Aluminum-coated silicon steel and method of production, pre-coated steel, process for producing a hot formed component

Abstract

The application provides an aluminized silicon steel and a preparation method thereof, a pre-coated steel and a production process of a hot-formed component. The aluminized silicon steel comprises a pre-coating layer arranged on a steel base. The pre-coating layer comprises an intermediate layer and an aluminized silicon coating layer. The nominal thickness of the aluminized silicon coating layer is 10-33 microns. The aluminized silicon coating layer contains Al-Si phases with a proportion of 5-40% and Al-Si-Fe phases with a proportion of 0.1-15%. The dispersion index of the Al-Si phases and the Al-Si-Fe phases in the aluminized silicon coating layer is greater than or equal to 0.05. In the aluminized silicon steel, the proportions of the Al-Si phases and the Al-Si-Fe phases in the aluminized silicon coating layer are appropriate, and the dispersion index is appropriate, which is helpful to the production of a hot-formed component with small grains. The hot-formed component has a double-layer Al-rich intermetallic compound layer, thereby improving the coating toughness and environmental tolerance of the hot-formed component, reducing the crack sensitivity, and improving the hydrogen brittleness resistance and corrosion resistance of the hot-formed component.

Description

[0001] The present patent application is a divisional application of the patent application with the application number 202410661792.0, the application date of May 27, 2024, and the invention name of "Aluminum-silicon plated steel and preparation method, pre-coated plated steel, and production process of hot-formed component". TECHNICAL FIELD

[0002] The present application relates to the field of hot-formed steel, in particular to aluminum-silicon plated steel and preparation method, pre-coated plated steel, and production process of hot-formed component. BACKGROUND

[0003] At present, the strength of commercially available hot-formed steel has exceeded 1500 MPa, and 2000 MPa hot-formed steel is becoming a hot spot for automotive steel. While pursuing strength, these hot-formed steels hope to obtain higher toughness and better crack sensitivity. The material strength of collision energy absorption has reached the 1000 MP level. The coating of traditional aluminum-silicon hot-formed steel has a typical four-layer structure, namely (a) interdiffusion layer; (b) intermediate layer; (c) Al-rich intermetallic compound layer; (d) surface layer. This structure can be produced within a wide hot-formed austenitizing processing window, not only obtaining higher strength, but also excellent welding performance of the coating.

[0004] With the increasing demand for material cost, a type of thin-coated hot-formed steel has appeared on the market, but the coating of this type of material is not conducive to welding process control, and the corrosion resistance of thin-coated layer is low. Moreover, with the increase of material strength to more than 2000 MPa, hydrogen embrittlement problem has become the focus of attention. The hot-formed austenitizing processing window that takes into account toughness and hydrogen embrittlement problem is the urgent demand of most customers at present. SUMMARY

[0005] The main purpose of the present application is to provide an aluminum-silicon plated steel, hot-formed component and production process thereof, to solve the technical problem that conventional aluminum-silicon plated steel cannot take into account toughness and hydrogen embrittlement.

[0006] To achieve the above-mentioned purpose, the present application provides an aluminum-silicon plated steel, comprising a steel base body and a pre-coating layer arranged on the steel base body.

[0007] The pre-coating layer comprises an intermediate layer and an aluminum-silicon coating layer; the nominal thickness of the aluminum-silicon coating layer is 10-33 microns; the aluminum-silicon coating layer contains Al-Si phase in a proportion of 5-40% and Al-Si-Fe phase in a proportion of 0.1-15%, and the dispersion index of the Al-Si phase and the Al-Si-Fe phase in the aluminum-silicon coating layer is greater than or equal to 0.05.

[0008] Si phase, the mass fraction of silicon in the Al-Si phase is 30-50%; the mass fraction of iron in the Al-Si-Fe phase is 10-35%, and the mass fraction of silicon is 3-15%.

[0009] Preferably, the aluminum-silicon coating contains the Al-Si phase in a proportion of 10-30% and the Al-Si-Fe phase in a proportion of 0.1-10%, wherein the mass fraction of silicon in the Al-Si phase is 30-50%; the mass fraction of iron in the Al-Si-Fe phase is 10-35%, and the mass fraction of silicon is 3-15%.

[0010] According to an embodiment of the present application, the Al-Si phase contains Al n Si m phase; wherein n:m=(1.0-3.0):1; the proportion of the Al n Si m phase in the Al-Si phase is ≥50%.

[0011] According to an embodiment of the present application, the Al n Si m phase contains at least one of Al4Si3 and Al4Si2.

[0012] According to an embodiment of the present application, the Al-Si-Fe phase contains Fe a Si b Al c phase; wherein a:b:c=(1-2):1:(4-9); the proportion of the Fe a Si b Al c phase in the Al-Si-Fe phase is ≥50%. The Fe a Si b Al c phase contains FeSiAl4 phase and Fe2SiAl7 phase.

[0013] The present application provides another aluminum-silicon plated steel, which comprises a steel substrate and a pre-coating layer arranged on the steel substrate; the pre-coating layer comprises an intermediate layer and an aluminum-silicon coating layer; the aluminum-silicon coating layer contains aluminum flowers; the nominal thickness of the aluminum-silicon coating layer is 10-20 μm, and the aluminum flowers satisfy the condition that the coordinate points formed by the aluminum flower area (mm 2 ) and the aluminum flower convexity (μm) are located in a first convex pentagon, and the first convex pentagon is formed by five points of (2, 3), (150, 3), (350, 7), (350, 35), and (2, 35).

[0014] According to an embodiment of the present application, the aluminum-silicon coating layer contains aluminum flowers; the nominal thickness of the aluminum-silicon coating layer is 19-33 μm, and the aluminum flowers satisfy the condition that the coordinate points formed by the aluminum flower area (mm2 and the coordinate point formed by the aluminum flower boundary length per unit area (1 / mm) and the aluminum flower convexity (μm) is located within a second convex pentagon, which is circumscribed by five points (4, 5), (170, 5), (400, 12), (400, 40), and (4, 40).

[0015] According to an embodiment of the present application, the aluminum-silicon plated layer includes aluminum flowers; the nominal thickness of the aluminum-silicon plated layer is 10-20 μm, and the aluminum flowers satisfy the condition that the coordinate point formed by the aluminum flower boundary length per unit area (1 / mm) and the aluminum flower convexity (μm) is located within a third convex pentagon, which is circumscribed by five points (0.1, 7), (0.17, 3), (10, 3), (10, 35), and (0.1, 35).

[0016] According to an embodiment of the present application, the aluminum-silicon plated layer includes aluminum flowers; the nominal thickness of the aluminum-silicon plated layer is 19-33 μm, and the aluminum flowers satisfy the condition that the coordinate point formed by the aluminum flower boundary length per unit area (1 / mm) and the aluminum flower convexity (μm) is located within a fourth convex pentagon, which is circumscribed by five points (0.08, 12), (0.16, 5), (8, 5), (8, 40), and (0.08, 40).

[0017] The present application discloses a preparation method of an aluminum-silicon plated steel, which comprises the following steps:

[0018] After annealing the steel substrate to be plated, the steel substrate to be plated is immersed in a plating solution to obtain an immersed plated steel substrate; the plating solution comprises, in mass percentage, Si: 8-11%; Fe: 1-4%; and the rest is Al and unavoidable impurities;

[0019] The immersed plated steel substrate is cooled to 570-650 °C at a speed of 2-20 °C / s and maintained at 570-650 °C for 1-20 seconds to obtain a primary-cooled immersed plated steel.

[0020] The primary-cooled immersed plated steel is cooled to 300 °C at an average cooling speed of 5-25 °C / s in a temperature adjusting device under the condition of a heating gas, and the holding time is 2-30 seconds to obtain a secondary-cooled immersed plated steel; the temperature of the temperature adjusting device is 300-570 °C; the temperature of the heating gas is ≥100 °C, and the total suspended particulate of the gas is ≤0.2 mg / m3.

[0021] The secondary-cooled immersed plated steel is cooled to room temperature to obtain a pre-coated plated steel.

[0022] According to an embodiment of the present application, the immersed plated steel substrate is cooled to 570 °C at a speed of 2-15 °C / s and maintained at 570 °C for 1-10 seconds to obtain a primary-cooled immersed plated steel.

[0023] According to the embodiment of the present application, the first cold immersion plated steel is cooled to 300℃ at an average cooling rate of 5-20℃ / s, and the holding time is 2-20 seconds, to obtain the second cold immersion plated steel.

[0024] According to the embodiment of the present application, the annealing temperature in the annealing step of the steel substrate to be plated is 700-850℃, and the annealing time is 1-20 minutes; and the temperature of the steel substrate to be plated after annealing entering the immersion plating solution is 600-700℃.

[0025] The present application also discloses a pre-coated plated steel, which is obtained by cold rolling and skin passing the plated aluminum-silicon steel; the pre-coated plated steel comprises a steel substrate and a skin-passed plated layer arranged on the steel substrate; the skin-passed plated layer is obtained by at least one of cold rolling and skin passing;

[0026] The skin-passed plated layer comprises an intermediate layer and an aluminum-silicon plated layer; the nominal thickness of the aluminum-silicon plated layer is 10-33μm; the aluminum-silicon plated layer contains Al-Si phase in a proportion of 5-40% and Al-Si-Fe phase in a proportion of 0.1-15%, and the dispersion index of the Al-Si phase and the Al-Si-Fe phase in the aluminum-silicon plated layer is ≥0.05;

[0027] The mass fraction of silicon in the Al-Si phase is 30-50%, and the mass fraction of iron in the Al-Si-Fe phase is 10-35%, and the mass fraction of silicon is 3-15%.

[0028] The present application also discloses a hot-formed component, which comprises a steel substrate and a component plated layer; the component plated layer is generated by interdiffusion between the steel substrate and the aluminum-silicon pre-coated layer;

[0029] The component plated layer comprises, in sequence, an interdiffusion layer, a first intermediate layer, a first Al-rich intermetallic compound layer, a second intermediate layer and a second Al-rich intermetallic compound layer; the interdiffusion layer is located at the innermost side of the component plated layer.

[0030] The first Al-rich intermetallic compound layer is in a discontinuous structure, and the proportion of the length of the layer is ≤80%; the second Al-rich intermetallic compound layer is in a quasi-continuous structure, and the proportion of the continuous length of the layer is ≥20%.

[0031] Preferably, the proportion of the length of the first Al-rich intermetallic compound layer is 1-50%; the proportion of the continuous length of the second Al-rich intermetallic compound layer is ≥50%; more preferably, the proportion of the continuous length of the second Al-rich intermetallic compound layer is 50-90%.

[0032] According to the embodiment of the present application, the component plated layer further comprises a surface layer located at the outer side of the second Al-rich intermetallic compound layer.

[0033] According to the embodiments of the present application, the grain size of the first intermediate layer, the second intermediate layer, and the surface layer is less than or equal to 30 μm; preferably, the grain size of the first intermediate layer, the second intermediate layer, and the surface layer is less than or equal to 25 μm; more preferably, the grain size of the first intermediate layer, the second intermediate layer, and the surface layer is less than or equal to 15 μm. The grain size of the intermediate layer of the coating of the present application is the average grain size of the coating observed in cross section.

[0034] According to the embodiments of the present application, the total thickness of the coating of the component is 5 μm to 60 μm; preferably, the total thickness of the coating of the component is 20 μm to 55 μm; preferably, the total thickness of the coating of the component is 26 μm to 50 μm; further preferably, the total thickness of the coating of the component is 30 μm to 50 μm.

[0035] The present application also discloses another hot-formed component, comprising a steel substrate and a coating of the component; the coating of the component is produced by interdiffusion between the steel substrate and an Al-Si pre-coating; the coating of the component has at least four Si concentration peaks in the thickness direction.

[0036] According to the embodiments of the present application, the at least four Si concentration peaks include a first Si concentration peak, a second Si concentration peak, a third Si concentration peak, and a fourth Si concentration peak from the surface of the coating of the component to the steel substrate.

[0037] The distance between the first Si concentration peak and the surface of the coating of the component is greater than or equal to 0.25 μm.

[0038] According to the embodiments of the present application, the distance between the first Si concentration peak and the surface of the coating of the component is greater than or equal to 0.45 μm.

[0039] According to the embodiments of the present application, the distance between the first Si concentration peak and the surface of the coating of the component is greater than or equal to 0.75 μm.

[0040] According to the embodiments of the present application, the distance between the first Si concentration peak and the surface of the coating of the component is greater than or equal to 1.5 μm.

[0041] According to the embodiments of the present application, the concentration value of the smallest peak among the at least four Si concentration peaks after deducting the background is greater than or equal to 0.01%.

[0042] According to the embodiments of the present application, the concentration value of the smallest peak is greater than or equal to 0.025%.

[0043] According to the embodiments of the present application, the concentration value of the smallest peak is greater than or equal to 0.05%.

[0044] According to the embodiments of the present application, the concentration value of the smallest peak is greater than or equal to 0.25%.

[0045] The application also discloses a production process of the hot-formed component, which comprises the following steps.

[0046] The aluminum-silicon plated steel or the pre-coated steel is heated to an austenite interval, the holding temperature range is 880-950 DEG C, the holding time is 3-15 minutes, the heating atmosphere is air, and the dew point is less than or equal to 0 DEG C.

[0047] The steel plate after holding is cooled, and the heated steel plate is pressed by a die within 10 seconds and cooled to below 200 DEG C.

[0048] The application also discloses a motor vehicle comprising the hot-formed component.

[0049] In the aluminum-silicon plated steel, the proportion of the Al-Si phase and the Al-Si-Fe phase in the aluminum-silicon coating is appropriate, and the dispersion index is appropriate, which is helpful to the small grain of the hot-formed component produced subsequently, the double-layer Al-rich intermetallic compound layer, the improvement of the coating toughness and environmental tolerance of the hot-formed component, the reduction of the crack sensitivity, the improvement of the hydrogen brittleness resistance and corrosion resistance of the hot-formed component. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained according to the structures shown in the drawings without creative labor.

[0051] Figure 1 is a typical aluminum flower pattern of the strip steel of the present application before hot forming;

[0052] Figure 2 is a typical aluminum flower pattern of the component of the present application after hot forming;

[0053] Figure 3 is a typical metallographic structure of the component of the present application after hot forming;

[0054] Figure 4 is a typical metallographic structure of the traditional hot-formed component after hot forming;

[0055] Figure 5 is a deformed coating structure of the component of the present application after hot forming;

[0056] Figure 6 is a deformed coating structure of the traditional hot-formed steel component after hot forming;

[0057] Figure 7 is a structure diagram of the pre-coating before hot forming;

[0058] Figure 8 is the plated structure of the component of the present application after hot forming;

[0059] Figure 9 is the plated structure of the conventional hot formed component after hot forming;

[0060] Figure 10 is the distribution of Si and Fe elements in the plated section of the Al-Si plated steel of the present application;

[0061] Figure 11 shows the area of aluminum flowers on the surface of the strip steel of the present application before hot forming ≥ 200 mm 2 ;

[0062] Figure 12 shows the area of aluminum flowers on the surface of the strip steel of the present application before hot forming ≤ 9 mm 2 ;

[0063] Figure 13 is the plated composition feature of the component of the present application after hot forming;

[0064] Figure 14 is the plated composition feature of the conventional component after hot forming.

[0065] The implementation, functional features and advantages of the present application will be further described with reference to the accompanying drawings. DETAILED DESCRIPTION

[0066] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0067] It should be noted that all directional indications, such as up, down, …, in the embodiments of the present application are only used to explain the relative positional relationship, movement condition, etc. between components in a certain posture (as shown in the drawings), and if the certain posture changes, the directional indications also change accordingly.

[0068] In addition, the description such as "first", "second" and the like in the present application is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one of the features.

[0069] Moreover, the technical solutions among various embodiments of the present application can be combined with each other, but it must be based on the fact that a person skilled in the art can realize the combination, and when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist and is not within the protection scope required by the present application.

[0070] The applicant has carried out a large number of studies on the hot-formed component, and the existing hot-formed component is mainly a four-layer structure, which specifically comprises: (a) a mutual diffusion layer; (b) an intermediate layer; (c) an Al-rich intermetallic compound layer; and (d) a surface layer. Moreover, the Al-rich intermetallic compound layer is a quasi-continuous structure layer. That is, in a metallographic diagram, the length of the Al-rich intermetallic compound layer accounts for a large proportion of the length of the structure layer, such as 90%. The overall visual metallographic diagram is basically in a continuous state. The length of the structure layer is the total length measured by the plating layer.

[0071] The inventor has found that there is often brittle Al-rich intermetallic compound at the interface between the mutual diffusion layer and the first intermediate layer (i.e., the surface of the mutual diffusion layer), and when the Al-rich intermetallic compound on the surface of the mutual diffusion layer is thick, the cracks generated on the surface of the plating layer will almost all propagate to the steel substrate during bending. However, when the Al-rich intermetallic compound on the surface of the mutual diffusion layer is reduced, the difficulty of crack propagation from the outside to the inside of the mutual diffusion layer increases, and even the mutual diffusion layer remains intact while the cracks are generated in the steel substrate, which indicates that reducing the thickness of the Al-rich intermetallic compound on the surface of the mutual diffusion layer helps to improve the plasticity of the mutual diffusion layer and further block the propagation of cracks from the surface to the inside of the steel substrate. Further research has found that the first Al-rich intermetallic compound layer is easy to merge with the Al-rich intermetallic compound on the surface of the mutual diffusion layer and disappear. This merging not only thickens the Al-rich intermetallic compound on the surface of the mutual diffusion layer, but also easily leads to the formation of sharp corners of the Al-rich intermetallic compound on the surface of the mutual diffusion layer, and stress concentration often occurs at the corners, thereby easily causing the generation and propagation of cracks. If the cracks at this position continue to propagate and expand, they will reach the interface between the steel substrate and the mutual diffusion layer, further promoting the cracking of the steel substrate.

[0072] After deformation (such as bending), a large number of cracks in the mutual diffusion layer will help hydrogen to invade the martensite structure of the steel substrate, so that the intact mutual diffusion layer not only improves the bending toughness of the material, but also improves the hydrogen embrittlement resistance of the material to a certain extent.

[0073] Therefore, the first Al-rich intermetallic compound layer is specially arranged to share the enrichment degree of Al-rich intermetallic compound in the interdiffusion layer, so as to improve the plasticity of the interdiffusion layer. When the thickness of the plated layer after hot forming exceeds 26 μm, there is enough Al-rich intermetallic compound in the plated layer to form. The Al-rich intermetallic compound on the surface of the interdiffusion layer is ingeniously decomposed and removed in part to form a new first Al-rich intermetallic compound layer, so as to improve the plasticity of the interdiffusion layer and reduce the number of crack penetrations.

[0074] In order to form the hot-formed component with the above structure, the raw material plated aluminum silicon steel or the finished plated aluminum silicon steel (i.e. the pre-coated steel below) for forming the same must meet specific conditions. The plated aluminum silicon steel or the finished plated aluminum silicon steel (i.e. the pre-coated steel below) is introduced below.

[0075] To achieve the above object, the present application provides a plated aluminum silicon steel, comprising a steel base body and a pre-plated layer arranged on the steel base body.

[0076] The pre-plated layer comprises an intermediate layer and an aluminum silicon plated layer. The nominal thickness of the aluminum silicon plated layer is 10 μm to 33 μm. The aluminum silicon plated layer contains Al-Si phase in a proportion of 5 to 40% and Al-Si-Fe phase in a proportion of 0.1 to 15%, and the dispersion index of the Al-Si phase and the Al-Si-Fe phase in the aluminum silicon plated layer is ≥0.05. Among them, the mass fraction of silicon in the Al-Si phase is 30 to 50%. The mass fraction of iron in the Al-Si-Fe phase is 10 to 35%, and the mass fraction of silicon is 3 to 15%.

[0077] The distribution of Si and Fe elements in the plated layer section can be scanned by an energy dispersive spectrometer (EDS). For example, Figure 10 The phases in the bright position of the distribution of Si and Fe elements in the plated layer are Al-Si and Al-Si-Fe, respectively. Then the image software (such as Image-pro Plus) is used to calculate the proportion of Al-Si and Al-Si-Fe in the plated layer. When calculating the proportion, the interdiffusion layer between the plated layer and the base body should be removed. In order to ensure the representativeness of the test results, the continuous plated layer section length ≥100 mm range can be accumulated for detection.

[0078] The plated aluminum silicon steel is generally formed by hot-dip plating of a steel base body. The steel base body includes a steel billet, a hot-rolled strip steel and a cold-rolled strip steel. The steel base body to be plated generally exists in the form of a flat steel strip. The size of the steel strip is referred to GB708-2006, and is also called steel strip, strip steel or steel plate in the industry. Such naming does not affect the explanation of the present application. Generally, the thickness of the steel base body to be plated is 0.5 to 3.5 mm.

[0079] The steel substrate to be plated, i.e. the steel material for hot-dip plating, includes hot-rolled steel plates and cold-rolled steel plates, or collectively referred to as steel strips. The steel substrate to be plated can exist in the geometric forms of coils, sheets, parts, etc. The steel substrate to be plated for continuous annealing is generally in the form of a coil. Regardless of the geometric form of the steel substrate to be plated, it does not affect the explanation of the present application. The steel strip after hot-dip plating is cut into steel plates of appropriate sizes, and after hot forming of the steel plates, parts, sheets, and other components in the required geometric sizes can be obtained. Regardless of the geometric form of the components after hot forming, it does not affect the explanation of the present application. The plating layer referred to in the present application can be a double-sided plating layer on the upper and lower surfaces, or a plating layer on one surface.

[0080] In some embodiments, the steel substrate is a boron-containing intrusion-resistant hot-formed steel for automobiles, including or including the component range: C: 0.18-0.45%, Mn: 0.3-3.0%, B: 0.0008-0.005%, and optional alloying elements. The tensile strength of the material after hot forming is ≥ 1500 MPa, and this embodiment is particularly directed to materials with a tensile strength ≥ 1800 MPa or more after hot forming.

[0081] In some embodiments, the steel material is a niobium-containing crash energy-absorbing hot-formed steel for automobiles, including or including the component range: C: 0.03-0.12%, Mn: 0.15-2.5%, Nb: 0.02-0.10%, and optional alloying elements, including optional B: 0.0008-0.005%. The tensile strength of the material after hot forming is ≤ 1500 MPa, and this embodiment is particularly directed to materials with a tensile strength of 900-1500 MPa after hot forming.

[0082] The aluminum-silicon plating layer of the aluminum-silicon plated steel includes (1) an intermediate layer; and (2) an aluminum-silicon plating layer. The aluminum-silicon plating layer contains Al-Si phases in a proportion of 5-40%, and the mass fraction of silicon in the Al-Si phases is 30-50%. The aluminum-silicon plating layer contains Al-Si-Fe phases in a proportion of 0.1-15%, and the mass fraction of iron in the Al-Si-Fe phases is 10-35%, and the mass fraction of silicon is 3-15%.

[0083] Through the inventors' intensive research, it has been found that by reasonably controlling the manufacturing process, a certain proportion of Al-Si phases and Al-Si-Fe phases can be prepared in the aluminum-silicon plating layer of the pre-plating strip steel (such as Figure 9). The Al-Si phase and the Al-Si-Fe phase are the key sources of the Al-rich intermetallic compound in the coating during the hot forming process. The distribution and amount of the Al-Si phase and the Al-Si-Fe phase in the pre-coating largely determine the location and amount of the Al-rich intermetallic compound after the hot forming. When the Al-Si phase and the Al-Si-Fe phase are more and dispersedly distributed in the pre-coating, it is beneficial to the generation of the first Al-rich intermetallic compound layer after the hot forming. When the Al-Si phase and the Al-Si-Fe phase are less and concentratedly distributed in the pre-coating, the first Al-rich intermetallic compound layer is difficult to appear after the hot forming, and instead, the single Al-rich intermetallic compound layer of the traditional hot-formed steel appears, so that the double Al-rich intermetallic compound layer of the present application cannot be obtained.

[0084] In order to obtain the above-mentioned double Al-rich intermetallic compound structure after the hot forming, the Al-Si phase and the Al-Si-Fe phase should be dispersedly distributed in the pre-coating, not gathered into linear shape, and not gathered into large block shape. The Al-Si phase should account for 5-40% in the aluminum-silicon coating, and the mass fraction of silicon in the Al-Si phase is 20-50%. The Al-Si-Fe phase should account for 0.1-15% in the aluminum-silicon coating, the mass fraction of iron in the Al-Si-Fe phase is 10-35%, and the mass fraction of silicon in the Al-Si-Fe phase is 3-15%. As a preferred, the Al-Si phase should account for 10-30% in the aluminum-silicon coating, and the mass fraction of silicon in the Al-Si phase is 30-50%. The Al-Si-Fe phase should account for 0.1-15% in the aluminum-silicon coating, the mass fraction of iron in the Al-Si-Fe phase is 10-35%, and the mass fraction of silicon in the Al-Si-Fe phase is 3-15%.

[0085] In order to better illustrate the features of the present application, the dispersion degree of the Al-Si phase and the Al-Si-Fe of the present application is explained by using the dispersion index. In the 20x100 square microns of the aluminum-silicon coating (1), each uniform size and significantly discontinuous Al-Si phase and Al-Si-Fe phase is simplified as the geometric center of the particle, or the Al-Si phase and Al-Si-Fe phase with a single area ≥1 square micron is simplified as a particle, and 3 adjacent particles are connected. If the triangle formed by connecting the 3 particles is a non-obtuse triangle, it is recorded as a type A triangle. If it is an obtuse triangle, it is recorded as a type B triangle. The dispersion index is defined as the proportion of the type A triangle to the total number of triangles. The larger the index, the greater the dispersion degree. For the present application, when the dispersion index is ≥0.05, the location has a tendency to form the first Al-rich intermetallic compound layer, that is, the 6-layer coating structure containing the double Al intermetallic compound (the first Al-rich intermetallic compound layer and the second layer) is easily formed after the hot forming. As a preferred, the local dispersion index is ≥0.1.

[0086] In the case of meeting the above conditions, the Al-Si phase and Al-Si-Fe phase of the plated layer will appear ③ less quantity, clear boundary. Otherwise, the Al-Si phase and Al-Si-Fe phase of the plated layer will appear ① more quantity, fuzzy boundary; ② less quantity, fuzzy boundary.

[0087] In order to avoid the local Al-Si phase and Al-Si-Fe phase gathering, and cause the Al-rich intermetallic compound on the surface of the mutual diffusion layer to be too thick and sharp, the dispersion distribution of the present application is particularly important for this position. The dispersion distribution can promote the formation of the first Al-rich intermetallic compound layer, and avoid the Al-rich intermetallic compound on the surface of the mutual diffusion layer to be too thick and sharp. While meeting the content ratio and dispersion index requirements of the Al-Si phase and Al-Si-Fe phase by using the present application, the proportion of the obtained discontinuous first Al-rich intermetallic compound layer to the considered structural layer will exceed 0.5%. As a preferred, the proportion of the first Al-rich intermetallic compound layer to the considered structural layer will exceed 1%. The proportion is the proportion of the length obtained by connecting the first Al-rich intermetallic compound layer to the length of the structural layer, that is, the total length measured by the plated layer.

[0088] The plated aluminum-silicon steel described above has a suitable ratio of Al-Si phase and Al-Si-Fe phase in the aluminum-silicon plated layer, and a suitable dispersion index, which is helpful for the subsequent production of hot-formed components with smaller grains, having a double-layer Al-rich intermetallic compound layer, thereby improving the plated layer toughness and environmental tolerance of the hot-formed components, reducing their crack sensitivity, and making the hot-formed components also have the advantages of improving hydrogen brittleness resistance, corrosion resistance, etc.

[0089] The applicant has also found that a large number of documents have analyzed the plated layer structure of the pre-plated layer of the existing hot-formed steel in detail, and believe that before austenitizing (before hot forming heating), the pre-plated layer of the strip steel is mainly composed of intermetallic compounds formed by pure Al and pure Si eutectic reaction. The plated layer is composed of 3 parts, the outermost layer is a pure Al layer, which includes a small amount of Si-rich phase and Fe-Al-Si ternary alloy; the middle layer is a Fe-Al-Si ternary alloy phase; the inner layer is a Fe-Al alloy layer, mainly composed of Fe2Al5 and FeAl3. The pure Si phase is in the form of a long strip, and the color is relatively bright. There is a bright intermediate layer between the plated layer and the steel substrate, with a thickness of about 5mm, which is analyzed as Fe2SiAl7 (τ5 phase). There is a thin compound layer composed of Fe2Al5 and FeAl3 between the intermetallic compound Fe2SiAl7 and the steel substrate.

[0090] The Al-Si phase mainly exists in the form of Al n Si m cluster structure, or contains no more than 1% Fe, and the atomic structure stability of these aluminum-silicon phases has a higher correlation with their bonding mode and binding energy.

[0091] In some embodiments, the Al-Si phase comprises Al n Si m phase. Wherein n:m=(1.0~3.0):1. The Al n Si m phase is ≥50% in the Al-Si phase. Specifically, the Al n Si m phase comprises at least one of Al4Si3 and Al4Si2.

[0092] The present application mainly controls the Al-Si phase with atomic ratio n:m ranging from 1.0 to 3.0, to obtain a certain proportion of the required Al-Si phase, which helps to form the structure of the plated layer after hot forming. Further, the key precipitated phase includes the phase with Al-Si atomic ratio ranging from 1.3 to 2.5, such as Al4Si3 and Al4Si2. Such Al-Si phase (including Al4Si3 and Al4Si2) is the required precipitated phase requirement of the present application. Due to the bonding properties of the phase, Al4Si3 and Al4Si2 cannot be stable, and the present application uses heat preservation cover, plated layer heating, high-purity dry air and other means during the control cooling process of the plated layer, which can improve the stability of Al4Si3 and Al4Si2, and obtain more particles and more effective Al-Si phase.

[0093] In some embodiments, the Al-Si-Fe phase comprises Fe a Si b Al c phase; wherein a:b:c=(1~2):1:(4~9); the Fe a Si b Al c phase is ≥50% in the Al-Si-Fe phase. The Fe a Si b Al c phase comprises FeSiAl4 phase and Fe2SiAl7 phase.

[0094] The Al-Si-Fe phase is the main existing form of Fe in the plated layer, and this phase is the product of the recombination of the Fe element of the steel matrix with the Al-Si phase after diffusing into the plating solution to form the Al-Si-Fe phase. Existing research shows that during the cooling process of the hot-dip plating solution, solid needle-shaped FeSiAl4 (τ6 phase) phase is generated in the plated layer. However, the inventors found that there is actually Fe2SiAl7 (τ5 phase) phase in the plated layer. Such Al-Si-Fe phase (mainly including τ5 and τ6 phases) is the required precipitated phase requirement of the present application.

[0095] In some embodiments, the aluminum-silicon coating includes aluminum flowers. The aluminum-silicon coating has a nominal thickness of 10-20 μm, and the aluminum flowers satisfy the condition that a coordinate point formed by the aluminum flower area (mm 2 ) and the aluminum flower convexity (μm) is located within a first pentagon defined by the five points (2, 3), (150, 3), (350, 7), (350, 35), and (2, 35).

[0096] The aluminum-silicon coated steel sheet forms a single aluminum solidification layer at about 600°C, and the phase structure of the aluminum-silicon solidification is a polygonal pattern of flowers formed during solidification. This polygonal pattern of flowers is referred to as "aluminum flowers."

[0097] The coating thickness and the aluminum flower area are related. The larger the coating thickness, the more likely the aluminum flowers grow. This is mainly related to the lower cooling speed of the thick coating. When the coating thickness is ≥ 10 μm, the aluminum flower area is controllable. When the coating thickness is ≥ 19 μm, the aluminum flower area is more suitable. The average thickness of the pre-coating is 10-33 μm. As a preferred embodiment, the average thickness of the pre-coating is 19-33 μm.

[0098] The inventors have found that the continuity of the first Al-rich intermetallic compound layer and the size of the aluminum flowers are related. A larger aluminum flower area can also retain more complete aluminum dendrites, reducing the number of aluminum grain boundaries. Grain boundaries often have more precipitates, which become the gathering place of diffusible hydrogen. Once the conditions are met, this diffusible hydrogen will transfer to the steel matrix. Complete grain defects are less likely to reduce diffusible hydrogen, which can hinder the invasion of hydrogen into the steel matrix to some extent. The hydrogen embrittlement resistance of the hot formed part and the bulky aluminum flowers are related. Therefore, increasing the aluminum flower area to 4 mm 2 or more, and maintaining the pre-coating thickness at 10 μm or more, helps to reduce the diffusible hydrogen content of the coating and alleviate the degree of hydrogen diffusion into the steel matrix. When the average aluminum flower area is ≥ 16 mm 2 or more, and the pre-coating thickness is maintained at 19 μm or more, the number of grain boundaries will be significantly reduced, and the amount of hydrogen diffusion along the aluminum flower grain boundaries into the interior will be reduced. In addition, when the aluminum flower area is 2 mm 2 or less, and the coating thickness is less than 10 μm, the protective effect of the aluminum flowers will be affected. The reason is that the thickness of the aluminum flower boundary is thin, the invasion distance of hydrogen at this location will be greatly reduced, and the invasion of hydrogen into the steel matrix becomes easier. Small aluminum flowers and thin coatings are not conducive to blocking hydrogen intake.

[0099] In the related art, since the above-mentioned protective effect of the aluminum flowers has not been discovered, it is believed that the aluminum flowers affect the appearance of the final hot formed part, and it is generally desired that the aluminum flower area is as small as possible, or that there are no aluminum flowers. For example, by controlling the coating process, the aluminum flowers are made smaller, or there are no aluminum flowers. Alternatively, the aluminum flowers are covered by spraying powder.

[0100] In the present application, the nominal thickness is the set thickness of the Al-Si coating, i.e. the target thickness of the Al-Si coating. For the purpose of comparison and illustration, the Al flower convexity referred to in the present application is the Al flower convexity of the strip steel after production without surface treatment (e.g. skin pass).

[0101] The present application requires a relatively large Al flower on the coating, and the relatively large Al flower will result in an increase in the local thickness difference of the coating. The growth of the Al flower is a nucleation and growth process, the Al flower center nucleates and grows first, and the thickness increases continuously during the growth process. The thickness is relatively large at this point. The Al flower edge solidifies and grows later than the center nucleation point, and the thickness is relatively thin at this point. When the Al flower area is 4mm 2 or more, the uneven thickness has an impact on the distribution of the Al-Si phase and the Al-Si-Fe phase of the coating. When the Al flower area is 16mm 2 or more, the uneven thickness is more obvious. After increasing the Al flower using the coating cooling process of the present application, a significant thickness difference can be seen under a microscope, and even the coating has a rough feeling when touched by hand.

[0102] The coating thickness at the center of the Al flower is larger than that at the boundary of the Al flower, which is one of the key factors for the formation of the 6-layer structure after hot forming. The existence of this difference is beneficial to the formation of sufficient Al-Si phase and Al-Si-Fe phase near the center of the Al flower in the pre-coating. The Al flower convexity (C) is defined as the difference between the three-point average of the maximum coating thickness near the center of the Al flower and the three-point average of the minimum thickness near the edge of the Al flower on the pre-coating strip steel. The Al flower convexity of the present application is generally ≥1μm. To meet the quality requirements of the present application, the Al flower convexity should be maintained at least ≥3μm, and when the Al flower convexity of the coating is ≥5μm, the effect of promoting the 6-layer structure after hot forming is more obvious. For materials with a larger thickness, the single-sided coating thickness is 19-33μm, and the Al flower convexity should be maintained at least ≥5μm.

[0103] Since the Al-Si phase and the Al-Si-Fe phase in the coating have been basically formed before skin pass and levelling of the coating, even if the Al flower convexity is <3μm after skin pass, it can also meet the requirements of the present application. Therefore, the Al flower coating convexity required by the present application is the Al flower coating convexity requirement before surface treatment (e.g. skin pass, rolling, hot forming). Generally, when the pre-coating thickness is set to 10-20μm (nominal thickness 10-20μm), the Al flower convexity can be 5-40μm due to the existence of the Al flower convexity, and therefore the maximum Al flower convexity can be ≥35μm. When the coating thickness is set to 19-33μm (nominal thickness 19-33μm), the pre-coating thickness range can be 10-50μm, and therefore the maximum Al flower convexity can be ≥40μm. Without the process treatment of the present application, it is difficult to obtain the convexity required by the present application.

[0104] The analysis finds that the aluminum flower convexity is related to the plating layer thickness and the aluminum flower size. Generally, the thinner the plating layer is, the smaller the aluminum flower convexity is, and the smaller the aluminum flower area is, the smaller the aluminum flower convexity is. In order to meet the requirements of the material performance after hot forming, the relationship among the aluminum flower convexity, the aluminum flower area and the plating layer thickness should meet the following requirements.

[0105] C≥a·S

[0106] In the above formula, C is the aluminum flower convexity, in units of μm; S is the aluminum flower area, in units of mm 2 ; a is a coefficient, in units of μm / mm 2 . For the convenience of calculation and illustration, the value of a is 0.02.

[0107] As a preference, (1) when the average thickness of the single-side plating layer is < 19 μm, the coefficient is 0.02, that is, C≥0.02S. But in order to meet the distribution requirements of the plating layer precipitates, when the average thickness of the single-side plating layer is < 19 μm, the aluminum flower convexity is at least 3 μm. (2) when the average thickness of the single-side plating layer is ≥ 19 μm, the coefficient is 0.03, that is, C≥0.03S. In order to meet the distribution requirements of the plating layer precipitates, when the average thickness of the single-side plating layer is ≥ 19 μm, the aluminum flower convexity is at least 5 μm.

[0108] Under ideal conditions, the growth of a single aluminum flower in three-dimensional space can be equiaxed, that is, the aluminum flower thickness is equal to the aluminum flower diameter, but the aluminum flower on the surface of the strip steel of the present application is relatively large, the thickness growth is limited, and it will not become equiaxed, but flat. The aluminum flower convexity of the present application should be controlled within an upper limit, otherwise it will result in too uneven surface of the plating layer. Generally, the aluminum flower convexity should be less than or equal to 0.8 times the average thickness of the single-side plating layer. As a preference, the aluminum flower convexity is less than or equal to 0.7 times the average thickness of the single-side plating layer. For the convenience of calculation and illustration, the maximum aluminum flower convexity should not exceed 40 μm.

[0109] The five points (2, 3), (150, 3), (350, 7), (350, 35), (2, 35) constituting the first pentagon are each a coordinate point formed by the aluminum flower area (mm 2 ) and the aluminum flower convexity (μm). Taking the coordinate point (2, 3) as an example, it indicates that the aluminum flower area (mm 2 ) of the point is 2, and the aluminum flower convexity (μm) is 3.

[0110] The nominal thickness of the aluminum-silicon plating layer is 10-20 μm, and the corresponding aluminum flower satisfies the aluminum flower area (mm 2and the aluminum flower convexity (μm) form a coordinate point within the first pentagon. In this condition, the continuity of the first Al-rich intermetallic compound layer of the hot-formed member can be reduced, and the structure of the double Al-rich intermetallic compound layer is more likely to be generated, thereby improving the coating toughness and environmental tolerance of the hot-formed member, reducing the crack sensitivity, and making the hot-formed member also have the advantages of improving the hydrogen embrittlement resistance, corrosion resistance, and the like.

[0111] In some embodiments, the aluminum-silicon coating layer includes an aluminum flower. The nominal thickness of the aluminum-silicon coating layer is 10-20 μm, and the aluminum flower satisfies the condition that the coordinate point formed by the unit area aluminum flower boundary length (1 / mm) and the aluminum flower convexity (μm) is within the third pentagon, and the third pentagon is formed by five points (0.1, 7), (0.17, 3), (10, 3), (10, 35), and (0.1, 35). 2 and the aluminum flower convexity (μm) form a coordinate point within the second pentagon. The second pentagon is formed by five points (4, 5), (170, 5), (400, 12), (400, 40), and (4, 40).

[0112] The definitions of the five points constituting the second pentagon are the same as those of the five points constituting the first pentagon, and are not repeated here. The nominal thickness of the aluminum-silicon coating layer is 19-33 μm, and the aluminum flower satisfies the condition that the coordinate point formed by the aluminum flower area (mm 2 and the aluminum flower convexity (μm) form a coordinate point within the second pentagon. In this condition, the continuity of the first Al-rich intermetallic compound layer of the hot-formed member can be reduced, and the structure of the double Al-rich intermetallic compound layer is more likely to be generated, thereby improving the coating toughness and environmental tolerance of the hot-formed member, reducing the crack sensitivity, and making the hot-formed member also have the advantages of improving the hydrogen embrittlement resistance, corrosion resistance, and the like.

[0113] In some embodiments, the aluminum-silicon coating layer includes an aluminum flower. The nominal thickness of the aluminum-silicon coating layer is 10-20 μm, and the aluminum flower satisfies the condition that the coordinate point formed by the unit area aluminum flower boundary length (1 / mm) and the aluminum flower convexity (μm) is within the third pentagon, and the third pentagon is formed by five points (0.1, 7), (0.17, 3), (10, 3), (10, 35), and (0.1, 35).

[0114] Since the invasion of hydrogen is more likely to occur at the aluminum flower grain boundary, it is more appropriate to control the cumulative length of the grain boundary per unit area rather than the area of the aluminum flower, and even more so than the simple length and width parameters of the aluminum flower in the conventional technology. However, an equiaxed aluminum flower can be obtained by the present application. The equiaxed aluminum flower means that the lengths of the edges of the aluminum flower in different directions are close to each other, that is, the aluminum flower has isotropy, and the overall profile is approximately circular. That is, under the condition of the same area, the perimeter of the equiaxed aluminum flower is smaller than that of a non-equiaxed aluminum flower (for example, the difference between the lengths of the edges is large, for example, the overall profile of the aluminum flower is approximately rectangular).

[0115] Therefore, compared with the traditional aluminum plating technology, the cumulative boundary length of the aluminum flower of the present application is greatly reduced, and even when the aluminum flower area is small, the total boundary length of the aluminum flower is smaller than that of the aluminum plating plate produced by the traditional technology without control. Therefore, the aluminum flower convexity (μm) and the aluminum flower boundary length (mm) are the key technologies to determine the performance of the material of the present application. Since the aluminum flower boundary length is not easy to measure, and the shape of the aluminum flower of the present application is basically close to equiaxed, the aluminum flower shape stability is high, so the relationship between the aluminum flower area and the aluminum flower convexity can be used instead of the aluminum flower convexity and the aluminum flower boundary length requirement.

[0116] Through research, this alternative measurement scheme is effective in the present application. For the traditional production process, even if the average area of the aluminum flower is within the required range of the present application, but due to the uncontrolled shape of the aluminum flower, the cumulative length of the aluminum flower boundary per unit area will exceed the requirements of the present application. The present application simultaneously provides the relationship requirements of the aluminum flower convexity and the aluminum flower boundary length per unit area.

[0117] Therefore, in the present embodiment, (1) when the nominal thickness of the single-sided plating layer is 10-20 μm, the aluminum flower boundary length per unit area (1 / mm) and the aluminum flower convexity (μm) should be within the pentagon formed by the five points of (0.1, 7), (0.17, 3), (10, 3), (10, 35), (0.1, 35).

[0118] And in some embodiments, the nominal thickness of the aluminum-silicon plating layer is 19-33 μm, and the aluminum flower satisfies the condition that the coordinate points formed by the aluminum flower boundary length per unit area (1 / mm) and the aluminum flower convexity (μm) are located within the fourth pentagon formed by the five points of (0.08, 12), (0.16, 5), (8, 5), (8, 40), (0.08, 40).

[0119] (2) the aluminum flower boundary length per unit area (1 / mm) and the aluminum flower convexity (μm) should be within the pentagon formed by the five points of (0.08, 12), (0.16, 5), (8, 5), (8, 40), (0.08, 40).

[0120] The convexity of the plating aluminum flower in the actual delivery state may be affected by the finishing and the straightening, and the convexity will decrease. However, this will not cause serious adverse effects on the distribution of Al-Si and Al-Si-Fe in the plating layer.

[0121] Since the aluminum flower prepared in the embodiments of the present application is close to equiaxed, the aluminum flower area defined in the present application, that is, the average area of the aluminum flower on the plating layer surface, is more conducive to the technical requirements of the present application compared with the prior art. Therefore, in some embodiments, the aluminum flower area is measured as follows:

[0122] (1) A 300 mm x 300 mm sample is taken at the position of 1 / 4 of the width of the steel strip plate;

[0123] (2) Respectively on the sample, the lower surface, along the transverse and longitudinal each draw 3 100 mm long straight line, straight line spacing greater than 50 mm;

[0124] (3) Respectively count the number of each line on the aluminum flowers, the number of aluminum flowers in the transverse direction to take the average a, the number of aluminum flowers in the longitudinal direction to take the average b;

[0125] (4) Calculate the aluminum flower area S, S = 100 x 100 / (a x b).

[0126] Note: The above sampling position is only a representative sample, such as the strip size does not meet the requirements, the sampling position and the line position can be adjusted, but the evaluation area is generally not less than 90000 mm 2 .

[0127] The application discloses a preparation method of aluminized silicon steel, comprising the following steps:

[0128] S100: after annealing the steel substrate to be plated, the steel substrate to be plated is immersed in the immersion plating solution to obtain an immersion plated steel substrate. The immersion plating solution comprises, in percentage by mass: Si: 8-11%; Fe: 1-4%; and the rest is Al and inevitable impurities.

[0129] The steel substrate to be plated (i.e. the strip steel) for hot dipping plating includes hot-rolled strip steel and cold-rolled strip steel, and the thickness is 0.5-3.5 mm.

[0130] The immersion plating solution is usually placed in an aluminum pot. The composition of the immersion plating solution can also be represented by the composition of the aluminum pot. That is, the composition of the aluminum pot: Si: 8-11%; Fe: 1-4%; and the rest is Al and inevitable impurities.

[0131] After annealing the steel substrate to be plated, it is put into the aluminum pot, and the temperature of entering the aluminum pot is the pot-in temperature. In some embodiments, the temperature of the annealed steel substrate to be plated entering the immersion plating solution is 600-700 DEG C. That is, the strip steel pot-in temperature is 600-700 DEG C.

[0132] S200: cooling the immersion plated steel substrate to 570 DEG C-650 DEG C at a speed of 2-20 DEG C / s, and maintaining at 570 DEG C-650 DEG C for 1-20 seconds to obtain a primary-cooled immersion plated steel.

[0133] In order to realize the above-mentioned Al-Si phase and Al-Si-Fe phase requirements and the uniformity requirement of the plated layer, the application adopts the method of controlling the cooling of the plated layer and simultaneously applying deformation to the plated layer. That is, the first-stage cooling of S200 step and the second-stage cooling of S300 step.

[0134] To achieve the above-mentioned Al-Si phase and Al-Si-Fe phase requirements, the strip steel is cooled by air after hot dipping, and the average cooling rate of the strip steel is controlled to be ≤ 50°C / s in the range from the exit of the aluminum pot to 300°C. As a preference, the average rate is 2-25°C / s. As a preference, the average rate of the coating from the exit of the aluminum pot to 570°C (first stage cooling) is 2-20°C / s. The average rate of the coating from 570°C to 300°C (second stage cooling) is 5-25°C / s. Controlling the cooling helps the above-mentioned partial Al-Si phase and Al-Si-Fe phase to precipitate.

[0135] In the first stage cooling, the holding temperature range is generally 570-650°C, and the holding time is 1-20 seconds. The holding box can also be replaced by heat insulation plates, which should be arranged on both sides of the upper and lower surfaces of the coating. The holding measure helps to prolong the time of the coating of the strip steel in the high temperature zone, maintain the surface tension of the aluminum flowers, and thus improve the aluminum flower convexity after solidification of the coating.

[0136] S300: The primary cooling dipped steel is placed in a temperature adjusting device, and is continuously cooled to 300°C at an average cooling rate of 5-25°C / s under the condition of heated gas, and the holding time is 2-30 seconds, to obtain the secondary cooling dipped steel. The temperature of the temperature adjusting device is 300-570°C. The temperature of the heated gas is ≥ 100°C, and the total suspended particulate of the gas is ≤ 0.2 mg / m3.

[0137] To obtain the aluminum flower convexity and aluminum flower area required by the present application, the cooling rate should be avoided to be too large, and the cooling rate of the second stage is less than or equal to 15°C / s. The cooling stage can be provided with a temperature adjusting device, the holding temperature of which is 300-570°C, and the holding time is 2-30 seconds. Preferably, the holding temperature is 300-570°C, and the holding time is 5-20 seconds.

[0138] The measures such as cooling and holding can not meet the requirements of the growth of the aluminum flowers. To meet the requirements of the aluminum flower area and convexity, the cooling stage of the present application is provided with a gas heating device, the gas temperature during heating is ≥ 300°C, the temperature range of the strip steel during heating is 300-650°C, and the heating rate of the strip steel needs to be controlled to be 0-25°C / s. The total suspended particulate (TSP) of the gas is ≤ 0.2 mg / m3. The purpose of controlling the upper limit of the TSP is to reduce the particulate matters contained in the gas, which can become the aluminum flower points, so as to increase the aluminum flowers, and thus increase the boundary length of the aluminum flowers per unit area.

[0139] The inventors have analyzed the effect of phase transition exothermicity of the material on the aluminum flower, and found that when the material has exothermicity during the cooling process, the temperature of the strip steel is maintained, which is beneficial to the growth of the aluminum flower, especially to the Al-Si and Al-Si-Fe phases to meet the dispersion index of the present application. Therefore, the energy applied by the above-mentioned heat preservation can be appropriately reduced, that is, the heating gas temperature in the cooling section can be appropriately reduced. Generally, when the composition meets C: 0.18-0.45%, Mn: 0.3-3.0%, B: 0.0008-0.005%, the annealing holding temperature is ≥730, and the holding time is ≥1 minute, the phase transition exothermicity exists during the cooling process after plating, and the gas temperature during heating in the cooling section can be appropriately reduced, such as controlling the upper limit of the gas temperature, i.e. ≤650℃. Further, when C: 0.28-0.45%, Mn: 0.3-3.0%, B: 0.0008-0.005%, the annealing holding temperature is ≥730, and the holding time is ≥1 minute, the gas temperature during heating in the cooling section is 640℃.

[0140] When the strip steel is added with a certain amount of Cr, Ni, V, Mo, the temperature range of exothermicity has a downward trend, and the auxiliary heating of the heating gas should be advanced to prevent the phase transition exothermicity time from being delayed and affecting the growth of the aluminum flower. Specifically, when the strip steel meets C: 0.18-0.45%, Mn: 0.3-3.0%, B: 0.0008-0.005%, Cr: 0.1-0.5%, the annealing holding temperature is ≥730, the holding time is ≥1 minute, and the temperature of the strip steel gas heating in the cooling stage is ≥305℃. Further, when the strip steel meets C: 0.18-0.45%, Mn: 0.3-3.0%, B: 0.0008-0.005%, Cr: 0.1-0.5%, Ni+V+Mo: 0.1-1.5%, the annealing holding temperature is ≥730, the holding time is ≥1 minute, and the temperature of the strip steel gas heating in the cooling stage is ≥310℃. Further, when the strip steel meets C: 0.28-0.45%, Mn: 0.3-3.0%, B: 0.0008-0.005%, Cr: 0.1-0.5%, Ni+V+Mo: 0.1-1.5%, and two of the three elements Ni, V, Mo simultaneously meet ≥0.1%, the annealing holding temperature is ≥730, the holding time is ≥1 minute, and the temperature of the strip steel gas heating in the cooling stage is ≥315℃.

[0141] S400: cooling the said two-cooling immersion plated steel to room temperature to obtain a pre-coated plated steel.

[0142] In this step, air and / or water can be used to cool the strip steel from 300℃ to room temperature.

[0143] In some embodiments, the galvannealed steel substrate is cooled at a rate of 2-15°C / s to 570°C and maintained at 570°C for 1-10 seconds to obtain a primary-cooled galvannealed steel.

[0144] In some embodiments, the primary-cooled galvannealed steel is cooled at an average cooling rate of 5-20°C / s to 300°C and maintained for 2-20 seconds to obtain a secondary-cooled galvannealed steel.

[0145] In some embodiments, the annealing temperature in the annealing step of the steel substrate to be plated is 700-850°C and the annealing time is 1-20 minutes.

[0146] The cold-rolled steel strip is annealed at a temperature of 700-880°C for 1-20 minutes. Preferably, the annealing temperature is 700-850°C and the annealing time is 3-15 minutes. For hot-rolled steel strips that are not cold-rolled, the annealing temperature of the steel strip can be lower than 700°C.

[0147] In some embodiments, between step S100 and step S200, a step of blowing (e.g., using a nozzle blowing system, i.e., an air knife) to remove excess plating solution on the surface is further included to obtain a steel strip with a pre-plating layer having an average thickness (single side) of 10-33 μm. Preferably, the pre-plating layer of the steel strip has an average thickness of 19-33 μm.

[0148] In some embodiments, after the step of blowing to remove excess plating solution on the surface, a step of applying at least an alternating magnetic field to the plating layer in liquid state is further included, and the frequency of the alternating magnetic field is ≥1 Hz.

[0149] The present application requires controlling the grain distribution direction of the Al-Si-Fe phase in the plating layer. After the steel strip exits the air knife, at least an alternating magnetic field is applied to the plating layer in liquid state to control the distribution of the Al-Si-Fe phase, and the frequency of the alternating magnetic field is ≥1 Hz. The alternating magnetic field also has a stirring effect on the plating layer, which prevents the formation of too many unfavorable as-cast plating grains, and this stirring is beneficial to changing the distribution state of the Al-Si phase and the Al-Si-Fe phase and improving the dispersion index. Appropriately increasing the frequency of the alternating magnetic field, such as ≥50 Hz, makes the electromagnetic stirring effect on the plating layer more significant.

[0150] The present application also discloses a pre-coated steel strip, which is obtained by cold-rolling and finishing a galvannealed steel strip. The pre-coated steel strip comprises a steel substrate and a finished plating layer disposed on the steel substrate. The finished plating layer is obtained by at least one of cold-rolling and finishing.

[0151] The optical finish coating comprises an intermediate layer and an aluminum-silicon coating layer. The nominal thickness of the aluminum-silicon coating layer is 10-33 μm. The aluminum-silicon coating layer contains Al-Si phase in a proportion of 5-40% and Al-Si-Fe phase in a proportion of 0.1-15%, and the dispersion index of the Al-Si phase and the Al-Si-Fe phase in the aluminum-silicon coating layer is ≥0.05.

[0152] The mass fraction of silicon in the Al-Si phase is 30-50%. The mass fraction of iron in the Al-Si-Fe phase is 10-35%, and the mass fraction of silicon is 3-15%.

[0153] The pre-coated steel is obtained by cold rolling and optical finishing of aluminum-silicon plated steel. The pre-coated steel also has aluminum flowers. The aluminum flower convexity of the pre-coated steel may be affected by optical finishing and tension leveling, and the convexity may decrease. However, this does not have a serious adverse effect on the distribution of Al-Si and Al-Si-Fe in the coating, and is basically the same as in the aluminum-silicon plated steel. Therefore, the proportions, compositions, and areas of the aluminum flowers of the Al-Si phase and the Al-Si-Fe phase of the pre-coated steel can be referred to the aluminum-silicon plated steel, and will not be described again.

[0154] The application also discloses a hot-formed component, comprising a steel base and a component coating layer. The component coating layer is generated by interdiffusion between the steel base and an aluminum-silicon pre-coating layer.

[0155] The component coating layer comprises, in sequence, an interdiffusion layer, a first intermediate layer, a first Al-rich intermetallic compound layer, a second intermediate layer, and a second Al-rich intermetallic compound layer. The interdiffusion layer is located at the innermost side of the component coating layer.

[0156] The first Al-rich intermetallic compound layer has a discontinuous structure, and the proportion of the length of the layer is ≤80%. The second Al-rich intermetallic compound layer has a quasi-continuous structure, and the proportion of the continuous length of the layer is ≥20%.

[0157] In order to more clearly describe the structure of the hot-formed component, a hot-formed component with a more complete structure is taken as an example for description, and the coating layer has a six-layer structure. It should be noted that the surface layer is not necessarily a structure.

[0158] The component coating layer after hot forming comprises (a) an interdiffusion layer; (b) a first intermediate layer; (c) a first Al-rich intermetallic compound layer; (d) a second intermediate layer; (e) a second Al-rich intermetallic compound layer; and (f) a surface layer.

[0159] Wherein:

[0160] (a) interdiffusion layer: thickness 5-18 μm, hardness of the layer HV50g 230-420. The layer contains, calculated as a weight percentage: 80-95% Fe, 4-10% Al, 0-5% Si. At the interface between the interdiffusion layer and the first intermediate layer there are intermetallic compounds of the same composition as the first Al-rich intermetallic layer.

[0161] (b) first intermediate layer: thickness 0-25 μm, hardness of the layer HV50g 800-1000. The layer contains, calculated as a weight percentage: 35-47% Fe, 50-61% Al, 0-2% Si.

[0162] (c) first Al-rich intermetallic layer: thickness 0-15 μm, hardness of the layer HV50g 450-650. The layer contains, calculated as a weight percentage: 50-70% Fe, 30-35% Al, 2-6% Si. The first Al-rich intermetallic layer has a discontinuous structure, the proportion of the continuous length of the layer ≤ 80%. Preferably, the first Al-rich intermetallic layer has a discontinuous structure, the proportion of the continuous length of the layer 1-50%. In the layer, the Al-rich intermetallic compounds should have a coating thickness unevenness, the area where the coating is thinner (coating thickness ≤ 26 μm) is more difficult to form and has a poorer continuity. The continuity of the first Al-rich intermetallic layer is affected by the heating regime, the heating process should be continuous heating, not segmented to set different heating temperatures. In particular, the set temperature should not exceed 940 °C, and at the same time the actual temperature of the component should not exceed 950 °C, otherwise when the holding time is long enough, the first Al-rich intermetallic layer formed at high temperature will be completely merged into the interdiffusion layer, so that the layer completely disappears.

[0163] The inventors have found that when the average area of the aluminum flowers of the pre-coating is ≥ 16 mm 2 , a larger amount of the first Al-rich intermetallic layer is easily obtained. In particular, when the average area of the aluminum flowers is ≥ 64 mm 2 , and the coating thickness of the pre-coated strip is 10 μm or more, the first Al-rich intermetallic layer has a stronger continuity, the proportion of the continuous length of the Al-rich intermetallic compounds in the layer is 1-30%. When the average area of the aluminum flowers is ≥ 64 mm 2 , and the coating thickness of the pre-coated strip is 19 μm or more, the first Al-rich intermetallic layer has a stronger continuity, the proportion of the continuous length of the Al-rich intermetallic compounds in the layer is 1-50%. And when the maximum area of the aluminum flowers is ≥ 100 mm 2, more typical, excellent 6-layer structure after hot forming. The continuity of the first Al-rich intermetallic layer is related to the change of the coating after hot forming, such as when the thickness of the coating after hot forming is less than 26 μm, the first Al-rich intermetallic layer almost merges with the interdiffusion layer due to the close distance between the first Al-rich intermetallic layer and the Al-rich intermetallic layer on the surface of the interdiffusion layer. In addition, the thickness of the interdiffusion layer is too large, which will affect the formation of the first Al-rich intermetallic layer, such as when the thickness of the interdiffusion layer is ≥ 16 μm, the first Al-rich intermetallic layer almost disappears. The effect of aluminum flowers on the formation of the first Al-rich intermetallic layer is mainly affected by the distribution of Al-Si phase and Al-Si-Fe phase in the pre-coating. When the aluminum flowers increase, more Al-Si phase and Al-Si-Fe phase are more likely to form near the center of the aluminum flowers. When the area of the aluminum flowers decreases, the aggregation effect decreases, and the double-layer Al-rich intermetallic structure effect decreases. The nucleation amount of Al-Si phase and Al-Si-Fe phase required by the present application has been controlled in the aluminum pot before plating. Then, through the subsequent process of the present application, the distribution of Al-Si phase and Al-Si-Fe phase gradually meets the requirements of the present application.

[0164] After hot forming, the present application should avoid the presence of too many traditional hot-formed steel 4-layer structures, or fewer structure layers. Because when the structure layer is too small, the Al-rich intermetallic layer on the surface of the interdiffusion layer will thicken. It cannot meet the requirements of the present application, and further leads to the decline of the plasticity, toughness and hydrogen embrittlement sensitivity of the material. However, even if the present application has some unavoidable less than 6-layer structure in the local part of the coating, i.e. the first Al-rich intermetallic layer is partially disappeared, but through the implementation of the technology of the present application, the plasticity, toughness and hydrogen embrittlement sensitivity of the interdiffusion layer of the material are also improved, which is related to the coating aluminum flowers, Al-Si phase and Al-Si-Fe phase distribution characteristics, etc. More importantly, the grains in the coating are refined.

[0165] (d) Second intermediate layer: The second intermediate layer has the same composition as the first intermediate layer. The first intermediate layer and the second intermediate layer will be fused together at the position where the continuity of the first Al-rich intermetallic layer is low, and the smaller the area of the aluminum flowers and the thinner the coating, the more likely this fusion will occur.

[0166] (e) Second Al-rich intermetallic layer: The second Al-rich intermetallic layer has the same composition as the first Al-rich intermetallic layer, and is a quasi-continuous structure, generally accounting for ≥ 20% of the continuous length of the layer.

[0167] In some embodiments, the continuity is improved, the Al-rich intermetallic compound occupies a proportion of ≥ 50% of the continuous length of the layer. As preferred, the second Al-rich intermetallic compound layer is quasi-continuous structure, occupying a proportion of 50-90% of the continuous length of the layer. The proportion of the second Al-rich intermetallic compound layer is reduced from the traditional lower limit of 90% to 50% because a part of the Al-rich intermetallic compound originally used to form the second layer also forms a new first Al-rich intermetallic compound layer. When a part of the second Al-rich intermetallic compound layer is fused with the first Al-rich intermetallic compound layer, the intermetallic compound in the second Al-rich intermetallic compound layer occupies a proportion of 50-75% of the continuous length of the layer.

[0168] (f) Surface layer: The composition of the surface layer is almost the same as that of the first intermediate layer and the second intermediate layer, and the layer contains, in percentage by weight: 35-47% of Fe, 50-61% of Al, and 0-2% of Si. The layer also contains less than 30% of Al-rich intermetallic compound, generally between 2-15% of Al-rich intermetallic compound, and the Al-rich intermetallic compound in the layer contains, in percentage by weight: 50-70% of Fe, 30-35% of Al, and 2-6% of Si. There can also be a layer of pure aluminum or aluminum oxide with a continuity of ≥ 90% on the outer surface of the surface layer. Therefore, after the surface layer is subdivided, the surface layer can be divided into 3 or even more layers, and for the sake of convenience, the present application and the traditional aluminum-silicon-coated hot-formed steel are collectively referred to as the surface layer.

[0169] It should be noted that there is a continuous Al-rich intermetallic compound layer at the interface between the interdiffusion layer and the first layer of the intermediate layer. The composition of this layer is the same as or similar to that of the first and second Al-rich intermetallic compound layers.

[0170] More importantly, the grains in the coating of the present application are finer after hot forming, and the grain boundaries of the coating increase. After hot forming, more grain boundaries in the coating are beneficial to the diffusion of hydrogen in the steel matrix through the grain boundaries, and the discontinuous Al-rich intermetallic compound layer reduces the plugging effect on the hydrogen in the matrix, thereby relieving the risk of hydrogen embrittlement of the material. The refinement of the grains in the coating is related to the distribution of Al-Si phases and Al-Si-Fe phases in the coating before hot forming. When the dispersion index requirement of the present application is met, the Al-Si phases and Al-Si-Fe phases easily hinder the grain growth of the coating during the hot forming process, which helps to refine the grains in the intermediate layer. As a result, the Al-rich intermetallic compound of the first layer and the second layer formed after hot forming separates the first layer and the second layer of the intermediate layer, making the grains finer, further improving the toughness of the coating, reducing the crack sensitivity, and improving the environmental resistance of the coating. It also has the advantages of improving the resistance to hydrogen embrittlement and corrosion resistance.

[0171] In some embodiments, the grain size of the first intermediate layer, the second intermediate layer, and the surface layer of the present application is generally less than or equal to 30 μm; preferably, the grain size of the intermediate layer can be less than or equal to 25 μm; preferably, the grain size of the first intermediate layer, the second intermediate layer, and the surface layer can be less than or equal to 20 μm. Further preferably, the grain size of the first intermediate layer, the second intermediate layer, and the surface layer can be less than or equal to 15 μm.

[0172] However, the traditional hot-formed steel does not have the distribution characteristics of the Al-Si phase and the Al-Si-Fe phase of the present application, and after hot forming, the intermediate layer of the coating has coarse grains and few grain boundaries. In addition, the Al-rich intermetallic compound layer is in a substantially continuous state and has high continuity, which is not conducive to the diffusion of hydrogen in the environment and has a high blocking effect on hydrogen, and the hydrogen embrittlement sensitivity is higher. At the same time, the coarse coating grains, the substantially continuous intermediate layer, and the Al-rich intermetallic compound layer of the traditional hot-formed steel make the coating more brittle.

[0173] It should be noted that by adjusting the hot forming process, the thickness of the interdiffusion layer can be changed, thereby reducing the thickness of the intermediate layer, so that the coating has less than 6 layers. However, the presence of a double Al-rich intermetallic compound layer in the coating also meets the requirements of the double Al-rich intermetallic compound layer of the present application.

[0174] The coating structure after hot forming of the present application can be detected and observed by metallographic method. The sample after hot forming is cut into a sample of about 10 mm x 20 mm, and the 20 mm side length is perpendicular to the rolling direction, which is the rolling direction of the steel substrate during cold rolling of the strip steel. The observation surface is a 20 mm coating cross section. The sample is carefully polished to ensure that the surface layer is not damaged. The sample is soaked in 4% nitric acid alcohol for a certain period of time, such as 20 seconds, which can show the structure characteristics of the coating under an optical microscope. Taking a 1.0 mm sample as an example, 50 samples are detected cumulatively, and the distance between each point is at least 50 mm, that is, it is necessary to avoid taking more than one sample within a radius of 50 mm on the component for detection. According to the observation of the 20 mm coating cross section of each sample, the total length of the coating cross section observed under the microscope should be ≥1000 mm for at least 50 samples. It is necessary to avoid sampling at the edge of the component, and when the component is large enough, the sampling position should be ≥50 mm away from the edge; when the component size is not enough, the sampling position should be as close to the middle of the component as possible, or multiple components are used for verification. At least one of these samples has a double Al-rich intermetallic compound layer in one field of view (1000x), that is, it shows the 6-layer structure characteristics of the present application. However, when the cumulative total length required for detection (the cumulative length is the total length of the coating cross section observed under the microscope for at least 50 samples ≥1000 mm) is not reached, but it is found that there are, for example Figure 3The 6-layer structure feature of the material after hot forming can be considered to meet the structural requirements of the present application. Generally, 50 samples are cumulatively detected (cumulative length is the length of the plating layer cross section observed under a microscope for at least 50 samples cumulatively observed), the distance between each point is at least 50 mm, and at least 5 samples each have one field of view (1000 times) with the double-layer Al-rich intermetallic compound layer of the present application. As a preferred embodiment, 50 samples are cumulatively detected, the distance between each point is at least 50 mm, and at least 10 samples each have one field of view (1000 times) with the double-layer Al-rich intermetallic compound layer of the present application.

[0175] Since the range of optical microscope detection is small, it is not convenient to effectively reflect the actual structural features of the plating layer. GDOES (glow discharge optical spectrometer) can be used to analyze the plating layer after hot forming, and the Al, Si, and Fe content distribution in the plating layer obtained from the detection can be used to obtain the structural features of the plating layer. Figure 13 is the Si concentration distribution feature of the plating layer of the component of the present application after hot forming, Figure 14 is the Si concentration distribution feature of the plating layer of the conventional component after hot forming.

[0176] As shown in Figure 13 , a minimum valley of Si concentration is found from the surface to the steel substrate, and a common tangent 1 and a common tangent 2 can be drawn to the left and right of the valley, respectively. Above the two common tangents, peak 1, peak 2, peak 3, and peak 4 can be found away from the common tangents. There is a surface oxidation Si concentration peak in the range of about 0-0.2 μm from the surface, which is not one of the four peaks. These peaks refer to the peak value of the difference between the Y axis relative to the common tangent, that is, the peak value formed by subtracting the common tangent concentration value in the common tangent area from the detected concentration. The minimum valley is generally the second valley, but it can also be the first or third valley. Similarly, a common tangent 1 and a common tangent 2 can be drawn to the left and right of the second valley, respectively, and peak 1, peak 2, peak 3, and peak 4 can be found above each tangent relative to the distance between the common tangents.

[0177] The third peak can not be significant due to the influence of structural stability, which can be measured by increasing the sampling area of GDOES. Taking a sample with a material thickness of 1.0 mm as an example, when the single sampling diameter of GDOES is 4 mm, 100 sampling points are cumulatively detected, the distance between each point is at least 50 mm, that is, GDOES detection is avoided as much as possible within a radius of 50 mm. The area of each detection point is 12.56 mm 2 , that is, the area of at least 100 samples cumulatively detected is ≥1256 mm 2. Sampling should be avoided at the edge of the component, and when the component is large enough, the sample detection position should be at least 50 mm away from the edge; when the component size is not enough, the position should be as close to the middle of the component as possible, or multiple components are used for verification. At least one sampling point has the peak value 1, peak value 2, peak value 3 and peak value 4 characteristics of the present application. Generally, when the single sampling diameter of GDOES is 4 mm, 100 sampling points are cumulatively detected, and the distance between each point is at least 50 mm, and at least 5 sampling points have the peak value 1, peak value 2, peak value 3 and peak value 4 characteristics of the present application. As a preferred embodiment, when the single sampling diameter of GDOES is 4 mm, 100 sampling points are cumulatively detected, and the distance between each point is at least 50 mm, and at least 10 sampling points have the peak value 1, peak value 2, peak value 3 and peak value 4 characteristics of the present application. As a preferred embodiment, when the single sampling diameter of GDOES is 4 mm, 100 sampling points are cumulatively detected, and the distance between each point is at least 50 mm, and at least 20 sampling points have the peak value 1, peak value 2, peak value 3 and peak value 4 characteristics of the present application. Further as a preferred embodiment, when the single sampling diameter of GDOES is 4 mm, 100 sampling points are cumulatively detected, and the distance between each point is at least 50 mm, and at least 50 sampling points have the peak value 1, peak value 2, peak value 3 and peak value 4 characteristics of the present application.

[0178] As Figure 14 , a common tangent line 1 can be drawn to the left of the valley bottom near the valley between the surface and the steel substrate. However, when looking for a tangent point to the right of the valley bottom, in addition to the interface between the coating and the substrate, no other significant tangent point can be found. Therefore, only peak value 1, peak value 2 and peak value 3 can be found above the common tangent line 1, which are away from the common tangent line. There is a surface oxidation Si concentration peak in the range of about 0-0.2 μm from the surface, which is not one of the three peaks. The lowest valley is generally the second valley, and it can also be the first valley. Similarly, a common tangent line can be drawn to the right of the valley bottom, and peak value 1, peak value 2 and peak value 3 can be found. From the outside to the inside of the microstructure, peak value 1 corresponds to the Al-rich intermetallic compound in the surface layer, peak value 2 corresponds to the Al-rich intermetallic compound layer, and peak value 3 corresponds to the Al-rich intermetallic compound between the interdiffusion layer and the intermediate layer (i.e. the surface of the interdiffusion layer).

[0179] When GDOES is used for detection, the cumulative detection area should be ≥1000 mm 2 , that is, when the single sampling diameter of GDOES is 4 mm, more than 100 sampling points are cumulatively detected, and the distance between each point is at least 50 mm, which can meet the detection requirements. However, when the cumulative total area required for detection is not reached, it is found that there are Figure 13The material after hot forming can also be considered to meet the structural requirements of the present application.

[0180] The present application has at least four peaks of Si concentration, i.e. peak 1, peak 2, peak 3 and peak 4. From the outside to the inside in the microstructure, peak 1 corresponds to the Al-rich intermetallic compound in the surface layer, peak 2 corresponds to the second layer of Al-rich intermetallic compound, peak 3 corresponds to the first layer of Al-rich intermetallic compound, and peak 4 corresponds to the Al-rich intermetallic compound between the interdiffusion layer and the first layer (i.e. the surface of the interdiffusion layer). There is a peak of Si concentration of surface oxidation in the range of about 0-0.2 μm from the surface, which is not one of the four peaks. Therefore, the peak 2 and peak 3 (double-layer Al-rich intermetallic compound layer) of the present application replace the conventional single-layer Al-rich intermetallic compound layer, reduce the segregation of Si concentration in the plating layer, improve the toughness of the plating layer and the crack sensitivity of the steel substrate, and further improve the bending performance of the material. On the other hand, the double-layer Al-rich intermetallic compound layer with high Si concentration not only refines the plating layer grains, but also blocks the entry of hydrogen elements, further improving the hydrogen embrittlement resistance of the material. This is because during the hot forming process, the small plating layer grains and the double-layer Al-rich intermetallic compound layer with high Si concentration are not conducive to the diffusion of external hydrogen into the steel substrate. The conventional single-layer Al-rich intermetallic compound not only leads to the coarsening of the plating layer grains, but also cannot block the diffusion of hydrogen into the steel substrate.

[0181] For the surface layer after hot forming, the present application has the effect of inward migration of the Al-rich intermetallic compound in the surface layer, so that the amount of Al-rich intermetallic compound exposed or close to the surface is reduced, and the surface layer is more uniform compared to the prior art. Figure 13 and Figure 14It is known that the Si concentration peak 1 in the hot formed coating of the present application is at a distance of 1.50 μm from the surface, while the Si concentration peak 1 in the hot formed coating of the conventional coating is at a distance of about 0.25 μm from the surface. This change can significantly improve the structural compactness of the coating surface, and is beneficial to improve the coating toughness and hydrogen resistance. It is obvious that this compact coating structure is also beneficial to improve the environmental corrosion resistance of the hot formed coating, because the inward migration of the Al-rich intermetallic compounds in the surface layer of the present application leaves less Al-rich intermetallic compounds on the surface, thereby reducing the number of effective primary cells formed by the Al-rich intermetallic compounds and the nearby coating, and reducing the reaction rate of the coating in the environment. In the neutral salt spray test, the present application has more excellent corrosion resistance than the conventional coating. Generally, the first peak value (peak 1) of Si concentration in the coating of the present application is at a distance of ≥0.25 μm from the surface. As a preferred embodiment, the first peak value (peak 1) of Si concentration in the coating of the present application is at a distance of ≥0.45 μm from the surface. As a preferred embodiment, the first peak value (peak 1) of Si concentration in the coating of the present application is at a distance of ≥0.75 μm from the surface. Another method for calculating the peak concentration is to obtain the peak value data by subtracting the background. Related software can be used for operation (such as Origin). After obtaining the background curve, the original data is subtracted from the background curve to obtain the required peak curve. Through this method, the influence of peak value on material performance can be effectively evaluated. In order to facilitate calculation and description, the background curve of the present application is the common tangent 1 and common tangent 2 cut below the Si concentration curve of the coating. It should be noted that after subtracting the background, there is a small false peak value at the lowest valley depth. This sharp peak is caused by the calculation method, and it appears after the intersection of the two common tangents deviates from the lowest valley value. This false peak value should be removed and not considered. Generally, after subtracting the background, the peak value reaches more than 4, and when the minimum peak concentration value is ≥0.01%, the segregation of Si in the coating can be alleviated, the coating toughness and hydrogen resistance of the material can be improved, and the corrosion resistance of the coating can be significantly improved. As a preferred embodiment, after subtracting the background, the peak value reaches more than 4, and the minimum peak concentration value is ≥0.025%. As a preferred embodiment, after subtracting the background, the peak value reaches more than 4, and the minimum peak concentration value is ≥0.05%, which can effectively improve the bending and hydrogen resistance of the material. Further, as a preferred embodiment, after subtracting the background, the peak value reaches more than 4, and the minimum peak concentration value is ≥0.25%, which can significantly improve the bending and hydrogen resistance of the material. Due to the error between the accuracy of each detection equipment, there will be differences in the detection results, but when the equipment accuracy is sufficient, the number of peaks will not change.

[0182] When the coating thickness before hot forming is less than 19 μm, it is difficult to form the double-layer Al-rich intermetallic compound layer of the present application in process control, and the thickness of each layer is significantly thinned, and the hydrogen resistance is decreased. These are one of the reasons why the present application recommends a pre-coating layer of more than 19 μm.

[0183] By reducing the thickness of the plating layer, the thickness of the surface layer can be removed or reduced, or the continuity of the surface layer is reduced, so that the plating layer has a 5-layer structure, but the plating layer still has the double-layer intermediate layer and the double-layer Al-rich intermetallic compound layer of the present application, and also meets the requirements of the double-layer Al-rich intermetallic compound layer of the present application.

[0184] Preferably, the first Al-rich intermetallic compound layer accounts for 1-50% of the length of the layer. The second Al-rich intermetallic compound layer accounts for ≥50% of the continuous length of the layer. More preferably, the second Al-rich intermetallic compound layer accounts for 50-90% of the continuous length of the layer.

[0185] In some embodiments, the plating layer of the component further comprises a surface layer located outside the second Al-rich intermetallic compound layer.

[0186] In some embodiments, the grain size of the first intermediate layer, the second intermediate layer, and the surface layer is ≤30 μm. Preferably, the grain size of the first intermediate layer, the second intermediate layer, and the surface layer is ≤25 μm. More preferably, the grain size of the first intermediate layer, the second intermediate layer, and the surface layer is ≤15 μm.

[0187] In some embodiments, the total thickness of the plating layer of the component is 5-60 μm. Preferably, the total thickness of the plating layer of the component is 20-55 μm. Preferably, the total thickness of the plating layer of the component is 26-50 μm. Further preferably, the total thickness of the plating layer of the component is 30-50 μm.

[0188] The present application also discloses a production process of a hot-formed component, comprising the following steps:

[0189] The above-mentioned aluminum-silicon plated steel or the above-mentioned pre-coated steel is heated to the austenite region, the holding temperature range is 880-950 ℃, and the holding time is 3-15 minutes. The heating atmosphere is air, and the dew point in the austenitizing furnace is ≤0 ℃.

[0190] The cooled steel plate is taken out of the furnace, and the heated steel plate is transferred to the stamping machine within 10 seconds, and then deformed by pressing with a mold while being cooled to below 200 ℃.

[0191] Specifically, the pre-plating steel plate is heated to the austenite region, the holding temperature range is 880-950 ℃, and the holding time is 3-15 minutes. The austenitizing furnace is filled with air, and the dew point in the austenitizing furnace is ≤0 ℃. The cooled steel plate is taken out of the furnace, and the heated steel plate is transferred to the stamping machine within 10 seconds, and then deformed by pressing with a mold while being cooled to below 200 ℃.

[0192] During the hot forming process, the surface aluminum flowers of the pre-plating layer will decompose, oxidize and reorganize, and the alloying will occur inside the plating layer. However, the surface of the component after the hot forming can be seen the aluminum flower pattern with the average area ≥ 16mm 2 of the hot-dip plating finishing process (also known as leveling) has a certain influence on the clarity of the aluminum flowers after the hot forming. When the leveling elongation increases, the identification of the aluminum flowers after the hot forming decreases. Similarly, the mold pressure of the hot forming process has a great influence on the clarity of the aluminum flowers after the hot forming. When the pressure increases, the identification of the aluminum flowers decreases. The surface of the component after the hot forming and the lower stamping mold also cannot identify the aluminum flowers. However, after the surface is polished by sandpaper (such as 1200 mesh), the pattern left by the aluminum flowers after the hot forming can be seen. Or adjust the light source parameters to facilitate observation.

[0193] The total thickness of the plating layer of the component after the hot forming is 5μm-60μm. As preferred, the total thickness of the plating layer of the component after the hot forming is 20μm-55μm. As preferred, the total thickness of the plating layer of the component after the hot forming is 26μm-50μm. Further as preferred, the total thickness of the plating layer of the component after the hot forming is 30μm-50μm.

[0194] The application further discloses a motor vehicle comprising the hot-formed component.

[0195] The technical solutions in the application will be clearly and completely described below in combination with the embodiments in the application. Obviously, the described embodiments are only some of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all the other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the application.

[0196] Embodiment 1

[0197] The following steel substrate to be plated is provided with the following chemical composition, and the material thickness is 1.5mm.

[0198] Table 1 Chemical composition of the steel substrate to be plated, in terms of wt.%

[0199] C Si Mn P S Al B Cr Ti Nb N 0.36 0.49 1.09 0.012 0.0003 0.034 0.0033 0.33 0.018 0.022 0.0051

[0200] The steel substrate to be plated provided in Table 1 is cleaned, dried, and then heated to the required annealing temperature for heat preservation. In this embodiment, the annealing temperature is 800℃, and the heat preservation time is 10 minutes.

[0201] The steel substrate to be plated provided in Table 1 is cooled, and the temperature of the steel substrate to be plated before entering the aluminum pot is controlled to be between 600-700℃, and in this embodiment, the temperature is 660℃.

[0202] The aluminum pot composition by mass fraction meets: Si: 8-11%; Fe: 1-4%; the rest is Al and inevitable impurities. The Si content of the aluminum pot of the present embodiment is 10%, the Fe content is 1.5%, and the rest is Al and inevitable impurities.

[0203] After the steel substrate to be plated is hot-dip plated, the excess plating solution is removed by using an air knife (a known technique) to obtain a pre-plated strip steel, and the thickness of the plating layer of the strip steel (the plating layer before hot forming is called a pre-plated layer) is 25 μm.

[0204] The strip steel after hot-dip plating of aluminum-silicon is cooled in two stages. The first stage of cooling is carried out after the plating layer of the strip steel is controlled until it is cooled to 570°C. The second stage of cooling is carried out from 570°C of the strip steel until it is cooled to 300°C. The cooling rate is shown in Table 2. The third stage of cooling: the strip steel is cooled from 300°C to room temperature by using air and / or water.

[0205] The Al-Si phase and the Al-Si-Fe phase of the steel coils numbered 1-5 are relatively coarse, and the dispersion index is relatively high. The aluminum-silicon plating layer should contain the Al-Si phase in a proportion of 20-40%, and the Al-Si phase includes Al n Si m phase. Wherein n:m=(1.0-3.0):1. The Al n Si m phase in the Al-Si phase is ≥50%; the aluminum-silicon plating layer should contain the Al-Si-Fe phase in a proportion of 5-15%. The Al-Si-Fe phase includes Fe a Si b Al c phase; wherein a:b:c=(1-2):1:(4-9); the Fe a Si b Al c phase in the Al-Si-Fe phase is ≥50%.

[0206] The Al-Si phase and the Al-Si-Fe phase of the steel coils numbered 6-7 are relatively fine, and the dispersion index is relatively low. The aluminum-silicon plating layer should contain the Al-Si phase in a proportion of 5-30%, and the Al-Si phase includes Al n Si m phase. Wherein n:m=(1.0-3.0):1. The Al n Si m phase in the Al-Si phase is ≥50%; the aluminum-silicon plating layer should contain the Al-Si-Fe phase in a proportion of 0.1-8%. The Al-Si-Fe phase includes Fe a Si b Al c phase; wherein a:b:c=(1-2):1:(4-9); the Fea Si b Al c The proportion of the phase in the Al-Si-Fe phase is ≥50%.

[0207] The Al-Si and Al-Si-Fe phases in steel coils numbered 8-10 are extremely fine, with low dispersion indices and are difficult to assess. The aluminum-silicon coating should contain ≤5% of the fine Al-Si phase, or these fine Al-Si phases should not be considered valid assessment targets. The aluminum-silicon coating should contain very little Al-Si-Fe; these fine Al-Si phases are not considered valid assessment targets.

[0208] Table 2 Coating Cooling Rate and Aluminum Flower Area

[0209]

[0210] like Figure 1 This is a typical surface aluminum flower morphology diagram. Figure 2 This is a typical image of surface aluminum flower marks after thermoforming. Figure 11 The aluminum flower area is ≥200mm² 2 (200~400mm) 2 ); Figure 12 The area of ​​the aluminum flower is ≤9mm 2 (4~9mm 2 ).

[0211] Examples of steel coils numbered 8-10 have insufficient aluminum run area and aluminum run crown, failing to meet the requirements of this invention. The aluminum run crown and aluminum run area of ​​coils numbered 1-7 meet the requirements of this invention.

[0212] It can be seen that the first stage of cooling largely determines the size of the aluminum flower area; the higher the cooling rate, the smaller the aluminum flower. The second stage also affects the size of the coated aluminum flower; the higher the cooling rate, the smaller the aluminum flower. Compared to the first stage, the cooling rate of the second stage has a smaller impact on the size of the aluminum flower.

[0213] Example 2

[0214] The steel substrate to be plated in Table 1 is cleaned and dried, and then heated to the required annealing temperature and held for 10 minutes. In this example, the temperature is 800°C.

[0215] The steel substrate to be plated in Table 1 is cooled, and the temperature of the steel substrate to be plated before entering the aluminum pot is controlled at 660℃.

[0216] In this embodiment, the aluminum pot contains 10% Si, 1.5% iron, and the remainder is Al and unavoidable impurities.

[0217] The excess plating solution is removed by air knife after hot dip plating of the steel substrate to be plated to obtain a pre-plated strip steel. The pre-plated thickness of the strip steel is controlled according to Table 3.

[0218] The strip steel after hot dip plating of aluminum silicon is cooled in two stages. The first stage of cooling is carried out after the completion of the coating control of the strip steel until it is cooled to 570°C at a cooling rate of 10°C / s. The second stage of cooling is carried out from 570°C of the strip steel until it is cooled to 300°C at a cooling rate of 10°C / s. The third stage of cooling: the strip steel is cooled from 300°C to room temperature by air and / or water.

[0219] Table 3 Pre-plated thickness and aluminum flower area

[0220]

[0221] It can be seen that the coating thickness has a certain influence on the aluminum flower area. This is mainly because the thinner the coating, the more nucleation points, and the more limited the aluminum flower dendrite growth. In summary, when the coating thickness is more than 10 μm, the aluminum flower area is ideal; when the coating thickness is more than 19 μm, the aluminum flower area is relatively stable; but when it exceeds 33 μm, the growth of the aluminum flower is not obvious.

[0222] Example 3

[0223] The steel substrate to be plated provided in Table 1 is cleaned, dried, and then heated to the desired annealing temperature for heat preservation. In this embodiment, the annealing temperature is 800°C, and the heat preservation time is 10 minutes.

[0224] The steel substrate to be plated provided in Table 1 is cooled, and the temperature of the steel substrate to be plated before entering the aluminum pot is controlled to be 660°C.

[0225] The Si content of the aluminum pot in this embodiment is 10%, the Fe content is 1.5%, and the rest is Al and unavoidable impurities.

[0226] The excess plating solution is removed by air knife after hot dip plating of the steel substrate to be plated to obtain a pre-plated strip steel. The pre-plated thickness of the strip steel is controlled according to Table 4.

[0227] The strip steel after hot dip plating of aluminum silicon is cooled in two stages. The first stage of cooling is carried out after the completion of the coating control of the strip steel until it is cooled to 570°C. The second stage of cooling is carried out from 570°C of the strip steel until it is cooled to 300°C. The third stage of cooling: the strip steel is cooled from 300°C to room temperature by air and / or water.

[0228] The pre-plated steel plate is heated to the austenite range, the holding range is 900℃, the holding time is 8 minutes. The austenitizing furnace is air, the dew point in the austenitizing furnace is ≥0℃, the dew points of each sample are controlled to be the same, and a certain amount of hydrogen is introduced into the austenitizing furnace. After holding, the steel plate is cooled, the time for taking out the heated steel plate from the furnace to the stamping machine is ≤10 seconds, and then the stamping machine is used for stamping and quenching, and the cooling is to below 200℃.

[0229] Table 4: The proportion of the first Al-rich intermetallic compound layer in the layer and the performance results obtained by different plating layer thicknesses and aluminum flower areas

[0230]

[0231]

[0232] Note: In order to obtain the three-point bending bending angle and four-point bending delayed cracking time of the material, the production process is adjusted in the experiment. It is only used to illustrate the performance improvement of the material of the present application, and does not represent the final service performance. The final service performance of the material is closely related to the hot forming process. The use of the material of the present application helps to improve the toughness and hydrogen embrittlement resistance of the material.

[0233] It can be seen that: the thicker the plating layer, the more conducive to obtaining the first Al-rich intermetallic compound layer, thereby improving the bending performance and enhancing the delayed cracking resistance. The larger the aluminum flower area, the more conducive to obtaining the first Al-rich intermetallic compound layer, thereby improving the bending performance and enhancing the delayed cracking resistance. The use of plating layer stamping is conducive to obtaining the first Al-rich intermetallic compound layer, and the delayed cracking resistance is also stronger.

[0234] Except that the T1 sample does not meet the requirements of the first Al-rich intermetallic compound layer of the present application, the other samples meet the hot forming thickness plating layer structure requirements. The plating layer of the hot formed component of the other samples includes (a) interdiffusion layer; (b) first intermediate layer; (c) first Al-rich intermetallic compound layer; (d) second intermediate layer; (e) second Al-rich intermetallic compound layer; (f) surface layer.

[0235] The plating layer structure of the sample after hot forming is analyzed. As Figure 3 is the plating layer diagram of T8 after hot forming, and the plating layer presents the typical 6-layer structure of the hot formed steel of the present application after hot forming. As Figure 4 is the plating layer diagram of T9 after hot forming, and the plating layer is the 4-layer structure of the existing hot formed steel after hot forming.

[0236] 2% tensile deformation is performed on the hot formed T8 and T9, and the plating layer crack morphology is observed. As Figure 5T8 is a diagram of the coating of the inventive hot formed after deformation, the coating is a hot formed steel with two layers of Al-rich intermetallic compounds. After deformation, the interdiffusion layer is plastic, the crack does not penetrate the interdiffusion layer, but the steel substrate has cracks.

[0237] As Figure 6 T9 is a diagram of the coating of the conventional hot formed after deformation, the coating is a hot formed steel with one layer of Al-rich intermetallic compounds. After deformation, the interdiffusion layer is fragmented, but the steel substrate is intact without cracks.

[0238] Figure 8 T10 is a diagram of the coating structure of the inventive hot formed component, the two layers of Al-rich intermetallic compounds divide the coating, the grains in the coating are finer, and the fine grains in the coating. The average grain size is less than or equal to 25 μm.

[0239] Figure 9 T11 is a diagram of the coating structure of the conventional hot formed component after hot forming, the grains in the coating are coarse. The average grain size is greater than or equal to 20 μm, especially the grains in the intermediate layer are coarse, and the maximum size of the cross section can exceed 30 μm. The grains in the intermediate layer penetrate through most of the coating, and the adverse effects of such coarse structure on the performance of the coating are significant.

[0240] Example 4

[0241] The steel substrate to be plated provided in Table 1 is cleaned, dried, and then heated to the desired annealing temperature for heat preservation, and in this example, the temperature is 800 °C, and the heat preservation time is 10 minutes.

[0242] The steel substrate to be plated provided in Table 1 is cooled, and the temperature of the steel substrate before entering the aluminum pot is controlled to be 660 °C.

[0243] The Si content of the aluminum pot in this example is 10%, the Fe content is 1.5%, and the rest is Al and unavoidable impurities.

[0244] Materials T14 to T17 with different dispersion indexes of Al-Si and Fe-Al-Si phases in the coating required for the experiment are prepared by the method of the present application, and the hot forming process is performed on these pre-coating samples. The hot forming process used in this example is that the heat preservation temperature is 930 °C, and the heat preservation time is 5 minutes. The austenitizing furnace is air, the dew point in the austenitizing furnace is ≥0 °C, the dew points of the samples are controlled to be the same, and a certain amount of hydrogen is introduced into the austenitizing furnace.

[0245] The Si concentration of the coating of the samples is detected by GDOES, and the required Si concentration peak data is obtained after deducting the background. The coating structure, peak data and related performance results of these materials are shown in Table 5.

[0246] It can be seen that the dispersion index of the embodiment is more favorable to form the Al-rich intermetallic compound layer of the required double layer of the application, that is, four Si concentration peaks appear. Further, the higher Si concentration peak is favorable to improve the bending angle and the resistance to delayed cracking of the material.

[0247] The neutral salt spray test method was used to study samples T14 to T17. The results show that all the test samples have slight red rust after 2 hours; the red rust area of T14 is larger after 12 hours, about 80%; the red rust area of T15 is about 60%, and the red rust area of T16 and T17 is about 50%. The samples were taken out and dried after 72 hours of salt spray test, and the unit area weight gain data of the samples was measured as shown in Table 5. The unit area weight gain reflects the oxidation degree of the plating layer in the oxidation environment, that is, the weight gain of the plating layer after obtaining oxygen and other elements. It can be seen that the weight gain caused by oxidation of the sample satisfying the four Si concentration peaks of the application is significantly lower than that of the sample with three Si concentration peaks. The higher the minimum Si concentration peak, the smaller the unit area weight gain; when the minimum Si concentration peak is more than 0.10%, the unit area weight gain is less than 2.7 mg / cm 2 It can be seen that the complete six-layer structure (four Si concentration peaks) after thermoforming can significantly improve the corrosion resistance of the plating layer.

[0248] Table 5 Influence of different dispersion indexes on the plating layer and performance

[0249]

[0250]

[0251] The above technical solutions of the application are only preferred embodiments of the application, and do not limit the patent scope of the application. Any equivalent structural transformation made by using the content of the specification and drawings, or direct / indirect application in other related technical fields is included in the patent protection scope of the application.

[0252] The present application discloses the following notes:

[0253] Note 1. An aluminum-silicon plated steel, characterized in that it comprises a steel base body and a pre-plating layer arranged on the steel base body.

[0254] The pre-plating layer comprises an intermediate layer and an aluminum-silicon plating layer; the nominal thickness of the aluminum-silicon plating layer is 10-33 μm; the aluminum-silicon plating layer contains Al-Si phase in a proportion of 5-40% and Al-Si-Fe phase in a proportion of 0.1-15%, and the dispersion index of the Al-Si phase and the Al-Si-Fe phase in the aluminum-silicon plating layer is ≥0.05.

[0255] The mass fraction of silicon in the Al-Si phase is 30-50%; the mass fraction of iron in the Al-Si-Fe phase is 10-35%, and the mass fraction of silicon is 3-15%.

[0256] Clause 2. The aluminized silicon steel according to Clause 1, characterized in that the aluminum-silicon coating layer contains the Al-Si phase in a proportion of 10-30% and the Al-Si-Fe phase in a proportion of 0.1-10%.

[0257] Clause 3. The aluminized silicon steel according to Clause 1, characterized in that the Al-Si phase includes the Al n Si m phase; wherein n:m=(1.0-3.0):1; the proportion of the Al n Si m phase in the Al-Si phase is ≥50%.

[0258] Clause 4. The aluminized silicon steel according to Clause 1, characterized in that the Al n Si m phase includes at least one of Al 4 Si 3 and Al 4 Si 2.

[0259] Clause 5. The aluminized silicon steel according to Clause 1, characterized in that the Al-Si-Fe phase includes the Fe a Si b Al c phase; wherein a:b:c=(1-2):1:(4-9); the proportion of the Fe a Si b Al c phase in the Al-Si-Fe phase is ≥50%.

[0260] Clause 6. The aluminized silicon steel according to Clause 5, characterized in that the Fe a S i b Al c phase includes the Fe Si Al 4 phase and the Fe 2 Si Al 7 phase.

[0261] Clause 7. An aluminized silicon steel, characterized in that it comprises a steel base body and a pre-coating layer arranged on the steel base body; the pre-coating layer comprises an intermediate layer and an aluminum-silicon coating layer;

[0262] The aluminum-silicon coating layer includes aluminum flowers; the nominal thickness of the aluminum-silicon coating layer is 10-20 μm, and the condition that the coordinate points formed by the aluminum flower area in mm 2 and the aluminum flower convexity in μm satisfy that the coordinate points are located in a first convex pentagon, and the first convex pentagon is formed by five points (2, 3), (150, 3), (350, 7), (350, 35), (2, 35).

[0263] Para 8. The aluminum-silicon plated steel according to Para 7, characterized in that the aluminum-silicon plated layer comprises aluminum flowers; the nominal thickness of the aluminum-silicon plated layer is 19-33 μm, and the aluminum flowers satisfy the condition that the coordinate points formed by the aluminum flower area in mm 2 and the aluminum flower convexity in μm are located within a second convex pentagon, the second convex pentagon being formed by the five points (4, 5), (170, 5), (400, 12), (400, 40), and (4, 40).

[0264] Para 9. The aluminum-silicon plated steel according to Para 7, characterized in that the aluminum-silicon plated layer comprises aluminum flowers; the nominal thickness of the aluminum-silicon plated layer is 10-20 μm, and the aluminum flowers satisfy the condition that the unit area aluminum flower boundary length in 1 / mm and the aluminum flower convexity in μm form coordinate points located within a third convex pentagon, the third convex pentagon being formed by the five points (0.1, 7), (0.17, 3), (10, 3), (10, 35), and (0.1, 35).

[0265] Para 10. The aluminum-silicon plated steel according to Para 7, characterized in that the aluminum-silicon plated layer comprises aluminum flowers; the nominal thickness of the aluminum-silicon plated layer is 19-33 μm, and the aluminum flowers satisfy the condition that the unit area aluminum flower boundary length in 1 / mm and the aluminum flower convexity in μm form coordinate points located within a fourth convex pentagon, the fourth convex pentagon being formed by the five points (0.08, 12), (0.16, 5), (8, 5), (8, 40), and (0.08, 40).

[0266] Para 11. A method for preparing an aluminum-silicon plated steel, characterized by comprising the following steps:

[0267] After annealing the steel substrate to be plated, the steel substrate to be plated is immersed in a plating solution to obtain an immersed steel substrate; the plating solution comprises, in mass percent: Si: 8-11%; Fe: 1-4%; and the balance being Al and unavoidable impurities;

[0268] The immersed steel substrate is cooled at a rate of 2-20°C / s to 570-650°C and maintained at 570-650°C for 1-20 seconds to obtain a first-cooled immersed steel;

[0269] The first-cooled immersed steel is cooled in a temperature adjusting device under the condition of a heating gas to an average cooling rate of 5-25°C / s to 300°C, with a holding time of 2-30 seconds, to obtain a second-cooled immersed steel; the temperature adjusting device has a temperature of 300-570°C; the heating gas has a temperature of ≥100°C and a total suspended particulate of ≤0.2 mg / m 3 ;

[0270] The second-cooled immersed steel is cooled to room temperature to obtain a pre-plated steel.

[0271] Para 12. The method for preparing the aluminized silicon steel according to Para 11, characterized in that the initial cooling of the plated steel substrate is performed at a rate of 2-15 °C / s to 570 °C and maintained at 570 °C for 1-10 seconds to obtain the initial cooling plated steel.

[0272] Para 13. The method for preparing the aluminized silicon steel according to Para 11, characterized in that the initial cooling of the initial cooling plated steel is performed at an average cooling rate of 5-20 °C / s to 300 °C and maintained for 2-20 seconds to obtain the secondary cooling plated steel.

[0273] Para 14. The method for preparing the aluminized silicon steel according to any one of Paras 11-13, characterized in that the annealing temperature in the annealing step of the steel substrate to be plated is 700-850 °C and the annealing time is 1-20 minutes; and the temperature of the annealed steel substrate to be plated when entering the plating bath is 600-700 °C.

[0274] Para 15. A pre-coated steel, characterized in that the pre-coated steel comprises a cold-rolled and / or bright-finished aluminized silicon steel; the pre-coated steel comprises a steel substrate and a bright-finished plated layer disposed on the steel substrate; the bright-finished plated layer is obtained by one of cold rolling and bright finishing;

[0275] the bright-finished plated layer comprises an intermediate layer and an aluminum-silicon plated layer; the nominal thickness of the aluminum-silicon plated layer is 10-33 μm; the aluminum-silicon plated layer contains an Al-Si phase in a proportion of 5-40% and an Al-Si-Fe phase in a proportion of 0.1-15%, and the dispersion index of the Al-Si phase and the Al-Si-Fe phase in the aluminum-silicon plated layer is ≥0.05;

[0276] wherein the mass fraction of silicon in the Al-Si phase is 30-50%; and the mass fraction of iron in the Al-Si-Fe phase is 10-35% and the mass fraction of silicon is 3-15%.

[0277] Para 16. A hot-formed component, characterized in that it comprises a steel substrate and a component plated layer; the component plated layer is generated by interdiffusion between the steel substrate and an aluminum-silicon pre-coated layer during hot forming.

[0278] the component plated layer comprises, in sequence, an interdiffusion layer, a first intermediate layer, a first Al-rich intermetallic compound layer, a second intermediate layer, and a second Al-rich intermetallic compound layer; the interdiffusion layer is located at the innermost side of the component plated layer.

[0279] the first Al-rich intermetallic compound layer is in a discontinuous structure and occupies a proportion of ≤80% of the length of the layer; and the second Al-rich intermetallic compound layer is in a quasi-continuous structure and occupies a proportion of ≥20% of the continuous length of the layer.

[0280] Clause 17. The hot formed component according to clause 16, characterized in that the first Al-rich intermetallic compound layer has a proportion of 1-50% of the length of the layer; the second Al-rich intermetallic compound layer has a proportion of > 50% of the length of the layer.

[0281] Clause 18. The hot formed component according to clause 17, characterized in that the second Al-rich intermetallic compound layer has a proportion of 50-90% of the length of the layer.

[0282] Clause 19. The hot formed component according to any one of clauses 16-18, characterized in that the component coating further comprises a surface layer outside the second Al-rich intermetallic compound layer.

[0283] Clause 20. The hot formed component according to clause 19, characterized in that the first intermediate layer, the second intermediate layer, the surface layer have an average grain size of < 30 pm.

[0284] Clause 21. The hot formed component according to clause 20, characterized in that the first intermediate layer, the second intermediate layer have an average grain size of < 25 pm.

[0285] Clause 22. The hot formed component according to clause 21, characterized in that the first intermediate layer, the second intermediate layer have an average grain size of < 15 pm.

[0286] Clause 23. The hot formed component according to any one of clauses 16-18, characterized in that the total thickness of the component coating is 5-60 pm.

[0287] Clause 24. The hot formed component according to clause 23, characterized in that the total thickness of the component coating is 20-55 pm.

[0288] Clause 25. The hot formed component according to clause 24, characterized in that the total thickness of the component coating is 26-50 pm.

[0289] Clause 26. The hot formed component according to clause 25, characterized in that the total thickness of the component coating is 30-50 pm.

[0290] Clause 27. A hot formed component, characterized by a steel substrate and a component coating; the component coating is produced by interdiffusion of the steel substrate and an aluminum-silicon pre-coating during hot forming;

[0291] The component coating has at least four peaks of Si concentration in the thickness direction.

[0292] Note 28. The hot formed component according to Note 27, characterized in that the at least four Si concentration peaks comprise a first Si concentration peak, a second Si concentration peak, a third Si concentration peak and a fourth Si concentration peak from the component's plated surface to the steel substrate.

[0293] The first Si concentration peak is > 0.25 pm from the component's plated surface.

[0294] Note 29. The hot formed component according to Note 28, characterized in that the first Si concentration peak is > 0.45 pm from the component's plated surface.

[0295] Note 30. The hot formed component according to Note 29, characterized in that the first Si concentration peak is > 0.75 pm from the component's plated surface.

[0296] Note 31. The hot formed component according to Note 30, characterized in that the first Si concentration peak is > 1.5 pm from the component's plated surface.

[0297] Note 32. The hot formed component according to Note 27, characterized in that the at least four Si concentration peaks, excluding background, have a minimum peak concentration value > 0.01%.

[0298] Note 33. The hot formed component according to Note 32, characterized in that the minimum peak concentration value is > 0.025%.

[0299] Note 34. The hot formed component according to Note 33, characterized in that the minimum peak concentration value is > 0.05%.

[0300] Note 35. The hot formed component according to Note 34, characterized in that the minimum peak concentration value is > 0.25%.

[0301] Note 36. A process for producing a hot formed component, characterized by the steps of:

[0302] heating the aluminum-silicon plated steel according to any one of Notes 1 to 10 or the pre-coated steel according to Note 15 to the austenite region, with a holding temperature range of 880 to 950 °C and a holding time of 3 to 15 minutes; the heating atmosphere is air with a dew point < 0 °C;

[0303] cooling the steel sheet after holding and taking out the heated steel sheet to deform using a die within 10 s while cooling to below 200 °C.

[0304] Note 37. A motor vehicle, characterized by comprising the hot formed component according to any one of Notes 16 to 35.

Claims

1. A thermoformed component, characterized in that, It includes a steel substrate and a component coating; the component coating is produced by the steel substrate and an aluminum-silicon pre-coating layer through mutual diffusion during the thermoforming process; The component coating comprises sequentially stacked interdiffusion layers, a first intermediate layer, a first Al-rich intermetallic compound layer, a second intermediate layer, a second Al-rich intermetallic compound layer, and a surface layer; the interdiffusion layer is located at the innermost side of the component coating. The first Al-rich intermetallic compound layer has a discontinuous structure, accounting for ≤80% of the length of the layer; the second Al-rich intermetallic compound layer has a quasi-continuous structure, accounting for ≥20% of the continuous length of the layer. The component coating has, along its thickness direction, respectively, corresponding to: The Al-rich intermetallic compounds within the surface layer, The second Al-rich intermetallic compound layer, The first Al-rich intermetallic compound layer, At least four Si concentration peaks of the Al-rich intermetallic compound between the interdiffusion layer and the first intermediate layer.

2. The thermoformed component according to claim 1, characterized in that, The at least four Si concentration peaks include a first Si concentration peak, a second Si concentration peak, a third Si concentration peak, and a fourth Si concentration peak from the surface of the component coating to the steel substrate; The distance between the first peak Si concentration and the surface of the component coating is ≥0.25μm.

3. The thermoformed component according to claim 2, characterized in that, The distance between the first peak Si concentration and the surface of the component coating is ≥0.45μm.

4. The thermoformed component according to claim 3, characterized in that, The distance between the first peak Si concentration and the surface of the component coating is ≥0.75μm.

5. The thermoformed component according to claim 4, characterized in that, The distance between the first Si concentration peak and the surface of the component coating is ≥1.5μm.

6. The thermoformed component according to claim 1, characterized in that, The minimum Si concentration peak, after subtracting the background, has a concentration value ≥ 0.01 wt%.

7. The thermoformed component according to claim 6, characterized in that, The minimum peak concentration is ≥0.025% by weight.

8. The thermoformed component according to claim 7, characterized in that, The concentration of the minimum peak value is ≥0.05% by weight.

9. The thermoformed component according to claim 8, characterized in that, The concentration of the minimum peak value is ≥0.25% by weight.

10. The thermoformed component according to any one of claims 1 to 9, characterized in that, The method for obtaining the at least four Si concentration peaks includes: Find the lowest Si concentration valley between the component coating and the steel substrate. Draw two common tangents to the left and right of the curve at this valley. Above the two common tangents, find the first Si concentration peak, the second Si concentration peak, the third Si concentration peak, and the fourth Si concentration peak, which are far from the common tangents.

11. The thermoformed component according to claim 10, characterized in that, The at least four Si concentration peaks do not include Si concentration peaks where surface oxidation exists within a distance of 0–0.2 μm from the surface.

12. A motor vehicle, characterized in that, Includes the thermoformed component according to any one of claims 1 to 11.

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