High-performance dual-phase steel DP590 and preparation method thereof

Abstract

The invention provides high-performance dual-phase steel DP590 and a preparation method thereof, and relates to the technical field of steel preparation. The method comprises the following steps: obtaining a continuous casting billet; the continuous casting blank is subjected to hot rolling, and a hot-rolled coil is obtained; the hot-rolled coil is subjected to cold rolling, and strip steel with the set thickness is obtained; the strip steel is subjected to annealing treatment; and the strip steel obtained after annealing treatment is galvanized and leveled, and the high-performance dual-phase steel DP590 is obtained. The annealing treatment comprises a quick heating stage, a soaking stage and a quick cooling stage. The residual stress of the cold hard coil in the heating and soaking sections is eliminated, recrystallization occurs in the heating process, an equiaxed structure is obtained, and abnormal growth of crystal grains is avoided at a proper heating speed; the uniform heating process is beneficial to structure uniformity, the proportion of austenite to ferrite is regulated and controlled, enough martensite is obtained in the subsequent cooling process, and therefore a good strength and plasticity matching relation is obtained; the rapid cooling section enables the strip steel to complete the hot galvanizing process in the high-speed operation process, and reasonable austenite and ferrite contents are obtained, so that the performance of the dual-phase steel DP590 reaches the standard.

Description

Technical Field

[0001] The present application relates to the technical field of dual-phase steel preparation, and in particular to a high-performance dual-phase steel DP590 and a preparation method thereof. Background Art

[0002] In pursuit of lightweight production and energy conservation and environmental protection, the production of low-cost, high-performance and high-strength steel has become a research hotspot. Among them, the dual-phase steel DP590 composed of hard martensite and soft ferrite based on phase transformation strengthening has the characteristics of good strength-plasticity matching, low yield ratio and alloy cost. It is widely used in the manufacture of automobile bumpers, longitudinal beams, suspension systems and other components, and is one of the current dominant materials for automobile structural parts.

[0003] In the prior art, the preparation of hot-dip galvanized dual-phase steel DP590 mainly adopts the traditional process of molten iron pretreatment → converter steelmaking → refining outside the furnace → continuous casting → hot rolling → acid rolling → hot-dip galvanizing, and finally obtains galvanized sheet. The process focuses on controlling the cold rolling annealing temperature and the medium-temperature transformation temperature. The cold rolling annealing adopts the method of first rapid cooling to the medium-temperature transformation temperature, and then controlling the martensitic phase transformation in the cooling stage after plating, that is: heating → uniform heating → slow cooling → medium-temperature transformation → martensitic phase transformation (cooling after plating). The control process of cold rolling annealing and medium-temperature transformation temperature in this technology is complicated. At the same time, the more complicated the furnace zone process is, the longer the furnace zone length is, and the belt speed is reduced, which not only greatly increases the manufacturing cost, but also reduces the production efficiency, and fails to achieve the purpose of energy saving, environmental protection and efficient manufacturing. Summary of the invention

[0004] The present application provides a high-performance dual-phase steel DP590 and a preparation method thereof to solve the following technical problem: how to improve the preparation efficiency.

[0005] In a first aspect, the present invention provides a method for preparing high performance dual-phase steel DP590, comprising the following steps:

[0006] Obtaining a continuous casting billet;

[0007] hot rolling the continuously cast slab to obtain a hot rolled coil;

[0008] cold rolling the hot rolled coil to obtain a steel strip having a set thickness;

[0009] annealing the steel strip;

[0010] The annealed steel strip is galvanized and leveled to obtain high performance dual-phase steel DP590;

[0011] The step of annealing the steel strip comprises:

[0012] Heating the steel strip and controlling the heating rate and the end point temperature;

[0013] The heated steel strip is subjected to uniform heating, and the duration of the uniform heating is controlled;

[0014] The steel strip after being homogenized is rapidly cooled, and the cooling rate and the terminal temperature are controlled to perform annealing treatment on the steel strip.

[0015] Optionally, the set thickness is 1.0 mm to 1.6 mm.

[0016] Optionally, the duration of the soaking is 0.78 min to 0.94 min.

[0017] Optionally, the terminal temperature of the heating is 750°C to 800°C; and / or the heating rate does not exceed 3°C / s.

[0018] Optionally, the cooling end temperature is 450°C to 480°C, and the cooling rate is 10°C / s to 15°C / s.

[0019] Optionally, the chemical composition of the continuous casting billet, calculated by mass fraction, is: C: 0.10% to 0.14%, Si: 0.05% to 0.30%, Mn: 1.70% to 2.10%, P: ≤0.02%, S: ≤0.01%, Alt: 0.02% to 0.06%, Ti: 0.02% to 0.03% and Fe.

[0020] Optionally, hot rolling the continuously cast slab to obtain a hot rolled coil specifically comprises:

[0021] Heating and keeping the continuous casting billet warm;

[0022] The heated continuous casting slab is subjected to rough rolling and finish rolling to obtain a hot rolled coil;

[0023] The target temperature of the heating is 1100° C. to 1300° C.; the insulation time is 150 min to 200 min.

[0024] Optionally, the rough rolling temperature is 1000°C to 1100°C, and the finish rolling temperature is 850°C to 950°C.

[0025] Optionally, the galvanizing temperature is the same as the cooling end point temperature;

[0026] Optionally, the galvanizing temperature is 450°C to 480°C.

[0027] Optionally, the elongation of the flattening treatment is less than 0.5%.

[0028] In a second aspect, an embodiment of the present application provides a high performance dual-phase steel DP590 produced by the preparation method described in the first aspect.

[0029] Optionally, the performance of the high performance dual phase steel DP590 at least satisfies one of the following: yield strength R P0.2 340MPa~440MPa; tensile strength Rm>590MPa; elongation after fracture A80≥21%.

[0030] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0031] The embodiment of the present application provides a method for preparing high-performance dual-phase steel DP590 and a preparation method thereof, comprising the following steps: obtaining a continuous casting billet; hot rolling the continuous casting billet to obtain a hot-rolled coil; cold rolling the hot-rolled coil to obtain a strip steel with a set thickness; annealing the strip steel; galvanizing and leveling the strip steel after annealing to obtain high-performance dual-phase steel DP590; annealing the strip steel, including heating the strip steel so that the strip steel undergoes recrystallization during the heating process to obtain an equiaxed structure; and controlling the heating rate and the end temperature to avoid abnormal grain growth; uniformly heating the heated strip steel and controlling the duration of the uniform heating; which is conducive to uniform equiaxed structure, regulating the ratio of austenite and ferrite, so that sufficient martensite is obtained in the subsequent cooling process, so that the alloy obtains a good strength-plasticity matching relationship. Rapidly cool the uniformly heated strip steel, control the cooling rate and the end temperature, so that the strip steel obtains reasonable austenite and ferrite content, so that the finished product performance meets the standard, and obtains high-performance dual-phase steel DP590.

[0032] The annealing method adopted in the preparation method shortens the soaking stage, reduces the slow cooling stage, shortens the annealing time and distance, and makes the production equipment integration effect better. Through energy-saving and efficient preparation technology, low-cost and high-performance hot-dip galvanized duplex steel DP590 is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0035] Figure 1 A schematic flow chart of a method for preparing high-performance dual-phase steel DP590 according to some embodiments of the present application;

[0036] Figure 2A schematic diagram of an annealing process according to some embodiments of the present application;

[0037] Figure 3 Schematic diagram of the transverse and longitudinal organization of the dual-phase steel DP590 sample obtained in Example 1;

[0038] Figure 4 Schematic diagram of the transverse and longitudinal organization of the dual-phase steel DP590 sample obtained in Example 2;

[0039] Figure 5 Schematic diagram of the transverse and longitudinal organization of the dual-phase steel DP590 sample obtained in Comparative Example 1;

[0040] Figure 6 Schematic diagram of the transverse and longitudinal organization of the dual-phase steel DP590 sample obtained in Comparative Example 2;

[0041] Figure 7 Schematic diagram of the transverse and longitudinal organization of the dual-phase steel DP590 sample obtained in Comparative Example 3. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0043] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a rigid limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range; in addition, whenever a numerical range is indicated in this document, it is meant to include any cited numbers (fractions or integers) within the indicated range.

[0044] In this document, the terms including "including" and "including" mean "including but not limited to". Relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "plurality" means two or more; "at least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items; for example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. "Parts" such as parts by weight and parts by mass indicate the proportional relationship between the components. In the proportional relationship involved in this article, the parameters that need to be described by proportion should be understood as the first term of the proportional formula in the order of description, and the proportional numbers should be understood as the second term of the proportional formula. For example, if the mass ratio of substance A, substance B and substance C is 1:2:3, then substance A, substance B and substance C should correspond to the proportional numbers in the proportional formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0045] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this article can be purchased from the market or prepared by existing methods.

[0046] Figure 1 A schematic flow chart of a method for preparing high-performance dual-phase steel DP590 according to some embodiments of the present application;

[0047] like Figure 1 As shown, in the first aspect, the embodiment of the present application provides a method for preparing high-performance dual-phase steel DP590, comprising the following steps:

[0048] Obtaining a continuous casting billet;

[0049] hot rolling the continuously cast slab to obtain a hot rolled coil;

[0050] cold rolling the hot rolled coil to obtain a steel strip having a set thickness;

[0051] annealing the steel strip;

[0052] The annealed steel strip is galvanized and leveled to obtain high performance dual-phase steel DP590;

[0053] The step of annealing the steel strip comprises:

[0054] Heating the steel strip and controlling the heating rate and the end point temperature;

[0055] The heated steel strip is subjected to uniform heating, and the duration of the uniform heating is controlled;

[0056] The steel strip after being homogenized is rapidly cooled, and the cooling rate and the terminal temperature are controlled to perform annealing treatment on the steel strip.

[0057] In the above embodiment, the molten steel is solidified into a continuous casting billet through a continuous casting process for subsequent processing; the continuous casting billet is hot rolled to obtain a hot rolled coil. Hot rolling is to roll the continuous casting billet into a coil of a certain thickness and width through a rolling mill at high temperature. This step helps to improve the organizational structure and performance of the steel; the hot rolled coil is cold rolled. Cold rolling is to further roll the hot rolled coil at room temperature to obtain a strip with a thinner thickness and more precise size. Cold rolling can further improve the strength and hardness of the steel, while improving its surface quality and processing performance.

[0058] The annealing process includes rapid heating, soaking and rapid cooling stages. The strip is rapidly heated so that the strip undergoes recrystallization during the heating process to obtain an equiaxed structure. The heating rate and the end temperature of the heating are controlled to avoid abnormal grain growth. The heated strip is soaked and the soaking duration is controlled to facilitate uniform equiaxed structure and regulate the ratio of austenite and ferrite so that sufficient martensite is obtained during the subsequent cooling process, thereby obtaining a good strength-plasticity matching relationship for the alloy. The soaked strip is rapidly cooled, and the cooling rate and the end temperature of the cooling are controlled so that the strip obtains a reasonable content of austenite and ferrite, thereby achieving the performance standard of the finished product and obtaining high-performance dual-phase steel DP590.

[0059] The annealing method adopted in the preparation method shortens the soaking stage, reduces the slow cooling stage, shortens the annealing time and distance, and makes the production equipment integration effect better. Through energy-saving and efficient preparation technology, low-cost and high-performance hot-dip galvanized duplex steel DP590 is obtained.

[0060] As an optional implementation manner, the soaking time is 0.78 min to 0.94 min.

[0061] In the above-mentioned embodiment, the soaking process is conducive to uniform organization, regulating the ratio of austenite and ferrite, so that sufficient martensite is obtained in the subsequent cooling process, so that the steel obtains a good strength-plasticity matching relationship. The reason for controlling the duration of the soaking section to be 0.78min to 0.94min is that on the basis of ensuring the original organization type and performance, the soaking time is shortened to achieve the purpose of energy saving and consumption reduction. At the same time, the soaking section in the production equipment can be shortened by about 133m, and efficient production can achieve the purpose of cost reduction. Exemplarily, the soaking duration can be 0.78min, 0.77min, 0.78min, 0.79min, 0.80min, 0.81min, 0.82min, 0.83min, 0.84min, 0.85min, 0.86min, 0.87min, 0.88min, 0.89min, 0.90min, 0.91min, 0.92min, 0.93min and 0.94min.

[0062] As an optional implementation manner, the terminal temperature of the heating is 750-800°C; and the heating rate does not exceed 3°C / s.

[0063] In the above embodiment, the reason for controlling the terminal temperature of the heating section to 750°C to 800°C is that this temperature range is the ferrite + austenite two-phase region of the strip; illustratively, the terminal temperature of the heating can be 750°C, 755°C, 760°C, 765°C, 770°C, 775, 780°C, 785°C, 790°C, 795°C or 800°C.

[0064] The reason for controlling the heating rate not to exceed 3°C / s is to avoid abnormal grain growth. Exemplarily, the heating rate may be 0.5°C / s, 1°C / s, 1.5°C / s, 2.0°C / s, 2.5°C / s or 3°C / s.

[0065] As an optional implementation manner, the cooling end temperature is 450°C to 480°C, and the cooling rate is 10°C / s to 15°C / s.

[0066] In the above embodiment, the reason for controlling the terminal temperature of the rapid cooling section to be 450°C to 480°C is that the temperature difference between the strip out of the furnace and the zinc pot should not be too large. Exemplarily, the terminal temperature of the rapid cooling section can be 450°C, 455°C, 460°C, 465°C, 470°C, 475°C or 480°C. The reason for controlling the cooling rate to be 10°C / s to 15°C / s is that the cooling rate within this range can enable the steel coil to obtain a reasonable austenite and ferrite content, so that the performance of the finished product meets the standard. Exemplarily, the cooling rate can be 10°C / s, 11°C / s, 12°C / s, 13°C / s, 14°C / s or 15°C / s.

[0067] As an optional embodiment, the chemical composition of the dual-phase steel DP590, calculated by mass fraction, includes: C: 0.10% to 0.14%, Si: 0.05% to 0.30%, Mn: 1.70% to 2.10%, P: ≤0.02%, S: ≤0.01%, Alt: 0.02% to 0.06%, Ti: 0.02% to 0.03% and Fe.

[0068] In the above embodiment, the reason for controlling the carbon content in the dual-phase steel DP590 to be 0.10% to 0.14% is that the carbon element cooperates with other elements to balance the strength and plasticity of the steel matrix. For example, the carbon content in the dual-phase steel DP590 may be 0.10%, 0.11%, 0.12%, 0.13% or 0.14%.

[0069] The reason why the silicon content is 0.05% to 0.30% is that the silicon content in this range combined with other elements can improve the strength of the steel matrix. For example, the silicon content in the dual-phase steel DP590 can be 0.05%, 0.10%, 0.15%, 0.20%, 0.25% and 0.30%;

[0070] The reason why the content of manganese is 1.70% to 2.10% is that the manganese in this range can cooperate with other elements to improve the strength of the steel matrix and the processing performance of the steel matrix. For example, the content of manganese in the dual-phase steel DP590 can be 1.70%, 1.80%, 1.90%, 2.0%, and 2.10%;

[0071] The reason why the content of titanium is 0.02% to 0.03% is that the addition of titanium can refine the grains, thereby improving the performance of the steel matrix. For example, the content of titanium in the dual-phase steel DP590 can be 0.02%, 0.022%, 0.024%, 0.026%, 0.028% or 0.03%;

[0072] The reason why the phosphorus content is not more than 0.02% is that within a suitable range, phosphorus can improve the strength and hardness of the steel matrix, while a too high content will sacrifice the plasticity of the steel matrix and reduce the deep drawing performance. For example, the phosphorus content in the dual-phase steel DP590 can be 0.005, 0.01, 0.015, or 0.02%;

[0073] The reason why the content of sulfur is not more than 0.01% is that the increase of sulfur will reduce the plasticity and toughness of the steel matrix and increase the brittleness of the steel matrix. For example, the content of sulfur in the dual-phase steel DP590 may be 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, 0.009% or 0.01%;

[0074] The reason why the content of aluminum is 0.02% to 0.06% is that appropriate aluminum can perform deoxidation and refine grains. For example, the content of aluminum in the dual-phase steel DP590 can be 0.02%, 0.03%, 0.04%, 0.05% or 0.06%.

[0075] As an optional implementation manner, hot rolling the continuously cast billet to obtain a hot rolled coil specifically comprises:

[0076] Heating and keeping the continuous casting billet warm;

[0077] The heated continuous casting slab is subjected to rough rolling and finish rolling to obtain a hot rolled coil;

[0078] The target temperature of the heating is 1100° C. to 1300° C.; the insulation time is 150 min to 200 min.

[0079] In the above embodiment, the target temperature of heating is controlled to be 1100°C to 1300°C because the main purpose of controlling the heating furnace at 1100°C to 1300°C is to improve the processing performance and product quality of steel. Heating the continuous casting billet to this range can significantly improve the plasticity of the steel and reduce the deformation resistance. Exemplarily, the target temperature of heating can be 1100°C, 1150°C, 1200°C, 1250°C or 1300°C.

[0080] After the steel billet is heated to the specified temperature, it takes a certain amount of time to complete the organizational transformation and grain uniformity. The reason for controlling the insulation time to be 150min to 200min is that these processes can proceed smoothly, ensure the uniformity of the internal organization of the steel billet, and reduce internal stress. At the same time, the temperature stress and cross-sectional temperature difference can be reduced, thereby improving the heating effect and rolling quality. Exemplarily, the insulation time can be 150min, 160min, 170min, 180min, 190min or 200min.

[0081] As an optional implementation manner, the rough rolling temperature is 1000°C to 1100°C, and the finish rolling temperature is 850°C to 950°C.

[0082] In the above embodiment, the temperature of the rough rolling is controlled to be 1000°C to 1100°C because the internal structure of the steel is completely transformed into austenite in this temperature range. Austenite has good plasticity and toughness, making the steel easier to deform and form in the subsequent finishing rolling process. Exemplarily, the temperature of the rough rolling can be 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C, 1090°C or 1100°C.

[0083] The reason for controlling the temperature of the finishing rolling to be 850°C to 950°C is that within this temperature range, the strip has good plasticity, is easy to process and shape, and reduces the risk of breakage and deformation. The appropriate temperature can ensure that the mechanical properties of the strip, such as tensile strength and elongation, meet the design requirements and meet the subsequent use requirements. Exemplarily, the temperature of the finishing rolling can be 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C or 950°C.

[0084] As an optional implementation, the cold rolling parameters include: setting different reduction rates for different hot rolling incoming material thicknesses and order thicknesses.

[0085] As an optional implementation, the galvanizing temperature is the same as the terminal temperature of the rapid cooling stage, which is 450° C. to 480° C.; and the elongation of the skin-passing is less than 0.5%.

[0086] In the above embodiment, the reason for controlling the galvanizing temperature to 450°C to 480°C is that this temperature is the same as the terminal temperature of the rapid cooling section, so that the strip can complete the hot-dip galvanizing process during high-speed operation and obtain reasonable austenite and ferrite contents, so that the performance of the finished product meets the standards.

[0087] The reason for controlling the elongation of skin-passing to be less than 0.5% is that skin-passing can slightly stretch the steel strip to reduce thickness error; it can reduce the internal stress on the surface of the steel strip, making its surface smoother, less prone to wrinkles or warping, and reducing surface unevenness; it can eliminate or reduce poor strip shape and surface defects. Exemplarily, the elongation of skin-passing can be 0.1%, 0.2%, 0.3%, 0.4%.

[0088] As an optional implementation, the process of obtaining the continuous casting billet specifically includes: desulfurizing the molten iron by KR desulfurization, then performing converter steelmaking and LF refining, optimizing the composition of the molten steel, and finally performing continuous casting to obtain the continuous casting billet for hot rolling.

[0089] In a second aspect, the embodiments of the present application provide high performance dual-phase steel DP590 produced by the method described in the first aspect.

[0090] As an optional implementation, the performance of the high performance dual phase steel DP590 at least satisfies one of the following: yield strength R P0.2 340MPa~440MPa; tensile strength Rm>590MPa; elongation after fracture A80≥21%.

[0091] The present application is further described below in conjunction with specific examples. The experimental methods in the following examples where specific conditions are not specified are usually measured in accordance with national standards / industry standards; if there are no corresponding national standards / industry standards, they are measured in accordance with common international standards, conventional conditions or conditions recommended by the manufacturer.

[0092] Example 1

[0093] This embodiment provides a method for preparing high performance dual-phase steel DP590, comprising the following steps:

[0094] S1: pre-treating the molten iron to obtain a continuous casting billet.

[0095] First, the molten iron is desulfurized by KR desulfurization, and then converter steelmaking and LF refining are performed, and continuous casting is performed to obtain a continuous casting billet for hot rolling; the composition table of the continuous casting billet is shown in Table 1;

[0096] Table 1 Composition of continuous casting slab in Example 1

[0097]

[0098] S2: Hot rolling the continuous casting slab obtained in step S1.

[0099] S21: heating the continuous casting billet to 1235° C. for 190 min;

[0100] S22: rolling the continuous casting billet that has reached the target heating temperature in step S21, respectively, through rough rolling and finish rolling, the rough rolling temperature is 1090° C., and the final rolling temperature is 890° C.; finally, laminar cooling is performed to 530° C. and coiling is performed to obtain a hot rolled coil;

[0101] S3: The hot-rolled coil obtained in step S22 is subjected to cold rolling + annealing + hot-dip galvanizing + leveling treatment to finally obtain a hot-dip galvanized finished coil.

[0102] The cold-rolled strip is annealed: the strip is heated to 780°C at a heating rate of 2.0°C / s; the strip is evenly heated at this temperature for 0.78 min; and then it is rapidly cooled, with the cooling endpoint temperature of the rapid cooling stage being 460°C and the cooling rate being 15°C / s.

[0103] The annealed strip steel is put into a zinc pot for hot-dip galvanizing, and finally hot-dip galvanized dual-phase steel DP590 is obtained. The hot-dip galvanized strip steel is flattened, the furnace speed is 120m / min, and the skin-clearing elongation is 0.4%. Finally, the finished coil of hot-dip galvanized dual-phase steel DP590 for automobiles is obtained. The mechanical properties of the final finished coil are shown in Table 2, and the transverse and longitudinal structures of the sample are shown in Table 2. Figure 3 shown.

[0104] Table 2 Mechanical properties of finished rolls in Example 1

[0105]

[0106] Example 2

[0107] This embodiment provides a method for preparing high performance dual-phase steel DP590, comprising the following steps:

[0108] S1: pre-treating the molten iron to obtain a continuous casting billet.

[0109] First, the molten iron is desulfurized by KR desulfurization, and then converter steelmaking and LF refining are performed, and continuous casting is performed to obtain a continuous casting billet for hot rolling; the composition table of the continuous casting billet is shown in Table 3;

[0110] Table 3 Composition of continuous casting slab in Example 1

[0111]

[0112] S2: Hot rolling the continuous casting slab obtained in step S1.

[0113] S21: heating the continuous casting billet to 1230° C. for 185 min;

[0114] S22: rolling the continuous casting billet that has reached the target heating temperature in step S21, respectively, through rough rolling and finish rolling, the rough rolling temperature is 1085°C, and the final rolling temperature is 890°C; finally, laminar cooling is performed to 520°C for coiling to obtain a hot rolled coil;

[0115] S3: The hot-rolled coil obtained in step S22 is subjected to cold rolling + annealing + hot-dip galvanizing + leveling treatment to finally obtain a hot-dip galvanized finished steel coil.

[0116] The cold-rolled strip is annealed: the strip is heated to 775°C at a heating rate of 2.5°C / s; the strip is evenly heated at this temperature for 0.85 min; and then it is rapidly cooled, with the cooling endpoint temperature of the rapid cooling stage being 470°C and the cooling rate being 13.5°C / s.

[0117] The annealed strip steel is put into a zinc pot for hot-dip galvanizing, and finally hot-dip galvanized dual-phase steel DP590 is obtained. The hot-dip galvanized strip steel is flattened, the furnace speed is 110m / min, and the skin-clearing elongation is 0.3%. Finally, the finished coil of hot-dip galvanized dual-phase steel DP590 for automobiles is obtained. The mechanical properties of the final finished coil are shown in Table 4, and the transverse and longitudinal structures of the sample are shown in Table 4. Figure 4 .

[0118] Table 4 Performance of finished coils obtained in Example 2

[0119]

[0120] Example 3

[0121] This embodiment provides a method for preparing high performance dual-phase steel DP590, comprising the following steps:

[0122] S1: pre-treating the molten iron to obtain a continuous casting billet.

[0123] First, the molten iron is desulfurized by KR desulfurization, and then converter steelmaking and LF refining are performed, and continuous casting is performed to obtain a continuous casting billet for hot rolling; the composition table of the continuous casting billet is shown in Table 5;

[0124] Table 5 Composition of continuous casting slab in Example 3

[0125]

[0126] S2: Hot rolling the continuous casting slab obtained in step S1.

[0127] S21: heating the continuous casting billet to 1215° C. for 195 min;

[0128] S22: rolling the continuous casting billet that has reached the target heating temperature in step S21, respectively, through rough rolling and finish rolling, the rough rolling temperature is 1080° C., and the final rolling temperature is 880° C.; finally, laminar cooling is performed to 530° C. and coiling is performed to obtain a hot rolled coil;

[0129] S3: The hot-rolled coil obtained in step S22 is subjected to cold rolling + annealing + hot-dip galvanizing + leveling treatment to finally obtain a hot-dip galvanized finished steel coil.

[0130] The cold-rolled strip is annealed: the strip is heated to 770°C at a heating rate of 2.5°C / s; the strip is evenly heated at this temperature for 0.94 min; and then it is rapidly cooled, with the cooling endpoint temperature of the rapid cooling stage being 470°C and the cooling rate being 12.5°C / s.

[0131] The annealed strip steel is put into a zinc pot for hot-dip galvanizing, and finally hot-dip galvanized dual-phase steel DP590 is obtained. The hot-dip galvanized strip steel is flattened, the furnace speed is 100m / min, and the skin-clearing elongation is 0.4%. Finally, the finished coil of hot-dip galvanized dual-phase steel DP590 for automobiles is obtained. The mechanical properties of the final finished coil are shown in Table 6, and the transverse and longitudinal structures of the sample are shown in Table 6. Figure 5 .

[0132] Table 6 Mechanical properties of finished rolls provided in Example 3

[0133]

[0134] Comparative Example 1

[0135] This comparative example provides a method for preparing high-performance dual-phase steel DP590, comprising the following steps:

[0136] S1: pre-treating the molten iron to obtain a continuous casting billet.

[0137] First, the molten iron is desulfurized by KR desulfurization, and then converter steelmaking and LF refining are performed, and continuous casting is performed to obtain a continuous casting billet for hot rolling; the composition table of the continuous casting billet is shown in Table 7;

[0138] Table 7 Composition of continuous casting slab in comparative example 1

[0139]

[0140] S2: Hot rolling the continuous casting slab obtained in step S1.

[0141] S21: heating the continuous casting billet to 1220° C. for 190 min;

[0142] S22: rolling the continuous casting billet that has reached the target heating temperature in step S21, respectively, through rough rolling and finish rolling, the rough rolling temperature is 1095°C, and the final rolling temperature is 880°C; finally, laminar cooling is performed to 540°C and coiling is performed to obtain a hot rolled coil;

[0143] S3: The hot-rolled coil obtained in step S22 is subjected to cold rolling + annealing + hot-dip galvanizing + leveling treatment to finally obtain a hot-dip galvanized finished steel coil.

[0144] The cold-rolled strip is annealed: the strip is heated to 770°C with a heating rate of 2.3°C / s; it is evenly heated at this temperature for 1.23 min, and then slowly cooled and rapidly cooled, wherein the end point temperature of the slow cooling is 680°C, the end point temperature of the rapid cooling stage is 460°C, and the cooling rate is 12.5°C / s.

[0145] The annealed strip steel is put into a zinc pot for hot-dip galvanizing, and finally hot-dip galvanized dual-phase steel DP590 is obtained. The hot-dip galvanized strip steel is flattened, the furnace speed is 100m / min, and the skin-clearing elongation is 0.4%. Finally, the finished coil of hot-dip galvanized dual-phase steel DP590 for automobiles is obtained. The mechanical properties of the final finished coil are shown in Table 8, and the transverse and longitudinal structures of the sample are shown in Table 8. Figure 6 .

[0146] Table 8 Dual-phase steel properties provided in Comparative Example 1

[0147]

[0148] Comparative Example 2

[0149] This comparative example provides a method for preparing high-performance dual-phase steel DP590, comprising the following steps:

[0150] S1: pre-treating the molten iron to obtain a continuous casting billet.

[0151] First, the molten iron is desulfurized by KR desulfurization, and then converter steelmaking and LF refining are performed, and continuous casting is performed to obtain a continuous casting billet for hot rolling; the composition table of the continuous casting billet is shown in Table 9;

[0152] Table 9 Composition of continuous casting slab in comparative example 2

[0153]

[0154] S2: Hot rolling the continuous casting slab obtained in step S1.

[0155] S21: heating the continuous casting billet to 1220° C. for 190 min;

[0156] S22: rolling the continuous casting billet that has reached the target heating temperature in step S21, respectively, through rough rolling and finish rolling, the rough rolling temperature is 1085°C, and the final rolling temperature is 880°C; finally, laminar cooling is performed to 540°C and coiling is performed to obtain a hot rolled coil;

[0157] S3: The hot-rolled coil obtained in step S22 is subjected to cold rolling + annealing + hot-dip galvanizing + leveling treatment to finally obtain a hot-dip galvanized finished steel coil.

[0158] The cold-rolled strip is annealed: the strip is heated to 775°C with a heating rate of 2.3°C / s; the strip is evenly heated at this temperature for 1.30 min; then it is slowly cooled and rapidly cooled, with the end point temperature of the slow cooling being 670°C, the end point temperature of the rapid cooling stage being 460°C, and the cooling rate being 12.5°C / s.

[0159] The annealed strip steel is put into a zinc pot for hot-dip galvanizing, and finally hot-dip galvanized dual-phase steel DP590 is obtained. The hot-dip galvanized strip steel is flattened, and the furnace speed is 95m / min and the skin-finishing elongation is 0.3%. Finally, the finished coil of hot-dip galvanized dual-phase steel DP590 for automobiles is obtained. The mechanical properties of the final finished coil are shown in Table 10, and the transverse and longitudinal structures of the sample are shown in Table 10. Figure 7 shown.

[0160] Table 10 Performance of finished coils obtained in Comparative Example 2

[0161]

[0162] Experimental data results:

[0163] It can be seen from the data in the table that the performance of the finished dual-phase steel DP590 coils obtained in Examples 1 to 3 meets the requirements of R P0.2 is 340-440MPa, Rm is greater than 590MPa, A80 ≥ 21%, while the finished coils obtained in Comparative Examples 1 and 2 have poor performance; from the transverse and longitudinal organization diagrams in the embodiments and the comparative examples, it can be seen that the dual-phase steels in Examples 1-3 are not subjected to slow cooling but directly subjected to rapid cooling, and the volume fractions of ferrite and martensite in the finished coils are greater than those in Comparative Examples 1-2, so that the tensile strength in the embodiments is higher than that in the comparative examples.

[0164] In summary, the preparation method of high-performance dual-phase steel DP590 provided in the present application modifies the process of the annealing furnace zone, shortens the soaking section, and removes the slow cooling section, which not only shortens the length of the annealing furnace zone, but also gives full play to the integrated technology preparation capability of the new production line, while greatly saving the annealing time; in addition, the method combines the matching steel composition optimization, hot rolling process, cold rolling process, hot-dip galvanizing process and light-finishing process, which can not only achieve energy saving, but also achieve the purpose of efficient production. Under the premise of shortening the time, low-cost, high-performance DP590 high-strength steel with RP0.2 of 340-440MPa, Rm greater than 590MPa, and A80≥21% can still be obtained, which meets the enterprise development direction of lightweighting in the automotive industry.

[0165] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. It will be apparent to those skilled in the art that various modifications to these embodiments are possible, and the general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown in the present application, but will conform to the widest range consistent with the principles and novel features applied for by the present application.

Claims

1. A method for preparing high performance dual-phase steel DP590, characterized in that: The following steps are involved: Obtaining a continuous casting billet; hot rolling the continuously cast slab to obtain a hot rolled coil; cold rolling the hot rolled coil to obtain a steel strip having a set thickness; annealing the steel strip; The annealed steel strip is galvanized and leveled to obtain high performance dual-phase steel DP590; The step of annealing the steel strip comprises: Heating the steel strip and controlling the heating rate and the end point temperature; The heated steel strip is subjected to uniform heating, and the duration of the uniform heating is controlled; The steel strip after being homogenized is rapidly cooled, and the cooling rate and the terminal temperature are controlled to perform annealing treatment on the steel strip.

2. The preparation method according to claim 1, characterized in that: The duration of the soaking is 0.78 min to 0.94 min.

3. The preparation method according to claim 1, characterized in that: The end point temperature of the heating is 750°C to 800°C; and / or, The heating rate does not exceed 3°C / s.

4. The preparation method according to claim 1, characterized in that: The cooling end point temperature is 450°C to 480°C; and / or, The cooling rate is 10°C / s to 15°C / s.

5. The preparation method according to claim 1, characterized in that: The chemical composition of the continuous casting billet is calculated by mass fraction, specifically: C: 0.10% to 0.14%, Si: 0.05% to 0.30%, Mn: 1.70% to 2.10%, P: ≤0.02%, S: ≤0.01%, Alt: 0.02% to 0.06%, Ti: 0.02% to 0.03% and Fe.

6. The preparation method according to claim 1, characterized in that: The hot rolling of the continuous casting billet to obtain a hot rolled coil specifically comprises: Heating and keeping the continuous casting billet warm; The heated continuous casting slab is subjected to rough rolling and finish rolling to obtain a hot rolled coil; The target temperature of the heating is 1100° C. to 1300° C.; the insulation time is 150 min to 200 min.

7. The preparation method according to claim 6, characterized in that: The rough rolling temperature is 1000°C to 1100°C; and / or, The temperature of the finish rolling is 850°C to 950°C.

8. The preparation method according to claim 1, characterized in that: The galvanizing temperature is the same as the cooling end point temperature; and / or, The elongation of the flattening process is less than 0.5%.

9. High performance dual-phase steel DP590 prepared by the preparation method according to any one of claims 1 to 8.

10. The high performance dual phase steel DP590 according to claim 9, characterized in that: The performance of the high performance dual phase steel DP590 at least meets the following conditions: yield strength R P0.2 340MPa~440MPa; tensile strength Rm>590MPa; elongation after fracture A80≥21%.

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