Low-anisotropy 220MPa-grade hot-dip aluminum-silicon phosphorus-containing high-strength steel for automobile and preparation method thereof

Abstract

According to the low-anisotropy 220MPa-grade hot-dip aluminum-silicon phosphorus-containing high-strength steel for the automobile and the preparation method of the low-anisotropy 220MPa-grade hot-dip aluminum-silicon phosphorus-containing high-strength steel, the hot-dip aluminum-silicon high-strength steel for the automobile covering part is prepared through low-cost component design and ingenious combination of heat treatment and the hot-dip aluminum-silicon technology, the yield strength of the high-strength steel ranges from 220MPa to 260MPa, the tensile strength is larger than or equal to 360MPa, the percentage elongation after fracture is larger than or equal to 41%, and the elongation after fracture is larger than or equal to 41%. The plastic strain ratio r value is larger than or equal to 2.1, the anisotropic special-shaped index delta r value is smaller than or equal to 0.3, and the work hardening index n value is larger than or equal to 0.21; and within 6 months after the steel plate is manufactured, the increment of the yield strength is smaller than or equal to 8 MPa, the reduction of the percentage elongation after fracture is smaller than or equal to 1%, the structure comprises ferrite, a TiN precipitated phase, a VC precipitated phase and a Cu-rich phase, and the steel for the high-strength automobile covering part has excellent forming performance, high surface quality, no timeliness and a small anisotropy value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of automobile steel manufacturing, more particularly, to a low anisotropy 220MPa grade hot-dip aluminum-silicon phosphorus-containing high-strength steel for automobiles and a preparation method thereof. BACKGROUND

[0002] Under the background of the implementation of the national double carbon policy, in order to improve the endurance mileage, enhance the durability and safety of new energy vehicles, lightweight has become an irreversible development trend. High-strength steel and ultra-high-strength steel have been widely used in safety components and structural components. However, the steel for outer panels, which accounts for nearly one-fourth of the total amount of automobile steel, still mainly uses soft steel with relatively thick thickness and low strength, which means that there is still a lot of room for improvement in the lightweight of outer panels. Automobile outer panels mainly cover various surface parts of the vehicle body, such as doors, side walls, roofs, and engine covers. These parts, as the appearance of the car, need to meet the diversified personalized modeling requirements and show high freshness. The automobile outer panels are mostly spatial curved surface structures with complex shapes and are exposed to the external environment for a long time, which requires the steel plates used to have excellent formability, dent resistance, corrosion resistance, and no aging problems.

[0003] At present, the commonly used steel for automobile outer panels is mainly IF steel and BH steel with hot-dip galvanized coating. IF steel is a kind of ultra-low carbon steel with appropriate alloying elements, which can convert carbon and nitrogen atoms in the steel into carbonitride. In this way, there are no interstitial atoms in the steel matrix, so that a pure ferrite structure is obtained, which gives the steel excellent formability and no aging. However, IF steel has the disadvantages of low strength and high anisotropy. BH steel retains part of the interstitial solid solution atoms C in a free state. When the steel plate is subjected to coating and baking treatment, the solid solution C atoms will diffuse and gather around the dislocations, thereby pinning the dislocations and hindering the movement of the dislocations, so that the strength of the steel plate is improved and the steel plate has excellent dent resistance. However, BH steel has the disadvantage of high anisotropy, and there is a serious natural aging phenomenon during storage. In addition, the above-mentioned steel plate for automobile outer panels uses a hot-dip galvanized coating to meet the corrosion resistance requirement, which is not good in economy due to the gradual decrease of zinc resources and the continuous rise of zinc prices. Therefore, it is urgent to develop a high-strength steel with high deep drawing performance and low anisotropy value, and to find a new hot-dip method that is compatible with the heat treatment system of high-strength steel, to meet the demand for high-strength steel with good surface quality and excellent performance in the future market.

[0004] The patent with the application number 201810795677.7 discloses a phosphorus-containing high-strength steel and a preparation method thereof, wherein the composition of the phosphorus-containing high-strength steel is as follows: C: 0.002%~0.008%, Si: 0.06%~0.1%, Mn: 0.9%~1.3%, P: 0.06%~0.10%, S: ≤0.005%, Alt: 0.025%~0.035%, and the rest is iron and inevitable impurity elements. The phosphorus-containing high-strength steel has a low elongation, and no alloying elements are added, so that the C and N atoms in the steel cannot be fixed, resulting in a low r value of the steel plate and poor forming performance of the steel plate. In addition, the steel plate adopts a hot-dip galvanizing annealing process, and the hot-dip aluminum-silicon annealing process is not involved. The patent with the application number 202311387544.3 discloses a 340MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel and a manufacturing method thereof, wherein the composition of the high-strength IF steel is as follows: C: ≤0.003%, Si: ≤0.03%, Mn: 0.35~0.65%, P: 0.03~0.075%, S ≤0.010%, Als: 0.020~0.045%, Nb: 0.008~0.015%, Ti: 0.02~0.03%, B: 0.0004~0.0010%, N ≤0.0035%, and the rest is Fe and inevitable impurities. The steel plate does not mention the anisotropy index, nor does it mention the natural aging problem. In addition, the steel plate adopts a hot-dip galvanized iron alloy annealing process, and the hot-dip aluminum-silicon annealing process is not involved. SUMMARY

[0005] The present application aims to overcome the above-mentioned defects in the prior art and provide a low-anisotropy 220MPa grade hot-dip aluminum-silicon phosphorus-containing high-strength steel for automobiles and a preparation method thereof. Through reasonable design of chemical composition and production process, combined with the hot-dip aluminum-silicon process, the prepared hot-dip aluminum-silicon phosphorus-containing high-strength steel has low anisotropy value and high forming performance, and excellent surface quality.

[0006] To achieve the above-mentioned purposes, the technical solutions of the present application are as follows: The application discloses a low-anisotropy 220MPa-grade hot-dip aluminum-silicon phosphorus-containing high-strength steel for automobiles, which comprises the following components in percentage by mass: C: 0.0030%-0.0075%, Si: 0.050%-0.100%, Mn: 0.30%-0.65%, P: 0.040%-0.090%, Cu: 0.50%-0.90%, V: 0.020%-0.090%, Ti: 0.010%-0.050%, Nb: 0.010%-0.025%, Al: 0.010%-0.050%, N: less than or equal to 0.003%, S: less than or equal to 0.003%, and the balance of Fe and inevitable impurities; wherein 6<= (V / C) <=12, 10<= (Ti / N) <=20 and 10<= (Cu / P) <=15 are met according to the percentage by mass of each element.

[0007] The application further discloses a preparation method of the low-anisotropy 220MPa-grade hot-dip aluminum-silicon phosphorus-containing high-strength steel for automobiles, which comprises smelting, hot rolling, pickling, cold rolling, hot-dip aluminum-silicon plating and finishing.

[0008] The application has the following beneficial effects: (1) The chemical composition of the steel plate of the application does not add expensive alloy elements, and the alloy cost of the steel plate is controlled.

[0009] (2) The application eliminates the interstitial atoms N and C in the steel by reasonably controlling the coupling addition amount of Ti and N and the coupling addition amount of V and C, effectively prevents natural aging, ensures that the yield strength of the steel plate is kept in the range of 220MPa-268MPa within 6 months, the elongation after fracture is greater than or equal to 40%, the increase of the yield strength is less than or equal to 8MPa, and the decrease of the elongation after fracture is less than or equal to 1%.

[0010] (3) The application significantly improves the strength of the steel plate by reasonably coupling the addition amount of Cu and P, strengthens the grain boundary, reduces the adverse effects of P segregation at the grain boundary, and reduces the risk of secondary processing brittleness of the steel plate; at the same time, the atmospheric corrosion resistance of the steel plate is improved, and the corrosion resistance of the steel plate in harsh environments is enhanced.

[0011] (4) The application controls the precipitation of precipitates by reasonable smelting, hot rolling, pickling, cold rolling, hot galvanizing, and finishing process, obtains {111} texture beneficial to deep drawing performance, and makes the steel plate have excellent deep drawing performance and anisotropy index Δr value ≤0.3.

[0012] (5) The application places the hot galvanizing process in the slow cooling section, on the one hand, reasonably controls the temperature and time of the hot galvanizing process and the slow cooling process, ensures the formation of Cu-rich phases in the steel plate, and strengthens the grain boundary; on the other hand, reduces the energy loss in the production process, and realizes low carbon and environmental protection.

[0013] (6) The application realizes that the 220MPa level automobile has excellent forming performance, high surface quality, no aging property, and small anisotropy value, the yield strength of the high-strength steel prepared is 220MPa~260MPa, the tensile strength is ≥360MPa, the elongation after fracture is ≥41%, the plastic strain ratio r value is ≥2.1, the anisotropy index Δr value is ≤0.3, and the work hardening index n value is ≥0.21; within 6 months after the steel plate is manufactured, the yield strength is maintained in the range of 220MPa~268MPa, the elongation after fracture is ≥40%, the increase of the yield strength is ≤8MPa, the decrease of the elongation after fracture is ≤1%, and the structure includes ferrite and TiN precipitated phase, VC precipitated phase and Cu-rich phase. DETAILED DESCRIPTION

[0014] The application will be further described below in combination with specific embodiments, but the application is not limited in any way by the embodiments.

[0015] The application discloses a low anisotropy 220MPa level hot galvanizing aluminum silicon phosphorus containing high-strength steel for automobiles, which comprises the following components in percentage by mass: C: 0.0030%~0.0075%, Si: 0.050%~0.100%, Mn: 0.30%~0.65%, P: 0.040%~0.090%, Cu: 0.50%~0.90%, V: 0.020%~0.090%, Ti: 0.010%~0.050%, Nb: 0.010%~0.025%, Al: 0.010%~0.050%, N≤0.003%, S≤0.003%, and the balance is Fe and inevitable impurities; wherein 6≤(V / C)≤12, 10≤(Ti / N)≤20, and 10≤(Cu / P)≤15 are calculated according to the mass percentage of each element.

[0016] Specifically, the reasons for the alloy design of the present application are as follows: C: C element is an important additive element in the present application. C element is one of the most economical elements to improve the strength of the steel plate. In order to ensure the non-aging property of the steel plate, the fewer the interstitial C atoms in the steel plate, the better. However, a certain amount of C element is also needed to ensure a certain strength. Therefore, the content of C element is required to be in the range of 0.0030% to 0.0075% according to the present application.

[0017] Si: Si is an important additive element in the present application. Si element effectively improves the strength of the steel plate through solid solution strengthening. After the atomic of Si element dissolves into the ferrite lattice, it causes lattice distortion, hinders dislocation movement, and thus enhances the ability of the steel plate to resist deformation. However, too high Si content will reduce the plasticity of the steel, making the steel plate more prone to brittle fracture when deformed under stress, and the toughness also decreases, which makes the performance worse when bearing impact load. More seriously, too high Si content will also greatly affect the welding performance of the steel plate, which is prone to produce welding defects during welding, and reduce the quality and reliability of the welded joint. Therefore, the content of Si element is required to be in the range of 0.050% to 0.100% according to the present application.

[0018] Mn: Mn is an important additive element in the present application. Mn element effectively improves the strength of the steel plate through solid solution strengthening mechanism. However, when the Mn content in the steel plate is too high, it will have a significant impact on the internal microstructure of the steel plate. Specifically, too high Mn content will exacerbate the unevenness of the grain size in the steel plate, which will reduce the deformation coordination between the grains during plastic deformation of the steel plate. At the same time, under the action of too high Mn content, the weld and heat-affected zone tend to generate a large number of hard and brittle phases, which changes the original chemical composition and organizational form of the weld metal. Therefore, the content of Mn element is required to be in the range of 0.30% to 0.65% according to the present application.

[0019] P: P is an important additive element in the present application. P element plays a role of solid solution strengthening, which effectively improves the strength and hardness of the steel plate. P is also one of the elements that can most effectively strengthen ferrite. And when P element is used in combination with Cu element, P element can improve the atmospheric corrosion resistance of the steel plate, and to some extent, enhance the corrosion resistance of the steel plate in harsh environments. However, too high P content can cause grain boundary embrittlement, leading to secondary processing brittleness. Therefore, the content of P element is required to be in the range of 0.040% to 0.090% according to the present application.

[0020] Cu: Cu is an important additive element in the present application. Cu element exists in the form of Cu-rich phase in the matrix of the steel, and during the aging stage, Cu atoms are segregated and enriched, and Cu-rich clusters of nanometer size begin to separate from the supersaturated matrix, which plays a role in precipitation strengthening and improves the grain boundary strength. Cu element also has the effect of reducing work hardening and improving the plasticity of the steel plate. However, too much Cu element will make the Cu-rich phase further grow and coarsen, and too little Cu element will affect the precipitation amount of the Cu-rich phase, which is not conducive to the strength of the steel plate. Therefore, the Cu element content range is 0.50%~0.90% in the present application. And it needs to meet: 10≤(Cu / P)≤15, to ensure that enough Cu is segregated at the grain boundary, to improve the strength while reducing the segregation of P at the grain boundary, to avoid the brittleness of the steel plate during secondary processing.

[0021] V: V is an important additive element in the present application. V element is a strong carbide forming element, which can combine with interstitial atoms carbon to form stable fine carbide VC, which plays a role in precipitation strengthening; at the same time, the fine and dispersed VC precipitates have the effect of refining the grain, improving the plasticity of the steel plate, and significantly reducing the anisotropy value of the steel plate. However, too much V element will increase the number and size of precipitates in the steel, which will further reduce the plasticity of the steel. Therefore, the V element content range is 0.020%~0.090% in the present application. And it needs to meet: 6≤(V / C)≤12, to ensure that there is enough V element to fix C, to effectively remove interstitial solid solution atoms from the steel plate, to ensure the non-aging property of the steel plate. It is beneficial to further enhance the {111} texture, improve the r value of the steel plate, and has a certain amount of remaining amount, which reduces the anisotropy value of the steel plate, and also plays a role in precipitation strengthening, but the remaining amount cannot be too high, which will cause the plasticity of the steel plate to decrease.

[0022] Ti: Ti is an important additive element in the present application. Ti element is a strong nitride forming element in the present application, which can combine with interstitial atoms nitrogen to form stable fine nitride TiN, which plays a role in fine grain strengthening and precipitation strengthening, which not only guarantees the good plasticity and forming property of the steel plate, but also significantly improves the strength of the steel plate. However, too much Ti element will be dissolved in the ferrite matrix to improve the strength and reduce the plasticity. Therefore, the Ti element content range is 0.010%~0.050% in the present application. And it needs to meet: 10≤(Ti / N)≤20, to ensure that there is enough Ti element to fix N, to effectively remove interstitial solid solution atoms from the steel plate, to ensure the non-aging property of the steel plate. And has a certain amount of remaining amount, which is beneficial to further enhance the {111} texture, improve the r value of the steel plate, and reduce the anisotropy value of the steel plate; but the remaining amount cannot be too high, which will cause the strength of the steel plate to rise and the plasticity to decrease.

[0023] Nb: Nb is an important additive element in the present application. Nb element forms precipitated phase with C and other interstitial elements to eliminate interstitial atoms, plays a role of precipitated strengthening, eliminates natural aging of the steel plate, improves the cold forming performance of the steel plate, and Nb element can refine the grain and reduce the anisotropy value of the steel plate; Nb element can also expand the rolling process window and improve the uniformity of the steel coil. However, excessive addition of Nb element will lead to excessive strength of the steel plate and decrease of plasticity. Therefore, the content of Nb element is required to be 0.010%~0.025% in the present application.

[0024] Al: Al is an important additive element in the present application. Al is added as a deoxidizer in the steelmaking process, and the main role is to remove oxygen dissolved in the molten steel during oxygen blowing smelting. However, when the content of Al is too high, too many inclusions will be formed. Therefore, the content of Al is required to be 0.010%~0.050% in the present application.

[0025] S: S element is a harmful element in steel, which easily consumes Mn element to form MnS inclusions, and damages the performance of the steel plate. The lower the content of S element is, the better. Considering the production cost of the steel, the content of S element is required to be controlled in the range of ≤0.003% in the present application.

[0026] N: N element is a harmful element in steel, which consumes beneficial micro-alloying element Ti, reduces the effects of precipitated strengthening and fine-grain strengthening, and also causes natural aging. At the same time, N element will cause deterioration of the elongation and welding performance of the steel plate. Therefore, the lower the content of N element is, the better. However, too low content of N element will lead to production difficulty and increase the cost. Therefore, the content of N element is required to be controlled in the range of ≤0.003% in the present application.

[0027] In a specific embodiment, the yield strength of the high-strength steel is 220MPa~260MPa, the tensile strength is ≥360MPa, the elongation after fracture is ≥41%, the plastic strain ratio r value is ≥2.1, the anisotropy index Δr value is ≤0.3, and the work hardening index n value is ≥0.21; within 6 months after the steel plate is manufactured, the yield strength is maintained in the range of 220MPa~268MPa, the elongation after fracture is ≥40%, and the increase of the yield strength is ≤8MPa, and the decrease of the elongation after fracture is ≤1%.

[0028] In a specific embodiment, the microstructure of the high-strength steel includes ferrite and TiN precipitated phase, VC precipitated phase and Cu-rich phase.

[0029] The present application also discloses a preparation method of the low-anisotropy 220MPa-grade hot-dip aluminum-silicon phosphorus-containing high-strength steel for automobiles as described above, which comprises smelting, hot rolling, pickling, cold rolling, hot-dip aluminum-silicon and finishing; specifically comprising the following steps: S1, in smelting, smelting raw materials are sequentially subjected to converter smelting and RH refining to obtain molten steel, and then the molten steel is continuously cast into a casting blank.

[0030] S2, in the hot rolling, the heating temperature is 1230-1310 DEG C, the furnace time is 100-180 min; then the steel plate is formed by hot rolling, the rough rolling temperature is 1080-1160 DEG C, the final rolling temperature is greater than or equal to 910 DEG C, and the coiling temperature is 650-750 DEG C.

[0031] Specifically, the hot rolling process parameters of the application are as follows: (1) the application controls the heating temperature to be between 1230 DEG C and 1310 DEG C, which helps to ensure that the billet is fully austenitized, facilitating subsequent rolling, and at the same time ensuring that the added Ti element fixes the N element, so that TiN is completely precipitated. The furnace time is 100-180 min, the appropriate heating temperature and holding time make the alloying elements in the slab fully solid-solute and uniformly distributed, ensure the uniformity of the slab composition, and play a role in controlling the original austenite grain size.

[0032] (2) the application controls the rough rolling temperature to be between 1080 DEG C and 1160 DEG C, and the final rolling temperature is greater than or equal to 910 DEG C. Too high rough rolling temperature will lead to coarse austenite grains, and coarse ferrite grains may be formed after rolling, reducing the plasticity and toughness of the steel plate. Too low rough rolling temperature cannot guarantee that the final rolling temperature is greater than or equal to 910 DEG C, and the final rolling temperature greater than or equal to 910 DEG C is to ensure that the entire hot rolling process is in the austenite single-phase region of the steel plate, avoiding austenite-ferrite two-phase region rolling and mixed crystal phenomenon.

[0033] (3) the application controls the coiling temperature to be between 650 DEG C and 750 DEG C, which is beneficial to the precipitation of carbide VC and the refinement of grains. Too low coiling temperature will lead to insufficient fixation of interstitial atoms, causing aging brittleness and reducing the formability of the steel plate. Too high coiling temperature will result in larger grain size, affecting the r value of the steel plate.

[0034] S3, in the pickling, the steel plate is subjected to pickling treatment to remove the iron oxide scale formed on the surface of the steel plate due to oxidation, so that the surface of the steel plate is smooth, and the pickling steel plate provides good surface conditions for the subsequent cold rolling process.

[0035] S4, in the cold rolling, the cold rolling reduction is controlled to be 80-90%, and the cold rolled steel plate is obtained.

[0036] Specifically, the present application controls the cold rolling reduction rate to be 80%~90%, and makes the grains fully crushed and elongated by cold rolling to improve the energy storage, and the energy storage of cold rolling deformation is the driving force for subsequent heat treatment recrystallization, and sufficient reduction rate can ensure sufficient deformation energy storage to promote subsequent recrystallization and texture formation to improve the strength and forming performance, which is beneficial to the rapid growth of {111} texture component, and the {111} texture positively affects the plastic strain ratio r value of the steel plate, therefore, controlling the cold rolling reduction rate to be 80%~90% is beneficial to obtaining a higher r value of the steel plate and obtaining excellent deep drawing performance. However, too high cold rolling reduction rate will increase the load of the cold rolling mill.

[0037] S5, the cold-rolled steel plate obtained by sequentially subjecting the cold-rolled steel plate to pickling and cold rolling is heated to an annealing isothermal temperature, the annealing isothermal temperature is 800℃~880℃, the annealing isothermal time is 50s~100s; then the steel plate is slowly cooled to a slow cooling temperature, the slow cooling temperature is 660℃~740℃, the slow cooling time is 15s~30s; then the slowly cooled steel plate is put into an aluminum-silicon plating solution to obtain a steel plate coating, the aluminum-silicon plating solution temperature is 650℃~740℃, the hot aluminum-silicon plating time is 3s~10s, and the total time of the hot aluminum-silicon plating time and the slow cooling time is ≥20s; and the slow cooling temperature is greater than or equal to the aluminum-silicon plating solution temperature but not more than 10℃; after the aluminum-silicon plating is completed, the steel plate is cooled to room temperature at a cooling rate ≥20℃ / s to obtain a cooled steel plate.

[0038] Specifically, the hot aluminum-silicon plating process parameters of the present application are as follows: (1) The present application controls the annealing isothermal temperature to be 800℃~880℃, and the annealing isothermal time to be 50s~100s, which provides sufficient energy for recrystallization to make the grains grow again to obtain a suitable recrystallized grain size to improve the strength and deep drawing performance of the steel plate. Limiting the annealing temperature and the annealing time is beneficial to the formation of {111} texture, which can improve the plastic strain ratio r value of the steel plate to prevent the steel plate from being prone to thinning and cracking during deep drawing, thereby improving the deep drawing performance.

[0039] (2) The present application controls the slow cooling temperature to be 660℃~740℃, and the slow cooling time to be 15s~30s, which has the following two effects: one is to ensure the formation of Cu-rich phase in the steel plate to strengthen the grain boundary and promote the strength of the steel plate; the other is to ensure the formation of fine and dispersed VC carbide precipitates to improve the strength and fatigue resistance of the steel plate; at the same time, the uniformly distributed precipitates can also hinder the grain growth to further refine the grain structure and improve the strength and plasticity of the steel plate.

[0040] (3) After the slow cooling of the steel plate, the steel plate enters the aluminum-silicon plating solution to obtain a steel plate coating, the temperature of the aluminum-silicon plating solution is 650-740°C, and the hot-dip aluminum-silicon time is 3-10s. Reasonable hot-dip aluminum-silicon temperature and hot-dip aluminum-silicon time can promote the formation of Cu-rich phase in the steel to a greater extent; the Cu-rich phase is segregated at the grain boundary, which can further strengthen the grain boundary structure. This grain boundary strengthening mechanism has a positive role in promoting the strength of the steel plate, so that the overall mechanical properties of the steel plate are enhanced. At the same time, it can also create favorable conditions for the precipitation of Nb and Ti-containing carbides, which can efficiently capture interstitial solid solution atoms in the steel plate, promote their transition from solid solution state to precipitated phase, and effectively reduce the influence of interstitial solid solution atoms on the matrix. From the perspective of crystallography, this process is conducive to the further development and strengthening of {111} texture. The strengthening of {111} texture can improve the anisotropy of the steel plate, which is beneficial to the deep drawing performance of the steel plate. In addition, the steel plate slow cooling temperature-aluminum-silicon plating solution temperature should be ≤10°C, and the hot-dip aluminum-silicon time + steel plate slow cooling time should be ≥20s, so as to promote the ferrite grains to tend to be uniform in the growth process and effectively avoid the phenomenon of discrete distribution of grain size. The uniform grain structure is significantly effective in improving the uniformity of the mechanical properties of the steel plate and reducing the anisotropy value caused by the difference in the structure of the steel plate. At the same time, it can avoid the disorderly adhesion of a large number of Fe-Al alloy particles on the surface of the steel plate and thus deteriorate the surface quality of the steel plate, and the uniform ferrite grain structure can ensure the stable progress of the continuous hot-dip aluminum-silicon process, laying a solid foundation for obtaining high-quality aluminum-silicon plated steel plate.

[0041] (4) After the completion of hot-dip aluminum-silicon, the steel plate is rapidly cooled to room temperature at a rate of ≥20°C / s, which can effectively control the thickness of the aluminum-silicon coating and make the steel strip structure uniform, while avoiding the generation of crystal flower type defects on the surface of the steel plate.

[0042] In a specific embodiment, the composition of the aluminum-silicon plating solution is as follows in terms of mass percentage: Si: 7-13%, Al: 87-93%, and the rest is Fe and unavoidable impurity elements. Specifically, the reasonable range of Si elements can significantly optimize the fluidity of the plating solution in the continuous hot-dip aluminum-silicon system. The improvement of the fluidity of the plating solution helps it to spread and infiltrate more smoothly on the surface of the steel plate during the continuous hot-dip process, providing a basic condition for forming a uniform aluminum-silicon coating, thereby effectively avoiding defects such as uneven coating thickness.

[0043] S6, in the finishing process, the cooled steel plate enters the finishing machine for shape adjustment, and the finishing elongation is controlled to be 0.5-1.0%, which can effectively eliminate the yield platform of the steel plate and improve the surface quality of the steel plate, so that the finished plate shape is flat and wave-free.

[0044] The following are specific embodiments Examples 1-15 The preparation method of the low anisotropy 220 MPa grade hot-dip aluminum silicon phosphorus-containing high-strength steel for automobiles of the embodiment comprises smelting, hot rolling, pickling, cold rolling, hot-dip aluminum silicon plating and finishing; and specifically comprises the following steps: In the smelting, the smelting raw materials are sequentially subjected to converter smelting and RH refining to obtain molten steel, and then the molten steel is continuously cast into a casting blank.

[0045] In the hot rolling, the casting blank is heated to a heating temperature, and the furnace time is controlled; and then the casting blank is hot-rolled into a steel plate.

[0046] In the pickling, the steel plate is subjected to pickling treatment to remove the iron oxide scale formed on the surface of the steel plate due to oxidation, so that the surface of the steel plate is smooth, and the pickling steel plate provides good surface conditions for the subsequent cold rolling process.

[0047] In the cold rolling, the cold rolling reduction rate is controlled to obtain a cold-rolled steel plate.

[0048] In the hot-dip aluminum silicon plating, the cold-rolled steel plate obtained by sequentially subjecting to pickling and cold rolling is heated to an annealing isothermal temperature, and the annealing isothermal time is controlled; then the steel plate is slowly cooled to a slow cooling temperature, and the slow cooling time is controlled; then the steel plate after slow cooling is put into an aluminum silicon plating solution to obtain a steel plate coating, and the total time of the hot-dip aluminum silicon plating time and the slow cooling time is greater than or equal to 20 s; and the slow cooling temperature is greater than or equal to the aluminum silicon plating solution temperature but not more than 10 DEG C; after the aluminum silicon plating is completed, the steel plate is cooled to room temperature to obtain a cooled steel plate.

[0049] In the finishing, the cooled steel plate is put into a finishing machine for shape adjustment, the finishing elongation is controlled, and the low anisotropy 220 MPa grade hot-dip aluminum silicon phosphorus-containing high-strength steel for automobiles is obtained.

[0050] The chemical composition of the example steel is listed in Table 1, the hot rolling and cold rolling process parameters of the example steel are listed in Table 2, the hot-dip aluminum silicon plating and finishing process parameters of the example steel are listed in Table 3, and the mechanical properties of the example steel are listed in Table 4.

[0051] Table 1 Chemical composition of the example steel, wt%

[0052] Table 2 Process parameters of hot rolling and cold rolling of the example steel

[0053] Table 3 Process parameters of hot-dip aluminum silicon plating of the example steel

[0054] Table 4 Mechanical properties of the example steel

[0055] As can be seen from the above examples, by means of low-cost component design and ingenious combination of heat treatment and hot-dip aluminum-silicon plating process, the hot-dip aluminum-silicon plated high-strength automobile covering steel is prepared, the yield strength of the high-strength steel is 220 MPa to 260 MPa, the tensile strength is greater than or equal to 360 MPa, the elongation after fracture is greater than or equal to 41%, the plastic strain ratio r value is greater than or equal to 2.1, the anisotropy index Δr value is less than or equal to 0.3, and the work hardening index n value is greater than or equal to 0.21; within 6 months after the steel plate is manufactured, the yield strength is maintained in the range of 220 MPa to 268 MPa, the elongation after fracture is greater than or equal to 40%, the increase of the yield strength is less than or equal to 8 MPa, the decrease of the elongation after fracture is less than or equal to 1%, the microstructure includes ferrite and TiN precipitated phase, VC precipitated phase and Cu-rich phase, and the high-strength automobile covering steel is realized to have excellent forming performance, high surface quality, no aging property and small anisotropy value.

[0056] The above-described examples only express several embodiments of the present application, and the description is relatively specific and detailed, but it should not be understood as limiting the scope of the patent application. It should be noted that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A low anisotropy 220 MPa grade hot dip aluminum silicon phosphorus containing high strength steel for automobiles, characterized by, The high-strength steel comprises the following components in percentage by mass: C: 0.0030%~0.0075%, Si: 0.050%~0.100%, Mn: 0.30%~0.65%, P: 0.040%~0.090%, Cu: 0.50%~0.90%, V: 0.020%~0.090%, Ti: 0.010%~0.050%, Nb: 0.010%~0.025%, Al: 0.010%~0.050%, N≤0.003%, S≤0.003%, the balance being Fe and inevitable impurities; wherein, 6≤(V / C)≤12, 10≤(Ti / N)≤20, and 10≤(Cu / P)≤15, which are calculated according to the corresponding mass percentages of the elements.

2. The low anisotropy 220 MPa grade hot-dip aluminum-silicon phosphorus containing high strength steel for automotive applications according to claim 1, characterized in that, The yield strength of the high-strength steel is 220MPa~260MPa, the tensile strength is ≥360MPa, the elongation after fracture is ≥41%, the plastic strain ratio r value is ≥2.1, the anisotropy index Δr value is ≤0.3, and the work hardening index n value is ≥0.

21. Within 6 months after the manufacture of the steel plate, the yield strength is maintained in the range of 220MPa~268MPa, the elongation after fracture is ≥40%, and the increase in yield strength is ≤8MPa, and the decrease in elongation after fracture is ≤1%.

3. The low anisotropy 220 MPa grade hot-dip aluminum-silicon phosphorus containing high strength steel for automotive applications according to claim 1, characterized in that, The microstructure of the high-strength steel comprises ferrite and TiN precipitates, VC precipitates, and Cu-rich phases.

4. A method for producing a low anisotropy 220 MPa grade hot dip Al-Si-P containing high strength steel for automobiles according to any one of claims 1 to 3, characterized by, The manufacturing process comprises smelting, hot rolling, pickling, cold rolling, hot galvanizing, and finishing; In the hot galvanizing, the cold-rolled steel plate obtained by sequentially subjecting the steel plate to the pickling and the cold rolling is heated to an annealing isothermal temperature, the annealing isothermal temperature is 800℃~880℃, and the annealing isothermal time is 50s~100s; then the steel plate is slowly cooled to a slow cooling temperature, the slow cooling temperature is 660℃~740℃, and the slow cooling time is 15s~30s; then the slowly cooled steel plate is put into an aluminum-silicon plating solution to obtain a plated steel plate, the aluminum-silicon plating solution temperature is 650℃~740℃, the hot galvanizing time is 3s~10s, and the total time of the hot galvanizing time and the slow cooling time is ≥20s; and the slow cooling temperature is greater than or equal to the aluminum-silicon plating solution temperature but not more than 10℃; after the aluminum-silicon plating is completed, the steel plate is cooled to room temperature at a cooling rate ≥20℃ / s to obtain a cooled steel plate, and then the finishing is performed to obtain the low-anisotropy 220MPa-grade hot galvanizing aluminum-silicon phosphorus-containing high-strength steel for automobiles.

5. The method of producing a low anisotropy 220 MPa grade hot dip Al-Si-P containing high strength steel for automobiles according to claim 4, characterized in that, The components of the aluminum-silicon plating solution are as follows in percentage by mass: Si: 7%~13%, Al: 87%~93%, and the balance being Fe and inevitable impurities.

6. The method of producing a low anisotropy 220 MPa grade hot dip Al-Si-P containing high strength steel for automobiles according to claim 4, characterized in that, In the hot rolling, the heating temperature is 1230℃~1310℃, and the furnace time is 100min~180min; then the steel plate is hot-rolled, the open rolling temperature is 1080℃~1160℃, the finish rolling temperature is ≥910℃, and the coiling temperature is 650℃~750℃.

7. The method of producing a low anisotropy 220 MPa grade hot dip Al-Si-P containing high strength steel for automobiles according to claim 4, characterized in that, In the smelting, the smelting raw materials are sequentially subjected to converter smelting and RH refining to obtain molten steel, and then the molten steel is continuously cast into a cast slab.

8. The method of producing a low anisotropy 220 MPa grade hot dip Al-Si-P containing high strength steel for automobiles according to claim 4, characterized in that, In the pickling, the steel plate is subjected to pickling treatment to remove the iron oxide scale formed on the surface of the steel plate due to oxidation, to obtain a pickled steel plate.

9. The method of producing a low anisotropy 220 MPa grade hot dip Al-Si-P containing high strength steel for automobiles according to claim 4, characterized in that, In the cold rolling, the cold rolling reduction is controlled to be 80-90%, and the cold rolled steel plate is obtained.

10. The method of producing a low anisotropy 220 MPa grade hot dip Al-Si-P containing high strength steel for automobiles according to claim 4, characterized in that, In the skin passing, the cooled steel plate is fed into a skin passing machine for shape adjustment, and the skin passing elongation is controlled to be 0.5-1.0%.

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