High-plasticity hot-dip aluminum-silicon 260 MPa-grade isotropic phosphorus-containing high-strength steel and preparation method thereof

Abstract

The invention discloses high-plasticity hot-dip aluminum-silicon 260 MPa grade isotropic phosphorus-containing high-strength steel and a preparation method thereof, the high-plasticity hot-dip aluminum-silicon 260 MPa grade isotropic phosphorus-containing high-strength steel is prepared through reasonable component design and ingenious combination of heat treatment and an aluminum-silicon plating process, the yield strength of the steel plate in the 0-degree direction and the yield strength of the steel plate in the 90-degree direction are 260-300 MPa, the yield strength of the steel plate in the 0-degree direction and the yield strength of the steel plate in the 90-degree direction are 260-300 MPa, and the yield strength of the steel plate in the 90-degree direction are 260-300 MPa. The tensile strength is larger than or equal to 400 MPa, the percentage elongation after fracture is larger than or equal to 39%, the plastic strain ratio r value is larger than or equal to 2.0, the work hardening index n value is larger than or equal to 0.20, it is ensured that the yield strength difference value of the steel plate in the 0-degree direction and the 90-degree direction is smaller than or equal to 5 MPa, the tensile strength difference value is smaller than or equal to 5 MPa, the percentage elongation after fracture is smaller than or equal to 0.5%, the plastic strain ratio r value difference value is smaller than or equal to 0.10, and the work hardening index n value difference value is smaller than or equal to 0.01, the isotropy is good, and high plasticity and high surface quality are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of automobile steel manufacturing, more particularly, to a high-plasticity hot-dip aluminum-silicon 260MPa-grade isotropic phosphorus-containing high-strength steel and a preparation method thereof. BACKGROUND

[0002] As an important means of transportation in modern society, automobiles involve the selection and application of numerous materials in their manufacturing. As the "clothing" of the automobile, the outer panel not only plays a decisive role in the appearance of the automobile, but also is related to the safety performance, durability and other key aspects of the automobile. The outer panel of the automobile, such as the door, the engine cover and other components, needs to go through multiple stamping processes to be shaped. Good formability can ensure that the steel sheet accurately deforms according to the shape of the die in the stamping process, reducing the generation of defects such as wrinkling and cracking. At present, the outer panel of the automobile is mainly IF steel and BH steel with pure zinc or zinc-iron alloy coating. The soft steel represented by IF steel and BH steel has the advantages of excellent plasticity and formability, but has the disadvantages of insufficient strength, poor lightweight effect, and large anisotropy, which is prone to surface scratches, orange peel and other defects caused by deformation differences. Moreover, with the decreasing zinc resources and the increasing price of pure zinc or zinc-iron alloy coating, the economy is not good. Therefore, it is urgent to develop a high-strength high-plasticity and isotropic steel sheet for automobile outer panel, combined with a new hot-dip method, to meet the increasing automobile manufacturing standards and market demand.

[0003] 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 low elongation, and no alloying elements are added, so that the C and N atoms in the steel cannot be fixed, resulting in low r value of the steel plate and poor forming performance of the steel plate. 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 isotropy and natural aging problem, and the steel plate adopts a hot-dip galvanized iron alloy annealing process, and the hot-dip aluminum-silicon annealing process is not involved. SUMMARY

[0004] The purpose of the present application is to overcome the above-mentioned defects existing in the prior art, and to provide a high-plasticity hot-dip aluminum-silicon 260MPa grade isotropic phosphorus-containing high-strength steel and a preparation method thereof. Through reasonable design of chemical composition and production process, combined with the hot-dip aluminum-silicon process, a high-plasticity hot-dip aluminum-silicon 260MPa grade isotropic phosphorus-containing high-strength steel is prepared.

[0005] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows: The application discloses a high-plasticity hot-dip aluminum-silicon-coated 260MPa-grade isotropic phosphorus-containing high-strength steel, which comprises the following components in percentage by mass: C: 0.0050%-0.0095%, Si: 0.10%-0.40%, Mn: 0.10%-0.40%, P: 0.030%-0.070%, Cu: 0.20%-0.70%, Ti: 0.050%-0.090%, Nb: 0.020%-0.060%, Re: 0.003%-0.015%, Al: 0.010%-0.050%, N: less than or equal to 0.003%, S: less than or equal to 0.003%, Re is La and Ce, and the balance is Fe and inevitable impurities; wherein, 5.0<= (Cu / P) <=10.0, 1.00<= (Ti+Nb) / (12C+4N+2S) <=1.50, and 0.50<= (La+Ce) / (C+1.2N) <=1.00 are calculated according to the corresponding mass percentages of the elements.

[0006] The application further discloses a preparation method of the high-plasticity hot-dip aluminum-silicon-coated 260MPa-grade isotropic phosphorus-containing high-strength steel, which comprises smelting, hot rolling, pickling, cold rolling, hot-dip aluminum-silicon coating and finishing. The cold-rolled steel plate obtained through the pickling and the cold rolling is heated to an annealing isothermal temperature, the annealing isothermal temperature is 830 DEG C-910 DEG C, and the annealing isothermal time is 90s-150s; then the steel plate is slowly cooled to a slow cooling temperature, the slow cooling temperature is 650 DEG C-710 DEG C, 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 steel plate coating, the temperature of the aluminum-silicon plating solution is 640 DEG C-710 DEG C, the aluminum-silicon plating time is 5s-10s, and the total time of the aluminum-silicon plating time and the slow cooling time is greater than or equal to 25s; and the slow cooling temperature is greater than or equal to the temperature of the aluminum-silicon plating solution but less than or equal to 10 DEG C; after the aluminum-silicon plating is completed, the steel plate is cooled to room temperature at a cooling rate greater than or equal to 20 DEG C / s to obtain a cooled steel plate, and then the finishing treatment is performed to obtain the high-plasticity hot-dip aluminum-silicon-coated 260MPa-grade isotropic phosphorus-containing high-strength steel.

[0007] The application has the following beneficial effects: (1) The chemical composition of the steel plate is reasonably designed in the C, Si, Mn and P system, and Ti, Nb, La and Ce alloy elements are added, so that the economy is better.

[0008] (2) The application realizes the improvement of the forming performance of the steel plate by reasonably coupling the adding amount of Ti and Nb, firstly, Ti can be combined with S to generate titanium sulfide (TiS) and titanium carbon sulfide (Ti4C2S2) and other compounds. The reaction can control the morphology and spatial distribution of sulfides on one hand, and weaken the deterioration effect of sulfur elements on the mechanical properties of the steel plate; on the other hand, TiC will grow epitaxially with Ti4C2S2 particles as the core, promote the increase of TiC grain size, and then help to form a dispersed distribution of titanium carbide phase, and finally realize the improvement of the forming performance of the steel plate. Secondly, ensure that there is enough amount of Ti, Nb to fix carbonitride, effectively remove the interstitial solid solution atoms in the steel plate, and eliminate the natural aging of the steel plate; secondly, form Ti(N,C), NbC and other carbonitrides to play the purpose of precipitation strengthening and fine-grain strengthening, which can further enhance the {111} texture, which is beneficial to the strength and plasticity of the steel plate. Finally, ensure a certain amount of Ti, Nb remaining amount to ensure the isotropy of the steel plate.

[0009] (3) The application strengthens the grain boundary by reasonably coupling the adding amount of Cu and P, reduces the negative influence of the segregation phenomenon of P elements at the grain boundary, and then reduces the risk of brittleness of the steel plate during secondary processing. At the same time, it also improves the resistance of the steel plate to atmospheric corrosion, and to a certain extent, strengthens the corrosion resistance of the steel plate in harsh environments.

[0010] (4) The application adds a certain amount of rare earth elements (La+Ce) to enrich the grain boundary through the diffusion mechanism, inhibit the generation of Fe(Nb+Ti)P and other precipitated phases of P elements, and strengthen the grain boundary. At the same time, by reasonably coupling the adding amount of rare earth elements (La+Ce) and C, N elements, the plasticity of the steel plate is significantly improved while the isotropy of the steel plate is ensured.

[0011] (5) The application places the hot-dip aluminum silicon process in the slow cooling section, on one hand, reasonably controls the temperature and time of the hot-dip aluminum silicon process and the slow cooling process, ensures the formation of Cu-rich clusters 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.

[0012] (6) The present application realizes a hot-dip aluminum-silicon 260MPa grade phosphorus-containing high-strength steel with high plasticity and isotropy, and also has high surface quality, no aging property, excellent forming property and other advantages, the yield strength in the 0° direction and the 90° direction is 260MPa-300MPa, the tensile strength is greater than or equal to 400MPa, the elongation after fracture is greater than or equal to 39%, the plastic strain ratio r value is greater than or equal to 2.0, and the work hardening index n value is greater than or equal to 0.20; the yield strength difference in the 0° direction and the 90° direction is less than or equal to 5MPa, the tensile strength difference is less than or equal to 5MPa, the elongation after fracture difference is less than or equal to 0.5%, the plastic strain ratio r value difference is less than or equal to 0.10, and the work hardening index n value difference is less than or equal to 0.01; the structure includes ferrite and Ti(N,C) precipitated phase, NbC precipitated phase and Cu-rich clusters. DETAILED DESCRIPTION

[0013] The present application is further described below in combination with specific examples, but the present application is not limited in any way by the examples.

[0014] The present application discloses a high-plasticity hot-dip aluminum-silicon 260MPa grade isotropic phosphorus-containing high-strength steel, which comprises the following components in mass percentage: C: 0.0050%-0.0095%, Si: 0.10%-0.40%, Mn: 0.10%-0.40%, P: 0.030%-0.070%, Cu: 0.20%-0.70%, Ti: 0.050%-0.090%, Nb: 0.020%-0.060%, Re: 0.003%-0.015%, Al: 0.010%-0.050%, N≤0.003%, S≤0.003%, Re is La and Ce, and the balance is Fe and inevitable impurities; wherein the 5.0≤(Cu / P)≤10.0, 1.00≤(Ti+Nb) / (12C+4N+2S)≤1.50, and 0.50≤(La+Ce) / (C+1.2N)≤1.00 are calculated according to the mass percentage of each element.

[0015] Specifically, the reasons for the alloy design of the present application are as follows: C: C element is an important added element in the present application. C element is one of the most economical elements for improving the strength of steel plate, and when the content of C element is too high, too much carbide and solid solution C is easily generated in the steel, which will cause the change of the crystal structure of the steel, so that the dislocation movement is more hindered, and the plastic strain ratio r value and the work hardening index n value of the steel are also reduced, thereby causing the forming property of the steel plate to be poor. Therefore, the content of C element is required to be in the range of 0.0050%-0.0095%.

[0016] Si: Si is an important additive element in the present application. Si element plays a role of solid solution strengthening, improving the strength of the steel plate. However, too high Si content will reduce the plasticity of the steel plate, and Si element will promote the oxidation of the steel during heating, forming loose oxide skin structure with poor adhesion, which is easy to fall off during subsequent rolling or processing, thereby affecting the surface quality of the steel plate. Therefore, the present application requires that the content of Si element is in the range of 0.10%~0.40%.

[0017] Mn: Mn is an important additive element in the present application. Mn element plays a role of solid solution strengthening, improving the strength of the steel plate. However, too high Mn content is easy to form MnS inclusions and banded structure, which seriously damages the strength and plasticity of the steel plate. Therefore, the present application requires that the content of Mn element is in the range of 0.10%~0.40%.

[0018] P: P is an important additive element in the present application. P element plays a role of solid solution strengthening, and P element is one of the most economical elements to improve the strength of the steel plate. 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 environment. However, too much P element is easy to precipitate in the grain boundary as Fe(Ti+Nb)P precipitated phase, causing the grain boundary brittleness of the steel, hindering the formation of {111} texture, reducing the forming performance of the steel plate, and at the same time, the plasticity will be deteriorated due to the segregation at the grain boundary; too little addition will not improve the strength of the steel plate enough. Therefore, the present application requires that the content of P element is in the range of 0.030%~0.070%.

[0019] Cu: Cu is an important additive element in the present application. Cu element is supersaturated in the form of Cu-rich phase in the steel, and will segregate and enrich during the aging stage, and precipitate in the form of nano-element, which plays a role of precipitation strengthening and improves the grain boundary strength. However, too much Cu element will make the Cu-rich phase coarse, and too little Cu element will affect the precipitation amount of Cu-rich phase, which is not conducive to the strength of the steel plate. Therefore, the present application requires that the content of Cu element is in the range of 0.20%~0.70%. And it needs to meet: 5.0≤(Cu / P)≤10.0, to ensure that enough Cu segregates in the grain boundary, which reduces the adverse effects of P segregation in the grain boundary, and increases the resistance to secondary processing brittleness of the steel plate.

[0020] Ti: Ti is an important additive element in the present application. Ti element is a strong carbon, nitride forming element, which can form stable and fine carbon, nitride, play a role of fine grain strengthening and precipitation strengthening, which not only ensures that the steel plate has good plasticity and forming performance, 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 present application requires that the content of Ti element is in the range of 0.050%~0.090%.

[0021] Nb: Nb is an important additive element in the present application. Nb element has strong affinity with carbon and nitrogen, forming extremely stable carbide and nitride, which are pinned at the grain boundary, producing drag effect on dislocation and grain boundary, significantly improving the strength of the steel plate. And Nb element has the effect of refining the grain, which can make the grain size of the steel smaller, increase the grain boundary area; Nb element can also improve the uniformity of the steel coil, refine the structure, and improve the plasticity of the steel plate. 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 in the range of 0.020%~0.060% in the present application. And it needs to meet: 1.00≤(Ti+Nb) / (12C+4N+2S)≤1.50, to ensure sufficient amount of Ti and Nb to fix the carbon and nitrogen, effectively remove the interstitial solid solution atoms in the steel plate, and achieve the purpose of precipitation strengthening and fine-grain strengthening, which is beneficial to the strength and plasticity of the steel plate. At the same time, it can further enhance the {111} texture, improve the r value of the steel plate, and have a certain amount of residual amount to ensure the isotropy of the steel plate. But the residual amount cannot be too high, otherwise it will lead to the increase of the strength of the steel plate and the decrease of the plasticity.

[0022] Rare earth elements (La+Ce): Rare earth elements (La+Ce) are important additive elements in the present application. The atomic radius of rare earth elements (La+Ce) is larger than that of iron, which can produce solid solution strengthening effect when dissolved in steel. At the same time, rare earth elements (La+Ce) have strong deoxidizing and desulfurizing ability, forming spherical sulfide or sulfur oxide instead of long strip-shaped manganese sulfide inclusions, which can improve the plasticity and r value of the steel plate. In addition, rare earth elements (La+Ce) can also enrich in the grain boundary through diffusion mechanism, so that the amount of FeTi and FeNb phases in the steel plate is small, the generation of Fe(Nb+Ti)P and other precipitated phases is inhibited, and the grain boundary is strengthened. Therefore, the content of rare earth elements (La+Ce) is required to be in the range of 0.003%~0.015% in the present application. And it needs to meet 0.50≤(La+Ce) / (C+1.2N)≤1.00, to ensure sufficient amount of rare earth elements (La+Ce) to reduce the activity of carbon and nitrogen, increase the solubility in steel, reduce the desorption amount, improve the plasticity of the steel plate, and ensure the isotropy of the steel plate.

[0023] Al: Al is an important additive element in the present application. Al is added as a deoxidizer in the steelmaking process, and its main function is to remove the oxygen dissolved in the molten steel during oxygen blowing. However, when the content of Al is too high, too many inclusions will be formed. Therefore, the content of Al is required to be in the range of 0.010%~0.050% in the present application.

[0024] S: S element is a harmful element in steel, which can easily consume Mn element to form MnS inclusions, damaging the performance of the steel plate. The lower the content of S element, 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.

[0025] N: N element is a harmful element in steel, N element will form nitride with Nb, Ti element, reduce the complex strengthening effect of Nb, Ti, meanwhile N element will cause the elongation and welding performance of steel plate to deteriorate. The lower the content of N element is, the better, but too low will lead to production difficulty and increase cost. Therefore, the content of N element is required to be controlled in the range of ≤0.003% in the application.

[0026] In a specific embodiment, the yield strength of the high-strength steel in the 0° direction and the 90° direction is 260MPa~300MPa, the tensile strength is ≥400MPa, the elongation after fracture is ≥39%, the plastic strain ratio r value is ≥2.0, and the work hardening index n value is ≥0.20; the yield strength difference of the high-strength steel in the 0° direction and the 90° direction is ≤5MPa, the tensile strength difference is ≤5MPa, the elongation after fracture difference is ≤0.5%, the plastic strain ratio r value difference is ≤0.10, and the work hardening index n value difference is ≤0.01.

[0027] In a specific embodiment, the microstructure of the high-strength steel includes ferrite and Ti(N,C) precipitates, NbC precipitates and Cu-rich clusters.

[0028] The application also discloses a preparation method of the high-plasticity hot-dip aluminum-silicon 260MPa-grade isotropic phosphorus-containing high-strength steel. S1, in the 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.

[0029] S2, in the hot rolling, the heating temperature is 1150℃~1260℃, and the furnace time is 60min~120min; then the steel plate is hot-rolled, the opening rolling temperature is 1020℃~1100℃, the final rolling temperature is ≥920℃, and the coiling temperature is 640℃~750℃.

[0030] Specifically, the key parameters of the hot rolling process of the application are as follows: (1) The application controls the heating temperature to be between 1150℃ and 1260℃, which helps to ensure that the added Ti element fixes the N element, so that TiN precipitates completely; at the same time, it ensures that the billet is fully austenitized, which is convenient for subsequent rolling. The furnace time is 60min~120min, the appropriate heating temperature and holding time make the microstructure of each part inside the steel plate consistent, avoiding uneven microstructure caused by temperature difference, so as to ensure that the steel plate has consistent mechanical properties throughout the cross section.

[0031] (2) The present application controls the rough rolling temperature to be between 1020℃-1100℃, and the finish rolling temperature to be greater than or equal to 920℃. Too high rough rolling temperature will result in coarse austenite grains, and coarse ferrite grains after rolling, which will reduce the plasticity and toughness of the steel plate. Too low rough rolling temperature cannot guarantee the finish rolling temperature to be greater than or equal to 920℃, and the finish rolling temperature greater than or equal to 920℃ is to guarantee the whole hot rolling process to be in the austenite single phase region, to avoid the austenite-ferrite two phase region rolling, and to avoid the mixed grain phenomenon.

[0032] (3) The present application controls the coiling temperature to be between 640℃-750℃, which is beneficial to the precipitation of carbides and the refinement of grains. Too low coiling temperature will result in insufficient fixation of interstitial atoms, which will cause aging brittleness and reduce the formability of the steel plate. Too high coiling temperature will produce more iron oxide scale, which will reduce the efficiency of subsequent pickling, and will cause the cooling speed of the hot-rolled plate to be uneven, resulting in poor head-tail performance.

[0033] 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 pickled steel plate provides good surface conditions for the subsequent cold rolling process.

[0034] S4, in the cold rolling, the cold rolling reduction rate is controlled to be between 75%-88% to obtain a cold-rolled steel plate.

[0035] Specifically, the cold rolling reduction rate is controlled to be between 75%-88%, so that the original grains of the steel plate are strongly elongated and broken, and the dislocation density inside the grains is increased, to provide more nucleation sites for recrystallization in the subsequent annealing process. At the same time, the cold rolling reduction rate in this range is beneficial to the enhancement of the deep drawing performance of the {111} texture, and is not conducive to the suppression of the deep drawing performance of the {100} texture. The {111} texture can make the steel plate have better plastic deformation ability during deep drawing, and improve the formability of the steel plate.

[0036] S5, in the hot aluminum-silicon plating, the cold-rolled steel plate obtained by the pickling and cold rolling is heated to an annealing isothermal temperature, the annealing isothermal temperature is 830℃-910℃, the annealing isothermal time is 90s-150s; then the steel plate is slowly cooled to a slow cooling temperature, the slow cooling temperature is 650℃-710℃, 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 640℃-710℃, the aluminum-silicon plating time is 5s-10s, and the total time of the aluminum-silicon plating time and the slow cooling time is greater than or equal to 25s; 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 greater than or equal to 20℃ / s to obtain a cooled steel plate.

[0037] In a specific embodiment, the components of the aluminum-silicon plating solution are as follows in terms of mass percentage: Si: 7% to 15%, Al: 85% to 93%, and the rest is Fe and inevitable impurity elements. Specifically, Al is the main component in the plating solution, and the formed plating layer has good corrosion resistance, oxidation resistance, and thermal conductivity. The addition of 7% to 15% of Si elements can inhibit the reaction between aluminum and iron, thin the compound layer between the plating layer and the steel plate substrate, and be beneficial to the forming performance of the steel plate.

[0038] Specifically, the key parameters of the hot aluminum-silicon plating process of the present application are as follows: (1) The present application controls the annealing isothermal temperature to be 830°C to 910°C, and the annealing time to be 90s to 150s, to ensure that the recrystallization behavior of the cold-rolled deformed structure occurs fully. If the temperature is too high, the grains may grow excessively, resulting in uneven grain size and thus reducing the mechanical properties such as strength and plasticity of the steel plate. If the temperature is too low, the grain growth is slow, and the desired grain size and uniformity of the structure may not be achieved, which also affects the performance of the steel plate. A reasonable isothermal time can make the second phase exist in the steel plate in a suitable size, shape, and distribution, making the internal structure of the steel plate more uniform.

[0039] (2) The present application controls the slow cooling temperature to be 650°C to 710°C, and the slow cooling time to be 15s to 30s. A reasonable slow cooling temperature and slow cooling isothermal time can ensure the formation of Cu-rich phase in the steel plate, strengthen the grain boundary, and promote the strength of the steel plate. At the same time, it can also ensure the precipitation of carbides, effectively remove interstitial solid solution atoms in the steel plate, and be beneficial to the formation of {111} texture which is beneficial to deep drawing performance.

[0040] (3) The present application designs a reasonable aluminum-silicon plating solution temperature of 640°C to 710°C, and an aluminum-silicon plating time of 5s to 10s, to further promote the precipitation of Cu-rich phase, strengthen the grain boundary, and at the same time ensure the precipitation of carbides to remove interstitial solid solution atoms in the steel plate, which is beneficial to the formation of {111} texture which is beneficial to deep drawing performance. In addition, the total time of aluminum-silicon plating time and slow cooling time needs to be ≥25s to ensure that the precipitated phase has more time for nucleation and growth, and can form precipitated phases with more uniform size and more dispersed distribution, which is beneficial to improving the strength and plasticity of the steel plate; at the same time, the structure is fully homogenized to ensure the isotropy of the steel plate. In addition, the slow cooling temperature of the steel plate minus the aluminum-silicon plating solution temperature needs to be ≤10°C to ensure that the ferrite grain grows more uniformly and avoids the occurrence of different grain sizes, which is beneficial to improving the mechanical property uniformity of the steel plate, making the performance of the steel plate more consistent at each part, improving the isotropy of the steel plate, and facilitating the continuous hot aluminum-silicon plating process, avoiding the adhesion of a large number of Fe-Al alloy particles to the surface of the steel plate due to temperature fluctuations, and affecting the surface quality of the steel plate.

[0041] (4) The present application cools to room temperature at a rapid cooling rate of greater than or equal to 20 DEG C / s after the completion of the aluminum-silicon plating, the large cooling rate can effectively control the thickness of the aluminum-silicon plating layer, and the uniform steel strip structure is obtained, and the generation of crystal flower type defects on the surface of the steel plate is avoided.

[0042] S6, in the finishing, the cooled steel plate is put into a finishing machine for shape adjustment, and the finishing elongation is controlled to be 0.3%~1.0%, so that the yield platform of the steel plate can be effectively eliminated, the surface quality of the steel plate is improved, the finished plate shape is flat and without wave shape, and the high plasticity hot-dip aluminum-silicon 260 MPa grade isotropic phosphorus-containing high-strength steel is obtained.

[0043] The following is a specific embodiment Embodiments 1-15 The preparation method of the high plasticity hot-dip aluminum-silicon 260 MPa grade isotropic phosphorus-containing high-strength steel in the embodiment comprises smelting, hot rolling, pickling, cold rolling, hot-dip aluminum-silicon plating and finishing, and specifically comprises the following steps: S1, 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.

[0044] S2, 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.

[0045] 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.

[0046] S4, in the cold rolling, the cold rolling reduction rate is controlled to obtain a cold rolled steel plate.

[0047] S5, 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, and 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 aluminum-silicon plating time and the slow cooling time is greater than or equal to 25s; 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 completion of the aluminum-silicon plating, the steel plate is cooled to room temperature to obtain a cooled steel plate.

[0048] S6, in the finishing, the cooled steel plate is put into a finishing machine for shape adjustment, and the finishing elongation is controlled, i.e. the high plasticity hot-dip aluminum-silicon 260 MPa grade isotropic phosphorus-containing high-strength steel is obtained.

[0049] The chemical composition of the steel in the examples is listed in Table 1, the hot rolling and cold rolling process parameters of the steel in the examples are listed in Table 2, the hot-dip aluminum-silicon plating and finishing process parameters of the steel in the examples are listed in Table 3, and the mechanical properties of the steel in the examples are listed in Table 4.

[0050] Table 1 Chemical composition of the example steels, wt%

[0051] Table 2 Process parameters for hot rolling and cold rolling of the example steels

[0052] Table 3 Process parameters for hot dip aluminizing and skin passing of the example steels

[0053] Table 4 Mechanical properties of the example steels

[0054] As can be seen from the above examples, by reasonable composition design and ingenious combination of heat treatment and aluminizing process, a 260MPa grade isotropic phosphorus-containing high-strength steel with high plasticity is prepared, the yield strengths of the steel plate in 0° direction and 90° direction are 260MPa-300MPa, the tensile strength is ≥400MPa, the elongation after fracture is ≥39%, the plastic strain ratio r value is ≥2.0, the work hardening index n value is ≥0.20, and the yield strength difference between 0° direction and 90° direction of the steel plate is ≤5MPa, the tensile strength difference is ≤5MPa, the elongation after fracture difference is ≤0.5%, the plastic strain ratio r value difference is ≤0.10, the work hardening index n value difference is ≤0.01, the microstructure includes ferrite and Ti(N,C) precipitates, NbC precipitates and Cu-rich clusters, the isotropy is good, and the steel plate has high plasticity and high surface quality.

[0055] The above 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, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A high-plasticity, hot-dip aluminized silicon, 260MPa grade, isotropic, phosphorus-containing high-strength steel, characterized in that, Includes the following components by mass percentage: C: 0.0050%~0.0095%, Si: 0.10%~0.40%, Mn: 0.10%~0.40%, P: 0.030%~0.070%, Cu: 0.20%~0.70%, Ti: 0.050%~0.090%, Nb: 0.020%~0.060%, Re: 0.003%~0.015%, Al: 0.010%~0.050%, N≤0.003%, S≤0.003%, Re is La and Ce, the balance is Fe and unavoidable impurities; where calculated according to the corresponding mass percentage of each element, 5.0≤(Cu / P)≤10.0, 1.00≤(Ti+Nb) / (12C+4N+2S)≤1.50, 0.50≤(La+Ce) / (C+1.2N)≤1.

00.

2. The high-plasticity hot-dip aluminized silicon 260MPa grade isotropic phosphorus-containing high-strength steel according to claim 1, characterized in that, The high-strength steel has a yield strength of 260MPa~300MPa in the 0° direction and 90° direction, a tensile strength of ≥400MPa, an elongation after fracture of ≥39%, a plastic strain ratio r value of ≥2.0, and a work hardening index n value of ≥0.

20. The high-strength steel has a yield strength difference of ≤5MPa between the 0° and 90° directions, a tensile strength difference of ≤5MPa, a post-fracture elongation difference of ≤0.5%, a plastic strain ratio r difference of ≤0.10, and a work hardening index n difference of ≤0.

01.

3. The high-plasticity hot-dip aluminized silicon 260MPa grade isotropic phosphorus-containing high-strength steel according to claim 1, characterized in that, The microstructure of the high-strength steel includes ferrite, Ti(N,C) precipitates, NbC precipitates, and Cu-rich clusters.

4. A method for preparing high-plasticity hot-dip aluminized silicon 260MPa grade isotropic phosphorus-containing high-strength steel as described in any one of claims 1-3, characterized in that, This includes smelting, hot rolling, pickling, cold rolling, hot-dip aluminizing and silicon coating, and finishing. In the hot-dip aluminized silicon process, the cold-rolled steel sheet, obtained by sequential pickling and cold rolling, is heated to an annealing isothermal temperature of 830℃~910℃ for 90s~150s. The steel sheet is then slowly cooled to a slow-cooling temperature of 650℃~710℃ for 15s~30s. The slowly cooled steel sheet is then immersed in an aluminized silicon plating bath at 640℃~710℃ for 5s~10s, with the total time for plating and slow cooling ≥25s. The slow-cooling temperature is greater than or equal to the aluminized silicon plating bath temperature but not exceeding 10℃. After aluminized silicon plating, the steel sheet is cooled to room temperature at a cooling rate ≥20℃ / s to obtain a cooled steel sheet, which is then subjected to a finishing process to obtain the high-plasticity hot-dip aluminized silicon 260MPa grade isotropic phosphorus-containing high-strength steel.

5. The method for preparing high-plasticity hot-dip aluminized silicon 260MPa grade isotropic phosphorus-containing high-strength steel according to claim 4, characterized in that, The composition of the aluminum-silicon plating solution, by mass percentage, is: Si: 7%~15%, Al: 85%~93%, with the remainder being Fe and unavoidable impurity elements.

6. The method for preparing high-plasticity hot-dip aluminized silicon 260MPa grade isotropic phosphorus-containing high-strength steel according to claim 4, characterized in that, In the hot rolling process, the heating temperature is 1150℃~1260℃, and the furnace time is 60min~120min; then, the steel plate is hot rolled into a steel plate with an initial rolling temperature of 1020℃~1100℃, a final rolling temperature of ≥920℃, and a coiling temperature of 640℃~750℃.

7. The method for preparing high-plasticity hot-dip aluminized silicon 260MPa grade isotropic phosphorus-containing high-strength steel according to claim 4, characterized in that, In the smelting process, the raw materials are successively smelted in a converter and refined with RH to obtain molten steel, and then the molten steel is continuously cast into billets.

8. The method for preparing high-plasticity hot-dip aluminized silicon 260MPa grade isotropic phosphorus-containing high-strength steel according to claim 4, characterized in that, In the pickling process, the steel plate is pickled to remove the iron oxide scale formed on the surface of the steel plate due to oxidation, thereby obtaining a pickled steel plate.

9. The method for preparing high-plasticity hot-dip aluminized silicon 260MPa grade isotropic phosphorus-containing high-strength steel according to claim 4, characterized in that, In the cold rolling process, the cold rolling reduction rate is controlled at 75%~88% to obtain the cold-rolled steel sheet.

10. The method for preparing high-plasticity hot-dip aluminized silicon 260MPa grade isotropic phosphorus-containing high-strength steel according to claim 4, characterized in that, In the finishing process, the cooled steel plate is fed into the finishing machine for plate shape adjustment, and the finishing elongation is controlled to be 0.3%~1.0%.

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