A quenching and partitioning steel and a processing method thereof

Abstract

The present invention discloses a quenching and partitioning steel and a processing method thereof, and belongs to the technical field of alloy steel preparation. The processing method comprises: preparing raw materials according to chemical composition requirements, smelting in a vacuum state, and then continuously casting or forging into slabs; hot rolling the slabs and removing surface impurities, then cold rolling, and then processing using a continuous annealing furnace; performing simulated baking varnish treatment on the obtained steel plates or formed parts, or first performing lap welding as required, and then performing baking varnish treatment. The performance of the quenching and partitioning steel obtained by the process disclosed in the present invention is significantly improved compared with the performance of traditional quenching and partitioning steel, and the performance of the obtained welded joints is better than that of welded joints under traditional welding processes.

Description

Technical Field

[0001] The invention relates to the technical field of alloy steel preparation, and in particular to a quenching and partitioning steel and a processing method thereof. Background Art

[0002] Steel materials, especially automotive steel materials, need to be transformed to promote and facilitate the realization of the dual carbon goals. At present, third-generation automotive steel materials such as quenching and partitioning steel have excellent strength and plasticity, providing important support for the lightweighting of automobiles, thereby reducing the industry's carbon footprint. In addition to promoting the realization of the dual carbon goals by increasing strength and plasticity to reduce the weight of the vehicle body, it is also necessary to start from the production process of automotive steel and reduce carbon emissions in the production process, thereby accelerating the realization of the dual carbon goals.

[0003] At present, the cold-rolled quenched and partitioned steel produced in the industry must undergo cold forming and painting processes before being applied to automobile bodies. That is, the cold-rolled quenched and partitioned steel currently produced in the industry is not combined with the subsequent forming and painting processes, which increases the cost and carbon emissions of the entire process from production to application. Summary of the invention

[0004] In view of the technical problems existing in the whole process of current quenching and partitioning steel production and application, the present invention discloses a quenching and partitioning steel and a processing method thereof.

[0005] According to a first aspect of the technical solution of the present invention, a method for processing quenched and partitioned steel is provided, comprising the following steps:

[0006] S1, prepare the raw materials according to the chemical composition requirements, melt them in a vacuum state, and then continuously cast or forge them into slabs;

[0007] S2, hot rolling the slab to remove surface impurities, then cold rolling it, and then treating it in a continuous annealing furnace;

[0008] S3, subjecting the steel plate or formed part obtained in step S2 to simulated paint treatment, or firstly performing overlap welding and then performing simulated paint treatment as required.

[0009] Furthermore, in step S2, the process parameters of the hot rolling treatment are:

[0010] The material is kept at 1473-1493K for 120-180min, and then hot rolled for five times, with the starting temperature of rolling at 1323-1353K and the ending temperature of rolling at 1053-1063K. After rolling, the material is water-cooled to 843-863K for coiling. The above process parameters can achieve the refinement of the material grains, and provide a technical route for the subsequent baking paint process to fully realize the distribution effect of the elements.

[0011] Furthermore, in step S2, the process parameters of the cold rolling process and the process parameters of the continuous annealing furnace process are:

[0012] Cold rolling is carried out at room temperature, with a total reduction rate of 60-70%; the starting temperature of the soaking section is 1063-1093K, the ending temperature of the soaking section is 1093-1113K, the starting temperature of the rapid cooling is 890-1050K, and the over-aging section is 663-693 K. Through the cold rolling and continuous annealing process parameters, the material grains are further refined, and a certain amount of metastable austenite exists in the organization, which provides a technical route for fully realizing the partitioning effect of elements in the subsequent baking process.

[0013] Furthermore, before the step S3, the steel plate in the continuous annealing state may be placed in a designed stamping die and stamped into a desired formed part at room temperature.

[0014] Furthermore, in step S3, the simulated paint treatment is: heating to 383-553K at a heating rate of 0.1-15K / s, keeping warm for 300-3300s; then cooling to room temperature at a cooling rate of 0.1-10K / s. The above parameters promote carbon distribution, realize the combination of distribution and paint concept, and obtain quenching and distribution steel with excellent mechanical properties.

[0015] Preferably, in step S3, the simulated paint baking treatment is: heating to a range of 443K at a heating rate of 0.2K / s, keeping warm for 1200s; and then cooling to room temperature at a cooling rate of 0.6K / s.

[0016] Furthermore, in step S3, the objects to be overlapped and welded are the steel plates in a continuously truncated state with different strengths and thicknesses obtained in step S2.

[0017] Furthermore, in step S3, the ratio of the thickness of the thicker steel plate to the thinner steel plate in the continuously retreated state of the steel plates with different strengths and thicknesses is ≤1.5.

[0018] According to a second aspect of the technical solution of the present invention, there is provided a quenching and partitioning steel, wherein the quenching and partitioning steel is prepared by the processing method according to any one of the above aspects, wherein the chemical composition (by weight percentage) of the quenching and partitioning steel comprises:

[0019] 0.15-0.21% C, 2.5-3.5% Mn, 1.5-1.79% Si, 0.02-0.04% Al, 0.009-1.48% Cr, the rest is Fe and unavoidable impurities, of which:

[0020] Carbon (C) can improve the stability of austenite in the structure, and it can also produce a solid solution strengthening effect to improve the strength of the material. In order to ensure that there is enough austenite in the paint baking process and that there is enough C to supply diffusion, the C content is at least 0.15 for the present invention. On the other hand, when the C content exceeds 0.21%, the welding performance will deteriorate. From the above perspectives, the C composition range is 0.15-0.21%, and more preferably 0.18-0.21%;

[0021] Manganese (Mn) can expand the austenite phase and increase the stability of austenite. In order to ensure the austenite ratio in the paint baking process of the present invention, in addition to the appropriate C content, Mn ≥ 2.5% is required. When the Mn content is too high, the segregation phenomenon in the organization is significant, resulting in performance deterioration. Therefore, the upper limit of Mn is set to 3.5%. From the above perspectives, the Mn range is set to 2.5-3.5%, and more preferably 2.8-3.0%;

[0022] Silicon (Si) can produce a solid solution strengthening effect and inhibit the formation of carbides. In order to reduce the precipitation of C in the form of carbides and ensure sufficient C supply for diffusion, the content of Si in the present invention is 1.5% or more. On the other hand, too high Si leads to deterioration of plasticity and welding performance, so the content of Si in the present invention should be ≤1.79%. From the above perspective, the content of Si is 1.5-1.79%, more preferably, 1.6-1.7%;

[0023] Aluminum (Al) as a supplementary element can play a role in deoxidation, but too much Al is not easy to produce continuously, so the range of Al is 0.02-0.04%, and more preferably Al is 0.03-0.04%;

[0024] Chromium (Cr) can increase the hardenability of the material, which is beneficial for adjusting the cooling process to obtain a structure containing martensite and austenite, but too much Cr will cause carbides to deteriorate the performance. From the above perspective, the Cr content is set to 0.009-1.48%, more preferably, 0.016-0.021%.

[0025] Among them, the concept of combining distribution and baking paint is realized through appropriate chemical content design and processing methods. The whole process from production to application is analyzed without adding additional steps, and quenching and distribution steel that is superior to traditional processes is obtained.

[0026] Preferably, the chemical composition of the quenching and partitioning steel (by weight percentage) includes: 0.20% C, 3.0% Mn, 1.7% Si, 0.04% Al, 0.021% Cr, and the remainder is Fe and unavoidable impurities.

[0027] Furthermore, the slab heating temperature is 1473K, the insulation time is 120min, the hot rolling start temperature is 1353K, the hot rolling end temperature is 1063K, the coiling temperature is 863K, the start temperature of the continuous annealing soaking section is 1063K, the end temperature of the soaking section is 1103K, the start temperature of the rapid cooling is 1050K, the temperature of the over-aging section is 663K, and the tensile strength of the steel plate after the continuous annealing process is 1228MPa.

[0028] Beneficial effects of the present invention:

[0029] The processing method proposed in the present invention realizes the process route of utilizing cold forming processing and baking varnish treatment, coupling the concepts of partitioning and baking varnish, thereby improving the performance of quenched and partitioned steel, and the processing method does not require the separate design of hot forming molds, which is highly efficient and low-cost.

[0030] The forming and painting processes are an indispensable part of the application of cold-rolled quenched and partitioned steel to automobile bodies. How to couple the design concepts of forming, painting and cold-rolled quenched and partitioned steel to improve the performance of quenched and partitioned steel without adding additional processes and costs is a technical problem that needs to be solved to promote the national dual carbon goals. The quenched and partitioned steel disclosed in the present invention avoids the high cost caused by adding high levels of microalloying elements, and ensures the realization of the concept of combining partitioning and painting through appropriate chemical composition design to obtain good mechanical properties, and obtains a microstructure containing austenite of suitable stability and strong martensite. The performance of the quenched and partitioned steel obtained by the process disclosed in the present invention is significantly improved compared with the performance of traditional quenched and partitioned steel, and the performance of the obtained welded joint is better than that of the welded joint under the traditional welding process. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the quenching and partitioning steel and its processing process flow in an embodiment of the present invention.

[0032] Figure 2 The figure is a comparison chart of the performance of the quenching and partitioning steel obtained in Example 1 of the present invention and that of traditional steel.

[0033] Figure 3 The figure is a comparison chart of the performance of the quenching and partitioning steel obtained in Example 2 proposed by the present invention and the traditional steel.

[0034] Figure 4 The figure is a comparison chart of the performance of the quenched and partitioned steel welded joint and the traditional welded joint obtained in Example 3 proposed by the present invention. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings of the specification, and the purpose, technical solutions and advantages of the present invention will be more clearly shown. It should be clear that the specific embodiments described are not intended to limit the present invention, but are only intended to explain the present invention.

[0036] The technical solution of the present invention provides a quenching and partitioning steel and a processing technology thereof. The chemical composition of the steel is (by weight percentage) 0.15-0.21% C, 2.5-3.5% Mn, 1.5-1.79% Si, 0.02-0.04% Al, 0.009-1.48% Cr, and the remainder is Fe and unavoidable impurities.

[0037] like Figure 1 As shown, the quenching and partitioning steel processing technology includes the following steps:

[0038] S1, prepare the raw materials according to the chemical composition requirements, melt them in a vacuum state, and then continuously cast or forge them into slabs;

[0039] S2, keep the slab at 1473-1493K for 120-180min, then perform five passes of hot rolling, with the starting temperature of rolling at 1323-1353K and the ending temperature of rolling at 1053-1063K. After rolling, water cool it to 843-863K for coiling; pickle the hot-rolled steel in a hydrochloric acid tank to remove impurities such as iron oxide on the surface, and then perform five passes of cold rolling; then use a continuous annealing furnace to treat the steel strip, with the starting temperature of the soaking section at 1063-1093K, the ending temperature of the soaking section at 1103K, the starting temperature of the rapid cooling at 1050K, and the temperature of the over-aging section at 663K;

[0040] S3, subjecting the obtained steel plate or formed part to simulated baking varnish treatment, or firstly performing overlap welding and then baking varnish treatment as required.

[0041] Before step S3, the steel sheet in the continuous annealing state may be placed in a designed stamping die and stamped into a desired formed part at room temperature.

[0042] The chemical composition (by weight percentage) of the quenching and partitioning steel includes: 0.15-0.21% C to ensure that a suitable amount of C diffuses into austenite during the heating and holding process, 2.5-3.5% Mn to ensure that a suitable austenite is obtained, 1.5-1.79% Si to inhibit the formation of carbides, 0.02-0.04% Al to obtain a ferrite structure with a suitable amount ratio, 0.009-1.48% Cr to ensure suitable hardenability, and the remaining balance is Fe and unavoidable impurities. The concept of combining partitioning and baking varnish is realized through appropriate chemical composition design and processing methods, and a quenching and partitioning steel superior to the traditional process is obtained without adding additional processes.

[0043] In step S3, the simulated paint treatment is: heating to a range of 383-553 K at a heating rate of 0.1-15 K / s, keeping warm for 300-3300 seconds; then cooling to room temperature at a cooling rate of 0.1-10 K / s. The object of lap welding is, for example, a steel plate in a continuously annealed state of different strengths and thicknesses obtained in step S2. The ratio of the thickness of the thicker steel plate to the thinner steel plate in the continuously annealed state of different strengths and thicknesses is ≤1.5.

[0044] Example 1

[0045] The chemical composition adopted is 0.20% C, 3.0% Mn, 1.7% Si, 0.04% Al, 0.021% Cr, and the remainder is Fe and unavoidable impurities;

[0046] First, the quenching and partitioning steel was processed, in which the slab was heated to 1473K, kept warm for 120min, the starting temperature of hot rolling was 1353K, the ending temperature of hot rolling was 1063K, the coiling temperature was 863K, the starting temperature of the continuous annealing and soaking section was 1063K, the ending temperature of the soaking section was 1103K, the starting temperature of the rapid cooling was 1050K, and the temperature of the over-aging section was 663K; then, it was heated to 443K at a heating rate of 0.2K / s and kept warm for 1200s; then it was cooled to room temperature at a cooling rate of 0.6K / s.

[0047] The mechanical properties of the quenched and partitioned steel obtained in this embodiment are compared with those of conventional quenched and partitioned steel. Figure 2 As shown, it can be seen that the yield strength and tensile strength of the quenched and partitioned steel obtained in this embodiment are improved while maintaining the total elongation.

[0048] Example 2

[0049] The chemical composition adopted is 0.18% C, 2.8% Mn, 1.6% Si, 0.03% Al, 0.016% Cr, and the rest is Fe and unavoidable impurities;

[0050] First, the quenching and partitioning steel was processed, in which the slab was heated to 1493K, kept warm for 180min, the starting temperature of hot rolling was 1323K, the ending temperature of hot rolling was 1053K, the coiling temperature was 843K, the starting temperature of the continuous annealing and soaking section was 1093K, the ending temperature of the soaking section was 1103K, the starting temperature of the rapid cooling was 1050K, and the temperature of the over-aging section was 663K; then, it was heated to 443K at a heating rate of 0.2K / s and kept warm for 1200s; then it was cooled to room temperature at a cooling rate of 0.6K / s.

[0051] Figure 3This is a comparison chart of the mechanical properties of the quenched and partitioned steel obtained by this embodiment and the mechanical properties of the conventional quenched and partitioned steel. It can be seen that the yield strength and tensile strength of the quenched and partitioned steel obtained by this embodiment are higher than those of the quenched and partitioned steel obtained by the traditional process, while the total elongation remains unchanged.

[0052] Example 3

[0053] The chemical composition adopted is 0.20% C, 3.0% Mn, 1.7% Si, 0.04% Al, 0.021% Cr, and the rest is Fe and inevitable impurities; the quenching and partitioning steel is processed, wherein the slab heating temperature is 1473K, the insulation is 120min, the hot rolling start temperature is 1353K, the hot rolling end temperature is 1063K, the coiling temperature is 863K, the start temperature of the continuous annealing and soaking section is 1063K, the end temperature of the soaking section is 1103K, the start temperature of the rapid cooling is 1050K, and the temperature of the over-aging section is 663K, and a steel plate with a tensile strength of 1228MPa is obtained.

[0054] The chemical composition adopted is 0.18% C, 2.8% Mn, 1.6% Si, 0.03% Al, 0.016% Cr, and the rest is Fe and inevitable impurities; the quenching and partitioning steel is processed, wherein the slab heating temperature is 1493K, the insulation is 180min, the hot rolling start temperature is 1323K, the hot rolling end temperature is 1053K, the coiling temperature is 843K, the start temperature of the continuous annealing and soaking section is 1093K, the end temperature of the soaking section is 1103K, the start temperature of the rapid cooling is 1050K, and the temperature of the over-aging section is 663K; a steel plate with a tensile strength of 1049MPa is obtained.

[0055] The two different steel plates were connected by resistance spot welding and overlap, and then heated to 443K at a heating rate of 0.2K / s and kept warm for 1200s; and then cooled to room temperature at a cooling rate of 0.6K / s.

[0056] Figure 4 It is a comparison chart of the performance of quenched and partitioned steel welded joints and quenched and partitioned steel welded joints produced by traditional processes. It can be seen from the figure that the maximum shear force and absorbed energy of the quenched and partitioned steel welded joints obtained by this embodiment are higher than those of the quenched and partitioned steel welded joints produced by traditional processes.

[0057] In summary, according to the quenching and partitioning steel and the processing method thereof of the present invention, the quenching and partitioning steel undergoes raw material preparation, smelting, hot rolling, pickling, cold rolling and continuous annealing processes, and then undergoes cold forming (and / or welding), and finally undergoes baking varnish treatment. The performance of the quenching and partitioning steel obtained by the process disclosed in the present invention is significantly improved compared with the performance of the traditional quenching and partitioning steel, and the performance of the obtained welded joint is better than that of the welded joint under the traditional welding process.

[0058] The above description shows and describes the preferred embodiments of the present application, and it should be understood that the present application is not limited to the form disclosed herein. The above preferred embodiments should not be regarded as excluding other embodiments, and they can also be applied under various other combinations, modifications and environmental conditions; and can be modified within the scope of the application concept described herein, based on the above teachings or the technology or knowledge of the relevant field. Without departing from the spirit and scope of the present application, the changes and modifications made by those skilled in the art should be within the scope of protection of the claims attached to the present application.

Claims

1. A method for processing quenching and partitioning steel, characterized in that: The quenching and partitioning steel processing method is used to prepare a quenching and partitioning steel welded joint, and the quenching and partitioning steel processing method comprises the following steps: S1, prepare the raw materials according to the chemical composition requirements, melt them in a vacuum state, and then continuously cast or forge them into slabs; S2, hot rolling the slab to remove surface impurities, then cold rolling, and then treating it in a continuous annealing furnace; wherein the process parameters for treating it in the continuous annealing furnace are: the start temperature of the soaking section is 1063-1093 K, the end temperature of the soaking section is 1093-1113 K, the start temperature of the rapid cooling is 890-1050 K, and the temperature of the over-aging section is 663-693 K; S3, overlap welding the steel plate or formed part obtained in step S2, and then perform a simulated paint treatment; wherein the simulated paint treatment is: heating to a range of 383-553 K at a heating rate of 0.1-15 K / s, keeping the temperature for 300-3300 s; then cooling to room temperature at a cooling rate of 0.1-10 K / s, The chemical composition of the quenching and partitioning steel includes, by weight percentage, 0.15-0.21% C, 2.5-3.5% Mn, 1.5-1.79% Si, 0.02-0.04% Al, 0.009-1.48% Cr, and the remainder is Fe and unavoidable impurities.

2. The method for processing quenched and partitioned steel according to claim 1, characterized in that: In step S2, the process parameters of the hot rolling process are: The steel was kept at 1473-1493 K for 120-180 min, and then hot rolled in five passes. The starting temperature of the rolling was 1323-1353 K, the ending temperature of the rolling was 1053-1063 K, and the steel was coiled by water cooling to 843-863 K after the rolling.

3. The method for processing quenched and partitioned steel according to claim 1, characterized in that: In step S2, the process parameters of the cold rolling process are: Cold rolling was carried out at room temperature with a total reduction of 60-70%.

4. The method for processing quenched and partitioned steel according to claim 1, characterized in that: Before step S3, the steel sheet in the continuous annealing state is placed in a designed stamping die and stamped into a desired formed part at a stamping temperature of room temperature.

5. The method for processing quenched and partitioned steel according to claim 1, characterized in that: In step S3, the simulated paint treatment is as follows: The samples were heated to 443 K at a heating rate of 0.2 K / s and kept at that temperature for 1200 s; then they were cooled to room temperature at a cooling rate of 0.6 K / s.

6. The method for processing quenched and partitioned steel according to claim 1, characterized in that: In step S3, the objects to be overlapped and welded are the steel plates in the continuously annealed state with different strengths and thicknesses obtained in step S2.

7. The method for processing quenched and partitioned steel according to claim 6, characterized in that: In the step S3, the ratio of the thickness of the thicker steel plate to the thinner steel plate in the continuously retreated state of the steel plates with different strengths and thicknesses is ≤1.

5.

8. The method for processing quenched and partitioned steel according to claim 1, characterized in that: The chemical composition of the quenching and partitioning steel includes: 0.20% C, 3.0% Mn, 1.7% Si, 0.04% Al, 0.021% Cr, and the remainder is Fe and unavoidable impurities.

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