Ti microalloyed thin-gauge automobile compartment steel with yield strength larger than 355MPa and production method of Ti microalloyed thin-gauge automobile compartment steel

Abstract

The invention discloses Ti microalloyed thin-gauge steel for an automobile compartment with the yield strength larger than 355 MPa and a production method of the Ti microalloyed thin-gauge steel. The Ti microalloyed thin-gauge steel for the automobile compartment comprises, by mass, 0.16%-0.18% of C, 0.03%-0.10% of Si, 0.55%-0.70% of Mn, smaller than or equal to 0.018% of P, smaller than or equal to 0.015% of S, 0.020%-0.045% of Alt, 0.030%-0.040% of Ti, 0.0010%-0.0030% of Ca and the balance Fe and inevitable impurities. Through the combined action of titanium element fine grain strengthening and precipitation strengthening, the steel still has good toughness while keeping high strength, and meanwhile, the thickness of a steel plate is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical plate production, and specifically relates to a Ti microalloyed steel with a yield strength greater than 355 MPa for a thin-gauge automobile body and a production method thereof. Background Art

[0002] With the rapid development of the domestic commercial automobile industry and the strengthening of resource conservation and environmental awareness, users have put forward higher requirements for reducing automobile weight, reducing fuel consumption, improving the strength of automobile structural parts and safety performance. Automobile steel shows a trend of lightweight and high strengthening. High-strength automobile body steel is mainly used to manufacture automobile compartments, including truck compartments, van compartments, etc. The manufacturing process and service conditions of the body steel require not only high strength, but also good plasticity, toughness, cold formability and excellent welding performance. Ti micro-alloyed thin-gauge automobile body steel is a steel widely used in the field of automobile manufacturing. The alloy element Ti can combine with C and N to form stable carbides and nitrides. It is not easy to dissolve during heating. It can effectively prevent the growth of austenite grains by pinning grain boundaries and solute dragging, thereby improving the strength of steel. Titanium can change the sulfide morphology in steel and reduce the transverse and longitudinal performance differences and cold forming performance of the material. With the increasing requirements of the automotive industry for energy conservation, emission reduction and lightweighting, combined with the ultra-strong fine-grain strengthening effect of titanium and the economy of ferrotitanium, the application prospects of Ti micro-alloyed automobile body steel will be broader.

[0003] In order to meet the market demand for automobile body steel, further expand market share, and enrich product variety structure, based on advanced equipment and process characteristics, a Ti micro-alloyed steel with a yield strength greater than 355MPa thin gauge automobile body steel was invented using reasonable composition design and process technology. Production results and user effects show that all performances of this product meet relevant technical requirements and user requirements.

[0004] Patent publication number CN 116121639 A discloses a method for producing low-carbon microalloy steel strip with a yield strength of more than 355 MPa, wherein the main chemical composition ratio is C: 0.15-0.19%, Si: 0.08-0.25%, Mn: 0.35-0.55%, Ti: 0.025-0.050%, Cr≤0.30%, Ni≤0.30%, Cu≤0.30%, Nb≤0.07%, Mo≤0.10%. The composition design of the invention is different from the present invention, which improves the product strength by increasing the content of the precious alloys Cr, Ni, Cu, Nb, and Mo, which increases the manufacturing cost, while the present invention does not add the above alloys, which significantly reduces the production cost.

[0005] Patent publication number CN 117070851 A discloses an economical 355MPa grade hot-rolled steel plate and its elongation stable control method, the main chemical composition ratio is C: 0.15-0.18%, Si: 0.20-0.35%, Mn: 0.95-1.15%, Nb: 0.01-0.03%, Ti: 0.005-0.015%. The composition design of this invention is different from the present invention. The composition design of this invention not only adds the precious alloy Nb element, but also has higher Si and Mn contents than the present invention. Too high Si content not only reduces welding performance, but also produces a large amount of red rust, resulting in poor surface quality. High Mn content is easy to segregate to form banded structure, making the mechanical properties of the material anisotropic, and the cross-sectional shrinkage rate is seriously reduced, which has an adverse effect on the subsequent processing and use of steel. In addition, high Mn content will make the welding performance of steel worse. The present invention not only reduces the cost but also avoids the above situation.

[0006] Patent publication number CN 113025898 A discloses a low-manganese, low-silicon, micro-titanium alloyed Q355B structural steel plate and its production method. Firstly, the thickness of the steel plate of the invention is 12-35 mm, while the thickness of the steel plate of the present invention is thinner at 3-8 mm. Secondly, the invention does not mention the key process parameters such as the intermediate billet thickness, cooling rate and microstructure analysis involved in the present invention. Summary of the invention

[0007] The purpose of the present invention is to provide a Ti microalloyed steel with a yield strength greater than 355 MPa for a thin-gauge automobile body and a production method thereof. The chemical composition of the thin-gauge automobile body steel mentioned in the present invention is reasonably designed. Through the combined effects of titanium element fine grain strengthening and precipitation strengthening, the steel has good toughness while maintaining high strength, and the thickness of the steel plate is reduced, which perfectly meets the demand for lightweight automobiles, and all performances meet the requirements of relevant standards and user needs.

[0008] The present invention is specifically implemented through the following technical solutions:

[0009] In one aspect of the present invention, the present invention provides a Ti microalloyed steel with a yield strength greater than 355 MPa for a thin gauge automobile body, wherein the chemical composition is as follows by mass percentage: C: 0.16-0.18%, Si: 0.03-0.10%, Mn: 0.55-0.70%, P≤0.018%, S≤0.015%, Alt: 0.020-0.045%, Ti: 0.030-0.040%, Ca: 0.0010-0.0030%, and the remainder is Fe and unavoidable inclusions;

[0010] The mechanical properties of the automobile body steel meet the following requirements: yield strength ≥355MPa, tensile strength 490-630MPa, and elongation ≥20%.

[0011] In some embodiments, the chemical composition of the steel for automobile body is calculated by mass percentage as follows: C: 0.162-0.176%, Si: 0.05-0.10%, Mn: 0.60-0.70%, P≤0.018%, S≤0.005%, Alt: 0.030-0.045%, Ti: 0.030-0.037%, Ca: 0.0015-0.0026%, and the rest is Fe and unavoidable inclusions.

[0012] In some embodiments, the chemical composition of the steel for automobile body is, by mass percentage, C: 0.171%, Si: 0.05%, Mn: 0.60%, P: 0.018%, S: 0.004%, Alt: 0.035%, Ti: 0.036%, Ca: 0.0015%, and the rest is Fe and unavoidable inclusions.

[0013] In some embodiments, the chemical composition of the steel for automobile body is, by mass percentage, C: 0.176%, Si: 0.08%, Mn: 0.68%, P: 0.016%, S: 0.003%, Alt: 0.045%, Ti: 0.030%, Ca: 0.0026%, and the rest is Fe and unavoidable inclusions.

[0014] In some embodiments, the chemical composition of the steel for automobile body is, by mass percentage, C: 0.165%, Si: 0.10%, Mn: 0.70%, P: 0.015%, S: 0.003%, Alt: 0.030%, Ti: 0.037%, Ca: 0.0018%, and the rest is Fe and unavoidable inclusions.

[0015] In some embodiments, the chemical composition of the steel for automobile body is, by mass percentage, C: 0.162%, Si: 0.06%, Mn: 0.63%, P: 0.017%, S: 0.002%, Alt: 0.035%, Ti: 0.035%, Ca: 0.0018%, and the rest is Fe and unavoidable inclusions.

[0016] In some embodiments, the mechanical properties of the automobile body steel meet the following requirements: yield strength 467-527 MPa, tensile strength 539-590 MPa, and elongation 26-29%.

[0017] Another aspect of the present invention provides a method for producing steel for automobile body, which comprises the following processes: smelting - continuous casting - slab heating - rolling - cooling - coiling; wherein:

[0018] The smelting-continuous casting process comprises: KR desulfurization-converter-LF refining-slab continuous casting-slow cooling, and the composition of the molten steel supplied to the casting machine comprises C: 0.16-0.18%, Si: 0.03-0.10%, Mn: 0.55-0.70%, P≤0.018%, S≤0.015%, Alt: 0.020-0.045%, Ti: 0.030-0.040%, Ca: 0.0010-0.0030%;

[0019] The slab heating process includes: sending the slab after surface cleaning into the heating furnace, strictly controlling the slab heating temperature, furnace time, soaking temperature, soaking time and furnace discharge temperature, the heating temperature is controlled at 1210±20°C, the furnace time is controlled at 160-270min, the soaking temperature is controlled at 1230±20°C, the soaking time is controlled at 25-60min, and the furnace discharge temperature is controlled at 1220±20°C;

[0020] The rolling process includes a rough rolling stage and a finishing rolling stage. The rough rolling stage adopts a 3+3 mode two-stand rolling mill for rough rolling, and the finishing stage adopts a 7-stand continuous variable crown rolling mill for finishing rolling. The finishing stage adopts speed increase rolling; the finishing rolling entrance thickness is 40mm, the starting rolling temperature of the finishing rolling is not less than 1030°C, and the final rolling temperature of the finishing rolling is 890±15°C;

[0021] The cooling process adopts laminar cooling equipment, the cooling mode is front dispersion, and the computer secondary system self-learning calculation results are adopted;

[0022] The coiling temperature is 600±15°C.

[0023] The beneficial effect of the present invention is to provide a Ti microalloyed steel with a yield strength greater than 355MPa for thin-gauge automobile body and a production method thereof through a reasonable chemical composition design. The microstructure of the product is composed of ferrite and pearlite, and the mechanical properties are as follows: yield strength 467-527MPa, tensile strength 539-590MPa, and elongation 26-29%. The product significantly improves the organization and performance of the steel by adding a trace amount of Ti element to the steel, so that the product has high strength and good toughness and welding performance. Since the addition of titanium element can improve the strength of the steel, thinner steel can be used to manufacture the automobile body under the premise of ensuring safety, which helps to reduce the weight of the car and improve fuel economy and environmental protection performance. In addition, the production method of the product is simple and easy, suitable for industrial mass production, and all performances meet the requirements of relevant standards and user needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a microstructural photograph of the Ti microalloyed steel for thin-gauge automobile body with a yield strength greater than 355 MPa produced in Example 1. DETAILED DESCRIPTION

[0025] The present invention is described in detail below through specific examples. The examples are intended to help understand the present invention but are not intended to limit the present invention.

[0026] Example 1

[0027] The molten iron is pre-treated for desulfurization, and the top and bottom combined blown converter is used to decarbonize and dephosphorize the molten iron to obtain molten steel. Argon is blown throughout the converter smelting process, scrap steel is added to the converter, and the converter tapping temperature is 1653℃. Then the molten steel after converter smelting is subjected to LF refining outside the furnace, and the refining temperature is ≥1566℃. The LF refining outside the furnace is subjected to temperature measurement and composition fine-tuning. The chemical composition of the LF refining casting machine is shown in Table 1. The overheat of the slab continuous casting is 26℃, and then the slab is cleaned, slowly cooled, and the quality of the continuous casting is checked. The slab heating temperature is 1218℃, the heating time is 258min, and the heated slab is dephosphorized by high-pressure water. The width is set by a fixed width press, and 2-stand rough rolling and 7-stand CVC finishing rolling are used. The finishing rolling start temperature is 1033℃, the finishing rolling final rolling temperature is 895℃, and the finished product thickness is 3.0mm. Laminar cooling adopts front dispersion cooling, cooling rate is 26℃ / s, and the temperature of steel strip is reduced to 600℃ for coiling. Finally, product performance test is carried out, as shown in Table 2 below. Figure 1 As shown, the microstructure diagram of the steel for automobile body obtained in this embodiment is shown, and it can be seen that the microstructure is ferrite and pearlite.

[0028] Example 2

[0029] The molten iron is pre-treated for desulfurization, and the top and bottom combined blown converter is used to decarbonize and dephosphorize the molten iron to obtain molten steel. Argon is blown throughout the converter smelting process, scrap steel is added to the converter, and the converter tapping temperature is 1647℃. Then the molten steel after converter smelting is subjected to LF refining outside the furnace, and the refining temperature is ≥1564℃. The LF refining outside the furnace is subjected to temperature measurement and composition fine-tuning. The chemical composition of the LF refining casting machine is shown in Table 1. The overheat of the slab continuous casting is 28℃, and then the slab is cleaned, slowly cooled, and the quality of the continuous casting is checked. The slab heating temperature is 1213℃, and the heating time is 265min. The heated slab is dephosphorized by high-pressure water. The width is set by a fixed width press, and 2-stand rough rolling and 7-stand CVC finishing rolling are used. The finishing rolling start temperature is 1036℃, the finishing rolling final temperature is 883℃, and the finished product thickness is 5.0mm. Laminar cooling adopts front dispersion cooling with a cooling rate of 28°C / s. The temperature of the steel strip is reduced to 603°C for coiling, and finally the product performance is tested, as shown in Table 2 below.

[0030] Example 3

[0031] The molten iron is pre-treated for desulfurization, and the top and bottom combined blown converter is used to decarbonize and dephosphorize the molten iron to obtain molten steel. Argon is blown throughout the converter smelting process, scrap steel is added to the converter, and the converter tapping temperature is 1645℃. Then the molten steel after converter smelting is subjected to LF refining outside the furnace, and the refining temperature is ≥1560℃. The LF refining outside the furnace is subjected to temperature measurement and composition fine-tuning. The chemical composition of the LF refining casting machine is shown in Table 1. The overheat of the slab continuous casting is 27℃, and then the slab is cleaned, slowly cooled, and the quality of the continuous casting is checked. The slab heating temperature is 1215℃, and the heating time is 258min. The heated slab is dephosphorized by high-pressure water. The width is set by a fixed width press, and 2-stand rough rolling and 7-stand CVC finishing rolling are used. The finishing rolling start temperature is 1031℃, the finishing rolling final temperature is 890℃, and the finished product thickness is 6.0mm. Laminar cooling adopts front dispersion cooling with a cooling rate of 27°C / s. The temperature of the steel strip is reduced to 608°C for coiling, and finally the product performance is tested, as shown in Table 2 below.

[0032] Example 4

[0033] The molten iron is pre-treated for desulfurization, and the top and bottom combined blown converter is used to decarbonize and dephosphorize the molten iron to obtain molten steel. Argon is blown throughout the converter smelting process, and scrap steel is added to the converter. The converter tapping temperature is 1641℃. Then the molten steel after converter smelting is subjected to LF refining outside the furnace, and the refining temperature is ≥1562℃. The LF refining outside the furnace is subjected to temperature measurement and composition fine-tuning. The chemical composition of the LF refining casting machine is shown in Table 1. The overheat of the slab continuous casting is 32℃, and then the slab is cleaned, slowly cooled, and the quality of the continuous casting is checked. The slab heating temperature is 1210℃, the heating time is 263min, and the heated slab is dephosphorized by high-pressure water. The width is set by a fixed width press, and 2-stand rough rolling and 7-stand CVC finishing rolling are used. The finishing rolling start temperature is 1030℃, the finishing rolling final temperature is 896℃, and the finished product thickness is 8.0mm. Laminar cooling adopts front dispersion cooling with a cooling rate of 26°C / s. The temperature of the steel strip is reduced to 602°C for coiling, and finally the product performance is tested, as shown in Table 2 below.

[0034] Comparative Example 1

[0035] The production method is the same as that shown in Example 1, except that the chemical composition of the LF refining feed casting machine is different from that used in Example 1, as shown in Table 1. Finally, the product performance test is carried out, as shown in Table 2.

[0036] Comparative Example 2

[0037] The production method is the same as that shown in Example 4, except that the chemical composition of the LF refining casting machine is different from that used in Example 4, as shown in Table 1. Finally, the product performance test is carried out, as shown in Table 2.

[0038] Comparative Examples 3-4

[0039] The production method of Comparative Examples 3-4 is the same as that of Example 1, except that the coiling temperature is different from that of Example 1, specifically, the coiling temperature of Comparative Example 3 is 540° C., and the coiling temperature of Comparative Example 4 is 660° C. Finally, the product performance is tested, as shown in Table 2 below.

[0040] Table 1: Chemical composition (wt%) of Examples 1 to 4 of the present invention Comparative Examples 1 to 4

[0041] Example C Si Mn P S Alt Ti Ca 1 0.171 0.05 0.60 0.018 0.004 0.035 0.036 0.0015 2 0.176 0.08 0.68 0.016 0.003 0.045 0.030 0.0026 3 0.165 0.10 0.70 0.015 0.003 0.030 0.037 0.0018 4 0.162 0.06 0.63 0.017 0.002 0.035 0.035 0.0018 Comparative Example 1 0.171 0.05 0.90 0.018 0.004 0.045 0.060 0.0015 Comparative Example 2 0.180 0.07 0.30 0.018 0.002 0.025 0.026 0.0016 Comparative Example 3 0.171 0.05 0.60 0.018 0.004 0.035 0.036 0.0015 Comparative Example 4 0.171 0.05 0.60 0.018 0.004 0.035 0.036 0.0015

[0042] The mechanical properties of the steel coils of Examples 1 to 4 of the present invention and Comparative Examples 1 to 4 were tested, and the test results are shown in Table 2.

[0043] Table 2: Mechanical properties of the steel coils of Examples 1 to 4 of the present invention and Comparative Examples 1 to 4

[0044]

[0045] As can be seen from the contents recorded in Tables 1 and 2 above, the mechanical properties of the thin-gauge automobile body steel with a yield strength greater than 355MPa provided by the present invention can meet the following requirements: yield strength ≥ 355MPa, tensile strength 490-630MPa, elongation ≥ 20%, preferably meet the following requirements: yield strength 467-527MPa, tensile strength 539-590MPa, elongation 26-29%, and the product significantly improves the organization and performance of the steel by adding a trace amount of Ti element to the steel, so that the product has high strength and good toughness and welding performance. Since the addition of titanium element can improve the strength of the steel, thinner steel can be used to manufacture the automobile body under the premise of ensuring safety, which helps to reduce the weight of the automobile, improve fuel economy and environmental protection performance. In addition, the product production method is simple and easy, suitable for industrial mass production, and all performances meet the requirements of relevant standards and user needs. According to the test results of comparative examples 1-2, when the chemical composition of the product cannot meet the requirements of the present invention, the mechanical properties of the product will be unqualified. For example, when the content of Mn and Ti in comparative example 1 is higher than the standard requirements, the product obtained has high strength and low elongation, and the bending test is unqualified, and the cold processing formability is poor during the later use; when the content of Mn and Ti in comparative example 2 is lower than the standard requirements, the strength of the product obtained is lower than the standard requirements, which cannot meet the needs of users. According to the results of comparative examples 3-4, when the chemical composition of the product meets the requirements of the present invention, but the production process cannot meet the requirements of the present invention, for example, when the coiling temperature is lower than or higher than the set value, the performance of the obtained product will also fail to meet the requirements. The low coiling temperature in comparative example 3 leads to high strength and unqualified bending test, which cannot meet the needs of users; the high coiling temperature in comparative example 4 will cause the product strength to be low, resulting in insufficient load-bearing capacity during subsequent use.

[0046] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A Ti microalloyed steel with a yield strength greater than 355 MPa for thin gauge automobile body, the chemical composition of which is as follows by mass percentage: C: 0.16-0.18%, Si: 0.03-0.10%, Mn: 0.55-0.70%, P≤0.018%, S≤0.015%, Alt: 0.020-0.045%, Ti: 0.030-0.040%, Ca: 0.0010-0.0030%, and the remainder is Fe and unavoidable inclusions; The mechanical properties of the automobile body steel meet the following requirements: yield strength ≥355MPa, tensile strength 490-630MPa, and elongation ≥20%.

2. The steel for automobile body according to claim 1, wherein the chemical composition, by mass percentage, is: C: 0.162-0.176%, Si: 0.05-0.10%, Mn: 0.60-0.70%, P≤0.018%, S≤0.005%, Alt: 0.030-0.045%, Ti: 0.030-0.037%, Ca: 0.0015-0.0026%, and the rest is Fe and unavoidable inclusions.

3. The steel for automobile body according to claim 1 or 2, wherein the chemical composition, by mass percentage, is: C: 0.171%, Si: 0.05%, Mn: 0.60%, P: 0.018%, S: 0.004%, Alt: 0.035%, Ti: 0.036%, Ca: 0.0015%, and the remainder is Fe and unavoidable inclusions.

4. The steel for automobile body according to claim 1 or 2, wherein the chemical composition, by mass percentage, is: C: 0.176%, Si: 0.08%, Mn: 0.68%, P: 0.016%, S: 0.003%, Alt: 0.045%, Ti: 0.030%, Ca: 0.0026%, and the remainder is Fe and unavoidable inclusions.

5. The steel for automobile body according to claim 1 or 2, wherein the chemical composition, by mass percentage, is: C: 0.165%, Si: 0.10%, Mn: 0.70%, P: 0.015%, S: 0.003%, Alt: 0.030%, Ti: 0.037%, Ca: 0.0018%, and the remainder is Fe and unavoidable inclusions.

6. The steel for automobile body according to claim 1 or 2, wherein the chemical composition, by mass percentage, is: C: 0.162%, Si: 0.06%, Mn: 0.63%, P: 0.017%, S: 0.002%, Alt: 0.035%, Ti: 0.035%, Ca: 0.0018%, and the remainder is Fe and unavoidable inclusions.

7. The steel for automobile body according to any one of claims 1 to 6, wherein the mechanical properties thereof meet the following requirements: yield strength 467-527 MPa, tensile strength 539-590 MPa, and elongation 26-29%.

8. The method for producing the automobile body steel according to any one of claims 1 to 7, comprising the following process: Smelting - continuous casting - slab heating - rolling - cooling - coiling; among which: The smelting-continuous casting process comprises: KR desulfurization-converter-LF refining-slab continuous casting-slow cooling, and the composition of the molten steel supplied to the casting machine comprises C: 0.16-0.18%, Si: 0.03-0.10%, Mn: 0.55-0.70%, P≤0.018%, S≤0.015%, Alt: 0.020-0.045%, Ti: 0.030-0.040%, Ca: 0.0010-0.0030%; The slab heating process includes: sending the slab after surface cleaning into the heating furnace, strictly controlling the slab heating temperature, furnace time, soaking temperature, soaking time and furnace discharge temperature, the heating temperature is controlled at 1210±20°C, the furnace time is controlled at 160-270min, the soaking temperature is controlled at 1230±20°C, the soaking time is controlled at 25-60min, and the furnace discharge temperature is controlled at 1220±20°C; The rolling process includes a rough rolling stage and a finishing rolling stage. The rough rolling stage adopts a 3+3 mode two-stand rolling mill for rough rolling, and the finishing stage adopts a 7-stand continuous variable crown rolling mill for finishing rolling. The finishing stage adopts speed increase rolling; the finishing rolling entrance thickness is 40mm, the starting rolling temperature of the finishing rolling is not less than 1030°C, and the final rolling temperature of the finishing rolling is 890±15°C; The cooling process adopts laminar cooling equipment, the cooling mode is front dispersion, and the computer secondary system self-learning calculation results are adopted; The coiling temperature is 600±15°C.

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