Method for improving performance stability of 550mpa grade steel for automobile seat

Abstract

The present application relates to a kind of methods for improving the performance stability of 550MPa grade automobile seat steel, comprising the following steps, smelting-casting-heating-coarse rolling-finish rolling-laminar cooling-coiling-pickling-finished product;The heating process, the temperature of furnace is controlled at 1220-1240 ℃, total in furnace time is greater than or equal to 180 min;The finish rolling process, the temperature of finish rolling is controlled at 880-900 ℃;The coiling process, the temperature of coiling is controlled at 560-580 ℃, and offline is placed in closed area and slowly cooled to room temperature;The pickling process, using a certain temperature hydrochloric acid is continuously removed through the oxide scale, and the temperature of acid liquor is controlled at 75-90 ℃.The method not only greatly improves the product quality of 550MPa grade automobile seat steel, but also effectively reduces the problems such as stamping cracking, inaccurate positioning, size mismatch, etc., and has good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical rolling technology, and in particular relates to a method for improving the performance stability of 550MPa grade automotive seat steel. Background Technology

[0002] With the rise of emerging domestic brands and increasingly fierce competition among automakers, a cost war has quietly begun. As this war intensifies, the focus is no longer solely on the price of steel raw materials, which significantly impact costs. With the automotive industry becoming increasingly automated and the stamping of parts becoming more complex and varied, end customers are placing higher demands on the stability of material coiling performance. Currently, domestic steel mills invest heavily in developing high-precision products, but research on the stability of material coiling performance is relatively limited. Therefore, improving the stability of material coiling performance is of great significance.

[0003] Chinese patent document CN 110055458 A discloses a method for producing hot-rolled pickled automotive steel sheets, with the following chemical composition and weight percentages: C: 0.02-0.04%, Si ≤ 0.05%, Mn: The composition is 0.20–0.30%, P ≤ 0.020%, S ≤ 0.020%, Nb ≤ 0.010–0.020%, Als ≤ 0.030–0.050%, N ≤ 0.008%, with the balance being Fe and unavoidable impurities. It primarily employs high-temperature coiling, reducing the difficulty of laminar flow cooling control, ensuring the stability of the continuous coiling process, and improving the shape quality and performance stability of the coil during continuous coiling.

[0004] Chinese patent document CN 112281075 A discloses a method for improving the overall performance stability of niobium-titanium composite reinforced 700MPa girder steel coils. The chemical composition and weight percentages are as follows: C: 0.06–0.09%, Mn: 1.50–1.85%, Si: 0.05–0.20%, P: ≤0.015%, S: ≤0.005%, Nb: 0.025–0.060%, Ti: 0.070–0.110%, Mo: ≤0.20%, N: 0.0040–0.0085%, Al… S The content of the steel is 0.025-0.055%, with the remainder being Fe and unavoidable impurities. It is mainly based on the principle that structure determines performance. By stabilizing the steel composition and altering some rolling and cooling processes, the internal structure of the steel is improved, thereby obtaining steel with more consistent properties.

[0005] Chinese patent document CN 110499457 A discloses a high-surface-quality 1200MPa grade hot-dip galvanized duplex steel and its production method. Its chemical composition and weight percentages are as follows: C: 0.07~0.10%, Si: 0.25~0.55%, Mn: 1~4%, P≤0.016%, S≤0.008%, Als: 0.01~0.05%, N≤0.006%, Ti: 0.04~0.08%, Nb: 0.015~0.055%, Mo: 0.15~0.45%, B: 0.008~0.010%, with the remainder being Fe and unavoidable impurities. The main process involves a U-shaped coiling technique and in-furnace pre-oxidation technology to obtain steel coils with stable mechanical properties at the beginning, middle, and end of the galvanizing process.

[0006] Chinese patent document CN 116200680 A discloses a cold-rolled ultra-high-strength steel with uniform through-coil performance and its production method. Its chemical composition and weight percentages are as follows: C: 0.125–0.14%, Mn: 1.80–2.40%, Als: 0.057–0.30%, Si: 0.55–0.80%, Nb: 0.005–0.035%, Cr: 0.47–0.65%, Ti: 0.005–0.034% or Ti: 0.056–0.060%, P: ≤0.015%, S: ≤0.004%, N: ≤0.003%, with the remainder being Fe and unavoidable impurities. The uniform through-coil performance is mainly achieved by increasing the homogenization temperature and time during the annealing process to promote sufficient recrystallization and recovery at the beginning, middle, and end of the coil.

[0007] Publication No. CN 110055458 A / CN 112281075 A mainly achieves the stability of continuous winding performance through winding temperature control, but does not reflect the key control process during rolling; Publication No. CN 110499457 A / CN 116200680 A achieves the stability of continuous winding performance through processes such as annealing, which are lengthy and costly. Summary of the Invention

[0008] This invention provides a method for improving the performance stability of 550MPa grade automotive seat steel that is simple in process, economical and practical, and suitable for large-scale promotion.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for improving the performance stability of 550MPa grade automotive seat steel includes the following steps: smelting, continuous casting, heating, rough rolling, finish rolling, laminar flow cooling, coiling, pickling, and finished product. The heating process involves controlling the furnace exit temperature at 1220-1240℃ and the total furnace time at ≥180min. The finishing rolling process is wherein the final rolling temperature is controlled at 880-900℃. In the winding process, the winding temperature is controlled at 560-580℃, and the product is placed in a closed area to cool slowly to room temperature after it comes off the line.

[0010] Preferably, in the continuous casting process, the steelmaking process cuts short-length billets, and the length of the billets is controlled at 7.5-8m.

[0011] Preferably, in the smelting process, the chemical composition and weight percentage of the molten steel are as follows: C: 0.05-0.06%, Si≤0.1%, Mn: 1.1-1.2%, P≤0.02%, S≤0.01%, Als: 0.02-0.04%, Ti: 0.05-0.06%, N≤0.006%, with the remainder being iron and unavoidable impurities.

[0012] Preferably, in the roughing process, the thickness of the intermediate billet in the hot rolling roughing process is controlled at 47-52mm; edge heaters are used to compensate for the temperature at 50-60℃, and heat insulation covers are used throughout the process.

[0013] Preferably, in the finishing rolling process, the cooling water volume between the stands is increased in finishing rolling F2-F5, and the water volume is controlled at 45-55%; in the speed-up rolling, the rolling speed is controlled at 15-18m / s after tensioning.

[0014] Preferably, in the pickling process, hydrochloric acid is used to continuously remove the iron oxide scale from the coil, with a hydrochloric acid concentration of 120-230 g / L and a hydrochloric acid temperature controlled at 75-90℃.

[0015] Preferably, the steel used for the seat has a yield strength of 500-560 MPa, a tensile strength of 550-620 MPa, a yield and tensile strength fluctuation of ≤20 MPa, and an elongation of 12-18%.

[0016] Compared with the prior art, the present invention has the following advantages: 1. Innovatively implement short-length billet rolling, supplemented by increasing the thickness of intermediate billets, and using edge heaters and heat insulation covers. Multiple methods are coupled to reduce the temperature drop at the head and tail and the edges during rolling, ensuring the temperature uniformity of the head and tail and the cross-section of the plate width during rolling, achieving uniformity of the coil structure, and achieving a yield strength of 500-560MPa, a tensile strength of 550-620MPa, and a fluctuation of yield and tensile strength of ≤20MPa throughout the coil. 2. Unlike the traditional method of reducing the cooling water volume between stands to reduce temperature drop, this invention increases the cooling water volume between stands by 10%, thereby increasing the rolling speed, shortening the rolling time, and further reducing the temperature drop at the beginning and end of the rolling process. This "two-pronged approach" achieves uniform temperature throughout the rolling process.

[0017] 3. This invention does not add any production equipment, has no increased cost, is economical and practical, and is suitable for large-scale promotion, providing technical support for the industry. This invention improves the stability of the coiled performance of 550MPa grade automotive seat steel by coupling methods such as steel slab control, intermediate billet control, and rolling process control. This method not only significantly improves the product quality of 550MPa grade automotive seat steel, but also effectively reduces problems such as stamping cracking, inaccurate positioning, and dimensional inconsistencies, showing good application prospects.

[0018] 4. This invention does not involve annealing or other processes, making the process simple, economical, practical, and suitable for large-scale promotion. Attached Figure Description

[0019] Figure 1 The above is a statistical chart showing the fluctuation of mechanical properties of steel coils throughout the winding process in Examples 1-5.

[0020] Figure 2 The above is a statistical chart showing the fluctuation of mechanical properties of steel coils throughout the winding process, which is used for Comparative Examples 1-3. Detailed Implementation

[0021] This invention provides a method for improving the performance stability of 550MPa grade automotive seat steel. The invention is further illustrated through these embodiments. Those skilled in the art should understand that these specific embodiments and examples are for illustrative purposes only and are not intended to limit the invention.

[0022] A method for improving the performance stability of 550MPa grade automotive seat steel includes the following steps: smelting-continuous casting-heating-rough rolling-finish rolling-laminar cooling-coiling-pickling-finished product; In the smelting process, the chemical composition and weight percentage of molten steel are as follows: C: 0.05-0.06%, Si≤0.1%, Mn: 1.1-1.2%, P≤0.02%, S≤0.01%, Als: 0.02-0.04%, Ti: 0.05-0.06%, N≤0.006%, with the remainder being iron and unavoidable impurities.

[0023] In the continuous casting process, steelmaking cuts short billets, with the billet length controlled at 7.5-8m.

[0024] The heating process involves controlling the furnace exit temperature at 1220-1240℃ and the total furnace time at ≥180min. In the roughing process, the thickness of the intermediate billet in the hot rolling roughing process is controlled at 47-52mm; edge heaters are used to compensate for the temperature at 50-60℃, and insulation covers are used throughout the process.

[0025] In the finishing rolling process, the final rolling temperature is controlled at 880-900℃; in the finishing rolling process, the cooling water volume between the stands is increased in finishing rolling F2-F5, and the water volume is controlled at 45-55%; in the speed-up rolling, the rolling speed after tensioning is controlled at 15-18m / s.

[0026] In the winding process, the winding temperature is controlled at 560-580℃, and the product is placed in a closed area to cool slowly to room temperature after it comes off the line. The pickling process uses hydrochloric acid at a certain temperature to continuously remove the iron oxide scale from the coil. The concentration of hydrochloric acid is 120-230 g / L, and the temperature of hydrochloric acid is controlled at 75-90℃.

[0027] The composition and weight percentage of the 550MPa grade automotive seat steel of the present invention and comparative examples are shown in Table 1. The production method of the 550MPa grade automotive seat steel of the present invention and comparative examples is shown in Table 2. The mechanical properties of the head, middle and tail of the 550MPa grade automotive seat steel of the present invention and comparative examples are shown in Table 3.

[0028] Table 1. Chemical composition (mass percentage) of 550MPa grade automotive seat steel in the embodiments and comparative examples of the present invention.

[0029] Table 2 Production process parameters for 550MPa grade automotive seat steel in embodiments and comparative examples of the present invention

[0030] Table 3 Mechanical properties of steel head, middle and tail sections for automotive seats of 550MPa grade according to embodiments and comparative examples of the present invention

[0031] like Figure 1-2 As shown, the 550MPa grade automotive seat steel produced in Examples 1-5 of this invention has a yield strength of 500-560MPa, a tensile strength of 550-620MPa, a continuous coil yield and tensile strength fluctuation of ≤20MPa, and an elongation of 12-18%. The 550MPa grade automotive seat steel produced in Comparative Examples 1-3 has a continuous coil yield and tensile strength fluctuation of ≥40MPa. Through the implementation of this invention, the mechanical property stability of the 550MPa grade automotive seat steel is significantly improved. This not only reduces the incidence of cracking and dimensional discrepancies caused by large performance fluctuations at the customer's end, improving customer production efficiency and gaining a good reputation, but also expands the market brand power and influence of the 550MPa grade automotive seat steel. This invention is economical, practical, and low-cost, with good application prospects.

[0032] This invention is not limited to the embodiments described above. Although some embodiments of this invention have been described, they are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for improving the performance stability of 550MPa grade automotive seat steel, comprising the following steps: smelting-continuous casting-heating-rough rolling-finish rolling-laminar cooling-coiling-pickling-finished product; characterized in that: In the smelting process, the molten steel has the following chemical composition and weight percentage: C: 0.05-0.06%, Si≤0.1%, Mn: 1.1-1.2%, P≤0.02%, S≤0.01%, Als: 0.02-0.04%, Ti: 0.05-0.06%, N≤0.006%, with the remainder being iron and unavoidable impurities; In the continuous casting process, steelmaking cuts short-length billets, with the billet length controlled at 7.5-8m; The heating process involves controlling the furnace exit temperature at 1220-1240℃ and the total furnace time at ≥180min. In the roughing process, the thickness of the hot-rolled roughing intermediate billet is controlled at 47-52mm; an edge heater is used to compensate for the temperature control at 50-60℃; and a heat insulation cover is used throughout the process. In the finishing rolling process, the cooling water volume between the stands is increased in finishing rolling F2-F5, and the water volume is controlled at 45-55%; the speed-up rolling is carried out, and the rolling speed is controlled at 15-18m / s after tensioning, and the final rolling temperature is controlled at 880-900℃. In the winding process, the winding temperature is controlled at 560-580℃, and the product is placed in a closed area to cool slowly to room temperature after it comes off the line.

2. The method for improving the performance stability of 550MPa grade automotive seat steel according to claim 1, characterized in that: The pickling process uses hydrochloric acid to continuously remove the iron oxide scale from the coil, with a hydrochloric acid concentration of 120-230 g / L and a hydrochloric acid temperature controlled at 75-90℃.

3. The method for improving the performance stability of 550MPa grade automotive seat steel according to claim 1, characterized in that: The steel used for the seats has a yield strength of 500-560MPa, a tensile strength of 550-620MPa, a yield and tensile strength fluctuation of ≤20MPa, and an elongation of 12-18%.

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