Preparation method of low-cost 300MPa-grade low-alloy high-strength steel

Abstract

The invention discloses a preparation method of low-cost 300MPa-grade low-alloy high-strength steel. The preparation method comprises the following steps: (1) smelting-continuous casting; (2) hot rolling; (3) pickling and cold rolling; (4) continuous annealing; the low-alloy high-strength steel comprises the following chemical components in percentage by mass: 0.050%-0.065% of C, less than or equal to 0.030% of Si, 0.30%-0.40% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, 0.015%-0.040% of Alt, 0.008%-0.013% of Nb, less than or equal to 0.0080% of N, 0.0008%-0.0020% of Ca and the balance of Fe and inevitable impurities. By optimizing the chemical components and the preparation process, the alloy cost and the process cost are remarkably reduced while it is guaranteed that the strength of the steel reaches the 300 MPa level, and industrial low-cost production is achieved.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical sheet technology, and particularly relates to a method for preparing low-cost 300MPa grade low alloy high-strength steel. Background Technology

[0002] Low-alloy high-strength steel is widely used in engineering structures, machinery manufacturing, and other fields. As a commonly used strength grade, 300MPa grade cold-rolled low-alloy high-strength steel often relies on high alloy element content or complex processes to ensure performance in current technologies, resulting in high production costs and making it difficult to meet market demand for low-cost, high-performance steel. Against this backdrop, developing a low-cost preparation method for 300MPa grade cold-rolled low-alloy high-strength steel that balances composition optimization, process simplification, and energy reduction is of significant practical importance for enhancing product market competitiveness, responding to national green manufacturing policies, and supporting the high-quality development of the automotive industry.

[0003] The 300MPa grade low-alloy high-strength steel invented by Chengdu Advanced Metal Materials Industry Technology Research Institute (patent name: Production method of cold-rolled low-alloy high-strength steel plate, application publication number CN 107177770 B) is also a 300MPa grade low-alloy high-strength steel, just like this invention. The core production process of the product is continuous annealing + finishing, while that of this invention is continuous annealing + leveling (0.9-1.4%). The main strengthening elements of the product are C + Mn (0.30-0.50%) + Nb (0.010-0.020%), while that of this invention is C + Mn (0.30-0.40%) + very low Nb (0.008-0.013%), and the Si content is much lower than that of the product (0.05-0.15%), making the alloy cost of this invention more advantageous. In addition, there are differences between the two in hot rolling furnace time, coiling temperature, and annealing soaking temperature. The 300MPa grade low-alloy high-strength steel developed by Tangsteel (patent name: Production Method of 260-330MPa Grade Low-alloy High-strength Steel, application publication number CN104928576A) is also a low-alloy high-strength steel with a yield strength of 300MPa, just like the product of this invention. The main production process of Tangsteel's product is annealing + leveling, while that of this invention is continuous annealing + leveling. The main strengthening elements of Tangsteel's product are C+Mn(0.60%) / C+Mn+Nb / C+Mn+Ti / C+Mn+Nb+Ti, while the main strengthening element of this invention is C+Mn+low Nb. This invention has a certain alloy cost advantage. In addition, the hot rolling final rolling temperature, cold rolling reduction rate, annealing temperature, and leveling mill elongation are also different. The 300MPa grade low-alloy high-strength steel developed by Wuhan Iron and Steel (Patent title: A multi-grade cold-rolled low-alloy high-strength steel with yield strength covering 300-340MPa and its manufacturing method, application publication number CN 109811267) A) Both are 300MPa grade low-alloy high-strength steels. In terms of composition, the main strengthening elements of Wuhan Iron and Steel's product are C + high Mn (0.7-1.0%) + Nb (0.015-0.040%), while that of this invention is C + low Mn (0.30-0.40%) + extremely low Nb (0.008-0.013%). The Mn and Nb contents are much lower than those of the product, resulting in a significant cost advantage. In terms of process, the heating temperature of Wuhan Iron and Steel's product is 1260-1300℃ (higher than that of this invention, 1200-1240℃). The process parameters of this invention are more suitable for low-alloy systems, and the annealing and heating temperatures are more in line with the requirements for low cost and energy saving. The thickness coverage (0.7-2.0mm) is more focused on commonly used automotive specifications. Summary of the Invention

[0004] The purpose of this invention is to provide a low-cost method for preparing 300MPa grade low-alloy high-strength steel. By optimizing the chemical composition and preparation process, while ensuring the steel strength reaches the 300MPa grade, the method significantly reduces alloy and process costs, achieving low-cost industrial production. Mechanical properties meet the following requirements: yield strength R... p0.2300~380MPa, tensile strength R m 380~480MPa, elongation A 80 ≥23%.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a low-cost method for preparing 300MPa grade low-alloy high-strength steel, comprising:

[0007] (1) Smelting-continuous casting production process: hot metal pretreatment-converter-LF refining-casting machine;

[0008] (2) Hot rolling production process: billet heating—rough rolling—finish rolling—coiling; the billet is in the furnace for 180 to 240 minutes, the furnace exit temperature is 1200 to 1240℃, the rough rolling adopts a 3+3 mode 2-stand rolling mill, and the finish rolling adopts a 7-stand continuous variable crown rolling mill; the final rolling temperature of the finish rolling is 900±20℃, and the thickness of the hot rolled steel strip is 3.0 to 5.5mm; the cooling adopts laminar flow cooling equipment, front-dispersive cooling mode, and the coiling temperature is 590±20℃;

[0009] (3) Pickling and cold rolling process: After the hot-rolled strip steel is pickled to remove the surface iron oxide scale, it is cold rolled by a 5-stand cold rolling mill with a cold rolling reduction rate of 64-77% to the target thickness of 0.7-2.0 mm.

[0010] (4) Continuous annealing process: After uncoiling the cold-hardened steel strip, it is welded and produced continuously. The furnace speed is 70-170 m / min, the soaking temperature is 755-810℃, the temperature is slowly cooled to 600-640℃, and then cooled to 380-450℃. The flattening elongation is 0.9-1.5%.

[0011] The chemical composition of the low-alloy high-strength steel, by mass percentage, is as follows: C: 0.050%–0.065%, Si: ≤0.030%, Mn: 0.30%–0.40%, P: ≤0.020%, S: ≤0.010%, Alt: 0.015%–0.040%, Nb: 0.008%–0.013%, N: ≤0.0080%, Ca: 0.0008%–0.0020%, with the remainder being Fe and unavoidable impurities.

[0012] 2. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 1, characterized in that the chemical composition of the low-alloy high-strength steel, by mass percentage, is: C: 0.052%–0.062%, Si: 0.017%–0.030%, Mn: 0.32%–0.37%, P: 0.010–0.019%, S: 0.002–0.007%, Alt: 0.028%–0.039%, Nb: 0.008%–0.011%, N: 0.0038–0.0049%, Ca: 0.0009%–0.0012%, with the remainder being Fe and unavoidable impurities.

[0013] 3. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 2, characterized in that the chemical composition of the low-alloy high-strength steel by mass percentage is: C: 0.057%, Si: 0.023%, Mn: 0.35%, P: 0.014%, S: 0.005%, Alt: 0.033%, Nb: 0.009%, N: 0.0043%, Ca: 0.0010%, with the remainder being Fe and unavoidable impurities.

[0014] 4. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 2, characterized in that the chemical composition of the low-alloy high-strength steel by mass percentage is: C: 0.054%, Si: 0.019%, Mn: 0.33%, P: 0.017%, S: 0.003%, Alt: 0.030%, Nb: 0.0085%, N: 0.0040%, Ca: 0.0011%, with the remainder being Fe and unavoidable impurities.

[0015] 5. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 2, characterized in that the chemical composition of the low-alloy high-strength steel by mass percentage is: C: 0.059%, Si: 0.027%, Mn: 0.36%, P: 0.012%, S: 0.006%, Alt: 0.036%, Nb: 0.010%, N: 0.0046%, Ca: 0.0009%, with the remainder being Fe and unavoidable impurities.

[0016] 6. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 2, characterized in that the chemical composition of the low-alloy high-strength steel by mass percentage is: C: 0.056%, Si: 0.025%, Mn: 0.35%, P: 0.015%, S: 0.005%, Alt: 0.034%, Nb: 0.009%, N: 0.0048%, Ca: 0.0011%, with the remainder being Fe and unavoidable impurities.

[0017] 7. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 2, characterized in that the chemical composition of the low-alloy high-strength steel by mass percentage is: C: 0.060%, Si: 0.021%, Mn: 0.34%, P: 0.018%, S: 0.0038%, Alt: 0.031%, Nb: 0.011%, N: 0.0043%, Ca: 0.00105%, with the remainder being Fe and unavoidable impurities.

[0018] 8. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claims 3-7, characterized in that the billet is in the furnace for 196-227 min and the furnace exit temperature is 1216-1236℃; the finishing rolling temperature is 892-905℃, the hot-rolled steel strip thickness is 3.0-5.5 mm, and the coiling temperature is 573-603℃.

[0019] 9. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 8, characterized in that the furnace speed is 78-155m / min, the soaking temperature is 758-808℃, the temperature is slowly cooled to 610-635℃, and then cooled to 391-430℃, with a flattening elongation of 0.99-1.49%.

[0020] 10. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 9, characterized in that the mechanical properties of the low-alloy high-strength steel strip are: yield strength R p0.2 310~329MPa, tensile strength R m 413~431MPa, elongation A 80 30.0%–34.0%.

[0021] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0022] This invention optimizes the types and contents of alloying elements, avoiding the use of high-cost alloys. Simultaneously, it employs a mature converter-LF refining-continuous casting-rolling process, significantly reducing production costs and making it suitable for large-scale industrial production. By rationally controlling the content and proportion of elements such as C, Mn, Nb, and Alt, the steel achieves a strength of 300 MPa while ensuring good toughness and plasticity, meeting engineering application requirements. Furthermore, the preparation process is based on conventional steelmaking and rolling processes, requiring no additional special equipment, exhibiting strong process stability, and is easy to promote and implement. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings.

[0024] Figure 1 This is a microstructure diagram of Embodiment 1 of the present invention. Detailed Implementation

[0025] The present invention will be described in detail below through specific embodiments. These embodiments are only intended to help understand the present invention and do not limit the scope of the present invention.

[0026] Example

[0027] According to the above steelmaking process requirements, the actual chemical composition of the slab is shown in Table 1.

[0028] Table 1 Chemical composition (wt%) of embodiments of the present invention

[0029]

[0030]

[0031] According to the above hot rolling process requirements, the hot rolling thickness is 3.0 to 5.5 mm, and the actual process is shown in Table 2.

[0032] Table 2 Hot rolling process of embodiments of the present invention

[0033]

[0034] According to the above requirements for cold rolling, continuous annealing, and leveling processes, the cold rolling thickness is 0.70 to 2.00 mm. The actual continuous annealing and leveling processes are shown in Table 3.

[0035] Table 3. Continuous shearing and leveling processes in embodiments of the present invention.

[0036]

[0037] The mechanical properties of the steel strip in this embodiment of the invention were tested, and the test results are shown in Table 4.

[0038] Table 4 Mechanical properties of steel strip in embodiments of the present invention

[0039]

[0040]

[0041] As shown in Table 4, the mechanical properties of the low-cost 300MPa grade cold-rolled low-alloy high-strength steel strip of this invention are as follows: yield strength R p0.2 310~329MPa, tensile strength R m 413~431MPa, elongation A 80 The content of the steel produced in this embodiment is 30.0% to 34.0%. In summary, the steel produced in this embodiment meets the requirements for 300MPa grade low-alloy high-strength steel.

[0042] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing low-cost 300MPa grade low-alloy high-strength steel, characterized in that, include: (1) Smelting-continuous casting production process: hot metal pretreatment-converter-LF refining-casting machine; (2) Hot rolling production process: billet heating—rough rolling—finish rolling—coiling; the billet is in the furnace for 180 to 240 minutes, the furnace exit temperature is 1200 to 1240℃, the rough rolling adopts a 3+3 mode 2-stand rolling mill, and the finish rolling adopts a 7-stand continuous variable crown rolling mill; the final rolling temperature of the finish rolling is 900±20℃, and the thickness of the hot rolled steel strip is 3.0 to 5.5mm; the cooling adopts laminar flow cooling equipment, front-dispersive cooling mode, and the coiling temperature is 590±20℃; (3) Pickling and cold rolling process: After the hot-rolled strip steel is pickled to remove the surface iron oxide scale, it is cold rolled by a 5-stand cold rolling mill with a cold rolling reduction rate of 64-77% to the target thickness of 0.7-2.0 mm. (4) Continuous annealing process: After uncoiling the cold-hardened steel strip, it is welded and produced continuously. The furnace speed is 70-170 m / min, the soaking temperature is 755-810℃, the temperature is slowly cooled to 600-640℃, and then cooled to 380-450℃. The flattening elongation is 0.9-1.5%. The chemical composition of the low-alloy high-strength steel, by mass percentage, is as follows: C: 0.050%–0.065%, Si: ≤0.030%, Mn: 0.30%–0.40%, P: ≤0.020%, S: ≤0.010%, Alt: 0.015%–0.040%, Nb: 0.008%–0.013%, N: ≤0.0080%, Ca: 0.0008%–0.0020%, with the remainder being Fe and unavoidable impurities.

2. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 1, characterized in that, The chemical composition of the low-alloy high-strength steel, by mass percentage, is as follows: C: 0.052%–0.062%, Si: 0.017%–0.030%, Mn: 0.32%–0.37%, P: 0.010–0.019%, S: 0.002–0.007%, Alt: 0.028%–0.039%, Nb: 0.008%–0.011%, N: 0.0038–0.0049%, Ca: 0.0009%–0.0012%, with the remainder being Fe and unavoidable impurities.

3. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 2, characterized in that, The chemical composition of the low-alloy high-strength steel, by mass percentage, is as follows: C: 0.057%, Si: 0.023%, Mn: 0.35%, P: 0.014%, S: 0.005%, Alt: 0.033%, Nb: 0.009%, N: 0.0043%, Ca: 0.0010%, with the remainder being Fe and unavoidable impurities.

4. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 2, characterized in that, The chemical composition of the low-alloy high-strength steel, by mass percentage, is as follows: C: 0.054%, Si: 0.019%, Mn: 0.33%, P: 0.017%, S: 0.003%, Alt: 0.030%, Nb: 0.0085%, N: 0.0040%, Ca: 0.0011%, with the remainder being Fe and unavoidable impurities.

5. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 2, characterized in that, The chemical composition of the low-alloy high-strength steel, by mass percentage, is as follows: C: 0.059%, Si: 0.027%, Mn: 0.36%, P: 0.012%, S: 0.006%, Alt: 0.036%, Nb: 0.010%, N: 0.0046%, Ca: 0.0009%, with the remainder being Fe and unavoidable impurities.

6. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 2, characterized in that, The chemical composition of the low-alloy high-strength steel, by mass percentage, is as follows: C: 0.056%, Si: 0.025%, Mn: 0.35%, P: 0.015%, S: 0.005%, Alt: 0.034%, Nb: 0.009%, N: 0.0048%, Ca: 0.0011%, with the remainder being Fe and unavoidable impurities.

7. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 2, characterized in that, The chemical composition of the low-alloy high-strength steel, by mass percentage, is as follows: C: 0.060%, Si: 0.021%, Mn: 0.34%, P: 0.018%, S: 0.0038%, Alt: 0.031%, Nb: 0.011%, N: 0.0043%, Ca: 0.00105%, with the remainder being Fe and unavoidable impurities.

8. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claims 3-7, characterized in that, The billet is in the furnace for 196–227 minutes and exits at 1216–1236℃; the final rolling temperature is 892–905℃, the hot-rolled strip thickness is 3.0–5.5 mm, and the coiling temperature is 573–603℃.

9. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 8, characterized in that, The furnace speed is 78–155 m / min, the soaking temperature is 758–808℃, the temperature is slowly cooled to 610–635℃, and then cooled to 391–430℃, with a flattening elongation of 0.99–1.49%.

10. The method for preparing low-cost 300MPa grade low-alloy high-strength steel according to claim 9, characterized in that, The mechanical properties of the low-alloy high-strength steel strip are: yield strength R p0.2 310~329MPa, tensile strength R m 413~431MPa, elongation A 80 30.0%–34.0%.

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