A production method for improving the performance stability of single high-Ti high-strength steel in CSP production lines

Abstract

This invention discloses a production method for improving the performance stability of single high-Ti high-strength steel in a CSP production line. The method comprises: hot metal desulfurization → converter top and bottom combined blowing → LF ladle refining → continuous casting → homogenization → controlled rolling → controlled cooling → coiling. Specifically, in the continuous casting stage, the slab thickness is 60–85 mm; in the homogenization stage, the homogenization furnace exit temperature is 1080–1160 °C; and in the controlled rolling stage, the process is carried out on a hot continuous rolling mill with an initial rolling temperature ≥1030 °C, a reduction rate of ≥50% for the first three passes, and a reduction rate of 10% for the F7 pass. ~20%, with a final rolling temperature of 860~900℃; in the controlled cooling stage, an ultra-fast cooling mode is first adopted, controlling the cooling rate at 92~130℃ / S and the cooling time at 3~9S; then, a low-speed cooling mode is adopted, controlling the cooling rate at 20~60℃ / S, cooling to 460~540℃ for coiling; this invention solves the problem of large strength fluctuation range of high-Ti high-strength steel with single content, while not increasing the cost or operational difficulty of existing production methods, and has the capability for mass production.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for producing thin-gauge, single-size, high-Ti, high-strength steel on a CSP production line. Background Technology

[0002] When developing steel products, while ensuring mechanical properties and user performance, efforts should be made to reduce or eliminate the addition of alloying elements in the product design as much as possible. In particular, in the development of high-strength steel products, inexpensive Ti is used to replace expensive Nb and V for microalloying. In recent years, the design of single high-Ti high-strength steel has received increasing attention.

[0003] Single high-Ti microalloyed products suffer from significant performance fluctuations and uneven strength distribution along the length of hot-rolled high-Ti steel coils due to factors such as the control level of Ti yield during smelting, fluctuations in effective Ti caused by the combination of Ti with impurity elements, and the narrow Ti precipitation strengthening process window requiring high control over the rolling process. The strength fluctuation range of the beginning, middle, and end of the coil is 100~250MPa. This large fluctuation range leads to application quality risks such as side bending and warping during cutting and blanking, difficulty in cold bending and forming, and easy cracking, which cannot meet the user's requirements.

[0004] Therefore, the performance stability of hot-rolled Ti steel coils is a major challenge in the development of this series of steel grades. How to improve the performance stability of thin-gauge, single-size, high-Ti, high-strength steel in CSP production lines has become an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a production method that controls the strength fluctuation range of thin-gauge, single-content high-Ti high-strength steel within 20~60MPa in CSP production lines, solving the problem of large strength fluctuation range in single-content high-Ti high-strength steel. At the same time, it does not increase the cost or the difficulty of operation compared to existing production methods, and has the capability for large-scale mass production.

[0006] To achieve the above objectives, the following technical solution is adopted:

[0007] A production method for improving the performance stability of single high-Ti high-strength steel in CSP production line includes hot metal desulfurization → converter top and bottom composite blowing → LF ladle furnace refining → continuous casting → homogenization → controlled rolling → controlled cooling → coiling.

[0008] During the continuous casting stage, the slab thickness is 60~85mm;

[0009] During the homogenization stage, the outlet temperature of the homogenization furnace is 1080~1160℃;

[0010] The controlled rolling stage is carried out in the hot continuous rolling mill. The initial rolling temperature is ≥1030℃, the reduction rate of the first three passes is ≥50%, the reduction rate of the F7 pass is 10~20%, and the final rolling temperature is 860~900℃.

[0011] During the controlled cooling stage, the ultra-fast cooling mode is first adopted, with the cooling speed controlled at 92~130℃ / S and the cooling time at 3~9S; then the low-speed cooling mode is adopted, with the cooling speed controlled at 20~60℃ / S, and the temperature is cooled to 460~540℃ for winding.

[0012] According to the above scheme, the chemical composition of the single high-Ti high-strength steel by mass percentage is: C: 0.01~0.06, Si: ≤0.2, Mn: 0.2~1.70, P: ≤0.015, Ti: 0.06~0.13, with the balance being balance iron and unavoidable impurities.

[0013] In the optimized scheme, the chemical composition of the single high-Ti high-strength steel meets the following requirements: S≤0.003%, N≤60ppm, O≤15ppm.

[0014] In the further optimized scheme, C: 0.02~0.05, Si: ≤0.18, Mn: 0.5~1.40, P: ≤0.012, Ti: 0.08~0.12.

[0015] In the further optimized scheme, C: 0.03~0.04, Si: ≤0.16, Mn: 0.7~1.20, P: ≤0.010, Ti: 0.10~0.12.

[0016] According to the above plan, the slab thickness is 70~80mm during the continuous casting stage.

[0017] According to the above scheme, during the heat soaking stage, the furnace outlet temperature is 1100~1140℃.

[0018] According to the above plan, the controlled rolling stage is carried out in the hot continuous rolling mill, with an initial rolling temperature of ≥1040℃, a reduction rate of ≥62% for the first three passes, a reduction rate of 12~18% for the F7 pass, and a final rolling temperature of 865~895℃.

[0019] According to the above scheme, during the controlled cooling stage, the ultra-fast cooling mode adopts water cooling with a cooling rate of 100~120℃ / S and a cooling time of 5~7S.

[0020] According to the above scheme, during the controlled cooling stage, the cooling rate in the low-speed cooling mode is 30~50℃ / S, and the coil is wound up when cooled to 480~520℃.

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

[0022] This invention controls the two-stage cooling process after rolling and finishing, and controls the cooling rate in stages to control the proportion of microstructure and precipitates formed at different cooling stages. This controls the contribution ratio of strength and impact toughness, and ultimately achieves the goal of controlling the strength fluctuation range of thin-gauge, single high-Ti high-strength steel in CSP production lines within 20~60MPa.

[0023] This invention successfully prepared a low-alloy high-strength steel product with a thickness ≥1.2-3mm and a Ti content of 0.06~0.13% (no other precious alloying elements need to be added to the steel). The test results show that the yield strength and tensile strength of the whole roll of steel fluctuate within 20~60MPa, the elongation is ≥16%, and the performance stability is very good, which solves the problem of large strength fluctuation of high-Ti steel.

[0024] The production method of this invention is relatively simple, enabling continuous mass production with stable quality, and further enriching the product types. Detailed Implementation

[0025] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0026] The specific implementation provides a single high-Ti high-strength steel molten steel, as shown in Table 1. Examples 1-3 use the above-mentioned molten steel, which is refined in an LF furnace after converter smelting; subsequently, the molten steel is continuously cast and rolled into thin slabs, with a slab thickness of 60-85mm; the slabs are heated in a soaking furnace at a temperature controlled at 1080-1160℃; rolling is performed on a 7-stand finishing mill, with a finishing rolling start temperature ≥1020℃, a reduction rate ≥50% for the first three passes, and a reduction rate of 10-20% for the F7 pass; post-rolling cooling: after exiting the finishing mill, it directly enters the ultra-fast cooling water mode, controlling the cooling rate at 92-130℃ / s, with an ultra-fast cooling section cooling time of 3-9s; then it enters the low-speed cooling mode, controlling the cooling rate at 20-60℃ / s, cooling to 460-540℃ before coiling; the rolled thickness is 1.2-3.0mm.

[0027] In the optimized scheme, the slab thickness is 70~80mm during the continuous casting stage.

[0028] In the optimized scheme, during the homogenization stage, the temperature of the homogenization furnace exiting the furnace is 1100~1140℃.

[0029] In the optimized scheme, the controlled rolling stage is carried out in the hot continuous rolling mill, with an initial rolling temperature of ≥1040℃, a reduction rate of ≥62% for the first three passes, a reduction rate of 12~18% for the F7 pass, and a final rolling temperature of 865~895℃.

[0030] In the optimized solution, during the controlled cooling stage, the ultra-fast cooling mode uses water cooling with a cooling rate of 100~120℃ / S and a cooling time of 5~7S.

[0031] In the optimized scheme, during the controlled cooling stage, the cooling speed in the low-speed cooling mode is 30~50℃ / S, and the temperature is cooled to 480~520℃ before winding.

[0032] Table 1. Chemical composition of steel (wt%)

[0033]

[0034] Comparative Examples 1-3 and Examples 1-3 used steel from the same furnace. The specific process is as follows: the cast steel billet thickness is 60-85 mm; the billet is heated in a soaking furnace at a temperature controlled at 1080-1160℃; it is rolled on a 7-stand finishing mill with an initial rolling temperature ≥1050℃ and a final rolling temperature controlled at 880-930℃. After finishing rolling, laminar flow cooling is performed. After cooling, coiling is carried out at a temperature of 600-660℃.

[0035] The specific production process parameters are shown in Table 2.

[0036] Table 2

[0037]

[0038] The properties of the high-Ti steels obtained in the above embodiments and comparative examples are shown in Table 3.

[0039] Table 3

[0040]

[0041] As can be seen from Table 3, compared with Comparative Examples 1-3, the steel products obtained in Examples 1-3 of the present invention have yield strength fluctuations within 30 MPa and tensile strength fluctuations within 40 MPa at the beginning, middle, and end of the steel coils, while the steel products obtained in the Comparative Examples have yield strength fluctuations within 82-182 MPa and tensile strength fluctuations within 111-211 MPa at the beginning, middle, and end of the steel coils. The strength stability of the Examples is significantly better than that of the Comparative Examples; the elongation of the Examples is also significantly better than that of the Comparative Examples.

[0042] In summary, in the production of high-Ti steel plate and coil products on the CSP production line, compared with traditional production methods, the new production process provided by this invention can indeed significantly improve the performance stability of the product, while also significantly increasing the elongation. Moreover, this improvement in performance stability and elongation is not due to the addition of expensive alloys, but rather to the innovative design of the process, which yields a microstructure that is conducive to the balance of strength and toughness, ultimately resulting in excellent mechanical properties and ensuring a good user experience.

Claims

1. A production method for improving the performance stability of single high-Ti high-strength steel in a CSP production line, characterized in that... The process includes hot metal desulfurization → converter top and bottom combined blowing → LF ladle furnace refining → continuous casting → homogenization → controlled rolling → controlled cooling → coiling; During the continuous casting stage, the slab thickness is 60~85mm; During the homogenization stage, the outlet temperature of the homogenization furnace is 1100~1140℃; The controlled rolling stage is carried out in the hot continuous rolling mill. The initial rolling temperature is ≥1030℃, the reduction rate of the first three passes is ≥50%, the reduction rate of the F7 pass is 10~20%, and the final rolling temperature is 860~900℃. During the controlled cooling stage, the ultra-fast cooling mode is first adopted, with the cooling speed controlled at 92~130℃ / S and the cooling time at 3~9S; then the low-speed cooling mode is adopted, with the cooling speed controlled at 35~50℃ / S, and the temperature is cooled to 460~540℃ for winding. The chemical composition of the single high-Ti high-strength steel by mass percentage is as follows: C: 0.01~0.06%, Si: ≤0.2%, Mn: 0.2~1.70%, P: ≤0.015%, Ti: 0.06~0.13%, S≤0.003%, N: ≤60ppm, O≤15ppm, with the balance being balance iron and unavoidable impurities; The thickness of the single high-Ti high-strength steel is 1.2-3mm.

2. The production method for improving the performance stability of single high-Ti high-strength steel in a CSP production line as described in claim 1, characterized in that... C： 0.02~0.05%, Si: ≤0.18%, Mn: 0.5~1.40%, P: ≤0.012%, Ti: 0.08~0.12%.

3. The production method for improving the performance stability of a single high-Ti high-strength steel in a CSP production line as described in claim 1, characterized in that C: 0.03~0.04%, Si: ≤0.16%, Mn: 0.7~1.20%, P: ≤0.010%, Ti: 0.10~0.12%.

4. The production method for improving the performance stability of single high-Ti high-strength steel in a CSP production line as described in claim 1, characterized in that... During the continuous casting stage, the slab thickness is 70~80mm.

5. The production method for improving the performance stability of single high-Ti high-strength steel in a CSP production line as described in claim 1, characterized in that... The controlled rolling stage is carried out on a hot continuous rolling mill with an initial rolling temperature of ≥1040℃, a reduction rate of ≥62% for the first three passes, a reduction rate of 12~18% for the F7 pass, and a final rolling temperature of 865~895℃.

6. The production method for improving the performance stability of single high-Ti high-strength steel in a CSP production line as described in claim 1, characterized in that... During the controlled cooling phase, the ultra-fast cooling mode uses water cooling with a cooling rate of 100~120℃ / S and a cooling time of 5~7S.

7. The production method for improving the performance stability of single high-Ti high-strength steel in a CSP production line as described in claim 1, characterized in that... During the controlled cooling stage, the temperature is cooled to 480~520℃ before winding.

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