Cold-rolled dual-phase steel for solving liquid level fluctuation of crystallizer of equal-diameter row roller casting machine and preparation method of cold-rolled dual-phase steel

Abstract

The invention relates to the technical field of ferrous metallurgy production, in particular to cold-rolled dual-phase steel for solving the problem of liquid level fluctuation of a crystallizer of an equal-diameter row roller casting machine, and the cold-rolled dual-phase steel comprises the following chemical components in percentage by weight: 0.06-0.075% of C; 0.35% to 0.60% of Si; mn: 1.70 to 2.0%; less than or equal to 0.015% of P; s < = 0.005%; 0.020% to 0.060% of Als (aluminum chloride); 0.01% to 0.02% of V; 0.01 to 0.03 percent of Ti; 0.03 to 0.08% of Mo; n is less than or equal to 0.0045%; 0 < = 0.0035%, and the balance Fe and inevitable residual elements. The method has the beneficial effects that the degradation rate of steel-making defects such as inclusion and peeling is greatly reduced; the crystallizer liquid level stability is improved, the crystallizer liquid level fluctuation range is reduced, the number of continuous casting furnaces is increased by 50%, the pulling speed is increased by more than 30%, and the production efficiency and the operation stability are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel metallurgical production, and particularly relates to a cold-rolled dual-phase steel for solving liquid level fluctuation of a crystallizer of an equal-diameter roller caster and a preparation method thereof. BACKGROUND

[0002] The cold-rolled dual-phase high-strength steel HC340 / 590DP is one of the most widely used grades in automobile structural parts due to its good strength-plasticity balance and cost advantage. The solidified shell in the continuous casting process has high high-temperature strength and relatively low plasticity, and is sensitive to process disturbance. When produced on the widely used equal-diameter roller caster, the liquid level of the crystallizer often fluctuates dramatically and irregularly (such as sudden large fluctuations or continuous oscillation), and the amplitude significantly exceeds the normal control range.

[0003] Such abnormal fluctuation leads to: 1) the risk of protective slag entrapment increases dramatically, causing subcutaneous or surface slag inclusion of the casting blank, which seriously affects the quality and qualification rate of the subsequent cold-rolled plate (especially high-surface automobile plate); 2) the number of defects such as surface deep vibration marks and cracks of the casting blank increases; 3) internal cracks may be induced; 4) the liquid level alarm is frequently triggered, and even the casting is interrupted, which reduces the production efficiency and operation stability.

[0004] The conventional control means has limited effect on solving such fluctuation of the cold-rolled dual-phase high-strength steel on the equal-diameter roller caster. The core reason is that the special segmented roller design of the equal-diameter roller caster easily produces and transmits mechanical stress disturbance upwards in the bending / straightening section; and the high-temperature shell characteristics of the cold-rolled dual-phase high-strength steel are extremely sensitive to such stress feedback, and the interaction between the two easily excites specific mode liquid surface oscillation. The existing technology cannot effectively block or inhibit such disturbance caused by the coupling of equipment structure and material characteristics.

[0005] Therefore, it is urgent to develop a crystallizer liquid level stabilizing method specially applicable to the equal-diameter roller caster production of mainstream cold-rolled dual-phase high-strength steel such as HC340 / 590DP, which can effectively prevent abnormal fluctuation induced by lower mechanical stress feedback and ensure product quality and production smoothness. SUMMARY

[0006] In order to overcome the deficiencies of the prior art, the present application provides a cold-rolled dual-phase steel for solving the crystallizer liquid level fluctuation of an equal-diameter roller caster and a preparation method thereof. In the case of using an equal-diameter roller caster, primary phase delta ferrite is formed in the solidification process by reducing the carbon content, and allotropy transformation occurs in the solid state to form austenite, thereby reducing the solidification shrinkage. By combining the characteristics of the equal-diameter roller caster, the process parameters such as pouring temperature, drawing speed, crystallizer water distribution, etc. are optimized to improve the stability of the crystallizer liquid level fluctuation within ±3mm, thereby ensuring the quality of the casting blank, improving the production efficiency and operation stability. The strength loss caused by the reduction of carbon is compensated by increasing the Mn content and adding Mo, V and Ti, while reducing the temperature of the fast cooling section and the overaging section in the continuous annealing process and improving the flatness and elongation control.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions: A cold-rolled dual-phase steel for solving the crystallizer liquid level fluctuation of an equal-diameter roller caster, the chemical composition of which is as follows in terms of weight percentage: C: 0.06-0.075%; Si: 0.35-0.60%; Mn: 1.70-2.0%; P≤0.015%; S≤0.005%; Als: 0.020%-0.060%; V: 0.01-0.02%; Ti: 0.01-0.03%; Mo: 0.03-0.08%; N≤0.0045%; O≤0.0035%, and the rest is Fe and inevitable residual elements.

[0008] Further, the yield strength of the cold-rolled dual-phase steel for solving the crystallizer liquid level fluctuation of an equal-diameter roller caster is 340-460MPa, the tensile strength is 590-680MPa, the elongation is 20%-38%, and n 90 ≥0.15.

[0009] The reasons for the chemical composition design of the present application are as follows: "Reducing carbon content, increasing manganese content, and adding molybdenum, titanium and vanadium" composition design: by reducing the carbon content, primary phase delta ferrite is formed in the solidification process, and allotropy transformation occurs in the solid state to form austenite, thereby reducing the solidification shrinkage. By optimizing the process parameters such as pouring temperature, drawing speed, crystallizer water distribution, etc., the equal-diameter roller crystallizer liquid level fluctuation is effectively solved, and the stability of the crystallizer liquid level fluctuation within ±3mm is ensured.

[0010] By increasing the manganese content and adding molybdenum to increase the hardenability, and titanium and vanadium to strengthen the relatively soft ferrite matrix by fine carbonitride precipitation. This combination of "martensite transformation strengthening + ferrite matrix precipitation strengthening" can effectively improve the strength while ensuring the plasticity. Titanium has a strong affinity with nitrogen, which can form stable TiN first. This not only refines the original austenite grains, but also "protects" vanadium, allowing it to dissolve more fully and precipitate finer VC / VN during subsequent processes, thereby more efficiently contributing to strength, and optimizing the fast cooling and overaging processes of cold rolling continuous annealing to compensate for the strength loss caused by decarburization.

[0011] A preparation method of a cold-rolled dual-phase steel for solving the mold level fluctuation of an equal-diameter casting roller machine, the production process of the cold-rolled dual-phase steel for solving the mold level fluctuation of the equal-diameter casting roller machine: hot metal pretreatment → converter smelting → secondary refining outside the furnace → continuous casting → heating → rough rolling and finish rolling → controlled cooling → coiling → pickling → continuous annealing → flattening → packaging; Among them, the continuous casting and continuous annealing processes are optimized, and the specific method is as follows: Continuous casting: Pouring temperature: 1550-1590℃, superheat ≤25℃; constant speed pouring, casting speed 1.1-1.5m / min; Crystallizer vibration amplitude <±3mm, vibration frequency 120-180cpm; The secondary cooling of continuous casting adopts strong cooling mode, and the specific water consumption is 1.0-1.6L / kg; the crystallizer water distribution is 4400±100L / min on the wide side and 550±50L / min on the narrow side; Low-carbon alloy steel protective slag is used, the tundish slag thickness is controlled to be ≤80mm, and carbon-free tundish covering agent is used; Continuous annealing: Heating and holding temperature: 795-810℃; slow cooling temperature: 690-720℃; continuous annealing speed: ≥90m / min; flattening elongation: 0.4-0.9%.

[0012] Further, the slow cooling temperature in the cooling and annealing is 690-720℃, the overaging 1 temperature is 280-300℃, the overaging 2 temperature is 260-285℃, and the overaging 3 temperature is 250-290℃.

[0013] Further, the flattening elongation is: The strip thickness d is ≤0.949mm, and the flattening elongation is 0.9%; The strip thickness d is 0.950-1.349mm, and the flattening elongation is 0.8%; The strip thickness d is 1.350-1.549mm, and the flattening elongation is 0.7%; Strip thickness d = 1.550 ~ 1.949mm, flat elongation: 0.6%; Strip thickness d ≥ 1.950mm, flat elongation: 0.4%.

[0014] Compared with the prior art, the beneficial effects of the present application are: 1) Reduce the risk of protective slag, avoid the inclusion of billet under the skin or surface, improve the quality and pass rate of subsequent cold rolled plate; reduce the defects such as deep scratch and crack on the surface of the billet, reduce the possibility of inducing internal cracks.

[0015] 2) The production efficiency and operation stability of the equal-diameter roller caster are improved, the crystallizer liquid level stability is improved, the crystallizer liquid level fluctuation amplitude is reduced to within ±3mm; the continuous casting furnace number is increased by more than 1 times compared with before (5-8 furnaces); the leakage rate is zero; the crystallizer water distribution: the wide surface is increased from 4000±100L / min to 4400±100L / min, and the narrow surface is increased from 500±50L / min to 550±50L / min, so that the billet shell is quickly formed to prevent the trend of increased crystallizer liquid level fluctuation.

[0016] 3) The constant caster speed is realized, and is stably controlled at 1.1-1.5%, the speed is increased by more than 30%, and the production efficiency is greatly improved.

[0017] 4) The billet quality is improved, the defects are reduced, the finished steel defect degradation rate is reduced from 23.82% to 3.45%, and the degradation rate is reduced by more than 90%.

[0018] 5) The mechanical properties of the cold rolled dual-phase steel product meet the user's requirements, the yield strength is 340-460MPa, the tensile strength is 590-680MPa, the elongation is 20%-38%, n 90 ≥0.15. The organization is F+M, and M accounts for 17-20%.

[0019] 6) Due to the large increase in continuous casting furnace number, the steel material consumption is reduced, the cost per ton of steel is saved by 10.22 yuan, and the cost reduction is 1.5%. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A cold rolled dual-phase steel metallographic diagram for solving the crystallizer liquid level fluctuation of the equal-diameter roller caster is described in the present application. DETAILED DESCRIPTION

[0021] The specific embodiments of the present application will be further described below in conjunction with the drawings: The production process of the steel of the present application is: hot metal pretreatment → converter smelting → secondary refining → continuous casting → heating → rough rolling, finish rolling → controlled cooling → coiling → pickling → continuous annealing → flattening → packaging. Among them, the continuous casting and continuous annealing process is optimized, and the specific method is as follows: Continuous casting: Pouring temperature: 1550~1590℃, superheat ≤25℃; constant speed casting, billet pulling speed: 1.1~1.5m / min; achieving constant casting machine pulling speed, increasing the number of consecutive casting furnaces, zero steel leakage rate, and improving production efficiency.

[0022] The crystallizer vibration amplitude is <±3mm, the vibration frequency is 120~180cpm, the stability of the crystallizer liquid level is improved, the fluctuation range of the crystallizer liquid level is reduced, the steelmaking defect rate is significantly reduced, and the production efficiency and operational stability are further improved. The secondary cooling in continuous casting adopts a forced cooling mode with a water flow rate of 1.0–1.6 L / kg. The water flow rate in the crystallizer is 4400±100 L / min for the wide section and 550±50 L / min for the narrow section. The purpose of secondary cooling is to forcefully and uniformly cool the surface of the billet, allowing it to solidify in a shorter time. The secondary cooling zone must ensure that the billet is free of surface and internal cracks, has no central segregation, and has a zero leakage rate during pouring.

[0023] Use low-carbon alloy steel protective slag, control the slag thickness in the tundish to ≤80mm, and use carbon-free tundish covering agent; Continuous annealing: Heating and heat preservation section temperature: 795~810℃; slow cooling section temperature: 690~720℃; rapid cooling section temperature: 280~300℃; over-aging section 1 temperature: 270~290℃; over-aging section 2 temperature: 260~285℃; over-aging section 3 temperature: 250~280℃; continuous annealing speed: ≥90m / min; The flattening elongation rate is set according to the thickness of the cold-rolled strip of duplex steel: Strip thickness d≤0.949mm, flattening elongation: 0.9%; Strip thickness d = 0.950~1.349mm, flattening elongation: 0.8%; Strip thickness d = 1.350~1.549mm, flattening elongation: 0.7%; Strip thickness d = 1.550~1.949mm, flattening elongation: 0.6%; Strip thickness d≥1.950mm, flattening elongation: 0.4%.

[0024] Examples: Preparation of DP590 cold-rolled products in Examples 1-4: The chemical composition and preparation process of the steel in the comparative examples all adopted conventional methods. The chemical composition of the steel in the examples of this invention is shown in Table 1; the continuous casting process parameters of the examples of this invention are shown in Table 2; the cold rolling continuous annealing process parameters of the examples of this invention are shown in Table 3; the performance of the finished products in the examples of this invention are shown in Table 4.

[0025] Table 1 - Chemical composition (wt, %) of the steel in the embodiments of the present invention: Table 2 - Continuous casting process parameters of the embodiments of the present invention: Table 3 - Cold rolling continuous annealing process parameters of the present invention: Table 4 - Performance of finished products from embodiments of the present invention: From the above embodiments, it can be concluded that through innovative design and process optimization of the HC340 / 590DP composition, the crystallizer level fluctuation of the equal-diameter roll casting machine is effectively controlled, with amplitudes within ±3, significantly increasing the number of consecutive casting heats, further improving the casting speed, greatly reducing the rate of steelmaking defect degradation, and meeting user requirements for mechanical properties: yield strength 371–407 MPa, tensile strength 622–670 MPa, elongation 23.64–25.58%, n 90 The value is 0.15 to 0.16, and the tissue is F+M, with M accounting for 17% to 20%.

[0026] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A cold-rolled duplex steel for solving the problem of liquid level fluctuation in the crystallizer of an equal-diameter roll casting machine, characterized in that, Its chemical composition by weight percentage is as follows: C: 0.06~0.075%; Si: 0.35~0.60%; Mn: 1.70~2.0%; P≤0.015%; S≤0.005%; Als: 0.020%~0.060%; V：0.01～0.02%； Ti: 0.01-0.03%; Mo: 0.03-0.08%; N≤0.0045%; O≤0.0035%, with the remainder being Fe and unavoidable residual elements.

2. The cold-rolled duplex steel for solving the liquid level fluctuation in the crystallizer of an equal-diameter roll casting machine according to claim 1, characterized in that, The cold-rolled duplex steel used to solve the liquid level fluctuation problem in the crystallizer of an equal-diameter roll casting machine has a yield strength of 340–460 MPa, a tensile strength of 590–680 MPa, and an elongation of 20%–38%. 90 ≥0.

15.

3. A method for preparing cold-rolled duplex steel to solve the liquid level fluctuation in the crystallizer of an equal-diameter roll casting machine according to any one of claims 1 to 2, characterized in that, The aforementioned production process for cold-rolled duplex steel to address liquid level fluctuations in the crystallizer of an equal-diameter roll casting machine is as follows: Hot metal pretreatment → converter smelting → ladle refining → continuous casting → heating → rough rolling and finish rolling → controlled cooling → coiling → pickling → continuous annealing → leveling → packaging. Optimizations are made to the continuous casting and continuous annealing processes, with the specific methods described below: Continuous casting: Casting temperature: 1550~1590℃, superheat ≤25℃; constant speed casting, billet pulling speed: 1.1~1.5m / min; The crystallizer vibration amplitude is <±3mm, and the vibration frequency is 120~180cpm; The secondary cooling of continuous casting adopts a strong cooling mode with a specific water flow rate of 1.0 to 1.6 L / kg; the water supply to the crystallizer is 4400 ± 100 L / min for the wide side and 550 ± 50 L / min for the narrow side. Use low-carbon alloy steel protective slag, control the slag thickness in the tundish to ≤80mm, and use carbon-free tundish covering agent; Continuous annealing: Heating and heat preservation section temperature: 795~810℃; slow cooling section temperature: 690~720℃; continuous annealing speed: ≥90m / min; flattening elongation: 0.4~0.9%.

4. The method for preparing cold-rolled duplex steel to solve the liquid level fluctuation in the crystallizer of an equal-diameter roll casting machine according to claim 3, characterized in that, The continuous annealing process includes a rapid cooling section at 280–300°C, an over-aging section 1 at 270–290°C, an over-aging section 2 at 260–285°C, and an over-aging section 3 at 250–280°C.

5. The method for preparing cold-rolled duplex steel to solve the liquid level fluctuation in the crystallizer of an equal-diameter roll casting machine according to claim 3, characterized in that, The flatness elongation: Strip thickness d≤0.949mm, flattening elongation: 0.9%; Strip thickness d = 0.950~1.349mm, flattening elongation: 0.8%; Strip thickness d = 1.350~1.549mm, flattening elongation: 0.7%; Strip thickness d = 1.550~1.949mm, flattening elongation: 0.6%; Strip thickness d≥1.950mm, flattening elongation: 0.4%.

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