Process method for controlling occurrence rate of longitudinal cracks on surface of continuous casting slab

Abstract

The invention relates to the technical field of ferrous metallurgy, in particular to a process method for controlling the occurrence rate of longitudinal cracks on the surface of a continuous casting sheet billet, which specifically comprises the steps of controlling the uniform growth of an initial billet shell in a crystallizer, optimizing the flowing state of molten steel in the crystallizer, adjusting the vibration parameters of the crystallizer and controlling the thickness of a casting powder liquid slag layer. And the carbon content in the steel is controlled to avoid a peritectic zone, the sulfur content and residual elements are limited, and the manganese-sulfur ratio is increased. By means of the narrow face and wide face differentiated cooling ratio and combination of the reasonable taper and heat flux ratio, heat transfer of the wide face and the narrow face is effectively balanced, local stress concentration is restrained, it is ensured that an initial blank shell evenly grows, the hot crack risk is reduced, the occurrence rate of continuous casting surface longitudinal cracks is controlled, and the stable and reliable quality of continuous casting slab production is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, and particularly relates to a process method for controlling the incidence rate of longitudinal surface cracks of continuous casting slabs. Background Art

[0002] In the continuous casting production of steel slabs, longitudinal surface cracks of slabs are relatively common quality defect problems. Especially for severe longitudinal cracks with large length and depth, the entire slab can be directly determined as scrapped, and even leakage of molten steel may occur along the longitudinal cracks during the continuous casting production process, causing serious harm to production and equipment and huge economic losses to the enterprise. In order to effectively control the incidence rate of longitudinal surface cracks of slabs, an effective and feasible process technology method is needed. For this, the present application proposes a process method for controlling the incidence rate of longitudinal surface cracks of continuous casting slabs. Summary of the Invention

[0003] In view of the above technical problems, the present invention overcomes the disadvantages of the prior art and provides a process method for controlling the incidence rate of longitudinal surface cracks of continuous casting slabs. By means of methods such as promoting uniform growth of the billet shell, controlling the flow of molten steel, selecting a suitable mold powder, setting reasonable mold vibration parameters, and adjusting the composition of molten steel, the incidence rate of longitudinal surface cracks in continuous casting is well controlled.

[0004] The process method for controlling the incidence rate of longitudinal surface cracks of continuous casting slabs in this solution includes the following steps: (1) Controlling the uniform growth of the initial billet shell in the mold: adjusting the cooling intensity of the mold through a weak cooling process, optimizing the mold taper, controlling the heat flux ratio between the narrow face and the wide face, and adjusting the mold cooling water parameters to stabilize the temperature of the meniscus copper plate; (2) Optimizing the flow state of molten steel in the mold: ensuring uniform flow of molten steel by centering the submerged nozzle, controlling the insertion depth of the nozzle and the fluctuation amplitude of the molten steel surface; (3) Adjusting the mold vibration parameters: adopting negative strip time control, adjusting the vibration frequency and amplitude, and limiting the vibration deviation; (4) Matching the performance of the mold powder: controlling the thickness of the liquid slag layer of the mold powder to be 10 - 15 mm; (5) Adjusting the composition of molten steel: controlling the carbon content in the steel to avoid the peritectic region, limiting the sulfur content and residual elements, and increasing the manganese-to-sulfur ratio.

[0005] The further limited technical solution of the present invention is: Further, in step (1), in the weak cooling process, the cooling water flow rate of the narrow face is specifically set to be 400 - 600 L / min, and the cooling water flow rate of the wide face is 4000 - 5000 L / min; The taper of the mold is 0.8% - 1.5%, and the ratio of the heat flux on the narrow face to that on the wide face is 0.6 - 1.0; through the differential cooling ratio of the narrow face (400 - 600 L / min) and the wide face (4000 - 5000 L / min), combined with a taper of 0.8% - 1.5% and a heat flux ratio of 0.6 - 1.0, the heat transfer between the narrow and wide faces is effectively balanced, and local stress concentration is inhibited; The temperature difference between the inlet and outlet of the cooling water is controlled within 8°C, and the temperature fluctuation range of the meniscus copper plate is ≤5°C, ensuring the uniform growth of the initial billet shell and reducing the risk of thermal cracking.

[0006] Furthermore, in step (2), the immersion depth of the submerged nozzle is 120 - 170 mm, and the fluctuation amplitude of the molten steel surface is 3 - 5 mm, ensuring the symmetry of the flow field in the mold and reducing the erosion of the solidification front; The outlet inclination angle of the submerged nozzle is 10° - 25°, and the outlet diameter is 30 - 50 mm to inhibit the side flow and effectively inhibit the side flow and slag entrainment.

[0007] Furthermore, in step (3), the negative slippage time is set to 0.2 - 0.3 s, the vibration frequency is 100 - 200 times / minute, and the amplitude is 2 - 6 mm, significantly improving the lubrication condition for the billet shell to release from the mold; The vibration deviation is controlled to be less than 0.2 mm both longitudinally and transversely, eliminating the periodic crack defects caused by mechanical stress.

[0008] Furthermore, in step (4), the viscosity of the mold powder is 0.1 - 0.5 Pa·s, the melting temperature is 1050 - 1200°C, and the alkalinity (CaO / SiO2) is 0.8 - 1.2, achieving the formation of a stable slag film and uniform heat transfer.

[0009] Furthermore, in step (5), the chemical composition of the molten steel is: the carbon content is controlled to be 0.05% - 0.10% or 0.16% - 0.25%, the sulfur content is ≤0.015%, and the manganese - sulfur ratio is ≥30, significantly reducing the harm of sulfur segregation and low - melting - point eutectic phases; The contents of copper, arsenic, and zinc are all ≤0.1%, and the total amount of nickel + chromium + molybdenum is ≤0.3%, effectively inhibiting the tendency of grain - boundary embrittlement.

[0010] Furthermore, the thickness of the continuous - casting slab is 200 - 300 mm, the casting speed is 0.8 - 1.5 m / min, and the superheat is controlled to be 15 - 30°C, forming a reasonable temperature gradient and avoiding surface defects caused by rapid cooling.

[0011] Furthermore, in step (1), the material of the mold copper plate is silver - copper alloy, and the surface coating thickness is 0.1 - 0.3 mm; In step (2), the bottom shape of the submerged nozzle is chamfered or arc - designed, and the chamfer angle is 30° - 60°.

[0012] The beneficial effects of the present invention are as follows: (1) By differentiating the cooling ratio between the narrow face and the wide face, combining a reasonable taper and heat flux ratio, the present invention effectively balances the heat transfer between the narrow face and the wide face, suppresses local stress concentration, with the cooling water temperature difference ≤ 8°C and the temperature fluctuation of the meniscus copper plate ≤ 5°C. Supplemented by the high thermal conductivity of the silver-copper alloy coating, it ensures the uniform growth of the initial billet shell and reduces the risk of thermal cracking; (2) The present invention is a process method for controlling the incidence rate of longitudinal surface cracks in continuous casting. By adopting methods such as promoting the uniform growth of the billet shell, controlling the flow of molten steel, selecting a suitable mold powder, setting reasonable mold oscillation parameters, and adjusting the composition of molten steel, it effectively controls the incidence rate of longitudinal surface cracks in continuous casting, realizes the stable and reliable quality of continuous casting slab production, and reduces the huge economic losses caused by longitudinal surface cracks on the slab surface. Specific embodiments

[0013] This embodiment takes the continuous caster for casting slabs with a thickness of 260 mm as an example.

[0014] A process method for controlling the incidence rate of longitudinal surface cracks in continuous casting slabs: (1) Uniform growth of the initial billet shell in the mold: The mold weakly cools the billet shell. The cooling water flow rate of the narrow face is set at 500 L / min, and the cooling water flow rate of the wide face is set at 4500 L / min; the mold taper is set at 1.2%; the ratio of the heat flux of the narrow face to the heat flux of the wide face of the mold is 0.8; the inlet and outlet water temperature of the mold is controlled within 8°C, and the temperature of the meniscus copper plate of the mold is controlled at a constant value.

[0015] (2) Rationality of the molten steel flow in the mold: The molten steel level in the mold fluctuates by ±3 - ±5 mm; the submerged entry nozzle is centered; the insertion depth of the nozzle is set at 120 mm - 170 mm.

[0016] (3) Mold oscillation: Reduce the mold oscillation deviation (longitudinal, transverse < 0.2 mm). The negative slippage time value t of the mold oscillation is 0.2 - 0.3 s.

[0017] (4) Suitable mold powder: The principle for selecting the mold powder is that the thickness of the liquid slag layer on the molten steel surface in the mold is 10 - 15 mm.

[0018] (5) Adjust the composition of molten steel: The carbon content in the steel avoids the peritectic region, and [C] is controlled at the lower limit or the upper limit; [s] in the steel < 0.015%, [Mn] / [s] > 30; the residual elements [Cu], [As], [Zn] are controlled < 0.1%.

[0019] In addition to the above embodiments, the present invention may have other implementation manners. All technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A process method for controlling the incidence rate of longitudinal surface cracks in continuous casting slabs, characterized in that It includes the following steps: (1) Control the uniform growth of the initial billet shell in the mold: Adjust the cooling intensity of the mold through the weak cooling process, optimize the mold taper, control the heat flux ratio between the narrow face and the wide face, and adjust the cooling water parameters of the mold to stabilize the temperature of the meniscus copper plate; (2) Optimize the molten steel flow state in the mold: Ensure uniform molten steel flow by aligning the submerged entry nozzle, controlling the insertion depth of the nozzle and the fluctuation amplitude of the molten steel surface level; (3) Adjust the mold vibration parameters: Adopt negative slippage time control, adjust the vibration frequency and amplitude, and limit the vibration deviation; (4) Match the properties of the mold powder: Control the thickness of the liquid slag layer of the mold powder to be 10 - 15 mm; (5) Adjust the molten steel composition: Control the carbon content in the steel to avoid the peritectic region, limit the sulfur content and residual elements, and increase the manganese-to-sulfur ratio.

2. The process method according to claim 1, wherein In step (1), in the weak cooling process, the cooling water flow rate of the narrow face is specifically set to be 400 - 600 L / min, and the cooling water flow rate of the wide face is 4000 - 5000 L / min; The mold taper is 0.8% - 1.5%, and the heat flux ratio between the narrow face and the wide face is 0.6 - 1.0; The temperature difference between the inlet and outlet of the cooling water is controlled within 8 °C, and the fluctuation range of the meniscus copper plate temperature ≤ 5 °C.

3. The process method according to claim 1, characterized in that, In step (2), the insertion depth of the submerged entry nozzle is 120 - 170 mm, and the fluctuation amplitude of the molten steel surface level is 3 - 5 mm; The outlet inclination angle of the submerged entry nozzle is 10° - 25°, and the outlet diameter is 30 - 50 mm to suppress the uneven flow.

4. The process method according to claim 1, characterized in that, In step (3), the negative slippage time is set to be 0.2 - 0.3 s, the vibration frequency is 100 - 200 times / minute, and the amplitude is 2 - 6 mm; The vibration deviation is controlled to be less than 0.2 mm both longitudinally and transversely.

5. The process method according to claim 1, wherein In step (4), the viscosity of the mold powder is 0.1 - 0.5 Pa·s, the melting temperature is 1050 - 1200 °C, and the alkalinity (CaO / SiO2) is 0.8 - 1.

2.

6. The process method according to claim 1, wherein In step (5), the molten steel composition is: the carbon content is controlled to be 0.05% - 0.10% or 0.16% - 0.25%, the sulfur content ≤ 0.015%, and the manganese-to-sulfur ratio ≥ 30; The contents of copper, arsenic, and zinc are all ≤ 0.1%, and the total amount of nickel + chromium + molybdenum ≤ 0.3%.

7. The process method according to claim 1, characterized in that, The thickness of the continuous casting slab is 200 - 300 mm, the casting speed is 0.8 - 1.5 m / min, and the superheat is controlled to be 15 - 30 °C.

8. The process method according to claim 1, characterized in that, In step (1), the material of the mold copper plate is silver-copper alloy, and the surface coating thickness is 0.1 - 0.3 mm; In step (2), the bottom shape of the submerged entry nozzle is chamfered or arc-designed, and the chamfer angle is 30° - 60°.