A method for controlling longitudinal subsurface crack of peritectic high-aluminum steel continuous casting billet

Abstract

The present application belongs to the technical field of metallurgical steelmaking, and particularly relates to a method for controlling longitudinal sub-skin cracks of peritectic high-aluminum steel continuous casting billets, and reducing the AL content of peritectic high-aluminum steel. The method comprises the following steps: designing a large-bell mouth sleeve insertion type casting starting, a silica gel sealing gasket, a peritectic alloy high-aluminum special-purpose protective slag, and a crystallizer special slag salvaging process; reducing the variation range of the immersion nozzle insertion depth; and adopting a weak cooling peritectic water distribution process. The method reduces the influence of Als element oxidation and reduction on the protective slag denaturation, prolongs the denaturation time of the protective slag, reduces the nitrogen content and secondary oxidation in the steel, reduces the influence of Al2O3 inclusions, promotes the uniform slag setting and uniform solidification of the high-aluminum steel protective slag, and successfully realizes the continuous casting production process, so that the longitudinal sub-skin cracks of the peritectic high-aluminum steel continuous casting billets are well controlled.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgical steelmaking, and particularly relates to a peritectic high-aluminum steel continuous casting billet subsurface longitudinal crack control method. BACKGROUND

[0002] Continuous casting thick slab surface longitudinal crack is a common defect of continuous casting billet, and the surface longitudinal crack of common medium-carbon high-manganese steel, peritectic steel and the like is more common than other steel grades. Peritectic high-aluminum steel (C content 0.13-0.15%, Mn content 1.50-1.80%, Al content 0.4-0.6%) involves peritectic reaction, high manganese and high aluminum, and is more prone to longitudinal cracks. The main mechanism is that the increase of AL2O3 in the slag and the decrease of SiO2 caused by the reaction of Als and SiO2 in the steel, the variation of the basicity and viscosity of the protective slag, the thickening of the crystallization phase of the slag film, the uneven subsurface longitudinal crack of the billet shell, and the uneven solidification of the billet shell, so that the probability of the occurrence of the subsurface longitudinal crack of the billet shell is higher, and the rolling quality of the continuous casting billet is seriously affected. SUMMARY

[0003] The purpose of the application is to provide a peritectic high-aluminum steel continuous casting billet subsurface longitudinal crack control method, to prolong the degeneration time of the protective slag, to reduce the influence of Al2O3 inclusions, and to promote the uniform subsurface slagging and uniform solidification of the high-aluminum steel protective slag.

[0004] The technical solution adopted by the application to solve the technical problem is: a peritectic high-aluminum steel continuous casting billet subsurface longitudinal crack control method, comprising the following steps:

[0005] (1) reducing the Al alloy addition amount, and controlling the Als content in the steel to 0.4-0.5%;

[0006] (2) reducing the nitrogen content in the steel and secondary oxidation, designing a bell mouth ladle bushing plug-in type casting start, and adopting a silica gel sealing gasket to reduce the source of gas absorption by the molten steel;

[0007] (3) designing a peritectic alloy high-aluminum special protective slag, and the mass fraction and physical and chemical properties of the protective slag are as follows: C solid 4.5-5.5%, SiO2 27-30%, CaO 37.5-45.5%, MgO 1.0-3.0%, Al2O3 3.0-6.0%, Fe2O3 0.8-1.1%, K2O+Na2O 2.0-5.0%, Li2O 1.8-3.5%, F 8.0-9.0%, R 1.3-1.38, volatile matter 1.5-4.5, density 0.65-0.80 g / ml, melting point 1140-1200℃, and viscosity 0.1-0.15 Pa·s;

[0008] (4) optimizing the setting of the ladle bushing argon blowing flow rate, and controlling the argon blowing flow rate to 70-90 L / min to ensure the micro-positive pressure control of the bowl mouth on the bushing and reduce the air entering the molten steel;

[0009] (5) Reduce the maximum casting speed, the maximum casting speed control to 1.4m / min;

[0010] (6) Design crystallizer special slagging process, relieve the influence of protective slag degeneration;

[0011] (7) Submerged nozzle insertion depth automatic change, slag line change range between 130-150mm, promote AL2O3 inclusion floating;

[0012] (8) Two cooling water adopts weak cooling peritectic water distribution process, specific water quantity setting 0.58kg / L.

[0013] Further, the crystallizer special slagging process method in step (6) is as follows:

[0014] a. Under normal circumstances, crystallizer slagging and new slag making every 4-5 heats; under abnormal circumstances, when finding that crystallizer liquid slag is sticky and clumpy, timely organize slagging and new slag making operation;

[0015] b. Protective slag consumption billet length measurement method, protective slag addition every 20kg calculates billet length once, measure billet length continuous increase more than 5m, organize slagging and new slag replacement;

[0016] c. Liquid slag thickness measurement, every 15 minutes measures once, find that liquid slag layer increases and is sticky, according to step b slag consumption billet length measurement, organize slagging and new slag replacement;

[0017] d. Normal casting speed reduces to 1.0m / min and starts slagging, prevents high speed roll slag, ensures that slag clumps and sticky liquid slag are taken out.

[0018] The present application has the following beneficial effects:

[0019] (1) Through component control, the influence of Als element oxidation and reduction on protective slag degeneration is reduced, and the degeneration time of protective slag is prolonged.

[0020] (2) Through process design, the nitrogen content in steel and secondary oxidation are reduced, and the influence of Al2O3 inclusion is reduced.

[0021] (3) Through design of peritectic alloy high aluminum special protective slag, process optimization, improvement of crystallizer special slagging process, submerged nozzle insertion depth and automatic slag line range, the uniformity of high aluminum steel protective slag is promoted, and the continuous casting production process is smooth, and the skin longitudinal crack defect of peritectic high aluminum steel billet is well controlled. DETAILED DESCRIPTION

[0022] The following is a specific embodiment of the present application, which further describes the technical solutions of the present application, but the protection scope of the present application is not limited to these embodiments. Any changes or equivalent replacements without departing from the concept of the present application are included in the protection scope of the present application.

[0023] A method for controlling longitudinal sub-skin cracks of a peritectic high-aluminum steel continuous casting billet, comprising the following steps:

[0024] (1) Reduce the Al alloy addition amount, reduce the Als content in the steel, control to 0.4-0.5%, reduce the influence of high content of aluminum element in acid melting on the protective slag.

[0025] (2) Reduce the nitrogen content in the steel and secondary oxidation, design the trumpet mouth ladle sleeve insertion type casting, use silica gel sealing pad, reduce the source of molten steel getter (O\N).

[0026] (3) Design peritectic alloy high-aluminum special protective slag, according to the characteristics of Al and protective slag SiO2 reaction in molten steel, deduce the composition after reaction, design to add lower Al2O3 component, at the same time consider Al2O3 adsorption denaturation, add a large amount of lithium carbonate to stabilize the viscosity and crystallization temperature of the protective slag. Practice has proved that after using this new type of protective slag, the melting flame of the protective slag in the mold is uniform and stable, and the surface quality of the billet is good. The mass fraction and physical and chemical properties of the protective slag are as follows.

[0027]

[0028] (4) Optimize the setting of the ladle sleeve argon blowing flow, increase from the original 40L / min to 70-90L / min, ensure the micro-positive pressure control of the bowl mouth on the sleeve, and reduce the air entering the molten steel.

[0029] (5) Reduce the maximum casting speed of the caster, control the maximum casting speed from 1.6m / min to 1.4m / min, reduce the impact on the flow field of the billet side, and promote the floating of inclusions in the steel.

[0030] (6) Design special slag salvaging process for mold, relieve the influence of protective slag denaturation:

[0031] a. Under normal circumstances, the mold is salvaged every 4-5 heats, and new slag is made once; in abnormal circumstances, the mold is salvaged and new slag is made in time when the liquid slag in the mold is found to be sticky and clumped;

[0032] b. Protective slag consumption and billet length measurement method, calculate the billet length every 2 bags (20 kg) of protective slag addition, and organize slag salvaging and new slag replacement when the continuously measured billet length increase exceeds 5m;

[0033] c. Liquid slag thickness measurement, measure every 15 minutes, and organize slag salvaging and new slag replacement according to step b (slag consumption and billet length measurement) when the liquid slag layer is found to be increased and sticky;

[0034] d. Start salvaging when the normal casting speed is reduced to 1.0m / min, to prevent high-speed slag rolling and ensure that slag clumps and sticky liquid slag are salvaged.

[0035] 7) Submerged nozzle insertion depth automatic change, slag line variation range between 130mm-180mm, optimization improvement variation range between 130-150mm, promote Al2O3 inclusion floating.

[0036] 8) Two cooling water adopts weak cooling crystallization water distribution process, specific water quantity is 0.58kg / L.

[0037] The present application is not limited to the above-mentioned embodiments, and any person should know that the structural changes made under the inspiration of the present application, any technical solution with the same or similar to the present application, falls within the scope of the present application.

[0038] The technology, shape, structure part not described in detail in the present application are all known technology.

Claims

1. A method for controlling subsurface longitudinal cracks in peritectic high-alumina steel continuously cast billets, characterized in that, Includes the following steps: (1) Reduce the amount of Al alloy added, and control the Al content in the steel to 0.4-0.5%; (2) Reduce the nitrogen content and secondary oxidation in the steel. Design a bell-mouth large-blade sleeve for insertion and use a silicone sealing gasket to reduce the source of gas absorption by the molten steel. (3) Design a special protective slag for peritectic alloy high alumina. The mass fraction and physicochemical properties of each substance in the protective slag are as follows: C solid 4.5-5.5%, SiO2 27-30%, CaO 37.5-45.5%, MgO 1.0-3.0%, Al2O3 3.0-6.0%, Fe2O3 0.8-1.1%, K2O+Na2O 2.0-5.0%, Li2O 1.8-3.5%, F 8.0-9.0%, R 1.3-1.38, volatile matter 1.5-4.5%, density 0.65-0.80 g / ml, melting point 1140-1200℃, viscosity 0.1-0.15 Pa·s; (4) Optimize the setting of the argon blowing flow rate of the large-scale sleeve, control the argon blowing flow rate to 70-90L / min, ensure the slight positive pressure control of the cup mouth at the upper edge of the sleeve, and reduce the air entering the molten steel; (5) Reduce the maximum casting speed of the casting machine to 1.4 m / min; (6) Design a special slag removal process for the crystallizer to mitigate the effects of protective slag degradation; The specific slag removal process for crystallizers is as follows: a. Under normal circumstances, slag should be skimmed and new slag should be prepared every 4-5 furnaces; in abnormal circumstances, if the liquid slag in the crystallizer is found to be viscous or clumped, slag skimming and new slag preparation should be organized in a timely manner. b. Protective slag consumption and billet length measurement method: Calculate the billet length every 20kg of protective slag added. If the billet length increases by more than 5m continuously, organize slag removal and replace with new slag. c. Measure the thickness of the liquid slag every 15 minutes. If the liquid slag layer is found to be increased and viscous, organize slag removal and replace the slag according to the slag consumption length measurement in step b. d. Reduce the normal pulling speed to 1.0 m / min and start slag removal to prevent high-speed slag entanglement and ensure that slag clumps and viscous liquid slag are removed; (7) The insertion depth of the submersible nozzle changes automatically, and the slag line varies between 130-150mm, which promotes the flotation of AL2O3 inclusions. (8) The secondary cooling water adopts a weak cooling peritectic water distribution process, and the specific water volume is set at 0.58 kg / L.

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