Production process of low-alloy welding electrode steel

Abstract

The invention relates to a low-alloy welding rod steel production process which comprises the steps of KR desulfurization, converter smelting, LF refining, RH vacuum degassing and continuous casting machine casting, the end point oxygen content of a converter is controlled within 800 ppm, and aluminum ingots are added for deoxidation according to the end point oxygen content; lime, wollastonite and a proper amount of fluorite are used in a refining furnace for slagging, the alkalinity of refining final slag is controlled to be 3.0-5.0, the fluidity of the refining slag is guaranteed, the use amount of calcium carbide in the process is controlled, and the end-point oxygen content is controlled to be within 200 ppm; after RH vacuum degassing is finished, the dissolved oxygen content target of molten steel is controlled within 30 ppm, and the problems that bubbles appear on a continuous casting blank and the quality of the casting blank is poor are effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, in particular to a production process of low-alloy welding rod steel. Background Art

[0002] Low-carbon, low-silicon, and low-manganese welding wire has good welding performance due to its low element content. It can reduce the porosity and crack tendency during welding and improve the quality and strength of the weld.

[0003] Silicon is the most commonly used deoxidizing element in welding wire. Since silicon has a stronger affinity with oxygen than iron, it is easy to generate SiO2 with a high melting point (1710℃), and the particles of the product are small and difficult to float out of the molten pool, which is easy to cause slag inclusion in the weld metal. Therefore, the steel used for welding rods generally requires low silicon (Si≤0.03%) and a manganese content below 0.60%, which ensures welding performance, but the production process is more difficult, the oxygen content in the molten steel is high, and bubble defects are easy to appear inside the ingot, which greatly affects the quality of the ingot. Although aluminum is one of the strong deoxidizing elements, aluminum deoxidation generates high melting point Al2O3 (2050℃), which is easy to cause slag inclusion in the weld. At the same time, aluminum-containing welding wire is easy to cause spatter. Too high aluminum content will also reduce the weld metal's resistance to thermal cracking. Therefore, the aluminum content in the welding wire must be strictly controlled and should not be too much. If the aluminum content in the welding wire is properly controlled, the hardness, yield point, and tensile strength of the weld metal will be slightly improved. Therefore, for low-carbon, low-silicon, and low-manganese welding wire steel, how to reduce the dissolved oxygen content in the molten steel and avoid the formation of bubbles inside the ingot is a key research topic for steel companies. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the above problems, the present invention provides a production process of low alloy welding rod steel. By combining theoretical analysis with actual on-site production, it is proposed to use aluminum ingots for deoxidation in a converter, control the basicity of the final slag and the final oxygen content, RH vacuum degassing and stabilize the continuous casting process. The Si content of the final product is controlled below 0.03%, and the dissolved oxygen content in the molten steel is controlled below 30 ppm, thereby solving the problems of bubbles in the continuous casting billet and the quality of the casting billet.

[0006] (II) Technical solution

[0007] In order to solve the technical problem, the present invention provides a low alloy welding electrode steel production process, the method comprising the following steps in sequence:

[0008] (1) Converter process: The oxygen content at the converter end point is controlled within 800 ppm. Lime and fluorite are used for slag washing before steel tapping. Aluminum ingots are added for deoxidation according to the oxygen content. Ferromanganese is added for alloying. Slag removal is performed after steel tapping is completed.

[0009] (2) Refining process: The LF refining furnace uses lime + wollastonite and an appropriate amount of fluorite to make slag, and the basicity of the final refined slag is required to be controlled between 2.0 and 5.0; carbon powder and calcium carbide are used for deoxidation to ensure the fluidity of the refined slag. After the LF refining, the oxygen content of the molten steel is controlled within 200ppm; after the LF refining, the molten steel is hoisted to the RH vacuum degassing, and the oxygen content is controlled during the vacuum treatment process. After the vacuum degassing, the molten steel is placed on the continuous casting machine for casting.

[0010] (3) Continuous casting process: The continuous casting intermediate tank must ensure the baking effect. After the pouring starts, the continuous casting impact zone and casting zone are covered with alkaline covering agent for continuous pouring. Carbonized rice husks are used for covering and insulation. The black liquid level must be guaranteed. The billet samples are taken online for inspection. The surface quality of the billet is good and no obvious pore defects are found.

[0011] Preferably, in step (1), 500 kg of lime and 50 kg of fluorite are used for slag washing, and 50-100 kg of aluminum ingots are added for deoxidation according to the oxygen content. Sampling after the furnace is required, and the Al content in the steel is 0.005%-0.015%.

[0012] Preferably, after the LF refining in step (2) is completed, the mixture is suspended to RH vacuum degassing, and oxygen is determined during the RH vacuum degassing for 8-10 minutes and 12-15 minutes respectively.

[0013] Preferably, after the continuous casting in step (3) is started, about 300 kg of alkaline covering agent is added to the impact zone and the casting zone for covering.

[0014] Beneficial effects of the present invention:

[0015] By combining theoretical analysis with actual production, it is proposed to use aluminum ingots for deoxidation in the converter, control the basicity of the final slag and the final oxygen content, RH vacuum degassing and stabilize the continuous casting process. The Si content of the final product is controlled below 0.03%, and the dissolved oxygen content in the molten steel is controlled below 30ppm, thus solving the problems of bubbles in the continuous casting billet and the quality of the billet. DETAILED DESCRIPTION

[0016] Example 1

[0017] Taking the smelting of SWRY-1 low-carbon, low-silicon, low-manganese steel as an example, a production process of low-alloy welding rod steel is described in detail:

[0018]

[0019] 1. Converter process: The bottom blowing of the converter requires argon blowing throughout the whole process. The final composition of the converter is C 0.038%, Si 0.003%, Mn0.092%, P 0.0091%, S 0.0101%, oxygen content 634ppm, and the tapping temperature is 1607℃. 70kg aluminum ingots, ferromanganese alloy, 500Kg lime + 50Kg fluorite are added to the tapping for slag washing, and then the slag removal station is used for slag removal treatment. The Al content in the molten steel sampled after the furnace is 0.0071%.

[0020] 2. Refining process: add 800kg lime + 400kg wollastonite + 200kg fluorite into the refining furnace, send electricity to raise the temperature and slag, use carbon powder and calcium carbide for deoxidation, add ferromanganese to fine-tune the composition, and the oxygen is set at 168ppm at the end of refining. The basicity of the final slag is tested to be 3.8, and the steel is hoisted to the RH vacuum furnace; the oxygen is set to 35.3ppm in RH vacuum degassing for 8 minutes, and the oxygen is set to 27.5ppm in vacuum for 12 minutes. After the vacuum is finished, soft blowing is performed for 15 minutes and hoisted to the continuous casting machine. The finished product composition is tested to be C 0.0557%, Si 0.018%, Mn 0.44%, P0.0095%, S 0.0061%, Ni 0.010%, Cr 0.031%, Cu 0.010%, Mo 0.0015%, Al 0.002%.

[0021] 3. Continuous casting process: After continuous casting starts, high alkalinity covering agent is used to cover the continuous casting impact zone and casting zone for continuous casting. 300 kg of high alkalinity covering agent is added to the impact zone and casting zone. Carbonized rice husk is used to cover and keep warm on the high alkalinity covering agent. The black liquid level must be guaranteed. Take billet samples online to check the surface quality of the billet, and there should be no obvious pore defects.

[0022] Example 2

[0023] Taking the smelting of SWRY-1 low-carbon, low-silicon, low-manganese steel as an example, a production process of low-alloy welding rod steel is described in detail:

[0024]

[0025] 1. Converter process: The bottom blowing of the converter requires argon blowing throughout the whole process. The final composition of the converter is C 0.033%, Si 0.002%, Mn0.10%, P 0.0098%, S 0.011%, oxygen content 664ppm, and the tapping temperature is 1612℃. 75kg of aluminum ingots, ferromanganese alloy, 500Kg of lime + 50Kg of fluorite are added to the tapping for slag washing, and then the slag removal station is used for slag removal treatment. Al0.0078% of the molten steel is sampled after the furnace.

[0026] 2. Refining process: add 800kg lime + 400kg wollastonite + 200kg fluorite into the refining furnace, send electricity to raise temperature and slag, use carbon powder and calcium carbide for deoxidation, add ferromanganese to fine-tune the composition, and set the oxygen at 168ppm after refining. Detect the basicity of the final slag of refining to 4.2, and hoist the steel to the RH vacuum furnace; RH vacuum degassing for 8 minutes to set the oxygen at 38.5ppm, vacuum for 12 minutes to set the oxygen at 26.4ppm, and vacuum soft blowing for 13 minutes after the end of vacuum to hoist to the continuous casting machine. The finished product composition is tested to be C 0.0637%, Si 0.020%, Mn 0.451%, P0.010%, S 0.0065%, Ni 0.009%, Cr 0.033%, Cu 0.010%, Mo 0.0016%, Al 0.0024%.

[0027] 3. Continuous casting process: After continuous casting starts, high-alkalinity covering agent is used to cover the continuous casting impact zone and casting zone for continuous casting. 300 kg of covering agent is added to the impact zone and casting zone, and carbonized rice husk is used to cover and keep warm on the covering agent. The black liquid level must be guaranteed. Take billet samples online to check the surface quality of the billet, and there is no obvious pore defect.

[0028] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A process for producing low alloy welding electrode steel, characterized in that: The method comprises the following steps in sequence: (1) Converter process: The oxygen content at the converter end point is controlled within 800 ppm. Lime and fluorite are used for slag washing before steel tapping. Aluminum ingots are added for deoxidation according to the oxygen content. Ferromanganese is added for alloying. Slag removal is performed after steel tapping is completed. (2) Refining process: The LF refining furnace uses lime + wollastonite and an appropriate amount of fluorite to make slag, and the basicity of the final refined slag is required to be controlled between 2.0 and 5.0; carbon powder and calcium carbide are used for deoxidation to ensure the fluidity of the refined slag. After the LF refining, the oxygen content of the molten steel is controlled within 200ppm; after the LF refining, the molten steel is hoisted to the RH vacuum degassing, and the oxygen content is controlled during the vacuum treatment process. After the vacuum degassing, the molten steel is placed on the continuous casting machine for casting; (3) Continuous casting process: The continuous casting intermediate tank must ensure the baking effect. After the pouring starts, the continuous casting impact zone and casting zone are covered with alkaline covering agent for continuous pouring. Carbonized rice husks are used for covering and insulation. The black liquid level must be guaranteed. The billet samples are taken online for inspection. The surface quality of the billet is good and no obvious pore defects are found.

2. The process for producing low alloy welding electrode steel according to claim 1, characterized in that: In step (1), 500 kg of lime and 50 kg of fluorite are used for slag washing, and 50-100 kg of aluminum ingots are added for deoxidation according to the oxygen content. Samples are taken after the furnace, and the Al content in the steel is 0.005%-0.015%.

3. The process for producing low alloy welding electrode steel according to claim 1, characterized in that: After the LF refining in step (2) is completed, the mixture is suspended to RH vacuum degassing, and oxygen is determined during RH vacuum degassing for 8-10 minutes and 12-15 minutes respectively.

4. The process for producing low alloy welding electrode steel according to claim 1, characterized in that: In step (3), after the continuous casting starts, about 300 kg of alkaline covering agent is added to the impact zone and the casting zone for covering.

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