Steelmaking process for small square billets of sulfur-containing, nitrogen-containing, aluminum-controlled non-quenched and tempered steel

Abstract

This invention discloses a steelmaking process for small square billets containing sulfur and nitrogen, with controlled aluminum content, aiming to provide a smelting process for small square billets of non-quenched and tempered steel that solves the problem of turbulence in continuous casting. The process involves controlling the final carbon content of the electric furnace, using ferrosilicon and low-aluminum, low-titanium ferrosilicon for manganese and silicon alloying; adding ferrovanadium in the LF ladle for vanadium alloying, and using low-aluminum, low-titanium ferrosilicon and metallic manganese for silicon and manganese alloying; simultaneously, adjusting the nitrogen content in the LF process by blowing nitrogen, slag formation, and feeding sulfur wire off the furnace; after the VD ladle, supplementary feeding is performed based on nitrogen and sulfur analysis results, followed by vacuuming; no composition adjustment is performed after VD; and the superheat and castability of the molten steel are appropriately improved in continuous casting. The advantages of this invention are: solving the problem of turbulence in continuous casting; using nitrogen instead of argon in the LF refining process to quickly reach the required nitrogen content in the molten steel; and using nitrogen instead of argon for circulation in VD, saving nitriding time and the amount of nitrogen wire alloy added; shortening the smelting cycle, improving production efficiency, and reducing costs.

Description

Technical Field

[0001] This invention belongs to the field of metal material smelting technology, and relates to a smelting process for sulfur-containing, nitrogen-containing, controlled-aluminum non-quenched and tempered steel. Background Technology

[0002] Sulfur content 0.065%–0.090%, nitrogen content (160–200) × 10 -6 Non-quenched and tempered steel with aluminum content not exceeding 0.010%, silicon content 0.65%–0.75%, and vanadium content 0.27%–0.31%. Due to the characteristics of this product, turbulence is prone to occur during continuous casting. This can cause defects such as billet rejoining and slag entrapment, or even interrupted casting, accompanied by a large amount of abnormal billet cutting waste, which has a significant impact on quality stability, smooth production, and the improvement of billet yield. Summary of the Invention

[0003] This invention discloses a smelting process for sulfur-containing, nitrogen-containing, and aluminum-controlled non-quenched and tempered steel. The purpose is to provide a smelting process for non-quenched and tempered steel small billets to solve the problem of turbulence in continuous casting. It can be applied to the production of products such as 36MnVS4L, 36MnVS4H, 38MnVS4, and 46MnVS6. The specific process route and steps are as follows: Process route: 60-ton electric furnace → 60-ton LF furnace refining → 60-ton VD vacuum furnace refining → continuous casting of 180mm×180mm square billet; Step 1, Electric Furnace Smelting: Add molten iron and returned steel to the electric furnace for smelting. When about 1 / 4 of the steel has been tapped, add alloys and slag materials in the following order: "silicon manganese, low-aluminum and low-titanium ferrosilicon, carbon raiser, refining slag, and lime" to create high-basicity slag. The high-basicity slag ratio is: 750 kg refining slag + 300 kg lime, with a slag basicity of 4-5. During the smelting process, bottom-blown argon gas is used for stirring to prevent over-oxidation of the molten steel, prevent slag from falling, and improve the rate of achieving the target alloy composition. Based on the target composition of the required steel grade C i The actual composition of molten steel is determined during tapping from the electric furnace. C i 0 molten steel weight M 1. Proportion of carbon, silicon, and manganese in alloying A i and yield h i Calculations are performed to add the required alloy to the ladle, while simultaneously controlling the temperature of the molten steel. T The test was conducted at 1°C. The amount of each alloy added was... W i The formula for calculating (kg) is: (1) Step 2, refining in the LF refining furnace: (1) In the early stage, high-alkalinity slag is produced, and in the later stage, silica is added to transform the slag into sulfur-retaining slag. (2) Diffusion deoxidation: Carbon powder and calcium carbide are used, with the amount of carbon powder and calcium carbide added being 1.0 to 1.7 kg / t of molten steel. Carbon powder is used to retain the slag after it turns white. (3) Enter the LF station to prevent the aluminum content from increasing and the tendency of turbulence from increasing after vanadium-iron alloying. Vanadium alloying is carried out in the saddle. During vanadium alloying, about 300 kg of vanadium-iron is added. Vanadium-iron alloy is added later according to the analysis results. (5) After the molten steel temperature reaches 1560℃, switch the bottom-blowing argon gas to bottom-blowing nitrogen gas for nitrogen adjustment. Before entering the VD (Vacuum-Deposit) stage, take a gas sample for analysis. The target nitrogen content value is calculated as (250~300)×10. -6 Control is advisable; (6) Before adjusting the sulfur composition in the LF furnace, add 200 kg of silica to change the slag composition. Before hoisting the ladle, feed the sulfur line with a sulfur composition of 0.080% and stir for 1 to 2 minutes to make the sulfur composition uniform. After sampling and analyzing the sulfur composition, hoist the ladle to the next process without waiting for the results. Step 3, VD vacuum furnace smelting: (1) The vacuum process uses nitrogen circulation instead of argon; (2) After the furnace is set up, the sulfur line is supplemented with feed according to the sulfur composition results of the last analysis of the LF furnace, with a sulfur content of 0.080%; (3) After the furnace is set up, the nitrogen composition is determined according to the final analysis results of the LF furnace, calculated as (250~300)×10 -6 Feed nitrogen line; (4) The ultimate vacuum degree shall not exceed 67 Pa, and the vacuum holding time shall be 3 min. (5) After opening the can, the nitrogen and sulfur content will be adjusted according to the analysis results, but the content of other components will not be adjusted. Nitrogen recovery rate calculation: (2) In the above formula, C N1 The nitrogen content before vacuuming of VD, C N2 This refers to the nitrogen content after vacuum refining in a VD furnace. Sulfur recovery rate calculation: (3) In the above formula, C S1 The sulfur content before vacuuming of VD, C S2 This refers to the sulfur content after vacuum refining in a VD furnace. Step 4, Continuous casting: The superheat of the molten steel obtained in step 3 is appropriately increased to 30℃~45℃, and full-process protective casting is carried out. Invention points of this invention: By controlling the final carbon content of the electric furnace, manganese and silicon alloys are formed using ferrosilicon and low-aluminum, low-titanium ferrosilicon. Ferrovanadium is added in the LF furnace ladle for alloying. To further reduce the aluminum content and considering cost, low-aluminum, low-titanium ferrosilicon and metallic manganese are used for silicon and manganese alloying. At the same time, the nitrogen content in the LF furnace is adjusted by blowing nitrogen gas, slag is formed, and sulfur is fed into the sulfur line at the station. After the VD furnace ladle, supplementary feeding is performed based on the nitrogen and sulfur analysis results, and then vacuum is applied to achieve the effect of no composition adjustment after VD. The superheat of the continuous casting is appropriately increased to improve the castability of the molten steel. Advantages of this invention: The problem of turbidity in continuous casting was solved; in the LF refining process, nitrogen gas was blown instead of argon gas to quickly bring the nitrogen content in the molten steel to the target composition requirements. At the same time, nitrogen gas was used instead of argon gas for circulation in VD, which can save nitriding time and the amount of nitrogen wire alloy added in the refining process; the smelting cycle was shortened, production efficiency was improved, and costs were reduced. Detailed Implementation

[0004] The present invention will now be described in detail with reference to the embodiments. Example 1 Smelting process of 38MnVS4 sulfur-containing, nitrogen-containing, controlled-aluminum steel. Target chemical composition of 38MnVS4 is shown in Table 1. Table 1 Target Chemical Composition (1) Electric Furnace Smelting: Molten iron and recycled steel are added to the converter for smelting. 11t of recycled steel and 55t of molten iron are added to the electric furnace for smelting, with a scrap steel ratio of 16.67%, to obtain molten steel. When the electric furnace has tapped about 1 / 4 of its capacity, i.e., about 15t of steel, alloys and slag are added in the following order: ferrosilicon manganese, low-aluminum and low-titanium ferrosilicon, carbon raiser, refining slag, and lime. The alloys and slag are added in this order: 476kg of ferrosilicon manganese, 350kg of low-aluminum and low-titanium ferrosilicon, 100kg of carbon raiser, 750kg of refining slag, and 300kg of lime. Bottom-blown argon gas is used for stirring during the smelting process. Before tapping, a sample is taken to measure the temperature and carbon content (C) of the molten steel. i 0 =0.08%, nitrogen content C N1 =0.0050%, molten steel temperature T1=1642℃, molten steel weight M0=55.7t. (2) LF furnace refining: 50kg of carbon powder and 50kg of calcium carbide are added for diffusion deoxidation before entering the LF station. To prevent the aluminum content from increasing and increasing the tendency for turbulence after ferrovanadium alloying, 308kg of ferrovanadium is added to the ladle for vanadium alloying. Then, low-aluminum, low-titanium ferrosilicon and metallic manganese are used for silicon and manganese alloying, and ferrochrome and nickel plates are used for chromium and nickel alloying. The first analysis shows that [C]=0.29%, [Si]=0.35%, [Mn]=0.73%, [Cr]=0.13%, and [V]=0.278%, and the content reaches the target value to obtain molten steel and refining slag. After the molten steel temperature reaches 1580℃, argon gas is switched to nitrogen blowing for nitrogen adjustment. Before entering the VD station, the nitrogen content is checked at LF station and found to be 270×10⁻⁶. -6 Before adjusting the sulfur composition in the LF furnace, add 200 kg of silica to change the slag composition. Before hoisting the ladle, feed the sulfur line with a sulfur composition of 0.080% and stir for 1 to 2 minutes to homogenize the sulfur composition. After sampling and analyzing the sulfur composition, hoist the ladle to the next process without waiting for the results. (3) Vacuum refining in a VD furnace: A nitrogen circulation vacuum was used for smelting, with an ultimate vacuum level less than 67 Pa and a holding time of 3 minutes. Nitrogen samples were taken after opening the furnace for analysis: 140 × 10⁻⁶ Pa. -6 Sulfur: 0.047%. The chemical composition analysis results are shown in Table 2. The nitrogen recovery rate h is 51.85% and the sulfur recovery rate h is 57.32%. Nitrogen and sulfur feed lines are added, and the nitrogen and sulfur content is adjusted, but the content of other components is not adjusted. After the composition and temperature are qualified, the ladle is hoisted into the continuous casting. Table 2 Chemical composition of VD samples taken after opening the can (4) Continuous casting: The superheat of the molten steel obtained in step 3 was appropriately increased to 37.3℃, and full-process protective pouring was performed, with a constant casting speed of 1.15 m / min. After pouring, the chemical composition of the billet was tested, and the test results are shown in Table 3. The chemical composition of the billet meets the target composition requirements. Table 3 Chemical composition of cast billet

Claims

1. A process for steelmaking small square billets containing sulfur, nitrogen, and controlled aluminum (non-quenched and tempered steel), characterized in that, The specific process route and steps are as follows: Process route: 60-ton electric furnace → 60-ton LF furnace refining → 60-ton VD vacuum furnace refining → continuous casting of 180mm×180mm square billet; Step 1, Electric Furnace Smelting: Molten iron and returned steel are added to the electric furnace for smelting. When about 1 / 4 of the steel is tapped, alloys and slag materials are added in the following order: "silicon manganese, low-aluminum and low-titanium ferrosilicon, carbon raiser, refining slag, and lime" to create high-basicity slag. Bottom-blown argon gas is used for stirring during the smelting process to prevent over-oxidation of the molten steel, prevent slag from falling, and improve the rate of achieving the target alloy composition. Step 2, refining in the LF refining furnace: (1) In the early stage, high-alkalinity slag is produced, and in the later stage, silica is added to transform the slag into sulfur-retaining slag. (2) Diffusion deoxidation: Carbon powder and calcium carbide are used, with the amount of carbon powder and calcium carbide added being 1.0 to 1.7 kg / t of molten steel. Carbon powder is used to retain the slag after it turns white. (3) Entering the LF station, to prevent the aluminum content from increasing and the tendency to turbulence from increasing after vanadium-iron alloying, vanadium alloying is carried out in the saddle bag. (4) No aluminum wire is added to the LF furnace base and process, and the aluminum content is not adjusted; in order to prevent the aluminum content from increasing during the refining process, low-aluminum and low-titanium ferrosilicon and metallic manganese are used for silicon and manganese alloying to control the aluminum content; ferrochrome and nickel plates are used for chromium and nickel alloying to make their content reach the target value. (5) After the molten steel temperature reaches 1560℃, switch the bottom-blowing argon gas to bottom-blowing nitrogen gas for nitrogen adjustment. Before entering the VD (Vacuum-Deposit) stage, take a gas sample for analysis. The target nitrogen content value is calculated as (250~300)×10. -6 Control is advisable; (6) Before adjusting the sulfur composition in the LF furnace, add 200 kg of silica to change the slag. Before hoisting the ladle, feed the sulfur line with a sulfur composition of 0.080%. Stir for 1 min to 2 min to make the sulfur composition uniform. After sampling and analyzing the sulfur composition, hoist the ladle to the next process without waiting for the results. Step 3, VD vacuum furnace smelting: (1) The vacuum process uses nitrogen circulation instead of argon; (2) After the furnace is set up, sulfur wire is added based on the sulfur composition results of the last analysis of the LF furnace; (3) After the furnace is set up, the nitrogen composition is determined according to the final analysis results of the LF furnace, calculated as (250~300)×10 -6 Feed nitrogen line; (4) The ultimate vacuum degree shall not exceed 67 Pa, and the vacuum holding time shall be 3 min; (5) After opening the can, the nitrogen and sulfur content will be adjusted according to the analysis results, but the content of other components will not be adjusted. Step 4, Continuous casting: The superheat of the molten steel obtained in step 3 is appropriately increased, and the entire process is protected during casting.

2. The steelmaking process for sulfur-containing, nitrogen-containing, controlled-aluminum non-quenched and tempered steel billets according to claim 1, characterized in that, Step 1, Electric furnace smelting: The high-basicity slag is produced, with a high-basicity slag ratio of 750kg refining slag + 300kg lime, and the slag basicity is 4-5; Step 2, LF refining furnace refining: For the vanadium alloying, add about 300 kg of ferrovanadium, and then add more ferrovanadium alloy according to the analysis results; The aluminum content is controlled to be no more than 0.010%; Step 3, VD vacuum furnace smelting: After the ladle is set up, the sulfur line is replenished with sulfur according to the sulfur composition results of the last analysis of the LF furnace, with a sulfur content of 0.080%; Step 4, continuous casting: The superheat of the molten steel obtained in step 3 is appropriately increased to 30℃~45℃.

3. The steelmaking process for sulfur-containing, nitrogen-containing, controlled-aluminum non-quenched and tempered steel billets according to claim 1 or 2, characterized in that, Smelting process of 38MnVS4 sulfur-containing, nitrogen-containing, controlled-aluminum steel; The target chemical composition of 38MnVS4 is shown in Table 1; Table 1 Target Chemical Composition (1) Electric Furnace Smelting: Molten iron and recycled steel are added to the converter for smelting. 11t of recycled steel and 55t of molten iron are added to the electric furnace for smelting, with a scrap steel ratio of 16.67%, to obtain molten steel. When the electric furnace has tapped about 1 / 4 of its capacity, i.e., about 15t of steel, alloys and slag are added in the following order: ferrosilicon manganese, low-aluminum and low-titanium ferrosilicon, carbon raiser, refining slag, and lime. The alloys and slag are added in this order: 476kg of ferrosilicon manganese, 350kg of low-aluminum and low-titanium ferrosilicon, 100kg of carbon raiser, 750kg of refining slag, and 300kg of lime. Bottom-blown argon gas is used for stirring during the smelting process. Before tapping, a sample is taken to measure the temperature and carbon content (C) of the molten steel. i 0 =0.08%, nitrogen content C N1 =0.0050%, molten steel temperature T1=1642℃, molten steel weight M0=55.7t; (2) LF furnace refining: 50kg of carbon powder and 50kg of calcium carbide are added for diffusion deoxidation before entering the LF station. To prevent the aluminum content from increasing and increasing the tendency for turbulence after ferrovanadium alloying, 308kg of ferrovanadium is added to the ladle for vanadium alloying. Then, low-aluminum, low-titanium ferrosilicon and metallic manganese are used for silicon and manganese alloying, and ferrochrome and nickel plates are used for chromium and nickel alloying. The first analysis shows that [C]=0.29%, [Si]=0.35%, [Mn]=0.73%, [Cr]=0.13%, and [V]=0.278%, and the content reaches the target value to obtain molten steel and refining slag. After the molten steel temperature reaches 1580℃, argon gas is switched to nitrogen blowing for nitrogen adjustment. Before entering the VD station, the nitrogen content is checked at LF station and found to be 270×10⁻⁶. -6 Before adjusting the sulfur composition in the LF furnace, add 200 kg of silica to change the slag. Before hoisting the ladle, feed the sulfur line with a sulfur composition of 0.080%, stir for 1 min to 2 min to homogenize the sulfur composition, take a sample for analysis, and hoist the ladle to the next process without waiting for the results. (3) Vacuum refining in a VD furnace: A nitrogen circulation vacuum was used for smelting, with an ultimate vacuum level less than 67 Pa and a holding time of 3 minutes. Nitrogen samples were taken after opening the furnace for analysis: 140 × 10⁻⁶ Pa. -6 Sulfur: 0.047%, chemical composition analysis results are shown in Table 2, nitrogen recovery rate h is 51.85%, sulfur recovery rate h is 57.32%, nitrogen line and sulfur line are supplemented, nitrogen and sulfur content is adjusted, other component content is not adjusted, after the composition and temperature are qualified, the ladle is hoisted into continuous casting. Table 2 Chemical composition of VD samples taken after opening the can (4) Continuous casting: The superheat of the molten steel obtained in step 3 is appropriately increased to 37.3℃, and full-process protective casting is carried out. The constant casting speed is 1.15m / min. After casting, the chemical composition of the billet is tested. The test results are shown in Table 3. The chemical composition of the billet meets the target composition requirements. Table 3 Chemical composition of cast billet

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