A smelting method for low-C and low-Si soft wire steel

Abstract

The present invention relates to a smelting method for low-C and low-Si soft wire steel. The chemical composition of the steel is C≤0.02%, Si≤0.005%, Mn≤0.25%, P≤0.020%, S≤0.020%, and the balance is Fe and inevitable impurities. The KR+BOF+LF+CC smelting technology is adopted. After KR desulfurization, the S content of the molten iron entering the furnace is ≤0.003%. The C content of the converter end point is ≤0.06%, the S content is ≤0.018%, the oxygen content of the converter tapping is ≥500ppm, and the converter tapping content is ≤0.003%. No deoxidizer is added during the process, and low-basicity, high-oxidizing slag is added after the furnace at a rate of ≥5kg / ton of steel. The LF refining process adopts slagging and heating, large argon stirring and oxygenation to remove carbon and silicon, with a constant oxygen level of ≥800ppm. After sampling and testing of C≤0.015% and Si≤0.005%, aluminum wire is fed to deoxidize the molten steel, and aluminum shots are sprinkled to deoxidize the ladle top slag to ensure that the constant oxygen level is controlled between 30 and 50ppm. Calcium treatment is then carried out, and the finished product, low-C and low-Si soft wire steel, with C≤0.02% and Si≤0.005%, has been successfully developed.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to a smelting method of low-C and low-Si soft wire steel. Background Art

[0002] With the development of the national economy, low-carbon and low-silicon steels have been widely used. As the carbon and silicon content in steel decreases, the toughness and plasticity of steel increase, the deformation resistance increases, and the safety factor increases, and its application is becoming more and more extensive.

[0003] Low-carbon steel refers to steel with a carbon content less than 0.02%. Due to its low carbon content, it is difficult to smelt. During the LF refining process, arc heating is used, the LF furnace electrodes are made of carbon, and alloying elements also contain a high amount of carbon, which leads to an increase in the carbon content of the molten steel during production. Therefore, only by controlling the initial carbon content to a low level of ≤0.015% can the carbon content of the finished product be controlled to ≤0.02% under the aforementioned subsequent carburization conditions. Currently, the smelting process for ultra-low-carbon, low-silicon steel (C ≤0.0030%, Si ≤0.005%) is based on either a converter (BOF)-RH (vacuum treatment)-continuous casting process or a converter-LF-RH (vacuum treatment)-RH (vacuum treatment)-continuous casting process. Both processes require RH vacuum decarburization, which uses carbon-oxygen and silicon-oxygen reactions to reduce the carbon and silicon contents in the steel.

[0004] Chinese Patent No. 2017102209049 discloses a method for smelting ultra-low carbon steel, which includes desulfurization, converter blowing, RH vacuum treatment, and continuous casting. This smelting process utilizes traditional converter and RH vacuum refining, which increases control difficulty.

[0005] Chinese patent CN202211596331.7 discloses a "Method for Smelting Low-Silicon Aluminum-Killed Low-Carbon Steel with Controllable Inclusions," which includes three stages: converter steelmaking, ladle argon blowing, and continuous casting. The process utilizes controlled oxygen and high-alumina-adsorbent ladle slag to control inclusion levels in the molten steel. This smelting process, which utilizes a converter combined with ladle argon blowing, a high-basicity, low-oxidizing slag system, and full aluminum deoxidation, makes it difficult to produce molten steel with Si content ≤ 0.005%. Summary of the Invention

[0006] The present invention aims to provide a smelting method for producing low-C and low-Si soft wire steel by electric furnace + LF refining, which can better solve the problem of increased carbon and silicon content in molten steel during the production process and develop continuous casting billets of low-C and low-Si soft wire.

[0007] Technical solution of the invention:

[0008] A smelting method for low-C and low-Si soft steel wire, (1) pre-treatment of sulfur: after KR desulfurization, the sulfur content of the molten iron entering the furnace is ≤ 0.003%;

[0009] (2) Converter smelting: End point C ≤ 0.06%, converter tapping oxygen ≥ 500ppm, converter slide plate blocking slag, no alloy or deoxidizer added during tapping, ≥ 6kg / ton of steel low basicity and high oxidation slag added during tapping; slag composition control range is T.Fe = 15% ~ 25%, CaO = 25% ~ 35%, MgO = 5% ~ 10%, SiO2 = 20% ~ 30%, Al2O3 = 5% ~ 15%, MnO = 3% ~ 10%;

[0010] (3) LF decarburization and siliconization operation: After the molten steel enters the station, it is powered on to heat up and slag, alloys are added during the smelting process, and large amounts of argon gas are used for stirring and oxygenation to remove carbon and silicon. The oxygen content is ≥800ppm, and the sample composition is C≤0.015%, Si≤0.005%;

[0011] (4) LF deoxidation operation: After the composition is qualified, aluminum wire is fed to deoxidize the molten steel according to the constant oxygen situation, and aluminum shots are sprinkled to deoxidize the ladle top slag. Calcium treatment operation is performed to ensure that the constant oxygen is controlled between 30 and 50 ppm to obtain low C and low Si soft wire steel with C ≤ 0.02% and Si ≤ 0.005%.

[0012] The present invention adopts KR+BOF+LF composite smelting technology, adopts high oxygen at the converter end point, no deoxidizer is added during the converter tapping process, low basicity and high oxidizing slag is added, LF slag making and heating, large argon stirring and oxygenation to remove carbon and silicon, and an oxygen setting of ≥800ppm. After sampling and testing of C≤0.015% and Si≤0.005%, aluminum wire is added to deoxidize the molten steel, aluminum shots are sprinkled to deoxidize the ladle top slag to ensure that the oxygen setting is controlled between 30 and 50ppm, and then calcium wire treatment is performed. A series of technologies have been successfully developed to successfully develop a finished product with low carbon and low silicon soft wire steel with C≤0.02% and Si≤0.005%, which can well meet the usage needs of customers.

[0013] The outstanding features and remarkable effects of the present invention are as follows: when LF does not have the ability to remove S, pretreatment and converter are used to carry out S removal operations; the LF refining process uses highly oxidizing molten steel and low-basicity highly oxidizing slag, and alloys are added to adjust the composition to carry out C and Si removal operations; oxygen control operations are carried out on the deoxidation of molten steel and fixed slag, the oxygen content of the molten steel for pouring is controlled between 30 and 50 ppm, and calcium treatment is carried out, thereby ensuring the castability of the molten steel and being able to well meet the usage requirements of customers. DETAILED DESCRIPTION

[0014] The production method of the present invention will be further described below with reference to the embodiments:

[0015] Example 1:

[0016] A method for smelting low-C, low-Si soft steel wire, wherein the molten steel contains C=0.0192%, Si=0.0021%, Mn=0.2189%, P=0.0045%, S=0.0132%, and the balance is Fe and unavoidable impurities. The method comprises the following steps:

[0017] (1) Pretreatment of sulfur removal: After KR sulfur removal, the sulfur content of the molten iron entering the furnace is 0.0028%.

[0018] (2) Converter smelting: C=0.0552% and S=0.0124% of the steel tapped from the converter. The oxygen content of the steel tapped from the converter is 512ppm. The slag is blocked by a slide plate. During the tapping process, 7.4kg / ton of low-alkalinity and high-oxidizing slag is added. The slag composition is controlled to be T.Fe=18.92%, CaO=31.84%, MgO=7.91%, SiO2=25.24%, Al2O3=8.62%, and MnO=6.86%.

[0019] (3) LF decarbonization and Si removal operation: The LF furnace was powered on for 15 minutes, the temperature was 1634°C, 20.5 kg of medium carbon MnFe was added, and no deoxidizer was added for deoxidation. During the smelting process, large argon was used for stirring for 10 minutes, and the oxygen was set at 856 ppm.

[0020] (4) LF deoxidation operation: Take samples for testing, the composition is C=0.0122%, Si=0.0001%, Mn=0.2242%, P=0.0043%, S=0.0131%, 685 meters of aluminum wire are fed into the molten steel, 60 kg of aluminum shots are sprinkled on the top slag of the ladle, and after ensuring 45 ppm, 150 meters of calcium wire are fed and soft blowing is carried out for 12 minutes.

[0021] Example 2:

[0022] A method for smelting low-C, low-Si soft steel wire, wherein the molten steel contains C=0.0162%, Si=0.0014%, Mn=0.2021%, P=0.0058%, S=0.0167%, and the balance is Fe and unavoidable impurities. The method comprises the following steps:

[0023] (1) Pretreatment of sulfur removal: After KR sulfur removal, the sulfur content of the molten iron entering the furnace is 0.0021%.

[0024] (2) Converter smelting: C=0.0467% and S=0.0152% of the steel tapped from the converter. The oxygen content of the steel tapped from the converter was 568ppm. The slag was blocked by a slide plate. During the tapping process, 7.1kg / ton of low-alkalinity and high-oxidizing slag was added. The slag composition was controlled to be T.Fe=19.46%, CaO=28.34%, MgO=9.65%, SiO2=27.73%, Al2O3=7.86%, and MnO=6.62%.

[0025] (3) LF decarbonization and Si removal operation: The LF furnace was powered on for 18 minutes, the temperature was 1646°C, 19.5 kg of medium carbon MnFe was added, and no deoxidizer was added for deoxidation. During the smelting process, large argon was used for stirring for 10 minutes, and the oxygen was set at 882 ppm.

[0026] (4) LF deoxidation operation: Take samples for testing, the composition is C=0.0081%, Si=0.0001%, Mn=0.2015%, P=0.0052%, S=0.0154%, 700 meters of aluminum wire is fed into the molten steel, 60 kg of aluminum shot is sprinkled on the top slag of the ladle, after ensuring 38 ppm, 150 meters of calcium wire is fed, and soft blowing is carried out for 11 minutes.

[0027] Example 3:

[0028] A method for smelting low-C, low-Si soft steel wire, wherein the molten steel contains 0.0184% C, 0.0018% Si, 0.1892% Mn, 0.0045% P, and 0.0168% S, with the remainder being Fe and unavoidable impurities. The method comprises the following steps:

[0029] (1) Pretreatment of S removal: After KR S removal, the S content of the molten iron entering the furnace is 0.0025%.

[0030] (2) Converter smelting: C=0.0492% and S=0.0161% of the steel tapped from the converter. The oxygen content of the steel tapped from the converter was 618 ppm. The slag was blocked by a slide plate. During the tapping process, 8.05 kg / ton of low-alkalinity, high-oxidizing slag was added. The slag composition was controlled to be T.Fe=21.24%, CaO=28.34%, MgO=8.67%, SiO2=26.87%, Al2O3=9.45%, and MnO=5.38%.

[0031] (3) LF decarbonization and Si removal operation: The LF furnace was powered on for 12 minutes, the temperature was 1642°C, 20.5 kg of medium carbon MnFe was added, and no deoxidizer was added for deoxidation. During the smelting process, large argon was used for stirring for 10 minutes, and the oxygen was set at 956 ppm.

[0032] (4) LF deoxidation operation: Take samples for testing, the composition is C=0.0117%, Si=0.0001%, Mn=0.1867%, P=0.0042%, S=0.0164%, feed 760 meters of aluminum wire into the molten steel, sprinkle 60 kg of aluminum shot on the top slag of the ladle, ensure 42 ppm, feed 150 meters of calcium wire, and soft blow for 12 minutes.

Claims

1. A method for smelting low-C and low-Si soft steel wire, characterized by: The chemical composition of the steel is C≤0.02%, Si≤0.005%, Mn≤0.25%, P≤0.020%, S≤0.020% by weight, with the balance being Fe and unavoidable impurities. The process steps include: (1) Pretreatment of sulfur: After KR desulfurization, the sulfur content of the molten iron entering the furnace is ≤ 0.003%; (2) Converter smelting: End point C ≤ 0.06%, converter tapping oxygen ≥ 500ppm, converter slide plate blocking slag, no alloy or deoxidizer added during tapping, ≥ 6kg / ton of steel low basicity and high oxidation slag added during tapping; slag composition control range is T.Fe = 15% ~ 25%, CaO = 25% ~ 35%, MgO = 5% ~ 10%, SiO2 = 20% ~ 30%, Al2O3 = 5% ~ 15%, MnO = 3% ~ 10%; (3) LF decarburization and siliconization operation: After the molten steel enters the station, it is powered on to heat up and slag, alloys are added during the smelting process, and large amounts of argon gas are used for stirring and oxygenation to remove carbon and silicon. The oxygen content is ≥800ppm, and the sample composition is C≤0.015%, Si≤0.005%; (4) LF deoxidation operation: After the composition is qualified, aluminum wire is fed to deoxidize the molten steel according to the constant oxygen situation, and aluminum shots are sprinkled to deoxidize the ladle top slag. Calcium treatment operation is performed to ensure that the constant oxygen is controlled between 30 and 50 ppm to obtain low C and low Si soft wire steel with C ≤ 0.02% and Si ≤ 0.005%.