A smelting method for improving cleanliness of austenitic stainless steel

Abstract

The present application belongs to the field of smelting, and particularly relates to a smelting method for improving cleanliness of austenitic stainless steel. The method comprises the following steps: melting raw materials in an electric furnace, tapping; AOD refining; LF refining. The present application controls the content of C and Si elements and the tapping temperature when the raw materials are melted in the electric furnace, controls the temperature of the molten steel in the AOD refining, performs primary reduction with FeSi and controls the content of Si, adds reducing slag material lime and fluorite for secondary reduction, controls the target requirement of the basicity of the reducing slag, adds aluminum particles, and the rest is reduced with silicon calcium block; in the LF refining, CaSi powder is used for diffusion deoxidation, Al is not used for deoxidation, the target of oxygen is controlled, the white slag retention time is controlled, the argon stirring time and the soft argon blowing time are controlled, and the ladle is poured, so that the current inclusion requirement of high-end 304 austenitic stainless steel can be solved, and the inclusions are reduced from 1.5 or 2.0 grade to <=1.0 grade.

Description

Technical Field

[0001] This invention relates to the field of metallurgy, and more particularly to a metallurgical method for improving the cleanliness of austenitic stainless steel. Background Technology

[0002] Cleanliness control of steel is an inevitable trend in the development of steel materials. Cleanliness is an important indicator reflecting the overall quality level of steel, usually evaluated by the content of harmful elements in molten steel and the quantity, morphology, and size of non-metallic inclusions. Among these, non-metallic inclusions are a significant factor affecting the cleanliness of molten steel. Austenitic stainless steel refers to stainless steel that has an austenitic structure at room temperature. Steel containing approximately 18% Cr, 8%~25% Ni, and approximately 0.1% C has a stable austenitic structure. 304 austenitic stainless steel is widely used in daily life. Some high-end 304 austenitic stainless steel products are used in the production of mobile phone cases and watch bracelets, thus requiring high surface quality. Currently, high-end 304 stainless steel suffers from surface scale defects and dot-like defects after polishing, seriously affecting the surface aesthetics of the finished product. This is mainly due to inclusions in the stainless steel. High-end 304 stainless steel requires inclusions of grades A, B, C, and D to be ≤1.0. However, due to immature production processes, current production often results in inclusion levels of 1.5-2.0, and in severe cases, even grade 2.5 inclusions. This level of inclusions cannot meet current production requirements. Therefore, controlling inclusions in 304 stainless steel is of great significance for enterprises to achieve the production of high-end 304 stainless steel. Summary of the Invention

[0003] To address the problem of high inclusion levels in existing 304 stainless steel processes due to immature technology, this invention proposes a smelting method to improve the purity of austenitic stainless steel.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] A smelting method for improving the cleanliness of austenitic stainless steel includes the following steps: melting raw materials in an electric furnace and tapping the steel; AOD refining; LF refining;

[0006] In the AOD refining process, reducing slag materials such as quicklime and fluorite are added to form slag. The target requirement for controlling the basicity of the reducing slag (R=CaO / SiO2) is 2.1-2.2, and 0.5-0.8 kg / t of aluminum particles are added.

[0007] In the LF refining process, CaSi powder diffusion deoxidation is used, and the soft blowing argon time is controlled at 15-20 min.

[0008] Preferably, in the steps of the smelting method for improving the cleanliness of austenitic stainless steel, the carbon content is 1.9-2.2% and the silicon content is ≤0.8% when the steel is tapped.

[0009] Further preferred is a tapping temperature of 1640-1660℃.

[0010] Preferably, AOD refining includes the following steps:

[0011] (1) AOD oxygen blowing decarbonization;

[0012] (2) Reduced once with FeSi;

[0013] (3) After the first reduction is completed, shake the furnace to remove slag. For the second reduction, add reducing slag materials such as lime and fluorite to form slag. The target requirement for the basicity of the reducing slag (R=CaO / SiO2) is 2.1-2.2. Add 0.5-0.8 kg / t steel of aluminum particles, and use the rest of the reduction with calcium silicate blocks.

[0014] In a further preferred embodiment, during step (1) AOD oxygen blowing decarburization, the temperature of the molten steel smelting with slag added is maintained at 1680-1730℃.

[0015] Further preferred, step (2) reduces Si to a target of 0.25-0.45% in one step.

[0016] Preferably, LF refining includes the following steps:

[0017] (1) After the LF is in place, the argon gas is turned on. The large argon gas is used to stir and break the slag shell. After the ladle car is driven to the heating station, the temperature is measured and a sample is taken. The argon gas flow rate is adjusted and the power is supplied to raise the temperature.

[0018] (2) CaSi powder diffusion deoxidation is used instead of Al deoxidation, and the oxygen control target is ≤25ppm;

[0019] (3) Take a sample after the slag has turned white and the temperature is ≥1560℃. Adjust the composition precisely according to the internal control composition standard based on the analysis results. The white slag should be kept for ≥20 minutes.

[0020] (4) After the composition meets the internal control standard range, start large argon gas stirring. After stirring for 8-10 minutes, the Ar gas ring diameter is ≥300mm and does not expose the steel liquid surface. Start feeding calcium wire at 4-6m / t. After feeding, start soft blowing argon operation. Soft blowing time is 15-20 minutes. Then, lift the ladle for pouring.

[0021] More preferably, the internal control component standard is:

[0022] C: ≤0.020%; Si: 0.30~0.50%; Mn: 0.95~1.05%; P: ≤0.035%; S: ≤0.001%; ​​Ni: 8.05~8.12%; Cr: 18.15~18.35%; Fe: Balance.

[0023] Further preferred pouring temperature: 1530~1540℃.

[0024] The raw materials mentioned in step (1) include scrap steel, high-carbon ferrochrome, aluminum granules, nickel plates, and high-carbon ferromanganese or ferrosilicon.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) By selecting and adjusting the amount of deoxidizer in the refining process of AOD and LF furnaces, this invention takes into account the adjustment of slag alkalinity, molten steel temperature control, argon blowing and stirring, etc., and finally the smelting product achieves the purpose of this invention.

[0027] (2) The present invention can solve the current requirements for inclusions in high-end 304 austenitic stainless steel, reducing the inclusion level from 1.5 or 2.0 to ≤1.0. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments. The advantages and features of the present invention will become clearer in the description. However, the embodiments are merely illustrative and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions without departing from the spirit and scope of the present invention, and such modifications and substitutions all fall within the protection scope of the present invention.

[0029] Example 1

[0030] A smelting method for improving the cleanliness of austenitic stainless steel includes the following steps:

[0031] (1) The electric furnace melts raw materials, including scrap steel, high carbon ferrochrome, aluminum granules, nickel plates, and high carbon ferromanganese. The steel has a C content of 1.9%, a Si content of 0.6%, and a tapping temperature of 1648℃.

[0032] (2) AOD furnace refining:

[0033] 1) During AOD oxygen blowing decarburization, the temperature of the molten steel smelted with slag-added materials was 1688℃;

[0034] 2) Single reduction process: FeSi reduction, with Si controlled at 0.28%;

[0035] 3) Secondary reduction: After the primary reduction is completed, the furnace is shaken and the slag is skimmed off. For the secondary reduction, lime and fluorite are added to form slag. The basicity of the reducing slag (R=CaO / SiO2) is controlled to a target of 2.1. 0.6 kg / t steel of aluminum granules are added, and the remainder is reduced with calcium silicate blocks.

[0036] (3) LF furnace refining:

[0037] 1) After the LF is in place, the argon gas is turned on. The large argon gas is used to stir and break the slag shell. After the ladle car is driven to the heating station, the temperature is measured and samples are taken. The argon gas flow rate is adjusted and the power is supplied to raise the temperature.

[0038] 2) CaSi powder diffusion deoxidation is used instead of Al deoxidation, and oxygen is controlled at 23 ppm.

[0039] 3) After the slag has turned white enough, take a sample at 1562℃. Adjust the composition precisely according to the internal control composition based on the analysis results. The white slag should be kept for 25 minutes.

[0040] 4) After the composition meets the internal control standard range, start large argon gas stirring. After stirring for 8 minutes (Ar gas ring diameter 350mm without exposed steel liquid surface), calcium treatment process: feed calcium wire 4m / t; after feeding, start soft blowing argon operation, soft blowing time 18 minutes, hang ladle pouring, pouring temperature: 1532℃.

[0041] In this embodiment, the ingredients are controlled according to the internal control standards in Table 1.

[0042] Table 1. Composition control standards for austenitic stainless steel in Example 1

[0043]

[0044] Example 2

[0045] A smelting method for improving the cleanliness of austenitic stainless steel includes the following steps:

[0046] (1) The raw materials for electric furnace melting include scrap steel, high carbon ferrochrome, aluminum granules, nickel plates, and high carbon ferromanganese. The steel tapping C content is 2.1%, the Si content is 0.8%, and the tapping temperature is 1658℃.

[0047] (2) AOD furnace:

[0048] 1) During AOD oxygen blowing decarburization, the temperature of the molten steel smelted with slag-added materials is 1708℃;

[0049] 2) Single-stage reduction process: FeSi reduction, with Si controlled at 0.3%;

[0050] 3) Secondary reduction: After the primary reduction is completed, the furnace is shaken and the slag is skimmed off. For the secondary reduction, lime and fluorite are added to form slag. The basicity of the reducing slag (R=CaO / SiO2) is controlled to a target of 2.2. 0.7 kg / t steel of aluminum granules is added, and the remainder is reduced with calcium silicate blocks.

[0051] (3) LF furnace:

[0052] 1) After the LF is in place, the argon gas is turned on. The large argon gas is used to stir and break the slag shell. After the ladle car is driven to the heating station, the temperature is measured and samples are taken. The argon gas flow rate is adjusted and the power is supplied to raise the temperature.

[0053] 2) CaSi powder diffusion deoxidation is used, without Al deoxidation. Oxygen control target: 20 ppm.

[0054] 3) After the slag has turned white enough, take a sample at 1568°C. Based on the analysis results, adjust the composition precisely according to the internal control composition (same as in Example 1). The white slag should be kept for 30 minutes.

[0055] 4) Argon gas stirring process: After the composition meets the internal control standard range, start large argon gas stirring. After stirring for 9 minutes (Ar gas ring diameter 320mm without exposed steel liquid surface), calcium treatment process: feed calcium wire 4.5m / t; soft blowing time 18min.

[0056] Pouring was done using a ladle, with a pouring temperature of 1535℃.

[0057] Comparative Example 1

[0058] A method for smelting austenitic stainless steel includes the following steps:

[0059] (1) The raw materials for electric furnace melting include scrap steel, high carbon ferrochrome, aluminum granules, nickel plates, and high carbon ferromanganese. The steel tapping C content is 2.0%, the Si content is 0.3%, and the tapping temperature is 1648℃.

[0060] (2) AOD furnace:

[0061] 1) During AOD oxygen blowing decarburization, the temperature of the molten steel smelted with slag-added materials is 1690℃;

[0062] 2) Single reduction process: Si content controlled at 0.3%;

[0063] 3) Secondary reduction: The basicity of the reduction slag (R=CaO / SiO2) is controlled to a target of 1.7, and 0.6 kg / t of aluminum particles are added;

[0064] (3) LF furnace:

[0065] 1) After the LF is in place, the argon gas is turned on. The large argon gas is used to stir and break the slag shell. After the ladle car is driven to the heating station, the temperature is measured, samples are taken, the argon gas flow is adjusted, and the power is supplied to raise the temperature.

[0066] 2) CaSi powder diffusion deoxidation is used, without Al deoxidation; oxygen control target is 20 ppm;

[0067] 3) The white residue should be kept for 24 minutes;

[0068] 4) Argon gas stirring process: After the composition meets the internal control standard range, start large-scale argon gas stirring for 8 minutes (Ar gas ring diameter 350mm, not exposed above the molten steel surface). Calcium treatment process: feed calcium wire 4m / t; soft blowing time 10 minutes. Ladle casting, casting temperature: 1535℃.

[0069] Comparative Example 2

[0070] A method for smelting austenitic stainless steel includes the following steps:

[0071] (1) The raw materials are melted in an electric furnace, and the steel has a C content of 1.9% and a Si content of 0.4% at the tapping temperature of 1645℃.

[0072] (2) AOD furnace:

[0073] 1) During AOD oxygen blowing decarburization, the temperature of the molten steel smelted with slag-added materials is 1700℃;

[0074] 2) Single-stage reduction process: FeSi reduction, with Si controlled at 0.40%;

[0075] 3) Secondary reduction: The basicity of the reduction slag (R=CaO / SiO2) is controlled to a target of 2.0, and 1 kg of aluminum particles are added per t of steel;

[0076] (3) LF furnace:

[0077] 1) After the LF is in place, the argon gas is turned on. The large argon gas is used to stir and break the slag shell. After the ladle car is driven to the heating station, the temperature is measured, samples are taken, the argon gas flow is adjusted, and the power is supplied to raise the temperature.

[0078] 2) Use Al for deoxygenation, with an oxygen control target of 21 ppm;

[0079] 3) The white residue should be kept for 24 minutes;

[0080] 4) Argon gas stirring process: After the composition meets the internal control standard range, start large-scale argon gas stirring for 8 minutes (Ar gas ring diameter 310mm, not exposed above the molten steel surface). Calcium treatment process: feed calcium wire 6m / t; soft blowing time 15 minutes. Ladle pouring, pouring temperature: 1535℃.

[0081] The head and tail positions of the steel ingots produced according to the steps described in Examples 1 and 2 and Comparative Examples 1 and 2 were inspected and analyzed, and the results are shown in Table 2.

[0082] Table 2. Inspection and analysis results of the head and tail positions of the steel ingots produced in the examples and comparative examples.

[0083]

[0084] Note: The top and bottom rows in the table above show the inspection results for the relative head and tail positions of the steel ingot.

[0085] By comparing the inclusion inspection results of the above embodiments and the comparative examples, the inclusion results of the products produced according to the process set in this scheme are all ≤1.0 grade, which meets the requirements of high-end 304 steel that all types of inclusions A, B, C, and D are required to be ≤1.0 grade. However, the inclusion levels of the finished products produced in the comparative examples exceed 1.0 grade for types B and D, and do not meet the requirements.

Claims

1. A smelting method for improving the cleanliness of austenitic stainless steel, characterized in that, Includes the following steps: Electric furnace melts raw materials and produces steel; AOD refining; LF refining; The AOD refining process includes the following steps: (1) AOD oxygen blowing decarbonization; (2) Reduced once with FeSi; (3) After the first reduction is completed, shake the furnace to remove slag. For the second reduction, add reducing slag materials such as lime and fluorite to form slag. The basicity of the reducing slag R=CaO / SiO2 is controlled to a target of 2.1-2.

2. Add 0.5-0.8 kg / t steel of aluminum particles, and use silicon-calcium blocks for the rest of the reduction. The LF refining process includes the following steps: (1) After the LF is in place, the argon gas is turned on. The large argon gas is used to stir and break the slag shell. After the ladle car is driven to the heating station, the temperature is measured and a sample is taken. After adjusting the argon gas flow rate, the power is turned on to raise the temperature. (2) CaSi powder diffusion deoxidation is used instead of Al deoxidation, and the oxygen control target is ≤25ppm; (3) Take a sample after the slag has turned white and the temperature is ≥1560℃. Adjust the composition precisely according to the internal control composition standard based on the analysis results. The white slag should be kept for ≥20 minutes. (4) After the composition meets the internal control standard range, start large argon gas stirring. After stirring for 8-10 minutes, the Ar gas ring diameter is ≥300mm and does not expose the steel liquid surface. Start feeding calcium wire at 4-6m / t. After feeding, start soft blowing argon operation. Soft blowing time is 15-20 minutes. Then, pour the ladle. The internal control component standard is as follows: C: ≤0.020%; Si: 0.30~0.50%; Mn: 0.95~1.05%; P: ≤0.035%; S: ≤0.001%; ​​Ni: 8.05~8.12%; Cr: 18.15~18.35%; Fe: Balance.

2. The smelting method for improving the cleanliness of austenitic stainless steel according to claim 1, characterized in that, When the steel is tapped, the carbon content is 1.9-2.2% and the silicon content is ≤0.8%.

3. The smelting method for improving the cleanliness of austenitic stainless steel according to claim 1, characterized in that, The tapping temperature is 1640-1660℃.

4. The smelting method for improving the cleanliness of austenitic stainless steel according to claim 1, characterized in that, During step (1) AOD oxygen blowing decarburization, the temperature of the molten steel smelting with slag added is maintained at 1680-1730℃.

5. The smelting method for improving the cleanliness of austenitic stainless steel according to claim 1, characterized in that, Step (2) Reduce Si once to control the target of 0.25-0.45%.

6. The smelting method for improving the cleanliness of austenitic stainless steel according to claim 1, characterized in that, The pouring temperature is 1530~1540℃.

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