Method for smelting nickel-saving austenitic stainless steel

Abstract

The invention discloses a method for smelting nickel-saving austenitic stainless steel, which adopts a process of'electric furnace + AOD converter + LF refining furnace ', the electric furnace adopts a full cold charge smelting mode, 400-series medium-sized stainless steel scrap, 300-series large slag steel, 400-series coping dust, nickel-copper alloy and coke are reasonably added, so that P is less than or equal to 0.05%, Cu is less than or equal to 0.25% and Ni is less than or equal to 1.15% in tapping of the electric furnace, and when molten steel of the electric furnace is added into the AOD converter for smelting, the molten steel of the electric furnace is molten in the LF refining furnace. The smelting process sequentially comprises the stages of oxidation, reduction and desulfurization, and finally fine adjustment is conducted on molten steel components and temperature in an LF refining furnace to obtain the target steel grade. Compared with SUS304 austenitic stainless steel, the nickel-saving austenitic stainless steel has the advantages that the capacity of manganese for stabilizing an austenitic structure is only second to the solid solution strengthening of nickel and nitrogen and the corrosion resistance of copper, compared with the SUS304 austenitic stainless steel, the content of Ni is reduced, the content of Mn, N and Cu is increased, the smelting and rolling processes are similar to those of the SUS304 austenitic stainless steel, and the production cost is reduced. The effect of replacing part of SUS304 austenitic stainless steel is achieved, and the smelting cost is saved.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel smelting, and in particular to a method for smelting nickel-saving austenitic stainless steel. Background Art

[0002] As nickel resources in the world become increasingly scarce and scarce, especially high-grade laterite resources are increasingly depleted, how enterprises can stand out and remain invincible in the increasingly competitive market environment has become a major survival issue faced by all stainless steel companies. The ability of nickel-saving austenitic stainless steel to stabilize austenite structure using Mn elements is second only to the solid solution strengthening of nickel and nitrogen and the corrosion resistance of copper. The smelting and rolling process is similar to that of SUS304 austenitic stainless steel. This type of steel can replace part of SUS304 austenitic stainless steel to reduce the smelting cost of austenitic stainless steel. Summary of the invention

[0003] The purpose of the present invention is to provide a method for smelting nickel-saving austenitic stainless steel, which can replace part of SUS304 austenitic stainless steel, and the reduction of nickel content in the steel reduces the smelting cost.

[0004] To achieve its purpose, the present invention adopts the following technical solution: The present invention adopts the process of "electric furnace + AOD converter + LF refining furnace" to smelt nickel-saving austenitic stainless steel, including electric furnace with 400 series medium-sized stainless steel scrap, 300 series large slag steel, 400 series grinding chips, nickel-copper alloy, coke full cold material smelting, AOD converter oxidation stage, reduction stage and desulfurization stage, LF refining furnace fine-tuning molten steel composition and temperature, to obtain nickel-saving austenitic stainless steel, to achieve partial replacement of SUS304 austenitic stainless steel. The specific process includes the following steps: Step 1, primary smelting in an electric furnace: 400 series medium-sized stainless steel scrap, 300 series large slag steel, 400 series grinding chips, nickel-copper alloy, coke and auxiliary materials are added into the electric furnace. After the electric furnace is arced, the first 2-5 minutes are powered by low voltage level 7-12. After the materials around the three-phase electrode are melted to form a molten pool, high power and high voltage level 12-25 are used for power supply, and short arc well penetration and long arc primary smelting are performed to obtain primary molten steel. The P content of the primary molten steel is ≤0.05%, the Cu content is ≤0.25%, and the Ni content is ≤1.15%; Step 2: AOD converter smelting: adding the molten steel in step 1 into the AOD converter for smelting; Oxidation stage: According to the content of each component in the primary molten steel and the controlled content of Cr, Mn and Ni in the AOD converter smelting stage, the amount of ferrochrome, electrolytic manganese, low-carbon silicon manganese and nickel 35 required for AOD converter smelting is calculated, and added into the AOD converter for alloy smelting to decarburize and retain chromium; Reduction stage: according to the oxygen blowing amount in the smelting process and the amount of molten steel in the converter, ferrosilicon and fluorite are added to reduce the slag, recover the Cr in the slag, and make the content of reduced Si in the molten steel greater than 0.2%. The amount of ferrosilicon added = 1.25 × (total oxygen consumption in smelting - oxygen consumption of carbon oxide - oxygen consumption of silicon oxide) / silicon content of ferrosilicon + steel output × alloyed silicon content / silicon content of ferrosilicon, where 1.25 means that 1 standard of oxygen requires 1.25 kg of Si, and the amount of fluorite added is 20-24 kg / ton of steel; Desulfurization stage: Desulfurization is carried out according to the S content in the reduction stage to obtain molten steel; Step 3: Use the LF refining furnace to fine-tune the composition and temperature of the molten steel, and then cast it on the continuous casting machine.

[0005] As a further preferred embodiment of the technical solution of the present invention, in step one, the auxiliary material is dolomite, and according to the Si content in the 400 series medium-sized stainless scrap steel, 300 series large slag steel, 400 series grinding chips, and nickel-copper alloy added in the ingredients, the auxiliary material dolomite is added according to the slag basicity of 1.4-1.7, and at the same time, according to the carbon content in the ingredients, coke is added to control the final carbon content to 2.0-2.5%; after power is supplied for smelting until the electric furnace starts arcing, power is supplied at a low voltage level of 12 in the first 3 minutes.

[0006] Furthermore, in step 1, when the charge temperature reaches above 900° C., oxygen is blown to assist melting, and nickel-copper alloy and slag-making material lime are added at the same time.

[0007] Furthermore, when blowing oxygen to assist melting, the oxygen blowing rate of the furnace door oxygen gun is 2000-3000NM 3 / h.

[0008] Furthermore, in step one, when a preliminary molten pool is formed in the electric furnace, the operating voltage level is adjusted to level 21, and when the charge temperature reaches above 1500°C, carbon powder is sprayed into the furnace to make foamed slag to submerge the arc, and when the height of the foamed slag reaches above 350mm, the power supply level is adjusted to level 23; the spraying amount of the carbon powder is 1.8-2.3Kg / ton of steel.

[0009] Furthermore, in step one, the material in the electric furnace is completely melted. After the oxygen blowing stage, the temperature of the molten steel is adjusted to above 1580°C to enter the reduction stage. The furnace door oxygen gun is used to spray small-grain ferrosilicon to the slag interface. The spraying amount of small-grain ferrosilicon is 2-2.5 kg / ton of steel. At the same time, the oxygen gun is switched to nitrogen for stirring.

[0010] Furthermore, in step one, lime powder is added along with the steel flow during the steel-making process of the electric furnace for desulfurization, and the amount of lime powder added is 0.5-1 kg / ton of steel.

[0011] Furthermore, in the oxidation stage, the controlled contents of Cr, Mn and Ni are Cr 13.1%, Mn 9% and Ni 1.1%.

[0012] Furthermore, in step 2, the amount of ferrosilicon added = 1.25 × (total oxygen consumption in smelting - oxygen consumption of carbon oxide - oxygen consumption of silicon oxide) / silicon content of ferrosilicon + steel output × alloyed silicon content / silicon content of ferrosilicon, wherein 1.25 means that 1 standard cubic meter of oxygen requires 1.25 kg of Si, and the amount of fluorite added is 20-24 kg / ton of steel.

[0013] Furthermore, in the desulfurization stage of step three, the desulfurization operation is to add lime and fluorite for desulfurization according to the reduced S content.

[0014] The beneficial effects of the present invention are: 1. The electric furnace of the present invention adopts a full cold material smelting mode. By reasonably adding 400 series medium-sized stainless scrap steel, 300 series large slag steel, 400 series grinding chips, nickel-copper alloy and coke, the P content of the steel tapped from the electric furnace is ≤0.05%, the Cu content is ≤0.25%, and the Ni content is ≤1.15%. When the molten steel from the electric furnace is added to the AOD converter for smelting, the smelting process includes an oxidation stage, a reduction stage and a desulfurization stage. Finally, the composition and temperature of the molten steel are finely adjusted in the LF refining furnace, and the continuous casting is directly performed after tapping. The ability of manganese to stabilize austenite structure is second only to the solid solution strengthening of nickel and nitrogen and the corrosion resistance of copper. Compared with SUS304 austenitic stainless steel, the nickel-saving austenitic stainless steel composition reduces the Ni content by about 6.5% and increases the contents of Mn, N and Cu. The smelting and rolling processes are similar to those of SUS304 austenitic stainless steel. It not only replaces part of SUS304 austenitic stainless steel, but also reduces the smelting cost by 200 yuan / ton of steel.

[0015] 2. The nickel-saving austenitic stainless steel smelting method of the present invention and the nickel-saving austenitic stainless steel prepared thereby not only save the use of nickel resources, but also find a new direction for the development of stainless steel. DETAILED DESCRIPTION

[0016] The implementation steps and implementation effects of the nickel-saving austenitic stainless steel smelting method of the present invention are described in detail below in conjunction with specific embodiments.

[0017] Example 1 The first step is to melt and smelt 400 series medium-sized stainless steel scrap, 300 series large slag steel, 400 series grinding chips, nickel-copper alloy and auxiliary materials in an electric furnace; specifically, the following steps are performed: 1.1 The full cold material smelting mode is adopted. Before the electric furnace arcs, 4921 kg of coke and 845 kg of light-burned dolomite are spread on the bottom of the furnace, and 56 tons of 400 series medium-sized stainless scrap steel, 39 tons of 300 series large slag steel, and 5.1 tons of 400 series grinding chips are added. Then power is supplied for smelting. After the electric furnace arcs, the power supply is provided at a low voltage level of 12 in the first 3 minutes.

[0018] 1.2 Entering the melting period, when the charge temperature reaches 950℃, oxygen blowing is carried out by oxygen lance at the furnace door, and the blowing rate is 2400NM 3 / h, and when the initial molten pool is formed, the furnace door oxygen lance is used to clean the scrap steel at the furnace door, and 390 kg of nickel-copper alloy and 1 t of slag-making lime are added at the same time.

[0019] 1.3 When a preliminary molten pool is formed in the electric furnace, the operating voltage level is adjusted to level 21, and when the charge temperature reaches 1500°C, 206 kg of carbon powder is sprayed into the furnace to make foamed slag. When the height of the foamed slag is 350 mm, the power supply level is reduced to level 23.

[0020] 1.4 After the materials in the furnace are completely melted, desiliconization and alloying operations are completed (i.e. oxygen blowing stage), the molten steel temperature is adjusted to 1580℃ to enter the reduction stage. 237Kg of small-grained ferrosilicon is sprayed to the slag interface using the furnace door oxygen gun, and the oxygen gun is switched to nitrogen for stirring.

[0021] 1.5 Desulfurization operation: In order to prevent the sulfur content of the converter from being too high, 60kg of lime powder is added with the steel flow during the steelmaking process of the electric furnace for desulfurization operation. After steelmaking, primary molten steel is obtained. The composition and content of the primary molten steel are: C 1.820%, Si 0.128%, Mn 0.095%, P 0.043%, S 0.050%, Cr 11.646%, Ni 0.992%, Cu 0.183%; The second step is to add the primary molten steel from the electric furnace into the AOD converter for smelting. 2.1 In the oxidation stage, according to the composition of the primary molten steel, 6798 kg of ferrochrome, 9073 kg of electrolytic manganese, 2605 kg of low-carbon silicon manganese, 1163 kg of ferronickel (nickel content 26.47%), 9.6 t of lime and 3 t of dolomite were added according to the composition of the AOD converter molten steel (Cr13.1%, Mn9% and Ni1.1%), and the alloy was smelted to decarburize and retain chromium. Before entering the reduction stage, temperature measurement and sampling were carried out, with C0.076%, Cr12.54% and temperature 1748°C.

[0022] 2.2 Reduction stage, that is, the materials in the electric furnace are completely melted, and the desiliconization and alloying operations are completed. The molten steel temperature is adjusted to 1585℃ to enter the reduction stage. According to the oxygen blowing amount (4808Nm 3) Add 2010Kg of ferrosilicon and 2328Kg of fluorite, and the reducing components are C0.048%, Si0.256%, Mn8.664%, P0.0385%, S0.003%, Cr13.002%, Ni0.973%, Cu0.133%, and N0.2115%.

[0023] 2.3 Desulfurization stage, according to the reduced S content S0.003%, 900Kg lime and 436Kg fluorite are added, the desulfurization time is 5min, and the steel is directly tapped after desulfurization to obtain AOD converter molten steel.

[0024] The third step is to use fine scrap steel to fine-tune the Cr and Ni components during LF refining. The molten steel from the AOD converter was injected into the LF refining furnace, and after adding 123 kg of high carbon ferrochrome, 66 kg of crude nickel and 150 kg of electrolytic copper, it was directly put into the continuous casting machine for casting. The composition and content of the finished product are shown in Table 1.

[0025] Table 1 Example 2 The first step is to melt and smelt 400 series medium-sized stainless steel scrap, 300 series large slag steel, 400 series grinding chips, nickel-copper alloy, coke and auxiliary materials in an electric furnace; specifically, the following steps are performed: 1.1 The full cold material smelting mode is adopted. Before the electric furnace arcs, 4837 kg of coke and 545 kg of light-burned dolomite are spread on the bottom of the furnace, and 53 tons of 400 series medium-sized stainless scrap steel, 40 tons of 300 series large slag steel, and 4.7 tons of 400 series grinding chips are added. Then power is supplied for smelting. After the electric furnace arcs, the power supply is provided at a low voltage level of 12 in the first 3 minutes.

[0026] 1.2 Entering the melting period, when the charge temperature reaches 940℃, oxygen blowing is carried out through the furnace door oxygen gun to assist melting, and the oxygen blowing rate is 2350NM 3 / h, and when the initial molten pool is formed, the furnace door oxygen lance is used to clean the scrap steel at the furnace door, and 380 kg of nickel-copper alloy and 1 t of slag-making lime are added at the same time.

[0027] 1.3 When a preliminary molten pool is formed in the electric furnace, the operating voltage level is adjusted to level 21, and when the charge temperature reaches 1505°C, 187 kg of carbon powder is sprayed into the furnace to make foamed slag. When the height of the foamed slag is 350 mm, the power supply level is reduced to level 23.

[0028] 1.4 After the materials in the furnace are completely melted, desiliconization and alloying operations are completed (i.e. oxygen blowing stage), the molten steel temperature is adjusted to 1590℃ to enter the reduction stage. 242Kg of small-grained ferrosilicon is sprayed to the slag interface using the furnace door oxygen gun, and the oxygen gun is switched to nitrogen for stirring.

[0029] 1.5 Desulfurization operation: In order to prevent the sulfur content of the converter from being too high, 70kg of lime powder is added with the steel flow during the steelmaking process of the electric furnace for desulfurization operation. After steelmaking, primary molten steel is obtained. The composition and content of the primary molten steel are: C 1.930%, Si 0.067%, Mn 0.126%, P 0.044%, S 0.054%, Cr 12.565%, Ni 0.722%, Cu 0.178%; The second step is to add the primary molten steel from the electric furnace into the AOD converter for smelting. 2.1 In the oxidation stage, according to the composition of the primary molten steel, 6798 kg of ferrochrome, 9073 kg of electrolytic manganese, 2605 kg of low-carbon silicon manganese, 1163 kg of ferronickel (nickel content 26.47%), 9.6 t of lime and 3 t of dolomite were added according to the composition of the AOD converter molten steel (Cr13.1%, Mn9% and Ni1.1%), and the alloy was smelted to decarburize and retain chromium. Before entering the reduction stage, temperature measurement and sampling were carried out, with C0.076%, Cr12.54% and temperature 1748°C.

[0030] 2.2 Reduction stage, that is, when the materials in the electric furnace are completely melted, desiliconization and alloying operations are completed, the molten steel temperature is adjusted to 1585℃ to enter the reduction stage. According to the oxygen blowing amount (4808Nm 3 ) Add 2010Kg of ferrosilicon and 2328Kg of fluorite, and the reducing components are C0.048%, Si0.256%, Mn8.664%, P0.0385%, S0.003%, Cr13.002%, Ni0.973%, Cu0.133%, and N0.2115%.

[0031] 2.3 Desulfurization stage, according to the reduced S content S0.003%, 900Kg lime and 436Kg fluorite are added, the desulfurization time is 5min, and the steel is directly tapped after desulfurization to obtain AOD converter molten steel.

[0032] The third step is to use fine scrap steel to fine-tune the Cr and Ni components during LF refining. The molten steel from the AOD converter was injected into the LF refining furnace, and after adding 123 kg of high carbon ferrochrome, 66 kg of crude nickel and 150 kg of electrolytic copper, it was directly put into the continuous casting machine for casting. The composition and content of the finished product are shown in Table 2.

[0033] Table 2 From the data in 1-2, we can see that the Ni content of nickel-saving austenitic stainless steel is about 7% lower than that of SUS304 steel, the Mn content is about 8% higher, the N content is about 0.1% higher, and a large amount of steelmaking waste is used in the electric furnace smelting process. In summary, the cost of nickel-saving austenitic stainless steel is about 200 yuan / ton lower than that of SUS304 austenitic stainless steel.

Claims

1. A method for smelting nickel-saving austenitic stainless steel, characterized in that: The following steps are involved: Step 1, primary smelting in an electric furnace: 400 series medium-sized stainless steel scrap, 300 series large slag steel, 400 series grinding chips, nickel-copper alloy, coke and auxiliary materials are added into the electric furnace. After the electric furnace is arced, the first 2-5 minutes are powered by low voltage level 7-12. After the materials around the three-phase electrode are melted to form a molten pool, high power and high voltage level 12-25 are used for power supply, and short arc well penetration and long arc primary smelting are performed to obtain primary molten steel. The P content of the primary molten steel is ≤0.05%, the Cu content is ≤0.25%, and the Ni content is ≤1.15%; Step 2: AOD converter smelting: adding the molten steel in step 1 into the AOD converter for smelting; Oxidation stage: According to the content of each component in the primary molten steel and the controlled content of Cr, Mn and Ni in the AOD converter smelting stage, the amount of ferrochrome, electrolytic manganese, low-carbon silicon manganese and nickel 35 required for AOD converter smelting is calculated, and added into the AOD converter for alloy smelting to decarburize and retain chromium; Reduction stage: according to the oxygen blowing amount in the smelting process and the amount of molten steel in the converter, ferrosilicon and fluorite are added to reduce the slag, and Cr in the slag is recovered to make the content of reduced Si in the molten steel greater than 0.2%; the amount of ferrosilicon added = 1.25 × (total oxygen consumption in smelting - oxygen consumption of carbon oxide - oxygen consumption of silicon oxide) / silicon content of ferrosilicon + steel output × alloyed silicon content / silicon content of ferrosilicon, where 1.25 means that 1 standard cubic meter of oxygen requires 1.25 kg of Si, and the amount of fluorite added is 20-24 kg / ton of steel; Desulfurization stage: Desulfurization is carried out according to the S content in the reduction stage to obtain molten steel; Step 3: Use the LF refining furnace to fine-tune the composition and temperature of the molten steel, and then cast it on the continuous casting machine.

2. A method for smelting nickel-saving austenitic stainless steel as claimed in claim 1, characterized in that: In step one, the auxiliary material is dolomite. According to the Si content in the 400 series medium-sized stainless scrap steel, 300 series large slag steel, 400 series grinding chips, and nickel-copper alloy added in the ingredients, the auxiliary material dolomite is added according to the slag basicity of 1.4-1.

7. At the same time, according to the carbon content in the ingredients, coke is added to control the final carbon content to 2.0-2.5%. After power is supplied for smelting until the electric furnace starts arcing, power is supplied at a low voltage level of 12 in the first 3 minutes.

3. A method for smelting nickel-saving austenitic stainless steel as claimed in claim 2, characterized in that: In step 1, when the charge temperature reaches above 900°C, oxygen is blown to assist melting, and nickel-copper alloy and slag-making material lime are added at the same time.

4. A method for smelting nickel-saving austenitic stainless steel as claimed in claim 3, characterized in that: When blowing oxygen to assist melting, the oxygen blowing rate of the furnace door oxygen gun is 2000-3000NM 3 / h.

5. A method for smelting nickel-saving austenitic stainless steel as claimed in claim 4, characterized in that: In step one, when a preliminary molten pool is formed in the electric furnace, the operating voltage level is adjusted to level 21, and when the charge temperature reaches above 1500°C, carbon powder is sprayed into the furnace to make foamed slag to bury the arc. When the height of the foamed slag reaches above 350mm, the power supply level is adjusted to level 23; the spraying amount of the carbon powder is 1.8-2.3Kg / ton of steel.

6. A method for smelting nickel-saving austenitic stainless steel as claimed in claim 5, characterized in that: In step 1, the materials in the electric furnace are completely melted. After the oxygen blowing stage, the temperature of the molten steel is adjusted to above 1580°C to enter the reduction stage. The furnace door oxygen gun is used to spray small-grained ferrosilicon to the slag interface. The spraying amount of small-grained ferrosilicon is 2-2.5Kg / ton of steel. At the same time, the oxygen gun is switched to nitrogen for stirring.

7. A method for smelting nickel-saving austenitic stainless steel as claimed in claim 6, characterized in that: In step 1, lime powder is added along with the steel flow for desulfurization during the steel-making process of the electric furnace, and the amount of lime powder added is 0.5-1 kg / ton of steel.

8. A method for smelting nickel-saving austenitic stainless steel according to any one of claims 1 to 7, characterized in that: In the step dioxide stage, the controlled contents of Cr, Mn and Ni are Cr 13.1%, Mn 9% and Ni 1.1%.

9. A method for smelting nickel-saving austenitic stainless steel as claimed in claim 8, characterized in that: In step 2, the amount of ferrosilicon added = 1.25 × (total oxygen consumption in smelting - oxygen consumption of carbon oxide - oxygen consumption of silicon oxide) / silicon content of ferrosilicon + steel output × alloyed silicon content / silicon content of ferrosilicon, where 1.25 means 1 standard cubic meter of oxygen requires 1.25 kg of Si, and the amount of fluorite added is 20-24 kg / ton of steel.

10. A method for smelting nickel-saving austenitic stainless steel as claimed in claim 9, characterized in that: In the desulfurization stage of step 2, the desulfurization operation is to add lime and fluorite for desulfurization according to the reduced S content.

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