Method for smelting nickel-saving austenitic stainless steel through low-cost full-cold-material process

Abstract

The invention discloses a method for smelting nickel-saving austenitic stainless steel through a low-cost full-cold-charge process. The method sequentially comprises an electric furnace smelting procedure, an AOD converter smelting procedure, an LF refining furnace smelting procedure and a molten steel casting procedure. Wherein in the electric furnace stage, stainless steel scrap full-cold materials are adopted for melting and primary smelting, 400-series stainless steel scrap and large slag steel are reasonably added, the theoretical charging P content of an electric furnace is smaller than or equal to 0.55%, the theoretical charging S content of the electric furnace is smaller than or equal to 0.15%, electric furnace smelting mother liquor is obtained, and when the electric furnace smelting mother liquor is added into an AOD converter for smelting, reduced Cr and Ni components are controlled according to the upper limit of the steel target value of the nickel-saving type austenitic stainless steel; during LF refining, fine adjustment is conducted on Cr and Ni components through fine scrap steel; according to the process, during electric furnace burdening, high-price 400-series stainless steel scrap is replaced with low-price large slag steel, the proportion of the slag steel in all the materials can reach 60% or above, and the purpose that the low-price materials are used to smelt stainless steel to the maximum extent is achieved.

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 using a low-cost all-cold material process. Background Art

[0002] Since the beginning of the 21st century, my country's stainless steel industry has developed rapidly, accounting for almost half of the world's stainless steel production. At the same time, China lacks chromium and nickel, and stainless steel scrap is in short supply. How to solve the problem of raw material supply for stainless steel production and achieve low-cost stainless steel smelting has become the focus of the industry. At present, my country's stainless steel raw materials have long relied on the international market, mainly imported in the form of chromite and nickel sulfide (or laterite nickel ore). In view of the progress of stainless steel smelting technology, various nickel-containing and chromium-containing raw materials can be used as raw materials for smelting stainless steel. Therefore, how to use cheap materials instead of high-priced materials for stainless steel smelting is an important research direction to reduce the cost of stainless steel production. Summary of the invention

[0003] The purpose of the present invention is to provide a method for smelting nickel-saving austenitic stainless steel by a low-cost all-cold material process. By smelting in an electric furnace with all scrap steel, combined with the refined control of components such as Cr and Ni by an AOD converter and an LF furnace, low-priced materials are used instead of high-priced materials to achieve low-cost smelting of nickel-saving austenitic stainless steel.

[0004] To achieve its purpose, the present invention adopts the following technical solution: A method for smelting nickel-saving austenitic stainless steel by a low-cost all-cold material process, which sequentially comprises an electric furnace smelting process, an AOD converter smelting process, an LF refining furnace smelting process and a molten steel casting process to obtain nickel-saving austenitic stainless steel; The electric furnace smelting process is to melt and smelt 400 series stainless steel scrap, 400 series bulk slag steel, nickel-copper alloy and auxiliary materials in an electric furnace, and comprises the following steps: Step 1: Batching: Since the slag steel has an irregular shape and a large amount of slag, it is not easy to conduct electricity. In order to prevent the electrode from breaking when the electric furnace starts the arc, a two-basket charging mode is adopted, namely, basket 1 and basket 2. The slag steel is distributed to the two baskets in a ratio of 1:2 and matched with 400 series stainless steel scrap for arc starting. At least 25 tons of 400 series stainless steel scrap is added to the first basket as the arc starting material. The conventional charging principle of the electric furnace basket is followed during the batching process. 400 series stainless steel scrap, large pieces of slag steel and auxiliary materials are added to the basket from bottom to top, so that the P content of the electric furnace is ≤0.55% and the S content is ≤0.15%; Step 2: Melting molten steel; Coke is spread on the bottom of the electric furnace to solve the problem of too low carbon content of the materials entering the furnace. After adding the materials in basket No. 1 to the electric furnace, send it to the electric furnace for smelting. After the materials around the three-phase electrode melt to form a preliminary molten pool, unscrew the furnace cover and add the materials in basket No. 2, and continue to send it to the electric furnace for smelting; after the materials in the electric furnace are completely melted, desiliconize by blowing oxygen, and at the same time, add 0.3-0.4t / furnace of nickel alloy through the high-level silo for alloying, and steel is tapped after reduction. In order to prevent the sulfur content entering the converter from being too high, lime powder is added with the steel flow during the tapping process for desulfurization, so that S in the electric furnace smelting mother liquor is less than 0.08%; In the steel melting process, different power supply levels are selected according to different smelting stages to achieve the purpose of short arc well penetration and long arc melting. In the arc starting stage of the electric furnace, 12-level voltage level is used for power supply; after the power supply is stable, 7-8-level voltage level is used for power supply in the well penetration stage; after the well penetration is completed, the power supply level is gradually reduced to 10-12 levels according to the melting status of the material in the furnace; The AOD converter smelting process is to add the electric furnace smelting mother liquor into the AOD converter, and then desulfurize and produce steel after going through the oxidation stage and the reduction stage in sequence. The reduced Cr content in the molten steel is 13.119% and the Ni content is 1.074%.

[0005] The smelting process of the LF refining furnace is to add fine scrap steel, dilute and fine-tune the Cr and Ni components, and the final molten steel composition is C 0.13-0.15%, Si 0.35-0.45%, Mn 9.00-9.20%, P≤0.050%, S≤0.0030%, Ni 1.10%-1.20%, Cr 13.20-13.40%, Cu0.20-0.30%, and N 0.145-0.155%.

[0006] As a further preferred embodiment of the technical solution of the present invention, in step 1 of the electric furnace smelting process, the weight ratio of 400 series stainless steel scrap, bulk slag steel and auxiliary materials is 41.2-38.1:59.5-60.2:6.7-6.3, and the auxiliary materials are lime, light-burned dolomite and coke.

[0007] Furthermore, in step 2 of the electric furnace smelting process, a large amount of chromium is oxidized during the oxygen blowing process of smelting stainless steel in the electric furnace. In order to increase the chromium recovery rate, a reduction operation is required; after desiliconization and alloying, the molten steel temperature is adjusted to >1580°C to enter the reduction stage. During the reduction stage, a furnace door oxygen gun is used to spray small-grain ferrosilicon to the slag interface. The spraying amount of small-grain ferrosilicon is 200kg-300kg. At the same time, the oxygen gun is switched to nitrogen for stirring, and the steel is tapped after reduction.

[0008] Furthermore, in step 2 of the electric furnace smelting process, when a preliminary molten pool is formed in the electric furnace, a furnace door oxygen lance is used to clean the scrap steel at the furnace door, and oxygen is blown to assist melting, so as to improve the melting efficiency of the scrap steel.

[0009] Furthermore, during the oxygen blowing to assist melting, the oxygen blowing rate of the furnace door oxygen lance is 2000-3000NM3 / h.

[0010] Furthermore, in step 2 of the electric furnace smelting process, when the power supply enters the well drilling stage smoothly, carbon powder is sprayed into the furnace to make foamed slag for buried arc, and the carbon powder spraying amount is 200kg / furnace, which can effectively improve the smelting efficiency.

[0011] Furthermore, in the oxidation stage of the AOD converter smelting process, ferrochrome, lime and dolomite are added according to the Cr and Ni components in the electric furnace smelting mother liquor, so that the Cr content of the molten steel in the AOD converter is 13.119% and the Ni content is 1.074%, thereby decarburizing and retaining chromium.

[0012] Furthermore, in the reduction stage of the AOD converter smelting process, ordinary ferrosilicon and fluorite are added according to the oxidation amount of Cr in the oxidation stage, and the slag is reduced to recover Cr in the steel slag, so that the reduced Si is greater than 0.20%.

[0013] Furthermore, the amount of fluorite added in the reduction stage of the AOD converter smelting process is 17-20% of the total slag.

[0014] Furthermore, in the AOD converter smelting process, S≤0.005% in the molten steel.

[0015] The beneficial effects of the present invention are: The invention provides a method for smelting nickel-saving austenitic stainless steel with low cost and all cold materials by "electric furnace + AOD converter + LF refining", wherein, in the electric furnace stage, all cold materials of stainless scrap steel are used for melting and primary refining, and by reasonably adding 400 series stainless scrap steel and large slag steel, the theoretical P content entering the electric furnace is made ≤0.55%, and the S content is ≤0.15%, so as to obtain electric furnace smelting mother liquor, and when the electric furnace smelting mother liquor is added into the AOD converter for smelting, the reduced Cr and Ni components are controlled according to the upper limit of the target value of the nickel-saving austenitic stainless steel; during LF refining, fine scrap steel is used to fine-tune the Cr and Ni components; when the process of the invention is used, inexpensive large slag steel is used to replace the expensive 400 series stainless scrap steel when proportioning the electric furnace, and the proportion of slag steel in all materials can reach more than 60%, thereby realizing the maximum use of inexpensive materials to smelt stainless steel. DETAILED DESCRIPTION

[0016] The implementation process and effects of the method for smelting nickel-saving austenitic stainless steel using a low-cost all-cold material process of the present invention are described in detail below through specific embodiments.

[0017] Example 1 The first step is to melt and smelt 400 series stainless steel scrap, 400 series bulk slag steel, nickel-copper alloy and auxiliary materials in an electric furnace; 1.1 Two baskets of material feeding mode are adopted, namely, basket 1 and basket 2. Basket 1 is charged with 27.5t of 400 series stainless steel scrap, 19.7t of 400 series large slag steel, and 0.39t of nickel-copper alloy from bottom to top, totaling 47.2t; basket 2 is charged with 13.7t of 400 series stainless steel scrap and 39.4t of 400 series large slag steel, totaling 53.1t; the total weight of materials entering the furnace is 100.3t. Theoretically, the P content of the electric furnace is 0.055%, the S content is 0.04%, and the Cu content is 0.180%.

[0018] 1.2 Adopt the full cold material smelting mode. Before the electric furnace starts the arc, 4.92Kg of coke is laid on the bottom of the furnace, and the No. 1 material basket is added into the furnace. The electric furnace is powered at a voltage level of 12 within the first 3 minutes after the arc is started. After the materials around the three-phase electrode are melted to form a preliminary molten pool, the furnace cover is unscrewed, the No. 2 material basket is added, and the power supply smelting continues. When the preliminary molten pool is formed, the furnace door oxygen gun is used to clean the scrap steel at the furnace door, and the oxygen blowing operation is performed, and the oxygen blowing rate is 3000NM3 / h. When the scrap steel material is completely melted and enters the flat pool operation, the voltage level is adjusted to 21. When the charge temperature reaches 1500℃, 206Kg of carbon powder is sprayed into the furnace to make slag. When the height of the foam slag is 350mm, the power supply level is reduced to 23. After the materials in the furnace are completely melted, desiliconization and alloying (nickel alloy addition is 0.3t / furnace) are completed, the temperature of the molten steel is adjusted to 1580℃ to enter the reduction stage, and 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. After the reduction is completed, the steel is tapped, and lime powder is manually added with the steel flow for desulfurization to obtain the electric furnace smelting mother liquor; the electric furnace smelting mother liquor has the following components: C1.82%, Si 0.128%, Mn 0.095%, P 0.044%, S0.05%, Cr 11.65%, Ni0.99%, Cu 0.183%.

[0019] The second step is to add the mother liquor from the electric furnace to the AOD converter for smelting; 2.1 Oxidation stage: the mother liquor smelted in the electric furnace is added to the AOD converter, and then 6798 kg of ferrochrome, 0.96 t of lime and 0.3 t of dolomite are added for oxidation reaction. The reaction stops when the Cr content in the molten steel is 13.002% and the Ni content is 0.973%; 2.2 Reduction stage, according to the oxygen blowing amount during the smelting process (4808Nm 3 ) and the Mn content in the molten steel (8.664%), 2010Kg of ordinary ferrosilicon and 2328Kg of fluorite were added, and the reducing components were C 0.1233%, Si 0.423%, Mn 9.151%, P 0.0374%, S0.003%, Cr 13.119%, Ni 1.074%, and Cu 0.119%.

[0020] 2.3 Desulfurization stage: add 900 kg of lime, desulfurize for 5 minutes until the S content in the molten steel is 0.0017%, then directly tap the steel.

[0021] In the third step, during LF refining, fine steel scrap is used to fine-tune the Cr and Ni components. 66Kg of crude nickel and 123Kg of high carbon ferrochrome were added in the LF area, and the final composition of the molten steel was C 0.1365%, Si 0.381%, Mn 9.18%, P 0.039%, S 0.0014%, Ni1.141%, Cr 13.269%, Cu 0.253%, N 0.0149%, and the steel was tapped; Step 4: Molten Steel Pouring The molten steel from the LF refining furnace is cast according to conventional processes to obtain nickel-saving austenitic stainless steel. The performance indicators of nickel-saving austenitic stainless steel in the final cold-rolled annealing state meet the standard requirements in the following table: .

[0022] Example 2 The first step is to melt and smelt 400 series stainless steel scrap, large slag steel, nickel-copper alloy and auxiliary materials in an electric furnace; 1.1 Two baskets of material feeding mode are adopted, namely, basket 1 and basket 2. Basket 1 is charged with 25.4t of 400 series stainless steel scrap, 20t of 400 series bulk slag steel, and 0.38t of nickel-copper alloy from bottom to top, totaling 45.78t; basket 2 is charged with 12.7t of 400 series stainless steel scrap and 40t of 400 series bulk slag steel, totaling 52.7t; the total weight of materials entering the furnace is 98.48t. Theoretically, the P content of the electric furnace is 0.055%, the S content is 0.04%, and the Cu content is 0.179%.

[0023] 1.2 Adopt the full cold material smelting mode. Before the electric furnace starts arcing, 4.83 kg of coke is laid on the bottom of the furnace, and the No. 1 material basket is added into the furnace. The electric furnace is powered at a 12-level voltage level within the first 3 minutes after arcing. After the materials around the three-phase electrode melt to form a preliminary molten pool, the furnace cover is unscrewed, and the No. 2 material basket is added, and the power supply for smelting continues. When the preliminary molten pool is formed, the furnace door oxygen gun is used to clean the scrap steel at the furnace door, and oxygen blowing is performed. The oxygen blowing rate is 3000 NM 3 / h. When the scrap steel is completely melted and enters the flat pool operation, the voltage level is adjusted to level 21. When the charge temperature reaches 1500℃, 187Kg of carbon powder is sprayed into the furnace to make slag. When the height of the foam slag is 350mm, the power supply level is reduced to level 23. After the materials in the furnace are completely melted, desiliconization and alloying (the amount of nickel alloy added is 0.3t / furnace) are completed, the molten steel temperature is adjusted to 1580℃ to enter the reduction stage. Use the furnace door oxygen gun to spray 230Kg of small-grained ferrosilicon to the steel slag interface, and switch the oxygen gun to nitrogen for stirring. After the reduction is completed, the steel is tapped, and lime powder is manually added again with the steel flow for desulfurization to obtain the electric furnace smelting mother liquor; the composition of the electric furnace smelting mother liquor is C 1.93%, Si 0.067%, Mn0.126%, P 0.045%, S 0.054%, Cr 12.57%, Ni0.72%, Cu 0.178%, The second step is to add the mother liquor from the electric furnace to the AOD converter for smelting; 2.1 Oxidation stage: the mother liquor smelted in the electric furnace is added to the AOD converter, and then 4208 kg of ferrochrome, 0.85 t of lime and 0.3 t of dolomite are added for oxidation reaction. The reaction stops when the Cr content in the molten steel is 13.232% and the Ni content is 0.85%; 2.2 In the reduction stage, according to the oxygen blowing amount in the smelting process (4627Nm3) and the Mn content in the molten steel (9.002%), 2109Kg of ordinary ferrosilicon and 1918Kg of fluorite were added, and the reducing components were C0.1094%, Si0.392%, Mn9.051%, P0.0367%, S0.0039%, Cr13.181%, Ni1.015%, and Cu0.127%.

[0024] 2.3 Desulfurization stage: add 900 kg of lime, desulfurize for 5 minutes until the S content in the molten steel is 0.0018%, then directly tap the steel.

[0025] In the third step, during LF refining, fine steel scrap is used to fine-tune the Cr and Ni components. 142 kg of crude nickel was added to the LF area, and the final molten steel composition was C 0.1414%, Si 0.39%, Mn 9.089%, P 0.037%, S 0.0015%, Ni 1.141%, Cr 13.296%, Cu 0.265%, N 0.0146%, and steel was tapped; Step 4: Molten Steel Pouring The molten steel from the LF refining furnace is cast according to conventional processes to obtain nickel-saving austenitic stainless steel. The performance indicators of nickel-saving austenitic stainless steel in the final cold-rolled annealing state meet the standard requirements in the following table: .

Claims

1. A method for smelting nickel-saving austenitic stainless steel using a low-cost all-cold material process, characterized in that: The method comprises an electric furnace smelting process, an AOD converter smelting process, an LF refining furnace smelting process and a molten steel casting process in sequence, so as to obtain nickel-saving austenitic stainless steel; The electric furnace smelting process is to melt and smelt 400 series stainless steel scrap, large slag steel and auxiliary materials in an electric furnace, including the following steps: Step 1: Batching: Use the No. 1 and No. 2 basket charging mode, distribute the slag steel into the two baskets at a ratio of 1:2, and use 400 series stainless steel scrap for arc starting, and at least 25 tons of 400 series stainless steel scrap should be added to the first basket; add 400 series stainless steel scrap, large slag steel and auxiliary materials from bottom to top, so that the P content of the electric furnace is ≤0.55%, the S content is ≤0.15%, and the Cu content is ≤0.2%; Step 2, molten steel smelting; Coke is spread on the bottom of the electric furnace, and the materials in the No. 1 basket are added to the electric furnace and then sent to the electric furnace for smelting. After the materials around the three-phase electrode are melted to form a preliminary molten pool, the materials in the No. 2 basket are added and the smelting is continued; after the materials in the electric furnace are completely melted, desiliconization is carried out by oxygen blowing operation, and at the same time, 0.3-0.4t / furnace of nickel alloy is added through the high-level silo for alloying, and the steel is tapped after reduction. During the tapping process, lime powder is added with the steel flow for desulfurization, and S in the electric furnace smelting mother liquor is obtained to be less than 0.08%; During the molten steel smelting process, the electric furnace arc starting stage adopts 12-level voltage level for power supply; after the power supply is stable, the drilling stage adopts 7-8-level voltage level for power supply; after the drilling is completed, the power supply level is lowered to 10-12 level according to the melting condition of the material in the furnace; The AOD converter smelting process is to add the electric furnace smelting mother liquor into the AOD converter, and then desulfurize and produce steel after the oxidation stage and the reduction stage in sequence, and the reduced Cr in the molten steel is ≥13%, and the reduced Ni is ≤1.2%; The smelting process of the LF refining furnace is to add fine scrap steel, dilute and fine-tune the Cr and Ni components, and the final molten steel composition is C 0.13-0.15%, Si 0.35-0.45%, Mn 9.00-9.20%, P≤0.050%, S≤0.0030%, Ni 1.10%-1.20%, Cr 13.20-13.40%, Cu 0.20-0.30%, and N 0.145-0.155%.

2. The method for smelting nickel-saving austenitic stainless steel by low-cost all-cold material process as claimed in claim 1, characterized in that: In step 1 of the electric furnace smelting process, the weight ratio of 400 series stainless steel scrap, bulk slag steel and auxiliary materials is 41.2-38.1:59.5-60.2:6.7-6.3, and the auxiliary materials are lime, light-burned dolomite and coke.

3. The method for smelting nickel-saving austenitic stainless steel by low-cost all-cold material process as claimed in claim 2, characterized in that: In step 2 of the electric furnace smelting process, after desiliconization and alloying, the molten steel temperature is adjusted to >1580°C to enter the reduction stage. During the reduction stage, the furnace door oxygen lance is used to spray 200kg-300kg of small-grained ferrosilicon to the slag interface, and the oxygen lance is switched to nitrogen for stirring. The steel is then tapped after reduction.

4. The method for smelting nickel-saving austenitic stainless steel by low-cost all-cold material process as claimed in claim 3, characterized in that: In step 2 of the electric furnace smelting process, when a preliminary molten pool is formed in the electric furnace, a furnace door oxygen lance is used to clean the scrap steel at the furnace door, and oxygen is blown to assist melting.

5. The method for smelting nickel-saving austenitic stainless steel by low-cost all-cold material process as claimed in claim 4, characterized in that: When blowing oxygen to assist melting, the oxygen blowing rate of the furnace door oxygen gun is 2000-3000NM 3 / h.

6. The method for smelting nickel-saving austenitic stainless steel by low-cost all-cold material process as claimed in claim 5, characterized in that: In step 2 of the electric furnace smelting process, when the power supply enters the well drilling stage stably, carbon powder is sprayed into the furnace to make foamed slag for buried arc, and the carbon powder spraying amount is 200kg / furnace.

7. The method for smelting nickel-saving austenitic stainless steel by low-cost all-cold material process as claimed in claim 1, characterized in that: The oxidation stage of the AOD converter smelting process is to add ferrochrome, lime and dolomite according to the Cr and Ni components in the electric furnace smelting mother liquor, so that the Cr content of the molten steel in the AOD converter is 13.119% and the Ni content is 1.074%.

8. The method for smelting nickel-saving austenitic stainless steel by low-cost all-cold material process as claimed in claim 7, characterized in that: The reduction stage of the AOD converter smelting process is to add ferrosilicon and fluorite according to the oxidation amount of Cr in the oxidation stage, reduce the slag to recover Cr in the steel slag, and reduce Si>0.20%.

9. The method for smelting nickel-saving austenitic stainless steel by low-cost all-cold material process as claimed in claim 8, characterized in that: The amount of fluorite added in the reduction stage of the AOD converter smelting process is 17-20% of the total slag.

10. A method for smelting nickel-saving austenitic stainless steel using a low-cost all-cold material process as claimed in any one of claims 1 to 9, characterized in that: In the AOD converter smelting process, S≤0.005% in the molten steel.