A method for smelting high-manganese and high-nitrogen stainless steel by using return material

Abstract

The present application relates to a kind of high manganese high nitrogen stainless steel smelting method using return material, using full return material batching;By non-vacuum induction furnace smelting to fully recover [Mn] in return material, [Cr] and other easily oxidized elements;By argon-oxygen converter stage temperature control, flow control, proportion control, oxygen blowing decarburization control alkalinity;Decarburization to ≤0.02% after using argon stirring further decarburization and removal of surplus oxygen in molten steel;After reduction and adding electrolytic manganese to compensate [Mn] lost by oxidation and burning;By argon stirring to remove hydrogen in molten steel;Through slagging after secondary slagging, deoxidation, desulfurization is carried out;Finally, by nitrogen to increase nitrogen, argon to remove surplus nitrogen, nitrogen alloying is carried out, fully utilize return material and effectively recover [Mn] in return material, [Cr] and other easily oxidized elements, realize low-cost industrial production of high manganese high nitrogen stainless steel.

Description

Technical Field

[0001] This invention belongs to the field of metal smelting technology, specifically relating to a method for smelting high-manganese and high-nitrogen stainless steel using recycled materials, which fully utilizes recycled materials and effectively recovers [Mn] and [Cr] from the recycled materials to achieve low-cost industrial production of high-manganese and high-nitrogen stainless steel. Background Technology

[0002] High-manganese, high-nitrogen stainless steel is a nickel-saving austenitic stainless steel, typically with [Mn] ≥ 15%, [Cr] ≥ 13%, and [N] ≥ 0.40%. It uses manganese and nitrogen to replace nickel, thus stabilizing the austenitic structure and reducing manufacturing costs. Due to its excellent corrosion resistance, high strength, and low magnetism, it is widely used in key components such as logging instruments. Currently, the industry generally uses a method of virgin material batching → electric arc furnace smelting → VOD or AOD decarburization and chromium preservation smelting → LF furnace manganese and nitrogen alloying. This smelting process is complex, consumes large amounts of metallic manganese, manganese nitride, chromium nitride, and other alloys, resulting in high production costs.

[0003] The recycling process can recover alloying elements from recycled materials, effectively reducing production costs. It also allows for the full recycling of recycled materials and scrapped parts, achieving resource-saving circular production. However, high-manganese, high-nitrogen stainless steel contains easily oxidized elements such as [Mn] and [Cr]. When using recycled materials for smelting, several challenges arise. First, the high manganese content introduced by the recycled materials makes decarburization of ultra-low carbon steel difficult, resulting in long smelting times, low production efficiency, and high steel temperatures due to excessive manganese oxidation, leading to severe refractory corrosion. Second, decarburization and manganese / chromium retention occur simultaneously, resulting in significant [Mn] and [Cr] element loss, large amounts of slag during smelting, and the need to replenish expensive alloys after decarburization to compensate for the loss of [Mn] and [Cr]. This makes industrial production extremely difficult. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for smelting high-manganese and high-nitrogen stainless steel using recycled materials. This method employs fully recycled material batching; smelting in a non-vacuum induction furnace to fully recover easily oxidizable elements such as [Mn] and [Cr] from the recycled material; oxygen blowing for decarburization in a staged controlled temperature, flow rate, proportion, and basicity environment using an argon-oxygen furnace; after decarburization to ≤0.02%, further decarburization and removal of excess oxygen from the molten steel using argon stirring; subsequent reduction and addition of electrolytic manganese to compensate for the [Mn] lost through oxidation; removal of hydrogen from the molten steel using argon stirring; secondary slag formation after slag removal for deoxidation and desulfurization; and finally, nitrogen alloying through nitrogen enrichment and argon removal of excess nitrogen. This method fully utilizes the recycled material and effectively recovers easily oxidizable elements such as [Mn] and [Cr] from it, achieving low-cost industrial production of high-manganese and high-nitrogen stainless steel.

[0005] The objective of this invention is achieved through the following technical solution: A method for smelting high-manganese, high-nitrogen stainless steel using recycled materials is characterized by the following process flow: batching → non-vacuum induction furnace smelting → argon-oxygen furnace decarburization and manganese / chromium preservation smelting → argon-oxygen furnace reduction → argon-oxygen furnace alloying → argon-oxygen furnace deoxidation and desulfurization → tapping steel. The specific steps are as follows: Step 1) Batching: All furnace charge should be high-manganese and high-nitrogen stainless steel return material heads or steel scraps. The surface of the return material should be dry and free from rust, moisture, oil, mud and sand. Add 3-5 kg / t of lime to the bottom of the furnace before charging. Step 2) Non-vacuum induction furnace smelting: After the furnace charge is full, power is supplied. After the furnace charge is melted and cleared, the temperature is controlled between 1540-1580℃ and samples are taken. 2-5 kg / t of silicon calcium powder and aluminum powder are added for deoxidation to fully reduce the [Mn] and [Cr] elements in the slag. After reduction, the temperature is controlled at 1550-1580℃ and the steel is tapped and added to the argon-oxygen furnace for smelting. Step 3) Decarburization and manganese / chromium preservation smelting in an argon-oxygen furnace: The molten steel from step 2) is added to the argon-oxygen furnace. Since the MnO formed after the oxidation of high-manganese steel will corrode the furnace lining, 15-25 kg / t of lime is added to the furnace beforehand to protect the lining. After adding the steel, the blast gun is turned on and smelting is carried out at an oxygen-nitrogen flow ratio of 5:1, with an oxygen flow rate of 50 Nm³ / min. 3 The process involves first oxidizing [Si] and some [Mn] and [Cr] elements in the returned material at a flow rate of 1:1; when the temperature is ≥1600℃, the material is blown at an oxygen-nitrogen flow rate ratio of 1:1, with an oxygen flow rate of 25 Nm³ / min. 3 / min; when the temperature is ≥1650℃, blowing is carried out at an oxygen-nitrogen flow ratio of 1:3, wherein the oxygen flow rate is 15Nm 3 / min, and add 50-70 kg / t of high-carbon ferrochrome to compensate for the [Cr] element lost by the return material, and add 30-50 kg / t of lime to control the alkalinity R≥5 at the end of oxidation; when the temperature is ≥1700℃, blow at an oxygen-nitrogen flow ratio of 1:5, wherein the oxygen flow rate is 10 Nm 3 The oxygen blowing rate is maintained at 50 Nm³ / min to control the temperature to ≤1750℃; when the carbon content in the steel is ≤0.02% by mass, oxygen blowing is stopped, and argon gas is used at a flow rate of 50 Nm³ / min. 3 Stir for 1-2 minutes per minute to further decarburize and remove excess oxygen from the molten steel, measure the temperature and take samples for analysis; Step 4) Argon-oxygen furnace reduction: When the carbon content of the molten steel is ≤0.01% by mass and the temperature is ≥1730℃, add 20-30 kg / t of ferrosilicon and 1-3 kg / t of aluminum to the furnace, using nitrogen at a flow rate of 50 Nm. 3 Stir for 3-6 minutes at a constant speed to reduce the volume; Step 5) Argon-oxygen furnace alloying: After reduction as in Step 4), some [Mn] will still be lost due to burn-off. Therefore, 60-90 kg / t of electrolytic manganese metal needs to be added to compensate for the lost [Mn]. 8-15 kg / t of aluminum is added for oxygen blowing and temperature raising to compensate for the decrease in molten steel temperature caused by the addition of electrolytic manganese metal. Afterwards, nitrogen flow rate is 60 Nm³. 3 After stirring for 4-8 minutes at a flow rate of 50 Nm³ / min, switch the stirring gas to argon gas. 3 Stir for 0.5-1 minutes at a constant speed to remove hydrogen introduced by electrolysis of manganese metal; Step 6) Argon-oxygen furnace deoxidation and desulfurization: After step 5), remove more than 60% of the slag by weight, and add 8-15 kg / t of lime, 3-6 kg / t of fluorite, and 1-2 kg / t of aluminum for deoxidation and desulfurization; after adding the slag, the nitrogen flow rate is 60 Nm. 3 Stirring at 25-40 min for nitrogen alloying, then switching the stirring gas to argon at a flow rate of 30 Nm. 3 Argon is blown at a low flow rate of 0.5-1 minute per minute to remove excess nitrogen from the molten steel. After the composition is qualified, the steel is tapped at a temperature of 1520-1560℃.

[0006] The chemical elements of the high-manganese and high-nitrogen stainless steel, by mass percentage, are: C=0.01~0.06%, Si=0.10~0.60%, Mn=15.00~22.00%, P≤0.025%, S≤0.005%, Ni=1.50~4.50%, Cr=13.00~21.00%, Mo=0.50~2.50%, Cu=0.10~0.50%, Nb=0.01~0.10%, N=0.40~0.60%, Al=0.005~0.020%, with the balance being Fe and other unavoidable impurity elements.

[0007] The method of the present invention has the following advantages: (1) This invention overcomes the problem that the existing technology cannot carry out ultra-low carbon decarburization production of primary steel with [Mn]≥15%. It adopts the smelting of cheap high manganese and high nitrogen steel full return material. On the one hand, it fully recycles and utilizes high manganese and high nitrogen stainless steel return material, scrapped parts, etc., to achieve resource-saving and circular production. On the other hand, it recovers alloy elements in the return material and effectively reduces production costs. (2) The slag is reduced by primary refining in a non-vacuum induction furnace to fully recover easily oxidizable elements such as [Mn] and [Cr] in high-manganese and high-nitrogen stainless steel; (3) By controlling the temperature, flow rate, ratio, and basicity of the argon-oxygen furnace in stages, oxygen blowing decarburization was achieved, and decarburization and manganese preservation and decarburization and chromium preservation were carried out simultaneously. The blowing temperature and slag basicity were controlled, and the furnace lining was protected from high temperature erosion and oxidation erosion. Argon gas was blown in at the end of the decarburization period, and the CO partial pressure was reduced by inert gas to further decarburize and remove excess oxygen, thus realizing the smelting of ultra-low carbon steel and avoiding the large-scale oxidation of [Mn] and [Cr] elements. (4) The loss of some [Mn] elements during the return material blowing process is compensated by electrolytic manganese metal and the temperature loss after adding alloy and slag is compensated by oxidation and heating. The hydrogen in the molten steel is removed by reducing the H partial pressure by blowing in argon gas. Deoxidation and desulfurization are carried out by secondary slag making. Nitrogen is alloyed by blowing nitrogen at a large flow rate and the excess nitrogen in the molten steel is removed by blowing argon at a small flow rate. Finally, steel is directly tapped at qualified temperature and composition in the argon-oxygen furnace. Detailed Implementation

[0008] The following examples illustrate specific implementations of the present invention. However, these examples are merely for illustrative purposes and do not limit the scope of the invention in any way.

[0009] A method for smelting high-manganese, high-nitrogen stainless steel using recycled materials, employing a 60-ton argon-oxygen furnace, includes the following specific steps: Step 1) Batching: Select 52 tons of dry, oil-free high-manganese, high-nitrogen steel ZYNM7 for the return feed head. Step 2) Non-vacuum induction furnace smelting: A 50-ton non-vacuum induction furnace is used for smelting. Before charging, 200 kg of lime is added to the bottom of the furnace. After the furnace is full, the power is turned on. After the furnace charge is melted and cleared, a sample is taken at a temperature of 1560℃. 150 kg of silicon calcium powder and 100 kg of aluminum powder are added in batches to deoxidize the slag. The steel is tapped at a temperature of 1580℃. Step 3) Argon-oxygen furnace decarburization and manganese and chromium preservation smelting: 1200 kg of lime is added to the furnace in advance. The composition of the initial molten steel is shown in Table 1.

[0010] Table 1. Composition of primary steel added to the argon-oxygen furnace (mass percentage, %), balance being Fe and impurity elements. component 0.05 0.35 19.00 0.016 0.002 18.40 2.60 0.80 0.48 0.12 0.007 Nitrogen gas is used for cooling, and the air gun is turned on for smelting, with an oxygen flow rate of 50 Nm. 3 / min, nitrogen flow rate 10Nm 3 / min; Temperature measured: 1620℃; Adjusted air gun oxygen flow rate to 25 Nm³ / min and nitrogen flow rate to 25 Nm³ / min. 3 Continue blowing at 1680℃; adjust the oxygen flow rate of the air gun to 15 Nm. 3 / min, nitrogen flow rate 45Nm 3Continue blowing at a rate of / min, adding 3550kg of high-carbon ferrochrome and 3000kg of lime in batches; the temperature is measured at 1710℃, and the oxygen flow rate of the air gun is adjusted to 10Nm. 3 / min, nitrogen flow rate 50Nm 3 Continue blowing at a rate of / min; when the carbon content is 0.02%, stop blowing oxygen with the air gun and switch from nitrogen to argon at a flow rate of 50 Nm. 3 Stir at 1 / min for 2 minutes, measure temperature at 1735℃, and take samples for analysis; Step 4) Argon-oxygen furnace reduction: The sample has a carbon content of 0.01%. After adding 1000 kg of ferrosilicon and 120 kg of aluminum, the nitrogen flow rate is 50 Nm3 / min and the mixture is stirred for 5 minutes for reduction. Step 5) Argon-oxygen furnace alloying: Add 5100 kg of electrolytic manganese and 750 kg of aluminum. Turn on the air gun to blow oxygen for 450 Nm3 and then stop blowing oxygen. Stir with nitrogen at a flow rate of 60 Nm3 / min for 6 minutes, then switch nitrogen to argon at a flow rate of 50 Nm3 / min and stir for 1 minute. Step 6) Deoxidation and desulfurization in argon-oxygen furnace: After removing more than 60% of the slag, add 600 kg of lime, 240 kg of fluorite, and 70 kg of aluminum to form slag. Stir with nitrogen at a flow rate of 60 Nm3 / min for 35 minutes, then switch to argon at a flow rate of 30 Nm3 / min and stir for 0.5 minutes. The sample composition is qualified, and the steel is tapped at 1530℃. The composition before tapping is shown in Table 2.

[0011] Table 2. Composition of molten steel before tapping (mass percentage, %) component 0.015 0.35 19.80 0.017 0.002 18.60 2.30 0.70 0.53 0.11 0.008 .

Claims

1. A method for smelting high-manganese, high-nitrogen stainless steel using recycled materials, characterized in that: The chemical elements of the high-manganese, high-nitrogen stainless steel, by mass percentage, are: C=0.01~0.06%, Si=0.10~0.60%, Mn=15.00~22.00%, P≤0.025%, S≤0.005%, Ni=1.50~4.50%, Cr=13.00~21.00%, Mo=0.50~2.50%, Cu=0.10~0.50%, Nb=0.01~0.10%, N=0.40~0.60%, Al=0.005~0.020%, with the balance being Fe and other unavoidable impurity elements. The process flow is as follows: batching → non-vacuum induction furnace smelting → argon-oxygen furnace decarburization and manganese / chromium preservation smelting → argon-oxygen furnace reduction → argon-oxygen furnace alloying → argon-oxygen furnace deoxidation and desulfurization → tapping. The specific steps are as follows: Step 1) Batching: All furnace charge should be high-manganese and high-nitrogen stainless steel return material heads or steel scraps. The surface of the return material should be dry and free from rust, moisture, oil, mud and sand. Add 3-5 kg / t of lime to the bottom of the furnace before charging. Step 2) Non-vacuum induction furnace smelting: After the furnace charge is full, power is supplied. After the furnace charge is melted and cleared, the temperature is controlled between 1540-1580℃ and samples are taken. 2-5 kg / t of silicon calcium powder and aluminum powder are added for deoxidation to fully reduce the [Mn] and [Cr] elements in the slag. After reduction, the temperature is controlled at 1550-1580℃ and the steel is tapped and added to the argon-oxygen furnace for smelting. Step 3) Decarburization and manganese / chromium preservation smelting in an argon-oxygen furnace: The molten steel from step 2) is added to the argon-oxygen furnace. Since the MnO formed after the oxidation of high-manganese steel will corrode the furnace lining, 15-25 kg / t of lime is added to the furnace beforehand to protect the lining. After adding the steel, the blast gun is turned on and smelting is carried out at an oxygen-nitrogen flow ratio of 5:1, with an oxygen flow rate of 50 Nm³ / min. 3 The process involves first oxidizing [Si] and some [Mn] and [Cr] elements in the returned material at a flow rate of 1:1; when the temperature is ≥1600℃, the material is blown at an oxygen-nitrogen flow rate ratio of 1:1, with an oxygen flow rate of 25 Nm³ / min. 3 / min; when the temperature is ≥1650℃, blowing is carried out at an oxygen-nitrogen flow ratio of 1:3, wherein the oxygen flow rate is 15Nm 3 / min, and add 50-70 kg / t of high-carbon ferrochrome to compensate for the [Cr] element lost by the return material, and add 30-50 kg / t of lime to control the alkalinity R≥5 at the end of oxidation; when the temperature is ≥1700℃, blow at an oxygen-nitrogen flow ratio of 1:5, wherein the oxygen flow rate is 10 Nm 3 The oxygen blowing rate is maintained at 50 Nm³ / min to control the temperature to ≤1750℃; when the carbon content in the steel is ≤0.02% by mass, oxygen blowing is stopped, and argon gas is used at a flow rate of 50 Nm³ / min. 3 Stir for 1-2 minutes per minute to further decarburize and remove excess oxygen from the molten steel, measure the temperature and take samples for analysis; Step 4) Argon-oxygen furnace reduction: When the carbon content of the molten steel is ≤0.01% by mass and the temperature is ≥1730℃, add 20-30 kg / t of ferrosilicon and 1-3 kg / t of aluminum to the furnace, using nitrogen at a flow rate of 50 Nm. 3 Stir for 3-6 minutes at a constant speed to reduce the volume; Step 5) Argon-oxygen furnace alloying: After reduction as in Step 4), some [Mn] will still be lost due to burn-off. Therefore, 60-90 kg / t of electrolytic manganese metal needs to be added to compensate for the lost [Mn]. 8-15 kg / t of aluminum is added for oxygen blowing and temperature raising to compensate for the decrease in molten steel temperature caused by the addition of electrolytic manganese metal. Afterwards, nitrogen flow rate is 60 Nm³. 3 After stirring for 4-8 minutes at a flow rate of 50 Nm³ / min, switch the stirring gas to argon gas. 3 Stir for 0.5-1 minutes at a constant speed to remove hydrogen introduced by electrolysis of manganese metal; Step 6) Argon-oxygen furnace deoxidation and desulfurization: After step 5), remove more than 60% of the slag by weight, and add 8-15 kg / t of lime, 3-6 kg / t of fluorite, and 1-2 kg / t of aluminum for deoxidation and desulfurization; after adding the slag, the nitrogen flow rate is 60 Nm. 3 Stirring at a flow rate of 30 Nm³ / min for 25-40 minutes to alloy nitrogen, then switching the stirring gas to argon at a flow rate of 30 Nm³ / min. 3 Argon is blown at a low flow rate of 0.5-1 minute per minute to remove excess nitrogen from the molten steel. After the composition is qualified, the steel is tapped at a temperature of 1520-1560℃.