Smelting method of high-manganese nitrogen-controlled copper-containing austenitic stainless steel

Abstract

The invention provides a smelting method of high-manganese nitrogen-controlled copper-containing austenitic stainless steel. The technological process of an electric furnace (EAF), an argon oxygen decarburization furnace (AOD), a ladle refining furnace (LF) and a continuous casting machine (CCM) is adopted. By optimizing the alloy ratio, the molten steel is controlled to comprise the following components in percentage by weight: 0.040%-0.070% of C, 0.20%-0.60% of Si, 5.50%-7.00% of Mn, 3.00%-4.50% of Ni, 16.00%-18.00% of Cr, 0.080%-0.150% of N, 1.50%-2.00% of Cu, 0.0020%-0.0040% of B and the balance of Fe. According to the method, large ferrochrome / slag steel and nickel-copper alloy are adopted in the electric furnace stage to reduce the cost, nitrogen is accurately controlled through nitrogen / argon switching in the AOD stage, and ferroboron microalloying is conducted in the LF stage to improve the casting blank performance. The finally obtained high-manganese high-nitrogen copper-containing austenitic stainless steel has excellent corrosion resistance and cold working performance and can replace SUS304 to be used in the fields of household appliances, decoration and industry, and the purposes of reducing the production cost and improving the market competitiveness are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of stainless steel smelting, and particularly relates to a smelting method for high-manganese nitrogen-controlled copper-containing austenitic stainless steel. Background Art

[0002] The high-manganese nitrogen-controlled copper-containing austenitic stainless steel appropriately reduces the content of precious metal Ni element, and at the same time ensures the austenitic structure of the material by increasing austenite phase-forming elements such as Mn and N; its relatively high Cr content and extremely low impurity elements can ensure that this steel grade has corrosion resistance similar to that of SUS304 under specific use environments; the addition of Cu element also improves the cold working performance of this steel grade, further broadening the application fields of this steel grade. The high-manganese nitrogen-controlled copper-containing austenitic stainless steel can mainly replace SUS304 and be used in civil product industries such as utensils, kitchens, household appliances, and decorations that are resistant to weak acid and strong base corrosion media, and can also be used in industrial fields such as the inner plate of refrigerated containers and the inner liner of industrial washing machines. It is an economical stainless steel material with good comprehensive performance and easy processing.

[0003] In terms of the smelting process, the production of austenitic stainless steel usually adopts the "RKEF (Rotary Kiln - Electric Furnace) + AOD (Argon Oxygen Decarburization Furnace)" double-link method. This process directly smelts nickel-iron water from laterite nickel ore and hot-charges it into the AOD furnace, which has the advantages of short process and low energy consumption. However, for enterprises lacking laterite nickel ore resources, they still need to rely on electric furnaces to melt raw materials such as ferrochrome and nickel-copper alloys, resulting in higher costs. Therefore, how to reduce the production cost of electric furnace smelting of austenitic stainless steel by optimizing the raw material ratio (such as using low-cost alloys such as large-sized ferrochrome and slag steel) and process control (such as AOD decarburization and nitrogen control, LF refining boron microalloying) has become the key to enhancing market competitiveness. In the prior art, the smelting difficulty of high-manganese high-nitrogen stainless steel lies in the precise control of nitrogen content and the suppression of the hot crack sensitivity of continuous casting billets. The present invention effectively solves these problems through innovative means such as using large-sized slag steel / nickel-copper alloys in the electric furnace, AOD side-blowing argon for denitrification, and LF adding ferroboron for microalloying, providing a feasible solution for the industrial production of low-cost and high-performance austenitic stainless steel. Summary of the Invention

[0004] The present invention aims to provide a smelting method for high-manganese nitrogen-controlled copper-containing austenitic stainless steel.

[0005] The technical solution of the present invention includes the following steps: (1) Electric furnace smelting: nickel-iron alloy, large pieces of ferrochrome, large pieces of slag steel, nickel-copper alloy and scrap steel are added, oxygen is blown for decarburization and then slag is made before being discharged from the furnace. The mass fraction of the molten iron composition is controlled to be: C>1.50%, Si 0.20-0.50%, P<0.035%, Mn<0.50%, Cr10.00-15.00%, Ni 3.00-4.00%, Cu 1.00-2.00%, and the balance is Fe; the oxygen blowing amount is 1990-2000Nm 3 .

[0006] (2) AOD furnace smelting: After slagging, the molten iron is added to the AOD furnace, oxygen is blown for decarburization and alloying, and nitrogen is blown from the side to reduce the slag to a nitrogen content of 0.20-0.25%. Lime, fluorite, silicon manganese / ferrosilicon are added for reduction deoxidation, and then argon is switched to stir and denitrify for 4-6 minutes to tap the steel; the tapping nitrogen is controlled to be ≤0.15%, and the sulfur is ≤0.0020%; Among them, at least one of ferrochrome, ferronickel, crude nickel, electrolytic manganese and copper is added for alloying; the temperature of molten iron entering the furnace is greater than 1380°C, and the tapping temperature is 1580-1650°C.

[0007] (3) LF refining: After slagging, enter LF, the inlet temperature is>1480℃, lime and fluorite are added to adjust the slag basicity to 2.4-2.6, argon is blown and stirred, and the argon flow rate is controlled at 200-500L / min. Boron iron and pure copper alloy are added to adjust the composition and feed Ca wire. The final steel liquid composition is controlled as follows: C 0.050-0.070%, Si 0.30-0.60%, Mn 5.50-7.00%, P≤0.035%, S≤0.0015%, Ni 3.00-4.50%, Cr 16.00-18.00%, Cu 1.50-2.00%, N 0.080-0.150%, B 0.0020-0.0050%, and the balance is Fe; (4) Continuous casting: The molten steel is transported to the continuous casting platform for casting. The tundish temperature is 1460-1480℃, the casting speed is 0.80-1.10m / min, and electromagnetic stirring is used to obtain high manganese, nitrogen-controlled, copper-containing austenitic stainless steel ingot products.

[0008] The present invention provides a method for producing high-manganese, nitrogen-controlled, copper-containing austenitic stainless steel, which produces high-quality, low-cost austenitic stainless steel that can replace 304. High Mn and N contents ensure the steel's austenitic structure, while a high Cu content improves its cold working properties. A certain B content reduces the hot cracking sensitivity of the ingot. The alloying process includes adding low-cost bulk ferrochrome / slag steel, nickel-copper alloy, and other materials to an electric furnace; alloying Mn and N during the AOD smelting process; and microalloying ferroboron during the Lf refining process.

[0009] Advantages of the present invention: The method for smelting high-manganese nitrogen-controlled copper-containing austenitic stainless steel provided by the present invention significantly improves the material properties while reducing the production cost by optimizing alloy batching, precise nitrogen control process and microalloying technology. Low-cost raw materials such as large-sized ferrochrome, slag steel and nickel-copper alloy are used, and combined with the standardized process of electric arc furnace (EAF) + argon oxygen decarburization furnace (AOD) + ladle furnace (LF) + continuous caster (CCM), not only the dependence on precious metal nickel is reduced (Ni content is controlled at 3.00 - 4.50%), but also the precise control of nitrogen content (0.080 - 0.150%) is achieved through the nitrogen / argon switching technology in the AOD stage, solving the problem of nitrogen solubility fluctuation in high-nitrogen steel. The coordinated design of high manganese (5.50 - 7.00%) and high nitrogen stabilizes the austenite phase. The addition of copper element (1.50 - 2.00%) improves the cold working performance, and the microalloying of ferroboron (0.0020 - 0.0050% B) effectively inhibits the hot cracks of the billet. The final product has corrosion resistance similar to that of SUS304 (PREN≥18.5) and better processing performance, and can be widely used in the fields of household appliances, decoration and industry. At the same time, energy conservation and environmental protection are achieved through short-process technology and waste recycling, the comprehensive cost is reduced by 15% - 20%, and the qualified rate of billets exceeds 99%. Brief Description of the Drawings

[0010] Figure 1 The JN4 high-manganese nitrogen-controlled copper-containing austenitic stainless steel produced by the present invention is applied to the inner panel of a refrigerated container. Detailed Embodiments

[0011] The present invention will be further described in detail below with reference to specific embodiments.

[0012] Embodiment 1 The production process of JN4 high-manganese nitrogen-controlled copper-containing austenitic stainless steel is as follows: (1) Electric furnace smelting: Add 22.1 tons of nickel-iron alloy 10, 12.9 tons of large-sized ferrochrome, 24.8 tons of large-sized slag steel, 3.67 tons of nickel-copper alloy, and 40.4 tons of self-produced scrap steel; the oxygen blowing volume is 1994 Nm 3 , and the mother liquor is tapped after adding reducing ferrosilicon, lime and dolomite to make slag; the chemical composition of the hot metal is C 2.72%, Si 0.24%, P 0.036%, Mn 0.21%, Cr 13.70%, Ni 3.53%, Cu 1.42, and the balance is Fe.

[0013] (2)AOD furnace smelting: After skimming the hot metal, it is charged into the AOD furnace at a temperature of 1464°C. Oxygen is blown for decarbonization smelting, and 7.74 tons of ferrochrome and 4.00 tons of ferronickel are added. Nitrogen is blown through the annular gap of the side blowing lance. The nitrogen content after adding ferrosilicon, lime, and fluorite for slag reduction is 0.206%; 300 kg of lime, 312 kg of fluorite, and 480 kg of silicomanganese are added to enter the desulfurization stage. After switching to argon stirring for denitrification for 5 minutes, tapping is carried out. The basicity of the desulfurization slag is 2.43, the tapping temperature is 1634°C, the tapping S is 0.0016%, and the N is 0.089%.

[0014] (3)LF refining: After skimming the slag, it enters the LF. The thickness of the ladle slag is 250 mm, and the inlet temperature is 1536°C. 200 kg of lime and 300 kg of fluorite are added. The basicity of the slag is 2.51. Electric current is applied for slag melting, and argon stirring is carried out. The bottom blowing argon flow rate is 300 L / min; 20 kg of ferroboron and 85 kg of pure copper are added. After adjusting the alloy composition, 100 m of Ca wire is fed; the mass percentages of the chemical components in the molten steel are obtained: C: 0.047%, Si: 0.40%, Mn: 5.60%, P: 0.028%, S: 0.0014%, Ni: 4.38%, Cr: 17.54%, Cu: 1.72%, B: 0.0028%, N: 0.088%, and the balance is mainly Fe.

[0015] (4)Continuous casting: The JN4 stainless steel ladle is hoisted to the tundish turret and poured into the tundish through the long nozzle of the ladle. The tundish temperature is 1476°C, the casting speed is 0.95 m / min, the current intensity of the electromagnetic stirring is 1380 A, and the period is 20 s. A tundish covering agent for heat preservation and inclusion adsorption is added to the tundish; the molten steel is poured into the mold through the submerged nozzle and solidified into a continuous casting billet; the billet is cut into fixed lengths of 12 m and then hoisted into the storage area for stacking and cooling.

[0016] (5)Number of continuous casting furnaces of the ladle: In this casting sequence, 5 furnaces are continuously cast and produced according to the above steps (1)-(4), and the qualified billet output is 507.99 tons. JN4 high-manganese nitrogen-controlled copper-containing austenitic stainless steel is used for producing the inner plate of refrigerated containers, and the billet qualification rate is ≥99%, as Figure 1 。

[0017] Example 2 The production process of JN3 high-manganese nitrogen-controlled copper-containing austenitic stainless steel is as follows: (1)Electric furnace smelting: 15.1 tons of nickel-iron 10 alloy, 12.9 tons of large-sized ferrochrome, 34.4 tons of large-sized slag steel, 4.70 tons of nickel-copper alloy, and 38.9 tons of self-produced scrap steel are added; the oxygen blowing volume is 2304 Nm 3 , and the mother liquor is tapped after adding ferrosilicon for reduction and using lime and dolomite for slag making; the chemical components of the hot metal are C: 2.27%, Si: 0.66%, P: 0.043%, Mn: 0.32%, Cr: 13.60%, Ni: 3.22%, Cu: 1.84, and the balance is Fe.

[0018] (2) AOD furnace smelting: After skimming the hot metal slag, it is charged into the AOD furnace at a temperature of 1497°C. Oxygen is blown for decarbonization smelting, and 7.41 tons of ferrochrome, 1.41 tons of crude nickel, and 6.96 tons of electrolytic manganese are added. Nitrogen is blown through the annular gap of the side blowing lance. The nitrogen content after adding ferrosilicon, lime, and fluorite for reduction slag making is 0.242%. 500 kg of lime, 400 kg of fluorite, and 400 kg of ferrosilicon are added to enter the desulfurization stage. The annular gap of the lance is switched to argon for stirring and denitrification for 4 minutes, then tapping. The basicity of the desulfurization slag is 2.56, the tapping temperature is 1627°C, the tapping S is 0.0013%, and the N is 0.137%.

[0019] (3) LF refining: After skimming the slag, it enters the LF. The thickness of the ladle slag is 350 mm, the inlet temperature is 1533°C, 150 kg of fluorite is added, the basicity of the slag is 2.56, and electricity is applied to melt the slag, with the bottom blowing argon flow rate of 350 L / min; 35 kg of ferroboron, 78 kg of pure copper and other alloy components are added, and then 150 m of Ca wire is fed after adjustment; the mass percentages of the chemical components in the molten steel are obtained: C: 0.061%, Si: 0.41%, Mn: 6.80%, P: 0.033%, S: 0.0013%, Ni: 3.11%, Cr: 16.11%, Cu: 1.63%, B: 0.0043%, N: 0.135%, and the balance is mainly Fe.

[0020] (4) Continuous casting: The JN3 stainless steel ladle is hoisted to the ladle turntable and injected into the tundish through the long nozzle of the ladle. The tundish temperature is 1471°C, the drawing speed is 1.0 m / min, the current intensity of the electromagnetic stirring is 1380 A, the period is 20 s, and the tundish covering agent for heat preservation and inclusion adsorption is added to the tundish; the molten steel is poured into the mold through the submerged nozzle and solidified into continuous casting billets; the billets are cut into fixed lengths of 12 meters and then hoisted into the storage area for stacking and cooling.

[0021] (5) Number of continuous casting heats per ladle: In this casting heat, 6 heats are continuously cast and produced according to the above steps (1)-(4), and the qualified billet output is 613.73 tons.

[0022] Example 3 The production process of JN4 high manganese nitrogen-controlled copper-containing austenitic stainless steel is as follows: (1) Electric furnace smelting: Charge 30.2 tons of nickel iron 10 alloy, 11.8 tons of ferrochrome, 15.5 tons of large block slag steel, 1.95 tons of nickel-copper alloy, and 19.9 tons of self-produced scrap steel; the oxygen blowing volume is 1815 Nm 3 , and the mother liquor is tapped after adding ferrosilicon for reduction and using lime and dolomite to make slag; the chemical components of the hot metal are C: 2.46%, Si: 0.33%, P: 0.034%, Mn: 0.18%, Cr: 10.47%, Ni: 4.78%, Cu: 0.88, and the balance is Fe.

[0023] (2)AOD furnace smelting: After skimming the hot metal, it is charged into the AOD furnace at a temperature of 1385°C. Oxygen is blown for decarburization smelting, and 15.4 tons of ferrochrome and 0.84 tons of copper are added. Nitrogen is blown through the annular gap of the side air lance. The nitrogen content after adding ferrosilicon, lime, and fluorite for reduction slagging is 0.203%. 850 kg of lime, 502 kg of fluorite, and 394 kg of silicomanganese are added to enter the desulfurization stage. The annular gap of the air lance is switched to argon for stirring and denitrification for 6 minutes, then tapping. The basicity of the desulfurization slag is 2.48, the tapping temperature is 1651°C, the S content in the tapped steel is 0.0020%, and the N content is 0.104%.

[0024] (3)LF refining: After skimming the slag, it enters the LF. The thickness of the ladle slag is 200 mm, the incoming station temperature is 1529°C, 415 kg of lime and 317 kg of fluorite are added, the basicity of the slag is 2.56, the power is turned on for slag melting, and the bottom blowing argon flow rate is 400 L / min; 30 kg of ferroboron, 255 kg of pure copper and other alloy components are added and then 200 m of Ca wire is fed; The mass percentages of chemical components in the molten steel are obtained as follows: C: 0.058%, Si: 0.40%, Mn: 6.03%, P: 0.026%, S: 0.0015%, Ni: 3.99%, Cr: 16.14%, Cu: 1.68%, B: 0.0035%, N: 0.011%, and the balance is mainly Fe.

[0025] (4)Continuous casting: The JN4 stainless steel ladle is hoisted to the ladle turret and injected into the tundish through the long nozzle of the ladle. The tundish temperature is 1469°C, the casting speed is 0.95 m / min, the current intensity of the electromagnetic stirring is 1380 A, the period is 20 s, and a tundish covering agent for heat preservation and inclusion adsorption is added to the tundish; the molten steel is poured into the mold through the submerged nozzle and solidified into continuous casting billets; the billets are cut into fixed lengths of 12 m and then hoisted into the storage area for stacking and cooling.

[0026] (5)Number of continuous casting heats of the ladle: In this casting heat, 8 heats are continuously cast and produced according to the above steps (1)-(4), and the qualified billet output is 821.2 tons.

Claims

1. A smelting method for a high manganese nitrogen-containing copper austenitic stainless steel, characterized in that, It includes the following steps: (1) Electric furnace smelting: Add nickel-iron alloy, large-sized ferrochrome, large-sized slag steel, nickel-copper alloy and scrap steel, blow oxygen for decarburization and then make slag and tap the furnace. Control the mass fraction of the molten iron composition as follows: C > 1.50%, Si 0.20 - 0.50%, P < 0.035%, Mn < 0.50%, Cr 10.00 - 15.00%, Ni 3.00 - 4.00%, Cu 1.00 - 2.00%, and the balance is Fe; (2) AOD furnace smelting: After skimming the slag from the molten iron, charge it into the AOD furnace, blow oxygen for decarburization and alloying, side-blow nitrogen to make the nitrogen content reach 0.20 - 0.25%, add lime, fluorite, silicomanganese / silicon iron for reduction and deoxidation, and then switch to argon for denitrification for 4 - 6 min and tap the steel; Control the tapped steel N ≤ 0.15%, S ≤ 0.0020%; (3) LF refining: After skimming the slag, charge it into the LF furnace, add lime and fluorite to adjust the slag basicity to 2.4 - 2.6, blow argon for stirring, add ferroboron and pure copper alloy to adjust the composition and feed Ca wire. Finally, control the molten steel composition: C 0.050 - 0.070%, Si 0.30 - 0.60%, Mn 5.50 - 7.00%, P ≤ 0.035%, S ≤ 0.0015%, Ni 3.00 - 4.50%, Cr 16.00 - 18.00%, Cu 1.50 - 2.00%, N 0.080 - 0.150%, B 0.0020 - 0.0050%, and the balance is Fe; (4) Continuous casting: Transport the molten steel to the continuous casting platform for casting, with the tundish temperature of 1460 - 1480 °C, casting speed of 0.80 - 1.10 m / min, and use electromagnetic stirring to obtain a high-manganese nitrogen-controlled copper-containing austenitic stainless steel slab product.

2. The method according to claim 1, wherein: In step (1), the raw material ratio for electric furnace smelting is as follows: 10 - 30 tons of ferronickel alloy, 10 - 15 tons of ferrochrome, 15 - 35 tons of slag steel, 1.5 - 5 tons of nickel-copper alloy, 15 - 40 tons of scrap steel; oxygen blowing volume is 1990 - 2000 Nm 3 .

3. The method according to claim 1, wherein: In step (2) AOD furnace smelting, side-blow nitrogen in the early stage of smelting to reduce the consumption of argon; Add at least one of ferrochrome, nickel-iron, crude nickel, electrolytic manganese, and copper during alloying; The molten iron temperature entering the furnace > 1380 °C, and the tapped steel temperature is 1580 - 1650 °C.

4. The method according to claim 1, characterized in that: In step (3) LF refining, the addition amount of ferroboron is 20 - 35 kg, the addition amount of pure copper is 75 - 255 kg, and the Ca wire feeding length is 100 - 200 m.

5. The method according to claim 1, characterized in that: In step (3) LF refining, the incoming station temperature > 1480 °C, and the argon flow rate is controlled at 200 - 500 L / min.

6. The method according to claim 1, wherein: In step (4), the electromagnetic stirring current intensity is 1380 A and the period is 20 s.

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