Process for smelting low-phosphorus, low-silicon, low-aluminum and low-sulfur precision alloy

Abstract

The invention discloses a process for smelting a low-phosphorus, low-silicon, low-aluminum and low-sulfur precision alloy, and belongs to the technical field of stainless steel smelting. According to the technology, relatively cheap nickel pig iron / ferronickel is adopted as a main raw material, after melting is conducted through an intermediate frequency furnace, iron removal and dephosphorization are conducted through AOD, control over the low oxygen content, the low sulfur content and the extremely low phosphorus content of molten steel is achieved, further refining is conducted through an LF furnace, casting forming is conducted through a die casting or continuous casting technology, and low-cost and batch stable production of the precision alloy is achieved. According to the method, full utilization of iron-nickel alloy resources is achieved, dependence on high-grade ferronickel resources and pure nickel resources in the precision alloy production process is reduced, zero consumption of the pure nickel resources is achieved, and the raw material cost is lower than that of a conventional process by 10000 yuan / t; compared with a vacuum induction furnace production method, the production efficiency of the method is greatly improved; the invention provides a new thought for smelting low-phosphorus low-silicon low-aluminum low-sulfur precision alloy in a stainless steel refining furnace.

Description

Technical Field

[0001] The invention relates to a process for smelting a low-phosphorus, low-silicon, low-aluminum and low-sulfur precision alloy, belonging to the technical field of stainless steel smelting. Background Art

[0002] Due to its low thermal expansion coefficient, precision alloys are widely used in key areas such as aviation molds and chip lead frames. This material is a key core material in the chip field. The precision alloy 4J42K developed by domestic suppliers has been used in small batches for the production of lead frames for deep drawing processes, but because the quality does not reach the level of imported materials, the precision strips used for high-end stamping and etching process lead frames are still all imported.

[0003] The supply of imported materials is expensive, has a long delivery period, and is even refused, which greatly affects the development of my country's chip industry and downstream related manufacturing industries. Domestic lead frame manufacturers are in urgent need of high-quality domestic precision alloy materials, so the development and industrialization of high-end precision alloy strips is imminent.

[0004] Precision alloys are expensive and require high purity of molten steel. The industry mainly uses pure nickel as raw material and uses vacuum induction furnaces for batching and production. The nominal tonnage of vacuum induction furnaces is small and the production efficiency is low, resulting in low efficiency, high cost and long cycle in the production of precision alloys.

[0005] With the development of laterite nickel ore application technology and the promotion of RKEF process, cheap nickel pig iron has become the main raw material of stainless steel, and the cost of stainless steel has been reduced. In recent years, the demand for pure nickel for new energy batteries has increased rapidly, and the price difference between pure nickel and nickel pig iron has become larger and larger, reaching 40,000 to 50,000 yuan / t. Nickel pig iron has a high content of residual elements (P, S, Si, etc.), and there are many problems in the batch use of nickel pig iron in precision alloys: ① The P content in nickel pig iron is high, and the Cr content is high, so it cannot be used directly in special varieties of steel; ② The nickel content of nickel pig iron and imported nickel iron is low, and high-nickel steel must be added with pure nickel; ③ Conventional production adopts the batching mode of "dephosphorized iron water / low-phosphorus scrap steel + pure nickel", and the raw material cost is extremely high.

[0006] Based on the above situation, it is urgent to develop a process for producing precision alloys with low cost, high efficiency and high quality. Summary of the invention

[0007] The present invention aims to provide a process for smelting low-phosphorus, low-silicon, low-aluminum and low-sulfur precision alloys, thereby improving the quality of domestic precision alloys, achieving low-cost smelting and improving production efficiency.

[0008] The present invention adopts the method of de-ironization + aluminum shot precise control pre-reduction to low-control P, Si, Al, and S elements, thereby improving the purity of molten steel and enhancing product quality; it can produce high-quality domestic precision alloy materials and get rid of the dependence on foreign imports; the present invention uses the method of de-ironization first, and can dephosphorize at the same time, and uses nickel iron to replace pure nickel to reduce costs; the present invention mainly utilizes the short-process steelmaking 30t medium frequency furnace nickel iron water prefabricated liquid + 45tAOD (30t and 45t are the nominal capacities of each metallurgical furnace respectively) refining scheme, which greatly improves the smelting efficiency.

[0009] The invention provides a process for smelting a low-phosphorus, low-silicon, low-aluminum, and low-sulfur precision alloy, and the process route is: batching→medium frequency furnace smelting→AOD smelting→LF furnace refining→die casting; relatively cheap nickel pig iron / nickel iron is used as a main raw material, and after being melted in a medium frequency furnace, technical means such as de-ironization and dephosphorization are carried out in AOD smelting to achieve low oxygen content (≤30ppm), low sulfur content (≤0.005%) and extremely low phosphorus content (≤0.005%) in the molten steel, and further refined in the LF furnace, and cast by a die casting process, so as to achieve low-cost and stable batch production of precision alloys.

[0010] The above process specifically comprises the following steps: (1) Preliminary preparation: calculate the amount of nickel iron to be added in advance; prepare materials in advance; AOD furnace shell age requirements: the previous furnace must not produce high-chromium steel; furnace age > 20 times must not produce this steel; prepare a special ladle (special ladle for high-nickel steel) in advance and clean it; close the nitrogen valve; (2) For top gun blowing, 30 tons of nickel-iron alloy material is added in batches of 5 tons each time. If the splashing is large at the furnace mouth, change to bottom gun blowing. The oxygen blowing amount is adjusted according to the amount of nickel-iron material added and the amount of molten steel.

[0011] (3) The temperature of the deironing and dephosphorization process is controlled at 1580-1700℃, and the oxygen flow rate of the top gun is 3300m 3 / h.

[0012] After the removal of P and iron, measure the temperature first, and then decide whether to remove the slag according to the condition of the slag (specifically, look at the color of the slag, and remove the slag when the color is white). The slag must be removed cleanly.

[0013] Sampling is performed to test the P and Ni content in order to ensure that P is removed from the molten steel, and the nickel value is used as a reference for subsequent material additions.

[0014] (4) After the P removal is complete, add aluminum pellets to increase the temperature and blow oxygen; the temperature is 1730-1770℃; according to the P and Cr content, if P≤0.002%, the next step is pre-reduction; if the P content is high (≥0.005%), continue to remove the P. After the P removal is completed, start the pre-reduction, add aluminum pellets for reduction, and confirm the sample to avoid the furnace waiting time too long, which may cause chromium to return.

[0015] (5) After reduction, according to the Al content, the amount of oxygen blown in from the beginning of the sample packaging is calculated to calculate the total amount of aluminum shots added. The target Al is calculated as 0.2%. The amount of Al added during reduction = the calculated total aluminum content - the amount of heated aluminum shots added during the alloying process.

[0016] (6) After reduction, the first reduction slag is scraped clean and the second slag adjustment is carried out. During the slag adjustment process, 30-60 kg of silicon calcium powder or aluminum shot can be added according to the reduction slag sample. The slag is adjusted to white slag and the S content is confirmed by sampling. Steel can be tapped only when S is ≤ 0.005%.

[0017] Further, the above process is described in detail as follows: Calculation of reduced aluminum shot value: After P removal, slag needs to be removed. The slag contains oxygen, and the oxygen blowing amount data cannot be accurately extracted during the reduction calculation. Pre-reduction can provide the aluminum value to calculate the amount of reduced aluminum added.

[0018] The use of high-controlled aluminum (≥0.3%) and high-temperature (1720-1750℃) desulfurization provides a new idea for desulfurization of low-silicon and low-aluminum steels.

[0019] The de-ironing + aluminum shot precision controlled pre-reduction method is adopted to control the low P, Si, Al, S elements, low oxygen content in molten steel, and extremely low phosphorus content, greatly improving the purity of molten steel.

[0020] The short-process steelmaking medium-frequency furnace nickel-iron prefabricated liquid + AOD refining solution was used to replace the vacuum induction furnace smelting method, shortening the smelting time and improving production efficiency.

[0021] In the final product obtained by the method of the present invention, P≤0.005%, Si≤0.15%, S≤0.005%, and Al≤0.1%.

[0022] Beneficial effects of the present invention: (1) Compared with pure nickel production, this process can reduce costs by about RMB 10,000 / t of steel. The calculation method is: the current price of nickel plate is RMB 127,000 / t, and the price of nickel iron is RMB 980 / nickel point (i.e. RMB 98,000 / t); taking the common grade 4J36 in precision alloy as an example, the Ni content is about 36%; if nickel plate is used as raw material, the cost of Ni alloy is 1*36%*12.7=45,700 / t of steel; if nickel iron is used as raw material, the cost of Ni alloy is 1*36%*9.8=35,000 / t of steel; (2) Compared with the vacuum induction furnace production method, the production efficiency of the method of the present invention is greatly increased; (3) Product P≤0.005%, superior to competitors; (4) Improve the quality of domestic precision alloys: This type of steel has high requirements for elements such as [C], [P], [S], [Cr], and [Co]; the steel purity requirement is high, and the residual Cr, P, and Si requirements are low; the product uses Al deoxidation, and the [Al] in the finished product is ≤0.08%. Based on the above conditions, the present invention uses de-ironization + aluminum shot precision controlled pre-reduction to control the low P, Si, Al, and S elements, improve the purity of molten steel and improve the quality, and can produce high-quality domestic precision alloy materials, getting rid of the dependence on foreign imports; (5) Reduce costs: Precision alloys are expensive, and the industry mainly uses pure nickel as raw material. The current price of nickel plate is 127,000 yuan / t, and the price of ferronickel is 980 yuan / nickel point. The price of nickel plate is too high. Therefore, we consider using the method of first removing iron and dephosphorizing at the same time, and using ferronickel instead of pure nickel to reduce costs; (6) Improve production efficiency: The industry mainly adopts vacuum induction furnace batching production, which has a small nominal tonnage and low production efficiency. The present invention mainly uses the short-process steelmaking 30t medium frequency furnace nickel iron water prefabricated liquid + 45t AOD (30t and 45t are the nominal capacities of each metallurgical furnace respectively) refining scheme to greatly improve the smelting efficiency. DETAILED DESCRIPTION

[0023] The specific implementation manner of the present invention is described in detail below in conjunction with the embodiments, but the specific implementation manner of the present invention is not limited to the following embodiments. Example 1

[0024] The specific finished product composition requirements of this precision alloy are shown in the following table:

[0025] This example is implemented on a 30t medium frequency furnace + 45tAOD + 45tLF furnace, and the specific implementation is as follows.

[0026] The process route involved in precision alloy production is: 30t medium frequency furnace → 45t AOD → 45t LF furnace (30t and 45t are the nominal capacities of each metallurgical furnace respectively).

[0027] The operation steps of this embodiment are: Ⅰ The raw material composition of the medium frequency furnace is: C 1.515%; Si 0.546%; Mn 0.055%; P 0.031%; S0.235%; Cr 0.1460%; Ni 20.24%; the rest is iron and unavoidable impurities; the loading weight is 34t; The steel-out temperature of the medium frequency furnace is 1625℃, and the power consumption of the medium frequency furnace is 530kwh / t per ton of steel.

[0028] Ⅱ The composition of the pre-melt entering the AOD furnace is: C 1.61%; Si 0.47%; Mn 0.045%; P 0.032%; S 0.228%; Cr 0.71%; Ni 20.20%; the rest is iron and unavoidable impurities; Ⅲ After the medium frequency furnace is tapped, AOD is added for smelting to remove P. The amount added is 33.5t (steel amount), the AOD gas volume flow ratio is O2: Ar=8:1, and 30t of nickel-iron alloy (composition is C 0.05%, Si 0.11%, P0.016%, S 0.068%, Cr 0.02%, Ni 32.07%, and the rest is iron and unavoidable impurities) is added in batches during the AOD oxygen blowing process. The AOD oxygen consumption in the process of removing P and Fe is 4500Nm 3 , lime consumption is 6t, fluorite consumption is 0.5t, the process temperature is controlled at 1580℃~1620℃, and slag discharge is carried out after P removal. The slag discharge must be ensured to be clean, and samples are taken after slag discharge for composition analysis.

[0029] The results of sampling and analysis are as follows: C 0.0071%; Si 0.004%; Mn 0.011%; P 0.001%; ​​S 0.047%; Cr 0.015%; Ni 41.086%; the rest are iron and unavoidable impurities; After AOD de-P and slag removal, the composition is adjusted by adding 1t of scrap steel (composition: C 0.4%, Si 0.5%, P 0.015%, the rest is iron and unavoidable impurities), 2t of lime, 0.5t of fluorite, and blowing oxygen 600Nm 3 After heating, deoxidation operation is carried out. The deoxidizer is aluminum shot, and the addition amount is 1.5t. After 10 minutes of reduction, slag discharge and sampling are carried out.

[0030] The results of sampling and analysis are as follows: C 0.0020%; Si 0.07%; Mn 0.05%; P 0.0015%; S 0.003%; Cr 0.09%; Ni 40.62%; N0.0011%; the rest are iron and unavoidable impurities; After AOD slag removal, 0.18t of electrolytic manganese (composition: C 0.01%, Si 0.006%, Mn 99.9%, and the rest are iron and inevitable impurities) is added and then steel is tapped. The weight of the tapped steel is 42.3t, the temperature of the steel is 1610℃, and samples are taken for composition analysis.

[0031] The final sampling component analysis results of AOD in the embodiment are as follows: C 0.0024%; Si 0.06%; Mn 0.42%; P 0.0017%; S 0.003%; Cr 0.110%; Ni 40.563%; N 0.0015%; the rest are iron and unavoidable impurities; After the Ⅳ AOD is tapped, the molten steel enters the LF station for treatment. The inlet temperature is 1575℃. The temperature is measured at 1627℃ 20 minutes after power supply. 1.5t of lime and 0.6t of fluorite are added in batches for slag making. After slag making, argon blowing and stirring are carried out. The outlet temperature of LF is 1542℃, and then casting operation is carried out.

[0032] The analysis results of the components of the final product sampled in Example V are as follows: C 0.0031%; Si 0.06%; Mn 0.41%; P 0.0018%; S 0.001%; ​​Cr 0.12%; Ni 40.88%; N0.0017%; the rest are iron and unavoidable impurities. Example 2

[0033] This example is implemented on a 30t medium frequency furnace + 45tAOD + 45tLF furnace, and the specific implementation is as follows.

[0034] The process route involved in precision alloy production is: 30t medium frequency furnace → 45t AOD → 45t LF furnace (30t and 45t are the nominal capacities of each metallurgical furnace respectively).

[0035] The operation steps of this embodiment are: Ⅰ The raw material composition of the medium frequency furnace is: C 1.734%; Si 0.44%; Mn 0.058%; P 0.033%; S 0.225%; Cr 0.108%; Ni 20.22%; the rest is iron and unavoidable impurities; the loading weight is 34t; The steel-out temperature of the medium frequency furnace is 1625℃, and the power consumption of the medium frequency furnace per ton of steel is 530Kwh / t.

[0036] Ⅱ The composition of the pre-melt entering the AOD furnace is: C 1.79%; Si 0.40%; Mn 0.051%; P 0.034%; S 0.228%; Cr 0.15%; Ni 20.29%; the rest is iron and unavoidable impurities; Ⅲ After the medium frequency furnace is tapped, AOD is added for smelting to remove P. The amount added is 33.5t (steel amount), the AOD gas volume flow ratio is O2: Ar=8:1, and 30t of nickel-iron alloy (composition is C: 0.05%, Si: 0.11%, P: 0.016%, S: 0.068%, Cr: 0.02%, Ni: 32.07%, and the rest is iron and unavoidable impurities) is added in batches during the AOD oxygen blowing process. The AOD oxygen consumption in the process of removing P and Fe is 4500Nm 3 , lime consumption is 6t, fluorite consumption is 0.5t, the process temperature is controlled at 1580℃~1620℃, and slag discharge is carried out after P removal. The slag discharge must be ensured to be clean, and samples are taken after slag discharge for composition analysis.

[0037] The results of sampling and analysis are as follows: C 0.0051%; Si 0.003%; Mn 0.001%; ​​P 0.001%; ​​S 0.027%; Cr 0.010%; Ni 41.156%; the rest are iron and unavoidable impurities; After AOD de-P and slag removal, the composition is adjusted by adding 1t of scrap steel (composition: C 0.4%, Si 0.5%, P 0.015%, the rest is iron and unavoidable impurities), 2t of lime, 0.5t of fluorite, and blowing oxygen 600Nm 3 After heating, deoxidation operation is carried out. The deoxidizer is aluminum shot, and the addition amount is 1.5t. After 10 minutes of reduction, slag discharge and sampling are carried out.

[0038] The results of sampling and analysis are as follows: C 0.0025%; Si 0.05%; Mn 0.001%; ​​P 0.0011%; S 0.003%; Cr 0.045%; Ni 40.95%; N 0.0011%; the rest are iron and unavoidable impurities; After AOD slag removal, 0.2t of electrolytic manganese (composition: C 0.01%, Si 0.006%, Mn 99.9%, the rest is iron and inevitable impurities) is added and then steel is tapped. The weight of the tapped steel is 42.3t, the temperature of the steel is 1620℃, and samples are taken for composition analysis.

[0039] The final sampling component analysis results of AOD in the embodiment are as follows: C 0.0019%; Si 0.07%; Mn 0.39%; P 0.0013%; S 0.003%; Cr 0.039%; Ni 40.98%; N0.0015%; the rest are iron and unavoidable impurities; IV After AOD tapping, the molten steel enters the LF station for treatment. The inlet temperature is 1580℃. The temperature is measured at 1631℃ 20 minutes after power supply. 1.5t lime and 0.6t fluorite are added in batches for slag making. After slag making, argon blowing and stirring are carried out. The outlet temperature of LF is 1545℃, and then casting is carried out.

[0040] The analysis results of the components of the final product sampled in Example V are as follows: C 0.0022%; Si 0.05%; Mn 0.38%; P 0.0014%; S 0.001%; ​​Cr 0.13%; Ni 40.78%; N 0.0017%; the rest are iron and unavoidable impurities.

Claims

1. A process for smelting low-phosphorus, low-silicon, low-aluminum and low-sulfur precision alloy, characterized in that: Nickel pig iron or nickel iron is used as the main raw material. After melting in a medium frequency furnace, AOD is used for deironing and dephosphorization to achieve low oxygen content, low sulfur content and extremely low phosphorus content in the molten steel, among which the oxygen content is ≤30ppm, the sulfur content is ≤0.005%, and the phosphorus content is ≤0.005%. It is further refined in a LF furnace and cast using a die casting process to achieve low-cost, stable batch production of precision alloys.

2. The process for smelting low-phosphorus, low-silicon, low-aluminum and low-sulfur precision alloy according to claim 1 is characterized in that: The temperature of the deironing and dephosphorization process is controlled at 1580-1700℃, and the oxygen flow rate of the top gun is 3300m 3 / h; After de-P and de-ironization is completed, measure the temperature first and then decide whether to remove the slag based on the slag condition.

3. The process for smelting low-phosphorus, low-silicon, low-aluminum and low-sulfur precision alloy according to claim 1 is characterized in that: After complete removal of P, add aluminum shots to increase the temperature and blow oxygen; the heating temperature is 1730-1770℃; if the P content is ≤0.002%, pre-reduction is performed in the next step; if the P content is ≥0.005%, continue to remove P.

4. The process for smelting low-phosphorus, low-silicon, low-aluminum and low-sulfur precision alloy according to claim 1, characterized in that: After reduction, the first reduction slag is scraped clean and the secondary slag adjustment is carried out. During the slag adjustment process, 30-60kg of silicon calcium powder or aluminum shot is added according to the reduction slag sample to adjust the slag to white slag. Samples are taken to confirm the S content. Steel can be tapped only when S≤0.005%.

5. The process for smelting low-phosphorus, low-silicon, low-aluminum and low-sulfur precision alloy according to claim 1, characterized in that: The deironing + aluminum shot precision controlled pre-reduction method is adopted to control the P, Si, Al, S elements and the oxygen content of the molten steel to improve the purity of the molten steel. In the obtained product, P≤0.005%, Si≤0.15%, S≤0.005%, Al≤0.1%.

6. The process for smelting a low-phosphorus, low-silicon, low-aluminum, low-sulfur precision alloy according to any one of claims 1 to 5, characterized in that The following steps are involved: Ⅰ. Determination of raw material composition of medium frequency furnace, steel tapping temperature of medium frequency furnace: 1625℃; Ⅱ. After the steel is tapped from the medium frequency furnace, it is added to the AOD furnace for smelting to remove P. The AOD gas flow ratio is O2: Ar=8:

1. During the AOD oxygen blowing process, 30t of nickel-iron alloy is added in batches. The temperature of the P and Fe removal process is controlled at 1580℃~1620℃. After the P removal is completed, the slag removal operation is carried out. The slag must be removed cleanly, and the composition is analyzed after the slag removal. Ⅲ. After AOD deslagging, the composition is adjusted. Scrap steel, lime and fluorite are added. After oxygen blowing and heating, deoxidation is carried out. The deoxidizer is aluminum shot. After 10 minutes of reduction, slagging and sampling are carried out. After AOD deslagging, electrolytic manganese is added and steel is tapped. Samples are taken for composition analysis. IV. After AOD tapping, the molten steel enters the LF station for treatment, lime and fluorite are added in batches for slag making, argon blowing and stirring are carried out after slag making, and the LF station is discharged, and then casting operation is carried out; V. The final product composition is: C≤0.050%, Si≤0.15%, Mn: 0.38-0.60%, P≤0.005%, S≤0.005%, Ni: 40.00-42.50%, and the rest is iron and unavoidable impurities.

7. The process for smelting low-phosphorus, low-silicon, low-aluminum and low-sulfur precision alloy according to claim 6, characterized in that: The composition of nickel-iron alloy is C: 0.05%, Si: 0.11%, P: 0.016%, S: 0.068%, Cr: 0.02%, Ni: 32.07%, and the rest is iron and inevitable impurities.

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