Method for smelting 310S stainless steel based on low-grade ferronickel alloy

Abstract

The present application belongs to the technical field of stainless steel smelting, and particularly relates to a method for smelting 310S stainless steel based on low-grade nickel-iron alloy. The method comprises the following steps: S1, pouring low-grade nickel-iron melt into No. 1 AOD furnace, resetting No. 1 AOD furnace for blowing, and obtaining first enriched nickel-iron melt; S2, entering blowing period; S3, entering screening furnace period; S4, pouring the enriched high-grade nickel-iron melt into a clean ladle for standby, then pouring chromium-iron melt into No. 2 AOD furnace which is fully roasted, and finally pouring the high-grade nickel-iron melt into the chromium-iron melt to form 310S mother liquor, and starting smelting; S5, entering steel-making period; S6, entering oxidation-reduction period; S7, entering refining period; S8, after soft blowing and slag breaking, deep deoxidation is performed to purify the steel melt; and S9, continuous casting. The smelting process can greatly reduce the cost per ton of steel, and can also fully meet the requirements of 310S stainless steel products on nickel, phosphorus and sulfur contents.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel smelting technology, specifically relating to a method for smelting 310S stainless steel based on low-grade nickel-iron alloy. Background Technology

[0002] 310S stainless steel is an austenitic stainless heat-resistant steel containing 24.00~26.00% chromium and 19.00~22.00% nickel. It has excellent resistance to high-temperature oxidation and good mechanical properties at both room temperature and high temperature. It is widely used to manufacture various furnace components, linings and other high-temperature containers.

[0003] Currently, 310S products on the market have high requirements for trace elements phosphorus and sulfur, with P≤0.030% and S≤0.001%. When the phosphorus and sulfur content of 310S slabs exceeds this range during the preparation process, severe edge cracking defects will appear on the edges of the rolled steel coils downstream, which seriously affects the product performance. Therefore, steel mills often use pure nickel as a smelting raw material. However, pure nickel is expensive, which greatly limits the production of 310S stainless steel.

[0004] The nickel-iron alloy produced by the RKEF process has become the main raw material for most austenitic stainless steels due to its low price. Its main components are 8-12% nickel, 0.4-1.0% sulfur, and 0.02-0.06% phosphorus. If 310S is directly smelted using the nickel-iron alloy produced by this process, the final product often has excessive sulfur and phosphorus content.

[0005] Pure nickel and low-grade nickel-iron alloys severely limit the production and application of 310S stainless steel in terms of price and composition, respectively. Therefore, in order to reduce smelting costs and meet the requirements for phosphorus and sulfur content in the final product, it is urgent to propose a new smelting method for 310S stainless steel. Summary of the Invention

[0006] To address the above problems, this invention aims to provide a method for smelting 310S stainless steel based on low-grade nickel-iron alloy. The method utilizes a low-grade nickel-iron alloy obtained through the RKEF process. The high-grade nickel-iron alloy obtained through this invention can completely replace expensive pure nickel as a raw material for 310S smelting. This invention's smelting process significantly reduces the cost per ton of steel while fully meeting the requirements for nickel, phosphorus, and sulfur content in 310S stainless steel products.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for smelting 310S stainless steel based on low-grade nickel-iron alloy, comprising the following steps: S1. Add low-grade nickel-iron molten metal into AOD furnace No. 1, reset AOD furnace No. 1 and blow it to obtain the first enriched nickel-iron molten metal. The low-grade nickel-iron molten metal comprises the following components in percentage: C: 1.0~4.0%, Si≤0.3%, P: 0.02~0.06%, S: 0.4~1.0%, Ni: 8~12%, with the balance being Fe; S2. Return AOD furnace No. 1 to the positive position and enter the blowing period; S3. Entering the screening furnace period, high-grade nickel-iron molten metal is obtained; S4. Pour the enriched high-grade nickel-iron molten metal into a clean steel ladle for later use. Then, add the molten chromium-iron molten metal into the fully baked No. 2 AOD furnace. Finally, add the high-grade nickel-iron molten metal into the molten chromium-iron molten metal to form 310S mother liquor and start smelting. S5 and No. 2 AOD furnaces have been reset and are entering the steelmaking stage; S6 and No. 2 AOD furnaces were reset and entered the oxidation-reduction period, during which slag was re-formed in the oxidation stage. S7 and No. 2 AOD furnaces were reset and entered the refining period, with slag re-forming and deep deoxidation; After soft blowing and slag breaking at the S8 and LF refining stations, deep deoxidation is carried out to purify the molten steel. S9, 310S stainless steel products are obtained through continuous casting.

[0008] In one embodiment of the present invention, the low-grade nickel-iron molten metal in step S1 is obtained by smelting nickel-iron alloy produced by the RKEF process in an electric furnace.

[0009] As one embodiment of the present invention, the blowing process in step S1 includes the early blowing stage, the middle blowing stage, the late blowing stage, and slag discharge.

[0010] As one embodiment of the present invention, the early stage of blowing in step S1 includes the following steps: blowing O2:N2 at a ratio of 4:1 to 3:1 in the side gun flow rate, adding lime to form slag (for desulfurization), and entering the middle stage of blowing after the lime is added.

[0011] As one embodiment of the present invention, the intermediate blowing stage in step S1 includes the following steps: blowing O2:N2 at a ratio of 5:1 to 4:1 for 3 to 5 minutes, and then entering the later blowing stage.

[0012] As one embodiment of the present invention, the later stage of the blowing process in step S1 includes the following steps: first, add 6 to 10 tons of enriched nickel slag into the furnace (at one time), then blow the slag with the side gun flow rate of O2:N2 at a ratio of 3:1 to 2:1 for 5 to 10 minutes, and control the slag temperature at 1400 to 1450°C.

[0013] As one embodiment of the present invention, the slag removal in step S1 includes the following steps: after the blowing is completed, the No. 1 AOD furnace is left to stand for 3 minutes before slag removal begins. The amount of slag in the furnace is controlled within 2 tons to avoid the iron from returning to sulfur and phosphorus. After the slag is completely removed, the No. 1 AOD furnace is returned to normal to obtain the first enriched nickel-iron molten iron.

[0014] In one embodiment of the present invention, the enriched nickel slag added in the later stage of blowing in step S1 originates from the screening furnace period in step S3.

[0015] The enriched nickel slag added in step S1 of this invention is derived from the enriched nickel slag recovered during the screening furnace period, and its main function is to replace part of the lime for cooling and dephosphorization.

[0016] In one embodiment of the present invention, the oxygen supply intensity of the side lances in the early, middle, and late stages of blowing in step S1 is 0.8~1.5m. 3 / (min·t). In this invention, the oxygen supply intensity of the side lance varies with the amount of iron blown, and its main function is to raise the temperature so that the slag reaches the set temperature.

[0017] In one embodiment of the present invention, the temperature of the slag in the early stage of blowing in step S1 is controlled at 1500~1550℃, and the blowing time is 2~5 minutes.

[0018] In one embodiment of the present invention, the lime is added 3 to 5 times in step S1, with 1 to 2 tons of lime added into the furnace at intervals of 2 to 4 minutes each time.

[0019] In step S1 of the smelting method of the present invention, nitrogen gas is introduced into the side lance to cool the side lance and the molten steel, while stirring the molten steel is beneficial for dephosphorization and desulfurization.

[0020] In one embodiment of the present invention, the CaO content in the lime during the initial blowing stage in step S1 is ≥85%. In this invention, the addition of lime is used for slag formation and desulfurization; adding lime in batches can effectively prevent excessive temperature drop.

[0021] In one embodiment of the present invention, the slag basicity in the early stage of blowing in step S1 is 3.5~6.0.

[0022] In one embodiment of the present invention, the composition of the enriched nickel slag added in the later stage of blowing in step S1 is Ni: 0.05~0.2%, CaO: 20~40%, SiO2: 3~5%, MgO: 1.0~3.0%, S: 0.1~0.3%, with the balance being iron oxides.

[0023] In one embodiment of the present invention, the composition of the first enriched nickel-iron molten metal in step S1 is C≤0.1%, Si≤0.005%, P≤0.02%, S:0.1~0.2%, Ni:15~18%, and the balance is Fe.

[0024] In step S1 of this invention, the early stage of blowing is mainly for nickel extraction and desulfurization; the middle stage of blowing is used to effectively increase the amount of oxygen blown to raise the slag temperature, which is beneficial for desulfurization; the later stage of blowing is used to effectively reduce the proportion of oxygen blown and add enriched nickel slag to cool down and create a dephosphorization environment.

[0025] In one embodiment of the present invention, the number of times the blowing period is entered in step S2 is at least once; the blowing period includes the early blowing period, the middle blowing period, the late blowing period and the slag discharge period.

[0026] As one embodiment of the present invention, the pre-blowing stage in step S2 includes the following steps: the side lance flow rate of O2:N2 is 5:1 to 3:1, the slag temperature is controlled at 1500 to 1550°C, after the blowing begins, 3 to 6 tons of nickel-iron alloy are added to the furnace in 3 to 5 batches, with each batch spaced 2 to 4 minutes apart, and 1 to 2 tons of lime are added after each addition of nickel-iron alloy to create high-basicity slag for desulfurization. After the lime is added, the mid-blowing stage begins; the basicity of the slag is 4.0 to 8.0.

[0027] As one embodiment of the present invention, the intermediate blowing stage in step S2 includes the following steps: blowing O2:N2 at a ratio of 5:1 to 4:1 for 3 to 5 minutes, and then entering the later blowing stage.

[0028] As one embodiment of the present invention, the later stage of the blowing process in step S2 includes the following steps: first, add 6 to 10 tons of enriched nickel slag into the furnace at one time, and then blow the slag for 5 to 10 minutes with the side lance flow rate of O2:N2 at a ratio of 3:1 to 2:1, and control the slag temperature at 1400 to 1450°C.

[0029] As one embodiment of the present invention, the slag removal in step S2 includes the following steps: after the first stage of the blowing period ends, the No. 1 AOD furnace is left to stand for 3 minutes before slag removal begins. The amount of slag in the furnace is controlled within 2 tons to avoid the iron from returning to sulfur and phosphorus. After the slag is completely removed, the No. 1 AOD furnace returns to positive, and the second enriched nickel-iron molten iron is obtained.

[0030] In one embodiment of the present invention, the number of times the blowing period is entered in step S2 is determined based on the nickel content in the second enriched nickel-iron molten metal: if the nickel content in the second enriched nickel-iron molten metal does not reach 70% of the target nickel content, the furnace is shaken back to normal after slag discharge, and the blowing period continues; the composition of the second enriched nickel-iron molten metal obtained at the end of the blowing period is C≤0.03%, Si≤0.001%, P≤0.01%, S≤0.1%, Ni: 30~35%, with the balance being Fe; the target nickel content is a nickel content of 40~45% in the enriched nickel-iron molten metal.

[0031] In one embodiment of the present invention, the nickel-iron alloy added in the early stage of smelting in step S2 originates from the RKEF process. In this invention, the addition of the nickel-iron alloy in step S2 is mainly used to increase the nickel content of the molten nickel in the No. 1 AOD furnace. Due to its low grade and large smelting volume, it needs to be added evenly in stages and batches. The nickel-iron alloy composition is: C: 1.0~4.0%, Si≤0.3%, P: 0.02~0.06%, S: 0.4~1.0%, Ni: 8~12%, with the balance being Fe.

[0032] In steps S1 and S2 of this invention, the early stage of blowing is mainly used for desulfurization of iron. Iron blowing needs to be carried out at a relatively low temperature (below 1600℃, where the oxygen affinity of iron and iron oxide is greater than that of nickel). A large amount of oxygen is used to oxidize Fe into iron oxide, and then the slag is discharged to enrich nickel points. Desulfurization requires a high basicity (above 2) and high temperature (above 1500℃) environment. Therefore, it is more appropriate to control the temperature at 1500~1550℃ in the early stage of blowing, and it is easier to desulfurize if the slag basicity is controlled above 3.5. In the middle stage of blowing, no materials are added, and the oxygen blowing intensity can be appropriately increased to raise the temperature (below 1600℃) for desulfurization. The later stage of blowing is mainly for dephosphorization of iron, which requires high basicity, low temperature (below 1450℃), and highly oxidizing slag.

[0033] This invention effectively ensures excellent iron blowing, desulfurization, and dephosphorization effects during the blowing process in steps S1 and S2, as well as the conditions such as the oxygen supply intensity of the side lances, the ratio of oxygen to nitrogen in the side lances, the method of adding lime, and the slag basicity. Furthermore, the enriched nickel slag discharged during the screening furnace stage in this invention's process is characterized by high basicity, high oxidizing power, and low phosphorus and sulfur content. This slag can be recycled in the smelting method of this invention and used for temperature reduction and dephosphorization in the later stages of blowing.

[0034] In existing smelting processes, lower temperatures and oxidizing environments are suitable for dephosphorization, while higher temperatures and reducing environments are suitable for desulfurization. Generally, dephosphorization and desulfurization processes need to be carried out separately during smelting. When the smelting temperature of stainless steel is above 1650℃, this temperature is not suitable for dephosphorization. Therefore, existing stainless steel is generally smelted using low-phosphorus mother liquor. However, in the smelting process of this invention, by adding the enriched nickel slag discharged during the screening process in step S3 in step S1, the enriched nickel ferroalloy process utilizes the enriched nickel slag to control the slag temperature and oxidizing properties. This allows the low-grade nickel-iron molten metal produced by the RKEF process to be rapidly dephosphorized after desulfurization, eliminating the need to separate the desulfurization and dephosphorization processes. High-efficiency desulfurization and dephosphorization can be achieved in the same stage, ultimately yielding high-grade nickel-iron molten metal.

[0035] The smelting method of this invention uses nickel-iron alloy produced by the RKEF process as raw material. Smelting high-grade nickel-iron requires a large amount of low-grade nickel-iron alloy. Therefore, in order to speed up the smelting process, a portion of the nickel-iron alloy is melted in step S1 in advance. At the same time, in order to make full use of the converter heat source and control the furnace temperature, the low-grade nickel-iron alloy is directly added to the furnace in step S2 for staged blowing, which can quickly achieve the enrichment effect of nickel content during the smelting process. This ensures that the content of nickel, phosphorus, sulfur, etc. in the obtained 310S mother liquor meets the requirements, and the final 310S stainless steel product can also achieve high quality.

[0036] In one embodiment of the present invention, the number of screening cycles in step S3 is at least once.

[0037] As one embodiment of the present invention, the screening furnace period in step S3 includes blowing and slag discharge.

[0038] In the smelting method of the present invention, after the blowing period, step S3 enters the screening furnace period. During the screening furnace period, no nickel-iron alloy is added. The main purpose is to raise the nickel content to the target value by blowing and removing slag.

[0039] In one embodiment of the present invention, the side lance flow rate of O2:N2 during the screening furnace period in step S3 is 2:1 to 1:2 during blowing, and the slag temperature is controlled at 1400 to 1450°C throughout the process.

[0040] As one embodiment of the present invention, the blowing process in step S3 includes the following steps: adding 4 to 8 tons of enriched nickel slag into the furnace in 3 to 5 batches, with each batch spaced 2 to 4 minutes apart; adding 1 to 2 tons of lime to make high-alkalinity slag after each batch of enriched nickel slag; and the blowing cycle for each stage is 10 to 20 minutes.

[0041] As one embodiment of the present invention, the slag removal in step S3 includes the following steps: after each stage of blowing is completed, the converter is moved to the slag dumping position and left to stand for 3 minutes before slag removal and temperature measurement. The amount of slag in the furnace is controlled to within 2 tons to avoid iron molten iron from undergoing sulfur and phosphorus reversion. After slag removal, the furnace is shaken back to the normal position.

[0042] In one embodiment of the present invention, the number of screening periods in step S3 is determined based on the nickel content of the enriched nickel-iron molten metal after slag removal: if the nickel content of the enriched nickel-iron molten metal after slag removal does not reach the target nickel content, the screening period enters the next stage to continue blowing. The composition of the enriched nickel-iron molten metal obtained in the last stage of the screening period is C≤0.01%, P≤0.005%, S≤0.1%, Ni: 40~45%, with the balance being Fe; the target nickel content is the nickel content in the enriched nickel-iron molten metal being 40~45%.

[0043] In step S3 of the smelting method of the present invention, the screening furnace period is mainly characterized by temperature-controlled iron blowing and slag removal. The phosphorus and sulfur content of the nickel-iron water during the screening furnace period is relatively low. Therefore, the discharged slag has high basicity and low sulfur and phosphorus content, and can be recycled directly.

[0044] In one embodiment of the present invention, the No. 2 AOD furnace mentioned in step S4 is a new furnace. Using a new furnace for steelmaking can prevent the high-sulfur and high-phosphorus nickel slag adhering to the furnace mouth and furnace wall of the No. 1 AOD furnace from falling off and causing sulfur and phosphorus reversion.

[0045] In one embodiment of the present invention, the molten chromium in step S4 has the following composition: C: 6-8%, Si: 2-4%, P≤0.03%, S: 0.03-0.1%, Cr: 48-53%, with the balance being Fe.

[0046] In one embodiment of the present invention, the 310S mother liquor in step S4 has the following composition: C: 2-3%, Si: 0.2-2.0%, P: 0.005-0.02%, S: 0.05-0.1%, Cr: 20-26%, Ni: 18-24%, and the balance is Fe.

[0047] As one embodiment of the present invention, step S5 includes the following steps: resetting the No. 2 AOD furnace and entering the steelmaking period, continuously supplying oxygen to the oxygen lance and raising the temperature to 1550°C to start slag formation and desulfurization, adding 2-3 tons of lime to the furnace in batches, controlling the alkalinity at 1.3-1.5, adding alloys during the process to adjust the temperature and composition, and shaking the furnace to remove slag after alloying is completed; the amount of residual slag in the furnace is controlled within 3 tons, and the sulfur content of the obtained steel is S≤0.05%; the alloy includes at least one of ferrosilicon, high-carbon ferrochrome, scrap iron, and nickel briquettes.

[0048] In the alloy composition selected in this invention, ferrosilicon is used for heating, while high-carbon ferrochrome, scrap iron, and nickel briquettes can be used to adjust the chromium and nickel content.

[0049] As one embodiment of the present invention, step S6 includes the following steps: resetting AOD furnace No. 2 and entering the oxidation-reduction period; in the oxidation stage, slag is re-formed, with the alkalinity controlled at 2.4~3.2; oxygen blowing is used to raise the temperature for decarburization and chromium preservation, with the temperature controlled at 1680~1720℃; in the reduction stage, ferrosilicon is added to reduce chromium oxide, manganese oxide, etc., with the alkalinity controlled at 2.2~3.0 and the temperature controlled above 1650℃; after the reduction is completed, the furnace is shaken to discharge slag for desulfurization, with the amount of residual slag in the furnace controlled within 3 tons, and the resulting reduced sulfur content is S≤0.002%.

[0050] As one embodiment of the present invention, step S7 includes the following steps: resetting the No. 2 AOD furnace, entering the refining period, re-slagging and adding 150~300 meters of aluminum wire for deep deoxidation, controlling the basicity at 2.0~2.5, fine-tuning the composition, shaking the furnace to tap the steel and transporting it to the LF refining station, and obtaining the steel mother liquor with S≤0.001%.

[0051] As one embodiment of the present invention, step S8 includes the following steps: after soft blowing and slag breaking at the LF refining station, 100-130 meters of aluminum wire is added for deep deoxidation to prevent sulfur reversion, and then 500-600 meters of calcium wire is added to purify the molten steel. The Ca / Al ratio is controlled at ≥0.13. After the composition and temperature meet the requirements, continuous casting is carried out.

[0052] Compared with the prior art, the present invention has the following beneficial effects: 1. The high-grade nickel-iron alloy smelted by the process of this invention can completely replace expensive pure nickel as a raw material for 310S smelting. Calculated solely from the cost of nickel raw materials, using low-grade nickel-iron alloy as raw material can save at least 8,170 yuan per ton of steel compared to pure nickel raw material, greatly reducing the cost per ton of steel. At the same time, the 310S stainless steel smelted by the smelting method of this invention can fully meet the requirements of 310S products for nickel, phosphorus, and sulfur content.

[0053] 2. In the method of the present invention, the enriched nickel slag discharged during the screening furnace period can be recycled in the entire process of enriching nickel-iron. Its high alkalinity, high oxidizing power, low sulfur and low phosphorus characteristics can quickly cool down to create dephosphorization conditions, so that the nickel-iron water can be quickly dephosphorized after desulfurization. Attached Figure Description

[0054] Figure 1 This is a process flow diagram of the method for smelting 310S stainless steel based on low-grade nickel-iron alloy according to the present invention.

[0055] Figure 2 This is a schematic diagram of the low-grade nickel-iron molten metal enrichment process in the method of the present invention. Detailed Implementation

[0056] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0057] Unless otherwise specified, the experimental methods used in the examples and comparative examples are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0058] Example 1

[0059] A method for smelting 310S stainless steel based on low-grade nickel-iron alloy includes the following steps: S1. Add low-grade nickel-iron molten metal into AOD furnace No. 1, reset AOD furnace No. 1 and blow it to obtain the first enriched nickel-iron molten metal. The low-grade nickel-iron molten metal comprises the following components in percentage: C: 1.0~4.0%, Si≤0.3%, P: 0.02~0.06%, S: 0.4~1.0%, Ni: 8~12%, with the balance being Fe; S2. Return AOD furnace No. 1 to the positive position and enter the blowing period; S3. Entering the screening furnace period, high-grade nickel-iron molten metal is obtained; S4. Pour the enriched high-grade nickel-iron molten metal into a clean steel ladle for later use. Then, add the molten chromium-iron molten metal into the fully baked No. 2 AOD furnace. Finally, add the high-grade nickel-iron molten metal into the molten chromium-iron molten metal to form 310S mother liquor and start smelting. S5 and No. 2 AOD furnaces have been reset and are entering the steelmaking stage; S6 and No. 2 AOD furnaces were reset and entered the oxidation-reduction period, during which slag was re-formed in the oxidation stage. S7 and No. 2 AOD furnaces were reset and entered the refining period, with slag re-forming and deep deoxidation; After soft blowing and slag breaking at the S8 and LF refining stations, deep deoxidation is carried out to purify the molten steel. S9, 310S stainless steel products are obtained through continuous casting.

[0060] In step S1, the low-grade nickel-iron molten metal is obtained by electric furnace smelting of nickel-iron alloy produced by the RKEF process. The blowing process described in step S1 includes the early blowing stage, the middle blowing stage, the late blowing stage, and slag removal. The pre-blowing stage described in step S1 includes the following steps: blowing with the side gun flow rate O2:N2 at a ratio of 4:1 to 3:1, adding lime to form slag (for desulfurization), and entering the mid-blowing stage after the lime is added; The intermediate stage of refining mentioned in step S1 includes the following steps: refining with the side gun flow rate O2:N2 at a ratio of 5:1 to 4:1 for 3 to 5 minutes, and then entering the later stage of refining; The later stage of the blowing process described in step S1 includes the following steps: First, add 6 to 10 tons of enriched nickel slag into the furnace (at one time), and then blow the slag with the side lance flow rate of O2:N2 at a ratio of 3:1 to 2:1 for 5 to 10 minutes, while controlling the slag temperature at 1400 to 1450°C. The slag removal in step S1 includes the following steps: After the blowing is completed, the No. 1 AOD furnace is left to stand for 3 minutes before slag removal begins. The amount of slag in the furnace is controlled within 2 tons to avoid the iron from returning to sulfur and phosphorus. After the slag is completely removed, the No. 1 AOD furnace is returned to normal to obtain the first enriched nickel-iron molten iron. The enriched nickel slag added in the later stage of blowing in step S1 comes from the screening furnace period in step S3. The enriched nickel slag added in step S1 of this embodiment comes from the enriched nickel slag recovered during the screening furnace period, and its main function is to replace part of the lime for cooling and dephosphorization. In step S1, the oxygen supply intensity of the side lance during the early, middle, and late stages of blowing is 0.8~1.5m. 3 / (min·t); In step S1, the temperature of the slag during the early stage of blowing is controlled at 1500~1550℃, and the blowing time is 2~5 minutes; The lime is added 3 to 5 times in step S1, with 1 to 2 tons of lime added into the furnace every 2 to 4 minutes each time; In step S1, the lime used in the early stage of smelting contains ≥85% CaO. In this invention, the addition of lime is used for slag formation and desulfurization; adding lime in batches effectively prevents excessive temperature drop. The slag basicity mentioned in step S1 during the early stage of blowing is 3.5~6.0; The composition of the nickel-enriched slag added in the later stage of blowing in step S1 is Ni: 0.05~0.2%, CaO: 20~40%, SiO2: 3~5%, MgO: 1.0~3.0%, S: 0.1~0.3%, with the balance being iron oxides; In step S1, the composition of the first enriched nickel-iron molten metal is C≤0.1%, Si≤0.005%, P≤0.02%, S:0.1~0.2%, Ni:15~18%, and the balance is Fe; The number of times the blowing period is entered in step S2 is at least once; the blowing period includes the early blowing period, the middle blowing period, the late blowing period, and the slag discharge period; The pre-blowing stage described in step S2 includes the following steps: O2:N2 is blown at a ratio of 5:1 to 3:1 using a side lance; the slag temperature is controlled at 1500-1550℃; after the start of blowing, 3-6 tons of nickel-iron alloy are added to the furnace in 3-5 batches, with each batch spaced 2-4 minutes apart. After each addition of nickel-iron alloy, 1-2 tons of lime are added to create high-basicity slag for desulfurization. After the lime is added, the mid-blowing stage begins; the slag basicity is 4.0-8.0. The intermediate stage of refining described in step S2 includes the following steps: refining with a side gun flow rate of O2:N2 at 5:1 to 4:1 for 3 to 5 minutes, and then entering the later stage of refining; The later stage of the blowing process described in step S2 includes the following steps: first, add 6 to 10 tons of enriched nickel slag into the furnace at one time, and then blow the slag with the side lance flow rate of O2:N2 at a ratio of 3:1 to 2:1 for 5 to 10 minutes, while controlling the slag temperature at 1400 to 1450°C; The slag removal in step S2 includes the following steps: after the first stage of the blowing period ends, the No. 1 AOD furnace is left to stand for 3 minutes before slag removal begins. The amount of slag in the furnace is controlled within 2 tons to avoid the iron from returning to sulfur and phosphorus. After the slag is completely removed, the No. 1 AOD furnace returns to positive, and the second enriched nickel-iron molten iron is obtained. The number of times the blowing period is entered in step S2 is determined based on the nickel content in the second enriched nickel-iron molten metal: if the nickel content in the second enriched nickel-iron molten metal does not reach 70% of the target nickel content, the furnace is shaken back to normal after slag discharge, and the blowing period continues; the composition of the second enriched nickel-iron molten metal obtained at the end of the blowing period is C≤0.03%, Si≤0.001%, P≤0.01%, S≤0.1%, Ni: 30~35%, with the balance being Fe; the target nickel content is 40~45% nickel content in the enriched nickel-iron molten metal; In one implementation method, the nickel-iron alloy added in the early stage of smelting in step S2 originates from the RKEF process. In this embodiment, the addition of nickel-iron alloy in the early stage of smelting in step S2 is mainly used to increase the nickel content of the molten nickel-iron in AOD furnace No. 1. Because of its low grade and large smelting volume, it needs to be added in stages and batches evenly. The composition of the nickel-iron alloy is C: 1.0~4.0%, Si≤0.3%, P: 0.02~0.06%, S: 0.4~1.0%, Ni: 8~12%, with the balance being Fe; The number of screening cycles mentioned in step S3 is at least once; The screening period mentioned in step S3 includes blowing and slag removal; In step S3, the side lance flow rate of O2:N2 during the screening furnace period is 2:1 to 1:2 during blowing, and the slag temperature is controlled at 1400 to 1450℃ throughout the process; The blowing process described in step S3 includes the following steps: 4 to 8 tons of enriched nickel slag are added to the furnace in 3 to 5 batches, with an interval of 2 to 4 minutes between each batch. After each addition of enriched nickel slag, 1 to 2 tons of lime are added to create high-alkalinity slag. The blowing cycle for each stage is 10 to 20 minutes. The slag removal in step S3 includes the following steps: after each stage of blowing is completed, the converter is moved to the slag dumping position and left to stand for 3 minutes before slag removal and temperature measurement. The amount of slag in the furnace is controlled to within 2 tons to avoid iron molten iron from turning sulfur and phosphorus. After slag removal, the furnace is shaken back to the normal position. The number of screening cycles in step S3 is determined based on the nickel content of the enriched nickel-iron molten metal after slag removal: if the nickel content of the enriched nickel-iron molten metal after slag removal does not reach the target nickel content, the screening cycle proceeds to the next stage to continue blowing. The composition of the enriched nickel-iron molten metal obtained in the last stage of the screening cycle is C≤0.01%, P≤0.005%, S≤0.1%, Ni: 40~45%, with the balance being Fe; the target nickel content is a nickel content of 40~45% in the enriched nickel-iron molten metal. The No. 2 AOD furnace mentioned in step S4 is a new furnace. Using a new furnace for steelmaking can prevent the high-sulfur and high-phosphorus nickel slag adhering to the furnace mouth and furnace wall of the No. 1 AOD furnace from falling off and causing sulfur and phosphorus reversion. The molten chromium in step S4 has the following composition: C: 6-8%, Si: 2-4%, P≤0.03%, S: 0.03-0.1%, Cr: 48-53%, with the balance being Fe; The 310S mother liquor in step S4 has the following composition: C: 2-3%, Si: 0.2-2.0%, P: 0.005-0.02%, S: 0.05-0.1%, Cr: 20-26%, Ni: 18-24%, with the balance being Fe; Step S5 includes the following steps: Reset AOD furnace No. 2 and enter the steelmaking stage. After the oxygen lance continuously supplies oxygen and raises the temperature to 1550℃, slag formation and desulfurization begin. Add 2-3 tons of lime to the furnace in batches, and control the alkalinity at 1.3-1.5. During this period, add alloys to adjust the temperature and composition. After alloying is completed, shake the furnace to remove slag. The amount of residual slag in the furnace is controlled within 3 tons, and the sulfur content of the obtained steel is S≤0.05%. The alloy includes at least one of ferrosilicon, high-carbon ferrochrome, scrap iron, and nickel briquettes. Step S6 includes the following steps: Reset AOD furnace No. 2 and enter the oxidation-reduction period. In the oxidation stage, slag is re-formed, and the basicity is controlled at 2.4~3.2. Oxygen is blown to raise the temperature for decarburization and chromium preservation, and the temperature is controlled at 1680~1720℃. In the reduction stage, ferrosilicon is added to reduce chromium oxide, manganese oxide, etc., and the basicity is controlled at 2.2~3.0 and the temperature is controlled above 1650℃. After the reduction is completed, the furnace is shaken to discharge slag for desulfurization. The amount of residual slag in the furnace is controlled within 3 tons, and the content of reduced sulfur obtained is S≤0.002%. Step S7 includes the following steps: Reset AOD furnace No. 2, enter the refining period, re-slag and add 150~300 meters of aluminum wire for deep deoxidation, control the basicity at 2.0~2.5, fine-tune the composition and then shake the furnace to tap the steel and transport it to the LF refining station. The resulting steel mother liquor has S≤0.001%. Step S8 includes the following steps: After the slag is broken by soft blowing at the LF refining station, 100-130 meters of aluminum wire is added for deep deoxidation to prevent sulfur reversion, and then 500-600 meters of calcium wire is added to purify the molten steel. The Ca / Al ratio is controlled at ≥0.13. After the composition and temperature meet the requirements, continuous casting is carried out.

[0061] Example 2: Smelting method for 150 tons of 310S stainless steel a. The composition of 70 tons of low-grade nickel-iron molten iron produced by the RKEF process is shown in Table 1 below: Table 1. Composition of a low-grade nickel-iron molten metal (wt%)

[0062] b. Add the above 70 tons of low-grade nickel-iron molten metal to AOD No. 1, and proceed according to step S1 in Example 1 to obtain 55 tons of low-phosphorus and low-sulfur nickel-iron molten metal, the composition of which is shown in Table 2 below: Table 2. Composition of low-phosphorus, low-sulfur, nickel-containing molten iron (wt%):

[0063] c. The composition of 165 tons of a certain low-grade nickel-iron alloy produced by the RKEF process is shown in Table 3 below: Table 3. Composition of a low-grade nickel-iron alloy (wt%)

[0064] d. The 165 tons of low-grade nickel-iron alloy were placed in batches into AOD No. 1 and processed according to steps S2-3 in Example 1 to obtain 63 tons of low-phosphorus and low-sulfur enriched nickel-iron molten metal. Its composition is shown in Table 4 below: Table 4. Composition of low-phosphorus and low-sulfur enriched nickel-iron molten iron (wt%)

[0065] e. Add 63 tons of low-phosphorus enriched nickel-iron molten steel to AOD furnace No. 2 containing 70 tons of chromium-iron molten steel, and proceed according to steps S5-7 in Example 1 to obtain 147 tons of low-phosphorus and low-sulfur 310S molten steel. The composition is shown in Table 5 below: Table 5. Composition of low-phosphorus and low-sulfur 310S molten steel (wt%)

[0066] The experimental results above show that the 310S stainless steel smelting method of the present invention, through a specific smelting process, can not only effectively utilize the low-grade nickel-iron alloy raw material produced by the RKEF process (which can completely replace high-priced pure nickel as the raw material for 310S stainless steel smelting) for smelting, significantly reducing the cost per ton of steel, but also the 310S stainless steel obtained by the final smelting is of high quality and can meet the requirements of 310S stainless steel products for nickel, phosphorus and sulfur content.

[0067] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for smelting 310S stainless steel based on low-grade nickel-iron alloy, characterized in that, Includes the following steps: S1. Add low-grade nickel-iron molten metal into AOD furnace No. 1, reset AOD furnace No. 1 and blow it to obtain the first enriched nickel-iron molten metal. The low-grade nickel-iron molten metal comprises the following components in percentage: C: 1.0~4.0%, Si≤0.3%, P: 0.02~0.06%, S: 0.4~1.0%, Ni: 8~12%, with the balance being Fe; S2. Return AOD furnace No. 1 to the positive position and enter the blowing period; S3. Entering the screening furnace period, high-grade nickel-iron molten metal is obtained; S4. Pour the high-grade nickel-iron molten metal into a clean steel ladle for later use. Then, add the molten chromium-iron molten metal into the fully baked No. 2 AOD furnace. Finally, add the high-grade nickel-iron molten metal into the molten chromium-iron molten metal to form 310S mother liquor and start smelting. S5 and No. 2 AOD furnaces have been reset and are entering the steelmaking stage; S6 and No. 2 AOD furnaces were reset and entered the oxidation-reduction period, during which slag was re-formed in the oxidation stage. S7 and No. 2 AOD furnaces were reset and entered the refining period, with slag re-forming and deep deoxidation; After soft blowing and slag breaking at the S8 and LF refining stations, deep deoxidation is carried out to purify the molten steel. S9, 310S stainless steel products are obtained through continuous casting.

2. The method for smelting 310S stainless steel based on low-grade nickel-iron alloy as described in claim 1, characterized in that, The low-grade nickel-iron molten metal mentioned in step S1 is obtained by smelting nickel-iron alloy produced by the RKEF process in an electric furnace. The blowing process described in step S1 includes the early blowing stage, the middle blowing stage, the late blowing stage, and slag removal.

3. The method for smelting 310S stainless steel based on low-grade nickel-iron alloy as described in claim 2, characterized in that, The pre-blowing stage described in step S1 includes the following steps: the side gun flow rate O2:N2 is blown at a ratio of 4:1 to 3:1, lime is added to form slag, and after the lime is added, the mid-blowing stage begins; The intermediate stage of refining mentioned in step S1 includes the following steps: refining with the side gun flow rate O2:N2 at a ratio of 5:1 to 4:1 for 3 to 5 minutes, and then entering the later stage of refining; The later stage of the blowing process described in step S1 includes the following steps: first, add 6 to 10 tons of enriched nickel slag into the furnace, then blow the slag at a flow rate of O2:N2 of 3:1 to 2:1 for 5 to 10 minutes, and control the slag temperature at 1400 to 1450°C. The slag removal in step S1 includes the following steps: After the blowing is completed, the No. 1 AOD furnace is left to stand for 3 minutes before slag removal begins. The amount of slag in the furnace is controlled within 2 tons to avoid sulfur and phosphorus return in the molten iron. After the slag is completely removed, the No. 1 AOD furnace is returned to normal to obtain the first enriched nickel-iron molten iron.

4. The method for smelting 310S stainless steel based on low-grade nickel-iron alloy as described in claim 3, characterized in that, The enriched nickel slag added in the later stage of blowing in step S1 comes from the screening furnace period in step S3. In step S1, the oxygen supply intensity of the side lance during the early, middle, and late stages of blowing is 0.8~1.5m. 3 / (min·t); In step S1, the temperature of the slag during the early stage of blowing is controlled at 1500~1550℃, and the blowing time is 2~5 minutes; The lime is added 3 to 5 times in step S1, with 1 to 2 tons of lime added into the furnace every 2 to 4 minutes each time; In step S1, the lime used in the early stage of smelting contains ≥85% CaO; The slag basicity mentioned in step S1 during the early stage of blowing is 3.5~6.0; The composition of the nickel-enriched slag added in the later stage of blowing in step S1 is Ni: 0.05~0.2%, CaO: 20~40%, SiO2: 3~5%, MgO: 1.0~3.0%, S: 0.1~0.3%, with the balance being iron oxides; In step S1, the composition of the first enriched nickel-iron molten metal is C≤0.1%, Si≤0.005%, P≤0.02%, S:0.1~0.2%, Ni:15~18%, and the balance is Fe.

5. The method for smelting 310S stainless steel based on low-grade nickel-iron alloy as described in claim 1, characterized in that, The number of times the blowing period is entered in step S2 is at least once; the blowing period includes the early blowing period, the middle blowing period, the late blowing period, and the slag discharge period; The pre-blowing stage described in step S2 includes the following steps: O2:N2 is blown at a ratio of 5:1 to 3:1 using a side lance; the slag temperature is controlled at 1500-1550℃; after the start of blowing, 3-6 tons of nickel-iron alloy are added to the furnace in 3-5 batches, with each batch spaced 2-4 minutes apart; after each addition of nickel-iron alloy, 1-2 tons of lime are added to create high-basicity slag for desulfurization; after the lime is added, the mid-blowing stage begins; the slag basicity is 4.0-8.

0. The intermediate stage of refining described in step S2 includes the following steps: refining with a side gun flow rate of O2:N2 at 5:1 to 4:1 for 3 to 5 minutes, and then entering the later stage of refining; The later stage of the blowing process described in step S2 includes the following steps: first, add 6 to 10 tons of enriched nickel slag into the furnace at one time, and then blow the slag with the side lance flow rate of O2:N2 at a ratio of 3:1 to 2:1 for 5 to 10 minutes, while controlling the slag temperature at 1400 to 1450°C; The slag removal in step S2 includes the following steps: after the first stage of the blowing period ends, the No. 1 AOD furnace is left to stand for 3 minutes before slag removal begins. The amount of slag in the furnace is controlled within 2 tons to avoid the iron from returning to sulfur and phosphorus. After the slag is completely removed, the No. 1 AOD furnace returns to positive, and the second enriched nickel-iron molten iron is obtained. The number of times the blowing period is entered in step S2 is determined based on the nickel content in the second enriched nickel-iron molten metal: if the nickel content in the second enriched nickel-iron molten metal does not reach 70% of the target nickel content, the furnace is shaken back to normal after slag discharge, and the blowing period continues; the composition of the second enriched nickel-iron molten metal obtained at the end of the blowing period is C≤0.03%, Si≤0.001%, P≤0.01%, S≤0.1%, Ni: 30~35%, with the balance being Fe; the target nickel content is 40~45% nickel content in the enriched nickel-iron molten metal; The nickel-iron alloy added in the early stage of blowing in step S2 comes from the RKEF process; the composition of the nickel-iron alloy is C: 1.0~4.0%, Si≤0.3%, P: 0.02~0.06%, S: 0.4~1.0%, Ni: 8~12%, and the balance is Fe.

6. The method for smelting 310S stainless steel based on low-grade nickel-iron alloy as described in claim 1, characterized in that, The number of screening cycles mentioned in step S3 is at least once; The screening period mentioned in step S3 includes blowing and slag removal; In step S3, the side lance flow rate of O2:N2 during the screening furnace period is 2:1 to 1:2 during blowing, and the slag temperature is controlled at 1400 to 1450℃ throughout the process; The blowing process described in step S3 includes the following steps: 4 to 8 tons of enriched nickel slag are added to the furnace in 3 to 5 batches, with an interval of 2 to 4 minutes between each batch. After each addition of enriched nickel slag, 1 to 2 tons of lime are added to create high-alkalinity slag. The blowing cycle for each stage is 10 to 20 minutes. The slag removal in step S3 includes the following steps: after each stage of blowing is completed, the converter is moved to the slag dumping position and left to stand for 3 minutes before slag removal and temperature measurement. The amount of slag in the furnace is controlled to within 2 tons to avoid iron molten iron from turning sulfur and phosphorus. After slag removal, the furnace is shaken back to the normal position. The number of screening cycles in step S3 is determined based on the nickel content of the enriched nickel-iron molten metal after slag removal: if the nickel content of the enriched nickel-iron molten metal after slag removal does not reach the target nickel content, the screening cycle proceeds to the next stage for continued blowing. The composition of the enriched nickel-iron molten metal obtained in the last stage of the screening cycle is C≤0.01%, P≤0.005%, S≤0.1%, Ni: 40~45%, with the balance being Fe; the target nickel content is a nickel content of 40~45% in the enriched nickel-iron molten metal.

7. The method for smelting 310S stainless steel based on low-grade nickel-iron alloy as described in claim 1, characterized in that, The No. 2 AOD furnace mentioned in step S4 is a new furnace; The molten chromium in step S4 has the following composition: C: 6-8%, Si: 2-4%, P≤0.03%, S: 0.03-0.1%, Cr: 48-53%, with the balance being Fe; The 310S mother liquor composition in step S4 is C: 2~3%, Si: 0.2~2.0%, P: 0.005~0.02%, S: 0.05~0.1%, Cr: 20~26%, Ni: 18~24%, with the balance being Fe.

8. The method for smelting 310S stainless steel based on low-grade nickel-iron alloy as described in claim 1, characterized in that, Step S5 includes the following steps: Reset AOD furnace No. 2 and enter the steelmaking period. After the oxygen lance continuously supplies oxygen and raises the temperature to 1550℃, slag formation and desulfurization begin. Add 2-3 tons of lime to the furnace in batches, and control the alkalinity at 1.3-1.

5. During this period, add alloys to adjust the temperature and composition. After the alloying is completed, shake the furnace to remove slag. The amount of residual slag in the furnace is controlled within 3 tons, and the sulfur content of the obtained steel is S≤0.05%. The alloy includes at least one of ferrosilicon, high-carbon ferrochrome, scrap iron, and nickel briquettes.

9. The method for smelting 310S stainless steel based on low-grade nickel-iron alloy as described in claim 1, characterized in that, Step S6 includes the following steps: Reset AOD furnace No. 2 and enter the oxidation-reduction period. In the oxidation stage, slag is re-formed, and the basicity is controlled at 2.4~3.

2. Oxygen is blown and the temperature is controlled at 1680~1720℃. In the reduction stage, ferrosilicon is added, and the basicity is controlled at 2.2~3.

0. The temperature is controlled above 1650℃. After the reduction is completed, the furnace is shaken to remove slag and desulfurize. The amount of residual slag in the furnace is controlled within 3 tons. The resulting reduced sulfur content is S≤0.002%.

10. The method for smelting 310S stainless steel based on low-grade nickel-iron alloy as described in claim 1, characterized in that, Step S7 includes the following steps: Reset AOD furnace No. 2, enter the refining period, re-slag and add 150~300 meters of aluminum wire for deep deoxidation, control the basicity at 2.0~2.5, fine-tune the composition, shake the furnace to tap the steel and transport it to the LF refining station. The resulting steel mother liquor has an S≤0.001%. Step S8 includes the following steps: After the slag is broken by soft blowing at the LF refining station, 100-130 meters of aluminum wire is added for deep deoxidation to prevent sulfur reversion, and then 500-600 meters of calcium wire is added to purify the molten steel. The Ca / Al ratio is controlled at ≥0.

13. After the composition and temperature meet the requirements, continuous casting is carried out.

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