A refining method for improving niobium recovery in stainless steel

Abstract

This invention discloses a refining method for improving niobium recovery from stainless steel, comprising the following steps: S1, adding niobium-containing stainless steel scrap to an electric arc furnace in batches for smelting; S2, adding ferrosilicon, carbon powder, and lime sequentially to the electric arc furnace for smelting; S3, after two-thirds of each batch of materials has melted, using a small flow rate of oxygen to aid melting; S4, when the molten steel reaches the required composition and temperature for tapping, transferring the molten steel to an AOD furnace for smelting; S5, when the temperature of the molten steel in the AOD furnace is not lower than 1550℃, adding lime for decarburization and oxidation smelting; S6, when the carbon content in the molten steel reaches the internal control target for the smelting steel grade, decarburization and oxidation are completed, and ferrosilicon, aluminum ingots, and fluorite are added to the AOD furnace respectively, while a large flow rate of argon is blown into the AOD furnace; S7, smelting until the silicon content in the molten steel is not lower than 0.4%, and the slag basicity in the furnace is not lower than 2.15. This invention is characterized by improving the niobium recovery rate from niobium-containing stainless steel scrap.

Description

Technical Field

[0001] This invention relates to a stainless steel refining method, and more particularly to a refining method for improving niobium recovery in stainless steel. Background Technology

[0002] With the increasing demand and production of stainless steel in my country, a large amount of stainless steel scrap is generated annually. How to recycle and utilize this scrap in the most economical and effective way is a pressing issue for smelting professionals. Among these, niobium, particularly niobium-containing stainless steel scrap, has high recycling value and deserves special attention. However, niobium is an easily oxidized element, and most stainless steel scrap is smelted in electric arc furnaces with ladle refining. The large amount of oxygen used in the smelting process leads to severe oxidation of niobium in the steel. Using traditional smelting methods, the niobium recovery rate from niobium-containing stainless steel scrap is very low, requiring the addition of ferroniobium in the later stages of smelting. Because ferroniobium alloys are expensive, this significantly increases the raw material cost of the product.

[0003] To improve the niobium recovery rate of niobium-containing stainless steel scrap, the traditional electric arc furnace (EAF) refining and smelting method has the following drawbacks: First, during EAF smelting, due to the varying shapes of the stainless steel scrap, oxygen blowing is necessary for smelting, leading to severe niobium oxidation. Because of the high impurity content in the stainless steel scrap, the large amount of slag in the furnace, and the poor stirring effect of the EAF, the oxidized niobium is generally difficult to reduce and recover within the EAF. Field smelting statistics show that the average niobium recovery rate of EAF is only 42%. Second, the stainless steel AAF refining process is divided into decarburization oxidation and reduction refining. In the early stage, a large amount of metal (including niobium) is oxidized. Existing stainless steel smelting processes add a large amount of ferrosilicon reducing agent in the later stage for metal reduction, resulting in slag with low basicity and a large amount of slag, which is not conducive to niobium recovery. Third, the traditional stainless steel AAF refining and reduction process still has shortcomings in terms of the combination of stirring capacity and the balance of deoxidizing element reactions in actual operation. Therefore, the existing smelting technology has a low niobium recovery rate from niobium-containing stainless steel scrap. On-site smelting statistics show that the average recovery rate of niobium is only 51%. Summary of the Invention

[0004] The purpose of this invention is to provide a refining method for improving niobium recovery from stainless steel. This invention is characterized by increasing the niobium recovery rate from niobium-containing stainless steel scrap.

[0005] The technical solution of this invention: A refining method for improving niobium recovery in stainless steel, comprising the following steps:

[0006] S1. Niobium-containing stainless steel scrap is added to an electric arc furnace in batches for smelting.

[0007] S2. According to the requirements of the steel grade being smelted, ferrosilicon, carbon powder and lime are added to the electric arc furnace in sequence for smelting.

[0008] S3. After two-thirds of each batch of material is melted, oxygen is blown at a low flow rate to aid melting.

[0009] S4. When the temperature of the molten steel reaches above 1500℃, all niobium-containing stainless steel scrap in the furnace is melted into molten steel, and oxygen blowing to aid melting is stopped; when the molten steel is smelted to the point where the composition and temperature meet the requirements for tapping, the molten steel is transferred to the AOD furnace for smelting.

[0010] S5. When the temperature of molten steel in the AOD furnace is not lower than 1550℃, lime shall be added according to the requirement that the basicity of the AOD slag is greater than 2.15, and decarburization and oxidation smelting shall be carried out.

[0011] S6. When the carbon content in the molten steel reaches the internal control target for the steel grade, the decarburization oxidation ends. Based on the AOD slag basicity being greater than 2.15, ferrosilicon, aluminum ingots, and fluorite are added to the AOD furnace respectively, and a large flow of argon gas is blown into the AOD furnace.

[0012] S7. The silicon content in the molten steel shall not be less than 0.4%, and the basicity of the slag in the furnace shall not be less than 2.15.

[0013] In the aforementioned refining method for improving niobium recovery in stainless steel, the batching step S1 specifically involves: mechanically packaging or cutting niobium-containing stainless steel scrap according to the size of the material to be fed into the furnace, adding it to the electric arc furnace in batches for smelting, with the weight of each batch not exceeding the maximum smelting capacity of the electric arc furnace, and adding the next batch of niobium-containing stainless steel scrap after the previous batch has been completely melted into molten steel.

[0014] In the aforementioned refining method for improving niobium recovery in stainless steel, in step S2, the required addition weight of ferrosilicon is 1.0%-1.2% for the silicon content of the molten steel, the addition weight of carbon powder is 2.0%-2.5% for the carbon content of the molten steel, and the addition weight of lime is 28-30 kg / ton of molten steel.

[0015] In the aforementioned refining method for improving niobium recovery in stainless steel, the oxygen flow rate for oxygen blowing in step S3 is 150-200 m³ / h. 3 The oxygen supply rate is 0.9-1.2 MPa per hour, and the oxygen blowing time is 10-15 minutes.

[0016] In the aforementioned refining method for improving niobium recovery in stainless steel, the tapping requirements in step S4 are that the silicon content in the molten steel is not less than 0.5%, the carbon content is not less than 1.2%, and the molten steel temperature is not less than 1650℃.

[0017] In the aforementioned refining method for improving niobium recovery in stainless steel, step S5, the decarburization oxidation smelting includes a first-stage decarburization oxidation and a second-stage decarburization oxidation. During the first-stage decarburization oxidation, the AOD furnace is filled with 1500 mg / L of pure oxygen. 3Oxygen is blown in at a flow rate of / h; when the decarburization of the molten steel reaches below 0.20%, the second stage of decarburization and oxidation begins.

[0018] In the aforementioned refining method for improving niobium recovery in stainless steel, during step S5, in the second stage of decarburization oxidation, the oxygen flow rate is gradually adjusted downwards to 450 m³ / h. 3 / h, and simultaneously blow in argon gas to ensure a total gas flow rate of 1500m³ / h. 3 / h.

[0019] In the aforementioned refining method for improving niobium recovery in stainless steel, in step S6, the high flow rate of argon gas is 900-1200 m³ / s. 3 / h, air gun pressure is 0.8-1.0MPa, molten steel is stirred for 6-8min.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] This invention improves the electric arc furnace (EAF) smelting and AOD (Alternating Dry Oxygen Deposition) refining processes for niobium-containing stainless steel scrap. Improvements include stricter requirements on the stainless steel raw material composition, oxygen blowing method, tapped steel composition, and temperature range control in the EAF smelting process. This allows the niobium recovery rate in the EAF smelting to reach over 65%. In the AOD furnace, control over slag basicity, temperature, and air blowing method enhances the refining and reduction effect, thereby increasing the niobium recovery rate to over 85% in the AOD smelting process. Ultimately, this increases the recycling value of niobium-containing stainless steel scrap, helps reduce raw material costs, and increases economic benefits. Detailed Implementation

[0022] The present invention will be further described below with reference to embodiments, but these embodiments are not intended to limit the scope of the invention. Example

[0023] A refining method for improving niobium recovery in stainless steel includes the following steps:

[0024] S1. The composition of the niobium-containing stainless steel scrap added to the electric arc furnace is screened and accepted. The accepted composition is Ni: 10.1%, Cr: 17.75%, Nb: 0.79%.

[0025] According to the requirement that the length, height and width of the material to be fed into the furnace should not exceed 1 meter, the niobium-containing stainless steel scrap is mechanically packaged or cut to meet the furnace size requirements of the electric arc furnace, so as to facilitate furnace smelting and rapid melting.

[0026] S2: The steel grade to be smelted is determined to be niobium-containing stainless steel TP347H. The amount of niobium-containing stainless steel scrap is 32 tons, which are loaded into three raw material tanks in three batches and added to the electric arc furnace in sequence. The next batch of niobium-containing stainless steel scrap is added after the previous batch has been completely melted into molten steel.

[0027] Because carbon and silicon react preferentially with oxygen compared to niobium, according to the requirements for steel smelting, the first batch of 12 tons of niobium-containing stainless steel scrap, 380 kg of ferrosilicon, 600 kg of carbon powder, and 900 kg of lime were sequentially added to an electric arc furnace for melting. After the first batch of niobium-containing stainless steel scrap was completely melted into a liquid state, the second and third batches of niobium-containing stainless steel scrap, 10 tons each, were added sequentially. Each batch of material was melted to two-thirds its maximum thickness before being smelted using a 180m... 3 A small flow rate of oxygen is supplied per hour to aid melting, with an oxygen supply pressure of 1.05 MPa and an oxygen blowing time of 12 minutes, to prevent excessive oxidation of niobium in the molten steel.

[0028] S3: After oxygen blowing to aid melting, the molten steel reaches a uniform temperature within the furnace, and the temperature rises rapidly. When the molten steel temperature reaches above 1500℃, all niobium-containing stainless steel scrap in the furnace is melted into molten steel. Oxygen blowing to aid melting stops, and the composition of the molten steel is analyzed as Si: 0.58%, C: 1.35%, Nb: 0.57%, Ni: 10.2%, Cr: 17.3%. The measured temperature of the molten steel is 1656℃, and the composition and temperature meet the requirements. The steel is then tapped and transferred to an AOD furnace for smelting.

[0029] S4: 30.6 tons of molten steel were poured into the AOD furnace to smelt low-carbon austenitic stainless steel. All transferred slag in the furnace was removed. A sample was taken for analysis of the steel composition: Si: 0.49%, C: 1.23%, Nb: 0.57%, Ni: 10.18%, Cr: 17.4%. The measured temperature of the molten steel was 1572℃, and the composition and temperature met the requirements for the steel grade. First, 1500 mg / L of pure oxygen was added to the AOD furnace. 3 Oxygen is blown in at a flow rate of / h, and 2100 kg of lime is added at the same time, according to the requirement that the basicity of AOD slag R=CaO / SiO2 is greater than 2.15, to enter the first stage of decarburization oxidation.

[0030] S5: The measured steel temperature is 1689℃, and the decarburization rate of the steel has reached below 0.20%, entering the second stage of decarburization and oxidation. The oxygen flow rate is gradually adjusted downwards to a minimum of 450 m³ / h. 3 / h, and simultaneously blow in argon gas to ensure a total gas flow rate of 1500m³ / h. 3 / h.

[0031] S6: The molten steel is decarburized to below 0.05%, decarburization oxidation is complete, and the reduction period begins. Sampling and analysis of the molten steel composition reveals C: 0.048%, Si: 0%, Nb: 0%, Ni: 10.6%, Cr: 15.9%, and a temperature of 1726℃. At this point, some metallic elements in the molten steel have been oxidized, with niobium being completely oxidized. Based on the AOD slag basicity R=CaO / SiO2 being greater than 2.15, 450 kg of ferrosilicon, 130 kg of aluminum ingots, and 200 kg of fluorite are added to the AOD furnace. Argon gas is then blown into the AOD furnace at a rate of 950 m³ / h. 3 / h flow rate, air gun pressure of 0.85MPa, molten steel stirring for 7min.

[0032] S7: Based on the AOD slag basicity requirements, the slag basicity R=CaO / SiO2 is calculated to be 2.58. A second sample analysis of the molten steel composition by weight percentage shows: C: 0.045%, Si: 0.44%, Nb: 0.49%, Ni: 10.05%, Cr: 17.38%. This achieves the goal of thorough mixing and reduction.

[0033] Tests showed that the Nb metal recovery rate in the molten steel reached 86%. Example

[0034] A refining method for improving niobium recovery in stainless steel includes the following steps:

[0035] S1. The composition of the niobium-containing stainless steel scrap added to the electric arc furnace is screened and accepted. The accepted composition is Ni: 9.2%, Cr: 18.1%, Nb: 0.63%.

[0036] According to the requirement that the length, height and width of the material to be fed into the furnace should not exceed 1 meter, the niobium-containing stainless steel scrap is mechanically packaged or cut to meet the furnace size requirements of the electric arc furnace, so as to facilitate furnace smelting and rapid melting.

[0037] S2: The steel grade to be smelted is determined to be niobium-containing stainless steel 30432, and the amount of niobium-containing stainless steel scrap is 32.5 tons. The scrap is loaded into three raw material tanks in three batches and added to the electric arc furnace in sequence. The next batch of niobium-containing stainless steel scrap is added after the previous batch has been completely melted into molten steel.

[0038] Because carbon and silicon react preferentially with oxygen compared to niobium, according to the requirements for steel smelting, the first batch of 12.5 tons of niobium-containing stainless steel scrap, 340 kg of ferrosilicon, 600 kg of carbon powder, and 850 kg of lime were sequentially added to an electric arc furnace for melting. After the first batch of niobium-containing stainless steel scrap was completely melted into a liquid state, the second and third batches of niobium-containing stainless steel scrap, 10 tons each, were added sequentially. After each batch of materials had melted to two-thirds its maximum volume, a 200m³ smelting furnace was used. 3 The oxygen supply is provided at a low flow rate of 0.97 MPa per hour for 11 minutes to aid melting, thus preventing excessive oxidation of niobium in the molten steel.

[0039] S3: After oxygen blowing to aid melting, the molten steel reaches a uniform temperature within the furnace, and the temperature rises rapidly. When the molten steel temperature reaches above 1500℃, all niobium-containing stainless steel scrap in the furnace is melted into molten steel. Oxygen blowing to aid melting stops, and the composition of the molten steel is analyzed as follows: Si: 0.65%, C: 1.48%, Nb: 0.48%, Ni: 9.3%, Cr: 17.95%. The measured temperature of the molten steel is 1667℃. The composition and temperature meet the requirements, and the steel is tapped and transferred to an AOD furnace for smelting.

[0040] S4: 30.8 tons of molten steel were poured into the AOD furnace to smelt low-carbon austenitic stainless steel. All transferred slag in the furnace was removed, and a sample was taken for analysis of the steel composition: Si: 0.52%, C: 1.35%, Nb: 0.48%, Ni: 9.25%, Cr: 18.00%. The measured temperature of the molten steel was 1576℃, and the composition and temperature met the requirements for the steel grade. First, 1500 mg / L of pure oxygen was added to the AOD furnace. 3 Oxygen is blown in at a flow rate of / h, and 2200 kg of lime is added at the same time, according to the requirement that the basicity of AOD slag R=CaO / SiO2 is greater than 2.15, to enter the first stage of decarburization oxidation.

[0041] S5: The measured steel temperature is 1696℃, and the decarburization rate of the steel has reached below 0.20%, entering the second stage of decarburization and oxidation. The oxygen flow rate is gradually adjusted downwards to a minimum of 450 m³ / h. 3 / h, and simultaneously blow in argon gas to ensure a total gas flow rate of 1500m³ / h. 3 / h.

[0042] S6: The molten steel is decarburized to below 0.05%, decarburization oxidation is complete, and the reduction period begins. Sampling and analysis of the molten steel composition shows C: 0.044%, Si: 0%, Nb: 0%, Ni: 9.68%, Cr: 16.55%, and a temperature of 1732℃. At this point, some metallic elements in the molten steel have been oxidized, with niobium being completely oxidized. Based on the AOD slag basicity R=CaO / SiO2 being greater than 2.15, 460 kg of ferrosilicon, 150 kg of aluminum ingots, and 200 kg of fluorite are added to the AOD furnace. Argon gas is then blown into the AOD furnace at a rate of 930 m³ / h. 3 / h flow rate, air gun pressure of 0.87MPa, molten steel stirring for 8min.

[0043] S7: Based on the AOD slag basicity requirements, the slag basicity R=CaO / SiO2 is calculated to be 2.65. A second sample analysis of the molten steel composition by weight percentage shows: C: 0.043%, Si: 0.49%, Nb: 0.43%, Ni: 9.07%, Cr: 18.36%. This achieves the goal of thorough mixing and reduction.

[0044] Tests showed that the Nb metal recovery rate in the molten steel reached 89.5%.

Claims

1. A refining method for improving niobium recovery in stainless steel, characterized in that: Includes the following steps: S1. Niobium-containing stainless steel scrap is added to an electric arc furnace in batches for smelting. S2. According to the requirements of the steel grade being smelted, ferrosilicon, carbon powder and lime are added to the electric arc furnace in sequence for smelting. S3. After two-thirds of each batch of material is melted, oxygen is blown at a low flow rate to aid melting. S4. When the temperature of the molten steel reaches above 1500℃, all niobium-containing stainless steel scrap in the furnace is melted into molten steel, and oxygen blowing to aid melting is stopped. When the molten steel is smelted to the point where the composition and temperature meet the requirements for tapping, the molten steel is transferred to an AOD furnace for further smelting. S5. When the temperature of molten steel in the AOD furnace is not lower than 1550℃, lime shall be added according to the requirement that the basicity of the AOD slag is greater than 2.15, and decarburization and oxidation smelting shall be carried out. S6. When the carbon content in the molten steel reaches the internal control target for the steel grade, the decarburization oxidation ends. Based on the AOD slag basicity being greater than 2.15, ferrosilicon, aluminum ingots, and fluorite are added to the AOD furnace respectively, and a large flow of argon gas is blown into the AOD furnace. S7. The silicon content in the molten steel shall not be less than 0.4%, and the basicity of the slag in the furnace shall not be less than 2.

15.

2. The refining method for improving niobium recovery in stainless steel according to claim 1, characterized in that: In step S1, the niobium-containing stainless steel scrap contains 0.4%-1.0% niobium by weight, 9%-11% nickel by weight, and 17%-20% chromium by weight.

3. The refining method for improving niobium recovery in stainless steel according to claim 1, characterized in that: The specific steps of step S1 are as follows: the niobium-containing stainless steel scrap is mechanically packaged or cut according to the size of the material to be put into the furnace, and added to the electric arc furnace in batches for smelting. The weight of each batch does not exceed the maximum smelting amount of the electric arc furnace. The next batch of niobium-containing stainless steel scrap is added after the previous batch of niobium-containing stainless steel scrap has been completely melted into molten steel.

4. The refining method for improving niobium recovery in stainless steel according to claim 1, characterized in that: In S2, the required addition weight of ferrosilicon in steelmaking is 1.0%-1.2% silicon content in the molten steel, the addition weight of carbon powder is 2.0%-2.5% carbon content in the molten steel, and the addition weight of lime is 28-30 kg / ton of molten steel.

5. The refining method for improving niobium recovery in stainless steel according to claim 1, characterized in that: In step S3, the oxygen blowing flow rate for oxygen blowing to aid melting is 150-200 m³ / h. 3 The oxygen supply rate is 0.9-1.2 MPa per hour, and the oxygen blowing time is 10-15 minutes.

6. The refining method for improving niobium recovery in stainless steel according to claim 1, characterized in that: The requirements for tapping the steel in step S4 are that the silicon content in the molten steel is not less than 0.5%, the carbon content is not less than 1.2%, and the temperature of the molten steel is not less than 1650℃.

7. The refining method for improving niobium recovery in stainless steel according to claim 1, characterized in that: In step S5, the decarburization oxidation smelting includes a first stage of decarburization oxidation and a second stage of decarburization oxidation. During the first stage of decarburization oxidation, the AOD furnace is filled with 1500 mg / L of pure oxygen. 3 Oxygen is blown in at a flow rate of / h; when the decarburization of the molten steel reaches below 0.20%, the second stage of decarburization and oxidation begins.

8. A refining method for improving niobium recovery in stainless steel according to claim 7, characterized in that: In step S5, during the second stage of decarbonization and oxidation, the oxygen flow rate is gradually adjusted downwards to 450 m³ / h. 3 / h, and simultaneously blow in argon gas to ensure a total gas flow rate of 1500m³ / h. 3 / h.

9. A refining method for improving niobium recovery in stainless steel according to claim 1, characterized in that: In step S6, the high flow rate of argon gas is 900-1200 m³ / h. 3 / h, air gun pressure is 0.8-1.0MPa, molten steel is stirred for 6-8min.