Method for smelting free-cutting austenitic stainless steel in AOD furnace

Abstract

The invention belongs to the technical field of stainless steel smelting, and particularly discloses a method for smelting free-cutting austenitic stainless steel in an AOD furnace, and the method for smelting free-cutting austenitic stainless steel in the AOD furnace comprises the following steps: S1, preparing AOD mixed steel; s2, preparation of AOD oxygen blowing decarburization; s3, preparation of reducing slag skimming operation; s4, preparing secondary slag; s5, adding ferrous sulfide to increase the sulfur component of the molten steel; the requirement of molten steel reduction deoxidation can be met by controlling the alkalinity of the reducing slag according to 1.5, the alkalinity of the reducing slag and the alkalinity of secondary slagging are set to be the same, the influence and fluctuation of the slag of the reducing slag on the alkalinity of the secondary slagging can be avoided, the purpose of stably controlling the sulfur component of the molten steel is achieved, and the problem that during reduction slagging, the alkalinity of the slag is controlled to be 2.0-2.3, and the sulfur content of the molten steel is reduced is solved. Slag in the furnace needs to be removed after reduction, and the slag in the furnace cannot be completely removed under the influence of the furnace profile.

Description

Technical Field

[0001] The present application relates to the technical field of stainless steel smelting, and more specifically, to a method for smelting free-cutting austenitic stainless steel in an AOD furnace. Background Art

[0002] Free-cutting austenitic stainless steel is widely used in machinery manufacturing, automobile, aerospace and other fields due to its good cutting performance, corrosion resistance and mechanical properties. The main chemical elements of this type of stainless steel are low C, high Cr, and a small amount of Ni, Mo and S elements are added. The production process of this material focuses on determining the optimal steel grade composition and accurately and stably controlling the S and Mn content of the material in alkaline electric furnace production.

[0003] The sulfur content requirement for free-cutting austenitic stainless steel is 0.20%-0.30%. The slag-forming agent lime added during steelmaking and slag-making reacts with the sulfur in the molten steel ([FeS]+(CaO)=(CaS)+[FeO]). According to metallurgical thermodynamic conditions, the higher the alkalinity, the better the desulfurization and the lower the sulfur content in the molten steel. When producing free-cutting stainless steel, the sulfur in the molten steel enters the slag, which will lead to insufficient sulfur content in the molten steel and the product being scrapped. During reduction slag-making, the slag alkalinity is controlled at 2.0-2.3. After reduction, the slag in the furnace needs to be removed. Affected by the furnace type, the slag in the furnace cannot be completely removed. Due to the residual high-alkalinity slag in the furnace, it is difficult to control the amount of lime and quartz sand added during secondary slag-making, resulting in fluctuations in alkalinity. When adding ferrosulphur to increase sulfur, if the slag alkalinity is too high, the slag desulfurization capacity is enhanced, and the sulfur in the molten steel enters the slag, resulting in insufficient sulfur content in the molten steel, resulting in product scrapping and other problems.

[0004] Therefore, it is urgent to study the method of reducing the slag basicity from 2.0 to 1.5 during AOD reduction slag making, and adding lime and quartz sand (main component SiO2, content of more than 98%) according to the basicity of 1.5 during secondary slag making. Since the basicity of reduction slag making and secondary slag making is the same, the weight of the residual reduction slag in the furnace will not affect the basicity of secondary slag making, thereby achieving the purpose of stably controlling the sulfur content of molten steel. Summary of the invention

[0005] The object of the present invention is to provide a method for smelting free-cutting austenitic stainless steel in an AOD furnace to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for smelting free-cutting austenitic stainless steel in an AOD furnace, comprising the following steps: S1. Preparation of AOD steel: The primary steel from the electric arc furnace and alloy furnace is added to the AOD steel through the ladle. Inside the furnace, the temperature of the molten steel after being added to the AOD furnace is 1450°C, and the composition is as follows: C, Si, Mn, Cr, Ni, Cu; S2. Preparation of AOD oxygen blowing decarburization: After adding steel, oxygen blowing decarburization begins in the AOD furnace. During the oxygen blowing period, the amount of lime added is calculated according to the oxygen blowing amount and alkalinity, and all of it is added into the furnace before 1 / 3 of the oxygen is blown; S3, preparation of reduction slag slagging operation: after oxygen blowing and decarburization, add metal oxides in ferrosilicon reduction slag, stir for 8 minutes and then remove the slag after reduction and desulfurization in the furnace. The slagging should be as clean as possible and the residue should be controlled within 1500kg; S4, secondary slag preparation: according to the basicity of 1.5, lime and quartz sand are added for secondary slag making. The total slag amount is 3000kg, the reduced slag residue is 1500kg, and the secondary slag amount is 1500kg. Then the amount of lime added is 900kg and the amount of quartz sand added is 600kg. S5. Add ferrosulphide to increase the sulfur content of molten steel: After secondary slag making, the slag basicity can be stably controlled at 1.5. Add ferrosulphide (S content 45%) to increase the sulfur content of molten steel to 0.20%-0.30%. After sampling, analyze the sulfur content by spectrum. When the content meets the requirements, AOD steelmaking is performed: The AOD-steel mixture includes the following raw materials in percentage by weight: C 1.85%; Si 0.63%; Mn 0.70%; Cr 17.10%; Ni 8.20%; Cu 2.0%.

[0007] Preferably, the metallurgical slag is obtained by adding lime and quartz sand for secondary slagging according to a basicity of 1.5, and the binary basicity of the metallurgical slag is calculated by the formula: basicity is CaO / SiO.

[0008] Preferably, the AOD makes reducing slag with a basicity of 1.5, and lime and quartz sand are added according to the basicity of 1.5 during secondary slag making. Since the basicity of the reducing slag is the same as that of the secondary slag making, the basicity of the slag can be stably controlled, thereby achieving the purpose of stably controlling the sulfur content of the molten steel.

[0009] Preferably, the total slag amount of the secondary slag making includes the following raw materials in parts by weight: Total slag volume 3000kg; Reduction slag residue 1500kg; Secondary slag production: 1500kg; Lime addition amount 900kg; The amount of quartz sand added is 600kg.

[0010] Preferably, in said S2, oxygen is blown for decarbonization, and the amount of lime added is calculated according to the oxygen blowing amount and alkalinity during oxygen blowing, and all of it is put into the furnace before 1 / 3 of the oxygen is blown.

[0011] Preferably, after the oxygen decarburization of S2 is completed, the metal oxides in the ferrosilicon reduction slag are added, and after stirring for 8 minutes, the slag after reduction and desulfurization in the furnace is removed. The slag is removed as cleanly as possible and the residue is controlled within 1500kg.

[0012] Preferably, during the AOD reduction slag making, the slag basicity is reduced from 2.0 to 1.5, and during the secondary slag making, lime and quartz sand (main component SiO2, content of more than 98%) are added according to the basicity of 1.5.

[0013] Preferably, in S5, the process of adjusting the composition includes: adding silica after alloying the molten steel, feeding sulfur wire after slag breaking, adjusting the S content, and then feeding Si-Ca wire according to the deoxidation condition and Si content, and then adding rare earth and Fe-B alloy.

[0014] Preferably, the slag basicity after the secondary slag making can be stably controlled at 1.5, and ferrosulfur (S content 45%) is added to increase the sulfur content of the molten steel to 0.20%-0.30%. The sulfur content is analyzed by spectroscopy after sampling, and AOD is used to tap the steel after the composition meets the requirements.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention can achieve the requirement of reducing and deoxidizing molten steel by controlling the basicity of the reducing slag to 1.5; 2. The present invention sets the basicity of the reducing slag to be the same as the basicity of the secondary slag making, thereby preventing the influence and fluctuation of the basicity of the secondary slag making caused by the residue of the reducing slag, thereby achieving the purpose of stably controlling the sulfur content of the molten steel. DETAILED DESCRIPTION

[0016] Unless the context clearly dictates otherwise, unmodified nouns and nouns modified by "the" include singular and plural referents.

[0017] As used in the specification and claims, the terms "comprises," "comprising," "having," "may," "containing," and variations thereof as used herein refer to open transitional phrases, terms, or words that require the presence of specified ingredients / steps and allow for the presence of other ingredients / steps. However, such descriptions should be interpreted as also describing compositions or methods as "consisting of" and "consisting essentially of" the recited ingredients / steps, which allows for the presence of only the specified ingredients / steps and any unavoidable impurities that may result therefrom, and excludes other ingredients / steps.

[0018] Numerical values ​​in the specification and claims of this application should be understood to include the same numerical values ​​when reduced to the same number of significant figures and numerical values ​​that differ from the stated value by less than the experimental error of ordinary measurement techniques of the type described in this application for determining the stated value.

[0019] All ranges disclosed herein are inclusive of the indicated endpoints and are independently combinable (eg, the range of "2 grams to 10 grams" includes the endpoints 2 grams and 10 grams, and all intermediate values).

[0020] The terms "about" and "approximately" can be used to include any numerical value that can be varied without changing the basic function of the value. When used with a range, "about" and "approximately" also disclose the range defined by the absolute values ​​of the two endpoints, for example, "about 2 to about 4" also discloses a range of "2 to 4". Generally, the terms "about" and "approximately" can refer to ±10% of the indicated number. However, for temperature, the term "approximately" refers to ±1°C.

[0021] Unless expressly stated otherwise, the percentages of elements are to be considered as percentages by weight of the alloy in question.

[0022] The present disclosure may refer to the temperature of certain method steps. It should be noted that these indicators generally refer to the temperature set by the heat source (such as a furnace), and not necessarily the temperature that the heated material must reach.

[0023] The present invention provides a method for smelting free-cutting austenitic stainless steel in an AOD furnace, comprising the following steps: S1, preparation of AOD and steel; The primary molten steel from the electric arc furnace and alloy furnace is added to the AOD furnace through the ladle. The temperature of the molten steel after adding it to the AOD furnace is 1450℃, and the composition is as follows: C, Si, Mn, Cr, Ni, Cu; S2, preparation of AOD oxygen blowing decarburization; After adding steel, oxygen decarburization begins in the AOD furnace. During the oxygen blowing period, the amount of lime added is calculated based on the oxygen blowing amount and alkalinity, and all of it is added into the furnace before 1 / 3 of the oxygen is blown; S3, preparation of reduction slag slagging operation; After oxygen decarburization is completed, add the metal oxides in the ferrosilicon reduction slag, stir for 8 minutes, and then remove the slag after reduction and desulfurization in the furnace. The slag should be removed as cleanly as possible and the residue should be controlled within 1500kg; S4, preparation of secondary slag; According to the basicity of 1.5, lime and quartz sand are added for secondary slagging. The total slag volume is 3000kg, the reduced slag residue is 1500kg, and the secondary slagging volume is 1500kg. The amount of lime added is 900kg and the amount of quartz sand added is 600kg. S5, adding ferrosulphur to increase the sulfur content of molten steel; After secondary slag making, the slag basicity can be stably controlled at 1.5. Sulfur iron (S content 45%) is added to increase the sulfur content of molten steel to 0.20%-0.30%. After sampling, the sulfur content is analyzed by spectroscopy. When the composition meets the requirements, AOD steelmaking is performed: The AOD-steel mixture includes the following raw materials in percentage by weight: C 1.85%; Si 0.63%; Mn 0.70%; Cr 17.10%; Ni 8.20%; Cu 2.0%.

[0024] The specific steps are as follows: according to the alkalinity of 1.5, lime and quartz sand are added for secondary slagging to obtain metallurgical slag. The binary alkalinity calculation formula of metallurgical slag is: the alkalinity is CaO / SiO, and AOD makes reducing slag with an alkalinity of 1.5. During the secondary slagging, lime and quartz sand are added according to the alkalinity of 1.5. Since the alkalinity of the reducing slag is the same as that of the secondary slagging, the alkalinity of the slag can be stably controlled, thereby achieving the purpose of stably controlling the sulfur content of the molten steel. During the oxygen blowing period, the amount of lime added is calculated according to the oxygen blowing amount and the alkalinity, and all of it is put into the furnace before 1 / 3 of the oxygen blowing. After the oxygen blowing and decarburization are completed, the metal oxides in the ferrosilicon reducing slag are added, and the slag after reduction and desulfurization in the furnace is removed after stirring for 8 minutes. , slag should be removed as cleanly as possible, and the residue should be controlled within 1500kg. The basicity of the slag is reduced from 2.0 to 1.5. During the secondary slag making, lime and quartz sand (main component SiO2, content of more than 98%) are added according to the basicity of 1.5. After the molten steel is alloyed, silica is added. After slag breaking, the sulfur wire is fed to adjust the S content, and then the Si-Ca wire is fed according to the deoxidation situation and Si content, and then rare earth and Fe-B alloy are added. After the secondary slag making, the slag basicity can be stably controlled at 1.5, and ferrous sulfur (S content 45%) is added to increase the sulfur content of the molten steel to 0.20%-0.30%. The sulfur content is analyzed by spectrum after sampling. AOD steelmaking is performed after the composition meets the requirements.

[0025] S1, preparation of AOD and steel; The primary molten steel from the electric arc furnace and alloy furnace is added to the AOD furnace through the ladle. The temperature of the molten steel after adding it to the AOD furnace is 1450℃, and the composition is as follows: C, Si, Mn, Cr, Ni, Cu; S2, preparation of AOD oxygen blowing decarburization; After adding steel, oxygen decarburization begins in the AOD furnace. During the oxygen blowing period, the amount of lime added is calculated based on the oxygen blowing amount and alkalinity, and all of it is added into the furnace before 1 / 3 of the oxygen is blown; S3, preparation of reduction slag slagging operation; After oxygen decarburization is completed, add the metal oxides in the ferrosilicon reduction slag, stir for 8 minutes, and then remove the slag after reduction and desulfurization in the furnace. The slag should be removed as cleanly as possible and the residue should be controlled within 1500kg; S4, preparation of secondary slag; According to the basicity of 1.5, lime and quartz sand are added for secondary slagging. The total slag volume is 3000kg, the reduced slag residue is 1500kg, and the secondary slagging volume is 1500kg. The amount of lime added is 900kg and the amount of quartz sand added is 600kg. S5, adding ferrosulphur to increase the sulfur content of molten steel; After secondary slag making, the slag basicity can be stably controlled at 1.5. Sulfur iron (S content 45%) is added to increase the sulfur content of molten steel to 0.20%-0.30%. After sampling, the sulfur content is analyzed by spectroscopy. When the composition meets the requirements, AOD steelmaking is performed: The AOD-steel mixture includes the following raw materials in percentage by weight: C 1.85%; Si 0.63%; Mn 0.70%; Cr 17.10%; Ni 8.20%; Cu 2.0%.

[0026] The specific steps are as follows: according to the alkalinity of 1.5, lime and quartz sand are added for secondary slagging to obtain metallurgical slag. The binary alkalinity calculation formula of metallurgical slag is: the alkalinity is CaO / SiO, and AOD makes reducing slag with an alkalinity of 1.5. During the secondary slagging, lime and quartz sand are added according to the alkalinity of 1.5. Since the alkalinity of the reducing slag is the same as that of the secondary slagging, the alkalinity of the slag can be stably controlled, thereby achieving the purpose of stably controlling the sulfur content of the molten steel. During the oxygen blowing period, the amount of lime added is calculated according to the oxygen blowing amount and the alkalinity, and all of it is put into the furnace before 1 / 3 of the oxygen blowing. After the oxygen blowing and decarburization are completed, the metal oxides in the ferrosilicon reducing slag are added, and the slag after reduction and desulfurization in the furnace is removed after stirring for 8 minutes. , slag should be removed as cleanly as possible, and the residue should be controlled within 1500kg. The basicity of the slag is reduced from 2.0 to 1.5. During the secondary slag making, lime and quartz sand (main component SiO2, content of more than 98%) are added according to the basicity of 1.5. After the molten steel is alloyed, silica is added. After slag breaking, the sulfur wire is fed to adjust the S content, and then the Si-Ca wire is fed according to the deoxidation situation and Si content, and then rare earth and Fe-B alloy are added. After the secondary slag making, the slag basicity can be stably controlled at 1.5, and ferrous sulfur (S content 45%) is added to increase the sulfur content of the molten steel to 0.20%-0.30%. The sulfur content is analyzed by spectrum after sampling. AOD steelmaking is performed after the composition meets the requirements.

[0027] Free-cutting austenitic stainless steel AOD smelting process S1, preparation of AOD and steel; The primary molten steel from the electric arc furnace and alloy furnace is added to the AOD furnace through the ladle. The temperature of the molten steel after adding it to the AOD furnace is 1450℃, and the composition is as follows: C, Si, Mn, Cr, Ni, Cu; S2, preparation of AOD oxygen blowing decarburization; After adding steel, oxygen decarburization begins in the AOD furnace. During the oxygen blowing period, the amount of lime added is calculated based on the oxygen blowing amount and alkalinity, and all of it is added into the furnace before 1 / 3 of the oxygen is blown; S3, preparation of reduction slag slagging operation; After oxygen decarburization is completed, add the metal oxides in the ferrosilicon reduction slag, stir for 8 minutes, and then remove the slag after reduction and desulfurization in the furnace. The slag should be removed as cleanly as possible and the residue should be controlled within 1500kg; S4, preparation of secondary slag; According to the basicity of 1.5, lime and quartz sand are added for secondary slagging. The total slag volume is 3000kg, the reduced slag residue is 1500kg, and the secondary slagging volume is 1500kg. The amount of lime added is 900kg and the amount of quartz sand added is 600kg. S5, adding ferrosulphur to increase the sulfur content of molten steel; After secondary slag making, the slag basicity can be stably controlled at 1.5. Sulfur iron (S content 45%) is added to increase the sulfur content of molten steel to 0.20%-0.30%. After sampling, the sulfur content is analyzed by spectroscopy. When the composition meets the requirements, AOD steelmaking is performed: The AOD-steel mixture includes the following raw materials in percentage by weight: C 1.85%; Si 0.63%; Mn 0.70%; Cr 17.10%; Ni 8.20%; Cu 2.0%.

[0028] The specific steps are as follows: according to the alkalinity of 1.5, lime and quartz sand are added for secondary slagging to obtain metallurgical slag. The binary alkalinity calculation formula of metallurgical slag is: the alkalinity is CaO / SiO, and AOD makes reducing slag with an alkalinity of 1.5. During the secondary slagging, lime and quartz sand are added according to the alkalinity of 1.5. Since the alkalinity of the reducing slag is the same as that of the secondary slagging, the alkalinity of the slag can be stably controlled, thereby achieving the purpose of stably controlling the sulfur content of the molten steel. During the oxygen blowing period, the amount of lime added is calculated according to the oxygen blowing amount and the alkalinity, and all of it is put into the furnace before 1 / 3 of the oxygen blowing. After the oxygen blowing and decarburization are completed, the metal oxides in the ferrosilicon reducing slag are added, and the slag after reduction and desulfurization in the furnace is removed after stirring for 8 minutes. , slag should be removed as cleanly as possible, and the residue should be controlled within 1500kg. The basicity of the slag is reduced from 2.0 to 1.5. During the secondary slag making, lime and quartz sand (main component SiO2, content of more than 98%) are added according to the basicity of 1.5. After the molten steel is alloyed, silica is added. After slag breaking, the sulfur wire is fed to adjust the S content, and then the Si-Ca wire is fed according to the deoxidation situation and Si content, and then rare earth and Fe-B alloy are added. After the secondary slag making, the slag basicity can be stably controlled at 1.5, and ferrous sulfur (S content 45%) is added to increase the sulfur content of the molten steel to 0.20%-0.30%. The sulfur content is analyzed by spectrum after sampling. AOD steelmaking is performed after the composition meets the requirements.

[0029] Free-cutting austenitic stainless steel AOD smelting process S1, preparation of AOD and steel; The primary molten steel from the electric arc furnace and alloy furnace is added to the AOD furnace through the ladle. The temperature of the molten steel after adding it to the AOD furnace is 1450℃, and the composition is as follows: C, Si, Mn, Cr, Ni, Cu; S2, preparation of AOD oxygen blowing decarburization; After adding steel, oxygen decarburization begins in the AOD furnace. During the oxygen blowing period, the amount of lime added is calculated based on the oxygen blowing amount and alkalinity, and all of it is added into the furnace before 1 / 3 of the oxygen is blown; S3, preparation of reduction slag slagging operation; After oxygen decarburization is completed, add the metal oxides in the ferrosilicon reduction slag, stir for 8 minutes, and then remove the slag after reduction and desulfurization in the furnace. The slag should be removed as cleanly as possible and the residue should be controlled within 1500kg; S4, preparation of secondary slag; According to the basicity of 1.5, lime and quartz sand are added for secondary slagging. The total slag volume is 3000kg, the reduced slag residue is 1500kg, and the secondary slagging volume is 1500kg. The amount of lime added is 900kg and the amount of quartz sand added is 600kg. S5, adding sulphur iron to increase the sulphur content of molten steel; After secondary slag making, the slag basicity can be stably controlled at 1.5. Sulfur iron (S content 45%) is added to increase the sulfur content of molten steel to 0.20%-0.30%. After sampling, the sulfur content is analyzed by spectroscopy. When the composition meets the requirements, AOD steelmaking is performed: The AOD-steel mixture includes the following raw materials in percentage by weight: C 1.85%; Si 0.63%; Mn 0.70%; Cr 17.10%; Ni 8.20%; Cu 2.0%.

[0030] The specific steps are as follows: according to the alkalinity of 1.5, lime and quartz sand are added for secondary slagging to obtain metallurgical slag. The binary alkalinity calculation formula of metallurgical slag is: the alkalinity is CaO / SiO, and AOD makes reducing slag with an alkalinity of 1.5. During the secondary slagging, lime and quartz sand are added according to the alkalinity of 1.5. Since the alkalinity of the reducing slag is the same as that of the secondary slagging, the alkalinity of the slag can be stably controlled, thereby achieving the purpose of stably controlling the sulfur content of the molten steel. During the oxygen blowing period, the amount of lime added is calculated according to the oxygen blowing amount and the alkalinity, and all of it is put into the furnace before 1 / 3 of the oxygen blowing. After the oxygen blowing and decarburization are completed, the metal oxides in the ferrosilicon reducing slag are added, and the slag after reduction and desulfurization in the furnace is removed after stirring for 8 minutes. , slag should be removed as cleanly as possible, and the residue should be controlled within 1500kg. The basicity of the slag is reduced from 2.0 to 1.5. During the secondary slag making, lime and quartz sand (main component SiO2, content of more than 98%) are added according to the basicity of 1.5. After the molten steel is alloyed, silica is added. After slag breaking, the sulfur wire is fed to adjust the S content, and then the Si-Ca wire is fed according to the deoxidation situation and Si content, and then rare earth and Fe-B alloy are added. After the secondary slag making, the slag basicity can be stably controlled at 1.5, and ferrous sulfur (S content 45%) is added to increase the sulfur content of the molten steel to 0.20%-0.30%. The sulfur content is analyzed by spectrum after sampling. AOD steelmaking is performed after the composition meets the requirements.

[0031] Free-cutting austenitic stainless steel AOD smelting process The main components and contents of the stainless steels smelted in Examples 1-3 were respectively detected according to the method for determining the multi-element content of stainless steel in Examples 1-3, and compared with the existing production requirements for producing this type of stainless steel. The results are shown in Table 1 Element content C(%) Si(%) Mn(%) Cr(%) Ni(%) Cu(%) Production requirements 1.85% 0.63% 0.70% 17.10% 8.20% 2.0% Table 1 The main components and contents of the stainless steels smelted in Examples 1-3 were respectively detected according to the method for determining the multi-element content of stainless steel in Examples 1-3, and compared with the existing production requirements for producing this type of stainless steel. The results are shown in Table 2 Total slag Reduction slag residue Secondary slag production Amount of lime added Quartz sand addition amount 3000kg 1500kg 1500kg 900kg 600kg Total slag volume 3000kg = Reduction slag residue 1500kg + Secondary slag volume 1500kg Secondary slag production: 1500kg = lime addition: 900kg + quartz sand addition: 600kg Table 2 Although the embodiments of the present invention have been shown and described, it is understandable to those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents. This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the embodiments as needed without any creative contribution. However, as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for smelting free-cutting austenitic stainless steel in an AOD furnace, characterized in that: The following steps are involved: S1. Preparation of AOD steel: The primary steel from the electric arc furnace and alloy furnace is added to the AOD steel through the ladle. Inside the furnace, the temperature of the molten steel after being added to the AOD furnace is 1450°C, and the composition is as follows: C, Si, Mn, Cr, Ni, Cu; S2. Preparation of AOD oxygen blowing decarburization: After adding steel, oxygen blowing decarburization begins in the AOD furnace. During the oxygen blowing period, the amount of lime added is calculated according to the oxygen blowing amount and alkalinity, and all of it is added into the furnace before 1 / 3 of the oxygen is blown; S3, preparation of reduction slag slagging operation: after oxygen blowing and decarburization, add metal oxides in ferrosilicon reduction slag, stir for 8 minutes and then remove the slag after reduction and desulfurization in the furnace. The slagging should be as clean as possible and the residue should be controlled within 1500kg; S4, secondary slag preparation: according to the basicity of 1.5, lime and quartz sand are added for secondary slag making. The total slag amount is 3000kg, the reduced slag residue is 1500kg, and the secondary slag amount is 1500kg. Then the amount of lime added is 900kg and the amount of quartz sand added is 600kg. S5. Add ferrosulphide to increase the sulfur content of molten steel: After secondary slag making, the slag basicity can be stably controlled at 1.

5. Add ferrosulphide (S content 45%) to increase the sulfur content of molten steel to 0.20%-0.30%. After sampling, analyze the sulfur content by spectrum. When the content meets the requirements, AOD steelmaking is performed: The AOD-steel mixture includes the following raw materials in percentage by weight: C 1.85%； Si 0.63%; Mn 0.70%; Cr 17.10%； Ni 8.20%; Cu 2.0%.

2. The method for smelting free-cutting austenitic stainless steel in an AOD furnace according to claim 1, characterized in that: The metallurgical slag is obtained by adding lime and quartz sand for secondary slagging according to a basicity of 1.

5. The binary basicity calculation formula of the metallurgical slag is: basicity is CaO / SiO.

3. The method for smelting free-cutting austenitic stainless steel in an AOD furnace according to claim 2, characterized in that: The AOD makes reducing slag with a basicity of 1.5, and lime and quartz sand are added according to the basicity of 1.5 during secondary slag making. Since the basicity of the reducing slag is the same as that of the secondary slag making, the basicity of the slag can be stably controlled, thereby achieving the purpose of stably controlling the sulfur content of molten steel.

4. The method for smelting free-cutting austenitic stainless steel in an AOD furnace according to claim 1, characterized in that: The total slag amount of the secondary slag making comprises the following raw materials in parts by weight: Total slag volume 3000kg; Reduction slag residue 1500kg; Secondary slag production: 1500kg; Lime addition amount 900kg; The amount of quartz sand added is 600kg.

5. The method for smelting free-cutting austenitic stainless steel in an AOD furnace according to claim 1, characterized in that: In the S2, oxygen is blown for decarbonization. During the oxygen blowing period, the amount of lime added is calculated according to the oxygen blowing amount and the alkalinity, and all of it is put into the furnace before 1 / 3 of the oxygen is blown.

6. The method for smelting free-cutting austenitic stainless steel in an AOD furnace according to claim 5, characterized in that: After the oxygen decarburization of S2 is completed, the metal oxides in the ferrosilicon reduction slag are added, and the slag after reduction and desulfurization in the furnace is removed after stirring for 8 minutes. The slag is removed as cleanly as possible and the residue is controlled within 1500kg.

7. The method for smelting free-cutting austenitic stainless steel in an AOD furnace according to claim 1, characterized in that: During the AOD reduction slag making process, the slag basicity is reduced from 2.0 to 1.5, and during the secondary slag making process, lime and quartz sand (main component SiO2, content of which is more than 98%) are added according to the basicity of 1.

5.

8. The method for smelting free-cutting austenitic stainless steel in an AOD furnace according to claim 1, characterized in that: In the S5, the process of adjusting the composition includes: after alloying the molten steel, adding silica, feeding sulfur wire after slag breaking, adjusting the S content, and then feeding Si-Ca wire according to the deoxidation situation and Si content, and then adding rare earth and Fe-B alloy.

9. The method for smelting free-cutting austenitic stainless steel in an AOD furnace according to claim 7, characterized in that: After the secondary slag making, the slag basicity can be stably controlled at 1.5, and ferrosulphide (S content 45%) is added to increase the sulfur content of molten steel to 0.20%-0.30%. After sampling, the sulfur content is analyzed by spectroscopy. When the content meets the requirements, AOD steelmaking is performed.

Images