CN108330245B - A kind of high-purity smelting method of stainless steel - Google Patents

Abstract

The invention discloses a high-purity smelting method of stainless steel, which comprises the following steps: under the protection of high-purity argon, performing master alloy smelting, AOD + LF external refining, VD vacuum refining and die casting steel ingot processes by adopting electric arcs, and obtaining the stainless steel ingot with low impurity content. According to the invention, the electric arc is used for smelting, and high-purity argon is introduced in the smelting process, so that the alloy can be effectively prevented from being oxidized, impurity elements are prevented from entering, and the burning loss of volatile elements is reduced; meanwhile, the content of P in the steel is reduced by methods of large slag amount, multiple slag flowing and the like in the smelting process; and adding aluminum particles for pre-deoxidation in LF refining. The smelting preparation method of the stainless steel is applied to the production of the stainless steel in the industrial production process.

Description

A kind of high-purity smelting method of stainless steel

technical field

The invention discloses a high-purity smelting method of stainless steel, which belongs to the field of stainless steel preparation.

Background technique

In the smelting process of stainless steel, the endogenous inclusions are mainly due to the deoxidizer (Al, FeSi, SiMn, etc.) added to the molten steel being oxidized to form Al ₂ O ₃ , SiO ₂ and MgO·Al ₂ during the deoxidation and alloying operation. O ₃ , SiO ₂ -MnO, Al ₂ O ₃ -SiO ₂ -MnO and other composite deoxidation products; alloy elements (Cr, Ti, Si, Mn) are partially oxidized to form FeO·Cr ₂ O ₃ , SiO ₂ -Cr ₂ O _3. A1 ₂ O ₃ -Cr ₂ O ₃ , Cr ₂ O ₃ -MnS, TiO ₂ and other inclusions; in the process of cooling, solidification and crystallization of molten steel, secondary deoxidation products will be formed due to temperature drop and local component segregation. When these products are too late to be discharged from the molten steel, they remain in the steel to form endogenous inclusions.

Al has strong deoxidation ability, but its deoxidation product from Al ₂ O ₃ has adverse effects on the properties of most grades of stainless steel, so its use in stainless steel smelting is greatly limited. It has been found from relevant research at home and abroad that when comprehensively considering the deoxidation, desulfurization and dephosphorization effects of stainless steel liquid, compound refining agents containing alkaline earth metal elements (barium, calcium and magnesium) and rare earth can be selected. Deoxidation, desulfurization and reductive dephosphorization ability, and the deoxidation product has a fast floating speed, and there is almost no residue in the steel. Unfortunately, most of the research in this area is still in the laboratory research stage, and it is rarely applied and promoted in the actual production of stainless steel.

The foreign inclusions in the finished stainless steel are large inclusions brought into the molten steel by the erosion and erosion of the refractory material during the smelting and pouring process, slag mixed into the molten steel (such as the steel slag in the AOD tapping process) and in the molten steel. Secondary oxidation during transportation and pouring, etc.

Nitride in stainless steel is mainly in the form of TiN, which is the product of [N] dissolved in steel and N ₂ in the air inhaled by molten steel during smelting and pouring, which interacts with [Ti] in steel . In addition, during the solidification process of molten steel, other types of nitrides such as CrN and Cr ₂ N will also be produced.

In short, in the process of smelting, when the content of O, N, S, N, etc. in the steel is high, it will cause the macrostructure of the steel ingot to shrink, shrink, and even form bubbles, and may also form inclusions such as oxides and nitrides, which become cracks. The vantage point for generation and expansion, severely degrades the mechanical properties of stainless steel. Therefore, it is necessary to purify the molten steel to control the content of O, N, and S within a lower range. However, for selected raw materials, the stability of the melting crucible and the alloy melting process are the keys to controlling the impurity content.

The patent [CN200410017115.8] discloses a smelting production method of N-containing duplex stainless steel, which adopts the method of "primary smelting in electric arc furnace + refining in AOD furnace". , flow control, to control the nitrogen content in molten steel, the required refining temperature is high and the refining time is long, which is easy to cause the burning loss of some volatile elements (such as Al, etc.) under vacuum, and the degassing effect is not ideal, the gas content Couldn't go down to the desired level.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a high-purity smelting method of stainless steel for the problems such as various defects, inclusions, and component segregation that are prone to occur in the industrial smelting and production process of stainless steel, using an arc to smelt the master alloy under the protection of high-purity argon gas, AOD+LF out-of-furnace refining, VD vacuum refining, die-casting steel ingots and other processes can obtain stainless steel ingots with low impurity content.

The technical scheme that specifically realizes the present invention is: a high-purity smelting method of stainless steel, comprising the following steps:

In the first step, the fully baked scrap steel and pig iron are subjected to arc smelting:

In electric arc smelting, a large amount of slag and multiple slag flows are used to control the harmful elements in the electric furnace smelting process: P≤0.05%, Si≤0.4%, As≤0.007%, Sn≤0.004%, Sb≤0.010%, Pb≤0.001% , Bi≤0.001%, Cu≤0.20% and electric furnace tapping temperature≥1600℃;

The second step: carry out AOD+LF refining outside the furnace; decarburize by adjusting the partial pressure of oxygen in the mixed gas in the AOD furnace; realize forced deoxidation and reduction of chromium oxide by reducing slag in the LF furnace, and fill the inert gas argon Gas accelerates the reduction reaction between steel and slag;

The third step: VD vacuum refining

After the product of the second step is poured into the slag, it is transferred to the VD furnace for vacuuming, and the vacuum degree is kept below 67Pa; the vacuum is maintained for 15 minutes to ensure that the alloying elements are evenly distributed in the molten steel, and then refined, the refining temperature is ≥1600 ° C, soft blowing Argon for 15 minutes, soft blowing argon temperature ≥ 1600 ℃, hanging bag sedative;

Step 4: Pouring Process

The pouring conditions are as follows: when the temperature is greater than or equal to 1580°C, the pouring is started, the ingot body injection rate is 600m ³ /h, the riser injection rate is 280m ³ /h, and the demolding time is 8.5 hours, completing the high-purity smelting of stainless steel.

Further, the amount of large slag is scrap steel ≥ 600kg/t.

Further, in the second step AOD furnace decarburization process:

The molten steel smelted by the electric furnace is sent to the AOD furnace through the ladle, and oxygen and argon are injected into the molten pool;

When the temperature in the AOD furnace is greater than or equal to 1600 °C, add ferrochromium and ferromolybdenum in batches, measure the temperature according to the flue gas and flame, and conduct temperature measurement and sampling;

When w([C])≥0.7%, pure oxygen is used for blowing in AOD, and when the temperature is >1580℃, w[(Cr)]=20%, carbon oxide;

When w([C])≤0.7%, adopt O ₂ , Ar continuous change method for decarburization, O ₂ : Ar=(2～3): 1,

When w([C])≤0.10%, pure argon is used for blowing, and the residual oxygen in the steel and Cr ₂ O ₃ in the slag are used for further decarburization. By adjusting the ratio of argon and oxygen, O ₂ : Ar=1: (2～ 3.5) While controlling the end point C≤0.06%, reduce the oxidation of chromium;

When w([C])≤0.03%, pure argon is used for smelting for 5-15 minutes, so that the dissolved oxygen in the molten steel can continue to be decarburized to remove harmful gas impurities, and the dosage of reducing agent Fe-Si can also be reduced.

Further, add lime according to the content of silicon in the molten steel, keep [Si]=lime addition/[(3.2～4.3)G], wherein, G is the total weight of the molten steel; wherein, the yield of Cr≥96 %, the yield of Mn ≥ 88%, the total alloy yield ≥ 96%

Compared with the prior art, the present invention has the following advantages:

(1) The present invention adopts electric arc to carry out preliminary melting of molten steel under the protection of high-purity argon gas, which can effectively control the pollution in the alloy melting process and reduce the content of inclusions.

(2) In the refining process of the present invention, AOD+LF is used for out-of-furnace refining. In the decarburization period, the effect of decarburization is realized by adjusting the partial pressure of oxygen in the mixed gas; in the reduction period, forced deoxidation is realized by filling the inert gas argon to realize the reduction of chromium oxide.

(3) VD vacuum refining is adopted in the alloy smelting process of the present invention, the molten steel is fully diffused in the process, and the process of soft blowing argon can further prevent the oxidation of molten steel and reduce inclusions.

Description of drawings

Fig. 1 is the stainless steel smelting flow chart of the present invention;

Fig. 2 is the change diagram of the whole [O] of the stainless steel smelting process of the present invention;

Fig. 3 is the change diagram of inclusion size and quantity in the stainless steel smelting process of the present invention;

Fig. 4 is the microstructure diagram of the stainless steel prepared by the present invention.

Detailed ways

The present invention will be described in detail below with reference to the embodiments and accompanying drawings.

A high-purity smelting method for stainless steel, using arc equipment to smelt under the protection of inert gas atmosphere, rapidly heating and cooling through arc equipment under high vacuum, and refining outside the AOD+LF furnace and VD vacuum refining to obtain low impurity, High purity stainless steel.

The specific parameters of the embodiment are as follows:

A steel plant produces 6 furnaces of 410S stainless steel by implementing the experimental method of the present invention, and its specific components are shown in Table 1. Among them, harmful impurity elements As≤0.007%, Sn≤0.004%, Sb≤0.010%, Pb≤0.001%, Bi≤0.001%, P≤0.0020%, Al≤0.015%, central looseness <1.0 grade, sulfide≤1.0 grade, oxide ≤ grade 1.5.

The ingredients are shown in Table 1

Table 1 Stainless steel chemical composition (wt.%)

project molten steel composition C 0.018～0.035 Si 0.30～0.45 Mn 0.25～0.35 P ≤0.033 S ≤0.005 Ni ≤0.30 Cr 12.00-13.25 N ≤0.030

Example 1

The fully baked scrap steel and pig iron are subjected to arc smelting, and the use of scrap steel and pig iron as the raw material supply of stainless steel has greater flexibility, and the molten iron and stainless steel return material can be adjusted according to the fluctuation of the market nickel price and stainless steel return material price and the supply situation. proportion.

(1) Arc smelting

The vacuum electric arc furnace is used for melting. When the vacuum degree of the vacuum induction melting furnace reaches 60Pa, the high-purity argon gas is introduced to 0.1MPa, and the temperature is rapidly increased until the charge is completely melted.

In order to obtain lower tapping P, adopt the method of large slag amount (≥600kg/t) and multiple slag flow, electric furnace tapping: P≤0.05%, Si≤0.4%, electric furnace tapping temperature ≥1600℃.

In the process of electric furnace smelting, the impurity elements are analyzed and recorded. The harmful elements As≤0.007%, Sn≤0.004%, Sb≤0.010%, Pb≤0.001%, Bi≤0.001%, Cu≤0.20%.

(2) Refining outside the furnace using AOD+LF. In the decarburization period, the effect of decarburization is realized by adjusting the partial pressure of oxygen in the mixed gas; in the reduction period, forced deoxidation is realized by filling the inert gas argon to realize the reduction of chromium oxide.

The molten steel smelted by the electric furnace is sent to the AOD furnace through the ladle, and oxygen and argon are injected into the molten pool to reduce the carbon content and increase the oxidation of chromium. In order to ensure rapid decarburization, reduce chromium loss and save argon, a low argon-to-oxygen ratio should be used in the initial stage of blowing. As the carbon content decreases, the argon to oxygen ratio is increased. Ferrosilicon and lime are added, and chromium oxide is converted into metal by intensifying argon stirring to produce low-sulfur stainless steel. When the temperature in the AOD furnace is ≥1600℃, add ferrochrome and ferromolybdenum in batches, measure the temperature according to the flue gas and flame, and conduct temperature measurement and sampling. When w([C])≥0.7%, use pure oxygen blowing in AOD. When the temperature is >1580℃, w[(Cr)]=20%, carbon dioxide is firstly oxidized; when w([C])≤0.7%, the decarburization is carried out by continuous change of O ₂ and Ar(N ₂ ), and O ₂ : Ar=2:1, the decarburization efficiency is increased by 6%; when w([C])≤0.10%, pure argon is used for blowing, and the residual oxygen in the steel and Cr ₂ O ₃ in the slag are used for further decarburization. Argon oxygen ratio, O ₂ : Ar=1:2, control end point C≤0.06%, reduce the oxidation of chromium while further increasing the decarburization rate, when w([C])≤0.03%, use pure argon gas Blowing for 5 to 15 minutes, so that the dissolved oxygen in the molten steel can continue to decarburize to remove harmful gas impurities, and it can also reduce the amount of reducing agent Fe-Si, and increase the temperature of molten steel from the original process of 1-4 ° C / s to a decrease of 3 -6°C/s. Lime is added according to the silicon content in the molten steel, keeping [Si]=the amount of lime added/[(3.2-4.3)G], where G is the total weight of the molten steel. Among them, the yield of Cr is ≥96%, the yield of Mn is ≥88%, and the total alloy yield is ≥96%.

LF refining process: LF refining adds aluminum particles for pre-deoxidation, desulfurization, slag pouring, and removal of P and Si in the slag. When w[S] in molten steel is less than 10×10 ^-6 , compared with the traditional reduction of Cr ₂ O ₃ by adding FeSi, the reduction refining time is shortened by 5-17 minutes, and the desulfurization efficiency is increased to 60%-90%. At this time, [H]≤1-3ppm, [O]≤30-60ppm.

(3) VD vacuum refining

VD vacuum refining: After pouring the slag, transfer to the vacuum position to vacuumize. Keep the vacuum degree below 67Pa; keep the vacuum for 15 minutes to ensure that the alloy elements are evenly distributed in the molten steel, and then carry out refining.

(4) pouring process

When the temperature is greater than or equal to 1580℃, the pouring starts, the injection rate of the ingot body is 600m ³ /h, the injection rate of the riser is 280m ³ /h, and the demolding time is 8.5 hours, and the high-purity smelting of stainless steel is completed.

The impurity content of stainless steel smelted by the above method is obviously reduced. Table 2, Table 3 and Table 4 respectively show the detection of chemical composition, inclusion composition and low magnification structure of molten steel at different stages.

Table 2 Chemical composition of molten steel at different stages

Table 3 Compositional changes of inclusions in stainless steel

Table 4 Low magnification structure detection of stainless steel

Example 2

The fully baked scrap steel and pig iron are subjected to arc smelting, and the scrap steel and pig iron are used as the raw materials of stainless steel. The supply has great flexibility, and the molten iron and stainless steel return can be adjusted according to the fluctuation of the market nickel price and stainless steel return material price and the supply situation. ratio of material.

(1) Arc smelting

The vacuum electric arc furnace is used for melting. When the vacuum degree of the vacuum induction melting furnace reaches 60Pa, the high-purity argon gas is introduced to 0.1MPa, and the temperature is rapidly increased until the charge is completely melted.

In order to obtain lower tapping P, adopt the method of large slag amount (≥600kg/t) and multiple slag flow, electric furnace tapping: P≤0.05%, Si≤0.4%, electric furnace tapping temperature ≥1600℃.

In the process of electric furnace smelting, the impurity elements are analyzed and recorded. The harmful elements As≤0.007%, Sn≤0.004%, Sb≤0.010%, Pb≤0.001%, Bi≤0.001%, Cu≤0.20%.

(2): Refining outside the furnace using AOD+LF. In the decarburization period, the effect of decarburization is realized by adjusting the partial pressure of oxygen in the mixed gas; in the reduction period, forced deoxidation is realized by filling the inert gas argon to realize the reduction of chromium oxide.

The molten steel smelted by the electric furnace is sent to the AOD furnace through the ladle, and oxygen and argon are injected into the molten pool to reduce the carbon content and increase the oxidation of chromium. In order to ensure rapid decarburization, reduce chromium loss and save argon, a low argon-to-oxygen ratio should be used in the initial stage of blowing. As the carbon content decreases, the argon to oxygen ratio is increased. Ferrosilicon and lime are added, and chromium oxide is converted into metal by intensifying argon stirring to produce low-sulfur stainless steel. When the temperature in the AOD furnace is ≥1600℃, add ferrochrome and ferromolybdenum in batches, measure the temperature according to the flue gas and flame, and conduct temperature measurement and sampling, when w([C])≥0.7%, use pure oxygen blowing in AOD When the temperature is >1580℃, w[(Cr)]=20%, carbon dioxide is firstly oxidized; when w([C])≤0.7%, decarburization is carried out by continuous change of O ₂ and Ar, O ₂ : Ar=2.5 : 1, the decarburization efficiency is increased by 6%; when w([C])≤0.10%, pure argon is used for blowing, and the residual oxygen in the steel and Cr ₂ O ₃ in the slag are used for further decarburization. By adjusting the ratio of argon and oxygen, O ₂ : Ar=1: 2.5, control the end point C≤0.06%, while further increasing the decarburization rate, reduce the oxidation of chromium, when w([C])≤0.03%, adopt pure argon to blow for 5～ For 15 minutes, the dissolved oxygen in the molten steel can continue to be decarburized to remove harmful gas impurities, and the dosage of the reducing agent Fe-Si can also be reduced. Lime is added according to the silicon content in the molten steel, keeping [Si]=the amount of lime added/[(3.2-4.3)G], where G is the total weight of the molten steel. Among them, the yield of Cr is ≥96%, the yield of Mn is ≥88%, and the total alloy yield is ≥96%.

LF refining process: LF refining adds aluminum particles for pre-deoxidation, desulfurization, slag pouring, and removal of P and Si in the slag. When w[S] in molten steel is less than 10×10 ^-6 , compared with the traditional reduction of Cr ₂ O ₃ by adding FeSi, the reduction refining time is shortened by 5-17 minutes, and the desulfurization efficiency is increased to 60%-90%. At this time, [H]≤1-3ppm, [O]≤30-60ppm.

(3) VD vacuum refining

VD vacuum refining: After pouring the slag, transfer to the vacuum position to vacuumize. Keep the vacuum degree below 67Pa; keep the vacuum for 15 minutes to ensure that the alloy elements are evenly distributed in the molten steel, and then carry out refining.

(4) pouring process

When the temperature is greater than or equal to 1580℃, the pouring starts, the injection rate of the ingot body is 600m ³ /h, the injection rate of the riser is 280m ³ /h, and the demolding time is 8.5 hours, and the high-purity smelting of stainless steel is completed.

The impurity content of stainless steel smelted by the above method is obviously reduced. Table 5 and Table 6 respectively show the chemical composition, inclusion composition and low-magnification detection of molten steel at different stages.

Table 5 Chemical composition of molten steel at different stages

Table 6 Compositional changes of inclusions in stainless steel

Example 3

The smelting of stainless steel uses high-quality scrap steel, pig iron or molten iron, and the fully baked alloy is initially melted.

(1) Arc smelting

The vacuum electric arc furnace is used for melting. When the vacuum degree of the vacuum induction melting furnace reaches 60Pa, the high-purity argon gas is introduced to 0.1MPa, and the temperature is rapidly increased until the charge is completely melted.

In order to obtain lower tapping P, adopt the method of large slag amount (≥600kg/t) and multiple slag flow, electric furnace tapping: P≤0.05%, Si≤0.4%, electric furnace tapping temperature ≥1600℃.

In the process of electric furnace smelting, the impurity elements are analyzed and recorded. The harmful elements As≤0.007%, Sn≤0.004%, Sb≤0.010%, Pb≤0.001%, Bi≤0.001%, Cu≤0.20%.

(2) Refining outside the furnace using AOD+LF. In the decarburization period, the effect of decarburization is realized by adjusting the partial pressure of oxygen in the mixed gas; in the reduction period, forced deoxidation is realized by filling the inert gas argon to realize the reduction of chromium oxide.

The molten steel smelted by the electric furnace is sent to the AOD furnace through the ladle, and oxygen and argon are injected into the molten pool to reduce the carbon content and increase the oxidation of chromium. In order to ensure rapid decarburization, reduce chromium loss, and save argon, a low argon-to-oxygen ratio should be used in the initial stage of blowing. As the carbon content decreases, the argon to oxygen ratio is increased. Ferrosilicon and lime are added, and chromium oxide is converted into metal by intensifying argon stirring to produce stainless steel. When the temperature in the AOD furnace is ≥1600℃, add ferrochrome and ferromolybdenum in batches, measure the temperature according to the flue gas and flame, and conduct temperature measurement and sampling, when w([C])≥0.7%, use pure oxygen blowing in AOD When the temperature is more than 1580℃, w[(Cr)]=20%, the carbon is oxidized first; when w([C])≤0.7%, the decarburization is carried out by continuously changing O ₂ and Ar(N ₂ ), and the O ₂ : Ar=3:1, the decarburization efficiency is increased by 6%; when w([C])≤0.10%, pure argon is used for blowing, and the residual oxygen in the steel and Cr ₂ O ₃ in the slag are used for further decarburization. Argon oxygen ratio, O ₂ : Ar=1:3, control end point C≤0.06%, reduce the oxidation of chromium while further increasing the decarburization rate, when w([C])≤0.03%, use pure argon gas Blowing for 5 to 15 minutes can make the dissolved oxygen in the molten steel continue to decarburize to remove harmful gas impurities, and can also reduce the amount of reducing agent Fe-Si. Lime is added according to the content of silicon in the molten steel, keeping [Si]=amount of lime added/[(3.2-4.3)G], where G is the total weight of the molten steel. Among them, the yield of Cr is ≥96%, the yield of Mn is ≥88%, and the total alloy yield is ≥96%.

LF refining process: LF refining adds aluminum particles for pre-deoxidation, desulfurization, slag pouring, and removal of P and Si in the slag. When w[S] in molten steel is less than 10×10 ^-6 , compared with the traditional reduction of Cr ₂ O ₃ by adding FeSi, the reduction refining time is shortened by 5-17 minutes, and the desulfurization efficiency is increased to 60%-90%. At this time, [H]≤1-3ppm, [O]≤30-60ppm.

(3) VD vacuum refining

VD vacuum refining: After pouring the slag, transfer to the vacuum position to vacuumize. Keep the vacuum degree below 67Pa; keep the vacuum for 15 minutes to ensure that the alloy elements are evenly distributed in the molten steel, and then carry out refining.

(4) pouring process

When the temperature is greater than or equal to 1580℃, the pouring starts, the injection rate of the ingot body is 600m ³ /h, the injection rate of the riser is 280m ³ /h, and the demolding time is 8.5 hours, and the high-purity smelting of stainless steel is completed.

The impurity content of stainless steel smelted by the above method is obviously reduced. Table 7 and Table 8 respectively show the chemical composition, inclusion composition and low-magnification detection of molten steel at different stages.

Table 7 Chemical composition of molten steel in different stages

Table 8 Compositional changes of inclusions in stainless steel

Example 4

For the smelting of stainless steel, high-quality scrap steel, pig iron or molten iron, and fully baked alloys are used for initial melting.

(1) Arc smelting

The vacuum electric arc furnace is used for melting. When the vacuum degree of the vacuum induction melting furnace reaches 60Pa, the high-purity argon gas is introduced to 0.1MPa, and the temperature is rapidly increased until the charge is completely melted.

In order to obtain lower tapping P, adopt the method of large slag amount (≥600kg/t) and multiple slag flow, electric furnace tapping: P≤0.05%, Si≤0.4%, electric furnace tapping temperature ≥1600℃.

In the process of electric furnace smelting, the impurity elements are analyzed and recorded. The harmful elements As≤0.007%, Sn≤0.004%, Sb≤0.010%, Pb≤0.001%, Bi≤0.001%, Cu≤0.20%.

(2) Refining outside the furnace using AOD+LF. In the decarburization period, the effect of decarburization is realized by adjusting the partial pressure of oxygen in the mixed gas; in the reduction period, forced deoxidation is realized by filling the inert gas argon to realize the reduction of chromium oxide.

The molten steel smelted by the electric furnace is sent to the AOD furnace through the ladle, and oxygen and argon are injected into the molten pool to reduce the carbon content and increase the oxidation of chromium. In order to ensure rapid decarburization, reduce chromium loss and save argon, a low argon-to-oxygen ratio should be used in the initial stage of blowing. As the carbon content decreases, the argon to oxygen ratio is increased. Ferrosilicon and lime are added, and chromium oxide is converted into metal by intensifying argon stirring to produce low-sulfur stainless steel. When the temperature in the AOD furnace is ≥1600℃, add ferrochrome and ferromolybdenum in batches, measure the temperature according to the flue gas and flame, and conduct temperature measurement and sampling. When w([C])≥0.7%, use pure oxygen blowing in AOD. When the temperature is >1580℃, w[(Cr)]=20%, carbon dioxide is firstly oxidized; when w([C])≤0.7%, decarburization is carried out by continuous change of O ₂ and Ar, O ₂ : Ar=3 : 1, the decarburization efficiency is increased by 6%; when w([C])≤0.10%, pure argon is used for blowing, and the residual oxygen in the steel and Cr ₂ O ₃ in the slag are used for further decarburization. By adjusting the ratio of argon and oxygen, O ₂ : Ar=1:3, control the end point C≤0.06%, while further increasing the decarburization rate, reduce the oxidation of chromium, when w([C])≤0.03%, use pure argon to blow 5～ 15min, the dissolved oxygen in the molten steel can continue to decarburize to remove harmful gas impurities, and it can also reduce the amount of reducing agent Fe-Si, and the molten steel temperature can be increased from 1-4℃/s in the original process to a decrease of 3-6℃/s. s. Lime is added according to the silicon content in the molten steel, keeping [Si]=the amount of lime added/[(3.2-4.3)G], where G is the total weight of the molten steel. Among them, the yield of Cr is ≥96%, the yield of Mn is ≥88%, and the total alloy yield is ≥96%.

LF refining process: LF refining adds aluminum particles for pre-deoxidation, desulfurization, slag pouring, and removal of P and Si in the slag. When w[S] in molten steel is less than 10×10 ^-6 , compared with the traditional reduction of Cr ₂ O ₃ by adding FeSi, the reduction refining time is shortened by 5-17 minutes, and the desulfurization efficiency is increased to 60%-90%. At this time, [H]≤1-3ppm, [O]≤30-60ppm.

(3) VD vacuum refining

VD vacuum refining: After pouring the slag, transfer to the vacuum position to vacuumize. Keep the vacuum degree below 67Pa; keep the vacuum for 15 minutes to ensure that the alloy elements are evenly distributed in the molten steel, and then carry out refining.

(4) pouring process

When the temperature is greater than or equal to 1580℃, the pouring starts, the injection rate of the ingot body is 600m ³ /h, the injection rate of the riser is 280m ³ /h, and the demolding time is 8.5 hours, and the high-purity smelting of stainless steel is completed.

The impurity content of stainless steel smelted by the above method is significantly reduced. Table 9 and Table 10 respectively show the chemical composition, inclusion composition and low-magnification detection of molten steel at different stages.

Table 9 Chemical composition of molten steel at different stages

Table 10 Compositional changes of inclusions in stainless steel

Principle of the present invention: The present invention is smelted by an electric arc smelting furnace, and high-purity argon gas is introduced into the smelting process, so it can effectively prevent the alloy from being oxidized, prevent the entry of impurity elements, and reduce the burning loss of volatile elements; , In the smelting process, the content of P in the steel is reduced by methods such as large slag amount (≥600kg/t) and multiple slag flows; LF refining adds aluminum particles for pre-deoxidation. In addition, the equipment can achieve rapid heating and cooling. When refining the master alloy, stainless steel with low impurities and high purity can be obtained. The smelting and preparation method of stainless steel is mainly used in the production of stainless steel in the industrial production process. Three-step smelting of stainless steel through electric furnace smelting→AOD+LF refining outside the furnace→VD vacuum refining→die casting ingot Burning loss of elements; use AOD+LF out-of-furnace refining and deoxidation, adjust the partial pressure of argon and oxygen in molten steel, and remove P, Si and other inclusions; use VD vacuum refining to further eliminate inclusions in molten steel, so as to achieve high-purity smelting .

Claims (5)

1. The high-purity smelting method of stainless steel is characterized by comprising the following steps of:

firstly, carrying out electric arc smelting on the fully baked scrap steel and pig iron:

in the electric arc smelting, a large amount of slag is adopted, the slag is flowed for many times, harmful elements P in the electric furnace smelting process are controlled to be less than or equal to 0.05 percent, Si is less than or equal to 0.4 percent, As is less than or equal to 0.007 percent, Sn is less than or equal to 0.004 percent, Sb is less than or equal to 0.010 percent, Pb is less than or equal to 0.001 percent, Bi is less than or equal to 0.001 percent, Cu is less than or equal to 0.20;

the second step is that: performing AOD + LF external refining; decarbonizing in an AOD furnace by adjusting the partial pressure of oxygen in the mixed gas; forced deoxidation and reduction of chromium oxide are realized in the LF furnace through reducing slag, and inert gas argon is filled to accelerate the reduction reaction between steel and slag; in the decarburization process of the AOD furnace:

the molten steel smelted by the electric furnace is sent into the AOD furnace through a ladle, and oxygen and argon are blown into a molten pool;

when the temperature in the AOD furnace is more than or equal to 1600 ℃, ferrochromium and ferromolybdenum are added in batches, and temperature measurement sampling is carried out according to the temperature measured by flue gas and flame;

when w ([ C ]) is more than or equal to 0.7%, adopting pure oxygen blowing at the AOD, and when the temperature is more than 1580 ℃, w [ (Cr) ] =20%, and oxidizing carbon;

when w ([ C ]]) Less than 0.7%, using O₂Ar decarburization in a continuously varying manner, O₂：Ar=（2~3）：1，

When w ([ C ]]) Less than or equal to 0.10 percent, blowing with pure argon, using residual oxygen in steel and Cr in slag₂O₃Further decarbonizing, adjusting the ratio of argon to oxygen, O₂：Ar=1：（2~3.5）

When w (C) is less than or equal to 0.03 percent, pure argon is adopted for blowing for 5 ~ 15min, so that the dissolved oxygen in the molten steel is continuously decarbonized to remove harmful gas impurities;

the third step: VD vacuum refining

Transferring the product obtained in the second step to a VD furnace for vacuumizing after deslagging, and keeping the vacuum degree below 67 Pa; keeping the vacuum for 15 minutes to ensure that the alloy elements are uniformly distributed in the molten steel, and then refining, wherein the refining temperature is more than or equal to 1600 ℃, the soft argon blowing temperature is more than or equal to 1600 ℃, and the ladle is calmed;

the fourth step: pouring process

The pouring conditions are specifically as follows: and when the temperature is more than or equal to 1580 ℃, pouring is started, the ingot casting speed is 600 m/h, the riser casting speed is 280 m/h, and the demolding time is 8.5 hours, so that the high-purity smelting of the stainless steel is completed.

2. The high purity smelting method of stainless steel according to claim 1, wherein the amount of the large slag in the first step is more than or equal to 600kg/t of scrap steel.

3. The high-purity smelting method of stainless steel according to claim 1, wherein in the second step of AOD furnace decarburization, lime is added according to the content of silicon in the molten steel, and the addition amount of [ Si ] = lime/[ (3.2 ~ 4.3.3) G ] is kept, wherein G is the total weight of the molten steel.

4. The high purity smelting method of stainless steel according to claim 1, wherein the LF refining process: adding aluminum particles for pre-deoxidation, desulfurization, deslagging and removing P, Si in deslagging in LF refining; w S in molten steel]＜10×10^-6，[H]≤1-3ppm，[O]≤30-60ppm。

5. The high purity smelting method of stainless steel according to claim 1, wherein in the second step of AOD + LF furnace refining, the AOD decarburization control end point C is less than or equal to 0.06% to satisfy the C component.

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