CN108330245B - High-purity smelting method for stainless steel - Google Patents

High-purity smelting method for stainless steel Download PDF

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CN108330245B
CN108330245B CN201810132857.7A CN201810132857A CN108330245B CN 108330245 B CN108330245 B CN 108330245B CN 201810132857 A CN201810132857 A CN 201810132857A CN 108330245 B CN108330245 B CN 108330245B
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陈�光
冯亚亚
卜春成
徐驰
潘曦
苏翔
韩娣娟
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Nanjing Tech University
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/005—Manufacture of stainless steel
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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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

High-purity smelting method for stainless steel
Technical Field
The invention discloses a high-purity smelting method of stainless steel, and belongs to the field of stainless steel preparation.
Background
During the smelting of stainless steel, the endogenous impurities are mainly deoxidized and alloyed, and the deoxidizer (Al, FeSi, SiMn, etc.) added into the molten steel is oxidized to produce Al2O3、SiO2And MgO. Al2O3、SiO2-MnO、Al2O3-SiO2-MnO and other complex deoxidation products; the alloying elements (Cr, Ti, Si, Mn) are partially oxidized to FeO. Cr2O3、SiO2-Cr2O3、A12O3-Cr2O3、Cr2O3-MnS、TiO2And the like; cooling, solidifying and crystallizing molten steelIn the process, secondary deoxidation products and the like are also formed due to temperature drop and local component segregation. When these products have no time to be discharged from the molten steel, they remain in the steel to form endogenous inclusions.
Al has stronger deoxidizing capacity, but the deoxidizing product is extracted from Al2O3The performance of stainless steel with most grades is adversely affected, so the use in the stainless steel smelting process is greatly limited. It is found from relevant research at home and abroad that when the deoxidation, desulfurization and dephosphorization effects of stainless steel liquid are comprehensively considered, a composite refining agent containing alkaline earth metal elements (barium, calcium and magnesium), rare earth and the like can be selected, and the composite refining agent not only has strong deoxidation, desulfurization and reduction dephosphorization capabilities, but also has high floating speed of a deoxidation product and almost no residue in steel. Unfortunately, the research on the aspect is still in the laboratory research stage, and the research is rarely applied and popularized in the practical production of stainless steel.
The foreign impurities in the stainless steel finished product are large-scale impurities brought into molten steel by scouring and erosion of refractory materials, slag mixed into the molten steel (such as steel slag mixed out in the AOD tapping process), secondary oxidation in the molten steel transportation and pouring processes, and the like in the smelting and pouring processes.
Nitrides in stainless steel liquid mainly appear in the form of TiN, which is [ N ] dissolved in steel]And N in the process of smelting and pouring, the molten steel is sucked into the air2And in steel [ Ti ]]The product of the action. In addition, CrN and Cr may be present in the molten steel during solidification2N, etc. other types of nitrides.
In conclusion, in the smelting process, when the content of O, N, S, N and the like in steel is higher, shrinkage cavities and shrinkage porosity of a steel ingot macrostructure can be caused, even bubbles are formed, and impurities such as oxides and nitrides can be formed, so that the impurities become favorable positions for generating and expanding cracks, and the mechanical property of the stainless steel is seriously reduced. Therefore, the molten steel needs to be purified, and the O, N, S content is controlled in a lower range. However, for the selected raw materials, the stability of the melting crucible and the alloy melting process are critical to controlling the impurity content.
The patent [ CN200410017115.8] discloses a smelting production method of N-containing duplex stainless steel, which adopts a mode of 'electric arc furnace primary smelting + AOD furnace refining', controls the content of nitrogen in molten steel by controlling the time and flow of nitrogen blown into the molten steel during the smelting of the AOD furnace, has high required refining temperature and long refining time, is easy to cause burning loss of volatile elements (such as Al and the like) under certain vacuum, has unsatisfactory degassing effect, and can not reduce the gas content to the expected level.
Disclosure of Invention
The invention aims to solve the problems of various defects, impurities, composition segregation and the like easily occurring in the industrial smelting production process of stainless steel, and provides a high-purity smelting method of stainless steel.
The technical scheme for concretely realizing the invention is as follows: a high-purity smelting method for stainless steel comprises the following steps:
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;
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: when the temperature is more than or equal to 1580 ℃, the casting is started, and the ingot body casting speed is 600m3H, riser injection speed 280m3And h, demoulding for 8.5 hours to finish the high-purity smelting of the stainless steel.
Furthermore, the large slag amount is more than or equal to 600kg/t of scrap steel.
Further, in the second step of AOD furnace decarburization process:
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 percent, adopting pure oxygen blowing at AOD, and when the temperature is more than 1580 ℃, changing w (Cr) to 20 percent, and oxidizing carbon;
when w ([ C ]]) Less than or equal to 0.7 percent, adopting 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 by adjusting the argon-oxygen ratio, O2: ar is 1: (2-3.5) controlling the end point C to be less than or equal to 0.06%, and simultaneously reducing the oxidation of chromium;
when w (C) is less than or equal to 0.03 percent, pure argon is adopted for blowing for 5-15 min, so that the dissolved oxygen in the molten steel is continuously decarbonized to remove harmful gas impurities, and the dosage of a reducing agent Fe-Si can be reduced
Further, lime is added according to the content of silicon in the molten steel, and the addition amount of [ Si ] ═ lime/[ (3.2-4.3) G ] is kept, wherein G is the total weight of the molten steel; wherein the yield of Cr is more than or equal to 96 percent, the yield of Mn is more than or equal to 88 percent, and the total alloy yield is more than or equal to 96 percent
Compared with the prior art, the invention has the following advantages:
(1) the invention adopts electric arc to carry out primary smelting of molten steel under the protection of high-purity argon, can effectively control pollution in the process of melting alloy and reduce the content of impurities.
(2) In the refining process, the AOD and LF external refining is adopted. In the decarburization period, the partial pressure of oxygen in the mixed gas is adjusted to realize the decarburization function; in the reduction period, the forced deoxidation is realized by filling inert gas argon, and the reduction of the chromium oxide is realized.
(3) According to the invention, VD vacuum refining is adopted in the alloy smelting process, molten steel is fully diffused in the process, and meanwhile, the oxidation of the molten steel can be further prevented and inclusions can be reduced in the soft argon blowing process.
Drawings
FIG. 1 is a flow diagram of stainless steel melting according to the present invention;
FIG. 2 is a diagram showing the change of the total [ O ] in the stainless steel smelting process according to the present invention;
FIG. 3 is a graph showing the change in size and amount of inclusions in a stainless steel smelting process according to the present invention;
FIG. 4 is a structural diagram of stainless steel produced by the present invention.
Detailed Description
The present invention will be described in detail below with reference to examples and the accompanying drawings.
A high-purity smelting method for stainless steel includes such steps as smelting in arc equipment under the protection of inertial gas, quickly heating and cooling in high vacuum, and performing AOD + LF external refining and VD vacuum refining to obtain high-purity stainless steel with low impurities.
The specific parameters of the examples are as follows:
the specific components of 6 furnaces 410S stainless steel produced by a certain steel plant by implementing the experimental method of the invention are shown in Table 1. Wherein, the harmful impurity element 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, P is less than or equal to 0.0020 percent, Al is less than or equal to 0.015 percent, the center porosity is less than 1.0 grade, sulfide is less than or equal to 1.0 grade, and oxide is less than or equal.
The components are shown in Table 1
Table 1 stainless steel chemical composition (wt.%)
Item Composition of molten steel
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 electric arc smelting, the scrap steel and pig iron are used as raw materials of stainless steel for supply, the flexibility is high, and the proportion of molten iron and stainless steel return can be adjusted according to fluctuation of the nickel price and the stainless steel return price in the market and supply conditions.
(1) Electric arc smelting
And (3) smelting by adopting a vacuum arc furnace, and when the vacuum degree of the vacuum induction smelting furnace reaches 60Pa, rapidly heating to completely melt the furnace burden when high-purity argon is introduced to 0.1 MPa.
In order to obtain lower tapping P, a method of large slag amount (more than or equal to 600kg/t) and multiple slag flowing is adopted, and electric furnace tapping: p is less than or equal to 0.05 percent, Si is less than or equal to 0.4 percent, and the tapping temperature of the electric furnace is more than or equal to 1600 ℃.
Impurity elements are analyzed and recorded in the electric furnace smelting process, harmful elements such As less than or equal to 0.007 percent of As, less than or equal to 0.004 percent of Sn, less than or equal to 0.010 percent of Sb, less than or equal to 0.001 percent of Pb, less than or equal to 0.001 percent of Bi and less than or equal to 0.20 percent of Cu.
(2) And performing secondary refining by adopting AOD and LF. In the decarburization period, the partial pressure of oxygen in the mixed gas is adjusted to realize the decarburization function; in the reduction period, the forced deoxidation is realized by filling inert gas argon, and the reduction of the chromium oxide is realized.
The molten steel smelted by the electric furnace is sent into the AOD furnace through a ladle, oxygen and argon are blown into a molten pool, the carbon content is reduced, and the oxidation of chromium is increased. In order to ensure quick decarburization, reduce chromium loss and save argon, a low argon-oxygen ratio is adopted at the initial stage of blowing. The argon-oxygen ratio is increased as the carbon content decreases. Adding ferrosilicon and lime, and converting chromium oxide into metal by enhancing argon blowing stirring to produce the low-sulfur stainless steel. When the temperature in the AOD furnace is more than or equal to 1600 ℃, ferrochromium and ferromolybdenum are added in batches, temperature measurement and sampling are carried out according to the temperature measured by flue gas and flame, and when w ([ C ])]) When the content is more than or equal to 0.7 percent, pure oxygen blowing is adopted at the AOD, and the temperature is higher>At 1580 deg.C, w [ (Cr)]First, carbon is oxidized, 20%; when w ([ C ]]) Less than or equal to 0.7 percent, adopting O2、Ar(N2) Decarburization in a continuously varying manner, O2: ar is 2: 1, the decarburization efficiency is improved by 6 percent; 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 by adjusting the argon-oxygen ratio, O2: ar is 1: 2, controlling the end point C to be less than or equal to 0.06 percent, further improving the decarburization speed and simultaneously reducing the oxidation of chromium when w ([ C ]]) When the temperature is less than or equal to 0.03 percent, pure argon is adopted for blowing for 5-15 min, so that the dissolved oxygen in the molten steel is continuously decarburized to remove harmful gas impurities, the dosage of a reducing agent Fe-Si can be reduced, and the temperature of the molten steel is reduced by 3-6 ℃/s from the original process by increasing 1-4 ℃/s. Adding lime according to the content of silicon in the molten steel and keeping the [ Si ]]Addition of ═ lime/[ (3.2-4.3) G]Wherein G is the total weight of the molten steel. Wherein the yield of Cr is more than or equal to 96 percent, and the yield of Mn is more than or equal to 88 percentThe total alloy yield is more than or equal to 96 percent.
And LF refining: and adding aluminum particles for pre-deoxidation, desulfurization, deslagging and removing P, Si in slag in LF refining. W S in molten steel]＜10×10-6Reducing Cr with FeSi added conventionally2O3Compared with the prior art, the reduction refining time is shortened by 5-17 min, and the desulfurization efficiency is improved to 60% -90%. At this time, [ H ]]≤1-3ppm，[O]≤30-60ppm。
(3) VD vacuum refining
VD vacuum refining: and transferring to a vacuum position for vacuumizing after deslagging. 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;
(4) pouring process
When the temperature is more than or equal to 1580 ℃, the casting is started, and the ingot body casting speed is 600m3H, riser injection speed 280m3And h, demoulding for 8.5 hours to finish the high-purity smelting of the stainless steel.
The impurity content of the stainless steel smelted by the method is obviously reduced, and the chemical components, inclusion components and macrostructure of molten steel in different stages are respectively detected in tables 2, 3 and 4.
TABLE 2 chemical composition of molten steel at different stages
Figure BDA0001575420460000061
TABLE 3 compositional changes of inclusions in stainless steels
Figure BDA0001575420460000062
TABLE 4 detection of macrostructures in stainless steel
Figure BDA0001575420460000063
Example 2
The fully baked scrap steel and pig iron are subjected to electric arc smelting, the scrap steel and the pig iron are used as raw materials of the stainless steel, the supply has high flexibility, and the proportion of molten iron and the stainless steel return can be adjusted according to the fluctuation of the nickel price and the stainless steel return price in the market and the supply condition.
(1) Electric arc smelting
And (3) smelting by adopting a vacuum arc furnace, and when the vacuum degree of the vacuum induction smelting furnace reaches 60Pa, rapidly heating to completely melt the furnace burden when high-purity argon is introduced to 0.1 MPa.
In order to obtain lower tapping P, a method of large slag amount (more than or equal to 600kg/t) and multiple slag flowing is adopted, and electric furnace tapping: p is less than or equal to 0.05 percent, Si is less than or equal to 0.4 percent, and the tapping temperature of the electric furnace is more than or equal to 1600 ℃.
Impurity elements are analyzed and recorded in the electric furnace smelting process, harmful elements such As less than or equal to 0.007 percent of As, less than or equal to 0.004 percent of Sn, less than or equal to 0.010 percent of Sb, less than or equal to 0.001 percent of Pb, less than or equal to 0.001 percent of Bi and less than or equal to 0.20 percent of Cu.
(2): and performing secondary refining by adopting AOD and LF. In the decarburization period, the partial pressure of oxygen in the mixed gas is adjusted to realize the decarburization function; in the reduction period, the forced deoxidation is realized by filling inert gas argon, and the reduction of the chromium oxide is realized.
The molten steel smelted by the electric furnace is sent into the AOD furnace through a ladle, oxygen and argon are blown into a molten pool, the carbon content is reduced, and the oxidation of chromium is increased. In order to ensure quick decarburization, reduce chromium loss and save argon, a low argon-oxygen ratio is adopted at the initial stage of blowing. The argon-oxygen ratio is increased as the carbon content decreases. Adding ferrosilicon and lime, and converting chromium oxide into metal by enhancing argon blowing stirring to produce the low-sulfur stainless steel. When the temperature in the AOD furnace is more than or equal to 1600 ℃, ferrochromium and ferromolybdenum are added in batches, temperature measurement and sampling are carried out according to the temperature measured by flue gas and flame, and when w ([ C ])]) When the content is more than or equal to 0.7 percent, pure oxygen blowing is adopted at the AOD, and the temperature is higher>At 1580 deg.C, w [ (Cr)]First, carbon is oxidized, 20%; when w ([ C ]]) Less than or equal to 0.7 percent, adopting O2Ar decarburization in a continuously varying manner, O2: ar ═ 2.5: 1, the decarburization efficiency is improved by 6 percent; 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 by adjusting the argon-oxygen ratio, O2: ar is 1: 2.5, controlling the end point C to be less than or equal to 0.06 percent, and further improving the decarburization speedWhile reducing the oxidation of chromium when w ([ C ]]) When the content is less than or equal to 0.03 percent, pure argon is adopted for blowing for 5-15 min, so that the dissolved oxygen in the molten steel is continuously decarbonized to remove harmful gas impurities, and the dosage of a reducing agent Fe-Si can be reduced. Adding lime according to the content of silicon in the molten steel and keeping the [ Si ]]Addition of ═ lime/[ (3.2-4.3) G]Wherein G is the total weight of the molten steel. Wherein the yield of Cr is more than or equal to 96%, the yield of Mn is more than or equal to 88%, and the total alloy yield is more than or equal to 96%.
And LF refining: and adding aluminum particles for pre-deoxidation, desulfurization, deslagging and removing P, Si in slag in LF refining. W S in molten steel]＜10×10-6Reducing Cr with FeSi added conventionally2O3Compared with the prior art, the reduction refining time is shortened by 5-17 min, and the desulfurization efficiency is improved to 60% -90%. At this time, [ H ]]≤1-3ppm，[O]≤30-60ppm。
(3) VD vacuum refining
VD vacuum refining: and transferring to a vacuum position for vacuumizing after deslagging. 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;
(4) pouring process
When the temperature is more than or equal to 1580 ℃, the casting is started, and the ingot body casting speed is 600m3H, riser injection speed 280m3And h, demoulding for 8.5 hours to finish the high-purity smelting of the stainless steel.
The impurity content of the stainless steel smelted by the method is obviously reduced, and the chemical components, inclusion components and macrostructure of molten steel in different stages are respectively detected in tables 5 and 6.
TABLE 5 chemical composition of molten steel at different stages
Figure BDA0001575420460000081
TABLE 6 compositional changes of inclusions in stainless steels
Figure BDA0001575420460000082
Example 3
The stainless steel is smelted by selecting high-quality scrap steel, pig iron or molten iron and performing primary melting on the fully baked alloy.
(1) Electric arc smelting
And (3) smelting by adopting a vacuum arc furnace, and when the vacuum degree of the vacuum induction smelting furnace reaches 60Pa, rapidly heating to completely melt the furnace burden when high-purity argon is introduced to 0.1 MPa.
In order to obtain lower tapping P, a method of large slag amount (more than or equal to 600kg/t) and multiple slag flowing is adopted, and electric furnace tapping: p is less than or equal to 0.05 percent, Si is less than or equal to 0.4 percent, and the tapping temperature of the electric furnace is more than or equal to 1600 ℃.
Impurity elements are analyzed and recorded in the electric furnace smelting process, harmful elements such As less than or equal to 0.007 percent of As, less than or equal to 0.004 percent of Sn, less than or equal to 0.010 percent of Sb, less than or equal to 0.001 percent of Pb, less than or equal to 0.001 percent of Bi and less than or equal to 0.20 percent of Cu.
(2) And performing secondary refining by adopting AOD and LF. In the decarburization period, the partial pressure of oxygen in the mixed gas is adjusted to realize the decarburization function; in the reduction period, the forced deoxidation is realized by filling inert gas argon, and the reduction of the chromium oxide is realized.
The molten steel smelted by the electric furnace is sent into the AOD furnace through a ladle, oxygen and argon are blown into a molten pool, the carbon content is reduced, and the oxidation of chromium is increased. In order to ensure quick decarburization, reduce chromium loss and save argon, a low argon-oxygen ratio is adopted at the initial stage of blowing. The argon-oxygen ratio is increased as the carbon content decreases. Adding ferrosilicon and lime, and converting chromium oxide into metal by reinforced argon blowing stirring to produce stainless steel. When the temperature in the AOD furnace is more than or equal to 1600 ℃, ferrochromium and ferromolybdenum are added in batches, temperature measurement and sampling are carried out according to the temperature measured by flue gas and flame, and when w ([ C ])]) When the content is more than or equal to 0.7 percent, pure oxygen blowing is adopted at the AOD, and the temperature is higher>At 1580 deg.C, w [ (Cr)]First, carbon is oxidized, 20%; when w ([ C ]]) Less than or equal to 0.7 percent, adopting O2、Ar(N2) Decarburization in a continuously varying manner, O2: ar is 3: 1, the decarburization efficiency is improved by 6 percent; 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 by adjusting the argon-oxygen ratio, O2: ar is 1: 3, controlling the end point C to be less than or equal to 0.06 percent, further improving the decarburization speed and reducing the oxygen of chromiumWhen w ([ C ]]) When the content is less than or equal to 0.03 percent, pure argon is adopted for blowing for 5-15 min, so that the dissolved oxygen in the molten steel is continuously decarbonized to remove harmful gas impurities, and the dosage of a reducing agent Fe-Si can be reduced. Adding lime according to the content of silicon in the molten steel and keeping the [ Si ]]Addition of ═ lime/[ (3.2-4.3) G]Wherein G is the total weight of the molten steel. Wherein the yield of Cr is more than or equal to 96%, the yield of Mn is more than or equal to 88%, and the total alloy yield is more than or equal to 96%.
And LF refining: and adding aluminum particles for pre-deoxidation, desulfurization, deslagging and removing P, Si in slag in LF refining. W S in molten steel]＜10×10-6Reducing Cr with FeSi added conventionally2O3Compared with the prior art, the reduction refining time is shortened by 5-17 min, and the desulfurization efficiency is improved to 60% -90%. At this time, [ H ]]≤1-3ppm，[O]≤30-60ppm。
(3) VD vacuum refining
VD vacuum refining: and transferring to a vacuum position for vacuumizing after deslagging. 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.
(4) Pouring process
When the temperature is more than or equal to 1580 ℃, the casting is started, and the ingot body casting speed is 600m3H, riser injection speed 280m3H, demoulding for 8.5 hours to finish the high-purity smelting of the stainless steel
The impurity content of the stainless steel smelted by the method is obviously reduced, and the chemical components, inclusion components and macrostructure of molten steel in different stages are respectively detected in tables 7 and 8.
TABLE 7 chemical composition of molten steel at different stages
Figure BDA0001575420460000101
TABLE 8 compositional changes of inclusions in stainless steels
Figure BDA0001575420460000102
Example 4
The stainless steel is smelted by selecting dried high-quality scrap steel, pig iron or molten iron and performing primary melting on fully baked alloy.
(1) Electric arc smelting
And (3) smelting by adopting a vacuum arc furnace, and when the vacuum degree of the vacuum induction smelting furnace reaches 60Pa, rapidly heating to completely melt the furnace burden when high-purity argon is introduced to 0.1 MPa.
In order to obtain lower tapping P, a method of large slag amount (more than or equal to 600kg/t) and multiple slag flowing is adopted, and electric furnace tapping: p is less than or equal to 0.05 percent, Si is less than or equal to 0.4 percent, and the tapping temperature of the electric furnace is more than or equal to 1600 ℃.
Impurity elements are analyzed and recorded in the electric furnace smelting process, harmful elements such As less than or equal to 0.007 percent of As, less than or equal to 0.004 percent of Sn, less than or equal to 0.010 percent of Sb, less than or equal to 0.001 percent of Pb, less than or equal to 0.001 percent of Bi and less than or equal to 0.20 percent of Cu.
(2) And performing secondary refining by adopting AOD and LF. In the decarburization period, the partial pressure of oxygen in the mixed gas is adjusted to realize the decarburization function; in the reduction period, the forced deoxidation is realized by filling inert gas argon, and the reduction of the chromium oxide is realized.
The molten steel smelted by the electric furnace is sent into the AOD furnace through a ladle, oxygen and argon are blown into a molten pool, the carbon content is reduced, and the oxidation of chromium is increased. In order to ensure quick decarburization, reduce chromium loss and save argon, a low argon-oxygen ratio is adopted at the initial stage of blowing. The argon-oxygen ratio is increased as the carbon content decreases. Adding ferrosilicon and lime, and converting chromium oxide into metal by enhancing argon blowing stirring to produce the low-sulfur stainless steel. When the temperature in the AOD furnace is more than or equal to 1600 ℃, ferrochromium and ferromolybdenum are added in batches, temperature measurement and sampling are carried out according to the temperature measured by flue gas and flame, and when w ([ C ])]) When the content is more than or equal to 0.7 percent, pure oxygen blowing is adopted at the AOD, and the temperature is higher>At 1580 deg.C, w [ (Cr)]First, carbon is oxidized, 20%; when w ([ C ]]) Less than or equal to 0.7 percent, adopting O2Ar decarburization in a continuously varying manner, O2: ar is 3: 1, the decarburization efficiency is improved by 6 percent; 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 by adjusting the argon-oxygen ratio, O2: ar is 1: 3, controlling the end point C to be less than or equal to 0.06 percent, further improving the decarburization speed and simultaneously reducing the oxidation of chromium when w ([ C ]]) When the content is less than or equal to 0.03%, the method is adoptedBlowing pure argon for 5-15 min to remove harmful gas impurities by continuously decarbonizing dissolved oxygen in the molten steel, and reducing the dosage of a reducing agent Fe-Si, wherein the temperature of the molten steel is increased by 1-4 ℃/s from the original process, and is reduced by 3-6 ℃/s. Adding lime according to the content of silicon in the molten steel and keeping the [ Si ]]Addition of ═ lime/[ (3.2-4.3) G]Wherein G is the total weight of the molten steel. Wherein the yield of Cr is more than or equal to 96%, the yield of Mn is more than or equal to 88%, and the total alloy yield is more than or equal to 96%.
And LF refining: and adding aluminum particles for pre-deoxidation, desulfurization, deslagging and removing P, Si in slag in LF refining. W S in molten steel]＜10×10-6Reducing Cr with FeSi added conventionally2O3Compared with the prior art, the reduction refining time is shortened by 5-17 min, and the desulfurization efficiency is improved to 60% -90%. At this time, [ H ]]≤1-3ppm，[O]≤30-60ppm。
(3) VD vacuum refining
VD vacuum refining: and transferring to a vacuum position for vacuumizing after deslagging. 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.
(4) Pouring process
When the temperature is more than or equal to 1580 ℃, the casting is started, and the ingot body casting speed is 600m3H, riser injection speed 280m3H, demoulding for 8.5 hours to finish the high-purity smelting of the stainless steel
The impurity content of the stainless steel smelted by the method is obviously reduced, and the chemical components, inclusion components and macrostructure of molten steel in different stages are respectively detected in tables 9 and 10.
TABLE 9 chemical composition of molten steel at different stages
Figure BDA0001575420460000121
TABLE 10 compositional changes of inclusions in stainless steels
Figure BDA0001575420460000122
The principle of the invention is as follows: the invention carries out smelting by the electric arc smelting furnace, 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 steel is reduced by methods of large slag amount (more than or equal to 600kg/t), multiple slag flowing and the like in the smelting process; and adding aluminum particles for pre-deoxidation in LF refining. In addition, the equipment can realize rapid temperature rise and temperature reduction, low-impurity high-purity stainless steel can be obtained when mother alloy refining is carried out, and the smelting preparation method of the stainless steel is mainly applied to the production of the stainless steel in the industrial production process. Stainless steel is smelted in three steps of electric furnace smelting → AOD + LF external refining → VD vacuum refining → die casting steel ingot, namely, the electric furnace is adopted for melting under the protection of high-purity argon, so that the pollution in the alloy melting process can be effectively controlled, and the burning loss of volatile elements is reduced; performing secondary refining and deoxidation by adopting AOD and LF, adjusting partial pressure of argon and oxygen in molten steel, and removing P, Si and other impurities; and VD vacuum refining is adopted to further eliminate inclusions in the molten steel, so that high-purity purification smelting is realized.

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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