CN108546867B - Smelting method of casting blank of duplex stainless steel - Google Patents

Smelting method of casting blank of duplex stainless steel Download PDF

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CN108546867B
CN108546867B CN201810344460.4A CN201810344460A CN108546867B CN 108546867 B CN108546867 B CN 108546867B CN 201810344460 A CN201810344460 A CN 201810344460A CN 108546867 B CN108546867 B CN 108546867B
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smelting
nitrogen
stainless steel
casting blank
duplex stainless
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CN108546867A (en
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邢长军
吴林
姚春发
宁小智
杨忠民
陈颖
王慧敏
李昭东
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ADVANCED STEEL TECHNOLOGY Co Ltd
Central Iron and Steel Research Institute
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Central Iron and Steel Research Institute
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C22C33/06—Making ferrous alloys by melting using master alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/006—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals with use of an inert protective material including the use of an inert gas
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/04—Refining by applying a vacuum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/05—Refining by treating with gases, e.g. gas flushing also refining by means of a material generating gas in situ
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/16—Remelting metals
    • C22B9/18—Electroslag remelting
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    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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Abstract

The invention discloses a smelting method of a casting blank of a duplex stainless steel, belongs to the technical field of stainless steel smelting, and solves the problem that the casting blank of the duplex stainless steel in the prior art is easy to have the defects of looseness, shrinkage cavity, subcutaneous air holes and the like. The smelting method adopts a smelting process combining vacuum smelting and atmosphere protection electroslag remelting, wherein the partial pressure of argon is controlled to be higher than atmospheric pressure in the vacuum smelting process, and the pressure of argon is controlled to be higher than atmospheric pressure in the electroslag remelting process. The smelting method can be used for smelting duplex stainless steel.

Description

Smelting method of casting blank of duplex stainless steel
Technical Field
The invention relates to a stainless steel smelting technology, and particularly provides a method for smelting a casting blank of duplex stainless steel.
Background
The duplex stainless steel has an austenite-ferrite duplex structure, has the characteristics of high strength, good toughness, excellent pitting corrosion resistance and excellent stress corrosion resistance, and becomes one of important steel types for stainless steel development in the future.
In the prior art, the content of alloy elements in the duplex stainless steel is high, and particularly, the content of nitrogen elements is more than 1500-3000ppm, and even higher. The nitrogen is added by adopting a high-pressure nitrogen increasing mode or a direct high-nitrogen alloy mode. However, in any of the above nitrogen increasing methods, the metallurgical quality of the duplex stainless steel is difficult to control, and defects such as porosity, shrinkage cavity, and subcutaneous porosity are likely to occur.
The Chinese patent application CN102888550A discloses a method for smelting high-purity high-nitrogen duplex stainless steel, which carries out smelting of the high-purity high-nitrogen duplex stainless steel by a composite process of vacuum melting, liquid steel nitrogen charging and refining, and adjusts the nitrogen content of the high-nitrogen duplex stainless steel by controlling the nitrogen pressure and the nitrogen charging and refining time during nitrogen charging. The nitrogen is filled in the technical core of nitrogen increase, so that the problem of production cost is solved, but the problems of high control difficulty, unstable metallurgical quality and the like exist.
Disclosure of Invention
In view of the above analysis, the present invention aims to provide a casting blank of duplex stainless steel and a smelting method thereof, which solve the problem that the casting blank of duplex stainless steel in the prior art is prone to have defects such as porosity, shrinkage cavity and subcutaneous air hole.
The purpose of the invention is mainly realized by the following technical scheme:
the invention provides a smelting method of a duplex stainless steel casting blank, which adopts a smelting process combining vacuum smelting and atmosphere protection electroslag remelting, wherein the partial pressure of argon is controlled to be higher than atmospheric pressure in the vacuum smelting process, and the pressure of the argon is controlled to be higher than atmospheric pressure in the electroslag remelting process.
Further, the method comprises the following steps:
step 1: calculating the limit nitrogen content under normal pressure according to the target composition of the duplex stainless steel casting blank, multiplying the limit nitrogen content under normal pressure by a corrected value to obtain the actual added mass percentage of the nitrogen element, wherein the corrected value is 0.7-0.9, and calculating the added amount of the ferrochrome nitride alloy according to the actual added mass percentage of the nitrogen element;
step 2: preparing a smelting material according to the composition of the duplex stainless steel casting blank by mass percent and the actually added mass percent of the N element, and carrying out vacuum primary smelting on the smelting material to obtain molten steel;
and step 3: refining the molten steel;
and 4, step 4: pressurizing and filling argon gas above the atmospheric pressure;
and 5: adding a raw material for improving the partial pressure of argon and calculating the obtained ferrochrome nitride according to the actual adding weight percentage of nitrogen content;
step 6: controlling the temperature of the molten steel to be higher than the melting point of the alloy, carrying out casting molding on the molten steel, and naturally cooling to obtain an ingot mold;
and 7: and carrying out nitrogen protection electroslag remelting on the ingot mold.
And 8: and cooling and solidifying the molten steel obtained after the electroslag remelting to obtain a duplex stainless steel casting blank.
Further, in step 1, the calculation formula of the limit nitrogen content under normal pressure is as follows:
Figure BDA0001631463340000021
Figure BDA0001631463340000031
in the formula (I), the compound is shown in the specification,
Figure BDA0001631463340000032
is nitrogen partial pressure, MPa, p0Is the standard atmospheric pressure, MPa,
Figure BDA0001631463340000033
the activity coefficient of nitrogen in the molten steel; t is the melting point of the alloy, K; omega m]Is the mass percentage of an alloy element m, wherein m is at least one of Cr, Ni, Mo, Mn, C, Si, P, S, Al, Ti, V, W and O; % N is the limiting nitrogen content at atmospheric pressure.
Further, in step 2, the vacuum primary refining comprises the following steps: and (3) putting the smelting material into a high-nitrogen steel multifunctional induction furnace, vacuumizing until the vacuum degree is less than 15Pa, and heating the smelting material until a molten pool appears to obtain molten steel.
Further, in the process of heating the smelting materials until a molten pool appears, the initial power of the high-nitrogen steel multifunctional induction furnace is 30KW-40KW, and the power is increased to 70KW-80KW at the rate of increasing 5KW every 5 min.
Further, in the step 3, a high-nitrogen steel multifunctional induction furnace is adopted for refining, the refining power is 40KW-50KW, the refining time is 30 min-40 min, and the vacuum degree is less than or equal to 5 Pa.
Further, in step 4, the argon pressure is 0.5-0.9 MPa.
Further, the argon pressure was calculated using the following formula:
Figure BDA0001631463340000035
pAris argon partial pressure, MPa, p0Is the standard atmospheric pressure, MPa,
Figure BDA0001631463340000034
the activity coefficient of nitrogen in the molten steel; % N is the limiting nitrogen content at atmospheric pressure; lgKNTo balance constant, lgKNT is the melting point of the alloy, K, 1467.6/T-1.28.
Further, in step 7, the nitrogen pressure is 0.1MPa to 0.3 MPa.
Further, in step 8, the cooling rate is 1.0 ℃/s to 1.5 ℃/s.
Compared with the prior art, the invention has the following beneficial effects:
1) according to the smelting method of the duplex stainless steel casting blank, provided by the invention, the alloy components can be controlled within a target range through vacuum smelting, but the uniformity is different, and after electroslag remelting is combined, the uniformity is further improved, so that the control precision is improved, and unexpected beneficial effects are obtained through the combination of the two methods. Specifically, the alloy elements are primarily smelted through a vacuum smelting process, but the obtained primary casting blank has serious subcutaneous pores and has the defects of loose tissue, shrinkage cavity, subcutaneous pores and the like; then, the primary casting blank is further processed through an atmosphere protection electroslag remelting process, deoxidation and degassing are carried out in the atmosphere protection electroslag remelting process to reduce the forming conditions of non-metallic inclusions, so that large-particle non-metallic inclusions in the primary casting blank are reduced, the structure of the primary casting blank becomes compact, the distribution of alloy components is uniform, particularly, nitrogen elements can be re-dissolved into remelting liquid drops through the atmosphere protection electroslag remelting process to eliminate the defects of a vacuum matrix, so that the defects of loose structure, shrinkage cavities, subcutaneous air holes and the like of the primary casting blank are reduced, the internal and surface quality of the casting blank are improved, the component control precision is improved, the high nitrogen yield of the duplex stainless steel casting blank is ensured, and meanwhile, the smelting method of the duplex stainless steel casting blank can stably keep a high yield.
2) According to the smelting method of the duplex stainless steel casting blank, the compactness of the casting blank structure and the uniformity of the distribution of alloy components are improved through the atmosphere protection electroslag remelting process, and the casting blank can keep good processing plasticity and toughness in a wider temperature interval, so that the smelting method can adapt to a smaller processing compression ratio.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof.
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The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention.
FIG. 1 is a schematic view of the bottom of a casting blank after vacuum melting of duplex stainless steel according to an embodiment of the present invention;
fig. 2 is a schematic view of an appearance of a casting blank after remelting electroslag in a duplex stainless steel atmosphere according to an embodiment of the present invention;
FIG. 3 is a schematic view of a casting blank after remelting electroslag in a duplex stainless steel atmosphere according to an embodiment of the present invention;
fig. 4 is a schematic diagram illustrating uniformity of an internal structure of a casting blank after remelting electroslag in a duplex stainless steel atmosphere according to an embodiment of the present invention;
fig. 5 is an appearance schematic diagram of a casting blank after remelting electroslag in a duplex stainless steel atmosphere protection provided by the second embodiment of the present invention;
fig. 6 is a schematic view of the lower part of a casting blank after remelting electroslag in a duplex stainless steel atmosphere protection provided by the second embodiment of the present invention.
Detailed Description
The preferred embodiments of the present invention are described in detail below.
In a first aspect, the invention provides a smelting method of a duplex stainless steel casting blank, which adopts a smelting process combining vacuum smelting and atmosphere protection electroslag remelting.
Compared with the prior art, the smelting method of the duplex stainless steel casting blank provided by the invention has the advantages that the alloy components can be controlled within a target range through vacuum smelting, the uniformity is different, the uniformity is further improved by combining with electroslag remelting, the control precision is improved, and unexpected beneficial effects are achieved by combining the two methods. Specifically, the alloy elements are primarily smelted through a vacuum smelting process, but the obtained primary casting blank has serious subcutaneous pores and has the defects of loose tissue, shrinkage cavity, subcutaneous pores and the like; then, the primary casting blank is further processed through an atmosphere protection electroslag remelting process, deoxidation and degassing are carried out in the atmosphere protection electroslag remelting process to reduce the forming conditions of non-metallic inclusions, so that large-particle non-metallic inclusions in the primary casting blank are reduced, the structure of the primary casting blank becomes compact, the distribution of alloy components is uniform, particularly, nitrogen elements can be re-dissolved into remelting liquid drops through the atmosphere protection electroslag remelting process to eliminate the defects of a vacuum matrix, so that the defects of loose structure, shrinkage cavities, subcutaneous air holes and the like of the primary casting blank are reduced, the internal and surface quality of the casting blank are improved, the component control precision is improved, the high nitrogen yield of the duplex stainless steel casting blank is ensured, and meanwhile, the smelting method of the duplex stainless steel casting blank can stably keep a high yield.
Meanwhile, the compactness of the casting blank structure and the distribution uniformity of alloy components are improved through an atmosphere protection electroslag remelting process, and the casting blank can keep good processing plasticity and toughness in a wider temperature interval, so that the casting blank can adapt to a smaller processing compression ratio.
Considering that the composition of the duplex stainless steel billet may affect the final quality of the billet, the composition of the duplex stainless steel billet is, for example, in mass percent: 0.02 to 0.03 percent of C, 0.6 to 0.75 percent of Mn, 0.40 to 0.48 percent of Si, 21.0 to 25.5 percent of Cr, 5.80 to 7.26 percent of Ni, 3.50 to 4.20 percent of Mo, 0.18 to 0.35 percent of N, and the balance of Fe and inevitable impurities.
Specifically, the smelting method of the duplex stainless steel casting blank comprises the following steps:
step 1: calculating the limit nitrogen content under normal pressure according to the composition of the duplex stainless steel casting blank, multiplying the limit nitrogen content under normal pressure by a corrected value to obtain the actual adding mass percentage of the nitrogen element, wherein the corrected value is 0.7-0.9, and calculating the adding amount of the ferrochrome nitride alloy according to the actual adding mass percentage of the nitrogen element.
Wherein, the calculation formula of the limit nitrogen content under normal pressure is as follows:
Figure BDA0001631463340000061
Figure BDA0001631463340000071
in the formula (I), the compound is shown in the specification,
Figure BDA0001631463340000072
is nitrogen partial pressure, MPa, p0Is the standard atmospheric pressure, MPa,
Figure BDA0001631463340000073
the activity coefficient of nitrogen in the molten steel; t is the melting point of the alloy, K; omega m]Is the mass percentage of an alloy element m, wherein m is at least one of Cr, Ni, Mo, Mn, C, Si, P, S, Al, Ti, V, W and O; % N is the limiting nitrogen content at atmospheric pressure, i.e., the amount of nitrogen saturated at atmospheric pressure.
Step 2: preparing smelting materials according to the composition of a duplex stainless steel casting blank by mass percent and the actually added mass percent of an N element, loading the smelting materials into a high-nitrogen steel multifunctional induction furnace, vacuumizing until the vacuum degree is less than 15Pa, transmitting power to heat the smelting materials, wherein the initial power of the high-nitrogen steel multifunctional induction furnace is 30KW-40KW, increasing the speed of 5KW every 5min, increasing the power to 70KW-80KW, smelting in vacuum until a molten pool appears, controlling the power to be stable, avoiding splashing, and obtaining molten steel.
It should be noted that the high-nitrogen steel multifunctional induction furnace is a specific furnace type, and a person skilled in the art can realize vacuum smelting of the smelting materials by controlling the power parameters of the high-nitrogen steel multifunctional induction furnace.
And step 3: refining the molten steel, wherein the refining power is 40KW-50KW, the refining time is 30 min-40 min, the vacuum degree is less than or equal to 5Pa, and removing impurity gas elements such as O, H, N and the like in the steel.
And 4, step 4: argon gas higher than atmospheric pressure is pressurized and filled into the furnace, so that the solubility of N in molten steel is improved, and the yield of N is ensured, which is the difference between the process and the conventional process.
Illustratively, the argon pressure is 0.5 to 0.9MPa, and specifically, the above-mentioned argon pressure can be calculated by the following formula:
Figure BDA0001631463340000081
pAris argon partial pressure, MPa, p0Is the standard atmospheric pressure, MPa,
Figure BDA0001631463340000082
the activity coefficient of nitrogen in the molten steel; % N is the limiting nitrogen content at atmospheric pressure; lgKNTo balance constant, lgKN1467.6/T-1.28, T is the melting point of the alloy, K; .
And 5: adding raw materials for improving argon partial pressure (which refers to raw materials containing volatile elements and increasing argon partial pressure after melting and volatilizing) and calculating the obtained ferrochrome nitride according to the actual added weight percentage of nitrogen content;
step 6: adding a deoxidizing agent, controlling the temperature of the molten steel to be 100-150 ℃ higher than the melting point of the alloy, so that the fluidity of the molten steel is improved, the depth of a shrinkage cavity is reduced, electrically pouring the molten steel into an ingot mold, performing casting molding, naturally cooling, discharging gas and breaking the cavity, and opening a furnace cover to obtain the ingot mold;
and 7: carrying out nitrogen protection electroslag remelting on the ingot mould, wherein nitrogen protection is carried out in the whole process, the nitrogen pressure is 0.1-0.3 MPa (for example, 0.2MPa), and the flow is 25 NL/min; the smelting period of the electroslag remelting adopts constant smelting speed control smelting, the smelting speed control equation V is 0.7 XD Kg/h, and D is the size of a water-cooled crystallizer and the unit mm.
The molten steel is solidified in the water-cooled crystallizer, and the cooling speed is high and reaches 1.0 ℃/s-1.5 ℃/s. The selective crystallization can not be fully developed, so that the composition segregation of the steel ingot is small, and the crystallization of the steel is carried out from bottom to top, the structure is uniform, and the defects of looseness, shrinkage cavities, subcutaneous air holes and the like are avoided.
In the above smelting method, the difficulties are the yield of N element in the vacuum smelting process, the segregation of N element, and the suppression of N element volatilization in the electroslag process. According to the invention, the partial pressure of argon in the furnace is controlled in the vacuum melting process (step 4) to control the yield of N element, the melting power is controlled (step 2-3) to control the segregation of N element, and the volatilization of N element in the electroslag remelting process is further inhibited by the pressure of the protective atmosphere in the electroslag remelting process (step 7), so that the smelting method of the duplex stainless steel casting blank can stably keep higher yield while ensuring higher nitrogen yield.
Example 1
The equipment adopts a 50Kg multifunctional induction melting furnace with the ultimate vacuum degree of 6.67 multiplied by 10-2Pa, power supply power of 160KW, frequency of 2500Hz, and charging amount of 36 Kg. The smelting target components of the No. 1 test steel are shown in the table 1.
Table 1: control range and control target of No. 1 test steel composition
C Mn Si Cr Ni Mo N
Target component 0.02 0.6 0.4 25.5 7.26 4.20 0.35
The method comprises the following specific steps:
(1) pure iron, metal chromium, nickel, molybdenum, vanadium and crucible carbon are put into a furnace. Ferrochromium nitride, manganese, carbon, silicon and a deoxidizer are filled into a storage bin.
(2) Evacuating the smelting chamber of the multifunctional induction furnace, starting to transmit electricity to heat furnace charge when the vacuum degree is less than 15Pa, and gradually increasing the power to 70KW at the rate of increasing 5KW every 5min by 40 KW.
(3) After the furnace burden is melted and cleared out of the molten pool, the power is controlled, splashing is avoided, and the vacuum degree is gradually reduced.
(4) Adjusting the power to be low, refining the mixture to 10Min, removing O, N, H degrees and the like, wherein the vacuum degree is less than or equal to 5 Pa.
(5) Alloying: partial deoxidizer is added from a charging opening step by step.
(6) Adjusting the pressure of the argon in the furnace to 0.6 MPa.
(7) Adding ferrochromium nitride, manganese, carbon and silicon.
(8) Adding a final deoxidizer, controlling the temperature of the molten steel to be 1500-.
(9) And (5) deflating, breaking the cavity, opening the furnace cover and taking out the ingot mold.
(10) And (4) welding the steel ingots together according to the finished product sizing, and carrying out nitrogen protection electroslag remelting.
(11) The electroslag remelting is started, most process parameters are conventional process parameters, wherein the process parameters comprise ① requiring whole-process nitrogen protection, the pressure is 0.2MPa, the flow rate is 25NL/min ②, the smelting period adopts constant smelting speed, the smelting speed control equation V is 0.7 XD Kg/h, and D is the size of a crystallizer and the unit mm.
FIG. 1 shows that only vacuum steel ingot is smelted, and as can be seen from FIG. 1, many bubbles exist under the skin, which seriously affects the yield.
Table 2: measured chemical composition of test Steel No. 1 (%)
C Mn Si Cr Ni Mo N
0.02 0.7 0.45 25.32 6.3 4.12 0.32
FIGS. 2-3 show the finished product of the present embodiment using vacuum melting and electroslag ingot, and it can be seen from FIGS. 2-3 that there are no subcutaneous bubbles.
After the analysis of the components, the yield of N was 99%, and segregation was substantially absent.
As can be seen from the low power of the electroslag ingot in FIG. 4, no metallurgical defects such as shrinkage cavity, porosity and white spots are found.
144Kg of feed material, 126Kg of weight of the semi-finished product of the electroslag ingot, no subcutaneous bubbles on the surface of the electroslag ingot, no shrinkage cavities at two ends and no looseness.
Example 2
The equipment adopts 200Kg of multifunctional induction melting furnace with the ultimate vacuum degree of 6.67 multiplied by 10-2Pa, power supply power of 200KW, frequency of 2000Hz, and charging amount of 160 Kg. The smelting target components of the 2# test steel are shown in the table 3.
Table 3: control range and control target of 2# component
C Mn Si Cr Ni Mo N
Target component 0.02 0.6 0.4 21.0 6.0 3.50 0.20
The method comprises the following specific steps:
(1) pure iron, metal chromium, nickel, molybdenum, vanadium and crucible carbon are put into a furnace. Ferrochromium nitride, manganese, carbon, silicon and a deoxidizer are filled into a storage bin.
(2) Evacuating the smelting chamber of the multifunctional induction furnace, starting to transmit electricity to heat furnace charge when the vacuum degree is less than 15Pa, and gradually increasing the power to 150KW at the speed of increasing 10KW every 5min by 50 KW.
(3) After the furnace burden is melted and cleared out of the molten pool, the power is controlled, splashing is avoided, and the vacuum degree is gradually reduced.
(4) Adjusting the power to be low, refining the mixture to 10Min, removing O, N, H degrees and the like, wherein the vacuum degree is less than or equal to 5 Pa.
(5) Alloying: partial deoxidizer is added from a charging opening step by step.
(6) Adjusting the pressure of the argon in the furnace to 0.5 MPa.
(7) Adding ferrochromium nitride, manganese, carbon and silicon.
(8) Adding a final deoxidizer, controlling the temperature of the molten steel to be 1500-.
(9) And (5) deflating, breaking the cavity, opening the furnace cover and taking out the ingot mold.
(10) And according to the finished product sizing, carrying out nitrogen protection electroslag remelting on the steel ingot.
(11) The electroslag remelting is started, most process parameters are conventional process parameters, wherein the process parameters comprise ① requiring whole-process nitrogen protection, the pressure is 0.2MPa, the flow rate is 25NL/min ②, the smelting period adopts constant smelting speed, the smelting speed control equation V is 0.7 XD Kg/h, and D is the size of a crystallizer and the unit mm.
Table 4: chemical composition of finished Steel (%)
C Mn Si Cr Ni Mo N
0.03 0.75 0.48 22.5 5.80 3.80 0.18
FIGS. 5-6 show the vacuum melting and electroslag ingot finished product of this example, without the presence of subcutaneous bubbles from FIGS. 5-6.
The feeding amount is 160Kg, the weight of the semi-finished product of the electroslag ingot is 140Kg, the outer surface of the electroslag ingot has no subcutaneous bubbles, and both ends have no shrinkage cavities and looseness.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.

Claims (2)

1. A smelting method of a duplex stainless steel casting blank is characterized in that a smelting process combining vacuum smelting and atmosphere protection electroslag remelting is adopted, the partial pressure of argon is controlled to be higher than atmospheric pressure in the vacuum smelting process, and the pressure of nitrogen is controlled to be higher than atmospheric pressure in the electroslag remelting process;
the smelting method of the duplex stainless steel casting blank comprises the following steps:
step 1: calculating the limit nitrogen content under normal pressure according to the target composition of the duplex stainless steel casting blank, multiplying the limit nitrogen content under normal pressure by a corrected value to obtain the actual added mass percentage of the nitrogen element, wherein the corrected value is 0.7-0.9, and calculating the added amount of the ferrochrome nitride alloy according to the actual added mass percentage of the nitrogen element;
step 2: preparing a smelting material according to the composition of the duplex stainless steel casting blank by mass percent and the actually added mass percent of the N element, and carrying out vacuum primary smelting on the smelting material to obtain molten steel;
and step 3: refining the molten steel;
and 4, step 4: pressurizing and filling argon gas above the atmospheric pressure;
and 5: adding ferrochromium nitride, manganese, carbon and silicon;
step 6: adding a deoxidizing agent, controlling the temperature of the molten steel to be 100-150 ℃ higher than the melting point of the alloy, performing casting molding on the molten steel, and naturally cooling to obtain an ingot mold;
and 7: carrying out nitrogen protection electroslag remelting on the ingot mould, and carrying out nitrogen protection in the whole process to ensure that nitrogen elements are dissolved into remelting liquid drops again;
and 8: cooling and solidifying the molten steel obtained after the electroslag remelting to obtain a two-phase stainless steel casting blank;
in the step 2, the vacuum primary refining comprises the following steps: putting the smelting material into a high-nitrogen steel multifunctional induction furnace, vacuumizing until the vacuum degree is less than 15Pa, and heating the smelting material until a molten pool appears to obtain molten steel; in the process of heating smelting materials until a molten pool appears, the initial power of the high-nitrogen steel multifunctional induction furnace is 30-40 Kw, and the power is increased to 70-80 Kw at the rate of increasing 5Kw every 5 min;
in the step 3, a high-nitrogen steel multifunctional induction furnace is adopted for refining, the refining power is 40-50 Kw, the refining time is 30-40 min, and the vacuum degree is less than or equal to 5 Pa;
in the step 4, the argon pressure is 0.5-0.9 MPa;
in the step 7, the nitrogen pressure is 0.2MPa to 0.3MPa, and the flow is 25 NL/min;
in the step 8, the cooling speed is 1.0 ℃/s-1.5 ℃/s;
the duplex stainless steel casting blank comprises the following components in percentage by mass: 0.02 to 0.03 percent of C, 0.6 to 0.75 percent of Mn, 0.40 to 0.48 percent of Si, 21.0 to 25.5 percent of Cr, 5.80 to 7.26 percent of Ni, 3.50 to 4.20 percent of Mo, 0.18 to 0.35 percent of N, and the balance of Fe and inevitable impurities.
2. The method for smelting a duplex stainless steel ingot according to claim 1, wherein in step 1, the calculation formula of the limiting nitrogen content under normal pressure is as follows:
Figure FDA0002249301240000021
Figure FDA0002249301240000022
in the formula (I), the compound is shown in the specification,
Figure FDA0002249301240000023
is nitrogen partial pressure, MPa, p0Is the standard atmospheric pressure, MPa,
Figure FDA0002249301240000024
the activity coefficient of nitrogen in the molten steel; t is the melting point of the alloy, K; omega m]Is the mass percentage of an alloy element m, wherein m is at least one of Cr, Ni, Mo, Mn, C, Si, P, S, Al, Ti, V, W and O; % N is the limiting nitrogen content at atmospheric pressure.
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