CN108441599B - Method for smelting nitrogen-containing stainless steel in vacuum induction furnace - Google Patents
Method for smelting nitrogen-containing stainless steel in vacuum induction furnace Download PDFInfo
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- C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
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Abstract
the invention provides a method for smelting nitrogen-containing stainless steel in a vacuum induction furnace, which comprises two steps of vacuum induction smelting and gas shielded electroslag remelting, wherein the vacuum induction smelting comprises the following steps: 1.1, heating; 1.2 charging and melting; 1.3 refining; 1.4 analyzing components; 1.5 gas analysis; the gas shielded electroslag remelting method comprises the following steps: 2.1 coating aluminum powder on the surface of the electrode rod prepared in the step 1.5; 2.2 remelting under the protection of argon or nitrogen; 2.3, finishing smelting. The method adopts a mode of vacuum induction smelting (VIM) and gas shielded electroslag remelting (PESR) to smelt the high-quality nitrogen-containing stainless steel.
Description
Technical Field
the invention relates to the technical field of stainless steel smelting, in particular to a method for smelting nitrogen-containing stainless steel in a vacuum induction furnace.
Background
the nitrogen as a strong austenite forming element is applied to various stainless steels, so that the mechanical property and the corrosion resistance of the stainless steel can be obviously improved, and even a part of expensive nickel can be replaced. With the understanding of the excellent performance of nitrogen-containing stainless steel, the development of high-nitrogen stainless steel is continuously improved and developed, but the high-nitrogen stainless steel is rarely popularized and applied in batches. An important factor restricting the production and application of high-quality nitrogen-containing stainless steel is the smelting problem. Because nitrogen is a gas element, the solubility of nitrogen in steel is low, and high-quality stainless steel generally requires accurate component control, high purity, and less phosphorus and sulfur content and inclusions in smelting. The vacuum smelting can improve the internal quality of steel and ensure the phosphorus and sulfur content and the inclusion level, but the control of the nitrogen content in the smelting process is a difficult point in the smelting process.
If a nitrogen content control method in the vacuum smelting process can be researched, the problem of batch production of high-quality nitrogen-containing stainless steel can be solved.
Disclosure of Invention
the invention aims to provide a method for smelting nitrogen-containing stainless steel in a vacuum induction furnace, which adopts a mode of vacuum induction smelting (VIM) and gas shielded electroslag remelting (PESR) to smelt high-quality nitrogen-containing stainless steel.
in order to achieve the above purpose, the invention provides the following technical scheme:
the method for smelting the nitrogen-containing stainless steel by using the vacuum induction furnace comprises two steps of vacuum induction smelting and gas protection electroslag remelting, wherein the vacuum induction smelting comprises the following steps:
1.1 temperature rise: heating the vacuum induction furnace for 1.5-2 hours by using low power at the initial stage of vacuum induction smelting, wherein the low power is between 250 and 450 KW;
1.2 Loading and thawing: after the temperature is raised in the step 1.1, the power is adjusted to 900KW for melting the steel material, the power is reduced to 200KW for boiling the molten steel, and all the raw material steel, part of electrolytic nickel, part of metal chromium and part of metal molybdenum are continuously added;
1.3 refining: after the melting in the step 1.2, measuring the temperature, entering a refining period after the temperature reaches or is higher than the liquidus line of the steel grade by 100-plus-200 ℃, and stirring after the temperature is kept for 10-15min by using the power of 500-plus-1000 KW in the refining period, wherein the stirring time is 3-5 min;
1.4 component analysis: reducing the power to 400KW for 250-;
Reducing the power to 400KW, taking the 2 nd component sample for analysis, finely adjusting the components according to the analysis result to supplement alloy elements and nitrides, adjusting the nitrogen content of the nitrides, adjusting the vacuum degree of the smelting chamber to 0-740 Torr, increasing the power to 1000KW, melting and stirring, wherein the stirring time is more than or equal to 1min, and a large amount of scum appears on the surface of the molten steel after melting;
Taking the 3 rd component sample for analysis, and reducing the vacuum degree to enable the nitrogen content of the molten pool to reach a target value if the nitrogen content exceeds the upper limit of the standard;
Analyzing the 4 th component sample, tapping and casting into electrode rods when the temperature of the molten steel is 40-120 ℃ higher than the liquidus,
1.5 gas analysis: after the electrode rod is cooled to room temperature, sampling at the tail part of the electrode rod to analyze the gas content;
The gas shielded electroslag remelting method comprises the following steps:
2.1 selecting a slag system corresponding to the steel grade,
coating aluminum powder on the surface of the electrode rod prepared in the step 1.5;
2.2 remelting under the protection of argon or nitrogen;
2.3, finishing smelting.
as a preferred embodiment, in the above method, in step 1.4, the nitride is one or a mixture of manganese nitride, chromium nitride and silicon nitride.
In a preferred embodiment, in the above method, the nitride is manganese nitride.
as a preferred embodiment, in the above method, in the step 2.1, aluminum powder is added to the slag system in a ratio of aluminum powder to slag weight of 1 to 2:1000, and the surface of the electrode rod prepared in the step 1.5 is coated with aluminum powder in a ratio of aluminum powder to electrode rod weight of 1 to 3: 3000.
As a preferred embodiment, in the above method, in the step 2.1, the slag is a binary premelting slag, which is a mixture of CaF2 and Al2O 3.
As a preferred embodiment, in the above method, in step 1.4, after the 3 rd component sample is analyzed, the vacuum degree is selected to be between 0 and 740 torr according to the higher value of the nitrogen content, and is maintained for 5 to 8 minutes.
as a preferred embodiment, in the above method, between the step 1.3 and the step 1.4, the following steps are further provided:
degassing: when the molten steel contains a large amount of oxygen, carbon is used for deoxidation to generate CO gas, and the CO gas is subjected to degassing treatment.
as a preferable embodiment, in the above method, in the step 1.4, as can be seen from the reaction formula Δ rGm, at that time, molten steel is degassed; otherwise, the molten steel absorbs gas.
as a preferred embodiment, in the above method, in the step 2.2, the remelting rate is controlled to 4.0 to 8.0 kg/min.
As a preferred embodiment, in the above method, in the step 1.1 to 1.3, the degree of vacuum is less than or equal to 0.3 Pa; preferably, in said step 1.2: continuously adding all raw material steel, electrolytic nickel accounting for 25-35% of the adding amount, metallic chromium accounting for 25-35% of the adding amount and metallic molybdenum accounting for 25-35% of the adding amount.
the analysis shows that the invention discloses a method for smelting nitrogen-containing stainless steel in a vacuum induction furnace, which adopts a mode of vacuum induction smelting (VIM) and gas shielded electroslag remelting (PESR) to smelt high-quality nitrogen-containing stainless steel, so that the high-quality nitrogen-containing stainless steel meets the requirements of required components and inclusions. The vacuum induction smelting (VIM) comprises the steps of heating, charging, melting, refining, component analysis, gas analysis and the like, and the gas shielded electroslag remelting (PESR) comprises the steps of aluminum coating, gas shielded remelting and the like. Adjusting pressure during vacuum induction smelting (VIM) to adjust nitrogen content, and coating aluminum by gas shielded electroslag remelting (PESR) to reduce oxygen content. Degassing treatment is carried out in the melting period and the refining period, so that the oxygen content in steel is reduced, and the formation of pores on the surface of a steel ingot is effectively avoided. In the component analysis stage, metal chromium is added into the molten steel to increase the solubility of nitrogen, and manganese nitride is added into the molten steel, the lower melting temperature of the manganese nitride can reduce the overflow of nitrogen from the molten steel, so that the nitrogen content of the high-quality nitrogen-containing stainless steel is increased, the temperature of the molten steel and the tapping temperature are well controlled in the smelting process, the nitrogen content in the molten steel is ensured, and the nitrogen content meets the component requirement.
Drawings
the accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. Wherein:
FIG. 1 is a schematic process flow diagram of the present invention.
FIG. 2 is a schematic process flow diagram of example 1 of the present invention.
FIG. 3 is a process flow chart of example 2 of the present invention.
Detailed Description
The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings. The various examples are provided by way of explanation of the invention, and not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. It is therefore intended that the present invention encompass such modifications and variations as fall within the scope of the appended claims and equivalents thereof.
according to the embodiment of the invention, the method for smelting the nitrogen-containing stainless steel in the vacuum induction furnace is provided, and the high-quality nitrogen-containing stainless steel is smelted in a mode of vacuum induction smelting (VIM) and gas shielded electroslag remelting (PESR), so that the high-quality nitrogen-containing stainless steel meets the requirements of required components and inclusions. The method solves the following technical problems:
1. How to control the nitrogen content to meet the component requirement;
2. How to reduce the oxygen content in the steel;
3. how to avoid the formation of pores on the surface of the steel ingot.
the three major factors influencing the nitrogen content in the operation process of smelting the high-quality nitrogen-containing stainless steel in the vacuum induction furnace are as follows:
1. influence of alloying elements on nitrogen content. The solubility of nitrogen in the ferroalloy solution is greatly affected by other alloying elements. Different alloy elements have different action coefficients on the solubility of nitrogen in steel, elements such as chromium Cr, manganese Mn, molybdenum Mo, vanadium V, niobium Nb and the like increase the solubility of nitrogen, and elements such as nickel Ni, copper Cu, silicon Si, carbon C and the like reduce the solubility of nitrogen. The influence of various elements on the solubility of nitrogen in molten steel can be effectively measured by using the activity coefficient. According to the current experimental results, the reasonable control of elements in the steel, particularly the control of chromium or manganese, can effectively improve the solubility of nitrogen.
2. The kind of nitride added and the method. The nitrogen-containing steel is smelted by a vacuum induction furnace, and nitrogen alloying is mainly carried out by adding nitride. Because the smelting system of the vacuum induction furnace is a low-pressure system, the nitrogen overflows on the surface of the molten steel due to the fact that the nitride is greatly melted and dissolved in the molten steel. If the nitride is added too early, the nitrogen dissolved in the molten steel can continuously participate in the overflow reaction on the surface of the molten steel, so that the dissolved nitrogen in the molten steel is less and less. In addition, if the melting temperature of the nitrides exceeds the temperature of the molten steel, the melting time is inevitably prolonged, and the higher melting temperature can promote the nitrogen to overflow from the molten steel. When the melting temperature of the nitride is lower than the temperature of the molten steel, the nitride is added into the molten steel to be rapidly melted and uniformly stirred; because the time is short, a large amount of supersaturated nitrogen dissolved in the molten steel is not overflowed before being cast into steel ingots and is left in the molten steel, thereby obtaining higher nitrogen content. Among several kinds of nitride alloys such as manganese nitride, chromium nitride, silicon nitride, etc., only manganese nitride has a low melting temperature of about 1200 ℃, and chromium nitride and silicon nitride have melting temperatures of over 1600 ℃. Therefore, when the vacuum induction furnace is used for smelting the nitrogen-containing steel, manganese nitride is preferably used.
3. influence of smelting parameters. According to henry's law, the solubility of nitrogen in steel decreases instead with increasing temperature. Therefore, the control of the temperature of the molten steel and the tapping temperature during smelting are important factors for ensuring the nitrogen content in the molten steel. The temperature is adjusted and controlled through the change of the transmitted power, and the temperature of the molten steel is measured through a thermocouple thermometer.
through the analysis, the method for solving the technical problems needs to start from two aspects of vacuum degree and nitrogen alloy adding time, solves the problem of oxygen content and avoids the formation of pores on the surface of the steel ingot, and can finish the smelting of the nitrogen-containing stainless steel.
As shown in fig. 1, the method comprises the steps of:
Vacuum Induction Melting (VIM):
Step 1.1, heating: in the initial stage of VIM smelting, the vacuum induction furnace is heated for 1.5-2 hours (such as 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours and 2 hours) by using low power, the low power is between 250 and 450KW (such as 250KW, 270KW, 290KW, 310KW, 330KW, 350KW, 370KW, 400KW, 420KW, 440KW and 450KW), and the vacuum degree is adjusted to be less than or equal to 0.3 Pa;
Step 1.2 charging and thawing: after the temperature is raised in the step 1.1, the power is adjusted to 700-type slag KW 900KW (for example, 700KW, 715KW, 730KW, 745KW, 760KW, 775KW, 790KW, 805KW, 820KW, 835KW, 850KW, 875KW, 880KW and 900KW) to melt the steel material, the power is reduced to 100-type slag KW 200KW (for example, 100KW, 110KW, 120KW, 130KW, 140KW, 150KW, 160KW, 170KW, 180KW, 190KW and 200KW) when the molten steel is boiled till the molten steel is not boiled violently, all raw material steel, partial electrolytic nickel, partial chromium metal and partial molybdenum metal are continuously added according to ingredient proportioning, and the vacuum degree is less than or equal to 0.
according to the ingredient composition of the target steel grade, the metals added to the steel grade need to be limited to a few types, and if the composition is changed, the possibility of adding other metals is provided. "all" means the whole of the raw steel required for the formulation of the composition, and "part" may be added in an amount of 25 to 35% of the formulation amount. Because the raw material steel and the alloy are solid, the raw material steel and the alloy can not be melted after being added. In addition the silo cannot accommodate all the raw steel. The main task of the melting period is to melt the charge smoothly.
Step 1.3, refining: after the melting in the step 1.2, measuring the temperature, wherein the temperature is changed according to the liquidus line of the steel, the temperature is changed to be up to or higher than 100-.
The main tasks of the refining period are to fully remove oxygen in steel, remove inclusion elements, improve the purity of molten steel and create conditions for adding manganese nitride.
when the degassing process is completed during the melting period and the refining period, and the steel contains a large amount of oxygen, the CO gas generated by deoxidation using carbon easily induces nitrogen dissolved in the molten steel to bubble and overflow, which is not favorable for obtaining a high nitrogen content. The degassing treatment can effectively avoid the formation of pores on the surface of the steel ingot and can improve the purity of the molten steel.
Step 1.4 component analysis: reducing power to 250-400KW (such as 250KW, 270KW, 290KW, 310KW, 330KW, 350KW, 370KW and 400KW), taking the 1 st component sample for analysis, finely adjusting components according to the analysis result, supplementing the residual chromium, electrolytic nickel and molybdenum in the added amount, increasing power to 500-1000KW (such as 500KW, 550KW, 600KW, 650KW, 700KW, 750KW, 800KW, 850KW, 900KW, 950KW and 1000KW), melting and stirring, wherein the stirring time is 3-5min (such as 3min, 4min and 5 min).
for example, the target composition of Cr is 22-24% and the composition of Cr of the 1 st composition is 19.5%, at which time 2.5% of Cr should be added to adjust the Cr composition to be at least close to the target lower limit.
Reducing the power to 250-one and 400KW (such as 250KW, 270KW, 290KW, 310KW, 330KW, 350KW, 370KW and 400KW), taking the 2 nd component sample for analysis, finely adjusting the components according to the analysis result, supplementing alloy and nitride, wherein the supplementing amount is determined according to the components of the molten pool at the moment, and the closer to the target components, the less the supplementing amount is; the farther away from the target component, the more the additional amount is, the more the nitride is used for adjusting the nitrogen content, the vacuum degree in the vacuum induction furnace is adjusted to 0-740 torr, the power is increased to 500 plus material 1000KW (for example, 500KW, 550KW, 600KW, 650KW, 700KW, 750KW, 800KW, 850KW, 900KW, 950KW and 1000KW), the mixture is melted and stirred, the stirring time is more than or equal to 1min, and a large amount of scum appears on the surface of the molten steel after the melting;
Wherein the added alloy element is one or a mixture of more of metal chromium, metal manganese, metal molybdenum, metal vanadium and metal niobium, preferably metal chromium, and the metal chromium can increase the solubility of nitrogen.
The supplementary nitride is one or a mixture of manganese nitride, chromium nitride and silicon nitride, preferably manganese nitride, the melting temperature of the manganese nitride is about 1200 ℃, and the lower melting temperature can reduce the overflow of nitrogen from the molten steel.
The adjustment of the numerical value of the vacuum degree in the vacuum induction furnace needs to be determined according to the used vacuum induction furnace and the nitrogen content, and the influence on the nitrogen content in the molten steel has the following three aspects:
1) Certain specifications and parameters of the vacuum induction furnace (such as the volume of a furnace chamber, the specification of a crucible for smelting and the like) influence the content of nitrogen in molten steel. The furnace chamber is small, and the diffusion of nitrogen to the furnace chamber can be reduced under the condition of unchanged pressure; the smaller the inner diameter of the crucible is, the smaller the specific surface area of the molten steel in contact with the outside is, and the smaller the chance of nitrogen participating in the overflow reaction is. The small furnace cavity and the small inner diameter of the crucible are beneficial to keeping higher nitrogen content in the molten steel.
2) wherein Δ rGm is Gibbs free energy (Gibbs free energy), which is a thermodynamic function introduced for judging the proceeding direction of the process in chemical thermodynamics, R is a constant, T is temperature, x is gas, w is percentage, p is partial pressure, which is even equilibrium partial pressure, chemical reactions all proceed toward reaction equilibrium, which is partial pressure currently proceeding (gas is two atoms, so lower corner mark is 2), which is partial pressure at equilibrium, 1/2 is open square root, according to the reaction formula Δ rGm, at that time, molten steel is degassed; otherwise, the molten steel absorbs gas. Therefore, the required adjustment of the vacuum degree during the nitrogen adding needs to be corrected according to a formula and actual parameters. The nitrogen absorption is maximum at 740 torr, but the oxygen content increases with it; as the degree of vacuum decreases, the amount of nitrogen absorbed decreases, and the oxygen content does not increase much.
3) According to the distribution coefficient relation of gas elements and alloy elements in steel, the saturation value of nitrogen in the molten pool under normal pressure can be calculated. The saturation value of nitrogen in the bath at atmospheric pressure is used to indicate whether the steel is producible. For example, 1Cr9Mo is 500ppm at normal pressure, and it is not practical for one user to request the N content to be between 600 and 800 ppm. The saturation value of nitrogen in the bath at atmospheric pressure is the limit of the nitrogen content that can be produced.
Taking the 3 rd component sample for analysis, if the nitrogen content exceeds the upper limit of the component requirement, reducing the vacuum degree to make the nitrogen content of the molten pool reach the target value, and selecting the vacuum degree between 0-740 torr (such as 50 torr, 80 torr, 150 torr, 220 torr, 260 torr, 300 torr, 400 torr, 450 torr, 480 torr, 620 torr and 730 torr) according to the higher value of the nitrogen content, and keeping for 5-8 minutes (such as 5 minutes, 6 minutes, 7 minutes and 8 minutes).
The vacuum degree required to be adjusted when the nitrogen is added needs to be corrected according to a formula and actual parameters. The final value to be reached by the nitrogen content is determined by the calculation amount corrected according to the formula and the actual parameters. If N absorbed by a steel is 5000ppm, the steel type composition requires that N be 4500ppm, and the vacuum degree can be achieved only at about 700 Torr. If the steel grade requires 1000ppm, the vacuum degree is 30-100 torr.
And (4) analyzing the 4 th component sample, and tapping and casting into an electrode rod when the temperature of the molten steel is 40-120 ℃ higher than the liquidus if the components are qualified. Preferably, tapping and casting the molten steel into the electrode rod when the temperature of the molten steel is 40-80 ℃ higher than the liquidus line.
And step 1.5, analyzing the gas, and sampling at the tail part of the electrode rod after the electrode rod is cooled to room temperature to analyze the gas content.
gas protection electroslag remelting:
2.1 selecting a slag system corresponding to the steel grade, adding aluminum powder into the slag system according to the weight ratio of the aluminum powder to the slag system of 1.5:1000,
Coating aluminum powder on the surface of the electrode rod prepared in the step 1.5 according to the weight ratio of the aluminum powder to the electrode rod of 1-3: 3000;
Preferably, aluminum powder is added into the slag system according to the weight ratio of the aluminum powder to the slag system of 1-2:1000, the slag is binary premelting slag, and the binary premelting slag is a mixture of CaF2 and Al2O 3.
and (3) coating aluminum powder on the surface of the electrode rod prepared in the step 1.5 according to the weight ratio of the aluminum powder to the electrode rod of 1-3: 3000.
2.2 remelting under the protection of argon or nitrogen, preferably argon;
Argon is adopted for whole smelting process, so that deoxidation operation is carried out, and the electroslag melting speed is controlled according to 4.0-8.0kg/min (such as 4.0kg/min, 4.5kg/min, 5.0kg/min, 5.5kg/min, 6.0kg/min, 6.5kg/min, 7.0kg/min, 7.5kg/min and 8.0 kg/min).
2.3, finishing smelting.
sampling steel ingots and analyzing chemical elements.
Example 1:
This example is a high quality austenitic stainless steel containing nitrogen, and the composition requirements and the formulation are shown in table 1.
Table 1: example 1 composition requirements and formulation design for high quality nitrogen containing austenitic stainless steel
In the embodiment, the material preparation design is carried out according to the composition requirement range of the high-quality nitrogen-containing stainless steel. The raw materials are ultra-low carbon pure iron, low S, P Cr, Ni and Mo metal materials, and low carbon manganese iron nitride is selected for nitrogen alloying. All furnace materials must be clean and dry, have no oil stain and rust and have accurate components. The C, O, N content of all raw materials was analyzed before smelting to ensure accurate dosing. The influence of the element content on the steel grade needs to be considered in the design of the ingredients.
As shown in FIG. 2, the method for preparing the nitrogen-containing stainless steel with the above composition design comprises the following steps:
The process route is as follows: and 6t vacuum induction smelting (VIM) pouring 2 steel ingots of 3 tons, and then carrying out electroslag remelting by using 3t gas protection. The parameters in the example are parameters of 6t vacuum induction smelting and 3t gas shielded electroslag furnace remelting.
vacuum Induction Melting (VIM):
step 1.1, heating: heating a vacuum induction furnace for 2 hours at low power of 250KW in the initial VIM smelting stage, and adjusting the vacuum degree to be less than or equal to 0.3 Pa;
step 1.2 charging and thawing: after the temperature is raised in the step 1.1, the power is adjusted to 900KW for melting the steel material, during the period, the power is reduced to 200KW when the molten steel is boiled until the molten steel is not boiled violently, 2961Kg of raw material steel, 1454Kg of electrolytic nickel, 1454Kg of metallic chromium and 135Kg of metallic molybdenum are continuously added, and the vacuum degree is less than or equal to 0.3 Pa.
Step 1.3, refining: after the melting in the step 1.2, measuring the temperature to 1577 ℃ (the liquidus of the steel grade is about 1395 ℃, measuring the temperature to be higher than the liquidus of the steel grade 182 ℃), entering a refining period, keeping for 9min by using high power 1000KW during the refining period, stirring for 4min, and keeping the vacuum degree to be less than or equal to 0.3 Pa.
step 1.4 component analysis: reducing the power to 250KW, taking the 1 st component sample for analysis (see Table 2), finely adjusting the components according to the analysis result, supplementing 32Kg of electrolytic nickel, 64Kg of metal chromium and 13Kg of metal molybdenum, increasing the power to 1000KW, melting and stirring for 3 min.
Reducing the power to 250KW, taking the 2 nd component sample for analysis (see table 2), supplementing 75Kg of metal chromium and 150Kg of manganese nitride according to the analysis result, wherein the manganese nitride is FeMn75N7 (the manganese content is 75% and the nitrogen content is 7%), adjusting the vacuum degree in the vacuum induction furnace to 740 torr, increasing the power to 1000KW, melting and stirring for 2min, and generating a large amount of scum on the surface of molten steel after melting;
Taking the 3 rd component sample for analysis (see table 2), if the nitrogen content exceeds the upper limit of the standard, reducing the vacuum degree to enable the nitrogen content of the molten pool to reach the target value, selecting the vacuum degree of 30 torr according to the higher value of the nitrogen content, and keeping the vacuum degree for 2 minutes.
Taking the 4 th component sample for analysis (see table 2), wherein the components are qualified, and tapping and casting the steel into two electrode rods when the temperature of the molten steel is 1456 ℃;
step 1.5 gas analysis (see table 2), after the electrode rods are cooled to room temperature, sampling is carried out on the tail parts of the electrode rods to analyze finished product samples, and the results show that one of the electrode rods has 0.139% of N and 84ppm of O, the other electrode rod has 0.134% of N and 84ppm of O, and the N content and the O content meet the numerical values specified in the component range.
Table 2: analytical sample information (unit:% wt)
gas protection electroslag remelting:
2.1 selecting a slag system corresponding to the steel grade, adding aluminum powder into the slag system according to the weight ratio of the aluminum powder to the slag system of 1-2:1000,
and (3) coating aluminum powder on the surface of the electrode rod prepared in the step 1.5 according to the weight ratio of the aluminum powder to the electrode rod of 1-3: 3000.
2.2 remelting under the protection of argon;
argon is adopted for protection in the whole smelting process, so that deoxidation operation is carried out, and the electroslag melting speed is controlled according to 6.5 kg/min.
2.3 finishing the smelting to obtain the high-quality nitrogen-containing austenitic stainless steel.
the ingot was sampled and analyzed for chemical elements and the oxygen content was reduced to 22ppm, see table 3.
Table 3: chemical elements for ingot sampling analysis (unit:% wt)
| Number of samples | C | Mn | Si | P | S | Ni | Cr | Mo | N | O(ppm) |
| Finished product 1 | 0.01 | 1.11 | 0.05 | 0.004 | 0.002 | 21.74 | 24.12 | 2.23 | 0.134 | 22 |
| Finished product 2 | 0.01 | 1.14 | 0.06 | 0.004 | 0.001 | 21.77 | 24.05 | 2.24 | 0.132 | 23 |
the inclusion test levels (rated according to GB/T10561) for the ingot samples are shown in Table 4 (the numerical parts in the table represent the inclusion level grades):
Table 4: level of inclusions examination (unit:% wt)
| Stage | A | B | C | D |
| thin line | 0.5 | 0.5 | 0.0 | 0.5 |
| coarse series | 0.0 | 0.0 | 0.0 | 0.5 |
example 2:
this example is a high quality austenitic stainless steel containing nitrogen, and the composition requirements and the formulation are shown in table 5.
Table 5: example 2 composition requirements and formulation design for high quality nitrogen containing austenitic stainless steel
In the embodiment, the material preparation design is carried out according to the composition requirement range of the high-quality nitrogen-containing stainless steel. The raw materials are ultra-low carbon pure iron, low S, P Cr, Ni and Mo metal materials, and low carbon manganese iron nitride is selected for nitrogen alloying. All furnace materials must be clean and dry, have no oil stain and rust and have accurate components. The C, O, N content of all raw materials was analyzed before smelting to ensure accurate dosing. The influence of the element content on the steel grade needs to be considered in the design of the ingredients.
As shown in FIG. 3, the method for preparing the nitrogen-containing stainless steel with the above composition design comprises the following steps:
The process route is as follows: and 6t vacuum induction smelting (VIM) pouring 2 steel ingots of 3 tons, and then carrying out electroslag remelting by using 3t gas protection. The parameters in the example are parameters of 6t vacuum induction smelting and 3t gas shielded electroslag furnace remelting.
vacuum Induction Melting (VIM):
Step 1.1, heating: in the initial stage of VIM smelting, the vacuum induction furnace is heated for 1.5 hours by using low power, the low power is 250KW, and the vacuum degree is adjusted to be less than or equal to 0.3 Pa;
Step 1.2 charging and thawing: after the temperature is raised in the step 1.1, the power is adjusted to 850KW to melt the steel material, the power is reduced to 150KW when the molten steel boils until the molten steel does not boil violently, 2938Kg of raw material steel, 1430Kg of electrolytic nickel, 1480Kg of metallic chromium and 129Kg of metallic molybdenum are continuously added, and the vacuum degree is less than or equal to 0.3 Pa.
Step 1.3, refining: after the melting in the step 1.2, measuring the temperature to 1589 ℃ (the liquidus of the steel grade is about 1400 ℃, the temperature is higher than the liquidus of the steel grade by 189 ℃), entering a refining period, keeping the temperature for 10min by using high power 900KW during the refining period, and then stirring for 5min, wherein the vacuum degree is less than or equal to 0.3 Pa.
Step 1.4 component analysis: the power is reduced to 300KW, the 1 st component sample is taken for analysis (see Table 6), the components are finely adjusted according to the analysis result, 85Kg of chromium metal, 25Kg of electrolytic nickel and 7Kg of molybdenum metal are added, the power is increased to 900KW, the melting and the stirring are carried out, and the stirring time is 3 min.
Reducing the power to 300KW, taking the 2 nd component sample for analysis (see table 6), supplementing 16Kg of metal chromium and 145Kg of manganese nitride according to the analysis result, wherein the manganese nitride is FeMn75N7, the manganese content is 75 percent, the nitrogen content is 7 percent, adjusting the vacuum degree in the vacuum induction furnace to 740 torr, increasing the power to 900KW for melting and stirring for 2min, and generating a large amount of scum on the surface of molten steel after melting;
Taking the 3 rd component sample for analysis (see table 6), if the nitrogen content exceeds the upper limit of the standard, reducing the vacuum degree to enable the nitrogen content of the molten pool to reach the target value, selecting the vacuum degree of 25 torr according to the higher value of the nitrogen content, and keeping the vacuum degree for 2 minutes.
Analyzing the 4 th component sample (see table 6), and obtaining qualified components, wherein the temperature of molten steel is 1478 ℃, tapping and casting into two electrode rods;
And step 1.5, analyzing the gas, sampling and analyzing a finished product sample at the tail part of the electrode rod after the electrode rod is cooled to room temperature, and displaying that the N content of one electrode rod is 0.123 percent and the O content is 68ppm, the N content of the other electrode rod is 0.119 percent and the O content is 68ppm, and the values meet the values specified in the component range.
Table 6: analytical sample information (unit:% wt)
| Number of samples | C | Mn | Si | P | S | Ni | Cr | Mo | Al | N |
| 1 | 0.01 | 0.03 | 0.04 | 0.006 | 0.003 | 22.64 | 22.74 | 2.06 | 0.012 | 0.0077 |
| 2 | 0.01 | 0.03 | 0.04 | 0.006 | 0.003 | 23.00 | 23.93 | 2.17 | 0.012 | 0.0049 |
| 3 | 0.01 | 1.75 | 0.05 | 0.006 | 0.003 | 21.99 | 24.86 | 2.14 | 0.006 | 0.164 |
| 4 | 0.01 | 1.78 | 0.05 | 0.006 | 0.003 | 22.09 | 25.19 | 2.17 | 0.006 | 0.128 |
| finished product 1 | 0.01 | 1.75 | 0.06 | 0.006 | 0.003 | 22.05 | 25.14 | 2.17 | 0.009 | 0.123 |
| finished product 2 | 0.01 | 1.76 | 0.06 | 0.005 | 0.003 | 22.07 | 25.03 | 2.16 | 0.007 | 0.119 |
Gas protection electroslag remelting:
2.1 selecting a slag system corresponding to the steel grade, adding aluminum powder into the slag system according to the weight ratio of the aluminum powder to the slag system of 1.5:1000,
The surface of the electrode rod prepared in step 1.5 was coated with aluminum powder at a ratio of 1:3000 in terms of the weight of aluminum powder to the weight of the electrode rod.
2.2 remelting under the protection of argon;
Argon is adopted for protection in the whole smelting process, so that deoxidation operation is carried out, and the electroslag melting speed is controlled according to 6.0 kg/min.
2.3 finishing the smelting to obtain the high-quality nitrogen-containing austenitic stainless steel.
the ingot was sampled and analyzed for chemical elements and the oxygen content was reduced to 21ppm, see table 7.
Table 7: chemical elements for ingot sampling analysis (unit:% wt)
| Number of samples | C | Mn | Si | P | S | Ni | Cr | Mo | N | O(ppm) |
| Finished product 1 | 0.01 | 1.73 | 0.05 | 0.005 | 0.002 | 21.97 | 24.63 | 2.17 | 0.116 | 21 |
| finished product 2 | 0.01 | 1.75 | 0.04 | 0.005 | 0.002 | 21.89 | 24.68 | 2.16 | 0.121 | 22 |
The inclusion levels (rated according to GB/T10561) for ingot samples are shown in Table 8 (the numerical parts in the table represent the inclusion level grades):
Table 8: level of inclusions examination (unit:% wt)
| Stage | A | B | C | D |
| thin line | 0.5 | 0.5 | 0.0 | 0.5 |
| Coarse series | 0.0 | 0.0 | 0.0 | 0.5 |
the two examples are illustrated by two steel grades, other steel grades being equally suitable for use in the present invention.
From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects:
The method adopts a mode of vacuum induction smelting (VIM) and gas shielded electroslag remelting (PESR) to smelt the high-quality nitrogen-containing stainless steel, so that the high-quality nitrogen-containing stainless steel meets the requirements of required components and inclusions.
the vacuum induction smelting (VIM) comprises the steps of heating, charging, melting, refining, component analysis, gas analysis and the like, and the gas shielded electroslag remelting (PESR) comprises the steps of aluminum coating, gas shielded remelting and the like.
adjusting pressure during vacuum induction smelting (VIM) to adjust nitrogen content, and coating aluminum by gas shielded electroslag remelting (PESR) to reduce oxygen content.
Degassing treatment is carried out in the melting period and the refining period, so that the oxygen content in steel is reduced, and the formation of pores on the surface of a steel ingot is effectively avoided. In the component analysis stage, metal chromium is added into the molten steel to increase the solubility of nitrogen, and manganese nitride is added into the molten steel, the lower melting temperature of the manganese nitride can reduce the overflow of nitrogen from the molten steel, so that the nitrogen content of the high-quality nitrogen-containing stainless steel is increased, the temperature of the molten steel and the tapping temperature are well controlled in the smelting process, the nitrogen content in the molten steel is ensured, and the nitrogen content meets the component requirement.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. The method for smelting the nitrogen-containing stainless steel by using the vacuum induction furnace is characterized by comprising two steps of vacuum induction smelting and gas shielded electroslag remelting, wherein the vacuum induction smelting comprises the following steps:
1.1 temperature rise: heating the vacuum induction furnace for 1.5-2 hours by using low power at the initial stage of vacuum induction smelting, wherein the low power is between 250 and 450 KW;
1.2 Loading and thawing: after the temperature is raised in the step 1.1, the power is adjusted to 900KW for melting the steel material, the power is reduced to 200KW for boiling the molten steel, and all the raw material steel, part of electrolytic nickel, part of metal chromium and part of metal molybdenum are continuously added;
1.3 refining: after the melting in the step 1.2, measuring the temperature, entering a refining period after the temperature reaches or is higher than the liquidus line of the steel grade by 100-plus-200 ℃, and stirring after the temperature is kept for 10-15min by using the power of 500-plus-1000 KW in the refining period, wherein the stirring time is 3-5 min;
1.4 component analysis: reducing the power to 400KW for 250-;
Reducing the power to 400KW, taking the 2 nd component sample for analysis, finely adjusting the components according to the analysis result to supplement alloy elements and nitrides, adjusting the nitrogen content of the nitrides, adjusting the vacuum degree of the smelting chamber to 0-740 Torr, increasing the power to 1000KW, melting and stirring, wherein the stirring time is more than or equal to 1min, and a large amount of scum appears on the surface of the molten steel after melting;
Taking the 3 rd component sample for analysis, and reducing the vacuum degree to enable the nitrogen content of the molten pool to reach a target value if the nitrogen content exceeds the upper limit of the standard;
Analyzing the 4 th component sample, tapping and casting into electrode rods when the temperature of the molten steel is 40-120 ℃ higher than the liquidus,
1.5 gas analysis: after the electrode rod is cooled to room temperature, sampling at the tail part of the electrode rod to analyze the gas content;
the gas shielded electroslag remelting method comprises the following steps:
2.1 selecting a slag system corresponding to the steel grade,
coating aluminum powder on the surface of the electrode rod prepared in the step 1.5;
2.2 remelting under the protection of argon or nitrogen;
2.3, finishing smelting;
In the step 1.4, the nitride is manganese nitride;
In the step 2.1, aluminum powder is added into the slag system according to the weight ratio of the aluminum powder to the slag system of 1-2:1000,
And (3) coating aluminum powder on the surface of the electrode rod prepared in the step 1.5 according to the weight ratio of the aluminum powder to the electrode rod of 1-3: 3000.
2. The method according to claim 1, characterized in that in step 2.1, the slag is a binary premelt slag, which is a mixture of CaF2 and Al2O 3.
3. The method according to claim 1, wherein in step 1.4, after the 3 rd component sample is analyzed, the vacuum degree is selected to be between 0 and 740 torr according to the higher value of the nitrogen content, and is maintained for 5 to 8 minutes.
4. Method according to claim 1, characterized in that between step 1.3 and step 1.4 there is further provided the step of:
Degassing: when the molten steel contains a large amount of oxygen, carbon is used for deoxidation to generate CO gas, and the CO gas is subjected to degassing treatment.
5. The method according to claim 1, wherein in step 1.4, as can be seen from the equation Δ rGm, the molten steel is degassed; otherwise, the molten steel absorbs gas.
6. The method as set forth in claim 1, wherein in the step 2.2, the remelting rate is controlled to 4.0 to 8.0 kg/min.
7. the method according to claim 1, wherein in step 1.1-1.3, the vacuum is less than or equal to 0.3 Pa.
8. the method according to claim 7, characterized in that in step 1.2: continuously adding all raw material steel, electrolytic nickel accounting for 25-35% of the adding amount, metallic chromium accounting for 25-35% of the adding amount and metallic molybdenum accounting for 25-35% of the adding amount.
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| CN101812625A (en) * | 2010-04-21 | 2010-08-25 | 中国科学院金属研究所 | Smelting process of 1Cr13 stainless steel |
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