CN112359217A - Supersaturated high-nitrogen stainless steel pressurizing electroslag remelting process - Google Patents
Supersaturated high-nitrogen stainless steel pressurizing electroslag remelting process Download PDFInfo
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Abstract
The invention belongs to the technical field of metal metallurgy, and particularly discloses a supersaturated high-nitrogen stainless steel pressurized electroslag remelting process which comprises the steps of early preparation, vacuumizing and pressurizing, primary electroslag remelting, slow cooling finishing, secondary electroslag remelting, finished product finishing and inspection acceptance marking. The method ensures that the nitrogen content reaches the target range by controlling the pressure of the pressurized electroslag remelting to be 10-20bar and controlling the pressure set value to be larger than the theoretical value and pressurizing by using nitrogen as inert gas; by optimizing the addition mode of the nitriding alloy, adopting secondary pressure electroslag remelting and controlling the secondary remelting pressure to be not less than primary remelting, the segregation of nitrogen elements is reduced, and the structural uniformity of the steel ingot is ensured; the density of the material is improved by optimizing the process control mode and the process parameters of the heat sealing top. The performance of the stainless steel product prepared by the invention reaches the international advanced level, and the blank of domestic supersaturated high-nitrogen martensitic stainless steel industrial production can be filled.
Description
Technical Field
The invention belongs to the technical field of metal metallurgy, and particularly relates to a supersaturated high-nitrogen stainless steel pressurized electroslag remelting process.
Background
The supersaturated high-nitrogen stainless steel is a steel type with the nitrogen content of more than 0.3 percent, has excellent performance, is widely applied in the fields of mechanical manufacture, aerospace, chemical engineering, biotechnology and the like, such as 30Cr15MoN steel, is high-nitrogen martensite cold-processed steel, and has excellent toughness (the impact toughness can reach 150j/cm when the Rockwell hardness is 56-57)23 times that of 1.4125 austenitic stainless steel), high corrosion resistance (3 times that of 1.4125 austenitic stainless steel), high annealing resistance (up to 50 ℃), and hardness up to 60 Rockwell hardness, and is used in the fields of main shaft bearings and ball bearings in the aerospace field and the manufacture of common machines. Because the research of the supersaturated high-nitrogen stainless steel is relatively late in China and the technologies of other countries are kept secret, the demand of the supersaturated high-nitrogen stainless steel always depends on import and the cost is huge.
Electroslag smelting is a special smelting method for refining metal by using resistance heat generated by passing current through liquid slag, and at present, two common methods are adopted in electroslag smelting: one is electroslag remelting realized by casting a consumable electrode and a crystallizer under the common condition, and the other is electroslag remelting realized by casting the consumable electrode and the crystallizer under the vacuum condition. The two methods can not meet the nitrogen content requirement of high-nitrogen steel, the nitrogen content in supersaturated high-nitrogen stainless steel is much higher than that in atmospheric pressure, so that the supersaturated high-nitrogen stainless steel can be smelted and solidified under the pressurizing condition, at present, a certain research is also made in the aspect of pressurizing electroslag remelting process in China aiming at the production of high-nitrogen steel, but the effect is not ideal, and the following problems mainly exist: firstly, the nitrogen content is greatly changed, and the target range cannot be reached every time; secondly, the prepared electroslag ingot has poor structural uniformity and great segregation of nitrogen elements; and thirdly, the upper end of the electroslag ingot has a longer loose section, and the compactness of the material is poor. Therefore, the quality of the supersaturated high-nitrogen stainless steel produced by pressurized electroslag remelting in China at present is far from the international advanced level, and the supersaturated high-nitrogen stainless steel cannot be practically applied.
Disclosure of Invention
In order to solve the problems, the invention provides a supersaturated high-nitrogen stainless steel pressurized electroslag remelting process, which can ensure that the nitrogen content reaches a target range, can solve the problems of poor material structure uniformity and density and improve the quality of finished products.
In order to achieve the purpose, the invention adopts the following specific technical scheme:
a supersaturated high-nitrogen stainless steel pressurizing electroslag remelting process comprises the following steps:
s1, preparing: the method can be any one of turning, grinding and shot blasting (the nitrogen content of the electrode bar of high-nitrogen steel is very low, such as 30Cr15MoN steel suitable for the process, the N content of the electrode bar is only about 0.04 wt%, and the N content can be increased by 0.35-0.44 wt% by the process); welding and manufacturing a consumable electrode and a dummy bar plate, and laying slag on the dummy bar plate; assembling a crystallizer;
s2, vacuumizing and pressurizing: before smelting and power transmission, vacuumizing a pressure bin of a crystallizer until the pressure reaches below 10mbar, and filling 0.5-1.5 bar of protective atmosphere;
s3, primary electroslag remelting: pressurizing electroslag remelting is carried out after electrification, the partial pressure of nitrogen is controlled to be 10-20bar, the pressure set value is larger than the theoretical value, and a nitriding alloy is added into a molten pool; the pressurized electroslag remelting comprises three processes of starting, smelting and heat sealing top, wherein the heat sealing top process adopts three control modes of power control, swing control and melting speed control, the swing value and the melting speed feeding are controlled in a stepped power reduction and simultaneous stage, and the heat sealing top time is more than 70 min;
s4, slow cooling and finishing;
s5, secondary electroslag remelting: pressurizing electroslag remelting is carried out again without adding nitriding alloy, the partial pressure of nitrogen is controlled to be 10-20bar, and the pressurizing electroslag remelting process is controlled to be the same as the step S3;
and S6, finishing the finished product and checking and accepting the label.
Preferably, the nitrogen pressure of the secondary electroslag remelting is not less than the nitrogen pressure of the primary electroslag remelting.
Preferably, the nitrogen pressure of the primary electroslag remelting and the secondary electroslag remelting is controlled at 16bar, and the nitrogen pressure of the primary electroslag remelting and the secondary electroslag remelting is an optimal choice from the aspects of efficiency and cost.
Preferably, in step S3, the alloy nitride is added through a screw conveyor from at least two inlets of the apparatus.
Preferably, in step S3, the nitride alloy is Si3N4。
Preferably, in step S3, the top-sealing time is 100min, the top-sealing process includes five stages, and the process control parameters are as follows:
0-10 min: swinging for 1.00 mOhm, and setting the melting speed to be 8.00 kg/min;
10-20 min: the power is reduced by 110.00 kW, the swing is 1.20 mOhm, and the melting speed is set to be 6.00 kg/min;
20-30 min: the power is reduced by 80.00 kW, the swing is 1.40 mOhm, and the melting speed is set to be 3.5 kg/min;
30-55 min: the power is reduced by 40.00 kW, the swing is 1.60 mOhm, and the melting speed is set to be 2.00 kg/min;
55-100 min: the power is reduced by 10.00 kW, the swing is 1.00 mOhm, and the melting speed is set to be 1.00 kg/min.
Preferably, the starting process of the pressurized electroslag remelting adopts power control and swing control, and the smelting process adopts power control, swing control and smelting speed control.
Preferably, the pressurized electroslag remelting is started by solid slag, the slag system is pre-melted slag, and the slag system comprises the following components in percentage by mass: CaF2 40~ 50%，Al2O3 0.30~0.40%，CaO 20~25%，SiO2 20~25%，MgO 10~15%。
Preferably, in step S2, the pressure chamber is filled with a 1.0bar protective atmosphere, and the filled gas composition is 50% argon and 50% nitrogen.
Preferably, the supersaturated high-nitrogen stainless steel is 30Cr15MoN steel, and the components of the supersaturated high-nitrogen stainless steel comprise the following components in percentage by mass: 0.28-0.34% of C, 0.30-0.80% of Si, 0.30-0.60% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, less than or equal to 14.50-16.00% of Cr14, 0.95-1.10% of Mo, less than or equal to 0.25% of Cu, 0.35-0.44% of N, less than or equal to 0.30% of Ni, less than or equal to 0.035% of Al, less than or equal to 0.0030% of Ti, and the balance of Fe.
The invention relates to a pressurized electroslag remelting process for producing supersaturated high-nitrogen stainless steel with nitrogen dissolving amount exceeding atmospheric pressure by using an electroslag remelting technology in a pressure state and adding a nitriding alloy through pressurized remelting, which effectively solves the problems of the existing pressurized electroslag remelting process through the following technical route:
firstly, the invention can ensure that the nitrogen content reaches the target range by controlling the pressure of the pressurized electroslag remelting to be 10-20bar and the pressure set value to be larger than the theoretical value and using nitrogen as inert gas for pressurizing. The reason is as follows: in the experiment, the N content is verified to accord with the Sievert law, a pressure theoretical value required by supersaturated high-nitrogen stainless steel to reach a nitrogen content target value is calculated according to an empirical formula, a set value is improved, the fault tolerance rate can be improved by higher pressure, and the influence of fluctuation of chemical components of a steel ingot on the solubility of the steel ingot is reduced; and nitrogen can be better alloyed by pressurizing with nitrogen as an inert gas.
Secondly, in order to reduce the segregation of nitrogen elements and ensure the structural uniformity of steel ingots, the invention optimizes the adding mode of the nitralloy in the first remelting process, namely improves the porosity of the alloy by conveying through a screw conveyor, and adds the nitralloy into a molten pool through at least two inlets of equipment, thereby ensuring the uniformity during adding; on the other hand, secondary electroslag remelting is adopted, and any alloy is not required to be added in the secondary remelting, so that the structure is more uniform. However, the nitrogen content is reduced in the process of adopting secondary electroslag remelting, and the problem of nitrogen element overflow is effectively solved by controlling the secondary remelting pressure to be not less than the primary remelting.
Then, aiming at the problems of loose sections at the upper end of the slag ingot and poor material compactness, the invention optimizes the hot capping process to solve the problem. The invention particularly adopts three control modes of power control, swing control and melting speed control in the heat sealing top process, wherein the power control is the step-type reduction of the control power, the swing control is to adjust the electrode position (the unit of swing is the resistance value, and the large resistance value is determined by the electrode position) when the power is reduced, and then to correspondingly adjust the melting speed (the melting speed is also gradually reduced) in each stage of the reduction of the power, namely the melting speed control.
The invention has the following beneficial effects:
1. the invention effectively solves the problems of the existing pressurized electroslag remelting process, can ensure the high solubility of nitrogen in steel and ensure that the nitrogen content in the steel reaches a target value; the nitrogen element is highly and uniformly distributed in the steel ingot, and the tissue uniformity is good; the hot-top sealing process is optimized, and the density and the utilization rate of the material are improved. In addition, the saturated high-nitrogen stainless steel electroslag remelting in the vacuum pressure bin solves the problem of hydrogen absorption of the traditional electroslag equipment.
2. The supersaturated high-nitrogen stainless steel prepared by the process has the advantages of high strength, high hardness, excellent mechanical property, good high temperature resistance and corrosion resistance, and the product performance reaches the international advanced level.
3. The invention can completely replace noble metal nickel with nitrogen, remarkably reduces the manufacturing cost, improves the safety of the material, expands the application field of the material and has good application prospect.
4. The invention can realize the mature production of the supersaturated high-nitrogen martensitic stainless steel in batches, breaks through the monopoly of other countries on the production of the high-performance supersaturated high-nitrogen stainless steel, and fills the blank of the domestic industrialized production of the supersaturated high-nitrogen martensitic stainless steel.
Drawings
FIG. 1: example 1 macroscopic topography of supersaturated high nitrogen stainless steel.
FIG. 2: example 1 quenched microstructure of supersaturated high nitrogen stainless steel.
FIG. 3: example 1 grain size diagram of supersaturated high nitrogen stainless steel.
FIG. 4: example 1 report on the detection of supersaturated high nitrogen stainless steel.
FIG. 5: example 1 heat-seal top cross-sectional view of a supersaturated ingot of high nitrogen stainless steel.
FIG. 6: and (3) metallographic structure diagram of the annealed steel ingot subjected to primary pressure electroslag remelting in the comparative example 1.
FIG. 7: and (3) a metallographic structure diagram of the annealed steel ingot subjected to secondary pressure electroslag remelting in the comparative example 1.
FIG. 8: comparative example 3 heat-seal top cross-sectional view of a supersaturated ingot of high nitrogen stainless steel.
Detailed Description
The invention is further described below with reference to the accompanying drawings and specific embodiments.
Example 1
The embodiment provides a pressurizing electroslag remelting process for supersaturated high-nitrogen stainless steel, wherein the supersaturated high-nitrogen stainless steel is 30Cr15MoN steel, and the supersaturated high-nitrogen stainless steel comprises the following chemical components in percentage by mass: 0.28-0.34% of C, 0.30-0.80% of Si, 0.30-0.60% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, less than or equal to 0.50-16.00% of Cr14.50, 0.95-1.10% of Mo, less than or equal to 0.25% of Cu, 0.35-0.44% of N, less than or equal to 0.30% of Ni, less than or equal to 0.035% of Al and less than or equal to 0.0030% of Ti, wherein the pressurized electroslag remelting process:
s1, preparing: the iron scale on the surface of the electrode bar is thoroughly removed; welding and manufacturing a consumable electrode and a dummy bar; laying slag on the dummy bar plate, wherein the electroslag remelting is started by solid slag, and the slag system is pre-melted slag and comprises the following components in percentage by mass: CaF2 43.22%，Al2O3 0.32%，CaO 22.05%，SiO2 21.48%，MgO 12.25 percent; assembling a crystallizer, wherein the nominal capacity of the crystallizer is 8t, and the average diameter of the crystallizer is phi 656 mm;
s2, vacuumizing and pressurizing: before smelting and power transmission, a pressure bin of a crystallizer is vacuumized, the pressure reaches below 10mbar, and then 1.0bar protective atmosphere (50% argon and 50% nitrogen) is filled;
s3, primary electroslag remelting: pressurizing electroslag remelting is carried out after electrification, and the partial pressure of nitrogen is controlled to be 16bar (the theoretical pressure value of supersaturated high-nitrogen stainless steel 30Cr15MoN required by reaching a nitrogen content target value is 7bar according to calculation of an empirical formula, and the pressure set value in actual production is larger than the theoretical value); and Si is fed by a screw conveyor3N4Accurately adding the nitrogen into the molten pool from two inlets of the device, wherein the nitrogen content in the electrode rod is 0.04 percent, and calculating Si according to a target value3N4The amount of (c) added; the pressurized electroslag remelting comprises three processes of starting, smelting and hot-sealing (each process has Si)3N4The addition of (1) and a start-up process, wherein the start-up process adopts two control modes of rate control and swing control, the melting and hot capping processes adopt three control modes of power control, swing control and melting speed control, and specific process parameters of each process are shown in the following tables 1-3:
TABLE 1 Start-Up Process parameters
TABLE 2 Process parameters of the smelting Process
TABLE 3 Heat Top seal Process parameters
S4, slowly cooling, finishing, inspecting and warehousing;
s5, secondary electroslag remelting: pressurizing electroslag remelting is carried out again without adding nitriding alloy, the nitrogen partial pressure is controlled to be 16bar, and the control and process parameters of the pressurizing electroslag remelting process are the same as those of the step S3;
and S6, finishing the finished product and checking and accepting the label.
The supersaturated high-nitrogen stainless steel 30Cr15MoN prepared in the example 1 is evaluated, and the results are as follows:
as shown in FIGS. 1 to 4, the low-power morphology, the quenched structure and the crystal grains of the 30Cr15MoN steel
According to the detection report of the steel, nitrogen and other elements meet the component requirements; the structure has no segregation, the grain size is high, the size is consistent, and the material uniformity is good; the steel has high strength and hardness and excellent mechanical property; as shown in fig. 5, the heat-sealed top section of the steel ingot has no heat-sealed top defects such as loose shrinkage cavity, slag wrapping and the like, and the structural compactness of the steel is good as can be seen by combining the structural picture shown in fig. 2.
Comparative example 1
This comparative example compares the metallographic structures of the steel ingots obtained by the primary pressure electroslag remelting and the secondary pressure electroslag remelting in example 1 after annealing, and as shown in fig. 6 to 7, the comparison of the metallographic structures of the steel ingots subjected to the primary pressure electroslag remelting and the steel ingots subjected to the secondary pressure electroslag remelting after annealing is obvious: large-particle chain-shaped and strip-shaped carbides exist in the metallographic structure of the steel ingot subjected to primary pressure electroslag remelting; after the secondary pressure electroslag remelting, the metallographic structure of the annealed steel ingot is more uniform, the structure performance is obviously improved, and the necessity of the secondary pressure electroslag remelting is reflected.
Comparative example 2
Compared with the embodiment 1, the nitrogen pressure in the secondary pressure electroslag remelting process is changed, and on the basis that the fixed pressure in the primary pressure electroslag remelting process is 16bar, the change situation of the nitrogen content of the steel ingot when different pressures are adopted in the secondary pressure electroslag remelting process is compared, and the result is shown in the following table 4:
TABLE 4 nitrogen content of 30Cr15MoN steel ingot smelted under different pressures
From the data in table 4, it can be seen visually that when the pressure of the secondary pressure electroslag remelting is lower than the pressure of the primary pressure electroslag remelting, a part of nitrogen elements in the steel ingot escapes, so that the nitrogen content is reduced and the product does not meet the standard requirement, and if the set pressure of the secondary pressure electroslag remelting exceeds the primary pressure electroslag remelting, the cost is greatly increased, so that the pressure value of the secondary pressure electroslag remelting is set to 16bar (namely, the pressure value is the same as the pressure value of the secondary pressure electroslag remelting), and the stability of the nitrogen element content in the steel ingot can be ensured by determining the pressure value of the secondary pressure electroslag remelting.
Comparative example 3
Compared with the example 1, the comparative example adopts different technological parameters (namely the technological parameters before optimization) of the heat capping process, and is different from the example 1 in that: the timing control for the different stages is different, as shown in table 5 below:
TABLE 5 Process parameters for the Hot Top seal Process of comparative example 3
As shown in fig. 8, for the heat seal top cross-sectional view of the supersaturated high nitrogen stainless steel ingot obtained by using the above process parameters, compared with fig. 5 (i.e., the heat seal top cross-sectional view of the ingot of example 1), there are significant heat seal top defects (loose shrinkage cavities and slag inclusions) which can seriously affect the quality of the ingot, whereas the heat seal top effect is significantly improved by adopting optimized heat seal top process parameters in example 1, and thus, it can be seen that the time control of each stage of the heat seal top process is crucial.
In conclusion, the process determines accurate parameters of each stage of the pressure electroslag remelting of the supersaturated high-nitrogen stainless steel, confirms that the high-quality supersaturated high-nitrogen stainless steel needs to be subjected to secondary electroslag remelting for further uniform components, determines the pressure condition of the secondary electroslag remelting, and finally ensures that the performance of the supersaturated high-nitrogen stainless steel produced by applying the process reaches the international advanced level.
At present, the annual effective yield of the 30Cr15MoN steel is 2000 tons, the import price of the supersaturated high-nitrogen stainless steel is 30 ten thousand per ton, and the price of the supersaturated high-nitrogen stainless steel produced in batches is 15 ten thousand per ton, which is equivalent to saving 3 billion yuan RMB for the country every year, and the economic benefit is very considerable.
This detailed description is to be construed as illustrative only and is not to be taken as limiting the invention, as any changes that may be made by a person skilled in the art after reading the present specification will be protected by the patent laws within the scope of the appended claims.
Claims (10)
1. A supersaturated high-nitrogen stainless steel pressurizing electroslag remelting process is characterized in that: the method comprises the following steps:
s1, preparing: the iron scale on the surface of the electrode bar is thoroughly removed; welding and manufacturing a consumable electrode and a dummy bar plate, and laying slag on the dummy bar plate; assembling a crystallizer;
s2, vacuumizing and pressurizing: before smelting and power transmission, vacuumizing a pressure bin of a crystallizer until the pressure reaches below 10mbar, and filling 0.5-1.5 bar of protective atmosphere;
s3, primary electroslag remelting: pressurizing electroslag remelting is carried out after electrification, the partial pressure of nitrogen is controlled to be 10-20bar, the pressure set value is larger than the theoretical value, and a nitriding alloy is added into a molten pool; the pressurized electroslag remelting comprises three processes of starting, smelting and heat sealing top, wherein the heat sealing top process adopts three control modes of power control, swing control and melting speed control, the swing value and the melting speed feeding are controlled in a stepped power reduction and simultaneous stage, and the heat sealing top time is more than 70 min;
s4, slow cooling and finishing;
s5, secondary electroslag remelting: pressurizing electroslag remelting is carried out again without adding nitriding alloy, the partial pressure of nitrogen is controlled to be 10-20bar, and the pressurizing electroslag remelting process is controlled to be the same as the step S3;
and S6, finishing the finished product and checking and accepting the label.
2. The pressurized electroslag remelting process for supersaturated high nitrogen stainless steel according to claim 1, wherein:
the nitrogen pressure of the secondary electroslag remelting is not less than that of the primary electroslag remelting.
3. The pressurized electroslag remelting process for supersaturated high nitrogen stainless steel according to claim 2, wherein: the nitrogen pressure of the primary electroslag remelting and the secondary electroslag remelting are controlled at 16 bar.
4. The pressurized electroslag remelting process for supersaturated high nitrogen stainless steel according to claim 1, wherein: in step S3, the alloy nitride is added through a screw conveyor from at least two inlets of the apparatus.
5. The pressurized electroslag remelting process for supersaturated high nitrogen stainless steel according to claim 1, wherein: in step S3, the nitride alloy is Si3N4。
6. The pressurized electroslag remelting process for supersaturated high nitrogen stainless steel according to claim 1, wherein: in step S3, the top heat sealing time is 100min, the top heat sealing process includes five stages, and the process control parameters are as follows:
0-10 min: swinging for 1.00 mOhm, and setting the melting speed to be 8.00 kg/min;
10-20 min: the power is reduced by 110.00 kW, the swing is 1.20 mOhm, and the melting speed is set to be 6.00 kg/min;
20-30 min: the power is reduced by 80.00 kW, the swing is 1.40 mOhm, and the melting speed is set to be 3.5 kg/min;
30-55 min: the power is reduced by 40.00 kW, the swing is 1.60 mOhm, and the melting speed is set to be 2.00 kg/min;
55-100 min: the power is reduced by 10.00 kW, the swing is 1.00 mOhm, and the melting speed is set to be 1.00 kg/min.
7. The pressurized electroslag remelting process for supersaturated high nitrogen stainless steel according to claim 1, wherein: the start process of the pressurized electroslag remelting adopts power control and swing control, and the smelting process adopts power control, swing control and smelting speed control.
8. The pressurized electroslag remelting process for supersaturated high nitrogen stainless steel according to claim 1, wherein: the pressurizing electroslag remelting is started by solid slag, and the slag system is pre-melted slag which comprises the following components in percentage by mass: CaF2 40~ 50%，Al2O3 0.30~0.40%，CaO 20~25%，SiO2 20~25%，MgO 10~15%。
9. The pressurized electroslag remelting process for supersaturated high nitrogen stainless steel according to claim 1, wherein: in step S2, a pressure chamber was filled with 1.0bar of protective atmosphere, and the filled gas consisted of 50% argon and 50% nitrogen.
10. The pressurized electroslag remelting process for supersaturated high-nitrogen stainless steel according to any one of claims 1 to 9, wherein: the supersaturated high-nitrogen stainless steel is 30Cr15MoN steel, and comprises the following components in percentage by mass: 0.28-0.34% of C, 0.30-0.80% of Si, 0.30-0.60% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, less than or equal to 14.50-16.00% of Cr14, 0.95-1.10% of Mo, less than or equal to 0.25% of Cu, 0.35-0.44% of N, less than or equal to 0.30% of Ni, less than or equal to 0.035% of Al, less than or equal to 0.0030% of Ti, and the balance of Fe.
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