CN113355584B - High-cobalt high-molybdenum superhard high-speed steel and method for improving hot working performance thereof - Google Patents

High-cobalt high-molybdenum superhard high-speed steel and method for improving hot working performance thereof Download PDF

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CN113355584B
CN113355584B CN202110652006.7A CN202110652006A CN113355584B CN 113355584 B CN113355584 B CN 113355584B CN 202110652006 A CN202110652006 A CN 202110652006A CN 113355584 B CN113355584 B CN 113355584B
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CN113355584A (en
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李花兵
冯浩
姜周华
焦卫超
朱红春
张树才
杨守星
贺彤
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Northeastern University China
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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Abstract

The invention belongs to the technical field of high-speed steel, and particularly relates to high-cobalt high-molybdenum superhard high-speed steel and a method for improving the hot working performance of the high-cobalt high-molybdenum superhard high-speed steel. The improvement method provided by the invention comprises the following steps: carrying out induction smelting on industrial pure iron, a chromium-containing raw material, a molybdenum-containing raw material, metal tungsten, metal cobalt, graphite, industrial silicon, a manganese-containing raw material and a vanadium-containing raw material to obtain molten steel; carrying out pressurized electroslag remelting on the cast ingot obtained by casting the molten steel to obtain an electroslag ingot; the solidification pressure in the pressurized electroslag remelting process is 1-2 MPa; and sequentially carrying out high-temperature heat treatment and forging on the electroslag ingot to obtain the high-cobalt high-molybdenum superhard high-speed steel forging. By increasing the pressure of the pressurized electroslag remelting and solidification, the cooling rate of an electroslag ingot is increased, and eutectic carbide is refined; simultaneously, M in the electroslag ingot is treated by high-temperature heat treatment 2 The C eutectic carbide is decomposed and spheroidized, the form and the size of the carbide are improved, and the hot workability and the processing yield of the high-cobalt high-molybdenum superhard high-speed steel are improved.

Description

High-cobalt high-molybdenum superhard high-speed steel and method for improving hot working performance thereof
Technical Field
The invention belongs to the technical field of high-speed steel, and particularly relates to high-cobalt high-molybdenum superhard high-speed steel and a method for improving the hot working performance of the high-cobalt high-molybdenum superhard high-speed steel.
Background
The high-speed steel has the advantages of high hardness, good wear resistance, excellent red hardness and the like, and is widely applied to the fields of cutters, high-load dies, aviation high-temperature bearings, high-performance rollers and the like. In recent years, with the rapid development of modern cutting processing technology, although high-speed steel faces the challenge of being replaced by materials such as hard alloy and the like, the high-speed steel can be used for manufacturing complex precision tools and impact-resistant and vibration-resistant cutting tools due to good processing performance, good strength and toughness matching and strong impact resistance, so far, the high-speed steel plays an important role in the field of tool materials, and particularly the demand of high-performance high-speed steel represented by M42 is still strong.
At present, the production flow of high-speed steel mainly takes a smelting process as a main process, namely smelting → LF + VD refining → electrode bar manufacturing for electroslag remelting → forging. However, due to the high content of alloying elements (Co, mo, W, cr, V, etc.) and the limited cooling capacity of conventional electroslag remelting, high-speed steel is prone to form serious segregation of carbon and alloying elements during solidification, and thus coarse network eutectic carbides are formed at grain boundaries. The existence of eutectic carbide can not only seriously cut the matrix, but also be used as a crack source and a crack propagation way, so that the grain boundary embrittlement of the high-speed steel is serious, the thermoplasticity is reduced, and further the high-speed steel is extremely easy to crack in the hot working processes of forging, rolling and the like, and the yield is low.
Disclosure of Invention
In view of the above, the present invention provides a high-cobalt high-molybdenum superhard high-speed steel and a method for improving the hot workability thereof. According to the invention, the hot processing performance of the high-cobalt high-molybdenum superhard high-speed steel is improved by improving the solidification pressure in the pressurized electroslag remelting process, adding a high-temperature heat treatment step and optimizing the forging process, so that the processing yield of the high-cobalt high-molybdenum superhard high-speed steel is improved.
In order to solve the technical problem, the invention provides a method for improving the hot working performance of high-cobalt high-molybdenum superhard high-speed steel, which comprises the following steps:
smelting industrial pure iron, a chromium-containing raw material, a molybdenum-containing raw material, metal tungsten, metal cobalt, graphite, industrial silicon, a manganese-containing raw material and a vanadium-containing raw material to obtain molten steel;
carrying out pressurized electroslag remelting on the cast ingot obtained by casting the molten steel to obtain an electroslag ingot; the solidification pressure in the pressurized electroslag remelting process is 1-2 MPa;
and sequentially carrying out high-temperature heat treatment and forging on the electroslag ingot to obtain the high-cobalt high-molybdenum superhard high-speed steel forging.
Preferably, the temperature of the high-temperature heat treatment is 1100-1140 ℃, and the heat preservation time is 6-10 h; the heating rate of heating to the temperature required by the heat treatment is 80-120 ℃/h.
Preferably, the voltage of the pressurized electroslag remelting is 33-40V, the current is 2200-3000A, and the pressure is 1-2 MPa.
Preferably, the smelting comprises the following steps:
carrying out induction smelting on industrial pure iron, a chromium-containing raw material, a molybdenum-containing raw material, metal tungsten and metal cobalt to obtain base molten steel;
adding partial graphite into the basic molten steel for vacuum carbon deoxidation to obtain pre-deoxidized molten steel;
adding a manganese-containing raw material, a vanadium-containing raw material, industrial silicon and residual graphite into the pre-deoxidized molten steel for alloying to obtain molten steel.
Preferably, the temperature of the induction melting is 1480-1530 ℃;
preferably, the vacuum degree of vacuum carbon deoxidation is less than 30Pa, the time is 20-30 min, and the temperature is 1430-1480 ℃.
Preferably, the alloying temperature is 1430-1480 ℃ and the time is 5-10 min.
Preferably, the high temperature heat treatment further comprises: coating the surface of the electroslag ingot with paint; the coating comprises an adhesive and powder, wherein the mass ratio of the adhesive to the powder is preferably 0.4-0.9: 1;
the powder comprises the following components in percentage by mass: 45 to 50% of SiO 2 ，22～26％Al 2 O 3 ，14～18％SiC，2～4％CeO 2 2-4% CaO, 5-8% white mud;
the adhesive is sodium silicate aqueous solution, and the density is 1.36-1.42 g/cm 3 。
Preferably, the forging temperature is 1090-1120 ℃ and the finish forging temperature is 960-980 ℃.
The invention also provides the ultra-hard high-speed steel with high cobalt, high molybdenum and the like prepared by the preparation method of the technical scheme, which comprises the following chemical components in percentage by mass: 0.9-1.2% of Mo, 8-10% of Co, 3-5% of Cr, 1-2.5% of W, 0.7-1.5% of V, 0.1-0.5% of Si, 0.1-0.5% of Mn, and the balance of Fe and inevitable impurities.
The invention provides a method for improving the hot working performance of high-cobalt high-molybdenum superhard high-speed steel, which comprises the following steps: smelting industrial pure iron, a chromium-containing raw material, a molybdenum-containing raw material, metal tungsten, metal cobalt, graphite, industrial silicon, a manganese-containing raw material and a vanadium-containing raw material to obtain molten steel; carrying out pressurized electroslag remelting on the cast ingot obtained by casting the molten steel to obtain an electroslag ingot; the solidification pressure in the pressurized electroslag remelting process is 1-2 MPa; and sequentially carrying out high-temperature heat treatment and forging on the electroslag ingot to obtain the high-cobalt high-molybdenum superhard high-speed steel forging. The invention can effectively reduce the air gap between the ingot and the crystallizer by improving the solidification pressure in the pressurizing electroslag remelting process, enhance the cooling effect of the crystallizer, and improve the cooling rate of the electroslag ingot, thereby refining the solidification structure, improving the distribution of eutectic carbide, and further improving the hot processing performance of the high-cobalt high-molybdenum superhard high-speed steel. The invention leads the M of the metastable state in the high-cobalt high-molybdenum superhard high-speed steel to be subjected to high-temperature heat treatment 2 C eutectic carbide is decomposed to generate M 6 C and MC stable carbides; m 2 The decomposition, the fracture and the spheroidization of the C eutectic carbide improve the continuity of a matrix and the form and the size of the carbide, thereby effectively improving the hot working performance of the high-cobalt high-molybdenum superhard high-speed steel and improving the processing yield of the high-cobalt high-molybdenum superhard high-speed steel.
Drawings
FIG. 1 is a microstructure diagram of an electroslag ingot prepared in example 1 after high-temperature heat treatment;
FIG. 2 is a microstructure diagram of an electroslag ingot prepared in example 2 after high-temperature heat treatment;
FIG. 3 is a microstructure diagram of a high-cobalt high-molybdenum superhard high-speed steel forging prepared in example 1;
FIG. 4 is a microstructure diagram of a high-cobalt high-molybdenum superhard high-speed steel forging prepared in example 2;
FIG. 5 is a surface topography of a high-cobalt high-molybdenum superhard high-speed steel forging prepared in example 1;
FIG. 6 is a surface topography map of a high-cobalt high-molybdenum superhard high-speed steel forging prepared in example 2;
FIG. 7 is a surface topography of a high-cobalt high-molybdenum superhard high-speed steel forging prepared in comparative example 1.
Detailed Description
The invention provides a method for improving the hot working performance of high-cobalt high-molybdenum superhard high-speed steel, which comprises the following steps:
smelting industrial pure iron, a chromium-containing raw material, a molybdenum-containing raw material, metal tungsten, metal cobalt, graphite, industrial silicon, a manganese-containing raw material and a vanadium-containing raw material to obtain molten steel;
carrying out pressurized electroslag remelting on the cast ingot obtained by casting the molten steel to obtain an electroslag ingot; the solidification pressure in the pressurized electroslag remelting process is 1-2 MPa;
and sequentially carrying out high-temperature heat treatment and forging on the electroslag ingot to obtain the high-cobalt high-molybdenum superhard high-speed steel forging.
The method comprises the steps of smelting industrial pure iron, a chromium-containing raw material, a molybdenum-containing raw material, metal tungsten, metal cobalt, graphite, industrial silicon, a manganese-containing raw material and a vanadium-containing raw material to obtain molten steel. In the present invention, the smelting preferably comprises the steps of:
carrying out induction smelting on industrial pure iron, a chromium-containing raw material, a molybdenum-containing raw material, metal tungsten and metal cobalt to obtain base molten steel;
adding partial graphite into the basic molten steel for vacuum carbon deoxidation to obtain pre-deoxidized molten steel;
and adding a manganese-containing raw material, a vanadium-containing raw material, industrial silicon and residual graphite into the pre-deoxidized molten steel for alloying and casting to obtain an ingot.
The invention carries out induction melting on industrial pure iron, chromium-containing raw materials, molybdenum-containing raw materials, metal tungsten and metal cobalt to obtain the basic molten steel. In the present invention, the chromium-containing feedstock preferably comprises metallic chromium or ferrochrome, more preferably metallic chromium. In the present invention, the molybdenum-containing raw material preferably includes metallic molybdenum or ferromolybdenum, and more preferably metallic molybdenum. The invention has no special requirements on the mass ratio of the industrial pure iron to the chromium-containing raw material to the molybdenum-containing raw material to the metal tungsten to the metal cobalt, and the industrial pure iron and chromium-containing raw material to the metal tungsten to the metal cobalt are proportioned according to the content of the chemical components of the required high-speed steel.
In the invention, the induction melting is preferably vacuum induction melting; the vacuum degree of the vacuum induction melting is preferably less than 10Pa, and more preferably 5-8 Pa; the temperature of the vacuum induction melting is preferably 1480-1530 ℃, and more preferably 1500-1510 ℃.
After the basic molten steel is obtained, partial graphite is added into the basic molten steel for vacuum carbon deoxidation to obtain pre-deoxidation molten steel. In the present invention, the mass percentage of the partial graphite to the total mass of the graphite is preferably 40 to 80%, and more preferably 50 to 60%. In the present invention, the mass ratio of the total mass of graphite to carbon in the ingot is preferably 1.03 to 1.08:1, more preferably 1.05 to 1.07:1. in the present invention, the graphite is used for deoxidation in addition to carbon in the target high-speed steel.
In the present invention, the process of adding part of the graphite to the base molten steel is preferably performed under a protective atmosphere, the protective atmosphere is preferably argon gas with a purity of not less than 99.999%, and the pressure of the protective atmosphere is preferably 0.01 to 0.05MPa, and more preferably 0.02 to 0.03MPa. In the present invention, the vacuum carbon deoxidation is preferably performed under vacuum conditions, and the degree of vacuum of the vacuum conditions is preferably less than 30Pa, and more preferably 10 to 20Pa. In the present invention, the temperature of the vacuum carbon deoxidation is preferably 1430 to 1480 ℃, more preferably 1450 to 1470 ℃. In the present invention, the time for the vacuum carbon deoxidation is preferably 20 to 30min, and more preferably 20 to 25min.
In the invention, the vacuum carbon deoxidation can effectively reduce the oxygen content in the molten steel, is beneficial to improving the cleanliness of the electroslag ingot and avoids oxygen element from deteriorating the thermoplasticity of the high-cobalt high-molybdenum superhard high-speed steel.
After the pre-deoxidized molten steel is obtained, the manganese-containing raw material, the vanadium-containing raw material, the industrial silicon and the residual graphite are added into the pre-deoxidized molten steel for alloying to obtain the molten steel. In the present invention, the manganese-containing raw material preferably includes metallic manganese and electrolytic manganese, more preferably metallic manganese. In the present invention, the vanadium-containing raw material preferably includes metal vanadium or ferrovanadium, more preferably metal vanadium. The invention has no special requirements on the mass ratio of the industrial silicon to the manganese-containing raw material to the vanadium-containing raw material, and the industrial silicon to the manganese-containing raw material to the vanadium-containing raw material is prepared according to the content of the chemical components of the required high-speed steel.
In the invention, a manganese-containing raw material, a vanadium-containing raw material, industrial silicon and residual graphite are added into the pre-deoxidized molten steel, preferably, the manganese-containing raw material, the vanadium-containing raw material, the industrial silicon and the residual graphite are sequentially added into the pre-deoxidized molten steel; the time interval for adding the manganese-containing raw material, the vanadium-containing raw material, the industrial silicon and the residual graphite is preferably 1-3 min, and more preferably 2min. The present invention preferably performs alloying during the addition process. In the present invention, the alloying process is preferably performed under a protective atmosphere, the protective atmosphere is preferably argon gas with a purity of 99.999% or more, and the pressure of the protective atmosphere is preferably 0.01 to 0.03MPa, and more preferably 0.02 to 0.03MPa. In the present invention, the temperature of the alloying is preferably 1430 to 1480 ℃, more preferably 1450 to 1470 ℃.
In the invention, after the manganese-containing raw material, the vanadium-containing raw material, the industrial silicon and the residual graphite are added into the pre-deoxidized molten steel, the addition of magnesium alloy and rare earth is preferably further included for deep deoxidation and deep desulfurization. In the present invention, the magnesium alloy preferably includes a nickel-magnesium alloy or an iron-magnesium alloy, and more preferably a nickel-magnesium alloy. In the present invention, the magnesium content in the magnesium alloy is preferably 5 to 20% by mass. In the present invention, the rare earth preferably comprises cerium or lanthanum, more preferably cerium. In the invention, the addition amount of magnesium in the magnesium alloy is preferably 0.006-0.012 kg, more preferably 0.008-0.10 kg based on one ton of high-cobalt high-molybdenum superhard high-speed steel; the amount of the rare earth added is preferably 0.3 to 0.6kg, more preferably 0.4 to 0.5kg.
According to the invention, by adding the magnesium alloy and the rare earth into the molten steel, oxygen and sulfur impurities in the molten steel can be further reduced, the cleanliness of the electroslag ingot is improved, and the oxygen and sulfur impurity elements are prevented from deteriorating the thermoplasticity of the high-cobalt high-molybdenum superhard high-speed steel.
After molten steel is obtained, casting ingots obtained by casting the molten steel to perform pressurized electroslag remelting to obtain electroslag ingots; the solidification pressure in the pressurizing electroslag remelting process is 1-2 MPa.
In the present invention, the temperature of the molten steel at the time of casting is preferably 1430 to 1480 ℃ and more preferably 1450 to 1470 ℃. In the present invention, the casting method further preferably comprises: and keeping the temperature of the molten steel at the casting temperature. In the present invention, the time for the heat-retention is preferably 2 to 4min, more preferably 3min. The invention has no special requirements on the casting and can adopt a conventional mode in the field.
In the present invention, the pressurized electroslag remelting is preferably performed in a pressurized electroslag remelting furnace. The invention preferably forges the cast ingot to obtain the consumable electrode which is suitable for the size of the pressurized electroslag remelting furnace crystallizer. The size of the consumable electrode is not specially limited, and the consumable electrode can be adapted to the size of the crystallizer of the pressurized electroslag remelting furnace. In an embodiment of the invention, the consumable electrode is a rod of 80mm diameter. In the present invention, the pressurized electroslag remelting process preferably further comprises: welding the consumable electrode to a dummy electrode and connecting the dummy electrode to an electrode holder; placing arc striking scraps in an arc striking ring at the center of a pressurized electroslag remelting furnace bottom water tank; and baking the pre-melted slag, and adding the baked pre-melted slag into a crystallizer of a pressurized electroslag remelting furnace for arc starting and slag making.
The present invention also preferably includes, prior to welding the consumable electrode to the dummy electrode: and polishing the surface of the consumable electrode. In the present invention, the present invention does not specifically limit the polishing operation, and a polishing operation conventional in the art may be used. The periphery of the consumable electrode is polished by the invention to remove oxide skin, so that oxygen enrichment in the electroslag ingot can be prevented.
In the present invention, the material of the arc ignition scrap is preferably the same as that of the target high speed steel. In the embodiment of the present invention, the amount of the arc ignition scrap is preferably 0.25 to 0.35kg, and more preferably 0.28 to 0.32kg. In the invention, a gasket is preferably arranged between the arc ignition ring and the pressurizing electroslag remelting furnace crystallizer, and the gasket is preferably made of cast iron. The diameter of the shim in embodiments of the invention is preferably 108 to 112mm, more preferably 110mm; the thickness of the gasket is preferably 8 to 12mm, more preferably 10mm. In the invention, the consumable electrode, the arc striking chips and the pressurized electroslag remelting furnace bottom water tank are in close contact, so that current can pass after electrification is ensured.
In the present invention, the pre-melted slag preferably comprises 55 to 65% of CaF by mass 2 ，15～25％CaO，15～25％Al 2 O 3 And unavoidable impurities; more preferably 58 to 62% CaF 2 ，18～22％CaO，18～22％Al 2 O 3 And inevitable impurities. In the present invention, the amount of the premelting slag is preferably 3 to 3.6kg, more preferably 3.3 to 3.5kg. In the invention, the baking temperature is preferably 600-800 ℃, and more preferably 650-750 ℃; the time is preferably 6 to 10 hours, more preferably 8 to 9 hours.
In the present invention, before the arc starting and slagging, the method further preferably comprises: and introducing argon into the pressurized electroslag remelting furnace. The purity of the argon is preferably more than or equal to 99.999 percent, the flow rate of the introduced argon is preferably 10-20 NL/min, more preferably 12-15 NL/min, and the time is preferably 4-10 min, more preferably 5-8 min. The invention removes the air in the pressurized electroslag remelting furnace by introducing argon. In the invention, the voltage for arc starting and slagging is preferably 25-33V, and more preferably 28-30V; the current is preferably 1200 to 2100A, more preferably 1600 to 2000A; the time is preferably 7 to 15min, more preferably 10 to 15min.
In the present invention, the voltage of the pressurized electroslag remelting is preferably 33 to 40V, more preferably 35 to 40V; the current is preferably 2200 to 3000A, more preferably 2200 to 2500A. In the present invention, the fluctuation of the voltage and current is preferably less than 5%. In the present invention, the melting rate of the pressurized electroslag remelting is preferably determined according to formula 1:
v = (0.35-0.45) × D kg/h formula 1;
wherein D is the size of the crystallizer of the pressurized electroslag remelting furnace and the unit is mm. In the examples of the present invention, the melt rate was specifically 50kg/h. In the present invention, the melting rate fluctuation is preferably less than 5%. In the present invention, the pressure of the pressurized electroslag remelting is preferably 1 to 2MPa, and more preferably 1.5 to 1.8MPa. In the present invention, the pressure is preferably formed by introducing argon gas into the melting chamber of the pressurized electroslag remelting furnace. In the invention, the solidification pressure in the pressurized electroslag remelting process is 1-2 MPa, preferably 1.5-1.8 MPa, and the solidification pressure refers to the gas pressure in the smelting chamber. The invention preferably fills argon into the melting chamber of the pressurized electroslag remelting furnace and simultaneously improves the pressure of the cooling water in the jacket of the crystallizer, so that the pressure of the cooling water is consistent with the pressure in the melting chamber. In the invention, the cooling mode of the pressurized electroslag remelting is cooling water cooling.
In the present invention, the pressurized electroslag remelting preferably further comprises: feeding and filling are carried out in a mode of gradually reducing current; and (5) closing the power supply, releasing pressure and taking out the electroslag ingot.
The invention adopts a mode of gradually reducing current to carry out feeding filling. In the present invention, the current is reduced by preferably 500 to 1000A, more preferably 600 to 800A, each time, so as to ensure sufficient feeding and filling and ensure flat feeding end face. In the present invention, the frequency of the current reduction is preferably 3 to 5 min/time, and more preferably 4 min/time.
After feeding and filling are finished, the electroslag ingot furnace closes a power supply, releases pressure and takes out the electroslag ingot. In the present invention, the pressure relief is preferably performed by reducing the pressure in the pressurized electroslag remelting furnace and in the crystallizer, and the pressure after the pressure relief is normal pressure. After the electroslag ingot is taken out, the electroslag ingot is preferably placed in a heat-insulating cover for slow cooling so as to prevent cracking.
After obtaining the electroslag ingot, sequentially carrying out high-temperature heat treatment and forging on the electroslag ingot to obtain the high-cobalt high-molybdenum superhard high-speed steel forging. In the present invention, the high temperature heat treatment preferably further comprises: coating the surface of the electroslag ingot with paint. In the present invention, the coating material preferably includes a binder and a powder material. In the invention, the adhesive is excellentSelected from sodium silicate aqueous solution (water glass), the density of the adhesive is preferably 1.36-1.42 g/cm 3 . In the invention, the powder material preferably comprises the following components in percentage by mass: 45 to 50% of SiO 2 ，22～26％Al 2 O 3 ，14～18％SiC，2～4％CeO 2 2-4% CaO, 5-8% white mud; the powder preferably comprises 45 to 50% by mass of SiO 2 More preferably 46 to 48%. The powder preferably contains 22 to 26% by mass of Al 2 O 3 More preferably 23 to 25%. In the invention, the low-melting-point sodium silicate is melted into a film at high temperature to bond silicon dioxide and aluminum oxide to form a compact glassy coating film to protect an electroslag ingot at a high-temperature stage. The powder preferably comprises, in mass%, 14 to 18% SiC, more preferably 15 to 17%. In the present invention, the SiC is mixed with O 2 The reaction reduces the oxygen potential around the coating and increases the protective effect of the coating at the low temperature stage. The powder preferably comprises, in mass percent, 2 to 4% CeO 2 More preferably 2.5 to 3.5%. In the invention, the cerium dioxide can improve the adhesion between the coating and the electroslag ingot, so that the coating can still be tightly combined with the electroslag ingot at high temperature. The powder preferably contains CaO in an amount of 2 to 4% by mass, more preferably 2.5 to 3.5% by mass. In the invention, the calcium oxide can improve the fluidity and lubricity of the coating at high temperature, so that the coating can uniformly cover the surface of the electroslag ingot. The powder material also preferably comprises 5 to 8 percent of white mud, more preferably 6 to 7 percent of white mud in percentage by mass.
In the present invention, the average particle size of the powder is preferably 100 to 200 mesh, more preferably 100 to 150 mesh. In the present invention, the mass ratio of the binder to the powder is preferably 0.4 to 0.9:1, more preferably 0.5 to 0.7:1. in the present invention, the thickness of the coating layer after coating is preferably 0.3 to 0.6mm, more preferably 0.4 to 0.5mm.
In the present invention, the coating has good chemical stability, moderate surface tension, strong adhesion, good wetting and high temperature resistance. The coating is coated on the surface of the electroslag ingot, so that the severe oxidation and decarburization of the electroslag ingot in the heat treatment process can be avoided; meanwhile, the oxidation burning loss amount and the decarburized layer thickness of the electroslag ingot in the heat treatment process can be obviously reduced.
In the present invention, the coating preferably further comprises: and drying the electroslag ingot coated with the coating. In the present invention, the temperature of the drying is preferably 20 to 50 ℃, more preferably 25 to 40 ℃; the time is preferably 8 to 15 hours, more preferably 9 to 12 hours.
In the present invention, the temperature of the high-temperature heat treatment is preferably 1100 to 1140 ℃, more preferably 1120 to 1130 ℃; the holding time is preferably 6 to 10 hours, more preferably 6 to 8 hours. In the present invention, the rate of temperature rise to the temperature required for the heat treatment is preferably 80 to 120 ℃/h, more preferably 80 to 100 ℃/h. In the present invention, the initial temperature of the temperature rise is preferably less than 200 ℃, more preferably less than 150 ℃. In the present invention, the high temperature heat treatment process causes M in a metastable state 2 C eutectic carbide is decomposed to generate M 6 C and MC stable carbides; the decomposition reaction is shown as formula 1:
M 2 C+γ(Fe)→M 6 c + MC is represented by formula 1.
In the present invention, the forging method preferably further comprises: preheating the hammering block; the temperature after preheating is preferably 150 to 200 ℃. In the present invention, the forging temperature is preferably 1090 to 1120 ℃, more preferably 1100 to 1110 ℃; the finish forging temperature is preferably 960 to 980 ℃, and more preferably 970 to 980 ℃. In the present invention, when the forging temperature is 1050 ℃ or more, tapping is preferable to prevent the ingot from cracking; when the temperature of the forging is 980-1050 ℃, heavy impact is preferred to ensure that the carbide in the forging can be broken. In the present invention, the number of times of forging is preferably 3 to 5 times, and the total forging ratio of forging is preferably 12 to 16.
According to the invention, the cracking tendency of the electroslag ingot in the forging process can be reduced by selecting different striking degrees at different forging temperatures, and meanwhile, coarse eutectic carbide in the electroslag ingot can be crushed, so that a fine and uniformly distributed structure of the carbide is obtained. The invention performs forging under a large forging ratio, can fully deform the high-speed steel, can effectively break an as-cast structure, further reduces the size of carbide and uniformly distributes the carbide.
In the present invention, the forging preferably further includes: and cooling the forged product, wherein the cooling rate of the cooling is preferably 80-120 ℃/h, and more preferably 80-100 ℃/h. In the invention, the cooling preferably comprises cooling the forged product in a heating furnace or cooling the forged product by covering a heat insulating material on the surface.
The invention also provides the high-speed steel prepared by the preparation method of the technical scheme, which comprises the following chemical components in percentage by mass:
Figure BDA0003111940730000091
Figure BDA0003111940730000101
in the invention, the high-speed steel preferably comprises the following chemical components in percentage by mass:
Figure BDA0003111940730000102
in order to further illustrate the present invention, the following embodiments are described in detail, but they should not be construed as limiting the scope of the present invention.
In the embodiment of the invention, the induction melting is carried out in a 50kg vacuum induction furnace, wherein the ultimate vacuum degree is 0.1Pa, and the charging amount is 40-45 kg.
In the embodiment of the invention, the pressurized electroslag remelting is carried out in a 50kg pressurized electroslag remelting furnace, the highest pressure of the pressurized electroslag remelting furnace is 7MPa, the rated power of a power supply is 500kW, the inner diameter D of a crystallizer is 130mm, and the weight of a consumable electrode is 30-50 kg.
In the embodiment of the invention, the purity of industrial pure iron and iron is 99.9wt%, the purity of metal chromium is 99.15wt%, the purity of metal molybdenum is 99.98wt%, the purity of metal cobalt is 99.94wt%, the purity of metal tungsten is 99.95wt%, the purity of metal vanadium is more than or equal to 99.9wt%, the purity of industrial silicon is 99.93wt%, the purity of metal manganese is 97.65wt%, the purity of graphite is more than or equal to 99.9wt%, the purity of nickel-magnesium alloy contains 19.65wt%, the purity of nickel is 80.37wt%, the purity of cerium is more than or equal to 99.5wt%, and the purity of argon in each step is more than or equal to 99.999%.
In the embodiment of the invention, the pre-melted slag comprises CaF 2 ：60±1％，Al 2 O 3 :20 +/-1%, caO:20 plus or minus 1 percent, and the balance of inevitable impurities.
Example 1
31.248kg industrial pure iron, 1.575kg metal chromium, 3.99kg metal molybdenum, 0.63kg metal tungsten and 3.36kg metal cobalt are placed in a crucible in a vacuum induction furnace, and induction melting is carried out under the conditions that the temperature is 1505 ℃, the vacuum degree is 5Pa, and basic molten steel is obtained;
filling argon with the purity of more than or equal to 99.999 percent into a vacuum induction furnace to ensure that the pressure in the furnace is 0.025MPa, adding 0.255kg of graphite (5 percent more on the basis of target components) into the primary molten steel in the argon atmosphere, starting a vacuum pump after the graphite is melted down to perform vacuum carbon deoxidation, wherein the vacuum degree of the vacuum carbon deoxidation is 15Pa, the temperature is 1480 ℃, and the time is 24min to obtain pre-deoxidized molten steel;
filling argon with the purity of more than or equal to 99.999 percent into the furnace to ensure that the pressure in the furnace is 0.02MPa, and sequentially adding 0.126kg of metal manganese, 0.483kg of metal vanadium, 0.126kg of industrial silicon, 0.230kg of graphite, 0.042kg of nickel-magnesium alloy and 0.021kg of cerium into the pre-deoxidized molten steel at the temperature of 1480 ℃ at intervals of 2min to obtain molten steel;
keeping the temperature of the molten steel at 1470 ℃ for 3min, and then casting to obtain a cast ingot; forging the cast ingot to obtain a consumable electrode with the diameter phi =80mm, welding the consumable electrode to a dummy electrode, and connecting the dummy electrode with an electrode holder;
placing 0.32kg of arc striking scraps (1.1% C,0.3% Si,0.3% Mn,3.75% Cr,9.5% Mo,8% Co,1.5% W,1.15% V and the balance Fe) in an arc striking ring at the center of a bottom tank of a pressurized electroslag remelting furnace (the consumable electrode, the arc striking scraps and the bottom tank of the pressurized electroslag remelting furnace are in close contact); wherein a gasket which has the diameter of 110mm, the thickness of 10mm and is made of cast iron is arranged between the arc striking ring and the water tank;
baking 3.35kg of premelting slag at 650 ℃ for 8 hours, adding the premelting slag into a crystallizer of a pressurized electroslag remelting furnace, and then sealing the pressurized electroslag furnace; starting a water supply system to introduce normal-pressure cooling water into the crystallizer; introducing argon gas with the flow rate of 15NL/min into the pressurized electroslag remelting furnace for 6min; carrying out arc starting and slagging for 12min under the conditions that the voltage is 28V and the current is 1600A;
after the arcing and slagging are finished, introducing argon into a smelting chamber of the pressurized electroslag remelting furnace to ensure that the pressure in the smelting chamber of the pressurized electroslag remelting furnace is 1.8MPa, the pressure of cooling water in a crystallizer jacket of the pressurized electroslag remelting furnace is 1.8MPa, and pressurized electroslag remelting (with the smelting speed of 50 kg/h) is carried out under the conditions that the voltage is 37V and the current is 2300A;
after the consumable electrode is smelted, feeding and filling are carried out in a mode of gradually reducing current, the current is reduced once every 4min, and the current is reduced by 550A each time;
after the completion of the shrinkage, closing an alternating current power supply, opening a vent valve of the pressurized electroslag furnace to release pressure, and synchronously reducing the pressure of cooling water in a crystallizer of the pressurized electroslag furnace to normal pressure to obtain an electroslag ingot; placing the electroslag ingot in a heat-preserving cover for cooling;
coating a coating with a thickness of 0.4mm on the surface of the electroslag ingot (powder composition: 48% SiO% 2 ，24％Al 2 O 3 ，16％SiC，3％CeO 2 3% CaO,6% white mud; the adhesive has a density of 1.38g/cm 3 An aqueous sodium silicate solution; the mass ratio of the binder to the powder is 0.6: 1) Then drying for 12h at 25 ℃; placing the electroslag ingot coated with the coating in a heating furnace with the initial temperature of 150 ℃ to raise the temperature to 1130 ℃ according to the temperature rise rate of 100 ℃/h, and carrying out high-temperature heat treatment for 6h;
preheating a hammer anvil to 150 ℃, forging the electroslag ingot after heat treatment (the forging starting temperature is 1100 ℃, and the final forging temperature is 980 ℃), tapping when the temperature is above 1050 ℃, tapping when the temperature is 980-1050 ℃, and returning to a heating furnace for reheating when the temperature is below 980 ℃; repeatedly forging for 3 times to obtain a round bar with the diameter of 40mm, wherein the total forging ratio is 12; and then, the forged product is placed in a heating furnace and cooled to room temperature according to the cooling rate of 100 ℃/h, and the high-cobalt high-molybdenum superhard high-speed steel forging is obtained.
Example 2
31.992kg industrial pure iron, 1.613kg chromium metal, 4.085kg molybdenum metal, 0.645kg tungsten metal and 3.440kg cobalt metal are placed in a crucible in an induction furnace, and induction melting is carried out under the conditions that the temperature is 1515 ℃ and the vacuum degree is 7Pa, so as to obtain basic molten steel;
filling argon with the purity of more than or equal to 99.999 percent into a vacuum induction furnace to ensure that the pressure in the furnace is 0.026MPa, adding 0.261kg of graphite (0.059 percent on the basis of target components) into the basic molten steel in the argon atmosphere, starting a vacuum pump after the graphite is melted down to perform vacuum carbon deoxidation, wherein the vacuum degree of the vacuum carbon deoxidation is 12Pa, the temperature is 1475 ℃, and the time is 25min to obtain pre-deoxidation molten steel;
argon with the purity of more than or equal to 99.999 percent is filled into the furnace to ensure that the pressure in the furnace is 0.03MPa, and 0.129kg of metal manganese, 0.495kg of metal vanadium, 0.129kg of industrial silicon, 0.240kg of graphite, 0.043kg of nickel-magnesium alloy and 0.022kg of cerium are added into the pre-deoxidized molten steel in sequence (at intervals of 2 min) at 1475 ℃ to be alloyed to obtain molten steel;
cooling the molten steel to 1472 ℃, preserving heat for 3min, and then casting to obtain a cast ingot; forging the cast ingot to obtain a consumable electrode with the diameter phi =80mm, welding the consumable electrode to a dummy electrode, and connecting the dummy electrode with an electrode holder;
placing 0.33kg of arc striking scraps (1.1% C,0.3% Si,0.3% Mn,3.75% Cr,9.5% Mo,8% Co,1.5% W,1.15% V and the balance Fe) in an arc striking ring at the center of the bottom tank of the pressurized electroslag remelting furnace (the consumable electrode, the arc striking scraps and the bottom tank of the pressurized electroslag remelting furnace are in close contact); wherein a gasket which has the diameter of 110mm, the thickness of 10mm and is made of cast iron is arranged between the arc ignition ring and the water tank;
baking 3.35kg of premelting slag at 650 ℃ for 8 hours, adding the premelting slag into a crystallizer of a pressurized electroslag remelting furnace, and then sealing the pressurized electroslag furnace; starting a water supply system to introduce normal-pressure cooling water into the crystallizer; introducing argon gas with the flow rate of 15NL/min into the pressurized electroslag remelting furnace for 6min; carrying out arc starting and slagging for 12min under the conditions that the voltage is 27V and the current is 1600A;
after the arc starting and slagging are finished, argon is introduced into a smelting chamber of the pressurized electroslag remelting furnace, so that the pressure in the smelting chamber of the pressurized electroslag remelting furnace is 1.8MPa, the pressure of cooling water in a crystallizer jacket of the pressurized electroslag remelting furnace is 1.8MPa, and pressurized electroslag remelting (with the smelting speed of 50 kg/h) is carried out under the conditions that the voltage is 38V and the current is 2250A;
when the consumable electrode is smelted, feeding filling is carried out in a mode of gradually reducing current, the current is reduced once every 4min, and the current is reduced by 550A each time;
after the completion of the shrinkage, closing an alternating current power supply, opening a vent valve of the pressurized electroslag furnace to release pressure, and synchronously reducing the pressure of cooling water in a crystallizer of the pressurized electroslag furnace to normal pressure to obtain an electroslag ingot; placing the electroslag ingot in a heat-preserving cover for cooling;
coating a coating material (powder composition: 48%; siO) having a thickness of 0.45mm on the surface of the electroslag ingot 2 ，24％Al 2 O 3 ，16％SiC，3％CeO 2 3% CaO,6% white mud; the adhesive has a density of 1.38g/cm 3 An aqueous sodium silicate solution; the mass ratio of the binder to the powder is 0.6: 1) Drying at 27 deg.C for 10 hr; placing the electroslag ingot coated with the coating in a heating furnace with the initial temperature of 100 ℃ to heat up to 1120 ℃ according to the heating rate of 100 ℃/h, and carrying out high-temperature heat treatment for 8h;
preheating a hammer anvil to 150 ℃, forging the electroslag ingot after heat treatment (the forging starting temperature is 1100 ℃, and the forging finishing temperature is 980 ℃), wherein tapping is carried out when the temperature is above 1050 ℃, tapping is carried out when the temperature is 980-1050 ℃, and returning to a heating furnace for reheating when the temperature is below 980 ℃; repeatedly forging for 3 times to obtain a round bar with the diameter of 40mm, wherein the total forging ratio is 12; and then the forged product is placed in a heating furnace and cooled to room temperature according to the cooling rate of 90 ℃/h, and the high-cobalt high-molybdenum superhard high-speed steel forging is obtained.
Comparative example 1
30.504kg industrial pure iron, 1.538kg metal chromium, 3.895kg metal molybdenum, 0.615kg metal tungsten and 3.280kg metal cobalt are placed in a crucible in an induction furnace, and induction melting is carried out at the temperature of 1490 ℃ and under the vacuum degree of 6Pa, so as to obtain base molten steel;
filling argon with the purity of more than or equal to 99.999 percent into a vacuum induction furnace to ensure that the pressure in the furnace is 0.025MPa, adding 0.244kg of graphite (5 percent more on the basis of target components) into the basic molten steel in the argon atmosphere, starting a vacuum pump after the graphite is melted down to perform vacuum carbon deoxidation, wherein the vacuum degree of the vacuum carbon deoxidation is 14Pa, the temperature is 1510 ℃, and the time is 25min to obtain pre-deoxidation molten steel;
argon with the purity of more than or equal to 99.999 percent is filled into the furnace to ensure that the pressure in the furnace is 40kPa, and 0.123kg of metal manganese, 0.472kg of metal vanadium, 0.123kg of industrial silicon, 0.230kg of graphite, 0.041kg of nickel-magnesium alloy and 0.020kg of cerium are added into the pre-deoxidized molten steel in sequence (at an interval of 3 min) at the temperature of 1505 ℃ to obtain alloyed molten steel;
cooling the alloying molten steel to 1467 ℃, preserving heat for 3min, and then casting to obtain a cast ingot; forging the cast ingot to obtain a consumable electrode with the diameter phi =80mm, welding the consumable electrode to a dummy electrode, and connecting the dummy electrode with an electrode holder;
placing 0.33kg of arc striking scraps (1.1% C,0.3% Si,0.3% Mn,3.75% Cr,9.5% Mo,8% Co,1.5% W,1.15% V and the balance Fe) in an arc striking ring at the center of the bottom tank of the pressurized electroslag remelting furnace (the consumable electrode, the arc striking scraps and the bottom tank of the pressurized electroslag remelting furnace are in close contact); wherein a gasket which has the diameter of 110mm, the thickness of 10mm and is made of cast iron is arranged between the arc ignition ring and the water tank;
baking 3.3kg of premelting slag at 650 ℃ for 9 hours, adding the premelting slag into a crystallizer of a pressurized electroslag remelting furnace, and then sealing the pressurized electroslag furnace; starting a water supply system to introduce normal-pressure cooling water into the crystallizer; introducing argon gas with the flow rate of 15NL/min into the pressurized electroslag remelting furnace for 6min; carrying out arc starting and slagging for 13min under the conditions that the voltage is 28V and the current is 1600A;
after the arc starting and slagging are finished, argon is introduced into the smelting chamber of the pressurized electroslag remelting furnace, so that the pressure in the smelting chamber of the pressurized electroslag remelting furnace is 0.1MPa, meanwhile, the pressure of cooling water in a crystallizer jacket of the pressurized electroslag remelting furnace is 0.1MPa, and pressurized electroslag remelting (with the smelting speed of 50 kg/h) is carried out under the conditions that the voltage is 37V and the current is 2250A;
after the consumable electrode is smelted, feeding filling is carried out in a mode of gradually reducing current, the current is reduced once every 4min, and the current is reduced 550A each time;
after the completion of the shrinkage, closing an alternating current power supply, opening a vent valve of the pressurized electroslag furnace to release pressure, and synchronously reducing the pressure of cooling water in a crystallizer of the pressurized electroslag furnace to normal pressure to obtain an electroslag ingot; placing the electroslag ingot in a heat-preserving cover for cooling;
coating a coating material (powder composition: 48%; siO) having a thickness of 0.4mm on the surface of the electroslag ingot 2 ，24％Al 2 O 3 ，16％SiC，3％CeO 2 3% CaO,6% white mud; the adhesive has a density of 1.38g/cm 3 An aqueous sodium silicate solution; the mass ratio of the binder to the powder is 0.6: 1) Then drying for 12h at room temperature and 25 ℃; preheating an anvil to 150 ℃, putting the electroslag ingot coated with the coating into a heating furnace at the temperature of 150 ℃ to be heated to 1120 ℃, preserving heat for 1h, and forging (the start forging temperature is 1100 ℃, and the finish forging temperature is 980 ℃), wherein when the temperature is above 1050 ℃, the ingot is tapped, when the temperature is 980-1050 ℃, the ingot is tapped, and when the temperature is below 980 ℃, the ingot is returned to the heating furnace for reheating; repeatedly forging for 3 times to obtain a round bar with the diameter of 40mm, wherein the total forging ratio is 12; and then the forged product is placed in a heating furnace and cooled to room temperature according to the cooling rate of 90 ℃/h, and the high-cobalt high-molybdenum superhard high-speed steel forging is obtained.
The microstructure of the electroslag ingots prepared in examples 1 and 2 after the high-temperature heat treatment was observed by a metallographic microscope to obtain a microstructure diagram, as shown in fig. 1 and 2. The observation sample was taken from a 1/2 radius portion of the electroslag ingot prepared in examples 1 and 2. As can be seen from FIGS. 1 and 2, M in the high-speed steel prepared by the preparation method provided by the present invention 2 The C eutectic carbide is fully decomposed, fractured and spheroidized, and the form and the size of the carbide are improved.
The microstructure of the superhard high-speed steel forging with high cobalt and high molybdenum prepared in the embodiments 1 and 2 is observed by a metallographic microscope to obtain a microstructure diagram, as shown in fig. 3 and 4. The observation sample is taken from the central part of the super-hard high-speed steel forging with high cobalt and high molybdenum prepared in the embodiments 1 and 2. As can be seen from FIGS. 3 and 4, the carbides in the high-speed steel prepared by the preparation method provided by the present invention are finely dispersed and uniformly distributed.
FIGS. 5 to 7 are surface topography maps of the high-cobalt high-molybdenum superhard high-speed steel forgings prepared in examples 1 and 2 and comparative example 1 respectively. Comparing fig. 5 to 7, it can be seen that the high-speed steel prepared by the preparation method of the present invention has good surface quality and no crack defect after forging, while the high-speed steel prepared by the comparative example has cracking and deep transverse cracks after forging, which indicates that the high-speed steel prepared by the preparation method of the present invention has good hot workability.
Although the present invention has been described in detail with reference to the above embodiments, it is only a part of the embodiments of the present invention, not all of the embodiments, and other embodiments can be obtained without inventive step according to the embodiments, and the embodiments are within the scope of the present invention.

Claims (7)

1. A method for improving the hot working performance of high-cobalt high-molybdenum superhard high-speed steel comprises the following steps:
smelting industrial pure iron, a chromium-containing raw material, a molybdenum-containing raw material, metal tungsten, metal cobalt, graphite, industrial silicon, a manganese-containing raw material and a vanadium-containing raw material to obtain molten steel;
carrying out pressurized electroslag remelting on the cast ingot obtained by casting the molten steel to obtain an electroslag ingot; the solidification pressure in the pressurized electroslag remelting process is 1 to 1.8MPa;
sequentially carrying out high-temperature heat treatment and forging on the electroslag ingot to obtain a high-cobalt high-molybdenum superhard high-speed steel forging; the temperature of the high-temperature heat treatment is 1100 to 1140 ℃, and the heat preservation time is 6 to 10 hours; the heating rate of heating to the temperature required by heat treatment is 80 to 120 ℃/h; the high-cobalt high-molybdenum superhard high-speed steel forging comprises the following chemical components in percentage by mass: 0.9 to 1.2 percent of C,8 to 10 percent of Mo,7~9 percent of Co,3~5 percent of Cr,1 to 2.5 percent of W,0.7 to 1.5 percent of V,0.1 to 0.5 percent of Si,0.1 to 0.5 percent of Mn, and the balance of Fe and inevitable impurities;
the forging temperature is 1090-1120 ℃, and the finish forging temperature is 960-980 ℃; the forging times are 3~5, and the total forging ratio of forging is 12 to 16; when the temperature of the forging is above 1050 ℃, flicking to prevent the steel ingot from cracking; when the temperature of the forging is 980-1050 ℃, the heavy impact is carried out to ensure that the carbide in the forging can be broken.
2. The method according to claim 1, wherein the voltage of the pressurized electroslag remelting ranges from 33 to 40V, the current ranges from 2200 to 3000A, and the pressure ranges from 1 to 2MPa.
3. The method of claim 1, wherein the smelting comprises the steps of:
carrying out induction melting on industrial pure iron, a chromium-containing raw material, a molybdenum-containing raw material, metal tungsten and metal cobalt to obtain basic molten steel;
adding partial graphite into the basic molten steel for vacuum carbon deoxidation to obtain pre-deoxidized molten steel;
adding a manganese-containing raw material, a vanadium-containing raw material, industrial silicon and residual graphite into the pre-deoxidized molten steel for alloying to obtain molten steel.
4. The method of claim 3, wherein the induction melting temperature is 1480 to 1530 ℃.
5. The method as claimed in claim 3, wherein the vacuum degree of vacuum carbon deoxidation is less than 30Pa, the time is 20 to 30min, and the temperature is 1430 to 1480 ℃.
6. The method as claimed in claim 3, wherein the alloying temperature is 1430 to 1480 ℃ and the alloying time is 5 to 10min.
7. The method of claim 1, further comprising, prior to the high temperature heat treatment: coating the surface of the electroslag ingot with paint; the coating comprises an adhesive and powder, wherein the mass ratio of the adhesive to the powder is 0.4-0.9: 1;
the powder comprises the following components in percentage by mass: 45 to 50% SiO 2 ，22~26% Al 2 O 3 ，14~18% SiC，2~4% CeO 2 2~4% CaO,5~8% white mud;
the adhesive is a sodium silicate aqueous solution, and the density of the adhesive is 1.36 to 1.42g/cm 3 。
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CN107576679B (en) * 2017-08-31 2020-05-19 辽宁科技大学 Method for calibrating local cooling speed of electroslag ingot in process of producing high-speed steel through electroslag remelting
CN109988971B (en) * 2019-04-16 2020-05-08 东北大学 Method for producing ultra-grade pure high-speed tool steel

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