EP4647516A1 - High-vanadium high-speed steel and preparation method therefor, and use thereof - Google Patents

High-vanadium high-speed steel and preparation method therefor, and use thereof

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Publication number
EP4647516A1
EP4647516A1 EP25150726.5A EP25150726A EP4647516A1 EP 4647516 A1 EP4647516 A1 EP 4647516A1 EP 25150726 A EP25150726 A EP 25150726A EP 4647516 A1 EP4647516 A1 EP 4647516A1
Authority
EP
European Patent Office
Prior art keywords
vanadium
speed steel
melt
preparation
speed
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP25150726.5A
Other languages
German (de)
French (fr)
Inventor
Yujie Wang
Haitao Jiang
Jiao Zhang
Hui Xing
Baode Sun
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Kunshan Micrograin Co Ltd
Shanghai Jiao Tong University
Original Assignee
Kunshan Micrograin Co Ltd
Shanghai Jiao Tong University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kunshan Micrograin Co Ltd, Shanghai Jiao Tong University filed Critical Kunshan Micrograin Co Ltd
Publication of EP4647516A1 publication Critical patent/EP4647516A1/en
Pending legal-status Critical Current

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    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C22C37/10—Cast-iron alloys containing aluminium or silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
    • B22D11/051—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds into moulds having oscillating walls
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
    • B22D11/053—Means for oscillating the moulds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D23/00—Casting processes not provided for in groups B22D1/00 - B22D21/00
    • B22D23/003—Moulding by spraying metal on a surface
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/52—Manufacture of steel in electric furnaces
    • C21C5/5264—Manufacture of alloyed steels including ferro-alloys
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C21D1/32—Soft annealing, e.g. spheroidising
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/58—Oils
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/84—Controlled slow cooling
    • 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
    • C21D5/00—Heat treatments of cast-iron
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/16—Remelting metals
    • C22B9/18—Electroslag remelting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/08—Making cast-iron alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • 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
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/36—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.7% by weight of carbon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations

Definitions

  • the present invention relates to the technical field of high-vanadium high-speed steel, and specifically to a high-vanadium high-speed steel and preparation method therefor, and use thereof.
  • the high-vanadium high-speed steel is easy to form coarse eutectic carbides due to its high contents of carbon and alloying elements, so that the segregation is serious and the microstructure is uneven, which seriously limits the mechanical property and the wear resistance. Therefore, the critical factors to improve comprehensive performances of the high-speed steel are defining the size of the carbide and improving the morphology and the microstructure homogeneity of the carbide.
  • the manufacturing methods mainly include the conventional casting, electroslag remelting, spray molding, and powder metallurgy.
  • the conventional casting and electroslag remelting in the above methods are widely used in mass industrial production, but the high-speed steel ingot by the two methods has coarse carbides, which are distributed in a continuous network.
  • the spray molding is a rapid solidification technology, which utilizes the refined liquid metal to form the droplet spraying flow after atomization, so that the semi-solidified particles are deposited on the base.
  • the microstructure refinement and the uniform composition of the metal can be realized by the rapid solidification, which eliminates the macro-segregation.
  • this method has problems of overspray of the spraying droplets, a low yield, a loose microstructure, and the inherent porosity.
  • the high-vanadium high-speed steel exists in the form of the ingot (i.e., it does not have the subsequent thermal mechanical deformation and only needs to carry out the heat treatment).
  • the ingot by the spray molding has a porosity up to about 20%, which is difficult to satisfy the use.
  • the microstructure is coarse; the distribution is uneven; the heat treatment process is complex and time-consuming, so that it is difficult to realize the desired comprehensive performance.
  • the object of the present invention is to provide a high-vanadium high-speed steel and preparation method therefor, and use thereof.
  • the present invention is realized in the following ways.
  • the present invention provides a preparation method of a high-vanadium high-speed steel, including:
  • the cooling rate is 45-75°C/h.
  • the high-vanadium high-speed steel casting billet is heated with a furnace in a tube furnace protected by an inert gas.
  • the raw materials are smelted by using an intermediate frequency induction furnace at a smelting temperature of 1480-1520°C; the intermediate frequency induction furnace is vacuumized to 100-400 Pa when smelting; and subsequently the inert gas is filled for protection.
  • a pressure difference between an inner chamber of the melt and an outer chamber during the melt impacting is 0.05-0.25 MPa, and a spraying speed is 0.75-1 .75 m/s.
  • a speed of the cooling platform moving downward is 50-120 mm/s.
  • the quenching and tempering treatment includes: preheating the annealing ingot at 600-750°C for 5-15min; then carrying out a quenching and holding a temperature at 1000-1230°C, wherein a holding duration is 10-30min, and then carrying out the quenching in oil to a room temperature; and then tempering 1-4 times at 520-600°C for 1h each time, wherein the tempering is carried out each time after air cooling to the room temperature.
  • the annealed ingot is preheated in a muffle furnace, and quenched in a tube furnace filled with an inert atmosphere.
  • the present invention provides a high-vanadium high-speed steel ingot, which is prepared by the using preparation method of the high-vanadium high-speed steel as described in any one of the foregoing embodiments.
  • an annealing hardness of the high-vanadium high-speed steel is 315-360 HV.
  • a tempering hardness of the high-vanadium high-speed steel is 863-980 HV.
  • a tempering bending strength of the high-vanadium high-speed steel is 1157-1404 MPa.
  • a vanadium content in the high-vanadium high-speed steel is 4-10%.
  • vanadium carbide in the ingot is in a shape of sphere, and is uniformly distributed in the base.
  • the vanadium carbide in the ingot is in a shape of sphere and block, and is distributed dispersedly, wherein vanadium carbide with a coarse size and an irregular shape does not appear.
  • the present invention provides the use of the high-vanadium high-speed steel, wherein the high-vanadium high-speed steel is as described in the foregoing embodiments, and can be used in the preparation of a roll, a hammer head, a ball mill liner, or a rotor body.
  • the present invention includes the following beneficial effects.
  • the preparation method of the high-vanadium high-speed steel provided by the present invention prepares the high-vanadium high-speed steel casting billet by adopting the melt impact method first, which can play roles of crushing grains and crushing primary carbides when performing the melt impacting, so as to improve the strength, toughness, and wear resistance of the high-vanadium high-speed steel, so as to improve the service life.
  • the melt impact method first can play roles of crushing grains and crushing primary carbides when performing the melt impacting, so as to improve the strength, toughness, and wear resistance of the high-vanadium high-speed steel, so as to improve the service life.
  • the melt impact method Compared with the prior spray molding method, the biggest difference is that the formed ingot microstructure is dense and uniform, and the carbide is fine.
  • the ingot prepared by the prior spray molding technique has inherent voids.
  • the ingot porosity still exists after the heat treatment since the forging process is not included in subsequence, so that the service life is greatly reduced.
  • the method of the present invention refines the grains and carbides, and greatly reduces the generation of porosity.
  • the utilization rate of the melt is higher, and there is no waste of the alloy melt.
  • the solidified ingot microstructure is uniform and dense. Additionally, the high-vanadium high-speed steel casting billet prepared by the melt impact method has fine and uniform carbide particles.
  • the carbide In order to prevent the aggregation and growth of the carbide, it adopts the rapid spheroidizing annealing process, wherein after it is heated to 820-910 °C with the furnace and held for 2-4h, it is cooled down to 450-550°C at a cooling rate larger than 40°C/h; and then it is air cooled to a room temperature, wherein the temperature cooling speed is fast, so as to realize the rapid annealing, so that the carbide in the high-vanadium high-speed steel is not easily agglomerated, and is uniformly distributed in conglobate shape, wherein the rapid spheroidizing annealing process is time-saving and high-efficient, and compared with the conventional annealing process, it greatly shortens the duration; and next, the quenching and tempering are carried out, which comprehensively improves the mechanical property of the high-vanadium high-speed steel.
  • the present invention provides a preparation method of a high-vanadium high-speed steel, including the following steps.
  • the raw materials is smelted to form a melt.
  • the raw materials are prepared according to the chemical element composition of vanadium, and are smelted to obtain the melt of the high-vanadium high-speed steel, wherein the raw materials in mass percentage include C: 2.0-2.5%, Cr: 4-6%, W: 2.5-6%, Mo: 3-7%, V: 4-10%, Si: 0.3-0.6%, Mn: 0.3-0.8%, and a balance of Fe.
  • the raw material is smelted by using an intermediate frequency induction furnace at a smelting temperature of 1480-1520°C; the intermediate frequency induction furnace is vacuumized to 100-400 Pa when smelting; and subsequently the inert gas is filled for protection.
  • the melt is impacted to a cooling platform to form a high-vanadium high-speed steel casting billet.
  • the melt is deposited on a pre-cooled cooling platform (such as a water-cooled copper mold) at a spraying speed of 0.75-1.75 m/s by the inert gas, at which time the melt is rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet.
  • a pre-cooled cooling platform such as a water-cooled copper mold
  • the impacting temperature of the high-vanadium high-speed steel of the above composition melt is controlled to be 1480-1520°C, wherein the superheat should not be too high, otherwise the grain of solidification microstructure will be coarse; and the fluidity is poor when it is lower than this temperature, which is not easy to realize the rapid impacting and easy to block the nozzle.
  • a pressure difference between an inner chamber of the melt and an outer chamber during the melt impacting is 0.05-0.25 MPa, wherein the pressure difference refers to a pressure difference between the chamber of the melt in the crucible and the outer chamber.
  • the specific realizing step can be described as: vacuumizing the chamber formed by the intermediate frequency induction furnace, and filling the inert atmosphere subsequently, at which time there is still a certain pressure difference with the outside; and filling the inert gas flow into the melt when the melt reaches the holding temperature, so as to promote the rapid spraying of the melt.
  • the structure is mainly controlled by means of airflow, which is easy to realize and operate.
  • the cooling platform can move up and down under the driving of the movement mechanism, so as to control a distance between the cooling platform and the nozzle of the intermediate frequency induction furnace, so as to perform the melt impacting better, wherein the speed of the downward movement of the cooling platform is 50-120 mm/s.
  • the present invention found by research that when lower than 50mm/s, it will have the problem of the lower quality of metallurgical bonding between layers, which is easy to cause a large amount of porosity defects; and when higher than 120mm/s, the melt of the next layer has arrived before the melt of the last layer forms a valid solidification thickness, which cannot play a crushing effect on the dendritic crystal.
  • the spheroidizing annealing treatment is carried out on the high-vanadium high-speed steel casting billet to obtain an annealed ingot, wherein the spheroidizing annealing treatment includes heating the high-vanadium high-speed steel casting billet to 820-910°C; holding for 2-4h; then cooling down to 450-550°C at a cooling rate larger than 40°C/h; then air cooling to a room temperature.
  • the high-vanadium high-speed steel casting billet is prepared by the melt impact method based on step S2 first, wherein the microstructure of the formed high-vanadium high-speed steel casting billet is uniform, and the size of the carbide is small. It needs to develop a new annealing process, which can meet the cutting condition, and at the same time prevent the aggregation and growth of the fine carbides. Therefore, the present invention adopts the above spheroidizing annealing treatment, which rapidly reduces the temperature to 450-550°C by a high-speed cooling method.
  • the duration of this process is only 1/4-1/3 of the duration of the conventional annealing process, which is energy saving and high-efficient, but also can realize that the vanadium carbide in the high-vanadium high-speed steel casting billet is in a shape of sphere; is uniformly distributed; has suitable hardness; and is convenient for the subsequent machining.
  • the cooling rate can be, for example, 45-75°C/h. In other embodiments of the present invention, the cooling rate can be, for example, any one of 45°C/h, 50°C/h, 55°C/h, 60°C/h, 65°C/h, 70°C/h, 75°C/h, or a range value between any two.
  • the high-vanadium high-speed steel casting billet is heated with a furnace in the tube furnace protected by the inert gas, and is protected by the inert gas, which can avoid the reaction between the chemical elements in the raw material and the oxygen, and at the same time the heating with the furnace can be better controlled.
  • the quenching and tempering treatment is performed on the annealed ingot, so as to obtain a resultant.
  • the quenching and tempering treatment includes: preheating the annealed ingot at 600-750°C for 5-15min; then carrying out a quenching when holding a temperature at 1000-1230°C, wherein a holding duration is 10-30min, and carrying out the quenching in oil to a room temperature; and then tempering 1-4 times at 520-600°C for 1h each time, wherein the tempering is carried out each time after air cooling to the room temperature.
  • the annealed ingot is preheated in a muffle furnace, and quenched in the tube furnace filled with the inert atmosphere.
  • the annealed ingot is fully preheated in 600-750°C first, which can prevent the annealed ingot from directly cracking during the heat preservation at 1000-1230°C.
  • the large amounts of carbides can be fully dissolved by quenching in the heat preservation at 1000-1230°C; and the carbides were sphered and isolated due to the high temperature diffusion dissolution and the driving from the interfacial tension, which is beneficial to improving the morphology of the carbide and to improving its toughness.
  • the dissolved alloying element is dissolved in the austenite to increase the hardenability of the alloy, and at the next quenching and cooling process, the base transforms to the strong martensite base.
  • the stress can be eliminated, so as to promote the dispersion and the precipitation of the secondary carbides, which improves the strength and hardness of the base.
  • the multiple tempering process allows the incomplete residual austenite to transform completely, so as to improve the strength and the hardness of the base.
  • the performance of the high-vanadium high-speed steel is improved by multiple quenching and tempering treatments, so that it has a high hardness, and the good strength and toughness.
  • the high-vanadium high-speed steel prepared by using the above preparation method of the high-vanadium high-speed steel has the excellent mechanical property, wherein the annealing hardness of the high-vanadium high-speed steel is 315-360 HV; the tempering hardness of the high-vanadium high-speed steel is 863-980 HV; and the tempering bending strength of the high-vanadium high-speed steel is 1157-1404 MPa. Meanwhile, the vanadium content in the high-vanadium high-speed steel is 4-10%. After the high-vanadium high-speed steel is annealed, the vanadium carbide in the ingot is in a shape of sphere, and is uniformly distributed in the base.
  • the vanadium carbide in the ingot is mainly in a shape of sphere and block, and is distributed dispersedly, wherein the vanadium carbide with a coarse size and an irregular shape does not appear.
  • the grain and the primary carbide are crushed by using the impacting effect of the melt, which in turn can improve the strength, toughness, and wear resistance of the high carbon alloy steel, so as to improve the service life.
  • the biggest difference is that the formed ingot microstructure is dense and uniform, and the carbide is fine.
  • the ingot prepared by the prior spray molding technique has inherent voids.
  • the preparation method of the high-vanadium high-speed steel provided by the present invention prepares the high-vanadium high-speed steel casting billet by using the melt impact method.
  • the high-vanadium high-speed steel casting billet prepared by the melt impact method has fine and uniform carbide particles. In order to prevent the aggregation and growth of the carbide, it adopts the rapid spheroidizing annealing process, which is time-saving and high-efficient, and compared with the conventional annealing process, it greatly shortens the duration. Next, the quenching and tempering treatment is carried out, which can comprehensively improve the mechanical property of the high-vanadium high-speed steel.
  • the high-vanadium high-speed steel obtained can be widely used to prepare the roll, hammer head, ball mill liner, or rotor body.
  • the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
  • Example is basically the same as Example 1, and the only difference is that the parameters of step (3) and step (4) are different.
  • the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
  • Example is basically the same as Example 1, and the only difference is that the parameters of step (3) and step (4) are different.
  • the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
  • Example is basically the same as Example 1, and the only difference is that the parameters of step (3) and step (4) are different.
  • the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
  • Example is basically the same as Example 1, and the only difference is that the parameters of step (3) and step (4) are different.
  • the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
  • Example is basically the same as Example 1, and the only difference is that the parameters of step (3) and step (4) are different.
  • the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
  • Example is essentially the same as Example 1, and differs only in that the parameters of steps (1) and (2) are different.
  • the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
  • Example is essentially the same as Example 1, and differs only in that the parameters of steps (1) and (2) are different.
  • the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
  • the Comparative Example is basically the same as Example 4, wherein the only difference is that step (3) adopts the conventional annealing process.
  • the specific steps were as follows.
  • the Comparative Example is basically the same as Example 4, wherein the only difference is that step (2) adopts the ingot prepared by the spray molding technology.
  • the specific steps were as follows.
  • the Comparative Example is basically the same as Example 4, wherein the only differences are that step (2) adopts the ingot prepared by the spray molding technology, and step (3) adopts the conventional annealing process.
  • the specific steps were as follows.
  • the Comparative Example is basically the same as Example 1, wherein the only difference is that the cooling rate in step (3) is different.
  • the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
  • the Comparative Example is basically the same as Example 1, wherein the only difference is that the cooling rate in step (3) is different.
  • the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
  • the Comparative Example is basically the same as Example 4, wherein the only difference is that no heat treatment was performed in the Comparative Example.
  • the specific steps were as follows.
  • the microstructures of the high-vanadium high-speed steels provided by the above Examples 1-8 and Comparative Examples 1-6 were statistically analyzed.
  • the carbide agglomeration condition was evaluated according to the standard of the national standard GB-T 14979-1994 method for evaluating non-uniformity of eutectic carbide of steel , wherein the uniform distribution could be defined as 1-2 levels, and the more uniform distribution was defined as 3-4 levels.
  • the porosity was evaluated according to the national standard GB 12823-91 grade and content of defect of steel casting , wherein the critical porosity of the steel casting was a smallest porosity under the casting process condition, wherein it was usually 3%-5%, and should not exceed 5%.
  • the low porosity in the example could be defined as smaller than 3%, and the high porosity was defined as 3%-5%.
  • the service life of the high-speed steel was evaluated according to the national standard GB-T16461-1996 life test of single edge turning tool.
  • the high-vanadium high-speed steels provided by Examples 1-8 and Comparative Examples 1-6 above were used to carry out the mechanical property test, wherein the test method of the annealing hardness was characterized by the Vickers indentation technique; the test method of the tempering hardness was characterized by the Vickers indentation technique; and the test method of the tempering bending strength was tested by three-point bending experiment.
  • the test method of the annealing hardness was characterized by the Vickers indentation technique
  • the test method of the tempering hardness was characterized by the Vickers indentation technique
  • the test method of the tempering bending strength was tested by three-point bending experiment.
  • the test result refers to Table 1 and Table 2.
  • Table 1 statistical table of microstructures of high-vanadium high-speed steels provided by different examples Material Carbide size (spherical particle) Carbide agglomeration condition Porosity Service life Example 4 2.26 ⁇ m uniform distribution low long Comparative Example 1 3.72 ⁇ m relatively uniform distribution low relatively long Comparative Example 2 2.07 ⁇ m uniform distribution relatively high short Comparative Example 3 3.68 ⁇ m relatively uniform distribution relatively high short Comparative Example 4 3.25 ⁇ m uniform distribution low relatively long Comparative Example 5 2.66 ⁇ m uniform distribution low relatively long Comparative Example 6 2.21 ⁇ m uniform distribution low short Table 2: statistical table of mechanical properties of high-vanadium high-speed steels provided by different examples Material Annealing hardness (HV) Tempering hardness (HV) Tempering bending strength (MPa) Hardness (HV) Bending strength (MPa) Example 1 360 863 1271 / / Example 2 345 864 1199 / / Example 3 315 954 1404 / / Example 4 360 894 1192 / /
  • the microstructure of the high-vanadium high-speed steel ingot prepared by the melt impact method is fine and dense, and it has both high tempering hardness and high bending strength.
  • the Comparative Example 1 adopts the conventional annealing process, which results in a significant increase in the carbide size, and it is up to 3.72 ⁇ m.
  • the Comparative Example 2 adopts the spray molding process to prepare the high-vanadium high-speed steel ingot, wherein the ingot has a higher porosity and the mechanical property is significantly lower than that of Example 4.
  • the step (2) adopts the ingot prepared by the spray molding technology, and at the same time the step (3) adopts the conventional annealing process, which results in a significant increase in the carbide size and a significant decrease in the mechanical property.
  • the Comparative Example 4 and the Comparative Example 5 adopt different cooling rates, wherein the cooling rate of the Comparative Example 4 is lower than the range value of the present invention, which results in a significant increase in the carbide size; and in Comparative Example 5, the cooling rate is too large; the spheroidizing annealing process is not sufficient; the microstructure softening is not sufficient; and it has the highest annealing hardness, which is not beneficial for cutting processing; and it cannot further reduce the carbide size, but the carbide size increases slightly; and the secondary solid solution effect is poor, which results in a certain reduction of the mechanical property.
  • the selection of a rapid spheroidizing annealing process for preparing the high-vanadium high-speed steel ingot by the melt impact method follows principles of time saving and high efficiency, so as to obtain the annealing hardness similar to that of the conventional annealing process under a long cycle and a high energy consumption, and the proper rapid spheroidizing annealing process avoids the aggregation and roughening of fine carbides.
  • the high-vanadium high-speed steel ingot prepared by the melt impact method has the satisfactory mechanical property.
  • the preparation method of the high-vanadium high-speed steel prepareds the high-vanadium high-speed steel casting billet by adopting the melt impact method first, which can play the role of crushing grains and crushing primary carbides when performing the melt impacting, so as to improve the strength, the toughness, and the wear resistance of the high-vanadium high-speed steel, so as to improve the service life.
  • the melt impact method can play the role of crushing grains and crushing primary carbides when performing the melt impacting, so as to improve the strength, the toughness, and the wear resistance of the high-vanadium high-speed steel, so as to improve the service life.
  • the melt impact method Compared with the prior spray molding method, the biggest difference is that the formed ingot microstructure is dense and uniform, and the carbide is fine.
  • the ingot prepared by the prior spray molding technology has inherent porosity.
  • the ingot porosity still exists after the heat treatment since the forging process is not included in subsequence, so that the service life is greatly reduced.
  • the method of the present invention refines the grains and carbides, and greatly reduces the generation of porosity.
  • the utilization rate of the melt is higher, and there is no waste of the alloy melt.
  • the solidified ingot microstructure is uniform and dense. Additionally, the high-vanadium high-speed steel casting billet prepared by the melt impact method has fine and uniform carbide particles.
  • the carbide In order to prevent the aggregation and growth of the carbide, it adopts the rapid spheroidizing annealing process, wherein after it is heated to 820-910°C with the furnace and held for 2-4h, it is cooled down to 450-550°C at a cooling rate larger than 40°C/h; and then it is air cooled to a room temperature, wherein the temperature cooling speed is fast, so as to realize the rapid annealing, so that the tungsten carbide in the high-vanadium high-speed steel is not easily agglomerated, and is uniformly distributed in conglobate shape.
  • the rapid spheroidizing annealing process is time-saving and high-efficient, wherein compared with the conventional annealing process, it greatly shortens the duration.
  • the quenching and the tempering are carried out, which comprehensively improve the mechanical property of the high-vanadium high-speed steel.

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Abstract

The present invention provides a high-vanadium high-speed steel and preparation method therefor, and use thereof, which relate to the technical field of high-vanadium high-speed steel. The preparation method includes: smelting raw materials to form a melt; impacting the melt to a cooling platform to form a high-vanadium high-speed steel casting billet; and performing a spheroidizing annealing treatment and a quenching and tempering treatment, so as to obtain a resultant. The spheroidizing annealing treatment includes: heating the high-vanadium high-speed steel casting billet to 820-910°C; holding for 2-4h; then cooling down to 450-550°C at a cooling rate larger than 40°C/h; and then air cooling to a room temperature. It can play roles of crushing grains and crushing primary carbides when performing the melt impacting, so that the formed ingot microstructure is dense and uniform, and the carbide is fine. The rapid spheroidizing annealing process is used to realize the rapid annealing, so that the carbide in the high-vanadium high-speed steel is not easily agglomerated, and is uniformly distributed in conglobate shape, which is time-saving and high-efficient, and is beneficial to improving the mechanical property of the high-vanadium high-speed steel.

Description

    Technical field
  • The present invention relates to the technical field of high-vanadium high-speed steel, and specifically to a high-vanadium high-speed steel and preparation method therefor, and use thereof.
    • Background art
  • The high-vanadium high-speed steel is easy to form coarse eutectic carbides due to its high contents of carbon and alloying elements, so that the segregation is serious and the microstructure is uneven, which seriously limits the mechanical property and the wear resistance. Therefore, the critical factors to improve comprehensive performances of the high-speed steel are defining the size of the carbide and improving the morphology and the microstructure homogeneity of the carbide. The manufacturing methods mainly include the conventional casting, electroslag remelting, spray molding, and powder metallurgy. The conventional casting and electroslag remelting in the above methods are widely used in mass industrial production, but the high-speed steel ingot by the two methods has coarse carbides, which are distributed in a continuous network. In the subsequent heat treatment process, the coarse and continuous network carbides are difficult to eliminate, which results in embrittlement of the grain boundary, so that the strength and toughness are reduced. The spray molding is a rapid solidification technology, which utilizes the refined liquid metal to form the droplet spraying flow after atomization, so that the semi-solidified particles are deposited on the base. The microstructure refinement and the uniform composition of the metal can be realized by the rapid solidification, which eliminates the macro-segregation. However, this method has problems of overspray of the spraying droplets, a low yield, a loose microstructure, and the inherent porosity. Importantly, as the roll material for hot rolling, the high-vanadium high-speed steel exists in the form of the ingot (i.e., it does not have the subsequent thermal mechanical deformation and only needs to carry out the heat treatment). The ingot by the spray molding has a porosity up to about 20%, which is difficult to satisfy the use.
  • In the above preparation methods, the microstructure is coarse; the distribution is uneven; the heat treatment process is complex and time-consuming, so that it is difficult to realize the desired comprehensive performance.
  • In view of this, the present invention is proposed.
    • Summary of the invention
  • The object of the present invention is to provide a high-vanadium high-speed steel and preparation method therefor, and use thereof.
  • The present invention is realized in the following ways.
  • In a first aspect, the present invention provides a preparation method of a high-vanadium high-speed steel, including:
    • smelting raw materials to form a melt, wherein the raw materials in mass percentage include C: 2.0-2.5%, Cr: 4-6%, W: 2.5-6%, Mo: 3-7%, V: 4-10%, Si: 0.3-0.6%, Mn: 0.3-0.8%, and a balance of Fe;
    • impacting the melt to a cooling platform to form a high-vanadium high-speed steel casting billet;
    • carrying out a spheroidizing annealing treatment on the high-vanadium high-speed steel casting billet to obtain an annealed ingot, wherein the spheroidizing annealing treatment includes heating the high-vanadium high-speed steel casting billet to 820-91 0°C; holding for 2-4h; then cooling down to 450-550°C at a cooling rate larger than 40°C/h; then air cooling to a room temperature; and
    • performing a quenching and tempering treatment on the annealed ingot, so as to obtain a resultant.
  • In an optional embodiment, the cooling rate is 45-75°C/h.
  • In an optional embodiment, the high-vanadium high-speed steel casting billet is heated with a furnace in a tube furnace protected by an inert gas.
  • In an optional embodiment, the raw materials are smelted by using an intermediate frequency induction furnace at a smelting temperature of 1480-1520°C; the intermediate frequency induction furnace is vacuumized to 100-400 Pa when smelting; and subsequently the inert gas is filled for protection.
  • In an optional embodiment, a pressure difference between an inner chamber of the melt and an outer chamber during the melt impacting is 0.05-0.25 MPa, and a spraying speed is 0.75-1 .75 m/s.
  • In an optional embodiment, a speed of the cooling platform moving downward is 50-120 mm/s.
  • In an optional embodiment, the quenching and tempering treatment includes: preheating the annealing ingot at 600-750°C for 5-15min; then carrying out a quenching and holding a temperature at 1000-1230°C, wherein a holding duration is 10-30min, and then carrying out the quenching in oil to a room temperature; and then tempering 1-4 times at 520-600°C for 1h each time, wherein the tempering is carried out each time after air cooling to the room temperature.
  • In an optional embodiment, the annealed ingot is preheated in a muffle furnace, and quenched in a tube furnace filled with an inert atmosphere.
  • In a second aspect, the present invention provides a high-vanadium high-speed steel ingot, which is prepared by the using preparation method of the high-vanadium high-speed steel as described in any one of the foregoing embodiments.
  • Preferably, an annealing hardness of the high-vanadium high-speed steel is 315-360 HV.
  • Preferably, a tempering hardness of the high-vanadium high-speed steel is 863-980 HV.
  • Preferably, a tempering bending strength of the high-vanadium high-speed steel is 1157-1404 MPa.
  • Preferably, a vanadium content in the high-vanadium high-speed steel is 4-10%.
  • Preferably, after the high-vanadium high-speed steel is annealed, vanadium carbide in the ingot is in a shape of sphere, and is uniformly distributed in the base.
  • Preferably, after the high-vanadium high-speed steel is tempered, the vanadium carbide in the ingot is in a shape of sphere and block, and is distributed dispersedly, wherein vanadium carbide with a coarse size and an irregular shape does not appear.
  • In a third aspect, the present invention provides the use of the high-vanadium high-speed steel, wherein the high-vanadium high-speed steel is as described in the foregoing embodiments, and can be used in the preparation of a roll, a hammer head, a ball mill liner, or a rotor body.
  • The present invention includes the following beneficial effects.
  • The preparation method of the high-vanadium high-speed steel provided by the present invention prepares the high-vanadium high-speed steel casting billet by adopting the melt impact method first, which can play roles of crushing grains and crushing primary carbides when performing the melt impacting, so as to improve the strength, toughness, and wear resistance of the high-vanadium high-speed steel, so as to improve the service life. Compared with the prior spray molding method, the biggest difference is that the formed ingot microstructure is dense and uniform, and the carbide is fine. The ingot prepared by the prior spray molding technique has inherent voids. For casting the high-vanadium high-speed steel, the ingot porosity still exists after the heat treatment since the forging process is not included in subsequence, so that the service life is greatly reduced. The method of the present invention refines the grains and carbides, and greatly reduces the generation of porosity. The utilization rate of the melt is higher, and there is no waste of the alloy melt. The solidified ingot microstructure is uniform and dense. Additionally, the high-vanadium high-speed steel casting billet prepared by the melt impact method has fine and uniform carbide particles. In order to prevent the aggregation and growth of the carbide, it adopts the rapid spheroidizing annealing process, wherein after it is heated to 820-910 °C with the furnace and held for 2-4h, it is cooled down to 450-550°C at a cooling rate larger than 40°C/h; and then it is air cooled to a room temperature, wherein the temperature cooling speed is fast, so as to realize the rapid annealing, so that the carbide in the high-vanadium high-speed steel is not easily agglomerated, and is uniformly distributed in conglobate shape, wherein the rapid spheroidizing annealing process is time-saving and high-efficient, and compared with the conventional annealing process, it greatly shortens the duration; and next, the quenching and tempering are carried out, which comprehensively improves the mechanical property of the high-vanadium high-speed steel.
    • Brief description of drawings
  • In order to more clearly illustrate the technical solutions of the examples of the present invention, the drawings to be used in the examples will be briefly introduced below. It should be understood that the following drawings only show certain examples of the present invention, and therefore should not be regarded as a limitation of the scope. Other relevant drawings can be obtained from these drawings by a person of ordinary skill in the art without inventive efforts.
    • Fig. 1 shows a metallographic microstructure of preparing a high-vanadium high-speed steel casting billet by a melt impact method provided by Example 4 of the present invention;
    • Fig. 2 shows a schematic diagram of a rapid spheroidizing annealing process of preparing a high-vanadium high-speed steel by a melt impact method provided by Example 4 of the present invention;
    • Fig. 3 shows a metallographic microstructure of a high-vanadium high-speed steel casting billet after a rapid spheroidizing annealing provided by Example 4 of the present invention; and
    • Fig. 4 shows a metallographic microstructure of a high-vanadium high-speed steel casting billet after quenching-tempering provided by Example 4 of the present invention.
    Detailed description of embodiments
  • In order to make the purpose, technical solutions and advantages of the examples of the present invention clearer, the technical solutions in the examples of the present invention will be described clearly and completely in the following. Where specific conditions are not indicated in the examples, they shall be performed based on the usual conditions or those recommended by manufacturers. The reagents or instruments used without indication of the manufacturers are conventional products that can be purchased commercially.
  • The present invention provides a preparation method of a high-vanadium high-speed steel, including the following steps.
    • S1: Smelting.
  • The raw materials is smelted to form a melt.
  • In the present invention, the raw materials are prepared according to the chemical element composition of vanadium, and are smelted to obtain the melt of the high-vanadium high-speed steel, wherein the raw materials in mass percentage include C: 2.0-2.5%, Cr: 4-6%, W: 2.5-6%, Mo: 3-7%, V: 4-10%, Si: 0.3-0.6%, Mn: 0.3-0.8%, and a balance of Fe.
  • The raw material is smelted by using an intermediate frequency induction furnace at a smelting temperature of 1480-1520°C; the intermediate frequency induction furnace is vacuumized to 100-400 Pa when smelting; and subsequently the inert gas is filled for protection.
    • S2: Melt impacting.
  • The melt is impacted to a cooling platform to form a high-vanadium high-speed steel casting billet.
  • Specifically, when the smelting reaches a preset temperature (1480-1520 °C), the melt is deposited on a pre-cooled cooling platform (such as a water-cooled copper mold) at a spraying speed of 0.75-1.75 m/s by the inert gas, at which time the melt is rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet.
  • The impacting temperature of the high-vanadium high-speed steel of the above composition melt is controlled to be 1480-1520°C, wherein the superheat should not be too high, otherwise the grain of solidification microstructure will be coarse; and the fluidity is poor when it is lower than this temperature, which is not easy to realize the rapid impacting and easy to block the nozzle.
  • A pressure difference between an inner chamber of the melt and an outer chamber during the melt impacting is 0.05-0.25 MPa, wherein the pressure difference refers to a pressure difference between the chamber of the melt in the crucible and the outer chamber. The specific realizing step can be described as: vacuumizing the chamber formed by the intermediate frequency induction furnace, and filling the inert atmosphere subsequently, at which time there is still a certain pressure difference with the outside; and filling the inert gas flow into the melt when the melt reaches the holding temperature, so as to promote the rapid spraying of the melt. The structure is mainly controlled by means of airflow, which is easy to realize and operate.
  • The cooling platform can move up and down under the driving of the movement mechanism, so as to control a distance between the cooling platform and the nozzle of the intermediate frequency induction furnace, so as to perform the melt impacting better, wherein the speed of the downward movement of the cooling platform is 50-120 mm/s. The present invention found by research that when lower than 50mm/s, it will have the problem of the lower quality of metallurgical bonding between layers, which is easy to cause a large amount of porosity defects; and when higher than 120mm/s, the melt of the next layer has arrived before the melt of the last layer forms a valid solidification thickness, which cannot play a crushing effect on the dendritic crystal.
    • S3: Spheroidizing annealing treatment.
  • The spheroidizing annealing treatment is carried out on the high-vanadium high-speed steel casting billet to obtain an annealed ingot, wherein the spheroidizing annealing treatment includes heating the high-vanadium high-speed steel casting billet to 820-910°C; holding for 2-4h; then cooling down to 450-550°C at a cooling rate larger than 40°C/h; then air cooling to a room temperature.
  • In the present invention, the high-vanadium high-speed steel casting billet is prepared by the melt impact method based on step S2 first, wherein the microstructure of the formed high-vanadium high-speed steel casting billet is uniform, and the size of the carbide is small. It needs to develop a new annealing process, which can meet the cutting condition, and at the same time prevent the aggregation and growth of the fine carbides. Therefore, the present invention adopts the above spheroidizing annealing treatment, which rapidly reduces the temperature to 450-550°C by a high-speed cooling method. It not only can shorten the duration of the annealing process (the duration of this process is only 1/4-1/3 of the duration of the conventional annealing process), which is energy saving and high-efficient, but also can realize that the vanadium carbide in the high-vanadium high-speed steel casting billet is in a shape of sphere; is uniformly distributed; has suitable hardness; and is convenient for the subsequent machining.
  • The cooling rate can be, for example, 45-75°C/h. In other embodiments of the present invention, the cooling rate can be, for example, any one of 45°C/h, 50°C/h, 55°C/h, 60°C/h, 65°C/h, 70°C/h, 75°C/h, or a range value between any two.
  • The high-vanadium high-speed steel casting billet is heated with a furnace in the tube furnace protected by the inert gas, and is protected by the inert gas, which can avoid the reaction between the chemical elements in the raw material and the oxygen, and at the same time the heating with the furnace can be better controlled.
    • S4: Quenching and tempering treatment.
  • The quenching and tempering treatment is performed on the annealed ingot, so as to obtain a resultant.
  • The quenching and tempering treatment includes: preheating the annealed ingot at 600-750°C for 5-15min; then carrying out a quenching when holding a temperature at 1000-1230°C, wherein a holding duration is 10-30min, and carrying out the quenching in oil to a room temperature; and then tempering 1-4 times at 520-600°C for 1h each time, wherein the tempering is carried out each time after air cooling to the room temperature. The annealed ingot is preheated in a muffle furnace, and quenched in the tube furnace filled with the inert atmosphere.
  • Since the high-vanadium high-speed steel contains a large amount of high-melting-point brittle carbides, in the quenching and tempering treatment of the present invention, the annealed ingot is fully preheated in 600-750°C first, which can prevent the annealed ingot from directly cracking during the heat preservation at 1000-1230°C. The large amounts of carbides can be fully dissolved by quenching in the heat preservation at 1000-1230°C; and the carbides were sphered and isolated due to the high temperature diffusion dissolution and the driving from the interfacial tension, which is beneficial to improving the morphology of the carbide and to improving its toughness. Additionally, the dissolved alloying element is dissolved in the austenite to increase the hardenability of the alloy, and at the next quenching and cooling process, the base transforms to the strong martensite base. During the tempering at 520-600°C, the stress can be eliminated, so as to promote the dispersion and the precipitation of the secondary carbides, which improves the strength and hardness of the base. The multiple tempering process allows the incomplete residual austenite to transform completely, so as to improve the strength and the hardness of the base. The performance of the high-vanadium high-speed steel is improved by multiple quenching and tempering treatments, so that it has a high hardness, and the good strength and toughness.
  • The high-vanadium high-speed steel prepared by using the above preparation method of the high-vanadium high-speed steel has the excellent mechanical property, wherein the annealing hardness of the high-vanadium high-speed steel is 315-360 HV; the tempering hardness of the high-vanadium high-speed steel is 863-980 HV; and the tempering bending strength of the high-vanadium high-speed steel is 1157-1404 MPa. Meanwhile, the vanadium content in the high-vanadium high-speed steel is 4-10%. After the high-vanadium high-speed steel is annealed, the vanadium carbide in the ingot is in a shape of sphere, and is uniformly distributed in the base. After the high-vanadium high-speed steel is tempered, the vanadium carbide in the ingot is mainly in a shape of sphere and block, and is distributed dispersedly, wherein the vanadium carbide with a coarse size and an irregular shape does not appear.
  • In the present invention, the grain and the primary carbide are crushed by using the impacting effect of the melt, which in turn can improve the strength, toughness, and wear resistance of the high carbon alloy steel, so as to improve the service life. Compared with the prior spray molding method, the biggest difference is that the formed ingot microstructure is dense and uniform, and the carbide is fine. The ingot prepared by the prior spray molding technique has inherent voids. For casting the high-vanadium high-speed steel, the ingot porosity still exists after the heat treatment since the forging process is not included in subsequence, so that the service life is greatly reduced. The preparation method of the high-vanadium high-speed steel provided by the present invention prepares the high-vanadium high-speed steel casting billet by using the melt impact method. It refines the grains and carbides, and greatly reduces the generation of porosity. The utilization rate of the melt is higher, and there is no waste of the alloy melt. The solidified ingot microstructure is uniform and dense. Additionally, the high-vanadium high-speed steel casting billet prepared by the melt impact method has fine and uniform carbide particles. In order to prevent the aggregation and growth of the carbide, it adopts the rapid spheroidizing annealing process, which is time-saving and high-efficient, and compared with the conventional annealing process, it greatly shortens the duration. Next, the quenching and tempering treatment is carried out, which can comprehensively improve the mechanical property of the high-vanadium high-speed steel. The high-vanadium high-speed steel obtained can be widely used to prepare the roll, hammer head, ball mill liner, or rotor body.
  • The features and performance of the present invention are described in further detail below in connection with the examples.
    • Example 1
  • The example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using an intermediate frequency induction furnace at a smelting temperature of 1480°C. During smelting, the intermediate frequency induction furnace was vacuumized to 250 Pa and subsequently the inert gas was filled for protection, so that a melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2.5%C, 5.0%Cr, 4%W, 3.0%Mo, 8%V, 0.5%Si, 0.3%Mn, and a balance of Fe.
    2. (2) When the smelting reached 1480°C, the melt was deposited by the inert gas on a pre-cooled water-cooled copper mold at a spraying speed of 1 .25m/s under a pressure difference of 0.15 MPa, wherein a movement speed of the water-cooled copper mold was 100 mm/s, at which time the melt was rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet, and then it was cooled to the room temperature.
    3. (3) The rapid spheroidizing annealing process was carried out on the ingot obtained by this process; a temperature of 850°C was held for 2h; it was cooled to 500°C at a rate of 50°C/h; and then it was air cooled.
    4. (4) It was held at a temperature of 1100°C for 15 min, and quenched in oil to the room temperature; and it was tempered twice at 560°C for 1h each time.
    Example 2
  • The Example is basically the same as Example 1, and the only difference is that the parameters of step (3) and step (4) are different.
  • Specifically, the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using an intermediate frequency induction furnace at a smelting temperature of 1480°C. During smelting, the intermediate frequency induction furnace was vacuumized to 250 Pa and subsequently the inert gas was filled for protection, so that the melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2.5%C, 5.0%Cr, 4%W, 3.0%Mo, 8%V, 0.5%Si, 0.3%Mn, and a balance of Fe.
    2. (2) When the smelting reached 1480°C, the melt was deposited by the inert gas on the pre-cooled water-cooled copper mold at the spraying speed of 1.25m/s under the pressure difference of 0.15 MPa, wherein the movement speed of the water-cooled copper mold was 100 mm/s, at which time the melt was rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet, and then it was cooled to the room temperature.
    3. (3) The rapid spheroidizing annealing process was carried out on the ingot obtained by this process; a temperature of 880°C was held for 2h; it was cooled to 500°C at the rate of 50°C/h; and then it was air cooled.
    4. (4) It was held at the temperature of 1150°C for 15 min, and quenched in oil to the room temperature; and it was tempered twice at 560°C for 1h each time.
    Example 3
  • The Example is basically the same as Example 1, and the only difference is that the parameters of step (3) and step (4) are different.
  • Specifically, the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using an intermediate frequency induction furnace at a smelting temperature of 1480°C. During smelting, the intermediate frequency induction furnace was vacuumized to 250 Pa and subsequently the inert gas was filled for protection, so that the melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2.5%C, 5.0%Cr, 4%W, 3.0%Mo, 8%V, 0.5%Si, 0.3%Mn, and a balance of Fe.
    2. (2) When the smelting reached 1480°C, the melt was deposited by the inert gas on the pre-cooled water-cooled copper mold at the spraying speed of 1.25m/s under the pressure difference of 0.15 MPa, wherein the movement speed of the water-cooled copper mold was 100 mm/s, at which time the melt was rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet, and then it was cooled to the room temperature.
    3. (3) The rapid spheroidizing annealing process was carried out on the ingot obtained by this process; a temperature of 910°C was held for 2h; it was cooled to 500°C at the rate of 50°C/h; and then it was air cooled.
    4. (4) It was held at the temperature of 1200°C for 15 min, and quenched in oil to the room temperature; and it was tempered twice at 560°C for 1h each time.
    Example 4
  • The Example is basically the same as Example 1, and the only difference is that the parameters of step (3) and step (4) are different.
  • Specifically, the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using the intermediate frequency induction furnace at the smelting temperature of 1480°C. During smelting, the intermediate frequency induction furnace was vacuumized to 250 Pa and subsequently the inert gas was filled for protection, so that the melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2.5%C, 5.0%Cr, 4%W, 3.0%Mo, 8%V, 0.5%Si, 0.3%Mn, and a balance of Fe.
    2. (2) When the smelting reached 1480°C, the melt was deposited by the inert gas on the pre-cooled water-cooled copper mold at the spraying speed of 1.25m/s under the pressure difference of 0.15 MPa, wherein the movement speed of the water-cooled copper mold was 100 mm/s, at which time the melt was rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet, and then it was cooled to the room temperature. Referring to Fig. 1, it can be seen from Fig. 1 that the microstructure of the high-vanadium high-speed steel casting billet is fine and distributed uniformly.
    3. (3) Referring to Fig. 2, the rapid spheroidizing annealing process was carried out on the ingot obtained by this process; a temperature of 850°C was held for 2h; it was cooled to 500°C at the rate of 50°C/h; and then it was air cooled. Referring to Fig. 3, it can be seen from Fig. 3 that the microstructure of the high-vanadium high-speed steel casting billet after the rapid spheroidizing annealing is fine and distributed uniformly.
    4. (4) It was held at the temperature of 1100°C for 15 min, and quenched in oil to the room temperature; and it was tempered three times at 560°C for 1h each time. Referring to Fig. 4, it can be seen from Fig. 4 that the microstructure of the high-vanadium high-speed steel casting billet after the spheroidizing temper is fine and distributed uniformly.
    Example 5
  • The Example is basically the same as Example 1, and the only difference is that the parameters of step (3) and step (4) are different.
  • Specifically, the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using the intermediate frequency induction furnace at the smelting temperature of 1480°C. During smelting, the intermediate frequency induction furnace was vacuumized to 250 Pa and subsequently the inert gas was filled for protection, so that the melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2.5%C, 5.0%Cr, 4%W, 3.0%Mo, 8%V, 0.5%Si, 0.3%Mn, and a balance of Fe.
    2. (2) When the smelting reached 1480°C, the melt was deposited by the inert gas on the pre-cooled water-cooled copper mold at the spraying speed of 1.25m/s under the pressure difference of 0.15 MPa, wherein the movement speed of the water-cooled copper mold was 100 mm/s, at which time the melt was rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet, and then it was cooled to the room temperature.
    3. (3) The rapid spheroidizing annealing process was carried out on the ingot obtained by this process; a temperature of 880°C was held for 2h; it was cooled to 500°C at the rate of 50°C/h; and then it was air cooled.
    4. (4) It was held at the temperature of 1150°C for 15 min, and quenched in oil to the room temperature; and it was tempered three times at 560°C for 1h each time.
    Example 6
  • The Example is basically the same as Example 1, and the only difference is that the parameters of step (3) and step (4) are different.
  • Specifically, the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using the intermediate frequency induction furnace at the smelting temperature of 1480°C. During smelting, the intermediate frequency induction furnace was vacuumized to 250 Pa and subsequently the inert gas was filled for protection, so that the melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2.5%C, 5.0%Cr, 4%W, 3.0%Mo, 8%V, 0.5%Si, 0.3%Mn, and a balance of Fe.
    2. (2) When the smelting reached 1480°C, the melt was deposited by the inert gas on the pre-cooled water-cooled copper mold at the spraying speed of 1.25m/s under the pressure difference of 0.15 MPa, wherein the movement speed of the water-cooled copper mold was 100 mm/s, at which time the melt was rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet, and then it was cooled to the room temperature.
    3. (3) The rapid spheroidizing annealing process was carried out on the ingot obtained by this process; a temperature of 910°C was held for 2h; it was cooled to 500°C at the rate of 50°C/h; and then it was air cooled.
    4. (4) It was held at the temperature of 1200°C for 15 min, and quenched in oil to the room temperature; and it was tempered three times at 560°C for 1h each time.
    Example 7
  • This Example is essentially the same as Example 1, and differs only in that the parameters of steps (1) and (2) are different.
  • Specifically, the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using the intermediate frequency induction furnace at the smelting temperature of 1500°C. During smelting, the intermediate frequency induction furnace was vacuumized to 100 Pa and subsequently the inert gas was filled for protection, so that the melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2%C, 4%Cr, 2.5%W, 5.0%Mo, 4%V, 0.3%Si, 0.5%Mn, and a balance of Fe.
    2. (2) When the smelting reaches 1500°C, the melt was deposited by the inert gas on the pre-cooled water-cooled copper mold at the spraying speed of 0.75m/s under the pressure difference of 0.05 MPa, wherein the movement speed of the water-cooled copper mold was 50 mm/s, at which time the melt was rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet, and then it was cooled to the room temperature.
    3. (3) The rapid spheroidizing annealing process was carried out on the ingot obtained by this process; a temperature of 850°C was held for 2h; it was cooled to 500°C at a rate of 50°C/h; and then it was air cooled.
    4. (4) It was held at the temperature of 1100°C for 15 min, and quenched in oil to the room temperature; and it was tempered twice at 560°C for 1h each time.
    Example 8
  • This Example is essentially the same as Example 1, and differs only in that the parameters of steps (1) and (2) are different.
  • Specifically, the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using the intermediate frequency induction furnace at the smelting temperature of 1520°C. During smelting, the intermediate frequency induction furnace was vacuumized to 400 Pa and subsequently the inert gas was filled for protection, so that the melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2.3%C, 6.0%Cr, 6%W, 7.0%Mo, 10%V, 0.6%Si, 0.8%Mn, and a balance of Fe.
    2. (2) When the smelting reaches 1520°C, the melt was deposited by the inert gas on the pre-cooled water-cooled copper mold at the spraying speed of 1.75m/s under the pressure difference of 0.25 MPa, wherein the movement speed of the water-cooled copper mold was 120 mm/s, at which time the melt was rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet, and then it was cooled to the room temperature.
    3. (3) The rapid spheroidizing annealing process was carried out on the ingot obtained by this process; a temperature of 850°C was held for 2h; it was cooled to 500°C at a rate of 50°C/h; and then it was air cooled.
    4. (4) It was held at the temperature of 1100°C for 15 min, and quenched in oil to the room temperature; and it was tempered twice at 560°C for 1h each time.
    Comparative Example 1
  • The Comparative Example is basically the same as Example 4, wherein the only difference is that step (3) adopts the conventional annealing process. The specific steps were as follows.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using the intermediate frequency induction furnace at the smelting temperature of 1480°C. During smelting, the intermediate frequency induction furnace was vacuumized to 250 Pa and subsequently the inert gas was filled for protection, so that the melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2.5%C, 5.0%Cr, 4%W, 3.0%Mo, 8%V, 0.5%Si, 0.3%Mn, and a balance of Fe.
    2. (2) When the smelting reached 1480°C, the melt was deposited by the inert gas on the pre-cooled water-cooled copper mold at the spraying speed of 1.25m/s under the pressure difference of 0.15 MPa, wherein the movement speed of the water-cooled copper mold was 100 mm/s, at which time the melt was rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet, and then it was cooled to the room temperature.
    3. (3) The conventional annealing process was carried out on the ingot obtained by this process, i.e., a temperature of 860°C was held for 40 h and then it was cooled with the furnace.
    4. (4) It was held at the temperature of 1100°C for 15 min, and quenched in oil to the room temperature; and it was tempered three times at 560°C for 1h each time.
    Comparative Example 2
  • The Comparative Example is basically the same as Example 4, wherein the only difference is that step (2) adopts the ingot prepared by the spray molding technology. The specific steps were as follows.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using the intermediate frequency induction furnace at the smelting temperature of 1480°C. During smelting, the intermediate frequency induction furnace was vacuumized to 250 Pa and subsequently the inert gas was filled for protection, so that the melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2.5%C, 5.0%Cr, 4%W, 3.0%Mo, 8%V, 0.5%Si, 0.3%Mn, and a balance of Fe.
    2. (2) When the smelting reached 1480°C, the high-temperature melt was atomized by the spray molding technology, wherein the melt formed a morphology mixed with solidity, semi-solidity, and liquid under a high-speed gas flow; it was mixed and deposited on the cooling base to form the high-vanadium high-speed steel casting billet; and then it was cooled to the room temperature.
    3. (3) The rapid spheroidizing annealing process was carried out on the ingot obtained by this process; a temperature of 850°C was held for 2h; it was cooled to 500°C at the rate of 50°C/h; and then it was air cooled.
    4. (4) It was held at the temperature of 1100°C for 15 min, and quenched in oil to the room temperature; and it was tempered three times at 560°C for 1h each time.
    Comparative Example 3
  • The Comparative Example is basically the same as Example 4, wherein the only differences are that step (2) adopts the ingot prepared by the spray molding technology, and step (3) adopts the conventional annealing process. The specific steps were as follows.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using the intermediate frequency induction furnace at the smelting temperature of 1480°C. During smelting, the intermediate frequency induction furnace was vacuumized to 250 Pa and subsequently the inert gas was filled for protection, so that the melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2.5%C, 5.0%Cr, 4%W, 3.0%Mo, 8%V, 0.5%Si, 0.3%Mn, and a balance of Fe.
    2. (2) When the smelting reached 1480°C, the high-temperature melt was atomized by the spray molding technology, wherein the melt formed a morphology mixed with solidity, semi-solidity, and liquid under a high-speed gas flow; it was mixed and deposited on the cooling base to form the high-vanadium high-speed steel casting billet; and then it was cooled to the room temperature.
    3. (3) The conventional annealing process was carried out on the ingot obtained by this process, i.e., a temperature of 860°C was held for 40 h and then it was cooled with the furnace.
    4. (4) It was held at the temperature of 1100°C for 15 min, and quenched in oil to the room temperature; and it was tempered three times at 560°C for 1h each time.
    Comparative Example 4
  • The Comparative Example is basically the same as Example 1, wherein the only difference is that the cooling rate in step (3) is different.
  • Specifically, the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using the intermediate frequency induction furnace at the smelting temperature of 1480°C. During smelting, the intermediate frequency induction furnace was vacuumized to 250 Pa and subsequently the inert gas was filled for protection, so that the melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2.5%C, 5.0%Cr, 4%W, 3.0%Mo, 8%V, 0.5%Si, 0.3%Mn, and a balance of Fe.
    2. (2) When the smelting reached 1480°C, the melt was deposited by the inert gas on the pre-cooled water-cooled copper mold at the spraying speed of 1.25m/s under the pressure difference of 0.15 MPa, wherein the movement speed of the water-cooled copper mold was 100 mm/s, at which time the melt was rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet, and then it was cooled to the room temperature.
    3. (3) The rapid spheroidizing annealing process was carried out on the ingot obtained by this process; a temperature of 850°C was held for 2h; it was cooled to 500°C at the rate of 30°C/h; and then it was air cooled.
    4. (4) It was held at the temperature of 1100°C for 15 min, and quenched in oil to the room temperature; and it was tempered three times at 560°C for 1h each time.
    Comparative Example 5
  • The Comparative Example is basically the same as Example 1, wherein the only difference is that the cooling rate in step (3) is different.
  • Specifically, the example provided a preparation method of the high-vanadium high-speed steel, including the following steps.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using the intermediate frequency induction furnace at the smelting temperature of 1480°C. During smelting, the intermediate frequency induction furnace was vacuumized to 250 Pa and subsequently the inert gas was filled for protection, so that the melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2.5%C, 5.0%Cr, 4%W, 3.0%Mo, 8%V, 0.5%Si, 0.3%Mn, and a balance of Fe.
    2. (2) When the smelting reached 1480°C, the melt was deposited by the inert gas on the pre-cooled water-cooled copper mold at the spraying speed of 1.25m/s under the pressure difference of 0.15 MPa, wherein the movement speed of the water-cooled copper mold was 100 mm/s, at which time the melt was rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet, and then it was cooled to the room temperature.
    3. (3) The rapid spheroidizing annealing process was carried out on the ingot obtained by this process; a temperature of 850°C was held for 2h; it was cooled to 500°C at the rate of 100°C/h; and then it was air cooled.
    4. (4) It was held at the temperature of 1100°C for 15 min, and quenched in oil to the room temperature; and it was tempered three times at 560°C for 1h each time.
    Comparative Example 6
  • The Comparative Example is basically the same as Example 4, wherein the only difference is that no heat treatment was performed in the Comparative Example. The specific steps were as follows.
    1. (1) The raw material was prepared according to the chemical element composition of vanadium, and was smelted by using the intermediate frequency induction furnace at the smelting temperature of 1480°C. During smelting, the intermediate frequency induction furnace was vacuumized to 250 Pa and subsequently the inert gas was filled for protection, so that the melt of the high-vanadium high-speed steel was obtained, wherein the raw material in mass percentage included 2.5%C, 5.0%Cr, 4%W, 3.0%Mo, 8%V, 0.5%Si, 0.3%Mn, and a balance of Fe.
    2. (2) When the smelting reached 1480°C, the pre-cooled water-cooled copper mold at the spraying speed of 1.25m/s under the pressure difference of 0.15 MPa, wherein the movement speed of the water-cooled copper mold was 100 mm/s, at which time the melt was rapidly solidified and molded, so as to form the high-vanadium high-speed steel casting billet, and then it was cooled to the room temperature without any heat treatment.
    Experimental Example
  • The microstructures of the high-vanadium high-speed steels provided by the above Examples 1-8 and Comparative Examples 1-6 were statistically analyzed. The carbide agglomeration condition was evaluated according to the standard of the national standard GB-T 14979-1994 method for evaluating non-uniformity of eutectic carbide of steel, wherein the uniform distribution could be defined as 1-2 levels, and the more uniform distribution was defined as 3-4 levels. The porosity was evaluated according to the national standard GB 12823-91 grade and content of defect of steel casting, wherein the critical porosity of the steel casting was a smallest porosity under the casting process condition, wherein it was usually 3%-5%, and should not exceed 5%. The low porosity in the example could be defined as smaller than 3%, and the high porosity was defined as 3%-5%. The service life of the high-speed steel was evaluated according to the national standard GB-T16461-1996 life test of single edge turning tool.
  • The high-vanadium high-speed steels provided by Examples 1-8 and Comparative Examples 1-6 above were used to carry out the mechanical property test, wherein the test method of the annealing hardness was characterized by the Vickers indentation technique; the test method of the tempering hardness was characterized by the Vickers indentation technique; and the test method of the tempering bending strength was tested by three-point bending experiment. When without carrying out the heat treatment, it only needed to test the hardness and the bending strength, wherein the test method of the hardness was characterized by the Vickers indentation technique; and the test method of the bending strength was characterized by the three-point bending experiment. The test result refers to Table 1 and Table 2. Table 1: statistical table of microstructures of high-vanadium high-speed steels provided by different examples
    Material Carbide size (spherical particle) Carbide agglomeration condition Porosity Service life
    Example 4 2.26 µm uniform distribution low long
    Comparative Example 1 3.72 µm relatively uniform distribution low relatively long
    Comparative Example 2 2.07 µm uniform distribution relatively high short
    Comparative Example 3 3.68 µm relatively uniform distribution relatively high short
    Comparative Example 4 3.25 µm uniform distribution low relatively long
    Comparative Example 5 2.66 µm uniform distribution low relatively long
    Comparative Example 6 2.21 µm uniform distribution low short
    Table 2: statistical table of mechanical properties of high-vanadium high-speed steels provided by different examples
    Material Annealing hardness (HV) Tempering hardness (HV) Tempering bending strength (MPa) Hardness (HV) Bending strength (MPa)
    Example 1 360 863 1271 / /
    Example 2 345 864 1199 / /
    Example 3 315 954 1404 / /
    Example 4 360 894 1192 / /
    Example 5 345 891 1157 / /
    Example 6 315 980 1258 / /
    Example 7 311 775 1391
    Example 8 350 929 1170
    Comparative Example 1 356 810 1014 / /
    Comparative Example 2 363 786 567 / /
    Comparative Example 3 349 792 550 / /
    Comparative Example 4 354 853 1173 / /
    Comparative Example 5 368 860 1155 / /
    Comparative Example 6 / / / 834 891
  • As can be seen from the above table, the microstructure of the high-vanadium high-speed steel ingot prepared by the melt impact method is fine and dense, and it has both high tempering hardness and high bending strength. The Comparative Example 1 adopts the conventional annealing process, which results in a significant increase in the carbide size, and it is up to 3.72 µm. The Comparative Example 2 adopts the spray molding process to prepare the high-vanadium high-speed steel ingot, wherein the ingot has a higher porosity and the mechanical property is significantly lower than that of Example 4. In Comparative Example 3, the step (2) adopts the ingot prepared by the spray molding technology, and at the same time the step (3) adopts the conventional annealing process, which results in a significant increase in the carbide size and a significant decrease in the mechanical property. The Comparative Example 4 and the Comparative Example 5 adopt different cooling rates, wherein the cooling rate of the Comparative Example 4 is lower than the range value of the present invention, which results in a significant increase in the carbide size; and in Comparative Example 5, the cooling rate is too large; the spheroidizing annealing process is not sufficient; the microstructure softening is not sufficient; and it has the highest annealing hardness, which is not beneficial for cutting processing; and it cannot further reduce the carbide size, but the carbide size increases slightly; and the secondary solid solution effect is poor, which results in a certain reduction of the mechanical property. Since the heat treatment is not carried out in Comparative Example 6, the secondary hardening and strengthening could not be realized, so that its mechanical property is significantly reduced. In the present invention, the selection of a rapid spheroidizing annealing process for preparing the high-vanadium high-speed steel ingot by the melt impact method follows principles of time saving and high efficiency, so as to obtain the annealing hardness similar to that of the conventional annealing process under a long cycle and a high energy consumption, and the proper rapid spheroidizing annealing process avoids the aggregation and roughening of fine carbides. In the subsequent quenching-tempering treatment, the high-vanadium high-speed steel ingot prepared by the melt impact method has the satisfactory mechanical property.
  • In summary, the preparation method of the high-vanadium high-speed steel provided by the present invention prepares the high-vanadium high-speed steel casting billet by adopting the melt impact method first, which can play the role of crushing grains and crushing primary carbides when performing the melt impacting, so as to improve the strength, the toughness, and the wear resistance of the high-vanadium high-speed steel, so as to improve the service life. Compared with the prior spray molding method, the biggest difference is that the formed ingot microstructure is dense and uniform, and the carbide is fine. The ingot prepared by the prior spray molding technology has inherent porosity. For casting the high-vanadium high-speed steel, the ingot porosity still exists after the heat treatment since the forging process is not included in subsequence, so that the service life is greatly reduced. The method of the present invention refines the grains and carbides, and greatly reduces the generation of porosity. The utilization rate of the melt is higher, and there is no waste of the alloy melt. The solidified ingot microstructure is uniform and dense. Additionally, the high-vanadium high-speed steel casting billet prepared by the melt impact method has fine and uniform carbide particles. In order to prevent the aggregation and growth of the carbide, it adopts the rapid spheroidizing annealing process, wherein after it is heated to 820-910°C with the furnace and held for 2-4h, it is cooled down to 450-550°C at a cooling rate larger than 40°C/h; and then it is air cooled to a room temperature, wherein the temperature cooling speed is fast, so as to realize the rapid annealing, so that the tungsten carbide in the high-vanadium high-speed steel is not easily agglomerated, and is uniformly distributed in conglobate shape. The rapid spheroidizing annealing process is time-saving and high-efficient, wherein compared with the conventional annealing process, it greatly shortens the duration. Next, the quenching and the tempering are carried out, which comprehensively improve the mechanical property of the high-vanadium high-speed steel.
  • The foregoing is merely preferred embodiments of the present invention and is not intended to limit the present invention, and the present invention has various modification changes for those skilled in the art. Any modifications, equivalent substitutions, and improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims (10)

  1. A preparation method of a high-vanadium high-speed steel, comprising:
    - smelting raw materials to form a melt, wherein the raw materials in mass percentage comprise C: 2.0-2.5%, Cr: 4-6%, W: 2.5-6%, Mo: 3-7%, V: 4-10%, Si: 0.3-0.6%, Mn: 0.3-0.8%, and a balance of Fe;
    - impacting the melt to a cooling platform to form a high-vanadium high-speed steel casting billet;
    - carrying out a spheroidizing annealing treatment on the high-vanadium high-speed steel casting billet to obtain an annealed ingot, wherein the spheroidizing annealing treatment comprises heating the high-vanadium high-speed steel casting billet to 820-910 °C; holding for 2-4 h; then cooling down to 450-550 °C at a cooling rate larger than 40 °C/h; then air cooling to a room temperature; and
    - performing a quenching and tempering treatment on the annealed ingot, so as to obtain a resultant.
  2. The preparation method of the high-vanadium high-speed steel according to claim 1, wherein the cooling rate is 45-75 °C/h.
  3. The preparation method of the high-vanadium high-speed steel according to claim 1, wherein the high-vanadium high-speed steel casting billet is heated with a furnace in a tube furnace protected by an inert gas.
  4. The preparation method of the high-vanadium high-speed steel according to claim 1, wherein the raw materials are smelted by using an intermediate frequency induction furnace at a smelting temperature of 1480-1520 °C; the intermediate frequency induction furnace is vacuumized to 100-400 Pa when smelting; and subsequently the inert gas is filled for protection.
  5. The preparation method of the high-vanadium high-speed steel according to claim 1, wherein a pressure difference between an inner chamber of the melt and an outer chamber during the melt impacting is 0.05-0.25 MPa, and a spraying speed is 0.75-1.75 m/s.
  6. The preparation method of the high-vanadium high-speed steel according to claim 1, wherein a speed of the cooling platform moving downward is 50-120 mm/s.
  7. The preparation method of the high-vanadium high-speed steel according to claim 1, wherein the quenching and tempering treatment comprises: preheating the annealed ingot at 600-750 °C for 5-15 min; then carrying out a quenching and holding a temperature at 1000-1230 °C, wherein a holding duration is 10-30min, and carrying out the quenching in oil to a room temperature; and then tempering 1-4 times at 520-600 °C for 1h each time, wherein the tempering is carried out each time after air cooling to the room temperature.
  8. The preparation method of the high-vanadium high-speed steel according to claim 7, wherein the annealed ingot is preheated in a muffle furnace, and quenched in a tube furnace filled with an inert atmosphere.
  9. A high-vanadium high-speed steel, wherein the high-vanadium high-speed steel is prepared by using the preparation method of the high-vanadium high-speed steel according to any one of claims 1-8, wherein:
    - preferably, an annealing hardness of the high-vanadium high-speed steel is 315-360 HV;
    - preferably, a tempering hardness of the high-vanadium high-speed steel is 863-980 HV;
    - preferably, a tempering bending strength of the high-vanadium high-speed steel is 1157-1404 MPa;
    - preferably, a vanadium content in the high-vanadium high-speed steel is 4-10%;
    - preferably, after the high-vanadium high-speed steel is annealed, vanadium carbide in the ingot is in a shape of sphere, and is uniformly distributed in a base; and
    - preferably, after the high-vanadium high-speed steel is tempered, vanadium carbide in the ingot is in a shape of sphere and block, and is distributed dispersedly, wherein vanadium carbide with a coarse size and an irregular shape does not appear.
  10. A use of the high-vanadium high-speed steel according to claim 9 in a preparation of a roll, a hammer head, a ball mill liner, or a rotor body.
EP25150726.5A 2024-05-07 2025-01-08 High-vanadium high-speed steel and preparation method therefor, and use thereof Pending EP4647516A1 (en)

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