WO2024062933A1 - 熱間工具鋼の製造方法および熱間工具鋼 - Google Patents

熱間工具鋼の製造方法および熱間工具鋼 Download PDF

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WO2024062933A1
WO2024062933A1 PCT/JP2023/032637 JP2023032637W WO2024062933A1 WO 2024062933 A1 WO2024062933 A1 WO 2024062933A1 JP 2023032637 W JP2023032637 W JP 2023032637W WO 2024062933 A1 WO2024062933 A1 WO 2024062933A1
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forging
work tool
cross
hot work
steel
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PCT/JP2023/032637
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English (en)
French (fr)
Japanese (ja)
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洋佑 中野
裕也 古賀
公太 片岡
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株式会社プロテリアル
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Priority to CN202380067704.8A priority Critical patent/CN119907721A/zh
Priority to JP2024548192A priority patent/JPWO2024062933A1/ja
Priority to EP23868056.5A priority patent/EP4592003A1/en
Priority to KR1020257009324A priority patent/KR20250054085A/ko
Publication of WO2024062933A1 publication Critical patent/WO2024062933A1/ja

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
    • B21J1/00—Preparing metal stock or similar ancillary operations prior, during or post forging, e.g. heating or cooling
    • B21J1/02—Preliminary treatment of metal stock without particular shaping, e.g. salvaging segregated zones, forging or pressing in the rough
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
    • B21J1/00—Preparing metal stock or similar ancillary operations prior, during or post forging, e.g. heating or cooling
    • B21J1/04—Shaping in the rough solely by forging or pressing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
    • B21J1/00—Preparing metal stock or similar ancillary operations prior, during or post forging, e.g. heating or cooling
    • B21J1/06—Heating or cooling methods or arrangements specially adapted for performing forging or pressing operations
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
    • B21J5/00—Methods for forging, hammering, or pressing; Special equipment or accessories therefor
    • 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
    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • 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
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • 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
    • C21D9/22—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for drills; for milling cutters; for machine cutting tools
    • 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
    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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
    • C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt
    • 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
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • 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
    • C21D2211/005—Ferrite

Definitions

  • the present invention relates to a method for producing hot work tool steel and hot work tool steel.
  • hot work tool steel As a material (hot work tool steel) applied to hot work tools, for example, SKD61 series alloy tool steel, which is a JIS steel type, is known. Such hot work tool steel is usually made from a steel ingot or a steel billet obtained by blooming a steel ingot, which is then subjected to various hot workings and heat treatments to form a specified forged material. Manufactured by annealing a forged material. The produced hot work tool steel is then subjected to a step of being machined into a desired hot tool shape in an annealed state with low hardness.
  • Hot work tool steel that has been machined into the shape of a hot work tool is generally subjected to finishing processing after being adjusted to a predetermined working hardness by quenching and tempering.
  • Quenching is an operation in which the hot tool material is heated to an austenite temperature range and rapidly cooled to transform the structure to martensite. Therefore, the composition of the hot tool material can be adjusted to a martensitic structure by quenching.
  • Patent Document 1 in order to obtain excellent toughness, a series of A method for producing hot work tool steel is disclosed, which is characterized by performing hot forging to introduce strain, and then soaking at a temperature of 1200 to 1300° C. for 6 hours or more.
  • the toughness of hot tools can be improved by making the martensitic structure finer.
  • the purpose is to make the prior austenite grain size found in the martensitic structure finer.
  • the annealed structure is defined as "the oversized cumulative distribution of ferrite crystal grains in a cross section based on the cross-sectional area of the ferrite crystal grains, and the grain size when the cumulative cross-sectional area is 90% of the total cross-sectional area is the equivalent circle diameter.
  • the authors propose a method to create an annealed structure with a grain size distribution of 25 ⁇ m or less.
  • Patent Document 2 specifies an annealing structure for obtaining hot work tool steel with excellent toughness.
  • solid forging with a processing ratio (cross-sectional area ratio) of 5 seconds or more is required, and since there is a limit to the size of the forged material that can be obtained by forging due to the size of the steel ingot, if the processing ratio cannot be increased for forged material with a large cross-sectional size, it is difficult to obtain a fine annealing structure.
  • Upsetting forging described in JIS-G-7101 is known as a means for producing a forged material having a cross-sectional area larger than that of a steel ingot.
  • the upsetting is usually carried out at a high temperature exceeding 1200° C., and grain growth occurs immediately, making it difficult to obtain a fine structure.
  • Patent Document 1 and Patent Document 2 do not mention such problems during forging, and there is still room for further investigation. Therefore, an object of the present invention is to provide a method for producing hot work tool steel having a fine annealed structure even if the cross-sectional size is large.
  • one aspect of the present invention is a method for producing hot work tool steel, which obtains hot work tool steel having a cross-sectional area of 200,000 mm 2 or more, in which a steel ingot is heated to 1100 to 1250°C, and then hot forged to form a steel.
  • a blooming forging process to obtain a piece; a first finishing forging process in which the steel billet is heated to 850 to 1020°C and upsetting forging is performed at an upsetting forging ratio of 1.6 or more to obtain an intermediate forging material; , a second finishing forging step in which the intermediate forging material is subjected to solid forging with a solid forging forming ratio of 2.0 to 4.0 to obtain a forging material; and a second finishing forging step. It is preferable to include a soaking step in which the steel ingot is heated to 1250° C. or higher before the blooming forging step.
  • the cross-sectional area is 200,000 mm or more
  • the cumulative cross-sectional area of the ferrite crystal grains in the structural cross-section is the total cross-sectional area in an oversized cumulative distribution based on the cross-sectional area of the ferrite crystal grains. It is a hot work tool steel having a grain size distribution in which the grain size at 90% of the diameter is 25 ⁇ m or less in equivalent circle diameter.
  • FIG. 2 is a schematic diagram for explaining the manufacturing method of the present invention. It is an optical micrograph of the cross-sectional structure of the hot work tool steel (sample No. 1) of the example of this invention. 1 is a grain boundary diagram obtained by electron beam backscatter diffraction (EBSD) of a hot work tool steel (sample No. 1) of an example of the present invention. It is an optical micrograph of the cross-sectional structure of the hot work tool steel (sample No. 2) of this invention example. 1 is a grain boundary diagram obtained by electron beam backscatter diffraction (EBSD) of a hot work tool steel (sample No. 2) of an example of the present invention.
  • EBSD electron beam backscatter diffraction
  • FIG. 1 is an optical microscope photograph of a cross-sectional structure of a hot work tool steel (sample No. 3) according to an embodiment of the present invention.
  • FIG. 2 is a grain boundary diagram obtained by electron beam backscatter diffraction (EBSD) of a hot work tool steel (sample No. 3) of an example of the present invention. It is an optical micrograph of the cross-sectional structure of hot work tool steel (sample No. 11) of a comparative example. It is a grain boundary diagram obtained by electron beam backscatter diffraction (EBSD) of hot work tool steel (sample No. 11) of a comparative example.
  • EBSD electron beam backscatter diffraction
  • the feature of the present invention is that, in the next step, the intermediate forging material obtained by upsetting forging the steel billet obtained by blooming forging at a predetermined temperature is subjected to finish forging at a ratio of solid forging. It is a place where you can obtain forged materials with fine ferrite grain size.
  • the hot work tool steel obtained by the production method of the present invention has an annealed structure and is used after being quenched and tempered. It is tool steel.
  • the effect of refining the hot-work tool steel structure obtained by the manufacturing method of the present invention can be achieved by implementing the manufacturing method of the present invention described later if the material is quenched and tempered to develop a martensitic structure. It is. Therefore, in order to achieve the above effects of the present invention, it is not necessary to specify the composition of the hot work tool steel.
  • the hot work tool steel according to the manufacturing method of the present invention has, in mass%, C: 0.3 to 0.5%, Cr: 3 It is preferable to have a component composition containing V: 0.0 to 6.0%, and further preferably to have a component composition containing V: 0.1 to 1.5%.
  • the hot work tool steel according to the manufacturing method of the present invention has C: 0.3 to 0.5%, Si: 2.0% or less, Mn: 1.5% or less, P: 0.05% or less, S : 0.05% or less, Cr: 3.0-6.0%, Mo and W alone or in combination (Mo+1/2W): 0.5-3.5%, V: 0.1-1.5 %, balance Fe and impurities.
  • C 0.3 to 0.5%
  • Si 2.0% or less
  • Mn 1.5% or less
  • P 0.05% or less
  • S 0.05% or less
  • Cr 3.0-6.0%
  • V 0.1-1.5 %
  • balance Fe and impurities balance Fe and impurities.
  • C 0.3 to 0.5% by mass (hereinafter simply referred to as "%")
  • C is a basic element of hot work tool materials, some of which dissolves in the matrix to provide strength, and some of which forms carbides to improve wear resistance and seizure resistance.
  • C dissolved as an interstitial atom is added together with substitutional atoms such as Cr that have a high affinity with C, it acts as an I (interstitial atom)-S (substitutional atom) effect; a drag resistance of solute atoms, and is expected to increase the strength of hot work tools.
  • substitutional atoms such as Cr that have a high affinity with C
  • Si 2.0% or less Si is a deoxidizing agent during steel manufacturing, but if it is too large, it will lead to the formation of ferrite in the tool structure after quenching and tempering. Therefore, the content is preferably 2.0% or less.
  • Si has the effect of improving the machinability of the material. In order to obtain this effect, addition of less than 0.2% may be sufficient, but addition of 0.2% or more is preferable.
  • Mn 1.5% or less
  • the content is preferably 1.5% or less.
  • Mn has the effect of increasing hardenability, suppressing the formation of ferrite in the tool structure, and obtaining appropriate quenching and tempering hardness.
  • the presence of MnS as a non-metallic inclusion has a great effect on improving machinability.
  • the addition amount may be less than 0.1%, but the addition amount is preferably 0.1% or more.
  • P 0.05% or less
  • P is usually an impurity element that is inevitably included in various hot tool materials. It is an element that segregates to prior austenite grain boundaries during heat treatment such as tempering and embrittles the grain boundaries. Therefore, in order to improve the toughness of hot tools, it is preferable to limit the content to 0.05% or less.
  • S 0.05% or less
  • S is an impurity element that is normally included unavoidably in various hot tool materials. And, it is an element that deteriorates the toughness of the material. Therefore, in order to improve the toughness of hot tools, it is preferable to limit the content to 0.05% or less.
  • S has the effect of improving machinability by combining with the Mn and existing as MnS, a non-metallic inclusion. In order to obtain this effect, addition of less than 0.03% may be sufficient, but addition of 0.03% or more is preferable.
  • Cr 3.0-6.0% Cr is an element that improves hardenability, forms carbides, and is effective in strengthening the matrix and improving wear resistance. It is a basic element of hot tool materials that also contributes to improving temper softening resistance and high-temperature strength. However, excessive addition causes a decrease in hardenability and high-temperature strength. Therefore, the content is preferably 3.0 to 6.0%. More preferably, it is 5.0% or less. In the present invention, since the effect of improving toughness is obtained by making the martensitic structure finer, it is possible to reduce Cr by the amount of this effect. In this case, for example, by controlling Cr to 5.0% or less, the high temperature strength can be further improved.
  • Mo and W alone or in combination can be added alone or in combination in order to precipitate or aggregate fine carbides during tempering to impart strength and improve softening resistance. Since W has an atomic weight approximately twice that of Mo, the amount added in this case can be defined as the Mo equivalent of (Mo+1/2W) (of course, only one of them may be added, or both may be added). (can also be added together). In order to obtain the above-mentioned effects, it is preferable to add 0.5% or more in terms of (Mo+1/2W). However, if it is too large, machinability and toughness will deteriorate, so the value of (Mo+1/2W) is preferably 3.5% or less.
  • V forms carbides and has the effect of strengthening the base, improving wear resistance, and tempering softening resistance.
  • the carbides distributed in the annealed structure act as pinning particles that suppress coarsening of austenite crystal grains during quenching and heating, and contribute to improving toughness. In order to obtain these effects, it is preferable to add 0.1% or more. In the present invention, it is preferable to add V in order to further refine the martensitic structure. However, if it is too large, the machinability and toughness will deteriorate due to an increase in carbide itself, so it is preferably 1.5% or less.
  • Ni 0-1.0%
  • Ni is an element that increases the viscosity of the base and reduces machinability. Therefore, the content is preferably 1.0% or less.
  • Ni is an element that suppresses the formation of ferrite in the tool structure.
  • C, Cr, Mn, Mo, W, etc. it imparts excellent hardenability to tool materials, forming a martensite-based structure even when the cooling rate during hardening is slow, preventing a decrease in toughness. It is an effective element for preventing.
  • it since it also improves the essential toughness of the matrix, it may be added as necessary in the present invention. When added, it may be added in an amount of less than 0.1%, but it is preferably added in an amount of 0.1% or more.
  • Co 0-1.0% Since Co reduces toughness, it is preferably 1.0% or less. On the other hand, Co forms an extremely dense and highly adhesive protective oxide film on the surface of the hot tool when the temperature rises during use. This oxide film prevents metal contact with the mating material, suppresses temperature rise on the tool surface, and provides excellent wear resistance. Therefore, Co may be added as necessary. When added, it may be less than 0.3%, but preferably 0.3% or more.
  • Nb 0-0.3% Since Nb causes a decrease in machinability and toughness, it is preferably 0.3% or less. On the other hand, Nb forms carbides and has the effect of strengthening the base and improving wear resistance. Moreover, it has the effect of increasing resistance to temper softening and, like V, suppressing coarsening of crystal grains and contributing to improvement of toughness. Therefore, Nb may be added as necessary. When added, it may be less than 0.01%, but preferably 0.01% or more.
  • the main elements that may remain in steel as unavoidable impurities are Cu, Al, Ca, Mg, O (oxygen), N (nitrogen), etc.
  • the content of these elements is preferably as low as possible. However, on the other hand, it may be contained in a small amount in order to obtain additional effects such as controlling the morphology of inclusions, improving other mechanical properties, and improving manufacturing efficiency. In this case, it is sufficient that Cu ⁇ 0.25%, Al ⁇ 0.025%, Ca ⁇ 0.01%, Mg ⁇ 0.01%, O ⁇ 0.01%, N ⁇ 0.03%. is the preferred regulatory upper limit of the present invention.
  • Hot work tool steel with an annealed structure is usually made from a steel ingot or a steel billet obtained by blooming a steel ingot as a starting material, which is then subjected to various hot workings and heat treatments to form a specified forged material.
  • This forged material is annealed and finished into a desired shape, such as a block shape.
  • FIG. 1 shows a schematic diagram for explaining the manufacturing method of the present invention (in the schematic diagram, the "shaded" surface of the steel piece or forged material is a common surface between each process). Note that the present invention is suitable for a method of manufacturing large-sized hot work tool steel having a cross-sectional area of 200,000 mm 2 or more.
  • a more preferable cross-sectional area is 300,000 mm 2 or more.
  • the aspect ratio in the cross section of the hot work tool steel is preferably 2 to 3.
  • the "cross-sectional area" in the present invention can be defined as the area of a cross-section perpendicular to the longitudinal direction of the forged material.
  • a blooming forging step is carried out in which a steel ingot obtained by casting is heated to 1100 to 1250° C. and then hot forged to obtain a steel billet.
  • the larger the size of the steel ingot obtained by casting the slower the solidification rate and the growth of coarse dendrites.
  • the heating temperature in the blooming forging process of the present invention is set to 1100 to 1250°C. Note that upsetting forging may be carried out during the blooming forging process depending on the cross-sectional area of the steel ingot and the cross-sectional area of the hot tool steel to be finally obtained.
  • annealing temperature at this time is preferably 600°C or higher. More preferably, the annealing temperature is higher than the austenite transformation point and lower than 900°C. Once the ferrite structure is transformed into the austenite structure, the effect of adjusting the crystal grain size can be expected.
  • the upsetting forming ratio is the ratio of the length L 1 of the steel billet shown in FIG. 1 to the length L 2 of the steel billet after upsetting, and is expressed by the formula 1/(L 2 /L 1 ). You can ask for it.
  • a preferable upper limit of the heating temperature in the first finish forging step is 1000°C.
  • a more preferable upper limit is 990°C.
  • the subsequent finish forging step is preferably carried out at a temperature below which the aforementioned pinning carbide is sufficiently present.
  • the lower limit temperature is preferably a temperature equal to or higher than the austenite transformation point. In the case of SKD61, which is a representative steel type of hot work tool steel, the austenite transformation point is around 850°C, so in the present invention, the lower limit of the heating temperature in the first finish forging step is set to 850°C.
  • the upsetting forging forming ratio in the first finish forging step is 1.6 or more. If the upsetting forging forming ratio is small, a sufficient cross-sectional area of the intermediate forging material after upsetting cannot be obtained. It becomes difficult to obtain a forged material with a large cross-sectional size. Although there is no upper limit for the upsetting forging ratio, if the cross-sectional area increases too much by increasing the forging ratio. Since the load required for forging increases and exceeds the pressing force of the forging machine, it can be set to about 2.0, for example. After upsetting forging, the shape is formed into an intermediate forging having a cross-sectional area necessary to obtain an actual forging forming ratio of 2.0 to 4.0 in accordance with the size of the forging obtained in the second finishing step.
  • a second finishing forging process is performed in which the intermediate forging material obtained through the first finishing forging process is subjected to solid forging with a solid forging forming ratio of 2.0 to 4.0 to obtain a forging material. do.
  • the actual forging forming ratio is the ratio of the cross-sectional area A 3 of the intermediate forging material shown in FIG. 1 to the cross-sectional area A 4 after the second finish forging step, and can be determined by the formula A 3 /A 4 .
  • This second finish forging may be started immediately after the first finish forging step is completed, but it may also be carried out after being placed in a heating furnace, reheated, and held. Note that there is no problem even if the temperature at which the second finish forging is performed is different from the temperature for the first finish forging. Preferably, it is carried out at the same temperature as the first finish forging temperature or at a lower temperature.
  • the forged material after the second finish forging step is annealed at a temperature equal to or higher than the austenite transformation point.
  • This step removes residual stress from the forged material after hot plastic working and sufficiently lowers the hardness, making it easier to machine into the shape of a hot tool such as a mold, which will be described later.
  • the annealing temperature at this time is preferably higher than the austenite transformation point and lower than 900°C.
  • the annealing temperature is too high, for example, solid solution of carbides in the forged material structure to the base will proceed, and during subsequent cooling from the annealing temperature, the carbides will preferentially re-precipitate at grain boundaries, resulting in the final It may have a negative effect on the carbide distribution in the product structure.
  • the manufacturing method of the present invention it is preferable to perform soaking in which the steel ingot is heated to 1250° C. or higher before the blooming forging step.
  • the components are diluted in the initially solidified region, and the components are concentrated in the most solidified region, and coarse eutectic carbides are formed.
  • the eutectic carbides become coarser and the segregation of components worsens.
  • the temperature is too high, a part of the steel ingot will melt and a liquid phase will be formed, making it impossible to maintain the shape of the steel ingot, so it is preferable to set the upper limit for each component of the material.
  • the soaking process can also serve as the process.
  • the temperature is low, the effects of solid solution and segregation diffusion of eutectic carbides are small, so it is preferable to carry out the heating at a temperature equal to or higher than the heating temperature of the blooming forging process.
  • the hot work tool steel (forged material) of the present invention obtained by the production method of the present invention has a large size with a cross-sectional area perpendicular to the longitudinal direction of 200,000 mm 2 or more (preferably 300,000 mm 2 or more), but has an annealed structure.
  • the grain size (D90) when the cumulative cross-sectional area is 90% of the total cross-sectional area is 25 ⁇ m in equivalent circle diameter. It has the following particle size distribution.
  • the prior austenite grain size after quenching and tempering is reduced to, for example, No. A fine structure of 9.0 or more can be stably obtained.
  • a preferable upper limit of D90 is 22 ⁇ m, and a more preferable upper limit of D90 is 20 ⁇ m.
  • the ferrite crystal grains of the present invention are obtained by taking a sample from the center of a cross section perpendicular to the longitudinal direction of the forged material, and forming an area of 400 ⁇ m x 400 ⁇ m on a plane parallel to the longitudinal direction (forging direction) of the sample. can be measured. This is because in the case of a forged material with a large cross-sectional area, crystal grains tend to become coarse in the center of the cross-section. Furthermore, if crystal grain refinement by recrystallization or phase transformation is insufficient, coarse grains extending in the forging direction may remain, and this can be confirmed by observing parallel surfaces.
  • the above measurements are performed on two or more cross sections of the forged material. Furthermore, it is preferable that the two or more cross sections include cross sections of both ends of the forged material after cutting the ends.
  • the above-mentioned ends are unnecessary parts that are not suitable for the product and are usually cut off.
  • the annealed structure according to the present invention is a structure containing carbides, the carbides act as pinning particles that suppress coarsening of austenite crystal grains during quenching and heating, further suppressing the growth of austenite crystals. These carbides exist as undissolved carbides in the structure in which the prior austenite grain size has been refined in the hot tool after quenching and tempering.
  • the "annealed structure" in the present invention refers to a structure obtained by an annealing treatment, and is preferably a structure whose hardness is softened to, for example, about 150 to 230 HBW in terms of Brinell hardness.
  • the hot work tool steel obtained by the manufacturing method of the present invention is prepared into a martensitic structure with a predetermined hardness by quenching and tempering, and is prepared into a hot work tool product. Then, the hot work tool steel is shaped into a hot work tool by various machining processes such as cutting and drilling.
  • the processing is preferably performed in a state where the material has low hardness (annealed state) before quenching and tempering. In this case, finishing processing may be performed after the quenching and tempering. Further, depending on the case, processing may be performed in a pre-hardened state after the quenching and tempering.
  • the temperature of this quenching and tempering varies depending on the composition of the material, the target hardness, etc., but it is preferable that the quenching temperature is approximately 1000 to 1100°C, and the tempering temperature is approximately 500 to 650°C. If the quenching temperature is high, the above-mentioned pinning carbide becomes solid solution in the matrix and crystal grain growth occurs, so it is preferable to set the temperature at which the pinning carbide sufficiently remains.
  • the quenching temperature is about 1000 to 1030°C
  • the tempering temperature is about 550 to 650°C.
  • the quenching and tempering hardness is preferably 50 HRC or less. More preferably 48HRC or less
  • a 10 t steel ingot having the composition shown in No. 11 in Table 1 was melted using a melting furnace. After soaking this steel ingot at a temperature of 1250°C or higher, it is subjected to blooming at 1160°C, and then annealed at 870°C to obtain a steel billet with a thickness of 700 mm x width of 1090 mm x length of 1680 mm, This steel piece was subjected to the process shown in No. 11 in Table 2, and the obtained forged material was annealed at 870°C to obtain a hot work tool steel as a comparative example.
  • the cross-sectional structures of the hot work tool steels (samples) No. 1 to No. 3 and No. 11 produced were observed.
  • the cross-sections observed were obtained by cutting unnecessary parts from both ends of the steel material.
  • the samples were sliced at a position of about 15 mm from both end faces so as to include the obtained cross-sections, and two plate-shaped test pieces were taken.
  • a test piece was cut out at a distance of about 10 mm to 20 mm from the center of the plate-shaped test piece, and a surface parallel to the forging direction (i.e., the length direction of the sample) was observed.
  • the observation was performed with an optical microscope (magnification 200 times), and the observed cross-sectional area was 0.16 mm 2 (400 ⁇ m ⁇ 400 ⁇ m).
  • the cross-sectional structures of the hot work tool steels No. 1 and No. 11 were almost entirely occupied by ferrite phase, and ferrite crystal grains occupied more than 99 area % of the observed cross section.
  • FIG. 6 shows the particle size distribution at one end surface of samples No. 1 and No. 11.
  • the vertical axis represents the cumulative cross-sectional area (%) of the crystal grains
  • the horizontal axis represents the equivalent circular diameter of the crystal grains. From the measurement results, No. 1 and No. 1 manufactured by the present invention. 2.No. The equivalent circle diameters where the cumulative cross-sectional area of No.
  • hot work tool steel is 90% (d90) of the total cross-sectional area are 18 ⁇ m, 18 ⁇ m, and 19 ⁇ m at the above one end surface, and 18 ⁇ m, 17 ⁇ m, and 15 ⁇ m at the other end surface, respectively. This was confirmed.
  • the equivalent circle diameter at which the cumulative cross-sectional area of hot work tool steel No. 11 obtained by the manufacturing method of Comparative Example is 90% (d90) of the total cross-sectional area is 30 ⁇ m at one end surface and 24 ⁇ m at the other end surface. Met. From the above, it was confirmed that the hot work tool steel of the example of the present invention had a finer structure than that of the comparative example.

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PCT/JP2023/032637 2022-09-21 2023-09-07 熱間工具鋼の製造方法および熱間工具鋼 WO2024062933A1 (ja)

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KR1020257009324A KR20250054085A (ko) 2022-09-21 2023-09-07 열간 공구강의 제조 방법 및 열간 공구강

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JP2007100194A (ja) 2005-10-07 2007-04-19 Daido Steel Co Ltd 熱間工具鋼の製造方法
WO2015182586A1 (ja) 2014-05-28 2015-12-03 日立金属株式会社 熱間工具材料および熱間工具の製造方法
WO2016208571A1 (ja) * 2015-06-22 2016-12-29 日立金属株式会社 高速度工具鋼鋼材の製造方法、高速度工具鋼製品の製造方法および高速度工具鋼製品
CN114015949A (zh) * 2021-11-11 2022-02-08 成都先进金属材料产业技术研究院股份有限公司 改善含钒冷作模具钢碳化物形态的方法
CN114951528A (zh) * 2021-02-23 2022-08-30 天津重型装备工程研究有限公司 一种用于改善高合金钢锻件性能的闭式锻造方法及工装

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JP6195166B2 (ja) 2014-03-24 2017-09-13 本田技研工業株式会社 自動車の車体構造

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Publication number Priority date Publication date Assignee Title
US6565683B1 (en) * 1996-06-21 2003-05-20 General Electric Company Method for processing billets from multiphase alloys and the article
JP2007100194A (ja) 2005-10-07 2007-04-19 Daido Steel Co Ltd 熱間工具鋼の製造方法
WO2015182586A1 (ja) 2014-05-28 2015-12-03 日立金属株式会社 熱間工具材料および熱間工具の製造方法
WO2016208571A1 (ja) * 2015-06-22 2016-12-29 日立金属株式会社 高速度工具鋼鋼材の製造方法、高速度工具鋼製品の製造方法および高速度工具鋼製品
CN114951528A (zh) * 2021-02-23 2022-08-30 天津重型装备工程研究有限公司 一种用于改善高合金钢锻件性能的闭式锻造方法及工装
CN114015949A (zh) * 2021-11-11 2022-02-08 成都先进金属材料产业技术研究院股份有限公司 改善含钒冷作模具钢碳化物形态的方法

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