WO2024252667A1 - Matériau d'acier - Google Patents

Matériau d'acier Download PDF

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Publication number
WO2024252667A1
WO2024252667A1 PCT/JP2023/021540 JP2023021540W WO2024252667A1 WO 2024252667 A1 WO2024252667 A1 WO 2024252667A1 JP 2023021540 W JP2023021540 W JP 2023021540W WO 2024252667 A1 WO2024252667 A1 WO 2024252667A1
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Prior art keywords
content
steel material
temperature
steel
tempering
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PCT/JP2023/021540
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English (en)
Japanese (ja)
Inventor
友彰 浜口
暁 大川
宏二 渡里
基成 西原
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Nippon Steel Corp
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Nippon Steel Corp
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Priority to CN202380098932.1A priority Critical patent/CN121285646A/zh
Priority to JP2025525911A priority patent/JPWO2024252667A1/ja
Priority to PCT/JP2023/021540 priority patent/WO2024252667A1/fr
Publication of WO2024252667A1 publication Critical patent/WO2024252667A1/fr
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • This disclosure relates to steel materials, and more specifically, to steel materials suitable for use in high-temperature environments, such as hot working tools.
  • Hot forging and hot extrusion processes use hot tools such as hot forging dies and extrusion tools.
  • the hot tools collide with or come into contact with high-temperature materials at temperatures of around 850 to 1300°C. For this reason, the steel used as hot tools is required to have excellent strength and toughness in high-temperature environments.
  • the strength and toughness required in high-temperature environments such as hot processing are referred to as "high-temperature strength” and "high-temperature toughness”.
  • Patent Document 1 International Publication No. 2005/182586
  • Patent Document 2 International Publication No. 2016/013273
  • Patent Document 3 JP 2018-165400 A
  • Patent Documents 1 to 3 do not address the issue of achieving both high-temperature strength and high-temperature toughness.
  • the objective of this disclosure is to provide a steel material that has excellent high-temperature strength and excellent high-temperature toughness.
  • the steel material disclosed herein has the following configuration:
  • a steel material The chemical composition, in mass%, is C: 0.20-0.60%, Si: 0.05-1.00%, Mn: 0.20-1.00%, P: 0.030% or less, S: 0.0300% or less, Cr: 5.60-7.00%, Mo: 1.00-4.00%, V: 0.10-1.50%, sol. Al: 0.0005-0.1000%, N: 0.0050-0.0500%, Ni: 0-2.00%, Cu: 0 to 0.050%, Nb: 0 to 0.1000%, Ti: 0 to 0.050%, and The balance is composed of Fe and impurities.
  • the total area ratio of martensite and bainite is 99% or more,
  • the average grain size of prior austenite grains is 150 ⁇ m or less,
  • the Cr content contained in the residue extracted from the steel material by electrolytic extraction is 0.5 to 3.0% by mass,
  • the Mo content in the residue is 0.2 to 2.0% by mass. Steel.
  • the steel material disclosed herein has excellent high-temperature strength and excellent high-temperature toughness.
  • the inventors have conducted research into steel materials that have excellent high-temperature strength and excellent high-temperature toughness. As a result, the inventors have come to the following findings.
  • the inventors investigated steel materials with excellent high-temperature strength and excellent high-temperature toughness from the viewpoint of chemical composition.
  • the steel materials had the following composition by mass: C: 0.20-0.60%, Si: 0.05-1.00%, Mn: 0.20-1.00%, P: 0.030% or less, S: 0.0300% or less, Cr: 5.60-7.00%, Mo: 1.00-4.00%, V: 0.10-1.50%, sol.
  • the inventors focused on precipitates in steel.
  • steel having the above-mentioned chemical composition several types of fine precipitates can form.
  • Precipitates in steel increase high-temperature strength through precipitation strengthening.
  • precipitates can also become the starting point of cracks and reduce high-temperature toughness. Therefore, the inventors thought that if specific precipitates are formed in appropriate amounts, it would be possible to increase the high-temperature strength of the steel while also preventing them from becoming the starting point of cracks and reducing high-temperature toughness.
  • the size of the precipitates that form in steel with the above-mentioned chemical composition is extremely fine, at the nano level. For this reason, it is difficult to quantitatively measure the number density of each type of precipitate using a scanning electron microscope or the like. However, by carrying out electrolytic extraction on steel and quantifying the chemical composition of the resulting extraction residue, it is possible to predict the precipitates in the steel.
  • the inventors therefore carried out electrolytic extraction on steel material having the above-mentioned chemical composition, and investigated the relationship between the components in the resulting residue and high-temperature strength and high-temperature toughness.
  • the inventors found that in steel material having the above-mentioned chemical composition and with an average crystal grain size of prior austenite grains of 150 ⁇ m or less, if the Cr content obtained in the extraction residue is 0.5 to 3.0% by mass and the Mo content is 0.2 to 2.0% by mass, excellent high-temperature strength and excellent high-temperature toughness can be obtained.
  • the steel material of this embodiment which was completed based on the above findings, has the following configuration.
  • a steel material The chemical composition, in mass%, is C: 0.20-0.60%, Si: 0.05-1.00%, Mn: 0.20-1.00%, P: 0.030% or less, S: 0.0300% or less, Cr: 5.60-7.00%, Mo: 1.00-4.00%, V: 0.10-1.50%, sol. Al: 0.0005-0.1000%, N: 0.0050-0.0500%, Ni: 0-2.00%, Cu: 0 to 0.050%, Nb: 0 to 0.1000%, Ti: 0 to 0.050%, and The balance is composed of Fe and impurities.
  • the total area ratio of martensite and bainite is 99% or more,
  • the average grain size of prior austenite grains is 150 ⁇ m or less,
  • the Cr content contained in the residue extracted from the steel material by electrolytic extraction is 0.5 to 3.0% by mass,
  • the Mo content in the residue is 0.2 to 2.0% by mass. Steel.
  • the steel material according to [1] The chemical composition is Ni: 0.01-2.00%, Cu: 0.001 to 0.050%, Nb: 0.0001 to 0.1000%, and Ti: 0.001 to 0.050%, Contains one or more selected from the group consisting of Steel.
  • the steel material according to [1] or [2], The steel material is a hot work tool; Steel.
  • the steel material of this embodiment satisfies the following characteristics 1 to 4.
  • the chemical composition is, in mass%, C: 0.20-0.60%, Si: 0.05-1.00%, Mn: 0.20-1.00%, P: 0.030% or less, S: 0.0300% or less, Cr: 5.60-7.00%, Mo: 1.00-4.00%, V: 0.10-1.50%, sol. Al: 0.0005-0.1000%, N: 0.0050-0.0500%, Ni: 0-2.00%, Cu: 0-0.050%, Nb: 0-0.1000%, Ti: 0-0.050%, and the balance: Fe and impurities.
  • the total area ratio of martensite and bainite is 99% or more.
  • the average grain size of prior austenite grains is 150 ⁇ m or less.
  • the Cr content contained in the residue extracted from the steel material by electrolytic extraction is 0.5 to 3.0% by mass, and the Mo content contained in the residue is 0.2 to 2.0% by mass.
  • Carbon (C) improves the hardenability of steel and increases the high-temperature strength of steel.
  • C also forms carbides and/or carbonitrides to increase the high-temperature strength of steel.
  • C also stabilizes austenite. Specifically, C expands the temperature range in which austenite can stably exist, and makes it easier to transform into austenite by holding the temperature for a short period of time during reverse transformation. %, the above-mentioned effects cannot be obtained sufficiently even if the contents of other elements are within the ranges of this embodiment.
  • the C content exceeds 0.60%, even if the contents of other elements are within the range of this embodiment, the carbides become coarse when used in a high-temperature environment.
  • the C content is 0.20 to 0.60%.
  • the lower limit of the C content is preferably 0.25%, more preferably 0.27%, and further preferably 0.29%.
  • the upper limit of the C content is preferably 0.55%, more preferably 0.52%, and further preferably 0.50%.
  • Si 0.05-1.00% Silicon (Si) deoxidizes steel. Si also improves the machinability of steel. Si also improves temper softening resistance and high temperature strength of steel. Si content is less than 0.05% If this is the case, even if the contents of other elements are within the ranges of this embodiment, the above-mentioned effects cannot be sufficiently obtained. On the other hand, if the Si content exceeds 1.00%, coarse oxides are generated even if the contents of other elements are within the range of this embodiment. Therefore, the high-temperature strength of the steel material is reduced, and the steel material The toughness of the steel decreases. Therefore, the Si content is 0.05 to 1.00%.
  • the lower limit of the Si content is preferably 0.07%, more preferably 0.08%, and further preferably 0.09%.
  • the upper limit of the Si content is preferably 0.90%, more preferably 0.80%, still more preferably 0.70%, still more preferably 0.60%, and still more preferably 0.55%. %.
  • Mn 0.20-1.00%
  • Manganese (Mn) deoxidizes steel. Mn also improves the hardenability and high temperature strength of steel. Mn also stabilizes austenite. When the Mn content is less than 0.20%, If there are any, the above-mentioned effects cannot be sufficiently obtained even if the contents of the other elements are within the ranges of this embodiment. On the other hand, if the Mn content exceeds 1.00%, Mn will segregate in the steel material even if the contents of other elements are within the ranges of this embodiment. As a result, the high-temperature strength of the steel material decreases, and The high temperature toughness of the steel decreases. Therefore, the Mn content is 0.20 to 1.00%.
  • the lower limit of the Mn content is preferably 0.22%, more preferably 0.25%, further preferably 0.27%, and further preferably 0.30%.
  • the upper limit of the Mn content is preferably 0.95%, more preferably 0.90%, still more preferably 0.85%, still more preferably 0.80%, and still more preferably 0.75%. %, and more preferably 0.70%.
  • Phosphorus (P) is an unavoidable impurity, and the P content is more than 0%. P segregates at grain boundaries. If the P content exceeds 0.030%, the hot workability, high-temperature strength, and high-temperature toughness of the steel material are reduced even if the contents of other elements are within the ranges of this embodiment. Therefore, the P content is 0.030% or less.
  • the P content is preferably as low as possible. However, an extreme reduction in the P content significantly increases the production cost. Therefore, in consideration of industrial production, the lower limit of the P content is preferably 0.001%, more preferably 0.003%, more preferably 0.005%, and even more preferably 0.010%.
  • the upper limit of the P content is preferably 0.028%, more preferably 0.025%, still more preferably 0.023%, still more preferably 0.020%, and still more preferably 0.015%.
  • S 0.0300% or less Sulfur (S) is an unavoidably contained impurity, and the S content is more than 0%. S segregates at grain boundaries or forms sulfides. If the S content exceeds 0.0300%, the hot workability, high-temperature strength, and high-temperature toughness of the steel material are reduced even if the contents of other elements are within the ranges of this embodiment. Therefore, the S content is 0.0300% or less.
  • the S content is preferably as low as possible. However, an extreme reduction in the S content significantly increases the production cost. Therefore, in consideration of industrial production, the preferred lower limit of the S content is 0.0001%, more preferably 0.0003%, and even more preferably 0.0005%.
  • the upper limit of the S content is preferably 0.0250%, more preferably 0.0200%, more preferably 0.0150%, more preferably 0.0100%, more preferably 0.0090%, more preferably 0.0070%, and more preferably 0.0060%.
  • Chromium (Cr) improves the hardenability of steel and increases the high-temperature strength of the steel. Cr also improves the temper softening resistance and increases the high-temperature strength and high-temperature toughness of the steel. Cr also forms carbides, It improves the high temperature strength of the steel material. If the Cr content is less than 5.60%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Cr content exceeds 7.00%, even if the contents of other elements are within the ranges of this embodiment, the strength of the steel material becomes too high, and in this case, the high temperature toughness of the steel material decreases. Therefore, the Cr content is 5.60 to 7.00%. The lower limit of the Cr content is preferably 5.63%, more preferably 5.66%, and further preferably 5.69%. The upper limit of the Cr content is preferably 6.97%, more preferably 6.94%, and further preferably 6.91%.
  • Mo Molybdenum
  • Mo enhances the high-temperature strength of steel by solid solution strengthening. Mo also forms carbides to enhance the high-temperature strength and high-temperature toughness of steel. Mo also enhances the wear resistance of steel. If the Mo content is less than 1.00%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Mo content exceeds 4.00%, the strength of the steel material becomes too high even if the contents of other elements are within the ranges of this embodiment. In this case, the machinability of the steel material decreases. or the high-temperature toughness of the steel material decreases. Therefore, the Mo content is 1.00 to 4.00%.
  • the lower limit of the Mo content is preferably 1.10%, more preferably 1.20%, still more preferably 1.30%, still more preferably 1.40%, and still more preferably 1.50%. %.
  • the upper limit of the Mo content is preferably 3.90%, more preferably 3.80%, and further preferably 3.70%.
  • V Vanadium (V) enhances the high-temperature strength of steel by solid solution strengthening. V also forms carbides and/or carbonitrides to enhance the high-temperature strength of steel. V content is less than 0.10% If this is the case, even if the contents of other elements are within the ranges of this embodiment, the above-mentioned effects cannot be sufficiently obtained. On the other hand, if the V content exceeds 1.50%, even if the contents of other elements are within the ranges of this embodiment, the carbides and/or carbonitrides become coarse when used in a high temperature environment. This reduces the high-temperature strength and high-temperature toughness of the steel material. Therefore, the V content is 0.10 to 1.50%.
  • the lower limit of the V content is preferably 0.15%, more preferably 0.20%, still more preferably 0.25%, still more preferably 0.30%, and still more preferably 0.35%. %, and more preferably 0.40%.
  • the upper limit of the V content is preferably 1.45%, more preferably 1.40%, even more preferably 1.30%, even more preferably 1.10%, and even more preferably 1.00%. %.
  • sol. Al 0.0005-0.1000%
  • Aluminum (Al) deoxidizes steel. If the sol. Al content is less than 0.0005%, the above effect can be sufficiently obtained even if the contents of other elements are within the range of this embodiment. I can't. On the other hand, if the sol.Al content exceeds 0.1000%, oxides are excessively generated. In this case, even if the contents of other elements are within the range of this embodiment, the high temperature strength and high temperature properties of the steel material are deteriorated. The toughness decreases. Furthermore, the machinability of the steel decreases. Therefore, the sol. Al content is 0.0005 to 0.1000%. The lower limit of the sol.
  • Al content is preferably 0.0010%, more preferably 0.0015%, and further preferably 0.0020%.
  • the upper limit of the sol. Al content is preferably 0.0900%, more preferably 0.0800%, still more preferably 0.0750%, still more preferably 0.0700%, and still more preferably 0. 0.0600%, more preferably 0.0500%, and even more preferably 0.0400%.
  • the Al content referred to in this specification means the content of "acid-soluble Al", that is, "sol. Al”.
  • N 0.0050-0.0500%
  • Nitrogen (N) forms nitrides and/or carbonitrides to increase the high-temperature strength of steel. N also increases the high-temperature strength of steel through solid solution strengthening. N also acts as an austenite stabilizing element. If the N content is less than 0.0050%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the N content exceeds 0.0500%, even if the contents of other elements are within the ranges of this embodiment, the nitrides and/or carbonitrides will become coarse when used in a high-temperature environment. This reduces the high-temperature strength and high-temperature toughness of the steel material.
  • the N content is 0.0050 to 0.0500%.
  • the lower limit of the N content is preferably 0.0060%, more preferably 0.0065%, and further preferably 0.0070%.
  • the upper limit of the N content is preferably 0.0400%, more preferably 0.0380%, and further preferably 0.0360%.
  • the remainder of the chemical composition of the steel material according to this embodiment is made up of Fe and impurities.
  • impurities in the chemical composition refer to substances that are mixed in from raw materials such as ore and scrap, or from the manufacturing environment, during the industrial production of steel material, and are acceptable to the extent that they do not adversely affect the steel material according to this embodiment.
  • the chemical composition of the steel material of this embodiment is further Ni: 0-2.00%, Cu: 0 to 0.050%, Nb: 0 to 0.1000%, and Ti: 0 to 0.050%, may contain one or more elements selected from the group consisting of: These optional elements will now be described.
  • the chemical composition of the steel material of the present embodiment may further contain one or more elements selected from the group consisting of Ni and Cu. All of these elements are optional elements and may not be contained. When contained, Ni and Cu contribute to stabilizing austenite.
  • Nickel (Ni) is an optional element and may not be contained, that is, the Ni content may be 0%.
  • Ni When Ni is contained, that is, when the Ni content exceeds 0%, Ni contributes to the stabilization of austenite in the same manner as Mn. If even a small amount of Ni is contained, the above effect can be obtained to some extent. However, if the Ni content exceeds 2.00%, even if the contents of other elements are within the ranges of this embodiment, the transformation point decreases, and in this case, the high-temperature strength of the steel material decreases. Therefore, the Ni content is 0 to 2.00%.
  • the lower limit of the Ni content is preferably 0.01%, more preferably 0.03%, and further preferably 0.05%.
  • the upper limit of the Ni content is preferably 1.80%, more preferably 1.60%, further preferably 1.40%, and further preferably 1.20%.
  • Cu 0-0.050% Copper (Cu) is an optional element and may not be contained, that is, the Cu content may be 0%.
  • Cu When Cu is contained, that is, when the Cu content exceeds 0%, Cu contributes to stabilizing austenite. Even if even a small amount of Cu is contained, the above effect can be obtained to some extent. However, if the Cu content exceeds 0.050%, the high temperature strength of the steel material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the Cu content is 0 to 0.050%.
  • the lower limit of the Cu content is preferably 0.001%, more preferably 0.003%, further preferably 0.005%, and further preferably 0.008%.
  • the upper limit of the Cu content is preferably 0.045%, more preferably 0.040%, further preferably 0.035%, and further preferably 0.030%.
  • the chemical composition of the steel material of the present embodiment may further contain one or more elements selected from the group consisting of Nb and Ti. These elements are optional elements and may not be contained. When contained, Nb and Ti increase the high temperature strength of the steel material.
  • Niobium (Nb) is an optional element and may not be contained, that is, the Nb content may be 0%.
  • Nb is contained, that is, when the Nb content is more than 0%, Nb forms carbides and/or carbonitrides to increase the high-temperature strength of the steel material. The effect is achieved to some extent. However, if the Nb content exceeds 0.1000%, even if the contents of other elements are within the ranges of this embodiment, the carbides and/or carbonitrides become coarse when used in a high temperature environment. This reduces the high-temperature strength and high-temperature toughness of the steel material. Therefore, the Nb content is 0 to 0.1000%.
  • the lower limit of the Nb content is preferably 0.0001%, more preferably 0.0003%, further preferably 0.0005%, and further preferably 0.0010%.
  • the upper limit of the Nb content is preferably 0.0800%, more preferably 0.0600%, still more preferably 0.0550%, still more preferably 0.0400%, and still more preferably 0.0300%. %, and more preferably 0.0200%.
  • Titanium (Ti) is an optional element and may not be contained, that is, the Ti content may be 0%.
  • Ti When Ti is contained, that is, when the Ti content is more than 0%, Ti forms carbides and/or carbonitrides, and increases the high-temperature strength of the steel material. The effect is achieved to some extent. However, if the Ti content exceeds 0.050%, even if the contents of other elements are within the ranges of this embodiment, the carbides and/or carbonitrides become coarse when used in a high temperature environment. This reduces the high-temperature strength and high-temperature toughness of the steel material. Therefore, the Ti content is 0 to 0.050%.
  • the lower limit of the Ti content is preferably 0.001%, more preferably 0.002%, and further preferably 0.003%.
  • the upper limit of the Ti content is preferably 0.040%, more preferably 0.030%, further preferably 0.020%, and further preferably 0.010%.
  • the total area ratio of martensite and bainite is less than 99%, ferrite is formed in the remainder of the microstructure. In this case, sufficient high-temperature strength or high-temperature toughness may not be obtained. On the other hand, if the total area ratio of martensite and bainite is 99% or more, excellent high-temperature strength and excellent high-temperature toughness are obtained.
  • the total area ratio of martensite and bainite in the microstructure of a steel material can be determined by the following method.
  • a test piece is taken from a position at a depth of 1 mm or more from the surface of the steel material.
  • the size of the test piece is not particularly limited, but is, for example, 20 mm x 15 mm x 15 mm.
  • the surface of the 20 mm x 15 mm is used as the observation surface.
  • the observation surface of the test piece is mirror-polished.
  • the mirror-polished observation surface is immersed in a nital etching solution for about 10 seconds to reveal the structure by etching.
  • the etched observation surface is observed using an optical microscope at 500x magnification.
  • the observation field has an area of 20,000 ⁇ m2 .
  • ferrite can be easily distinguished from martensite and bainite in the observation field based on the contrast. Therefore, ferrite in the observation field is identified and the area of the identified ferrite is determined.
  • the area of ferrite is divided by the total area of the observation field to determine the area ratio (%) of ferrite.
  • the determined area ratio of ferrite is an integer value rounded off to one decimal place. Using the obtained area ratio of ferrite, the total area ratio (%) of martensite and bainite is calculated by the following formula.
  • Total area ratio of martensite and bainite (%) 100 - area ratio of ferrite
  • the average grain size of the prior austenite grains is 150 ⁇ m or less. If the average grain size of the prior austenite grains is 150 ⁇ m or less, the steel material can have excellent high-temperature strength and excellent high-temperature toughness.
  • the upper limit of the average grain size of the prior austenite grains is preferably 140 ⁇ m, more preferably 130 ⁇ m, still more preferably 120 ⁇ m, still more preferably 110 ⁇ m, and still more preferably 100 ⁇ m.
  • the lower limit of the average grain size of the prior austenite grains is not particularly limited.
  • the lower limit of the average grain size of the prior austenite grains is preferably 10 ⁇ m, more preferably 15 ⁇ m, and even more preferably 20 ⁇ m.
  • the average grain size ( ⁇ m) of the prior austenite grains of the steel material according to the present embodiment is determined by the following method. First, a test piece is taken from a position at a depth of 1 mm or more from the surface of the steel material.
  • the size of the test piece is not particularly limited, but for example, the test piece has a surface (observation surface) of 10 mm ⁇ 10 mm.
  • the observation surface of the test piece is mirror-polished.
  • An arbitrary 800 ⁇ m ⁇ 800 ⁇ m field of view of the observation surface is subjected to EBSD (Electron Backscattering Diffraction) analysis as described in Non-Patent Document 1 to obtain crystal orientation information of martensite and bainite.
  • the step size in the EBSD analysis is not particularly limited, but the step size is set to 1 ⁇ m, for example.
  • the grain boundaries of the prior austenite grains in the field of view are identified based on the obtained crystal orientation information and the Kurdjumov-Sachs relationship.
  • the circle equivalent diameter ( ⁇ m) of each prior austenite grain in the field of view in which the grain boundaries of the prior austenite grains are identified is obtained.
  • the prior austenite grains to be targeted are all included in the field of view. Furthermore, prior austenite grains identified as having an area of 1 ⁇ m2 or less are deemed to be erroneously detected and are excluded.
  • the circle equivalent diameter means the diameter of a circle when the area of each prior austenite grain is converted into a circle having the same area.
  • the arithmetic mean value of the circle equivalent diameters of each prior austenite grain thus obtained is defined as the average grain size ( ⁇ m) of the prior austenite grains.
  • the average grain size of the prior austenite grains is an integer value rounded off to the nearest whole number.
  • the Cr content contained in the residue extracted from the steel material by electrolytic extraction is 0.5 to 3.0% by mass
  • the Mo content contained in the residue is 0.2 to 2.0% by mass.
  • the steel material of the present embodiment has precipitates containing Cr and/or Mo.
  • the precipitates containing Cr and/or Mo are referred to as "CrMo-containing precipitates".
  • the CrMo-containing precipitates increase the high-temperature strength of steel materials used in high-temperature environments. If the Cr content in the residue is less than 0.5% or the Mo content is less than 0.2%, the amount of CrMo-containing precipitates formed in the steel material is insufficient. In this case, sufficient high-temperature strength cannot be obtained.
  • the Cr content in the residue exceeds 3.0% or the Mo content exceeds 2.0%, CrMo-containing precipitates are generated excessively and coarsened in the steel material, and the strength in the prior austenite grains in the steel material becomes excessively high, resulting in insufficient high temperature toughness. Therefore, the Cr content contained in the residue is 0.5 to 3.0%, and the Mo content contained in the residue is 0.2 to 2.0%.
  • the lower limit of the Cr content in the residue is preferably 0.6%, more preferably 0.7%, and even more preferably 0.8%.
  • the upper limit of the Cr content in the residue is preferably 2.8%, more preferably 2.6%, further preferably 2.4%, and further preferably 2.2%.
  • the lower limit of the Mo content in the residue is preferably 0.3%, and more preferably 0.4%.
  • the upper limit of the Mo content in the residue is preferably 1.8%, more preferably 1.6%, further preferably 1.4%, and further preferably 1.2%.
  • the Cr content and Mo content contained in the extraction residue are determined by the following method.
  • a test piece is taken from a position at a depth of 1 mm or more from the surface of the steel material.
  • the size of the test piece is not particularly limited, but for example, it is a round bar test piece with a diameter of 15 mm and a length of 70 mm.
  • the longitudinal direction of the round bar test piece is parallel to the surface of the steel material.
  • the collected test pieces are subjected to constant current electrolysis using a 10% AA-based solution (a solution containing, by volume, 10% acetylacetone, 1% tetramethylammonium chloride, and 89% methanol solution). Specifically, the procedure is as follows.
  • preliminary electrolysis is performed to remove any deposits (surface scale and impurities) on the surface of the test piece.
  • electrolysis is performed on the area from the surface of the scale to a depth of 100 ⁇ m at room temperature (15-30°C) with a current of 1000 mA.
  • the test piece is immersed in an alcohol solution.
  • ultrasonic cleaning is performed to remove any deposits on the surface of the test piece.
  • the mass of the test piece from which the deposits have been removed i.e., the mass of the test piece before constant current electrolysis, is measured.
  • constant current electrolysis is performed on the test piece. Specifically, a new 10% AA-based solution is prepared. Then, using the prepared new 10% AA-based solution, the current density is maintained at 30 mA/ cm2 at room temperature, and the region from the surface of the test piece to a depth of about 100 ⁇ m is electrolyzed. The depth of the electrolyzed region is determined from the mass difference (reduction amount) (g) of the test piece before and after constant current electrolysis, and the surface area of the test piece, assuming the specific gravity of the sample to be 7.8 g/ cm3 . After constant current electrolysis, the test piece is immersed in an alcohol solution. Then, ultrasonic cleaning is performed to remove the deposits on the surface of the test piece. The mass of the test piece from which the deposits have been removed is measured, and this is taken as the mass (g) of the test piece after constant current electrolysis.
  • the 10% AA solution used in the constant current electrolysis and the alcohol solution used in the subsequent ultrasonic cleaning are suction filtered through a filter with a mesh size of 0.2 ⁇ m to extract the residue.
  • the extracted residue is subjected to chemical elemental analysis using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry). Specifically, the residue is dissolved in acid to obtain a solution. The solution is subjected to chemical elemental analysis using ICP-AES to obtain the Cr mass contained in the residue and the Mo mass contained in the residue. The Cr content (mass%) contained in the residue is obtained based on the Cr mass (g) contained in the residue and the mass difference (g) of the test piece before and after constant current electrolysis.
  • the mass difference of the test piece before and after constant current electrolysis corresponds to the mass of the test piece dissolved by constant current electrolysis.
  • the Cr content contained in the residue means the Cr content (mass%) contained in the residue when the chemical composition of the steel material is 100%.
  • the Mo content (mass%) contained in the residue is obtained based on the Mo mass (g) contained in the residue and the mass difference (g) of the test piece before and after constant current electrolysis.
  • the Mo content in the residue means the Mo content (mass%) contained in the residue when the chemical composition of the steel material is taken as 100%.
  • the Cr content (mass%) and Mo content (mass%) contained in the residue are numerical values rounded off to one decimal place.
  • the steel material of this embodiment that satisfies the above characteristics 1 to 4 has excellent high-temperature strength and excellent high-temperature toughness.
  • the high temperature strength of steel is measured by the following method.
  • a round bar tensile test piece is taken from a position 1 mm deep or more from the surface of the steel material.
  • the diameter of the parallel part of the round bar tensile test piece is 6 mm, and the gauge length is 30 mm.
  • the longitudinal direction of the round bar tensile test piece is parallel to the surface of the steel material.
  • a high temperature tensile test in accordance with JIS G 0567:2020 is carried out. Specifically, the round bar tensile test piece is held at 650 ° C for 10 minutes.
  • a tensile test is carried out at atmospheric pressure on the round bar tensile test piece at 650 ° C to obtain the tensile strength (MPa). If the obtained tensile strength is 500 MPa or more, the steel material is judged to have "excellent high temperature strength".
  • a V-notch test piece is taken from a position 1 mm or more deep from the surface of the steel material.
  • the size of the V-notch test piece is 10 mm x 10 mm x 55 mm.
  • the longitudinal direction of the V-notch test piece is parallel to the surface of the steel material.
  • a V-notch is formed at the center of one of the surfaces of the V-notch test piece that is parallel to the longitudinal direction.
  • the V-notch has a depth of 2 mm, a V-notch angle of 45°, and a V-notch tip R of 0.25 mm.
  • the V-notch test piece is held at 600°C for 30 minutes. After holding, a Charpy impact test is carried out in accordance with JIS Z 2242:2018 using the 600°C V-notch test piece to determine the absorbed energy (J). If the obtained absorbed energy is 80J or more, the steel is determined to have "excellent high-temperature toughness.”
  • the steel material of this embodiment is used in high-temperature environments and is widely applicable to applications requiring high-temperature strength and high-temperature toughness.
  • the steel material of this embodiment is suitable for use as hot work tools.
  • hot work tools include hot press dies, hot forging dies, die casting dies, and hot extrusion tools.
  • An example of a method for manufacturing a steel material according to this embodiment includes the following steps.
  • a material having a chemical composition that satisfies the characteristic 1 is prepared. Specifically, molten steel is prepared, the content of each element in the chemical composition of which satisfies the characteristic 1.
  • the prepared molten steel is used to carry out the well-known A material is manufactured by the above-mentioned casting method. For example, an ingot is manufactured by an ingot casting method. Or, a bloom is manufactured by a continuous casting method. Through the above-mentioned steps, a material (ingot or bloom) is manufactured.
  • Hot working step In the hot working process, hot working is performed on the material prepared in the material preparation process to form an intermediate steel material having the shape of the final product. Examples of hot working include hot forging, hot rolling, and hot extrusion. Before the hot working, the material is heated. The heating temperature is not particularly limited, but is, for example, 1150 to 1300°C. Hot working may be performed multiple times.
  • the quenching temperature T0 exceeds 1100° C., the average grain size of the prior austenite grains in the steel material becomes too large and exceeds 150 ⁇ m. Therefore, the quenching temperature T0 is 1100° C. or less.
  • the lower limit of the quenching temperature T0 is sufficient as long as it is equal to or higher than the AC3 point, and is, for example, 900° C.
  • the holding time at the quenching temperature T0 is defined as the quenching time t0. If the quenching time t0 exceeds 7.0 hours, the austenite grains will coarsen. As a result, the average grain size of the prior austenite grains in the steel will become too large, exceeding 150 ⁇ m. Therefore, the quenching time t0 is 7.0 hours or less. There is no particular lower limit to the quenching time t0, but it is, for example, 0.5 hours, and more preferably 1.0 hour.
  • the cooling rate CR0 after holding for the quenching time t0 is 0.10 to 1.00°C/sec.
  • the cooling rate CR0 is achieved by water cooling or oil cooling.
  • Step 4 In the method for producing a steel material according to the present embodiment, tempering is performed twice (first tempering step and second tempering step). In the microstructure of the intermediate steel material after the quenching step, not only martensite but also retained austenite is present. Therefore, in the first tempering step, the retained austenite in the intermediate steel material is transformed into martensite. By transforming the retained austenite into martensite, CrMo-containing precipitates are formed throughout the structure in the next second tempering step. can be generated uniformly.
  • the conditions for the first tempering step are as follows. (Condition 4) Tempering temperature T1 in step 4: 500 to 550° C. (Condition 5) Cooling rate CR1 in step 4: 0.10° C./sec or more
  • tempering temperature T1 is less than 500°C, the transformation from the retained austenite to martensite may be insufficient. In this case, the total area ratio of martensite and bainite may be reduced. Furthermore, precipitates other than the CrMo-containing precipitates (Fe 2 Mo) may be generated. In this case, the amount of the CrMo-containing precipitates generated may be insufficient.
  • the tempering temperature T1 exceeds 550°C, the transformation from the retained austenite to martensite is completed, but the formation of CrMo-containing precipitates is promoted. As a result, excessive CrMo-containing precipitates are formed and coarsened during the second tempering process. As a result, the Cr content and/or Mo content in the residue becomes too high.
  • Cooling rate CR1 If the cooling rate CR1 after holding at the tempering temperature T1 is less than 0.10°C/sec, the retained austenite may not transform into martensite during the cooling process. In this case, the total area ratio of martensite and bainite is reduced. Furthermore, CrMo-containing precipitates are generated excessively and coarsened during the second tempering step. As a result, the Cr content and/or Mo content in the residue becomes too high.
  • the upper limit of the cooling rate CR1 is not particularly limited, but is, for example, 1.00° C./sec.
  • Step 5 Second tempering step
  • CrMo-containing precipitates that satisfy characteristic 4 are generated.
  • the conditions in the second tempering step are as follows. (Condition 6) Tempering temperature T2 in step 5: greater than 550° C. to 650° C. (Condition 7) Sum of the tempering time t1 in step 4 and the tempering time t2 in step 5: 10.0 to 40.0 hours
  • tempering temperature T2 exceeds 650° C., CrMo-containing precipitates are generated in excess and become coarse, and in this case, sufficient high-temperature toughness cannot be obtained.
  • the tempering temperature T2 is 550° C. or lower, the amount of CrMo-containing precipitates formed is insufficient, and in this case, sufficient high-temperature strength cannot be obtained. Therefore, the tempering temperature T2 is greater than 550°C and greater than 650°C.
  • the holding time at the tempering temperature T1 in the first tempering step in step 4 is defined as the tempering time t1 (hours).
  • the holding time at the tempering temperature T2 in the second tempering step in step 5 is defined as the tempering time t2 (hours).
  • the total time of the tempering time t1 and the tempering time t2 exceeds 40.0 hours, the tempering time is too long, and in this case, CrMo-containing precipitates are generated in excess and become coarse. Therefore, the total time of the tempering time t1 and the tempering time t2 is 10.0 to 40.0 hours.
  • the above manufacturing process allows the production of steel that satisfies features 1 to 4.
  • the effects of the steel material of this embodiment will be explained in more detail below using examples.
  • the conditions in the following examples are one example of conditions adopted to confirm the feasibility and effects of the steel material of this embodiment. Therefore, the steel material of this embodiment is not limited to this one example of conditions.
  • the ingot was hot forged to produce a rectangular intermediate steel material.
  • the ingot was heated to a temperature of 1150-1300°C during hot forging.
  • a quenching process was carried out on the intermediate steel material.
  • the quenching temperature T0 (°C), quenching time t0 (hours), and cooling rate CR0 (°C/sec) during the quenching process were as shown in Table 2.
  • the first tempering process was carried out on the intermediate steel material after the quenching process.
  • the tempering temperature T1 (°C), tempering time t1 (hours), and cooling rate CR1 (°C/sec) in the first tempering process were as shown in Table 2.
  • the second tempering process was carried out on the intermediate steel material after the first tempering process.
  • the tempering temperature T2 (°C) and tempering time t2 (hours) in the second tempering process were as shown in Table 2. Steel materials with each test number were manufactured using the above manufacturing process.
  • the total area ratio (%) of martensite and bainite of the steel material of each test number was determined by the method described in [Method for measuring total area ratio of martensite and bainite] above.
  • the test specimens were taken from a position at a depth of 1 mm or more from the surface of the steel material.
  • the size of the test specimen was 20 mm x 15 mm x 15 mm, and the surface of the 20 mm x 15 mm was used as the observation surface.
  • the obtained total area ratio of martensite and bainite is shown in the "M+B total area ratio (%)" column in Table 3.
  • the average grain size ( ⁇ m) of the prior austenite grains of the steel material of each test number was determined by the method described in [Method for determining the average grain size of prior austenite grains] above.
  • the test specimens were taken from a depth position of 1 mm or more from the surface of the steel material of each test number.
  • the test specimens had a surface of 10 mm ⁇ 10 mm.
  • the 10 mm ⁇ 10 mm surface was used as the observation surface.
  • the step size in the EBSD analysis was 1 ⁇ m.
  • the obtained average grain size of the prior austenite grains is shown in the "Average grain size ( ⁇ m)" column in Table 3.
  • the tensile strength (MPa) of the steel material of each test number at 650°C was determined by the method described in the above [High-temperature strength evaluation method].
  • the round bar tensile test specimens were taken from a position at a depth of 1 mm or more from the surface of the steel material.
  • the diameter of the parallel part of the round bar tensile test specimen was 6 mm, and the gauge length was 30 mm.
  • the obtained tensile strengths are shown in the "High-temperature tensile strength (MPa)" column in Table 3.
  • test number 27 the C content was too high.
  • the tensile strength at 650°C was less than 500 MPa, and excellent high-temperature strength was not obtained.
  • the absorbed energy at 600°C was less than 80 J, and excellent high-temperature toughness was not obtained.
  • test number 28 the Cr content was too high. As a result, the Cr content in the extraction residue was too high. As a result, the absorbed energy at 600°C was less than 80 J, and excellent high-temperature toughness was not obtained.
  • the Cr content was too low.
  • the tensile strength at 650°C was less than 500 MPa, and excellent high-temperature strength was not obtained.
  • the absorbed energy at 600°C was less than 80 J, and excellent high-temperature toughness was not obtained.
  • the quenching temperature T0 was too high.
  • the average grain size of the prior austenite grains exceeded 150 ⁇ m.
  • the tensile strength at 650°C was less than 500 MPa, and excellent high-temperature strength was not obtained.
  • the absorbed energy at 600°C was less than 80 J, and excellent high-temperature toughness was not obtained.
  • the quenching time t0 was too long.
  • the average grain size of the prior austenite grains exceeded 150 ⁇ m.
  • the tensile strength at 650°C was less than 500 MPa, and excellent high-temperature strength was not obtained.
  • the absorbed energy at 600°C was less than 80 J, and excellent high-temperature toughness was not obtained.
  • the tempering temperature T1 in the first tempering step was too low.
  • the total area ratio of martensite and bainite was low.
  • the Cr content and Mo content contained in the extraction residue were too low.
  • the tensile strength at 650°C was less than 500 MPa, and excellent high-temperature strength was not obtained.
  • the absorbed energy at 600°C was less than 80 J, and excellent high-temperature toughness was not obtained.
  • test numbers 37 and 38 the tempering temperature T1 in the first tempering step was too high. As a result, the Cr and Mo contents in the extraction residue were too high. As a result, the absorbed energy at 600°C was less than 80 J, and excellent high-temperature toughness was not obtained.
  • test numbers 39 and 40 air cooling was used in the first tempering step, and the cooling rate CR1 was too slow. As a result, the total area ratio of martensite and bainite was less than 99%, and the Cr and Mo contents in the extraction residue were too high. As a result, the absorbed energy at 600°C was less than 80 J, and excellent high-temperature toughness was not obtained.
  • test numbers 41 and 42 the tempering temperature T2 in the second tempering step was too low. As a result, the Cr and Mo contents in the extraction residue were too low. As a result, the tensile strength at 650°C was less than 500 MPa, and excellent high-temperature strength was not obtained.
  • test numbers 45 and 46 the total tempering time (t1 + t2) in the first and second tempering steps was too short. As a result, the Cr and Mo contents in the extraction residue were too low. As a result, the tensile strength at 650°C was less than 500 MPa, and excellent high-temperature strength was not obtained.

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  • Heat Treatment Of Steel (AREA)

Abstract

L'invention concerne un matériau d'acier présentant une excellente résistance à température élevée et une excellente ténacité à température élevée. Ce matériau d'acier comprend une composition chimique comprenant, en % en masse, de 0,20 à 0,60 % de C, de 0,05 à 1,00 % de Si, de 0,20 à 1,00 % de Mn, jusqu'à 0,030 % de P, jusqu'à 0,0300 % de S, de 5,60 à 7,00 % de Cr, de 1,00 à 4,00 % de Mo, de 0,10 à 1,50 % de V, de 0,0005 à 0,1000 % d'Al sol., de 0,0050 à 0,0500 % de N, le reste étant du Fe et des impuretés inévitables, présente une proportion surfacique totale de martensite et de bainite supérieure ou égale à 99 %, et comprend des grains cristallins d'austénite antérieure présentant un diamètre moyen de grain cristallin inférieur ou égal à 150 μm. Un résidu extrait du matériau d'acier par un procédé d'extraction électrolytique présente une teneur en Cr de 0,5 à 3,0 % en masse et une teneur en Mo de 0,2 à 2,0 % en masse.
PCT/JP2023/021540 2023-06-09 2023-06-09 Matériau d'acier Ceased WO2024252667A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2014025103A (ja) * 2012-07-26 2014-02-06 Daido Steel Co Ltd 熱間工具鋼
WO2015182586A1 (fr) * 2014-05-28 2015-12-03 日立金属株式会社 Matériau d'outil pour travail à chaud et procédé pour la fabrication d'un outil pour travail à chaud
JP2016017200A (ja) * 2014-07-08 2016-02-01 大同特殊鋼株式会社 金型用鋼及び温熱間金型
JP2018165400A (ja) * 2017-03-28 2018-10-25 大同特殊鋼株式会社 焼入れ時に粗大な結晶粒が発生しない焼鈍鋼材およびその製造方法
WO2023022222A1 (fr) * 2021-08-20 2023-02-23 日本製鉄株式会社 Matériau d'acier

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2014025103A (ja) * 2012-07-26 2014-02-06 Daido Steel Co Ltd 熱間工具鋼
WO2015182586A1 (fr) * 2014-05-28 2015-12-03 日立金属株式会社 Matériau d'outil pour travail à chaud et procédé pour la fabrication d'un outil pour travail à chaud
JP2016017200A (ja) * 2014-07-08 2016-02-01 大同特殊鋼株式会社 金型用鋼及び温熱間金型
JP2018165400A (ja) * 2017-03-28 2018-10-25 大同特殊鋼株式会社 焼入れ時に粗大な結晶粒が発生しない焼鈍鋼材およびその製造方法
WO2023022222A1 (fr) * 2021-08-20 2023-02-23 日本製鉄株式会社 Matériau d'acier

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