WO2021095831A1 - Hot-work tool steel having exceptional high-temperature strength and toughness - Google Patents

Hot-work tool steel having exceptional high-temperature strength and toughness Download PDF

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WO2021095831A1
WO2021095831A1 PCT/JP2020/042367 JP2020042367W WO2021095831A1 WO 2021095831 A1 WO2021095831 A1 WO 2021095831A1 JP 2020042367 W JP2020042367 W JP 2020042367W WO 2021095831 A1 WO2021095831 A1 WO 2021095831A1
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carbides
toughness
hot
tool steel
temperature strength
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PCT/JP2020/042367
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French (fr)
Japanese (ja)
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章生 美谷
真理 妙瀬田
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山陽特殊製鋼株式会社
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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
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

  • This application relates to hot tool steel with excellent high temperature strength and toughness, which is used as a hot tool for hot forging dies and the like.
  • JIS-SKD61 is generally used as a hot tool for hot press forging, hot extrusion or die casting (for example, a die), and a hot tool for hammer forging (for example, a die). ), JIS-SKT4 is generally used.
  • JIS-SKD61 is a hot tool steel (for example, mold steel) that has both strength and toughness at a relatively high level, but it often breaks early due to cracks during use, and is not always sufficient in terms of toughness. is not it. Further, the toughness of JIS-SKD61 is insufficient to suppress the extension of thermal fatigue cracks.
  • JIS-SKT4 emphasizes toughness so that it can withstand a large impact due to hammer forging, but its wear resistance is insufficient due to its low softening resistance. Further, when the die-engraved surface is repeatedly lowered for the purpose of regeneration processing, the hardness is lowered in the central portion due to the low hardenability, and cracks, sagging, etc. occur due to insufficient strength. Furthermore, since the applicable hardness is low, wear resistance or strength is insufficient, and it is not suitable for hot press forging or hot extrusion (see, for example, Patent Document 1).
  • the applicant has so far proposed an invention of a hot tool steel having excellent toughness and high temperature strength in order to improve the life of a hot tool such as a mold (see, for example, Patent Document 2).
  • a hot tool such as a mold
  • the precipitation state of carbides before the use of a hot tool such as a mold that is, before the hot tool is exposed to a high temperature environment is not considered, and the softening resistance is not taken into consideration. That is, the high temperature strength is still insufficient.
  • Hot work tool steel by precipitating secondary carbides such as M 2 C, MC to use at high temperatures, softening resistance, i.e. high-temperature strength is obtained.
  • softening resistance i.e. high-temperature strength
  • the amount of secondary carbides precipitated during high-temperature use decreases, so there is a problem that high high-temperature strength cannot be obtained.
  • the problem to be solved by the present invention is that in hot tool steel produced by quenching in an electric furnace or a vacuum induction melting furnace, carbides remaining in the steel in the melting step (preliminary step). Is solid-melted in the quenching process of steel to obtain steel having excellent toughness by controlling the size of carbides to be small, and further, the solid-melting of carbides precipitates fine carbides during high-temperature use as a hot tool. It is to increase the amount of effective carbon for this purpose and to obtain excellent high temperature strength by precipitating fine carbides.
  • the present invention as the first hot tool steel, C: 0.20 to 0.60%, Si: 0.1 to 0.3%, Mn: 0 in mass%. .5 to 2.0%, Ni: 0.5 to 2.5%, Cr: 1.6 to 2.6%, Mo: 0.3 to 2.0%, V: 0.05 to 0.80 Provided is a hot tool steel having excellent high temperature strength and toughness, which contains% and is characterized in that the balance is composed of Fe and unavoidable impurities.
  • the second hot tool steel C: 0.20 to 0.60%, Si: 0.1 to 0.3%, Mn: 0.5 to 2.0 in mass%. %, Ni: 0.5 to 2.5%, Cr: 1.6 to 2.6%, Mo: 0.3 to 2.0%, V: 0.05 to 0.80%, and the balance
  • a hot tool steel composed of Fe and unavoidable impurities and is characterized in that the number of carbides having a circle equivalent diameter of 1 ⁇ m or more per 10,000 ⁇ m 2 in the hot tool steel before use is 150 or less. It is a hot tool steel having excellent high temperature strength and toughness.
  • a hot tool steel having excellent high temperature strength and toughness is provided.
  • the impact value of the Charpy impact test is increased by setting the number of carbides having a circle equivalent diameter of 1 ⁇ m or more per 10,000 ⁇ m 2 in the hot tool steel before use to 150 or less.
  • Hot tool steel or the like having a hardness of 85 J / cm 2 or more and a hardness reduction value (decrease value from the initial hardness (for example, 39 to 41 HRC)) of 14 HRC or less after holding at 600 ° C. for 100 hours, etc.
  • a hot tool steel having excellent toughness and high temperature strength can be obtained.
  • The% of the content of C, Si, Mn, Ni, Cr, Mo and V is mass%, and among the chemical components forming the steel, other than C, Si, Mn, Ni, Cr, Mo and V.
  • the rest of is Fe and unavoidable impurities.
  • C 0.20 to 0.60%
  • C is an element necessary for obtaining high temperature strength, hardness and wear resistance by ensuring sufficient hardenability of steel and forming carbides. If the C content is less than 0.20%, sufficient high-temperature strength cannot be obtained. On the other hand, if the C content is more than 0.60%, solidification segregation is promoted, carbides are likely to be crystallized, and toughness is impaired. Further, due to the aggregation of the generated carbide, high temperature strength cannot be expected and the toughness is also lowered. Therefore, the content of C is set to 0.20 to 0.60%. The content of C is preferably 0.40 to 0.60%.
  • Si 0.1-0.3%
  • Si is an element necessary to obtain a deoxidizing effect during steelmaking and to obtain an effect of ensuring hardenability of steel. If the Si content is less than 0.1%, each of the above effects cannot be obtained. On the other hand, if the Si content is more than 0.3%, the toughness is lowered. Therefore, the Si content is set to 0.1 to 0.3%. The Si content is preferably 0.1 to 0.2%.
  • Mn 0.5-2.0% Mn is an element necessary for obtaining a deoxidizing effect during steelmaking and for obtaining an effect of ensuring hardenability of steel. If the Mn content is less than 0.5%, each of the above effects cannot be obtained. On the other hand, if the Mn content is more than 2.0%, the toughness is lowered. Therefore, the Mn content is set to 0.5 to 2.0%. The Mn content is preferably 0.5 to 1.4%.
  • Ni 0.5-2.5%
  • Ni is an element necessary for improving toughness. If the Ni content is less than 0.5%, sufficient toughness cannot be obtained. On the other hand, since Ni is an expensive element, the cost increases when the content of Ni is more than 2.5%. Therefore, the Ni content is set to 0.5 to 2.5%.
  • the Ni content is preferably 1.1 to 2.3%.
  • Cr 1.6-2.6% Cr is an element necessary for ensuring hardenability. If the Cr content is less than 1.6%, sufficient hardenability cannot be obtained. On the other hand, if the Cr content is more than 2.6%, Cr-based carbides are excessively formed during quenching and tempering, which lowers high-temperature strength, softening resistance and toughness. Therefore, the Cr content is set to 1.6 to 2.6%. The Cr content is preferably 1.6 to 2.4%.
  • Mo 0.3-2.0%
  • Mo is an element necessary for obtaining precipitated carbides that contribute to hardenability, secondary curing, and high-temperature strength, and for fine carbides that have become unsolidified during quenching to suppress coarsening of crystal grains. .. If the Mo content is less than 0.3%, the above effect cannot be obtained. On the other hand, even if Mo is added in excess of 2.0%, not only the above effect is saturated, but also the toughness is lowered due to the coarse aggregation of carbides, and the cost is high. Therefore, the Mo content is set to 0.3 to 2.0%. The Mo content is preferably 0.3 to 1.7%.
  • V 0.05 to 0.80% V deposits fine and hard carbides and carbonitrides during tempering or when used as a hot tool, contributing to strength and abrasion resistance, and during quenching, fine carbides and carbonitrides are crystal grains. It is an element necessary to suppress the coarsening of and suppress the decrease in toughness. If the V content is less than 0.05%, the above effect cannot be obtained. On the other hand, if the V content is more than 0.80%, coarse crystallized carbides are produced during solidification, and the toughness is inhibited. Therefore, the V content is set to 0.05 to 0.80%. The V content is preferably 0.05 to 0.20%.
  • Hot tool before use Number of carbides with a circle equivalent diameter of 1 ⁇ m or more per 10,000 ⁇ m 2 : 150 or less Used hot (high temperature) as a hot tool for hot forging dies, etc.
  • the previous hot tool steel is referred to as "before use" hot tool steel. Since the hot tool comes into contact with the work material heated to a high temperature for the purpose of improving workability or controlling the structure to obtain desired characteristics after hot work, the surface of the hot tool is transferred by heat from the work material. The vicinity is exposed to a considerable temperature (for example, 180 to 1300 ° C.) before use.
  • the number of carbides with a circle equivalent diameter of 1 ⁇ m or more per 10,000 ⁇ m 2 is more than 150, the amount of carbon dissolved in the matrix is insufficient and hot.
  • the amount of fine and hard carbides that precipitate during high-temperature use as a tool and contribute to the improvement of high-temperature strength decreases, and sufficient high-temperature strength cannot be obtained.
  • the number of carbides having a circle equivalent diameter of 1 ⁇ m or more per 10,000 ⁇ m 2 is more than 150, stress is concentrated on the carbides and used as a crack starting point or a propagation path. To act, it inhibits the toughness of steel. Therefore, in the second hot tool steel, the number of carbides having a circle-equivalent diameter of 1 ⁇ m or more per 10,000 ⁇ m 2 in the hot tool steel before use is 150 or less.
  • the number of carbides having a circle-equivalent diameter of 1 ⁇ m or more per 10,000 ⁇ m 2 is measured using a steel material after quenching and tempering as described in Examples.
  • the carbides are, for example, M 2 C, MC, M 3 C, M 7 C 3 , M 23 C 6, and the like.
  • M represents a metal element.
  • the hot work tool steel of the present invention by M 2 C, secondary carbides MC like precipitates at high temperatures used, softening resistance, i.e. high-temperature strength is obtained.
  • softening resistance i.e. high-temperature strength
  • the amount of secondary carbides precipitated during high-temperature use will decrease and high high-temperature strength cannot be obtained, and if there are many coarse carbides in the stage before high-temperature use. , There are problems such as low toughness.
  • the obtained steel materials of the invention steel and the comparative steel are heat-treated at 840 to 1000 ° C. for a sufficient time (for example, 30 minutes) to obtain an austenite structure and solid-solve the carbides, respectively. , Oil-cooled quenching was carried out. Next, each of the hardened steel materials was heated to 500 to 700 ° C., and then air-cooled and tempered to adjust the quality to 39 to 41 HRC.
  • the hardened and tempered steel materials were machined into test materials for each test for measuring the amount of carbides, evaluating toughness, and evaluating high-temperature strength, respectively. Then, using the test materials for each test, each test of measurement of carbide amount, evaluation of toughness, and evaluation of high temperature strength was carried out as follows.
  • Comparative steel No. 17 since the C content (0.71%) is larger than the upper limit value (0.60%) of the present invention, the number of carbides having a circle equivalent diameter of 1 ⁇ m or more per 10,000 ⁇ m 2 is more than 150, and , Ni content (0.4%) is less than the lower limit (0.5%) of the present invention. Therefore, the toughness is low (the impact value of the Charpy impact test at room temperature is less than 85 J / cm 2 ), and the high temperature strength is also low (the amount of decrease from the initial hardness exceeds 14 HRC).
  • the number of the above carbides is more than 150. Therefore, the toughness is low (the impact value of the Charpy impact test at room temperature is less than 85 J / cm 2).
  • Comparative steel No. 22 since the Ni content (0.4%) is less than the lower limit value (0.5%) of the present invention, the toughness is low (the impact value of the Charpy impact test at room temperature is less than 85 J / cm 2). Further, since the V content (0.03%) is less than the lower limit value (0.05%) of the present invention, the high temperature strength is low (the amount of decrease from the initial hardness exceeds 14 HRC).
  • Comparative steel No. 24 since the C content (0.66%) is larger than the upper limit value (0.60%) of the present invention, the number of carbides having a circle equivalent diameter of 1 ⁇ m or more per 10,000 ⁇ m 2 is more than 150. Therefore, the toughness is low (the impact value of the Charpy impact test at room temperature is less than 85 J / cm 2 ), and the high temperature strength is also low (the amount of decrease from the initial hardness exceeds 14 HRC).
  • Comparative steel No. In 28 the number of carbides having a circle-equivalent diameter of 1 ⁇ m or more per 10,000 ⁇ m 2 is more than 150. Therefore, the toughness is low (the impact value of the Charpy impact test at room temperature is less than 85 J / cm 2 ), and the high temperature strength is also low (the amount of decrease from the initial hardness exceeds 14 HRC).

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Abstract

In order to provide hot-work tool steel having exceptional high-temperature strength and toughness, the present invention provides: hot-work tool steel that contains, in terms of mass%, 0.20-0.60% of C, 0.1-0.3% of Si, 0.5-2.0% of Mn, 0.5-2.5% of Ni, 1.6-2.6% of Cr, 0.3-2.0% of Mo, and 0.05-0.80% of V, the balance being Fe and unavoidable impurities; and hot-work tool steel that contains, in terms of mass%, 0.20-0.60% of C, 0.1-0.3% of Si, 0.5-2.0% of Mn, 0.5-2.5% of Ni, 1.6-2.6% of Cr, 0.3-2.0% of Mo, and 0.05-0.80% of V, the balance being Fe and unavoidable impurities, and the hot-work tool steel being configured so that the number of carbides having a size such that the equivalent circle diameter is 1 μm or greater is 150 or less per 10,000 μm2 in the hot-work tool steel prior to use.

Description

高温強度及び靭性に優れる熱間工具鋼Hot tool steel with excellent high temperature strength and toughness
　この出願は、熱間鍛造金型等の熱間工具として使用される、高温強度及び靭性に優れる熱間工具鋼に関する。 This application relates to hot tool steel with excellent high temperature strength and toughness, which is used as a hot tool for hot forging dies and the like.
　熱間プレス鍛造、熱間押出し又はダイカスト用の熱間工具（例えば、金型）には、ＪＩＳ－ＳＫＤ６１が汎用的に用いられており、また、ハンマー鍛造用の熱間工具（例えば、金型）には、ＪＩＳ－ＳＫＴ４が汎用的に使用されている。 JIS-SKD61 is generally used as a hot tool for hot press forging, hot extrusion or die casting (for example, a die), and a hot tool for hammer forging (for example, a die). ), JIS-SKT4 is generally used.
　ＪＩＳ－ＳＫＤ６１は強度と靭性の双方を比較的高位で兼備した熱間工具鋼（例えば、金型用鋼）であるが、使用中の割れによる早期破損が生じることが多く、靭性面では必ずしも十分ではない。また、ＪＩＳ－ＳＫＤ６１の靭性は、熱疲労亀裂の伸展を抑制するためには、不足している。 JIS-SKD61 is a hot tool steel (for example, mold steel) that has both strength and toughness at a relatively high level, but it often breaks early due to cracks during use, and is not always sufficient in terms of toughness. is not it. Further, the toughness of JIS-SKD61 is insufficient to suppress the extension of thermal fatigue cracks.
　ＪＩＳ－ＳＫＴ４は、ハンマー鍛造による大きな衝撃にも耐え得るように、靭性を重視している一方で、軟化抵抗性が低いために、耐摩耗性が不足する。また、再生加工を目的とした型彫り面の引下げを繰返して行うと、焼入れ性が低いために中心部では硬さ低下が生じてしまい、強度不足から割れ、へたり等が発生する。さらには、適用可能な硬さが低いために、耐摩耗性又は強度が不足し、熱間プレス鍛造又は熱間押出しの用途には向いていない（例えば、特許文献１参照）。 JIS-SKT4 emphasizes toughness so that it can withstand a large impact due to hammer forging, but its wear resistance is insufficient due to its low softening resistance. Further, when the die-engraved surface is repeatedly lowered for the purpose of regeneration processing, the hardness is lowered in the central portion due to the low hardenability, and cracks, sagging, etc. occur due to insufficient strength. Furthermore, since the applicable hardness is low, wear resistance or strength is insufficient, and it is not suitable for hot press forging or hot extrusion (see, for example, Patent Document 1).
　出願人は、これまでに、金型等の熱間工具の寿命向上のために、優れた靭性及び高温強度を有する熱間工具鋼の発明を提案している（例えば、特許文献２参照）。しかし、この発明の提案では、金型等の熱間工具が使用される前、すなわち熱間工具が高温環境に曝される高温使用前の炭化物の析出状態について考慮されておらず、軟化抵抗性、すなわち高温強度がなお不十分である。 The applicant has so far proposed an invention of a hot tool steel having excellent toughness and high temperature strength in order to improve the life of a hot tool such as a mold (see, for example, Patent Document 2). However, in the proposal of the present invention, the precipitation state of carbides before the use of a hot tool such as a mold, that is, before the hot tool is exposed to a high temperature environment is not considered, and the softening resistance is not taken into consideration. That is, the high temperature strength is still insufficient.
特開２０１３－２１３２５５号公報Japanese Unexamined Patent Publication No. 2013-21255 特開２０１１－１９５９１７号公報Japanese Unexamined Patent Publication No. 2011-195917
　熱間工具鋼は、高温使用時にＭ２Ｃ、ＭＣ等の二次炭化物が析出することで、軟化抵抗性、すなわち高温強度が得られる。しかし、熱間工具鋼では、高温使用前の段階で炭化物が多いと、高温使用中における二次炭化物の析出量が減少するので、高い高温強度が得られない問題がある。 Hot work tool steel, by precipitating secondary carbides such as M 2 C, MC to use at high temperatures, softening resistance, i.e. high-temperature strength is obtained. However, in hot tool steel, if there is a large amount of carbides in the stage before high-temperature use, the amount of secondary carbides precipitated during high-temperature use decreases, so there is a problem that high high-temperature strength cannot be obtained.
　そこで、本発明が解決しようとする課題は、電気炉又は真空誘導溶解炉で溶製して製造される熱間工具鋼において、その溶製工程（前工程）で鋼中に残存している炭化物を、鋼の焼入れ工程において固溶させて、炭化物サイズを小さく制御することによって優れた靭性を有する鋼とし、さらに、炭化物の固溶により、熱間工具として高温使用中に微細な炭化物を析出させるための有効炭素量を増加させ、微細な炭化物の析出により優れた高温強度を得ることである。 Therefore, the problem to be solved by the present invention is that in hot tool steel produced by quenching in an electric furnace or a vacuum induction melting furnace, carbides remaining in the steel in the melting step (preliminary step). Is solid-melted in the quenching process of steel to obtain steel having excellent toughness by controlling the size of carbides to be small, and further, the solid-melting of carbides precipitates fine carbides during high-temperature use as a hot tool. It is to increase the amount of effective carbon for this purpose and to obtain excellent high temperature strength by precipitating fine carbides.
　上記課題を解決するために、本発明は、第１の熱間工具鋼として、質量％で、Ｃ：０．２０～０．６０％、Ｓｉ：０．１～０．３％、Ｍｎ：０．５～２．０％、Ｎｉ：０．５～２．５％、Ｃｒ：１．６～２．６％、Ｍｏ：０．３～２．０％、Ｖ：０．０５～０．８０％を含有し、残部がＦｅ及び不可避不純物からなることを特徴とする、高温強度及び靭性に優れる熱間工具鋼を提供する。 In order to solve the above problems, the present invention, as the first hot tool steel, C: 0.20 to 0.60%, Si: 0.1 to 0.3%, Mn: 0 in mass%. .5 to 2.0%, Ni: 0.5 to 2.5%, Cr: 1.6 to 2.6%, Mo: 0.3 to 2.0%, V: 0.05 to 0.80 Provided is a hot tool steel having excellent high temperature strength and toughness, which contains% and is characterized in that the balance is composed of Fe and unavoidable impurities.
　また、本発明は、第２の熱間工具鋼として、質量％で、Ｃ：０．２０～０．６０％、Ｓｉ：０．１～０．３％、Ｍｎ：０．５～２．０％、Ｎｉ：０．５～２．５％、Ｃｒ：１．６～２．６％、Ｍｏ：０．３～２．０％、Ｖ：０．０５～０．８０％を含有し、残部がＦｅ及び不可避不純物からなる熱間工具鋼であって、使用前の熱間工具鋼における１０，０００μｍ２当りの円相当径１μｍ以上の大きさの炭化物の個数が１５０個以下であることを特徴とする、高温強度及び靭性に優れる熱間工具鋼である。 Further, according to the present invention, as the second hot tool steel, C: 0.20 to 0.60%, Si: 0.1 to 0.3%, Mn: 0.5 to 2.0 in mass%. %, Ni: 0.5 to 2.5%, Cr: 1.6 to 2.6%, Mo: 0.3 to 2.0%, V: 0.05 to 0.80%, and the balance Is a hot tool steel composed of Fe and unavoidable impurities, and is characterized in that the number of carbides having a circle equivalent diameter of 1 μm or more per 10,000 μm 2 in the hot tool steel before use is 150 or less. It is a hot tool steel having excellent high temperature strength and toughness.
　本発明によれば、高温強度及び靭性に優れる熱間工具鋼が提供される。特に、本発明によれば、使用前の熱間工具鋼における１０，０００μｍ２当りの円相当径１μｍ以上の大きさの炭化物の個数を１５０個以下とすることにより、シャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ２以上であり、かつ、６００℃で１００時間保持後の硬さの減少値（初期硬さ（例えば、３９～４１ＨＲＣ）からの減少値）が１４ＨＲＣ以下である熱間工具鋼等、靭性及び高温強度に優れる熱間工具鋼が得られる。 According to the present invention, a hot tool steel having excellent high temperature strength and toughness is provided. In particular, according to the present invention, the impact value of the Charpy impact test is increased by setting the number of carbides having a circle equivalent diameter of 1 μm or more per 10,000 μm 2 in the hot tool steel before use to 150 or less. Hot tool steel or the like having a hardness of 85 J / cm 2 or more and a hardness reduction value (decrease value from the initial hardness (for example, 39 to 41 HRC)) of 14 HRC or less after holding at 600 ° C. for 100 hours, etc. A hot tool steel having excellent toughness and high temperature strength can be obtained.
　以下、実施例に先立って、本発明の熱間工具鋼における化学成分の含有量の限定理由を化学成分毎に説明し、さらに、使用前の熱間工具鋼における１０，０００μｍ２当りの円相当径１μｍ以上の大きさの炭化物の個数の限定理由について説明する。なお、Ｃ、Ｓｉ、Ｍｎ、Ｎｉ、Ｃｒ、Ｍｏ及びＶの含有量に関する％は、質量％であり、鋼を形成する化学成分のうち、Ｃ、Ｓｉ、Ｍｎ、Ｎｉ、Ｃｒ、Ｍｏ及びＶ以外の残部は、Ｆｅ及び不可避不純物である。 Hereinafter, prior to the examples, the reasons for limiting the content of the chemical components in the hot tool steel of the present invention will be described for each chemical component, and further, the equivalent of a circle per 10,000 μm 2 in the hot tool steel before use. The reason for limiting the number of carbides having a diameter of 1 μm or more will be described. The% of the content of C, Si, Mn, Ni, Cr, Mo and V is mass%, and among the chemical components forming the steel, other than C, Si, Mn, Ni, Cr, Mo and V. The rest of is Fe and unavoidable impurities.
　Ｃ：０．２０～０．６０％
　Ｃは、鋼の十分な焼入れ性を確保し、炭化物を形成させることで、高温強度、硬度及び耐摩耗性を得るために必要な元素である。Ｃの含有量が０．２０％より少ないと十分な高温強度が得られない。一方、Ｃの含有量が０．６０％より多いと凝固偏析を助長し、炭化物の晶出が生じやすくなり靭性を阻害する。また、生成した炭化物の凝集により、高温強度が望めず、靭性も低下する。そこで、Ｃの含有量は０．２０～０．６０％とする。Ｃの含有量は、好ましくは０．４０～０．６０％とする。 C: 0.20 to 0.60%
C is an element necessary for obtaining high temperature strength, hardness and wear resistance by ensuring sufficient hardenability of steel and forming carbides. If the C content is less than 0.20%, sufficient high-temperature strength cannot be obtained. On the other hand, if the C content is more than 0.60%, solidification segregation is promoted, carbides are likely to be crystallized, and toughness is impaired. Further, due to the aggregation of the generated carbide, high temperature strength cannot be expected and the toughness is also lowered. Therefore, the content of C is set to 0.20 to 0.60%. The content of C is preferably 0.40 to 0.60%.
　Ｓｉ：０．１～０．３％
　Ｓｉは、製鋼時の脱酸効果を得るため及び鋼の焼入れ性確保の効果を得るために必要な元素である。Ｓｉの含有量が０．１％より少ないと上記の各効果を得ることができない。一方、Ｓｉの含有量が０．３％より多いと靭性を低下させる。そこで、Ｓｉの含有量は０．１～０．３％とする。Ｓｉの含有量は、好ましくは０．１～０．２％とする。 Si: 0.1-0.3%
Si is an element necessary to obtain a deoxidizing effect during steelmaking and to obtain an effect of ensuring hardenability of steel. If the Si content is less than 0.1%, each of the above effects cannot be obtained. On the other hand, if the Si content is more than 0.3%, the toughness is lowered. Therefore, the Si content is set to 0.1 to 0.3%. The Si content is preferably 0.1 to 0.2%.
　Ｍｎ：０．５～２．０％
　Ｍｎは、製鋼時の脱酸効果を得るため及び鋼の焼入れ性確保の効果を得るために必要な元素である。Ｍｎの含有量が０．５％より少ないと上記の各効果を得ることができない。一方、Ｍｎの含有量が２．０％より多いと靭性を低下させる。そこで、Ｍｎの含有量は０．５～２．０％とする。Ｍｎの含有量は、好ましくは０．５～１．４％とする。 Mn: 0.5-2.0%
Mn is an element necessary for obtaining a deoxidizing effect during steelmaking and for obtaining an effect of ensuring hardenability of steel. If the Mn content is less than 0.5%, each of the above effects cannot be obtained. On the other hand, if the Mn content is more than 2.0%, the toughness is lowered. Therefore, the Mn content is set to 0.5 to 2.0%. The Mn content is preferably 0.5 to 1.4%.
　Ｎｉ：０．５～２．５％
　Ｎｉは、靭性の向上のために必要な元素である。Ｎｉの含有量が０．５％より少ないと十分な靭性が得られない。一方、Ｎｉは、高価な元素であるので、Ｎｉの含有量が２．５％より多いとコストが上昇する。そこで、Ｎｉの含有量は０．５～２．５％とする。Ｎｉの含有量は、好ましくは１．１～２．３％とする。 Ni: 0.5-2.5%
Ni is an element necessary for improving toughness. If the Ni content is less than 0.5%, sufficient toughness cannot be obtained. On the other hand, since Ni is an expensive element, the cost increases when the content of Ni is more than 2.5%. Therefore, the Ni content is set to 0.5 to 2.5%. The Ni content is preferably 1.1 to 2.3%.
　Ｃｒ：１．６～２．６％
　Ｃｒは、焼入れ性を確保するために必要な元素である。Ｃｒの含有量が１．６％より少ないと十分な焼入れ性が得られない。一方、Ｃｒの含有量が２．６％より多いと焼入焼戻し時にＣｒ系の炭化物が過多に形成され、高温強度、軟化抵抗性及び靭性を低下させる。そこで、Ｃｒの含有量は１．６～２．６％とする。Ｃｒの含有量は、好ましくは１．６～２．４％とする。 Cr: 1.6-2.6%
Cr is an element necessary for ensuring hardenability. If the Cr content is less than 1.6%, sufficient hardenability cannot be obtained. On the other hand, if the Cr content is more than 2.6%, Cr-based carbides are excessively formed during quenching and tempering, which lowers high-temperature strength, softening resistance and toughness. Therefore, the Cr content is set to 1.6 to 2.6%. The Cr content is preferably 1.6 to 2.4%.
　Ｍｏ：０．３～２．０％
　Ｍｏは、焼入れ性、二次硬化及び高温強度に寄与する析出炭化物を得るため、また、焼入れ時に未固溶となった微細な炭化物が結晶粒の粗大化を抑制するために必要な元素である。Ｍｏの含有量が０．３％より少ないと、上記の効果が得られない。一方、Ｍｏは２．０％より過剰に添加しても、上記の効果は飽和するばかりか、炭化物が粗大に凝集することにより靭性を低下させ、また、コスト高となる。そこで、Ｍｏの含有量は０．３～２．０％とする。Ｍｏの含有量は、好ましくは０．３～１．７％とする。 Mo: 0.3-2.0%
Mo is an element necessary for obtaining precipitated carbides that contribute to hardenability, secondary curing, and high-temperature strength, and for fine carbides that have become unsolidified during quenching to suppress coarsening of crystal grains. .. If the Mo content is less than 0.3%, the above effect cannot be obtained. On the other hand, even if Mo is added in excess of 2.0%, not only the above effect is saturated, but also the toughness is lowered due to the coarse aggregation of carbides, and the cost is high. Therefore, the Mo content is set to 0.3 to 2.0%. The Mo content is preferably 0.3 to 1.7%.
　Ｖ：０．０５～０．８０％
　Ｖは、焼戻し時又は熱間工具として使用時に、微細で硬質な炭化物及び炭窒化物を析出し、強度や耐摩耗性に寄与し、また、焼入れ時には、微細な炭化物及び炭窒化物が結晶粒の粗大化を抑制し、靭性の低下を抑制するために必要な元素である。Ｖの含有量が０．０５％よりも少ないと、上記の効果は得られない。一方、Ｖの含有量が０．８０％より多いと、凝固時に粗大な晶出炭化物が生成され、靭性が阻害される。そこで、Ｖの含有量は、０．０５～０．８０％とする。Ｖの含有量は、好ましくは０．０５～０．２０％とする。 V: 0.05 to 0.80%
V deposits fine and hard carbides and carbonitrides during tempering or when used as a hot tool, contributing to strength and abrasion resistance, and during quenching, fine carbides and carbonitrides are crystal grains. It is an element necessary to suppress the coarsening of and suppress the decrease in toughness. If the V content is less than 0.05%, the above effect cannot be obtained. On the other hand, if the V content is more than 0.80%, coarse crystallized carbides are produced during solidification, and the toughness is inhibited. Therefore, the V content is set to 0.05 to 0.80%. The V content is preferably 0.05 to 0.20%.
　使用前の熱間工具鋼における１０，０００μｍ２当りの円相当径１μｍ以上の大きさの炭化物の個数：１５０個以下
　熱間鍛造金型等の熱間工具として熱間（高温）で使用される前の熱間工具鋼を、「使用前」の熱間工具鋼と称する。熱間工具は、例えば、加工性向上又は熱間加工後に所望の特性を得るための組織制御等を目的に高温に加熱された被加工材と接触するため、被加工材からの熱移動により表面近傍が相当の温度（例えば１８０～１３００℃）に曝されて使用される。 Hot tool before use Number of carbides with a circle equivalent diameter of 1 μm or more per 10,000 μm 2 : 150 or less Used hot (high temperature) as a hot tool for hot forging dies, etc. The previous hot tool steel is referred to as "before use" hot tool steel. Since the hot tool comes into contact with the work material heated to a high temperature for the purpose of improving workability or controlling the structure to obtain desired characteristics after hot work, the surface of the hot tool is transferred by heat from the work material. The vicinity is exposed to a considerable temperature (for example, 180 to 1300 ° C.) before use.
　使用前の熱間工具鋼において、１０，０００μｍ２当りの円相当径１μｍ以上の大きさの炭化物の個数が１５０個より多いと、マトリックスに固溶している炭素の量が不足し、熱間工具として高温使用中に析出して高温強度の向上に寄与する微細で硬質な炭化物の量が減少し、十分な高温強度が得られない。また、使用前の熱間工具鋼において、１０，０００μｍ２当りの円相当径１μｍ以上の大きさの炭化物の個数が１５０個より多いと、炭化物に応力が集中して割れの起点や伝播経路として作用するために、鋼の靭性を阻害する。そこで、第２の熱間工具鋼では、使用前の熱間工具鋼における１０，０００μｍ２当りの円相当径１μｍ以上の大きさの炭化物の個数は１５０個以下とする。 In hot tool steel before use, if the number of carbides with a circle equivalent diameter of 1 μm or more per 10,000 μm 2 is more than 150, the amount of carbon dissolved in the matrix is insufficient and hot. The amount of fine and hard carbides that precipitate during high-temperature use as a tool and contribute to the improvement of high-temperature strength decreases, and sufficient high-temperature strength cannot be obtained. Further, in the hot tool steel before use, if the number of carbides having a circle equivalent diameter of 1 μm or more per 10,000 μm 2 is more than 150, stress is concentrated on the carbides and used as a crack starting point or a propagation path. To act, it inhibits the toughness of steel. Therefore, in the second hot tool steel, the number of carbides having a circle-equivalent diameter of 1 μm or more per 10,000 μm 2 in the hot tool steel before use is 150 or less.
　１０，０００μｍ２当りの円相当径１μｍ以上の大きさの炭化物の個数は、実施例に記載されるように、焼入れ焼戻し後の鋼材を用いて計測される。炭化物は、例えば、Ｍ２Ｃ、ＭＣ、Ｍ３Ｃ、Ｍ７Ｃ３、Ｍ２３Ｃ６等である。なお、Ｍは、金属元素を表す。 The number of carbides having a circle-equivalent diameter of 1 μm or more per 10,000 μm 2 is measured using a steel material after quenching and tempering as described in Examples. The carbides are, for example, M 2 C, MC, M 3 C, M 7 C 3 , M 23 C 6, and the like. In addition, M represents a metal element.
　本発明の熱間工具鋼は、高温使用時にＭ２Ｃ、ＭＣ等の二次炭化物が析出することで、軟化抵抗性、すなわち高温強度が得られる。しかし、高温使用前の段階で炭化物が多いと、高温使用中の二次炭化物の析出量が減少して高い高温強度が得られず、また、高温使用前の段階で粗大な炭化物が多く存在すると、靭性が低くなる等の問題がある。 The hot work tool steel of the present invention, by M 2 C, secondary carbides MC like precipitates at high temperatures used, softening resistance, i.e. high-temperature strength is obtained. However, if there is a large amount of carbides in the stage before high-temperature use, the amount of secondary carbides precipitated during high-temperature use will decrease and high high-temperature strength cannot be obtained, and if there are many coarse carbides in the stage before high-temperature use. , There are problems such as low toughness.
　以下、本発明の実施例について具体的に説明する。 Hereinafter, examples of the present invention will be specifically described.
　先ず、表１に示す化学成分を含有し、残部がＦｅ及び不可避不純物からなる発明鋼（Ｎｏ．１～１６）及び比較鋼（Ｎｏ．１７～３３）を、それぞれ１００ｋｇ、真空誘導溶解炉にて溶製し、インゴットに造塊した。次いで、これらのインゴットを１２２０℃に加熱し、角１５ｍｍの角材に鍛伸し、発明鋼及び比較鋼の鋼材を得た。 First, 100 kg each of the invention steels (No. 1 to 16) and the comparative steels (No. 17 to 33) containing the chemical components shown in Table 1 and the balance consisting of Fe and unavoidable impurities were placed in a vacuum induction melting furnace. It was melted and ingot into an ingot. Next, these ingots were heated to 1220 ° C. and forged into square lumber having a square of 15 mm to obtain steel materials of invention steel and comparative steel.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　得られた発明鋼及び比較鋼の鋼材を、それぞれ、オーステナイト組織を得るとともに炭化物を固溶させるのに十分な時間（例えば、３０分間）、８４０～１０００℃で熱処理して炭化物を固溶した後、油冷する焼入れを実施した。次いで、焼入れ後の鋼材を、それぞれ、５００～７００℃に加熱した後、空冷する焼戻しを実施し、３９～４１ＨＲＣに調質した。 The obtained steel materials of the invention steel and the comparative steel are heat-treated at 840 to 1000 ° C. for a sufficient time (for example, 30 minutes) to obtain an austenite structure and solid-solve the carbides, respectively. , Oil-cooled quenching was carried out. Next, each of the hardened steel materials was heated to 500 to 700 ° C., and then air-cooled and tempered to adjust the quality to 39 to 41 HRC.
　焼入れ焼戻し後の鋼材を、それぞれ、炭化物量の測定、靭性の評価、高温強度の評価を行うための、各試験用の供試材に機械加工した。次いで、各試験用の供試材を用いて、炭化物量の測定、靭性の評価、高温強度の評価の各試験を以下のように実施した。 The hardened and tempered steel materials were machined into test materials for each test for measuring the amount of carbides, evaluating toughness, and evaluating high-temperature strength, respectively. Then, using the test materials for each test, each test of measurement of carbide amount, evaluation of toughness, and evaluation of high temperature strength was carried out as follows.
［炭化物量の評価］
　供試材の中心をバフ研磨にて鏡面研磨した後、ピクリン酸アルコール溶液でマトリックスを腐食させ、薄い灰色又は白色に見える炭化物が多く観察される箇所を３０視野選択し、電子顕微鏡にて１０，０００倍で観察し、円相当径１μｍ以上の炭化物個数を、画像解析により計測した。結果を表１に示す。１０，０００μｍ２当たりの円相当径１μｍ以上の炭化物個数が１５０個以下のものを、表１の炭化物個数の欄に「○」と表示し、１０，０００μｍ２当たりの円相当径１μｍ以上の炭化物個数が１５０個より多いものを、表１の炭化物個数の欄に「×」と表示する。 [Evaluation of carbide content]
After mirror-polishing the center of the test material by buffing, the matrix is corroded with an alcohol picrinate solution, 30 fields are selected where many light gray or white carbides are observed, and 10 with an electron microscope. The number of carbides having a diameter equivalent to a circle of 1 μm or more was measured by image analysis by observing at 000 times. The results are shown in Table 1. If the number of carbides with a circle-equivalent diameter of 1 μm or more per 10,000 μm 2 is 150 or less, “○” is displayed in the column of the number of carbides in Table 1, and the carbides with a circle-equivalent diameter of 1 μm or more per 10,000 μm 2 are displayed. Those having more than 150 pieces are indicated by "x" in the column of the number of carbides in Table 1.
［靭性の評価］
　供試材から、ＪＩＳＺ２２４２規格の角１０ｍｍ、長さ５５ｍｍ、２ｍｍＵノッチからなる試験片を形成し、常温でシャルピー衝撃試験を行うことで靭性を評価した。結果を表１に示す。衝撃値が８５Ｊ／ｃｍ２以上のものを、表１の靭性の欄に「○」と表示し、衝撃値が８５Ｊ／ｃｍ２未満のものを、表１の靱性の欄に「×」と表示する。 [Evaluation of toughness]
A test piece having a JISZ2242 standard angle of 10 mm, a length of 55 mm, and a 2 mm U notch was formed from the test material, and the toughness was evaluated by performing a Charpy impact test at room temperature. The results are shown in Table 1. Those with an impact value of 85 J / cm 2 or more are indicated by "○" in the toughness column of Table 1, and those with an impact value of less than 85 J / cm 2 are indicated by "x" in the toughness column of Table 1. To do.
［高温強度の評価］
　供試材を、６００℃で１００時間保持後空冷し、室温におけるＨＲＣ硬さを測定し、初期硬さ（３９～４１ＨＲＣ）からの減少値に基づいて、高温強度を評価した。結果を表１に示す。減少値が１４ＨＲＣ以下となったものを、表１の高温強度の欄に「○」と表示し、減少値が１４ＨＲＣを超えたものを、表１の高温強度の欄に「×」と表示する。 [Evaluation of high temperature strength]
The test material was held at 600 ° C. for 100 hours and then air-cooled, the HRC hardness at room temperature was measured, and the high temperature strength was evaluated based on the decrease value from the initial hardness (39 to 41 HRC). The results are shown in Table 1. If the decrease value is 14 HRC or less, "○" is displayed in the high temperature intensity column of Table 1, and if the decrease value exceeds 14 HRC, "x" is displayed in the high temperature intensity column of Table 1. ..
　発明鋼のＮｏ．１～１６では、炭化物個数、靭性、高温強度の各欄の評価が全て「○」であった。 Invention steel No. In 1 to 16, the evaluations in each column of the number of carbides, toughness, and high temperature strength were all "◯".
　これに対して、比較鋼のＮｏ．１７～３３では、炭化物個数、靭性、高温強度の各欄の評価が全て「○」のものはなかった。 On the other hand, the comparative steel No. In 17 to 33, none of the evaluations in each column of the number of carbides, toughness, and high temperature strength were "○".
　比較鋼のＮｏ．１７では、Ｃの含有量（０．７１％）が本発明の上限値（０．６０％）より多いため、１０，０００μｍ２当りの円相当径１μｍ以上の炭化物個数が１５０個より多く、また、Ｎｉの含有量（０．４％）が本発明の下限値（０．５％）より少ない。このため、靭性が低く（常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ２未満）、高温強度も低い（初期硬さからの減少量が１４ＨＲＣを超える）。 Comparative steel No. In No. 17, since the C content (0.71%) is larger than the upper limit value (0.60%) of the present invention, the number of carbides having a circle equivalent diameter of 1 μm or more per 10,000 μm 2 is more than 150, and , Ni content (0.4%) is less than the lower limit (0.5%) of the present invention. Therefore, the toughness is low (the impact value of the Charpy impact test at room temperature is less than 85 J / cm 2 ), and the high temperature strength is also low (the amount of decrease from the initial hardness exceeds 14 HRC).
　比較鋼のＮｏ．１８、２３、２５、２７では、１０，０００μｍ２当りの円相当径１μｍ以上の炭化物個数が１５０個より多い。このため、高温強度が低い（初期硬さからの減少量が１４ＨＲＣを超える）。 Comparative steel No. In 18, 23, 25, and 27, the number of carbides having a circle-equivalent diameter of 1 μm or more per 10,000 μm 2 is more than 150. Therefore, the high temperature strength is low (the amount of decrease from the initial hardness exceeds 14 HRC).
　比較鋼のＮｏ．１９では、Ｃｒの含有量（１．５％）が本発明の下限値（１．６％）より少なく（これにより、焼入れ性が不十分となる）、１０，０００μｍ２当りの円相当径１μｍ以上の炭化物個数が１５０個より多い。このため、靭性が低い（常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ２未満）。 Comparative steel No. In 19, the Cr content (1.5%) is less than the lower limit (1.6%) of the present invention (which results in insufficient hardenability), and the equivalent circle diameter of 10,000 μm 2 is 1 μm. The number of the above carbides is more than 150. Therefore, the toughness is low (the impact value of the Charpy impact test at room temperature is less than 85 J / cm 2).
　比較鋼のＮｏ．２０では、Ｍｏの含有量（０．２％）が本発明の下限値（０．３％）より少ない（これにより、焼入れ性が不十分となる）。このため、高温強度が低い（初期硬さからの減少量が１４ＨＲＣを超える）。 Comparison steel No. At 20, the Mo content (0.2%) is less than the lower limit (0.3%) of the present invention (which results in inadequate hardenability). Therefore, the high temperature strength is low (the amount of decrease from the initial hardness exceeds 14 HRC).
　比較鋼のＮｏ．２１では、１０，０００μｍ２当りの円相当径１μｍ以上の炭化物個数が１５０個より多い。このため、靭性が低い（常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ２未満）。 Comparative steel No. In 21, the number of carbides having a circle-equivalent diameter of 1 μm or more per 10,000 μm 2 is more than 150. Therefore, the toughness is low (the impact value of the Charpy impact test at room temperature is less than 85 J / cm 2).
　比較鋼のＮｏ．２２では、Ｎｉの含有量（０．４％）が本発明の下限値（０．５％）より少ないため、靭性が低い（常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ２未満）。また、Ｖの含有量（０．０３％）が本発明の下限値（０．０５％）より少ないため、高温強度が低い（初期硬さからの減少量が１４ＨＲＣを超える）。 Comparative steel No. In No. 22, since the Ni content (0.4%) is less than the lower limit value (0.5%) of the present invention, the toughness is low (the impact value of the Charpy impact test at room temperature is less than 85 J / cm 2). Further, since the V content (0.03%) is less than the lower limit value (0.05%) of the present invention, the high temperature strength is low (the amount of decrease from the initial hardness exceeds 14 HRC).
　比較鋼のＮｏ．２４では、Ｃの含有量（０．６６％）が本発明の上限値（０．６０％）より多いため、１０，０００μｍ２当りの円相当径１μｍ以上の炭化物個数が１５０個より多い。このため、靭性が低く（常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ２未満）、高温強度も低い（初期硬さからの減少量が１４ＨＲＣを超える）。 Comparative steel No. In No. 24, since the C content (0.66%) is larger than the upper limit value (0.60%) of the present invention, the number of carbides having a circle equivalent diameter of 1 μm or more per 10,000 μm 2 is more than 150. Therefore, the toughness is low (the impact value of the Charpy impact test at room temperature is less than 85 J / cm 2 ), and the high temperature strength is also low (the amount of decrease from the initial hardness exceeds 14 HRC).
　比較鋼のＮｏ．２６では、Ｃｒの含有量（２．８％）が本発明の上限値（２．６％）より多いため（これにより、焼入れ焼戻し時にＣｒ系の炭化物が過多に形成される）、１０，０００μｍ２当りの円相当径１μｍ以上の炭化物個数が１５０個より多い。このため、靭性が低く（常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ２未満）、高温強度も低い（初期硬さからの減少量が１４ＨＲＣを超える）。 Comparative steel No. In No. 26, since the Cr content (2.8%) is higher than the upper limit value (2.6%) of the present invention (this causes excessive formation of Cr-based carbides during quenching and tempering), 10,000 μm. The number of carbides having a circle-equivalent diameter of 1 μm or more per 2 is more than 150. Therefore, the toughness is low (the impact value of the Charpy impact test at room temperature is less than 85 J / cm 2 ), and the high temperature strength is also low (the amount of decrease from the initial hardness exceeds 14 HRC).
　比較鋼のＮｏ．２８では、１０，０００μｍ２当りの円相当径１μｍ以上の炭化物個数が１５０個より多い。このため、靭性が低く（常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ２未満）、高温強度も低い（初期硬さからの減少量が１４ＨＲＣを超える）。 Comparative steel No. In 28, the number of carbides having a circle-equivalent diameter of 1 μm or more per 10,000 μm 2 is more than 150. Therefore, the toughness is low (the impact value of the Charpy impact test at room temperature is less than 85 J / cm 2 ), and the high temperature strength is also low (the amount of decrease from the initial hardness exceeds 14 HRC).
　比較鋼のＮｏ．２９では、Ｖの含有量（０．０３％）が本発明の下限値（０．０５％）より少ない。このため、高温強度が低い（初期硬さからの減少量が１４ＨＲＣを超える）。 Comparison steel No. At 29, the V content (0.03%) is less than the lower limit (0.05%) of the present invention. Therefore, the high temperature strength is low (the amount of decrease from the initial hardness exceeds 14 HRC).
　比較鋼のＮｏ．３０では、１０，０００μｍ２当りの円相当径１μｍ以上の炭化物個数が１５０個より多い。このため、高温強度が低い（初期硬さからの減少量が１４ＨＲＣを超える）。 Comparative steel No. At 30, the number of carbides having a circle-equivalent diameter of 1 μm or more per 10,000 μm 2 is more than 150. Therefore, the high temperature strength is low (the amount of decrease from the initial hardness exceeds 14 HRC).
　比較鋼のＮｏ．３１では、Ｍｏの含有量（２．１％）が本発明の上限値（２．０％）より多く、１０，０００μｍ２当りの円相当径１μｍ以上の炭化物個数が１５０個より多い（Ｍｏの含有量が多いため、焼入れ時に固溶しきらない炭化物が粗大凝集する）。このため、靭性が低く（常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ２未満）、高温強度も低い（初期硬さからの減少量が１４ＨＲＣを超える）。 Comparative steel No. In 31, the Mo content (2.1%) is larger than the upper limit (2.0%) of the present invention, and the number of carbides having a circle equivalent diameter of 1 μm or more per 10,000 μm 2 is more than 150 (Mo). Due to its high content, carbides that do not completely dissolve during quenching coagulate coarsely). Therefore, the toughness is low (the impact value of the Charpy impact test at room temperature is less than 85 J / cm 2 ), and the high temperature strength is also low (the amount of decrease from the initial hardness exceeds 14 HRC).
　比較鋼のＮｏ．３２では、Ｃの含有量（０．１３％）が本発明の下限値（０．２％）より少ない。このため、高温強度が低い（初期硬さからの減少量が１４ＨＲＣを超える）。 Comparison steel No. At 32, the C content (0.13%) is less than the lower limit (0.2%) of the present invention. Therefore, the high temperature strength is low (the amount of decrease from the initial hardness exceeds 14 HRC).
　比較鋼のＮｏ．３３では、１０，０００μｍ２当りの円相当径１μｍ以上の炭化物個数が１５０個より多い。このため、高温強度が低い（初期硬さからの減少量が１４ＨＲＣを超える）。 Comparative steel No. In 33, the number of carbides having a circle-equivalent diameter of 1 μm or more per 10,000 μm 2 is more than 150. Therefore, the high temperature strength is low (the amount of decrease from the initial hardness exceeds 14 HRC).

Claims (2)

  1. 　質量％で、Ｃ：０．２０～０．６０％、Ｓｉ：０．１～０．３％、Ｍｎ：０．５～２．０％、Ｎｉ：０．５～２．５％、Ｃｒ：１．６～２．６％、Ｍｏ：０．３～２．０％、Ｖ：０．０５～０．８０％を含有し、残部がＦｅ及び不可避不純物からなることを特徴とする、高温強度及び靭性に優れる熱間工具鋼。 By mass%, C: 0.20 to 0.60%, Si: 0.1 to 0.3%, Mn: 0.5 to 2.0%, Ni: 0.5 to 2.5%, Cr: High temperature strength characterized by containing 1.6 to 2.6%, Mo: 0.3 to 2.0%, V: 0.05 to 0.80%, and the balance consisting of Fe and unavoidable impurities. Hot tool steel with excellent toughness.
  2. 　質量％で、Ｃ：０．２０～０．６０％、Ｓｉ：０．１～０．３％、Ｍｎ：０．５～２．０％、Ｎｉ：０．５～２．５％、Ｃｒ：１．６～２．６％、Ｍｏ：０．３～２．０％、Ｖ：０．０５～０．８０％を含有し、残部がＦｅ及び不可避不純物からなる熱間工具鋼であって、使用前の熱間工具鋼における１０，０００μｍ２当りの円相当径１μｍ以上の大きさの炭化物の個数が１５０個以下であることを特徴とする、高温強度及び靭性に優れる熱間工具鋼。 By mass%, C: 0.20 to 0.60%, Si: 0.1 to 0.3%, Mn: 0.5 to 2.0%, Ni: 0.5 to 2.5%, Cr: A hot tool steel containing 1.6 to 2.6%, Mo: 0.3 to 2.0%, V: 0.05 to 0.80%, and the balance consisting of Fe and unavoidable impurities. A hot tool steel having excellent high temperature strength and toughness, characterized in that the number of carbides having a circle equivalent diameter of 1 μm or more per 10,000 μm 2 in the hot tool steel before use is 150 or less.
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Citations (6)

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Publication number Priority date Publication date Assignee Title
JPS6130654A (en) * 1984-07-21 1986-02-12 Kanto Tokushu Seikou Kk Steel for roll shell for continuously casting aluminum
JP2003268486A (en) * 2002-03-11 2003-09-25 Nippon Koshuha Steel Co Ltd Tool steel for hot working
JP2011195917A (en) * 2010-03-23 2011-10-06 Sanyo Special Steel Co Ltd Hot work tool steel excellent in toughness
JP2013213255A (en) * 2012-04-02 2013-10-17 Sanyo Special Steel Co Ltd Hot working die steel
JP2019019374A (en) * 2017-07-15 2019-02-07 山陽特殊製鋼株式会社 Hot tool steel excellent in hardening property and toughness
JP2019019397A (en) * 2017-07-20 2019-02-07 山陽特殊製鋼株式会社 Preharden hot tool steel excellent in machinability

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6130654A (en) * 1984-07-21 1986-02-12 Kanto Tokushu Seikou Kk Steel for roll shell for continuously casting aluminum
JP2003268486A (en) * 2002-03-11 2003-09-25 Nippon Koshuha Steel Co Ltd Tool steel for hot working
JP2011195917A (en) * 2010-03-23 2011-10-06 Sanyo Special Steel Co Ltd Hot work tool steel excellent in toughness
JP2013213255A (en) * 2012-04-02 2013-10-17 Sanyo Special Steel Co Ltd Hot working die steel
JP2019019374A (en) * 2017-07-15 2019-02-07 山陽特殊製鋼株式会社 Hot tool steel excellent in hardening property and toughness
JP2019019397A (en) * 2017-07-20 2019-02-07 山陽特殊製鋼株式会社 Preharden hot tool steel excellent in machinability

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