JP2005113161A - Hot tool steel - Google Patents
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- JP2005113161A JP2005113161A JP2003345056A JP2003345056A JP2005113161A JP 2005113161 A JP2005113161 A JP 2005113161A JP 2003345056 A JP2003345056 A JP 2003345056A JP 2003345056 A JP2003345056 A JP 2003345056A JP 2005113161 A JP2005113161 A JP 2005113161A
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Abstract
Description
本発明は、熱間鍛造用金型、ダイカスト金型及び押し出し用金型等に使用される熱間工具鋼に関する。 The present invention relates to hot tool steel used for hot forging dies, die casting dies, extrusion dies, and the like.
近時、熱間鍛造用金型、ダイカスト金型及び熱間押し出し用金型等の熱間加工用金型は、大型化し、形状も複雑になっている。また、成形効率を向上させるために、型面からの冷却が過酷になっており、更に、鍛造加工及び鋳造加工の精度を向上させるために、金型のコーナー部がより先鋭化し、その肉厚も薄くなっている。 Recently, hot working dies such as hot forging dies, die casting dies, and hot extrusion dies have become larger and more complicated in shape. In addition, the cooling from the mold surface is severe to improve the molding efficiency, and the corner of the mold is sharpened and the wall thickness is increased to improve the accuracy of forging and casting. Is also thinner.
このように形状が複雑で、肉厚が薄く、コーナー部のＲが小さい大型の金型を製造する場合、金型の内部品質を向上させるために、その製造工程において熱処理が施される。その際、油焼入れ等により急冷されることがあるが、熱処理後に金型材料を急冷すると、変形又は割れが発生して、金型作製が不能になることが多いため、通常は、熱処理後の金型材料は徐冷されている。しかしながら、熱処理後に徐冷すると、金型材料である鋼材の組織がマルテンサイトからベイナイトとなり、靱性が低下するため、早期大割れが発生しやすくなり、金型の寿命が短くなる。 Thus, when manufacturing a large mold having a complicated shape, a thin wall thickness, and a small corner portion R, heat treatment is performed in the manufacturing process in order to improve the internal quality of the mold. At that time, it may be rapidly cooled by oil quenching, etc., but if the mold material is rapidly cooled after heat treatment, deformation or cracking often occurs, making it impossible to make the mold. The mold material is slowly cooled. However, when the steel is gradually cooled after the heat treatment, the structure of the steel material, which is a mold material, changes from martensite to bainite, and the toughness is reduced, so that early large cracks are likely to occur and the life of the mold is shortened.
熱間鍛造加工、ダイカスト加工及び熱間押し出し加工等の熱間加工においては、金型の型面の変形及び熱膨張の僅かな違いにより、製品の寸法及び形状に不良が発生するため、金型が早期に寿命に達するという事例が増加してきている。従来の熱間加工用金型に使用されている熱間工具鋼の場合、材料の偏析又は炭化物及び非金属介在物等の影響により、方向によって熱膨張差に違いがある。即ち、熱膨張率に異方性がある。例えば、金型を４００℃より高い温度に加熱したり、１００℃以下まで冷却したりする場合、金型の熱膨張差が大きな引張応力となり、応力が集中しやすいコーナーＲ部からコーナーエッジ割れが発生する。そこで、コーナーエッジ割れの発生を抑制して金型を長寿命化するため、熱膨張率が小さく、熱膨張率に異方性がない熱間工具鋼が求められている。 In hot working such as hot forging, die casting and hot extrusion, there is a problem in the size and shape of the product due to slight differences in the mold surface deformation and thermal expansion. Increasingly, cases have reached the end of their lives. In the case of hot tool steel used in conventional hot working molds, there is a difference in thermal expansion difference depending on the direction due to segregation of materials or the influence of carbides and non-metallic inclusions. That is, the coefficient of thermal expansion has anisotropy. For example, when the mold is heated to a temperature higher than 400 ° C. or cooled to 100 ° C. or less, the difference in thermal expansion of the mold becomes a large tensile stress, and the corner edge cracks from the corner R portion where the stress tends to concentrate. Occur. Therefore, in order to extend the life of the mold by suppressing the occurrence of corner edge cracking, there is a need for a hot tool steel having a low coefficient of thermal expansion and no anisotropy in the coefficient of thermal expansion.
従来、Ｓｉ、Ｐ、Ｓ及びＯの含有量を低減すると共に、Ａｓ、Ｓｎ、Ｃｕ、Ｂ、Ｐｂ、及びＢｉ等の微量不純物元素の含有量を低減することにより、靱性を向上させて、金型の長寿命化を図った熱間工具鋼がある（特許文献１参照。）。また、Ｃ、Ｓｉ、Ｍｎ、Ｎｉ、Ｃｒ及びＣｕの含有量を規定し、Ｍｏ、Ｗ、Ｖ、Ｔｉ、Ｎｂ、Ｚｒ及びＣｏの含有量を所定の値以下に規制し、更に、Ｃａ、Ｍｇ、Ａｌ、Ｂ及びＲＥＭ等の微量成分の含有量を規定することにより、靱性、耐ヒートチェック性及び耐衝撃性を向上させて、金型の長寿命化を図った熱間工具鋼も提案されている（特許文献２参照）。 Conventionally, while reducing the contents of Si, P, S and O, and reducing the contents of trace impurity elements such as As, Sn, Cu, B, Pb, and Bi, the toughness is improved, and gold There is a hot work tool steel that extends the life of the mold (see Patent Document 1). Further, the contents of C, Si, Mn, Ni, Cr and Cu are defined, the contents of Mo, W, V, Ti, Nb, Zr and Co are regulated to a predetermined value or less, and further, Ca, Mg Hot tool steel that has improved toughness, heat check resistance and impact resistance by prescribing the contents of trace components such as Al, B and REM has been proposed. (See Patent Document 2).
更に、金型製造時の熱処理（焼入れ）時に発生する問題を解決するため、種々の焼入れ方法が提案されている（例えば、特許文献３乃至５参照。）。例えば、特許文献３及び４に記載の焼入れ方法は、オーステナイト化温度から複合冷却変更温度まで徐冷することにより、ベーナイト組織にならないようにして、熱歪みを少なくすると共に、靱性及び耐ヒートチェック性を向上させている。また、特許文献５に記載の熱間加工用ダイスの製造方法は、先ず、冷却材に投入して急冷し、その後、マルテンサイト変態点に到達する前に冷却材から引き上げて、常温まで徐冷している。これにより、焼入れ時の割れの発生を抑制し、靱性及び強度を向上させ、金型を長寿命化している。 Furthermore, various quenching methods have been proposed in order to solve the problems that occur during heat treatment (quenching) during mold manufacture (see, for example, Patent Documents 3 to 5). For example, in the quenching methods described in Patent Documents 3 and 4, by gradually cooling from the austenitizing temperature to the composite cooling change temperature, the bainite structure is not formed, the thermal strain is reduced, and the toughness and heat check resistance are reduced. Has improved. Moreover, the manufacturing method of the die for hot working described in Patent Document 5 is first charged into the coolant and rapidly cooled, and then pulled up from the coolant before reaching the martensite transformation point and gradually cooled to room temperature. doing. Thereby, generation | occurrence | production of the crack at the time of quenching is suppressed, toughness and intensity | strength are improved, and the metal mold | die is lengthened.
しかしながら、上述の従来の技術には以下に示す問題点がある。形状が複雑で、肉厚が薄く、コーナー部のＲが小さい大型の金型においては、高精度な製品を成形するために、金型の変形を抑制する高温強度及びコーナーＲ部におけるヒートクラックに対する耐割れ性の向上が必要である。特許文献１及び２に記載の熱間工具鋼のように、金型に使用する熱間工具鋼を高合金化すると、焼入れ性が低下するという問題がある。また、特許文献３乃至５に記載の焼入れ方法のように、熱処理方法についての検討もなされているが、これらの方法は鋼材の検討が十分になされていない。 However, the conventional techniques described above have the following problems. In large molds with complex shapes, thin wall thickness, and small corner R, high-temperature strength that suppresses deformation of the mold and heat cracks at the corner R are required to form highly accurate products. Improvement of crack resistance is necessary. Like hot tool steel of patent documents 1 and 2, when hot tool steel used for a metallic mold is made into a high alloy, there is a problem that hardenability falls. Moreover, although the heat processing method is also examined like the hardening method of patent documents 3 thru | or 5, these methods are not fully examined about steel materials.
本発明はかかる問題点に鑑みてなされたものであって、熱膨張率が小さく、熱膨張率に異方性がなく、形状が複雑でコーナー部のＲが小さい金型においてもヒートクラックに対する耐割れ性が優れた熱間工具鋼を提供することを目的とする。 The present invention has been made in view of such problems, and is resistant to heat cracks even in a mold having a low coefficient of thermal expansion, no anisotropy in the coefficient of thermal expansion, a complicated shape, and a small corner R. An object of the present invention is to provide a hot work tool steel having excellent crackability.
本発明に係る熱間工具鋼は、Ｃ：０．３０乃至０．４５質量％、Ｓｉ：０．０５乃至０．２５質量％、Ｍｎ：０．５０乃至０．７０質量％、Ｃｒ：５．３０乃至５．７５質量％、Ｍｏ：３．００乃至３．５０質量％、Ｖ：０．６５乃至０．９５質量％、Ｎｉ：０．４５乃至０．７５質量％、Ｃｏ：０．４５乃至０．７５質量％を含有し、Ｓを０．００５質量％以下、Ｐを０．００１０質量％以下、Ｗ：０．００５０質量％以下に規制し、残部がＦｅ及び不可避的不純物からなり、ＪＩＳＧ０５５５に規定されている非金属介在物の清浄度がｄＡ６０×４００で０．００５％以下、ｄＢ６０×４００で０．００５％以下であると共に、焼き鈍ししたときに、粒径が１μｍを超える炭化物及び非金属介在物の総面積率が０．００４％以下であり、粒径が１μｍ以下の炭化物及び非金属介在物の総面積率が１５．０％以上であり、前記炭化物及び非金属介在物のアスペクト比が１．０乃至１．３である。 The hot work tool steel according to the present invention has C: 0.30 to 0.45 mass%, Si: 0.05 to 0.25 mass%, Mn: 0.50 to 0.70 mass%, Cr: 5. 30 to 5.75 mass%, Mo: 3.00 to 3.50 mass%, V: 0.65 to 0.95 mass%, Ni: 0.45 to 0.75 mass%, Co: 0.45 to Containing 0.75% by mass, S is controlled to 0.005% by mass or less, P is controlled to 0.0010% by mass or less, W: 0.0050% by mass or less, and the balance consists of Fe and unavoidable impurities. The cleanliness of non-metallic inclusions specified in the above is 0.005% or less at dA60 × 400 and 0.005% or less at dB60 × 400. The total area ratio of metal inclusions is 0.004% or less, There is a total area ratio of the following carbide and non-metallic inclusions 1μm 15.0% or more, the aspect ratio of the carbide and non-metallic inclusions is 1.0 to 1.3.
本発明においては、熱膨張率を低減する効果がある炭化物及び非金属介在物を積極的に添加すると共に、異方性がある形状の添加物を軽減することにより、熱膨張率の異方性を低減することができる。 In the present invention, anisotropy of the thermal expansion coefficient is achieved by positively adding carbides and non-metallic inclusions that have the effect of reducing the thermal expansion coefficient and reducing additives having an anisotropic shape. Can be reduced.
また、本発明の熱間工具鋼においては、偏析部におけるＣ及びＣｒの濃度と非偏析部におけるＣ及びＣｒの濃度との比（偏析部の濃度／比偏析部の濃度）が１．４乃至１．９であり、偏析部におけるＷ及びＭｎの濃度と非偏析部におけるＷ及びＭｎの濃度との比が１．２以下であり、偏析部のアスペクト比が１．０乃至１．３であり、偏析部と非偏析部の面積比（偏析部の面積／非偏析部の面積）が１．３以上であることが好ましい。これにより、偏析部の形状が球状になり、更に、熱間工具鋼中に均一分散することができる。その結果、炭化物及び非金属介在物と同様に、熱膨張率を低減すると共に、熱膨張率の異方性がなくなり等方体になる。 In the hot tool steel of the present invention, the ratio of the concentration of C and Cr in the segregation part and the concentration of C and Cr in the non-segregation part (concentration of the segregation part / concentration of the specific segregation part) is 1.4 to 1.4. 1.9, the ratio of the concentration of W and Mn in the segregation part to the concentration of W and Mn in the non-segregation part is 1.2 or less, and the aspect ratio of the segregation part is 1.0 to 1.3 The area ratio between the segregation part and the non-segregation part (area of the segregation part / area of the non-segregation part) is preferably 1.3 or more. Thereby, the shape of a segregation part becomes spherical shape and can be uniformly disperse | distributed in hot tool steel. As a result, as with carbides and non-metallic inclusions, the coefficient of thermal expansion is reduced, and the anisotropy of the coefficient of thermal expansion is eliminated to form an isotropic body.
更に、本発明の熱間工具鋼においては、例えば、鍛伸方向の熱膨張係率（Ｌ方向の熱膨張率）と、前記鍛伸方向に対して垂直な方向における熱膨張係率（Ｗ方向の熱膨張率）との比（Ｌ方向の熱膨張率／Ｗ方向の熱膨張率）が、１．０００乃至１．０１５である。これにより、熱膨張率が異方性から等方性になるため、金型のコーナーエッジ部の早期割れが改善される。 Furthermore, in the hot work tool steel of the present invention, for example, the thermal expansion coefficient in the forging direction (thermal expansion coefficient in the L direction) and the thermal expansion coefficient in the direction perpendicular to the forging direction (W direction) (Thermal expansion coefficient in the L direction / thermal expansion coefficient in the W direction) is 1.000 to 1.015. Thereby, since the coefficient of thermal expansion changes from anisotropy to isotropic, early cracking of the corner edge portion of the mold is improved.
本発明によれば、Ｃ、Ｓｉ、Ｍｎ、Ｃｒ、Ｍｏ、Ｖ、Ｎｉ及びＣｏの含有量を上述の範囲内にし、Ｓ及びＰの含有量を規制し、更に、非金属介在物の清浄度、焼き鈍ししたときの粒径が１μｍを超える炭化物及び非金属介在物の総面積率及び粒径が１μｍ以下の炭化物及び非金属介在物の総面積率、並びに炭化物及び非金属介在物のアスペクト比を上述の範囲内にすることにより、熱膨張率が小さく、熱膨張率の異方性がない等方熱膨張性の熱間工具鋼を得ることができる。本発明の熱間工具鋼を使用して製造された金型は、過酷な熱的応力及び機械的応力の作用に対して、コーナーエッジ部における耐衝撃割れ性が優れており、複雑な製品を精度よく成形することができる。 According to the present invention, the contents of C, Si, Mn, Cr, Mo, V, Ni, and Co are within the above range, the contents of S and P are regulated, and the cleanliness of nonmetallic inclusions The total area ratio of carbides and non-metallic inclusions having a grain size exceeding 1 μm when annealed, the total area ratio of carbides and non-metallic inclusions having a particle diameter of 1 μm or less, and the aspect ratio of carbide and non-metallic inclusions By making it in the above-mentioned range, an isotropic thermally expandable hot tool steel having a small coefficient of thermal expansion and no anisotropy of the coefficient of thermal expansion can be obtained. Molds manufactured using the hot tool steel of the present invention have excellent impact cracking resistance at corner edges against the effects of severe thermal stress and mechanical stress, making complex products It can be molded with high accuracy.
以下、本発明に係る熱間工具鋼について詳細に説明する。本発明の熱間工具鋼は、Ｃ：０．３０乃至０．４５質量％、Ｓｉ：０．０５乃至０．２５質量％、Ｍｎ：０．５０乃至０．７０質量％、Ｃｒ：５．３０乃至５．７５質量％、Ｍｏ：３．００乃至３．５０質量％、Ｖ：０．６５乃至０．９５質量％、Ｎｉ：０．４５乃至０．７５質量％、Ｃｏ：０．４５乃至０．７５質量％を含有し、Ｓを０．００５質量％以下、Ｐを０．００１０質量％以下、Ｗ：０．００５０質量％以下に規制し、残部がＦｅ及び不可避的不純物からなり、ＪＩＳＧ０５５５に規定されている非金属介在物の清浄度がｄＡ６０×４００で０．００５％以下、ｄＢ６０×４００で０．００５％以下であると共に、焼き鈍ししたときに、粒径が１μｍを超える炭化物及び非金属介在物の総面積率が０．００４％以下であり、粒径が１μｍ以下の炭化物及び非金属介在物の総面積率が１５．０％以上であり、前記炭化物及び非金属介在物のアスペクト比が１．０乃至１．３である。 Hereinafter, the hot work tool steel according to the present invention will be described in detail. The hot work tool steel of the present invention has C: 0.30 to 0.45 mass%, Si: 0.05 to 0.25 mass%, Mn: 0.50 to 0.70 mass%, Cr: 5.30. To 5.75 mass%, Mo: 3.00 to 3.50 mass%, V: 0.65 to 0.95 mass%, Ni: 0.45 to 0.75 mass%, Co: 0.45 to 0 .75% by mass, S is controlled to 0.005% by mass or less, P is controlled to 0.0010% by mass or less, W: 0.0050% by mass or less, and the balance is Fe and inevitable impurities. The specified cleanness of nonmetallic inclusions is 0.005% or less at dA60 × 400, 0.005% or less at dB60 × 400, and when annealed, carbides and nonmetals having a particle size exceeding 1 μm The total area ratio of inclusions is 0.004% or less, and the particle size is μm below the carbide and the total area ratio of the nonmetallic inclusions is 15.0% or more, the aspect ratio of the carbide and non-metallic inclusions is 1.0 to 1.3.
熱間工具鋼の高温強度を上げるためには、例えば、汎用鋼であるＪＩＳ規格ＳＫＤ６１鋼とＪＩＳ規格ＳＫＤ８鋼との関係のように、Ｃｒ添加量を少なくして、Ｗ及びＮｉ等を添加すればよい。しかしながら、Ｃｒ添加量を少なくすると、焼入れ性が劣化し、大きな金型においては、組織がマルテンサイトからベイナイトになって靱性が低下する。また、本発明者等の検討により、Ｃｒ添加量を少なくした熱間工具鋼を、熱間鍛造用金型、ダイカスト金型及び押し出し用金型等の各種熱間加工用金型に使用した場合、加熱及び冷却を繰り返すと、熱及び応力により著しく硬度軟化が促進されて、その硬度が低下することが判明した。更に、本発明者等は、この応力軟化現象を抑制するためには、Ｍｏ系炭化物の生成量を増やし、Ｖ系炭化物をできるだけ少なくすることが有効であることを見出した。即ち、熱間工具鋼の高温強度向上には、Ｃｒ含有量、Ｍｏ含有量及びＶ含有量を最適化することが有効である。そこで、本発明の熱間工具鋼においては、Ｃ含有量を０．３０乃至０．４５質量％、Ｍｏ含有量を３．００乃至３．５０質量％、Ｖ含有量を０．６５乃至０．９５質量％とする。 In order to increase the high-temperature strength of hot work tool steel, for example, as in the relationship between JIS standard SKD61 steel and JIS standard SKD8 steel, which are general purpose steels, the amount of Cr added should be reduced and W, Ni, etc. should be added. That's fine. However, if the amount of Cr added is reduced, the hardenability deteriorates, and in a large mold, the structure changes from martensite to bainite and the toughness decreases. In addition, when the hot tool steel with a reduced amount of Cr added is used for various hot working dies such as a hot forging die, die casting die and extrusion die as a result of the study by the present inventors. It has been found that when heating and cooling are repeated, hardness and softening are remarkably promoted by heat and stress, and the hardness decreases. Furthermore, the present inventors have found that in order to suppress this stress softening phenomenon, it is effective to increase the amount of Mo-based carbide generated and to reduce the amount of V-based carbide as much as possible. That is, it is effective to optimize the Cr content, the Mo content, and the V content in order to improve the high temperature strength of the hot tool steel. Therefore, in the hot tool steel of the present invention, the C content is 0.30 to 0.45 mass%, the Mo content is 3.00 to 3.50 mass%, and the V content is 0.65 to 0.00. 95% by mass.
また、熱膨張率が小さい材料としては、Ｆｅ−Ｎｉ系合金であるインバー及びアンバー等が挙げられるが、これらの材料は、一般に、Ｎｉ含有量が２０％を超えるものが多いため、コストが増加すると共に、高温強度が得られないという問題があり、実用的ではない。例えば、ＪＩＳ規格ＳＫＤ６１鋼の熱膨張率を小さくするためには、熱膨張率が小さい基地と、熱膨張率が小さく靱性等の機械的性質に影響を与えない第２相とを組み合わせることが有効である。表１に炭化物、酸化物及び窒化物の熱膨張率を示す。なお、表１には比較のため、Ｆｅの熱膨張率も併せて示す。本発明者等は、表１に示すような熱膨張率が小さい材料で第２相を形成すると、その体積率が多い程熱膨張率を低下させる効果が大きいことを見出した。 In addition, examples of materials having a low coefficient of thermal expansion include invar and amber, which are Fe-Ni alloys, but these materials generally have a Ni content exceeding 20%, which increases costs. In addition, there is a problem that high-temperature strength cannot be obtained, which is not practical. For example, in order to reduce the thermal expansion coefficient of JIS standard SKD61 steel, it is effective to combine a base having a low thermal expansion coefficient with a second phase that has a low thermal expansion coefficient and does not affect mechanical properties such as toughness. It is. Table 1 shows the thermal expansion coefficients of carbides, oxides, and nitrides. Table 1 also shows the thermal expansion coefficient of Fe for comparison. The present inventors have found that when the second phase is formed of a material having a low coefficient of thermal expansion as shown in Table 1, the effect of decreasing the coefficient of thermal expansion is greater as the volume ratio is higher.
但し、熱膨張率には、第２相を構成する粒子の鍛伸方向における長さと鍛伸方向に垂直な方向における長さとの比、即ち、第２相中の粒子のアスペクト比も影響する。このため、本発明の熱間工具鋼においては、熱膨張率の異方性をなくして等方性にするため、第２相を形成する炭化物及び非金属介在物のアスペクト比を１．０乃至１．３にする。 However, the ratio of the length in the forging direction of the particles constituting the second phase to the length in the direction perpendicular to the forging direction, that is, the aspect ratio of the particles in the second phase, also affects the coefficient of thermal expansion. For this reason, in the hot tool steel of the present invention, the aspect ratio of carbides and non-metallic inclusions forming the second phase is set to 1.0 to 1.0 in order to eliminate the anisotropy of the thermal expansion coefficient and make it isotropic. Set to 1.3.
また、本発明者等は、熱膨張率の異方性には、第２相中の粒子の形状以外に偏析状態も影響することを見出した。ＪＩＳＧ０５５５に規定されている清浄度で、ＭｎＳ及びケイ酸塩等のＡ系介在物は粘性変形介在物である。また、Ａｌ２Ｏ３等のＢ系介在物は加工方向に集団をなして、不連続的に粒状介在物として並んだものである。このような、Ａ系介在物及びＢ系介在物の含有量を少なくする程、熱膨張率の異方性をなくす効果があり、これらを含有しないことがより好ましい。下記表２乃至６に、偏析部におけるＣｒ、Ｓｉ、Ｗ、Ｃ及びＭｎの濃度と熱膨張率との関係を示す。下記表２乃至６に示すように、偏析部におけるＷ及びＭｎの含有量が増すと熱膨張率が高くなり、Ｃ及びＣｒの含有量が増すと熱膨張率は低下する。そこで、本発明の熱間工具鋼においては、熱膨張率の小さい第２相粒子の面積率を増加させると共に、熱膨張率を高くするＷ及びＭｎの含有量を抑制して、Ｃｒ及びＣ等の熱膨張率を低下させる成分のみを、球状に近い形状で偏析させて、均一分散させる。これにより、熱膨張率が小さくなると共に、熱膨張率に異方性がなくなる。 Further, the present inventors have found that the segregation state affects the anisotropy of the thermal expansion coefficient in addition to the shape of the particles in the second phase. A-type inclusions such as MnS and silicate are viscous deformation inclusions with the cleanliness specified in JIS G0555. Further, B-based inclusions such as Al 2 O 3 form a group in the processing direction and are discontinuously arranged as granular inclusions. The smaller the contents of such A-based inclusions and B-based inclusions, the more effective is to eliminate the anisotropy of the thermal expansion coefficient, and it is more preferable not to contain them. Tables 2 to 6 below show the relationship between the concentration of Cr, Si, W, C and Mn in the segregation part and the thermal expansion coefficient. As shown in Tables 2 to 6 below, the thermal expansion coefficient increases as the W and Mn contents in the segregation portion increase, and the thermal expansion coefficient decreases as the C and Cr contents increase. Therefore, in the hot tool steel of the present invention, the area ratio of the second phase particles having a small coefficient of thermal expansion is increased, and the contents of W and Mn that increase the coefficient of thermal expansion are suppressed, and Cr, C, etc. Only the component that lowers the coefficient of thermal expansion is segregated in a nearly spherical shape and uniformly dispersed. As a result, the coefficient of thermal expansion becomes small and the coefficient of thermal expansion has no anisotropy.
更に、金型のコーナーエッジ部における早期割れを改善するためには、高温強度の向上並びに炭化物及び非金属介在物の微細化が有効である。本発明者等は、耐溶損性及び耐ヒートチェック性については、初期ヒートトラック発生に影響を与えない炭化物及び非金属介在物の粒径範囲があることを見出しており、特願２００２−２８２９８において、耐溶損性及び耐ヒートチェック性に影響与える粒径が１．０μｍを超える炭化物及び非金属介在物の量を少なくして、非削性を改善する効果が大きい粒径が１．０μｍ以下の炭化物及び非金属介在物の量を多くした熱間工具鋼を提案している。また、特願２００２−２８２９８に記載しているように、本発明者等は、粒径が１．０μｍ以下の炭化物及び非金属介在物の面積率を１０．５％以上にし、粒径が１．０μを越える炭化物及び非金属介在物の面積率を０．００４％以下にすることにより、被削性が向上することも見出している。そして、更に鋭意実験研究を行った結果、本発明者等は、炭化物及び非金属介在物等の形状によっては、炭化物及び非金属介在物の長手方向と幅方向と熱膨張率に差が生じて、コーナーＲ部より発生するコーナーエッジ割れが助長することを見出した。熱膨張率が大きく、熱膨張率に異方性があると、金型のコーナーエッジ部に引張応力が集中しやすく、早期に大割れする原因となる。そこで、金型のコーナーエッジ部における早期割れを改善するためには、熱膨張率を低くして、熱膨張率の異方性を低減することが好ましい。 Furthermore, in order to improve early cracking at the corner edge portion of the mold, it is effective to improve the high-temperature strength and refine the carbide and nonmetallic inclusions. The present inventors have found that there is a particle size range of carbides and non-metallic inclusions that do not affect the initial heat track generation with respect to the resistance to melting and heat check, and in Japanese Patent Application No. 2002-28298. The particle size having a large effect of improving the non-machinability by reducing the amount of carbides and non-metallic inclusions having a particle size exceeding 1.0 μm which affects the erosion resistance and heat check resistance is 1.0 μm or less. A hot work tool steel with increased amounts of carbides and non-metallic inclusions is proposed. In addition, as described in Japanese Patent Application No. 2002-28298, the inventors set the area ratio of carbides and non-metallic inclusions having a particle size of 1.0 μm or less to 10.5% or more, and the particle size is 1 It has also been found that the machinability is improved by setting the area ratio of carbides and non-metallic inclusions exceeding 0.0μ to 0.004% or less. As a result of further earnest experimental research, the present inventors have found that, depending on the shape of carbides and non-metallic inclusions, there is a difference in the thermal expansion coefficient between the longitudinal direction and the width direction of the carbides and non-metallic inclusions. It was found that the corner edge cracking generated from the corner R portion is promoted. If the coefficient of thermal expansion is large and the coefficient of thermal expansion is anisotropic, tensile stress tends to concentrate on the corner edge portion of the mold, causing large cracks at an early stage. Therefore, in order to improve early cracking at the corner edge portion of the mold, it is preferable to lower the thermal expansion coefficient and reduce the anisotropy of the thermal expansion coefficient.
更にまた、本発明者等は、Ｃｒ添加量を多くして、Ｎｉ及びＭｏを添加することで焼入れ性が著しく改善することを見出した。しかしながら、これらの元素を多量に添加すると、熱間工具鋼内に偏析が発生しやすくなって粗大な炭化物の析出量が増加するため、靱性が著しく低下すると共に、金型のコーナーエッジ部の早期割れが発生しやすくなる。このような靱性の低下及びコーナーエッジ部の早期割れを助長する偏析部の発生及び粗大な炭化物の析出を制御するためには、ＥＳＲ（Electroslag Remelting：エレクトロスラグリメルティング）法又はＶＡＲ（Vacuum Arc Remelting：真空アーク再溶解）法等の特殊溶解法を適用して、凝固速度を速くすることが有効である。 Furthermore, the present inventors have found that the hardenability is remarkably improved by increasing the Cr addition amount and adding Ni and Mo. However, if these elements are added in a large amount, segregation is likely to occur in the hot tool steel and the amount of coarse carbides precipitated increases, so that the toughness is remarkably lowered and the corner edge portion of the mold is prematurely removed. Cracks are likely to occur. In order to control the occurrence of segregation part and the precipitation of coarse carbides that promote the deterioration of toughness and early cracking of the corner edge part, the ESR (Electroslag Remelting) method or VAR (Vacuum Arc Remelting) method is used. : It is effective to increase the solidification rate by applying a special melting method such as vacuum arc remelting).
但し、凝固速度を速くすると、操業中の凝固範囲、即ち、溶解している液相の体積が少なくなり、更に凝固速度を速めると、マクロ偏析している電極母材部分のみが溶解して凝固するようになり、電極母材の偏析がそのまま鋼材に転写されてしまう。このような鋼材に通常の鍛造法を適用した場合、偏析方向とその垂直方向とでは熱膨張率及び靱性に差が生じるため、ヒートチェック性が悪化する。そこで、本発明の熱間工具鋼においては、ＥＳＲ等の特殊溶解法により均一に偏析を発生させた鋼材を、据え込み鍛造を繰り返し行う等して、その偏析部の形状を球状に近付ける。これにより、従来、機械的性質を劣化させると考えられていた偏析部を積極的に利用することができ、熱膨張率等の特性を著しく改善することができる。 However, if the solidification rate is increased, the solidification range during operation, that is, the volume of the dissolved liquid phase decreases, and if the solidification rate is further increased, only the electrode base material portion that is macrosegregated is dissolved and solidified. As a result, the segregation of the electrode base material is directly transferred to the steel material. When a normal forging method is applied to such a steel material, a difference occurs in the coefficient of thermal expansion and the toughness between the segregation direction and the vertical direction, and therefore the heat check property is deteriorated. Therefore, in the hot tool steel of the present invention, the segregated portion is brought close to a spherical shape by repeatedly performing upset forging on a steel material that has been uniformly segregated by a special melting method such as ESR. Thereby, the segregation part which was conventionally considered to deteriorate the mechanical properties can be positively utilized, and characteristics such as the thermal expansion coefficient can be remarkably improved.
上述のように、本発明の熱間工具鋼は、鍛伸方向に延びやすい硫化物系介在物の量及び大きさを極限まで減じると共に、酸化物系介在物も極小量に減らし、熱膨張の異方性を改善し、Ｍｎ及びＷが偏析することを極力抑え、Ｃ及びＣｒを含む偏析部の形状を溶解方法及び鍛造方法を制限することにより、均一で、且つ球状に近い形状にすることにより、熱膨張率の異方性をなくしたものである。 As described above, the hot work tool steel of the present invention reduces the amount and size of sulfide inclusions that tend to extend in the forging direction to the minimum, and also reduces the oxide inclusions to a minimum amount, thereby reducing thermal expansion. Improve anisotropy, suppress segregation of Mn and W as much as possible, and limit the shape of the segregated part containing C and Cr to a uniform and nearly spherical shape by limiting the melting method and forging method. Thus, the anisotropy of the thermal expansion coefficient is eliminated.
なお、電気炉精錬、炉外精錬及びＥＳＲ等の特殊溶解等を行った後、通常の鍛造加工方法により鋼塊の断面積の（１／４）まで小さく伸ばす（４Ｓ）だけでは、偏析部が長く引き延ばされるだけで、偏析部を球状に近い形状にすることはできない。そこで、本発明の熱間工具鋼を溶解及び造塊する際には、長さ方向に据え込み鍛造を行い、径方向に鍛造する際には偏析をせん断するように加工することが好ましい。これらの工程を繰り返すことにより、偏析形状を制御することができる。また、偏析部を均一分散するためには、消耗電極式再溶解等に使用する電極母材にも上記鍛造法を適用することが有効である。 In addition, after performing special melting, etc., such as electric furnace refining, out-of-furnace refining, and ESR, the segregation part can be formed by simply extending to (1/4) the cross-sectional area of the steel ingot by a normal forging method (4S). The segregation part cannot be made into a shape close to a sphere simply by being elongated for a long time. Therefore, it is preferable to perform upsetting forging in the length direction when melting and ingoting the hot tool steel of the present invention, and to process segregation when forging in the radial direction. By repeating these steps, the segregation shape can be controlled. Further, in order to uniformly disperse the segregated portion, it is effective to apply the forging method to an electrode base material used for consumable electrode type remelting or the like.
以下、本発明の熱間工具鋼の組成限定理由について説明する。 Hereinafter, the reasons for limiting the composition of the hot tool steel of the present invention will be described.
Ｃ：０．３０乃至０．４５質量％
Ｃは熱膨張率を小さくする効果がある炭化物を含む偏析部を形成する主要成分である。また、Ｃは、焼入れ（熱処理）時に基地に固溶して必要な焼入れ硬さを付与し、また焼き戻し時においては特殊炭化物を形成して析出して軟化抵抗及び高温強度を付与すると共に、残留炭化物を形成して高温における耐摩耗性を付与する。更に、焼入れ加熱時の結晶粒の粗大化を防ぐ作用も有する。但し、Ｃ含有量が０．３０質量％未満の場合、上述の添加効果は得られない。一方、Ｃ含有量が０．４５質量％を超えると、炭化物の量が必要以上に増加して、熱間工具鋼として必要な靱性が保持できず、また高温強度の低下も招く。よって、Ｃ含有量は０．３０乃至０．４５質量％とする。
C: 0.30 to 0.45 mass%
C is a main component that forms a segregated portion containing carbides that has the effect of reducing the coefficient of thermal expansion. In addition, C is dissolved in the base at the time of quenching (heat treatment) to give necessary quenching hardness, and at the time of tempering, it forms and deposits special carbide to give softening resistance and high temperature strength, Residual carbides are formed to provide high temperature wear resistance. Furthermore, it has the effect | action which prevents the coarsening of the crystal grain at the time of quenching heating. However, when the C content is less than 0.30% by mass, the above-described addition effect cannot be obtained. On the other hand, when the C content exceeds 0.45% by mass, the amount of carbide increases more than necessary, and the toughness necessary for hot tool steel cannot be maintained, and the high-temperature strength decreases. Therefore, the C content is 0.30 to 0.45 mass%.
Ｓｉ：０．０５乃至０．２５質量％
Ｓｉは一般に、脱酸元素として使用されており、その含有量が０．０５質量％未満ではその効果が得られない。また、Ｓｉは、耐酸化性又は５００乃至６００℃における焼き戻し軟化抵抗を高め、またＡ１変態点を上げる効果があり、その添加量は、目的及び用途により調整することができる。一方、Ｓｉは、偏析を助長する元素であるが、熱膨張率を抑制する効果はなく、Ｓｉ含有量が０．２５質量％を超えると、靱性の低下を招くと共に、熱伝導性が過度に低下する。よって、Ｓｉ含有量は０．０５乃至０．２５質量％とする。
Si: 0.05 to 0.25% by mass
Si is generally used as a deoxidizing element, and if its content is less than 0.05% by mass, the effect cannot be obtained. Further, Si is tempering enhance softening resistance in oxidation resistance or 500 to 600 ° C., also has the effect of increasing the A 1 transformation point, the amount added can be adjusted depending on the purpose and application. On the other hand, Si is an element that promotes segregation, but there is no effect of suppressing the coefficient of thermal expansion, and if the Si content exceeds 0.25 mass%, the toughness is reduced and the thermal conductivity is excessive. descend. Therefore, the Si content is 0.05 to 0.25% by mass.
Ｍｎ：０．５０乃至０．７０質量％
Ｍｎは、基地に固溶して焼入れ性を高める効果が大きいが、その含有量が０．５０質量％未満ではその効果が得られない。一方、Ｍｎ含有量が少ない程、熱膨張率は小さくなる。特に、Ｍｎ含有量が０．７０質量％を超えると、偏析し、熱膨張率を高くすると共に、焼き鈍し硬さが過度に高くなり、被切削性が低下する。また、Ｍｎ含有量が０．７０質量％を超えると、Ａ１変態点が過度に低下する。よって、Ｍｎ含有量は０．５乃至０．７質量％とする。
Mn: 0.50 to 0.70 mass%
Mn has a large effect of improving the hardenability by dissolving in a matrix, but if its content is less than 0.50% by mass, the effect cannot be obtained. On the other hand, the smaller the Mn content, the smaller the coefficient of thermal expansion. In particular, when the Mn content exceeds 0.70% by mass, segregation occurs and the coefficient of thermal expansion is increased, and the annealing and hardness are excessively increased, so that the machinability is lowered. Further, if the Mn content exceeds 0.70 mass%, A 1 transformation point is excessively lowered. Therefore, the Mn content is 0.5 to 0.7% by mass.
Ｃｒ：５．３０乃至５．７５質量％
Ｃｒは熱膨張率を抑制するために必要不可欠な偏析を構成すると共に、応力軟化を抑制する効果がある。また、工具として必要とされる焼入れ性を付与する最も重要な元素である。更に、耐酸化性、耐摩耗性及び高温強度の向上、Ａ１変態点の上昇、残留炭化物を形成することによる焼入れ加熱時の結晶粒粗大化の抑制、焼き戻し時に特殊炭化物を析出することによる昇温時における軟化抵抗の改善等の効果もある。但し、Ｃｒ含有量が５．３０質量％未満では、耐錆び性が劣化して、冷却水等により金型が錆びやすくなる。一方、Ｃｒ含有量が５．７５質量％を超えると、Ｃｒ炭化物を過度に形成するため、高温強度が低下する。よって、Ｃｒ含有量は５．３０乃至５．７５質量％とする。
Cr: 5.30 to 5.75% by mass
Cr constitutes segregation essential for suppressing the coefficient of thermal expansion and has the effect of suppressing stress softening. Moreover, it is the most important element which imparts the hardenability required as a tool. Furthermore, by oxidation resistance, improvement of wear resistance and high temperature strength, increase of A 1 transformation point, the suppression of coarsening of crystal grains during heating for quenching due to the formation of the residual carbides, to precipitate special carbides during tempering There are also effects such as improvement of softening resistance at the time of temperature rise. However, when the Cr content is less than 5.30% by mass, the rust resistance is deteriorated, and the mold is easily rusted by cooling water or the like. On the other hand, if the Cr content exceeds 5.75% by mass, Cr carbide is excessively formed, so that the high-temperature strength decreases. Therefore, the Cr content is set to 5.30 to 5.75% by mass.
Ｍｏ：３．００乃至３．５０質量％
Ｍｏは応力軟化を抑制する効果がある。また、特殊炭化物を形成する元素であり、残留炭化物を形成して、加熱時の組織粗大化を防止する効果もある。更に、焼き戻し時に微細な特殊炭化物を析出するため、焼き戻し軟化抵抗及び高温強度を向上させる最も重要な添加元素である。更にまた、Ａ１変態点を高める効果もある。但し、Ｍｏ含有量が３．００質量％未満では、前述の効果が得られず、Ｍｏ含有量が３．５０質量％を超えると、粗大な炭化物を形成するため、靱性の過度の低下を招く。よって、Ｍｏ含有量は３．００乃至３．５０質量％とする。
Mo: 3.00 to 3.50 mass%
Mo has an effect of suppressing stress softening. Moreover, it is an element that forms a special carbide, and also has the effect of forming a residual carbide and preventing the coarsening of the structure during heating. Further, it is the most important additive element for improving temper softening resistance and high-temperature strength because fine special carbides precipitate during tempering. Furthermore, there is also the effect of increasing the A 1 transformation point. However, when the Mo content is less than 3.00% by mass, the above-described effects cannot be obtained. When the Mo content exceeds 3.50% by mass, coarse carbides are formed, resulting in an excessive decrease in toughness. . Therefore, the Mo content is set to 3.00 to 3.50 mass%.
Ｖ：０．６５乃至０．９５質量％
Ｖは強力な炭化物形成元素であり、残留炭化物を形成して結晶を粒微細化する効果が大きく、高温における耐摩耗性を向上させる効果もある。また、Ｖは、偏析を助長する元素ではあるが、熱膨張率を低くする効果はない。Ｖ含有量が０．６５質量％未満では、耐高温軟化性が低下し、ダイカスト等の高温金属に接触した際に、金型が軟化してしまう。一方、Ｖ含有量が０．９５質量％を超えると、ＶＣ等の炭化物が多量に生成するため靱性が低下する。よって、Ｖ含有量は０．６５乃至０．９５質量％とする。
V: 0.65 to 0.95 mass%
V is a strong carbide-forming element, has a great effect of forming residual carbides to refine crystals and has an effect of improving wear resistance at high temperatures. V is an element that promotes segregation, but has no effect of lowering the coefficient of thermal expansion. When the V content is less than 0.65% by mass, the high-temperature softening resistance decreases, and the mold softens when it comes into contact with a high-temperature metal such as die casting. On the other hand, if the V content exceeds 0.95% by mass, a large amount of carbide such as VC is produced, so that the toughness is lowered. Therefore, the V content is set to 0.65 to 0.95 mass%.
Ｎｉ：０．４５乃至０．７５質量％
Ｎｉは基地に固溶して靱性を高める効果がある。また、焼入れ性を高めるために目的及び用途により添加される。Ｎｉも前述のＶと同様に、偏析を助長する元素ではあるが、熱膨張率を低くする効果はない。Ｎｉ含有量が０．４５質量％未満では、耐錆び性が低下して、金型内の冷却孔が冷却水等により錆びやすくなるとなり、Ｎｉ含有量が０．７５質量％を超えると、焼き鈍し硬さを過度に高くし、被切削性が低下すると共に、Ａ１変態点が過度に低下する。よって、Ｎｉ含有量は０．４５乃至０．７５質量％とする。
Ni: 0.45 to 0.75% by mass
Ni has the effect of increasing the toughness by solid solution in the base. Further, it is added depending on the purpose and application in order to enhance the hardenability. Ni, like V described above, is an element that promotes segregation, but has no effect of lowering the coefficient of thermal expansion. When the Ni content is less than 0.45% by mass, the rust resistance is lowered, and the cooling holes in the mold are easily rusted by cooling water or the like. When the Ni content exceeds 0.75% by mass, annealing is performed. the hardness was excessively high, together with the cutting resistance decreases, a 1 transformation point is excessively lowered. Therefore, the Ni content is 0.45 to 0.75% by mass.
Ｃｏ：０．４５乃至０．７５質量％
Ｃｏは基地に固溶して高温強度を高める作用がある。また、Ｃｏを添加することにより、焼入れ加熱時におけるオーステナイト中への炭化物の固溶限の向上、焼き戻し時における特殊炭化物の析出量の増加、昇温時における析出炭化物の凝集抵抗の向上等の効果が得られ、高温強度特性を改善することができる。更に、昇温時に、表面に緻密な酸化皮膜を形成するため、高温でも耐摩耗性及び耐焼付き性が向上する。なお、Ｃｏは、偏析を助長する元素であるが、熱膨張率を低下させる効果はない。Ｃｏ含有量が０．４５質量％未満では、前述のＮｉと同様に、耐錆び性が低下して金型内の冷却孔が錆びやすくなるとなる。一方、Ｃｏ含有量が０．７５質量％を超えると、靱性が低下する。よって、Ｃｏ含有量は０．４５乃至０．７５質量％とする。
Co: 0.45 to 0.75% by mass
Co has the effect of increasing the high temperature strength by dissolving in the base. In addition, by adding Co, the solid solubility limit of carbides in austenite during quenching heating, the amount of precipitation of special carbides during tempering, the improvement of aggregation resistance of precipitated carbides during temperature rise, etc. An effect is acquired and a high temperature strength characteristic can be improved. Furthermore, since a dense oxide film is formed on the surface when the temperature is raised, the wear resistance and seizure resistance are improved even at high temperatures. Note that Co is an element that promotes segregation, but has no effect of reducing the coefficient of thermal expansion. When the Co content is less than 0.45% by mass, the rust resistance is lowered and the cooling holes in the mold are easily rusted as in the case of Ni described above. On the other hand, if the Co content exceeds 0.75% by mass, the toughness decreases. Therefore, the Co content is 0.45 to 0.75% by mass.
Ｓ：０．００５質量％以下、Ｐ：０．０１０質量％以下
Ｓ及びＰは、偏析を助長する元素であるが、偏析部が熱膨張率を低下させる効果はない。また、ＳはＭｎと化合して熱膨張率に異方性を生じさせるＭｎＳを生成するため、Ｓ含有量は０．００５質量％以下に規制する。なお、Ｓは含有していないことがより好ましい。更に、Ｐは靱性を低下させるため、Ｐ含有量は０．０１０％以下に規制する。
S: 0.005% by mass or less, P: 0.010% by mass or less S and P are elements that promote segregation, but the segregation part does not have an effect of reducing the coefficient of thermal expansion. Further, since S combines with Mn to generate MnS that causes anisotropy in the thermal expansion coefficient, the S content is restricted to 0.005 mass% or less. In addition, it is more preferable that S is not contained. Furthermore, since P reduces toughness, the P content is restricted to 0.010% or less.
Ｗ：０．００５０質量％以下
Ｗは熱膨張率を大きくすると共に偏析の発生を助長する。しかしながら、Ｗは原料に微量に含まれているため、不純物として添加されてしまう。そこで、本発明の熱間工具鋼においては、Ｗ含有量を０．００５０質量％以下に規制する。なお、Ｗは含有していないことがより好ましい。
W: 0.0050 mass% or less W increases the coefficient of thermal expansion and promotes the occurrence of segregation. However, since W is contained in a trace amount in the raw material, it is added as an impurity. Then, in the hot tool steel of this invention, W content is controlled to 0.0050 mass% or less. In addition, it is more preferable that W is not contained.
炭化物及び非金属介在物
一般に、炭化物及び非金属介在物の含有量が増すと、機械的特性が劣化する。しかしながら、その大きさ及び形状を制御することにより、熱膨張率を低下させる効果が得られる。例えば、Ａｌ２Ｏ３、ＳｉＯ２及びＭｎＯ等の非金属介在物、並びにＭｏ２Ｃ、ＶＣ及びＮｂＣ等の炭化物のように、熱膨張係数が低い化合物を積極的に添加することにより、熱膨張率を低下させることができる。但し、焼入れした場合は、炭化物を形成している元素が固溶した状態で固化するため、炭化物量は変化する。一方、焼き鈍しした場合には、一旦固溶した元素が再度炭化物を形成するため、１μｍ以上の炭化物量は変化せず、１μｍ以下の炭化物量が半分程度に減少する。そこで、本発明においては、焼き鈍ししたときに、粒径が１μｍを超える炭化物及び非金属介在物の総面積率を０．００４％以下とし、粒径が１μｍ以下の炭化物及び非金属介在物の総面積率を１５．０％以上とする。焼き鈍し材において、粒径が１μｍを超える粗大な炭化物及び非金属介在物の総面積率が０．００４％を超えると、靱性が著しく低下する。一方、粒径が１μｍ以下の炭化物及び非金属介在物であれば、靱性は低下しない。但し、粒径が１μｍ以下の炭化物及び非金属介在物の総面積率が１５．０％未満であると、熱膨張率を低下させる効果が得られない。なお、焼き入れ材においては、粒径が１μｍ以下の炭化物及び非金属介在物の総面積率が１０．０％以上であることが好ましい。
Carbides and non-metallic inclusions In general, mechanical properties deteriorate as the content of carbides and non-metallic inclusions increases. However, by controlling the size and shape, the effect of reducing the coefficient of thermal expansion can be obtained. For example, non-metallic inclusions such as Al 2 O 3 , SiO 2, and MnO, and carbides such as Mo 2 C, VC, and NbC can be added to positively add a compound having a low coefficient of thermal expansion. The rate can be reduced. However, when quenched, the amount of carbide changes because the elements forming the carbide are solidified in a solid solution state. On the other hand, when annealing is performed, the element once solid-dissolved forms carbide again, so that the amount of carbide of 1 μm or more does not change, and the amount of carbide of 1 μm or less decreases to about half. Therefore, in the present invention, when annealed, the total area ratio of carbides and non-metallic inclusions having a particle size exceeding 1 μm is 0.004% or less, and the total of carbides and non-metallic inclusions having a particle size of 1 μm or less. The area ratio is 15.0% or more. In the annealed material, if the total area ratio of coarse carbides and non-metallic inclusions having a particle size exceeding 1 μm exceeds 0.004%, the toughness is remarkably reduced. On the other hand, if the carbide and non-metallic inclusions have a particle size of 1 μm or less, the toughness is not lowered. However, if the total area ratio of carbides and non-metallic inclusions having a particle size of 1 μm or less is less than 15.0%, the effect of reducing the thermal expansion coefficient cannot be obtained. In the quenching material, the total area ratio of carbides and non-metallic inclusions having a particle size of 1 μm or less is preferably 10.0% or more.
また、鍛造加工により変形して、熱膨張率に異方性を生じさせるＭｎＳ等の介在物の含有量を低減することにより、熱膨張率に異方性がない熱間工具鋼を提供することができる。そこで、本発明においては、炭化物及び非金属介在物のアスペクト比を１．０乃至１．３の範囲にする。炭化物及び非金属介在物のアスペクト比が１．０の場合は、これらの形状が球状であるため、最も理想的な形状である。なお、アスペクト比が１．３を超えると熱膨張率に異方性が生じる。更に、本発明においては、ＪＩＳＧ０５５５に規定されているＡ系介在物の清浄度ｄＡ６０×４００を０．００５％以下、Ｂ系介在物の清浄度ｄＢ６０×４００を０．００５％以下にする。これにより、熱膨張率が等方性である熱間工具鋼を得ることができる。 Also, to provide hot tool steel having no anisotropy in the thermal expansion coefficient by reducing the content of inclusions such as MnS that are deformed by forging and cause anisotropy in the thermal expansion coefficient. Can do. Therefore, in the present invention, the aspect ratio of carbides and non-metallic inclusions is set in the range of 1.0 to 1.3. When the aspect ratio of carbides and non-metallic inclusions is 1.0, these shapes are spherical, which is the most ideal shape. When the aspect ratio exceeds 1.3, anisotropy occurs in the thermal expansion coefficient. Furthermore, in the present invention, the cleanness dA60 × 400 of the A-based inclusions specified in JISG0555 is 0.005% or less, and the cleanness dB60 × 400 of the B-based inclusions is 0.005% or less. Thereby, the hot tool steel with an isotropic thermal expansion coefficient can be obtained.
また、Ｎは基地又は炭化物中に固溶して結晶粒を微細化し、靱性を高める効果がある。更に、オーステナイトフォーマーとして作用するため、Ｃ含有量が少ない場合においても、焼入れ加熱時にフェライトが残存することを防ぎ、靱性に優れた合金を得ることができる。Ｎは上述のような効果が必要な場合に、目的及び用途に応じて適宜添加することができるが、Ｃｒ等の熱間工具鋼の合金組成の範囲内で添加可能な限界量が存在するため、Ｎ含有量は０．２０質量％以下にすることが好ましい。 Further, N has an effect of increasing the toughness by solid solution in the matrix or carbide to refine the crystal grains. Furthermore, since it functions as an austenite former, even when the C content is small, it is possible to prevent the ferrite from remaining during quenching heating and to obtain an alloy having excellent toughness. N can be appropriately added depending on the purpose and application when the above-described effects are required, but there is a limit amount that can be added within the range of the alloy composition of hot tool steel such as Cr. The N content is preferably 0.20% by mass or less.
更に、Ｎｉ及びＴｉは強力な炭化物形成元素であり、結晶粒を微細化し、焼き戻し時において凝集抵抗が特に大きい微細炭化物を析出するため、６５０℃以上の高温域における軟化抵抗及び高温強度を高める効果がある。但し、これらの総含有量が０．５質量％を超えると、固溶しにくい粗大な炭化物を形成して靱性が低下する。そこで、Ｎｉ及びＴｉの総含有量は０．５質量％以下にすることが好ましい。 Furthermore, Ni and Ti are strong carbide-forming elements, which refine crystal grains and precipitate fine carbides with particularly high agglomeration resistance during tempering, thus increasing softening resistance and high-temperature strength at high temperatures of 650 ° C. or higher. effective. However, if the total content thereof exceeds 0.5% by mass, coarse carbides that are difficult to dissolve are formed and the toughness is lowered. Therefore, the total content of Ni and Ti is preferably 0.5% by mass or less.
更にまた、Ｃｕ、Ｂ、Ａｌ及びＢｅは、金属間化合物を形成する。これらの金属間化合物は、熱間工具鋼内で析出するため、昇温時における軟化抵抗及び高温強度を改善する効果がある。但し、これらの含有量が、総量で３．００質量％を超えると靱性が低下する。よって、Ｃｕ、Ｂ、Ａｌ及びＢｅの総含有量は、３．００質量％以下にすることが好ましい。 Furthermore, Cu, B, Al and Be form an intermetallic compound. Since these intermetallic compounds precipitate in the hot tool steel, they have the effect of improving the softening resistance and the high temperature strength at the time of temperature rise. However, when these contents exceed 3.00 mass% in total, toughness will fall. Therefore, the total content of Cu, B, Al and Be is preferably set to 3.00% by mass or less.
一般に、鋼材内に偏析が生じていると靱性が低下するため、偏析部は少ない方が好ましいが、本発明の熱間工具鋼においては、熱膨張率等を低下させるため、あえて偏析部を残している。そして、本発明においては、Ｗ及びＭｎのように、熱間工具鋼の特性を劣化させる偏析成分については、偏析部における濃度と非偏析部における濃度との比（＝偏析部の濃度／非偏析部の濃度）を１．２以下とし、Ｃ及びＣｒのように、熱膨張率低減に効果がある成分については、偏析部における濃度と非偏析部における濃度との比（＝偏析部の濃度／非偏析部の濃度）を１．４乃至１．９とすることが好ましい。偏析部におけるＷ及びＭｎの濃度と非偏析部におけるＷ及びＭｎの濃度との比が、１．２を超えると、上記表６に示すように、偏析部に含まれるＭｎにより熱膨張率が大きくなり、熱膨張率に異方性が生じる。一方、上記表２に示すように、Ｃｒの偏析は、熱膨張率を低下させる効果がある。但し、偏析部におけるＣ及びＣｒの濃度と非偏析部におけるＣ及びＣｒの濃度との比が、１．４未満では熱膨張率が低下せず、１．９を超えると多量のＣｒ系炭化物が偏析部に生成するため、熱膨張率の差が大きくなると共に靱性が低下する。 Generally, when segregation occurs in the steel material, the toughness is reduced, so it is preferable that the number of segregation parts is small.However, in the hot tool steel of the present invention, the segregation part is left unintentionally in order to reduce the coefficient of thermal expansion. ing. In the present invention, the segregation component such as W and Mn, which deteriorates the properties of the hot tool steel, is a ratio between the concentration in the segregation part and the concentration in the non-segregation part (= concentration in the segregation part / non-segregation). The concentration of the segregation part and the concentration in the non-segregation part (= concentration of the segregation part / The concentration of the non-segregation part) is preferably 1.4 to 1.9. When the ratio of the concentration of W and Mn in the segregation part and the concentration of W and Mn in the non-segregation part exceeds 1.2, as shown in Table 6 above, the thermal expansion coefficient is large due to Mn contained in the segregation part. Thus, anisotropy occurs in the coefficient of thermal expansion. On the other hand, as shown in Table 2 above, the segregation of Cr has the effect of reducing the coefficient of thermal expansion. However, if the ratio of the concentration of C and Cr in the segregation part and the concentration of C and Cr in the non-segregation part is less than 1.4, the thermal expansion coefficient does not decrease, and if it exceeds 1.9, a large amount of Cr-based carbides are present. Since it produces | generates in a segregation part, toughness falls while the difference of a thermal expansion coefficient becomes large.
このように、偏析部も前述の炭化物及び非金属介在物と同様に熱膨張率の異方性に関係する。そこで、熱膨張率が小さい偏析部を有効に利用するためには、偏析部と非偏析部との面積比（＝偏析部の面積／比偏析部の面積）を１．３以上とすることが好ましい。また、偏析部のアスペクト比を１．０乃至１．３とすることにより、偏析部の熱膨張率を等方性にして、熱膨張率の異方性をなくすことができる。 As described above, the segregation part is related to the anisotropy of the thermal expansion coefficient as in the case of the above-described carbide and nonmetallic inclusion. Therefore, in order to effectively use the segregation part having a small coefficient of thermal expansion, the area ratio between the segregation part and the non-segregation part (= area of the segregation part / area of the segregation part) should be 1.3 or more. preferable. Moreover, by setting the aspect ratio of the segregation part to 1.0 to 1.3, the thermal expansion coefficient of the segregation part is made isotropic, and anisotropy of the thermal expansion coefficient can be eliminated.
また、本発明の熱間工具鋼においては、鍛伸方向の熱膨張率（Ｌ方向熱膨張率）と鍛伸方向に垂直な方向の熱膨張率（Ｔ方向熱膨張率）の比（＝Ｔ方向熱膨張率／Ｌ方向熱膨張率）が１．０００乃至１．０１５であることが好ましい。これにより、等方熱膨張性にすることができるため、金型のコーナーエッジ部の早期割れを抑制することができる。 In the hot work tool steel of the present invention, the ratio of the thermal expansion coefficient in the forging direction (L direction thermal expansion coefficient) and the thermal expansion coefficient in the direction perpendicular to the forging direction (T direction thermal expansion coefficient) (= T (Directional thermal expansion coefficient / L thermal expansion coefficient) is preferably 1.000 to 1.015. Thereby, since it can be made isotropic thermal expansibility, the early crack of the corner edge part of a metal mold | die can be suppressed.
以下、本発明の実施例の効果について、本発明の範囲から外れる比較例と比較して説明する。本発明の実施例及び比較例として、下記表７に示す組成の熱間工具鋼を、４０ｔ電気炉−炉外精錬にて３乃至１８ｔの鋼塊とし、その鋼塊を消耗電極として再溶解した。その後、１２３０℃で加熱して、２５００ｔ鋳造プレス機により、鋼塊の高さが（１／２）又は（１／３）になるまで鋼塊の長さ方向へ据え込み鍛造した。その際の条件は、送り量と厚さとの比（＝送り量／厚さ）を０．１乃至０．２、圧下率を１乃至３％とした。この据え込み鍛造を繰り返し行うことにより、偏析部をせん断して、偏析部の形状を種々に変化させた。その後、８３０℃で焼き鈍し焼鈍して、３００乃至５００ｍｍ角の試料を作製した。各試料の鍛造条件、炭化物及び非金属介在物の面積率、非金属介在物の清浄度、非金属介在物のアスペクト比を下記表８に、偏析部と非偏析部との濃度比、偏析部のアスペクト比及び熱膨張率を下記表９に示す。 Hereinafter, the effect of the Example of this invention is demonstrated compared with the comparative example which remove | deviates from the scope of the present invention. As examples and comparative examples of the present invention, hot tool steel having the composition shown in Table 7 below was made into a steel ingot of 3 to 18 t by 40 t electric furnace-external refining, and the steel ingot was remelted as a consumable electrode. . Then, it heated at 1230 degreeC and upset and forged in the length direction of the steel ingot by the 2500t casting press until the height of the steel ingot became (1/2) or (1/3). The conditions at that time were such that the ratio between the feed amount and the thickness (= feed amount / thickness) was 0.1 to 0.2, and the rolling reduction was 1 to 3%. By repeatedly performing this upsetting forging, the segregation part was sheared and the shape of the segregation part was changed variously. Then, it annealed at 830 degreeC and annealed and produced the 300-500 mm square sample. The forging conditions of each sample, the area ratio of carbide and non-metallic inclusions, the cleanliness of non-metallic inclusions, and the aspect ratio of non-metallic inclusions are shown in Table 8 below. The concentration ratio between the segregated portion and the non-segregated portion, the segregated portion Table 9 shows the aspect ratio and thermal expansion coefficient.
なお、各試料の組織観察は、その横断面における中心部の長手方向で実施した。具体的には、粒径が１μｍ以下の炭化物及び非金属介在物の面積率の測定は、先ず、焼き鈍し材を研磨した後、ピクリン酸＋３％硝酸溶液に浸漬して、金属組織を現出させた。そして、これらの金属組織をＳＥＭ（Scanning Electron Microscope：走査型電子顕微鏡）により、４０００倍で写真撮影した。このＳＥＭ写真を、画像解析して炭化物及び非金属介在物の面積率及び平均粒径を求めた。一方、粒径が１μｍを超える炭化物及び非金属介在物の面積率の測定は、焼き鈍し材を研磨した後、シュウ酸で腐食させて金属組織を現出させ、この金属組織をＳＥＭにより１０００倍で写真撮影し、１ｍｍ２の視野内の画像解析を実施することにより測定した。 In addition, the structure observation of each sample was implemented in the longitudinal direction of the center part in the cross section. Specifically, the area ratio of carbides and non-metallic inclusions having a particle size of 1 μm or less is measured by first polishing the annealed material and then immersing it in picric acid + 3% nitric acid solution to reveal the metal structure. It was. These metal structures were photographed at a magnification of 4000 using a scanning electron microscope (SEM). This SEM photograph was subjected to image analysis to determine the area ratio and average particle size of carbides and non-metallic inclusions. On the other hand, the area ratio of carbides and non-metallic inclusions having a particle size exceeding 1 μm is measured by polishing the annealed material and then corroding with oxalic acid to reveal the metal structure. Photographs were taken and measured by performing image analysis within a 1 mm 2 field of view.
また、非金属介在物の清浄度は、ＪＩＳ Ｇ０５５５に規定されている方法により求めた。なお、本実施例及び比較例の熱間工具鋼においては、全ての試料において、Ａ系介在物の清浄度ｄＡが０．００５％以下で、Ｂ系介在物の清浄度ｄＢが０．００５％以下であった。 Further, the cleanliness of the nonmetallic inclusions was determined by the method defined in JIS G0555. In the hot working tool steels of this example and the comparative example, the cleanness dA of the A-based inclusions is 0.005% or less and the cleanliness dB of the B-based inclusions is 0.005% in all samples. It was the following.
更に、清浄度を測定した試験片中の炭化物及び非金属介在物の最大長さを、この最大長さに対して垂直な幅で割った値のうち、最大値から１０点の平均値をとり、これを炭化物及び非金属介在物のアスペクト比とした。なお、本実施例の熱間工具鋼における炭化物及び非金属介在物のアスペクト比は、１．０乃至１．３の範囲内であった。 Furthermore, among the values obtained by dividing the maximum lengths of carbides and non-metallic inclusions in the test piece whose cleanliness was measured by the width perpendicular to the maximum length, an average value of 10 points from the maximum value was taken. This was defined as the aspect ratio of carbides and non-metallic inclusions. In addition, the aspect ratio of the carbide | carbonized_material and nonmetallic inclusion in the hot tool steel of a present Example was in the range of 1.0 thru | or 1.3.
偏析部及び非偏析部におけるＷ及びＭｏ並びにＣ及びＣｒの濃度の測定は、Ｘ線マイクロアナライザにて、ビーム径を３μｍに調整し、各元素について、３０ｍｍの長さを測定した。このとき、測定領域中に偏析部が１０乃至３０個存在するようにするため、その測定領域内における最高濃度部から１０点測定値を抽出し、これを平均化して偏析部の濃度とした。また、最低濃度部から１０点測定値を抽出し、これを平均化して非偏析部の濃度とした。そして、最高濃度部の濃度（ＣＰＳ：Count Per Second）を最低濃度部の濃度（ＣＰＳ）で除して、偏析部と非偏析部との濃度比を求めた。 In the segregation part and the non-segregation part, the W, Mo, C, and Cr concentrations were measured by adjusting the beam diameter to 3 μm with an X-ray microanalyzer and measuring the length of 30 mm for each element. At this time, in order to make 10 to 30 segregation portions exist in the measurement region, 10-point measurement values were extracted from the highest concentration portion in the measurement region and averaged to obtain the concentration of the segregation portion. Further, 10-point measurement values were extracted from the lowest concentration part, and averaged to obtain the concentration of the non-segregated part. And the density | concentration ratio of a segregation part and a non-segregation part was calculated | required by dividing | segmenting the density | concentration (CPS: Count Per Second) of the highest density part by the density | concentration (CPS) of the lowest density part.
偏析部と非偏析部との面積比は、縦３０ｍｍ、横３０ｍｍ、高さ５０ｍｍの鋼材を、１０３０℃で３０分間保持した後油冷し、長手方向におけるミクロ組織をナイタール腐食液（アルコール＋３％硝酸溶液）で腐食させ、光学顕微鏡により倍率を５０倍で撮影した写真の色の濃い部分の面積を白い部分の面積で割った値とした。 The area ratio between the segregation part and the non-segregation part is as follows. A steel material having a length of 30 mm, a width of 30 mm, and a height of 50 mm is held at 1030 ° C. for 30 minutes and then oil-cooled. Nitric acid solution) was corroded, and the area of the dark portion of the photograph taken with an optical microscope at a magnification of 50 was divided by the area of the white portion.
偏析部のアスペクト比の測定は、先ず、試料の中央部から３０ｍｍ角の試験片を採取し、この試験片をナイタール腐食液（アルコール＋３％硝酸）で腐食させ、偏析部を現出させた。そして、試験片中のミクロ組織（１ｍｍ×１ｍｍの視野面積）中における、各偏析部の最大長さを各偏析部の中心部の幅で割った値のうち、最大値から１０点の平均値をとり、これを偏析部のアスペクト比とした。 In measuring the aspect ratio of the segregation part, first, a 30 mm square test piece was collected from the center of the sample, and this test piece was corroded with a nital corrosive solution (alcohol + 3% nitric acid) to reveal the segregation part. And among the values obtained by dividing the maximum length of each segregation part by the width of the center part of each segregation part in the microstructure (1 mm × 1 mm viewing area) in the test piece, an average value of 10 points from the maximum value This was taken as the aspect ratio of the segregation part.
熱膨張率の測定は、試料を９８０℃乃至１０８０℃で３０分加熱した後に焼入れをし、５００乃至６７０℃に２時間加熱して焼き戻しし、この焼き戻し工程を２回繰り返すことにより、硬さを４５±１ＨＲＣに調整した後、電気炉で３０℃（加熱開始温度：Ｔ１）から６００℃（加熱終了温度：Ｔ２）まで加熱した。そして、加熱前の試料寸法をＬ１、加熱後の試験片寸法をＬ２として、下記数式１から熱膨張率αを算出した。 The coefficient of thermal expansion was measured by heating the sample at 980 ° C. to 1080 ° C. for 30 minutes and then quenching, heating to 500 to 670 ° C. for 2 hours, tempering, and repeating this tempering process twice. After adjusting the thickness to 45 ± 1 HRC, heating was performed from 30 ° C. (heating start temperature: T 1 ) to 600 ° C. (heating end temperature: T 2 ) in an electric furnace. Then, the sample dimensions L 1 before heating, the specimen dimensions after heating as L 2, was calculated α thermal expansion coefficient from the following equation 1.
次に、本実施例及び比較例の熱間工具鋼のコーナー割れ寿命を評価するため、ヒートチェック試験を実施した。先ず、直径が４５ｍｍ、長さが６０ｍｍの試料を、前述の熱膨張率の測定と同様に、９８０℃乃至１０８０℃に３０分加熱した後に焼入れをし、５００乃至６７０℃に２時間加熱して焼き戻しし、この焼き戻し工程を２回繰り返して、硬さを４５±１ＨＲＣに調整し、更にその長さ方向に、コーナー部の形状が１Ｒで長さが０．２５ｍｍの溝を形成した試験片を作製した。この試験片を、高周波誘導加熱法にて加熱し、表面温度が５００℃に達したときに水をかけて１００℃まで冷却した。この加熱及び冷却工程を繰り返し、５０回毎に割れ（幅４０μｍ程度）を確認し、目視で割れが見えたときの試験回数をその試料の寿命とした。 Next, a heat check test was carried out in order to evaluate the corner crack life of the hot work tool steels of this example and the comparative example. First, a sample having a diameter of 45 mm and a length of 60 mm was heated to 980 ° C. to 1080 ° C. for 30 minutes and then quenched, and heated to 500 to 670 ° C. for 2 hours, as in the measurement of the coefficient of thermal expansion described above. Tempering, this tempering process was repeated twice, the hardness was adjusted to 45 ± 1 HRC, and a groove with a corner shape of 1R and a length of 0.25 mm was formed in the length direction. A piece was made. This test piece was heated by a high frequency induction heating method, and when the surface temperature reached 500 ° C., it was cooled to 100 ° C. with water. This heating and cooling process was repeated, and cracks (about 40 μm wide) were confirmed every 50 times, and the number of tests when the cracks were visually observed was regarded as the life of the sample.
なお、各試料片に溝を形成したのは、実際の金型のコーナー部を再現するためである。図１は横軸に溝部のＲの度合いをとり、縦軸にコーナ割れ寿命をとって、試験片の溝形状と耐コーナー割れ性との関係を示すグラフ図である。ＳＫＤ６１−１（従来品）、比較例２−２及び実施例２−１にＲが異なる溝を形成した試験片を、前述の方法でヒートチェック試験を行ったところ、図１に示すように、溝部のＲが小さくなるほど寿命が短くなった。また、比較例２−２に１Ｒの溝が形成された試験片は、ＳＫＤ６１−１に１Ｒの溝が形成された試験片と同等の寿命であったが、溝が形成されていない（（１／Ｒ）＝０）比較例２−２の試験片では、溝が形成されていないＳＫＤ６１−１の試験片に比べてコーナー割れ寿命が向上していた。一方、実施例２−１の試験片は、溝形状にかかわらずＳＫＤ６１−１よりもコーナー割れ寿命が優れていた。このように、溝を形成していない試験片でヒートチェック性試験を行うと、組成を多少変更しただけでもコーナー割れ寿命が向上し、実際に金型として使用した場合の結果とは異なることがある。そこで、本実施例においては、試験条件をより厳しくするため、１Ｒの溝を形成した試験片を使用してヒートチェック性試験を行った。その結果を上記表９に示す。 The reason why the grooves are formed in each sample piece is to reproduce the corner portion of the actual mold. FIG. 1 is a graph showing the relationship between the groove shape of the test piece and the corner crack resistance, with the horizontal axis representing the degree of R of the groove and the vertical axis representing the corner crack life. When a heat check test was performed on the test pieces in which grooves different in R were formed in SKD61-1 (conventional product), Comparative Example 2-2 and Example 2-1, as shown in FIG. The service life was shortened as R of the groove portion decreased. Further, the test piece in which the 1R groove was formed in Comparative Example 2-2 had the same life as the test piece in which the 1R groove was formed in SKD61-1, but the groove was not formed ((1 / R) = 0) In the test piece of Comparative Example 2-2, the corner crack life was improved as compared with the test piece of SKD61-1 in which no groove was formed. On the other hand, the test piece of Example 2-1 had a better corner crack life than SKD61-1, regardless of the groove shape. In this way, when the heat check property test is performed with a test piece having no groove formed, the corner crack life is improved even if the composition is slightly changed, which may differ from the result when actually used as a mold. is there. Therefore, in this example, in order to make the test conditions stricter, a heat check test was performed using a test piece in which a 1R groove was formed. The results are shown in Table 9 above.
上記表７乃至９に示すように、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｃｒ、Ｍｏ、Ｖ、Ｎｉ又はＣｏの含有量、金属炭化物及び非金属介在物の面積率、非金属介在物の清浄度及び／又は非金属介在物のアスペクト比が本発明の範囲から外れる比較例１−１乃至比較例２−２の試験片は、熱膨張率が高く、コーナー割れ寿命も８００回以下であり、従来品であるＳＫＤ６１−１、ＳＫＤ６１−２と同等以下であった。一方、本発明の範囲内である実施例１−１乃至実施例３−２の試料は、熱膨張率が従来品であるＳＫＤ６１−１、ＳＫＤ６１−２より低く、コーナー割れ寿命も２０００回以上と、優れた特性を示した。更に、Ｌ方向熱膨張率とＷ方向の熱膨張率との比が０．９８５乃至１．０１５であり、従来品に比べて熱膨張率の異方性が大幅に改善されていた。特に、Ｌ方向熱膨張率とＷ方向の熱膨張率との比が１．０００乃至１．０１５の範囲内である実施例２−１及び実施例２−２の試験片は、コーナー割れ寿命が優れていた。 As shown in Tables 7 to 9 above, the content of C, Si, Mn, P, S, Cr, Mo, V, Ni or Co, the area ratio of metal carbide and nonmetal inclusions, and cleanness of nonmetal inclusions The test pieces of Comparative Examples 1-1 to 2-2, in which the degree and / or the aspect ratio of the nonmetallic inclusions are out of the scope of the present invention, have a high coefficient of thermal expansion and a corner crack life of 800 times or less, It was equal to or less than that of the conventional products SKD61-1 and SKD61-2. On the other hand, the samples of Examples 1-1 to 3-2, which are within the scope of the present invention, have a lower coefficient of thermal expansion than conventional products SKD61-1, SKD61-2, and the corner crack life is 2000 times or more. Showed excellent properties. Furthermore, the ratio of the thermal expansion coefficient in the L direction to the thermal expansion coefficient in the W direction was 0.985 to 1.015, and the anisotropy of the thermal expansion coefficient was greatly improved as compared with the conventional product. In particular, the test pieces of Example 2-1 and Example 2-2 in which the ratio of the thermal expansion coefficient in the L direction and the thermal expansion coefficient in the W direction is in the range of 1.000 to 1.015 have a corner crack life. It was excellent.
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| JP2008223122A (en) * | 2007-03-15 | 2008-09-25 | Fuji Wpc:Kk | Method for strengthening alloy steel for hot-working die, and alloy steel of hot-working die for restraining generation of heat-fatigue crack with this method |
| EP2055798A1 (en) | 2007-10-31 | 2009-05-06 | Daido Tokushuko Kabushiki Kaisha | Tool steel and manufacturing method thereof |
| WO2009116371A1 (en) | 2008-03-19 | 2009-09-24 | コニカミノルタオプト株式会社 | Method for producing wafer lens |
| WO2009116448A1 (en) | 2008-03-19 | 2009-09-24 | コニカミノルタオプト株式会社 | Method for producing molded body or wafer lens |
| WO2010035540A1 (en) | 2008-09-25 | 2010-04-01 | コニカミノルタオプト株式会社 | Apparatus and method for manufacturing wafer lens |
| WO2010137368A1 (en) | 2009-05-29 | 2010-12-02 | コニカミノルタオプト株式会社 | Method for producing wafer lens, and method and apparatus for producing wafer lens laminate |
| CN104280413A (en) * | 2014-10-16 | 2015-01-14 | 江苏省沙钢钢铁研究院有限公司 | Method for counting length-width ratio of manganese sulfide impurity in steel |
| WO2021039861A1 (en) | 2019-08-26 | 2021-03-04 | ダイキン工業株式会社 | Injection molding method |
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| JP2008223122A (en) * | 2007-03-15 | 2008-09-25 | Fuji Wpc:Kk | Method for strengthening alloy steel for hot-working die, and alloy steel of hot-working die for restraining generation of heat-fatigue crack with this method |
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| WO2009116371A1 (en) | 2008-03-19 | 2009-09-24 | コニカミノルタオプト株式会社 | Method for producing wafer lens |
| WO2009116448A1 (en) | 2008-03-19 | 2009-09-24 | コニカミノルタオプト株式会社 | Method for producing molded body or wafer lens |
| EP2759395A1 (en) | 2008-03-19 | 2014-07-30 | Konica Minolta Opto, Inc. | Method for producing a wafer lens |
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| WO2021039861A1 (en) | 2019-08-26 | 2021-03-04 | ダイキン工業株式会社 | Injection molding method |
| CN113604733A (en) * | 2021-07-05 | 2021-11-05 | 昆山东大特钢制品有限公司 | High-temperature-resistant and high-toughness high-end hot-work die steel and production process thereof |
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