JP5881276B2 - Hot tool steel with excellent toughness, short-time and long-term softening resistance - Google Patents
Hot tool steel with excellent toughness, short-time and long-term softening resistance Download PDFInfo
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- 229910001315 Tool steel Inorganic materials 0.000 title claims description 9
- 230000007774 longterm Effects 0.000 title 1
- 238000012360 testing method Methods 0.000 claims description 10
- 229910052721 tungsten Inorganic materials 0.000 claims description 9
- 229910052750 molybdenum Inorganic materials 0.000 claims description 7
- 229910052720 vanadium Inorganic materials 0.000 claims description 6
- 229910052799 carbon Inorganic materials 0.000 claims description 5
- 229910052804 chromium Inorganic materials 0.000 claims description 5
- 229910052748 manganese Inorganic materials 0.000 claims description 5
- 229910052710 silicon Inorganic materials 0.000 claims description 5
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims description 2
- 229910000831 Steel Inorganic materials 0.000 description 12
- 239000010959 steel Substances 0.000 description 12
- 230000000694 effects Effects 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 5
- 238000005242 forging Methods 0.000 description 5
- 150000001247 metal acetylides Chemical class 0.000 description 5
- 238000005496 tempering Methods 0.000 description 4
- 238000000034 method Methods 0.000 description 3
- 238000010791 quenching Methods 0.000 description 3
- 230000000171 quenching effect Effects 0.000 description 3
- 229910001563 bainite Inorganic materials 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000009863 impact test Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000005275 alloying Methods 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000001934 delay Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000000644 propagated effect Effects 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
Description
本発明は、使用負荷の大きい熱間鍛造金型などに使用される特に高靭性、短時間および長時間の高軟化抵抗性の熱間工具鋼に関する。 The present invention relates to a hot tool steel having particularly high toughness, a short time and a long softening resistance for use in a hot forging die having a large service load.
熱間で使用されるハンマー型鍛造用などの大型金具や使用負荷の大きい金型には、熱疲労や衝撃に耐えうる高温強度と靭性を兼ね備えている必要がある。そのため、従来から熱間工具の分野には、例えばＪＩＳ規格の鋼種であるＳＫＴ４やＳＫＤ６１などが使用されている。しかし、近年の塑性加工技術の進歩に伴い製品の大型化、複雑化が進み、また、金型を分割せず一体化するなど、金型の使用環境はますます厳しくなってきており、ＳＫＴ４は靭性に優れているが、高温強度が低く、またＳＫＤ６１は高温強度に優れているが、硬さが高いため、ＳＫＴ４に比べ靭性が劣るという性質があり、十分な熱間工具寿命を実現し難くなっている。 Large metal fittings for forging hammer dies used in hot conditions and dies having a large load are required to have high-temperature strength and toughness that can withstand thermal fatigue and impact. Therefore, conventionally, for example, SKT4 and SKD61, which are JIS standard steel types, have been used in the field of hot tools. However, with recent advances in plastic processing technology, the size and complexity of products have increased, and the mold usage environment has become increasingly severe, such as integrating the mold without dividing it. Excellent toughness but low high-temperature strength, and SKD61 is excellent in high-temperature strength, but because of its high hardness, it has the property of inferior toughness compared to SKT4, making it difficult to achieve a sufficient hot tool life. It has become.
熱間工具が寿命に至るまでの主な現象として、金型のコーナー部からの大割れや金型の表面におけるヒートチェックが上げられる。金型のコーナー部には応力が集中し易いため、突発的または衝撃的な応力によって亀裂や欠けが生じることがあり、その亀裂や欠けが進展していくことで起こるのが大割れである。ヒートチェックは、鍛造品との接触により高温度化した金型表面に対するその後の強制冷却による引張応力が作用して、亀裂が発生および進展する現象で、加熱および冷却に伴う熱疲労現象である。このようなヒートチェックが生じると、鍛造品を正確な形状に変形させることが出来なくなる。さらに、ヒートチェックにより生じた亀裂に応力が集中することで亀裂が進展し、金型の大割れに至ることもある。 Major phenomena until the hot tool reaches the end of its life include large cracks from the corners of the mold and heat check on the surface of the mold. Since stress tends to concentrate on the corners of the mold, cracks or chips may occur due to sudden or impact stress, and large cracks occur as the cracks or chips progress. The heat check is a phenomenon in which a tensile stress due to subsequent forced cooling acts on a die surface that has been heated to high temperature by contact with a forged product, and cracks are generated and propagated. This is a thermal fatigue phenomenon accompanying heating and cooling. When such a heat check occurs, the forged product cannot be deformed into an accurate shape. Further, the stress develops in the crack generated by the heat check, so that the crack progresses and may lead to a large crack of the mold.
つまり、金型寿命を向上するための対策としては次の点が考えられる。すなわち、コーナー部からの大割れを抑制するためには、金型の靭性を高めることが重要である。また、ヒートチェックを抑制するためには強度、靭性、軟化抵抗を高めることが重要である。ここで軟化抵抗を高めることの意味は次の点にある。すなわち、軟化抵抗が低ければ常温での硬さは高くても鍛造を繰り返すうちに金型は軟化してくる。その結果、金型表面の強度が低下しヒートチェックが生じ易くなる。そこで金型の軟化抵抗を高めておくことで、金型表面で発生するヒートチェックを抑制することができる。 That is, the following points can be considered as measures for improving the mold life. That is, it is important to increase the toughness of the mold in order to suppress large cracks from the corner portion. In order to suppress heat check, it is important to increase strength, toughness, and softening resistance. Here, the meaning of increasing the softening resistance is as follows. That is, if the softening resistance is low, the mold softens as the forging is repeated even if the hardness at normal temperature is high. As a result, the strength of the mold surface is lowered and heat check is likely to occur. Therefore, by increasing the softening resistance of the mold, it is possible to suppress the heat check generated on the mold surface.
このようなことから、靭性や高温強度を改善して熱間工具の寿命を向上させようとする技術がいくつか提案されている。例えば、Ｎｂ、Ｔａ、ＴｉやＺｒの添加により結晶粒を微細化して靭性を高める手法が提案されている（例えば、特許文献１参照。）。しかし、上述の特許文献１は、結晶粒の微細化は靭性と常温強度の向上には有効であるものの、高温強度は逆に低下してしまう場合もあるという問題を有していた。また、残留炭化物の量を規定することにより靭性および高温強度を改善する手法が提案されている（例えば、特許文献２参照。）。しかし、靭性および高温強度は焼入れ後のマルテンサイト組織やベイナイト組織などの組織の影響を大きく受けるため、靭性および高温強度を高いレベルで制御するためには残留炭化物量を規定するだけでは不十分であり、また、Ｃｒ、Ｍｏ、Ｗ、Ｖといった希少金属を多量に添加するため、製造コストが嵩み、寿命向上のメリットが少なくなってしまっている。 For this reason, several techniques have been proposed for improving toughness and high-temperature strength to improve the life of hot tools. For example, a technique for increasing the toughness by refining crystal grains by adding Nb, Ta, Ti, or Zr has been proposed (see, for example, Patent Document 1). However, although the above-mentioned Patent Document 1 is effective for improving toughness and room temperature strength, the refinement of crystal grains has a problem that the high temperature strength may decrease. Further, a technique for improving toughness and high-temperature strength by regulating the amount of residual carbide has been proposed (see, for example, Patent Document 2). However, because toughness and high-temperature strength are greatly affected by the structure of martensite structure and bainite structure after quenching, it is not sufficient to specify the amount of residual carbide to control toughness and high-temperature strength at a high level. In addition, since a large amount of rare metals such as Cr, Mo, W, and V are added, the manufacturing cost is increased and the merit of improving the life is reduced.
本発明が解決しようとする課題は、金型の寿命向上のために、優れた靭性、短時間および長時間の軟化抵抗性、および高温強度を有する熱間工具鋼を提供することである。 The problem to be solved by the present invention is to provide a hot work tool steel having excellent toughness , short-time and long-time softening resistance, and high-temperature strength in order to improve the life of the mold.
本発明の課題を解決するための手段は、請求項１の発明では、質量％で、Ｃ：０．２０〜０．６０％、Ｓｉ：０．１０〜０．３０％、Ｍｎ：０．５〜２．０％、Ｖ：０．０５〜０．８０％、を含有し、さらにＮｉ：０．５〜２．５％、Ｃｒ：１．６〜２．６％のうちの１種または２種を、Ｎｉ＋Ｃｒ＞３．０％を満たす範囲で含有し、さらにＭｏ：０．３０〜２．０％、Ｗ：０．６〜４．０％のうちの１種または２種（ただし、２種の場合、１／２Ｗ＋Ｍｏ≦２．０％を満たす範囲）を含有し、さらに、Ｆ（Ｃ、Ｓｉ、Ｍｎ、Ｎｉ、Ｖ、Ｍｏ、Ｗ）＝１８７Ｃ［％］＋５４Ｓｉ［％］＋３７Ｍｎ［％］＋４Ｎｉ［％］−Ｃｒ［％］−２７（Ｍｏ＋１／２Ｗ）［％］＋１６９Ｖ［％］の値がＦ≦１７１を満たし、残部Ｆｅおよび不可避の不純物からなることを特徴とする靱性および軟化抵抗性に優れた熱間工具鋼である。
なお、軟化抵抗性に優れたとは、熱間工具鋼の試験片を６００℃の炉中に３〜１００時間保持した後の室温における保持前の硬さと保持後の硬さの差異の少ないことで、これは３〜１０時間保持の短時間と１０超〜１００時間保持の長時間の両保持時間で共に軟化抵抗性に優れていることである。
Means for solving the problems of the present invention are as follows. In the invention of claim 1, by mass%, C: 0.20 to 0.60%, Si: 0.10 to 0.30%, Mn: 0.5 -2.0%, V: 0.05-0.80%, and also Ni: 0.5-2.5%, Cr: 1.6-2.6 % 1 type or 2 The seed is contained within a range satisfying Ni + Cr> 3.0%, and further, one or two of Mo: 0.30 to 2.0% and W: 0.6 to 4.0% (however, 2 In the case of a seed, it contains ½ W + Mo ≦ 2.0%), and F (C, Si, Mn, Ni, V, Mo, W) = 187 C [%] + 54 Si [%] + 37 Mn [% ] + 4Ni [%]-Cr [%]-27 (Mo + 1/2 W) [%] + 169 V [%] satisfies F ≦ 171, the remainder Fe and inevitable impurities It is made of a hot work tool steel excellent in toughness and softening resistance characterized.
The excellent softening resistance means that there is little difference between the hardness before holding at room temperature after holding the test piece of hot tool steel in a furnace at 600 ° C. for 3 to 100 hours and the hardness after holding. This is excellent in softening resistance in both a short holding time of 3 to 10 hours and a long holding time of more than 10 to 100 hours.
上記の手段としたことで、使用負荷の大きい熱間鍛造金型などの使用に際して、ヒートチェック、亀裂の進展、大割れに対する抵抗性が高く、金型寿命が大幅に改善された熱間工具鋼を提供することができる極めて優れた効果を奏するものである。 By using the above means, hot tool steel with high resistance to heat check, crack propagation, and large cracking, and greatly improved die life when using hot forging dies with a large load. It is possible to provide extremely excellent effects.
優れた靱性および軟化抵抗性を持たせるために、従来の鋼成分について多くの改良研究を重ねた結果、本発明者らは、以下の（１）および（２）に記載の特性を見出した。 As a result of many studies on improvement of conventional steel components in order to provide excellent toughness and softening resistance, the present inventors have found the characteristics described in the following (1) and (2).
（１）靭性はＦ（Ｃ、Ｓｉ、Ｍｎ、Ｎｉ、Ｖ、Ｍｏ、Ｗ）＝１８７Ｃ［％］＋５４Ｓｉ［％］＋３７Ｍｎ［％］＋４Ｎｉ［％］−Ｃｒ［％］−２７（Ｍｏ＋１／２Ｗ）［％］＋１６９Ｖ［％］の値がＦ≦１７１を満たすとき、高い靭性が得られる。また、（２）軟化抵抗性は、使用時間の長さにより効果的な合金元素が異なり、短時間の場合はＭｏおよびＷの添加量に依存し、ＭｏおよびＷの量が、質量％で、（Ｍｏ＋１／２Ｗ）≧０.３０％であれば、高い軟化抵抗性が得られる。さらに、使用時間が長時間の場合、軟化抵抗性に効果のあるＣｒの添加量だけでなく、軟化抵抗性には影響しないといわれているＮｉを加えた（Ｎｉ＋Ｃｒ）の添加量に軟化抵抗性は依存しており、質量％で、（Ｎｉ＋Ｃｒ）≦３．０％の場合には、軟化抵抗性が極端に悪化することを見出した。 (1) Toughness is F (C, Si, Mn, Ni, V, Mo, W) = 187C [%] + 54Si [%] + 37Mn [%] + 4Ni [%] − Cr [%] − 27 (Mo + 1 / 2W) When the value of [%] + 169 V [%] satisfies F ≦ 171, high toughness is obtained. In addition, (2) softening resistance varies depending on the effective alloying element depending on the length of use time. In a short time, it depends on the amount of addition of Mo and W, and the amount of Mo and W is in mass%. When (Mo + 1 / 2W) ≧ 0.30%, high softening resistance is obtained. Furthermore, when the usage time is long, not only the addition amount of Cr effective in softening resistance but also the addition amount of Ni (Ni + Cr), which is said to have no effect on the softening resistance, is softening resistance. It was found that the softening resistance is extremely deteriorated when the mass ratio is (Ni + Cr) ≦ 3.0%.
このことから、高い靱性、軟化抵抗性および製造コストのバランスから、Ｍｏ：０．３０〜２．０％を含有し、Ｎｉ：０．５〜２．５％、Ｃｒ：１．６〜２．６％のうちの１種または種を、Ｎｉ＋Ｃｒ＞３．０％を満たす範囲に含有する必要がある。 From this, Mo: 0.30-2.0% is contained from the balance of high toughness, softening resistance, and manufacturing cost, Ni: 0.5-2.5%, Cr: 1.6-2. It is necessary to contain one or 6 % of 6 % in a range satisfying Ni + Cr> 3.0%.
次に上記以外の本成分の限定理由について述べる。なお、％は質量％を示す。 Next, the reasons for limitation of this component other than the above will be described. In addition,% shows the mass%.
Ｃは、焼入焼戻しによりマトリックス中に溶け込み、マトリックスの強度および焼入れ性を向上させると共に焼戻しにより炭化物を形成し、高温強度および耐摩耗性を与える元素である。従って、上記の特性を確保するために下限を０．２０％とした。ただし、多すぎると靱性および軟化抵抗性を低下させることからを０．６０％以下とした。望ましくは０．３５〜０．５５％である。 C is an element that dissolves in the matrix by quenching and tempering, improves the strength and hardenability of the matrix, forms carbides by tempering, and provides high-temperature strength and wear resistance. Therefore, the lower limit is set to 0.20% in order to ensure the above characteristics. However, if the amount is too large, the toughness and the softening resistance are lowered. Desirably, it is 0.35 to 0.55%.
Ｓｉは、脱酸剤として有用である。そのためには０．１０％以上の添加が必要である。Ｓｉは、また被削性や熱間での耐酸化性を向上させる。しかし、０．５０％を超えると靱性を低下させることから０．５０％以下とした。望ましくは０．１０〜０．３０％である。 Si is useful as a deoxidizer. For that purpose, addition of 0.10% or more is necessary. Si also improves machinability and hot oxidation resistance. However, if it exceeds 0.50%, the toughness is lowered, so it was made 0.50% or less. Desirably, it is 0.10 to 0.30%.
Ｍｎは、高温強度を低下させるベイナイトの生成を遅らせる元素であり、また脱酸剤としても必要な元素であり、これらの効果を確保するためには０．５％以上の添加が必要である。しかし、過度に添加すると靱性を低下させると共に、焼きなまし硬さを高くし被削性を低下させることから２．０％以下とした。望ましくは０．６〜１．５％である。 Mn is an element that delays the formation of bainite that lowers the high-temperature strength, and is also an element that is necessary as a deoxidizing agent. To ensure these effects, 0.5% or more must be added. However, when added excessively, the toughness is lowered and the annealing hardness is increased to lower the machinability, so the content was made 2.0% or less. Desirably, it is 0.6 to 1.5%.
Ｎｉは、焼入れ性および靱性を向上させる元素であり、０．５％以上の添加により有効な効果が現れる。しかしながら、２．５％を超えると高温強度を低下させることから２．５％以下とした。望ましくは１．２〜２．０％である。 Ni is an element that improves hardenability and toughness, and an effective effect appears when 0.5% or more is added. However, if it exceeds 2.5%, the high temperature strength is lowered, so it was made 2.5% or less. Desirably, it is 1.2 to 2.0%.
Ｃｒは、適度な添加により焼入れ性、軟化抵抗性および高温強度を向上させ、さらに、Ｃと結合して炭化物を形成し耐摩耗性を向上させる元素であり、これらの硬化をうるためには１．０％以上の添加が必要である。しかし、４．０％を超えて添加するとＣｒ炭化物の凝集を招き、軟化抵抗性を低下させるが、実施例の表１の発明鋼に基づいてＣｒの範囲は１．６〜２．６％とした。 Cr is an element that improves hardenability, softening resistance, and high-temperature strength by appropriate addition, and further forms a carbide by combining with C to improve wear resistance. Addition of 0.0% or more is necessary. However, if added over 4.0%, Cr carbide agglomerates and softening resistance is lowered, but the Cr range is 1.6-2.6% based on the inventive steel of Table 1 of the examples. I did .
Ｖは、耐摩耗性および軟化抵抗性を向上させる元素であり、０．０５％以上の添加で効果が得られる。しかし、０．８０％を超えて添加すると過剰に炭化物を形成し靱性を低下させることから上限を０．８０％とした。望ましくは０．１０〜０．５０％である。 V is an element that improves wear resistance and softening resistance, and an effect can be obtained by adding 0.05% or more. However, if added over 0.80%, carbides are excessively formed and the toughness is lowered, so the upper limit was made 0.80%. Desirably, it is 0.10 to 0.50%.
ＭｏおよびＷは、焼戻しにより微細な炭化物を形成し、高温強度および軟化抵抗性を向上させる。なお、この効果を得るためのＷ添加量はＭｏ添加量に比べ２倍必要である。しかしながら、過度の添加により巨大炭化物および偏析を生成し、靱性を低下させることから上限をＭｏ当量（Ｍｏ＋１／２Ｗ）で２．０％とした。望ましくはＭｏ当量（Ｍｏ＋１／２Ｗ）で０．３〜１．６％である。 Mo and W form fine carbides by tempering and improve high temperature strength and softening resistance. In order to obtain this effect, the amount of W added is twice as much as the amount of Mo added. However, since excessive carbides generate giant carbides and segregation and lower toughness, the upper limit was made 2.0% in terms of Mo equivalent (Mo + 1/2 W). Desirably, the Mo equivalent (Mo + 1 / 2W) is 0.3 to 1.6%.
以下、本発明の実施例を表１に示し、本発明の範囲から外れる比較例と比較して、発明の効果について具体的に説明する。
表１に示した実施例のＮｏ．２、Ｎｏ．５〜８の組成からなる発明鋼と、比較例のＮｏ．１０〜１６の組成からなる比較鋼について、それぞれ１００ｋｇを真空誘導溶解炉にて溶製して出鋼し、さらに平均径１９０ｍｍの鋳塊にそれぞれ鋳込んだ。これらの鋳塊を１５ｍｍ×１５ｍｍの角材（以下、「角１５ｍｍ」という。）に鍛伸し、次いで後述する形状に機械加工して供試材とし、各供試材の特性についてそれぞれ試験した。
Examples of the present invention are shown in Table 1 below, and the effects of the present invention will be specifically described in comparison with comparative examples that are out of the scope of the present invention.
No. of the example shown in Table 1 . 2, no. Invention steels having compositions of 5 to 8 and No. of Comparative Example. About 10 to 16 comparative steels each having a composition of 10 to 100 kg were melted in a vacuum induction melting furnace to be extracted, and further cast into ingots having an average diameter of 190 mm. These ingots were forged into 15 mm × 15 mm squares (hereinafter referred to as “square 15 mm”), then machined into the shapes described below to give specimens, and the characteristics of each specimen were tested.
試験は上述の供試材の発明鋼と比較鋼におけるシャルピー衝撃試験および軟化抵抗性試験を行って、それぞれの鋼のヒートチェック、すなわち亀裂の進展や大割れの可能性をみた。それぞれの試験方法を次に示す。
１）シャルピー衝撃試験は、ＪＩＳ規定の３号角１０ｍｍ、長さ５５ｍｍからなるＵノッチの試験片に対し、硬さが３９〜４１ＨＲＣになるように焼入焼戻して、常温で試験を行って、それぞれの靱性をみた。
２）軟化抵抗性試験は、角１５ｍｍ、長さ１５ｍｍの試験片に対し、３９〜４１ＨＲＣになるように焼入焼戻した試験片を、６００℃に加熱した炉の中に３〜１００時間保持した後、それぞれの鋼の試験片について室温におけるＨＲＣ硬さを測定し、軟化抵抗性をみた。
In the test, the Charpy impact test and the softening resistance test were performed on the above-described invented steels and comparative steels, and the heat check of each steel, that is, the possibility of crack growth and large cracks was observed. Each test method is shown below.
1) The Charpy impact test was performed by quenching and tempering a U-notch test piece consisting of JIS standard No. 3 corner 10 mm and length 55 mm to a hardness of 39 to 41 HRC, and testing at room temperature. The toughness of
2) In the softening resistance test, a test piece quenched and tempered to 39 to 41 HRC with respect to a test piece having a corner of 15 mm and a length of 15 mm was held in a furnace heated to 600 ° C. for 3 to 100 hours. Then, the HRC hardness at room temperature was measured for each steel specimen, and the softening resistance was observed.
上述の試験の結果を表２に示す。表２において、靱性の評価は、シャルピー衝撃値が８０Ｊ／ｃｍ2以上であれば◎、７０Ｊ／ｃｍ2以上であれば○、７０Ｊ／ｃｍ2未満であれば×と評価した。また、軟化抵抗性は、保持時間が３〜１０時間の短時間のときは、初期ＨＲＣ硬さからの低下が１ポイント以下であれば◎、１ポイントより多い場合は×とした。また、保持時間が１０超〜１００時間の長時間のときは、１０時間後の硬さからの低下が１０ポイント以下であれば◎、１０ポイントより多い場合は×とした。
表２に示すように、Ｎｏ．２、Ｎｏ．５〜８の発明鋼はいずれの鋼種も、Ｎｏ．１０〜１６の比較鋼よりも靱性および短時間と長時間の軟化抵抗性に優れているので、これらの鋼成分からなる工具鋼はヒートチェックが抑制され、亀裂が進展して大割れを起こしにくくなっており、熱間鍛造用の金型として優れた工具鋼である。
The results of the above test are shown in Table 2. In Table 2, evaluation of the toughness, the Charpy impact value is equal to 80 J / cm 2 or more ◎, if 70 J / cm 2 or more ○, was evaluated as × when less than 70 J / cm 2. The softening resistance was evaluated as ◎ if the decrease from the initial HRC hardness was 1 point or less when the holding time was 3 to 10 hours, and x when it was more than 1 point. In addition, when the holding time is longer than 10 to 100 hours, if the decrease from the hardness after 10 hours is 10 points or less, ◎, and if it is more than 10 points, the result is x.
As shown in Table 2, no. 2, no. No. 5-8 invention steels are No. Because it has better toughness and short-time and long-time softening resistance than 10-16 comparative steels, tool steels composed of these steel components are less susceptible to heat checks and cracks that are difficult to cause large cracks. It is an excellent tool steel as a die for hot forging.
Claims (1)
なお、軟化抵抗性に優れたとは、熱間工具鋼の試験片を６００℃の炉中に３〜１００時間保持した後の室温における保持前の硬さと保持後の硬さの差異の少ないことで、これは３〜１０時間保持の短時間と１０超〜１００時間保持の長時間の両保持時間で共に軟化抵抗性に優れていることである。 In mass%, C: 0.20-0.60%, Si: 0.10-0.30%, Mn: 0.5-2.0%, V: 0.05-0.80% And further containing one or two of Ni: 0.5 to 2.5% and Cr: 1.6 to 2.6 % in a range satisfying Ni + Cr> 3.0%, and further Mo: Contains one or two of 0.30 to 2.0%, W: 0.6 to 4.0% (however, in the case of two, a range satisfying 1 / 2W + Mo ≦ 2.0%) Furthermore, F (C, Si, Mn, Ni, V, Mo, W) = 187 C [%] + 54 Si [%] + 37 Mn [%] + 4 Ni [%] − Cr [%] − 27 (Mo + ½ W) [% ] + 169V [%] value satisfying F ≦ 171, and consists of the balance Fe and inevitable impurities, and has excellent toughness and softening resistance Tool steel.
The excellent softening resistance means that there is little difference between the hardness before holding at room temperature after holding the test piece of hot tool steel in a furnace at 600 ° C. for 3 to 100 hours and the hardness after holding. This is excellent in softening resistance in both a short holding time of 3 to 10 hours and a long holding time of more than 10 to 100 hours.
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| JP2013213255A (en) * | 2012-04-02 | 2013-10-17 | Sanyo Special Steel Co Ltd | Hot working die steel |
| CN103334061B (en) * | 2013-06-18 | 2016-01-20 | 上海大学 | High thermal conductivity large section die-casting die steel and preparation thereof and heat treating method |
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| JP6894166B2 (en) * | 2017-07-20 | 2021-06-23 | 山陽特殊製鋼株式会社 | Pre-hardened hot tool steel with excellent machinability |
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