JP6654328B2 - High hardness and high toughness cold tool steel - Google Patents
High hardness and high toughness cold tool steel Download PDFInfo
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- 229910001315 Tool steel Inorganic materials 0.000 title claims description 20
- 229910000831 Steel Inorganic materials 0.000 claims description 44
- 239000010959 steel Substances 0.000 claims description 44
- 238000010791 quenching Methods 0.000 claims description 39
- 230000000171 quenching effect Effects 0.000 claims description 39
- 150000001247 metal acetylides Chemical class 0.000 claims description 29
- 238000005496 tempering Methods 0.000 claims description 29
- 229910001566 austenite Inorganic materials 0.000 claims description 25
- 230000000717 retained effect Effects 0.000 claims description 24
- 229910052799 carbon Inorganic materials 0.000 claims description 9
- 229910052804 chromium Inorganic materials 0.000 claims description 8
- 229910052748 manganese Inorganic materials 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 3
- 239000000463 material Substances 0.000 description 16
- 238000012360 testing method Methods 0.000 description 14
- 230000000694 effects Effects 0.000 description 10
- 230000000052 comparative effect Effects 0.000 description 8
- 239000013078 crystal Substances 0.000 description 8
- 238000005482 strain hardening Methods 0.000 description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 5
- 238000005096 rolling process Methods 0.000 description 5
- 239000002436 steel type Substances 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 238000011282 treatment Methods 0.000 description 4
- 230000000007 visual effect Effects 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 3
- 229910000734 martensite Inorganic materials 0.000 description 3
- 150000004767 nitrides Chemical class 0.000 description 3
- 238000005299 abrasion Methods 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000005242 forging Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
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- 238000005097 cold rolling Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
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- 238000003754 machining Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 238000004663 powder metallurgy Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
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- 238000012545 processing Methods 0.000 description 1
- 230000009291 secondary effect Effects 0.000 description 1
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- 229910052721 tungsten Inorganic materials 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
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Description
本発明は、鍛造金型、フォーミングロールあるいは転造ダイスなどの使用条件が特に過酷な冷間加工用として好適な高硬度で高靱性な冷間工具鋼に関し特に冷間加工用の金型並びに工具用の鋼に関する。 The present invention relates to a high-hardness and high-toughness cold tool steel suitable for use in cold working where the use conditions such as forging dies, forming rolls or rolling dies are particularly severe. For steel.
近年、冷間加工技術の発展に伴って、より高硬度の被加工材を冷間で加工したり、その加工量が増大するなどして、冷間加工条件が過酷化している。そのため、冷間工具鋼に対しては、６３ＨＲＣ以上の硬さがあり、かつ、靭性の高い材料が求められている。また、冷間工具鋼は焼入れ後に５００℃以上の焼戻しを行ったとき、焼入れ前の寸法に比べて膨張（以下「変寸」と称する。）するため、仕上加工が必要であり、経済性の観点から、この変寸が小さい方が良い。 In recent years, with the development of cold working technology, cold working conditions have become severer due to the cold working of higher hardness workpieces and the increase in the amount of working. Therefore, a material having a hardness of 63 HRC or more and a high toughness is required for the cold tool steel. Further, when tempered at 500 ° C. or more after quenching, the cold tool steel expands (hereinafter referred to as “deformation”) as compared with the dimension before quenching, and thus requires a finishing process and is economical. From the viewpoint, it is better that the size change is small.
ところで、冷間工具鋼の鋼材としてＨＲＣ６３を超える硬さを有する材料として、例えば、ＪＩＳで規定される高速度工具鋼のＳＫＨ５１が挙げられ、また、加工硬化の大きいステンレス鋼またはＨＲＣ４０程度の調質鋼などの難加工材の転造に対する転造ダイス用鋼が提案されており（例えば、特許文献１参照。）、また、Ｃ、Ｍｏ、Ｗ、Ｖ，Ｃｏなどの合金元素を多量に加えて、多量の硬質炭化物を析出させることで、高硬度を得ており、低温焼入れが可能な鋼が提案されている（例えば、特許文献２参照。）。しかし、これらの鋼は粗大な一次炭化物が多く、そのために靭性および疲労強度が低いだけでなく、金型材料費が高くなる問題がある。 By the way, as a material having a hardness exceeding HRC63 as a steel material of a cold tool steel, for example, SKH51 of a high-speed tool steel specified by JIS can be mentioned, and stainless steel having a large work hardening or a temper of about HRC40. Rolling die steel for rolling of difficult-to-machine materials such as steel has been proposed (for example, see Patent Document 1), and a large amount of alloying elements such as C, Mo, W, V, and Co are added. There has been proposed a steel which has a high hardness by precipitating a large amount of hard carbide and which can be hardened at a low temperature (for example, see Patent Document 2). However, these steels have a large amount of coarse primary carbides, and thus have the problems of not only low toughness and fatigue strength but also high mold material costs.
さらに、直径換算して直径が１０μｍ以上の炭化物の個数と介在物の清浄度を抑制した高い硬さと高い靱性をあわせ備えた、精密加工用の工具鋼が提案されている（例えば、特許文献３参照。）。しかし、この鋼は炭窒化物が疎になる部分が多いために、炭窒化物によるピン止めが働きにくく、結晶粒の粗大化を招き、靭性が低下する場合が見られるので、使用条件が過酷な冷間加工用として、十分な特性を有しているとは言えない。 Further, a tool steel for precision machining has been proposed that has both high hardness and high toughness in which the number of carbides having a diameter of 10 μm or more in terms of diameter and the cleanliness of inclusions are suppressed (for example, Patent Document 3). reference.). However, this steel has many parts where carbonitrides are sparse, so pinning by carbonitrides is difficult to work, causing coarsening of crystal grains and decreasing toughness. It cannot be said that it has sufficient properties for cold working.
上述したような問題を解消するために、発明者は鋭意開発を進めた結果、合金成分式、鋼材中の一次炭化物の単位面積あたりに占める面積率および個数、さらに焼入れ後の残留オーステナイト量、および、焼入れ焼戻し後の炭化物の面積を規定することで焼入れ時に結晶粒の粗大化を起こすことなく、かつ、変寸の少ない、焼戻し後の硬さが６３ＨＲＣ以上となる高硬度で高靭性な冷間工具鋼が得られることを見出した。 In order to solve the above-described problems, the inventor has intensively developed the alloy composition formula, the area ratio and the number of primary carbides per unit area in the steel material per unit area, and the residual austenite amount after quenching, and By defining the area of the carbide after quenching and tempering, it is possible to prevent the crystal grains from coarsening during quenching, and to reduce the size change. The hardness after tempering is 63 HRC or more. It has been found that tool steel can be obtained.
本発明が解決しようとする課題は、焼入れ時に結晶粒の粗大化を起こすことなく、変寸の少ない、焼戻し後の硬さが６３ＨＲＣ以上となる高硬度で高靭性な冷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 high-hardness and high-toughness cold tool steel which has a small size change and a hardness after tempering of 63 HRC or more without causing coarsening of crystal grains during quenching. That is.
上記の課題を解決するための本発明の手段は、第１の手段では、質量％で、Ｃ：０．６〜０．９％、Ｓｉ：０．７〜０．９％、Ｍｎ：０．１〜０．６％、Ｃｒ：４．０〜６．５％未満、（Ｍｏ＋Ｗ／２）：２．０超〜５．０％、（Ｖ＋Ｎｂ／２）：０．１〜０．６％、および、Ｎ：１００超〜５００ｐｐｍを有し、残部Ｆｅおよび不可避不純物からなる鋼で、この鋼の焼入れ時の残留オーステナイトの安定性を表す値であるＲはＲ＝５１．４×Ｃ（％）−４．２×Ｃｒ（％）−４４．４×Ｖ（％）＋０．１×Ｎ（ｐｐｍ）で示され、Ｒ：１５．０〜３１．０であり、５００℃以上の焼戻し後の硬さ：６３ＨＲＣ以上で、５０００００μｍ2中の一次炭化物の個数：２００個以上で、かつ、５０００００μｍ2中の一次炭化物の面積率：０．５〜３．０％であることを特徴とする高硬度で高靱性な冷間工具鋼である。 Means of the present invention for solving the above-mentioned problems are as follows. In the first means, C: 0.6 to 0.9%, Si: 0.7 to 0.9%, Mn: 0. 1 to 0.6%, Cr: 4.0 to less than 6.5%, (Mo + W / 2): more than 2.0 to 5.0%, (V + Nb / 2): 0.1 to 0.6%, And N: a steel having more than 100 to 500 ppm, the balance being Fe and unavoidable impurities, and R representing the stability of retained austenite at the time of quenching of this steel is R = 51.4 × C (%) -4.2 × Cr (%)-44.4 × V (%) + 0.1 × N (ppm), R: 15.0 to 31.0, and hardness after tempering at 500 ° C. or more Length: 63HRC or more, number of primary carbides in 500,000 μm 2 : 200 or more, and area ratio of primary carbides in 500,000 μm 2 : 0.5 to 3. It is a high hardness and high toughness cold tool steel characterized by being 0%.
第２の手段では、質量％で、Ｃ：０．６〜０．９％、Ｓｉ：０．７〜０．９％、Ｍｎ：０．１〜０．６％、Ｃｒ：４．０〜６．５％未満、（Ｍｏ＋Ｗ／２）：２．０超〜５．０％、（Ｖ＋Ｎｂ／２）：０．１〜０．６％、および、Ｎ：１００超〜５００ｐｐｍを有し、残部Ｆｅおよび不可避不純物からなる鋼で、この鋼の焼入れ時の残留オーステナイトの安定性を表す値であるＲはＲ＝５１．４×Ｃ（％）−４．２×Ｃｒ（％）−４４．４×Ｖ（％）＋０．１×Ｎ（ｐｐｍ）で示され、Ｒ：１５．０〜３１．０であり、５００℃以上の焼戻し後の硬さ：６３ＨＲＣ以上で、５０００００μｍ2中の一次炭化物の個数：２００個以上で、かつ、５０００００μｍ2中の一次炭化物の面積率：０．５〜３．０％であり、さらに焼入れ後の残留オーステナイト量は１２〜３０％であることを特徴とする高硬度で高靱性な冷間工具鋼である。 In the second means, in mass%, C: 0.6 to 0.9%, Si: 0.7 to 0.9%, Mn: 0.1 to 0.6%, Cr: 4.0 to 6%. 0.5%, (Mo + W / 2): more than 2.0 to 5.0%, (V + Nb / 2): 0.1 to 0.6%, and N: more than 100 to 500 ppm, with the balance Fe R, which is a value representing the stability of retained austenite during quenching of the steel, is R = 51.4 × C (%) − 4.2 × Cr (%) − 44.4 × V (%) + 0.1 × N (ppm), R: 15.0 to 31.0, hardness after tempering at 500 ° C. or more: 63HRC or more, number of primary carbides in 500,000 μm 2 : 200 or more, and the area ratio of primary carbide in 500,000 μm 2 : 0.5 to 3.0%, and residual austena after quenching It is a high hardness and high toughness cold tool steel characterized in that the iron content is 12 to 30%.
第３の手段では、質量％で、Ｃ：０．６〜０．９％、Ｓｉ：０．７〜０．９％、Ｍｎ：０．１〜０．６％、Ｃｒ：４．０〜６．５％未満、（Ｍｏ＋Ｗ／２）：２．０超〜５．０％、（Ｖ＋Ｎｂ／２）：０．１〜０．６％、および、Ｎ：１００超〜５００ｐｐｍを有し、残部Ｆｅおよび不可避不純物からなる鋼で、この鋼の焼入れ時の残留オーステナイトの安定性を表す値であるＲはＲ＝５１．４×Ｃ（％）−４．２×Ｃｒ（％）−４４．４×Ｖ（％）＋０．１×Ｎ（ｐｐｍ）で示され、Ｒ：１５．０〜３１．０であり、５００℃以上の焼戻し後の硬さ：６３ＨＲＣ以上で、５０００００μｍ2中の一次炭化物の個数：２００個以上で、かつ、５０００００μｍ2中の一次炭化物の面積率：０．５〜３．０％であり、さらに焼入れ焼戻し後の平均炭化物面積は２５μｍ2以下であることを特徴とする高硬度で高靱性な冷間工具鋼である。 In the third means, in mass%, C: 0.6 to 0.9%, Si: 0.7 to 0.9%, Mn: 0.1 to 0.6%, Cr: 4.0 to 6%. 0.5%, (Mo + W / 2): more than 2.0 to 5.0%, (V + Nb / 2): 0.1 to 0.6%, and N: more than 100 to 500 ppm, with the balance Fe R, which is a value representing the stability of retained austenite during quenching of the steel, is R = 51.4 × C (%) − 4.2 × Cr (%) − 44.4 × V (%) + 0.1 × N (ppm), R: 15.0 to 31.0, hardness after tempering at 500 ° C. or more: 63HRC or more, number of primary carbides in 500,000 μm 2 : 200 or more and the area ratio of primary carbide in 500,000 μm 2 : 0.5 to 3.0%, and furthermore, the average carbonization after quenching and tempering It is a high hardness and high toughness cold tool steel characterized by having an object area of 25 μm 2 or less.
第４の手段では、質量％で、Ｃ：０．６〜０．９％、Ｓｉ：０．７〜０．９％、Ｍｎ：０．１〜０．６％、Ｃｒ：４．０〜６．５％未満、（Ｍｏ＋Ｗ／２）：２．０超〜５．０％、（Ｖ＋Ｎｂ／２）：０．１〜０．６％、および、Ｎ：１００超〜５００ｐｐｍを有し、残部Ｆｅおよび不可避不純物からなる鋼で、この鋼の焼入れ時の残留オーステナイトの安定性を表す値であるＲはＲ＝５１．４×Ｃ（％）−４．２×Ｃｒ（％）−４４．４×Ｖ（％）＋０．１×Ｎ（ｐｐｍ）で示され、Ｒ：１５．０〜３１．０であり、５００℃以上の焼戻し後の硬さ：６３ＨＲＣ以上で、５０００００μｍ2中の一次炭化物の個数：２００個以上で、かつ、５０００００μｍ2中の一次炭化物の面積率：０．５〜３．０％であり、さらに焼入れ後の残留オーステナイト量は１２〜３０％であり、焼入れ焼戻し後の平均炭化物面積は２５μｍ2以下であることを特徴とする高硬度で高靱性な冷間工具鋼である。 In the fourth means, in mass%, C: 0.6 to 0.9%, Si: 0.7 to 0.9%, Mn: 0.1 to 0.6%, Cr: 4.0 to 6%. 0.5%, (Mo + W / 2): more than 2.0 to 5.0%, (V + Nb / 2): 0.1 to 0.6%, and N: more than 100 to 500 ppm, with the balance Fe R, which is a value representing the stability of retained austenite during quenching of the steel, is R = 51.4 × C (%) − 4.2 × Cr (%) − 44.4 × V (%) + 0.1 × N (ppm), R: 15.0 to 31.0, hardness after tempering at 500 ° C. or more: 63HRC or more, number of primary carbides in 500,000 μm 2 : 200 or more, and the area ratio of primary carbide in 500,000 μm 2 : 0.5 to 3.0%, and residual austena after quenching It is a high hardness, high toughness cold tool steel characterized by having an iron content of 12 to 30% and an average carbide area after quenching and tempering of 25 μm 2 or less.
本発明の鋼は、５００℃以上の高温焼戻しで硬さが６３ＨＲＣ以上の高硬度であり、冷間工具鋼としたときに、高温焼戻しにより変寸して膨張することなく正確な寸法の工具が得られ、高硬度の被加工材を効率よく正確に加工することができ、特に冷間加工用の金型、成型用ロール、転造ダイスなどとして優れた特性を有する高硬度で高靱性な冷間加工用の鋼材である。 The steel of the present invention has a high hardness of 63 HRC or more at a high temperature tempering of 500 ° C. or more, and when it is used as a cold tool steel, a tool having accurate dimensions without being deformed and expanded due to the high temperature tempering. It is possible to efficiently and accurately process high-hardness workpieces and obtain high-hardness, high-toughness cold-rolling with excellent properties, especially as molds for cold working, forming rolls, and rolling dies. It is a steel material for hot working.
先ず、本発明の実施の形態を記載するに先立って、本発明の手段の鋼の化学成分の限定理由並びに残留オーステナイトの安定性を表す値のＲ、焼戻し後の硬さ、５０００００μｍ2中の一次炭化物の個数、５０００００μｍ2中の一次炭化物の炭化物面積率、焼入れ後の残留オーステナイト量および焼入れ焼戻し後の平均炭化物面積における限定理由について以下に説明する。なお、％は質量％である。 First, prior to describing the embodiments of the present invention, the reason for limiting the chemical composition of the steel of the means of the present invention and the value R representing the stability of retained austenite, the hardness after tempering, the primary hardness in 500,000 μm 2 The reasons for limiting the number of carbides, the area ratio of primary carbides in 500,000 μm 2 , the amount of retained austenite after quenching, and the average carbide area after quenching and tempering will be described below. In addition,% is mass%.
Ｃ：０．６〜０．９％
Ｃは、硬質炭化物を形成し、硬さ、耐摩耗性を向上させるとともに焼入れ性を高める元素であり、Ｃが０．６％未満であるとこれらの効果は得られない。一方、Ｃが０．９％より多いと粗大な炭化物を形成し、靱性および加工性を悪化する。そこで、Ｃは０．６〜０．９％とし、望ましくは０．７〜０．９％とする。
C: 0.6-0.9%
C is an element that forms hard carbide, improves hardness and wear resistance, and enhances hardenability. If C is less than 0.6%, these effects cannot be obtained. On the other hand, if C is more than 0.9%, coarse carbides are formed, and toughness and workability deteriorate. Therefore, C is set to 0.6 to 0.9%, preferably 0.7 to 0.9%.
Ｓｉ：０．７〜０．９％
Ｓｉは、脱酸剤として作用し、かつ基地の硬さを増し、焼入れ性を向上させる元素であり、Ｓｉが０．７％未満であるとこれらの効果は得られない。一方、Ｓｉが０．９％より多いと靱性および加工性を悪化する。そこで、Ｓｉは０．７〜０．９％とする。
Si: 0.7 to 0.9%
Si is an element that acts as a deoxidizing agent, increases the hardness of the matrix, and improves the hardenability. If Si is less than 0.7%, these effects cannot be obtained. On the other hand, when Si is more than 0.9%, toughness and workability deteriorate. Therefore, Si is set to 0.7 to 0.9%.
Ｍｎ：０．１〜０．６％
Ｍｎは、脱酸材として作用しかつ焼入れ性を増す元素であり、Ｍｎが０．１％未満であるとこれらの効果は得られない。一方、Ｍｎが０．６％より多いと鋼のマトリックスを脆化し靱性を悪化する。そこで、Ｍｎは０．１〜０．６％とし、望ましくは０．２〜内０．６％とする。
Mn: 0.1-0.6%
Mn is an element that acts as a deoxidizing agent and increases quenchability. If Mn is less than 0.1%, these effects cannot be obtained. On the other hand, when Mn is more than 0.6%, the steel matrix becomes brittle and the toughness is deteriorated. Therefore, Mn is set to 0.1 to 0.6%, preferably 0.2 to 0.6%.
Ｃｒ：４．０〜６．５％未満
Ｃｒは、硬質炭化物を形成し、硬さ、耐摩耗性を向上させるとともに、焼入れ性を高める元素であり、Ｃｒが４．０％未満であるとその効果を得られない。一方、Ｃｒが６．５％以上であると、粗大な炭化物を形成し、靱性および加工性を悪化する。そこでＣｒは４．０〜６．５％未満とし、望ましくは４．５〜６．３％とする。
Cr: 4.0 to less than 6.5% Cr is an element that forms a hard carbide, improves hardness and abrasion resistance, and enhances hardenability. When Cr is less than 4.0%, Cr is an element. No effect. On the other hand, when Cr is 6.5% or more, coarse carbides are formed, and toughness and workability deteriorate. Therefore, Cr is set to 4.0 to less than 6.5%, and preferably 4.5 to 6.3%.
（Ｍｏ＋Ｗ／２）：２．０超〜５．０％
（Ｍｏ＋Ｗ／２）は、硬質炭化物を形成し、硬さ、耐摩耗性を向上させるとともに、焼入れ性、焼戻し軟化抵抗性を高める働きをする。そのためには、（Ｍｏ＋Ｗ／２）は２．０％超が必要である。一方、（Ｍｏ＋Ｗ／２）は粗大な炭化物を形成し、靱性および加工性を悪化する。そこで、（Ｍｏ＋Ｗ／２）は２．０超〜５．０％とし、望ましくは２．６〜４．０％とする。
(Mo + W / 2): more than 2.0 to 5.0%
(Mo + W / 2) forms a hard carbide, improves the hardness and abrasion resistance, and functions to enhance the quenchability and the temper softening resistance. For that purpose, (Mo + W / 2) needs to be more than 2.0%. On the other hand, (Mo + W / 2) forms coarse carbides and deteriorates toughness and workability. Therefore, (Mo + W / 2) is set to more than 2.0 to 5.0%, and preferably to 2.6 to 4.0%.
（Ｖ＋Ｎｂ／２）：０．１〜０．６％
（Ｖ＋Ｎｂ／２）は、硬質炭化物を形成し、硬さ、耐摩耗性を向上させるとともに、焼入れ時の結晶粒の粗大化を抑制する効果があり、靱性の向上に寄与する働きをする。そのためには、（Ｖ＋Ｎｂ／２）は０．１％以上が必要である。一方、（Ｖ＋Ｎｂ／２）は粗大な炭窒化物を形成し靱性および加工性を悪化する。そこで、（Ｖ＋Ｎｂ／２）は０．１〜０．６％とし、望ましくは０．３〜０．５％とする。
(V + Nb / 2): 0.1 to 0.6%
(V + Nb / 2) forms a hard carbide, improves hardness and wear resistance, and has an effect of suppressing coarsening of crystal grains during quenching, and contributes to improvement in toughness. For that purpose, (V + Nb / 2) needs to be 0.1% or more. On the other hand, (V + Nb / 2) forms a coarse carbonitride and deteriorates toughness and workability. Therefore, (V + Nb / 2) is set to 0.1 to 0.6%, preferably 0.3 to 0.5%.
Ｎ：１００超〜５００ｐｐｍ
Ｎは、窒化物を形成するために必要な元素であり、形成された窒化物が耐摩耗性を向上させるとともに結晶粒の粗大化を防止し靱性の低下を抑制する働きをする。しかし、Ｎが１００ｐｐｍ以下であるとこれらの効果は得られない。一方、Ｎが５００ｐｐｍより多いと、粗大な窒化物を形成し、靱性および加工性を悪化する。そこで、Ｎは１００超〜５００ｐｐｍとし、望ましくは１２０〜４００ｐｐｍとする。
N: more than 100 to 500 ppm
N is an element necessary for forming a nitride, and the formed nitride functions to improve wear resistance, prevent coarsening of crystal grains, and suppress a decrease in toughness. However, if N is 100 ppm or less, these effects cannot be obtained. On the other hand, if N is more than 500 ppm, coarse nitrides are formed, and toughness and workability deteriorate. Therefore, N is set to be more than 100 to 500 ppm, preferably 120 to 400 ppm.
Ｒ：１５．０〜３１．０
Ｒは、本願発明の化学成分の範囲を満たす鋼の焼入れ時の残留オーステナイトの安定性を表す値であり、ＣおよびＮが増えることで、焼入れ時に残留オーステナイトが安定化しやすくなるが、Ｃｒ、Ｖが増えると、炭窒化物が形成されやすくなり、特にＶは焼入れ温度に加熱されても固溶しにくい炭窒化物を形成するため、残留オーステナイトの安定性に寄与するＣおよびＮの影響を低下させる。すなわち、Ｒが大きいほど残留オーステナイトは安定となる。
ところで、残留オーステナイトは５００℃以上で焼き戻した時に、マルテンサイト化して二次硬化に寄与するが、マルテンサイト化が起こることで、膨張して焼入れ前の寸法からの変寸が大きくなるため、残留オーステナイトの安定性が高すぎると、残留オーステナイトが多く残るようになり、焼入れ前の寸法からの変寸が大きくなる。そこで、Ｒは３１．０以下とする。ただし、残留オーステナイトの安定性が低すぎると、マルテンサイト化が低温で進みやすく、二次炭化物が析出したときに起こる析出硬化の温度域と重ならなくなるため、焼戻し後の硬さが６３ＨＲＣ以上得られなくなる。そこで、Ｒは１５．０以上とする。以上の理由から、Ｒは１５．０〜３１．０とし、望ましくは１７．０〜２９．０とする。
R: 15.0-31.0
R is a value indicating the stability of retained austenite during quenching of steel satisfying the range of the chemical components of the present invention. As C and N increase, the retained austenite is easily stabilized during quenching. Increases, carbonitrides are likely to be formed, and in particular, V forms carbonitrides which are hardly dissolved even when heated to a quenching temperature, so that the effects of C and N, which contribute to the stability of retained austenite, are reduced. Let it. That is, the larger R is, the more stable the retained austenite is.
By the way, when the retained austenite is tempered at 500 ° C. or more, it becomes martensite and contributes to secondary hardening.However, the martensitization occurs, which causes expansion and deformation from the dimension before quenching becomes large. If the stability of the retained austenite is too high, a large amount of the retained austenite remains, and the size change from the dimension before quenching becomes large. Therefore, R is set to 31.0 or less. However, if the stability of the retained austenite is too low, martensitization is likely to proceed at low temperatures and does not overlap the temperature range of precipitation hardening that occurs when secondary carbides precipitate, so that the hardness after tempering is 63 HRC or more. Can not be. Therefore, R is set to 15.0 or more. For the above reasons, R is set to 15.0 to 31.0, preferably 17.0 to 29.0.
５００℃以上の焼戻し後の硬さ：６３ＨＲＣ以上
５００℃以上の焼戻し後の硬さは、本発明の冷間工具鋼を塑性加工用のダイスまたは圧延ロールなどするときに必要であり、特に高硬度である金属材料の加工には、工具鋼の硬さが６３ＨＲＣより低いと加工できない。そこで、本発明の冷間工具鋼における、５００℃以上の焼戻し後の硬さを６３ＨＲＣ以上とする。
Hardness after tempering of 500 ° C or more: 63HRC or more Hardness after tempering of 500 ° C or more is necessary when the cold tool steel of the present invention is used as a die or a rolling roll for plastic working, and particularly high hardness. When the hardness of the tool steel is lower than 63 HRC, the processing cannot be performed on the metal material having the following condition. Therefore, the hardness after tempering at 500 ° C. or higher in the cold tool steel of the present invention is 63 HRC or higher.
５０００００μｍ2中の一次炭化物の個数：２００個以上
５０００００μｍ2中の一次炭化物の個数は焼入れ処理後に残っている５０００００μｍ2中の炭化物の個数をいう。ところで、本発明鋼における５０００００μｍ2中の一次炭化物の個数が２００個より少ないと、冷間工具鋼として必要な耐摩耗性が得られない。また、結晶粒のピン止め効果も得られない。そこで、必要な耐摩耗性とピン止め効果を有するものとするために、５０００００μｍ2中の一次炭化物の個数は２００個以上とする。
The number of primary carbides in 500000μm 2: 200 or more 500000Myuemu number of primary carbides in 2 refers to the number of carbides in 500000Myuemu 2 remaining after quenching. By the way, if the number of primary carbides in 500,000 μm 2 of the steel of the present invention is less than 200, the wear resistance required as a cold tool steel cannot be obtained. Further, the effect of pinning the crystal grains cannot be obtained. Therefore, in order to have the necessary wear resistance and pinning effect, the number of primary carbides in 500,000 μm 2 is set to 200 or more.
５０００００μｍ2中の一次炭化物の炭化物面積率：０．５〜３．０％
一次炭化物は結晶粒のピン止めに寄与することが出来るが、５０００００μｍ2中の一次炭化物の炭化物面積率が０．５％未満では結晶粒のピン止め効果が得られない。一方、この面積率が３．０％を超えると、炭化物同士の距離が近くなって、割れの伝播が起きやすくなり、靱性が低下する。そこで、５０００００μｍ2中の一次炭化物の炭化物面積率は、０．５〜３．０％とし、望ましくは０．５〜１．８％とする。
Carbide area ratio of primary carbide in 500,000 µm 2 : 0.5 to 3.0%
The primary carbides can contribute to the pinning of the crystal grains, but if the carbide area ratio of the primary carbides in 500,000 μm 2 is less than 0.5%, the effect of pinning the crystal grains cannot be obtained. On the other hand, if this area ratio exceeds 3.0%, the distance between the carbides becomes short, and the propagation of cracks easily occurs, and the toughness is reduced. Therefore, the carbide area ratio of the primary carbide in 500,000 μm 2 is set to 0.5 to 3.0%, preferably 0.5 to 1.8%.
焼入れ後の残留オーステナイト量は１２〜３０％
焼入れ後の残留オーステナイトは、５００℃以上で焼戻し行ったときに、マルテンサイト化して二次効果に寄与する。しかし、焼入れ後の残留オーステナイト量が１２％より少な過ぎると、マルテンサイト化による二次硬化が十分に得られない。そこで残留オーステナイト量は１２％以上とする。しかし、焼入れ後の残留オーステナイト量が３０％より多いと、焼戻し後の変寸が大きくなる。そこで、焼入れ後の残留オーステナイト量は１２〜３０％とし、望ましくは、１４〜２５％とする。
The amount of retained austenite after quenching is 12-30%
The retained austenite after quenching turns into martensite when tempered at 500 ° C. or higher, and contributes to the secondary effect. However, if the amount of retained austenite after quenching is less than 12%, secondary hardening due to martensite formation cannot be sufficiently obtained. Therefore, the amount of retained austenite is set to 12% or more. However, when the amount of retained austenite after quenching is more than 30%, the size change after tempering becomes large. Therefore, the amount of retained austenite after quenching is set to 12 to 30%, preferably, 14 to 25%.
焼入れ焼戻し後の平均炭化物面積は、２５μｍ2以下
焼入れ焼戻し後の平均炭化物面積は、２５μｍ2を超えると、割れ起点になりやすい炭化物サイズのものが多くなり靱性が低下する。そこで、焼入れ焼戻し後の平均炭化物面積は、２５μｍ2以下とする。
The average carbide area after quenching and tempering is 25 μm 2 or less. If the average carbide area after quenching and tempering exceeds 25 μm 2 , carbides that tend to be crack initiation points increase and the toughness decreases. Therefore, the average carbide area after quenching and tempering is set to 25 μm 2 or less.
ここで、本願発明の実施の形態について説明する。先ず、本願の請求項１〜４に係る発明の鋼であり、表１に示す供試材である発明鋼のＮｏ．１〜３６と、それらの比較例である表２に示す供試材である比較鋼のＮｏ．３７〜５２の、各供試材の鋼の１００Ｋｇを真空誘導炉で溶製し、得られた鋼を、断面の縦辺および横辺それぞれが５０ｍｍである角材に鍛伸した。次いで、これらの角材を図１に示すように、１０５０℃に加熱した後、空冷して焼入れ処理し、その後、５００〜６００℃に加熱して空冷する焼戻し処理を２回以上繰り返した。表１および表２に供試材の化学成分とＲ値を示す。 Here, an embodiment of the present invention will be described. First, the steel of the invention according to Claims 1 to 4 of the present application, which is a test material shown in Table 1, is the steel of the invention. Nos. 1 to 36 and the comparative steel Nos. 37 to 52, 100 kg of the steel of each test material was melted in a vacuum induction furnace, and the obtained steel was forged into a square bar having a vertical side and a horizontal side each having a cross section of 50 mm. Next, as shown in FIG. 1, after heating these square pieces to 1050 ° C., they were air-cooled and quenched, and thereafter, tempering treatments of heating to 500 to 600 ° C. and air-cooled were repeated twice or more. Tables 1 and 2 show the chemical components and R values of the test materials.
上記の表１の各発明鋼および表２の各比較鋼の供試材について、５００〜６００℃の２回以上の繰返し焼戻し処理温度で、最も高い硬さとなったものを評価した。この硬さが６３ＨＲＣ以上のときは○とし、６３ＨＲＣよりも低いときは×として、表３および表４に示した。 With respect to the test materials of the invention steels in Table 1 and the comparative steels in Table 2, those having the highest hardness at two or more repeated tempering temperatures of 500 to 600 ° C. were evaluated. When the hardness was 63 HRC or more, the result was indicated by “、”, and when the hardness was lower than 63 HRC, the result was indicated by “X”.
上記の焼入れ処理した各発明鋼および各比較鋼の供試材を用いて、中心部から、縦８ｍｍ、横８ｍｍ、長さ８ｍｍの試験片を割り出し、Ｘ線回折により残留オーステナイト量（％）を求めて、表３および表４に示した。 Using the test material of each of the invention steels and the comparative steels subjected to the above quenching treatment, a test piece having a length of 8 mm, a width of 8 mm, and a length of 8 mm was determined from the center, and the amount of retained austenite (%) was determined by X-ray diffraction. The results are shown in Tables 3 and 4.
さらに、上記の焼入れ焼戻し処理した各発明鋼および各比較鋼の供試材を用いて、中心部から、縦１５ｍｍ、横１５ｍｍ、長さ１５ｍｍの試験片を割り出し、光学顕微鏡の１００倍の視野で、３箇所ランダムに撮影し、画像解析装置を使用して、それぞれの５０００００μｍ2視野内の一次炭化物個数および一次炭化物面積率をそれらの画像から測定し、その平均を求めて、表３および表４に示した。 Further, a test piece having a length of 15 mm, a width of 15 mm, and a length of 15 mm was determined from the center using a test material of each of the invention steels and the comparative steels subjected to the above-mentioned quenching and tempering, and was viewed with a 100-fold visual field of an optical microscope. The number of primary carbides and the area ratio of primary carbides in each of the 500,000 μm 2 visual fields were measured from the images by randomly photographing three places and using an image analyzer, and the average thereof was determined. Tables 3 and 4 It was shown to.
さらに、上記の焼入れ焼戻し処理した各発明鋼および各比較鋼の供試材を用いて、中心部から、縦１５ｍｍ、横１５ｍｍ、長さ１５ｍｍの試験片を割り出し、ナイタールにより腐食し、光学顕微鏡の１００倍の視野でランダムに撮影し、画像解析装置を使用して、それぞれの５０００００μｍ2視野内の炭化物の平均面積をそれらの画像から求めて、表３および表４に示した。 Further, a test piece having a length of 15 mm, a width of 15 mm, and a length of 15 mm was determined from the center using the test material of each of the invention steels and the comparative steels subjected to the above quenching and tempering treatments, and was corroded with nital. Photographs were taken at random in a 100-fold visual field, and the average area of carbide in each 500,000 μm 2 visual field was determined from those images using an image analyzer, and is shown in Tables 3 and 4.
また、発明鋼および比較鋼の靱性は、シャルピー衝撃値で評価した。シャルピー衝撃試験は、上記の焼入れ焼戻し処理した各発明鋼および各比較鋼の供試材の中心部から、縦１０ｍｍ、横１０ｍｍ、長さ５５ｍｍからなる、図２に示す１０Ｒ−２ｍｍＣノッチのシャルピー試験片を割り出し、実施した。６３ＨＲＣ以上の硬さが得られるＪＩＳ鋼種であるＳＫＨ５１の粉末冶金により製造した鋼は、６３ＨＲＣで２５Ｊ／ｃｍ2のシャルピー衝撃値が得られるため、この２５Ｊ／ｃｍ2のシャルピー衝撃値を基準として、３０Ｊ／ｃｍ2より高いシャルピー衝撃値が得られれば、靱性に優れているとして◎とし、２５Ｊ／ｃｍ2より高く３０Ｊ／ｃｍ2以下であれば、靱性がよいとして○とし評価して、表３および表４に示した。 Further, the toughness of the inventive steel and the comparative steel was evaluated by a Charpy impact value. The Charpy impact test is a 10R-2mmC notch shown in FIG. 2, which is 10 mm long, 10 mm wide and 55 mm long from the center of the test material of each invention steel and each comparative steel subjected to the above quenching and tempering treatment. Pieces were indexed and performed. A steel manufactured by powder metallurgy of SKH51, which is a JIS steel type capable of obtaining a hardness of 63 HRC or more, has a Charpy impact value of 25 J / cm 2 at 63 HRC. Therefore, based on the Charpy impact value of 25 J / cm 2 , When a Charpy impact value higher than 30 J / cm 2 was obtained, the toughness was evaluated as excellent, and when it was higher than 25 J / cm 2 and 30 J / cm 2 or less, the toughness was evaluated as good. And Table 4.
上記した鍛伸後の各発明鋼および各比較鋼の供試材を用いて、縦５０ｍｍ、横５０ｍｍ、長さ１００ｍｍからなる試験片を割り出し、長さ方向の寸法を測定した後、上記の焼入れ焼戻し処理を行ない、再度、長さ方向の寸法を測定して、熱処理前からの変寸した長さを求めた。ところで、ＳＫＨ５１は０．１ｍｍ膨張するので、この０．１ｍｍを基準の変寸とし、膨張が０〜０．１ｍｍ未満であればよいとして○とし、０．１ｍｍ以上であれば悪いとして×として表３および表４に示した。 Using the test material of each invention steel and each comparative steel after forging described above, a test piece having a length of 50 mm, a width of 50 mm, and a length of 100 mm was indexed, and the length in the length direction was measured. Tempering was performed, and the length in the length direction was measured again to determine the length that was changed before the heat treatment. By the way, since the SKH51 expands by 0.1 mm, this 0.1 mm is set as a reference size change, and if the expansion is 0 to less than 0.1 mm, it is evaluated as ○. 3 and Table 4.
以上の表１および表３から、本発明鋼の化学成分であるＣ、Ｓｉ、Ｍｎ、（Ｍｏ＋Ｗ／２）、（Ｖ＋Ｎｂ／２）の含有量が、各々１つでも請求項の範囲から高く外れた鋼種はシャルピー衝撃値が低いため、靱性が低い。（Ｍｏ＋Ｗ／２）、残留オーステナイト量およびＲ置が各々１つでも低く外れた鋼種は、硬さが６３ＨＲＣ以上でない。Ｎが低く外れた鋼種はシャルピー衝撃値が低いため、靱性が低い。Ｒ値が高くはずれた鋼種は、変寸が大きい。一次炭化物面積率が低く、一次炭化物個数が少ない鋼種はシャルピー衝撃値が低いため、靱性が低いことが分かる。 From the above Tables 1 and 3, even one content of each of C, Si, Mn, (Mo + W / 2), and (V + Nb / 2), which are the chemical components of the steel of the present invention, deviates significantly from the scope of the claims. Steel grades have low Charpy impact values and thus low toughness. (Mo + W / 2), the steel type in which at least one of the retained austenite amount and the R value deviated from each other had a hardness of not more than 63 HRC. Steels with low N values have low Charpy impact values and thus low toughness. A steel type with a high R value deviates greatly. It can be seen that a steel type having a low primary carbide area ratio and a small number of primary carbides has a low Charpy impact value, and thus has low toughness.
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| JP7214313B2 (en) * | 2018-12-04 | 2023-01-30 | 山陽特殊製鋼株式会社 | High toughness cold work tool steel with high wear resistance |
| JP2020111766A (en) * | 2019-01-08 | 2020-07-27 | 山陽特殊製鋼株式会社 | Cold tool steel |
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| JP2960496B2 (en) * | 1989-12-12 | 1999-10-06 | 日立金属株式会社 | Cold tool steel |
| JP3821974B2 (en) * | 1999-01-14 | 2006-09-13 | 山陽特殊製鋼株式会社 | Cold work tool steel |
| AU2003241253C1 (en) * | 2002-06-13 | 2009-05-14 | Uddeholms Ab | Cold work steel and cold work tool |
| JP5988732B2 (en) * | 2012-07-02 | 2016-09-07 | 山陽特殊製鋼株式会社 | Cold work tool steel with high hardness and toughness |
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