JP4186340B2 - Hot work tool steel with excellent wear resistance - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、熱間鍛造用金型、押し出し型、ダイカスト金型等に使用される被削性と工具寿命に優れた熱間工具鋼に関するものである。
【０００２】
【従来の技術】
熱間での鍛造、押し出し、ダイカスト等の金型に使用される工具鋼は、金型の寿命を向上させるために高温強度や靱性の改善以外に、金型作製時における加工時間の短縮や切削工具寿命の延命等を図るための被削性の向上も必要となる。
【０００３】
合金工具鋼鋼材としては、ＪＩＳ Ｇ ４４０４に多種類のものが規定されているが、中でも５ＣｒーＭｏーＶ系のＳＫＤ６１やＳＫＤ６２等、３Ｃｒー３Ｍｏ−Ｖ系のＳＫＤ７、及び、ＮｉーＣｒーＭｏーＶ系のＳＫＴ３やＳＫＴ４等、が熱間工具用として多用されている。しかしながら、これらの合金工具鋼鋼材では、前記した熱間工具鋼に要求される特性を満足することは不可能である。
【０００４】
このような状況に対して、快削元素を添加して被削性を高めようとする技術がいくつか提案されている。
例えば特開平９ー２１７１４７号では、Ｓ、Ｔｅを非金属介在物として鋼中に介在させることによって、切削加工時に応力集中源として作用させ、切削抵抗の低下並びに切削屑の破砕性を高めることにより、被削性を向上させるものが提案されている。また、特開平４ー３５８０４０号では、被削性の低下の原因となる炭化物量を低減させるものが提案されている。
【０００５】
【発明が解決しようとする課題】
しかしながら、特開平９ー２１７１４７号で提案された熱間工具鋼では、ある程度の被削性の向上は認められるものの、Ｓ、Ｔｅの非金属介在物が靱性や高温強度の低下を招くという欠点がある。また、特開平４ー３５８０４０号で提案された熱間工具鋼では、炭化物量の低下に伴って高温強度が低下し、工具寿命を低下させるという欠点がある。
すなわち、現状の技術においては、被削性と靱性、高温強度を全て満足する熱間工具鋼を得ることは非常に困難であった。
【０００６】
本発明は、上記した課題に鑑みてなされたものであり、被削性に優れ、工具寿命の延命を可能とする熱間工具鋼を提供することを目的としている。
【０００７】
【課題を解決するための手段】
上記した目的を達成するために、本発明に係る耐摩耗性に優れた熱間工具鋼では、
重量％で、
Ｃ ：０．４０〜０．６０％、
Ｓｉ：０．２０を超え、１．２０％以下、
Ｍｎ：０．２０〜１．５０％、
Ｎｉ：１．００〜２．００％、
Ｃｒ：１．００〜２．７０％、
Ｍｏ：０．３０〜２．００％、
Ｖ ：０．１０％を超え、０．８０％未満、
Ａｌ：０．００５％以上、０．１０％未満、
を含有し、残部はＦｅおよび不可避的不純物で、この不可避的不純物中のＰは０．０１５％以下、Ｓは０．００５％以下、Ｎは０．０１５％以下であり、焼入時の組織がマルテンサイト＋ベイナイトであって、かつ、前記組織におけるベイナイト量が５〜８０％であることとしている。そして、このようにすることで、被削性を維持し、高温強度と靱性の相反する特性を兼ね備えさせることができる。
【０００８】
【発明の実施の形態】
上記した目的を達成するために、本発明者らは、熱間工具鋼の特性に及ぼす合金元素について種々の検討を行い、以下の事柄を知見した。
【０００９】
▲１▼靱性
靱性に及ぼすＳｉ含有量と焼入組織の影響を図１に示す。
図１は後述する実施例における鋼種Ｎｏ．１〜１８を用いて、靱性（破壊靱性値）に及ぼすＳｉ含有量並びに焼入組織の影響を示した図であるが、この図１より、明らかなように、焼入時の組織がマルテンサイトの場合（図１中の●印）の靱性は、一般に報告されているように、Ｓｉ含有量の低減により改善され、Ｓｉ含有量が１．２重量％でも熱間工具鋼として必要な２５０ｋｇｆ／ｍｍ2 以上の靱性値が得られることが判る。
【００１０】
また、マルテンサイト＋ベイナイトの場合（図１中の■印）の靱性は、マルテンサイト単独の場合と比較して低くなるものの、Ｓｉ含有量の依存性はマルテンサイト単独の場合よりも弱くなっている。そして、全てがベイナイトの場合（図１中の▲印）には、熱間工具鋼として必要な靱性値は、Ｓｉ含有量に係わらず必要な値よりも低いものの、Ｓｉ含有量の依存性が全くなくなることを、本発明者らは今回の検討で初めて見出した。
【００１１】
▲２▼高温強度
高温強度に及ぼすＳｉ含有量と焼入時の組織の影響を図２に示す。
図２は後述する実施例における鋼種Ｎｏ．１〜１８を用いて、高温強度（６００℃の０．２％耐力）に及ぼすＳｉ含有量並びに焼入組織の影響を示した図であるが、この図２より、高温強度も靱性と同様にＳｉ含有量の増加に伴って低下し、焼入時の組織は、マルテンサイト単独の場合（図２中の●印）と比較してマルテンサイト＋ベイナイトの場合（図２中の■印）に、さらに、ベイナイト単独の場合（図２中の▲印）に高温強度に優れることを、本発明者らは今回の検討で初めて見出した。
【００１２】
▲３▼被削性
被削性に及ぼすＳｉ含有量と焼入時の組織の影響を図３に示す。
図３は後述する実施例における鋼種Ｎｏ．１〜１８を用いて、被削性（切削工具の寿命に至るまでの切削長）に及ぼすＳｉ含有量並びに焼入組織の影響を示した図であるが、この図３より、被削性の向上にはＳｉ含有量が０．２重量％以上でないと効果が得られないことが判る。さらに、焼入時における組織（図３中の●印：マルテンサイト単独の場合、■印：マルテンサイト＋ベイナイトの場合、▲印：ベイナイト単独の場合）の依存性が無いことも判る。また、硬さの依存性もないことが判っていることから、被削性の向上には、Ｓｉ含有量の増加が最も有効であることが判明した。
【００１３】
上記した▲１▼〜▲３▼の知見より、Ｓｉ含有量を増加させることは被削性の向上に最も有効である反面、靱性の低下を招くだけでなく高温強度も低下させること、及び、Ｓｉ含有量を増加させてもベイナイト組織を有するようにすることで、高温強度の低下を抑えることができるようになることが判る。
【００１４】
また、上記した▲１▼▲２▼の知見、すなわち、ベイナイト率の増加に伴って靱性が低下し、高温強度が上昇する理由は、ベイナイトとマルテンサイトから析出する炭化物の形態に依存していることによると考えられる。つまり、焼き戻し後のベイナイトは、マルテンサイトと比較すると、粗大な炭化物が析出するために靱性が低下し、また、Ｍｏ2 Ｃが微細析出するために高温強度が上昇するからと考えられる。
【００１６】
本発明に係る耐摩耗性に優れた熱間工具鋼は、上記した本発明者らの知見に基づき、高温強度と靱性の相反する特性を兼ね備えさせると共に、上記した知見に加え、被削性を維持し高温強度、靱性の全てに優れる成分系を調査した結果に基づいて成されたものであり、重量％で、Ｃ：０．４０〜０．６０％、Ｓｉ：０．２０を超え、１．２０％以下、Ｍｎ：０．２０〜１．５０％、Ｎｉ：１．００〜２．００％、Ｃｒ：１．００〜２．７０％、Ｍｏ：０．３０〜２．００％、Ｖ：０．１０％を超え、０．８０％未満、Ａｌ：０．００５％以上、０．１０％未満、を含有し、残部はＦｅおよび不可避的不純物で、この不可避的不純物中のＰは０．０１５％以下、Ｓは０．００５％以下、Ｎは０．０１５％以下であり、焼入時の組織がマルテンサイト＋ベイナイトであって、かつ、前記組織におけるベイナイト量が５〜８０％であることを要旨とする耐摩耗性に優れた熱間工具鋼である。
【００１７】
以下に、本発明に係る耐摩耗性に優れた熱間工具鋼における化学成分を限定する理由について説明する。
Ｃ：Ｃは鋼の焼入性を高め、靱性を向上させ、焼き戻し時に炭窒化物として二次析出して高温強度を向上させる作用を有する。しかし、その含有量が０．４０％未満では添加効果が乏しく、０．６０％を超えて含有させると、被削性の低下を引き起こすため、本発明では望ましくはその含有量を０．４０〜０．６０％とした。
【００１８】
Ｓｉ：Ｓｉは鋼の被削性を向上する作用を有する（図１参照）。しかし、その含有量が０．２０％以下では添加効果に乏しく、１．２０％を超えると靱性（図２参照）及び高温強度（図３参照）を低下させ、熱間工具寿命の低下を引き起こす。そこで、本発明では望ましくはその含有量を０．２０％を超え、１．２０％以下とした。
【００１９】
Ｍｎ：Ｍｎは鋼の焼入性を向上させて靱性を高めるのに有効な元素である。しかし、その含有量が０．２０％未満では添加効果が得られず、１．５０％を超えると偏析が生じて靱性、強度の低下を招くようになるので、本発明では望ましくはその含有量を０．２０〜１．５０％とした。
【００２０】
Ｎｉ：ＮｉもＭｎと同様に焼入性を向上させて靱性を改善するのに有効な元素であるが、その含有量が１．００％未満ではその効果が乏しく、２．００％を超えると変態点を下げて高温強度の低下を招く。従って、本発明では望ましくはその含有量を１．００〜２．００％とした。
【００２１】
Ｃｒ：Ｃｒは靱性、耐摩耗性の向上に有効な元素であるが、その含有量が１．００％未満では十分な効果が得られず、２．７０％を超えると高温強度の低下を招くようになるので、本発明では望ましくはその含有量を１．００〜２．７０％とした。
【００２２】
Ｍｏ：Ｍｏは鋼の焼入性と焼き戻し軟化抵抗を向上させて、靱性と高温強度を高める作用を有する。しかし、その含有量が０．３０％未満では添加効果が得られない。一方、２．００％を超えると被削性、靱性が低下する。従って、本発明では望ましくはその含有量を０．３０〜２．００％とした。
【００２３】
Ｖ：Ｖは高温強度を高めるのに必要な元素である。Ｖの含有量が０．１０％以下であるとその効果が乏しく、０．８％以上では被削性と靱性を悪化させる。そこで、本発明では望ましくはその含有量を０．１０％を超え、０．８０％未満とした。
【００２４】
Ａｌ：Ａｌは鋼の脱酸の安定化及び均質化を図るのに有効な元素であり、その含有量が０．００５％未満ではその効果を得ることができない。また、０．１０％以上では被削性の低下や鋼中の地きずの原因となる。そのため、本発明では望ましくはその含有量を０．００５％以上、０．１０％未満とした。
【００２５】
本発明に係る熱間工具鋼では、不純物元素としてのＰ，Ｓ及びＮの含有量を、それぞれ下記の通り規制する。
Ｐ：Ｐは含有量が多いと偏析が大きくなり、靱性の低下や熱亀裂の発生を助長するので、その含有量は可能な限り少ないことが望ましい。そこで、本発明ではその含有量を０．０１５％以下に限定した。
【００２６】
Ｓ：Ｓは硫化物を形成し、被削性を向上させるが、靱性を低下させるので、含有量は可能な限り少ないことが望ましい。そこで、本発明ではその含有量を０．００５％以下に限定した。
【００２７】
Ｎ：ＮはＶと窒化物を形成して焼入加熱時の固溶Ｖ量を減少させる。固溶Ｖ量が少ないと焼き戻し時に二次析出するＶ炭窒化物の量が減少し、高温強度が低下する。そこで、本発明ではその含有量を０．０１５％以下に限定した。
【００２８】
焼入組織：焼入組織のベイナイト率は、厚さ１０ｍｍの素材を焼入れした際に、水冷した場合の素材の硬さをＨ１、室温まで２０時間かけて冷却した場合の素材の硬さをＨ２とし、実際に熱処理をしたときの素材の硬さをＨとしたとき、次式により算出される。なお、硬さはビッカース硬さで表示する。
ベイナイト率（％）＝１００−｛（Ｈ−Ｈ２）／（Ｈ１−Ｈ２）｝×１００
【００２９】
本発明者らの実験によれば、ベイナイト率が０（１００％マルテンサイト）〜４％の場合には、高温強度の向上には不十分であり、ベイナイト率が８０％を超える場合は靱性が低下する。そこで、本発明ではベイナイト率を５〜８０％のマルテンサイト＋ベイナイト混合組織に限定した。
【００３０】
【実施例】
本発明に係る熱間工具鋼の効果を実施例に基づいて説明する。
下記表１に示す化学組成を有する本発明鋼（Ｎｏ．７〜Ｎｏ．１２）、及び＊印を付した部分が本発明で規定するベイナイト率或いは成分範囲から外れた比較鋼（Ｎｏ．１〜Ｎｏ．６及びＮｏ．１３〜Ｎｏ．３８）を、電気炉で溶製して得た鋼塊を分塊し、鍛錬比５以上で鍛造した後、８００〜８５０℃で焼鈍をした。
【００３１】
焼入組織を変化させるために、厚さを１０〜８００ｍｍにし、９００〜１０５０℃から水冷、油冷、炉冷により焼入を実施した。そして、引き続き、焼き戻しを５５０〜６４０℃で行い、硬さＨＳ５５〜６０に調整して金型を製造し、そして下記の各種試験を実施した。
【００３２】
被削性試験は、フライス加工( 工具材質：ＰＶＤコーテッド超硬（Ｋ２０）、切削条件：Ｖ＝５０ｍ／ｍｉｎ、ｆ＝０．１８ｍｍ／刃、ｄ＝３．０ｍｍ）により切削工具寿命までの切削長を測定した。
【００３３】
高温強度試験は、ＪＩＳ １４Ａ号試験片（直径Ｄ＝６ｍｍ）にてＪＩＳ Ｇ
０５６７に準拠し、６００℃の試験温度で行い、０．２％耐力を測定した。
破壊靱性試験はＡＳＴＭ Ｅ３９９−８３に準じて測定した。
【００３４】
経験的に切削長が１ｍ以上で被削性に優れ、破壊靱性値が２５０ｋｇｆ／ｍｍ 3/2 以上、かつ、６００℃の０．２％耐力が５５ｋｇｆ／ｍｍ2 以上のとき工具寿命が優れることが判っている。
【００３５】
下記表１に示される本発明鋼は、下記表２に示すように、切削長、破壊靱性値、６００℃の０．２％耐力の全てが所定値を満足し、比較鋼と比較して優れていることが判る。
被削性向上にはＳｉ含有量の増加が最も有効であるが、これまではＳｉ含有量の増加により、高温強度の低下を伴っていたものが、本発明鋼では、焼入組織をベイナイト率が５〜８０％のマルテンサイト＋ベイナイト混合組織にすることにより、Ｓｉによる高温強度低下分を補うことができた。また、その他成分により靱性の低下も抑えることができた。本発明鋼を熱間鍛造金型として評価した例を下記表３に示しているが、いずれも比較鋼よりも寿命が長いことが判る。
【００３６】
【表１】
【表２】
【表３】
【発明の効果】
以上説明したように、本発明に係る熱間工具鋼は従来技術では成しえなかった被削性、靱性、高温強度の全てを完備し、熱間鍛造、押し出し、ダイカストに用いられる金型やマンドレル等に使用した場合には、その製造費の削減、並びに、工具寿命を延ばすことが可能で、産業上の効果は非常に大きい。
【図面の簡単な説明】
【図１】靱性（破壊靱性値）に及ぼすＳｉ含有量ならびに焼入組織の影響を示す図である。
【図２】高温強度（６００℃の０．２％耐力）に及ぼすＳｉ含有量ならびに焼入組織の影響を示す図である。
【図３】被削性（切削工具の寿命に至るまでの切削長）に及ぼすＳｉ含有量ならびに焼入組織の影響を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hot tool steel excellent in machinability and tool life used for a hot forging die, an extrusion die, a die casting die and the like.
[0002]
[Prior art]
Tool steel used for hot forging, extrusion, die casting and other dies, in addition to improving high-temperature strength and toughness in order to improve the life of the dies, shortening the machining time and cutting during die production It is also necessary to improve machinability in order to extend the tool life.
[0003]
As JIS G 4404, many types of alloy tool steels are defined. Among them, 5Cr-Mo-V type SKD61 and SKD62, 3Cr-3Mo-V type SKD7, and Ni-Cr- Mo-V type SKT3, SKT4, etc. are frequently used for hot tools. However, with these alloy tool steels, it is impossible to satisfy the characteristics required for the hot tool steel described above.
[0004]
In response to such a situation, several techniques for adding a free-cutting element to improve machinability have been proposed.
For example, in Japanese Patent Laid-Open No. 9-217147, by interposing S and Te in steel as non-metallic inclusions, it acts as a stress concentration source at the time of cutting, thereby reducing the cutting resistance and increasing the friability of cutting waste. Something that improves machinability has been proposed. Japanese Patent Application Laid-Open No. 4-358040 proposes a technique for reducing the amount of carbide that causes a decrease in machinability.
[0005]
[Problems to be solved by the invention]
However, in the hot work tool steel proposed in Japanese Patent Laid-Open No. 9-217147, although some improvement in machinability is recognized, there is a drawback that non-metallic inclusions of S and Te cause a decrease in toughness and high temperature strength. is there. In addition, the hot tool steel proposed in Japanese Patent Laid-Open No. 4-358040 has the disadvantage that the high-temperature strength decreases with a decrease in the amount of carbide and the tool life decreases.
In other words, with the current technology, it has been very difficult to obtain a hot work tool steel that satisfies all of machinability, toughness, and high temperature strength.
[0006]
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a hot tool steel that has excellent machinability and can extend the tool life.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, in the hot work tool steel excellent in wear resistance according to the present invention,
% By weight
C: 0.40 to 0.60%,
Si: more than 0.20, 1.20% or less,
Mn: 0.20 to 1.50%,
Ni: 1.00 to 2.00%,
Cr: 1.00 to 2.70%,
Mo: 0.30 to 2.00%,
V: more than 0.10%, less than 0.80%,
Al: 0.005% or more, less than 0.10%,
The balance is Fe and inevitable impurities, P in the inevitable impurities is 0.015% or less, S is 0.005% or less, N is 0.015% or less, and the structure at the time of quenching There has been a possible I martensite + bainite der and bainite amount in the tissue is 5 to 80%. And by doing in this way, machinability can be maintained and it can have the characteristic which high temperature strength and toughness conflict.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In order to achieve the above-described object, the present inventors have made various studies on alloy elements affecting the properties of hot tool steel and have found the following matters.
[0009]
(1) Toughness FIG. 1 shows the influence of Si content and hardened structure on toughness.
FIG. 1 shows the steel type No. 1 to 18 show the influence of the Si content and the quenched structure on the toughness (fracture toughness value). As is clear from FIG. 1, the structure at the time of quenching is martensite. The toughness in this case (marked with ● in FIG. 1) is improved by reducing the Si content, as generally reported, and even if the Si content is 1.2 wt%, 250 kgf / It can be seen that a toughness value of mm 2 or more is obtained.
[0010]
Further, although the toughness in the case of martensite + bainite (marked by ■ in FIG. 1) is lower than that in the case of martensite alone, the dependence on the Si content is weaker than in the case of martensite alone. Yes. And when all are bainite (▲ mark in FIG. 1), although the toughness value required as a hot tool steel is lower than the required value regardless of the Si content, the dependency of the Si content is The present inventors have found for the first time in this study that they will disappear completely.
[0011]
(2) High temperature strength FIG. 2 shows the influence of the Si content and the structure during quenching on the high temperature strength.
FIG. 2 shows the steel type No. 1 to 18 show the influence of the Si content and the quenching structure on the high temperature strength (0.2% proof stress at 600 ° C.). From FIG. 2, the high temperature strength is similar to the toughness. As the Si content increases, the structure at the time of quenching is in the case of martensite + bainite (marked with ■ in Fig. 2) compared to martensite alone (marked with ● in Fig. 2). Furthermore, the present inventors have found for the first time in this examination that bainite alone is excellent in high-temperature strength (indicated by a triangle in FIG. 2).
[0012]
(3) Machinability FIG. 3 shows the influence of the Si content and the structure during quenching on the machinability.
FIG. 3 shows the steel type No. 1 to 18 show the influence of the Si content and the hardened structure on the machinability (cutting length until the life of the cutting tool). From FIG. It can be seen that the effect cannot be obtained unless the Si content is 0.2% by weight or more. Furthermore, it can be seen that there is no dependency on the structure at the time of quenching (in FIG. 3, mark ●: martensite alone, mark ■: martensite + bainite, mark ▲: bainite alone). Further, since it has been found that there is no dependence on hardness, it has been found that increasing the Si content is the most effective for improving machinability.
[0013]
From the above findings (1) to (3), increasing the Si content is most effective for improving machinability, but not only lowering toughness but also reducing high-temperature strength, and It can be seen that even if the Si content is increased, a decrease in high-temperature strength can be suppressed by having a bainite structure.
[0014]
In addition, the findings of the above (1), (2), that is, the reason why the toughness decreases and the high temperature strength increases as the bainite ratio increases, depends on the form of carbides precipitated from bainite and martensite. It is thought that. That is, it is considered that bainite after tempering has lower toughness due to precipitation of coarse carbides and higher strength at high temperatures due to fine precipitation of Mo 2 C compared to martensite.
[0016]
The hot work tool steel with excellent wear resistance according to the present invention is based on the above-mentioned findings of the present inventors, and has both high temperature strength and toughness conflicting properties, and in addition to the above-described knowledge, machinability. It was made on the basis of the results of investigating a component system that was maintained and excellent in all of the high-temperature strength and toughness. By weight percent, C: 0.40 to 0.60%, Si: more than 0.20, 20% or less, Mn: 0.20 to 1.50%, Ni: 1.00 to 2.00%, Cr: 1.00 to 2.70%, Mo: 0.30 to 2.00%, V : More than 0.10%, less than 0.80%, Al: 0.005% or more and less than 0.10%, the balance being Fe and inevitable impurities, P in the inevitable impurities is 0 .015% or less, S is 0.005% or less, N is 0.015% or less, and the structure at the time of quenching is martenser. A preparative + bainite, and an excellent hot work tool steel in wear resistance that summarized in that bainite amount in the tissue is 5 to 80%.
[0017]
Below, the reason for limiting the chemical component in the hot tool steel excellent in abrasion resistance according to the present invention will be described.
C: C enhances the hardenability of the steel, improves the toughness, and has a function of improving the high temperature strength by secondary precipitation as carbonitride during tempering. However, if the content is less than 0.40%, the effect of addition is poor, and if the content exceeds 0.60%, the machinability is lowered. Therefore, in the present invention, the content is preferably 0.40 to 0.40%. The content was 0.60%.
[0018]
Si: Si has the effect of improving the machinability of steel (see FIG. 1). However, if the content is 0.20% or less, the effect of addition is poor, and if it exceeds 1.20%, the toughness (see FIG. 2) and the high-temperature strength (see FIG. 3) are lowered and the hot tool life is reduced. . Therefore, in the present invention, the content is desirably more than 0.20% and not more than 1.20%.
[0019]
Mn: Mn is an element effective for improving the hardenability of steel and increasing toughness. However, if the content is less than 0.20%, the effect of addition cannot be obtained, and if it exceeds 1.50%, segregation occurs, leading to a decrease in toughness and strength. Was set to 0.20 to 1.50%.
[0020]
Ni: Ni is also an element effective for improving hardenability and improving toughness in the same manner as Mn. However, when its content is less than 1.00%, its effect is poor, and when it exceeds 2.00% Lowering the transformation point leads to a decrease in high temperature strength. Therefore, in the present invention, the content is desirably 1.00 to 2.00%.
[0021]
Cr: Cr is an element effective for improving toughness and wear resistance. However, if its content is less than 1.00%, a sufficient effect cannot be obtained, and if it exceeds 2.70%, high temperature strength is reduced. Therefore, in the present invention, the content is desirably 1.00 to 2.70%.
[0022]
Mo: Mo has the effect of improving the toughness and high temperature strength by improving the hardenability and temper softening resistance of the steel. However, if the content is less than 0.30%, the effect of addition cannot be obtained. On the other hand, if it exceeds 2.00%, the machinability and toughness deteriorate. Therefore, in the present invention, the content is desirably 0.30 to 2.00%.
[0023]
V: V is an element necessary for increasing the high temperature strength. If the V content is 0.10% or less, the effect is poor, and if it is 0.8% or more, the machinability and toughness are deteriorated. Therefore, in the present invention, the content is desirably more than 0.10% and less than 0.80%.
[0024]
Al: Al is an element effective for stabilizing and homogenizing deoxidation of steel. If the content is less than 0.005%, the effect cannot be obtained. On the other hand, if the content is 0.10% or more, machinability is deteriorated and a ground defect in the steel is caused. Therefore, in the present invention, the content is desirably 0.005% or more and less than 0.10%.
[0025]
The hot work tool steel according to the present invention, P as an impurity element, the content of S and N, regulates as their respective following.
P: When the content of P is large, segregation increases and promotes the reduction of toughness and the occurrence of thermal cracks. Therefore, the content of P is desirably as small as possible. Thus, the content of Waso present invention is limited to 0.015% or less.
[0026]
S: S forms sulfides and improves machinability, but lowers toughness, so the content is preferably as small as possible. Thus, the content of Waso present invention is limited to 0.005% or less.
[0027]
N: N forms nitrides with V to reduce the amount of dissolved V during quenching heating. If the amount of solute V is small, the amount of V carbonitride that is secondarily precipitated during tempering decreases and the high-temperature strength decreases. Thus, the content of Waso present invention is limited to 0.015% or less.
[0028]
Hardened structure: The bainite ratio of the hardened structure is the hardness of the material when water-cooled when the material having a thickness of 10 mm is quenched, and the hardness of the material when cooled to room temperature over 20 hours is H2. And when the hardness of the material when actually heat-treated is H, it is calculated by the following equation. The hardness is displayed as Vickers hardness.
Bainite ratio (%) = 100 − {(H−H2) / (H1−H2)} × 100
[0029]
According to the experiments by the present inventors, when the bainite ratio is 0 (100% martensite) to 4%, it is insufficient for improving the high-temperature strength, and when the bainite ratio exceeds 80%, the toughness is increased. descend. Therefore, in the present invention, the bainite ratio is limited to a martensite + bainite mixed structure of 5 to 80%.
[0030]
【Example】
The effect of the hot tool steel according to the present invention will be described based on examples.
The present invention steel having a chemical composition shown in Table 1 (No.7~No.1 2), and * subjected part mark off the bainite ratio or composition range specified in the present onset bright comparative steel (No. 1 to No. 6 and No. 13 to No. 38 ) were ingots obtained by melting in an electric furnace, forged at a forging ratio of 5 or more, and then annealed at 800 to 850 ° C.
[0031]
In order to change the quenching structure, the thickness was set to 10 to 800 mm, and quenching was performed from 900 to 1050 ° C. by water cooling, oil cooling, and furnace cooling. Subsequently, tempering was performed at 550 to 640 ° C., the mold was manufactured by adjusting the hardness to HS 55 to 60, and the following various tests were performed.
[0032]
The machinability test is performed by milling (tool material: PVD coated carbide (K20), cutting conditions: V = 50 m / min, f = 0.18 mm / tooth, d = 3.0 mm) until cutting tool life. The length was measured.
[0033]
The high-temperature strength test is performed using a JIS 14A test piece (diameter D = 6 mm).
In accordance with 0567, the test was conducted at a test temperature of 600 ° C., and 0.2% proof stress was measured.
The fracture toughness test was measured according to ASTM E399-83.
[0034]
Empirically, the tool length is excellent when the cutting length is 1 m or more, the machinability is excellent, the fracture toughness value is 250 kgf / mm 3/2 or more, and the 0.2% proof stress at 600 ° C. is 55 kgf / mm 2 or more. Is known.
[0035]
As shown in Table 2 below, the steel of the present invention shown in Table 1 below is superior to the comparative steel in that the cutting length, fracture toughness value, and 0.2% proof stress at 600 ° C. all satisfy predetermined values. You can see that
Increasing the Si content is the most effective for improving machinability, but up until now there was a decrease in high-temperature strength due to the increase in Si content. By using a martensite + bainite mixed structure with 5 to 80%, it was possible to compensate for the decrease in high-temperature strength due to Si. Moreover, the fall of toughness could be suppressed by other components. An example of evaluating the steel of the present invention as a hot forging die is shown in Table 3 below, and it can be seen that all have a longer life than the comparative steel.
[0036]
[Table 1]
[Table 2]
[Table 3]
【The invention's effect】
As explained above, the hot work tool steel according to the present invention has all the machinability, toughness, and high temperature strength that could not be achieved by the prior art, and is used for hot forging, extrusion, die casting and die casting. When used for a mandrel or the like, the manufacturing cost can be reduced and the tool life can be extended, and the industrial effect is very great.
[Brief description of the drawings]
FIG. 1 is a diagram showing the influence of Si content and quenched structure on toughness (fracture toughness value).
FIG. 2 is a diagram showing the influence of Si content and quenched structure on high-temperature strength (0.2% yield strength at 600 ° C.).
FIG. 3 is a diagram showing the influence of Si content and hardened structure on machinability (cutting length until the life of a cutting tool).
Claims (1)
Ｃ ：０．４０〜０．６０％、
Ｓｉ：０．２０を超え、１．２０％以下、
Ｍｎ：０．２０〜１．５０％、
Ｎｉ：１．００〜２．００％、
Ｃｒ：１．００〜２．７０％、
Ｍｏ：０．３０〜２．００％、
Ｖ ：０．１０％を超え、０．８０％未満、
Ａｌ：０．００５％以上、０．１０％未満、
を含有し、残部はＦｅおよび不可避的不純物で、この不可避的不純物中のＰは０．０１５％以下、Ｓは０．００５％以下、Ｎは０．０１５％以下であり、焼入時の組織がマルテンサイト＋ベイナイトであって、かつ、前記組織におけるベイナイト量が５〜８０％であることを特徴とする耐摩耗性に優れた熱間工具鋼。% By weight
C: 0.40 to 0.60%,
Si: more than 0.20, 1.20% or less,
Mn: 0.20 to 1.50%,
Ni: 1.00 to 2.00%,
Cr: 1.00 to 2.70%,
Mo: 0.30 to 2.00%,
V: more than 0.10%, less than 0.80%,
Al: 0.005% or more, less than 0.10%,
Containing, the balance of Fe and unavoidable impurities, P is 0.015% in the unavoidable impurities less, S 0.005% below, N is the Ri der 0.015% or less, the baked Nyutoki tissue a martensite + bainite, and wear resistance superior hot work tool steel bainite amount in the tissue you wherein 5% to 80% der Rukoto.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP26866499A JP4186340B2 (en) | 1999-09-22 | 1999-09-22 | Hot work tool steel with excellent wear resistance |
| US09/664,766 US6478898B1 (en) | 1999-09-22 | 2000-09-19 | Method of producing tool steels |
| EP00308357A EP1087030B9 (en) | 1999-09-22 | 2000-09-22 | Method of producing tool steel and tool |
| DE60021670T DE60021670T2 (en) | 1999-09-22 | 2000-09-22 | Method for producing a tool steel and tool |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP26866499A JP4186340B2 (en) | 1999-09-22 | 1999-09-22 | Hot work tool steel with excellent wear resistance |
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| JP4186340B2 true JP4186340B2 (en) | 2008-11-26 |
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| SE533283C2 (en) | 2008-03-18 | 2010-08-10 | Uddeholm Tooling Ab | Steel, process for manufacturing a steel blank and process for manufacturing a detail of the steel |
| JP5881276B2 (en) * | 2010-03-23 | 2016-03-09 | 山陽特殊製鋼株式会社 | Hot tool steel with excellent toughness, short-time and long-term softening resistance |
| CN105483502A (en) * | 2015-12-03 | 2016-04-13 | 浙江腾龙精线有限公司 | Production method for spring wire |
| WO2017109233A1 (en) * | 2015-12-24 | 2017-06-29 | Rovalma, S.A | Long durability high performance steel for structural, machine and tooling applications |
| CN109266965A (en) * | 2018-11-01 | 2019-01-25 | 宁波钢铁有限公司 | A kind of hot rolled strip and its preparation and application |
| CN110656294B (en) * | 2019-10-31 | 2021-08-03 | 宝钢轧辊科技有限责任公司 | Working roll special for tin-plating finisher and manufacturing method thereof |
| CN113621876A (en) * | 2021-06-02 | 2021-11-09 | 中航上大高温合金材料股份有限公司 | Manufacturing method of high-performance hot-work die steel |
| JP7320095B1 (en) * | 2022-03-02 | 2023-08-02 | 山陽特殊製鋼株式会社 | Alloy tool steel for hot working |
| CN114717389B (en) * | 2022-04-18 | 2023-09-22 | 燕山大学 | Wear-resistant low-temperature bainite hot work die steel and preparation method thereof |
| CN115386690A (en) * | 2022-08-25 | 2022-11-25 | 阳江合金材料实验室 | Method for preparing 7Cr17MoV stainless steel with improved hardness and stainless steel |
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