JP5359582B2 - Hardened tool steel material - Google Patents
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Abstract
Description
本発明は、焼入れ焼戻しにより、均一微細な結晶粒を得ることができる金属組織を有する焼入れ用工具鋼素材に関するものである。 The present invention relates to a tool steel material for quenching having a metal structure capable of obtaining uniform fine crystal grains by quenching and tempering.
焼入れ焼戻しにより均一微細な結晶粒を得る手法として、焼入れ用工具鋼素材の製造過程で変態を繰り返すことが挙げられる。この方法は熱間加工後にマルテンサイト、ベイナイト変態域まで冷却し、その後Ａｃ３点以上で完全にオーステナイト変態させ、焼きなましを行った後、焼入れ焼戻しするといった熱処理方法がその例である。
また、焼入れ用工具鋼素材の焼きなまし状態での金属組織は、炭化物を均一に分散させた金属組織であるほうが好ましいとされる。
しかし、原因不明の結晶粒異常成長が報告されており、その原因としては
(１)逆マルテンサイト変態説(非特許文献１)、
(２)結晶方位規制説(非特許文献２)、
(３)残留オーステナイト合体説(非特許文献３)
などが知られている。
As a technique for obtaining uniform fine crystal grains by quenching and tempering, it is possible to repeat transformation in the process of manufacturing a tool steel material for quenching. An example of this method is a heat treatment method in which the steel is cooled to a martensite and bainite transformation region after hot working, then completely austenite transformed at the Ac3 point or higher, annealed, and then quenched and tempered.
In addition, the metal structure in the annealed state of the tool steel material for quenching is preferably a metal structure in which carbides are uniformly dispersed.
However, unexplained abnormal grain growth has been reported.
(1) Reverse martensitic transformation theory (Non-Patent Document 1),
(2) Crystal orientation regulation theory (Non-Patent Document 2),
(3) Residual austenite coalescence theory (Non-patent Document 3)
Etc. are known.
従来の結晶粒微細化方法では、焼きなまし状態での金属組織が均一な組織であっても、焼入れ焼戻し後に均一微細な結晶粒を得ることができない現象が起こりえた。これは、焼入れ処理の保持温度、加熱速度、冷却速度等の条件が不適当であった時に起こり易く、これらの解決手法として、保持温度の見直し、急速加熱、急速冷却による対策が行われてきた。
しかし、昨今の製品の大型化に伴いこれらの対策では物理的に対策不可能な事例も生じてきた。例えば、加熱速度が遅いと結晶粒が粗大に成長するため、加熱速度をできるだけ速くする対策がとられているが、製品の熱伝達係数は一定であり、製品が大型になるほど加熱速度は遅くなり、また、冷却速度も遅くなる傾向にあった。また、原因不明の結晶粒の異常成長が報告されており、完全に均一微細な結晶粒を得ることができないという課題があった。
本発明の目的は、焼入れ焼戻しにより、より確実に均一微細な結晶粒を得ることができる金属組織を有する焼入れ用工具鋼素材を提供することである。
In the conventional crystal grain refinement method, even if the metal structure in the annealed state is a uniform structure, a phenomenon that uniform fine crystal grains cannot be obtained after quenching and tempering may occur. This is likely to occur when conditions such as the holding temperature, heating rate, and cooling rate of the quenching process are inappropriate, and as a solution to these problems, measures have been taken by reviewing the holding temperature, rapid heating, and rapid cooling. .
However, with the recent increase in size of products, there have been cases where these measures cannot be physically addressed. For example, if the heating rate is slow, the crystal grains grow coarsely, so measures are taken to increase the heating rate as much as possible, but the heat transfer coefficient of the product is constant, and the heating rate becomes slower as the product becomes larger. Also, the cooling rate tended to be slow. Further, abnormal growth of crystal grains of unknown cause has been reported, and there has been a problem that it is impossible to obtain completely uniform fine crystal grains.
The objective of this invention is providing the tool steel raw material for hardening which has a metal structure which can obtain a uniform fine crystal grain more reliably by quenching and tempering.
本発明は上述の課題に鑑みてなされたものである。
すなわち本発明は、質量％でＣ：０．１〜０．８％、Ｓｉ：２．０％以下、Ｍｎ：２．０％以下、Ｃｒ：１．０〜１５．０％、Ｍｏ：１０．０％以下を含有し、更にＮｉ：４．０％以下、Ｖ：４．０％以下、Ｗ：１０．０％以下、Ｃｏ：１０．０％以下、の何れか１種以上を含有して残部はＦｅ及び不可避的不純物でなる焼入れ用工具鋼素材であって、該工具鋼素材の金属組織を１００００倍で観察した時、１００μｍ２中に円相当径０．１〜０．５μｍの炭化物個数が３００個以上形成されている炭化物が密な領域Ａと、該領域Ａに対して、１００μｍ２中に円相当径０．１〜０．５μｍの炭化物個数が１００個以上少ない炭化物が疎な領域Ｂとが混在する金属組織でなる焼入れ用工具鋼素材である。
好ましくは、領域Ｂの１００μｍ２中に見られる円相当径０．１〜０．５μｍの炭化物個数は２００個以上である焼入れ用工具鋼素材である。
The present invention has been made in view of the above problems.
That is, in the present invention, C: 0.1 to 0.8% , Si: 2.0% or less, Mn: 2.0% or less, Cr: 1.0 to 15.0%, Mo: 10. It contains 0% or less, and further contains at least one of Ni: 4.0% or less, V: 4.0% or less, W: 10.0% or less, Co: 10.0% or less. The balance is a tool steel material for quenching composed of Fe and inevitable impurities , and the number of carbides having an equivalent circle diameter of 0.1 to 0.5 μm in 100 μm 2 when the metallographic structure of the tool steel material is observed at a magnification of 10,000 times Region A in which 300 or more of the carbides are formed, and a region in which the number of carbides having an equivalent circle diameter of 0.1 to 0.5 μm in 100 μm 2 is less than 100 in the region A. It is a tool steel material for quenching made of a metal structure mixed with B.
Preferably, it is a tool steel material for quenching in which the number of carbides having an equivalent circle diameter of 0.1 to 0.5 μm found in 100 μm 2 of the region B is 200 or more.
本発明によれば、従来の結晶粒微細化には炭化物を均一に分散させるという知見とは全く異なる考え方で焼入れ用工具鋼素材の金属組織を制御することで、より確実に均一微細な結晶粒を得ることができる。 According to the present invention, by controlling the metallographic structure of the tool steel material for quenching with a completely different concept from the knowledge of uniformly dispersing carbide in conventional crystal grain refinement, it is possible to more reliably obtain uniform crystal grains. Can be obtained.
上述したように、本発明の最大の特徴は、焼入れ焼戻しにより均一微細な結晶粒を得ることができる焼入れ用工具鋼素材の金属組織にある。以下に本発明を詳しく説明する。
先ず、本発明では質量％でＣ：０．１〜０．８％を含有する焼入れ用工具鋼素材を本発明の対象とする。
Ｃ含有量を０．１〜０．８％とした理由は、Ｃ量が０．１％未満では、Ｃ量が少なすぎて、特に結晶粒内においてＣが不足し炭化物が析出しなく、０．８％以上ではＣが過剰になり、炭化物が密な領域と炭化物が疎な領域との差がなくなり、焼入れ焼戻しにより均一微細な結晶粒を得るための金属組織を得ることができなくなるためである。
好ましくはＣ：０．２〜０．６％であり、更に好ましくは０．２５〜０．５５％である。
As described above, the greatest feature of the present invention resides in the metal structure of a tool steel material for quenching that can obtain uniform fine crystal grains by quenching and tempering. The present invention is described in detail below.
First, in this invention, the tool steel raw material for hardening containing C: 0.1-0.8% by mass% is made into the object of this invention.
The reason why the C content is 0.1 to 0.8% is that when the C content is less than 0.1%, the C content is too small, particularly in the crystal grains, C is insufficient and carbides are not precipitated. If it is .8% or more, C becomes excessive, there is no difference between the carbide dense region and the carbide sparse region, and it becomes impossible to obtain a metal structure for obtaining uniform fine crystal grains by quenching and tempering. is there.
Preferably it is C: 0.2-0.6%, More preferably, it is 0.25-0.55%.
次に金属組織について説明する。
金属組織において、本発明の焼入れ用工具鋼素材と、従来好ましいと言われていた焼入れ用工具鋼素材とは大きく異なる。
従来好ましいとされている金属組織に調整した焼入れ用工具鋼素材として３５０ｍｍ(t)×３５０ｍｍ(w)×１５００ｍｍ(l)の大型化鋼材から金属組織観察用試験片を切出し、観察した。従来方法により得られた焼入れ用工具鋼素材(焼入れ前の焼きなまし状態)の金属組織を図４に示す。
観察は焼入れ用工具鋼素材から切出した試験片を４％ナイタール腐食後、走査電子顕微鏡(ＳＥＭ)を用いて１００００倍で観察したものであり、１００μｍ２中に円相当径０．１〜０．５μｍの炭化物が１００〜１５０個形成された炭化物が均一に分散させた金属組織である。なお、従来材の化学組成はＣ：０．３９％、Ｓｉ：０．９６％、Ｍｎ：０．４３％、Ｃｒ：５．１１％、Ｍｏ：１．２１％、Ｎｉ：０．２３％、Ｖ：０．８１％含有して残部はＦｅであり、金属組織調整方法は後述する実施例にて示すことにする。
Next, the metal structure will be described.
In the metal structure, the tool steel material for quenching according to the present invention is greatly different from the tool steel material for quenching which has been said to be preferable in the past.
A specimen for observation of metal structure was cut out from a large steel material of 350 mm (t) × 350 mm (w) × 1500 mm (l) as a tool steel material for quenching adjusted to a metal structure which has been considered to be preferable. FIG. 4 shows the metal structure of the tool steel material for quenching (annealed state before quenching) obtained by the conventional method.
Observed after 4% nital corrosion test pieces cut out from the tool steel material for hardening, which was observed at 10,000-fold using a scanning electron microscope (SEM), circle equivalent diameter from 0.1 to 0 in 100 [mu] m 2. A metal structure in which 100 to 150 carbides of 5 μm are uniformly dispersed. The chemical composition of the conventional material is C: 0.39%, Si: 0.96%, Mn: 0.43%, Cr: 5.11%, Mo: 1.21%, Ni: 0.23%, V: 0.81% contained with the balance being Fe, and the metal structure adjustment method will be shown in the examples described later.
続いて、本発明で規定する金属組織について説明する。化学組成は上記の従来材と同じである。
本発明の金属組織は、１００００倍で観察した時、１００μｍ２中に円相当径０．１〜０．５μｍの炭化物個数が３００個以上形成されている炭化物が密な領域Ａを有し、この領域Ａに対して、１００μｍ２中に円相当径０．１〜０．５μｍの炭化物個数が１００個以上少ない炭化物が疎な領域Ｂが混在する金属組織を呈する。
すなわち、本発明で規定する金属組織は、従来材の金属組織に見られる炭化物個数より多くの炭化物が形成され、且つ炭化物が密集する、炭化物が密な領域を有するため、炭化物が微細・不均一分散と言う、特殊な金属組織を呈する。
なお、金属組織は、１００００倍で観察した時、１００μｍ２中に円相当径０．１〜０．５μｍの炭化物個数が３００個以上形成されている炭化物が密な領域を領域Ａとし、領域Ａと比較し炭化物が疎な領域(１００μｍ２中に円相当径０．１〜０．５μｍの炭化物個数が領域Ａに対し、１００個以上少ない)を領域Ｂとして記す。
Then, the metal structure prescribed | regulated by this invention is demonstrated. The chemical composition is the same as the above-mentioned conventional material.
The metal structure of the present invention has a dense region A in which 300 or more carbides having an equivalent circle diameter of 0.1 to 0.5 μm are formed in 100 μm 2 when observed at a magnification of 10,000 times. The region A exhibits a metal structure in which a region B in which the number of carbides having an equivalent circle diameter of 0.1 to 0.5 μm is less than 100 is sparse is mixed in 100 μm 2 .
That is, the metal structure defined in the present invention has a carbide dense region in which a larger number of carbides than the number of carbides found in the metal structure of the conventional material are formed, and the carbides are dense. It exhibits a special metal structure called dispersion.
When the metallographic structure is observed at a magnification of 10,000, the region A is defined as a region having a dense carbide in which 300 or more carbides having an equivalent circle diameter of 0.1 to 0.5 μm are formed in 100 μm 2. A region where carbides are sparse compared to (the number of carbides having an equivalent circle diameter of 0.1 to 0.5 μm in 100 μm 2 is 100 or more less than region A) is referred to as region B.
本発明の焼入れ用工具鋼素材として３５０ｍｍ(t)×３５０ｍｍ(w)×１５００ｍｍ(l)の大型化鋼材から金属組織観察用試験片を切出し、観察した。
観察は焼入れ用工具鋼素材から切出した試験片を４％ナイタール腐食後、走査電子顕微鏡(ＳＥＭ)を用いて１００００倍で観察したものであり、領域Ａを図１に、領域Ｂを図２に示す。上述した領域Ａと領域Ｂの観察は、観察面をランダムに選んだ１０視野以上の視野にて炭化物の分布状況を測定するものとするが、領域Ａは旧オーステナイト粒界かその近傍に見られ、領域Ｂは旧オーステナイト粒の粒内に相当する個所に見られることが多い。
そのため、ランダムに観察する視野には、旧オーステナイト粒界かその近傍の個所と、旧オーステナイト粒内の２つの視野は必須で観察する。
As a tool steel material for quenching according to the present invention, a specimen for metallographic observation was cut out from a large-sized steel material of 350 mm (t) × 350 mm (w) × 1500 mm (l) and observed.
The observation was made by observing a specimen cut out from a tool steel material for quenching at a magnification of 10,000 using a scanning electron microscope (SEM) after 4% nital corrosion. Region A in FIG. 1 and region B in FIG. Show. In the observation of the above-described region A and region B, the distribution state of carbide is measured in a field of view of 10 fields or more with the observation surface selected at random, but the area A is found at or near the prior austenite grain boundary. The region B is often found in a portion corresponding to the inside of the prior austenite grains.
Therefore, for the visual field to be observed at random, the prior austenite grain boundary or its vicinity and the two visual fields in the prior austenite grain are essential.
本発明において上述の炭化物が密な領域Ａと炭化物が疎な領域Ｂとが混在する金属組織とすることが重要であり、この混合組織とすることで、焼き入れ焼戻し後に均一微細な結晶粒を得ることができる。
この結晶粒微細化機構は、領域Ａは０．１〜０．５μｍと微細な炭化物が数多く存在し、領域Ｂは領域Ａに対し炭化物の個数が１００個以上少ないため、焼き入れ加熱すると固溶した炭素濃度は領域Ａが領域Ｂより高くなり、領域Ａの変態点が領域Ｂの変態点より低くなり、領域Ａから優先的にオーステナイトへ変態する。
領域Ａより先に変態したオーステナイトは粒成長するが、次いで領域Ｂもオーステナイトへ変態し、領域Ａより先に変態したオーステナイトの成長を抑制する効果があるためである。また、微細な炭化物が多数析出しているため、焼き入れ加熱により生成するオーステナイトの核生成サイトが増加し、お互いの結晶粒が粒成長を抑制しあうことで焼き入れ焼戻し後に均一微細な結晶粒を得ることができると考えている。
In the present invention, it is important to have a metal structure in which the above-described carbide-rich region A and carbide-sparse region B are mixed. By using this mixed structure, uniform fine crystal grains can be obtained after quenching and tempering. Can be obtained.
In this grain refinement mechanism, region A has many fine carbides of 0.1 to 0.5 μm, and region B has less than 100 carbides compared to region A. The carbon concentration of the region A is higher than that of the region B, the transformation point of the region A is lower than the transformation point of the region B, and transformation from the region A to austenite is performed preferentially.
This is because the austenite transformed prior to the region A is grain-grown, but the region B is also transformed to austenite and has the effect of suppressing the growth of austenite transformed prior to the region A. In addition, since many fine carbides are precipitated, the number of nucleation sites of austenite generated by quenching heating increases, and each crystal grain suppresses grain growth, so that uniform fine crystal grains after quenching and tempering. I believe you can get
そのため、領域Ａと領域Ｂとの間には、結晶粒微細化機構が得られるに必要な炭素濃度と、部分的な炭素濃度の差が必要になる。しかも、固溶し易い大きさの炭化物個数が特定個数以上の差をもって存在しなければ上記の結晶粒微細化効果は得られない。
そのため、焼入れ加熱時に基地に固溶し易すく、且つ結晶粒微細化が得られるに必要な、優先的な変態が実現できる大きさとして、０．１〜０．５μｍの大きさの炭化物サイズとその個数が３００個以上と規定した。この本発明で規定する炭化物個数が少なくても、或いは／更に炭化物のサイズが０．１〜０．５μｍの大きさ以外となっても、結晶粒微細化機構が得られるに必要な炭素濃度は不十分となるか、部分的な炭素濃度の差が不十分となり結晶粒微細化効果が得られない。
また、結晶粒微細化に必要な炭素濃度差を得るために炭化物が疎な領域Ｂは領域Ａよりも１００μｍ２中に円相当径０．１〜０．５μｍの炭化物が１００個以上少ないと規定した理由は、炭化物個数の差が領域Ａと領域Ｂとで１００個未満であると炭素の濃度差が少なく、結晶粒微細化効果が得られないためである。
Therefore, a difference between the carbon concentration necessary for obtaining a crystal grain refining mechanism and a partial carbon concentration is required between the region A and the region B. In addition, if the number of carbides having a size that is easy to dissolve is not greater than a specific number, the above-described crystal grain refining effect cannot be obtained.
Therefore, it is easy to dissolve in the base at the time of quenching heating, and as a size capable of realizing the preferential transformation necessary to obtain crystal grain refinement, a carbide size of 0.1 to 0.5 μm and The number was defined as 300 or more. Even if the number of carbides defined in the present invention is small or / and the size of the carbide is other than 0.1 to 0.5 μm, the carbon concentration necessary for obtaining the crystal grain refining mechanism is Insufficient or partial difference in carbon concentration is insufficient, and the effect of crystal grain refinement cannot be obtained.
Further, in order to obtain a carbon concentration difference necessary for crystal grain refinement, the region B in which the carbides are sparse is defined as having 100 or less carbides having an equivalent circle diameter of 0.1 to 0.5 μm in the region 100 μm 2 than the region A. The reason for this is that if the difference in the number of carbides is less than 100 between region A and region B, the difference in carbon concentration is small and the effect of crystal grain refinement cannot be obtained.
ところで、結晶粒微細化機構が得られるに必要な炭素濃度と、部分的な炭素濃度の差をより確実に実現するには、領域Ａ、領域Ｂ共に、固溶し易い大きさの炭化物が主体となっているのが良く、１００００倍で観察した時に確認できる炭化物総個数の８０％以上(好ましくは９０％以上、更に好ましくは９５％以上)が０．１〜０．５μｍの大きさであるのが良い。
また、領域Ａの０．１〜０．５μｍの大きさの炭化物個数といっても、観察する視野によって個数のバラツキが生じるため、領域Ｂを特定するための領域Ａの炭化物個数は、少なくとも１００００倍を３視野観察・測定した平均値を領域Ａの炭化物個数の基準とすると良い。
なお、領域Ｂの炭化物個数の下限としては２００個未満となると結晶粒微細化効果が得にくくなることから領域Ｂの１００μｍ２中に円相当径０．１〜０．５μｍの炭化物個数の下限は２００個とするのが良い。
また、領域Ａとしては、１００μｍ２中に円相当径０．１〜０．５μｍの炭化物が３００個以上の範囲で多く含まれるほど、焼入れ加熱時のオーステナイト生成の核となり、より焼入れ焼戻しによる結晶粒微細化が望める。領域Ａの炭化物個数の上限は例えば含有するＣ量や、炭化物形成元素量によって変化するため、上限を設定するのは難しいが、経験的には、実質的に１００μｍ２中に円相当径０．１〜０．５μｍの炭化物が６００個程度形成されるのが限界である。
By the way, in order to more surely realize the difference between the carbon concentration necessary for obtaining the crystal grain refining mechanism and the partial carbon concentration, both the region A and the region B are mainly composed of carbides having a size that is easily dissolved. 80% or more (preferably 90% or more, more preferably 95% or more) of the total number of carbides that can be confirmed when observed at 10000 times is 0.1 to 0.5 μm. Is good.
Further, even if the number of carbides having a size of 0.1 to 0.5 μm in the region A is varied depending on the field of view to be observed, the number of carbides in the region A for specifying the region B is at least 10,000. The average value obtained by observing and measuring the double field of view is preferably used as a reference for the number of carbides in the region A.
In addition, as the lower limit of the number of carbides in the region B is less than 200, it is difficult to obtain a crystal grain refining effect. Therefore, the lower limit of the number of carbides having an equivalent circle diameter of 0.1 to 0.5 μm in 100 μm 2 of the region B is 200 is good.
Further, as the region A, the more the carbide having an equivalent circle diameter of 0.1 to 0.5 μm is contained in the range of 300 or more in 100 μm 2 , the core of austenite generation at the time of quenching heating, and the more the crystal by quenching and tempering Fine grain can be expected. C amount and the upper limit of the carbide number of region A containing for example, to vary with a carbide forming element content, but it is difficult to set an upper limit, Empirically, the circle equivalent diameter 0 in substantially 100 [mu] m 2. The limit is that about 600 1-0.5 μm carbides are formed.
本発明の金属組織の更に好ましい形態について説明する。
本発明の金属組織は、残留オーステナイトが実質的にないことが望ましい。残留オーステナイトが過度に残留すると焼きなまし状態で時効割れの原因となったり、焼き入れ加熱時に残留オーステナイトを起点に粗大なオーステナイトが生成される恐れがある。そのため、本発明では残留オーステナイトは実質的にないことが望ましい。
なお、残留オーステナイトが実質的にないというのは、エックス線回折にて定量的に測定し、残留オーステナイトは０を含む１％以内であれば残留オーステナイトが実質的にないとする。
A more preferable embodiment of the metal structure of the present invention will be described.
The metal structure of the present invention desirably has substantially no retained austenite. If the retained austenite remains excessively, it may cause aging cracking in the annealed state, or coarse austenite may be generated starting from the retained austenite during quenching heating. Therefore, in the present invention, it is desirable that there is substantially no retained austenite.
The fact that there is substantially no retained austenite is measured quantitatively by X-ray diffraction, and the retained austenite is substantially absent if it is within 1% including 0.
本発明の熱処理方法に適用する工具鋼の組成としては、質量％で０．１〜０．８％、Ｓｉ：２．０％以下、Ｍｎ：２．０％以下、Ｃｒ：１．０〜１５．０％、Ｍｏ：１０．０％以下を含有し、更にＮｉ：４．０％以下、Ｖ：４．０％以下、Ｗ：１０．０％以下、Ｃｏ：１０．０％以下、の何れか１種以上を含有して残部はＦｅ及び不可避的不純物でなるものを用いると良い。
以下に、前記の好ましい組成の範囲について説明する。なお、含有量は質量％で表している。
Ｓｉ：２．０％以下
Ｓｉは工具鋼において溶解時の脱酸剤として添加される。しかし、多量に添加すると靱性が低下する。そのため、本発明では２．０％以下とした。好ましくは０．１５〜１．２０％である。
Ｍｎ：２．０％以下
Ｍｎは工具鋼において溶解時の脱酸および脱硫剤として添加される。しかし、多量に添加すると靱性が低下する。そのため、本発明では２．０％以下とした。好ましくは０．３０〜１．００％である。
Ｃｒ：１．０〜１５．０％
Ｃｒは工具鋼において焼入れ性を向上させ、引張り強さや靱性を改善するという目的で添加される。しかし、多量に添加すると逆に靱性が低下する。そのため本発明では１．０〜１５．０％とした。好ましくは１．０〜１３．０％、更に好ましくは１．０〜６．０％である。
Ｍｏ：１０．０％以下
Ｍｏは工具鋼において焼入れ性を向上させる。また、焼戻しにより微細な炭化物を形成し、高温引張り強さを増大させるという目的で添加される。しかし、多量に添加すると逆に靱性が低下する。そのため本発明では１０．００％以下とした。好ましくは０．２０〜５．００％であり、更に好ましくは０．２０〜２．５％である。
The set formed of tool steel to be applied to the heat treatment method of the present invention, from .1 to 0.8% by mass%, Si: 2.0% or less, Mn: 2.0% or less, Cr: 1.0 to 15.0%, Mo: 10.0% or less, Ni: 4.0% or less, V: 4.0% or less, W: 10.0% or less, Co: 10.0% or less It is preferable to use at least one of them and the balance being Fe and unavoidable impurities .
Below, the range of the said preferable composition is demonstrated. In addition, content is represented by the mass%.
Si: 2.0% or less Si is added as a deoxidizer during melting in tool steel. However, when added in a large amount, the toughness decreases. Therefore, in the present invention, it was made 2.0% or less. Preferably it is 0.15 to 1.20%.
Mn: 2.0% or less Mn is added as a deoxidizing and desulfurizing agent during melting in tool steel. However, when added in a large amount, the toughness decreases. Therefore, in the present invention, it was made 2.0% or less. Preferably it is 0.30 to 1.00%.
Cr: 1.0-15.0%
Cr is added for the purpose of improving hardenability in tool steel and improving tensile strength and toughness. However, if added in a large amount, the toughness is reduced. Therefore, in this invention, it was set as 1.0 to 15.0%. Preferably it is 1.0 to 13.0%, and more preferably 1.0 to 6.0%.
Mo: 10.0% or less Mo improves hardenability in tool steel. Further, it is added for the purpose of forming fine carbides by tempering and increasing the high-temperature tensile strength. However, if added in a large amount, the toughness is reduced. Therefore, in the present invention, it was made 10.00% or less. Preferably it is 0.20 to 5.00%, More preferably, it is 0.20 to 2.5%.
Ｎｉ：４．００％以下
Ｎｉは工具鋼において焼入れ性を向上させ、靱性を改善するという目的で添加される。しかし、多量に添加すると変態点を下げ、高温強度が低下する。そのため本発明では４．００％以下とした。好ましくは２．０％以下である。
Ｖ：４．００％以下
Ｖは工具鋼において結晶粒を細かくし靱性を向上させる。また、焼戻しにより高硬度の炭窒化物を形成し、引張強度を増大させるという目的で添加される。しかし、多量に添加すると逆に靱性が低下する。そのため本発明では４．００％以下とした。好ましくは０．１０〜１．１０％である。
Ｗ：１０．００％以下
Ｗは工具鋼において焼入れ性を向上させる。また、焼戻しにより微細な炭化物を形成し、高温引張り強さを増大させるという目的で添加される。しかし、多量に添加すると逆に靱性が低下する。そのため本発明では４．００％以下とした。好ましくは０．１０〜１．１０％である。
Ni: 4.00% or less Ni is added for the purpose of improving hardenability and improving toughness in tool steel. However, if added in a large amount, the transformation point is lowered and the high-temperature strength is lowered. Therefore, in the present invention, it was made 4.00% or less. Preferably it is 2.0% or less.
V: 4.00% or less V improves the toughness by making crystal grains finer in tool steel. Further, it is added for the purpose of forming a high hardness carbonitride by tempering and increasing the tensile strength. However, if added in a large amount, the toughness is reduced. Therefore, in the present invention, it was made 4.00% or less. Preferably it is 0.10 to 1.10%.
W: 10.00% or less W improves hardenability in tool steel. Further, it is added for the purpose of forming fine carbides by tempering and increasing the high-temperature tensile strength. However, if added in a large amount, the toughness is reduced. Therefore, in the present invention, it was made 4.00% or less. Preferably it is 0.10 to 1.10%.
Ｃｏ：１０．００％以下
Ｃｏは工具鋼において赤熱硬性を増し、高温引張強度を増大させるという目的で添加される。本発明では１０．００％以下とした。
以上、説明する元素以外は実質的にＦｅとしているが、不可避的に含有する不純物も当然含まれる。また、例えばＮｂ、Ｔｉは、結晶粒を微細化するのに有効な元素であるため、靱性が劣化させない程度の０．２０％以下の範囲で含有させても良い。
また、Ａｌは炭素の拡散を早くする元素であり、パーライト変態で炭化物の析出を促進させる効果があるため、０．２０％以下の範囲で含有させても良い。
Co: 10.00% or less Co is added for the purpose of increasing red hot hardness and increasing high-temperature tensile strength in tool steel. In the present invention, it was made 10.00% or less.
As mentioned above, although it is substantially Fe except the element demonstrated, naturally the impurity contained inevitably is also contained. Further, for example, Nb and Ti are effective elements for refining crystal grains, and therefore may be contained in a range of 0.20% or less to the extent that toughness does not deteriorate.
Al is an element that accelerates the diffusion of carbon, and has the effect of promoting precipitation of carbides by pearlite transformation. Therefore, Al may be contained in a range of 0.20% or less.
以下に本発明の金属組織を有する焼入れ用工具鋼素材の製造方法を図５に示すヒートパターンを用いて説明する。
炭化物が析出するに必要な０．１〜０．８％のＣ含有量を有し、好ましくは上述した好適な範囲内の化学組成を有する工具鋼の素材を１０５０〜１２５０℃に加熱して熱間加工を行う(図５には図示なし)。加熱温度は工具鋼素材の塑性加工性を考慮し、完全にオーステナイト組織とするため１０５０℃以上とした。また、１２５０℃以上では工具鋼素材が部分的溶融する可能性があるため１０５０〜１２５０℃の範囲とした。好ましくは１０７０〜１１７０℃の範囲内である。また、加熱・保持の時間は長時間保持するにつれ、オーステナイト結晶粒が粗大に成長することを考慮して適宜決定すればよく、３〜１０時間程度であれば十分である。
なお、工具鋼素材の熱間加工では自由鍛造、型打鍛造といった熱間鍛造を適用するとよく、熱間加工のその他の条件としては、熱間加工終了温度は工具鋼素材の表面温度が９５０〜１０５０℃の範囲であれば良く、鍛造比は熱間加工においてより歪を蓄積させるため５より大きいことが好ましい。
The manufacturing method of the tool steel raw material for hardening which has the metal structure of this invention below is demonstrated using the heat pattern shown in FIG.
A tool steel material having a C content of 0.1 to 0.8% necessary for precipitation of carbides and preferably having a chemical composition within the above-mentioned preferred range is heated to 1050 to 1250 ° C. Inter-working is performed (not shown in FIG. 5). Considering the plastic workability of the tool steel material, the heating temperature was set to 1050 ° C. or higher in order to obtain a complete austenite structure. Moreover, since the tool steel raw material may partially melt at 1250 ° C. or higher, the temperature range is set to 1050 to 1250 ° C. Preferably it exists in the range of 1070-1170 degreeC. Further, the heating and holding time may be appropriately determined in consideration of the fact that the austenite crystal grains grow coarsely as it is held for a long time, and about 3 to 10 hours is sufficient.
In the hot working of the tool steel material, it is preferable to apply hot forging such as free forging and die forging. As other conditions for the hot working, the hot working finish temperature is 950 to 950. It may be in the range of 1050 ° C., and the forging ratio is preferably larger than 5 in order to accumulate more strain in hot working.
そして、上記の熱間加工終了後、工具鋼素材の表面温度が５００〜７００℃となるまで空冷以上の冷却速度で冷却を行う(図５中の(１))。
熱間加工終了後の工具鋼素材温度は結晶粒界に炭化物が析出可能な温度にある。熱間加工終了後に過剰に結晶粒界に炭化物が析出した場合、焼入れ焼戻しを行うと、炭化物が結晶粒界に残存し、靱性を阻害するという問題がある。そのため、結晶粒界に炭化物が析出し難い７００℃以下の温度域まで冷却を急ぐ必要がある。
この時の冷却は、粒界炭化物のノーズにかからない程度の速さで冷却することとし、工具鋼素材の断面寸法がおおよそ３００ｍｍ(t)×３００ｍｍ(w)よりも小さいものは空冷とし、それ以上に大きいものは、ファンにてカゼを当てて強制冷却すると良く、おおよそ２５℃／ｍｉｎの速さであれば良い。
そして、上記の冷却により結晶粒界に炭化物が析出し難い７００℃以下の温度域まで冷却を行うが、過度に低い温度まで冷却するとオーステナイトがベイナイトに変態する可能性があり、ベイナイト変態してしまうとその後の等温保持にて炭化物の析出を制御できないという問題がある。これを抑制するために、空冷以上での冷却の下限は５００℃とした。
And after completion | finish of said hot processing, it cools with the cooling rate more than air cooling until the surface temperature of a tool steel raw material becomes 500-700 degreeC ((1) in FIG. 5).
The tool steel material temperature after hot working is at a temperature at which carbides can be precipitated at the grain boundaries. In the case where carbide is excessively precipitated at the crystal grain boundary after the hot working is finished, there is a problem that if quenching and tempering is performed, the carbide remains in the crystal grain boundary and the toughness is inhibited. For this reason, it is necessary to urge cooling to a temperature range of 700 ° C. or lower where carbides are unlikely to precipitate at the grain boundaries.
Cooling at this time is performed at a speed that does not affect the nose of the grain boundary carbide, and if the cross-sectional dimension of the tool steel material is smaller than about 300 mm (t) x 300 mm (w), air cooling is performed. Larger ones may be forcedly cooled by applying a fan with a fan, and may be about 25 ° C./min.
Then, cooling is performed to a temperature range of 700 ° C. or less where carbides are not easily precipitated at the grain boundaries by the above cooling, but austenite may be transformed into bainite when cooled to an excessively low temperature, resulting in bainite transformation. And there is a problem that the precipitation of carbide cannot be controlled by the subsequent isothermal holding. In order to suppress this, the lower limit of cooling above air cooling was set to 500 ° C.
次に、工具鋼素材の表面温度が５００〜７００℃となるまで空冷以上の冷却速度で冷却の後、加熱炉に工具鋼の素材を入材し、４００〜７００℃の温度に加熱・保持を行う(図５中の(２))。
４００〜７００℃に限定した理由は７００℃より高いと先に述べた通り結晶粒界に炭化物が析出し、４００℃より低いとベイナイトに変態する可能性があるためである。なお、加熱・保持の時間は長時間保持すると、その時点でベイナイトに変態する可能性があると言ったことを考慮して適宜決定すればよく、０．５〜５時間程度であれば十分である。この処理により、被熱処理材の中心部までパーライトノーズ以下の温度に均熱化をする。
Next, after cooling at a cooling rate of air cooling or higher until the surface temperature of the tool steel material reaches 500 to 700 ° C., the tool steel material is placed in a heating furnace and heated and held at a temperature of 400 to 700 ° C. Perform ((2) in FIG. 5).
The reason why the temperature is limited to 400 to 700 ° C. is that if the temperature is higher than 700 ° C., carbides precipitate at the grain boundaries as described above, and if the temperature is lower than 400 ° C., there is a possibility of transformation into bainite. Note that the heating / holding time may be appropriately determined in consideration of the fact that, when held for a long time, there is a possibility of transformation to bainite at that time, and it is sufficient if it is about 0.5 to 5 hours. is there. By this treatment, the temperature is equalized to a temperature equal to or lower than the pearlite nose up to the center of the heat-treated material.
次に、前記４００〜７００℃の温度に加熱・保持した工具鋼素材の素材温度を高める加熱を行なって（図５中の（３））工具鋼素材温度をパーライトノーズからマイナス１００℃の温度域に高め、該パーライトノーズからマイナス１００℃の温度域にて加熱・保持を行い（図５中の（４））、冷却（図５中の（５））して工具鋼中間素材とする。
パーライトノーズからマイナス１００℃の温度域としたのは、この範囲内では図１に示すような旧オーステナイト粒界近傍は炭化物が密に、旧オーステナイト粒内部は炭化物が疎に析出した金属組織が得られるためであり、焼鈍後に行う焼入れ焼戻しによって結晶粒微細化を達成するに必要な金属組織に調整するためである。
パーライトノーズより高温側では炭化物がほぼ均一に分散したパーライト組織となり、パーライトノーズからマイナス１００℃より低い温度では、パーライト変態が終了するまでの時間が長くなり、旧オーステナイト粒界近傍は炭化物が密に、旧オーステナイト粒内部は炭化物が疎に析出した金属組織を得がたいという問題があり、焼鈍後に行う焼入れ焼戻しによって結晶粒径の微細化がはかれない。そのため、本発明ではパーライトノーズからマイナス１００℃の温度域とした。
なお、加熱・保持の時間はパーライト変態開始後、パーライト変態終了まで保持するといったことを考慮して適宜決定すればよく、１０〜５０時間程度であれば十分である。
Next, heating is performed to increase the material temperature of the tool steel material heated and held at the temperature of 400 to 700 ° C. ((3) in FIG. 5). The tool steel material temperature is changed from pearlite nose to a temperature range of −100 ° C. Then, heating and holding from the pearlite nose in a temperature range of minus 100 ° C. ((4) in FIG. 5) and cooling ((5) in FIG. 5) to obtain a tool steel intermediate material.
The temperature range of −100 ° C. from the pearlite nose is that within this range, as shown in FIG. 1, a metal structure in which carbides are densely deposited in the vicinity of the prior austenite grain boundaries and carbides are loosely precipitated in the former austenite grains is obtained. This is to adjust the metal structure necessary to achieve grain refinement by quenching and tempering after annealing.
On the higher temperature side than the pearlite nose, the carbide has a pearlite structure in which the carbides are almost uniformly dispersed, and at a temperature lower than minus 100 ° C. from the pearlite nose, the time until the pearlite transformation is completed becomes long. In the former austenite grains, there is a problem that it is difficult to obtain a metal structure in which carbides are sparsely precipitated, and the crystal grain size is not refined by quenching and tempering after annealing. Therefore, in this invention, it was set as the temperature range of minus 100 degreeC from pearlite nose.
The heating / holding time may be appropriately determined in consideration of holding from the start of pearlite transformation to the end of pearlite transformation, and it is sufficient if it is about 10 to 50 hours.
以下の実施例で本発明を更に詳しく説明する。
まず表１に示す組成の工具鋼を溶解し、１０Ｔｏｎの鋼塊を得た。この鋼塊を３分割し、１分割材を本発明とする工具鋼素材、１分割材を従来例の工具鋼素材とした。
The following examples further illustrate the present invention.
First, tool steel having the composition shown in Table 1 was melted to obtain a 10-ton steel ingot. The steel ingot was divided into three parts, and a tool steel material according to the present invention was used as a one-piece material, and a tool steel material of a conventional example was used as the one-piece material.
この工具鋼素材を１１００℃に加熱し、８時間保持を行った。そして、熱間鍛造(熱間プレス)にて熱間加工を行った。この時の加工率は１８％(鍛造比５．５)とし、３５０ｍｍ(t)×３５０ｍｍ(w)×１５００ｍｍ(l)に仕上げた。熱間加工終了温度は表面温度が９５０℃であった。
そして、工具鋼素材の表面温度が５５０℃となるまでファンにてカゼを吹き当てることによる強制冷却を行い(図５中の(１))、熱間加工時に固溶していた炭素がその冷却過程において結晶粒界にネット状の炭化物として析出するということを防止するために、９００℃付近もカゼを吹き当てる強制冷却とした。なお、表面温度は放射温度計を用いて測定した。
その後４５０℃の加熱炉に工具鋼素材を入材し、４５０℃の温度で３時間保持を行い(図５中の(２))、次いで前記４５０℃の温度に加熱・保持した素材の素材温度をパーライトノーズからマイナス１００℃の温度域内の７２５℃の温度に素材温度を高める加熱を行い(図５中の(３))、２０時間保持を行った後(図５中の(４))、炉冷し(図５中の(５))て焼入れ用工具鋼素材とした。なお、表１に示す工具鋼のパーライトノーズの温度は７７５℃であった。
また、従来例として、マルテンサイト、ベイナイト変態域まで冷却し、その後Ａｃ３点以上で完全にオーステナイト変態させ、焼きなましを行った従来材の焼入れ用工具鋼素材とした。なお、熱間鍛造条件は本発明の焼入れ用の工具鋼素材製造条件と同一とした。
This tool steel material was heated to 1100 ° C. and held for 8 hours. And hot working was performed by hot forging (hot pressing). The processing rate at this time was 18% (forging ratio 5.5), and finished to 350 mm (t) × 350 mm (w) × 1500 mm (l). The hot working finish temperature was 950 ° C. at the surface temperature.
Then, forced cooling is performed by blowing a case with a fan until the surface temperature of the tool steel material reaches 550 ° C. ((1) in FIG. 5), and the carbon that has been dissolved during hot working is cooled. In order to prevent precipitation as a net-like carbide in the crystal grain boundary during the process, forced cooling was performed by spraying caseo at around 900 ° C. The surface temperature was measured using a radiation thermometer.
After that, the tool steel material is put into a 450 ° C. heating furnace, held at a temperature of 450 ° C. for 3 hours ((2) in FIG. 5), and then the material temperature of the material heated and held at the temperature of 450 ° C. Is heated from the pearlite nose to a temperature of 725 ° C. within the temperature range of minus 100 ° C. ((3) in FIG. 5), and after holding for 20 hours ((4) in FIG. 5), The furnace steel was cooled ((5) in FIG. 5) to obtain a tool steel material for quenching. The temperature of the pearlite nose of the tool steel shown in Table 1 was 775 ° C.
Moreover, as a conventional example, the steel was cooled to the martensite and bainite transformation region, and then completely austenite transformed at the Ac3 point or higher, thereby obtaining a conventional tool steel material for quenching that was annealed. The hot forging conditions were the same as the conditions for producing the tool steel material for quenching according to the present invention.
この本発明の工具鋼及び比較例の焼入れ用工具鋼素材から金属組織観察用の試験片を切り出して、金属組織観察を行った。４％ナイタール腐食後、査電子顕微鏡(ＳＥＭ)を用いて１００００倍で金属組織を１０視野観察し、その画像を三谷商事株式会社製画像解析ソフト「ＷｉｎＲＯＯＦ(Ｒ)」にて解析することで１００μｍ２中に存在する炭化物個数及び炭化物サイズを確認した。
本発明にて得られた金属組織を図３に示す。図３(ａ)は１００倍の電子顕微鏡写真であり、図３(ｂ)は図３(ａ)中に白枠で囲った部分の拡大写真(×４００)である。図３で白く見える個所は領域Ａであり、黒色の個所が領域Ｂである。領域Ａは旧オーステナイト粒界とその近傍に見られるのが分かる。なお、炭化物が密な領域Ａを図１に、炭化物が疎な領域Ｂを図２に示す。図１及び図２は１００００倍の電子顕微鏡写真である。従来材も焼入れ用工具鋼素材から切出した試験片を４％ナイタール腐食後、走査電子顕微鏡(ＳＥＭ)を用いて１００００倍で観察した。従来材の金属組織を図４に示す。
A test specimen for observing the metal structure was cut out from the tool steel of the present invention and the quenched tool steel material of the comparative example, and the metal structure was observed. After 4% Nital corrosion, 10 fields of view of the metal structure were observed at 10,000 times using a scanning electron microscope (SEM), and the image was analyzed with image analysis software “WinROOF®” manufactured by Mitani Corporation. The number of carbides present in 2 and the carbide size were confirmed.
The metal structure obtained by the present invention is shown in FIG. FIG. 3A is a 100 × electron micrograph, and FIG. 3B is an enlarged photograph (× 400) of a portion surrounded by a white frame in FIG. 3A. The portion that appears white in FIG. 3 is the region A, and the black portion is the region B. It can be seen that region A is seen at the prior austenite grain boundary and its vicinity. A region A in which carbides are dense is shown in FIG. 1, and a region B in which carbides are sparse is shown in FIG. 1 and 2 are 10000 × electron micrographs. A test piece cut from a tool steel material for quenching was also observed at 10,000 times using a scanning electron microscope (SEM) after 4% nital corrosion. The metal structure of the conventional material is shown in FIG.
そして、本発明の焼入れ用工具鋼素材及び従来材の焼入れ用工具鋼素材からエックス線回折用試験片を採取し、広角エックス線回折装置を用い、測定条件はターゲットＣｏ、電圧４０ＫＶ、電流２００ｍＡにて残留オーステナイトの有無を確認し、本発明材及び従来材の残留オーステナイトは確認できなかった(残留オーステナイト量は０％だった)。
また、本発明の焼入れ用工具鋼素材及び従来材の焼入れ用工具鋼素材の走査電子顕微鏡(ＳＥＭ)を用いて１００００倍で観察した時、１００μｍ２中に円相当径０．１〜０．５μｍの炭化物の個数の結果については表２及び表３に示す。
Then, specimens for X-ray diffraction were sampled from the quenching tool steel material of the present invention and the conventional quenching tool steel material, and remained at a target Co, a voltage of 40 KV, and a current of 200 mA using a wide-angle X-ray diffraction apparatus. The presence or absence of austenite was confirmed, and the retained austenite of the present invention material and the conventional material could not be confirmed (the amount of retained austenite was 0%).
Further, when observed at 10,000 times using a scanning electron microscope (SEM) of the quenching tool steel material of the present invention and the conventional quenching tool steel material, an equivalent circle diameter of 0.1 to 0.5 μm in 100 μm 2 Tables 2 and 3 show the results of the number of carbides.
先ず、画像解析の結果から、本発明の焼入れ用工具鋼素材の金属組織は、炭化物の析出形態としては、ある一定方向に連なって析出するのではなく、それぞれの炭化物が方位性を持たず分散し、針状比が１〜２と言った、特徴的な金属組織となっていた。
また、金属組織を１００００倍で観察した時、１００μｍ２中に円相当径０．１〜０．５μｍの炭化物個数が３００個以上形成されている炭化物が密な領域Ａを有し、該金属組織中には１００μｍ２中に円相当径０．１〜０．５μｍの炭化物個数が領域Ａに対し、１００個以上少ない炭化物が疎な領域Ｂが混在する金属組織であることを確認した。
従来材においては、焼入れ用工具鋼素材から切出した試験片を４％ナイタール腐食後、走査電子顕微鏡(ＳＥＭ)を用いて１００００倍で観察したものであり、１００μｍ２中に円相当径０．１〜０．５μｍの炭化物がおよそ１００〜１５０個形成された炭化物が均一に分散する金属組織であった。
First, from the results of image analysis, the metal structure of the tool steel material for quenching according to the present invention is not precipitated continuously in a certain direction as a carbide precipitation form, but each carbide is dispersed without orientation. However, it had a characteristic metal structure with an acicular ratio of 1-2.
Further, when the metal structure is observed at a magnification of 10,000, the carbide structure in which 300 or more carbides having an equivalent circle diameter of 0.1 to 0.5 μm are formed in 100 μm 2 has a dense region A, and the metal structure It was confirmed that in 100 μm 2 , the number of carbides having an equivalent circle diameter of 0.1 to 0.5 μm in the region A was a metal structure in which a region B in which 100 or more carbides were sparse was mixed.
In the conventional material, a specimen cut from a tool steel material for quenching was observed at 10,000 times using a scanning electron microscope (SEM) after 4% nital corrosion, and an equivalent circle diameter of 0.1 in 100 μm 2. It was a metal structure in which approximately 100 to 150 carbides of ˜0.5 μm were uniformly dispersed.
次に、本発明の工具鋼、比較例の工具鋼をＡｃ３点以上の温度の１０３０℃に加熱して焼入れし、その後、６００℃にて焼戻しを１回行った。なお、加熱保持時間は焼入れ時が２時間、焼戻し時は７時間とした。
本発明の工具鋼及び比較例の工具鋼から金属組織観察用の試験片を切り出し、平均結晶粒度を測定した結果を表４に示す。
Next, the tool steel of the present invention and the tool steel of the comparative example were heated to 1030 ° C. at a temperature of Ac3 point or higher and quenched, and then tempered once at 600 ° C. The heating and holding time was 2 hours during quenching and 7 hours during tempering.
Table 4 shows the results of cutting out test pieces for observing the metal structure from the tool steel of the present invention and the tool steel of the comparative example and measuring the average crystal grain size.
以上説明したように本願発明の金属組織を有する焼入れ用工具鋼素材を用い、焼入れ焼戻しを行うことで、均一微細な結晶粒を得ることができ、且つ平均結晶粒度番号で８番より細粒となり、靱性が大幅に向上する効果がある。 As explained above, by using the tool steel material for quenching having the metal structure of the present invention and quenching and tempering, uniform fine crystal grains can be obtained, and the average grain size number becomes finer than No. 8. The toughness is greatly improved.
本願発明の金属組織を有する焼入れ用工具鋼素材を用いれば、焼入れ焼戻しにより均一微細な結晶粒を得ることから工具鋼の靱性が要求される用途に利用可能である。 If the tool steel material for quenching having the metal structure of the present invention is used, uniform fine crystals can be obtained by quenching and tempering, so that it can be used for applications requiring toughness of tool steel.
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