JP5212772B2 - Hot work tool steel with excellent toughness and high temperature strength - Google Patents
Hot work tool steel with excellent toughness and high temperature strength Download PDFInfo
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Description
本発明は、プレス金型や鍛造金型、ダイカスト金型、押出工具といった多種の熱間工具に供して最適な、靭性および高温強度を向上させた熱間工具鋼に関するものである。 The present invention relates to a hot tool steel having improved toughness and high-temperature strength that is optimal for use in various hot tools such as press dies, forging dies, die casting dies, and extrusion tools.
熱間工具は、高温の被加工材や硬質な被加工材と接触しながら使用されるため、熱疲労や衝撃に耐えうる強度と靭性を兼ね備えている必要がある。そのため、従来熱間工具の分野には、例えばＪＩＳ鋼種であるＳＫＤ６１系の合金工具鋼が用いられていた。さらに最近では、熱間工具を使用して製造される製品の製造時間の短縮や複雑形状の成形のために被加工材が高温化してきていることや、製品の複数同時加工に伴って金型等の熱間工具も大型化してきていることなどから、熱間工具材料にはさらに高い高温強度と大型サイズでも内部まで高い靭性を確保できることが求められている。 Since a hot tool is used while being in contact with a high-temperature work material or a hard work material, it must have both strength and toughness that can withstand thermal fatigue and impact. For this reason, in the field of hot tools, for example, SKD61-based alloy tool steel, which is a JIS steel type, has been used. More recently, the temperature of workpieces has increased due to the shortening of the manufacturing time of products manufactured using hot tools and the formation of complex shapes, and dies due to the simultaneous processing of multiple products. Since hot tools such as these are becoming larger, hot tool materials are required to be able to secure high toughness up to the inside even at higher high-temperature strength and large size.
合金工具鋼の靭性と高温強度を改善することを目的として、化学組成の範囲を定めることにより靭性を維持しつつ高温強度を改善する手法や（特許文献１参照）、残留炭化物の量を規定することにより靭性および高温強度を改善する手法が提案されている（特許文献２参照）。
しかし、上述の特許文献１は、靭性の具体的な測定値が無いことから靭性のレベルを評価することはできないが、本発明者が行った検討結果から判断するに、靭性および高温強度を十分に高いレベルで兼備するためには化学組成の範囲の限定が不十分である。また、上述の特許文献２の方法においても、靭性および高温強度は焼入れ後のマルテンサイト組織やベイナイト組織などの組織の影響を大きく受けるため、靭性および高温強度を高いレベルで制御するためには残留炭化物量を規定するだけでは不十分である。 However, although the above-mentioned Patent Document 1 cannot evaluate the toughness level because there is no specific measurement value of toughness, the toughness and the high-temperature strength are sufficient to judge from the examination results made by the present inventors. In order to achieve a high level, the range of the chemical composition is not sufficiently limited. In the method of Patent Document 2 described above, the toughness and the high temperature strength are greatly affected by the structure such as the martensite structure and the bainite structure after quenching. It is not enough to specify the amount of carbide.
本発明の目的は、より確実に優れた靭性および高温強度を有する熱間工具鋼を提供することである。 An object of the present invention is to provide a hot work tool steel having more reliably superior toughness and high temperature strength.
本発明者が鋭意研究を行った結果、靭性および高温強度には焼入れ後の組織が大きく影響することを突き止め、優れた靭性および高温強度を兼ね備えるために好適な焼入れ後の組織を明らかにした。そして、好適な焼入れ後の組織を得るためには、各元素の含有量を最適な範囲に制御することによってこそ得られる、その極めて狭い好組成域が存在することを見出し、本発明に到達した。 As a result of intensive studies by the present inventors, it was found that the structure after quenching greatly affects toughness and high-temperature strength, and a structure after quenching suitable for combining excellent toughness and high-temperature strength was clarified. And in order to obtain a suitable structure after quenching, the inventors have found that there is an extremely narrow favorable composition range obtained by controlling the content of each element to an optimum range, and have reached the present invention. .
すなわち本発明は、質量％で、Ｃ：０．３４〜０．４０％、Ｓｉ：０．３５〜０．４５％、Ｍｎ：０．４５〜０．７５％、Ｎｉ：０〜０．５％未満、Ｃｒ：４．９〜５．５％、ＭｏおよびＷは単独または複合で（Ｍｏ＋１／２Ｗ）：２．５〜２．９％、Ｖ：０．５〜０．７％、残部Ｆｅおよび不可避的不純物からなることを特徴とする靭性および高温強度に優れた熱間工具鋼である。本発明の熱間工具鋼は、例えばその硬さを４０ＨＲＣ以上に調質して使用すればよいが、特に４５ＨＲＣ以上の高硬さ域において、その優れた靭性および高温強度の兼備効果を発揮する。 That is, the present invention is mass%, C: 0.34 to 0.40%, Si: 0.35 to 0.45 %, Mn: 0.45 to 0.75%, Ni: 0 to 0.5% Less than, Cr: 4.9 to 5.5%, Mo and W alone or in combination (Mo + 1 / 2W): 2.5 to 2.9%, V: 0.5 to 0.7%, balance Fe and It is a hot work tool steel excellent in toughness and high temperature strength characterized by comprising inevitable impurities. The hot tool steel of the present invention may be used after adjusting its hardness to 40 HRC or higher, for example, and exhibits excellent toughness and high temperature strength, particularly in a high hardness region of 45 HRC or higher. .
ここで、本発明の熱間工具鋼に好ましくは、それを構成するＣ，Ｓｉ，Ｍｎ，Ｎｉ，Ｃｒ，Ｍｏ，Ｗ、Ｖの各元素のうちのＣ，Ｍｎ，Ｎｉ，Ｃｒ，Ｍｏ，Ｗ、Ｖの１種または２種以上が、さらに下記の狭組成域を満たすことである。これにおいては、勿論、その全てを満たすことが望ましい。
Ｃ ：０．３５〜０．３９％、
Ｍｎ：０．５ 〜０．７ ％、
Ｎｉ：０．０１〜０．３ ％、
Ｃｒ：５．０ 〜５．４ ％、
ＭｏおよびＷは単独または複合で（Ｍｏ＋１／２Ｗ）：２．６〜２．８％、
Ｖ ：０．５５〜０．６５％
Here, preferably the hot work tool steel of the invention, C constituting it, Si, Mn, Ni, Cr , Mo, W, C of each element of V, Mn, Ni, Cr, Mo, W 1 or 2 or more of V further satisfy | fills the following narrow composition range. In this, of course, it is desirable to satisfy all of them.
C: 0.35~0.39%,
M n: 0.5 ~0.7%,
Ni: 0.01 to 0.3%,
Cr: 5.0 to 5.4%,
Mo and W are single or combined (Mo + 1 / 2W): 2.6 to 2.8%,
V: 0.55-0.65%
本発明によれば熱間工具鋼の靭性および高温強度を非常に高いレベルで兼備することができる。そして、この効果は、４０ＨＲＣ以上の硬さ域においては勿論のこと、例えば４５ＨＲＣ以上、更には４６ＨＲＣ以上の高硬さ域に調質した時においては、最大限に発揮される。よって、多種熱間の用途・環境に適用が可能な熱間工具鋼の実用化にとって有効な技術となる。 According to the present invention, it is possible to combine the toughness and high temperature strength of hot tool steel at a very high level. And this effect is exhibited to the maximum when it is tempered in a high hardness region of 45 HRC or more, further 46 HRC or more, as well as in a hardness region of 40 HRC or more. Therefore, this is an effective technique for practical application of hot tool steel that can be applied to various uses and environments.
上述したように、本発明の重要な特徴は各元素の含有量を最適な範囲に制御することにある。すなわち、各元素の含有量を限定的な範囲に制御するだけで、製造方法は従来のままで、広い範囲の焼入れ冷却速度でも靭性および高温強度を高いレベルで兼備できる組織を得ることができる狭組成域が存在するのであって、それを特定できたところに特徴を有する。すなわち、基本元素においては、Ｃ−Ｃｒ量の関係は従来のバランスを踏襲しながらも、これに相互関係する他の炭化物形成元素のＭｏ，Ｗ，Ｖの最適調整と、そして、これら基本元素の調整による結果特性には多大な影響を及ぼすＳｉやＮｉの調整こそが重要なのである。以下、本発明鋼の狭組成域で構成される成分限定の理由について述べる。 As described above, an important feature of the present invention is that the content of each element is controlled within an optimum range. That is, only by controlling the content of each element to a limited range, the manufacturing method remains the same, and a narrow structure capable of obtaining a high level of toughness and high-temperature strength even with a wide range of quenching cooling rates can be obtained. There is a composition range, and it is characterized by the fact that it can be specified. That is, in the basic element, the relationship of the amount of C—Cr follows the conventional balance, but the optimum adjustment of Mo, W, V of other carbide forming elements interrelated to this, and the basic element It is important to adjust Si and Ni, which have a great influence on the resulting characteristics of the adjustment. Hereinafter, the reason for limiting the components constituted by the narrow composition range of the steel of the present invention will be described.
Ｃは、一部が基地中に固溶して強度を付与し、一部は炭化物を形成することで耐摩耗性や耐焼付き性を高める、熱間工具鋼には重要な必須元素である。また、固溶した侵入型原子であるＣは、ＣｒなどのＣと親和性の大きい置換型原子と共添加した場合、Ｉ（侵入型原子）−Ｓ（置換型原子）効果；溶質原子の引きずり抵抗として作用し高強度化する効果も期待される。ただし、含有量が０．３４質量％未満では工具部材として十分な硬さ、耐摩耗性を確保できなくなる。他方、過度の添加は靭性や熱間強度の低下を招くため上限を０．４０質量％とする。好ましくは０．３５〜０．３９％、更に好ましくは０．３６〜０．３８％である。 C is an essential essential element for hot work tool steel, part of which is dissolved in the matrix to give strength, and part of it forms carbides to improve wear resistance and seizure resistance. Further, when C, which is a solid interstitial atom, is co-added with a substitution atom having a high affinity with C, such as Cr, the I (interstitial atom) -S (substitution atom) effect; solute atom dragging The effect of increasing the strength by acting as a resistance is also expected. However, if the content is less than 0.34 mass%, sufficient hardness and wear resistance as a tool member cannot be secured. On the other hand, excessive addition causes a decrease in toughness and hot strength, so the upper limit is made 0.40% by mass. Preferably it is 0.35-0.39%, More preferably, it is 0.36-0.38%.
Ｓｉは、製鋼時の脱酸剤であるとともに被削性を高める元素である。これらの効果を得るためには０．３５質量％以上の添加が必要であるが、多過ぎると針状のベイナイトを生成させて靭性を低下させたり、焼入れ冷却時のベイナイト組織中のセメンタイト系の炭化物の析出を抑制することによって間接的に焼戻し時の合金炭化物の析出・凝集・粗大化を促進して高温強度を低下させたりするので０．４５質量％以下とする。 Si is an element that enhances machinability as well as a deoxidizer during steelmaking. In order to obtain these effects, addition of 0.35 % by mass or more is necessary. However, if it is too much, needle-like bainite is generated to reduce toughness, or the cementite type in the bainite structure during quenching cooling. By suppressing the precipitation of carbides, the precipitation, aggregation and coarsening of alloy carbides during tempering are indirectly promoted to lower the high temperature strength, so the content is made 0.45 % by mass or less .
Ｍｎは、焼入性を高め、フェライトの生成を抑制し、適度の焼入れ焼戻し硬さを得る効果がある。また、非金属介在物ＭｎＳとして組織中に存在すれば、被削性の向上に大きな効果がある。これらの効果を得るためには０．４５質量％以上の添加が必要であるが、多過ぎると基地の粘さを上げて被削性を低下させるので０．７５質量％以下とする。好ましくは０．５〜０．７％である。 Mn has the effect of improving hardenability, suppressing the formation of ferrite, and obtaining appropriate quenching and tempering hardness. Moreover, if it exists in a structure | tissue as nonmetallic inclusion MnS, there exists a big effect in the improvement of a machinability. In order to obtain these effects, it is necessary to add 0.45% by mass or more, but if it is too much, the viscosity of the base is increased and the machinability is lowered, so the content is made 0.75% by mass or less. Preferably it is 0.5 to 0.7%.
Ｎｉは、フェライトの生成を抑制する元素である。また、Ｃ、Ｃｒ、Ｍｎ、Ｍｏ、Ｗなどとともに本発明鋼に優れた焼入性を付与し、緩やかな焼入冷却速度の場合にも、マルテンサイト主体の組織を形成させ、靭性の低下を防ぐために重要な添加元素であり、さらに基地の本質的な靭性改善効果を与えることから、例えば０．０１％以上といった添加の好ましい元素である。そして、本発明にとって何よりも重要なことは、このＮｉを添加した場合であっても、上限を厳重に規制管理することであって、つまり、多過ぎると基地の粘さを上げて被削性を低下させたり、高温強度を低下させたりするので、０．５質量％未満とする必要がある。好ましくは、０．３質量％以下に規制することである。 Ni is an element that suppresses the formation of ferrite. In addition, it provides excellent hardenability to the steel of the present invention together with C, Cr, Mn, Mo, W, etc., and even in the case of a slow quenching cooling rate, it forms a martensite-based structure and reduces toughness. It is an important additive element for preventing, and further provides an essential toughness improving effect of the base, so that it is a preferable element to be added, for example, 0.01% or more. And, the most important thing for the present invention is that even when Ni is added, the upper limit is strictly controlled and controlled. Or lowers the high temperature strength, it is necessary to make it less than 0.5% by mass. Preferably, it is restricted to 0.3% by mass or less.
Ｃｒは焼入れ性を高めて、また、炭化物を形成して基地の強化や耐摩耗性を向上させる効果を有する元素であり、焼戻し軟化抵抗および高温強度の向上にも寄与する、本発明の熱間工具鋼には必須の元素である。これらの効果を得るため４．９質量％以上添加する必要がある。ただし、過度の添加は焼入れ性や高温強度の低下を招くため、上限を５．５質量％とする。好ましくは５．０〜５．４％、更に好ましくは５．１〜５．３％である。 Cr is an element having an effect of improving hardenability and forming carbides to improve the strengthening and wear resistance of the base, and contributes to the improvement of temper softening resistance and high temperature strength. It is an essential element for tool steel. In order to obtain these effects, it is necessary to add 4.9% by mass or more. However, excessive addition causes a decrease in hardenability and high temperature strength, so the upper limit is set to 5.5% by mass. Preferably it is 5.0 to 5.4%, more preferably 5.1 to 5.3%.
ＭｏおよびＷは、焼入性を高めるとともに、焼戻しにより微細炭化物を析出させて強度を付与し、軟化抵抗を向上させるために単独または複合で添加できる。ＷはＭｏの約２倍の原子量であることからＭｏ＋１／２Ｗで規定することができる（当然、いずれか一方のみの添加としても良いし、双方を共添加することもできる）。そして、前記した効果を得るためには（Ｍｏ＋１／２Ｗ）で２．５質量％以上の添加が必要である。多過ぎると被削性の低下や針状ベイナイトの生成による靭性の低下を招くので、（Ｍｏ＋１／２Ｗ）で２．９質量％以下とする。好ましくは（Ｍｏ＋１／２Ｗ）で２．６〜２．８％である。 Mo and W can be added singly or in combination to enhance hardenability, precipitate fine carbides by tempering, impart strength, and improve softening resistance. Since W has an atomic weight approximately twice that of Mo, it can be defined as Mo + 1 / 2W (of course, either one may be added or both may be added together). And in order to acquire an above-described effect, addition of 2.5 mass% or more is required by (Mo + 1 / 2W). If the amount is too large, the machinability is lowered and the toughness is lowered due to the formation of acicular bainite. Therefore, (Mo + 1 / 2W) is 2.9% by mass or less. Preferably, it is 2.6 to 2.8% in (Mo + 1 / 2W).
Ｖは、炭化物を形成し、基地の強化や耐摩耗性向上の効果を有する。また、焼戻し軟化抵抗を高めるとともに結晶粒の粗大化を抑制し、靭性向上に寄与する。この効果を得るためには０．５質量％以上を添加する必要があるが、多過ぎると被削性や靭性の低下を招くので０．７質量％以下とする。好ましくは０．５５〜０．６５％である。 V forms carbides and has the effect of strengthening the base and improving wear resistance. In addition, it increases temper softening resistance and suppresses coarsening of crystal grains, thereby contributing to improvement of toughness. In order to obtain this effect, it is necessary to add 0.5% by mass or more, but if it is too much, the machinability and toughness are lowered, so the content is made 0.7% by mass or less. Preferably it is 0.55-0.65%.
なお、不可避的不純物として、残留する可能性のある主な元素は、Ｐ、Ｓ、Ｃｏ、Ｃｕ、Ａｌ、Ｃａ、Ｍｇ、Ｏ、Ｎ等である。本発明の作用効果を最大限に達成するためには、これらはできるだけ低い方が望ましいが、一方では、介在物の形態制御や、その他の機械的特性、あるいは製造効率の向上などの、付加的な作用効果を得る目的のもとでは、多少の含有および／または添加することもできる。この場合、質量％で、Ｐ≦０．０３％、Ｓ≦０．０１％、Ｃｏ≦０．０５％、Ｃｕ≦０．２５％、Ａｌ≦０．０２５％、Ｃａ≦０．０１％、Ｍｇ≦０．０１％、Ｏ≦０．０１％、Ｎ≦０．０３％であれば、本発明の熱間工具鋼の基本特性に特に大きな影響を及ぼさないと考えられるので、この範囲であれば許容でき、好ましい規制上限である。 Note that main elements that may remain as inevitable impurities are P, S, Co, Cu, Al, Ca, Mg, O, N, and the like. In order to achieve the maximum effect of the present invention, these should be as low as possible. However, on the other hand, there are additional features such as inclusion shape control, other mechanical properties, and improvement in production efficiency. Some contents and / or additions may be added for the purpose of obtaining various effects. In this case, by mass%, P ≦ 0.03%, S ≦ 0.01%, Co ≦ 0.05%, Cu ≦ 0.25%, Al ≦ 0.025%, Ca ≦ 0.01%, Mg ≦ 0.01%, O ≦ 0.01%, N ≦ 0.03%, it is considered that the basic characteristics of the hot work tool steel of the present invention is not particularly affected, so in this range It is acceptable and is a preferred upper limit of regulation.
表１に本発明鋼、比較鋼および従来鋼の化学成分を示す。比較鋼は本発明の限られた狭成分範囲から外れている化学組成の鋼、従来鋼は現在一般的に使用されている、当然のことながら本発明の成分範囲外の熱間工具鋼である。 Table 1 shows chemical components of the steels of the present invention, comparative steels and conventional steels. The comparative steel is a steel having a chemical composition that is outside the limited narrow component range of the present invention, and the conventional steel is a hot-work tool steel that is, of course, currently outside the component range of the present invention. .
これらの本発明鋼、比較鋼および従来鋼は、真空誘導溶解炉にて１０ｋｇずつ溶製した鋼塊に、１２５０℃で５時間の均質化熱処理を施した後、１１５０℃で熱間鍛造することによって３０ｍｍ厚さ×６０ｍｍ幅の鋼材を作製した。その後、８６０℃で焼なまし処理したのち、１０３０℃で焼入れ処理した。焼入れは加圧ガス冷却にて行い、焼入温度（１０３０℃）から焼入温度と室温（２０℃）との中間の温度（５２５℃）まで冷却するのに要する時間を半冷時間と定義した場合（例えば、１０３０℃から５２５℃まで冷却するのに１０分かかる場合「半冷１０分」と表す）、急冷に対応するものとして半冷３分程度、大型サイズの鋼材の中心部のように冷却速度が遅くなる部分に対応するものとして半冷４０分程度で冷却した。その後、種々の温度で焼戻し処理して、４６ＨＲＣの硬さに調質した。 These steels of the present invention, comparative steels and conventional steels are subjected to homogenization heat treatment at 1250 ° C. for 5 hours on a steel ingot made in 10 kg increments in a vacuum induction melting furnace, and then hot forged at 1150 ° C. Thus, a steel material having a thickness of 30 mm and a width of 60 mm was produced. Then, after annealing at 860 ° C., quenching was performed at 1030 ° C. Quenching is performed by pressurized gas cooling, and the time required for cooling from the quenching temperature (1030 ° C.) to an intermediate temperature (525 ° C.) between the quenching temperature and room temperature (20 ° C.) is defined as a semi-cooling time. In the case (for example, when it takes 10 minutes to cool from 1030 ° C. to 525 ° C., it is expressed as “semi-cooled 10 minutes”). It was cooled in about 40 minutes semi-cooling as a part corresponding to the part where the cooling rate becomes slow. Thereafter, it was tempered at various temperatures and tempered to a hardness of 46HRC.
上記のようにして作製した表１の本発明鋼、比較鋼および従来鋼から、鍛造後の鋼材の幅方向に試験片の長手方向、鋼材の長手方向に試験片のノッチ方向がくるように（すなわちＴ方向から採取）して作製した２ｍｍＵノッチシャルピー衝撃試験片を用いて、室温でシャルピー衝撃試験した結果を表２に示す。このＴ方向から採取し、比較的高硬度である４６ＨＲＣに調質した試験片でシャルピー衝撃試験を行った場合、鍛造組織の影響を受けて衝撃値が低くなりやすいため、３４（Ｊ／ｃｍ２）を越える衝撃値が得られれば優れた靭性を有すると言える。特に４０（Ｊ／ｃｍ２）を越える衝撃値が得られればその靭性は極めて優れている。 From the present invention steel, comparative steel and conventional steel of Table 1 produced as described above, the longitudinal direction of the test piece is in the width direction of the steel material after forging, and the notch direction of the test piece is in the longitudinal direction of the steel material ( Table 2 shows the results of a Charpy impact test at room temperature using a 2 mm U-notch Charpy impact test piece prepared by sampling from the T direction. When a Charpy impact test is performed with a specimen taken from the T direction and tempered to 46 HRC having a relatively high hardness, the impact value tends to be low due to the influence of the forged structure, so 34 (J / cm 2 It can be said that it has excellent toughness if an impact value exceeding) is obtained. In particular, if an impact value exceeding 40 (J / cm 2 ) is obtained, the toughness is extremely excellent.
表２の結果より、焼入れ時に急冷を行えば、本発明の組成外である比較鋼や従来鋼であってもマルテンサイトを主体とした組織とできるので、Ｔ方向から採取した試験片でも比較的高い衝撃値が得られる。しかしながら、焼入れ時に冷却が半冷４０分程度に遅くなった場合、比較鋼２１はもとよりＭｏ量が低いことに加えて、Ｎｉも無添加であるため、比較鋼２２はＭｏ量が低いために、それぞれ焼入れ性が劣り、そしてベイナイト主体の組織となってしまうために衝撃値も低くなる。また、比較鋼２４〜２７は、Ｓｉ量が多すぎるためにベイナイトの中でも針状ベイナイト組織が発達して衝撃値が低くなる。 From the results of Table 2, if quenching is performed at the time of quenching, even comparative steels and conventional steels outside the composition of the present invention can have a structure mainly composed of martensite. High impact value can be obtained. However, when the cooling is slowed down to about 40 minutes during quenching, in addition to the comparative steel 21 not only having a low Mo amount, but also Ni is not added, the comparative steel 22 has a low Mo amount. In each case, the hardenability is inferior, and the impact value is low because the structure is mainly composed of bainite. Moreover, since comparative steels 24-27 have too much Si amount, a needle-like bainite structure develops among bainite, and an impact value becomes low.
従来鋼３１はもとよりＭｏ量が低いことに加えて、低めのＣ量とＮｉも無添加であるために焼入れ性がかなり劣り、衝撃値が最も低い。従来鋼３２はＭｏ量が多すぎるために針状ベイナイト組織が発達して衝撃値が低くなる。 In addition to the low Mo content as well as the conventional steel 31, not only the lower C content and Ni are added, but the hardenability is considerably inferior and the impact value is the lowest. In the conventional steel 32, since the amount of Mo is too large, the acicular bainite structure develops and the impact value becomes low.
これらに対して、化学組成を最適に調整した本発明鋼１〜１３は、冷却速度が遅くなってもベイナイト組織、中でも特に針状ベイナイト組織の生成を抑制しているため、優れた靭性を維持している。なお、比較鋼２３は、本発明による最適組成と比べて靭性を高める元素であるＮｉのみが高く外れた組成のため、冷却速度が遅くなっても靭性は良好である。 On the other hand, the inventive steels 1 to 13 whose chemical compositions are optimally adjusted maintain excellent toughness because they suppress the formation of bainite structure, especially acicular bainite structure even when the cooling rate is slow. doing. Note that the comparative steel 23 is a composition in which only Ni, which is an element that enhances toughness as compared with the optimum composition according to the present invention, is out of the composition, so that the toughness is good even when the cooling rate is slow.
次に、表１の本発明鋼および、比較鋼の中で衝撃値が良好だった比較鋼２３を用いて高温強度を比較した。引張試験片は、鍛造後の鋼材の長手方向に試験片の長手方向がくるように採取し（すなわち、Ｌ方向から採取し）、６５０℃で高温引張試験した際の引張強さで評価した。引張試験は、試験片が６５０℃に達した後１０分保持してから開始した。結果を表３に示す。 Next, the high temperature strength was compared using the steel of the present invention in Table 1 and the comparative steel 23 having a good impact value among the comparative steels. The tensile test piece was sampled so that the longitudinal direction of the test piece was in the longitudinal direction of the steel material after forging (that is, sampled from the L direction), and evaluated by the tensile strength when a high-temperature tensile test was performed at 650 ° C. The tensile test was started after the test piece was held for 10 minutes after reaching 650 ° C. The results are shown in Table 3.
本発明の最適組成の狭範囲から外れている比較鋼２３は、Ｎｉ含有量が多すぎることにより、靭性には優れていたが高温強度が劣ることが分かる。一方、本発明鋼はいずれも高い高温強度を有していることが分かる。 It can be seen that the comparative steel 23, which is out of the narrow range of the optimum composition of the present invention, was excellent in toughness but inferior in high-temperature strength due to the excessive Ni content. On the other hand, it can be seen that the steels of the present invention all have high high-temperature strength.
本発明を適用して熱間工具鋼の靭性および高温強度を向上させることによって、プレス金型や鍛造金型、ダイカスト金型、押出工具といった多種の熱間工具への適用はもちろんのこと、さらに使用負荷が大きい金型等の熱間工具部材にも適用できる。 By applying the present invention to improve the toughness and high-temperature strength of hot work tool steel, it can be applied to various hot tools such as press dies, forging dies, die casting dies and extrusion tools. The present invention can also be applied to a hot tool member such as a mold having a large use load.
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