JP7149250B2 - Hot work tool steel with excellent high temperature strength and toughness - Google Patents
Hot work tool steel with excellent high temperature strength and toughness Download PDFInfo
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- JP7149250B2 JP7149250B2 JP2019206589A JP2019206589A JP7149250B2 JP 7149250 B2 JP7149250 B2 JP 7149250B2 JP 2019206589 A JP2019206589 A JP 2019206589A JP 2019206589 A JP2019206589 A JP 2019206589A JP 7149250 B2 JP7149250 B2 JP 7149250B2
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
Description
この出願は、熱間鍛造金型に使用される、高温強度と靭性に優れる熱間工具鋼に関する。 This application relates to hot work tool steel that is used in hot forging dies and has excellent high temperature strength and toughness.
熱間プレス鍛造や熱間押出し熱間ダイカスト用の金型には、ＪＩＳ－ＳＫＤ６１が汎用的に用いられており、また、熱間ハンマー鍛造用の金型には、ＪＩＳ－ＳＫＴ４が汎用的に使用されている。
ＪＩＳ－ＳＫＤ６１は強度と靭性の双方を比較的高位で兼備した金型用鋼であるが、使用中の割れによる早期破損が生じることが多く、靭性面では必ずしも十分ではない。また、ＪＩＳ－ＳＫＤ６１の靭性は、熱疲労亀裂の伸展を抑制するためには、不足している。
ＪＩＳ－ＳＫＴ４は、ハンマー鍛造による大きな衝撃にも耐え得るように、靭性を重視している一方で、軟化抵抗性が低いために、耐摩耗性が不足する。また、再生加工を目的とした型彫り面の引下げを繰返して行うと、焼入れ性が低いために中心部では硬さ低下が生じてしまい、強度不足から割れやへたりなどが発生する。さらには、適用可能な硬さが低いために、耐摩耗性や強度が不足し、熱間プレス鍛造や熱間押出しの用途には向いていない（例えば、特許文献１参照。）。
JIS-SKD61 is commonly used for dies for hot press forging and hot extrusion hot die casting, and JIS-SKT4 is commonly used for dies for hot hammer forging. in use.
JIS-SKD61 is a mold steel that has both strength and toughness at a relatively high level. Also, the toughness of JIS-SKD61 is insufficient to suppress the extension of thermal fatigue cracks.
JIS-SKT4 emphasizes toughness so that it can withstand a large impact due to hammer forging, but it lacks wear resistance due to its low softening resistance. In addition, if the engraving surface is repeatedly lowered for the purpose of reprocessing, the hardenability is low, so the hardness of the central portion decreases, and cracks and settling occur due to lack of strength. Furthermore, since the applicable hardness is low, wear resistance and strength are insufficient, and it is not suitable for hot press forging or hot extrusion (see, for example, Patent Document 1).
出願人は、これまでに、金型の寿命向上のために、優れた靭性および高温強度を有する熱間工具鋼の発明を提案している（例えば、特許文献２参照。）。しかし、この発明の提案では、使用前の炭化物の析出状態について考慮されておらず、軟化抵抗性、すなわち高温強度がなお不十分である。 The applicant has so far proposed an invention of a hot work tool steel having excellent toughness and high-temperature strength in order to improve the life of a mold (see, for example, Patent Document 2). However, the proposal of this invention does not take into account the state of precipitation of carbides before use, and the softening resistance, that is, the high-temperature strength, is still insufficient.
熱間工具鋼は、高温使用時にＭ2ＣやＭＣの二次炭化物が析出することで、軟化抵抗すなわち高温強度が得られる。しかし、熱間工具鋼は、使用前の段階で炭化物が多いと、使用中における二次炭化物の析出量が減少するので、高い高温強度が得られない問題がある。 Hot work tool steel can obtain softening resistance, ie, high temperature strength, by precipitation of secondary carbides of M 2 C and MC when used at high temperatures. However, if the hot work tool steel contains a large amount of carbides before use, the amount of precipitated secondary carbides decreases during use, so there is a problem that high high-temperature strength cannot be obtained.
そこで、本発明が解決しようとする課題は、電気炉または真空誘導溶解炉で溶製して製造の熱間工具鋼において、その溶製工程（前工程）で鋼中に残存している炭化物を、鋼の焼入れ工程において固溶させて、炭化物サイズを小さく制御することによって優れた靭性を有する鋼とし、さらに、炭化物の固溶により、熱間工具鋼として使用中に微細な炭化物を析出させるための有効炭素量を増加させ、微細な炭化物の析出により優れた高温強度を得ることである。 Therefore, the problem to be solved by the present invention is to remove carbides remaining in the steel in the melting process (pre-process) in hot work tool steel manufactured by melting in an electric furnace or a vacuum induction melting furnace. , In order to make a steel with excellent toughness by controlling the carbide size to a small size by dissolving it in the steel quenching process, and to precipitate fine carbides during use as a hot work tool steel due to the dissolution of carbides. It is to increase the effective carbon content of the steel and obtain excellent high temperature strength by precipitation of fine carbides.
本願発明の課題を解決するための手段は、第１の手段では、質量％で、Ｃ：０．２０～０．６０％、Ｓｉ：０．１～０．３％、Ｍｎ：０．５～２．０％、Ｎｉ：０．５～２．５％、Ｃｒ：１．６～２．６％、Ｍｏ：０．３～２．０％、Ｖ：０．０５～０．８０％を有し、残部Ｆｅおよび不可避不純物からなることを特徴とする高温強度および靭性に優れる熱間工具鋼である。 Means for solving the problems of the present invention are, in mass%, C: 0.20 to 0.60%, Si: 0.1 to 0.3%, Mn: 0.5 to 2.0%, Ni: 0.5-2.5%, Cr: 1.6-2.6%, Mo: 0.3-2.0%, V: 0.05-0.80% It is a hot work tool steel having excellent high-temperature strength and toughness, characterized by containing Fe and unavoidable impurities as the balance.
第２の手段では、質量％で、質量％で、Ｃ：０．２０～０．６０％、Ｓｉ：０．１～０．３％、Ｍｎ：０．５～２．０％、Ｎｉ：０．５～２．５％、Ｃｒ：１．６～２．６％、Ｍｏ：０．３～２．０％、Ｖ：０．０５～０．８０％を有し、残部Ｆｅおよび不可避不純物からなる鋼であって、該鋼の使用前の１０，０００μｍ2当りの円相当径１μｍ以上の大きさの炭化物の個数は１５０個以下であることを特徴とする高温強度および靭性に優れる熱間工具鋼である。 In the second means, in mass %, C: 0.20 to 0.60%, Si: 0.1 to 0.3%, Mn: 0.5 to 2.0%, Ni: 0 .5 to 2.5%, Cr: 1.6 to 2.6%, Mo: 0.3 to 2.0%, V: 0.05 to 0.80%, the balance from Fe and unavoidable impurities A hot work tool having excellent high-temperature strength and toughness, characterized in that the number of carbides having an equivalent circle diameter of 1 μm or more per 10,000 μm 2 of the steel before use is 150 or less. Steel.
本発明は、上記の手段により得られた鋼の使用前の１０，０００μｍ2当りの円相当径１μｍ以上の大きさの炭化物の個数を１５０個以下とすることにより、シャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ2以上であり、初期硬さの３９～４１ＨＲＣから６００℃で１００時間保持後の硬さの減少値が１４ＨＲＣ以下となるなど、靭性および高温強度に優れた熱間工具鋼が得られる。 In the present invention, the number of carbides having an equivalent circle diameter of 1 μm or more per 10,000 μm 2 of the steel obtained by the above means before use is 150 or less, so that the impact value in the Charpy impact test is It is 85 J/cm 2 or more, and the hardness decrease value after holding at 600° C. for 100 hours is 14 HRC or less from the initial hardness of 39 to 41 HRC. .
先ず、発明を実施するための形態の説明に先立って、本願発明による熱間工具鋼の化学成分の含有量の限定理由を各化学成分毎に説明し、さらに本願発明鋼における使用前における１０，０００μｍ2当りの円相当径１μｍ以上の大きさの炭化物の個数の限定理由について説明する。なお、含有量における％は、質量％であり、各化学成分の残部はＦｅおよび不可避不純物であり鋼を形成する。 First, prior to the description of the mode for carrying out the invention, the reasons for limiting the content of the chemical components of the hot work tool steel according to the present invention will be explained for each chemical component, and furthermore, the 10, The reason for limiting the number of carbides having an equivalent circle diameter of 1 μm or more per 000 μm 2 will be explained. In addition, % in the content is mass %, and the balance of each chemical component is Fe and unavoidable impurities to form steel.
Ｃ：０．２０～０．６０％
Ｃは、本発明鋼の十分な焼入れ性を確保し、炭化物を形成させることで、高温強度、硬度、および耐摩耗性を得るために必要な元素である。Ｃが０．２０％より少ないと十分な高温強度が得られない。一方、Ｃが０．６０％より多いと凝固偏析を助長し、炭化物の晶出が生じやすくなり靭性を阻害する。また、生成した炭化物の凝集により、高温強度が望めず、靭性も低下する。そこで、Ｃは０．２０～０．６０％とする。より好ましくは、０．４０～０．６０％とする。
C: 0.20-0.60%
C is an element necessary for ensuring sufficient hardenability of the steel of the present invention and forming carbides to obtain high-temperature strength, hardness, and wear resistance. If C is less than 0.20%, sufficient high-temperature strength cannot be obtained. On the other hand, when C is more than 0.60%, solidification segregation is promoted, and carbides are likely to crystallize, impairing toughness. Moreover, due to the agglomeration of the generated carbides, high-temperature strength cannot be expected, and toughness is also lowered. Therefore, C is set to 0.20 to 0.60%. More preferably, it is 0.40 to 0.60%.
Ｓｉ：０．１～０．３％
Ｓｉは、製鋼時の脱酸効果を得るためおよび本発明鋼の焼入れ性確保の効果を得るために必要な元素である。Ｓｉが０．１％より少ないと上記の各効果を得ることが出来ない。一方、Ｓｉが０．３％より多いと靭性を低下させる。そこで、Ｓｉは０．１～０．３％とする。
Si: 0.1-0.3%
Si is an element necessary for obtaining the deoxidizing effect during steelmaking and for obtaining the effect of securing the hardenability of the steel of the present invention. If Si is less than 0.1%, the above effects cannot be obtained. On the other hand, when Si is more than 0.3%, toughness is lowered. Therefore, Si should be 0.1 to 0.3%.
Ｍｎ：０．５～２．０％
Ｍｎは、製鋼時の脱酸効果を得るためおよび本発明鋼の焼入れ性確保の効果を得るために必要な元素である。Ｍｎが０．５％より少ないと上記の各効果を得ることが出来ない。一方、Ｍｎが２．０％より多いと靭性を低下させる。そこで、Ｍｎは０．５～２．０％とする。
Mn: 0.5-2.0%
Mn is an element necessary for obtaining the deoxidizing effect during steelmaking and for obtaining the effect of securing the hardenability of the steel of the present invention. If Mn is less than 0.5%, the above effects cannot be obtained. On the other hand, when Mn is more than 2.0%, toughness is lowered. Therefore, Mn is set to 0.5 to 2.0%.
Ｎｉ：０．５～２．５％
Ｎｉは、靭性の向上のために必要な元素であり、０．５％より少ないと十分な靭性が得られない。一方、Ｎｉは、高価な元素であるので２．５％より多いとコストが上昇する。そこで、Ｎｉは０．５～２．５％とする。
Ni: 0.5-2.5%
Ni is an element necessary for improving toughness, and if less than 0.5%, sufficient toughness cannot be obtained. On the other hand, Ni is an expensive element, so if it exceeds 2.5%, the cost increases. Therefore, Ni should be 0.5 to 2.5%.
Ｃｒ：１．６～２．６％
Ｃｒは、焼入れ性を確保するために必要な元素であり、１．６％より少ないと十分な焼入れ性が得られない。一方、Ｃｒは２．６％より多いと焼入焼戻し時にＣｒ系の炭化物が過多に形成され、高温強度、軟化抵抗性および靭性を低下させる。そこで、Ｃｒは１．６～２．６％とする。
Cr: 1.6-2.6%
Cr is an element necessary for ensuring hardenability, and if it is less than 1.6%, sufficient hardenability cannot be obtained. On the other hand, if the Cr content is more than 2.6%, an excessive amount of Cr-based carbides are formed during quenching and tempering, deteriorating high-temperature strength, softening resistance and toughness. Therefore, Cr is set to 1.6 to 2.6%.
Ｍｏ：０．３～２．０％
Ｍｏは、焼入れ性、二次硬化および高温強度に寄与する析出炭化物を得るため、また、焼入れ時に未固溶となった微細な炭化物が結晶粒の粗大化を抑制するために必要な元素である。しかし、Ｍｏが、０．３％より少ないと、上記の効果が得られない。一方、Ｍｏは２．０％より過剰に添加しても、上記の効果は飽和するばかりか、炭化物が粗大に凝集することにより靭性を低下させ、また、コスト高となる。そこでＭｏは０．３～２．０％とする。
Mo: 0.3-2.0%
Mo is an element necessary for obtaining precipitated carbides that contribute to hardenability, secondary hardening, and high-temperature strength, and for suppressing coarsening of crystal grains by fine carbides that are not dissolved during quenching. . However, if Mo is less than 0.3%, the above effect cannot be obtained. On the other hand, even if Mo is added in excess of 2.0%, not only does the above effect saturate, but also the carbides coarsely aggregate to lower the toughness and increase the cost. Therefore, Mo should be 0.3 to 2.0%.
Ｖ：０．０５～０．８０％
Ｖは、焼戻し時または熱間工具鋼として使用時に、微細で硬質な炭化物および炭窒化物を析出し、強度や耐摩耗性に寄与し、また、焼入れ時には、微細な炭化物および炭窒化物が結晶粒の粗大化を抑制し、靭性の低下を抑制するために必要な元素である。しかし、Ｖが０．０５％よりも少ないと、上記の効果は得られない。一方、Ｖが０．８０％より多いと、凝固時に粗大な晶出炭化物が生成され、靭性が阻害される。そこで、Ｖは０．０５～０．８０％とする。より好ましくは、０．０５～０．２０％とする。
V: 0.05-0.80%
V precipitates fine hard carbides and carbonitrides during tempering or when used as hot work tool steel, contributing to strength and wear resistance. It is an element necessary for suppressing coarsening of grains and suppressing deterioration of toughness. However, if V is less than 0.05%, the above effect cannot be obtained. On the other hand, when V is more than 0.80%, coarse crystallized carbides are formed during solidification, impairing toughness. Therefore, V is set to 0.05 to 0.80%. More preferably, it is 0.05 to 0.20%.
発明鋼の使用前の１０，０００μｍ2当りの円相当径１μｍ以上の大きさの炭化物の個数：１５０個以下
発明鋼の熱間鍛造や金型等の熱間での鋼として使用する前の本発明鋼を、「使用前」の状態と称する。さて、使用前の１０，０００μｍ2当りの円相当径１μｍ以上の大きさの炭化物の個数が１５０個より多すぎると、マトリックスに固溶している炭素の量が不足し、熱間工具鋼として使用中に微細な硬質の炭化物が析出することで、高温強度の向上に寄与する微細で硬質な炭化物の量が減少し、十分な高温強度が得られない。また、使用前の１０，０００μｍ2当りの円相当径１μｍ以上の大きさの炭化物の個数が１５０個より多すぎると、当該鋼に応力が集中して割れの起点や伝播経路として作用するために、鋼の靭性を阻害する。
そこで、第２の手段では、発明鋼の使用前の１０，０００μｍ2当りの円相当径１μｍ以上の大きさの炭化物の個数は１５０個以下とする。
Number of carbides with equivalent circle diameter of 1 μm or more per 10,000 μm 2 of invention steel before use: 150 or less Inventive steel is referred to as "before use" condition. Now, if the number of carbides with a circle-equivalent diameter of 1 μm or more per 10,000 μm 2 before use is more than 150, the amount of carbon dissolved in the matrix will be insufficient, resulting in an insufficient hot work tool steel. Precipitation of fine hard carbides during use reduces the amount of fine hard carbides that contribute to the improvement of high-temperature strength, and sufficient high-temperature strength cannot be obtained. In addition, if the number of carbides with an equivalent circle diameter of 1 μm or more per 10,000 μm 2 before use is more than 150, stress concentrates on the steel and acts as a starting point or propagation path for cracks. , impairs the toughness of the steel.
Therefore, in the second means, the number of carbides having an equivalent circle diameter of 1 μm or more per 10,000 μm 2 of the inventive steel before use is 150 or less.
次いで、発明を実施するための形態について、以下に実施例を参照しつつ説明する。 Next, modes for carrying out the invention will be described below with reference to examples.
この発明を実施するための形態では、本発明鋼の高温使用時にＭ２ＣやＭＣの二次炭化物が析出することで、軟化抵抗すなわち高温強度が得られる。しかし、使用前の段階で、炭化物が多いと、使用中の二次炭化物の析出量が減少して高い高温強度が得られず、また、使用前に粗大な炭化物が多く存在すると、靭性が低くなるなどの問題がある。 In the mode for carrying out the present invention, softening resistance, that is, high temperature strength, is obtained by precipitation of secondary carbides of M 2 C and MC when the steel of the present invention is used at high temperatures. However, if there is a large amount of carbides before use, the amount of secondary carbides precipitated during use will decrease, preventing high-temperature strength from being obtained. There are problems such as
以下、本発明の実施例について具体的に説明する。先ず、表１に示す発明鋼のＮｏ．１～１６、および比較鋼のＮｏ．１７～３３の化学成分を有し、残部Ｆｅおよび不可避不純物からなる各発明鋼および各比較鋼のそれぞれを１００ｋｇ真空誘導溶にて溶製し、各発明鋼および各比較鋼のそれぞれのインゴットに造塊した。
さらに、これらのインゴットを１２２０℃に加熱して角１５ｍｍの角材に鍛伸した。
Examples of the present invention will be specifically described below. First, the invention steel Nos. shown in Table 1 were tested. 1 to 16, and comparative steel nos. 100 kg of each invention steel and each comparison steel having a chemical composition of 17 to 33, the balance being Fe and inevitable impurities, was melted by vacuum induction melting, and each ingot of each invention steel and each comparison steel was produced. clumped.
Further, these ingots were heated to 1220° C. and forged into 15 mm squares.
これらの各発明鋼および各比較鋼の角材をそれぞれ８４０～１０００℃に加熱し、オーステナイト組織を得るとともに、炭化物を固溶させるのに十分な時間、例えば、３０分の熱処理を施して炭化物を固溶した後、油冷する焼入れを実施した。
さらに、これらを５００～７００℃に加熱後、空冷する焼戻しを実施した。
これらの実施により、各鋼材を３９～４１ＨＲＣに調質した。
調質した各発明鋼および各比較鋼の角材を、炭化物量の測定、靭性の評価、高温強度の評価を行うための、各試験用の供試材に機械加工した。
The square bars of each of the invention steels and each of the comparative steels are heated to 840 to 1000° C. to obtain an austenite structure, and heat treatment is performed for a time sufficient to solidify the carbides, for example, 30 minutes, to solidify the carbides. After melting, quenching by oil cooling was performed.
Furthermore, after heating these to 500 to 700° C., they were tempered by air cooling.
Through these practices, each steel was tempered to 39-41 HRC.
The quenched square bars of each invention steel and each comparative steel were machined into specimens for each test for measuring carbide content, evaluating toughness, and evaluating high temperature strength.
次いで、これらの各試験用の供試材を用いて、炭化物量の測定、靭性の評価、高温強度の評価の各試験を以下のように実施した。 Next, using these test materials for each test, the following tests were performed for measuring the amount of carbides, evaluating toughness, and evaluating high-temperature strength.
炭化物量の評価は、上記の３９～４１ＨＲＣの調質材からなる各Ｎｏ．の発明鋼および各Ｎｏ．の比較鋼の供試材の中心をバフ研磨にて鏡面研磨した後、炭化物が多く観察される箇所を３０視野選択し、電子顕微鏡にて１０，０００倍で観察される円相当径１μｍ以上の炭化物個数を、画像解析により計測した。
この結果、１０，０００μｍ2当たりの円相当径１μｍ以上の炭化物個数が１５０個以下のものを、表１の炭化物個数の欄に○と表示し、１０，０００μｍ2当たりの円相当径１μｍ以上の炭化物個数が１５０個より多いものを、表１の炭化物個数の欄に×と表示して、炭化物量の評価とした。
The amount of carbides was evaluated using each No. of the heat refining materials of 39 to 41 HRC. of the invention steel and each No. After the center of the test material of the comparative steel was mirror-polished by buffing, 30 fields of view where many carbides were observed were selected, and a circle equivalent diameter of 1 μm or more observed at 10,000 times with an electron microscope The number of carbides was counted by image analysis.
As a result, those having 150 or less carbides with an equivalent circle diameter of 1 μm or more per 10,000 μm 2 are marked with ○ in the column of the number of carbides in Table 1, and those with an equivalent circle diameter of 1 μm or more per 10,000 μm 2 Those with more than 150 carbides were marked with x in the column of the number of carbides in Table 1, and the amount of carbides was evaluated.
靭性の評価は、上記の焼入焼戻し材からなる各Ｎｏ．の発明鋼および各Ｎｏ．の比較鋼の供試材から、ＪＩＳ規格の３号角１０ｍｍ、長さ５５ｍｍからなるＵノッチ試験片を形成し、これらの各Ｕノッチ試験片に対し、硬さが３９～４１ＨＲＣになるように焼入焼戻して、常温でシャルピー衝撃試験を行うことで靭性を評価した。すなわち、衝撃値が８５Ｊ／ｃｍ2以上となったものを、表１の靭性の欄に○とし、衝撃値が８５Ｊ／ｃｍ2未満のものを×として、それぞれ評価した。 Evaluation of toughness was performed on each No. of the above quenched and tempered materials. of the invention steel and each No. A U-notch test piece having a JIS standard No. 3 square of 10 mm and a length of 55 mm was formed from the test material of the comparative steel, and each of these U-notch test pieces was sintered so that the hardness was 39 to 41 HRC. After being annealed and subjected to a Charpy impact test at room temperature, the toughness was evaluated. That is, those having an impact value of 85 J/cm 2 or more were evaluated as ○ in the toughness column of Table 1, and those having an impact value of less than 85 J/cm 2 were evaluated as x.
高温強度の評価は、上記の焼入焼戻し材からなる各Ｎｏ．の発明鋼および各Ｎｏ．の比較鋼の供試材を、６００℃で１００時間保持後空冷し、室温におけるＨＲＣ硬さを各Ｎｏ．の発明鋼および各Ｎｏ．の比較鋼ごとに測定し、それらの初期硬さの３９～４１ＨＲＣからの減少値をもって高温強度の評価とした。減少値が１４ＨＲＣ以下となったものを表１の高温強度の欄に○と表示し、減少値が１４ＨＲＣより超えたものを表１の高温強度の欄に×と表示した。 Evaluation of high-temperature strength was performed on each No. of the above quenched and tempered materials. of the invention steel and each No. of comparative steels were held at 600° C. for 100 hours and then air-cooled. of the invention steel and each No. was measured for each of the comparative steels, and the high-temperature strength was evaluated by the decrease value from the initial hardness of 39 to 41 HRC. Those with a reduction value of 14 HRC or less are marked with ◯ in the high temperature strength column of Table 1, and those with a reduction value of more than 14 HRC are marked with x in the high temperature strength column of Table 1.
発明鋼のＮｏ．１～１６の各Ｎｏ．のものは、炭化物個数、靭性、高温強度の各欄の評価が全て○であった。 Invented steel No. Each No. 1 to 16. In the case of , the evaluation in each column of the number of carbides, toughness, and high-temperature strength was all good.
これに対して比較鋼のＮｏ．１７～３３の各Ｎｏ．のものは、炭化物個数、靭性、高温強度の各欄の評価が全て○のものはなかった。 On the other hand, comparative steel No. Each No. 17 to 33. None of the samples were evaluated as ○ in each column of the number of carbides, toughness, and high-temperature strength.
すなわち、比較鋼のＮｏ．１７は、Ｃ量が０．７１％と本願発明の上限値の０．６０％より多く、１０，０００μｍ2当りの円相当径１μｍ以上の炭化物個数が多いので炭化物数が×であり、またＮｉ量が０．４％と本願発明の下限の０．５％より少ないため、靭性は常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ2低く×であり、かつ高温強度は初期硬さからの減少量が１４ＨＲＣより多いので×である。 That is, the comparison steel No. In No. 17, the amount of C is 0.71%, which is more than the upper limit of 0.60% of the present invention, and the number of carbides having a circle equivalent diameter of 1 μm or more per 10,000 μm 2 is large, so the number of carbides is x. Since the amount is 0.4%, which is less than the lower limit of 0.5% of the present invention, the impact value of the Charpy impact test at room temperature is 85 J / cm 2 lower, and the high temperature strength is x. Since the amount of decrease is more than 14HRC, it is x.
比較鋼のＮｏ．１８、２３、２５、２７は、１０，０００μｍ2当りの円相当径１μｍ以上の炭化物個数が１５０個より多く×であり、高温強度は初期硬さからの減少量が１４ＨＲＣより多いので×である。 Comparative steel No. 18, 23, 25, and 27, the number of carbides with an equivalent circle diameter of 1 μm or more per 10,000 μm 2 is more than 150, and the high-temperature strength is x because the amount of decrease from the initial hardness is more than 14 HRC. .
比較鋼のＮｏ．１９は、Ｃｒ量が１．５％と本願発明の下限値の１．６％より少なく、焼入れ性が不十分で、１０，０００μｍ2当りの円相当径１μｍ以上の炭化物個数が多いので炭化物数の欄が×であり、靭性は常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ2より低いので×である。 Comparative steel No. In No. 19, the Cr content is 1.5%, which is less than the lower limit of 1.6% of the present invention, and the hardenability is insufficient. is x, and the toughness is x because the impact value in the Charpy impact test at room temperature is lower than 85 J/cm 2 .
比較鋼のＮｏ．２０は、Ｍｏ量が０．２％と本願発明の下限値の０．３％より少ないので焼入れ性が不十分で、高温強度は初期硬さからの減少量が１４ＨＲＣより多く×である。 Comparative steel No. In No. 20, the amount of Mo is 0.2%, which is less than the lower limit of 0.3% of the present invention, so the hardenability is insufficient, and the high-temperature strength decreases more than 14 HRC from the initial hardness.
比較鋼のＮｏ．２１は、１０，０００μｍ2当りの円相当径１μｍ以上の炭化物個数が多いので炭化物数が×であり、靭性は常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ2より低いので×である。 Comparative steel No. No. 21 has a large number of carbides having an equivalent circle diameter of 1 μm or more per 10,000 μm 2 , so the number of carbides is x.
比較鋼のＮｏ．２２は、Ｎｉ量が０．４％と本願発明の下限値の０．５％より少なく、靭性は常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ2より低く×であり、かつＶ量が０．０３％と本願発明の下限値の０．０５％より少ないので、高温強度は初期硬さからの減少量が１４ＨＲＣより多く×である。 Comparative steel No. In No. 22, the Ni content is 0.4%, which is less than the lower limit of 0.5% of the present invention, the toughness is x, the impact value of the Charpy impact test at room temperature is lower than 85 J / cm 2 , and the V content is Since it is 0.03%, which is less than the lower limit of 0.05% of the present invention, the amount of decrease from the initial hardness of the high temperature strength is more than 14 HRC, which is x.
比較鋼のＮｏ．２４は、Ｃ量が０．６６％と本願発明の上限値の０．６０％より多いので、１０，０００μｍ2当りの円相当径１μｍ以上の炭化物個数が多いので炭化物数が×であり、靭性は常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ2より低く×であり、かつ高温強度は初期硬さからの減少量が１４ＨＲＣより多いので×である。 Comparative steel No. In No. 24, the C content is 0.66%, which is more than the upper limit of 0.60% of the present invention, so the number of carbides with an equivalent circle diameter of 1 μm or more per 10,000 μm 2 is large, so the number of carbides is ×, and the toughness is x because the impact value in the Charpy impact test at room temperature is lower than 85 J/cm 2 and the high-temperature strength is x because the amount of decrease from the initial hardness is more than 14 HRC.
比較鋼のＮｏ．２６は、Ｃｒ量が２．８％と本願発明の上限値の２．６％より多く、１０，０００μｍ2当りの円相当径１μｍ以上の炭化物個数が多いので炭化物数が×であり、さらに、焼入焼戻し時にＣｒ系の炭化物が過多に形成され、靭性が常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ2より低く×となり、高温強度・軟化抵抗性を低下させ、かつ高温強度は初期硬さからの減少量が１４ＨＲＣより多いので×である。 Comparative steel No. In No. 26, the Cr content is 2.8%, which is more than the upper limit of 2.6% of the present invention, and the number of carbides having a circle-equivalent diameter of 1 μm or more per 10,000 μm 2 is large, so the number of carbides is x. An excessive amount of Cr - based carbide is formed during quenching and tempering. It is x because the amount of decrease from hardness is greater than 14HRC.
比較鋼のＮｏ．２８は、１０，０００μｍ2当りの円相当径１μｍ以上の炭化物個数が多いので炭化物数が×であり、靭性は常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ2より低く×であり、かつ高温強度は初期硬さからの減少量が１４ＨＲＣより多いので×である。 Comparative steel No. No. 28 has a large number of carbides with an equivalent circle diameter of 1 μm or more per 10,000 μm 2 , so the number of carbides is x, and the toughness is x because the impact value in the Charpy impact test at room temperature is lower than 85 J / cm 2 , and The high temperature strength is x because the amount of decrease from the initial hardness is more than 14 HRC.
比較鋼のＮｏ．２９は、Ｖ量が０．０３％と本願発明の下限値の０．０５％より少ないので、高温強度は初期硬さからの減少量が１４ＨＲＣより多く×である。 Comparative steel No. In No. 29, the amount of V is 0.03%, which is less than the lower limit of 0.05% of the present invention.
比較鋼のＮｏ．３０は、１０，０００μｍ2当りの円相当径１μｍ以上の炭化物個数が多いので炭化物数が×であり、高温強度は初期硬さからの減少量が１４ＨＲＣより多いので×である。 Comparative steel No. No. 30 has a large number of carbides with an equivalent circle diameter of 1 μm or more per 10,000 μm 2 , so the number of carbides is x, and the high-temperature strength is x because the decrease from the initial hardness is more than 14 HRC.
比較鋼のＮｏ．３１は、Ｍｏ量が２．１％と本願発明の下限値の２．０％より多く、１０，０００μｍ2当りの円相当径１μｍ2以上の炭化物個数が多いので炭化物数が×であり、靭性はＭｏが多いので炭化物が粗大凝集することにより靭性を低下させ、常温でのシャルピー衝撃試験の衝撃値が８５Ｊ／ｃｍ2より低く×であり、かつ高温強度は初期硬さからの減少量が１４ＨＲＣより多いので×である。 Comparative steel No. In No. 31, the Mo content is 2.1%, which is more than the lower limit of 2.0% of the present invention, and the number of carbides having a circle-equivalent diameter of 1 μm 2 or more per 10,000 μm 2 is large, so the number of carbides is x, and the toughness Since there is a large amount of Mo, carbides coarsely aggregate to reduce toughness, the impact value in the Charpy impact test at room temperature is lower than 85 J / cm 2 , and the high-temperature strength decreases from the initial hardness by 14HRC. It is x because it is more.
比較鋼のＮｏ．３２は、Ｃ量が本願発明の下限値の０．２％より少なく、高温強度は初期硬さからの減少量が１４ＨＲＣより多いので×である。 Comparative steel No. 32, the C content is less than the lower limit of 0.2% of the present invention, and the high temperature strength decreases from the initial hardness by more than 14 HRC, so it is x.
比較鋼のＮｏ．３３は、１０，０００μｍ2当りの円相当径１μｍ以上の炭化物個数が多いので炭化物数が×であり、高温強度は初期硬さからの減少量が１４ＨＲＣより多いので×である。 Comparative steel No. In No. 33, the number of carbides with an equivalent circle diameter of 1 μm or more per 10,000 μm 2 is large, so the number of carbides is x.
Claims (1)
% by mass, C: 0.20 to 0.60%, Si: 0.1 to 0.3%, Mn: 0.5 to 2.0%, Ni: 0.5 to 2.5%, Cr: 1.6% to 2.6%, Mo: 0.3% to 2.0%, V: 0.05% to 0.80%, and the balance is Fe and inevitable impurities. A hot work tool steel excellent in high-temperature strength and toughness, wherein the number of carbides having an equivalent circle diameter of 1 μm or more per 10,000 μm 2 is 150 or less.
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