JP3279086B2 - Machine structural steel with excellent delayed fracture resistance - Google Patents
Machine structural steel with excellent delayed fracture resistanceInfo
- Publication number
- JP3279086B2 JP3279086B2 JP19395494A JP19395494A JP3279086B2 JP 3279086 B2 JP3279086 B2 JP 3279086B2 JP 19395494 A JP19395494 A JP 19395494A JP 19395494 A JP19395494 A JP 19395494A JP 3279086 B2 JP3279086 B2 JP 3279086B2
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- steel
- delayed fracture
- fracture resistance
- content
- machine structural
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Description
【0001】[0001]
【産業上の利用分野】本発明は、140kgf/mm2以上の引張
強さを有し、かつ、耐遅れ破壊性に優れた高張力ボルト
やPC鋼棒、更には大型機械用の高張力鋼板に使用され
る機械構造用鋼に関する。The present invention relates to a high-tensile bolt or a PC steel rod having a tensile strength of 140 kgf / mm 2 or more and excellent in delayed fracture resistance, and a high-tensile steel plate for a large machine. The present invention relates to steel for machine structural use used for:
【0002】[0002]
【従来の技術】近年、特に構造物の大型化、自動車やト
ラックおよび土木・鉱山機械などの軽量化に伴い、今ま
で以上に高強度な機械構造用鋼、特に高張力ボルトやP
C鋼棒の開発が必要とされている。2. Description of the Related Art In recent years, particularly with the enlargement of structures and the weight reduction of automobiles, trucks, civil engineering and mining equipment, steel for machine structural use having higher strength than ever, especially high tension bolts and P
There is a need for the development of C steel bars.
【0003】従来、一般に使用されている機械構造用鋼
は、引張強度100kgf/mm2レベルでは例えば、 0.4%C−
1.05%Cr−0.23%Moの組成を有するJIS G 4105(1989)に
規定されたSCM440の低合金鋼、引張強度130kgf/mm2レベ
ルでは、例えば、0.17%C−3%Ni− 1.6%Cr− 0.5%
Moの組成を有するJIS G 4103(1989)に規定されたSNCM61
6 の低合金鋼の熱間圧延材に焼入れ焼戻し処理を施すこ
とによって製造されている。また、引張強度174kgf/mm2
レベルのものは、上記の低合金鋼の熱間圧延材に熱処理
条件を変えて焼入れ焼戻し処理を施すことによって製造
されている。しかしこれらの機械構造用鋼を実用に供し
た場合、使用中に遅れ破壊を生じることがあるため、高
張力ボルトやPC鋼棒を始めとして自動車や土木用機械
の重要保安部品として用いるに際し、品質の安定性に欠
けることが問題となっていた。Conventionally, the commonly used machine structural steel, tensile strength 100 kgf / mm 2 level, for example, 0.4% C-
JIS G 4105 (1989) to a defined SCM440 low alloy steel having a composition of 1.05% Cr-0.23% Mo, the tensile strength of 130 kgf / mm 2 level, for example, 0.17% C-3% Ni- 1.6% Cr- 0.5%
SNCM61 specified in JIS G 4103 (1989) with Mo composition
It is manufactured by quenching and tempering the hot-rolled material of low alloy steel of No. 6. In addition, tensile strength 174kgf / mm 2
The low-grade steel is manufactured by subjecting the above-described low-alloy steel hot-rolled material to a quenching and tempering treatment under different heat treatment conditions. However, when these mechanical structural steels are put to practical use, they may cause delayed fracture during use. Therefore, when used as important security parts for automobiles and civil engineering machines, including high-tensile bolts and PC steel rods, they are required to be of high quality. Lack of stability has been a problem.
【0004】なお、遅れ破壊とは静荷重下におかれた鋼
がある時間経過後に突然脆性的に破断する現象であり、
外部環境から鋼中に侵入した水素による一種の水素脆性
とされている。[0004] Delayed fracture is a phenomenon in which a steel placed under a static load suddenly breaks brittlely after a certain period of time.
It is considered to be a kind of hydrogen embrittlement due to hydrogen penetrating into steel from the external environment.
【0005】このようなことから、上記の機械構造用鋼
においては、今のところその強度レベルを引張強さで10
0kgf/mm 2 以下にすることが実用上望ましいとされてい
る。[0005] For these reasons, in the above-mentioned steel for machine structural use, at present, its strength level is 10% in terms of tensile strength.
It is said that it is practically desirable to make it 0 kgf / mm 2 or less.
【0006】これに対して、上記の通常の低合金鋼より
耐遅れ破壊性の優れた鋼として、例えば、18%Ni−7.5
%Co−5%Mo− 0.5%Ti− 0.1%Alの組成を有する18%
Niマルエージング鋼があるが、極めて高価であるために
経済性の観点から用途が限られている。そこで、経済性
を考慮した高強度かつ耐遅れ破壊性に優れた構造用鋼お
よび高強度ボルト用鋼が、例えば、特開昭58−84960
号、同61−117248号、同58−157921号および同58−6121
9 号の各公報で提案されている。更に、特開平3−2437
45号公報や特開平2−145746号公報等に、各種成分を添
加して耐遅れ破壊性を改善した鋼およびその製造法が提
案されているが、靱性や水素透過性の点で必ずしも十分
とは言えない。[0006] On the other hand, as a steel having more excellent delayed fracture resistance than the above-mentioned ordinary low alloy steel, for example, 18% Ni-7.5
18% having a composition of% Co-5% Mo-0.5% Ti-0.1% Al
Although there is Ni maraging steel, its use is limited from the viewpoint of economy because it is extremely expensive. Therefore, structural steel and high-strength bolt steel having high strength and excellent delayed fracture resistance in consideration of economy are disclosed in, for example, JP-A-58-84960.
No. 61-117248, No. 58-157921 and No. 58-6121
It is proposed in each gazette of Issue 9. Further, JP-A-3-2437
No. 45 and Japanese Unexamined Patent Publication (Kokai) No. 2-145746, etc., have proposed a steel having improved delayed fracture resistance by adding various components and a method for producing the same, but are not necessarily sufficient in terms of toughness and hydrogen permeability. I can't say.
【0007】[0007]
【発明が解決しようとする課題】本発明は上記した産業
界の要請に応えるべく、140kgf/mm2以上の引張強度を有
し、かつ耐遅れ破壊性に優れた機械構造用鋼を提供する
ことを目的とするもので例えば、橋梁用高張力ボルト等
のように恒久的に使用するのではなくて、定期的な補修
あるいは取り替えを前提とし、一定期間内に遅れ破壊の
発生の恐れのない140kgf/mm2以上の引張強さを有する機
械構造用鋼を安価で提供することを目的とする。このよ
うな用途としては、各種構造物用高張力鋼、自動車、土
木機械、産業機械用のボルト用鋼および高張力鋼板があ
り、これらに本発明鋼を使用することによって上記の産
業界の要求に応えることができる。SUMMARY OF THE INVENTION The present invention provides a steel for machine structural use having a tensile strength of 140 kgf / mm 2 or more and excellent in delayed fracture resistance in order to meet the above-mentioned demands of the industry. For example, instead of being used permanently like high-tension bolts for bridges, etc., it is premised on periodic repair or replacement, and there is no risk of delayed failure within a certain period of 140 kgf An object of the present invention is to provide a mechanical structural steel having a tensile strength of at least / mm 2 at a low cost. Such applications include high-strength steels for various structures, steels for bolts and high-strength steel sheets for automobiles, civil engineering machines, industrial machines, and the use of the steel of the present invention in these. Can respond to.
【0008】すなわち、本発明は所定の期間ならば遅れ
破壊の発生する危険がなく、従って定期的な取り替えを
前提として安全に使用できる140kgf/mm2以上の引張強さ
を有する機械構造用鋼を安価で提供することを目的とし
てなされたものである。That is, the present invention provides a steel for machine structural use having a tensile strength of 140 kgf / mm 2 or more that can be safely used on the premise of periodic replacement without the risk of delayed fracture occurring for a predetermined period. It is intended to be provided at a low price.
【0009】[0009]
【課題を解決するための手段】これまでにCr含有量が低
くCuを添加した耐遅れ破壊性に優れた構造用鋼は開発さ
れているが、Cuの耐遅れ破壊性向上に対する機構の解明
は十分ではなかった。[Means for Solving the Problems] Structural steels with low Cr content and added Cu with excellent delayed fracture resistance have been developed so far. Was not enough.
【0010】そこで本発明者は、まずCu添加が耐遅れ破
壊性に及ぼす影響について研究した結果、Cuは腐食速度
を下げることにより水素の侵入を抑制し、遅れ破壊の原
因である水素脆化を防止することにより耐遅れ破壊性を
向上するという知見を得た。Therefore, the present inventor first studied the effect of the addition of Cu on delayed fracture resistance, and found that Cu suppresses the invasion of hydrogen by lowering the corrosion rate and reduces hydrogen embrittlement, which is the cause of delayed fracture. It has been found that the prevention improves the delayed fracture resistance.
【0011】本発明鋼はこれまでの鋼より更に強度増加
を確実にするためにCの含有量を高めた。そこで、これ
によるCuの水素侵入抑制効果の低下を防ぐため、本発明
者はCu以外に水素侵入抑制効果を持つ元素を調査した。
その結果、これまでに開発されている多くの耐遅れ破壊
性に優れた構造用鋼に添加されているMoが、水素過電圧
を下げることにより水素侵入抑制効果を示し、この効果
により遅れ破壊の原因となる水素脆化を防止して耐遅れ
破壊性を向上させることを知見した。そこで、Cuおよび
Mo以外の元素の含有量は一定として、すなわち、重量%
で、C: 0.8%、Si:1.25%、Mn:0.33%、P: 0.004
%、S: 0.006%、Cr: 1.0%、Al:0.10%、Ni:0.45
%、Nb: 0.171%、V:0.05%とし、Cuを無添加または
0.3重量%添加した鋼に水素侵入抑制機構の異なるMoを
追加添加して、更なる水素侵入抑制効果を期待したが、
図1に示すように、この化学組成の鋼に対しては顕著な
効果は得られなかった。The steel of the present invention has a higher C content in order to further increase the strength of the conventional steel. Therefore, in order to prevent the decrease in the effect of suppressing hydrogen intrusion of Cu due to this, the present inventors investigated elements other than Cu that have the effect of suppressing hydrogen intrusion.
As a result, Mo, which has been added to many of the structural steels with excellent delayed fracture resistance, which has been developed up to now, has the effect of suppressing hydrogen intrusion by reducing hydrogen overvoltage, and this effect causes delayed fracture. It has been found that the hydrogen embrittlement which prevents the occurrence of the above phenomenon is prevented and the delayed fracture resistance is improved. So, Cu and
The content of elements other than Mo is constant, that is,
And C: 0.8%, Si: 1.25%, Mn: 0.33%, P: 0.004
%, S: 0.006%, Cr: 1.0%, Al: 0.10%, Ni: 0.45
%, Nb: 0.171%, V: 0.05%, without adding Cu
The addition of Mo with a different hydrogen intrusion suppression mechanism to steel with 0.3% by weight addition was expected to further suppress hydrogen intrusion.
As shown in FIG. 1, no remarkable effect was obtained for steel having this chemical composition.
【0012】そこで、更に実験、研究を重ねた結果、図
2に示すように、CuとMoを複合添加し、更にCr含有量を
増加させることにより水素侵入抑制効果が飛躍的に向上
し、Cu単独添加鋼にCrを含有させた場合よりも有効であ
るという新しい知見を得た。Therefore, as a result of further experiments and studies, as shown in FIG. 2, the effect of suppressing hydrogen intrusion is dramatically improved by adding Cu and Mo in combination and further increasing the Cr content. A new finding was found that it was more effective than the case where Cr was contained in a single additive steel.
【0013】なお、図2の結果は、Mo添加鋼(Mo:0.50
%、C:0.81%、Si:1.26%、Mn:0.35%、P: 0.005
%、S: 0.008%、Cu: 0.3%、Cr: 3.3%、sol.Al:
0.10%、Ni:0.46%、Nb: 0.173%、V:0.05%)およ
びMo非添加鋼(Mo: 0.003%、Mo以外の化学組成は、Mo
添加鋼に同じ)でのものである。The results of FIG. 2 show that Mo-added steel (Mo: 0.50
%, C: 0.81%, Si: 1.26%, Mn: 0.35%, P: 0.005
%, S: 0.008%, Cu: 0.3%, Cr: 3.3%, sol.Al:
0.10%, Ni: 0.46%, Nb: 0.173%, V: 0.05%) and Mo-free steel (Mo: 0.003%, chemical composition other than Mo is Mo
(Same as additive steel).
【0014】また、これまでに低P・低S化による粒界
偏析の軽減および清浄化が耐遅れ破壊性を向上すること
が知られており、本発明鋼においてもPおよびSの含有
量を低下させて、耐遅れ破壊性の一層の向上を図った。It has been known that reduction of grain boundary segregation and purification by low P and low S improve delayed fracture resistance. The steels of the present invention have a low P and S content. It is intended to further improve the delayed fracture resistance.
【0015】本発明は上記の知見に基づいてなされたも
ので、その要旨は下記(1)〜(5)の耐遅れ破壊性に
優れた機械構造用鋼にある。The present invention has been made on the basis of the above findings, and the gist of the invention lies in the following (1) to (5): steel for machine structural use having excellent delayed fracture resistance.
【0016】(1)重量%で、C:0.56〜0.90%、Si:
0.5〜2.0 %、Mn: 0.5%未満、P: 0.015%以下、
S:0.01%以下、Cu:0.10〜1.00%、Cr: 1.5〜5.0
%、Mo:0.05〜1.0 %、Al:0.01〜0.10%、Nb: 0.005
〜0.20%、Ni:0.05〜0.50%、V:0.01〜0.30%を含有
し、かつ、Cu+Mo≧ 0.4%を満たし、残部は実質的にFe
および不可避的不純物からなる耐遅れ破壊性に優れた機
械構造用鋼。(1) By weight%, C: 0.56 to 0.90%, Si:
0.5 to 2.0%, Mn: less than 0.5%, P: 0.015% or less,
S: 0.01% or less, Cu: 0.10-1.00%, Cr: 1.5-5.0
%, Mo: 0.05 to 1.0%, Al: 0.01 to 0.10%, Nb: 0.005
0.20%, Ni: 0.05-0.50%, V: 0.01-0.30%, and Cu + Mo ≧ 0.4%, the balance being substantially Fe
And mechanical structural steel with excellent delayed fracture resistance consisting of unavoidable impurities.
【0017】(2)上記(1)に記載の成分に加えて更
に、重量%で、0.01〜0.15%のZrを含有し、かつ、Cu+
Mo≧ 0.4%を満たすことを特徴とする耐遅れ破壊性に優
れた機械構造用鋼。(2) In addition to the components described in the above (1), the composition further contains 0.01 to 0.15% by weight of Zr and contains Cu +
A mechanical structural steel with excellent delayed fracture resistance, characterized by satisfying Mo ≧ 0.4%.
【0018】(3)上記(1)に記載の成分に加えて更
に、重量%で、0.01〜0.10%のTi及び0.0003〜0.0050%
のBのうちの1種以上を含有し、かつ、Cu+Mo≧ 0.4%
を満たすことを特徴とする耐遅れ破壊性に優れた機械構
造用鋼。(3) In addition to the components described in the above (1), 0.01 to 0.10% of Ti and 0.0003 to 0.0050% by weight are further added.
Contains at least one of B and Cu + Mo ≧ 0.4%
A mechanical structural steel with excellent delayed fracture resistance, characterized by satisfying the following conditions.
【0019】(4)上記(1)に記載の成分に加えて更
に、重量%で、0.01〜0.15%のZr、ならびに0.01〜0.10
%のTiおよび0.0003〜0.0050%のBのうちの1種以上を
含有し、かつ、Cu+Mo≧ 0.4%を満たすことを特徴とす
る耐遅れ破壊性に優れた機械構造用鋼。(4) In addition to the component described in the above (1), 0.01 to 0.15% by weight of Zr, and 0.01 to 0.10% by weight.
% Ti and one or more of 0.0003 to 0.0050% B, and satisfy Cu + Mo ≧ 0.4%, and are excellent in delayed fracture resistance.
【0020】(5)焼入れ焼戻し組織からなる上記
(1)〜(4)のいずれかに記載の耐遅れ破壊性に優れ
た機械構造用鋼。(5) The machine structural steel according to any one of the above (1) to (4), which has a quenched and tempered structure and is excellent in delayed fracture resistance.
【0021】[0021]
【作用】以下に、本発明における鋼の化学組成および組
織を上記のように限定する理由について述べる。なお、
「%」は「重量%」を意味する。The reasons for limiting the chemical composition and structure of steel in the present invention as described above will be described below. In addition,
“%” Means “% by weight”.
【0022】(A)鋼の化学組成 C: Cは炭化物を形成し析出強度によって鋼を強化し、ま
た、焼入時に安定なマルテンサイト組織を生成させて変
態強度によっても鋼を強化するので高強度化する上で必
須の元素である。また、焼入性の増加および結晶の細粒
化にも有効な成分である。0.56%未満では焼入性の劣化
をきたし、また、炭化物の析出量が少なく強度を損な
う。一方、0.90%を超える場合には、焼入時の焼割れ感受
性が増加し、加えて鋼が著しく硬化して延性、溶接性お
よび加工性が低下する。従って、C量は0.56〜0.90%と
する。(A) Chemical composition of steel C: C forms a carbide and strengthens the steel by precipitation strength, and also forms a stable martensite structure during quenching and strengthens the steel by transformation strength. It is an essential element for strengthening. Further, it is an effective component for increasing hardenability and refining crystals. If it is less than 0.56 %, the hardenability deteriorates, and the amount of carbide precipitated is small, resulting in a loss of strength. On the other hand, when the content exceeds 0.90%, the susceptibility to quenching during quenching increases, and in addition, the steel is significantly hardened, and the ductility, weldability, and workability decrease. Therefore, the C content is set to 0.56 to 0.90%.
【0023】Si:Siは鋼の脱酸および強度増加のために
有効な元素である。その含有量が 0.5%未満では前記作
用に所望の効果が得られず、他方その含有量が 2.0%を
超えると鋼の清浄性が損なわれ靱性が劣化する場合があ
るため、本発明ではその含有量を0.5〜2.0 %と定め
た。Si: Si is an effective element for deoxidizing steel and increasing strength. If the content is less than 0.5%, the desired effect cannot be obtained in the above-mentioned action, while if the content exceeds 2.0%, the cleanliness of steel may be impaired and the toughness may be deteriorated. The amount was defined as 0.5-2.0%.
【0024】Mn:Mnは脱酸のほか、焼入性向上に有効な
元素であるが、多量に含有させると粒界脆化現象が生
じ、遅れ破壊の発生を促進する。更にMnはSと結合し
て、これが割れの起点となることからも、耐遅れ破壊性
の改善のためには極力その含有量を低下させなければな
らない。従って、耐遅れ破壊性の改善を目的とする本発
明ではMnの含有量を 0.5%未満とした。なおMn含有量は
実質的に0でもよい。Mn: Mn is an element effective for improving dequenching and hardenability, but when contained in a large amount, grain boundary embrittlement occurs to promote delayed fracture. Furthermore, since Mn combines with S and this serves as a starting point of cracking, its content must be reduced as much as possible to improve delayed fracture resistance. Therefore, in the present invention for the purpose of improving delayed fracture resistance, the content of Mn is set to less than 0.5%. The Mn content may be substantially zero.
【0025】P:Pはいかなる熱処理を施してもその粒
界偏析を完全に消滅することはできず、かつ粒界強度を
低下させ耐遅れ破壊性を劣化させるため、本発明では不
純物としてのPの上限を 0.015%とした。P: P cannot completely eliminate the grain boundary segregation by any heat treatment, and also reduces the grain boundary strength and deteriorates the delayed fracture resistance. Is set to 0.015%.
【0026】S:Sは前述したようにMnと結合して割れ
の起点となり、更に単独でも粒界に偏析して遅れ破壊の
原因となる水素脆化を促進するため、極力その含有量を
低く制限することが必要である。したがって、本発明で
は不純物としてのS含有量を0.01%以下とした。S: As described above, S combines with Mn to serve as a starting point of cracking. Further, S alone promotes hydrogen embrittlement which segregates at the grain boundary and causes delayed fracture. It is necessary to limit. Therefore, in the present invention, the content of S as an impurity is set to 0.01% or less.
【0027】Cu:Cuは外部環境からの鋼中への水素侵入
を抑制すると共に、Nb、MoおよびCrと複合添加すること
よって鋼の焼戻し軟化抵抗を著しく高めることができる
ので高い焼戻し温度が取れることと相まって、耐遅れ破
壊性を向上する作用を有する。しかしその含有量が0.10
%未満ではその効果が小さく、一方、1.00%を超えて含
有させると溶接性、熱間加工性および靱性の劣化をきた
すので、本発明ではCuの含有量を0.10〜1.00%とした。Cu: Cu suppresses the intrusion of hydrogen into the steel from the external environment and, when combined with Nb, Mo and Cr, can significantly increase the tempering softening resistance of the steel, so that a high tempering temperature can be obtained. This has the effect of improving delayed fracture resistance. But its content is 0.10
%, The effect is small. On the other hand, when the content exceeds 1.00%, the weldability, hot workability and toughness are deteriorated. Therefore, in the present invention, the Cu content is set to 0.10 to 1.00%.
【0028】Cr:Crは鋼の焼入性を向上させ、かつ鋼に
焼戻し軟化抵抗を付与する作用がある。Cr: Cr has the effect of improving the hardenability of steel and imparting temper softening resistance to steel.
【0029】特に、NbやCuとの複合添加で著しい焼戻し
軟化抵抗を鋼に付与するが、その添加量が 1.5%未満で
はCuとMo複合添加による水素侵入抑制効果が発揮され
ず、耐遅れ破壊性を飛躍的に向上させることができな
い。一方、Crは高価な合金元素であるため経済性を考慮
し、本発明ではその含有量を1.5〜5.0%と定めた。In particular, the addition of Nb or Cu in combination gives remarkable temper softening resistance to steel. However, if the addition amount is less than 1.5 %, the effect of suppressing the intrusion of hydrogen by the addition of Cu and Mo is not exhibited, resulting in delayed fracture resistance. The performance cannot be improved dramatically. On the other hand, since Cr is an expensive alloy element, its content is set to 1.5 to 5.0% in the present invention in consideration of economic efficiency.
【0030】Mo:Moは機構は異なるがCuと同様に水素侵
入抑制効果を示す。また鋼の焼入性を向上させ、かつ鋼
に焼戻し軟化抵抗を付与する作用があり、特に、Cu、N
b、Crとの複合添加で焼戻し軟化抵抗を著しく増大さ
せ、高い焼戻し温度の採用を可能にして耐遅れ破壊性の
改善に有効である。しかしその含有量が0.05%未満では
前記の効果が十分に得られず、一方、 1.0%を超えて添
加してもその効果は飽和し、コストの上昇を招くだけで
あるため、本発明ではその含有量を0.05〜1.0 %と定め
た。Mo: Mo has a different mechanism, but exhibits an effect of suppressing hydrogen intrusion similarly to Cu. It also has the effect of improving the hardenability of steel and imparting tempering softening resistance to steel.
The addition of b and Cr in combination significantly increases the tempering softening resistance, enables the use of a high tempering temperature, and is effective in improving delayed fracture resistance. However, if the content is less than 0.05%, the above-mentioned effects cannot be sufficiently obtained. On the other hand, if the content exceeds 1.0%, the effects are saturated and only the cost is increased. The content was determined to be 0.05-1.0%.
【0031】 Al: Alは鋼の脱酸の安定化、均質化および細粒化を図るのに
有効であるが、0.01%未満では所望の効果を得ることが
できず、一方、0.10%を超えて含有させてもその効果は
飽和してしまい、また介在物の増大により疵が発生し靱
性も劣化するので、本発明ではその含有量を0.01〜0.10
%と定めた。[0031] Al: Al is the stabilization of deoxidation of steel, is effective to achieve homogenization and comminution, is less than 0.01% can not be obtained the desired effect, whereas, the 0.1 0% beyond its effect when the content becomes saturated, and since flaws due to the increase in inclusions is deteriorated also occurs toughness, the content thereof in the present invention 0.01 to 0.1 0
%.
【0032】Nb:Nbを添加することにより鋼における細
粒化が促進され、粒界偏析が軽減されて耐遅れ破壊性が
一段と向上する。しかし、 0.005%未満では所望の効果
が得られず、一方、0.20%を超えると強度、延性などが
損なわれる。従って、その含有量を 0.005〜0.20%とし
た。Nb: By adding Nb, grain refinement in the steel is promoted, grain boundary segregation is reduced, and delayed fracture resistance is further improved. However, if it is less than 0.005%, the desired effect cannot be obtained, while if it exceeds 0.20%, strength, ductility, etc. are impaired. Therefore, its content was made 0.005 to 0.20%.
【0033】Ni:Niは鋼の靱性を高めるのに有効である
と共に、Cuチェッキングによる熱間加工性の低下を防ぐ
効果がある。しかしその含有量が0.05%未満では前記作
用に所望の効果が得られない。一方、0.50%を超えると
その効果が飽和し、またNiは高価な合金元素であるため
経済性を考慮して本発明ではその含有量を0.05〜0.50%
とした。Ni: Ni is effective in increasing the toughness of the steel and also has the effect of preventing a decrease in hot workability due to Cu checking. However, if the content is less than 0.05%, the desired effect cannot be obtained. On the other hand, if the content exceeds 0.50%, the effect is saturated, and Ni is an expensive alloy element, so that the content is 0.05 to 0.50% in the present invention in consideration of economy.
And
【0034】V:Vの添加はNbの場合と同様に鋼の細粒
化の促進作用があり、粒界偏析の軽減により耐遅れ破壊
性を一段と向上させる。しかし、0.01%未満では所望の
効果が得られず、一方、0.30%を超えると靱性が損なわ
れる。従って、その含有量を0.01〜0.30%とした。V: The addition of V has the effect of promoting the grain refinement of steel as in the case of Nb, and further enhances delayed fracture resistance by reducing grain boundary segregation. However, if it is less than 0.01%, the desired effect cannot be obtained, while if it exceeds 0.30%, the toughness is impaired. Therefore, the content is set to 0.01 to 0.30%.
【0035】Cu+Mo:CuとMoの複合添加は本発明におい
て重要な要素である。これらの水素侵入抑制機構の異な
る元素を組み合わせることにより、水素侵入抑制効果は
各元素の単独添加で得られる効果を相乗的に向上させる
ことができる。しかし、図3に示すように、その合計含
有量が 0.4%未満では所望の効果が得られない。従っ
て、耐遅れ破壊性の飛躍的向上を目的とする本発明で
は、CuとMoの合計含有量を 0.4%以上とした。なお図3
で用いた鋼は、C:0.82%、Si:1.31%、Mn:0.15%、
P:0.013%、S:0.01%、Cr: 4.0%、Al: 0.015
%、Nb:0.09%、Ni: 0.009%、V:0.02%の成分のも
のでCuとMoをそれぞれ0.04〜0.31%、0.04〜0.31%の範
囲で変えて、Cu+Moの量を調整した。Cu + Mo: The complex addition of Cu and Mo is an important factor in the present invention. By combining these elements having different hydrogen intrusion suppressing mechanisms, the effect of suppressing hydrogen intrusion can be synergistically improved by the effect of adding each element alone. However, as shown in FIG. 3, if the total content is less than 0.4%, the desired effect cannot be obtained. Therefore, in the present invention for the purpose of dramatically improving delayed fracture resistance, the total content of Cu and Mo is set to 0.4% or more. FIG. 3
The steels used in were: C: 0.82%, Si: 1.31%, Mn: 0.15%,
P: 0.013%, S: 0.01%, Cr: 4.0%, Al: 0.015
%, Nb: 0.09%, Ni: 0.009%, V: 0.02%, and the amount of Cu + Mo was adjusted by changing Cu and Mo in the ranges of 0.04 to 0.31% and 0.04 to 0.31%, respectively.
【0036】本発明の耐遅れ破壊性に優れた機械構造用
鋼には、上記の成分に加えて更に、Zr、TiおよびBのう
ちの1種以上を含んでいても良い。これらの合金元素の
作用効果と望ましい含有量は下記の通りである。The steel for machine structural use having excellent delayed fracture resistance according to the present invention may further contain one or more of Zr, Ti and B in addition to the above components. The effects and desirable contents of these alloy elements are as follows.
【0037】Zr:Zrは鋼中に炭化物を球状微細に分散さ
せて耐遅れ破壊性を一層改善させる効果を有するため、
特に高強度鋼の場合に高い耐遅れ破壊性を確保する目的
で含有させるが、0.01%未満ではその効果が小さく、一
方、0.15%を超えて含有させると靱性劣化をきたすよう
になる。従って、Zrを添加する場合には0.01〜0.15%の
含有量とするのがよい。Zr: Zr has the effect of dispersing carbides finely and spherically in steel to further improve delayed fracture resistance.
Particularly, in the case of high-strength steel, the content is included for the purpose of securing high delayed fracture resistance. However, if the content is less than 0.01%, the effect is small, while if it exceeds 0.15%, toughness is deteriorated. Therefore, when Zr is added, the content is preferably 0.01 to 0.15%.
【0038】TiおよびB:TiおよびBは鋼の焼入性を著
しく高めて高強度化し、かつ粒界を強化することにより
耐遅れ破壊性をいっそう改善する作用を有している。特
に製品寸法が大きい場合には高強度を確保する目的で添
加するが、それぞれTi:0.01%未満、B:0.0003%未満
では所望の効果が得られず、また、Ti、BはそれぞれT
i:0.10%、B:0.0050%を超えて含有させると、鋼の
靱性を劣化するようになる。従って、これらの合金元素
を1種以上添加する場合は、Ti:0.01〜0.10%、B:0.
0003〜0.0050%の含有量とするのがよい。Ti and B: Ti and B have the effect of remarkably enhancing the hardenability of the steel to increase the strength, and further improving the delayed fracture resistance by strengthening the grain boundaries. Especially when the product size is large, it is added for the purpose of securing high strength. However, if the content is less than 0.01% for Ti and less than 0.0003% for B, the desired effects cannot be obtained.
If the content exceeds i: 0.10% and B: 0.0050%, the toughness of the steel deteriorates. Therefore, when one or more of these alloying elements are added, Ti: 0.01 to 0.10%, B: 0.
The content is preferably from 0003 to 0.0050%.
【0039】(B)鋼の組織 上記した化学組成を有する鋼であっても、140kgf/mm2以
上の引張強さと良好な耐遅れ破壊性とを具備させるには
焼入れ焼戻し組織とするのが望ましい。そのための熱処
理例としては、通常の熱間圧延(加熱温度:1000〜1250
℃)を行い、圧延後、直ちにAr3点以上の温度(好まし
くは 850〜1020℃)から油や空気で焼入れするか、また
は 850〜1050℃、好ましくは 920〜1020℃に再加熱して
から油や空気で焼入れを施して低温変態生成物 (マルテ
ンサイトやベイナイト) となし、これをAc1点以下の温
度で焼戻しする処理がある。しかし、本発明鋼の組織
は、必ずしも焼入れ焼戻し(QT)組織である必要はな
い。何故ならば、本発明鋼は使用中の水素侵入量を低減
させて耐遅れ破壊性を向上させるものであるため内部組
織にそれほど依存しないからである。例えば、熱間圧延
のまま、または焼入れのまま(As Q)などの組織でも
後述の実施例に示すように、140kgf/mm2以上の引張り強
さと優れた耐遅れ破壊性を示す。(B) Structure of Steel Even if the steel has the above-mentioned chemical composition, it is desirable to use a quenched and tempered structure to provide a tensile strength of 140 kgf / mm 2 or more and good delayed fracture resistance. . Examples of heat treatments for this purpose include ordinary hot rolling (heating temperature: 1000 to 1250
℃), and immediately after rolling, quenching with oil or air from a temperature of 3 points or more (preferably 850 to 1020 ° C) or reheating to 850 to 1050 ° C, preferably 920 to 1020 ° C There is a process of quenching with oil or air to produce low-temperature transformation products (martensite or bainite), and tempering this at a temperature of 1 point or less of Ac. However, the structure of the steel of the present invention does not necessarily need to be a quenched and tempered (QT) structure. The reason for this is that the steel of the present invention does not depend so much on the internal structure because it reduces the amount of hydrogen penetration during use and improves delayed fracture resistance. For example, a structure such as hot rolled or quenched (As Q) shows a tensile strength of 140 kgf / mm 2 or more and excellent delayed fracture resistance, as shown in Examples described later.
【0040】ただし、焼入れままの鋼は引張強さは高い
が、降伏点が低く機械構造用鋼として使用する場合に使
用中に応力緩和の増大が生じるという問題がある。However, as-quenched steel has a high tensile strength, but has a low yield point, and has a problem that stress relaxation increases during use when used as a machine structural steel.
【0041】従って、鋼に所定の強度と耐遅れ破壊性を
付与するためには焼入れ後焼戻し処理をして、鋼の組織
を焼入れ焼戻し組織(主として焼戻しマルテンサイト組
織)とするのが望ましい。Therefore, in order to impart a predetermined strength and delayed fracture resistance to the steel, it is desirable to perform a tempering treatment after quenching to make the structure of the steel a quenched and tempered structure (mainly a tempered martensite structure).
【0042】[0042]
【実施例】次に本発明を一実施例により比較鋼と対比し
ながら説明する。なお、これらの実施例は本発明の効果
を示す例示であって、本発明の技術的範囲を何ら制限す
るものではない。まず通常の方法によって、下記表1〜
3に示す成分組成の鋼(No.1〜44)を50kg大気溶解炉に
て溶製した。鋼1〜37は本発明の組成を有しているもの
であり、鋼38〜44は表2中 *印を付した点で、本発明の
範囲から外れた組成の鋼である。また、鋼45〜47は従来
鋼であり、45はJIS G 4105(1989)のSCM440、46はJIS G
4103(1989)のSNCM616 鋼、47は特開昭58−84960 号記載
の鋼である。Next, the present invention will be described by way of an example in comparison with comparative steel. It should be noted that these examples are exemplifications showing the effects of the present invention, and do not limit the technical scope of the present invention at all. First, by the usual method, the following Table 1
A steel (No. 1 to 44) having the composition shown in No. 3 was melted in a 50 kg atmospheric melting furnace. Steels 1 to 37 have the composition of the present invention, and steels 38 to 44 are steels having compositions out of the range of the present invention at the points marked * in Table 2. Further, steels 45 to 47 are conventional steels, 45 is SCM440 of JIS G 4105 (1989), and 46 is JIS G
4103 (1989) SNCM616 steel and 47 are steels described in JP-A-58-84960.
【0043】鋼1〜4、9〜13、15、16、20〜24、28〜
30、32、36〜39、43および44は、1100〜1200℃で熱間鍛
造および熱間圧延して厚さ15mmの板材とし、 950℃に再
加熱して45分保持し油焼入れした後、 600℃で焼戻して
空冷し、その組織が焼入れ焼戻し組織で、その引張強さ
が140kgf/mm2以上となるように調整して遅れ破壊性を
調査した。また、45〜47の従来鋼についても同様の焼入
れ焼戻し処理を行った。すなわち45、46、47についてそ
れぞれ870,900,950℃に再加熱して45分保持した後油焼
き入れし、その後45、46は500℃で、47は600℃で焼戻し
を施した。さらに、上記以外の熱間圧延まま材(No.5、
17、25、33、40) 、焼入れまま材(No.6、18、26、34、
41) 、熱間圧延後加速冷却を施した鋼(No.7、27、35、
42) についても調査した。加速冷却条件は 400〜500 ℃
までを10〜15℃/sの冷却速度となるように水冷をした。The steel 1 to 4, 9 to 13 and 15, 16,20~24,28~
30, 32 , 36 to 39 , 43 and 44 are hot forged and hot rolled at 1100 to 1200 ° C. to make a 15 mm thick plate, reheated to 950 ° C., held for 45 minutes, and oil quenched. It was tempered at 600 ° C. and air-cooled, and its structure was a quenched and tempered structure, and its tensile strength was adjusted to be 140 kgf / mm 2 or more, and delayed fracture property was investigated. The same quenching and tempering treatment was performed on 45 to 47 conventional steels. That is, 45, 46, and 47 were reheated to 870, 900, and 950 ° C., respectively, held for 45 minutes, and then oil-quenched, and thereafter, tempered at 500 ° C. for 45 and 46 and 600 ° C. for 47. Furthermore, other hot rolled as-rolled materials (No. 5,
17, 25, 33, 40), as-quenched material (No. 6, 18, 26, 34,
41), steel that has been subjected to accelerated cooling after hot rolling (No. 7 , 27, 35,
42) was also investigated. Accelerated cooling condition is 400 ~ 500 ℃
Water cooling was performed so that the cooling rate was 10 to 15 ° C / s.
【0044】なお遅れ破壊性の調査は、定荷重試験方法
によった。すなわち、図4に示すような形状、寸法の試
験片1を図5に示すように定荷重試験機8にセットし
て、pH=2のワルポール液(塩酸と酢酸ナトリウム水溶
液の混合液)2をポンプ3で循環させた環境下で 750時
間の間重錘4で静荷重 (引張応力: 140kgf/mm2)をか
け、試験片1を陰極として対極6との間に定電流 (1mA
/cm2) を流して試験片1に水素をチャージしながら、破
断の発生の有無を観察した。試験温度は温度調節装置7
で25℃に保持した。この試験結果は表4〜6に、破断し
なかったものは○、破断したものは×で各鋼の強度レベ
ルを添えて示した。なお、図4中において数字はmmの単
位の長さを示す。The examination of delayed fracture was carried out by a constant load test method. That is, a test piece 1 having a shape and dimensions as shown in FIG. 4 was set on a constant load tester 8 as shown in FIG. 5, and a Walpole solution (mixed solution of hydrochloric acid and sodium acetate aqueous solution) 2 having a pH of 2 was prepared. A static load (tensile stress: 140 kgf / mm 2 ) is applied to the weight 4 for 750 hours in an environment circulated by the pump 3, and a constant current (1 mA) is applied between the test piece 1 as a cathode and the counter electrode 6.
/ cm 2 ) and charged the specimen 1 with hydrogen while observing the occurrence of fracture. The test temperature is controlled by the temperature controller 7
At 25 ° C. The results of this test are shown in Tables 4 to 6, with ○ for those that did not break, and X for those that did break, together with the strength level of each steel. The numbers in FIG. 4 indicate the unit length in mm.
【0045】試験環境としてpH=2は、実使用環境にお
いて実現可能な最も厳しい環境に相当する。したがっ
て、この結果は実使用のうち最も厳しい環境での耐遅れ
破壊性を評価するものと考えられる。試験温度としての
25℃は遅れ破壊試験を行う上での一つの標準温度であ
る。As the test environment, pH = 2 corresponds to the most severe environment that can be realized in an actual use environment. Therefore, it is considered that this result evaluates the delayed fracture resistance in the severest environment among actual use. Test temperature
25 ° C is one standard temperature for performing the delayed fracture test.
【0046】表4〜6より、本発明の鋼は定荷重破断時
間がいずれも 750時間を超えていることから耐遅れ破壊
性に優れていることが明らかである。また、靱性の点で
はシャルピー試験のシェルフエネルギー値が高くなって
いることから、および延性の点では高温圧縮試験の変形
必要応力が小さくなっていることから、それぞれ改善さ
れていることがわかる。From Tables 4 to 6, it is clear that the steels of the present invention are excellent in delayed fracture resistance since the constant load rupture time exceeds 750 hours. Further, it can be seen that the toughness is improved because the shelf energy value in the Charpy test is high, and the ductility is improved because the required stress for deformation in the high temperature compression test is small.
【0047】すなわち、本発明によると140kgf/mm2以上
の引張強さを有する機械構造用鋼を得ることができ、前
述したように定期補修または取り替えを前提とし、必要
な耐遅れ破壊性の程度の明確な用途の鋼には、本発明に
おける機械構造用鋼を広範囲に使用できる。That is, according to the present invention, a steel for machine structural use having a tensile strength of 140 kgf / mm 2 or more can be obtained. The steel for machine structural use according to the present invention can be used for a wide range of steels having a clear application.
【0048】[0048]
【表1】 [Table 1]
【0049】[0049]
【表2】 [Table 2]
【0050】[0050]
【表3】 [Table 3]
【0051】[0051]
【表4】 [Table 4]
【0052】[0052]
【表5】 [Table 5]
【0053】[0053]
【表6】 [Table 6]
【0054】[0054]
【発明の効果】上記したごとく、本発明は140kgf/mm2以
上の引張強さを有し、かつ耐遅れ破壊性に優れた機械構
造用鋼で、定期補修または取り替えを前提とした一定期
間内での遅れ破壊発生の恐れのない、特に高張力ボルト
やPC鋼棒、更には大型機械用の高張力鋼板に使用され
る機械構造用鋼に安価な低合金高強度鋼として提供する
ことができる産業上有効な発明である。As described above, the present invention is a steel for machine structural use having a tensile strength of 140 kgf / mm 2 or more and excellent in delayed fracture resistance within a certain period of time assuming regular repair or replacement. It can be provided as an inexpensive low-alloy high-strength steel for machine structural steel used for high-tensile bolts and PC steel rods, especially for high-tensile steel plates for large-sized machines, without the risk of delayed fracture occurring at high temperatures. This is an industrially effective invention.
【図1】Cr:1%を含有するCu添加鋼及びCu無添加鋼に
おける、Mo含有量と水素透過量との関係を示す図であ
る。FIG. 1 is a diagram showing the relationship between the Mo content and the hydrogen permeation amount in a Cu-added steel containing Cr: 1% and a Cu-free steel.
【図2】Cu:0.3 %を含有するMo添加鋼及び Mo 無添加
鋼における、Cr含有量と水素透過量との関係を示す図で
ある。FIG. 2 is a diagram showing the relationship between the Cr content and the hydrogen permeation amount in a Mo-added steel containing 0.3% of Cu and a Mo-free steel.
【図3】(Cr+Mo)含有量と水素透過量との関係を示す
図である。FIG. 3 is a diagram showing a relationship between a (Cr + Mo) content and a hydrogen permeation amount.
【図4】実施例における定荷重試験で用いた試験片とノ
ッチの形状および寸法を示す図であり、(イ)は試験片
を示し、(ロ)は試験片のノッチ部の詳細を示す。FIG. 4 is a view showing the shape and dimensions of a test piece and a notch used in a constant load test in an example, where (a) shows a test piece and (b) shows details of a notch portion of the test piece.
【図5】定荷重試験方法の概要を示す図である。FIG. 5 is a diagram showing an outline of a constant load test method.
1:試験片、2:ワルポール液、3:ポンプ、4:重
錘、5:ポテンシオスタット、6:対極、7:温度調節
装置、8:定荷重試験機1: test piece, 2: Walpole liquid, 3: pump, 4: weight, 5: potentiostat, 6: counter electrode, 7: temperature controller, 8: constant load tester
フロントページの続き (58)調査した分野(Int.Cl.7,DB名) C22C 38/00 301 C22C 38/48 Continuation of front page (58) Field surveyed (Int. Cl. 7 , DB name) C22C 38/00 301 C22C 38/48
Claims (5)
2.0 %、Mn: 0.5%未満、P: 0.015%以下、S:0.01
%以下、Cu:0.10〜1.00%、Cr: 1.5〜5.0 %、Mo:0.
05〜1.0 %、Al:0.01〜0.10%、Nb: 0.005〜0.20%、
Ni:0.05〜0.50%、V:0.01〜0.30%を含有し、かつ、
Cu+Mo≧ 0.4%を満たし、残部は実質的にFeおよび不可
避的不純物からなる耐遅れ破壊性に優れた機械構造用
鋼。C .: 0.56 to 0.90%, Si: 0.5 to 0.9% by weight.
2.0%, Mn: less than 0.5%, P: 0.015% or less, S: 0.01
% Or less, Cu: 0.10 to 1.00%, Cr: 1.5 to 5.0%, Mo: 0.
05 to 1.0%, Al: 0.01 to 0.10%, Nb: 0.005 to 0.20%,
Ni: 0.05 to 0.50%, V: 0.01 to 0.30%, and
A steel for machine structural use that satisfies Cu + Mo ≧ 0.4% and the balance is substantially composed of Fe and unavoidable impurities and has excellent delayed fracture resistance.
%で、0.01〜0.15%のZrを含有し、かつ、Cu+Mo≧ 0.4
%を満たし、残部は実質的にFeおよび不可避的不純物か
らなる耐遅れ破壊性に優れた機械構造用鋼。2. The composition according to claim 1, further comprising, by weight%, 0.01 to 0.15% of Zr, and Cu + Mo ≧ 0.4.
%, The balance being substantially Fe and unavoidable impurities, and excellent in delayed fracture resistance.
%で、0.01〜0.10%のTi及び0.0003〜0.0050%のBのう
ちの1種以上を含有し、かつ、Cu+Mo≧ 0.4%を満た
し、残部は実質的にFeおよび不可避的不純物からなる耐
遅れ破壊性に優れた機械構造用鋼。3. The composition according to claim 1, further comprising at least one of 0.01% to 0.10% Ti and 0.0003% to 0.0050% B by weight, and Cu + Mo ≧ 0.4%. , The balance being substantially Fe and unavoidable impurities, and excellent in delayed fracture resistance for machine structural use.
%で、0.01〜0.15%のZr、ならびに0.01〜0.10%のTi及
び0.0003〜0.0050%のBのうちの1種以上を含有し、か
つ、Cu+Mo≧ 0.4%を満たし、残部は実質的にFeおよび
不可避的不純物からなる耐遅れ破壊性に優れた機械構造
用鋼。4. The composition according to claim 1, further comprising, by weight, 0.01 to 0.15% of Zr, and 0.01 to 0.10% of Ti and 0.0003 to 0.0050% of B. And a mechanical structure steel which satisfies Cu + Mo ≧ 0.4% and the balance is substantially composed of Fe and unavoidable impurities and has excellent delayed fracture resistance.
いずれかに記載の耐遅れ破壊性に優れた機械構造用鋼。5. The steel for machine structural use according to claim 1, wherein said steel has a quenched and tempered structure and has excellent delayed fracture resistance.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP19395494A JP3279086B2 (en) | 1994-08-18 | 1994-08-18 | Machine structural steel with excellent delayed fracture resistance |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP19395494A JP3279086B2 (en) | 1994-08-18 | 1994-08-18 | Machine structural steel with excellent delayed fracture resistance |
Publications (2)
Publication Number | Publication Date |
---|---|
JPH0860291A JPH0860291A (en) | 1996-03-05 |
JP3279086B2 true JP3279086B2 (en) | 2002-04-30 |
Family
ID=16316527
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JP19395494A Expired - Fee Related JP3279086B2 (en) | 1994-08-18 | 1994-08-18 | Machine structural steel with excellent delayed fracture resistance |
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JP (1) | JP3279086B2 (en) |
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AU2001271469A1 (en) * | 2000-06-29 | 2002-01-14 | Borg Warner, Inc. | Carbide coated steel articles and method of making them |
JP5913214B2 (en) * | 2013-07-05 | 2016-04-27 | 株式会社神戸製鋼所 | Bolt steel and bolts, and methods for producing the same |
KR101822292B1 (en) | 2016-08-17 | 2018-01-26 | 현대자동차주식회사 | High strength special steel |
KR101822295B1 (en) * | 2016-09-09 | 2018-01-26 | 현대자동차주식회사 | High strength special steel |
JP7479794B2 (en) * | 2019-04-16 | 2024-05-09 | 高周波熱錬株式会社 | PC steel with excellent delayed fracture resistance and its manufacturing method |
-
1994
- 1994-08-18 JP JP19395494A patent/JP3279086B2/en not_active Expired - Fee Related
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