JPH05148580A - Steel for bolt excellent in delayed breakdown characteristic - Google Patents

Steel for bolt excellent in delayed breakdown characteristic

Info

Publication number
JPH05148580A
JPH05148580A JP33985791A JP33985791A JPH05148580A JP H05148580 A JPH05148580 A JP H05148580A JP 33985791 A JP33985791 A JP 33985791A JP 33985791 A JP33985791 A JP 33985791A JP H05148580 A JPH05148580 A JP H05148580A
Authority
JP
Japan
Prior art keywords
steel
delayed fracture
strength
present
less
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
JP33985791A
Other languages
Japanese (ja)
Inventor
Norihisa Yamamoto
典久 山本
Kazue Nomura
一衛 野村
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Aichi Steel Corp
Original Assignee
Aichi Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Aichi Steel Corp filed Critical Aichi Steel Corp
Priority to JP33985791A priority Critical patent/JPH05148580A/en
Publication of JPH05148580A publication Critical patent/JPH05148580A/en
Pending legal-status Critical Current

Links

Abstract

PURPOSE:To stably attain excellent delayed breakdown characteristics even after heat-treating by decreasing content of Si, Mn, S, Cr, Ti, by increasing content of Mo and adding V in a steel composition. CONSTITUTION:The composition of steel for bolt consists of 0.30-0.50% C, <=0.15% SiO, <=0.40% Mn, <=0.01% S, <=0.25% Cr, 0.8-2.0% Mo, 0.05-0.30% V, <=0.003% Ti, 0.005-0.070% Al, 0.01-0.025% N in weight ratio and balance Fe and inevitable impurities. The steel has lack of quenching property even if adding Mo in some case because of low content of Mn and Cr. In this case, lack of quenching property is made up by adding 0.2-3.0% Ni.

Description

【発明の詳細な説明】Detailed Description of the Invention

【0001】[0001]

【産業上の利用分野】本発明は、遅れ破壊特性の優れた
高強度ボルト用鋼に関する。
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high strength bolt steel having excellent delayed fracture characteristics.

【0002】[0002]

【従来の技術】建築、橋梁、自動車等では、部品の締結
のために数多くのボルトが使用されている。ボルトは、
溶接が不可能ないし不適切な箇所での使用に適している
が、溶接に比べ重量の点で不利になることや、前記部品
の軽量化や、自動車等では燃費低減に対する要求が非常
に強いため、強度の高いボルトが強く要望されてきてい
る。
2. Description of the Related Art In construction, bridges, automobiles, etc., many bolts are used for fastening parts. Bolt
It is suitable for use in places where welding is not possible or inappropriate, but it is disadvantageous in terms of weight compared to welding, the weight of the above parts is reduced, and there is a strong demand for fuel consumption reduction in automobiles etc. There is a strong demand for high strength bolts.

【0003】現在、高強度ボルトは、JISB1051-1991
強度ランク別に分けて、9.8 、10.9、12.9のように規定
されており、その材料として、現在SCM435、SCM440とい
ったCr-Mo 鋼の焼入焼もどし材が最も広く使用されてい
る。
Currently, high-strength bolts are stipulated in JISB1051-1991 according to strength rank, such as 9.8, 10.9, and 12.9. As its material, quench-hardening of Cr-Mo steel such as SCM435 and SCM440 is currently used. The most widely used material is reversion material.

【0004】[0004]

【発明が解決しようとする課題】前記したJIS 規格で、
最も強度の高いものは、12.9(引張強さ124kgf/mm2
上、硬さHv 435以下)の強度区分のボルトである。しか
し、これと同等かそれ以上に強度が増加すると、すなわ
ち、引張強さが130kgf/mm2以上になると、長時間使用し
た時に、ほとんど塑性変形を伴わずに破壊するという遅
れ破壊と言われている現象が生じやすくなる。従って、
従来から使用されているSCM440等、JIS 規格のCr-Mo 鋼
を使用して、引張強さが130kgf/mm2を超えるように熱処
理を施すことは容易であるが、前記した遅れ破壊現象が
無視できない程度に大きくなってしまうため、引張強さ
を130kgf/mm2以上とし、軽量化を図ることが困難であっ
た。
[Problems to be Solved by the Invention] According to the aforementioned JIS standard,
The ones with the highest strength are bolts in the strength category of 12.9 (tensile strength 124 kgf / mm 2 or more, hardness Hv 435 or less). However, if the strength is equal to or higher than this, that is, if the tensile strength is 130 kgf / mm 2 or more, it is said to be delayed fracture, which causes almost no plastic deformation when used for a long time. The phenomenon that it is likely to occur. Therefore,
Using JIS standard Cr-Mo steel such as SCM440 that has been used conventionally, it is easy to heat treat it so that the tensile strength exceeds 130 kgf / mm 2 , but the delayed fracture phenomenon described above is ignored. Since it becomes so large that it cannot be achieved, it was difficult to reduce the tensile strength by setting it to 130 kgf / mm 2 or more.

【0005】上記問題に対応するため、130kgf/mm2以上
での使用を目的とした鋼種が数多く開発されている。し
かし、実操業上の熱処理はRXガス等を用いた雰囲気中
で行われることが多く、研究・試作段階で行われる真空
中で熱処理する場合に比べ、高強度域の遅れ破壊特性の
低下が顕著となり、適切な対策方法も見出されておら
ず、実用化の障害となっていた。
To cope with the above problems, many steel grades have been developed for use at 130 kgf / mm 2 or more. However, the heat treatment in actual operation is often performed in an atmosphere using RX gas, etc., and the delayed fracture characteristics in the high-strength region are markedly reduced compared to the heat treatment in a vacuum performed in the research / trial stage. Therefore, an appropriate countermeasure method has not been found, which has been an obstacle to practical use.

【0006】本発明は、通常の雰囲気熱処理炉において
130kgf/mm2以上の高い引張強さになるように熱処理した
場合においても、優れた遅れ破壊特性の得られる高強度
ボルト用鋼を提供することを目的とする。
The present invention is applied to a conventional atmosphere heat treatment furnace.
An object of the present invention is to provide a steel for high strength bolts which can obtain excellent delayed fracture characteristics even when heat-treated to have a high tensile strength of 130 kgf / mm 2 or more.

【0007】[0007]

【課題を解決するための手段】本発明者は、ボルト材を
雰囲気熱処理炉にて熱処理した場合の高強度域の遅れ破
壊特性を低下させる原因を研究調査した結果、以下の知
見を得た。RXガス等を用いた雰囲気焼入炉にて熱処理
を施したボルトの中で、遅れ破壊特性が悪いものを良い
ものと比較調査した結果、ボルト表層に過剰炭素領域が
観察されるとともに、粒界に酸化物の生成が認められ、
この影響により遅れ破壊特性が低下していることをつき
とめた。そこで、本発明者等は表層への炭素の浸入(以
下軽浸炭と記す。)と粒界酸化を防ぐことができれば、
遅れ破壊特性が向上すると考えた。
Means for Solving the Problems The present inventor has obtained the following findings as a result of research and investigation into the cause of deterioration of delayed fracture characteristics in a high strength region when a bolt material is heat-treated in an atmosphere heat treatment furnace. Among bolts that were heat-treated in an atmosphere quenching furnace using RX gas, etc., a comparative examination was conducted with those with poor delayed fracture characteristics as good ones. The formation of oxides in
We have found that the delayed fracture characteristics are degraded by this effect. Therefore, if the present inventors can prevent carbon infiltration into the surface layer (hereinafter referred to as light carburization) and grain boundary oxidation,
We thought that delayed fracture characteristics would improve.

【0008】軽浸炭と粒界酸化は、真空焼入炉を用いれ
ば防止できるが、生産性が悪く、設備も高価であり、コ
スト高となって実用的でなく、実操業において使用が困
難である。そこで、本発明者等は通常の雰囲気熱処理炉
による処理を行った場合でも遅れ破壊特性が低下しない
ボルト用鋼の開発を進めた。
Light carburization and intergranular oxidation can be prevented by using a vacuum quenching furnace, but the productivity is poor, the equipment is expensive, the cost is high, it is not practical, and it is difficult to use in actual operation. is there. Therefore, the inventors of the present invention proceeded with the development of a steel for bolts in which the delayed fracture characteristics are not deteriorated even when the treatment is performed in a normal atmosphere heat treatment furnace.

【0009】軽浸炭を防止するためには、熱処理炉内の
雰囲気ガスのカーボン・ポテンシャル(以下C.P.と記
す。)を下げることが有効と考えられるが、逆に脱炭や
粒界酸化が生じやすくなるため、C.P.値の変更には慎重
に対応しなければならない。通常C.P.値は鋼に含有する
炭素量などを基準として鋼種ごとに管理されている。し
かし、最適なC.P.値は、鋼種間あるいはロット毎の合金
組成の違い、炭化物の分布状態などによって変化するた
め、実操業において、軽浸炭と脱炭がともに生じないよ
うにC.P.値を管理することは難しい。そこで本発明者等
は、C.P.値を変化させないで軽浸炭を抑えられる条件に
ついて調査を進めた結果、Cr量が高いほど軽浸炭が起き
やすいことを突き止めた。
In order to prevent light carburization, it is considered effective to lower the carbon potential (hereinafter referred to as CP) of the atmosphere gas in the heat treatment furnace, but conversely decarburization and grain boundary oxidation are likely to occur. Therefore, it is necessary to be careful to change the CP value. Normally, the CP value is controlled for each steel type based on the amount of carbon contained in the steel. However, the optimum CP value varies depending on the alloy composition between steel types or lots and the distribution state of carbides.Therefore, in actual operation, control the CP value so that both light carburization and decarburization do not occur. Is difficult Therefore, the present inventors have conducted an investigation on the conditions under which the light carburization can be suppressed without changing the CP value, and have found that the lighter carburization is more likely to occur as the Cr content is higher.

【0010】また、粒界酸化と鋼成分との関係について
も検討を進めた結果、酸化しやすい元素であるSi、Mn、
Crを低減すると、効果があることを見出した。しかし、
これらの元素を低減すると、必要な焼入性が得られず、
かつ焼もどし温度を低く設定しないと130kgf/mm2以上の
引張強さが得られなくなり、靱性が低下して、却って遅
れ破壊特性が低下する。本発明鋼は従来鋼に比べ高強度
で使用することを目的としており、同一強度を得るため
の焼もどし温度を高く設定でき、高強度としても靱性が
低下しないような配慮が必要である。
As a result of further study on the relationship between grain boundary oxidation and steel components, Si, Mn, which are oxidizable elements,
It was found that reducing Cr is effective. But,
If these elements are reduced, the required hardenability cannot be obtained,
In addition, unless the tempering temperature is set low, the tensile strength of 130 kgf / mm 2 or more cannot be obtained, the toughness deteriorates, and the delayed fracture property rather deteriorates. The steel of the present invention is intended to be used at a higher strength than conventional steels, and it is necessary to set a high tempering temperature to obtain the same strength, and it is necessary to consider so that the toughness does not deteriorate even if the strength is high.

【0011】そこで、Moの増量とV の添加により焼もど
し軟化抵抗の向上を図り、さらに前記Moの増量と適量の
C の添加により必要な焼入性を確保して、この問題を克
服した。また、必要に応じてNiを適量添加すれば、遅れ
破壊特性を低下させることなく、焼入性の大小をコント
ロールできることがわかった。
Therefore, by increasing the amount of Mo and adding V, the tempering softening resistance is improved, and the amount of Mo and the appropriate amount are increased.
This problem was overcome by ensuring the required hardenability by adding C. It was also found that the hardenability can be controlled by adding an appropriate amount of Ni as needed without deteriorating the delayed fracture property.

【0012】一方、結晶粒微細化に効果のある元素であ
るTi、Nbをボルト用鋼に適用した場合の弊害について
は、今まで考慮されていなかったが、調査した結果、T
i、Nbの炭窒化物が存在すると、遅れ破壊時の破壊の起
点となって強度を低下させることと、不純物として存在
するTi、NbがN と結びつくことによって、AlN の生成を
阻害し、AlN の結晶粒微細化効果に悪影響を及ぼすこと
がわかった。そこで、本発明では、不純物として含有さ
れる可能性があるTiについては、含有率の上限を厳しく
規制し、Nbについては積極添加しないこととした。
On the other hand, the adverse effects of applying Ti and Nb, which are elements effective for grain refinement, to bolt steels have not been taken into consideration until now.
The presence of carbonitrides of i and Nb decreases the strength at the starting point of fracture during delayed fracture, and Ti and Nb that exist as impurities combine with N to inhibit the formation of AlN and It has been found that the grain refining effect of is adversely affected. Therefore, in the present invention, for Ti that may be contained as an impurity, the upper limit of the content rate is strictly regulated, and Nb is not positively added.

【0013】以上得られた知見をもとに完成した本発明
は、重量比にしてC:0.30〜0.50% 、Si:0.15%以下、Mn:
0.40%以下、V:0.05〜0.30% 、S:0.010%以下、Cr:0.25%
以下、Mo:0.8〜2.0%、Ti:0.003% 以下、Al:0.005〜0.07
0%、N:0.010 〜0.025%を含有し、残部がFeおよび不可避
的不純物元素からなることを特徴とする遅れ破壊特性の
優れたボルト用鋼であり、第2発明は焼入性を向上させ
て太径のボルトの製造を可能にするため、第1発明鋼に
Niを0.2 〜3.0%含有させたものである。
The present invention completed on the basis of the findings obtained above, C: 0.30 to 0.50% by weight, Si: 0.15% or less, Mn:
0.40% or less, V: 0.05 to 0.30%, S: 0.010% or less, Cr: 0.25%
Below, Mo: 0.8-2.0%, Ti: 0.003% or less, Al: 0.005-0.07
A steel for bolts having excellent delayed fracture characteristics, characterized by containing 0%, N: 0.010 to 0.025%, and the balance being Fe and unavoidable impurity elements. The second invention is to improve hardenability. In order to enable the production of large diameter bolts,
It contains 0.2 to 3.0% of Ni.

【0014】以下に本発明のボルト用鋼の成分限定理由
を説明する。 C:0.30〜0.50% C は必要な焼入性と強度を確保するための必須元素であ
る。本発明の目的を達成するためには、従来鋼に比べ高
い焼もどし温度にて140kgf/mm2以上の引張強さを得る必
要があり、下限を0.30% とした。しかし、多量に含有さ
せると、靱性が低下し、粒界炭化物が増加して、逆に遅
れ破壊特性が低下するため、上限を0.50% とした。
The reasons for limiting the components of the steel for bolts of the present invention will be described below. C: 0.30 to 0.50% C is an essential element for ensuring the necessary hardenability and strength. In order to achieve the object of the present invention, it is necessary to obtain a tensile strength of 140 kgf / mm 2 or higher at a tempering temperature higher than that of conventional steel, and the lower limit was made 0.30%. However, when contained in a large amount, the toughness decreases, grain boundary carbides increase, and conversely the delayed fracture property deteriorates. Therefore, the upper limit was made 0.50%.

【0015】Si:0.15%以下 Siは脱酸剤として効果のある元素であるが、焼入時の高
温加熱時に起きる粒界酸化を助長し、遅れ破壊強度を低
下させる。従って、極力低下させる必要があるため、上
限を0.15% とした。
Si: 0.15% or less Si is an element effective as a deoxidizing agent, but it promotes grain boundary oxidation that occurs during high temperature heating during quenching and reduces delayed fracture strength. Therefore, the upper limit is set to 0.15% because it is necessary to reduce it as much as possible.

【0016】Mn:0.40%以下 Mnは、従来鋼においては、焼入性向上のために添加され
る元素であるが、Siと同様に焼入時の高温加熱時に起き
る粒界酸化を助長するとともに、セメンタイト中に固溶
して、析出したセメンタイトの成長を促進し、遅れ破壊
強度を低下させるため、極力低下させる必要があり、上
限を0.40% とした。
Mn: 0.40% or less Mn is an element added to improve the hardenability in conventional steels, but like Si, promotes grain boundary oxidation that occurs during high temperature heating during quenching, and The solid solution in cementite promotes the growth of the precipitated cementite and reduces the delayed fracture strength, so it is necessary to reduce it as much as possible, and the upper limit was made 0.40%.

【0017】S:0.010%以下 S は通常不純物として含有し、鋼中にMnS 等の非金属介
在物として存在している。この非金属介在物は遅れ破壊
特性を低下させるため、S は極力低減する必要があり、
上限を0.010%とした。
S: 0.010% or less S is usually contained as an impurity and present in steel as a non-metallic inclusion such as MnS. Since this non-metallic inclusion deteriorates the delayed fracture property, it is necessary to reduce S as much as possible.
The upper limit was 0.010%.

【0018】Cr:0.25%以下 Crは焼入性を上げるのに効果のある元素であるが、前述
したように軽浸炭と粒界酸化を助長し、遅れ破壊特性を
低下させる元素でもある。従って、遅れ破壊特性の向上
を最重要視している本発明では、極力低減する必要があ
るので、上限を0.25% とした。
Cr: 0.25% or less Cr is an element effective in improving hardenability, but as described above, it is also an element that promotes light carburization and grain boundary oxidation and deteriorates delayed fracture characteristics. Therefore, in the present invention in which the improvement of delayed fracture characteristics is most important, it is necessary to reduce as much as possible, so the upper limit was made 0.25%.

【0019】Mo:0.80 〜2.00% Mn、Crを低減している本発明にとって、Moは必要な焼入
性を確保するために不可欠な元素である。また、Moは焼
もどし軟化抵抗を付与するという効果も有する。このよ
うな効果を十分に得るためには従来鋼に比べ増量して、
0.80% 以上の含有が必要である。しかし、多量に含有さ
せても効果が飽和するとともに、粗大炭化物を生成して
遅れ破壊特性を低下させる可能性があるため、上限を2.
00% とした。
Mo: 0.80 to 2.00% In the present invention in which Mn and Cr are reduced, Mo is an essential element for ensuring the required hardenability. Mo also has the effect of imparting temper softening resistance. In order to fully obtain such effects, the amount should be increased compared to conventional steel,
It is necessary to contain 0.80% or more. However, even if contained in a large amount, the effect will be saturated, and there is a possibility that coarse carbides will be formed and the delayed fracture property will be deteriorated.
It was set to 00%.

【0020】V:0.05〜0.30% Vは結晶粒を微細化するとともに、焼もどし時に炭化物
となって微細析出し、焼もどし軟化抵抗を向上させる効
果のある元素である。これにより、同一の強度を得るの
により高い焼もどし温度にすることができるため、その
効果を十分に得るために、0.05% 以上添加することにし
た。しかし、多量に含有させてもその効果が飽和すると
ともに、コスト増となるため、上限を0.30%とした。
V: 0.05 to 0.30% V is an element which has the effect of refining the crystal grains and, at the time of tempering, finely forming carbides during the tempering to improve the tempering softening resistance. With this, a higher tempering temperature can be obtained to obtain the same strength, so in order to sufficiently obtain the effect, it was decided to add 0.05% or more. However, even if contained in a large amount, the effect is saturated and the cost increases, so the upper limit was made 0.30%.

【0021】Ti:0.003% 以下 Tiは鋼中に不純物として含有している元素であるが、通
常は特に規制されていない。しかし、Tiが存在すると応
力集中効果の大きいTiN が析出して粒界が脆化し、遅れ
破壊特性が低下するため、極力低減する必要があり、上
限を0.003%とした。
Ti: 0.003% or less Ti is an element contained as an impurity in steel, but is not particularly restricted. However, when Ti is present, TiN, which has a large stress concentration effect, precipitates and embrittles the grain boundaries, degrading delayed fracture characteristics. Therefore, it is necessary to reduce it as much as possible, and the upper limit was made 0.003%.

【0022】Al:0.005〜0.070% Alは脱酸剤として効果があるとともに、鋼中で窒化物(A
lN) を形成して結晶粒を微細化する効果を有する。従っ
て0.005%以上含有させる必要がある。しかし、多量に含
有させると、形成されるAlN が粗大化して、かえって結
晶粒微細化効果が低下するため、上限を0.070%とした。
Al: 0.005-0.070% Al is effective as a deoxidizing agent, and at the same time nitrides (A
lN) has the effect of refining the crystal grains. Therefore, it is necessary to contain 0.005% or more. However, if a large amount of AlN 3 is contained, the formed AlN becomes coarse and the grain refining effect is rather reduced, so the upper limit was made 0.070%.

【0023】N:0.010〜0.025% Nは前述したように、Alと窒化物を形成し、結晶粒微細
化に効果のある元素であり、0.010%以上、好ましくは0.
012%以上の含有が必要である。しかし、多量に含有させ
ると、製鋼時にブローホールが発生して製造が困難にな
るので、上限を0.025%とした。
N: 0.010 to 0.025% As described above, N is an element that forms a nitride with Al and is effective in refining crystal grains, and is 0.010% or more, preferably 0.
It is necessary to contain 012% or more. However, if a large amount is contained, blowholes are generated during steelmaking and manufacturing becomes difficult, so the upper limit was made 0.025%.

【0024】Ni:0.2〜3.0% 本発明はMn、Crを低減しているため、Moを添加しても焼
入性が不足する場合がある。その場合は、必要に応じNi
を添加して、焼入性の不足を補うことが必要であり、下
限を0.2%とした。しかし、多量に含有させても効果が飽
和するとともにコスト高となるため、上限を3.0%とし
た。
Ni: 0.2 to 3.0% In the present invention, since Mn and Cr are reduced, the hardenability may be insufficient even if Mo is added. In that case, if necessary, Ni
It is necessary to make up for the lack of hardenability by adding 0.1%, and the lower limit was made 0.2%. However, even if a large amount is contained, the effect is saturated and the cost increases, so the upper limit was made 3.0%.

【0025】[0025]

【実施例】次に本発明鋼の特徴を、比較鋼、従来鋼と比
較して、実施例でもって明らかにする。表1に実施例で
使用した供試材の化学成分を示す。表1において、1〜
9鋼は本発明鋼で、1〜5鋼は第1発明、6〜9鋼は第
2発明に該当する鋼である。また、10〜15鋼は部分的に
本発明の成分範囲外である比較鋼であり、16鋼は従来鋼
であるJIS-SCM440である。
EXAMPLES Next, the characteristics of the steel of the present invention will be clarified by examples in comparison with comparative steel and conventional steel. Table 1 shows the chemical components of the test materials used in the examples. In Table 1, 1 to
Steel No. 9 is the steel of the present invention, Steel Nos. 1 to 5 are the first inventions, and Steel Nos. 6 to 9 are the steels corresponding to the second invention. Further, 10 to 15 steels are comparative steels which are partially outside the composition range of the present invention, and 16 steels are JIS-SCM440 which is a conventional steel.

【0026】[0026]

【表1】 [Table 1]

【0027】表1に示す成分を有する供試材を電気炉に
より溶解し、分塊圧延により鋼片を製造し、線材への圧
延前に鋼片の一部を採取して、焼入温度及び焼もどし温
度と引張強さとの関係を調査した。そして、引張強さが
145kgf/mm2程度となる熱処理条件を求め、以下に説明す
る方法で評価を行った。調査の結果得られた熱処理条件
を表2に示す。従来鋼に比べ、本発明鋼は焼もどし軟化
抵抗が大きく、同一の強度を得るのに焼もどし温度を高
くできることがわかる。
The test materials having the components shown in Table 1 were melted in an electric furnace, and slab rolling was used to produce a steel slab. A part of the steel slab was sampled before rolling into a wire rod, and the quenching temperature and The relationship between tempering temperature and tensile strength was investigated. And the tensile strength
A heat treatment condition of about 145 kgf / mm 2 was obtained and evaluated by the method described below. Table 2 shows the heat treatment conditions obtained as a result of the investigation. It can be seen that the steel of the present invention has a higher temper softening resistance than the conventional steel, and the tempering temperature can be increased to obtain the same strength.

【0028】次に、圧延によりφ15mmの線材を製造し、
表2に示す条件で熱処理を施した材料について、後述す
る方法で引張試験、遅れ破壊試験を行い、本発明鋼の性
能を評価した。試験結果を前述の表2に合わせて示す。
引張試験は、前記線材より JIS14号A 試験片を作製し、
前記条件で熱処理を施した後、引張速度1mm/min の条件
で行った。
Next, a wire material of φ15 mm is manufactured by rolling,
The materials heat-treated under the conditions shown in Table 2 were subjected to a tensile test and a delayed fracture test by the methods described below to evaluate the performance of the steel of the present invention. The test results are also shown in Table 2 above.
Tensile test, JIS14 A test piece was made from the wire,
After the heat treatment under the above conditions, the tensile speed was 1 mm / min.

【0029】遅れ破壊試験は、線材よりボルトを製造
し、熱処理した後、5%HCl 溶液中に30分浸漬して水素を
吸蔵させた後、種々の応力で締め付けて放置し、 200時
間以内に破断しない最大の応力の引張強さに対する比
(遅れ破壊強度比)を求めるという方法で行った。な
お、ボルトの熱処理は、一般に広く用いられているRX
ガスを使用した雰囲気熱処理炉(C.P.値は炭素含有量と
同一とした。) と真空熱処理炉の両方を使用して行い、
雰囲気の違いによる遅れ破壊特性への影響を評価した。
In the delayed fracture test, bolts were manufactured from wire rods, heat-treated, immersed in a 5% HCl solution for 30 minutes to absorb hydrogen, tightened under various stresses, and allowed to stand within 200 hours. The method was carried out by obtaining the ratio of the maximum stress that does not break to the tensile strength (delayed fracture strength ratio). In addition, the heat treatment of the bolt is performed by the widely used RX.
Performed using both an atmosphere heat treatment furnace using gas (CP value was the same as the carbon content) and a vacuum heat treatment furnace.
We evaluated the effect of delayed atmosphere on delayed fracture characteristics.

【0030】[0030]

【表2】 [Table 2]

【0031】表2から明らかなように、比較鋼である10
〜15鋼を本発明鋼の実施例である1〜9鋼と比較する
と、10鋼はC 含有率が低いため、焼もどし温度を低くし
ないと必要な引張強度が得られず、靱性が低下して遅れ
破壊特性が劣るものであり、11〜13鋼は軽浸炭あるいは
粒界酸化が原因となって遅れ破壊特性を低下させる元素
であるSi、Mn、Cr含有率が高いため、真空熱処理の場合
には優れた特性を示すが、雰囲気中で熱処理した場合の
遅れ破壊特性が劣るものであり、14鋼はS 含有率が高
く、15鋼はTi含有率が高いため、MnS あるいはTiN の影
響で遅れ破壊特性が劣るものである。
As is clear from Table 2, the comparative steel is 10
When steel Nos. 15 to 15 are compared with steels 1 to 9 which are examples of the steel of the present invention, steel 10 has a low C content, so unless the tempering temperature is lowered, the required tensile strength cannot be obtained and the toughness decreases. 11 to 13 steels have a high content of Si, Mn, and Cr, which are elements that reduce delayed fracture characteristics due to light carburization or grain boundary oxidation, However, the 14th steel has a high S content and the 15th steel has a high Ti content.Therefore, due to the influence of MnS or TiN, Delayed fracture characteristics are inferior.

【0032】また、従来鋼であるSCM440は本願発明鋼に
比べ焼もどし軟化抵抗が小さく、粒界酸化、非金属介在
物等により遅れ破壊特性を低下する元素が低減されてい
ないので、本発明鋼に比べ著しく遅れ破壊特性が劣るも
のである。
Further, SCM440, which is a conventional steel, has a smaller resistance to temper softening than the steel of the present invention, and the elements that deteriorate delayed fracture properties due to grain boundary oxidation, non-metallic inclusions, etc. are not reduced, so the steel of the present invention is Compared with, the delayed fracture characteristics are significantly inferior.

【0033】これに対して本発明鋼である1〜9鋼は、
粒界酸化、非金属介在物等の原因により遅れ破壊特性を
低下させる元素であるSi、Mn、S 、Cr、Ti等の元素を極
力低減し、その結果もたらされる焼入性の低下を遅れ破
壊特性に影響の小さいMoの増量あるいは必要に応じNiを
添加することによって補い、かつ適量のC の添加と前記
Moの増量およびV の添加によって焼もどし温度を高く設
定することを可能にしたことによって、通常の雰囲気熱
処理炉で熱処理して145kgf/mm2程度の高い引張強さとし
た場合においても、優れた遅れ破壊特性を得ることがで
きた。
On the other hand, the steels 1 to 9 of the present invention are
Elements such as Si, Mn, S, Cr and Ti, which are elements that deteriorate delayed fracture characteristics due to grain boundary oxidation, non-metallic inclusions, etc., are reduced as much as possible, and the resulting decrease in hardenability is delayed fracture. The amount of Mo, which has a small effect on the properties, is compensated by increasing the amount of Mo or adding Ni as necessary, and adding an appropriate amount of C and
By making it possible to set the tempering temperature high by increasing the amount of Mo and adding V, excellent delay is obtained even when heat treatment is performed in a normal atmosphere heat treatment furnace to obtain a high tensile strength of about 145 kgf / mm 2. The destructive property could be obtained.

【0034】[0034]

【発明の効果】以上説明したように、本発明のボルト用
鋼は従来鋼とは異なり、引張強さを高めても遅れ破壊現
象が起きにくいため、高い応力で使用することが可能で
ある。また通常の雰囲気熱処理炉によって熱処理しても
安定して優れた遅れ破壊特性を得ることができる。従っ
て、この特性を有効利用することにより、自動車等溶接
で固定が不可能な多くの箇所をより小さなボルトで固定
が可能となり、軽量化、省エネルギー化へ大きく寄与す
ることができる。
As described above, unlike the conventional steel, the bolt steel of the present invention can be used under high stress because delayed fracture phenomenon does not easily occur even if the tensile strength is increased. Further, even if heat treatment is performed in a normal atmosphere heat treatment furnace, excellent delayed fracture characteristics can be stably obtained. Therefore, by effectively utilizing this characteristic, many places that cannot be fixed by welding, such as an automobile, can be fixed with smaller bolts, which can greatly contribute to weight saving and energy saving.

Claims (2)

【特許請求の範囲】[Claims] 【請求項1】 重量比にしてC:0.30〜0.50% 、Si:0.15%
以下、Mn:0.40%以下、S:0.010%以下、Cr:0.25%以下、M
o:0.8〜2.0%、V:0.05〜0.30% 、Ti:0.003% 以下、Al:0.
005〜0.070%、N:0.010 〜0.025%を含有し、残部がFeお
よび不可避的不純物元素からなることを特徴とする遅れ
破壊特性の優れたボルト用鋼。
1. C: 0.30 to 0.50%, Si: 0.15% by weight
Below, Mn: 0.40% or less, S: 0.010% or less, Cr: 0.25% or less, M
o: 0.8 to 2.0%, V: 0.05 to 0.30%, Ti: 0.003% or less, Al: 0.
A steel for bolts having excellent delayed fracture characteristics, characterized by containing 005 to 0.070% and N: 0.010 to 0.025%, and the balance being Fe and inevitable impurity elements.
【請求項2】 重量比にしてC:0.30〜0.50% 、Si:0.15%
以下、Mn:0.40%以下、S:0.010%以下、Cr:0.25%以下、M
o:0.8〜2.0%、V:0.05〜0.30% 、Ti:0.003% 以下、Al:0.
005〜0.070%、N:0.010 〜0.025%とNi:0.2〜3.0%を含有
し、残部がFeおよび不可避的不純物元素からなることを
特徴とする遅れ破壊特性の優れたボルト用鋼。
2. C: 0.30 to 0.50%, Si: 0.15% by weight
Below, Mn: 0.40% or less, S: 0.010% or less, Cr: 0.25% or less, M
o: 0.8 to 2.0%, V: 0.05 to 0.30%, Ti: 0.003% or less, Al: 0.
A steel for bolts having excellent delayed fracture characteristics, which contains 005 to 0.070%, N: 0.010 to 0.025% and Ni: 0.2 to 3.0%, and the balance being Fe and inevitable impurity elements.
JP33985791A 1991-11-27 1991-11-27 Steel for bolt excellent in delayed breakdown characteristic Pending JPH05148580A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP33985791A JPH05148580A (en) 1991-11-27 1991-11-27 Steel for bolt excellent in delayed breakdown characteristic

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP33985791A JPH05148580A (en) 1991-11-27 1991-11-27 Steel for bolt excellent in delayed breakdown characteristic

Publications (1)

Publication Number Publication Date
JPH05148580A true JPH05148580A (en) 1993-06-15

Family

ID=18331484

Family Applications (1)

Application Number Title Priority Date Filing Date
JP33985791A Pending JPH05148580A (en) 1991-11-27 1991-11-27 Steel for bolt excellent in delayed breakdown characteristic

Country Status (1)

Country Link
JP (1) JPH05148580A (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1746176A1 (en) 2005-07-22 2007-01-24 Nippon Steel Corporation Steel with excellent delayed fracture resistance and tensile strength of 1600 MPa class or more, its shaped articles, and methods of production of the same
JP2009221539A (en) * 2008-03-17 2009-10-01 Jfe Steel Corp High-strength steel having excellent delayed cracking resistance
WO2023167318A1 (en) * 2022-03-04 2023-09-07 日本製鉄株式会社 Steel material

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1746176A1 (en) 2005-07-22 2007-01-24 Nippon Steel Corporation Steel with excellent delayed fracture resistance and tensile strength of 1600 MPa class or more, its shaped articles, and methods of production of the same
US7754029B2 (en) 2005-07-22 2010-07-13 Nippon Steel Corporation Steel with excellent delayed fracture resistance and tensile strength of 1801 MPa class or more, and its shaped article
JP2009221539A (en) * 2008-03-17 2009-10-01 Jfe Steel Corp High-strength steel having excellent delayed cracking resistance
WO2023167318A1 (en) * 2022-03-04 2023-09-07 日本製鉄株式会社 Steel material

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