JP2824058B2 - Low alloy steel for soft nitriding - Google Patents
Low alloy steel for soft nitridingInfo
- Publication number
- JP2824058B2 JP2824058B2 JP62050245A JP5024587A JP2824058B2 JP 2824058 B2 JP2824058 B2 JP 2824058B2 JP 62050245 A JP62050245 A JP 62050245A JP 5024587 A JP5024587 A JP 5024587A JP 2824058 B2 JP2824058 B2 JP 2824058B2
- Authority
- JP
- Japan
- Prior art keywords
- nitrocarburizing
- less
- alloy steel
- steel
- ferrite
- 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.)
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Description
【発明の詳細な説明】
［産業上の利用分野］
本発明は靭性に優れ、硬化深さの大きな機械部品とし
て有用な軟窒化用低合金鋼に関する。
［従来の技術］
軟窒化法は、浸炭焼入れと異なり、歪は小さく、ガス
窒化のように長時間の加熱処理を必要とせず、短時間の
処理によって、高い表面硬さと、優れた疲労強度が得ら
れる処理であり、機械部品の量産に適した方法である。
従来は軟窒化法に適した鋼がなく、やむを得ず例えば
S45C、SCM345等の強靭鋼およびSACM645の窒化用鋼等が
用いられている。又、調質処理をせずに軟窒化を行い、
フェライトとパーライト組織を主体とする材料を得るこ
とも知られている。
［発明が解決しようとする問題点］
上記従来軟窒化処理を施されたS54C、SCM435等の強靭
鋼については表面硬さおよび硬化深さ等に問題があり、
SACM645の窒化用鋼については、硬化深さやコストの点
で満足すべきものでない、又、調質処理をせずに軟窒化
を行いフェライトとパーライト組織を主体とする材料と
したものは、軟窒化後の靭性が著しく低下し、衝撃的な
荷重がかかる機械部品には適用できない。
そこで、さきに軟窒化処理で高い硬さと大きな硬化深
さが得られ、優れた疲労強度を有する軟窒化専用の鋼に
ついて開発（特公昭60−43431号公報参照）したが、製
造コストの点に問題があり、より低コストで耐疲労性の
良い鋼の開発が望まれている。
［問題点を解決するための手段］
本発明は、非調質状態で軟窒化処理し、結果としてベ
ーナイト＋フェライト＋パーライトの混合組織が形成さ
れることにより、優れた耐疲労性を発揮する低合金鋼組
成に関するもので、C:0.15〜0.30％、Si:0.15〜0.5％、
Mn:1.0〜2.0％、Cr:0.7％以下、V:0.05超〜0.30％、So
l.Al:0.02〜0.10％を含み、残部Feと不可避的不純物よ
りなる組成、および該組成にS:0.1％以下あるいはPb:0.
1％以下のうち１種又は２種を含む組成、並びにC:0.15
〜0.30％、Si:0.15〜0.5％、Mn:1.0〜2.0％、Cr:0.7％
以下、V:0.05超〜0.30％、Sol.Al:0.02〜0.10％、B:0.0
005〜0.0040％にさらにTi:0.020〜0.050％又はNb:0.020
〜0.050％のうち１種又は２種あるいはさらにS:0.1％以
下又はPb:0.1％以下のうち１種あるいは２種を含み、残
部Feと不可避的不純物よりなる組成である。
すなわち、種々の実験を行った結果、耐疲労強度に対
しては心部強度を一定以上に保てばHv600〜650程度の表
面硬さで十分であり、表面硬さを高くするためには窒化
時に窒化物を生成しやすいCr、Al、Ｖを添加すれば良い
が、あまり多量に添加することは経済的ではなく、ま
た、硬化深さを損なうこととなり、耐ピッチングおよび
耐疲労強度に関してはむしろ硬化深さの大きいことが有
利であることがわかった。
また、軟窒化後の衝撃性を改善するためには、心部の
ミクロ組織をベーナイト＋フェライト＋パーライトの混
合組織にする必要があることも確認された。
すなわち、本発明では軟窒化処理後所要の表面硬さを
得るために一定以上の心部硬さがえられ、かつミクロ組
織がベーナイト＋フェライト＋パーライト組織が得られ
るようにＣ、Mn量を調整し、窒化時に窒素と結合して、
高い表面硬さを与えるために主としてＶの添加を行い、
Cr、Alは補助的に少量加えた。これらの成分および他の
諸成分を含めて、組成を特許請求の範囲に示すように限
定した理由を以下に述べる。
C:Cは強度確保のために必要な基本成分であり、心部強
度確保のため最低限0.15％以上必要である。しかし0.03
0％を越えると心部の延性・靭性が低下し、鍛造後の冷
却時にベーナイトの発生を阻害し、軟窒化後の衝撃値を
著しく低下させる。
Si:Siは通常脱酸剤として添加されるが、この目的に対
して0.15％以上の添加で十分効果を発揮し、0.5％を越
えるとフェライトを硬化し、被削性に悪い影響を与え
る。
Mn:Mnは強度を確保するために必須の成分である。本発
明鋼では前述のようにＣの量を制限しているため、Mnに
よって強度の確保を行う必要があり、このため1.0％以
上を必要とし、特に心部強度に対しては1.50％以上が望
ましい。しかし2.0％を越えると被削性に悪い影響を与
える。
Cr:Crは窒化時に表面硬さを高くするのに効果がある
が、ＶおよびAlと共存するとき１％までの添加では効果
は明白でなく、硬化深さに対してはむしろマイナスに作
用し、本発明鋼では心部強度維持のための添加が主体で
あり、余り多く加えることは経済的でないので0.7％に
上限を設定した。
V:Vは窒化時の表面硬さと硬化深さを得るのに必須の元
素であり、0.05％を超える添加によって硬化深さを増加
し、0.20％以上では微増となり、0.3％を越えると硬化
深さを減少する。また表面硬さはＶの添加とともに上昇
するが、硬化深さと表面硬さより、0.3％を越える添加
はコストに見合うほど硬化が得られず、さらに靭性の低
下をもたらす。
Al:Alは窒化時に窒化物を生成した表面硬さ向上に効果
があるが、Ｖと複合して添加する場合0.1％までの添加
で十分にHv600〜650を確保することが可能であり、ま
た、結晶粒の調整効果も十分であり、1.0％を越えると
窒化深さを浅くし、また被削性に悪い影響を与える。Al
の添加は主として結晶粒の調整用として用いるので、本
発明においては上限を0.10％とした。
S:Sは被削性を向上させるため必要に応じて添加される
が、0.1％を越えると熱間加工性を阻害する。
Pb:Pbは被削性を向上するために必要に応じて添加され
るが、0.1％をこえるとガス軟化性を阻害する。
B:Bは焼き入れ性の向上に効果があり、質量効果を小さ
くするため必要に応じて添加されるが、この目的に対し
ては0.0005％以上の添加が必要であり、0.0040％を越え
ると鉄−ボロン化合物の析出によって靭性を低下させ
る。
Ti、Nb:Ti、NbはＢを添加する前の脱窒剤として使用
し、この目的に対して0.020％以上の添加が必要で、0.0
50％を越える添加は被削性に好ましくない。
上述の組成を有する本発明鋼は、Ac3点以上の温度に
加熱して鍛造等の熱間加工、あるいはAc3点以上の温度
に加熱して焼きならしあるいは焼きなましを行い、必要
に応じて冷間加工（鍛造、引き抜き切削）を行って、軟
窒化処理を行い、前述のような優れた軟窒化特性を示す
鋼となる。
［実施例］
本発明の実施例を比較例とともに述べる。
表１に示す組成を有する鋼種を高周波溶解炉で溶製
し、1250℃で熱間鍛造により25mmφに鍛伸し各種試験に
供した。
軟窒化特性
軟窒化処理はRX＋NH3の混合ガス雰囲気中で570℃×3h
r保持することで行い、窒化後の各試料の断面硬さを測
定し、表面硬さおよび硬化深さを測定した。表面硬さは
表面より0.05mm位置での硬さとし、硬化深さはHv450を
示す表面からの深さとした。結果を表２に示す。表２の
結果から本発明鋼は十分な表面硬さと十分な硬化深さを
示すことがわかる。
軟窒化後の衝撃試験結果
JIS3号衝撃試験片（2mm Uノッチ）に570℃×3Hrのガ
ス軟窒化処理を行って、衝撃試験を行った。結果を表３
に示す。表３に示すように、本発明鋼は比較材に較べて
軟窒化処理後も十分な衝撃値を示している。疲労強度
570℃×3Hrのガス軟窒化処理を行った本発明鋼の回転
曲げ疲労試験（小野式）の結果を第１図に示す。第１図
によれば、本発明鋼は58および55kgf/mm2の耐久限を示
し、切り欠き材についても52kgf/mm2の切り欠き強さを
示し、優れた疲労特性を示している。
［発明の効果］
本発明の低合金鋼は、圧延あるいは鍛造のままないし
焼ならしあるいは焼なまし状態のいわゆる非調質状態で
軟窒化処理することにより、軟窒化特性を有し、靭性に
優れ硬化深さの大きな製品が得られるものであり、衝撃
的な荷重がかかる機械部品の製造に適した材料である。Description: TECHNICAL FIELD The present invention relates to a low alloy steel for nitrocarburizing which has excellent toughness and is useful as a mechanical part having a large hardening depth. [Prior art] Unlike carburizing and quenching, the nitrocarburizing method has a small distortion, does not require a long-time heat treatment unlike gas nitriding, and has a high surface hardness and excellent fatigue strength by a short-time treatment. This is a process that can be obtained, and is a method suitable for mass production of mechanical parts. Conventionally, there is no steel suitable for the nitrocarburizing method.
High-strength steels such as S45C and SCM345, and nitriding steels such as SACM645 are used. Also, nitrocarburizing without tempering treatment,
It is also known to obtain a material mainly composed of ferrite and a pearlite structure. [Problems to be Solved by the Invention] There is a problem in the surface hardness and hardening depth of the tough steels such as S54C and SCM435 which have been subjected to the conventional nitrocarburizing treatment,
SACM645 steel for nitriding is not satisfactory in terms of hardening depth and cost.In addition, soft-nitriding without tempering treatment and using a material mainly composed of ferrite and pearlite structure However, it is not applicable to mechanical parts subjected to impact load. Therefore, we developed a special steel for nitrocarburizing, which had high hardness and large hardening depth by nitrocarburizing treatment and had excellent fatigue strength (see Japanese Patent Publication No. 60-43431). There is a problem, and it is desired to develop a steel with lower cost and good fatigue resistance. [Means for Solving the Problems] The present invention provides a low-temperature alloy exhibiting excellent fatigue resistance by performing a soft nitriding treatment in a non-heat-treated state, thereby forming a mixed structure of bainite + ferrite + pearlite. Concerning alloy steel composition, C: 0.15-0.30%, Si: 0.15-0.5%,
Mn: 1.0 to 2.0%, Cr: 0.7% or less, V: more than 0.05 to 0.30%, So
l. Al: A composition containing 0.02 to 0.10%, with the balance being Fe and unavoidable impurities, and S: 0.1% or less or Pb: 0.
Composition containing one or two of 1% or less, and C: 0.15
~ 0.30%, Si: 0.15 ~ 0.5%, Mn: 1.0 ~ 2.0%, Cr: 0.7%
Hereinafter, V: more than 0.05 to 0.30%, Sol.Al: 0.02 to 0.10%, B: 0.0
005 to 0.0040% and Ti: 0.020 to 0.050% or Nb: 0.020
The composition contains one or two of 0.05% or less, or one or two of S: 0.1% or less and Pb: 0.1% or less, with the balance being Fe and unavoidable impurities. In other words, as a result of conducting various experiments, surface hardness of about Hv600 to 650 is sufficient if the core strength is maintained at a certain level or more with respect to fatigue resistance, and nitriding is required to increase surface hardness. Sometimes it is good to add Cr, Al, V, which easily produces nitride, but it is not economical to add too much, and it will impair the hardening depth, and rather with respect to pitting resistance and fatigue resistance, A large cure depth has been found to be advantageous. It was also confirmed that in order to improve the impact resistance after nitrocarburizing, it was necessary to make the core microstructure a mixed structure of bainite + ferrite + pearlite. That is, in the present invention, the C and Mn contents are adjusted so that a core hardness of a certain level or more can be obtained in order to obtain a required surface hardness after the nitrocarburizing treatment, and a microstructure of bainite + ferrite + pearlite can be obtained. And combines with nitrogen during nitriding,
V is mainly added to give high surface hardness,
Cr and Al were added in small amounts in an auxiliary manner. The reasons for limiting the composition, including these and other components, as set forth in the claims are set forth below. C: C is a basic component necessary for securing strength, and at least 0.15% or more is required for securing core strength. But 0.03
If it exceeds 0%, the ductility and toughness of the core deteriorate, and the generation of bainite is inhibited during cooling after forging, and the impact value after nitrocarburizing is significantly reduced. Si: Si is usually added as a deoxidizer, but for this purpose, addition of 0.15% or more exerts a sufficient effect, and if it exceeds 0.5%, ferrite is hardened, and the machinability is adversely affected. Mn: Mn is an essential component for ensuring strength. In the steel of the present invention, since the amount of C is limited as described above, it is necessary to secure the strength by Mn. Therefore, 1.0% or more is required, and in particular, the core strength is 1.50% or more. desirable. However, if it exceeds 2.0%, the machinability is adversely affected. Cr: Cr is effective in increasing the surface hardness during nitriding, but when coexisting with V and Al, the effect is not clear when added up to 1%, and acts rather negatively on the hardening depth. In addition, the steel of the present invention is mainly added for maintaining the core strength, and it is not economical to add too much, so the upper limit is set to 0.7%. V: V is an element essential for obtaining the surface hardness and hardening depth during nitriding. The hardening depth increases with the addition of more than 0.05%, slightly increases with more than 0.20%, and hardens with more than 0.3%. Decrease. Further, the surface hardness increases with the addition of V. However, depending on the hardening depth and the surface hardness, if the addition exceeds 0.3%, hardening cannot be obtained to meet the cost, and the toughness further decreases. Al: Al is effective in improving the surface hardness of the nitride formed during nitridation, but when added in combination with V, addition of up to 0.1% can sufficiently secure Hv 600 to 650. Also, the effect of adjusting the crystal grains is sufficient. If it exceeds 1.0%, the nitriding depth is reduced and the machinability is adversely affected. Al
Is mainly used for adjusting crystal grains, so the upper limit is set to 0.10% in the present invention. S: S is added as necessary to improve machinability, but if it exceeds 0.1%, hot workability is impaired. Pb: Pb is added as needed to improve machinability, but if it exceeds 0.1%, gas softening is impaired. B: B is effective for improving the hardenability and is added as needed to reduce the mass effect. However, for this purpose, 0.0005% or more must be added. The toughness is reduced by precipitation of the iron-boron compound. Ti, Nb: Ti and Nb are used as denitrifying agents before B is added. For this purpose, addition of 0.020% or more is necessary.
Addition exceeding 50% is not preferable for machinability. The present invention steel having a composition described above, hot working such as forging is heated to Ac 3 point or more of the temperature, or heated to Ac 3 point or higher temperatures do normalizing or annealing, the as needed Cold-working (forging, drawing and cutting) is performed and nitrocarburizing is performed to obtain a steel exhibiting the above-described excellent nitrocarburizing properties. [Examples] Examples of the present invention will be described together with comparative examples. Steel types having the compositions shown in Table 1 were melted in a high-frequency melting furnace, forged at 1250 ° C. by hot forging to 25 mmφ, and subjected to various tests. Soft nitriding characteristics Soft nitriding is performed in a mixed gas atmosphere of RX + NH 3 at 570 ° C x 3h
r The holding was performed, and the cross-sectional hardness of each sample after nitriding was measured, and the surface hardness and the curing depth were measured. The surface hardness was a hardness at a position of 0.05 mm from the surface, and the curing depth was a depth from the surface showing Hv450. Table 2 shows the results. The results in Table 2 show that the steel of the present invention has a sufficient surface hardness and a sufficient hardening depth. Impact test results after nitrocarburizing A JIS No. 3 impact test piece (2 mm U notch) was subjected to gas nitrocarburizing treatment at 570 ° C x 3 hours, and an impact test was performed. Table 3 shows the results
Shown in As shown in Table 3, the steel of the present invention shows a sufficient impact value even after the nitrocarburizing treatment as compared with the comparative material. FIG. 1 shows the results of a rotary bending fatigue test (Ono equation) of the steel of the present invention subjected to a gas nitrocarburizing treatment at a fatigue strength of 570 ° C. × 3 Hr. According to FIG. 1, the steel of the present invention exhibits a durability limit of 58 and 55 kgf / mm 2 , and the notched material also exhibits a notch strength of 52 kgf / mm 2 and exhibits excellent fatigue properties. [Effects of the Invention] The low-alloy steel of the present invention has a nitrocarburizing property by being subjected to nitrocarburizing treatment in a so-called non-tempered state in a rolled or forged state, in a normalized or annealed state, and has a toughness. It is an excellent material that can provide a product with a large hardening depth and is suitable for the production of mechanical parts subjected to impact loads.
【図面の簡単な説明】
第１図は実施例と比較例の疲労強度の試験結果を示すグ
ラフである。BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing test results of fatigue strength of Examples and Comparative Examples.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 福住 達夫 東京都江東区東雲１−９−31 三菱製鋼 株式会社東京製作所内 (56)参考文献 特開 昭59−179759（ＪＰ，Ａ) 特開 昭59−16949（ＪＰ，Ａ) 特開 昭59−16948（ＪＰ，Ａ) 特公 昭55−3424（ＪＰ，Ｂ２) 特公 昭61−27460（ＪＰ，Ｂ２) ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tatsuo Fukuzumi 1-9-31 Shinonome, Koto-ku, Tokyo Mitsubishi Steel Tokyo Manufacturing Co., Ltd. (56) References JP-A-59-179759 (JP, A) JP-A-59-16949 (JP, A) JP-A-59-16948 (JP, A) Tokiko Sho 55-3424 (JP, B2) Tokiko Sho 61-27460 (JP, B2)
Claims (1)
％、Cr:0.7％以下、V:0.05超〜0.30％、Sol.Al:0.02〜
0.10％を含み、残部Feと不可避的不純物よりなる非調質
状態で軟窒化処理し、結果としてベーナイト＋フェライ
ト＋パーライトの混合組織が形成される軟窒化用低合金
鋼。 ２．C:0.15〜0.30％、Si:0.15〜0.5％、Mn:1.0〜2.0
％、Cr:0.7％以下、V:0.05超〜0.30％、Sol.Al:0.02〜
0.10％、さらにS:0.1％以下あるいはPb:0.1％以下のう
ち１種又は２種を含み、残部Feと不可避的不純物よりな
る非調質状態で軟窒化処理し、結果としてベーナイト＋
フェライト＋パーライトの混合組織が形成される軟窒化
用低合金鋼。 ３．C:0.15〜0.30％、Si:0.15〜0.5％、Mn:1.0〜2.0
％、Cr:0.7％以下、V:0.05超〜0.30％、Sol.Al:0.02〜
0.10％、B:0.0005〜0.0040％、さらにTi0.020〜0.050％
又はNb:0.020〜0.050％のうち１種又は２種を含み残部F
eと不可避的不純物よりなる非調質状態で軟窒化処理
し、結果としてベーナイト＋フェライト＋パーライトの
混合組織が形成される軟窒化用低合金鋼。 ４．C:0.15〜0.30％、Si:0.15〜0.5％、Mn:1.0〜2.0
％、Cr:0.7％以下、V:0.05超〜0.30％、Sol.Al:0.02〜
0.10％、B:0.0005〜0.0040％、さらにTi0.020〜0.050％
又はNb:0.020〜0.050％のうち１種あるいは２種を含
み、さらにS:0.1％以下又はPb:0.1％以下のうちの１種
あるいは２種を含み、残部Feと不可避的不純物よりなる
非調質状態で軟窒化処理し、結果としてベーナイト＋フ
ェライト＋パーライトの混合組織が形成される軟窒化用
低合金鋼。(57) [Claims] C: 0.15-0.30%, Si: 0.15-0.5%, Mn: 1.0-2.0
%, Cr: 0.7% or less, V: more than 0.05 ~ 0.30%, Sol.Al: 0.02 ~
A low-alloy steel for nitrocarburizing that contains 0.10% and is nitrocarburized in a non-refined state consisting of the balance of Fe and unavoidable impurities, resulting in the formation of a mixed structure of bainite + ferrite + pearlite. 2. C: 0.15-0.30%, Si: 0.15-0.5%, Mn: 1.0-2.0
%, Cr: 0.7% or less, V: more than 0.05 ~ 0.30%, Sol.Al: 0.02 ~
0.10%, further contains one or two of S: 0.1% or less and Pb: 0.1% or less, and is subjected to nitrocarburizing treatment in a non-tempered state consisting of the balance of Fe and unavoidable impurities. As a result, bainite +
A low alloy steel for nitrocarburizing in which a mixed structure of ferrite and pearlite is formed. 3. C: 0.15-0.30%, Si: 0.15-0.5%, Mn: 1.0-2.0
%, Cr: 0.7% or less, V: more than 0.05 ~ 0.30%, Sol.Al: 0.02 ~
0.10%, B: 0.0005-0.0040%, and Ti0.020-0.050%
Or Nb: one or two of 0.020 to 0.050% and the balance F
A low-alloy steel for nitrocarburizing that undergoes nitrocarburizing treatment in a non-tempered state consisting of e and unavoidable impurities, resulting in the formation of a mixed structure of bainite + ferrite + pearlite. 4. C: 0.15-0.30%, Si: 0.15-0.5%, Mn: 1.0-2.0
%, Cr: 0.7% or less, V: more than 0.05 ~ 0.30%, Sol.Al: 0.02 ~
0.10%, B: 0.0005-0.0040%, and Ti0.020-0.050%
Or one or two of Nb: 0.020 to 0.050%, and one or two of S: 0.1% or less or Pb: 0.1% or less, and the balance of Fe and unavoidable impurities Low-alloy steel for nitrocarburizing which is subjected to nitrocarburizing treatment in a homogeneous state, resulting in the formation of a mixed structure of bainite + ferrite + pearlite.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP62050245A JP2824058B2 (en) | 1987-03-06 | 1987-03-06 | Low alloy steel for soft nitriding |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP62050245A JP2824058B2 (en) | 1987-03-06 | 1987-03-06 | Low alloy steel for soft nitriding |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS63216950A JPS63216950A (en) | 1988-09-09 |
| JP2824058B2 true JP2824058B2 (en) | 1998-11-11 |
Family
ID=12853604
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP62050245A Expired - Fee Related JP2824058B2 (en) | 1987-03-06 | 1987-03-06 | Low alloy steel for soft nitriding |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2824058B2 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0565594A (en) * | 1991-09-09 | 1993-03-19 | Sanyo Special Steel Co Ltd | Soft-nitriding steel |
| JP5904057B2 (en) * | 2012-08-27 | 2016-04-13 | 新日鐵住金株式会社 | Age hardening type steel for soft nitriding and age hardening type steel for soft nitriding |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5916949A (en) * | 1982-07-16 | 1984-01-28 | Sumitomo Metal Ind Ltd | Soft-nitriding steel |
| JPS59179759A (en) * | 1983-03-31 | 1984-10-12 | Daido Steel Co Ltd | Soft-nitriding steel |
-
1987
- 1987-03-06 JP JP62050245A patent/JP2824058B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPS63216950A (en) | 1988-09-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| LAPS | Cancellation because of no payment of annual fees |