JP2000160287A - Nitriding non-heat treated forged parts and manufacture thereof - Google Patents
Nitriding non-heat treated forged parts and manufacture thereofInfo
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- JP2000160287A JP2000160287A JP10331002A JP33100298A JP2000160287A JP 2000160287 A JP2000160287 A JP 2000160287A JP 10331002 A JP10331002 A JP 10331002A JP 33100298 A JP33100298 A JP 33100298A JP 2000160287 A JP2000160287 A JP 2000160287A
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- nitriding
- steel
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- heat treated
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- Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Articles (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、高い疲労強度およ
び優れた曲げ矯正性をもつ非調質窒化鍛造部品およびそ
の製造方法に関する。本発明の鍛造部品は、自動車エン
ジン等に使用されるクランク軸の用途に好適である。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-heat treated nitrided forged part having high fatigue strength and excellent bending straightness, and a method for producing the same. The forged part of the present invention is suitable for use in a crankshaft used for an automobile engine or the like.
【０００２】[0002]
【従来の技術】例えば自動車エンジン用クランク軸のよ
うに高い疲労強度が要求される鍛造部品では、熱間鍛造
後、冷却し、必要に応じ機械加工を行った後、高周波焼
入れや窒化処理などの表面強化の処理を行うことが多
い。窒化処理は疲労強度向上の点では高周波焼入れに若
干劣るものの、表面に硬質の化合物層が生成し、耐焼付
き性や耐かじり性の点では著しく優れるため、窒化処理
を行う鍛造部品（以下、窒化鍛造部品という）も多い。2. Description of the Related Art Forged parts that require high fatigue strength, such as crankshafts for automobile engines, are cooled after hot forging, machined as required, and then subjected to induction hardening or nitriding. In many cases, surface strengthening treatment is performed. Nitriding is slightly inferior to induction quenching in terms of improvement in fatigue strength, but since a hard compound layer is formed on the surface and extremely superior in terms of seizure resistance and galling resistance, forged parts to be subjected to nitriding (hereinafter referred to as nitriding) Forged parts).
【０００３】図１は、調質鋼および非調質鋼の窒化鋼鍛
造部品の製造法を示す工程図であり、同図(a) は調質鋼
の場合、同図(b) は非調質鋼の場合である。同図(a) に
示すように、調質鋼では鋼片は熱間鍛造後、放冷または
空冷（非図示）され、調質処理により金属組織形態が調
整されるのに対し、同図(b) では、鋼片は鍛造のままの
組織である。次いで、窒化処理を行う。ただし、同図に
示すように、クランク軸のような機械加工が必要な鍛造
部品の場合、窒化処理後では表面が硬化し、機械加工が
困難なため、窒化処理前に必要に応じて旋盤、ドリル等
の切削あるいは研削などの機械加工を行う。また、窒化
処理後の鍛造部品には曲がりが生じる場合があり、必要
に応じ適当な曲げ矯正を行って製品とする。[0003] Fig. 1 is a process chart showing a method of manufacturing a forged steel part of a tempered steel and a non-heat treated steel. Fig. 1 (a) shows the case of a tempered steel, and Fig. This is the case for high quality steel. As shown in FIG. 2A, in the tempered steel, the slab is cooled or air-cooled (not shown) after hot forging, and the metal structure is adjusted by the tempering treatment. In b), the billet is an as-forged structure. Next, a nitriding treatment is performed. However, as shown in the figure, in the case of a forged part that requires machining such as a crankshaft, the surface hardens after nitriding, making machining difficult. Carry out machining such as cutting or grinding with a drill. In addition, the forged part after the nitriding treatment may be bent, and the product is subjected to appropriate bending correction if necessary.
【０００４】近年、図１(b) に示すように、コスト削減
や生産リードタイムの縮小のために調質処理を省略して
鍛造のままで製品に供する、いわゆる非調質化が多くの
窒化鍛造部品に対して検討されている。しかしながら、
調質処理を省略することによってある種の性能が劣化す
ることがあり、非調質化できない部品もある。[0004] In recent years, as shown in FIG. 1 (b), in order to reduce costs and shorten production lead time, so-called non-temper-izing has been performed in many cases where the tempering process is omitted and the product is used as it is forged. Considered for forged parts. However,
Omitting the refining process can degrade certain types of performance, and some parts cannot be non-refined.
【０００５】性能劣化の第一には、疲労強度低下の問題
がある。鍛造後に調質処理を行わずに窒化処理を施した
部品（以下、非調質窒化鋼という）の疲労限度は、同一
組成の鋼を鍛造後に調質処理を行って窒化処理を施した
部品（以下、調質窒化鋼という）のそれよりも低い。[0005] The first problem of performance degradation is the problem of reduced fatigue strength. The fatigue limit of a part that has been subjected to nitriding without tempering after forging (hereinafter referred to as non-heat-treated nitrided steel) is the same as that of a part that has been subjected to tempering after tempering after forging steel of the same composition ( (Hereinafter referred to as tempered nitrided steel).
【０００６】第二には、曲げ矯正性劣化の問題がある。
これは鍛造部品が窒化処理時の加熱および冷却により変
形し、曲げ矯正しなければならないときの問題である。
曲げ矯正時には表面に大きな塑性ひずみが発生しき裂を
生じる。非調質窒化鋼にき裂が発生する限界のひずみ量
（以下、曲げ矯正可能ひずみ量という）は、調質窒化鋼
のそれよりも小さい。一般に、曲げ矯正時にき裂が発生
することによって部品の疲労限度は著しく低くなる。[0006] Second, there is a problem of deterioration in bending straightness.
This is a problem when the forged part is deformed by heating and cooling during the nitriding treatment and has to be straightened.
At the time of straightening, a large plastic strain occurs on the surface and cracks occur. The limit amount of strain at which cracks occur in the non-heat-treated nitrided steel (hereinafter referred to as a bendable strain) is smaller than that of the tempered nitrided steel. In general, the occurrence of cracks during straightening significantly reduces the fatigue limit of a part.
【０００７】窒化鍛造部品の中でもクランク軸は窒化処
理後に曲げ矯正を行うことが多いので、非調質窒化鋼の
適用が困難である。[0007] Among the nitriding forged parts, the crankshaft is often subjected to bending correction after nitriding, so that it is difficult to apply non-heat-treated nitrided steel.
【０００８】これまで、析出硬化元素を高濃度に含有さ
せることによって、鍛造のままで、調質処理を施さずに
高い疲労限度を得る発明がなされた。Heretofore, there has been an invention in which a high hardening limit is contained in a high concentration of a precipitation hardening element so that a high fatigue limit can be obtained without subjecting the steel to forging treatment.
【０００９】例えば、特開平８−１４４０１８号公報に
は、Ｃｒ、Ｖ、Ａｌを適量含有させ、窒化処理による表
面硬化をねらうとともに、窒化による心材の強度低下を
防止できるとする鋼材が開示されている。For example, Japanese Patent Application Laid-Open No. 8-144018 discloses a steel material containing Cr, V, and Al in appropriate amounts to prevent surface hardening due to nitriding and to prevent a decrease in the strength of a core material due to nitriding. I have.
【００１０】特開平１−１７７３３８号公報には、Ｍ
ｎ、Ｃｒ、Ｍｏ、Ｖを適量含有させ、窒化処理による表
面硬化により疲労強度を向上させるとする鋼材が開示さ
れている。[0010] JP-A-1-177338 discloses M
There is disclosed a steel material that contains appropriate amounts of n, Cr, Mo, and V and improves fatigue strength by surface hardening by nitriding treatment.
【００１１】これらはいずれも強力な析出硬化元素であ
るバナジウム（Ｖ）やクロム（Ｃｒ）を高濃度に含有し
た鋼であり高価である。また窒化処理後の曲げ矯正性
は、後述する実施例が示すようにきわめて劣るものとな
る。また、これらの公報には、疲労限度および曲げ矯正
性を同時に改善する技術は開示されていない。All of these are steels containing high concentrations of vanadium (V) and chromium (Cr), which are strong precipitation hardening elements, and are expensive. Further, the bending straightening property after the nitriding treatment is extremely inferior as shown in the examples described later. Further, these publications do not disclose techniques for simultaneously improving the fatigue limit and the bending straightness.
【００１２】[0012]
【発明が解決しようとする課題】本発明の目的は、鍛造
後の調質が不要で、窒化処理後の曲げ矯正時に発生する
き裂がない、またはき裂が発生する限界のひずみ量が高
く、かつ疲労限度の高い非調質窒化鍛造部品およびその
製造方法を提供することにある。具体的には、代表的な
焼入焼もどし処理を行ったＳ４８Ｃ鋼の窒化調質鍛造部
品に対比して、疲労限度は１．２倍以上、曲げ矯正可能
ひずみ量は同等以上の性能を有する非調質窒化鍛造部品
とその製造方法を提供することにある。SUMMARY OF THE INVENTION An object of the present invention is to eliminate the need for refining after forging, to eliminate cracks that occur during bending correction after nitriding, or to increase the critical strain amount at which cracks occur. Another object of the present invention is to provide a non-heat treated nitrided forged part having a high fatigue limit and a method of manufacturing the same. More specifically, as compared with a typical quenched and tempered S48C steel nitrided tempered forged part, the fatigue limit is 1.2 times or more and the bendable strain amount is equal to or more than that. An object of the present invention is to provide a non-heat-treated nitrided forged part and a method for manufacturing the same.
【００１３】[0013]
【課題を解決するための手段】一般に、窒化処理によっ
て形成される窒化層は、最表面の化合物層とその下の拡
散層からなる。拡散層と母材部の境界付近には、高い残
留応力が生じている。非調質窒化鋼で疲労破壊が発生す
る起点は、拡散層内あるいは拡散層と母材の境界部であ
り、また曲げ矯正で問題となるき裂は拡散層表面でのき
裂である。以下の説明で「表面」というとき、化合物層
を除いた拡散層の表面側をいうものとする。In general, a nitrided layer formed by a nitriding treatment comprises a compound layer on the outermost surface and a diffusion layer thereunder. A high residual stress is generated near the boundary between the diffusion layer and the base material. The starting point of the fatigue fracture in the non-heat-treated nitrided steel is in the diffusion layer or at the boundary between the diffusion layer and the base material, and the crack that poses a problem in bending correction is a crack on the surface of the diffusion layer. In the following description, “surface” refers to the surface side of the diffusion layer excluding the compound layer.
【００１４】本発明者らは非調質窒化鋼の疲労強度およ
び曲げ矯正性について種々検討し、以下の知見を得た。The present inventors have conducted various studies on the fatigue strength and bending straightness of the non-heat treated nitrided steel, and have obtained the following findings.
【００１５】(a) 非調質窒化鋼の疲労限度が低い原因は
以下による。非調質窒化鋼の残留応力は疲労限度を低下
させる主たる原因である。(A) The reason why the fatigue limit of the non-heat treated nitrided steel is low is as follows. Residual stress in non-heat treated nitrided steel is a major cause of lower fatigue limit.
【００１６】非調質窒化鋼では析出硬化元素を含まない
鋼であっても、硬さは表面で著しく高くなり、内部に向
かって急勾配で低下する。そのため、表面には高い圧縮
残留応力が発生するが、母材と拡散層との境界付近で
は、この圧縮残留応力と均衡する引張残留応力が生じて
いる。In non-heat-treated nitrided steel, even if the steel does not contain a precipitation hardening element, the hardness is extremely high on the surface and decreases steeply toward the inside. Therefore, a high compressive residual stress is generated on the surface, but a tensile residual stress is generated near the boundary between the base material and the diffusion layer, which balances the compressive residual stress.
【００１７】拡散層と母材との境界付近で引張残留応力
が高くなるのは、拡散層側表面のみ硬さが著しく高く、
かつ硬化層深さが小さいことから来ているものと推定さ
れる。これは外部から入った窒素が内部に入りにくく表
面にとどまっていることを意味する。この原因を窒化処
理時の窒素の拡散挙動から見ると、下記のように考えら
れる。The reason why the tensile residual stress becomes high near the boundary between the diffusion layer and the base material is that the hardness is extremely high only on the diffusion layer side surface,
It is also presumed that this is due to the small depth of the hardened layer. This means that nitrogen entering from the outside hardly enters the inside and stays on the surface. From the viewpoint of the diffusion behavior of nitrogen during nitriding, the cause is considered as follows.
【００１８】非調質鋼は、１１００℃以上に加熱後１０
００℃以上で鍛造を終了し、そのまま放冷または空冷す
るので、組織は巨大な旧オーステナイト粒界に沿った薄
いネット状フェライトと、残りの部分のパーライトから
構成される。また、非調質鋼のフェライト体積率は、調
質鋼（焼準処理）のそれに比較して小さい。これは、非
調質鋼のオーステナイト粒径が大きい分だけ焼入れ性が
大きく、フェライト変態が抑制されるためである。Non-heat treated steel is heated to 1100 ° C.
Since the forging is finished at 00 ° C. or more and the cooling is performed as it is, the structure is composed of a thin net-like ferrite along a giant old austenite grain boundary and the rest of pearlite. The ferrite volume fraction of the non-heat treated steel is smaller than that of the heat treated steel (normalized treatment). This is because the hardenability is large due to the large austenite grain size of the non-heat treated steel, and the ferrite transformation is suppressed.
【００１９】これに対して、調質鋼の組織は微細なオー
ステナイトから変態した、微細なフェライトとパーライ
トの混合組織（焼準の場合）、またはきわめて微細なラ
ス（網目状組織）と炭化物からなるマルテンサイトまた
はベイナイト組織（焼入れ焼戻しの場合）、のいずれか
である。On the other hand, the structure of the tempered steel is composed of a fine structure of ferrite and pearlite (in the case of normalization) transformed from fine austenite, or an extremely fine lath (network structure) and carbide. Either martensite or bainite structure (in the case of quenching and tempering).
【００２０】窒化処理を行う時、窒素の拡散速度はフェ
ライト中では大きく、パーライト中では層状セメンタイ
トに拡散を阻害されるために拡散速度は著しく小さい。During the nitriding treatment, the diffusion rate of nitrogen is high in ferrite and is extremely low in pearlite because diffusion is inhibited by layered cementite.
【００２１】非調質鋼ではフェライトが旧オーステナイ
ト粒界に薄く集中しているために、内部への窒素の拡散
はフェライトを通ってしかできない。従って、外部から
入った窒素は内部に入りにくい。このため、拡散層深さ
が浅くなって硬さ分布は急勾配になり、母材部の境界付
近に引張残留応力が発生すると考えられる。In the non-heat-treated steel, the diffusion of nitrogen into the inside can be performed only through the ferrite because the ferrite is concentrated in the austenite grain boundary thinly. Therefore, nitrogen that has entered from the outside hardly enters the inside. For this reason, it is considered that the hardness distribution becomes steep as the depth of the diffusion layer becomes shallow, and tensile residual stress is generated near the boundary of the base material.
【００２２】これに対して、調質処理を行った組織では
微細なフェライトが粒界に限らず組織全体に分布してい
るので、組織全体にわたって窒素の拡散経路が存在す
る。そのため、調質鋼では窒化処理を施すと表面から内
部にまで緩やかな硬さ分布ができ、引張残留応力は小さ
いと推定される。On the other hand, since fine ferrite is distributed not only in the grain boundaries but in the entire structure in the structure subjected to the tempering treatment, there is a nitrogen diffusion path throughout the structure. Therefore, it is presumed that the tempered steel has a gentle hardness distribution from the surface to the inside when the nitriding treatment is performed, and the tensile residual stress is small.
【００２３】(b) 非調質窒化鋼の曲げ矯正可能ひずみ量
が低下する原因は以下による。鋼の表面硬さが高いほど
曲げ矯正の際き裂を生じやすい。しかし、き裂長さは表
面硬さだけでは一義的に決まらない。前述したように、
非調質鋼の組織はフェライト変態が抑制された混粒とな
る。曲げ矯正時に発生するき裂は、パーライト粒を一単
位として進展し粒界のフェライトで停止するため、一旦
き裂が発生するとき裂長さは大きくなる。これに対して
調質鋼では、微細なフェライト粒が組織全体に分布して
いるので、曲げ矯正によってき裂が発生してもさほど進
展しないと考えられる。(B) The cause of the decrease in the amount of strain that can be bent in non-heat-treated nitrided steel is as follows. The higher the surface hardness of steel, the easier it is for cracks to occur during bending straightening. However, the crack length cannot be uniquely determined only by the surface hardness. As previously mentioned,
The structure of the non-heat treated steel is a mixed grain in which the ferrite transformation is suppressed. The crack generated at the time of bending correction propagates as a unit of pearlite grains and stops at ferrite at the grain boundary, so that once a crack occurs, the crack length increases. On the other hand, in the tempered steel, since fine ferrite grains are distributed throughout the structure, it is considered that even if a crack is generated by bending straightening, the crack does not progress much.
【００２４】以上をまとめると、(a) 窒化層深さが浅い
ことが、疲労強度低下の原因になっている、(b) 窒化処
理後の表面硬さを上昇させると、曲げ矯正性を悪化させ
る、ことに集約される。To summarize the above, (a) the shallow depth of the nitride layer causes a decrease in fatigue strength. (B) If the surface hardness after the nitriding treatment is increased, the bending straightening property is deteriorated. Let's get together.
【００２５】従って非調質窒化鋼では、き裂の起点とな
る拡散層／母材境界層の高い引張残留応力を低減するた
め、母材を窒素原子が拡散しやすい組織にして、拡散層
の厚さを大きくし、硬さ勾配をなだらかにすることと、
窒化によって表面を過度に硬化させないことが必要であ
る。Therefore, in the non-heat-treated nitrided steel, in order to reduce the high tensile residual stress in the diffusion layer / base metal boundary layer that is the starting point of a crack, the base metal is made to have a structure in which nitrogen atoms are easily diffused, and Increasing the thickness, making the hardness gradient gentle,
It is necessary that the surface is not excessively hardened by nitriding.
【００２６】以上の検討から、窒化用鋼としてはフェラ
イト主体組織とするか、それが困難な場合はフェライト
＋パーライト組織よりもマルテンサイトあるいはベイナ
イトの単相組織が望ましい。From the above studies, it is preferable to use a ferrite-based structure as the nitriding steel or, if it is difficult, a martensite or bainite single phase structure rather than a ferrite + pearlite structure.
【００２７】非調質にてマルテンサイトあるいはベイナ
イト組織が得られればよいが、マルテンサイト単相とす
るには焼入性向上元素であるＣｒなどを多量に含有させ
る必要があり、曲げ矯正性の点から好ましくない。発明
者らは、ベイナイト組織が緩冷却によって得られること
に着目し、適正な化学組成の範囲および適正な窒化処理
条件を見出した。It is sufficient that a martensite or bainite structure can be obtained without tempering. However, in order to obtain a martensite single phase, it is necessary to contain a large amount of Cr, which is an element for improving hardenability, and the bending straightening property is reduced. Not preferred from the point. The present inventors have paid attention to the fact that a bainite structure is obtained by slow cooling, and have found an appropriate range of chemical composition and appropriate nitriding conditions.
【００２８】上記の知見に基づいて完成した本発明の要
旨は以下の(1) 〜(3) にある。 (1) 化学組成が重量％で、Ｃ：０．１５〜０．３５％、
Ｍｎ：１．００〜３．００％、Ｃｒ：０〜０．１５％、
Ｖ：０〜０．０２％、Ｃｕ：０．５０〜１．５０％、Ｎ
ｉ：Ｃｕ含有量の０．４倍以上を含有し、Ｂ、Ｎおよび
Ｔｉの含有量が、Ｂsol ＝Ｂ−（１１／１４）｛Ｎ−
（１４／４８）Ｔｉ｝で定義されるＢsolで０．００１
０〜０．００３０％であり、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非調質窒化鍛造部
品。The gist of the present invention completed on the basis of the above findings is as described in the following (1) to (3). (1) Chemical composition by weight%, C: 0.15 to 0.35%,
Mn: 1.00 to 3.00%, Cr: 0 to 0.15%,
V: 0 to 0.02%, Cu: 0.50 to 1.50%, N
i: contains 0.4 times or more of the Cu content, and the content of B, N and Ti is Bsol = B− (11/14) ｛N−
(14/48) 0.001 in Bsol defined by Ti｝
0 to 0.0030%, the balance being Fe and unavoidable impurity elements, characterized by non-heat treated nitrided forged parts.
【００２９】(2) 前記(1) 項に記載の非調質窒化鍛造部
品がさらに、Ｓ：０．０４〜０．１０％、Ｃａ：０．０
００３〜０．００３０％、Ｐｂ：０．０５〜０．２０％
のうち１種以上の元素を含有することを特徴とする非調
質窒化鍛造部品。(2) The non-heat treated nitrided forged part according to the above item (1) further comprises S: 0.04 to 0.10%, Ca: 0.0
003 to 0.0030%, Pb: 0.05 to 0.20%
A non-heat treated nitrided forged part comprising at least one element selected from the group consisting of:
【００３０】(3) 化学組成が重量％で、Ｃ：０．１５〜
０．３５％、Ｍｎ：１．００〜３．００％、Ｃｒ：０〜
０．１５％、Ｖ：０〜０．０２％、Ｃｕ：０．５０〜
１．５０％、Ｎｉ：Ｃｕ含有量の０．４倍以上を含有
し、Ｂ、ＮおよびＴｉの含有量が、Ｂsol ＝Ｂ−（１１
／１４）｛Ｎ−（１４／４８）Ｔｉ｝で定義されるＢso
lで０．００１０〜０．００３０％であり、残部がＦｅ
および不可避的不純物元素からなる鋼材を熱間鍛造後、
放冷または空冷し、必要に応じて機械加工を行い、熱処
理をすることなく窒化処理を５００〜５８０℃で行い、
引き続き不活性ガス雰囲気中、５００〜５８０℃で後熱
処理を行い、その後、放冷、空冷または炉冷することを
特徴とする非調質窒化鍛造部品の製造方法。(3) The chemical composition is% by weight and C: 0.15 to
0.35%, Mn: 1.00 to 3.00%, Cr: 0
0.15%, V: 0 to 0.02%, Cu: 0.50
1.50%, containing 0.4 times or more of Ni: Cu content, and the content of B, N and Ti is Bsol = B- (11
/ 14) Bso defined by {N- (14/48) Ti}
l is 0.0010 to 0.0030%, and the balance is Fe
And after hot forging steel material consisting of unavoidable impurity elements,
Allow to cool or air cool, machine if necessary, perform nitriding at 500-580 ° C without heat treatment,
A method for producing a non-heat-treated nitrided forged part, comprising: performing a post-heat treatment at 500 to 580 ° C. in an inert gas atmosphere, followed by cooling, air cooling, or furnace cooling.
【００３１】[0031]
【発明の実施の形態】本発明の各構成元素の作用および
各元素の化学組成を限定した理由は次の通りである。以
下の組成％は重量％を示す。BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the action of each constituent element and the chemical composition of each element of the present invention are as follows. The following composition percentages indicate weight percentages.
【００３２】Ｃ：０．１５〜０．３５％、Ｃは強度およ
び疲労強度確保のため必要な成分である。さらにベイナ
イト単相組織を得るための基本成分である。０．１５％
未満では強度不足かつベイナイト生成が困難である。し
かし０．３５％を超えて含有させると、鍛造性や被削性
が劣化する。したがって上限を０．３５％とした。好適
範囲は０．２０〜０．３０％である。C: 0.15 to 0.35%, C is a component necessary for securing strength and fatigue strength. Further, it is a basic component for obtaining a bainite single phase structure. 0.15%
If it is less than the above, strength is insufficient and bainite formation is difficult. However, when the content exceeds 0.35%, forgeability and machinability deteriorate. Therefore, the upper limit is set to 0.35%. The preferred range is 0.20 to 0.30%.
【００３３】Ｍｎ：１．００〜３．００％、Ｍｎは、製
鋼時の脱酸剤として不可欠であるとともに強度確保のた
め、またベイナイト単相組織を得るために効果的な元素
である。そのため、下限は１．００％としなければなら
ない。３．００％を超えて過剰に含有させると被削性が
劣化するとともに曲げ矯正性が低下する。従って、Ｍｎ
含有量は１．００〜３．００％とする。好適範囲は１．
５０〜２．５０％である。Mn: 1.00 to 3.00%, Mn is an element which is indispensable as a deoxidizing agent at the time of steel making and is effective for ensuring strength and for obtaining a bainite single phase structure. Therefore, the lower limit must be set to 1.00%. If it is contained in excess of 3.00%, the machinability deteriorates and the bending straightness decreases. Therefore, Mn
The content is 1.00 to 3.00%. The preferred range is 1.
50 to 2.50%.
【００３４】Ｃｒ：０〜０．１５％、Ｃｒは不純物とし
て混入する以外は添加しない。少ないほどよい。Ｃｒを
含有すると窒化処理により窒化物を生成し表面の硬さを
高め、曲げ矯正性を顕著に劣化させるためである。しか
し、含有量を過度に低減させると精錬コストが増大する
ので、０．１５％までは許容する。Cr: 0 to 0.15%, Cr is not added except that it is mixed as an impurity. The smaller the better. This is because when Cr is contained, nitrides are formed by nitriding treatment to increase the hardness of the surface and to significantly degrade the bending straightness. However, if the content is excessively reduced, the refining cost increases, so that the content is allowed up to 0.15%.
【００３５】Ｖ：０〜０．０２％、ＶはＣｒと同様の作
用で曲げ矯正性を顕著に劣化させるので、少ないほどよ
い。不純物として混入する以外には添加しない。しか
し、含有量を過度に低減させると精錬コストが増大する
ので、０．０２％までは許容する。V: 0 to 0.02%, V remarkably deteriorates the bending straightening property by the same action as Cr, so the smaller the better, the better. It is not added except for mixing as an impurity. However, if the content is excessively reduced, the refining cost increases, so that the content is allowed up to 0.02%.
【００３６】Ｃｕ：０．５０〜１．５０％、Ｃｕは析出
強化元素として母材の強度増加による疲労強度向上に効
果的であり、特に窒化時の加熱により著しく析出し強度
が向上するので、クランク軸のように窒化前の軟らかい
状態で機械加工を済ませるものについては有効な元素で
ある。ただし、強化量は窒化処理時の温度に敏感であ
り、これについては後述する。析出効果を得るためには
０．５０％以上含有させる必要がある。一方、１．５０
％を超えて含有させても効果は飽和し、鍛造中に脆化す
るので０．５０％〜１．５０％とする。Cu: 0.50 to 1.50%, Cu is effective as a precipitation strengthening element for improving the fatigue strength by increasing the strength of the base material. It is an effective element for a machine which is machined in a soft state before nitriding, such as a crankshaft. However, the strengthening amount is sensitive to the temperature during the nitriding treatment, which will be described later. In order to obtain a precipitation effect, it is necessary to contain 0.50% or more. On the other hand, 1.50
%, The effect saturates and becomes brittle during forging, so the content is made 0.50% to 1.50%.
【００３７】Ｎｉ：Ｃｕ含有量の０．４倍以上、Ｃｕは
液体脆化を生じやすい元素であり、前記のようにＣｕを
含有させると熱間鍛造中に材料が割れることがある。こ
れを防止するため、Ｃｕと金属化合物をつくるＮｉを含
有させる。その含有量はＣｕの０．４倍以上が必要であ
る。Ni: Cu is 0.4 times or more the Cu content, and Cu is an element that easily causes liquid embrittlement. If Cu is contained as described above, the material may crack during hot forging. In order to prevent this, Ni that forms a metal compound with Cu is contained. Its content needs to be 0.4 times or more of Cu.
【００３８】Ｂ、ＴｉおよびＮ： Ｂsol ＝Ｂ−（１１／１４）｛Ｎ−（１４／４８）Ｔ
ｉ｝で定義されるＢsolとして０．００１０〜０．００
３０％とする。B, Ti and N: B sol = B− (11/14) ｛N− (14/48) T
0.0010 to 0.00 as Bsol defined by i｝
30%.
【００３９】この関係式はベイナイト組織を確保するた
めの固溶Ｂを基本に導出したものである。Ｂを微量含有
させると焼入れ性が向上するため、ベイナイト組織が容
易に形成される。この効果を得るためには少なくとも固
溶Ｂの状態で０．００１０％以上を確保する必要があ
る。固溶Ｂが０．００３０％を超えると靭性が損なわれ
るので、０．００３０％を超えないようにする。This relational expression is derived based on solid solution B for securing a bainite structure. When a small amount of B is contained, the hardenability is improved, so that a bainite structure is easily formed. In order to obtain this effect, it is necessary to secure at least 0.0010% in the state of solid solution B. If the solute B exceeds 0.0030%, the toughness is impaired, so the content should not exceed 0.0030%.
【００４０】含有Ｂがすべて固溶Ｂとはならない。Ｂは
Ｎと結合してＢＮを形成しやすく、固溶Ｂが失われるた
めである。従って、Ｔｉ添加によってＮを固定する必要
があり、Ｔｉの含有量は、固溶Ｂを上述のように確保す
るべく決められる。Ｂ、Ｎ、Ｔｉの原子量から上述のＢ
sol の式が得られる。All of the contained B do not become solid solution B. This is because B easily bonds to N to form BN, and solid solution B is lost. Therefore, it is necessary to fix N by adding Ti, and the content of Ti is determined so as to secure solid solution B as described above. From the atomic weights of B, N, and Ti,
The formula of sol is obtained.
【００４１】Ｂ単独の好ましい範囲は０．００２０〜
０．００４０％、Ｎ単独の好ましい範囲は０．００２０
〜０．００６０％、Ｔｉ単独の好ましい範囲は０．００
４０〜０．０２５０である。The preferred range of B alone is 0.0020 to
0.0040%, a preferable range of N alone is 0.0020.
To 0.0060%, a preferable range of Ti alone is 0.00
40 to 0.0250.
【００４２】その他の元素： Ｓｉ：鋼材の常用元素としてのＳｉは脱酸剤として使用
する元素であり、特に規定するものではなく、通常の
０．０５〜０．６０％の範囲が好適である。Other elements: Si: Si as a common element in steel materials is an element used as a deoxidizing agent, and is not particularly specified, but is preferably in the range of 0.05 to 0.60%. .
【００４３】Ｐ：Ｐは強化元素として有効な元素である
が、本発明のようにＣｕ等による強化が得られるのであ
れば特に下限値を規定するものではない。多量に含有す
ると靭性が劣化するため、上限を０．１００％とするの
が好ましい。P: P is an element effective as a strengthening element, but the lower limit is not particularly limited as long as strengthening by Cu or the like is obtained as in the present invention. If it is contained in a large amount, the toughness is deteriorated. Therefore, the upper limit is preferably set to 0.100%.
【００４４】Ｍｏ：Ｍｏも疲労強度向上に有効な元素で
あるが、特に下限値を規定するものではない。また多量
に含有させてもコストアップになる上、効果は小さいた
め０．４０％以下とするのが好ましい。Mo: Mo is also an element effective for improving the fatigue strength, but does not particularly define the lower limit. In addition, even if it is contained in a large amount, the cost is increased, and the effect is small.
【００４５】さらに、被削性が要求される場合には、下
記３元素のうち１種以上を意図的に含有させることが望
ましい。When machinability is required, it is desirable to intentionally contain one or more of the following three elements.
【００４６】Ｓ：０．０４〜０．１０％、Ｓは被削性の
向上に効果があり、０．０４％以上が望ましく、０．１
０％を超えると連続鋳造スラブに中心偏析等の欠陥を生
じる。従って、０．０４〜０．１０％とするのが望まし
い。さらに好適範囲は０．０４〜０．０７％である。S: 0.04% to 0.10%, S is effective in improving machinability, and is preferably 0.04% or more, and 0.1% or more.
If it exceeds 0%, defects such as center segregation occur in the continuously cast slab. Therefore, it is desirable to set it to 0.04 to 0.10%. A more preferred range is 0.04 to 0.07%.
【００４７】Ｃａ：０．０００３〜０．００３０％、Ｃ
ａは被削性の向上に効果があるので、０．０００３％以
上含有するのが望ましく、０．００３０％を超えると大
型介在物の混入が避けられないので、０．０００３〜
０．００３０％とするのが望ましい。さらに好適範囲は
０．００１０〜０．００３０％である。Ca: 0.0003-0.0030%, C
Since a is effective in improving machinability, a is desirably contained at 0.0003% or more. If it exceeds 0.0030%, mixing of large inclusions cannot be avoided.
It is desirable to set it to 0.0030%. A more preferred range is 0.0010 to 0.0030%.
【００４８】Ｐｂ：０．０５〜０．２０％、Ｐｂは被削
性の向上に効果があるので０．０５％以上含有するのが
望ましく、０．２０％を超えて含有すると介在物が多く
なり疲労限度が著しく低下する。従って０．０５〜０．
２０％とするのが望ましい。さらに好適範囲は０．０５
〜０．１６％である。Pb: 0.05 to 0.20%, Pb is effective in improving machinability, so it is desirable to contain Pb at 0.05% or more, and if it exceeds 0.20%, there are many inclusions. The fatigue limit is significantly reduced. Therefore, 0.05-0.
It is desirable to set it to 20%. Further preferred range is 0.05
０．１0.16%.
【００４９】つぎに上記の本発明鋼による窒化クランク
軸の製造方法について述べる。本発明の鋼材を加熱し、
鍛造加工を行い目的の形状とする。鍛造時の加熱温度は
低いほど好ましいが、その分プレスの能力が必要となる
ため、一般的な条件として１２００℃を標準とし、プレ
スの能力に応じて１１５０〜１２５０℃の範囲で決め
る。Next, a method of manufacturing a nitrided crankshaft using the steel of the present invention will be described. Heating the steel material of the present invention,
Forging is performed to obtain the desired shape. The lower the heating temperature during forging is, the more preferable it is. However, since the press capacity is necessary, 1200 ° C. is standardized as a general condition, and the temperature is determined in the range of 1150 to 1250 ° C. according to the press capacity.
【００５０】鍛造後は製造コストの点から放冷（大気中
の自然冷却）とするのが好ましい。ただし、製造時間短
縮のため送風等による若干の空冷を行っても問題はな
い。その後、窒化処理までの間に焼準または焼入れ焼も
どしなどの調質処理を行う必要はない。After the forging, it is preferable to allow cooling (natural cooling in the air) from the viewpoint of manufacturing cost. However, there is no problem even if a slight air cooling is performed by air blowing or the like to shorten the manufacturing time. Thereafter, it is not necessary to perform a tempering treatment such as normalizing or quenching and tempering before the nitriding treatment.
【００５１】冷却後の材料には必要に応じて切削、研削
などの機械加工を行う。その後窒化処理を行う。The material after cooling is subjected to machining such as cutting and grinding as required. Thereafter, a nitriding treatment is performed.
【００５２】ここでは窒化処理として雰囲気ガスによる
軟窒化処理を例に述べる。窒化処理の効果の指標とする
パラメータは表面硬さ（ここでは深さ０．０５ｍｍすな
わち拡散層の化合物層直下の硬さ）と窒化層深さであ
る。これは、先にも述べたように、曲げ矯正性は表面硬
さに強く依存し、疲労強度は窒化層深さに強く依存する
ためである。Here, a nitrocarburizing treatment using an atmosphere gas will be described as an example of the nitriding treatment. The parameters used as indicators of the effect of the nitriding treatment are the surface hardness (in this case, a depth of 0.05 mm, that is, the hardness immediately below the compound layer of the diffusion layer) and the depth of the nitride layer. This is because, as described above, the bending straightness strongly depends on the surface hardness, and the fatigue strength strongly depends on the nitrided layer depth.
【００５３】これら２つの指標について軟窒化温度およ
び軟窒化時間、さらに軟窒化後の後熱処理温度、冷却方
法等について広範囲に検討を行った結果、以下の結論が
得られた。The following conclusions were obtained as a result of extensively examining the nitrocarburizing temperature and nitrocarburizing time, the post-heating temperature after nitrocarburizing, the cooling method, and the like for these two indices.
【００５４】なお、窒化処理雰囲気のガス混合比につい
ては従来の条件、すなわち、ＮＨ3：ＲＸガス＝１：１
にて効果が得られることを確認している。また、ＲＸガ
スとは、浸炭性を持つ吸熱性ガスであり、ＣＯ、Ｎ2 、
Ｈ2 からなるガスである。The gas mixture ratio in the nitriding treatment atmosphere is the same as the conventional condition, that is, NH 3 : RX gas = 1: 1.
Has confirmed that the effect can be obtained. The RX gas is an endothermic gas having a carburizing property, such as CO, N 2 ,
It is a gas composed of H 2 .
【００５５】軟窒化処理：一般に軟窒化温度の上昇及び
長時間化により表面硬さおよび有効硬化層深さは単調に
増加する。しかしながら、本発明に係るベイナイト組織
鋼の組織は軟窒化温度に相当する５００〜６００℃で組
織および硬さが顕著に変化する。これは過飽和に固溶し
た炭素およびＣｕがそれぞれＦｅx Ｃ（ｘ＝２または
３）およびＣｕ析出物として析出し強度向上に寄与する
が、さらに進行すると析出物が粗大化し強度に寄与しな
くなるためである。[0055] Soft nitriding treatment: Generally, the surface hardness and the effective hardened layer depth monotonously increase as the soft nitriding temperature rises and becomes longer. However, the structure and hardness of the bainite-structured steel according to the present invention change remarkably at 500 to 600 ° C. corresponding to the nitrocarburizing temperature. This is because carbon and Cu dissolved in supersaturation precipitate as Fe x C (x = 2 or 3) and Cu precipitates, respectively, and contribute to the improvement of strength. However, as the progress proceeds further, the precipitates become coarse and do not contribute to the strength. It is.
【００５６】さらに引き続き行う後熱処理の効果を含
め、実用窒化層深さを最大にし、かつ表面硬さを最小に
する適正な条件が存在する。定量的に検討を行った結
果、十分な窒化層深さを得るには５００℃以上が必要
で、また析出物による強化の寄与を失わないためには５
８０℃以下とすべきである。好ましくは５３０〜５６０
℃であり、さらに５４５〜５５５℃が好ましい。なお、
この温度は通常軟窒化処理で用いられている温度（５７
０〜５８０℃）より低い。There are proper conditions for maximizing the practical nitrided layer depth and minimizing the surface hardness, including the effect of the subsequent post-heat treatment. As a result of a quantitative study, it is necessary to obtain a temperature of 500 ° C. or more to obtain a sufficient nitrided layer depth.
It should be below 80 ° C. Preferably 530-560
° C, and more preferably 545-555 ° C. In addition,
This temperature is the temperature normally used in the nitrocarburizing treatment (57
0-580 ° C).
【００５７】また窒化処理時間については、時間ととも
に窒化層深さは深くなるが、効果が飽和することを考慮
し、通常の窒化処理と同じ３ｈｒ程度とするのがよい。
もちろん必要に応じて処理時間を変化させてもかまわな
い。The nitriding time increases with time, but it is preferable to set the nitriding time to about 3 hours, which is the same as that of normal nitriding, in consideration of the effect being saturated.
Of course, the processing time may be changed as needed.
【００５８】なお、窒化処理方法は前記のガス軟窒化の
ほか、短時間で処理可能な窒化方法ならいずれでも可能
であり、たとえば塩浴窒化、イオン窒化を行ってもよ
い。その場合も前記の５００〜５８０℃の温度で処理す
るべきである。The nitriding method may be any of the above-mentioned gas nitrocarburizing methods, as long as it can be performed in a short time. For example, salt bath nitriding or ion nitriding may be performed. In this case, the treatment should be performed at the above-mentioned temperature of 500 to 580 ° C.
【００５９】軟窒化後の後熱処理：軟窒化による硬さ分
布を好ましい形状、すなわち曲げ矯正性の点から表面硬
さを低く、疲労限度の点から窒化層深さを深くために
は、適当な温度で保持すればよい。これは表面に濃縮し
たＮ原子を試験片内部に拡散させるためである。ただし
軟窒化処理と同様、高い温度ではＦｅx ＣやＣｕ析出物
が粗大化し強度すなわち硬さが低下するため適正な温度
が存在する。Post-heat treatment after nitrocarburizing: In order to make the hardness distribution by nitrocarburizing a preferable shape, that is, to lower the surface hardness from the point of bending straightening and to increase the depth of the nitrided layer from the point of fatigue limit, an appropriate What is necessary is just to hold at temperature. This is to diffuse the N atoms concentrated on the surface into the test piece. However as with soft nitriding, Fe x C and Cu precipitates intensity or hardness coarsened is proper temperature is present to lower at higher temperatures.
【００６０】定量的に検討した結果、硬さ分布を適切な
形にするためには５００℃以上が必要で、また析出物に
よる強化の寄与を失わないためには５８０℃以下とすべ
きであることが明らかになった。好ましくは５３０〜５
６０℃であり、さらに好ましくは５４５〜５５５℃であ
る。As a result of a quantitative study, it is necessary that the temperature be 500 ° C. or higher in order to make the hardness distribution appropriate, and the temperature should be 580 ° C. or lower in order not to lose the contribution of strengthening due to precipitates. It became clear. Preferably 530 to 5
It is 60 degreeC, More preferably, it is 545-555 degreeC.
【００６１】また時間については、時間とともに硬さ分
布は適正な形状に変化するが、長時間処理しても効果が
飽和することを考慮し、１〜３ｈｒ程度とするのがよ
い。As for time, the hardness distribution changes to an appropriate shape with time, but it is preferable to set the hardness distribution to about 1 to 3 hours in consideration of the fact that the effect is saturated even if the treatment is performed for a long time.
【００６２】この処理は通常の軟窒化処理のように軟窒
化後、油焼入したものを再加熱して行ってもよいが、別
の製造工程が一つ増えることになり、非調質化による工
程省略の効果がなくなる。したがって軟窒化後、同じ軟
窒化炉の中での継続して後熱処理するのが効果的であ
る。具体的には、軟窒化処理後、炉内を窒素ガス、Ａｒ
ガス等の不活性ガスで置換し、あるいは雰囲気を真空に
して高温を保持するのがよい。This treatment may be carried out by reheating the quenched oil after nitrocarburizing as in the ordinary nitrocarburizing treatment. However, another additional production step is required, and The effect of the omission of the process is eliminated. Therefore, it is effective to carry out post-heat treatment continuously in the same nitrocarburizing furnace after nitrocarburizing. Specifically, after the nitrocarburizing treatment, nitrogen gas and Ar
It is preferable to replace the gas with an inert gas such as a gas, or to maintain the high temperature by evacuating the atmosphere.
【００６３】冷却方法：後熱処理後の冷却方法によって
残留応力分布が異なる。従来の窒化鍛造鋼材料では軟窒
化処理後、油焼入することにより、表面に高い圧縮残留
応力を発生させ、表面の疲労限度は増加させている。し
かし、本発明鋼ではむしろ母材部−拡散層境界での疲労
き裂の発生が問題である。この部位の残留応力は表面の
残留応力と均衡する引張応力となるため好ましくない。
残留応力測定を行った結果、空冷以下の速度で冷却すれ
ば試験片内部に発生する引張残留応力は無視しうるほど
に小さくなるので、空冷、放冷または炉冷とする。液体
冷却を用いてはならない。生産リードタイムの点から
は、炉冷では冷却に数時間〜数十時間かかるため冷却フ
ァンを用いた空冷が好ましい。Cooling method: The residual stress distribution differs depending on the cooling method after the post heat treatment. In a conventional nitrided forged steel material, high compressive residual stress is generated on the surface by oil quenching after the soft nitriding treatment, and the surface fatigue limit is increased. However, in the steel of the present invention, the occurrence of a fatigue crack at the boundary between the base material and the diffusion layer is rather a problem. The residual stress at this portion is not preferable because it becomes a tensile stress balanced with the residual stress on the surface.
As a result of the residual stress measurement, if the cooling is performed at a speed lower than the air cooling, the tensile residual stress generated inside the test piece becomes so small as to be negligible. Do not use liquid cooling. From the viewpoint of production lead time, air cooling using a cooling fan is preferable because furnace cooling requires several hours to several tens of hours for cooling.
【００６４】[0064]
【実施例】表１に、試作した本発明例および比較例の鋼
を２４種類（Ｚ１〜Ｚ２４）および従来例の鋼であるＳ
４８Ｃ鋼の２鋼種（Ｚ２５〜２６）の化学組成を示す。
以下、鋼種番号と試験片番号とを対応させて記す。EXAMPLES Table 1 shows 24 types of steels (Z1 to Z24) of the prototypes of the present invention and comparative examples and S which is a conventional steel.
The chemical composition of two steel types (Z25 to 26) of 48C steel is shown.
Hereinafter, the steel type number and the test piece number will be described in association with each other.
【００６５】[0065]
【表１】 [Table 1]
【００６６】図２はクランク軸を模擬した試験片の形状
を示す概要図で、同図(a) は側面図、同図(b) は正面図
である。同図において、１はジャーナル部、２はピン
部、３はフィレットＲ部である。FIG. 2 is a schematic view showing the shape of a test piece simulating a crankshaft. FIG. 2 (a) is a side view and FIG. 2 (b) is a front view. In the figure, 1 is a journal, 2 is a pin, and 3 is a fillet R.
【００６７】表１に示す鋼を１５０ｋｇ大気中溶解炉で
溶製した後に、得られた鋼片を１２００℃まで加熱し、
図２に示す粗形状に熱間鍛造し放冷した。After the steel shown in Table 1 was melted in a 150 kg air melting furnace, the obtained steel slab was heated to 1200 ° C.
It was hot forged into the rough shape shown in FIG. 2 and allowed to cool.
【００６８】ただし従来例については熱間鍛造後、焼入
れ焼戻し処理として、８５０℃で３０分保持後水冷し、
引き続き６１０℃で３０分保持後空冷した。なお、供試
材Ｚ１７は熱間鍛造時に割れたので、試験を中止した。
これは、Ｃｕの含有量が高いため、熱間での脆化による
と考えられる。However, in the conventional example, after hot forging, as a quenching and tempering treatment, it was kept at 850 ° C. for 30 minutes and then water-cooled.
Subsequently, the mixture was kept at 610 ° C. for 30 minutes and air-cooled. Note that the test material Z17 was broken during hot forging, so the test was stopped.
This is considered to be due to hot embrittlement due to the high Cu content.
【００６９】各試験片について組織を調査したところ、
Ｚ１１とＺ１３を除き、体積率で９５％以上のベイナイ
ト組織であった。またＺ１１とＺ１３では体積率で２０
％以上のパーライトが見られた。Ｚ１１についてはＣ量
が不足しており、Ｚ１３ではＭｎ量が不足しているため
と考えられる 試験片のピン部２を旋盤で機械加工した後、以下の条件
で軟窒化処理を行った。本発明例および比較例の試験片
については、ガス比ＲＸ：ＮＨ3 ＝１：１の雰囲気中で
試験片を５５０℃に加熱し１８０分保持した後、ガスを
Ａｒガスと置換し、引き続き５５０℃で１８０分保持し
その後空冷した。When the structure of each test piece was examined,
Except for Z11 and Z13, the bainite structure had a volume ratio of 95% or more. For Z11 and Z13, the volume ratio is 20.
% Or more of pearlite was found. The pin portion 2 of the test piece, which is considered to be due to the lack of the amount of C in Z11 and the amount of Mn in Z13, was machined with a lathe and then soft-nitrided under the following conditions. With respect to the test pieces of the present invention example and the comparative example, the test pieces were heated to 550 ° C. in an atmosphere having a gas ratio of RX: NH 3 = 1: 1 and held for 180 minutes, and then the gas was replaced with Ar gas. The mixture was kept at 180 ° C. for 180 minutes, and then air-cooled.
【００７０】また従来例の鋼種については従来通りの条
件として、ガス比ＲＸ：ＮＨ3 ＝１：１の雰囲気中に試
験片を５７０℃に加熱し１８０分保持した後、１５０℃
の油中に焼入し、後熱処理は行わなかった。For the steel type of the conventional example, the test piece was heated to 570 ° C. in an atmosphere with a gas ratio of RX: NH 3 = 1: 1 and held for 180 minutes, and then kept at 150 ° C.
And no post-heat treatment was performed.
【００７１】鋼種Ｚ１については、軟窒化条件の影響を
詳細に明らかにするため、軟窒化処理温度、後熱処理温
度、冷却方法の各条件を種々変化させ試験を行った。In order to clarify the effect of the nitrocarburizing conditions on the steel type Z1, a test was conducted by changing various conditions of the nitrocarburizing treatment temperature, the post heat treatment temperature, and the cooling method.
【００７２】表２に鋼種Ｚ１から採取した試験片（Ｚ１
−１〜Ｚ１−１５）の軟窒化条件、後熱処理条件および
冷却条件を示す。Table 2 shows test pieces (Z1) taken from steel type Z1.
-1 to Z1-15) soft nitriding conditions, post heat treatment conditions and cooling conditions are shown.
【００７３】[0073]
【表２】 [Table 2]
【００７４】疲労試験は室温大気中で、試験片のジャー
ナル部１の端部およびピン部２の中央部を支持した３点
曲げ荷重制御両振りにて、繰返し速度５Ｈｚで実施し、
破断繰返し数が１０7 回となる応力振幅を疲労限度と定
義した。この応力は、疲労き裂が発生するピン部２のフ
ィレットＲ部３における応力であり、長さ１ｍｍのひず
みゲージによる測定値から換算したものである。The fatigue test was carried out in a room temperature atmosphere at a repetition rate of 5 Hz with a three-point bending load control swing supporting the end of the journal 1 and the center of the pin 2 of the test piece.
The stress amplitude at which the number of repeated fractures was 10 7 was defined as the fatigue limit. This stress is a stress in the fillet R portion 3 of the pin portion 2 where a fatigue crack occurs, and is converted from a value measured by a strain gauge having a length of 1 mm.
【００７５】一方、曲げ矯正性は同試験片による静的曲
げ試験により評価した。疲労試験時にひずみゲージを貼
付した場所と同一の場所にひずみゲージを貼付し、室温
大気中にて曲げを負荷し、ひずみゲージの断線をき裂の
発生と見なし、その時のひずみ量を曲げ矯正可能ひずみ
量とした。曲げ矯正可能ひずみ量はばらつきが大きいた
め、１鋼種につき４回の試験を行い、その平均値で評価
した。On the other hand, the bending straightness was evaluated by a static bending test using the same test piece. A strain gauge is attached to the same place where the strain gauge was attached at the time of the fatigue test, bending is applied in the atmosphere at room temperature, and the breakage of the strain gauge is regarded as the occurrence of a crack, and the strain amount at that time can be straightened. The amount of strain was used. Since the amount of bendable strain was large, the test was performed four times for each steel type, and the average value was evaluated.
【００７６】また被削性についてもＺ１７を除くすべて
の鋼に対して工具寿命の試験を行った。表３に、疲労、
曲げおよび被削性の試験結果を示す。Regarding the machinability, a tool life test was performed on all steels except Z17. Table 3 shows the fatigue,
The test results of bending and machinability are shown.
【００７７】[0077]
【表３】 [Table 3]
【００７８】表３に示すように、本発明例の試験片は、
疲労限度および曲げ矯正可能ひずみ量の両方において目
標値（Ｓ４８Ｃを素材とする軟窒化調質クランク軸と対
比して疲労強度は２割り増しの６０ｋｇｆ／ｍｍ2 、曲
げ矯正可能ひずみ量は同等の１．５％）を達成してい
た。これに対して、比較例の試験片および試験片Ｚ１
５，Ｚ２３、Ｚ２４は目標値の疲労限度と曲げ矯正可能
ひずみ量を同時に達成するものは存在しなかった。Ｚ１
５，Ｚ２３，Ｚ２４は本発明の請求項１の規定は満たす
ものの、それぞれ、Ｓが過大（Ｚ１５）、Ｃａが過大
（Ｚ２３）、Ｐｂが過大（Ｚ２４）であるため、疲労限
度が満足すべきものではなかった。これらは被削性向上
のために添加したＳ、Ｃａ、Ｐｂが悪影響を及ぼしたも
のと考えられる。As shown in Table 3, the test piece of the present invention example
In both the fatigue limit and the amount of strain that can be corrected, the target value (the fatigue strength is 60 kgf / mm 2 , which is 20% higher than that of the nitrocarburized tempered crankshaft using S48C as the material), and the amount of strain that can be bent is 1. 5%). On the other hand, the test piece of the comparative example and the test piece Z1
None of 5, Z23 and Z24 simultaneously achieved the target fatigue limit and the amount of strain that can be corrected. Z1
5, Z23 and Z24 satisfy the requirements of claim 1 of the present invention, but have an excessive S (Z15), an excessive Ca (Z23), and an excessive Pb (Z24), so that the fatigue limit should be satisfied. Was not. It is considered that S, Ca, and Pb added for improving machinability had an adverse effect.
【００７９】被削性は、Ｓ４８Ｃ鋼にＰｂを０．０５％
含有する鋼に調質処理を行ったクランク軸を基準とし
た。これと同等以上の工具寿命となったものを良好
（○）とした。本発明例の鋼種のうちＳ、ＣａまたはＰ
ｂを所定量含有したもの（表１の本発明例１）は、疲労
限度と曲げ矯正性を同時に満たし、かつ良好な被削性を
もつことがわかった。The machinability was determined by adding 0.05% of Pb to S48C steel.
Based on the crankshaft in which the steel contained was subjected to tempering treatment. A tool having a tool life equal to or longer than this was evaluated as good (良好). S, Ca or P among steel types of the present invention
It was found that those containing b in a predetermined amount (Example 1 of Table 1 in Table 1) simultaneously satisfied the fatigue limit and the bending straightness and had good machinability.
【００８０】一方、本発明例の鋼種の内、Ｓ、Ｃａまた
はＰｂを所定量含有しないもの（表１の本発明例２）は
被削性が劣っていた。On the other hand, among the steel types of the present invention, those not containing a predetermined amount of S, Ca or Pb (Example 2 of Table 1) were inferior in machinability.
【００８１】表４には各種の軟窒化処理条件および後熱
処理条件で処理を行った試験片の試験結果を示す。本発
明の範囲内の処理にて疲労強度と曲げ矯正性の目標値を
達成できることがわかった。Table 4 shows the test results of the test pieces that were processed under various soft nitriding conditions and post heat treatment conditions. It has been found that the target values of fatigue strength and bending straightness can be achieved by the treatment within the range of the present invention.
【００８２】[0082]
【表４】 [Table 4]
【００８３】[0083]
【発明の効果】本発明による非調質窒化鍛造部品を用い
れば、従来の調質処理を行った窒化鍛造部品と同等以上
の疲労限度と、従来と同等の曲げ矯正性を確保できる。
また、この窒化鍛造部品の製造においては調質処理を省
略できるため、大きなコスト削減が可能である。By using the non-heat treated nitrided forged part according to the present invention, it is possible to secure a fatigue limit equal to or higher than that of a conventional heat treated nitrided forged part, and a bending straightness equivalent to the conventional one.
In addition, in the production of this nitrided forged part, the tempering treatment can be omitted, so that a large cost reduction can be achieved.
【図１】調質鋼および非調質鋼の窒化鋼鍛造部品の製造
法を示す工程図であり、同図(a) は調質鋼の場合、同図
(b) は非調質鋼の場合である。BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram showing a method for producing a forged part of a tempered steel and a non-heat treated steel nitrided steel.
(b) is the case of non-heat treated steel.
【図２】クランク軸を模擬した試験片の形状を示す概要
図で、同図(a) は側面図、同図(b) は正面図である。FIG. 2 is a schematic view showing the shape of a test piece simulating a crankshaft, wherein FIG. 2 (a) is a side view and FIG. 2 (b) is a front view.
１ ジャーナル部 ２ ピン部 ３ フィレットＲ部 1 Journal 2 Pin 3 Fillet R
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.7 識別記号 ＦＩ テーマコート゛(参考） Ｃ２１Ｄ 9/30 Ｃ２１Ｄ 9/30 Ａ Ｃ２２Ｃ 38/58 Ｃ２２Ｃ 38/58 38/60 38/60 Ｃ２３Ｃ 8/24 Ｃ２３Ｃ 8/24 Ｆターム(参考） 4E087 AA10 BA01 BA02 CB01 CB04 DB04 DB11 DB14 DB15 DB16 DB24 HA32 HA82 4K028 AA02 AB01 AB06 4K032 AA01 AA02 AA05 AA08 AA11 AA14 AA15 AA16 AA17 AA21 AA23 AA27 AA28 AA29 AA31 AA35 AA36 CA02 CA03 CD05 CF01 CF02 CF03 4K042 AA16 BA04 CA02 CA05 CA06 CA10 CA12 CA13 DA06 DC02 DC05 DE03 DE04 ──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. 7 Identification symbol FI theme coat ゛ (Reference) C21D 9/30 C21D 9/30 A C22C 38/58 C22C 38/58 38/60 38/60 C23C 8/24 C23C 8/24 F term (reference) 4E087 AA10 BA01 BA02 CB01 CB04 DB04 DB11 DB14 DB15 DB16 DB24 HA32 HA82 4K028 AA02 AB01 AB06 4K032 AA01 AA02 AA05 AA08 AA11 AA14 AA15 AA16 AA17 AAA AA AA AA AA AA AA AA A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A CF03 4K042 AA16 BA04 CA02 CA05 CA06 CA10 CA12 CA13 DA06 DC02 DC05 DE03 DE04
Claims (3)
０．３５％、Ｍｎ：１．００〜３．００％、Ｃｒ：０〜
０．１５％、Ｖ：０〜０．０２％、Ｃｕ：０．５０〜
１．５０％、Ｎｉ：Ｃｕ含有量の０．４倍以上を含有
し、Ｂ、ＮおよびＴｉの含有量が、Ｂsol ＝Ｂ−（１１
／１４）｛Ｎ−（１４／４８）Ｔｉ｝で定義されるＢso
l で０．００１０〜０．００３０％であり、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非
調質窒化鍛造部品。1. The chemical composition in weight%, C: 0.15
0.35%, Mn: 1.00 to 3.00%, Cr: 0
0.15%, V: 0 to 0.02%, Cu: 0.50
1.50%, containing 0.4 times or more of Ni: Cu content, and the content of B, N and Ti is Bsol = B- (11
/ 14) Bso defined by {N- (14/48) Ti}
l is 0.0010 to 0.0030%, and the balance is Fe
And a non-heat treated nitrided forged part comprising an unavoidable impurity element.
さらに、Ｓ：０．０４〜０．１０％、Ｃａ：０．０００
３〜０．００３０％、Ｐｂ：０．０５〜０．２０％のう
ち１種以上の元素を含有することを特徴とする非調質窒
化鍛造部品。2. The non-heat treated nitrided forged part according to claim 1, further comprising: S: 0.04 to 0.10%, Ca: 0.000%
A non-heat treated nitrided forged part containing at least one element among 3 to 0.0030% and Pb: 0.05 to 0.20%.
０．３５％、Ｍｎ：１．００〜３．００％、Ｃｒ：０〜
０．１５％、Ｖ：０〜０．０２％、Ｃｕ：０．５０〜
１．５０％、Ｎｉ：Ｃｕ含有量の０．４倍以上を含有
し、Ｂ、ＮおよびＴｉの含有量が、Ｂsol ＝Ｂ−（１１
／１４）｛Ｎ−（１４／４８）Ｔｉ｝で定義されるＢso
l で０．００１０〜０．００３０％であり、残部がＦｅ
および不可避的不純物元素からなる鋼材を熱間鍛造後、
放冷または空冷し、必要に応じて機械加工を行い、熱処
理をすることなく窒化処理を５００〜５８０℃で行い、
引き続き不活性ガス雰囲気中、５００〜５８０℃で後熱
処理を行い、その後、放冷、空冷または炉冷することを
特徴とする非調質窒化鍛造部品の製造方法。3. The chemical composition in weight%, C: 0.15
0.35%, Mn: 1.00 to 3.00%, Cr: 0
0.15%, V: 0 to 0.02%, Cu: 0.50
1.50%, containing 0.4 times or more of Ni: Cu content, and the content of B, N and Ti is Bsol = B- (11
/ 14) Bso defined by {N- (14/48) Ti}
l is 0.0010 to 0.0030%, and the balance is Fe
And after hot forging steel material consisting of unavoidable impurity elements,
Allow to cool or air cool, machine if necessary, perform nitriding at 500-580 ° C without heat treatment,
A method for producing a non-heat-treated nitrided forged part, comprising: performing a post-heat treatment at 500 to 580 ° C. in an inert gas atmosphere, followed by cooling, air cooling, or furnace cooling.
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| Application Number | Priority Date | Filing Date | Title |
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| JP33100298A JP3915284B2 (en) | 1998-11-20 | 1998-11-20 | Non-tempered nitriding forged parts and manufacturing method thereof |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP33100298A JP3915284B2 (en) | 1998-11-20 | 1998-11-20 | Non-tempered nitriding forged parts and manufacturing method thereof |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2000160287A true JP2000160287A (en) | 2000-06-13 |
| JP3915284B2 JP3915284B2 (en) | 2007-05-16 |
Family
ID=18238740
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP33100298A Expired - Fee Related JP3915284B2 (en) | 1998-11-20 | 1998-11-20 | Non-tempered nitriding forged parts and manufacturing method thereof |
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| Country | Link |
|---|---|
| JP (1) | JP3915284B2 (en) |
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| JP2006002814A (en) * | 2004-06-16 | 2006-01-05 | Honda Motor Co Ltd | Forming method of nitrided sliding face |
| EP1857563A1 (en) * | 2005-02-25 | 2007-11-21 | Sumitomo Metal Industries, Ltd. | Non-tempered steel soft nitrided component |
| US7416616B2 (en) | 2003-09-01 | 2008-08-26 | Sumitomo Metal Industries, Ltd. | Non-heat treated steel for soft-nitriding |
| US7622009B2 (en) | 2001-03-21 | 2009-11-24 | Honda Giken Kogyo Kabushiki Kaisha | Steel material |
| US7655100B2 (en) | 2001-03-21 | 2010-02-02 | Honda Giken Kogyo Kabushiki Kaisha | Method for preparation of steel material |
| CN102825189A (en) * | 2012-09-20 | 2012-12-19 | 江苏金源锻造股份有限公司 | Preparation method of GH4169 alloy pipe |
| JP2013133539A (en) * | 2011-12-27 | 2013-07-08 | Toyota Motor Corp | Method for surface treatment of iron base material |
| WO2014136348A1 (en) * | 2013-03-07 | 2014-09-12 | 新日鐵住金株式会社 | Untempered soft-nitrided component |
| WO2016035519A1 (en) * | 2014-09-02 | 2016-03-10 | 新日鐵住金株式会社 | Non-tempered soft-nitrided component |
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|---|---|---|---|---|
| US7622009B2 (en) | 2001-03-21 | 2009-11-24 | Honda Giken Kogyo Kabushiki Kaisha | Steel material |
| US7655100B2 (en) | 2001-03-21 | 2010-02-02 | Honda Giken Kogyo Kabushiki Kaisha | Method for preparation of steel material |
| US7416616B2 (en) | 2003-09-01 | 2008-08-26 | Sumitomo Metal Industries, Ltd. | Non-heat treated steel for soft-nitriding |
| JP2006002814A (en) * | 2004-06-16 | 2006-01-05 | Honda Motor Co Ltd | Forming method of nitrided sliding face |
| JP4520223B2 (en) * | 2004-06-16 | 2010-08-04 | 本田技研工業株式会社 | Method for forming nitriding sliding surface |
| EP1857563A1 (en) * | 2005-02-25 | 2007-11-21 | Sumitomo Metal Industries, Ltd. | Non-tempered steel soft nitrided component |
| EP1857563A4 (en) * | 2005-02-25 | 2010-08-04 | Honda Motor Co Ltd | Non-tempered steel soft nitrided component |
| JP2013133539A (en) * | 2011-12-27 | 2013-07-08 | Toyota Motor Corp | Method for surface treatment of iron base material |
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| US9956950B2 (en) | 2013-03-07 | 2018-05-01 | Nippon Steel & Sumitomo Metal Corporation | Non-thermal refined soft-nitrided component |
| WO2016035519A1 (en) * | 2014-09-02 | 2016-03-10 | 新日鐵住金株式会社 | Non-tempered soft-nitrided component |
| JPWO2016035519A1 (en) * | 2014-09-02 | 2017-07-27 | 新日鐵住金株式会社 | Non-tempered soft nitriding parts |
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