JP5503170B2 - Case-hardened steel with excellent maximum grain reduction characteristics - Google Patents

Case-hardened steel with excellent maximum grain reduction characteristics Download PDF

Info

Publication number
JP5503170B2
JP5503170B2 JP2009070684A JP2009070684A JP5503170B2 JP 5503170 B2 JP5503170 B2 JP 5503170B2 JP 2009070684 A JP2009070684 A JP 2009070684A JP 2009070684 A JP2009070684 A JP 2009070684A JP 5503170 B2 JP5503170 B2 JP 5503170B2
Authority
JP
Japan
Prior art keywords
less
steel
excluding
case
inclusions
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.)
Expired - Fee Related
Application number
JP2009070684A
Other languages
Japanese (ja)
Other versions
JP2010222634A (en
Inventor
成朗 岡本
陽介 新堂
睦久 永濱
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.)
Kobe Steel Ltd
Original Assignee
Kobe Steel Ltd
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 Kobe Steel Ltd filed Critical Kobe Steel Ltd
Priority to JP2009070684A priority Critical patent/JP5503170B2/en
Publication of JP2010222634A publication Critical patent/JP2010222634A/en
Application granted granted Critical
Publication of JP5503170B2 publication Critical patent/JP5503170B2/en
Expired - Fee Related legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Description

本発明は自動車、建築機械、その他産業機械において浸炭処理等の表面硬化処理をして使用される鋼部品を製造するのに有用な肌焼鋼に関する。   The present invention relates to a case-hardened steel useful for producing steel parts used for surface hardening treatment such as carburizing treatment in automobiles, construction machines, and other industrial machines.

自動車、建築機械、その他産業機械において耐摩耗性、高疲労強度などが要求される部品を製造するには、肌焼鋼が利用されている。肌焼鋼としてはSCr、SCM、SNCMなどが多用されており、鍛造や切削などの機械加工を利用してこれら肌焼鋼を部品形状に成形した後、浸炭、窒化、浸炭窒化などの表面硬化処理を施し、その後必要に応じて研磨することで鋼部品が製造されている。近年、鋼部品の製造コストを低減するために、切削加工による負荷を低減することが求められている。例えば、切削加工を鍛造に切り替えたり、熱間鍛造を温間又は冷間鍛造に変更して寸法精度を高めることによって鍛造後の切削量を低減している。しかし、温間又は冷間鍛造した後、表面硬化処理すると、結晶粒が粗大化し易くなる。   Case-hardened steel is used to manufacture parts that require wear resistance, high fatigue strength, and the like in automobiles, construction machines, and other industrial machines. SCr, SCM, SNCM, etc. are frequently used as case hardening steel. After these case hardening steels are formed into parts using machine processing such as forging and cutting, surface hardening such as carburizing, nitriding, carbonitriding, etc. Steel parts are manufactured by processing and then polishing as necessary. In recent years, in order to reduce the manufacturing cost of steel parts, it is required to reduce the load caused by cutting. For example, the amount of cutting after forging is reduced by switching the cutting process to forging or changing hot forging to warm or cold forging to increase dimensional accuracy. However, if the surface hardening treatment is performed after warm forging or cold forging, the crystal grains are likely to be coarsened.

表面硬化処理の際の結晶粒の粗大化を防止する技術として、例えば、特許文献1〜3などにはNbを利用する技術が開示されている。特許文献1はNbを0.005〜0.20%添加することを提案しており、鋼中のNbはC、NおよびAlと結合して極めて微細な析出物を生成し、粗大化の防止に有効であると説明している。特許文献2はNbを0.001〜0.1%添加することを提案しており、Nbは鋼中のCやNと結合してNb炭化物、Nb窒化物、Nb炭窒化物などの析出物を生成すること、この析出物が鋼中に微細分散すると結晶粒の粗大化防止に有効であること、微細分散させるためには、これら析出物を固溶させることのできる温度で加熱した後、オーステナイト域では速やかに冷却すればよいことなどが説明されている。特許文献3はNbを0.015〜0.050%程度添加しており、Nbの炭化物を一旦全て固溶させることで、微細均一な析出を促して結晶粒の成長を抑制できると説明している。   As a technique for preventing crystal grain coarsening during the surface hardening treatment, for example, Patent Documents 1 to 3 disclose a technique using Nb. Patent Document 1 proposes that 0.005 to 0.20% of Nb is added, and Nb in the steel combines with C, N and Al to form extremely fine precipitates, preventing coarsening. It is explained that it is effective. Patent Document 2 proposes that 0.001 to 0.1% of Nb is added, and Nb combines with C and N in the steel and precipitates such as Nb carbide, Nb nitride, and Nb carbonitride. In order to finely disperse the precipitate in the steel, it is effective for preventing the coarsening of the crystal grains, and in order to finely disperse the precipitate, after heating at a temperature at which these precipitates can be dissolved, It is explained that the austenite region should be cooled quickly. Patent Document 3 explains that Nb is added in an amount of about 0.015 to 0.050%, and that all the carbides of Nb are once dissolved to promote fine and uniform precipitation and suppress the growth of crystal grains. Yes.

しかし、特許文献1〜3のようにNb析出物を一旦固溶させる方法でNb量が0.05%未満になると、十分な数量の析出物が得られず、結晶粒粗大化防止効果が低下するという不具合があった。そこで特許文献4は、Nbを0.05〜0.30%添加している。なお特許文献4でも、結晶粒粗大化防止に有効な微細析出物を生成させるため、鋳造時に生成した粗大な析出物を一旦固溶させなければならないとしており、分塊圧延前の加熱温度(T1;℃)と加熱時間(t;分)を、4000≦(T1+273)×log10(t×60)を満足するようにしなければならないとしている(なお特許文献4には、4000≦(T1+273)×log10(t)と記載されているが、実施例の欄の計算結果から逆算すると、4000≦(T1+273)×log10(t×60)が正しい)。 However, if the amount of Nb is less than 0.05% by the method of once dissolving Nb precipitates as in Patent Documents 1 to 3, a sufficient amount of precipitates cannot be obtained, and the effect of preventing crystal grain coarsening is reduced. There was a bug to do. Therefore, in Patent Document 4, 0.05 to 0.30% of Nb is added. In Patent Document 4, it is said that the coarse precipitates produced during casting must be once dissolved in order to produce fine precipitates effective for preventing the coarsening of crystal grains, and the heating temperature (T1) before the batch rolling is performed. ; ° C.) and heating time (t; minutes) must satisfy 4000 ≦ (T1 + 273) × log 10 (t × 60) (in Patent Document 4, 4000 ≦ (T1 + 273) × Although it is described as log 10 (t), 4000 ≦ (T1 + 273) × log 10 (t × 60) is correct when calculated backward from the calculation result in the column of Example.

特開平9−78184号公報JP-A-9-78184 特開2000−63943号公報Japanese Patent Application Laid-Open No. 2000-63943 特開2007−39732号公報JP 2007-39732 A 特開2007−162128号公報JP 2007-162128 A

特許文献4のようにすることで、多数の微細Nb析出物を析出させることができ、結晶粒粗大化防止特性を向上することができる。本発明の目的は、特許文献4の技術を改善し、結晶粒をさらに高度に制御することにある。   By making it like patent document 4, many fine Nb precipitates can be precipitated and a crystal grain coarsening prevention characteristic can be improved. An object of the present invention is to improve the technique of Patent Document 4 and to control the crystal grains to a higher degree.

特許文献1〜3及び特許文献4はいずれもNb析出物を一旦固溶することで、これらを微細析出させている。しかし、この技術によればNbが少ない場合には微細Nb析出物の数が不足する(特許文献1〜3)。Nbを所定量以上添加することで、微細Nb析出物を確保することができ、結晶粒の粗大化を防止できる(特許文献4)。   In each of Patent Literatures 1 to 3 and Patent Literature 4, Nb precipitates are once solid-dissolved to finely precipitate them. However, according to this technique, when Nb is small, the number of fine Nb precipitates is insufficient (Patent Documents 1 to 3). By adding Nb in a predetermined amount or more, fine Nb precipitates can be secured, and coarsening of crystal grains can be prevented (Patent Document 4).

ところが本発明者らがさらに検討を重ねたところ、特許文献4の技術によれば、殆どの結晶粒は粗大化が防止されているが、極一部に特異的に大きくなった結晶粒が存在していること(混粒)が判明した。そしてその原因について検討を進めたところ、粗大なNb析出物が僅かでも残ると、表面硬化処理における加熱時に粗大なNb析出物がオストワルド成長し、周辺の微細なNb析出物が消失する結果、極一部に特異的に結晶粒が大きくなることが判明した。そこで微細Nb析出物を多数分散して結晶粒の粗大化を防止しつつも、最大となる結晶粒を縮小化できる技術(混粒を防止できる技術)を目指してさらに検討を進めたところ、むしろNb析出物の僅かな固溶すら防止するようにしつつ、Nbの添加量を必要最小限にまで絞り込むようにすれば、結晶粒粗大化防止特性を示す十分量の微細Nb析出物が得られ、かつ粗大なNb析出物を著しく低減して混粒現象も防止できることを見出し、本発明を完成した。   However, as a result of further studies by the present inventors, according to the technique of Patent Document 4, the coarsening of most crystal grains is prevented, but there are crystal grains that are specifically enlarged in a very small part. (Mixed grain) was found. As a result of investigation on the cause, if even a small amount of coarse Nb precipitate remains, the coarse Nb precipitate grows Ostwald during heating in the surface hardening treatment, and the surrounding fine Nb precipitate disappears. It was found that the crystal grains were specifically enlarged in some areas. Therefore, when further studies were conducted with the aim of a technique (a technique capable of preventing mixed grains) that can reduce the largest crystal grain while dispersing a large number of fine Nb precipitates to prevent the coarsening of the crystal grains, rather, If the amount of Nb added is reduced to the necessary minimum while preventing even a slight solid solution of Nb precipitates, a sufficient amount of fine Nb precipitates exhibiting the prevention of grain coarsening can be obtained, In addition, the inventors have found that coarse Nb precipitates can be remarkably reduced to prevent the mixed grain phenomenon, and the present invention has been completed.

すなわち、本発明に係る肌焼鋼は、C:0.1〜0.3%(質量%の意味。化学成分の含有量について%を使う場合は、以下、同じく質量%を意味するものとする)、Si:1.5%以下(0%を含まない)、Mn:2%以下(0%を含まない)、Cr:2.5%以下(0%を含まない)、及びNb:0.01〜0.05%を含有し、残部が鉄及び不可避的不純物からなり、式(1)を満足している。このような肌焼鋼は、最大結晶粒の縮小化特性に優れている。
A/[Nb]≦0.7 …(1)
(式中、Aは、面積20μm2以上のNb系介在物の面積率(%)を示す。[Nb]は鋼中のNb含有量(質量%)を示す)
That is, the case-hardened steel according to the present invention is C: 0.1 to 0.3% (meaning mass%. When% is used for the content of chemical components, hereinafter, the same means mass%. ), Si: 1.5% or less (not including 0%), Mn: 2% or less (not including 0%), Cr: 2.5% or less (not including 0%), and Nb: 0. It contains 01-0.05%, the balance consists of iron and inevitable impurities, and satisfies the formula (1). Such a case-hardened steel is excellent in the reduction characteristics of the maximum crystal grains.
A / [Nb] ≦ 0.7 (1)
(In the formula, A represents the area ratio (%) of Nb-based inclusions having an area of 20 μm 2 or more. [Nb] represents the Nb content (mass%) in the steel)

前記肌焼鋼には、Mo:2.0%以下(0%を含まない)、B:0.005%以下(0%を含まない)、Cu:0.1%以下(0%を含まない)、Ni:3%以下(0%を含まない)などを適宜添加してもよい。なお前記不可避不純物は、例えば、P:0.03%以下(0%を含まない)、S:0.03%以下(0%を含まない)、Al:0.06%以下(0%を含まない)、N:0.05%以下(0%を含まない)などである。   In the case-hardened steel, Mo: 2.0% or less (not including 0%), B: 0.005% or less (not including 0%), Cu: 0.1% or less (not including 0%) ), Ni: 3% or less (excluding 0%), etc. may be added as appropriate. The inevitable impurities include, for example, P: 0.03% or less (not including 0%), S: 0.03% or less (not including 0%), Al: 0.06% or less (including 0%) N), N: 0.05% or less (not including 0%).

本発明の肌焼鋼は、前記化学組成の鋼材を平均100℃/h以上の速度で加熱し、分塊圧延した後、さらに温度850〜1050℃に再加熱してから熱間圧延することによって製造でき、前記分塊圧延の加熱温度T1(℃)と加熱時間t(分)が式(2)、(3)を満足している。
1100≦T1≦1350 …(2)
(T1+273)×log10(t×60)<4000 …(3)
本発明には前記肌焼鋼を冷間加工した後、表面硬化熱処理した鋼材も含まれる。
The case-hardened steel of the present invention is obtained by heating the steel material having the above-mentioned chemical composition at an average speed of 100 ° C./h or more, rolling it in pieces, and then re-heating it to a temperature of 850 to 1050 ° C. The heating temperature T1 (° C.) and the heating time t (minute) of the above-mentioned block rolling satisfy the formulas (2) and (3).
1100 ≦ T1 ≦ 1350 (2)
(T1 + 273) × log 10 (t × 60) <4000 (3)
The present invention also includes a steel material that is cold-worked and then subjected to a surface hardening heat treatment.

本発明によれば、Nb析出物の僅かな固溶すら防止するようにして、Nbの添加量を必要最小限にまで絞り込んでいるため、オストワルド成長するような粗大なNb系介在物を著しく低減でき、肌焼鋼の最大結晶粒の縮小化特性を高めることができる。   According to the present invention, the amount of Nb added is narrowed down to the minimum necessary so as to prevent even a slight solid solution of Nb precipitates, so that the coarse Nb-based inclusions that cause Ostwald growth are significantly reduced. And the reduction characteristics of the maximum crystal grains of the case-hardened steel can be enhanced.

図1は従来の肌焼鋼の組織を示す概念図である。FIG. 1 is a conceptual diagram showing the structure of a conventional case-hardened steel. 図2は本発明の肌焼鋼の組織の一例を示す概念図である。FIG. 2 is a conceptual diagram showing an example of the structure of the case hardening steel of the present invention. 図3は実験例で得られた鋼材を焼鈍するときのヒートパターンを示す図である。FIG. 3 is a view showing a heat pattern when the steel material obtained in the experimental example is annealed. 図4は実験例で得られた鋼材をガス浸炭するときのヒートパターンを示す図である。FIG. 4 is a view showing a heat pattern when gas carburizing the steel material obtained in the experimental example. 図5は実験例で得られた鋼材を真空浸炭するときのヒートパターンを示す図である。FIG. 5 is a diagram showing a heat pattern when vacuum carburizing the steel material obtained in the experimental example. 図6は式(1)の左辺(A/[Nb])と最大結晶粒の粒度番号との関係を示す図である。FIG. 6 is a diagram showing the relationship between the left side (A / [Nb]) of equation (1) and the grain size number of the largest crystal grain.

本発明は、部品形状に加工した後で表面硬化処理するのに適した鋼材、すなわち肌焼鋼を対象とする。そして表面硬化処理における加熱時に結晶粒が粗大化するのを防止するため、Nbが添加されている。Nbは、微細な介在物(炭化物、炭窒化物など)を形成し、表面硬化処理の加熱時に結晶粒が粗大化するのを防止するのに有用である。この効果を有効に発揮させるため、Nbは、0.01%以上、好ましくは0.015%以上、さらに好ましくは0.020%以上とした。なお従来は、この程度のNb添加量では、結晶粒粗大化防止効果が不足するが、後述するように本発明では、鋳造後のNbがその後に固溶しないようにしているため、微量なNb添加でも有効活用でき、十分な結晶粒粗大化防止効果を示すことができる。   The present invention is directed to a steel material suitable for surface hardening after being processed into a part shape, that is, case-hardened steel. And Nb is added in order to prevent a crystal grain coarsening at the time of the heating in a surface hardening process. Nb is useful for forming fine inclusions (such as carbides and carbonitrides) and preventing crystal grains from becoming coarse during heating in the surface hardening treatment. In order to effectively exhibit this effect, Nb is set to 0.01% or more, preferably 0.015% or more, and more preferably 0.020% or more. Conventionally, with this amount of Nb addition, the effect of preventing the coarsening of crystal grains is insufficient. However, as described later, in the present invention, Nb after casting is prevented from forming a solid solution thereafter, so that a small amount of Nb is added. Even if it is added, it can be used effectively and a sufficient effect of preventing coarsening of crystal grains can be exhibited.

ところでNbが増えると、粗大なNb系介在物が残りやすくなる。そして本発明者らの検討によれば、微細なNb系介在物を多量に生成させても、粗大なNb系介在物が僅かでも残っていると、混粒が生じることが判明した。図1は、この混粒の生成機構を説明するための概念図であって、図1(a)は加熱前の鋼組織を示し、図1(b)は加熱後の鋼組織を示している。加熱前の鋼組織では、図1(a)に示される様に、微細なNb系介在物1が多数存在する中で、1つの粗大なNb系介在物が存在している。この鋼が加熱されると、粗大なNb系介在物2がオストワルド成長し、周辺の微細なNb系介在物1を吸収する。その結果、粗大なNb系介在物2の周辺では、微細なNb系介在物1が疎となり、結晶粒の成長を抑制できなくなる。そのため粗大なNb系介在物2が存在する場所に、粗大な結晶粒(異常粒)12が生成し、混粒が生じる(図1(b))。   By the way, when Nb increases, coarse Nb-based inclusions tend to remain. According to the study by the present inventors, it has been found that even if a large amount of fine Nb-based inclusions are produced, mixed grains are produced if even a small amount of coarse Nb-based inclusions remain. FIG. 1 is a conceptual diagram for explaining the mixed grain formation mechanism. FIG. 1 (a) shows a steel structure before heating, and FIG. 1 (b) shows a steel structure after heating. . In the steel structure before heating, as shown in FIG. 1A, a large number of fine Nb-based inclusions 1 exist, and one coarse Nb-based inclusion exists. When this steel is heated, coarse Nb-based inclusions 2 are Ostwald-grown, and the surrounding fine Nb-based inclusions 1 are absorbed. As a result, the fine Nb-based inclusions 1 are sparse around the coarse Nb-based inclusions 2 and the growth of crystal grains cannot be suppressed. Therefore, coarse crystal grains (abnormal grains) 12 are generated in the place where the coarse Nb-based inclusions 2 are present, and mixed grains are generated (FIG. 1B).

そこで本発明では、粗大なNb系介在物を根絶するために、Nbの添加量を必要最小限に絞ることとした。図2(a)は、Nb添加量を必要最小限に絞ったときの鋼組織であり、図2(b)は、この鋼組織を表面硬化処理の為に加熱した後の鋼組織を示す。図2(a)に示される様に、Nbの添加量を必要最小限に絞ると、微細なNb系介在物1が殆どとなる鋼組織を形成できる。このような鋼組織にしておけば、図2(b)に示されるように、微細なNb系介在物1の消失を防止でき、鋼全体に亘って結晶粒粗大化防止効果を示され、異常粒(混粒)を防止できる。Nb添加量は、0.05%以下、好ましくは0.045%以下、さらに好ましくは0.040%以下である。   Therefore, in the present invention, in order to eradicate coarse Nb-based inclusions, the amount of Nb added is limited to the necessary minimum. FIG. 2A shows a steel structure when the Nb addition amount is reduced to a necessary minimum, and FIG. 2B shows the steel structure after the steel structure is heated for surface hardening treatment. As shown in FIG. 2A, when the amount of Nb added is reduced to the necessary minimum, a steel structure in which the fine Nb-based inclusions 1 are almost formed can be formed. If such a steel structure is used, as shown in FIG. 2 (b), the disappearance of fine Nb-based inclusions 1 can be prevented, and the effect of preventing grain coarsening is shown throughout the steel. Particles (mixed particles) can be prevented. The Nb addition amount is 0.05% or less, preferably 0.045% or less, and more preferably 0.040% or less.

本発明の肌焼鋼は、さらにC:0.1〜0.3%、Si:1.5%以下(0%を含まない)、Mn:2%以下(0%を含まない)、及びCr:2.5%以下(0%を含まない)を必須元素として含有する。各成分の添加理由は、以下の通りである。   The case-hardened steel of the present invention further includes C: 0.1 to 0.3%, Si: 1.5% or less (not including 0%), Mn: 2% or less (not including 0%), and Cr : 2.5% or less (excluding 0%) is contained as an essential element. The reason for adding each component is as follows.

Cは部品として必要な芯部硬さを確保する上で重要な元素であり、少ないと硬さ不足により、部品としての静的強度が不足する。逆にCが多すぎると硬くなりすぎ、鍛造性や切削性が低下する。従ってCは、0.1〜0.3%、好ましくは0.12〜0.28%である。さらに好ましくは0.15〜0.25%とする。   C is an important element for securing the core hardness necessary for a part, and if it is small, the static strength as a part is insufficient due to insufficient hardness. On the contrary, when C is too much, it becomes too hard, and forgeability and machinability deteriorate. Therefore, C is 0.1 to 0.3%, preferably 0.12 to 0.28%. More preferably, the content is 0.15 to 0.25%.

Siは焼戻し処理時の硬さ低減を抑制するため、表面硬化処理部品表層の硬さを確保するのに有効な元素である。しかし、添加量の増大に伴って材料の変形抵抗が増し、鍛造性を低下させる。従ってSiは、1.5%以下、好ましくは0.03〜1.3%、さらに好ましくは0.1〜1.0%とする。   Si is an effective element for ensuring the hardness of the surface layer of the surface-hardened treated part in order to suppress the hardness reduction during the tempering process. However, as the addition amount increases, the deformation resistance of the material increases and the forgeability decreases. Therefore, Si is 1.5% or less, preferably 0.03 to 1.3%, more preferably 0.1 to 1.0%.

Mnは脱酸材として作用し酸化物系介在物量を低減して鋼材の内部品質を高める作用を発揮するとともに、表面硬化処理(浸炭など)後の焼き入れ時の焼入性を著しく向上させる効果を持つ。しかし、Mnの増加に伴い縞状偏析が顕著となり、材質のバラツキが大きくなって冷間加工性に悪影響を与える。従ってMnは、2%以下、好ましくは0.1〜1.5%、さらに好ましくは0.3〜1.0%とする。   Mn acts as a deoxidizer, reduces the amount of oxide inclusions and enhances the internal quality of the steel, and significantly improves the hardenability during quenching after surface hardening (such as carburizing) have. However, as the Mn increases, striped segregation becomes prominent, resulting in large variations in material and adversely affecting cold workability. Therefore, Mn is 2% or less, preferably 0.1 to 1.5%, more preferably 0.3 to 1.0%.

Crは、Mnと同様に表面硬化処理(浸炭など)後の焼き入れ時の焼入性を著しく向上させる効果を持つ。またCrは、炭化物に固溶して炭化物の硬さを向上させる効果があるため耐摩耗性の向上に有効である。そのため歯車や軸受などの摺動部品には適量添加する。ところが過度に含有させると、素材の硬度が高くなりすぎて被削性、鍛造性が不良となる。従ってCrは、2.5%以下、好ましくは0.3〜2.0%、さらに好ましくは0.6〜1.5%とする。   Cr, like Mn, has the effect of significantly improving the hardenability during quenching after surface hardening (such as carburizing). In addition, Cr is effective in improving wear resistance because it has the effect of improving the hardness of the carbide by dissolving in the carbide. Therefore, an appropriate amount is added to sliding parts such as gears and bearings. However, if it is contained excessively, the hardness of the material becomes too high and the machinability and forgeability become poor. Therefore, Cr is 2.5% or less, preferably 0.3 to 2.0%, more preferably 0.6 to 1.5%.

本発明の肌焼鋼は、必要に応じて他の成分を含有していてもよい。他の成分としては、Mo、B、Cu、Niなどが例示でき、これらは単独で添加してもよく、適宜組み合わせて添加してもよい。Mo、B、Cu、Niなどの好ましい添加量及び添加理由は、以下の通りである。   The case hardening steel of this invention may contain the other component as needed. Examples of other components include Mo, B, Cu, Ni, and the like. These may be added alone or in appropriate combination. Preferred addition amounts and reasons for addition of Mo, B, Cu, Ni, etc. are as follows.

Mo:2.0%以下(0%を含まない)
Moは表面硬化処理(浸炭など)後の焼入れ時の焼入性を著しく向上させる効果を持つのに加え、耐衝撃強度の向上に有効である。しかし、過度に添加すると素材硬さが高くなるため被削性が不良となる。従ってMoは、2.0%以下、好ましくは0.01〜1.0%、さらに好ましくは0.1〜0.5%とする。
Mo: 2.0% or less (excluding 0%)
Mo has an effect of remarkably improving the hardenability at the time of quenching after surface hardening treatment (such as carburizing), and is effective in improving the impact strength. However, if it is added excessively, the material hardness increases, so that the machinability becomes poor. Therefore, Mo is 2.0% or less, preferably 0.01 to 1.0%, more preferably 0.1 to 0.5%.

B:0.005%以下(0%を含まない)
Bは微量で鋼材の焼入性を大幅に向上させる効果があることに加え、結晶粒界を強化し衝撃強度を高める作用があるため添加してもよい。しかし、過剰に添加すると、窒化物を生成して冷間及び熱間加工性を低下させる。従ってBは、0.005%以下、好ましくは0.0001〜0.004%、さらに好ましくは0.001〜0.003%とする。
B: 0.005% or less (excluding 0%)
B may be added in a small amount because it has the effect of significantly improving the hardenability of the steel material and has the effect of strengthening the grain boundaries and increasing the impact strength. However, if added excessively, nitrides are produced and cold and hot workability are reduced. Therefore, B is 0.005% or less, preferably 0.0001 to 0.004%, more preferably 0.001 to 0.003%.

Cu:0.1%以下(0%を含まない)
CuはFeより酸化されにくい元素であるため、鋼材の耐食性を向上させる。しかし、過剰に添加すると、鋼材の熱間延性が低下する。従ってCuは、0.1%以下、好ましくは0.01〜0.05%、さらに好ましくは0.01〜0.03%とする。
Cu: 0.1% or less (excluding 0%)
Since Cu is an element that is less likely to be oxidized than Fe, it improves the corrosion resistance of the steel material. However, when it adds excessively, the hot ductility of steel materials will fall. Therefore, Cu is 0.1% or less, preferably 0.01 to 0.05%, more preferably 0.01 to 0.03%.

Ni:3%以下(0%を含まない)
NiはCuとともに鋼材の耐食性を向上させる元素であり、単独で添加してもよいが、Cuと組み合わせて添加することが望ましい。また、Niは鋼材の耐衝撃性を向上させる効果もある。しかし過剰に添加すると鋼材の製造コストが上昇する。従ってNiは、3%以下、好ましくは0.01〜2.5%、さらに好ましくは0.03〜2.0%とする。
Ni: 3% or less (excluding 0%)
Ni is an element that improves the corrosion resistance of the steel together with Cu, and may be added alone, but it is desirable to add it in combination with Cu. Ni also has the effect of improving the impact resistance of the steel material. However, when it adds excessively, the manufacturing cost of steel materials will rise. Therefore, Ni is 3% or less, preferably 0.01 to 2.5%, more preferably 0.03 to 2.0%.

本発明の肌焼鋼では、上記以外の成分(残部)は、通常、鉄及び不可避的不純物である。なお不可避的不純物とは、原料(主原料、副原料など)や製造設備などから混入してくる不純物を意味し、例えば、P、S、Al、Nなどが挙げられる。P、S、Al、Nなどの好ましい量は、以下の通りである。   In the case-hardened steel of the present invention, the components other than the above (remainder) are usually iron and inevitable impurities. The inevitable impurities mean impurities mixed in from raw materials (main raw materials, auxiliary raw materials, etc.) and manufacturing equipment, and examples thereof include P, S, Al, and N. Preferred amounts of P, S, Al, N, etc. are as follows.

P:0.03%以下(0%を含まない)
Pは結晶粒界に偏析して部品の衝撃特性を低減させるため、少ないほど好ましい。従ってPは、例えば、0.03%以下、好ましくは0.02%以下、さらに好ましくは0.015%以下とする。
P: 0.03% or less (excluding 0%)
P is preferably as small as possible because it segregates at the grain boundaries and reduces the impact characteristics of the part. Therefore, P is, for example, 0.03% or less, preferably 0.02% or less, and more preferably 0.015% or less.

S:0.03%以下(0%を含まない)
SはMnと結合してMnS系介在物を生成し、部品の疲労強度、衝撃強度を低下させるためなるべく低減する方が好ましい。従ってSは、例えば、0.03%以下、好ましくは0.025%以下、さらに好ましくは0.020%以下とする。なおSは、切削性向上に寄与する場合がある。従ってSは、例えば、0.001%以上、好ましくは0.005%以上、さらに好ましくは0.010%以上としてもよい。
S: 0.03% or less (excluding 0%)
It is preferable that S is reduced as much as possible in order to combine with Mn to produce MnS inclusions and reduce the fatigue strength and impact strength of the part. Therefore, S is, for example, 0.03% or less, preferably 0.025% or less, and more preferably 0.020% or less. Note that S may contribute to improvement in machinability. Therefore, S may be, for example, 0.001% or more, preferably 0.005% or more, and more preferably 0.010% or more.

Al:0.06%以下(0%を含まない)
Alは溶製時に脱酸材として作用して酸化物系介在物量を低減して鋼材の内部品質を高める作用を示すが、スラグとして除去しきれずに残ったAlは粗大で硬い非金属介在物(Al23)を生成して疲労特性を低下させるなど、不純物として作用する。従って鋼中に残るAlは少ないほど好ましく、例えば、0.06%以下、好ましくは0.04%以下、さらに好ましくは0.02%以下とする。
Al: 0.06% or less (excluding 0%)
Al acts as a deoxidizer during melting and reduces the amount of oxide inclusions to increase the internal quality of the steel, but the remaining Al that cannot be removed as slag is coarse and hard non-metallic inclusions ( It acts as an impurity, for example, by generating Al 2 O 3 ) and reducing fatigue characteristics. Therefore, the less Al remaining in the steel, the better. For example, 0.06% or less, preferably 0.04% or less, and more preferably 0.02% or less.

N:0.05%以下(0%を含まない)
Nが多いと粗大なNb系介在物が生成して衝撃強度を低下させるとともに、鋼材の硬さ、変形抵抗を増大させ鍛造性が低下する。従ってNは少ないほど好ましく、例えば、0.05%以下、好ましくは0.04%以下、さらに好ましくは0.03%以下とする。なおNを完全に除去することはできず、むしろどうしても残るN(例えば、0.005%以上、好ましくは0.010%以上、さらに好ましくは0.015%以上のN)は、微細なNb系介在物を生成するのに利用される。
N: 0.05% or less (excluding 0%)
When N is large, coarse Nb-based inclusions are generated and impact strength is lowered, and the hardness and deformation resistance of the steel material are increased, and forgeability is lowered. Accordingly, N is preferably as small as possible, for example, 0.05% or less, preferably 0.04% or less, and more preferably 0.03% or less. Note that N cannot be completely removed, but the remaining N (for example, 0.005% or more, preferably 0.010% or more, more preferably 0.015% or more) is a fine Nb-based material. Used to generate inclusions.

本発明の肌焼鋼では、上述した通り、Nb量を必要最小限に抑制しており、これをできるだけ固溶させることなく利用する。このようにすることで、微細なNb系介在物を確保した上で、粗大なNb系介在物を著しく低減できる。粗大なNb系介在物を著しく低減することで、最大結晶粒を縮小化でき、混粒を防止できる。また冷間鍛造性も向上できる。なおNb添加量が少なくなるほど、粗大なNb系介在物の量も少なくなるため、粗大なNb系介在物の許容量はNb添加量に応じて定める。すなわち本発明の肌焼鋼は、式(1)を満足する。
A/[Nb]≦0.7 …(1)
(式中、Aは、面積20μm2以上のNb系介在物の面積率(%)を示す。[Nb]は鋼中のNb含有量(質量%)を示す)
In the case hardening steel of the present invention, as described above, the amount of Nb is suppressed to the minimum necessary, and this is utilized without making it as solid as possible. By doing in this way, while ensuring a fine Nb-type inclusion, a coarse Nb-type inclusion can be reduced significantly. By significantly reducing coarse Nb-based inclusions, the maximum crystal grains can be reduced and mixed grains can be prevented. Also, cold forgeability can be improved. In addition, since the amount of coarse Nb-based inclusions decreases as the Nb addition amount decreases, the allowable amount of coarse Nb-based inclusions is determined according to the Nb addition amount. That is, the case-hardened steel of the present invention satisfies the formula (1).
A / [Nb] ≦ 0.7 (1)
(In the formula, A represents the area ratio (%) of Nb-based inclusions having an area of 20 μm 2 or more. [Nb] represents the Nb content (mass%) in the steel)

式(1)は面積20μm2以上のNb系介在物を粗大な介在物として位置づけ、その量が低減されていることを意味する。面積20μm2を基準としたのは、Nb系介在物がオストワルド成長するには一定以上のサイズが必要なためである。好ましい式(1)の左辺(A/[Nb])は、0.6以下、特に0.5以下である。なお式(1)の左辺(A/[Nb])の下限は特に制限されないが、小さくし過ぎても制御が難しくなるだけであって効果が飽和する。従って式(1)の左辺(A/[Nb])の下限は、例えば、0.01以上(特に0.1以上)であってもよい。 Formula (1) means that Nb-based inclusions having an area of 20 μm 2 or more are positioned as coarse inclusions, and the amount thereof is reduced. The reason why the area is 20 μm 2 is that the Nb-based inclusions require a certain size or more for Ostwald growth. The left side (A / [Nb]) of the preferred formula (1) is 0.6 or less, particularly 0.5 or less. Note that the lower limit of the left side (A / [Nb]) of equation (1) is not particularly limited, but even if it is too small, the control only becomes difficult and the effect is saturated. Therefore, the lower limit of the left side (A / [Nb]) of the formula (1) may be, for example, 0.01 or more (particularly 0.1 or more).

本発明の肌焼鋼は、上記範囲に成分調整した鋳片を、Nb系介在物をできるだけ固溶させることなく加工(圧延など)することによって製造できる。例えば線材(棒鋼など)を製造する際には、分塊圧延、熱間圧延などするが、これらの加熱の際にNbの固溶を防止する。分塊圧延や熱間圧延の加熱温度は、鋼種に応じて適宜設定されるが、1100℃以上の温度に加熱して分塊圧延する際には、Nb系介在物が固溶し易くなるため、1100℃以上に加熱して分塊圧延するときの加熱時間を厳密に制御することが推奨される。 The case-hardened steel of the present invention can be produced by processing (rolling or the like) a slab whose component has been adjusted to the above range, without causing Nb-based inclusions to dissolve as much as possible. For example, when producing a wire (such as a steel bar), a block rolling, a hot rolling or the like is performed, but the solid solution of Nb is prevented during the heating. Although the heating temperature of the partial rolling and hot rolling is appropriately set according to the steel type, when heating to a temperature of 1100 ° C. or higher and performing the partial rolling , the Nb-based inclusions are easily dissolved. It is recommended to strictly control the heating time t when heating to 1100 ° C. or higher and performing batch rolling .

本発明の肌焼鋼は、温度1100〜1350℃に加熱してから分塊圧延し、次いで温度850〜1050℃に再加熱してから熱間圧延することによって製造されることが多い。従って分塊圧延の加熱時間を極力短くすることが推奨され、例えば、分塊圧延の加熱温度T1(℃)と加熱時間t(分)が式(3)を満足するようにすることが望ましい。
(T1+273)×log10(t×60)<4000 …(3)
式(3)の左辺((T1+273)×log10(t×60))はさらに小さくてもよく、例えば、2000以下、特に0以下であってもよい。
The case-hardened steel of the present invention is often manufactured by heating to a temperature of 1100 to 1350 ° C., then performing batch rolling, then reheating to a temperature of 850 to 1050 ° C. and then hot rolling. Therefore, it is recommended to shorten the heating time of the partial rolling as much as possible. For example, it is desirable that the heating temperature T1 (° C.) and the heating time t (minute) of the partial rolling satisfy the expression (3).
(T1 + 273) × log 10 (t × 60) <4000 (3)
The left side of (3) ((T1 + 273) × log 10 (t × 60)) may be even smaller, for example, 2000 or less, particularly 0 or less.

またNbの固溶をできるだけ防止するためには、温度1100〜1350℃への加熱を速やかに行うことが望ましい。温度1100〜1350℃に加熱する際の平均加熱速度(室温から最高温度まで加熱するのに要した時間と、その間の上昇温度で定まる加熱速度)は、例えば、100℃/h以上、好ましくは200℃/h以上(例えば、200〜300℃/h程度)、特に250℃/h以上である。   In order to prevent Nb from being dissolved as much as possible, it is desirable to quickly heat to a temperature of 1100 to 1350 ° C. The average heating rate at the time of heating to 1100 to 1350 ° C. (the time required for heating from room temperature to the maximum temperature and the heating rate determined by the rising temperature therebetween) is, for example, 100 ° C./h or more, preferably 200 C / h or more (for example, about 200 to 300 ° C./h), particularly 250 ° C./h or more.

上記のようにして得られた肌焼鋼は、冷間加工などによって適当な部品(例えば、歯車、シャフト類、無段変速機(CVT)プーリ、等速ジョイント(CVJ)、軸受など)の形状にした後、表面硬化処理(浸炭、窒化、浸炭窒化など。特に、浸炭又は浸炭窒化処理)することで、鋼部品にできる。   The case-hardened steel obtained as described above has the shape of appropriate parts (for example, gears, shafts, continuously variable transmission (CVT) pulley, constant velocity joint (CVJ), bearing, etc.) by cold working or the like. Then, surface hardening treatment (carburizing, nitriding, carbonitriding, etc., in particular carburizing or carbonitriding) can be used to make steel parts.

以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも勿論可能であり、それらはいずれも本発明の技術的範囲に包含される。   EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

実験例1
転炉溶製によって表1に示す成分の鋳片を作製し、この鋳片を所定温度まで加熱した後分塊圧延することによって大きさ155mm×155mm×10mのビレットを得た。得られたビレットを再加熱して熱間圧延(棒鋼圧延)することで、直径46mmの棒鋼を製造した。分塊圧延前の加熱条件及び熱間圧延(棒鋼圧延)前の加熱条件は、表2に示す通りである。なお分塊圧延前の加熱速度は、表3及び表4に示す。
Experimental example 1
A slab having the components shown in Table 1 was prepared by melting in a converter, and the slab was heated to a predetermined temperature and then subjected to block rolling to obtain a billet having a size of 155 mm × 155 mm × 10 m. The obtained billet was reheated and hot-rolled (steel rolling) to produce a steel bar having a diameter of 46 mm. Table 2 shows the heating conditions before the block rolling and the heating conditions before the hot rolling (bar rolling). Tables 3 and 4 show the heating rates before the batch rolling.

実験例1で得られた棒鋼の各特性を以下のようにして評価した。
1)冷間鍛造性(70%プレス)
棒鋼を温度760℃で5時間加熱した後、8時間かけて680℃まで冷却してから炉冷した(球状化焼鈍又は軟化焼鈍。図3)。焼鈍後の棒鋼から直径15mm×高さ22.5mmの円柱状試験片を切り出し、この試験片を高さ方向に圧縮した(加工率70%)。試験片の表面を実体顕微鏡(倍率20倍)で観察して割れの有無を確認し、以下の基準に基づいて冷間鍛造性を評価した。
良好:割れ無し
不良:割れ有り
Each characteristic of the steel bar obtained in Experimental Example 1 was evaluated as follows.
1) Cold forgeability (70% press)
The steel bar was heated at a temperature of 760 ° C. for 5 hours, then cooled to 680 ° C. over 8 hours, and then furnace-cooled (spheroidizing annealing or softening annealing. FIG. 3). A cylindrical test piece having a diameter of 15 mm and a height of 22.5 mm was cut out from the annealed steel bar, and the test piece was compressed in the height direction (processing rate: 70%). The surface of the test piece was observed with a stereomicroscope (magnification 20 times) to confirm the presence or absence of cracks, and the cold forgeability was evaluated based on the following criteria.
Good: No cracking Bad: Cracking

2)面積20μm2以上のNb系介在物の面積率(A)
棒鋼のt/4(tは棒鋼の直径)位置からL断面(軸心を含む断面)のサンプルを切り出し、研磨した。研磨面をEPMA(Electron Probe Microanalyzer)で測定した。面積が20μm2以上の介在物の組成を調べ、Nb含有量が5質量%以上の介在物をNb系介在物とし、その面積率を算出した。EPMAの測定条件は下記の通りである。
2) Area ratio of Nb inclusions with an area of 20 μm 2 or more (A)
A sample of the L cross section (cross section including the axis) was cut out from the t / 4 (t is the diameter of the steel bar) position of the steel bar and polished. The polished surface was measured with EPMA (Electron Probe Microanalyzer). The composition of inclusions having an area of 20 μm 2 or more was examined, and inclusions having an Nb content of 5% by mass or more were defined as Nb inclusions, and the area ratio was calculated. The measurement conditions of EPMA are as follows.

EPMA分析装置:JXA−8100型電子プローブマイクロアナライザー(日本電気株式会社製)
分析装置(EDS):SystemSix(サーモフィッシャーサイエンティフィック社製)
加速電圧:15kV
操作電流:4nA
測定面積:100mm2以上
観察倍率:200倍
EPMA analyzer: JXA-8100 type electron probe microanalyzer (manufactured by NEC Corporation)
Analyzer (EDS): SystemSix (manufactured by Thermo Fisher Scientific)
Acceleration voltage: 15 kV
Operating current: 4nA
Measurement area: 100 mm 2 or more Observation magnification: 200 times

3)混粒防止特性(最大結晶粒の粒度番号)
棒鋼を図3に示す焼鈍処理した後、切削加工して円柱体(直径15mm×高さ22.5mm)を作成し、ストローク速度18spm(平均歪速度8.5秒-1)で75%の圧縮加工を行って試験片を作製した。
3) Mixed grain prevention properties (size number of the largest crystal grain)
After the steel bar was annealed as shown in FIG. 3, it was cut to create a cylindrical body (diameter 15 mm × height 22.5 mm), and 75% compression at a stroke speed of 18 spm (average strain speed of 8.5 sec −1 ). Processing was performed to produce a test piece.

得られた試験片を図4に示すガス浸炭条件(浸炭期条件:温度950℃、時間70分、浸炭ガス:プロパンガス、カーボンポテンシャル0.8。拡散期条件:温度850℃、時間60分、浸炭ガス:プロパンガス、カーボンポテンシャル0.8。焼入れ条件:80℃、油冷)又は図5に示す真空浸炭条件(真空浸炭期条件:温度950℃、時間29分、浸炭ガス:アセチレンガス。拡散期条件:温度860℃、時間49分、浸炭ガス:アセチレンガス、カーボンポテンシャル0.8。焼入れ条件:60℃、油冷)で処理した。   The obtained test piece was subjected to gas carburizing conditions shown in FIG. 4 (carburizing condition: temperature 950 ° C., time 70 minutes, carburizing gas: propane gas, carbon potential 0.8. Diffusion period condition: temperature 850 ° C., time 60 minutes, Carburizing gas: propane gas, carbon potential 0.8, quenching conditions: 80 ° C., oil cooling) or vacuum carburizing conditions (vacuum carburizing period conditions: temperature 950 ° C., time 29 minutes), carburizing gas: acetylene gas. Periodic conditions: temperature 860 ° C., time 49 minutes, carburizing gas: acetylene gas, carbon potential 0.8, quenching conditions: 60 ° C., oil cooling).

相当歪0.7となる箇所の旧オーステナイト粒の粒度番号GhをJIS G0551に従って求めた。より詳細には、計数方法(附属書3)によって、平均結晶粒度番号を求めた。また観察視野800μm×800μmの中で最も粗大な結晶粒の粒度番号を比較法によって求め、これを最大結晶粒度番号とした。
結果を表3〜4に示す。
また式(1)の左辺(A/[Nb])を計算し、表3〜4に示す。さらにこの左辺(A/[Nb])と最大結晶粒との関係を図6に示す。
The grain size number Gh of the prior austenite grains at the location where the equivalent strain was 0.7 was determined according to JIS G0551. More specifically, the average grain size number was determined by a counting method (Appendix 3). Further, the grain size number of the coarsest crystal grain in the observation field of view 800 μm × 800 μm was determined by a comparative method, and this was set as the maximum crystal grain size number.
The results are shown in Tables 3-4.
Moreover, the left side (A / [Nb]) of Formula (1) is calculated and shown in Tables 3-4. Further, the relationship between the left side (A / [Nb]) and the maximum crystal grain is shown in FIG.

No.48〜49に示すようにNbが過剰な場合には、製造条件V〜VIを採用して溶体化処理を十分にしても、最大の結晶粒を小さくすることはできず、混粒状態を生じる。
これらに対して、Nbの添加量を必要最小限にまで絞り込み、Nb析出物の僅かな固溶すら防止すべく製造条件I〜IVを採用すると(No.1〜43)、微細なNb系介在物を確保しつつも粗大なNb系介在物を極めて小さくでき、式(1)の左辺(A/[Nb])を小さくできるため、結晶粒の粗大化を防止すると共に最大の結晶粒も小さくできる(混粒を防止できる)。
No. When Nb is excessive as shown in 48 to 49, even if the manufacturing conditions V to VI are adopted and the solution treatment is sufficient, the maximum crystal grain cannot be reduced, and a mixed grain state is generated. .
On the other hand, when Nb addition amount is narrowed down to the necessary minimum and manufacturing conditions I to IV are employed to prevent even a slight solid solution of Nb precipitates (No. 1 to 43), fine Nb-based intervening Coarse Nb-based inclusions can be made extremely small while securing the material, and the left side (A / [Nb]) of formula (1) can be made small, so that the crystal grains can be prevented from becoming coarse and the maximum crystal grains can be made small. Yes (can prevent mixed grains).

なおNbの量が不足すると(No.44〜47)、平均の結晶粒が粗大化する。また粗大な介在物の面積率A自体は小さくなるが、Nb量自体が少なくなっているため、式(1)の左辺(A/[Nb])が大きくなる。そのため最大の結晶粒を小さくできない。   When the amount of Nb is insufficient (Nos. 44 to 47), the average crystal grains become coarse. Moreover, although the area ratio A itself of a coarse inclusion becomes small, since the Nb amount itself is small, the left side (A / [Nb]) of Formula (1) becomes large. Therefore, the maximum crystal grain cannot be reduced.

本発明の肌焼鋼は、加工性(特に冷間鍛造性)に優れ、表面硬化処理後の混粒を防止できるため、自動車、建築機械、その他産業機械における鋼部品(例えば、歯車、シャフト類、無段変速機(CVT)プーリ、等速ジョイント(CVJ)、軸受など)を製造するのに有用である。   The case-hardened steel of the present invention is excellent in workability (especially cold forgeability) and can prevent mixed grains after the surface hardening treatment. Therefore, steel parts (for example, gears, shafts) in automobiles, construction machinery, and other industrial machines. , Continuously variable transmission (CVT) pulley, constant velocity joint (CVJ), bearing, etc.).

1 微細なNb系介在物
2 粗大なNb系介在物
11 微細な結晶粒
12 粗大な結晶粒
1 Fine Nb-based inclusions 2 Coarse Nb-based inclusions 11 Fine crystal grains 12 Coarse crystal grains

Claims (6)

C :0.1〜0.3%(質量%の意味。化学成分の含有量について%を使う場合は、以下、同じく質量%を意味するものとする)、
Si:1.5%以下(0%を含まない)、
Mn:2%以下(0%を含まない)、
Cr:2.5%以下(0%を含まない)、及び
Nb:0.01〜0.05%
を含有し、残部が鉄及び不可避的不純物からなり、式(1)を満足すると共に、旧オーステナイト粒の最大結晶粒度番号が5.2番以上であることを特徴とする最大結晶粒の縮小化特性に優れた肌焼鋼。
A/[Nb]≦0.7 …(1)
(式中、Aは、面積20μm2以上のNb系介在物の面積率(%)を示す。[Nb]は鋼中のNb含有量(質量%)を示す)
C: 0.1 to 0.3% (meaning mass%. When using% for the content of chemical components, hereinafter, the same shall mean mass%),
Si: 1.5% or less (excluding 0%),
Mn: 2% or less (excluding 0%),
Cr: 2.5% or less (excluding 0%), and Nb: 0.01 to 0.05%
The balance is made of iron and inevitable impurities, satisfies the formula (1), and the maximum grain size number of the prior austenite grains is 5.2 or more. Case-hardened steel with excellent properties.
A / [Nb] ≦ 0.7 (1)
(In the formula, A represents the area ratio (%) of Nb-based inclusions having an area of 20 μm 2 or more. [Nb] represents the Nb content (mass%) in the steel)
前記不可避不純物には、P、S、Al、及びNが含まれ、これらの含有量が以下の通りである請求項1に記載の肌焼鋼。
P :0.03%以下(0%を含まない)
S :0.03%以下(0%を含まない)
Al:0.06%以下(0%を含まない)
N :0.05%以下(0%を含まない)
The case-hardened steel according to claim 1, wherein the inevitable impurities include P, S, Al, and N, and the contents thereof are as follows.
P: 0.03% or less (excluding 0%)
S: 0.03% or less (excluding 0%)
Al: 0.06% or less (excluding 0%)
N: 0.05% or less (excluding 0%)
さらにMo:2.0%以下(0%を含まない)を含有する請求項1又は2に記載の肌焼鋼。   Furthermore, the case hardening steel of Claim 1 or 2 containing Mo: 2.0% or less (excluding 0%). さらにB:0.005%以下(0%を含まない)を含有する請求項1〜3のいずれかに記載の肌焼鋼。   Furthermore, B: 0.005% or less (0% is not included) The case hardening steel in any one of Claims 1-3. さらにCu:0.1%以下(0%を含まない)及びNi:3%以下(0%を含まない)から選択される少なくとも一種を含有する請求項1〜4のいずれかに記載の肌焼鋼。   Furthermore, skin hardening in any one of Claims 1-4 containing at least 1 type selected from Cu: 0.1% or less (excluding 0%) and Ni: 3% or less (not including 0%). steel. 請求項1〜5のいずれかに記載の肌焼鋼を冷間加工した後、表面硬化熱処理した鋼材。   A steel material subjected to surface hardening heat treatment after cold working the case-hardened steel according to any one of claims 1 to 5.
JP2009070684A 2009-03-23 2009-03-23 Case-hardened steel with excellent maximum grain reduction characteristics Expired - Fee Related JP5503170B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2009070684A JP5503170B2 (en) 2009-03-23 2009-03-23 Case-hardened steel with excellent maximum grain reduction characteristics

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2009070684A JP5503170B2 (en) 2009-03-23 2009-03-23 Case-hardened steel with excellent maximum grain reduction characteristics

Publications (2)

Publication Number Publication Date
JP2010222634A JP2010222634A (en) 2010-10-07
JP5503170B2 true JP5503170B2 (en) 2014-05-28

Family

ID=43040141

Family Applications (1)

Application Number Title Priority Date Filing Date
JP2009070684A Expired - Fee Related JP5503170B2 (en) 2009-03-23 2009-03-23 Case-hardened steel with excellent maximum grain reduction characteristics

Country Status (1)

Country Link
JP (1) JP5503170B2 (en)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP5643622B2 (en) * 2010-11-30 2014-12-17 株式会社神戸製鋼所 Case-hardened steel and machine structural parts using the same
US9410232B2 (en) 2011-11-01 2016-08-09 Nippon Steel & Sumitomo Metal Corporation Method for producing steel component
JP5737193B2 (en) * 2012-01-06 2015-06-17 新日鐵住金株式会社 Processing crack sensitivity evaluation method
JP6211784B2 (en) * 2013-03-29 2017-10-11 山陽特殊製鋼株式会社 Manufacturing method of automotive machine parts having excellent fatigue strength and automotive machine parts by the method
JP5790693B2 (en) * 2013-03-29 2015-10-07 Jfeスチール株式会社 Case-hardened steel for cold forging
CN109628834A (en) * 2018-12-29 2019-04-16 中国第汽车股份有限公司 A kind of nickelic niobium-containing high-strength carburizing Steel material of heavy-duty transmission axis tooth part

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6660105B1 (en) * 1997-07-22 2003-12-09 Nippon Steel Corporation Case hardened steel excellent in the prevention of coarsening of particles during carburizing thereof, method of manufacturing the same, and raw shaped material for carburized parts
JP4149576B2 (en) * 1998-08-24 2008-09-10 株式会社神戸製鋼所 Method for producing high-temperature carburizing steel and high-temperature carburizing steel obtained by the method
JP3804041B2 (en) * 2000-03-28 2006-08-02 新日本製鐵株式会社 High temperature carburizing steel with excellent high temperature carburizing properties and hot forged parts for high temperature carburizing
JP3954772B2 (en) * 2000-04-26 2007-08-08 新日本製鐵株式会社 Shaped material for high-temperature carburized parts with excellent grain coarsening prevention characteristics and manufacturing method thereof
JP3907986B2 (en) * 2001-09-14 2007-04-18 山陽特殊製鋼株式会社 Method for producing case-hardened steel with excellent cold workability and grain size characteristics
JP4212941B2 (en) * 2003-03-31 2009-01-21 愛知製鋼株式会社 Method for manufacturing hot forged parts for high temperature carburizing and hot forged parts for high temperature carburizing manufactured by the method
JP4956146B2 (en) * 2005-11-15 2012-06-20 株式会社神戸製鋼所 Case-hardened steel excellent in forgeability and prevention of grain coarsening, its manufacturing method, and carburized parts

Also Published As

Publication number Publication date
JP2010222634A (en) 2010-10-07

Similar Documents

Publication Publication Date Title
JP5432105B2 (en) Case-hardened steel and method for producing the same
JP5385656B2 (en) Case-hardened steel with excellent maximum grain reduction characteristics
JP4775506B1 (en) Bearing steel
JP5862802B2 (en) Carburizing steel
JP5231101B2 (en) Machine structural steel with excellent fatigue limit ratio and machinability
JP5400089B2 (en) Bearing steel excellent in rolling fatigue life characteristics, ingot material for bearing, and production method thereof
JP2007162128A (en) Case hardening steel having excellent forgeability and crystal grain-coarsening prevention property, its production method and carburized component
JP4775505B1 (en) Bearing ingot material with excellent rolling fatigue life and method for producing bearing steel
JP2015096657A (en) Case hardened steel and carburized material
JP4941252B2 (en) Case-hardened steel for power transmission parts
JP5503170B2 (en) Case-hardened steel with excellent maximum grain reduction characteristics
JP4464862B2 (en) Case-hardening steel with excellent grain coarsening resistance and cold workability that can be omitted for soft annealing.
JP4464861B2 (en) Case hardening steel with excellent grain coarsening resistance and cold workability
JP4502929B2 (en) Case hardening steel with excellent rolling fatigue characteristics and grain coarsening prevention characteristics
JP4569961B2 (en) Manufacturing method of parts for ball screw or one-way clutch
JP5649838B2 (en) Case-hardened steel and method for producing the same
JP2012237052A (en) Case-hardened steel excellent in cold forgeability and suppressing ability of crystal grain coarsening, and method for manufacturing the same
JP4488228B2 (en) Induction hardening steel
JP5976581B2 (en) Steel material for bearings and bearing parts with excellent rolling fatigue characteristics
JP5869919B2 (en) Case-hardening bar steel with excellent cold workability
JP6256416B2 (en) Case-hardened steel
JP4411096B2 (en) Steel wire rod and steel bar for case hardening with excellent cold forgeability after spheronization
JP2020164936A (en) Cementation steel and method for producing the same
JP2021028414A (en) Steel for carburized gear, carburized gear, and manufacturing method of carburized gear
JP2011208262A (en) Method for producing case hardening steel having high fatigue strength

Legal Events

Date Code Title Description
A621 Written request for application examination

Free format text: JAPANESE INTERMEDIATE CODE: A621

Effective date: 20110901

A977 Report on retrieval

Free format text: JAPANESE INTERMEDIATE CODE: A971007

Effective date: 20130627

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20130702

A521 Written amendment

Free format text: JAPANESE INTERMEDIATE CODE: A523

Effective date: 20130902

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20131112

A521 Written amendment

Free format text: JAPANESE INTERMEDIATE CODE: A523

Effective date: 20140109

TRDD Decision of grant or rejection written
A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

Effective date: 20140311

R150 Certificate of patent or registration of utility model

Ref document number: 5503170

Country of ref document: JP

Free format text: JAPANESE INTERMEDIATE CODE: R150

A61 First payment of annual fees (during grant procedure)

Free format text: JAPANESE INTERMEDIATE CODE: A61

Effective date: 20140314

LAPS Cancellation because of no payment of annual fees