JP4556770B2 - Carburizing steel and method for producing the same - Google Patents

Carburizing steel and method for producing the same Download PDF

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JP4556770B2
JP4556770B2 JP2005156038A JP2005156038A JP4556770B2 JP 4556770 B2 JP4556770 B2 JP 4556770B2 JP 2005156038 A JP2005156038 A JP 2005156038A JP 2005156038 A JP2005156038 A JP 2005156038A JP 4556770 B2 JP4556770 B2 JP 4556770B2
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伸隆 黒澤
邦和 冨田
高明 豊岡
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JFE Steel Corp
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本発明は、浸炭用鋼およびその製造方法に関し、特に自動車用鋼材や建設機械用鋼材に適用して好適なものである。   The present invention relates to carburizing steel and a method for producing the same, and is particularly suitable for application to steel for automobiles and steel for construction machinery.

自動車のクランクシャフトや歯車には、優れた疲労特性、耐摩耗性および耐ピッチング性が求められ、C量が0.2mass%前後のクロム鋼、クロムモリブデン鋼およびニッケルクロムモリブデン鋼等を所望の形状に成形後、浸炭処理や浸炭窒化処理を施すことにより製造されている。   Crankshafts and gears of automobiles are required to have excellent fatigue characteristics, wear resistance, and pitting resistance. Chromium steel, chrome molybdenum steel, nickel chrome molybdenum steel, etc. with a C content of around 0.2 mass% are in the desired shape. It is manufactured by carburizing or carbonitriding after molding.

上記の浸炭処理や浸炭窒化処理において、焼入れ時に熱処理歪が生じると、歯車の場合には歯形状が狂うため、仕上げ加工、研磨工程が必要となり、また軸条部品の場合には曲がりが生じるため、これを矯正することが必要となり、いずれの場合も生産性が阻害され、コストが上昇する。
かような熱処理歪は、浸炭処理中にオーステナイト結晶粒が粗大化し、焼入れ性が不安定となり、マルチンサイト変態時の膨張による応力不均一に起因して生じるとされ、その解消が課題となっている。
In the above carburizing and carbonitriding processes, if heat treatment distortion occurs during quenching, the tooth shape will be incorrect in the case of gears, and finishing and polishing processes will be required, and in the case of shaft parts, bending will occur. It is necessary to correct this, and in either case, productivity is hindered and costs increase.
It is said that such heat treatment strain is caused by coarsening of austenite grains during carburizing treatment, resulting in unstable hardenability, and non-uniform stress due to expansion during martensitic transformation. Yes.

特許文献1および特許文献2には、鋼の熱履歴とAl,Nb,N量を調整し、AlとNb窒化物のピン止め効果によって粗大粒の発生を抑制することが提案されているが、この技術では粗大粒発生の抑制効果の安定性の点で問題がある。
また、特許文献3および特許文献4には、Al,Nb,Tiなどの窒化物、炭化物、炭窒化物形成元素の含有量と、各析出物の大きさ、分布密度、ベイナイト組織分率、フェライトバンド評点および圧延条件を制御することによって、上記課題の解決を図っているが、種々の寸法形状を圧延により製造する実操業においては、これら多数のパラメータを制御することは事実上困難である。
Patent Document 1 and Patent Document 2 propose that the thermal history of steel and the amounts of Al, Nb, and N are adjusted to suppress the generation of coarse grains by the pinning effect of Al and Nb nitride. This technique has a problem in terms of stability of the effect of suppressing the generation of coarse particles.
Patent Document 3 and Patent Document 4 include the contents of nitrides, carbides, carbonitride-forming elements such as Al, Nb, Ti, etc., the size, distribution density, bainite structure fraction, ferrite of each precipitate. Although the above problems are solved by controlling the band score and rolling conditions, it is practically difficult to control these many parameters in the actual operation of manufacturing various dimensions and shapes by rolling.

上記の問題を解決するものとして、特許文献5には、鋼中のC,Ti,Moの含有量を次式(I)の範囲に制御することにより、浸炭部品をフェライト単相組織とし、フェライト相中に粒径が10nm未満の微細析出物を分散析出させることによって、浸炭処理時の粗大粒の発生を防止し、熱処理歪の少なくすることが提案されている,
0.5 ≦ (C/12)/{(Ti/48)+(Mo/96)}≦ 1.5 ---(I)
しかしながら、特許文献5に記載の技術では、浸炭層以外の内部については、その強度、靱性を十分に確保することができず、上述したクランクシャフトや歯車に適用するには改善の余地を残していた。
As a solution to the above problem, Patent Document 5 discloses that the content of C, Ti, and Mo in steel is controlled within the range of the following formula (I) to make the carburized component a ferrite single phase structure, and ferrite It has been proposed to prevent the generation of coarse particles during carburizing treatment and reduce heat treatment strain by dispersing fine precipitates with a particle size of less than 10 nm in the phase.
0.5 ≤ (C / 12) / {(Ti / 48) + (Mo / 96)} ≤ 1.5 --- (I)
However, the technique described in Patent Document 5 cannot sufficiently secure the strength and toughness of the interior other than the carburized layer, and leaves room for improvement to be applied to the crankshaft and gears described above. It was.

特開昭58−45354号公報JP 58-45354 A 特開昭61−261427号公報JP 61-261427 A 特開平11−50191号公報Japanese Patent Laid-Open No. 11-50191 特開平11−335777号公報JP 11-335777 A 特開2OO3−321731号公報Japanese Patent Laid-Open No. 2OO3-321731

本発明は、上記の実状に鑑み開発されたもので、浸炭層以外の内部の強度および靱性を確保しつつ、浸炭時には結晶粒の微細化を効果的に達成することができる浸炭用鋼を、その有利な製造方法と共に提案することを目的とする。   The present invention was developed in view of the above-mentioned actual situation, while ensuring the internal strength and toughness other than the carburized layer, carburizing steel that can effectively achieve grain refinement during carburizing, The object is to propose together with its advantageous manufacturing method.

さて、発明者らは、上記の課題を解決すべく、浸炭層以外の内部組織について鋭意検討を重ねた結果、以下に述べる知見を得た。
a)浸炭処理後に浸炭層以外の内部組織の強度および強性の向上を図るには、鋼組織を、フェライトと、パーライト及び/又はベイナイトが混在する組織とすることが有利である。
b)上記のような内部組織を得るためには、C含有量を0.1〜0.4mass%程度に高める必要がある。
c)C含有量が多い場合、微細炭化物を析出させるためには、上掲式(I)からも明らかなように、炭化物となって微細析出物を形成するTiやMoの量を増加させる必要があるが、C含有量を高くして、フェライトと、パーライト及び/又はベイナイトが混在する組織にした場合、上掲式(I)を満足するように成分調整を行っても十分な微細析出物は得られない。
As a result of intensive studies on the internal structure other than the carburized layer in order to solve the above problems, the inventors have obtained the following knowledge.
a) In order to improve the strength and strength of the internal structure other than the carburized layer after the carburizing treatment, it is advantageous that the steel structure is a structure in which ferrite and pearlite and / or bainite are mixed.
b) In order to obtain the above internal structure, it is necessary to increase the C content to about 0.1 to 0.4 mass%.
c) When the C content is high, in order to precipitate fine carbides, it is necessary to increase the amount of Ti and Mo that form carbides and form fine precipitates, as is clear from the above formula (I). However, when the C content is increased to make a structure in which ferrite and pearlite and / or bainite are mixed, sufficient fine precipitates can be obtained even if the components are adjusted to satisfy the above formula (I). Cannot be obtained.

そこで、発明者らは、上記の問題を解決すべく鋭意研究を重ねた結果、浸炭処理時に粗大粒の発生を防止するのに有用な微細析出物を効果的に生成させるためには、鋼成分とくに不純物として混入するS,N量を厳密に制御することが重要であることを新たに見出し、本発明を完成するに至ったのである。   Therefore, as a result of intensive studies to solve the above problems, the inventors have made it difficult to effectively produce fine precipitates useful for preventing the generation of coarse grains during carburizing treatment. In particular, the inventors have newly found out that it is important to strictly control the amounts of S and N mixed as impurities, and have completed the present invention.

すなわち、本発明の要旨構成は次のとおりである。
1.質量%で、
C:0.1〜0.4%、
Si:0.5%以下、
Mn:2.0%以下、
Al:0.1%以下、
Ti:0.1〜0.5%
Mo:0.05〜1.0%
S:0.005%以下および
N:0.004%以下
を、下記式(1)を満足する範囲において含有し、残部はFeおよび不可避的不純物の組成になり、鋼組織が、フェライトと、パーライト及び/又はベイナイトからなり、該フェライトの組織分率が50%以上で、かつフェライト相中に粒径:20nm未満の微細析出物が1×103個/μm3以上分散していることを特徴とする浸炭用鋼。

0.3 ≦ (C/12)/〔{Ti−(48S/32)−(48N/14)}/48+(Mo/96)〕≦ 2.0 --- (1)
That is, the gist configuration of the present invention is as follows.
1. % By mass
C: 0.1 to 0.4%
Si: 0.5% or less,
Mn: 2.0% or less,
Al: 0.1% or less,
Ti: 0.1-0.5%
Mo: 0.05-1.0%
S: 0.005% or less and N: 0.004% or less are contained within the range satisfying the following formula (1), the balance is composed of Fe and inevitable impurities, and the steel structure is ferrite, pearlite and / or bainite. For carburizing, characterized in that the ferrite has a structure fraction of 50% or more and fine precipitates having a particle size of less than 20 nm are dispersed in the ferrite phase at 1 × 10 3 particles / μm 3 or more. steel.
Record
0.3 ≤ (C / 12) / [{Ti- (48S / 32)-(48N / 14)} / 48+ (Mo / 96)] ≤ 2.0 --- (1)

2.前記鋼の組成が、さらに質量%で、
Cr:2.0%以下、
Nb:0.1%以下、
V:0.15%以下および
W:1.5%以下
のうちから選んだ1種または2種以上を含有し、かつ前記(1)式に代えて下記式(1)′を満足することを特徴とする上記1に記載の浸炭用鋼。

0.3 ≦ (C/12)/〔{Ti−(48S/32)−(48N/14)}/48+(Mo/96)+(Cr/52)+(Nb/93)
+(V/51)+(W/184)〕≦ 2.0 --- (1)′
2. The composition of the steel is further mass%,
Cr: 2.0% or less,
Nb: 0.1% or less,
It contains one or more selected from V: 0.15% or less and W: 1.5% or less, and satisfies the following formula (1) ′ instead of the above formula (1) The carburizing steel according to 1.
Record
0.3 ≤ (C / 12) / [{Ti- (48S / 32)-(48N / 14)} / 48+ (Mo / 96) + (Cr / 52) + (Nb / 93)
+ (V / 51) + (W / 184)] ≦ 2.0 --- (1) '

3.質量%で、
C:0.1〜0.4%、
Si:0.5%以下、
Mn:2.0%以下、
Al:0.1%以下、
Ti:0.1〜0.5%
Mo:0.05〜1.0%
S:0.005%以下および
N:0.004%以下
を、下記式(1)を満足する範囲において含有し、残部はFeおよび不可避的不純物の組成になる鋼素材を、1100℃以上に加熱後、熱間加工したのち冷却するに際し、該熱間加工時および冷却過程における800〜500℃の温度範囲の冷却速度を1.0℃/s以下とすることを特徴とする浸炭用鋼の製造方法。

0.3 ≦ (C/12)/〔{Ti−(48S/32)−(48N/14)}/48+(Mo/96)〕≦ 2.0 --- (1)
3. % By mass
C: 0.1 to 0.4%
Si: 0.5% or less,
Mn: 2.0% or less,
Al: 0.1% or less,
Ti: 0.1-0.5%
Mo: 0.05-1.0%
S: 0.005% or less and N: 0.004% or less in a range satisfying the following formula (1), with the balance being hot after heating a steel material having a composition of Fe and inevitable impurities to 1100 ° C or higher A method for producing carburized steel, characterized in that, when cooled after processing, the cooling rate in the temperature range of 800 to 500 ° C during hot processing and in the cooling process is 1.0 ° C / s or less.
Record
0.3 ≤ (C / 12) / [{Ti- (48S / 32)-(48N / 14)} / 48+ (Mo / 96)] ≤ 2.0 --- (1)

4.前記鋼素材の組成が、さらに質量%で、
Cr:2.0%以下、
Nb:0.1%以下、
V:0.15%以下および
W:1.5%以下
のうちから選んだ1種または2種以上を含有し、かつ前記(1)式に代えて下記式(1)′を満足することを特徴とする上記3に記載の浸炭用鋼の製造方法。

0.3 ≦ (C/12)/〔{Ti−(48S/32)−(48N/14)}/48+(Mo/96)+(Cr/52)+(Nb/93)
+(V/51)+(W/184)〕≦ 2.0 --- (1)′
4). The composition of the steel material is further mass%,
Cr: 2.0% or less,
Nb: 0.1% or less,
It contains one or more selected from V: 0.15% or less and W: 1.5% or less, and satisfies the following formula (1) ′ instead of the above formula (1) 3. A method for producing carburizing steel according to 3.
Record
0.3 ≤ (C / 12) / [{Ti- (48S / 32)-(48N / 14)} / 48+ (Mo / 96) + (Cr / 52) + (Nb / 93)
+ (V / 51) + (W / 184)] ≦ 2.0 --- (1) '

本発明によれば、浸炭層以外の鋼材内部について強度および靱性を確保した上で、浸炭処理時に結晶粒の微細化が達成できる浸炭用鋼を得ることができる。   ADVANTAGE OF THE INVENTION According to this invention, the steel for carburization which can achieve refinement | miniaturization of a crystal grain at the time of a carburizing process can be obtained, after ensuring intensity | strength and toughness about the inside of steel materials other than a carburized layer.

以下、本発明の浸炭用鋼の鋼組織、成分組成および製造条件について具体的に説明する。
鋼組織
本発明に係る浸炭用鋼は、その鋼組織を、フェライトと、パーライト及び/又はベイナイトが混在する組織とし、かつフェライトの組織分率を全組織の50%以上とする。
浸炭処理前の鋼組織が、パーライト及び/又はベイナイトが混入していない組織であるということは、浸炭後にも同様な組織になるということであり、とすると、浸炭層以外の内部組織では、十分な強度および靱性を確保できず、歯車やクランクシャフト等の部品としての軽量化が困難となる。
また、フェライトの組織分率が50%未満では、後述するように、所望の微細析出物を析出させることができず、浸炭処理時の結晶粒の粗大化を防止できない。
以上のことから、鋼組織は、フェライトと、パーライト及び/又はベイナイトとし、該フェライトの組織分率を50%以上に限定した。
Hereinafter, the steel structure, component composition, and production conditions of the carburizing steel of the present invention will be specifically described.
Steel structure The carburizing steel according to the present invention has a steel structure in which ferrite and pearlite and / or bainite are mixed, and the ferrite structure fraction is 50% or more of the entire structure.
The fact that the steel structure before carburizing treatment is a structure in which pearlite and / or bainite are not mixed means that the same structure is obtained after carburizing. Strength and toughness cannot be ensured, and it is difficult to reduce the weight of components such as gears and crankshafts.
In addition, when the ferrite structure fraction is less than 50%, as will be described later, desired fine precipitates cannot be precipitated, and coarsening of crystal grains during carburization cannot be prevented.
From the above, the steel structure was ferrite, pearlite, and / or bainite, and the structure fraction of the ferrite was limited to 50% or more.

ここに、フェライトの組織分率は50〜95%、一方パーライト及び/又はベイナイトの組織分率は5〜50%とすることが好ましい。また、冷間加工性を確保する観点からは、フェライトの組織分率は70〜95%、パーライト及び/又はベイナイトの組織分率は5〜30%とすることが好ましい。なお、鋼組織としては、その他にもマルテンサイトや残留オーステナイトが混入する場合があるが、これらの混入量が10%以下であれば何ら問題はない。
なお、各組織分率は、断面組織観察(200倍の光学顕微鏡組織観察)により、面積率で求めることができる。
Here, the structure fraction of ferrite is preferably 50 to 95%, while the structure fraction of pearlite and / or bainite is preferably 5 to 50%. Further, from the viewpoint of ensuring cold workability, the ferrite structure fraction is preferably 70 to 95%, and the pearlite and / or bainite structure fraction is preferably 5 to 30%. In addition, as the steel structure, martensite and retained austenite may be mixed, but there is no problem if the mixed amount is 10% or less.
In addition, each structure fraction can be calculated | required by an area ratio by cross-sectional structure | tissue observation (200 times optical microscope structure | tissue observation).

微細析出物
さらに、本発明では、フェライト組織中に、粒径:20nm未満の微細析出物が1×103個/μm3以上分散している必要がある。粒径が20nm未満の析出物の存在により、浸炭処理時の結晶粒界のピンニング効果により粒成長が効果的に防止される。この粒径:20nm未満の析出物の個数が1×103個/μm3未満では、上記したピンニング効果が不十分となり粒成長抑制効果が得られない 。
なお、微細析出物の個数は、以下の方法により求める。電子顕微鏡試料を、ツインジェット法を用いた電解研磨法で作成し、加速電圧:200kVで観察する。その際、微細析出物が母相に対して計測可能なコントラストになるように母相の結晶方位を制御し、析出物の数え落としが無いように焦点を正焦点からずらしたデフォーカス法で観察した。
また、析出物粒子の計測を行った領域の試料の厚さは、電子エネルギー損失分光法を用い、弾性散乱ピーク強度と非弾性散乱ピーク強度を測定することで算出する。
この方法により、粒子数の計測と試料厚さの計測を同じ領域について実施することができる。粒子数および粒子径の測定は、試料の0.5×0.5μmの領域4箇所について行い、1μm2当たりに分布する析出物を粒径ごとの個数として算出する。
本発明では、このようにして求めた粒径:2Onm未満の析出物の数を1×103個/μm3以上の範囲に規定する。なお、20nm未満の析出物の数は1×104個/μm3以上であることがより好ましい。
Further, in the present invention, it is necessary that fine precipitates having a particle size of less than 20 nm are dispersed in the ferrite structure at 1 × 10 3 particles / μm 3 or more. Due to the presence of precipitates having a particle size of less than 20 nm, grain growth is effectively prevented by the pinning effect of the crystal grain boundaries during the carburizing process. When the number of precipitates having a particle size of less than 20 nm is less than 1 × 10 3 / μm 3 , the pinning effect described above is insufficient and the effect of suppressing grain growth cannot be obtained.
The number of fine precipitates is determined by the following method. An electron microscope sample is prepared by an electropolishing method using a twin jet method and observed at an acceleration voltage of 200 kV. At that time, the crystal orientation of the parent phase is controlled so that the fine precipitates have a measurable contrast with respect to the parent phase, and the focus is shifted from the normal focus so that the precipitates are not counted and observed by the defocus method. did.
Further, the thickness of the sample in the region where the precipitate particles are measured is calculated by measuring the elastic scattering peak intensity and the inelastic scattering peak intensity using electron energy loss spectroscopy.
By this method, the number of particles and the sample thickness can be measured in the same region. The number of particles and the particle diameter are measured at four locations of a 0.5 × 0.5 μm region of the sample, and the precipitates distributed per 1 μm 2 are calculated as the number for each particle diameter.
In the present invention, the number of precipitates having a particle size of less than 2 Onm determined in this manner is defined in a range of 1 × 10 3 / μm 3 or more. The number of precipitates less than 20 nm is more preferably 1 × 10 4 / μm 3 or more.

成分組成
上述した組織が得られ、しかも本発明の浸炭用鋼の用途である歯車やクランクシャフトといった機械構造部品として必要な特性を確保するために、本発明では成分組成を以下のように限定する。なお、以下、各成分の含有量(%)は全て質量%を意味するものとする。
Ingredient composition In order to secure the characteristics required for mechanical structural parts such as gears and crankshafts that are used for the carburizing steel of the present invention, the composition of the present invention is limited as follows. . Hereinafter, the content (%) of each component means mass%.

C:0.1〜0.4%
Cは、必要な強度を得るために添加する。しかしながら、C量が0.1%未満では必要な強度を確保することができず、一方 0.4%を超えると硬くなり、冷間加工性を確保することが難しくなるだけでなく、浸炭後の芯部靱性が劣化するので、C量は0.1〜0.4%の範囲に限定する。より好ましくは0.2〜0.4%の範囲である。
C: 0.1-0.4%
C is added to obtain the required strength. However, if the C content is less than 0.1%, the required strength cannot be ensured. On the other hand, if it exceeds 0.4%, it becomes hard and it becomes difficult to ensure cold workability, but also the core toughness after carburizing. Therefore, the C content is limited to a range of 0.1 to 0.4%. More preferably, it is 0.2 to 0.4% of range.

Si:0.5%以下
Siは、強度、延性を向上させるために添加するが、含有量が0.5%を超えるとその効果が飽和するだけでなく、冷間加工時の変形抵抗が高くなって加工性が低下するため、Si量は0.5%以下に限定する。
Si: 0.5% or less
Si is added to improve the strength and ductility, but when the content exceeds 0.5%, not only the effect is saturated, but also the deformation resistance during cold working increases and the workability decreases. Si amount is limited to 0.5% or less.

Mn:2.0%以下
Mnは、強度、焼入れ性を向上させるために添加するが、含有量が2.0%を超えるとその効果は飽和するだけでなく、冷間加工時の変形抵抗が高くなって加工性が低下するため、Mnは2.0%以下に限定する。
Mn: 2.0% or less
Mn is added to improve strength and hardenability. However, if the content exceeds 2.0%, the effect is not only saturated, but also deformation resistance during cold working increases and workability decreases. , Mn is limited to 2.0% or less.

Al:0.1%以下
Alは、脱酸剤として有用であり、また強度及び延性を向上させる効果もあるので、0.1%を上限として添加する。
Al: 0.1% or less
Al is useful as a deoxidizer and also has the effect of improving strength and ductility, so 0.1% is added as the upper limit.

Ti:0.1〜0.5%
Tiは、Ti系炭化物や、Moと共にTi−Mo系炭化物を含む析出物を微細に析出させ、ピンニング効果を向上させる上で有用な元素である。しかしながら、含有量が0.1%未満では析出物量が少なすぎて粗大粒の抑制に必要なピンニング効果が得られず、一方0.5%を超えると析出物が粗大化し、上記したピンニング効果が低下するので、Tiは0.1〜0.5%の範囲に限定する。
Ti: 0.1-0.5%
Ti is an element useful for improving the pinning effect by finely depositing Ti-based carbides and precipitates containing Ti-Mo-based carbides together with Mo. However, if the content is less than 0.1%, the amount of precipitates is too small to obtain the pinning effect necessary for suppressing coarse grains, while if it exceeds 0.5%, the precipitates become coarse and the above-mentioned pinning effect is reduced. Ti is limited to a range of 0.1 to 0.5%.

Mo:0.05〜1.0%
Moは、Mo系炭化物や、Tiと共にTi−Mo系炭化物を含む析出物を微細に析出させ、ピンニング効果を向上させる上で有用な元素である。しかしながら、含有量が0.05%未満では析出物量が少なすぎて粗大粒の抑制に必要なピンニング効果が得られず、一方1.0%を超えて含有させるとベイナイト相のみならず、マルテンサイト相を形成するようになるので、Moは0.05〜1.0%の範囲に限定する。
Mo: 0.05-1.0%
Mo is an element useful for improving the pinning effect by finely depositing Mo-based carbides and precipitates containing Ti-Mo-based carbides together with Ti. However, if the content is less than 0.05%, the amount of precipitates is too small to obtain the pinning effect necessary for suppressing coarse grains. On the other hand, if the content exceeds 1.0%, not only the bainite phase but also the martensite phase is formed. Therefore, Mo is limited to a range of 0.05 to 1.0%.

S:0.005%以下
Sは、本発明のような高Ti鋼においては粗大なTiSを形成し、ピンニング効果に寄与しないだけでなく、むしろ粗大なTiSが存在するとTiおよびMo系の炭化物の析出サイトとなって、ピンニング効果に有効な微細析出物量を減少させる。ここに、Sが0.005%を超えて含有された場合には、上記の弊害が著しいので、Sは0.005%以下に制限することが重要である。
S: 0.005% or less S does not contribute to the pinning effect in the high Ti steel as in the present invention and does not contribute to the pinning effect, but rather in the presence of coarse TiS, precipitation sites of Ti and Mo-based carbides. Thus, the amount of fine precipitates effective for the pinning effect is reduced. Here, when the S content exceeds 0.005%, the above-described adverse effects are remarkable, so it is important to limit S to 0.005% or less.

N:0.004%以下
Nも、本発明のような高Ti鋼においては粗大なTiNを形成し、ピンニング効果に寄与しないだけでなく、むしろ粗大なTiNが存在するとTiおよびMo系の炭化物の析出サイトとなって、ピンニング効果に有効な微細析出物量を減少させる。ここに、Nが0.004%を超えて含有された場合には、上記の弊害が著しいので、Nは0.004%以下に制限することが重要である。
N: 0.004% or less N also forms coarse TiN in the high Ti steel as in the present invention, which not only contributes to the pinning effect but rather precipitates sites of Ti and Mo-based carbides when coarse TiN is present. Thus, the amount of fine precipitates effective for the pinning effect is reduced. Here, when N is contained in excess of 0.004%, the above-described adverse effects are remarkable. Therefore, it is important to limit N to 0.004% or less.

以上、本発明の基本成分の好適組成範囲について説明したが、本発明では、各々の元素が単に上記の範囲を満足するだけでは不十分で、C,Ti,Mo,SおよびNについては、次式(1)の要件を満たすことが肝要である。
0.3 ≦ (C/12)/〔{Ti−(48S/32)−(48N/14)}/48+(Mo/96)〕≦ 2.0 --- (1)
上掲式は、析出物の大きさ及び個数に影響を与えるもので、この式を満たす範囲でそれぞれの元素が含有された場合、後述する製造方法に従って製造すれば、粒径:20nm未満の微細析出物が1×103個/μm3以上分散した所望組織を得ることができる。
The preferred composition range of the basic component of the present invention has been described above. However, in the present invention, it is not sufficient that each element simply satisfies the above range. For C, Ti, Mo, S and N, It is important to satisfy the requirement of formula (1).
0.3 ≤ (C / 12) / [{Ti- (48S / 32)-(48N / 14)} / 48+ (Mo / 96)] ≤ 2.0 --- (1)
The above formula affects the size and number of precipitates. When each element is contained within the range satisfying this formula, if it is manufactured according to the manufacturing method described later, the particle size is less than 20 nm. A desired structure in which precipitates are dispersed at 1 × 10 3 particles / μm 3 or more can be obtained.

さらに、本発明では、以下に述べる元素を適宜含有させることができる。
Cr≦2.0%、Nb≦0.1%、V≦0.15%、W≦1.5%のうちから選んだ1種または2種以上
Crは、強度および靱性を向上させるのに有効なだけでなく、Tiと共に微細な炭化物を形成する有用元素であるが、含有量が2.0%を超えると硬さの上昇を招き冷間鍛造性が劣化するため、2.0%以下とする。
Nbは、Tiと共に微細析出物を形成して強度上昇に寄与する。また、組織を微細化し、結晶粒の整粒化により延性を向上させる効果もあるが、0.1%を超えて含有させると過度に微細化し、延性が低下するため、0.1%以下とする。
Vは、Tiと共に微細析出物を形成して強度上昇に寄与する。また、組織を微細化し、結晶粒の整粒化により延性を向上させる効果もあるが、0.15%を超えて含有させると過度に微細化し、延性が低下するため、0.15%以下とする。
Wは、Tiと共に微細析出物を形成して強度上昇に寄与する。また、組織を微細化し、結晶粒の整粒化により延性を向上させる効果もあるが、1.5%を超えて含有させると過度に微細化し、延性が低下するため、1.5%以下とする。
Furthermore, in the present invention, the following elements can be appropriately contained.
One or more selected from Cr ≤ 2.0%, Nb ≤ 0.1%, V ≤ 0.15%, W ≤ 1.5%
Cr is not only effective for improving strength and toughness, but is also a useful element that forms fine carbides with Ti. However, if its content exceeds 2.0%, it causes an increase in hardness and cold forgeability. Since it deteriorates, it should be 2.0% or less.
Nb contributes to the strength increase by forming fine precipitates together with Ti. In addition, there is an effect of improving the ductility by refining the structure and adjusting the crystal grains, but if it exceeds 0.1%, it becomes excessively fine and the ductility is lowered, so the content is made 0.1% or less.
V contributes to an increase in strength by forming fine precipitates together with Ti. Moreover, although there exists an effect which improves a ductility by refine | miniaturizing a structure | tissue and adjusting the grain size of a crystal grain, when it contains exceeding 0.15%, since it refines | miniaturizes excessively and a ductility falls, it is 0.15% or less.
W forms a fine precipitate together with Ti and contributes to an increase in strength. In addition, there is an effect of improving the ductility by refining the structure and adjusting the grain size, but if it exceeds 1.5%, it becomes excessively fine and the ductility is lowered, so the content is made 1.5% or less.

また、Cr,Nb,V,Wのうちから選んだ1種または2種以上を添加する場合には、上掲式(1)と同じ理由から、次式(1)′の要件を満足させる必要がある。
0.3 ≦ (C/12)/〔{Ti−(48S/32)−(48N/14)}/48+(Mo/96)+(Cr/52)+(Nb/93)
+(V/51)+(W/184)〕≦ 2.0 --- (1)′
Further, when adding one or more selected from Cr, Nb, V, and W, it is necessary to satisfy the requirement of the following formula (1) ′ for the same reason as the above formula (1). There is.
0.3 ≤ (C / 12) / [{Ti- (48S / 32)-(48N / 14)} / 48+ (Mo / 96) + (Cr / 52) + (Nb / 93)
+ (V / 51) + (W / 184)] ≦ 2.0 --- (1) '

なお、上記した元素以外の残部は、Feおよび不可避的不純物である。   The balance other than the above elements is Fe and inevitable impurities.

次に、本発明の製造条件について説明する。
上述した好適成分組成になる鋼素材を、1100℃以上に加熱後、仕上げ加工温度:800℃以上、1000℃以下で熱間加工したのち、800〜500℃の温度範囲を1.0℃/s以下の速度で冷却する必要がある。以下、各処理条件を上記のように限定した理由について説明する。
Next, the manufacturing conditions of the present invention will be described.
After heating the steel material with the preferred composition described above to 1100 ° C or higher, and then hot working at a finishing temperature of 800 ° C or higher and 1000 ° C or lower, the temperature range from 800 to 500 ° C is 1.0 ° C / s or lower. Need to cool at speed. Hereinafter, the reason why each processing condition is limited as described above will be described.

加熱温度:1100℃以上
本発明では、熱間加工前の加熱時に炭化物を十分に固溶させ、熱間加工時およびその後の冷却過程で微細析出物を析出させる。この際、加熱温度が1100℃未満では、炭化物をマトリックス中に十分に固溶させることができないため、熱間加工後に粗大な炭化物が生成し易く、浸炭時に粗大粒の発生を抑制することができない。そのため、熱間加工に際しては加熱温度を1100℃以上とする必要がある。好ましくは1150℃以上、より好ましくは1200℃以上である。
Heating temperature: 1100 ° C. or higher In the present invention, carbides are sufficiently dissolved during heating before hot working, and fine precipitates are deposited during hot working and after cooling. At this time, if the heating temperature is less than 1100 ° C., carbides cannot be sufficiently dissolved in the matrix, so that coarse carbides are likely to be generated after hot working, and generation of coarse particles during carburization cannot be suppressed. . Therefore, it is necessary to set the heating temperature to 1100 ° C. or higher during hot working. Preferably it is 1150 degreeC or more, More preferably, it is 1200 degreeC or more.

800〜500℃の温度範囲の冷却速度:1.0℃/s以下
熱間加工時およびその後の冷却過程において、800〜500℃の温度範囲の冷却速度が1.0℃/s超となると微細析出物が十分に析出しない。さらに、フェライトの組織分率が小さくなり、浸炭時に粗粒化が発生し易くなるだけでなく、圧延材の硬さが上昇し、冷間鍛造性が劣化する。そのため、冷却速度は1.0℃/s以下に制限する。好ましくは0.5℃/s以下、より好ましくは0.3℃/s以下である。
なお、冷却速度を小さくする方法としては、圧延また鍛造ラインの後方に保温カバーまたは熱源付き保温カバーを設置し、これにより徐冷を行う方法が挙げられる。
Cooling rate in the temperature range of 800 to 500 ° C: 1.0 ° C / s or less During the hot working and the subsequent cooling process, if the cooling rate in the temperature range of 800 to 500 ° C exceeds 1.0 ° C / s, fine precipitates are sufficient Does not precipitate. Furthermore, the ferrite structure fraction is reduced, and not only is coarsening easily generated during carburizing, but the hardness of the rolled material is increased and cold forgeability is deteriorated. Therefore, the cooling rate is limited to 1.0 ° C./s or less. Preferably it is 0.5 ° C./s or less, more preferably 0.3 ° C./s or less.
In addition, as a method for reducing the cooling rate, there is a method in which a heat insulation cover or a heat insulation cover with a heat source is installed behind the rolling or forging line, thereby gradually cooling.

なお、熱間加工時の仕上げ加工温度が800℃未満では、バンド組織が形成され易く、浸炭加熱 の逆変態時に混粒が生じ、粗大粒発生の原因となる。一方、仕上げ温度が1000℃を超えると、加工材の硬さが硬くなって冷間鍛造性が劣化する。以上の理由から、熱間加工時の仕上げ加工温度は800〜1000℃とすることが好ましい。
ここで、熱間加工は、浸炭処理直前の熱間加工のことを言い、棒鋼に対して、熱間加工を施さず、冷間加工や切削加工により部品形状に成形した後に浸炭処理を施す場合には、棒鋼製造時の熱間圧延時に上記の加熱温度、仕上げ加工条件、その後の冷却条件を適用すればよい。また、部品形状に成形を行うに当たって熱間鍛造工程を経る場合には、熱間鍛造時に上記の加熱温度、仕上げ加工条件、その後の冷却条件を適用すればよい。
If the finishing temperature during hot working is less than 800 ° C., a band structure is likely to be formed, and mixed grains are formed during reverse transformation of carburizing heating, causing coarse grains. On the other hand, when the finishing temperature exceeds 1000 ° C., the work material becomes hard and cold forgeability deteriorates. For the above reasons, the finishing temperature during hot working is preferably 800 to 1000 ° C.
Here, hot working refers to hot working immediately before carburizing treatment. When hot working is not performed on steel bars, carburizing treatment is performed after forming into a part shape by cold working or cutting. The above heating temperature, finishing process conditions, and subsequent cooling conditions may be applied during hot rolling at the time of manufacturing the steel bar. In addition, when a hot forging process is performed in forming a part shape, the above heating temperature, finishing process conditions, and subsequent cooling conditions may be applied during hot forging.

表1に示す種々の成分組成になる鋼を、100kg真空溶解炉にて溶製し、150mm角に鍛伸後、ダミービレットに溶接し、熱間圧延を表2に示す種々の加熱温度、仕上げ温度および冷却速度の条件下で行い、直径:20〜35mmの棒鋼を製造した。
かくして得られた棒鋼から微細析出物観察用試料を採取し、析出物サイズと量を求めた。また、同様にしてミクロ組織観察用試料を採取して組織観察を行い、フェライト面積率を求めた。
Steels with various compositions shown in Table 1 are melted in a 100 kg vacuum melting furnace, forged to 150 mm square, welded to a dummy billet, and hot-rolled with various heating temperatures and finishes shown in Table 2. Steel bars having a diameter of 20 to 35 mm were manufactured under conditions of temperature and cooling rate.
A sample for observing fine precipitates was collected from the steel bar thus obtained, and the size and amount of the precipitates were determined. Similarly, a sample for microstructural observation was collected and subjected to structural observation to determine the ferrite area ratio.

なお、微細析出物の個数および全析出物に占める割合は、以下の方法により求めた。
電子顕微鏡試料を、ツインジェット法を用いた電解研磨法で作成し、加速電圧:200kVで観察する。その際、微細析出物が母相に対して計測可能なコントラストになるように母相の結晶方位を制御し、析出物の数え落としが無いように焦点を正焦点からずらしたデフォーカス法で観察を行った。また、析出物粒子の計測を行った領域の試料の厚さは、電子エネルギー損失分光法を用い、弾性散乱ピーク強度と非弾性散乱ピーク強度を測定することで算出した。この方法により、粒子数の計測と試料厚さの計測を同じ領域について実施することができる。粒子数および粒子径の測定は、試料の0.5×0.5μmの領域4ヶ所について行い、1μm3当たりに分布する析出物を粒径ごとに算出し、粒径が20nm未満の析出物量を求めた。
The number of fine precipitates and the ratio of the total precipitates were obtained by the following method.
An electron microscope sample is prepared by an electropolishing method using a twin jet method and observed at an acceleration voltage of 200 kV. At that time, the crystal orientation of the parent phase is controlled so that the fine precipitates have a measurable contrast with respect to the parent phase, and the focus is shifted from the normal focus so that the precipitates are not counted and observed by the defocus method. Went. Moreover, the thickness of the sample in the region where the precipitate particles were measured was calculated by measuring the elastic scattering peak intensity and the inelastic scattering peak intensity using electron energy loss spectroscopy. By this method, the number of particles and the sample thickness can be measured in the same region. The number of particles and the particle size were measured at four locations of a 0.5 × 0.5 μm region of the sample, and the precipitates distributed per 1 μm 3 were calculated for each particle size, and the amount of precipitates having a particle size of less than 20 nm was determined.

また、フェライト面積率は、200倍の光学顕微鏡を用いて、試料の断面組織を観察することにより求めた。   Moreover, the ferrite area ratio was calculated | required by observing the cross-sectional structure | tissue of a sample using a 200 times optical microscope.

さらに、圧延ままの棒鋼から8mmφ×12mmの据え込み試験片を作成し、圧下率:70%の据え込みを行った後、浸炭シミュレーションを行った。浸炭シミュレーンョンの条件は、950〜1025℃に3時間加熱−水冷である。その後、切断面を研磨・エッチングを行い、旧オーステナイト粒径を観察して粗粒発生温度(結晶粒粗大化温度)を求めた。浸炭処理は通常900〜950℃の温度域で行われるため、粗粒化温度が950℃以下のものは結晶粒粗大化特性に劣ると判定した。なお、旧オーステナイト粒度の測定はJIS G O551に準拠し、400倍で10視野測定し、粒度番号5以下の粗粒が1つでも存在すれば粗粒発生と判定した。   Furthermore, an upsetting test piece of 8 mmφ × 12 mm was made from the rolled steel bar, and after upsetting at a rolling reduction of 70%, carburization simulation was performed. The conditions for carburizing simulation are heating to 950-125 ° C. for 3 hours and water cooling. Thereafter, the cut surface was polished and etched, and the prior austenite grain size was observed to determine the coarse grain generation temperature (crystal grain coarsening temperature). Since the carburizing process is normally performed in the temperature range of 900 to 950 ° C., it was determined that those having a coarsening temperature of 950 ° C. or lower are inferior in crystal grain coarsening characteristics. The prior austenite grain size was measured according to JIS G O551, measured 10 times at 400 times, and if any coarse grain having a grain size number of 5 or less was present, it was determined that coarse grains were generated.

またさらに、得られた棒鋼からJIS Z 2202に規定するシャルピー衝撃試験用の2mmUノッチ3号試験片を作成し、JIS Z 2242に準拠して試験温度:20℃でシャルピー衝撃試験を行い、吸収エネルギーを測定した。   Furthermore, a 2 mm U-notch No. 3 test piece for Charpy impact test specified in JIS Z 2202 was created from the obtained steel bar, and Charpy impact test was conducted at a test temperature of 20 ° C in accordance with JIS Z 2242. Was measured.

No.1,2,4,5,6,8,9,11,12,13,14,15,24, 25および28は発明例で、いずれも熱間圧延後のフェライト組織分率が50%以上で、かつ20nm未満の析出物を1×103個/μm3以上含有していた。その結果、いずれも浸炭シミュレーション実験時の粗粒化温度は1025℃以上という優れた特性を得た。また、吸収エネルギーも70J/cm2以上という優れた値が得られた。
なお、鋼a(No.1)および鋼c(No.5)において、圧延後の棒鋼を740℃×5時間加熱の球状化焼鈍処理を行ったものについても上記と同様に据え込み率:70%の冷間鍛造を行った後、浸炭シミュレーションを行ったが、ともに1025℃でも粗大粒の発生は認められなかった。
このように、本発明鋼は、冷間鍛造の前に焼鈍工程を経由する場合においても、優れた粗大粒防止特性を有していた。
Nos. 1, 2, 4, 5, 6, 8, 9, 11, 12, 13, 14, 15, 24, 25 and 28 are invention examples, all of which have a ferrite structure fraction of 50% after hot rolling. As described above, precipitates of less than 20 nm were contained at 1 × 10 3 pieces / μm 3 or more. As a result, in each case, an excellent characteristic that the coarsening temperature during the carburizing simulation experiment was 1025 ° C or higher was obtained. Also, an excellent value of absorbed energy of 70 J / cm 2 or more was obtained.
In steel a (No. 1) and steel c (No. 5), the steel bar after rolling was subjected to spheroidizing annealing at 740 ° C. for 5 hours, as in the above, the upsetting ratio: 70 % Carburizing simulation was performed after cold forging, and no coarse grains were observed even at 1025 ° C.
Thus, the steel of the present invention had excellent coarse grain prevention characteristics even when passing through the annealing process before cold forging.

これに対し、No.3,7,10はそれぞれ、熱間圧延条件が本発明の適正範囲を外れたため、フェライト組織分率と析出物の個数のいずれかあるいは両方が本発明の要件を満足せず、その結果、粗大粒発生温度は950℃以下と、粗大化防止特性に劣っている。
また、No.16は、S量が本発明の上限を超えて多量に含有されていて、粗大な析出物が形成されるため、微細析出物が減少し、粗大化防止特性に劣っている。
No.17は、N量が本発明の上限を超えて多量に含有されていて、粗大な析出物が形成されるため、微細析出物が減少し、粗大化防止特性に劣っている。
No.18は、Ti量が本発明の適正範囲より少ないため、微細析出物が減少し、粗大化防止特性に劣っている。
No.19は、Ti量が本発明の適正範囲より多すぎることから、粗大な析出物が形成された結果、微細析出物が減少し、粗大化防止特性に劣っている。
No.20は、Moが含有されていないため、微細析出物が減少し、粗大化防止特性に劣っている。
No.21は、Mo量が本発明の適正範囲より多いため、フェライト組織率が50%未満となり、粗大化防止特性に劣る。
No.22は、A値が本発明で規定した適正範囲より小さいため、粗大な析出物が形成されて微細析出物が減少し、粗大化防止特性が劣化している。
No.23は、A値が本発明で規定した適正範囲より大きいため、やはり粗大な析出物が形成されて微細析出物が減少し、粗大化防止特性が劣化している。
No.26は、加熱温度が本発明の下限を大きく下回っていたため、微細析出物が減少し、粗大化防止特性に劣っている。また、吸収エネルギーも10J/cm2と靱性も劣っていた。
No.27は、加熱温度が本発明の下限を下回っていたため、微細析出物の量や粗大化防止特性は満足されたものの、吸収エネルギーが30J/cm2と靱性に劣っていた。
On the other hand, in each of Nos. 3, 7, and 10, the hot rolling conditions were outside the appropriate range of the present invention, so either or both of the ferrite structure fraction and the number of precipitates satisfied the requirements of the present invention. As a result, the coarse grain generation temperature is 950 ° C. or less, which is inferior in the coarsening prevention characteristics.
Further, No. 16 contains a large amount of S exceeding the upper limit of the present invention, and coarse precipitates are formed, so that fine precipitates are reduced and the coarsening prevention property is poor.
No. 17 contains a large amount of N in excess of the upper limit of the present invention, and coarse precipitates are formed, so that fine precipitates are reduced and the coarsening prevention properties are poor.
In No. 18, since the Ti amount is less than the appropriate range of the present invention, fine precipitates are reduced and the coarsening prevention property is inferior.
In No. 19, since the amount of Ti is too much larger than the proper range of the present invention, coarse precipitates are formed. As a result, fine precipitates are reduced and the coarsening prevention property is poor.
Since No. 20 does not contain Mo, fine precipitates are reduced and the coarsening prevention property is inferior.
In No. 21, since the amount of Mo is larger than the appropriate range of the present invention, the ferrite structure ratio is less than 50%, and the coarsening prevention property is inferior.
In No. 22, since the A value is smaller than the appropriate range specified in the present invention, coarse precipitates are formed, fine precipitates are reduced, and the coarsening prevention characteristics are deteriorated.
In No. 23, since the A value is larger than the appropriate range specified in the present invention, coarse precipitates are also formed, the fine precipitates are reduced, and the coarsening prevention characteristics are deteriorated.
In No. 26, since the heating temperature was much lower than the lower limit of the present invention, fine precipitates were reduced and the coarsening prevention property was inferior. Further, the absorbed energy was 10 J / cm 2 and the toughness was inferior.
In No. 27, since the heating temperature was lower than the lower limit of the present invention, the amount of fine precipitates and the coarsening prevention characteristic were satisfied, but the absorbed energy was inferior to 30 J / cm 2 and toughness.

Claims (4)

質量%で、
C:0.1〜0.4%、
Si:0.5%以下、
Mn:2.0%以下、
Al:0.1%以下、
Ti:0.1〜0.5%
Mo:0.05〜1.0%
S:0.005%以下および
N:0.004%以下
を、下記式(1)を満足する範囲において含有し、残部はFeおよび不可避的不純物の組成になり、鋼組織が、フェライトと、パーライト及び/又はベイナイトからなり、該フェライトの組織分率が50%以上で、かつフェライト相中に粒径:20nm未満の微細析出物が1×103個/μm3以上分散していることを特徴とする浸炭用鋼。

0.3 ≦ (C/12)/〔{Ti−(48S/32)−(48N/14)}/48+(Mo/96)〕≦ 2.0 --- (1)
% By mass
C: 0.1 to 0.4%
Si: 0.5% or less,
Mn: 2.0% or less,
Al: 0.1% or less,
Ti: 0.1-0.5%
Mo: 0.05-1.0%
S: 0.005% or less and N: 0.004% or less are contained within the range satisfying the following formula (1), the balance is composed of Fe and inevitable impurities, and the steel structure is ferrite, pearlite and / or bainite. For carburizing, characterized in that the ferrite has a structure fraction of 50% or more and fine precipitates having a particle size of less than 20 nm are dispersed in the ferrite phase at 1 × 10 3 particles / μm 3 or more. steel.
Record
0.3 ≤ (C / 12) / [{Ti- (48S / 32)-(48N / 14)} / 48+ (Mo / 96)] ≤ 2.0 --- (1)
前記鋼の組成が、さらに質量%で、
Cr:2.0%以下、
Nb:0.1%以下、
V:0.15%以下および
W:1.5%以下
のうちから選んだ1種または2種以上を含有し、かつ前記(1)式に代えて下記式(1)′を満足することを特徴とする請求項1に記載の浸炭用鋼。

0.3 ≦ (C/12)/〔{Ti−(48S/32)−(48N/14)}/48+(Mo/96)+(Cr/52)+(Nb/93)
+(V/51)+(W/184)〕≦ 2.0 --- (1)′
The composition of the steel is further mass%,
Cr: 2.0% or less,
Nb: 0.1% or less,
It contains one or more selected from V: 0.15% or less and W: 1.5% or less, and satisfies the following formula (1) ′ in place of the formula (1) Item 2. The carburizing steel according to Item 1.
Record
0.3 ≤ (C / 12) / [{Ti- (48S / 32)-(48N / 14)} / 48+ (Mo / 96) + (Cr / 52) + (Nb / 93)
+ (V / 51) + (W / 184)] ≦ 2.0 --- (1) '
質量%で、
C:0.1〜0.4%、
Si:0.5%以下、
Mn:2.0%以下、
Al:0.1%以下、
Ti:0.1〜0.5%
Mo:0.05〜1.0%
S:0.005%以下および
N:0.004%以下
を、下記式(1)を満足する範囲において含有し、残部はFeおよび不可避的不純物の組成になる鋼素材を、1100℃以上に加熱後、熱間加工したのち冷却するに際し、該熱間加工時および冷却過程における800〜500℃の温度範囲の冷却速度を1.0℃/s以下とすることを特徴とする浸炭用鋼の製造方法。

0.3 ≦ (C/12)/〔{Ti−(48S/32)−(48N/14)}/48+(Mo/96)〕≦ 2.0 --- (1)
% By mass
C: 0.1 to 0.4%
Si: 0.5% or less,
Mn: 2.0% or less,
Al: 0.1% or less,
Ti: 0.1-0.5%
Mo: 0.05-1.0%
S: 0.005% or less and N: 0.004% or less in a range satisfying the following formula (1), with the balance being hot after heating a steel material having a composition of Fe and inevitable impurities to 1100 ° C or higher A method for producing carburized steel, characterized in that, when cooled after processing, the cooling rate in the temperature range of 800 to 500 ° C during hot processing and in the cooling process is 1.0 ° C / s or less.
Record
0.3 ≤ (C / 12) / [{Ti- (48S / 32)-(48N / 14)} / 48+ (Mo / 96)] ≤ 2.0 --- (1)
前記鋼素材の組成が、さらに質量%で、
Cr:2.0%以下、
Nb:0.1%以下、
V:0.15%以下および
W:1.5%以下
のうちから選んだ1種または2種以上を含有し、かつ前記(1)式に代えて下記式(1)′を満足することを特徴とする請求項3に記載の浸炭用鋼の製造方法。

0.3 ≦ (C/12)/〔{Ti−(48S/32)−(48N/14)}/48+(Mo/96)+(Cr/52)+(Nb/93)
+(V/51)+(W/184)〕≦ 2.0 --- (1)′
The composition of the steel material is further mass%,
Cr: 2.0% or less,
Nb: 0.1% or less,
It contains one or more selected from V: 0.15% or less and W: 1.5% or less, and satisfies the following formula (1) ′ in place of the formula (1) Item 4. A method for producing carburizing steel according to Item 3.
Record
0.3 ≤ (C / 12) / [{Ti- (48S / 32)-(48N / 14)} / 48+ (Mo / 96) + (Cr / 52) + (Nb / 93)
+ (V / 51) + (W / 184)] ≦ 2.0 --- (1) '
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JPH0610092A (en) * 1992-03-06 1994-01-18 Kawasaki Steel Corp High tensile strength thin steel sheet for press forming and its manufacture
JPH073391A (en) * 1993-06-17 1995-01-06 Kobe Steel Ltd Surface hardened high strength parts small in heat treating strain
JPH1112684A (en) * 1997-06-19 1999-01-19 Kobe Steel Ltd Case hardening steel for cold forging
JPH11335777A (en) * 1998-05-22 1999-12-07 Nippon Steel Corp Case hardening steel excellent in cold workability and low carburizing strain characteristics, and its production

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0610092A (en) * 1992-03-06 1994-01-18 Kawasaki Steel Corp High tensile strength thin steel sheet for press forming and its manufacture
JPH073391A (en) * 1993-06-17 1995-01-06 Kobe Steel Ltd Surface hardened high strength parts small in heat treating strain
JPH1112684A (en) * 1997-06-19 1999-01-19 Kobe Steel Ltd Case hardening steel for cold forging
JPH11335777A (en) * 1998-05-22 1999-12-07 Nippon Steel Corp Case hardening steel excellent in cold workability and low carburizing strain characteristics, and its production

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