JP5804832B2 - Steel material made of carburizing steel with excellent torsional fatigue properties - Google Patents
Steel material made of carburizing steel with excellent torsional fatigue properties Download PDFInfo
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- JP5804832B2 JP5804832B2 JP2011167621A JP2011167621A JP5804832B2 JP 5804832 B2 JP5804832 B2 JP 5804832B2 JP 2011167621 A JP2011167621 A JP 2011167621A JP 2011167621 A JP2011167621 A JP 2011167621A JP 5804832 B2 JP5804832 B2 JP 5804832B2
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- 229910000831 Steel Inorganic materials 0.000 title claims description 56
- 239000010959 steel Substances 0.000 title claims description 56
- 239000000463 material Substances 0.000 title claims description 21
- 238000005255 carburizing Methods 0.000 title description 11
- 239000012535 impurity Substances 0.000 claims description 4
- 239000000126 substance Substances 0.000 claims description 4
- 229910052748 manganese Inorganic materials 0.000 claims description 3
- 229910052710 silicon Inorganic materials 0.000 claims description 3
- 229910052799 carbon Inorganic materials 0.000 claims description 2
- 229910052802 copper Inorganic materials 0.000 claims description 2
- 229910052750 molybdenum Inorganic materials 0.000 claims description 2
- 229910052758 niobium Inorganic materials 0.000 claims description 2
- 229910052757 nitrogen Inorganic materials 0.000 claims description 2
- 229910052760 oxygen Inorganic materials 0.000 claims description 2
- 229910052698 phosphorus Inorganic materials 0.000 claims description 2
- 229910052717 sulfur Inorganic materials 0.000 claims description 2
- 230000002542 deteriorative effect Effects 0.000 claims 1
- 229910052742 iron Inorganic materials 0.000 claims 1
- 230000000694 effects Effects 0.000 description 13
- 230000000052 comparative effect Effects 0.000 description 8
- 229910000746 Structural steel Inorganic materials 0.000 description 5
- 238000005520 cutting process Methods 0.000 description 5
- 238000011282 treatment Methods 0.000 description 5
- 238000009661 fatigue test Methods 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 238000000137 annealing Methods 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 150000004767 nitrides Chemical class 0.000 description 3
- 230000002159 abnormal effect Effects 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 230000006698 induction Effects 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- 230000000171 quenching effect Effects 0.000 description 2
- 230000003679 aging effect Effects 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000012447 hatching Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 238000005121 nitriding Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000005496 tempering Methods 0.000 description 1
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- Heat Treatment Of Steel (AREA)
Description
本発明は、例えば自動車や産業機械などに使用されるギヤやシャフトなどの動力伝達部品として用いられる機械構造用鋼からなる鋼材に関し、特にガス浸炭を行って部品を製造した場合にねじり疲労強度に優れた機械構造用鋼からなる鋼材に関する。 The present invention relates to a steel material made of mechanical structural steel used as power transmission parts such as gears and shafts used in automobiles, industrial machines, etc., and particularly torsional fatigue strength when parts are manufactured by gas carburizing. The present invention relates to a steel material made of excellent mechanical structural steel.
自動車の駆動系に使用される部品、特にシャフト類はねじり疲労強度が問題となることが多い。そこで、このねじり疲労強度を向上するために、高周波焼入れ部品がよく用いられる（例えば、特許文献１参照。）。ところで、歯車と一体になったシャフトなどで、形状が非常に複雑な部品は、素材を焼入れ処理する前に切削などをして所要の形状に加工する必要がある。しかし、高周波焼入れ用鋼材はＣ含有量が０．４〜０．７％程度と高く、被削性に劣るために、このような歯車と一体になったシャフト類などの部品には適用が難しい。そこで、より高い被削性を要求される部品に対しては、高周波焼入れ用鋼材よりＣ含有量を低くし、Ｃ含有量を０．１〜０．２７％程度として、被削性の向上した浸炭用鋼とし、この鋼からなる鋼材を用いて所定の形状に切削加工した後、浸炭処理あるいは浸炭浸窒処理して表面硬度を高めるあるいは転動疲労寿命を高めるなどの方法を用いている（例えば、特許文献２参照。）。
Torsional fatigue strength is often a problem for parts used in automobile drive systems, particularly shafts. Therefore, in order to improve the torsional fatigue strength, an induction-hardened component is often used (see, for example, Patent Document 1). By the way, a part having a very complicated shape such as a shaft integrated with a gear needs to be processed into a required shape by cutting or the like before quenching the material. However, induction hardening steel has a high C content of about 0.4 to 0.7% and is inferior in machinability, so it is difficult to apply to parts such as shafts integrated with such gears. . Therefore, for parts requiring higher machinability, the C content is made lower than that of the steel for induction hardening, and the C content is set to about 0.1 to 0.27%, thereby improving the machinability. Carburizing steel, and after cutting into a predetermined shape using a steel material made of this steel, carburizing treatment or carburizing and nitriding treatment is used to increase the surface hardness or increase the rolling fatigue life ( For example, see
さらに、浸炭処理部品は、高周波焼入れ部品よりも高い曲げ疲労強度が得られることも知られており、浸炭処理部品のねじり疲労強度の向上に対してもニーズが高まっている。 Furthermore, it is also known that carburized parts can obtain higher bending fatigue strength than induction-hardened parts, and there is an increasing need for improving the torsional fatigue strength of carburized parts.
本発明が解決しようとする課題は、自動車や産業機械などに使用されるギヤやシャフトなどの動力伝達用の部品として用いられる機械構造用鋼からなり、被削性の低下を抑えてねじり疲労強度の向上を図った鋼材を提供することである。 The problem to be solved by the present invention is made of mechanical structural steel used as power transmission parts such as gears and shafts used in automobiles and industrial machines, and torsional fatigue strength is suppressed by reducing the machinability. It is providing the steel material which aimed at improvement.
上記の課題を解決するための本発明の手段は、請求項１の発明では、質量％で、Ｃ：０．１５〜０．３５％、Ｓｉ：０．３０〜０．９５％、Ｍｎ：０．１０〜１．００％、Ｐ：０．０３０％以下、Ｓ：０．０３０％以下、Ｃｒ：１．２０〜２．３０％、Ｃｕ：０．３０％以下、Ａｌ：０．００８〜０．１００％、Ｏ：０．００３０％以下、Ｎ：０．００２０〜０．０３００％を含有し、Ｎｉ：０．０９〜０．６８％、Ｍｏ：１．０％以下の１種または２種を含有し、残部Ｆｅ及び不可避不純物からなり、下記の（１）式を満足し、被削性を低下させることなくねじり疲労強度に優れた機械構造用鋼からなる鋼材である。
６．０％≧２Ｃ＋５Ｓｉ＋Ｃr−３Ｍｎ≧２．０％・・・（１）
The means of the present invention for solving the above-mentioned problems is that, in the invention of
6.0% ≧ 2C + 5Si + Cr-3Mn ≧ 2.0% (1)
請求項２の発明では、請求項１の化学成分に加え、さらにＴｉ：０．０２０〜０．２００％、Ｎｂ：０．０２〜０．２０、Ｂ：０．０００３〜０．００５０％のうち少なくとも１種以上を含有し、残部Ｆｅ及び不可避不純物からなり、下記の（１）式を満足し、被削性を低下させることなくねじり疲労強度に優れた機械構造用鋼からなる鋼材である。
６．０％≧２Ｃ＋５Ｓｉ＋Ｃr−３Ｍｎ≧２．０％・・・（１）
In the invention of
6.0% ≧ 2C + 5Si + Cr-3Mn ≧ 2.0% (1)
本発明の鋼の化学成分の限定理由を以下に説明する。なお、％は質量％である。
Ｃ：０．１５〜０．３５ ％
Ｃは、強度を付与するために必要な元素である。Ｃが０．１５％未満では、強度を確保することができない。一方、Ｃが０．３５％を超えると靭性が低下すると共に鋼素材の硬さが上昇して加工性が低下する。そこで、Ｃは０．１５〜０．３５ ％とし、望ましくは０．４５〜０．６５％とする。
The reason for limiting the chemical composition of the steel of the present invention will be described below. In addition,% is the mass%.
C: 0.15-0.35%
C is an element necessary for imparting strength. If C is less than 0.15%, the strength cannot be ensured. On the other hand, when C exceeds 0.35%, the toughness is lowered and the hardness of the steel material is increased, so that the workability is lowered. Therefore, C is 0.15 to 0.35%, preferably 0.45 to 0.65%.
Ｓｉ：０．３０〜０．９５％
Ｓｉは、鋼の脱酸に有効な元素であり、鋼に必要な焼入性および強度を付与する。またＳｉは、一定量以上の添加で浸炭異常層深さを浅くする効果がある。しかし、Ｓｉが０．３０％未満では、焼戻し軟化抵抗特性が低く、ガス浸炭時の浸炭異常層深さは深くなる。一方、Ｓｉが０．９５％を超えると素材の硬度が高くなり、加工性が劣化する。そこで、Ｓｉは０．３０〜０．９５％とし、望ましくは０．４５〜０．６５％とする。
Si: 0.30 to 0.95%
Si is an element effective for deoxidation of steel and imparts the hardenability and strength necessary for steel. Moreover, Si has the effect of making the carburizing abnormal layer depth shallow by addition of a certain amount or more. However, when Si is less than 0.30%, the temper softening resistance characteristic is low, and the carburizing abnormal layer depth during gas carburizing becomes deep. On the other hand, when Si exceeds 0.95%, the hardness of the material increases and the workability deteriorates. Therefore, Si is set to 0.30 to 0.95%, preferably 0.45 to 0.65%.
Ｍｎ：０．１０〜１．００％
Ｍｎは、鋼の脱酸に有効な元素であり、鋼に必要な焼入性を付与するが、０．１０％未満では効果が十分得られない。一方、Ｍｎが１．００％を超えると機械加工性を低下させる。そこで、Ｍｎは０．１０〜１．００％とし、望ましくは０．２５〜０．４０％とする。
Mn: 0.10 to 1.00%
Mn is an element effective for deoxidation of steel and imparts the hardenability necessary for steel, but if it is less than 0.10%, the effect is not sufficiently obtained. On the other hand, when Mn exceeds 1.00%, machinability is lowered. Therefore, Mn is set to 0.10 to 1.00%, preferably 0.25 to 0.40%.
Ｐ：≦０．０３０％
Ｐは、粒界に偏析して衝撃強度や疲労特性を低下させる。そこで、Ｐは０．０３０％以下とする。
P: ≦ 0.030%
P segregates at the grain boundaries and lowers the impact strength and fatigue characteristics. Therefore, P is set to 0.030% or less.
Ｓ：≦０．０３０％
Ｓは、ＭｎＳの形成により横方向の靭性や疲労強度を低下させる。そこで、Ｓは０．０３０％以下とする。
S: ≦ 0.030%
S reduces the toughness and fatigue strength in the lateral direction due to the formation of MnS. Therefore, S is set to 0.030% or less.
Ｃｒ：１．２０〜２．３０％
Ｃｒは、鋼に必要な焼入性を付与するが、１．２０％未満ではその効果が十分得られない。一方、Ｃｒが２．３０％を超えると、浸炭を阻害し、また素材硬度を上昇させて機械加工性を低下する。そこで、Ｃｒは１．２０〜２．３０％とし、望ましくは１．５０〜２．２０％とする。
Cr: 1.20 to 2.30%
Cr imparts the hardenability necessary for steel, but if it is less than 1.20%, the effect cannot be sufficiently obtained. On the other hand, if Cr exceeds 2.30%, carburization is hindered, and the material hardness is increased to lower the machinability. Therefore, Cr is 1.20 to 2.30%, preferably 1.50 to 2.20%.
Ｃｕ：≦０．３０％
Ｃｕは、スクラップから含有される不可避な元素であるが、時効性を有し、強度を向上させる効果がある。しかし、Ｃｕが０．３０％を超えると、熱間加工性が低下する。そこで、Ｃｕは０．３０％以下とする。
Cu: ≦ 0.30%
Cu is an inevitable element contained from scrap, but has aging properties and an effect of improving strength. However, when Cu exceeds 0.30%, the hot workability decreases. Therefore, Cu is made 0.30% or less.
Ａｌ：０．００８〜０．１００％
Ａｌは、鋼の脱酸に有効な元素であり、Ｎと結合してＡｌＮとして結晶粒粗大化抑制効果をもたらすが、０．００８％未満ではその効果が得られない。一方、Ａｌが０．１００％を超えると大型アルミナ系介在物を形成し、疲労特性および加工性が低下する。そこで、Ａｌは０．００８〜０．１００％とし、望ましくは０．０１０〜０．０５０％とする。
Al: 0.008 to 0.100%
Al is an element effective for deoxidation of steel, and combines with N to produce an effect of suppressing grain coarsening as AlN. However, if it is less than 0.008%, the effect cannot be obtained. On the other hand, if Al exceeds 0.100%, large alumina inclusions are formed, and fatigue characteristics and workability are deteriorated. Therefore, Al is made 0.008 to 0.100%, preferably 0.010 to 0.050%.
Ｏ：≦０．００３０％
Ｏは、鋼中に不可避に含有される元素であり、０．００３０％を超えると酸化物の増加により加工性や疲労強度が低下する。そこで、Ｏは０．００３０％以下とし、望ましくは０．００２０％以下とする。
O: ≦ 0.0030%
O is an element inevitably contained in the steel, and when it exceeds 0.0030%, workability and fatigue strength decrease due to an increase in oxides. Therefore, O is set to 0.0030% or less, preferably 0.0020% or less.
Ｎ：０．００２０〜０．０３００％
Ｎは、ＡｌＮやＮｂ窒化物として微細析出し、結晶粒粗大化を防止する効果があるが、０．００２０％未満ではその効果が得られない。一方、Ｎが０．０３００％を超えると窒化物が増加し、疲労強度や加工性が低下する。そこで、Ｎは０．００２０〜０．０３００％とする。
N: 0.0020 to 0.0300%
N is finely precipitated as AlN or Nb nitride and has an effect of preventing coarsening of crystal grains, but if it is less than 0.0020%, the effect cannot be obtained. On the other hand, when N exceeds 0.0300%, nitride increases and fatigue strength and workability decrease. Therefore, N is set to 0.0020 to 0.0300%.
Ｎｉ：０．０９〜０．６８％
Ｎｉは鋼の焼入性および靭性の向上に有効な元素である。ところで、本願の実施例である表１の発明鋼のＮｏ．５及びＮｏ．８の値に基づき、Ｎｉの下限値を０．０９％としている。また、Ｎｏ．７を削除したので、Ｎｏ．１２の値に基づき、Ｎｉの上限値を０．６８％としている。そこで、Ｎｉは０．０９〜０．６８％とする。
Ni: 0.09 to 0.68%
Ni is an element effective for improving the hardenability and toughness of steel. By the way, No. of invention steel of Table 1 which is an example of this application. 5 and no. Based on the value of 8, the lower limit value of Ni is 0.09%. No. 7 has been deleted. Based on the value of 12, the upper limit value of Ni is 0.68%. Therefore, Ni is set to 0.09 to 0.68% .
Ｍｏ：≦１．０％
Ｍｏは、鋼の焼入性、靭性および焼戻し軟化抵抗特性の向上に必要な元素である。しかし、Ｍｏが１．０％より多すぎると加工性を低下させ、かつ、鋼材コストが上昇する。そこで、Ｍｏは１．０％以下とする。
Mo: ≦ 1.0%
Mo is an element necessary for improving the hardenability, toughness and temper softening resistance characteristics of steel. However, if Mo is more than 1.0%, the workability is lowered and the steel material cost is increased. Therefore, Mo is set to 1.0% or less.
Ｔｉ：０．０２０〜０．２００％
Ｔｉは、鋼中のＣと結びついて炭化物を微細に形成し、結晶粒粗大化を防止する効果をもたらすが、その効果を得る場合には、０．０２０％以上添加する必要がある。一方、Ｔｉが０．２００％を超えて添加すると、機械加工性が低下する。そこでＴｉは０．０２０〜０．２００％とする。
Ti: 0.020 to 0.200%
Ti combines with C in the steel to form carbides finely and brings about an effect of preventing crystal grain coarsening. To obtain this effect, it is necessary to add 0.020% or more. On the other hand, when Ti is added in excess of 0.200%, the machinability is lowered. Therefore, Ti is set to 0.020 to 0.200%.
Ｎｂ：０．０２〜０．２０％
Ｎｂは、炭窒化物あるいは窒化物を形成し、結晶粒粗大化抑制効果をもたらすが、０．０２％未満ではその効果が得られない。一方、Ｎｂが０．２０％を超えると析出物の量が過剰となり、加工性が低下する。そこで、Ｎｂは０．０２〜０．２０％とし、望ましくは０．０３〜０．０７％とする。
Nb: 0.02 to 0.20%
Nb forms carbonitrides or nitrides and brings about an effect of suppressing the coarsening of crystal grains, but if less than 0.02%, the effect cannot be obtained. On the other hand, if Nb exceeds 0.20%, the amount of precipitates becomes excessive, and the workability deteriorates. Therefore, Nb is 0.02 to 0.20%, preferably 0.03 to 0.07%.
Ｂ：０．０００３〜０．００５０％
Ｂは、極少量の含有によって鋼の焼入性が著しく向上する元素である。そこで、Ｂは０．０００３〜０．００５０％とする。
B: 0.0003 to 0.0050%
B is an element that significantly improves the hardenability of the steel when contained in a very small amount. Therefore, B is set to 0.0003 to 0.0050%.
６．０％≧２Ｃ＋５Ｓｉ＋Ｃr−３Ｍｎ ≧２．０％・・・（１）とする理由
ねじり疲労強度を高める場合、合金元素の添加により芯部硬度を上げることが有効である。しかしながら、むやみに合金元素を添加した場合、被削性の低下が懸念される。
（１）式におけるＣ、Ｓｉ、Ｃｒ、Ｍｎの４元素は全て焼入性を上昇させる元素であり、これらの元素の添加によりねじり疲労強度の向上が見込まれる。ただし、Ｍｎは加工性改善のために行われる焼鈍処理などの熱処理時にミクロ組織の偏析を助長し、鋼のミクロ組織を不均一にする。従って、２Ｃ＋５Ｓｉ＋Ｃr−３Ｍｎで表すパラメータを２．０％以上から６．０％以下と制御しておくことで、不均一な鋼組織を抑制し、被削性を確保すると共にねじり疲労強度の向上が図れる。なお、２．０％より低いとねじり疲労強度向上の効果が見られない。また、６．０％より高くなると被削性が低下してしまう。
6.0% ≧ 2C + 5Si + Cr−3Mn ≧ 2.0% (1) Reason for Increasing Torsional Fatigue Strength It is effective to increase the core hardness by adding an alloy element. However, when an alloy element is added unnecessarily, there is a concern that the machinability is lowered.
The four elements C, Si, Cr, and Mn in the formula (1) are all elements that increase the hardenability, and the addition of these elements is expected to improve the torsional fatigue strength. However, Mn promotes the segregation of the microstructure at the time of heat treatment such as an annealing process for improving workability, and makes the microstructure of the steel non-uniform. Therefore, by controlling the parameter represented by 2C + 5Si + Cr-3Mn from 2.0% to 6.0%, the non-uniform steel structure is suppressed, the machinability is secured and the torsional fatigue strength is improved. I can plan. If it is less than 2.0%, the effect of improving torsional fatigue strength is not observed. Further, if it exceeds 6.0%, the machinability is lowered.
本発明は、上記の手段の機械構造用鋼からなる鋼材とし、この鋼材にガス浸炭を行うことで、鋼組織の均一性が向上し、かつ、被削性を低下することなく、ねじり疲労強度に優れた機械構造用鋼の鋼材からなる自動車や産業機械などに使用のギヤやシャフトなどの動力伝達用の部品が得られる。 The present invention is a steel material made of mechanical structural steel of the above means, and by performing gas carburization on this steel material, the uniformity of the steel structure is improved, and the torsional fatigue strength is reduced without reducing the machinability. It is possible to obtain parts for power transmission such as gears and shafts used in automobiles and industrial machines made of steel for machine structural use, which is excellent in machine structure.
表１に示す化学成分の組成の鋼を１００ｋｇ真空溶解炉で溶製し、得られた鋼を１２５０℃に加熱して５時間保持した後、直径３５ｍｍの棒鋼に製造した。続いて、９３０℃に６０分保持した後空冷して焼準した。次に直径３５ｍｍの棒鋼から、図１に示す形状（両端の上下が非対称であるのは、試験時に試験片が動かないようにするためである）のねじり疲労試験片１を作製し、図２に示すヒートパターンの条件により、９３０℃に加熱保持して０．５時間の均熱処理、３．０時間の浸炭処理、２．５時間の拡散処理からなる、ガス浸炭による浸炭焼入と１８０℃の焼戻しを実施し焼準材を得た。その後、試験条件を、片振り（０°から片方向だけに負荷を掛ける）、周波数５Ｈｚにて、下記に示すねじり疲労試験を実施した。
Steel having the chemical composition shown in Table 1 was melted in a 100 kg vacuum melting furnace, and the obtained steel was heated to 1250 ° C. and held for 5 hours, and then manufactured into a bar steel having a diameter of 35 mm. Subsequently, it was kept at 930 ° C. for 60 minutes and then air-cooled and normalized. Next, a torsional
被削性の評価は、上記で得た焼準材と、この焼準材とした後に、図３に示すように、１時間当たり３００℃の昇温速度で７９５℃に加熱して２．０時間保持し、５．０時間掛けて７２０℃に温度を下げ、さらに３．０時間掛けて６７０℃に温度を下げ、この温度から空冷により冷却する焼鈍処理を行った焼鈍材とにより実施し、その結果を表２に示す。 The evaluation of machinability was performed by using the normalizing material obtained above and the normalizing material, and then heating to 795 ° C. at a heating rate of 300 ° C. per hour as shown in FIG. Hold for a time, lower the temperature to 720 ° C. over 5.0 hours, further lower the temperature to 670 ° C. over 3.0 hours, and carry out the annealing with cooling treatment from this temperature by air cooling, The results are shown in Table 2.
表２の疲労限度は、上記の焼準材に対してねじり疲労試験の条件を、片振り、周波数が５Ｈｚ、疲労限度が２．０×１０6サイクルにおける値とし、この値の数字が大きいほど高強度であることを示している。 The fatigue limit shown in Table 2 is the value of the torsional fatigue test for the above-mentioned normalizing materials, with a single swing, a frequency of 5 Hz, and a fatigue limit of 2.0 × 10 6 cycles. It shows high strength.
同じく、表２の被削性は、焼準材、焼鈍材ともに被削性試験条件を、切込み量が０．５ｍｍ、切削速度が毎秒１５０ｍ、送り量が０．２５ｍｍ／ｒｅｖ、試験時間が１０分とし、バイトの逃げ面の摩耗量で評価し、この値の数字が大きいほど被削性は低下していることを示している。 Similarly, the machinability shown in Table 2 is based on the machinability test conditions for both the normalizing material and the annealed material, with a cutting depth of 0.5 mm, a cutting speed of 150 m / sec, a feed rate of 0.25 mm / rev, and a test time of 10 The amount of wear on the flank face of the cutting tool was evaluated, and the larger the value, the lower the machinability.
同じく、表２において、疲労限度の目標値は、比較鋼Ｎｏ．１４の１．０に対して１．２以上とする。さらに、被削性の目標値は、比較鋼Ｎｏ．１４の１．０に対して１．３以下とする。 Similarly, in Table 2, the target value of the fatigue limit is comparative steel No. It is 1.2 or more with respect to 1.0 of 14. Furthermore, the target value of machinability is the comparative steel No. It is 1.3 or less with respect to 1.0 of 14.
表２において、本願の発明鋼のＮｏ．１〜６およびＮｏ．８〜１２は、６．０％≧２Ｃ＋５Ｓｉ＋Ｃr−Ｍｎ≧２．０％・・・（１）式を満足している。一方、比較鋼のＮｏ．１４〜２９は、本願の発明鋼に対する比較鋼であり、この全ての鋼種において６．０％≧２Ｃ＋５Ｓｉ＋Ｃr−Ｍｎ≧２．０％・・・（１）式を満足していない。 In Table 2, No. of inventive steel of the present application . 1-6 and no. 8 to 12 satisfy 6.0% ≧ 2C + 5Si + Cr—Mn ≧ 2.0% (1). On the other hand, no. 14 to 29 are comparative steels for the invention steel of the present application, and in all of these steel types, 6.0% ≧ 2C + 5Si + Cr—Mn ≧ 2.0% (1) is not satisfied.
本願の発明鋼は、比較鋼のＮｏ．１４に比べてねじり疲労強度は向上し、かつ被削性の低下は見られない。
一方、比較鋼Ｎｏ．１６、Ｎｏ．１７、Ｎｏ．２０〜２２およびＮｏ．２９は比較鋼Ｎｏ．１４に比べてねじり疲労強度は向上している。しかし、それらはいずれも被削性が低下しており、本願の発明鋼とは異なる。さらに、比較鋼Ｎｏ．１５、Ｎｏ．１８、Ｎｏ．１９およびＮｏ．２３〜２８は、比較鋼Ｎｏ．１４に比べて被削性の低下は見られない。しかし、それらは、いずれもねじり疲労強度が向上しておらず本願の発明鋼とは異なる。
The invention steel of the present application is a comparative steel No. Compared to 14, torsional fatigue strength is improved and machinability is not reduced .
On the other hand, Comparative Steel No. 16, no. 17, no. 20-22 and no. No. 29 is a comparative steel No. 29. Compared to 14, the torsional fatigue strength is improved. However, all of them have reduced machinability and are different from the invention steel of the present application. Furthermore, comparative steel No. 15, no. 18, no. 19 and no. Nos. 23 to 28 are comparative steel Nos. Compared to 14, no reduction in machinability is seen. However, none of them has improved torsional fatigue strength and is different from the invention steel of the present application.
１ ねじり疲労試験片 1 Torsional fatigue test piece
Claims (2)
６．０％≧２Ｃ＋５Ｓｉ＋Ｃｒ−３Ｍｎ≧２．０％・・・（１） In mass%, C: 0.15 to 0.35%, Si: 0.30 to 0.95%, Mn: 0.10 to 1.00%, P: 0.030% or less, S: 0.030 %: Cr: 1.20-2.30%, Cu: 0.30% or less, Al: 0.008-0.100%, O: 0.0030% or less, N: 0.0020-0.0300 Ni: 0.09 to 0.68%, Mo: 1.0% or less of one or two types, and the balance consisting of Fe and inevitable impurities, satisfying the following formula (1) A steel material made of steel for machine structural use having excellent torsional fatigue strength without reducing machinability.
6.0% ≧ 2C + 5Si + Cr-3Mn ≧ 2.0% (1)
６．０％≧２Ｃ＋５Ｓｉ＋Ｃr−３Ｍｎ≧２．０％・・・（１） In addition to the chemical component of claim 1, containing at least one of Ti: 0.020 to 0.200%, Nb: 0.02 to 0.20, B: 0.0003 to 0.0050% , A steel material made of steel for machine structural use, which is composed of the balance Fe and inevitable impurities and has excellent torsional fatigue strength without deteriorating machinability, which satisfies the following formula (1).
6.0% ≧ 2C + 5Si + Cr-3Mn ≧ 2.0% (1)
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