JP6102183B2 - Induction hardening steel and manufacturing method thereof - Google Patents
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- 229910000831 Steel Inorganic materials 0.000 title claims description 93
- 239000010959 steel Substances 0.000 title claims description 93
- 230000006698 induction Effects 0.000 title claims description 52
- 238000004519 manufacturing process Methods 0.000 title claims description 14
- 238000005204 segregation Methods 0.000 claims description 71
- 239000011159 matrix material Substances 0.000 claims description 43
- 239000000463 material Substances 0.000 claims description 32
- 238000000034 method Methods 0.000 claims description 26
- 238000002791 soaking Methods 0.000 claims description 24
- 238000005096 rolling process Methods 0.000 claims description 23
- 238000009792 diffusion process Methods 0.000 claims description 18
- 238000000137 annealing Methods 0.000 claims description 16
- 229910052750 molybdenum Inorganic materials 0.000 claims description 16
- 229910052748 manganese Inorganic materials 0.000 claims description 15
- 239000000203 mixture Substances 0.000 claims description 14
- 229910052759 nickel Inorganic materials 0.000 claims description 14
- 229910052804 chromium Inorganic materials 0.000 claims description 13
- 230000008018 melting Effects 0.000 claims description 13
- 238000002844 melting Methods 0.000 claims description 13
- 229910052799 carbon Inorganic materials 0.000 claims description 12
- 229910052698 phosphorus Inorganic materials 0.000 claims description 12
- 229910052710 silicon Inorganic materials 0.000 claims description 12
- 229910052802 copper Inorganic materials 0.000 claims description 9
- 238000005242 forging Methods 0.000 claims description 9
- 229910052717 sulfur Inorganic materials 0.000 claims description 9
- 239000012535 impurity Substances 0.000 claims description 8
- 229910052720 vanadium Inorganic materials 0.000 claims description 8
- 238000005266 casting Methods 0.000 claims description 5
- 238000005336 cracking Methods 0.000 description 12
- 238000004453 electron probe microanalysis Methods 0.000 description 10
- 238000010791 quenching Methods 0.000 description 9
- 238000013507 mapping Methods 0.000 description 8
- 239000002184 metal Substances 0.000 description 7
- 229910052751 metal Inorganic materials 0.000 description 7
- 238000012360 testing method Methods 0.000 description 7
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- 230000000171 quenching effect Effects 0.000 description 4
- 238000004458 analytical method Methods 0.000 description 3
- 230000005496 eutectics Effects 0.000 description 3
- 238000012546 transfer Methods 0.000 description 3
- 239000010953 base metal Substances 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005530 etching Methods 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 238000004080 punching Methods 0.000 description 2
- 238000005496 tempering Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910000655 Killed steel Inorganic materials 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 238000005211 surface analysis Methods 0.000 description 1
- 238000009849 vacuum degassing Methods 0.000 description 1
Description
本発明は、高周波焼入れ用鋼材およびその製造方法に関するものである。 The present invention relates to a steel material for induction hardening and a method for producing the same.
従来、鋼材に対して高周波焼入れを行い、鋼材の強度を高めたり、高硬度化することが、例えば軸受鋼などの用途において行われている。このような高周波焼入れにより鋼材の強度や硬度を高めようとする場合に問題となるのが、高周波焼入れ時の焼割れである。この焼割れを防止するためには、まず、偏析の少ない鋼材を用いる必要がある。
ところで、上記の軸受鋼などの用途では、軸受けのサイズの大型化にともない大断面の鋳片を用いて製造する必要がある。この場合、連続鋳造材でなく造塊材を用いることにより鋳片の大断面化に対応しなければならない。
Conventionally, induction hardening is performed on a steel material to increase the strength of the steel material or increase the hardness, for example, in applications such as bearing steel. A problem that arises when the strength and hardness of a steel material is increased by induction hardening is quench cracking during induction hardening. In order to prevent this burning crack, it is first necessary to use a steel material with little segregation.
By the way, in applications such as the above-mentioned bearing steel, it is necessary to manufacture using a slab having a large cross section as the size of the bearing increases. In this case, it is necessary to cope with an increase in the cross section of the slab by using an agglomerated material instead of a continuous cast material.
かような造塊材において、偏析を抑制する技術として、特許文献１には、鋳型上部に押湯部を設けるキルド鋼の造塊に際し、押湯部下端における鋳型短辺長さＨ２と押湯部溶鋼体積Ｖ、溶鋼と接触する押湯枠表面積Ａ，押湯枠の総括厚みｌ、押湯枠の総括熱伝導率λとが特定の関係を満足するようにして造塊を行なう技術が開示されている。 As a technique for suppressing segregation in such an agglomerated material, Patent Document 1 discloses that, in the case of ingot making of killed steel in which a feeder part is provided on the upper part of the mold, the mold short side length H 2 at the lower end of the feeder part and the pushing part are pressed. There is a technique for ingot forming such that the molten steel volume V, the surface area A of the feeder frame in contact with the molten steel, the overall thickness l of the feeder frame, and the overall thermal conductivity λ of the feeder frame satisfy a specific relationship. It is disclosed.
また、特許文献２には、偏析を少なくする金属の造塊方法として、鋳型上部に金属製の押し湯枠を設け、この押し湯枠の上端部まで溶湯を注入することにより、押し湯枠上端部近傍の溶湯を凝固させることで鋳塊を閉塞し、その後、鋳塊を鋳型から取り出し、鋳型内相当位置および押し湯枠内相当位置の鋳塊内部に未凝固の溶湯が存在する時期に、鋳塊の下端部から上端部に向けて、溶質成分の濃化した溶湯を順次しごき出すように、鋳塊の側面を全長にわたり圧下する方法が開示されている。 Further, in Patent Document 2, as a method for ingoting metal to reduce segregation, a metal hot water frame is provided on the upper part of the mold, and the molten metal is poured into the upper end of the hot water frame to thereby obtain an upper end of the hot metal frame. The ingot is closed by solidifying the molten metal in the vicinity of the part, and then the ingot is taken out from the mold, and when the unsolidified molten metal is present inside the ingot at the position corresponding to the position in the mold and the position corresponding to the inside of the feeder frame, A method is disclosed in which the side surface of the ingot is squeezed over the entire length so as to sequentially squeeze out the molten metal having a concentrated solute component from the lower end portion to the upper end portion of the ingot.
さらに、特許文献３には、溶鋼中のＭｎおよびＰの含有量（％）の積を求め、この積値が０．６０／偏析係数で求まる値よりも小さくなる、造塊法を選択し、ＭｎおよびＰの偏析に起因する異常組織の発生を抑止する方法が開示されている。 Further, in Patent Document 3, the product of the contents (%) of Mn and P in the molten steel is obtained, and the ingot method is selected in which this product value is smaller than the value obtained by 0.60 / segregation coefficient, A method for suppressing the occurrence of abnormal tissue due to segregation of Mn and P is disclosed.
しかしながら、特許文献１に開示されている、鋳造時に押し湯枠を設けて偏析を少なくする方法では、大きなマクロ偏析を少なくすることはできても、ミクロ偏析を改善するには不十分である。 However, the method disclosed in Patent Document 1 that provides a feeder frame during casting to reduce segregation is insufficient to improve microsegregation even though large macrosegregation can be reduced.
また、特許文献２に開示されている、鋳塊の側面を全長にわたって圧下する方法では、これを実施するための装置が大掛かりとなるため、大量生産には不向きである。 In addition, the method of reducing the side surface of the ingot that is disclosed in Patent Document 2 over the entire length is not suitable for mass production because an apparatus for carrying out this operation is large.
さらに、特許文献３に開示されている方法は、ＭｎおよびＰの偏析を抑制するものであり、例えば軸受鋼などのＭｏやＣｒなどを含む場合において偏析を抑制する方途を与えるものではなかった。 Furthermore, the method disclosed in Patent Document 3 suppresses segregation of Mn and P, and does not provide a way to suppress segregation when, for example, Mo or Cr such as bearing steel is included.
上記したいずれの技術においても、例えば軸受け鋼に必須の高周波焼入れ時の焼割れを防止するための手段を具体的に与えるところはなく、その提供が希求されていた。
そこで、本発明は、この問題を解決し、ミクロ偏析を制御して高周波焼入れ時の焼割れが確実に防止される、造塊法による高周波焼入れ用鋼材を提供すると共に、造塊法による場合であっても大掛かりな装置を必要とせずに、該高周波焼入れ用鋼材を製造するための方法について提案することを目的とする。
In any of the above-described techniques, there is no specific means for preventing quench cracking during induction hardening, which is essential for bearing steel, for example, and the provision thereof has been desired.
Therefore, the present invention solves this problem and provides a steel material for induction hardening by an ingot-making method in which microsegregation is controlled to reliably prevent cracking during induction hardening. Even if it exists, it aims at proposing about the method for manufacturing this steel material for induction hardening, without requiring a large-scale apparatus.
発明者らは、造塊法により鋳造された鋼材に、適切な温度並びに時間の下で均熱拡散焼鈍を施し、ミクロ偏析をＤＩ（偏析部）／ＤＩ（マトリックス）を指標として該指標が5.00未満となるまで低減することより、高周波焼入れ時の焼割れが格段に減少できることを見出し、本発明を完成させた。 The inventors have performed soaking diffusion annealing at an appropriate temperature and time on a steel material cast by the ingot-making method, and microsegregation is represented by DI (segregation part) / DI (matrix) as an index, and the index is 5.00. The inventors have found that the cracking at the time of induction hardening can be remarkably reduced by reducing it to less than less, and the present invention has been completed.
すなわち、本発明の要旨は、次のとおりである。
１．造塊法により鋳造され、さらに鍛造及び／又は圧延が施されてなる高周波焼入れ用鋼材であって、質量％で、Ｃ：0.30〜0.70％、Si：0.15〜0.35％、Mn：0.50〜1.0％、Ｐ：0.030％以下、Ｓ：0.030％以下、Al：0.50％以下、Cr：0.75〜1.6％およびMo：0.15〜0.35％を含有し、残部Feおよび不可避的不純物からなる成分組成であり、かつ偏析部における下記式（１）にて求められるＤＩ値：ＤＩ（偏析部）とマトリックスにおける下記式（１）にて求められるＤＩ値：ＤＩ（マトリックス）との比ＤＩ（偏析部）／ＤＩ（マトリックス）が5.00未満であることを特徴とする高周波焼入れ用鋼材。
記
ＤＩ＝（0.171＋0.001×C＋0.265×C2）×（1＋Mn×3.3333）×（1+0.7×Si）×（1＋2.16×Cr）×（１＋３×Mo）×（1＋0.365×Cu）×（1＋0.363×Ni）×（1+1.73×Ｖ）×25.4 ・・・（１）
但し、式中のＣ、Mn、Si、Cr、Mo、Ni、CuおよびＶは、各元素の含有量（質量％）
That is, the gist of the present invention is as follows.
1. It is a steel for induction hardening that is cast by the ingot-making method, and further subjected to forging and / or rolling, and in mass%, C: 0.30 to 0.70%, Si: 0.15 to 0.35%, Mn: 0.50 to 1.0% And P: 0.030% or less, S: 0.030% or less, Al: 0.50% or less, Cr: 0.75 to 1.6% and Mo: 0.15 to 0.35%, and a component composition consisting of the balance Fe and inevitable impurities, and DI value obtained by the following formula (1) in the segregation part: DI (segregation part) and DI value obtained by the following formula (1) in the matrix: DI (matrix) ratio DI (segregation part) / DI ( A steel for induction hardening characterized by a matrix) of less than 5.00.
DI = (0.171 + 0.001 × C + 0.265 × C 2 ) × (1 + Mn × 3.3333) × (1 + 0.7 × Si) × (1 + 2.16 × Cr) × (1 + 3 × Mo) × (1 + 0.365 × Cu) x (1 + 0.363 x Ni) x (1 + 1.73 x V) x 25.4 (1)
However, C, Mn, Si, Cr, Mo, Ni, Cu and V in the formula are the contents of each element (% by mass).
２．前記成分組成が、さらに、質量％で、Ni：1.8％以下を含有することを特徴とする前記１に記載の高周波焼入れ用鋼材。 2. 2. The steel material for induction hardening as described in 1 above, wherein the component composition further contains, by mass%, Ni: 1.8% or less.
３．質量％で、Ｃ：0.30〜0.70％、Si：0.15〜0.35％、Mn：0.50〜1.0％、Ｐ：0.030％以下、Ｓ：0.030％以下、Al：0.50％以下、Cr：0.75〜1.6％、Mo：0.15〜0.35％を含有し残部Feおよび不可避的不純物からなる成分組成である鋼塊を造塊法により鋳造し、鋳造後の鋼塊を、該鋼塊の融点（℃）×0.85〜融点（℃）×0.99の温度範囲にて均熱拡散焼鈍を行い、偏析部における下記式（１）式で求められるＤＩ値：ＤＩ（偏析部）とマトリックスにおける下記式（１）で求められるＤＩ値：ＤＩ（マトリックス）との比ＤＩ（偏析部）／ＤＩ（マトリックス）を5.00未満とすることを特徴とする高周波焼入れ用鋼材の製造方法。
記
ＤＩ＝（0.171＋0.001×C＋0.265×C2）×（1＋Mn×3.3333）×（1+0.7×Si）×（1＋2.16×Cr）×（１＋３×Mo）×（1＋0.365×Cu）×（1＋0.363×Ni）×（1+1.73×Ｖ）×25.4 ・・・（１）
但し、式中のＣ、Mn、Si、Cr、Mo、Ni、CuおよびＶは、各元素の含有量（質量％）
3. In mass%, C: 0.30 to 0.70%, Si: 0.15 to 0.35%, Mn: 0.50 to 1.0%, P: 0.030% or less, S: 0.030% or less, Al: 0.50% or less, Cr: 0.75 to 1.6%, Mo: A steel ingot containing 0.15-0.35% and comprising the remainder Fe and inevitable impurities is cast by the ingot-making method, and the steel ingot after casting is melted at the melting point (° C.) × 0.85 to melting point of the steel ingot. (° C) x 0.99 Diffusion annealing in a temperature range, DI value obtained by the following formula (1) in the segregation part: DI (segregation part) and DI value obtained by the following formula (1) in the matrix : DI (matrix) ratio DI (segregation part) / DI (matrix) is less than 5.00.
DI = (0.171 + 0.001 × C + 0.265 × C 2 ) × (1 + Mn × 3.3333) × (1 + 0.7 × Si) × (1 + 2.16 × Cr) × (1 + 3 × Mo) × (1 + 0.365 × Cu) x (1 + 0.363 x Ni) x (1 + 1.73 x V) x 25.4 (1)
However, C, Mn, Si, Cr, Mo, Ni, Cu and V in the formula are the contents of each element (% by mass).
４．前記成分組成が、さらに、質量％で、Ni：1.8％以下を含有することを特徴とする前記３に記載の高周波焼入れ用鋼材の製造方法。 4). 4. The method for producing a steel material for induction hardening according to 3 above, wherein the component composition further contains, by mass%, Ni: 1.8% or less.
５．前記均熱拡散焼鈍は、前記鋼塊に対し圧延および／または鍛造を施した後に行うことを特徴とする前記３または４に記載の高周波焼入れ用鋼材の製造方法。 5. 5. The method for producing a steel material for induction hardening according to 3 or 4 above, wherein the soaking and diffusion annealing is performed after rolling and / or forging the steel ingot.
本発明によれば、造塊法により鋳造した後の鋼におけるミクロ偏析について、高周波焼入れ時の焼割れが回避できる規定を具体的に与えることができるため、高周波焼入れにより鋼材を高強度化あるいは高硬度化する場合に、非常に有用である。 According to the present invention, the microsegregation in steel that has been cast by the ingot method can be specifically provided with provisions that can avoid quenching cracks during induction hardening. This is very useful when hardening.
まず、本発明の高周波焼入れ用鋼は、高周波焼入れにより転送面の硬化処理が行なわれる軸受鋼としての用途に適している。したがって、本発明では、軸受用途を念頭におき、成分組成を限定した。以下、本発明における各成分含有量の限定理由から順に説明する。
なお、以下の説明において各元素の含有量に関する「％」表示は、すべて「質量％」を意味する。
First, the induction hardening steel of the present invention is suitable for use as a bearing steel in which the transfer surface is hardened by induction hardening. Therefore, in the present invention, the component composition is limited with bearing application in mind. Hereinafter, it demonstrates in order from the reason for limitation of each component content in this invention.
In the following description, the “%” display relating to the content of each element means “mass%”.
Ｃ：0.30〜0.70％
Ｃは、鋼の強度を高め高周波焼入れによる硬化組織の疲労特性、とりわけ、鋼材を軸受鋼として適用した場合に、高周波焼入れにより強化が行われる転送面の耐転動疲労寿命特性を向上するのに有効な元素であり、本発明では0.30％以上含有させる。一方、0.70％を超えて含有すると、素材の鋳造中に巨大共晶炭化物が生成し、耐焼割れ性の低下を招く。以上のことから、Ｃ量は0.30〜0.70％とする。
C: 0.30 to 0.70%
C improves the fatigue characteristics of hardened structure by induction hardening by increasing the strength of steel, especially the rolling fatigue life characteristics of the transfer surface that is strengthened by induction hardening when steel is applied as bearing steel. It is an effective element, and is contained by 0.30% or more in the present invention. On the other hand, if the content exceeds 0.70%, giant eutectic carbides are produced during the casting of the material, resulting in a decrease in the resistance to fire cracking. From the above, the C amount is set to 0.30 to 0.70%.
Si：0.15〜0.35％
Siは、脱酸剤として、また、固溶強化により鋼の強度を高め、高周波焼入れによる硬化組織の疲労特性、とりわけ、鋼材を軸受鋼として適用した場合に、高周波焼入により強化が行われる転送面の耐転動疲労寿命特性を向上するために添加される元素であり、本発明では、0.15％以上添加する。しかし、0.35％超の添加は、鋼中の酸素と結合し、酸化物として鋼中に残存して転動疲労寿命特性の劣化を招く。さらに、偏析部に濃化した場合には、共晶炭化物を生成し易くする。以上のことから、Siの上限は0.35％とする。
Si: 0.15-0.35%
Si is a deoxidizer and strengthens steel by solid solution strengthening. Fatigue characteristics of hardened structure by induction hardening, especially when steel is applied as bearing steel, transfer is strengthened by induction hardening. It is an element added to improve the rolling fatigue life characteristics of the surface. In the present invention, it is added in an amount of 0.15% or more. However, addition of more than 0.35% combines with oxygen in the steel and remains in the steel as an oxide, leading to deterioration of rolling fatigue life characteristics. Further, when concentrated in the segregation part, eutectic carbide is easily generated. From the above, the upper limit of Si is 0.35%.
Mn：0.5〜1.0％
Mnは、焼入れ性を向上し、鋼の強靭性を高め、鋼材の疲労特性、特に、耐転動疲労寿命特性を向上するために添加される元素であり、本発明では、0.5％以上添加する。しかし、1.0％を超える添加は、転動疲労寿命特性を低下させる。また、偏析部に濃化した場合には、非金属介在物を生成し易くする。以上のことから、Mnの上限は1.0％とする。
Mn: 0.5-1.0%
Mn is an element added to improve the hardenability, increase the toughness of the steel, and improve the fatigue properties of the steel material, especially the rolling fatigue life resistance. In the present invention, Mn is added in an amount of 0.5% or more. . However, addition exceeding 1.0% deteriorates rolling fatigue life characteristics. Moreover, when it concentrates in a segregation part, it makes it easy to produce | generate a nonmetallic inclusion. From the above, the upper limit of Mn is 1.0%.
Ｐ：0.030％以下
Ｐは、鋼の母材靭性、転動疲労寿命を低下させる有害な元素であり、できるかぎり低減することが好ましい。特に、Ｐの含有量が0.030％を超えると、母材靭性および転動疲労寿命の低下が大きくなる。よって、Ｐは0.030％以下とする。好ましくは、0.020％以下である。なお、工業的にはＰ含有量を０％とすることは困難であり、0.002％以上で不可避に含有されることが多い。
P: 0.030% or less P is a harmful element that lowers the base metal toughness and rolling fatigue life of steel, and is preferably reduced as much as possible. In particular, when the P content exceeds 0.030%, the reduction in the base metal toughness and rolling fatigue life becomes large. Therefore, P is set to 0.030% or less. Preferably, it is 0.020% or less. Industrially, it is difficult to make the P content 0%, and in many cases it is unavoidably contained at 0.002% or more.
Ｓ：0.030％以下
Ｓは、非金属介在物であるMnSとして鋼中に存在する。軸受鋼は転動疲労の起点となり易い酸化物が少ないため、MnSが鋼中に多量に存在すると転動疲労寿命の低下を招く。従って、できるかぎり低減することが好ましく、本発明では、0.030％以下とする。好ましくは、0.020％以下である。なお、工業的にはＳ含有量を０％とすることは困難であり、0.0001％以上で不可避に含有されることが多い。
S: 0.030% or less S is present in steel as MnS which is a nonmetallic inclusion. Since bearing steel has few oxides that are likely to be the starting point of rolling fatigue, if a large amount of MnS is present in the steel, the rolling fatigue life is reduced. Therefore, it is preferable to reduce as much as possible, and in the present invention, it is 0.030% or less. Preferably, it is 0.020% or less. Industrially, it is difficult to make the S content 0%, and in many cases it is unavoidably contained at 0.0001% or more.
Al： 0.50％以下
Alは、脱酸剤として、また、窒化物を生成させてオーステナイト粒を微細化し、靭性並びに転動疲労寿命特性を向上させるために添加される元素であり、添加してもよい。この効果を発現させるためには、0.005％以上添加することが好ましい。しかし、0.50％を超えて添加すると、粗大な酸化物系介在物が鋼中に存在するようになり、鋼の転動疲労寿命特性の低下を招く。以上のことから、Al含有量の上限は0.50％とする。好ましくは、0.45％以下である。
Al: 0.50% or less
Al is an element that is added as a deoxidizer and also for forming nitrides to refine austenite grains and improving toughness and rolling fatigue life characteristics. In order to exhibit this effect, 0.005% or more is preferably added. However, if added over 0.50%, coarse oxide inclusions will be present in the steel, leading to a reduction in the rolling fatigue life characteristics of the steel. From the above, the upper limit of the Al content is 0.50%. Preferably, it is 0.45% or less.
Cr：0.75〜1.6％
Crは、Mnと同様に鋼の強靭性を高め、鋼材の耐転動疲労寿命特性を向上するために添加する元素であり、本発明では、0.75％以上添加する。しかし、1.6％を超える添加は、共晶炭化物を生成させ易くするため、転動疲労寿命特性を低下させるため、Crの上限は1.6％とする。
Cr: 0.75-1.6%
Cr, like Mn, is an element added to increase the toughness of the steel and improve the rolling fatigue life characteristics of the steel material. In the present invention, Cr is added at 0.75% or more. However, the addition exceeding 1.6% facilitates the formation of eutectic carbides and lowers the rolling fatigue life characteristics, so the upper limit of Cr is 1.6%.
Mo：0.15〜0.35％
Moは、焼入れ性や焼戻し後の強度を高め、鋼の転動疲労寿命特性を向上する元素であり、0.15％以上添加する。しかし、0.35％を超える添加は、Ｖ偏析、逆Ｖ偏析あるいは中心偏析部にMoの濃化層を形成し、Moの偏析度を悪化させ、鋼材の耐転動疲労寿命特性の低下をまねくため、Moの上限は0.35％とする。
Mo: 0.15-0.35%
Mo is an element that enhances hardenability and strength after tempering and improves the rolling fatigue life characteristics of steel, and is added in an amount of 0.15% or more. However, addition of more than 0.35% causes a Mo segregation layer to be formed in the V segregation, reverse V segregation or central segregation part, thereby deteriorating the degree of Mo segregation and leading to a decrease in rolling fatigue life characteristics of the steel. The upper limit of Mo is 0.35%.
さらに、上記した基本成分に加えて、以下に示す成分を適宜添加することが可能である。
Ni：1.8％以下
Niは、焼入れ性や焼戻し後の強度を高め、鋼の転動疲労寿命特性を向上する元素であり、必要とする強度に応じて選択して添加することができる。このような効果を得るためには、Niは0.005％以上添加することが好ましい。しかし、Niは1.8％を超えて添加すると、却って鋼の被削性が低下するため、Niは1.8％を上限として添加することが好ましい。
Furthermore, in addition to the basic components described above, the following components can be appropriately added.
Ni: 1.8% or less
Ni is an element that increases the hardenability and strength after tempering and improves the rolling fatigue life characteristics of steel, and can be selected and added according to the required strength. In order to obtain such an effect, Ni is preferably added in an amount of 0.005% or more. However, if Ni is added in excess of 1.8%, the machinability of the steel is lowered, so it is preferable to add Ni up to 1.8%.
本発明の高周波焼入れ用鋼材においては、上記以外の成分は、Feおよび不可避的不純物である。 In the steel for induction hardening of the present invention, the components other than the above are Fe and inevitable impurities.
さらに、本発明の高周波焼入れ用鋼材では、偏析部における下記式（１）で求められるＤＩ値：ＤＩ（偏析部）とマトリックスにおける下記式（１）で求められるＤＩ値：ＤＩ（マトリックス）との比ＤＩ（偏析部）／ＤＩ（マトリックス）が5.00未満である必要がある。
記
ＤＩ＝（0.171＋0.001×C＋0.265×C2）×（1＋Mn×3.3333）×（1+0.7×Si）×（1＋2.16×Cr）×（１＋３×Mo）×（1＋0.365×Cu）×（1＋0.363×Ni）×（1+1.73×Ｖ）×25.4 ・・・（１）
但し、式中のＣ、Mn、Si、Cr、Mo、Ni、CuおよびＶは、各元素の含有量（質量％）
Furthermore, in the steel for induction hardening of the present invention, the DI value obtained by the following formula (1) in the segregation part: DI (segregation part) and the DI value obtained by the following formula (1) in the matrix: DI (matrix). The ratio DI (segregation part) / DI (matrix) needs to be less than 5.00.
DI = (0.171 + 0.001 × C + 0.265 × C 2 ) × (1 + Mn × 3.3333) × (1 + 0.7 × Si) × (1 + 2.16 × Cr) × (1 + 3 × Mo) × (1 + 0.365 × Cu) x (1 + 0.363 x Ni) x (1 + 1.73 x V) x 25.4 (1)
However, C, Mn, Si, Cr, Mo, Ni, Cu and V in the formula are the contents of each element (% by mass).
発明者らは、造塊法により鋳造されたものを用いる場合、高周波焼入れ時に焼割れが発生する率が高い理由を調査し、成分元素の偏析によるものであることがわかった。図１には、高周波焼入により焼割れが発生した箇所におけるＥＰＭＡマッピングの例を示す。図１に例示されるように、焼割れが発生した箇所においては、Ｓ，Ｐ、Ｃ，Ｍｏの偏析が認められた。ここで、図１中のＳ／Ｓ０、Ｐ／Ｐ０、Mo／Mo０は、偏析度を意味するものであり、面分析を行った領域のうち、Ｓ，Ｐ，Mo強度値が高い部分を横切る線上にてライン分析を実施し、それぞれ元素の最大値Ｓ、Ｐ、Moと平均値Ｓ０、Ｐ０、Mo０とから求められる値である。 When using what was cast by the ingot-making method, the inventors investigated the reason why the rate of occurrence of quenching cracks during induction hardening was high, and found that this was due to segregation of the component elements. FIG. 1 shows an example of EPMA mapping at a place where a quench crack is generated by induction hardening. As illustrated in FIG. 1, segregation of S, P, C, and Mo was observed in the places where the burning cracks occurred. Here, S / S 0 , P / P 0 , and Mo / Mo 0 in FIG. 1 mean the degree of segregation, and the S, P, and Mo intensity values are high in the area subjected to surface analysis. The line analysis is performed on the line crossing the part, and the values are obtained from the maximum values S, P, Mo and the average values S 0 , P 0 , Mo 0 of the respective elements.
さらに、発明者らは、偏析が発生している箇所で焼割れが発生し易い理由が、偏析部では合金元素の濃化によりその他の部分よりも焼入れ性が高まり、偏析部とマトリックス部とで焼入れ性の差が大きくなることが、高周波焼入による焼割れの原因であるとの知見を得た。そこで、焼入れ性の指標として一般的に用いられているＤＩ値、つまり上記（１）式で求められるＤＩ値について、偏析部における値をマトリックスにおける値に対して大きくしすぎないようにすれば、焼割れが発生する危険は減少することを見出した。 In addition, the inventors have found that segregation is likely to cause cracking in the segregation part, because the segregation part has higher hardenability than the other part due to the concentration of the alloy elements, and the segregation part and the matrix part It was found that the difference in hardenability was the cause of quench cracking due to induction hardening. Therefore, for the DI value generally used as an index of hardenability, that is, the DI value obtained by the above formula (1), if the value in the segregation part is not made too large relative to the value in the matrix, It has been found that the risk of burning cracks is reduced.
以下、ＤＩ（偏析部）／ＤＩ（マトリックス）が5.00未満と特定する、知見を得るに至った実験結果について説明する。
Ｃ：0.45％、Si：0.25％、Mn：0.75％、Ｐ：0.010％、Ｓ：0.001％、Ni：0.01％、Cr：1.05％およびMo：0.25％を含み、残部Feおよび不可避的不純物からなる、成分組成の鋼塊を造塊法によって鋳造し、得られた鋼塊を図２に示す製造方法に従って高周波焼入れ用鋼材とした。
Hereinafter, the experimental results that led to the acquisition of knowledge that DI (segregation part) / DI (matrix) is specified to be less than 5.00 will be described.
C: 0.45%, Si: 0.25%, Mn: 0.75%, P: 0.010%, S: 0.001%, Ni: 0.01%, Cr: 1.05% and Mo: 0.25%, and the balance consists of Fe and inevitable impurities The steel ingot having the component composition was cast by the ingot-making method, and the obtained steel ingot was used as a steel material for induction hardening according to the manufacturing method shown in FIG.
すなわち、造塊法によりトップ部1334mm×1226mm、ボトム部1278mm×862mm、高さ2700mmの鋼塊を鋳造し、得られた鋼塊に対して均熱温度および均熱時間を変化させて均熱拡散焼鈍を行い、その後、450mm角×6000mmあるいは600mm角×6000mmに熱間圧延し、熱間鍛造により1000mmφの円柱状鋼片に据え込んだ。得られた円柱状鋼片の径方向中心部にポンチング加工により穿孔し、さらにローリング鍛造により外径2500mmφ、内径2300mmφのリング状に成形した。ここで、同一の均熱拡散焼鈍を行なったものについて10個ずつのリング状の成形品を作製した。 In other words, a steel ingot with a top part of 1334 mm x 1226 mm, a bottom part of 1278 mm x 862 mm, and a height of 2700 mm was cast by the ingot-making method, and the soaking temperature and soaking time were changed for the resulting steel ingot to achieve soaking diffusion After annealing, it was hot-rolled to 450 mm square x 6000 mm or 600 mm square x 6000 mm and placed in a 1000 mmφ cylindrical steel slab by hot forging. The obtained cylindrical steel piece was punched by punching at the center in the radial direction, and further formed into a ring shape having an outer diameter of 2500 mmφ and an inner diameter of 2300 mmφ by rolling forging. Here, ten ring-shaped molded articles were produced for those subjected to the same soaking diffusion annealing.
得られた鋼材の、リングの内径部に対して高周波焼入れを施した。ここで、このような方法にて成形されたリングの内径部に対して高周波焼入れを行なう場合、リング内径部は、造塊時に特に偏析が生じやすい鋼塊の中心部相当の位置となる。よって、偏析による焼割れが特に生じやすい。 The obtained steel was subjected to induction hardening on the inner diameter part of the ring. Here, when induction hardening is performed on the inner diameter portion of the ring formed by such a method, the inner diameter portion of the ring is located at a position corresponding to the center portion of the steel ingot which is particularly susceptible to segregation during ingot forming. Therefore, burn cracking due to segregation is particularly likely to occur.
そして、高周波焼入れ後の焼入部からＥＰＭＡマッピング用試験片を採取し、偏析部分について上記（１）式で求められるＤＩ（偏析部）の値を求めた。ここで（１）式中の偏析部の各元素の含有量は、ＥＰＭＡライン分析により各元素のピークの含有量とし、また、マトリックス中の各元素の含有量は、ＥＰＭＡライン分析により、偏析部以外の部分の含有量の平均値とした。 And the test piece for EPMA mapping was extract | collected from the quenching part after induction hardening, and the value of DI (segregation part) calculated | required by said (1) Formula about the segregation part was calculated | required. Here, the content of each element in the segregation part in the formula (1) is the peak content of each element by EPMA line analysis, and the content of each element in the matrix is determined by the EPMA line analysis. It was set as the average value of content of parts other than.
また、リング状の成形品について高周波焼入れ後の焼割れの有無を目視で確認し、焼割れが発生したものについては、焼割れ部分から試験片を採取し、焼割れが発生していないものについては、任意の位置から径方向断面組織観察用の試験片を採取し、径方向断面に対して塩酸エッチングを行ってから観察して偏析の最も大きい箇所を特定し、この箇所からＥＰＭＡマッピング用試験片を採取した。 Also, for ring-shaped molded products, visually check for the presence or absence of cracking after induction hardening, and for those that have cracked, take a test piece from the cracked part and do not crack. Takes a specimen for observing a radial cross-sectional structure from an arbitrary position, observes after performing hydrochloric acid etching on the radial cross-section, identifies the place with the largest segregation, and from this point, tests for EPMA mapping Pieces were collected.
次いで、ＤＩ（偏析部）／ＤＩ（マトリックス）で焼割れ発生率を整理した。ここで、割れ発生率は、各拡散焼鈍条件につきリング状の成形品１０個中の焼割れ発生した成形品の個数から求めた。そして、ひとつの拡散焼鈍条件につき成形品１０個のうち、ＤＩ（偏析部）／ＤＩ（マトリックス）が最大の値を示した成形品のＤＩ（偏析部）／ＤＩ（マトリックス）を、その拡散焼鈍条件において得られたＤＩ（偏析部）／ＤＩ（マトリックス）の代表値とし、この代表値で割れ発生率を整理した。その結果を図３に示す。図３から、ＤＩ（偏析部）／ＤＩ（マトリックス）が5.00未満であれば、割れ発生率は０％とできることがわかった。 Subsequently, the occurrence rate of burning cracks was arranged by DI (segregation part) / DI (matrix). Here, the crack generation rate was determined from the number of molded products in which cracking occurred in 10 ring-shaped molded products for each diffusion annealing condition. Then, among 10 molded products per diffusion annealing condition, DI (segregated portion) / DI (matrix) of the molded product having the maximum value of DI (segregated portion) / DI (matrix) is the diffusion annealed. The representative value of DI (segregation part) / DI (matrix) obtained under the conditions was used, and the crack occurrence rate was arranged based on this representative value. The result is shown in FIG. From FIG. 3, it was found that if DI (segregation part) / DI (matrix) is less than 5.00, the crack generation rate can be 0%.
したがって、本発明では、ＤＩ（偏析部）／ＤＩ（マトリックス）が5.00未満であることを必須要件とした。なお、本発明は、Ｎｉを積極的に添加していない場合もあり、また、Ｃｕ、Ｖは積極的に添加しないものであるが、Ｎｉ、Ｃｕ、Ｖ無添加鋼であっても不可避的不純物として、これらがそれぞれ0.1％以下の範囲で含有されることを許容するため、ＤＩ値を求めるにあたっては、鋼中のＮｉ、Ｃｕ、Ｖ含有量についても求め、式（１）中にＮｉ、Ｃｕ、Ｖ含有量の値として用いているものとする。 Therefore, in the present invention, the essential requirement is that DI (segregation part) / DI (matrix) is less than 5.00. In the present invention, Ni may not be positively added, and Cu and V are not positively added, but even Ni, Cu, and V-free steels are unavoidable impurities. In order to allow these to be contained within a range of 0.1% or less, in determining the DI value, the contents of Ni, Cu, and V in the steel are also determined. , And used as a value of V content.
上記の例では、ＤＩ（偏析部）／ＤＩ（マトリックス）を高周波焼入れ後の成形材において求めたが、これは割れが発生した場合に偏析部の位置の特定が極めて容易となるためである。すなわち、高周波焼入れ前の鋼材や成形品においてＤＩ（偏析部）／ＤＩ（マトリックス）を測定する場合は、マクロ試験などにより、まず大まかに偏析位置を特定する作業が必要となる点が繁雑である。しかも、ＤＩ（偏析部）／ＤＩ（マトリックス）の値自体は、高周波焼入れの前後で実質的に同じであった。これは高周波焼入れに伴う加熱保持時間が通常数秒〜数分程度、最長でも30分程度の処理であり、したがって成分の拡散が問題となるレベルではないためと考えられる。 In the above example, DI (segregation part) / DI (matrix) was determined in the molded material after induction hardening, because it is very easy to specify the position of the segregation part when cracking occurs. That is, when measuring DI (segregation part) / DI (matrix) in a steel material or a molded product before induction hardening, it is complicated that a work for specifying a segregation position roughly is first required by a macro test or the like. . Moreover, the value of DI (segregation part) / DI (matrix) itself was substantially the same before and after induction hardening. This is presumably because the heat holding time associated with induction hardening is usually a few seconds to a few minutes, and the longest is about 30 minutes. Therefore, the diffusion of components is not at a problematic level.
次に、本発明の高周波焼入れ用鋼材の製造方法について説明する。
上述した成分組成となる鋼を溶製した後、これを造塊法により鋳造して鋼塊とする。鋳造後の鋼塊に対して均熱拡散焼鈍を行うことによって、上記のＤＩ（偏析部）／ＤＩ（マトリックス）が5.00未満を満足させる。
Next, the manufacturing method of the steel material for induction hardening of this invention is demonstrated.
After melting the steel having the component composition described above, it is cast by an ingot-making method to form a steel ingot. By performing soaking diffusion annealing on the steel ingot after casting, the above DI (segregation part) / DI (matrix) satisfies less than 5.00.
ここで、均熱拡散焼鈍に際しては、均熱温度を、鋼塊の融点（℃）×0.85〜融点（℃）×0.99の温度範囲とする。なぜなら、均熱温度が融点×0.85より低いと、偏析元素の拡散が十分とならず、ＤＩ（偏析部）／ＤＩ（マトリックス）が5.00未満を達成できない。また、均熱拡散焼鈍時間が長くなり、生産性が阻害される。一方、均熱温度が融点×0.99より高いと、濃化偏析部が再溶解する危険性が高くなる。したがって、造塊後の鋼塊を鋼塊の融点（℃）×0.85〜融点（℃）×0.99の温度範囲で均熱拡散焼鈍する必要がある。 Here, in soaking diffusion annealing, the soaking temperature is set to a temperature range of melting point (° C.) × 0.85 to melting point (° C.) × 0.99 of the steel ingot. This is because if the soaking temperature is lower than the melting point × 0.85, the segregation element does not diffuse sufficiently, and DI (segregation part) / DI (matrix) cannot be less than 5.00. Moreover, soaking diffusion annealing time becomes long and productivity is inhibited. On the other hand, if the soaking temperature is higher than the melting point x 0.99, the risk of re-dissolution of the concentrated segregation part increases. Therefore, it is necessary to perform soaking diffusion annealing on the steel ingot after ingot forming in the temperature range of melting point (° C.) × 0.85 to melting point (° C.) × 0.99 of the steel ingot.
なお、この温度範囲での必要な均熱時間は、鋼の成分組成毎に異なるが、均熱時間が長ければ長い程、ＤＩ（偏析部）／ＤＩ（マトリックス）は１に近い値となるため、上記式（１）を満足するようになる必要均熱時間を実験により求めておけばよい。
この均熱拡散焼鈍は、造塊後の鋼塊に圧延や鍛造を施した後に行ってもよい。
The necessary soaking time in this temperature range varies depending on the steel composition, but the longer the soaking time, the closer DI (segregation part) / DI (matrix) is to 1. What is necessary is just to obtain | require the required soaking time which will satisfy | fill said Formula (1) by experiment.
This soaking diffusion annealing may be performed after rolling or forging the steel ingot after ingot forming.
表１に示す成分組成である鋼を公知の転炉精錬、真空脱ガス法により溶製し、造塊法によりトップ部1334mm×1226mm、ボトム部1278mm×862mm、高さ2700mmの鋼塊を鋳造した。得られた鋼塊に対して表２に示す均熱温度および均熱時間にて均熱拡散焼鈍を行い、その後、図２で示したように450mm角×6000mmあるいは600mm角×6000mmに熱間圧延し、さらに、熱間鍛造により1000mmφの円柱状鋼片とした。得られた円柱状鋼片の径方向中心部にポンチング加工により穿孔し、さらにローリング鍛造により外径2500mm、内径2300mmのリング状に成形し、これを高周波焼入れ用の素材とした。 Steel having the composition shown in Table 1 was melted by a known converter refining and vacuum degassing method, and a steel ingot having a top portion of 1334 mm x 1226 mm, a bottom portion of 1278 mm x 862 mm, and a height of 2700 mm was cast by the ingot forming method. . The steel ingot obtained was subjected to soaking diffusion annealing at the soaking temperature and soaking time shown in Table 2, and then hot rolled to 450 mm square x 6000 mm or 600 mm square x 6000 mm as shown in FIG. Furthermore, a 1000 mmφ cylindrical steel piece was obtained by hot forging. The obtained cylindrical steel pieces were punched by punching at the center in the radial direction, and further formed into a ring shape having an outer diameter of 2500 mm and an inner diameter of 2300 mm by rolling forging, which was used as a material for induction hardening.
得られた素材の、リングの内径部に対して高周波焼入れを施した。高周波焼入れは、焼入れ深さが３mmとなる条件で行った。その後、リング内径部について目視にて焼割れの発生の有無を確認した。 The obtained material was induction hardened on the inner diameter of the ring. Induction hardening was performed under the condition that the hardening depth was 3 mm. Then, the presence or absence of occurrence of burning cracks was visually confirmed for the inner diameter part of the ring.
また、高周波焼入れ部から、ＥＰＭＡマッピング用試験片を採取し、ＥＰＭＡマッピングにより、偏析部およびマトリックスのＤＩ値を求め、各サンプルについて、ＤＩ（偏析部）／ＤＩ（マトリックス）の値を求めた。ここで、焼割れが発生したものについては、焼割れ発生部からＥＰＭＡマッピング用試験片を採取した。焼割れが発生していないものについては、任意の位置から径方向断面組織観察用の試験片を採取し、径方向断面に対して塩酸エッチングを行なってから観察して偏析の最も大きい箇所を特定し、この箇所からＥＰＭＡマッピング用試験片を採取した。
表２に、焼割れの有無の確認結果、ＤＩ値（マトリックス）、ＤＩ（偏析部）／ＤＩ（マトリックス）を示す。
Moreover, the test piece for EPMA mapping was extract | collected from the induction hardening part, DI value of the segregation part and a matrix was calculated | required by EPMA mapping, and the value of DI (segregation part) / DI (matrix) was calculated | required about each sample. Here, about what a crack crack generate | occur | produced, the test piece for EPMA mapping was extract | collected from the crack crack generation part. For specimens that have not been cracked, collect specimens for observing the radial cross-sectional structure from any position, and then perform hydrochloric acid etching on the radial cross-section to observe and identify the location with the greatest segregation. Then, an EPMA mapping test piece was collected from this location.
Table 2 shows the results of confirming the presence or absence of burning cracks, the DI value (matrix), and DI (segregation part) / DI (matrix).
ＤＩ（偏析部）／ＤＩ（マトリックス）が5.00未満とした本発明の高周波焼入れ用鋼は、焼割れの発生が認められなかったが、ＤＩ（偏析部）／ＤＩ（マトリックス）が5.00以上である比較例においては、焼割れの発生が認められた。また、ＤＩ（偏析部）／ＤＩ（マトリックス）が5.00未満の鋼材を得るためには均熱拡散焼鈍における均熱時間を調整すればよいことが表２（たとえば素材No.３〜６）から分かるが、表２の素材No.４と７より、均熱温度を（鋼材の融点（℃）×0.85〜融点（℃）×0.99の範囲内で）調整してもよいことが分かる。 In the induction hardening steel of the present invention in which DI (segregation part) / DI (matrix) was less than 5.00, no occurrence of quench cracking was observed, but DI (segregation part) / DI (matrix) was 5.00 or more. In the comparative example, the occurrence of burning cracks was observed. Moreover, in order to obtain steel materials with DI (segregation part) / DI (matrix) less than 5.00, it is understood from Table 2 (for example, materials Nos. 3 to 6) that the soaking time in soaking diffusion annealing may be adjusted. However, it can be seen from the material Nos. 4 and 7 in Table 2 that the soaking temperature may be adjusted (within the range of the melting point (° C.) × 0.85 to the melting point (° C.) × 0.99 of the steel material).
Claims (7)
記
ＤＩ＝（0.171＋0.001×C＋0.265×C2）×（1＋Mn×3.3333）×（1+0.7×Si）×（1＋2.16×Cr）×（１＋３×Mo）×（1＋0.365×Cu）×（1＋0.363×Ni）×（1+1.73×Ｖ）×25.4 ・・・（１）
但し、式中のＣ、Mn、Si、Cr、Mo、Ni、CuおよびＶは、各元素の含有量（質量％） In mass%, C: 0.30~0.70%, Si : 0.15~0.35%, Mn: 0.50~1.0%, P: 0.030% or less, S: 0.030% or less, Al: 0.50% or less, Cr: from .75 to 1.6% And Mo: 0.15 to 0.35%, a component composition comprising the balance Fe and inevitable impurities, and a DI value obtained by the following formula (1) in the segregation part: DI (segregation part) and the following formula in the matrix A steel material for induction hardening characterized in that the DI value obtained in (1): ratio DI (segregation part) / DI (matrix) to DI (matrix) is less than 5.00.
DI = (0.171 + 0.001 × C + 0.265 × C 2 ) × (1 + Mn × 3.3333) × (1 + 0.7 × Si) × (1 + 2.16 × Cr) × (1 + 3 × Mo) × (1 + 0.365 × Cu) x (1 + 0.363 x Ni) x (1 + 1.73 x V) x 25.4 (1)
However, C, Mn, Si, Cr, Mo, Ni, Cu and V in the formula are the contents of each element (% by mass).
記
ＤＩ＝（0.171＋0.001×C＋0.265×C2）×（1＋Mn×3.3333）×（1+0.7×Si）×（1＋2.16×Cr）×（１＋３×Mo）×（1＋0.365×Cu）×（1＋0.363×Ni）×（1+1.73×Ｖ）×25.4 ・・・（１）
但し、式中のＣ、Mn、Si、Cr、Mo、Ni、CuおよびＶは、各元素の含有量（質量％） In mass%, C: 0.30 to 0.70%, Si: 0.15 to 0.35%, Mn: 0.50 to 1.0%, P: 0.030% or less, S: 0.030% or less, Al: 0.50% or less, Cr: 0.75 to 1.6%, Mo: A steel ingot containing 0.15-0.35% and comprising the remainder Fe and inevitable impurities is cast by the ingot-making method, and the steel ingot after casting is melted at the melting point (° C.) × 0.85 to melting point of the steel ingot. (° C) x 0.99 Diffusion annealing in a temperature range, DI value obtained by the following formula (1) in the segregation part: DI (segregation part) and DI value obtained by the following formula (1) in the matrix : DI (matrix) ratio DI (segregation part) / DI (matrix) is less than 5.00.
DI = (0.171 + 0.001 × C + 0.265 × C 2 ) × (1 + Mn × 3.3333) × (1 + 0.7 × Si) × (1 + 2.16 × Cr) × (1 + 3 × Mo) × (1 + 0.365 × Cu) x (1 + 0.363 x Ni) x (1 + 1.73 x V) x 25.4 (1)
However, C, Mn, Si, Cr, Mo, Ni, Cu and V in the formula are the contents of each element (% by mass).
記
ＤＩ＝（0.171＋0.001×C＋0.265×C 2 ）×（1＋Mn×3.3333）×（1+0.7×Si）×（1＋2.16×Cr）×（１＋３×Mo）×（1＋0.365×Cu）×（1＋0.363×Ni）×（1+1.73×Ｖ）×25.4 ・・・（１）
但し、式中のＣ、Mn、Si、Cr、Mo、Ni、CuおよびＶは、各元素の含有量（質量％） A method for producing a steel for induction hardening, which is cast by an ingot-making method and further subjected to forging and / or rolling, wherein the induction hardening steel is in mass%, C: 0.30 to 0.70%, Si: 0.15 to Containing 0.35%, Mn: 0.50 to 1.0%, P: 0.030% or less, S: 0.030% or less, Al: 0.50% or less, Cr: 0.75 to 1.6% and Mo: 0.15 to 0.35%, the balance Fe and inevitable It is a component composition composed of impurities, and the DI value obtained by the following formula (1) in the segregation part: DI (segregation part) and the DI value obtained by the following formula (1) in the matrix: DI (matrix) Ratio DI (segregation part) / DI (matrix) is less than 5.00, The manufacturing method of the steel materials for induction hardening characterized by the above-mentioned .
Record
DI = (0.171 + 0.001 × C + 0.265 × C 2 ) × (1 + Mn × 3.3333) × (1 + 0.7 × Si) × (1 + 2.16 × Cr) × (1 + 3 × Mo) × (1 + 0.365 × Cu ) × (1 + 0.363 × Ni) × (1 + 1.73 × V) × 25.4 (1)
However, C, Mn, Si, Cr, Mo, Ni, Cu and V in the formula are the contents of each element (% by mass).
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