JP3549978B2 - Induction hardening steel with excellent cold workability - Google Patents

Description

【００３２】
【表２】

【００３３】
圧延棒鋼の内、一部の材料については、７００℃×３時間→空冷の条件で簡易焼鈍を行った。焼鈍を行った材料は、表２の３列目にＡの記号をつけて示す。
これらの材料から、平行部直径２０ｍｍの静的捩り試験片、捩り疲労試験片を採取した。
静的捩り試験片、捩り疲労試験片について周波数８．５ｋＨｚ で高周波焼入れを行い、その後１７０℃×１時間の条件で焼戻しを行った。いずれも、有効硬化層深さは約５ｍｍである。その後、静的捩り試験、捩り疲労試験を行った。捩り疲労特性は１×１０^４ サイクルでの時間強度で評価した。
【００３４】
また被削性はハイスドリルによる寿命速度を用いて評価した。用いたドリルはＪＩＳ−ＳＫＨ５１で直径３ｍｍのハイスドリルであり、穴あけ条件は送り０．２５ｍｍ／ｒｅｖ 、穴深さ９ｍｍ、切削油はスピンドル油を用い、２リットル／分である。評価試験は、切削速度を種々変化させて各切削速度における切削不能になるまでのドリル寿命から切削速度−ドリル寿命曲線を求め、この曲線から寿命穴あけ総深さが１０００ｍｍでドリル寿命となる最大切削速度を求め、これを寿命速度とした。
【００３５】
表２に熱処理の有無、各供試材の硬さ、ハイスドリル寿命、静的捩り強度、捩り疲労強度を示す。表２の「熱処理」の欄に記号「Ａ」を付けている水準は、圧延棒鋼を７００℃×３時間→空冷の条件で簡易焼鈍を行った後に硬さ他の評価を行ったことを示す。一方、無印の水準は圧延材を熱処理なしで、硬さ他の評価を行ったことを示す。ハイスドリル寿命は、比較鋼３１のドリル寿命速度を１００とした時の相対値で示した。
【００３６】
また、捩り疲労過程での材質劣化挙動を評価するために、応力振幅７００ＭＰａ で１×１０^４ サイクル疲労試験を行った試験片について、（ｉ）表面での圧縮残留応力の減衰量および（ｉｉ）フェライト（２１１）面のＸ線回折ピークの半価幅の減衰量を評価した。Ｘ線回折ピークの半価幅の減衰量は、疲労過程での正味の硬さの低下量を評価するために用いた。Ｘ線発生源としては、Ｃｒ管球を使用した。
【００３７】
【表３】

【００３８】
【表４】

【００３９】
表２のＮｏ． １〜３０は本発明鋼である。本発明鋼材では、比較鋼３１と比較して、概ね硬さは軟らかく、ドリル寿命も優れている。また、静的捩り強度、捩り疲労強度は比較鋼３１と比較して、同一炭素量でみると、いずれも優れている。静的捩り破壊の破面はいずれも粒界割れを含む破面であり、本発明鋼が優れた捩り強度を示すのは、Ｍｏ添加他により粒界強度が増加した効果による。また、疲労過程での残留応力減衰量、疲労過程での半価幅減衰量は、比較鋼３１と比較して、同一炭素量でみると、いずれも抑制されている。これから、本発明鋼が優れた捩り強度を示すのは、Ｍｏ添加他により疲労過程での材質劣化が抑制された効果、および粒界強度が増加した効果による。
【００４０】
一方、比較鋼３３はＣの含有量が本発明の範囲を上回った場合であり、同一炭素量の本発明鋼に比較して、静的捩り強度、捩り疲労強度が劣っている。
比較鋼３４はＴｉの含有量が本発明の範囲を上回った場合であり、比較鋼材３５はＮの含有量が本発明の範囲を上回った場合であり、いずれも、同一炭素量の本発明鋼に比較して、硬さが硬く、ドリル寿命も悪く、また静的捩り強度、捩り疲労強度が劣っている。
【００４１】
比較鋼３６はＭｏの含有量が本発明の範囲を下回った場合であり、比較鋼材３８はＰの含有量が本発明の範囲を上回った場合であり、いずれも、同一炭素量の本発明鋼に比較して、静的捩り強度、捩り疲労強度が劣っている。
比較鋼３７，３９はＳｉ，Ｍｎの含有量が本発明の範囲を上回った場合であり、いずれも、同一炭素量の本発明鋼に比較して、硬さが硬く、ドリル寿命も悪い。
【００４２】
また、比較鋼３２はＭｎ，Ｍｏの含有量が本発明の範囲を下回り、ＴｉとＮの含有量が本発明の範囲を上回った場合である。比較鋼３１はＪＩＳ規格のＳ５３Ｃ鋼にＴｉ，Ｂを添加した鋼であり、Ｓｉ，Ｍｎ，Ｍｏ，Ｔｉ，Ｎの含有量が本願発明の範囲と異なった場合である。いずれも、同一炭素量の本発明鋼に比較して、硬さが硬く、ドリル寿命も悪く、また静的捩り強度、捩り疲労強度が劣っている。
【００４３】
【発明の効果】
以上述べたごとく、本発明の高周波焼入れ用鋼を用いることにより、素材の段階で優れた冷間加工性を有し、高周波焼入れにより優れた捩り強度特性、捩り疲労強度特性を有する部品を実現することが可能となり、産業上の効果は極めて顕著なるものがある。
【図面の簡単な説明】
【図１】自動車の動力伝達系を構成する部品を示す正面図で、（Ａ）はスプライン部を有するシャフト、（Ｂ）はフランジ付シャフト、（Ｃ）は外筒部付シャフトをそれぞれ示す。
【符号の説明】
１０…シャフト
１１，１２…スプライン部
２０，２１…シャフト
２２…フランジ
３０，３１，３２…シャフト
３３…外筒部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a steel for induction hardening having excellent cold workability, and more specifically, the shaft 10 having the spline portions 11 and 12 shown in FIGS. 21. Among the components constituting a power transmission system of an automobile, such as shafts 30 to 32 having an outer cylindrical portion 33, those related to steel suitable for components manufactured by processes including forming by cold working and induction hardening. It is.
[0002]
[Prior art]
Shaft parts constituting a power transmission system of an automobile are usually manufactured by forming medium carbon steel into a predetermined part shape by cold working such as cutting and rolling, and performing induction hardening-tempering. With the increase in the output of automobile engines and the compliance with environmental regulations, there is a strong tendency to improve torsional strength and torsional fatigue strength. On the other hand, with the increase in strength, the cold workability at the stage before induction hardening deteriorates and the productivity deteriorates, so both cold workability and high strength after induction hardening are required. I have.
[0003]
In contrast, Japanese Patent Publication No. 38847/1989 discloses that C: more than 0.35 to 0.65%, Si: 0.15% or less, Mn: 0.6% or less, and B: 0.0005 to 0. 005%, Ti: 0.05% or less, Al: 0.015 to 0.05%, N: 0.010% or less Using cold forging steel as a material, cold forging and induction hardening are applied to the machine. A method for manufacturing a machine structural component, which comprises manufacturing a structural component, is shown. One of the features of the present invention is that the Mn content is regulated to 0.6% or less. Further, as is apparent from Table 1 on pages 3 and 4 of the publication, the amount of Ti added is in the range of 0.02 to 0.04%. The cold workability of the steel described in the publication is not always sufficient, and sufficient strength as a shaft part cannot be realized.
[0004]
JP-A-5-179400 discloses that C: 0.38 to 0.45%, Si: 0.35% or less, Mn: more than 1.0 to 1.5%, and B: 0.0005 to 0.5%. Direct cutting-induction quenching with fine grain structure of 0035%, Ti: 0.01 to 0.05%, Al: 0.01 to 0.06%, N: 0.010% or less and ferrite grain size number 6 or more A steel material is shown. As described above, the Mn content of the present invention is more than 1.0 to 1.5%, and in the shaft component, sufficient static torsional strength after induction hardening can be obtained, but cold workability is low. Not very good. Further, in this publication, no consideration is given to the torsional fatigue strength which is one of the important characteristics for the induction hardened shaft part. Dominant factors differ between static torsional strength, which is a material resistance to a static load, and torsional fatigue strength, which is a material resistance to a repeated load, and are different characteristics. Therefore, at present, the present material is not always applied to parts requiring torsional fatigue strength characteristics.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide steel which is excellent in cold workability such as cutting and rolling before induction hardening, and which has excellent torsional strength and torsional fatigue strength after induction hardening, which is excellent in induction hardened parts. Things.
[0006]
[Means for Solving the Problems]
The present inventors have excellent cold workability at the material stage, and to achieve a component having excellent torsional strength characteristics and torsional fatigue strength characteristics by induction hardening, perform intensive studies and obtain the following knowledge. Obtained.
(1) The following method is effective to ensure cold workability at the stage of raw material.
[0007]
(I) Si and P which are solid solution hardening elements are reduced.
(Ii) Mn, which is a solid solution hardening element, is not added in a large amount. Instead, the hardenability is supplemented by the addition of B.
(Iii) Further, the quenchability is supplemented by using Mo which forms a carbide independently of cementite.
(2) Further, in order to ensure cold workability, it is essential to optimize the amounts of Ti and N.
In order to bring out the above-described effect of improving the hardenability of B, it is necessary to add Ti to reduce solid solution N. However, the addition of a large amount of Ti (Ti: 0.02 to 0.04%) as disclosed in Table 1 on page 3 to 4 of JP-B 1-38847 causes the following harmful effects. cause.
[0008]
(I) TiN or TiC precipitates in the cooling process of the bar rolling before the cold working or in the cooling process of the softening annealing, and in the steel with a large amount of Ti added, the precipitation hardening causes the hardness to increase rather.
(Ii) A large amount of precipitation of TiN and TiC significantly deteriorates machinability and causes cracking during cold working such as rolling, so that cold workability of high Ti steel is significantly deteriorated.
[0009]
It is considered that the cold workability of the technique disclosed in Japanese Patent Publication No. 38847/1990 is not always sufficient due to the adverse effect of a large amount of Ti addition on such cold workability. In order to suppress the adverse effect of Ti on cold workability and to bring out the effect of improving the hardenability of B, it is necessary to limit Ti to less than 0.005 to 0.020%. N: It is necessary to control in the range of 0.0015 to less than 0.0050 % .
(3) Next, torsional fatigue fracture of the induction hardened material occurs in the following process.
[0010]
A. Cracks occur at the boundary between the surface or the hardened layer and the core.
B. The crack propagates initially in a plane parallel or perpendicular to the axial direction. This is referred to below as Mode III destruction.
C. Brittle fracture occurs with grain boundary cracking at a plane of 45 degrees in the axial direction, resulting in final fracture. This is hereinafter referred to as mode I destruction.
(4) The hardened layer undergoes material deterioration during the torsional fatigue process. That is, in the torsional fatigue process, the surface compressive residual stress is attenuated and the hardness is reduced. The more easily the material deteriorates in the fatigue process, the earlier the fatigue cracks occur. The following method is effective to suppress such material deterioration during the torsional fatigue process.
[0011]
(I) Mo and Si are added. However, Si is added in an appropriate amount in consideration of deterioration in workability.
(Ii) Hardenability is ensured by adding Mn-B. However, Mn is added in an appropriate amount in consideration of deterioration in workability. Do not add a large amount of Cr, an element that stabilizes cementite.
(5) The mode III fracture described in the column of the above torsional fatigue fracture process “B.” is a ductile fracture accompanied by a dimple pattern. If a large number of precipitates such as TiN are present, this becomes a core of the ductile fracture and becomes a mode III fracture. Is more likely to occur. That is, the conventional boron steel containing 0.020% or more of Ti and 0.005% or more of N tends to cause ductile fracture with TiN as a nucleus. One of the causes of the insufficient strength characteristics of the technology disclosed in Japanese Patent Publication No. 1-38847 and the widespread use thereof is considered to be the cause. Therefore, from the viewpoint of improving the mode III fracture strength, it is necessary to regulate the amounts of Ti and N in the ranges of Ti: 0.005 to less than 0.020% and N: 0.0015 to less than 0.005%. .
(6) In order to suppress the brittle fracture mode I accompanied by grain boundary cracking at a plane of 45 degrees in the axial direction described in the section of the above torsional fatigue fracture process “C.”, grain boundary strengthening by the following method is required. It is valid.
[0012]
(I) Addition of B, Mo, Si. However, Si is added in an appropriate amount in consideration of deterioration in workability. B is due to the effect of driving out grain boundary segregation P from the grain boundaries. Mo and Si are due to the effect of miniaturizing carbides precipitated at the grain boundaries.
(Ii) Reduction of P, Cu, O amounts.
(Iii) A reduction in the amount of TiN precipitates by optimizing the amounts of Ti and N.
(7) Next, the static torsional fracture of the induction hardened material is accompanied by grain boundary cracking when the strength is higher than a certain level. That is, the static torsional strength is determined by the grain boundary strength. Therefore, in order to improve the static torsional strength, grain boundary strengthening by the above-described method is effective.
[0013]
The present invention has been made based on the above novel findings, and the gist of the present invention is as follows.
As a weight ratio, C: 0.40 to 0.60%, Si: 0.01 to 0.15%, Mn: more than 0.6 to less than 1.0%, S: 0.01 to 0.15%, Mo: 0.01 to 0.70%, Ti: 0.005 to less than 0.020%, Al: 0.010 to 0.06%, B: 0.0005 to 0.005%, N: 0.0015 Less than 0.0050%, if necessary, one or two kinds of Ni: 0.05 to 3.00%, Cr: 0.03 to 0.70%, V: 0.03 to 0.3 %, Nb: one or two kinds of 0.005 to 0.1%, P: 0.020% or less, Cu: 0.02% or less , O: 0.0020% or less, the balance being Is an induction hardening steel excellent in cold workability, characterized by comprising iron and unavoidable impurities.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The reason for limiting the component content range of the present invention as described above will be described.
C: 0.40 to 0.60%
C is an element effective for increasing the hardness of the induction hardened layer, but if it is less than 0.40%, the hardness is insufficient, and if it exceeds 0.60%, the hardness before induction hardening is increased. The content was determined to be 0.40 to 0.60% because the hardness becomes too hard to deteriorate the cold workability, and carbide precipitation at the austenite grain boundaries becomes remarkable, deteriorating the grain boundary strength.
[0015]
Si: 0.01 to 0.15%
Si is added as a deoxidizing element and for the purpose of strengthening the grain boundary. However, if the content is less than 0.01%, the effect is insufficient. On the other hand, since Si increases the material hardness by solid solution hardening, addition of more than 0.15% deteriorates cold workability such as machinability at a stage before induction hardening. For the above reasons, the content is set to 0.01 to 0.15%.
[0016]
Mn: more than 0.6 to less than 1.0% Mn is (i) improvement of hardenability and formation of MnS in steel, (ii) refinement of austenite grains during induction hardening heating, and (iii) coating It is added for the purpose of improving machinability. However, below 0.6%, this effect is insufficient. On the other hand, when Mn is excessively added, the pearlite fraction of the raw material before induction hardening is increased, thereby increasing the raw material strength and deteriorating the cold workability. In particular, this tendency becomes remarkable when 1.0% or more is added. For the above reasons, the content of Mn is set to more than 0.6 to less than 1.0%.
[0017]
S: 0.01-0.15%
S forms MnS in steel and is added for the purpose of miniaturizing austenite grains and improving machinability during induction hardening and heating, but the effect is insufficient at 0.01% or less. On the other hand, when the content exceeds 0.15%, the effect is saturated, and rather, grain boundary segregation is caused to cause grain boundary embrittlement. For the above reasons, the content of S is set to more than 0.01 to 0.15%.
[0018]
Mo: 0.01 to 0.70%
Mo is added for the purpose of (i) suppressing the deterioration of the material during the torsional fatigue process, (ii) increasing the grain boundary strength by causing grain boundary segregation at the austenite grain boundary, and (iii) improving the hardenability. However, if the content is less than 0.01%, this effect is insufficient. On the other hand, excessive addition exceeding 0.70% saturates the effect and causes deterioration of cold workability. 0.70%.
[0019]
Ti: less than 0.005 to 0.020% Ti is combined with N in the steel to form TiN, which is added for the purpose of preventing BN precipitation by completely fixing solid solution N, that is, securing solid solution B. . However, if the content is less than 0.005, the effect is insufficient. On the other hand, if the content is excessively added at 0.020% or more, cracking at the time of cold working with a large amount of TiN or TiC and deterioration of the mode III fracture strength in the final part. Therefore, the content was made 0.005 to less than 0.020%.
[0020]
Al: 0.010-0.06%
Al is added as a deoxidizing element and a grain refining element, but if its content is less than 0.010%, its effect is insufficient. Mode III Since the breaking strength is deteriorated, the content is set to 0.010 to 0.06%.
[0021]
B: 0.0005 to 0.005%
B is added for the purpose of increasing the hardenability by segregating at the austenite grain boundaries in the solid solution state. At the same time, there is also an effect of increasing grain boundary strength by driving out grain boundary impurities such as P and Cu from the grain boundaries. Grain boundary strengthening increases torsional strength and torsional fatigue strength. However, if the content is less than 0.0005%, the effect is insufficient. On the other hand, the excessive addition exceeding 0.005% rather causes grain boundary embrittlement, so that the content is limited to 0.0005 to 0.005%. did.
[0022]
N: 0.0015 to less than 0.0050 % N is added for the purpose of refining austenite grains during high-frequency heating by precipitation of carbonitrides such as AlN, but the effect is insufficient if less than 0.0015%. . On the other hand, if the content is 0.0050% or more , BN is precipitated to reduce solid solution B, and cold work cracking due to precipitation of a large amount of TiN and deterioration of the mode III fracture strength in the final part are caused. Was set to 0.0015 to less than 0.0050 % .
[0023]
P: 0.020% or less P increases the material hardness by solid solution hardening, and deteriorates cold forgeability at a stage before induction hardening. Further, segregation at the austenite grain boundaries is caused, and the grain boundary strength is reduced, so that the brittle fracture under torsional stress is easily caused, and thus the strength is reduced. In particular, when P exceeds 0.020%, the strength is remarkably reduced, so 0.020% was made the upper limit. In order to further strengthen the grain boundary, the content is preferably 0.015% or less.
[0024]
Cu: 0.02% or less Cu also causes grain boundary segregation at austenite grain boundaries similarly to P, causing a reduction in strength. In particular, when Cu exceeds 0.02% , the strength is remarkably reduced. Therefore , the upper limit is set to 0.02% .
O: 0.0020% or less O causes grain boundary segregation to cause grain boundary embrittlement, forms hard oxide-based inclusions in steel, facilitates brittle fracture under torsional stress, and reduces strength. Cause. In particular, when O exceeds 0.0020%, the strength decreases remarkably, so the upper limit was made 0.0020%.
[0025]
Next, the invention steels according to claims 2 and 4 are steels in which (i) suppression of a decrease in hardness during torsional fatigue process and (ii) improvement of hardenability are achieved by adding Cr and Ni.
Ni: 0.05 to 3.00%
Cr: 0.03 to 0.70%
All of these elements improve the hardenability and suppress the decrease in hardness during the torsional fatigue process. Ni also has the effect of improving the toughness near the grain boundaries and suppressing brittle fracture. This effect is insufficient if Ni is less than 0.05 and Cr is less than 0.03%, while if Cr is more than 0.7%, cementite in the structure before induction hardening is stabilized, and cementite is heated during induction hardening. Becomes difficult, and the hardness of the effect layer after induction hardening becomes insufficient. Further, the addition of a large amount of Ni exceeding 3.0% saturates the effect and is not preferable from the viewpoint of economy. Furthermore, these excessive additions cause deterioration of cold workability. For the above reasons, the content was limited to the above range.
[0026]
Next, the third and fourth aspects of the present invention are steels in which austenite grains during high-frequency heating are refined to increase the strength by preventing grain boundary destruction.
V: 0.03-0.3%
Nb: 0.005 to 0.1%
V and Nb form carbonitrides in the steel and have the effect of reducing austenite grains during high-frequency heating. However, when the V content is less than 0.03% and the Nb content is less than 0.005%, the effect is insufficient. On the other hand, when the V content exceeds 0.3% and the Nb content exceeds 0.1%, the effect is insufficient. Are saturated, and rather cause deterioration of the cold workability and strength of the final product. Therefore, these contents are set to V: 0.03 to 0.3% and Nb: 0.005 to 0.1%. .
[0027]
Here, one of the causes of the occurrence of cracks in the process of torsional fatigue is uneven hardness of the hardened layer. Target component of the present invention steels, cold work remains hot rolling - besides When induction hardening, after a heat treatment of simple annealing or the like in the hot rolling after A _3-point temperature below, cold working - It may be induction hardened. However, the structure that has undergone heat treatment such as simple annealing after hot rolling is greatly affected by the structure of the rolled material. Therefore, even when such a heat treatment is performed after hot rolling, it is important to optimize the texture of the rolled material in order to suppress the unevenness in hardness of the hardened layer during induction hardening. If the structure of the rolled material has a ferrite fraction of more than 35% and a ferrite crystal grain size of more than 30 μm, the hardened layer will have remarkable unevenness in hardness, which tends to cause torsional fatigue failure. Therefore, it is desirable that the ferrite structure fraction of the structure of the rolled material be 35% or less and the ferrite crystal grain size be 30 μm or less. However, in the steel of the present invention, the present structure factor is not particularly limited.
[0028]
Further, in the steel for induction hardening according to the present invention, the manufacturing conditions are not particularly limited, and any conditions may be used as long as the requirements of the present invention are satisfied. For example, in order to further improve the cold workability, the steel material is manufactured by hot rolling at a finishing temperature of 750 to 900 ° C, and an average cooling rate in a temperature range of 700 to 500 ° C after the finish rolling; There is a method of performing the reaction under a condition of 1.7 ° C./sec, but the present invention is not particularly limited. In the production of a part using the steel of the present invention, heat treatment such as simple annealing, normal annealing, and normalizing can be performed as necessary.
[0029]
Hereinafter, the effects of the present invention will be more specifically described with reference to examples.
[0030]
【Example】
A steel material having the composition shown in Table 1 was rolled into a steel bar having a diameter of 34 mm. From this steel bar, an optical microscope observation specimen was sampled, corroded with a 5% nital solution, observed at 200 times and 400 times, and the ferrite fraction and the ferrite crystal grain size were determined. Table 1 shows the ferrite fraction and the ferrite crystal grain size.
[0031]
[Table 1]

[0032]
[Table 2]

[0033]
For some of the rolled steel bars, simple annealing was performed under the condition of 700 ° C. × 3 hours → air cooling. The annealed material is indicated by the symbol A in the third column of Table 2.
From these materials, static torsional test pieces and torsional fatigue test pieces having a parallel portion diameter of 20 mm were collected.
The static torsional test specimen and the torsional fatigue test specimen were subjected to induction hardening at a frequency of 8.5 kHz, and thereafter tempered at 170 ° C. × 1 hour. In each case, the effective hardened layer depth is about 5 mm. Thereafter, a static torsional test and a torsional fatigue test were performed. The torsional fatigue properties were evaluated by the time strength at 1 × 10 ⁴ cycles.
[0034]
The machinability was evaluated using the life speed of a high speed drill. The drill used was a high-speed drill having a diameter of 3 mm according to JIS-SKH51. The drilling conditions were 0.25 mm / rev in feed, 9 mm in depth, and 2 liters / minute using spindle oil as cutting oil. In the evaluation test, a cutting speed-drill life curve was obtained from the drill life until cutting became impossible at various cutting speeds at various cutting speeds, and from this curve the maximum cutting at which the total life drilling depth was 1000 mm and the drill life was reached. The speed was determined and this was taken as the life speed.
[0035]
Table 2 shows the presence or absence of heat treatment, hardness of each test material, life of high speed drill, static torsional strength, and torsional fatigue strength. The level indicated by the symbol "A" in the column of "Heat treatment" in Table 2 indicates that the hardness and other evaluations were performed after the rolled steel bars were subjected to simple annealing under the condition of 700 ° C. × 3 hours → air cooling. . On the other hand, an unmarked level indicates that the rolled material was evaluated for hardness and other properties without heat treatment. The high-speed drill life was shown as a relative value when the drill life speed of the comparative steel 31 was set to 100.
[0036]
In addition, in order to evaluate the material deterioration behavior in the torsional fatigue process, (i) the attenuation of the compressive residual stress on the surface and (ii) the test specimens that were subjected to a 1 × 10 ⁴ cycle fatigue test at a stress amplitude of 700 MPa. The attenuation of the half width of the X-ray diffraction peak on the ferrite (211) plane was evaluated. The attenuation of the half width of the X-ray diffraction peak was used to evaluate the net decrease in hardness during the fatigue process. As an X-ray source, a Cr tube was used.
[0037]
[Table 3]

[0038]
[Table 4]

[0039]
No. of Table 2 1 to 30 are steels of the present invention. The steel material of the present invention is generally softer in hardness and has a longer drill life than the comparative steel 31. In addition, the static torsional strength and the torsional fatigue strength are all superior to the comparative steel 31 when viewed at the same carbon amount. The fracture surfaces of static torsional fracture are all fracture surfaces including grain boundary cracks, and the reason why the steel of the present invention exhibits excellent torsional strength is due to the effect of increasing the grain boundary strength by addition of Mo and the like. In addition, the residual stress attenuation amount in the fatigue process and the half width width attenuation amount in the fatigue process are all suppressed as compared with the comparative steel 31 in terms of the same carbon amount. From this, the reason why the steel of the present invention exhibits excellent torsional strength is due to the effect of suppressing the material deterioration in the fatigue process due to the addition of Mo and the effect of increasing the grain boundary strength.
[0040]
On the other hand, the comparative steel 33 is the case where the content of C exceeds the range of the present invention, and is inferior in static torsional strength and torsional fatigue strength as compared with the steel of the present invention having the same carbon content.
Comparative steel 34 is a case where the content of Ti exceeds the range of the present invention, and comparative steel material 35 is a case where the content of N exceeds the range of the present invention. , The hardness is high, the drill life is poor, and the static torsional strength and torsional fatigue strength are inferior.
[0041]
Comparative steel 36 is a case where the content of Mo is lower than the range of the present invention, and comparative steel 38 is a case where the content of P is higher than the range of the present invention. , The static torsional strength and the torsional fatigue strength are inferior.
Comparative steels 37 and 39 are cases in which the contents of Si and Mn exceed the range of the present invention, and both have higher hardness and a shorter drill life than the steels of the present invention having the same carbon content.
[0042]
In the comparative steel 32, the contents of Mn and Mo are lower than the range of the present invention, and the contents of Ti and N are higher than the range of the present invention. Comparative steel 31 is a steel in which Ti and B are added to JIS standard S53C steel, and the content of Si, Mn, Mo, Ti, and N is different from the range of the present invention. In each case, the hardness is high, the drill life is poor, and the static torsional strength and torsional fatigue strength are inferior to those of the steel of the present invention having the same carbon content.
[0043]
【The invention's effect】
As described above, by using the steel for induction hardening of the present invention, a component having excellent cold workability at the material stage and having excellent torsional strength characteristics and torsional fatigue strength characteristics by induction hardening is realized. And the industrial effect is extremely remarkable.
[Brief description of the drawings]
FIG. 1 is a front view showing parts constituting a power transmission system of an automobile, (A) shows a shaft having a spline portion, (B) shows a shaft with a flange, and (C) shows a shaft with an outer cylinder portion.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Shaft 11, 12 ... Spline part 20, 21 ... Shaft 22 ... Flange 30, 31, 32 ... Shaft 33 ... Outer cylinder part

Claims (4)

In mass%,
C: 0.40 to 0.60%,
Si: 0.01 to 0.15%,
Mn: more than 0.6 to less than 1.0%,
S: 0.01-0.15%,
Mo: 0.01-0.70%,
Ti: 0.005 to less than 0.020%,
Al: 0.010-0.06%,
B: 0.0005 to 0.005%,
N: 0.0015 to less than 0.0050 % ,
P: 0.020% or less,
Cu: 0.02% or less,
O: limited to 0.0020% or less,
Induction hardening steel with excellent cold workability, characterized in that the balance consists of iron and unavoidable impurities. In mass%,
C: 0.40 to 0.60%,
Si: 0.01 to 0.15%,
Mn: more than 0.6 to less than 1.0%,
S: 0.01-0.15%,
Mo: 0.01-0.70%,
Ti: 0.005 to less than 0.020%,
Al: 0.010-0.06%,
B: 0.0005 to 0.005%,
N: 0.0015 to less than 0.0050 % ,
further,
Ni: 0.05 to 3.00%,
Cr: 0.03 to 0.70%
Containing one or two of the following,
P: 0.020% or less,
Cu: 0.02% or less,
O: limited to 0.0020% or less,
Induction hardening steel with excellent cold workability, characterized in that the balance consists of iron and unavoidable impurities. In mass%,
C: 0.40 to 0.60%,
Si: 0.01 to 0.15%,
Mn: more than 0.6 to less than 1.0%,
S: 0.01-0.15%,
Mo: 0.01-0.70%,
Ti: 0.005 to less than 0.020%,
Al: 0.010-0.06%,
B: 0.0005 to 0.005%,
N: 0.0015 to less than 0.0050 % ,
further,
V: 0.03-0.3%,
Nb: 0.005 to 0.1%
Containing one or two of the following,
P: 0.020% or less,
Cu: 0.02% or less,
O: limited to 0.0020% or less,
Induction hardening steel with excellent cold workability, characterized in that the balance consists of iron and unavoidable impurities. In mass%,
C: 0.40 to 0.60%,
Si: 0.01 to 0.15%,
Mn: more than 0.6 to less than 1.0%,
S: 0.01-0.15%,
Mo: 0.01-0.70%,
Ti: 0.005 to less than 0.020%,
Al: 0.010-0.06%,
B: 0.0005 to 0.005%,
N: 0.0015 to less than 0.0050 % ,
further,
Ni: 0.05 to 3.00%,
Cr: 0.03 to 0.70%
Containing one or two of the following,
further,
V: 0.03-0.3%,
Nb: 0.005 to 0.1%
Containing one or two of the following,
P: 0.020% or less,
Cu: 0.02% or less,
O: limited to 0.0020% or less,
Induction hardening steel with excellent cold workability, characterized in that the balance consists of iron and unavoidable impurities.

Images