JP3705462B2 - Manufacturing method of gear with excellent tooth surface strength - Google Patents

Description

【００４１】
表１に示すように、発明例１〜４ではいずれもピッティング寿命が長く、摩耗深さは小さいものとなっていた。
【００４２】
これに対して、比較例１〜３ではピッティング寿命が短く、摩耗深さは大きいものとなっていた。
【００４３】
（実施例２）
表２に示す鋼を素材とし、９２０℃で６０分間保持後冷却する焼ならしを行い、さらに、図４（ａ）に示すような中央太径部の直径が２６ｍｍ，中央太径部の長さが２８ｍｍ，両側細径部の直径がともに２２ｍｍ，全長が１３０ｍｍのローラーピッティング試験用試験片Ｓ_１を機械加工により製作すると共に、図５に示すような直径が７０ｍｍ，厚さが１０ｍｍのピンオンディスク摩耗試験用円盤試験片Ｓ_２を機械加工により製作した。
【００４４】
次いで、図３に示す温度−時間説明図において、温度Ｔ_１，時間ｔ_１，雰囲気ガスＮ_１，Ｎ_２がそれぞれ表２に示す条件でかつ雰囲気カーボンポテンシャルＣ．Ｐ．が１．１の条件、および、温度Ｔ_２，時間ｔ_２，雰囲気ガスＮ_１，Ｎ_２がそれぞれ表２に示す条件でかつ雰囲気カーボンポテンシャルＣ．Ｐ．が０．９５の条件による浸炭処理と浸窒処理とを同時に行ったのち、空冷（Ａ．Ｃ．）した。
【００４５】
続いて、各試験片Ｓ_１，Ｓ_２を再加熱してオーステナイト化し、温度Ｔ_３，時間ｔ_３，雰囲気ガスＮ_３がそれぞれ表２に示す条件による浸窒処理を再度行ったのち、温度１８０℃のソルト浴中に浸漬する焼入れ（Ｓ．Ｑ．）を行った。
【００４６】
そして、各試験片Ｓ_１，Ｓ_２の最表面のＣ量，最表面のＮ量，Ｎの侵入深さ、有効硬化深さ，有効硬化深さに対するＮの侵入深さを調べたところ、表３に示す結果であった。
【００４７】
さらに、図４（ａ）に示したローラーピッティング試験用試験片Ｓ_１を用いて、図４（ｂ）に示すような直径が１３０ｍｍ，厚さが１８ｍｍのローラー（ＳＣｒ４２０鋼の浸炭焼入れ品）Ｒを相手材とし、接触圧力：３．７ＧＰａ，すべり率：−４０％、潤滑油温度：８０℃の条件によるローラーピッティング試験を行って、ピッティング寿命を調べたところ、同じく表３に示す結果であった。
【００４８】
さらにまた、図５に示した円盤試験片Ｓ_２を用いて、同じく図５に示すような本体部の直径が８ｍｍ，本体部先端の半径が１００ｍｍＲ，鍔部の直径が１２ｍｍのピン（ＳＫ３の熱処理品）Ｐを相手材として、接触圧力：１５０ＭＰａ，摺動速度：０．２８ｍ／ｓの条件によるピンオンディスク摩耗試験を行って摩耗深さを調べたところ、同じく表３に示す結果であった。
【００４９】
なお、表１の比較例１１は浸炭・浸窒温度を低くかつ再浸窒温度を高くして行った場合を示し、比較例１２，１３は浸炭・浸窒温度を高くかつ再浸窒温度を低くして行った場合を示しており、これらの場合についても同様の評価試験を行ったところ、同じく表３に示す結果であった。
【００５０】
【表２】

【００５１】
【表３】

【００５２】
表２，表３に示すように、発明例１１〜１３ではいずれもピッティング寿命が長く、摩耗深さは小さいものとなっていた。
【００５３】
これに対して、比較例１１〜１３ではピッティング寿命が短く、摩耗深さは大きいものとなっていた。
【図面の簡単な説明】
【図１】 本発明による表面硬化組織を有する歯車における表面からの深さとＣ量およびＮ量との関係を概略的に示すグラフである。
【図２】 従来例による表面硬化組織を有する歯車における表面からの深さとＣ量およびＮ量との関係を概略的に示すグラフである。
【図３】 浸炭・浸窒処理および再浸窒処理条件を示す温度−時間説明図である。
【図４】 ローラーピッティング試験片の平面説明（図４（ａ））およびローラーピッティング試験要領を示す斜面説明図（図４（ｂ））である。
【図５】 ピンオンディスク型摩耗試験要領を示す正面説明図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a gear excellent in tooth surface strength used as a gear among machine elements used in various machine structures such as automobiles, industrial machines, and agricultural machines.
[0002]
[Prior art]
This type of gear is required to have excellent pitting resistance and wear resistance (or scoring resistance) on the tooth surface. To improve wear resistance (or scoring resistance), surface hardening treatment such as carburizing quenching or carbonitriding quenching is performed to increase the surface hardness or increase the curing depth. The method is widely adopted.
[0003]
When such a surface hardening treatment is performed, the relationship between the depth from the surface, the C amount and the N amount is, for example, as shown in FIG. 9% by weight) gradually decreases in the depth direction, and the N amount (0.1 to 0.3% by weight) on the outermost surface decreases sharply in the depth direction. .
[0004]
Therefore, in recent years, the surface pressure load on the gear tends to further increase, and as a countermeasure, chrome-containing steel is carburized to reduce abnormal structures with poor hardenability, and the temperature is slightly lowered after carburizing. Thus, the nitriding treatment is continued, or the reheating treatment is carried out before the nitriding treatment, as disclosed in JP-A-62-33755 (JP-B-7-13293) and JP-A-62-33757 ( Japanese Patent Publication No. 7-13294 (Japanese Patent Publication No. 7-13294), and Japanese Patent Application Laid-Open No. 49-10124 (Japanese Patent Publication No. 54-) in which residual austenite produced by carbonitriding is work-hardened to improve load capacity. The method described in Japanese Patent No. 17699) was considered.
[0005]
[Problems to be solved by the invention]
However, the surface pressure load tends to increase further, and there is a case where the contact surface is accompanied by more heat generation than conventional (for example, heat generation of 300 ° C. or more). There is a problem that the reduction of abnormal structure and the utilization of residual austenite by work hardening are not sufficient for improving the pitting resistance and wear resistance (or scoring resistance). The problem was to solve the problem.
[0006]
OBJECT OF THE INVENTION
The present invention has been made by paying attention to such conventional problems, and has excellent tooth surface strength with further improved pitting resistance and wear resistance (or scoring resistance) on the tooth surface. It aims at providing the manufacturing method of a gearwheel.
[0007]
[Means for Solving the Problems]
In view of the fact that the surface pressure load is further increased and the contact surface has been accompanied by heat generation more than conventional (for example, heat generation of 300 ° C. or more), even in such a case, It has been found that it is effective to form a hardened surface layer that is difficult to soften even at around 300 ° C in order to further improve pitting and wear resistance (or scoring resistance). Focusing on carbonitriding that further utilizes nitrogen, we have developed an optimal distribution in the depth direction of nitrogen that is effective in improving temper softening resistance and developed a heat treatment method that can provide such an optimal distribution. The present invention has been achieved.
[0008]
That is, the manufacturing method of the gear excellent in the tooth surface strength according to the present invention is made of case-hardened steel for machine structure as described in claim 1, and the C amount of the outermost surface is 0.5 weight. % And 0.9% by weight or less, and the N amount on the outermost surface is 0.3% by weight or more and 0.8% by weight or less, the N amount is equal to the C amount, and the penetration depth of N is A method of manufacturing a gear having a surface-hardened structure that reaches a depth of at least 80% of an effective hardening depth, which is a depth at which a hardness Hv550 is obtained, and is a gear material made of case-hardened steel for mechanical structure On the other hand, after performing the nitriding treatment at the same time as the carburizing treatment at a temperature of 800 ° C. or more and 950 ° C. or less, cooling, and further reheating to an austenitizing temperature of 800 ° C. or more and 930 ° C. or less and performing the nitriding treatment again. By hardening, the hardened surface structure not only C but N Is characterized in that it consists of a solid solution was dense martensite.
[0014]
[Effects of the Invention]
In the manufacturing method of the gear excellent in tooth surface strength according to the present invention, as the material, carbon structural hardened steel such as S09CK, S15CK, S20CK, nickel-chromium such as SNC415, SNC815, SNCM220, SNCM415, SNCM420, SNCM616, SNCM815, etc. Nickel, Chrome, Molybdenum, etc., SCr415, SCr420, etc., Chrome, SCM415, SCM418, SCM420, SCM421, SCM421, SCM822, etc. Case-hardened steel is used for mechanical structural alloys such as steels.
[0015]
In this case, in the case-hardened steel containing chromium, it is more desirable to use a Cr content of 0.3 to 3.0% by weight, and Cr is used in this type of case-hardened steel. Since it has the effect | action which contributes to the improvement of hardenability, in order to acquire such an effect | action, it is desirable to set it as 0.3 weight% or more, but since too much will reduce toughness. It is desirable to make it 0% by weight or less.
[0016]
Further, in the case-hardening steel containing vanadium, it is more desirable to use a V content of 0.1 to 0.5% by weight, and V is toughness in this kind of case-hardening steel. In order to obtain such an action, it is desirable to make it 0.1% by weight or more, but even if it is too much, the effect is not improved and the toughness is lowered. Therefore, the content is preferably 0.5% by weight or less.
[0017]
In addition to this, it goes without saying that C, Si, Mn, P, S, Ni, Mo, and the like are also preferably in a range suitable for this type of case-hardened steel.
[0018]
In addition, Al, Ti, Zr, Nb, N, etc., which have a grain refinement effect, or Pb, S, Ca, Se, Te, Bi, etc., which have a machinability improving effect, are included. It may be a thing.
[0019]
Then, after machining into gear material by performing plastic working or cutting using such hardened steel for machine structure, this gear material is subjected to nitriding treatment at the same time as carburizing treatment and then cooled. Further, by reheating to the austenitizing temperature, performing nitriding again, and then quenching, a gear having excellent tooth surface strength according to the present invention is manufactured.
[0020]
More specifically, when the gear material is cooled after being subjected to the nitriding process at the same time as the carburizing process, the cooling is performed after the carburizing process is performed simultaneously with the carburizing process at a temperature of 800 ° C. or more and 950 ° C. or less.
[0021]
In addition, after quenching after reheating to the austenitizing temperature after cooling and then quenching, reheating to austenitizing temperature of 800 ° C. or more and 930 ° C. or less after cooling and again performing nitriding treatment Then quench.
[0022]
Thus, for example, as shown in FIG. 1, the C amount on the outermost surface is 0.5 wt% or more and 0.9 wt% or less, and the N amount on the outermost surface is 0.3 wt% or more and 0.8 wt% or less. %, And the amount of penetration of N reaches the depth of at least 80% of the effective hardening depth, which is the depth at which the hardness Hv550 is obtained. A gear having an excellent tooth surface strength is obtained which has a hardened structure and the surface hardened structure is formed of a dense martensite structure in which not only C but also N is dissolved.
[0025]
In the manufacturing method of the gear according to the present invention, the N amount in the surface layer portion is made equal to the C amount, and N penetrates to a depth of 80% or more of the effective hardening depth at which the hardness Hv550 is obtained. Therefore, even in the case of a load where the contact surface pressure is high and the slip rate greatly fluctuates, it has excellent pitting resistance and wear resistance (or scoring resistance).
[0026]
In addition, since reheating and quenching is performed at the time of manufacture, the amount of retained austenite (γ _R ) is relatively small and the decrease in hardness is small despite the large amount of N.
[0027]
Furthermore, the surface hardened structure is a martensite structure in which not only C but also N is dissolved, and since the structure is dense, the resistance to crack growth is large, which is advantageous for extending the life. ing.
[0028]
【The invention's effect】
According to the method of manufacturing a gear having excellent tooth surface strength according to the present invention, the hardened steel for machine structure is used as a raw material, and the amount of C on the outermost surface is not less than 0.5% by weight and not more than 0.9% by weight. Effective hardening in which the amount of N on the surface is not less than 0.3% by weight and not more than 0.8% by weight, the amount of N is the same as the amount of C, and the penetration depth of N is the depth at which hardness Hv550 is obtained It is possible to obtain a gear having a hardened surface structure that reaches a depth of at least 80% of the depth, and excellent pitting resistance even under a load where the contact surface pressure is high and the slip ratio varies greatly. Long-life gear that has wear resistance and excellent tooth surface strength, and that is reheat-quenched, so that the amount of retained austenite is small despite the large amount of N and the hardness is small. The great effect that it is possible to produce Is et al.
[0030]
In addition, the hardened surface structure is made of a dense martensite structure in which not only C but also N is dissolved, so that the resistance to crack growth is large and the tooth surface strength is advantageous for extending the service life. The great effect is that it is possible to provide an excellent gear.
[0033]
【Example】
(Example 1)
The steel shown in Table 1 is used as a raw material, and normalizing is performed by holding at 920 ° C. for 60 minutes and then cooling. Further, the diameter of the central large diameter portion is 26 mm as shown in FIG. Saga 28mm, both side small-diameter portion of diameter are both 22 mm, with the overall length is produced by machining a roller pitting test specimen _{S 1} of 130 mm, a diameter as shown in FIG. 5 70 mm, thickness 10mm of the pin-on-disk wear test disc test piece S ₂ was fabricated by machining.
[0034]
Next, in the temperature-time explanatory diagram shown in FIG. 3, the temperature T ₁ = 900 ° C., the time t ₁ = 240 minutes, the atmospheric gas N ₁ , N ₂ = 6 vol% NH ₃ gas, the atmospheric carbon potential C.I. P. = 1.1, temperature T ₂ = 840 ° C., time t ₂ = 100 minutes, atmospheric gas N ₁ , N ₂ = 8 vol% NH ₃ gas, atmospheric carbon potential C.I. P. = Carrying treatment and nitriding treatment under the condition of 0.95 were performed at the same time, followed by air cooling (AC).
[0035]
Subsequently, each test piece S ₁ , S ₂ is reheated to a temperature T ₃ = 850 ° C. to austenite, and is subjected to a nitriding treatment with an atmosphere gas N ₃ = 8 vol% NH ₃ gas for a time t ₃ = 150 minutes. After performing again, quenching (SQ) was performed by dipping in a salt bath at a temperature of 180 ° C.
[0036]
Then, C of each test piece S _1, S ₂ on the outermost surface, N of the outermost surface, the penetration depth of the N, the effective hardening depth, were examined penetration depth of the N to the effective hardening depth, also The results are shown in Table 1.
[0037]
Furthermore, using a roller pitting test specimen _{S 1} shown in FIG. 4 (a), FIG. 4 the diameter as shown in (b) is 130 mm, a thickness of 18mm roller (SCr420 steel carburized products) A roller pitting test was conducted by using R as a counterpart material, contact pressure: 3.7 GPa, slip rate: -40%, lubricating oil temperature: 80 ° C., and the pitting life was examined. It was a result.
[0038]
Furthermore, by using the disc test piece _{S 2} shown in FIG. 5, like the diameter of the body portion as shown in FIG. 5 is 8 mm, the radius of the main body tip 100MmR, the diameter of the flange portion is 12mm pins (SK3 of Heat-treated product) When the wear depth was examined by conducting a pin-on-disk wear test under the conditions of contact pressure: 150 MPa and sliding speed: 0.28 m / s with P as the counterpart material, the results shown in Table 1 were also obtained. It was.
[0039]
In addition, the comparative example 1 of Table 1 shows the case where only the carburizing treatment is performed, the comparative example 2 shows the case where the conventional carbonitriding quenching is performed, and the comparative example 3 shows the case where the excessive nitriding treatment is performed. In these cases, the same evaluation test was conducted.
[0040]
[Table 1]

[0041]
As shown in Table 1, in each of Invention Examples 1 to 4, the pitting life was long and the wear depth was small.
[0042]
In contrast, in Comparative Examples 1 to 3, the pitting life was short and the wear depth was large.
[0043]
(Example 2)
The steel shown in Table 2 is used as a raw material, and normalizing is performed by holding at 920 ° C. for 60 minutes and then cooling. Further, the diameter of the central large diameter portion is 26 mm as shown in FIG. Saga 28mm, both side small-diameter portion of diameter are both 22 mm, with the overall length is produced by machining a roller pitting test specimen _{S 1} of 130 mm, a diameter as shown in FIG. 5 70 mm, thickness 10mm of the pin-on-disk wear test disc test piece S ₂ was fabricated by machining.
[0044]
Next, in the temperature-time explanatory diagram shown in FIG. 3, the temperature T ₁ , the time t ₁ , and the atmospheric gases N ₁ and N ₂ are the conditions shown in Table 2 and the atmospheric carbon potential C.I. P. Of the atmospheric carbon potential C., the conditions of the temperature T ₂ , the time t ₂ , the atmospheric gases N ₁ and N ₂ are the conditions shown in Table 2 and the atmospheric carbon potential C.I. P. Was subjected to carburizing treatment and nitriding treatment under the condition of 0.95 at the same time, followed by air cooling (AC).
[0045]
Subsequently, the test pieces S ₁ and S ₂ were reheated to austenite, and after the nitriding treatment was performed again under the conditions shown in Table 2 for the temperature T ₃ , the time t ₃ , and the atmosphere gas N ₃ , the temperature 180 Quenching (SQ) was performed by immersion in a salt bath at 0 ° C.
[0046]
Then, C of each test piece S _1, S ₂ on the outermost surface, N of the outermost surface, the penetration depth of the N, the effective hardening depth, were examined penetration depth of the N to the effective hardening depth, the table The result is shown in FIG.
[0047]
Furthermore, using a roller pitting test specimen _{S 1} shown in FIG. 4 (a), FIG. 4 the diameter as shown in (b) is 130 mm, a thickness of 18mm roller (SCr420 steel carburized products) A roller pitting test was conducted under the conditions of using R as a counterpart material, contact pressure: 3.7 GPa, slip ratio: -40%, lubricating oil temperature: 80 ° C., and the pitting life was examined. It was a result.
[0048]
Furthermore, by using the disc test piece _{S 2} shown in FIG. 5, like the diameter of the body portion as shown in FIG. 5 is 8 mm, the radius of the main body tip 100MmR, the diameter of the flange portion is 12mm pins (SK3 of Heat-treated product) When the wear depth was examined by performing a pin-on-disk wear test under the conditions of contact pressure: 150 MPa and sliding speed: 0.28 m / s using P as the counterpart material, the results shown in Table 3 were also obtained. It was.
[0049]
In addition, Comparative Example 11 in Table 1 shows a case where the carburizing / nitriding temperature is low and the renitriding temperature is high, and Comparative Examples 12 and 13 are a high carburizing / nitriding temperature and the renitriding temperature is high. The results are shown in Table 3 when the same evaluation test was performed for these cases.
[0050]
[Table 2]

[0051]
[Table 3]

[0052]
As shown in Tables 2 and 3, in each of Invention Examples 11 to 13, the pitting life was long and the wear depth was small.
[0053]
On the other hand, in Comparative Examples 11 to 13, the pitting life was short and the wear depth was large.
[Brief description of the drawings]
FIG. 1 is a graph schematically showing a relationship between a depth from a surface, a C amount, and an N amount in a gear having a surface hardened structure according to the present invention.
FIG. 2 is a graph schematically showing a relationship between a depth from a surface, a C amount, and an N amount in a gear having a hardened surface structure according to a conventional example.
FIG. 3 is a temperature-time explanatory diagram showing carburizing / nitrogenizing treatment and renitriding treatment conditions.
FIG. 4 is a plan view of a roller pitting test piece (FIG. 4 (a)) and a slope explanatory view (FIG. 4 (b)) showing a roller pitting test procedure.
FIG. 5 is an explanatory front view showing a pin-on-disk type abrasion test procedure.

Claims (1)

  Hardened steel for machine structures is used as the raw material, the amount of C on the outermost surface is 0.5% to 0.9% by weight, and the amount of N on the outermost surface is 0.3% to 0.8% by weight. And the surface hardening structure | tissue which has reached the depth of at least 80% of the effective hardening depth which is the depth by which N amount is made into the amount of C, and N penetration depth is the depth from which hardness Hv550 is obtained A gear material made of case-hardened steel for mechanical structure is cooled at a temperature of 800 ° C. to 950 ° C. and then subjected to a nitriding treatment at the same time as a carburizing treatment, and further to 800 ° C. By reheating to an austenitizing temperature of 930 ° C. or lower and performing nitriding again and then quenching, the surface hardened structure is composed of a dense martensite structure in which not only C but also N is dissolved. Gear with excellent tooth surface strength Manufacturing method.

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