JP2008069436A - Component carburized under reduced pressure and its production method - Google Patents

Component carburized under reduced pressure and its production method Download PDF

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JP2008069436A
JP2008069436A JP2006251187A JP2006251187A JP2008069436A JP 2008069436 A JP2008069436 A JP 2008069436A JP 2006251187 A JP2006251187 A JP 2006251187A JP 2006251187 A JP2006251187 A JP 2006251187A JP 2008069436 A JP2008069436 A JP 2008069436A
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JP4940849B2 (en
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Kinsei Kino
欣成 嬉野
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Toyota Motor Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a component carburized under the reduced pressure combining high fatigue resistance and pitting resistance, and to provide its production method. <P>SOLUTION: The component carburized under the reduced pressure is obtained by subjecting a case hardening steel having a composition comprising, by mass, 0.05 to 0.4% C, 0.05 to 0.7% Si, 0.1 to 2.0% Mn, 0.003 to 0.020% N, and one or more kinds selected from 0.005 to 0.1% Nb, 0.01 to 0.1% Al and 0.01 to 0.4% Ti, and the balance Fe with inevitable impurities to forming into a prescribed shape, and subjecting the same to carburization under the reduced pressure, and, after the carburization under the reduced pressure, the depth of a crystal grain coarsened region comprising the crystal grains of ≥80μm is ≤0.25% of the depth of the carburized layer hardened to ≥650 HV. Regarding this production method, the above steel is subjected to hot forging at high temperature, is thereafter subjected to the precipitation treatment of carbonitrides, and is thereafter subjected to carburization treatment under the reduced pressure. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は所定形状に形成された肌焼鋼に減圧浸炭処理を施した減圧浸炭部品とその製造方法とに関する。   The present invention relates to a reduced-pressure carburized component obtained by subjecting a case-hardened steel formed in a predetermined shape to a reduced-pressure carburizing treatment, and a manufacturing method thereof.

自動車、建設車両、建設機械等に使用される歯車やシャフトなどの動力伝達に使用される鋼部品には、浸炭処理により表面に硬化層を形成する肌焼鋼が多用されている。これは、前記部品には優れた耐疲労特性と耐ピッチング性とを同時に要求されるため、表面は浸炭処理により硬い組織として耐ピッチング性を確保し、内部は低Ｃのままとして高い耐疲労特性を持たせるためである。   For steel parts used for power transmission such as gears and shafts used in automobiles, construction vehicles, construction machines, and the like, case-hardened steel that forms a hardened layer on the surface by carburizing treatment is often used. This is because the parts are required to have excellent fatigue resistance and pitting resistance at the same time, so the surface is hardened by carburizing treatment to ensure pitting resistance and the inside remains low C and high fatigue resistance. It is for having.

近年、これら部品の高強度化とともに大幅な製造コスト低減が大きな課題となっており、浸炭処理時間が短縮できる高温減圧浸炭処理が注目されている。   In recent years, with the increase in strength of these parts, a significant reduction in manufacturing cost has become a major issue, and high-temperature reduced-pressure carburizing treatment that can shorten the carburizing treatment time has attracted attention.

このような高温減圧浸炭処理は、処理時間の短縮には極めて効果的な処理方法であるが、従来からよく知られているように、浸炭処理後にオーステナイト粒が粗大化したり、混粒が生じるという問題がある。これは、減圧下での浸炭処理ではピン止め粒子である炭窒化物（ＡｌＮ、Ｎｂ（Ｃ、Ｎ））が脱窒素により表層部で欠落してしまい、このため表層部の結晶粒の粗大化が生じるからである。   Such a high-temperature vacuum carburizing process is an extremely effective processing method for shortening the processing time, but, as is well known in the past, austenite grains are coarsened or mixed grains are generated after carburizing process. There's a problem. This is because carbonitride (AlN, Nb (C, N)), which is a pinning particle, is lost in the surface layer portion due to denitrification in the carburizing process under reduced pressure, and thus the crystal grains in the surface layer portion are coarsened. This is because.

特許文献１には、高温減圧浸炭処理であっても結晶粒の粗大化を防止することができ、熱処理コストの低減を可能とする高温減圧浸炭による熱間鍛造部品の製造方法が提案されている。この製造方法は、特定組成の肌焼き鋼を用いて熱間鍛造後に浸炭処理する際に、熱間鍛造する直前の加熱温度および鍛造温度を高温度化するとともに、熱間鍛造母材を製造するための仕上圧延時の加熱および圧延温度をも高温度化することによって、浸炭処理前における炭窒化物を可能な限り固溶させることを特徴としている。   Patent Document 1 proposes a method for manufacturing a hot forged part by high-temperature vacuum carburization that can prevent coarsening of crystal grains even in high-temperature vacuum carburization treatment, and can reduce heat treatment costs. . In this manufacturing method, when carburizing after hot forging using a case-hardened steel having a specific composition, the heating temperature immediately before hot forging and the forging temperature are increased, and a hot forged base material is manufactured. Therefore, the carbonitride before the carburizing treatment is dissolved as much as possible by increasing the heating and rolling temperature during finish rolling.

しかし、特許文献１では、結晶粒の粗大化と減圧浸炭部品の耐疲労特性や耐ピッチング性との関係についての記載がなく、どのような浸炭層を形成すれば、所要の耐疲労特性や耐ピッチング性を有する減圧浸炭部品が得られるかは不明である。また、仕上圧延時の加熱や圧延温度、あるいは、熱間鍛造する直前の加熱温度や鍛造温度を所定の高温範囲に管理することは、極めて煩雑であり且つ製造コストを増加させる要因ともなる。
特開２００５−１３９５２３号公報 However, Patent Document 1 does not describe the relationship between the coarsening of crystal grains and the fatigue resistance and pitting resistance of reduced-pressure carburized parts. What kind of carburized layer is formed, the required fatigue resistance and resistance It is unclear whether a vacuum carburized part having pitching properties can be obtained. Moreover, it is extremely complicated and increases the production cost to manage the heating and rolling temperature during finish rolling, or the heating temperature and forging temperature immediately before hot forging within a predetermined high temperature range.
JP 2005-139523 A

本発明は上記の問題に鑑みてなされたもので、高い耐疲労特性と耐ピッチング性とを兼ね備える減圧浸炭部品とその製造方法を提供することを課題とする。   This invention is made | formed in view of said problem, and makes it a subject to provide the reduced pressure carburized components which have high fatigue resistance and pitching resistance, and its manufacturing method.

本発明の減圧浸炭部品は、質量比で、Ｃ：０．０５〜０．４％、Ｓｉ：０．０５〜０．７％、Ｍｎ：０．１〜２．０％、Ｎ：０．００３〜０．０２０％、およびＮｂ：０．００５〜０．１％、ＡＬ：０．０１〜０．１％、Ｔｉ：０．０１〜０．４％のうち一種以上を含有し、残部Ｆｅ及び不可避的不純物からなる肌焼き鋼を所定形状に成形し減圧浸炭してなり、該減圧浸炭後に８０μｍ以上の結晶粒を含む結晶粒粗大化領域の深さが６５０ＨＶ以上に硬化した浸炭層の深さの０．２５以下であることを特徴とする。   The reduced pressure carburized parts of the present invention are, by mass ratio, C: 0.05 to 0.4%, Si: 0.05 to 0.7%, Mn: 0.1 to 2.0%, N: 0.003. -0.020%, and Nb: 0.005-0.1%, AL: 0.01-0.1%, Ti: contain one or more of 0.01-0.4%, the balance Fe and The depth of the carburized layer formed by shaping the case-hardened steel made of inevitable impurities into a predetermined shape and carburizing under reduced pressure, and hardening the grain coarsening region containing crystal grains of 80 μm or more to 650 HV or more after the vacuum carburizing. Of 0.25 or less.

本発明の減圧浸炭部品は、結晶粒の粒径が８０μｍ以上の結晶粒を含む結晶粒粗大化領域の深さが、６５０ＨＶ以上に硬化した浸炭層の深さの０．２５以下であるので、曲げ疲労強度が高くかつ、ピッチング強度が高い。   In the reduced pressure carburized component of the present invention, the depth of the grain coarsened region containing crystal grains having a grain size of 80 μm or more is 0.25 or less of the depth of the carburized layer hardened to 650 HV or more. Bending fatigue strength is high and pitching strength is high.

本発明の減圧浸炭部品は、上記の合金組成に加えて、質量比で、Ｃｒ：０．２〜２．０％をさらに含有することができる。ＣｒはＭｎとともに焼入れ性を向上させる効果を有するので所望の内部硬さを得ることができる。   The reduced-pressure carburized component of the present invention can further contain Cr: 0.2 to 2.0% by mass ratio in addition to the above alloy composition. Since Cr has the effect of improving the hardenability together with Mn, a desired internal hardness can be obtained.

本発明の減圧浸炭部品の製造方法は、質量比で、Ｃ：０．０５〜０．４％、Ｓｉ：０．０５〜０．７％、Ｍｎ：０．１〜２．０％、Ｎ：０．００３〜０．０２０％、およびＮｂ：０．００５〜０．１％、ＡＬ：０．０１〜０．１％、Ｔｉ：０．０１〜０．４％のうち一種以上を含有し、残部Ｆｅ及び不可避的不純物からなる鋼材を溶製・鋳造して熱間圧延する素材製造工程と、該素材を加熱して熱間鍛造する熱間鍛造工程と、該熱間鍛造後の鋼材を加熱冷却して固溶した炭窒化物を析出させる析出処理工程と、該析出処理した鋼材を所定形状に成形する成形工程と、浸炭層を形成して該成形した鋼材を強化する減圧浸炭処理工程を有することを特徴とする。   The manufacturing method of the reduced pressure carburized parts of this invention is C: 0.05-0.4%, Si: 0.05-0.7%, Mn: 0.1-2.0%, N: by mass ratio. 0.003 to 0.020%, and Nb: 0.005 to 0.1%, AL: 0.01 to 0.1%, Ti: 0.01 to 0.4%, containing one or more types, A material manufacturing process in which a steel material composed of the remaining Fe and inevitable impurities is melted and cast and hot rolled, a hot forging process in which the material is heated and hot forged, and the steel material after hot forging is heated. A precipitation treatment step for precipitating the carbonitride that has been cooled and solid-dissolved, a forming step for forming the precipitation-treated steel material into a predetermined shape, and a reduced-pressure carburization treatment step for strengthening the formed steel material by forming a carburized layer. It is characterized by having.

本発明の減圧浸炭部品の製造方法は、熱間圧延後の素材を高温に加熱してから熱間鍛造を施すので、ピン止め効果を発揮する炭窒化物を完全に固溶するとともに、その後の析出処理で炭窒化物を均一微細に析出させることができる。このため減圧浸炭処理部品の結晶の粗大化を抑制することができる。   The method of manufacturing a reduced-pressure carburized part according to the present invention performs hot forging after heating the material after hot rolling to a high temperature, so that the carbonitride exhibiting the pinning effect is completely solid solution, and then Carbonitride can be uniformly and finely precipitated by the precipitation treatment. For this reason, the coarsening of the crystal | crystallization of a vacuum carburizing process component can be suppressed.

本発明の製造方法において、熱間鍛造時の素材の加熱は、１２００〜１３００℃で１０分以上加熱保持することが望ましい。素材をこの温度範囲で加熱してから熱間鍛造することで、熱間鍛造中に炭窒化物を完全に固溶させることができる。   In the production method of the present invention, it is desirable to heat and hold the raw material during hot forging at 1200 to 1300 ° C. for 10 minutes or more. By heating the material in this temperature range and then performing hot forging, the carbonitride can be completely dissolved during hot forging.

本発明の製造方法において、析出処理工程は、熱間鍛造工程の冷却段階で９００〜６５０℃の範囲を５℃／分以下の冷却速度で冷却する工程であることが望ましい。熱間鍛造工程の冷却段階で冷却速度を制御して炭窒化物を析出させることで、全体の工程を短縮することができ生産性を向上できる。   In the production method of the present invention, the precipitation treatment step is desirably a step of cooling the range of 900 to 650 ° C. at a cooling rate of 5 ° C./min or less in the cooling stage of the hot forging step. By controlling the cooling rate in the cooling step of the hot forging process to precipitate carbonitride, the entire process can be shortened and productivity can be improved.

また、析出処理工程は、熱間鍛造終了後、再度９００〜１０００℃で２０分以上加熱保持する工程としてもよい。析出処理工程を熱間鍛造工程と切り離すことで生産の自由度を増すことができる。   Moreover, a precipitation process process is good also as a process of heating and hold | maintaining again at 900-1000 degreeC for 20 minutes or more after completion | finish of hot forging. The degree of freedom in production can be increased by separating the precipitation treatment step from the hot forging step.

本発明の製造方法において、減圧浸炭処理工程は、減圧下において９００〜１０５０℃で浸炭処理する工程であることが望ましい。かかる高温で浸炭処理することで浸炭時間を短縮して製造コストを大幅に低減することができる。   In the production method of the present invention, the reduced pressure carburizing treatment step is desirably a step of carburizing at 900 to 1050 ° C. under reduced pressure. Carburizing at such a high temperature can shorten the carburizing time and greatly reduce the manufacturing cost.

本発明の減圧浸炭部品は、その化学成分組成と、減圧浸炭処理後における結晶粒粗大化領域の有効硬化層深さに対する比率とを所望の耐疲労特性と耐ピッキング性とを具備するように限定したところに特徴がある。   The reduced pressure carburized parts of the present invention are limited so that the chemical composition and the ratio of the grain coarsened region to the effective hardened layer depth after the reduced pressure carburization treatment have desired fatigue resistance and picking resistance. There is a feature.

まず、本発明における減圧浸炭用鋼の化学成分組成の限定理由について説明する。
Ｃ：０．０５〜０．４％
浸炭処理を行った部品に要求される強度と内部硬さを確保するためには、０．０５％以上のＣを含有する必要がある。しかし、０．４％を超えて含有させると内部の靱性が劣化し、また、被削性をも低下させるため、上限を０．４％とした。 First, the reason for limiting the chemical composition of the steel for reduced pressure carburization in the present invention will be described.
C: 0.05-0.4%
In order to ensure the strength and internal hardness required for the carburized parts, it is necessary to contain 0.05% or more of C. However, if the content exceeds 0.4%, the internal toughness deteriorates and the machinability also decreases, so the upper limit was made 0.4%.

Ｓｉ：０．０５〜０．７％
Ｓｉは鋼の製造時において脱酸のために必要な元素であり、最低でも０．０５％以上の含有が必要である。しかしながら、多量に含有させると冷間鍛造性を低下させるので上限を０．７％とした。 Si: 0.05-0.7%
Si is an element necessary for deoxidation during the production of steel, and it must be contained at least 0.05%. However, if it is contained in a large amount, the cold forgeability is lowered, so the upper limit was made 0.7%.

Ｍｎ：０．１〜２．０％
Ｍｎは、焼入れ性を向上させて必要な内部硬さを得るために必須の元素であり、最低でも０．１％以上含有させる必要がある。しかしながら、多量に含有させると、内部の靱性が劣化するとともに、被削性が低下するので上限を２．０％とした。 Mn: 0.1 to 2.0%
Mn is an essential element for improving hardenability and obtaining necessary internal hardness, and it is necessary to contain Mn at least 0.1%. However, if contained in a large amount, the internal toughness deteriorates and the machinability decreases, so the upper limit was made 2.0%.

Ｃｒ：０．２〜２．０％
ＣｒはＭｎと同様に焼入れ性を向上させる効果を有する元素であり、Ｍｎと同時添加する場合には、０．２％以上含有させるとよい。しかしながら、多量に含有させると、内部の靱性が劣化するとともに、被削性が低下するので上限を２．０％とした。 Cr: 0.2 to 2.0%
Cr is an element having an effect of improving the hardenability like Mn, and when added simultaneously with Mn, it is preferable to contain 0.2% or more. However, if contained in a large amount, the internal toughness deteriorates and the machinability decreases, so the upper limit was made 2.0%.

Ｎ：０．００３〜０．０２０％
Ｎは、ＡｌやＮｂと結合してＡｌＮやＮｂ（Ｃ，Ｎ）となって鋼中に存在し、浸炭処理後の異常粒成長を防止するために効果のある元素である。この効果を十分に得るためには、０．００３％以上のＮを含有させる必要がある。しかし、ＡｌＮやＮｂ（Ｃ，Ｎ）の析出量には適量があり、多すぎると浸炭初期粒径が細かくなってかえって異常粒成長が起きやすくなってしまう。これ故、上限を０．０２０％とした。 N: 0.003-0.020%
N combines with Al and Nb to form AlN and Nb (C, N) in the steel, and is an element effective for preventing abnormal grain growth after carburizing treatment. In order to obtain this effect sufficiently, it is necessary to contain 0.003% or more of N. However, there is an appropriate amount of precipitation of AlN and Nb (C, N), and if it is too much, the initial carburized grain size becomes fine, and abnormal grain growth tends to occur. Therefore, the upper limit was made 0.020%.

Ｎｂ：０．００５〜０．１％
Ｎｂは炭窒化物となって鋼中に存在し、特にＡｌに比べて高温での浸炭処理における結晶粒異常成長を防止する効果の大きい元素である。Ｎｂの添加量が少ない場合、特に１０５０℃以上の浸炭では、浸炭処理前に析出していた炭窒化物の一部が固溶し、ピン止め効果に寄与する炭窒化物の量が不足して粗粒化抑制効果が充分得られなくなるので、下限を０．００５％とした。一方、多量に含有させると熱間鍛造時の加熱によってＮｂ（Ｃ，Ｎ）が十分に固溶した状態とならずに、粗大なＮｂ（Ｃ，Ｎ）の析出物が残存した状態となってピン止め効果が低下する。よって、上限を０．１％に規定した。 Nb: 0.005 to 0.1%
Nb is a carbonitride and exists in steel, and is an element that has a greater effect of preventing abnormal grain growth in carburizing treatment at a higher temperature than Al. When the amount of Nb added is small, especially in carburizing at 1050 ° C. or higher, a part of the carbonitride precipitated before the carburizing treatment is dissolved, and the amount of carbonitride that contributes to the pinning effect is insufficient. Since the effect of suppressing coarsening cannot be obtained sufficiently, the lower limit was made 0.005%. On the other hand, if it is contained in a large amount, Nb (C, N) is not sufficiently dissolved by heating during hot forging, but coarse Nb (C, N) precipitates remain. The pinning effect is reduced. Therefore, the upper limit is defined as 0.1%.

Ａｌ：０．０１〜０．１％
Ａｌは酸素と結合しやすい元素であり、Ｓｉと同様に溶製時の脱酸に必要な元素である。また、鋼中でＡｌＮとして存在し、ピン止め効果により浸炭処理後の異常粒成長を防止する効果もある。従って、これらの効果を十分に得られるようにするために下限を０．０１％とした。しかしながら、多量に含有させると、鋼中に硬質なＡｌ２Ｏ３介在物が増加して、疲労強度や被削性への悪影響が大きくなるため、上限を０．１％とした。 Al: 0.01 to 0.1%
Al is an element that easily binds to oxygen, and is an element necessary for deoxidation at the time of melting, similar to Si. Moreover, it exists as AlN in steel, and has an effect which prevents the abnormal grain growth after a carburizing process by the pinning effect. Therefore, the lower limit is made 0.01% so that these effects can be sufficiently obtained. However, if contained in a large amount, hard Al 2 O 3 inclusions increase in the steel, and the adverse effect on fatigue strength and machinability increases, so the upper limit was made 0.1%.

Ｔｉ：０．０１〜０．４％
Ｔｉは、ＣやＮと結合して炭化物や窒化物を生成し結晶粒を微細化して靱性や疲労強度を向上させる効果を有する。その効果を有効に発揮させるためには、０．０１％以上含有させる必要がある。しかし、多量に含有させるとその効果は飽和してしまい、大型の介在物が生成してかえって靱性を低下させるため、上限を０．４％とした。 Ti: 0.01 to 0.4%
Ti combines with C and N to produce carbides and nitrides, and has the effect of refining crystal grains to improve toughness and fatigue strength. In order to exhibit the effect effectively, it is necessary to contain 0.01% or more. However, if contained in a large amount, the effect is saturated, and large inclusions are generated, which in turn decreases the toughness, so the upper limit was made 0.4%.

次に、８０μｍ以上の結晶粒を含む結晶粒粗大化領域の深さを６５０ＨＶ以上に硬化した浸炭層の深さの０．２５以下に限定する理由について説明する。   Next, the reason why the depth of the coarse grain region including crystal grains of 80 μm or more is limited to 0.25 or less of the depth of the carburized layer cured to 650 HV or more will be described.

減圧浸炭部品の曲げ疲労強度は、浸炭処理後のオーステナイト粒の粗大化や混粒層の発生によって低下する。   The bending fatigue strength of reduced-pressure carburized parts decreases due to coarsening of austenite grains after carburizing treatment and generation of mixed grain layers.

本発明者は、浸炭処理後の表面結晶粒の粗大化部における平均結晶粒径と曲げ疲労強度との関係を検討し、図１に示すように最大結晶粒径が８０μｍを境にして曲げ疲労強度が大きく変化することに着目した。すなわち、平均結晶粒径が８０μｍ未満では曲げ疲労強度が高く、平均結晶粒径が８０μｍ以上になると曲げ疲労強度は急激に低下し、破面観察により曲げ疲労強度が高い場合には、疲労破断が浸炭層の表面を起点として生じており、曲げ疲労強度が低い場合には、内部を起点とする疲労破断であることを見出した。   The present inventor examined the relationship between the average crystal grain size and the bending fatigue strength in the coarsened portion of the surface crystal grains after the carburizing treatment, and bending fatigue with a maximum crystal grain size of 80 μm as shown in FIG. We paid attention to the fact that the strength changes greatly. That is, when the average crystal grain size is less than 80 μm, the bending fatigue strength is high, and when the average crystal grain size is 80 μm or more, the bending fatigue strength sharply decreases. It was found that the fracture occurred starting from the surface of the carburized layer and the fracture starting from the inside when the bending fatigue strength was low.

また、８０μｍ以上の結晶粒が存在する粗大化部を有する場合には、減圧浸炭部品の曲げ疲労強度は、図２に示すように結晶粒の粗大化領域の最大深さｔとビッカース硬さが６５０ＨＶ以上である有効硬化層深さＴとの割合によって変化し、この割合が０．２５を境にして大きく変化することを見出した。ここで、結晶粒粗大化領域の最大深さｔとは、８０μｍ以上の結晶粒が存在する領域の１０視野、すなわち、８０μｍ以上の結晶粒が存在する１０箇所の粗大化部の中で最も深いものと定義される減圧浸炭後の部品表面からの距離である。また、ビッカース硬さが６５０ＨＶ以上である有効硬化層深さＴとは、部品表面から厚さ方向にビッカース硬さ分布を測定したときに、その分布がＨＶ６５０以上である部品表面からの距離である。そして、粗大化領域最大深さ／６５０ＨＶ以上硬化層厚さ（ｔ／Ｔ）が０．２５以下であれば、曲げ疲労による破断の起点が表面起点であり、０．２５を超えると内部起点となるという知見を得た。   In addition, in the case of having a coarsened portion where crystal grains of 80 μm or more exist, the bending fatigue strength of the reduced pressure carburized parts is the maximum depth t and Vickers hardness of the coarsened region of crystal grains as shown in FIG. It changed with the ratio with the effective hardened layer depth T which is 650HV or more, and it discovered that this ratio changed a lot 0.25 as a boundary. Here, the maximum depth t of the crystal grain coarsened region is the deepest of the 10 fields of view where the crystal grains of 80 μm or more exist, that is, the deepest part among the ten coarsened portions where the crystal grains of 80 μm or greater exist. It is the distance from the part surface after vacuum carburization, which is defined as one. The effective hardened layer depth T having a Vickers hardness of 650 HV or higher is a distance from the surface of the component having a distribution of HV 650 or higher when the Vickers hardness distribution is measured in the thickness direction from the component surface. . If the hardened layer thickness (t / T) is 0.25 or less when the coarsening region maximum depth / 650 HV or more, the starting point of fracture due to bending fatigue is the surface starting point. I got the knowledge that

この理由は現状では明らかではないが、通常、自動車部品の多く、とりわけ浸炭処理を施すトランスミッションギヤは複雑な形状のため、表面への応力集中が発生して表面起点破壊を生じるが、表面近傍に結晶粒の粗大化が発生すると粒内すべりの発生により、内部起点破壊が生じるためと推察される。   The reason for this is not clear at present, but normally, many car parts, especially transmission gears that are carburized, have a complicated shape, causing stress concentration on the surface and causing surface-origin fractures. It is inferred that when the coarsening of crystal grains occurs, internal origin fracture occurs due to the occurrence of intra-slip.

以上の特徴を有する本発明の減圧浸炭部品は、優れた耐疲労特性と耐ピッチング性とを有する。従来は、実際にこれらの試験を実施しなければ減圧浸炭部品の曲げ耐疲労特性や耐ピッチング性を保証できなかった。しかし、かかる試験には大がかりな装置と高度な試験技術が必要であり、さらに評価に時間がかかるという問題があった。ところが、本発明の減圧浸炭部品では、減圧浸炭部品の一部を試験片として採取し、その結晶粒や断面の硬さ分布を測定することで、容易に減圧浸炭部品の耐疲労特性や耐ピッチング性を評価してその適否を判断することができる。すなわち、簡便で且つ高精度の減圧浸炭部品の品質管理が可能となるわけである。   The reduced-pressure carburized component of the present invention having the above characteristics has excellent fatigue resistance and pitting resistance. Conventionally, the bending fatigue resistance and the pitting resistance of vacuum carburized parts could not be guaranteed unless these tests were actually performed. However, such a test requires a large-scale apparatus and advanced test technology, and further requires a long time for evaluation. However, in the reduced pressure carburized part of the present invention, a part of the reduced pressure carburized part is collected as a test piece, and the hardness distribution of the crystal grains and the cross section is measured. Appropriateness can be judged by evaluating sex. That is, it is possible to easily and accurately control the quality of the reduced pressure carburized parts.

このような減圧浸炭部品の製造方法は、上記の特定組成を有する鋼材を溶製・鋳造して熱間圧延する素材製造工程と、この素材を加熱して熱間鍛造する熱間鍛造工程と、熱間鍛造後の鋼材を加熱冷却して固溶した炭窒化物を析出させる析出処理工程と、析出処理した鋼材を所定形状に成形する成形工程と、浸炭層を形成して成形した鋼材を強化する減圧浸炭処理工程を有する。   Such a reduced pressure carburized parts manufacturing method includes a raw material manufacturing process in which a steel material having the above specific composition is melted and cast and hot rolled, and a hot forging process in which this material is heated and hot forged, Strengthening the steel material that has been formed by forming a carburized layer, forming a carburized layer, and forming a carburized layer that precipitates the carbonitride that has been solidified by heating and cooling the steel material after hot forging. A reduced pressure carburizing process.

本発明においては、特定組成の鋼塊を調製してこの鋼塊を圧延などで所望の圧延素材とするまでは、周知の方法で行うことができる。   In this invention, it can carry out by a well-known method until the steel ingot of a specific composition is prepared and this steel ingot is made into a desired rolling raw material by rolling or the like.

本発明では、熱間鍛造前の圧延素材に１２００〜１３００℃で１０分以上の加熱保持を施す。従って、熱間鍛造中に炭窒化物（ＡｌＮ、Ｎｂ（Ｃ、Ｎ））を完全に固溶させることができる。ここで、加熱温度を１２００〜１３００℃としたのは、加熱温度が１２００℃未満では未固溶の炭窒化物が残存して異常粒成長を完全に防止できなくなる場合があるからであり、１３００℃を超えて高温では、設備的制約を生じることがあるからである。   In the present invention, the rolled material before hot forging is heated and held at 1200 to 1300 ° C. for 10 minutes or more. Therefore, carbonitride (AlN, Nb (C, N)) can be completely dissolved during hot forging. Here, the reason why the heating temperature is set to 1200 to 1300 ° C. is that if the heating temperature is less than 1200 ° C., undissolved carbonitride may remain and abnormal grain growth may not be completely prevented. This is because, when the temperature is higher than ° C., equipment limitations may occur.

本発明の製造方法では、以上の加熱工程に続いて炭窒化物を析出させる析出処理工程を有するが、その形態は以下のいずれでも良い。   Although the manufacturing method of the present invention includes a precipitation treatment step of depositing carbonitride following the above heating step, any of the following forms may be employed.

析出処理工程の第１の形態は、熱間鍛造後の冷却段階で９００〜６５０℃の間を５℃／ｍｉｎ以下の冷却速度で徐冷する形態である。この温度範囲で徐冷することで鋼中に微細な炭窒化物（ＡｌＮ、Ｎｂ（Ｃ、Ｎ））を均一に分散析出させることができる。ここで、冷却速度が５℃／ｍｉｎを超えて速いと炭窒化物の析出が不十分となることがあるので好ましくない。また、徐冷温度範囲を９００〜６５０℃の間としたのは、徐冷開始温度が９００℃より高温では冷却に長時間を要して生産性を阻害する虞があり、また、６５０℃未満では炭窒化物の析出が不十分となることがあるので適当ではない。   The 1st form of a precipitation process process is a form which anneals between 900-650 degreeC with the cooling rate of 5 degrees C / min or less in the cooling step after hot forging. By slow cooling in this temperature range, fine carbonitrides (AlN, Nb (C, N)) can be uniformly dispersed and precipitated in the steel. Here, if the cooling rate is faster than 5 ° C./min, the precipitation of carbonitride may be insufficient, which is not preferable. Also, the slow cooling temperature range is set to 900 to 650 ° C. If the slow cooling start temperature is higher than 900 ° C., it may take a long time for cooling and hinder productivity, and less than 650 ° C. In this case, carbonitride precipitation may be insufficient.

また、析出処理工程の第２の形態は、熱間鍛造終了後、鍛造された鋼材を一旦冷却してから再度９００〜１０００℃に加熱して２０分以上保持する形態である。このように炭窒化物の析出温度で再加熱しても、第１の形態と同様に鋼中に微細な炭窒化物（ＡｌＮ、Ｎｂ（Ｃ、Ｎ））を均一に分散析出することができる。   Moreover, the 2nd form of a precipitation process process is a form which once heats forging steel material after completion | finish of hot forging, then heats again to 900-1000 degreeC, and hold | maintains for 20 minutes or more. Thus, even if reheating is performed at the carbonitride precipitation temperature, fine carbonitrides (AlN, Nb (C, N)) can be uniformly dispersed and precipitated in the steel as in the first embodiment. .

ここで、温度の下限を９００℃としたのは、９００℃未満では、析出する炭窒化物が微細になりすぎ、且つ数が多くなるため、浸炭初期の結晶粒径が細かくなり、粒成長の駆動力が高くなって高温浸炭中の異常粒成長を防止できなくなる可能性が高くなるからであり、上限を１０００℃としたのは、析出した炭窒化物が大きく、且つ少なくなってしまうために浸炭初期から粒径が大きくなって処理後においても大きい状態のままとなってしまうからである。   Here, the lower limit of the temperature is set to 900 ° C. When the temperature is less than 900 ° C., the precipitated carbonitride becomes too fine and the number increases, so that the crystal grain size at the initial stage of carburization becomes fine and the grain growth is reduced. This is because the driving force increases and the possibility that abnormal grain growth during high-temperature carburization cannot be prevented increases, and the upper limit is set to 1000 ° C. because the precipitated carbonitride is large and decreases. This is because the particle size increases from the initial stage of carburization and remains large even after the treatment.

本発明の製造方法では、減圧浸炭処理工程は、減圧下の雰囲気に浸炭ガスを導入して所定形状の鋼材を９００〜１０５０℃の範囲で加熱する工程であり、加熱時間は従来の減圧浸炭処理と同様とすればよい。   In the production method of the present invention, the reduced pressure carburizing treatment step is a step of introducing a carburizing gas into an atmosphere under reduced pressure to heat a steel material having a predetermined shape in a range of 900 to 1050 ° C., and the heating time is a conventional reduced pressure carburizing treatment. The same as above.

本発明の減圧浸炭部品の製造方法によれば、析出処理工程は上記のいずれの形態であっても、炭窒化物は母材内に均一微細に析出するので、その後に９００〜１０５０℃の範囲で加熱する高温減圧浸炭処理を施しても、結晶粒の粗大化を抑制することができる。   According to the method for producing a reduced pressure carburized part of the present invention, the carbonitride is uniformly and finely precipitated in the base material even if the precipitation treatment step is in any of the above forms, and thereafter in the range of 900 to 1050 ° C. Even if a high-temperature vacuum carburizing treatment is performed by heating at a high temperature, coarsening of crystal grains can be suppressed.

以下、本発明について実施例によってさらに詳しく説明する。   Hereinafter, the present invention will be described in more detail with reference to examples.

（１）供試材の作製
所定の原料を溶製・鋳造して表１に示す化学成分組成を有する供試鋼Ａ〜Ｄを得た。表１に示す供試鋼のうち、Ａ鋼とＢ鋼とは本発明の要件を満足する鋼であり、Ｃ鋼とＤ鋼は一部の成分が本発明の規定範囲を逸脱する比較鋼である。 (1) Preparation of test materials Test steels A to D having the chemical composition shown in Table 1 were obtained by melting and casting predetermined raw materials. Among the test steels shown in Table 1, Steel A and Steel B are steels that satisfy the requirements of the present invention, and Steel C and Steel D are comparative steels in which some components deviate from the specified range of the present invention. is there.

Figure 2008069436
Figure 2008069436

これらの供試鋼を熱間圧延して直径５０ｍｍの圧延素材を得た。次いでこの圧延素材を加熱条件１で加熱し、直ちに熱間鍛造して直径３０ｍｍの鍛造材を得た。鍛造後、加熱条件２で析出処理を行うとともに、この析出処理材を所定形状に機械加工して後述する各試験用の試験片を作製した。続いてこれらの試験片にそれぞれの浸炭条件で減圧浸炭処理を施して供試材１〜１７を得た。各供試材の加熱条件１、加熱条件２、浸炭条件を表２に示す。   These test steels were hot-rolled to obtain a rolled material having a diameter of 50 mm. The rolled material was then heated under heating condition 1 and immediately hot forged to obtain a forged material having a diameter of 30 mm. After forging, precipitation treatment was performed under heating condition 2, and this precipitation-treated material was machined into a predetermined shape to produce test pieces for each test described later. Subsequently, these test pieces were subjected to reduced pressure carburizing treatment under the respective carburizing conditions to obtain test materials 1 to 17. Table 2 shows the heating conditions 1, heating conditions 2 and carburizing conditions of each specimen.

Figure 2008069436
Figure 2008069436

（２）試験方法
各々の供試材について（ａ）８０μｍ以上の結晶粒が存在する結晶粒粗大化領域の
最大深さｔ／６５０ＨＶ以上硬化層深さＴ、（ｂ）回転曲げ疲労強度、および（ｃ）ピッチング強度を測定した。以下に各試験方法を説明する。 (2) Test method For each test material (a) Maximum depth t / 650HV or more of hardened layer depth T of crystal coarsening region where crystal grains of 80 μm or more exist, (b) Rotating bending fatigue strength, and (C) Pitting strength was measured. Each test method will be described below.

（ａ）８０μｍ以上の結晶粒が存在する結晶粒粗大化領域の最大深さｔ／６５０ＨＶ以上硬化層深さＴ（ｔ／Ｔ）
組織観察用試験片の仕上げ加工面をピクリン酸で腐食して、光学顕微鏡（倍率は５０倍）で８０μｍ以上の結晶粒が存在する粗大化部の１０視野を観察した。粗大化部の断面１０を図３に模式的に示す。図３は結晶粒径が８０μｍ以上の結晶粒Ｃを含む断面である。なお、図３ａで１１は組織観察用試験片の仕上げ面（表面）であり、１２は浸炭層、１３は母相である。 (A) Maximum depth t / 650 HV or more of hardened layer depth T (t / T) in a crystal grain coarsened region where crystal grains of 80 μm or more exist
The finished processed surface of the test piece for structure observation was corroded with picric acid, and 10 visual fields of the coarsened portion where crystal grains of 80 μm or more were present were observed with an optical microscope (magnification is 50 times). A cross section 10 of the coarsened portion is schematically shown in FIG. FIG. 3 is a cross section including crystal grains C having a crystal grain size of 80 μm or more. In FIG. 3a, reference numeral 11 denotes a finished surface (surface) of the structure observation specimen, 12 denotes a carburized layer, and 13 denotes a matrix.

図３ａにおいて、結晶粒粗大化領域の最大深さｔは、８０μｍ以上の結晶粒が存在する領域の１０視野中で最大の表面１１からの距離（μｍ）である。   In FIG. 3a, the maximum depth t of the crystal grain coarsened region is the maximum distance (μm) from the surface 11 in ten fields of view in the region where crystal grains of 80 μm or more exist.

また、６５０ＨＶ以上硬化層深さＴは、マイクロビッカース硬度が６５０ＨＶ以上である組織観察用試料片断面１０の表面１１からの距離である。図３では仕上げ面１１から試料片断面の深さ方向に０．１μｍピッチで（×で示す）順次マイクロビッカース硬度（荷重：３００ｇ）を測定し、図３ｂに示すような深さ方向の硬度分布グラフを作成して６５０ＨＶ以上の深さＴ（μｍ）を求める。   Further, the hardened layer depth T of 650 HV or higher is a distance from the surface 11 of the cross-sectional specimen 10 for tissue observation having a micro Vickers hardness of 650 HV or higher. In FIG. 3, micro Vickers hardness (load: 300 g) is sequentially measured from the finished surface 11 in the depth direction of the sample piece cross section at a pitch of 0.1 μm (indicated by ×), and the hardness distribution in the depth direction as shown in FIG. A graph is created to obtain a depth T (μm) of 650 HV or higher.

このようにして得られたｔとＴからｔ／Ｔを算出した。   T / T was calculated from t and T thus obtained.

（ｂ）回転曲げ疲労強度（ＭＰａ）
回転曲げ疲労強度（ＭＰａ）は、小野式回転曲げ疲労試験により求めた。小野式回転曲げ疲労試験は、図４に示す形状の試験片２０を用い、ＪＩＳ−Ｚ２２７４の「金属材料の回転曲げ疲れ試験方法」に準じて行った。なお、回転数は３０００ｒｐｍとし、ノッチ部における応力集中係数は１．７８とした。そして、１０７回以上回転させても破断しない曲げ応力（１０７回耐久応力）を回転曲げ疲労強度（ＭＰａ）とした。 (B) Rotating bending fatigue strength (MPa)
The rotational bending fatigue strength (MPa) was determined by an Ono type rotational bending fatigue test. The Ono type rotating bending fatigue test was performed according to JIS-Z2274 “Rotating bending fatigue test method of metal material” using the test piece 20 having the shape shown in FIG. The rotational speed was 3000 rpm, and the stress concentration factor at the notch was 1.78. The bending stress (10 7 times endurance stress) that does not break even when rotated 10 7 times or more was defined as rotational bending fatigue strength (MPa).

なお、破断起点箇所は破断した各試験片の破断面をＳＥＭ（走査型電子顕微鏡）で観察して判定した。表面を起点として破断面が内部に向かって流れているものを表面起点、表面から数百μｍ入ったところから内部及び表面に向かって破面が流れているものを内部起点と判定した。なお、起点部にはフィッシュアイが認められることが多い。   In addition, the fracture starting point location was determined by observing the fracture surface of each fractured specimen with a scanning electron microscope (SEM). A surface where the fracture surface flows toward the inside starting from the surface was determined as the surface origin, and a surface where the fracture surface flows from a position several hundred μm from the surface toward the inside and the surface was determined as the internal origin. In many cases, fish eyes are recognized at the starting point.

（ｃ）ピッチング強度（ＭＰａ）
ピッチング強度（ＭＰａ）は、図５、６に示すローラピッチング試験により求めた。ローラピッチング試験は、図５、６に示すごとく、中央部分に試験部３１１を有する小ローラ３１と、円盤状の大ローラ３２とを用いて行った。なお、大ローラ３２は小ローラ３１の相手材であり、本実施例ではＳＣＭ２０材に浸炭処理を施して作製した。 (C) Pitting strength (MPa)
The pitching strength (MPa) was determined by a roller pitching test shown in FIGS. As shown in FIGS. 5 and 6, the roller pitching test was performed using a small roller 31 having a test portion 311 at the center and a disk-shaped large roller 32. The large roller 32 is a counterpart material of the small roller 31, and in the present embodiment, the SCM 20 material was subjected to carburizing treatment.

小ローラ３１には、図６ａに示すごとく、全長Ｌが１３０ｍｍの中央部分に、幅Ｗが２８ｍｍ、外径Ｄ１が２６ｍｍの試験部３１１が形成されている。また、大ローラ３２は、図６ｂに示すように、厚みＦが１８ｍｍ、外径Ｄ２が１３０ｍｍの円板であって、その端部３２１は図６ｃに示すごとく、クラウニング半径３００ｍｍの曲面に形成されている。   As shown in FIG. 6a, the small roller 31 is formed with a test portion 311 having a width W of 28 mm and an outer diameter D1 of 26 mm in a central portion having an overall length L of 130 mm. Further, as shown in FIG. 6b, the large roller 32 is a disc having a thickness F of 18 mm and an outer diameter D2 of 130 mm, and its end 321 is formed in a curved surface having a crowning radius of 300 mm as shown in FIG. 6c. ing.

そして、図５に示すように、軸３２９にセットした大ローラ３２の端部３２１と小ローラ３１の試験部３１１とを当接させた状態で、それぞれの周速に差を付けて回転させる。具体的には、小ローラ３１の回転数を２０００ｒｐｍとし、すべり率（周速差）を−２０％とした。また、潤滑は油温１２０℃のＡＴＦ（オートマチックトランスミッションフルード）により行った。   Then, as shown in FIG. 5, in a state where the end 321 of the large roller 32 set on the shaft 329 and the test unit 311 of the small roller 31 are in contact with each other, the peripheral speed is rotated with a difference. Specifically, the rotation speed of the small roller 31 was 2000 rpm, and the slip ratio (circumferential speed difference) was −20%. The lubrication was performed by ATF (automatic transmission fluid) having an oil temperature of 120 ° C.

そして、小ローラ３１と大ローラ３２との間に一定の面圧を負荷した状態で回転させてピッチング発生までの小ローラ３１の総回転数を求める。これを面圧を変化させて繰り返し行い、小ローラ３１を１０７回以上回転させてもピッチングが発生しない面圧（１０７回耐久面圧）をピッチング強度（ＭＰａ）とした。なお、ローラピッチング試験機としては、コマツエンジニアリング（株）製のものを用いた。 Then, the rotation is performed with a constant surface pressure applied between the small roller 31 and the large roller 32, and the total rotation speed of the small roller 31 until the occurrence of pitching is obtained. This was repeated by changing the surface pressure, and the surface pressure at which no pitching occurred even when the small roller 31 was rotated 10 7 times or more (10 7 times durable surface pressure) was defined as the pitching strength (MPa). A roller pitching tester manufactured by Komatsu Engineering Co., Ltd. was used.

（３）試験結果
結果を表２に併記した。表２から、ｔ／Ｔが０．２５以下である本発明例は、いずれも回転曲げ疲労強度が４００ＭＰａ以上、ピッチング強度も２４００ＭＰａ以上であり比較例に比べて優れていることが分かる。そして、破断起点はいずれも表面であった。 (3) Test results The results are shown in Table 2. From Table 2, it can be seen that all of the present invention examples having t / T of 0.25 or less have a rotational bending fatigue strength of 400 MPa or more and a pitching strength of 2400 MPa or more, which is superior to the comparative example. And the break origin was all on the surface.

本発明の減圧浸炭部品は、高い曲げ疲労強度やピッチング強度を要求される歯車などの動力伝達部品に好適である。例えば、自動車、建設車両、建設機械等に使用される歯車やシャフトなどの動力伝達に使用される鋼部品であって、特に自動車のトランスミッション歯車やＣＶＴのシーブなどには最適である。また、曲げ疲労試験やローラピッチング試験といった多大な時間を要する試験を行うことなく、その耐久性やピッチング性を判定することができるので減圧浸炭部品の品質管理手段として有用である。   The reduced pressure carburized parts of the present invention are suitable for power transmission parts such as gears that require high bending fatigue strength and pitching strength. For example, steel parts used for power transmission such as gears and shafts used in automobiles, construction vehicles, construction machines, etc., and particularly suitable for transmission gears of automobiles and sheaves of CVTs. Further, since durability and pitching performance can be determined without performing a time-consuming test such as a bending fatigue test or a roller pitching test, it is useful as a quality control means for reduced pressure carburized parts.

粗大化部平均結晶粒径と曲げ疲労強度との関係を概念的に示すグラフである。It is a graph which shows notionally a relation between a coarsening part average crystal grain size and bending fatigue strength. 結晶粒の粗大化領域深さｔ／６５０ＨＶ以上に硬化した浸炭層の深さＴによる曲げ疲労強度の変化を概念的に示すグラフである。It is a graph which shows notionally the change of the bending fatigue strength by the depth T of the carburized layer hardened to the coarsening area depth t / 650HV or more of a crystal grain. 浸炭層の断面を説明する模式図である。（ａ）は結晶粒の粗大化領域深さｔ、（ｂ）は６５０ＨＶ以上に硬化した浸炭層の深さＴを説明する図である。It is a schematic diagram explaining the cross section of a carburized layer. (A) is a figure explaining the coarsening area | region depth t of a crystal grain, (b) is explaining the depth T of the carburized layer hardened to 650HV or more. 曲げ疲労試験に供する試験片形状を示す図である。It is a figure which shows the test piece shape with which it uses for a bending fatigue test. ローラピッチング試験方法を説明する概要図である。It is a schematic diagram explaining a roller pitching test method. ローラピッチング試験の試験片形状を説明する概要図である。（ａ）は小ローラ、（ｂ）は大ローラ、（ｃ）は大ローラの端部形状である。It is a schematic diagram explaining the test piece shape of a roller pitching test. (A) is a small roller, (b) is a large roller, and (c) is an end shape of the large roller.

符号の説明Explanation of symbols

１１：表面 １２：浸炭層 １３：母相 ２０：曲げ疲労試験片 ３１：小ローラ ３１１：試験部 ３２：大ローラ ３２１：大ローラの端部 11: Surface 12: Carburized layer 13: Matrix 20: Bending fatigue test piece 31: Small roller 311: Test section 32: Large roller 321: End of large roller

Claims (7)

質量比で、Ｃ：０．０５〜０．４％、Ｓｉ：０．０５〜０．７％、Ｍｎ：０．１〜２．０％、Ｎ：０．００３〜０．０２０％、およびＮｂ：０．００５〜０．１％、ＡＬ：０．０１〜０．１％、Ｔｉ：０．０１〜０．４％のうち一種以上を含有し、残部Ｆｅ及び不可避的不純物からなる肌焼き鋼を所定形状に成形し減圧浸炭してなり、該減圧浸炭後に８０μｍ以上の結晶粒を含む結晶粒粗大化領域の深さが６５０ＨＶ以上に硬化した浸炭層の深さの０．２５以下であることを特徴とする減圧浸炭部品。   By mass ratio, C: 0.05-0.4%, Si: 0.05-0.7%, Mn: 0.1-2.0%, N: 0.003-0.020%, and Nb : 0.005 to 0.1%, AL: 0.01 to 0.1%, Ti: 0.01 to 0.4%, containing one or more, and the case-hardened steel consisting of the remaining Fe and inevitable impurities Is carburized under reduced pressure and carburized under reduced pressure, and after the vacuum carburization, the depth of the grain coarsened region containing crystal grains of 80 μm or more is 0.25 or less of the depth of the carburized layer cured to 650 HV or higher. Vacuum carburized parts characterized by 質量比で、Ｃｒ：０．２〜２．０％をさらに含有する請求項１に記載の減圧浸炭部品。   The reduced-pressure carburized component according to claim 1, further containing Cr: 0.2 to 2.0% by mass ratio. 質量比で、Ｃ：０．０５〜０．４％、Ｓｉ：０．０５〜０．７％、Ｍｎ：０．１〜２．０％、Ｎ：０．００３〜０．０２０％、およびＮｂ：０．００５〜０．１％、ＡＬ：０．０１〜０．１％、Ｔｉ：０．０１〜０．４％のうち一種以上を含有し、残部Ｆｅ及び不可避的不純物からなる鋼材を溶製・鋳造して熱間圧延する素材製造工程と、該素材を加熱して熱間鍛造する熱間鍛造工程と、該熱間鍛造後の鋼材を加熱冷却して固溶した炭窒化物を析出させる析出処理工程と、該析出処理した鋼材を所定形状に成形する成形工程と、浸炭層を形成して該成形した鋼材を強化する減圧浸炭処理工程を有することを特徴とする減圧浸炭部品の製造方法。   By mass ratio, C: 0.05-0.4%, Si: 0.05-0.7%, Mn: 0.1-2.0%, N: 0.003-0.020%, and Nb : 0.005-0.1%, AL: 0.01-0.1%, Ti: contain one or more of 0.01-0.4%, dissolve the steel material consisting of the remainder Fe and inevitable impurities A raw material manufacturing process for producing and casting and hot rolling, a hot forging process for heating and hot forging the raw material, and heating and cooling the steel material after hot forging to precipitate a solid solution carbonitride A low-pressure carburized component comprising: a precipitation treatment step to be formed; a forming step for forming the precipitation-treated steel material into a predetermined shape; and a reduced-pressure carburization treatment step for strengthening the formed steel material by forming a carburized layer. Method. 前記素材の加熱は、１２００〜１３００℃で１０分以上加熱保持する処理である請求項３に記載の減圧浸炭部品の製造方法。   The method of manufacturing a vacuum carburized part according to claim 3, wherein the heating of the material is a process of heating and holding at 1200 to 1300 ° C for 10 minutes or more. 前記析出処理は、前記熱間鍛造工程の冷却段階で９００〜６５０℃の範囲を５℃／分以下の冷却速度で冷却する処理である請求項３または４に記載の減圧浸炭部品の製造方法。   5. The method for producing a reduced-pressure carburized component according to claim 3, wherein the precipitation treatment is a treatment of cooling a range of 900 to 650 ° C. at a cooling rate of 5 ° C./min or less in the cooling stage of the hot forging step. 前記析出処理は、９００〜１０００℃で２０分以上加熱保持する処理である請求項３または４に記載の減圧浸炭部品の製造方法。   The method for producing a reduced-pressure carburized component according to claim 3 or 4, wherein the precipitation treatment is a treatment of heating and holding at 900 to 1000 ° C for 20 minutes or more. 前記減圧浸炭処理は、減圧下において９００〜１０５０℃で浸炭処理する請求項３〜６のいずれかに記載の減圧浸炭部品の製造方法。   The said reduced-pressure carburizing process is a manufacturing method of the reduced-pressure carburized component in any one of Claims 3-6 which carburize at 900-1050 degreeC under pressure reduction.
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