JP7196707B2 - Forged member for nitriding and its manufacturing method, and surface hardened forged member and its manufacturing method - Google Patents
Forged member for nitriding and its manufacturing method, and surface hardened forged member and its manufacturing method Download PDFInfo
- Publication number
- JP7196707B2 JP7196707B2 JP2019049911A JP2019049911A JP7196707B2 JP 7196707 B2 JP7196707 B2 JP 7196707B2 JP 2019049911 A JP2019049911 A JP 2019049911A JP 2019049911 A JP2019049911 A JP 2019049911A JP 7196707 B2 JP7196707 B2 JP 7196707B2
- Authority
- JP
- Japan
- Prior art keywords
- nitriding
- hardness
- treatment
- forged member
- manufacturing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Images
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
Description
本発明は、窒化用鍛造部材及びその製造方法、並びに表面硬化鍛造部材及びその製造方法に関する。 TECHNICAL FIELD The present invention relates to a nitriding forged member and its manufacturing method, and a surface hardened forged member and its manufacturing method.
自動車に用いられるギヤに代表される高い疲労強度が必要とされる部品には、表面硬化を目的とした浸炭、高周波熱処理等が施されている。これらの表面硬化処理はオーステナイト（γ）変態域まで加熱して処理を行い、その後、焼入れをするために、熱またはマルテンサイト変態に起因した歪の発生が問題視されている。 Parts that require high fatigue strength, such as gears used in automobiles, are subjected to carburizing, high-frequency heat treatment, etc. for the purpose of surface hardening. Since these surface hardening treatments are performed by heating to the austenite (γ) transformation region and then quenching, the generation of strain due to heat or martensite transformation is regarded as a problem.
この歪の問題については、γ変態温度よりも低い温度で処理が行われる窒化処理（ガス窒化処理）を採用することによって解決が可能である。窒化処理（ガス窒化処理）は、一般的にアンモニア（ＮＨ3）に窒素（Ｎ2）等を加えたガスを用いる通常の窒化処理と、アンモニア（ＮＨ3）にＲＸガス等を加えたガスを用いて炭素（Ｃ）の浸入拡散処理も兼ねる軟窒化処理がある。いずれの窒化処理によっても、例えば表面から０．２ｍｍ程度以上の深さまで所望の硬化効果を得るためには、比較的長時間の処理を必要とし、高い生産性を確保することは困難である。 This strain problem can be solved by adopting a nitriding treatment (gas nitriding treatment) in which the treatment is performed at a temperature lower than the γ transformation temperature. In the nitriding treatment (gas nitriding treatment), a normal nitriding treatment using a gas obtained by adding nitrogen (N 2 ) or the like to ammonia (NH 3 ) or a gas obtained by adding RX gas or the like to ammonia (NH 3 ) is used. There is a nitrocarburizing treatment that also serves as a carbon (C) infiltration diffusion treatment. In any nitriding treatment, in order to obtain the desired hardening effect, for example, to a depth of about 0.2 mm or more from the surface, a relatively long treatment time is required, and it is difficult to ensure high productivity.
例えば、特許文献１及び２においては、窒化処理により表面の高硬度化を行った例が示されているが、いずれにおいても９時間以上の長時間の処理時間を行うことが示されている。
For example,
また、強度向上を実現することだけを考えれば、窒化処理前の窒化用鍛造部材の硬さ（芯部及び表面を含む全体の硬さ）を上昇させておくことも有効である。しかし、鍛造部材の硬さの上昇は、切削性を悪化させるという問題がある。ギヤ等の鋼部材は、寸法精度を確保するために切削加工を行うことが必須であるところ、窒化用鍛造部材の硬さ（芯部及び表面の硬さ）の上昇による切削性の悪化は大きな問題となる。そのため、強度改善のために、窒化用鍛造部材の硬さを上昇させるという選択を行うことは困難である。 Moreover, if only the improvement of strength is considered, it is also effective to increase the hardness of the forged member for nitriding before nitriding treatment (the hardness of the whole including the core and the surface). However, increasing the hardness of the forged member has the problem of deteriorating machinability. Steel parts such as gears must be machined to ensure dimensional accuracy, but the increase in hardness (hardness of core and surface) of forged parts for nitriding significantly deteriorates machinability. It becomes a problem. Therefore, it is difficult to choose to increase the hardness of the forged member for nitriding in order to improve the strength.
本発明は、かかる背景に鑑みてなされたものであり、熱間鍛造後窒化処理前において、製造上問題のない切削性を確保しつつ、従来よりも、より短時間の窒化処理により、深い硬化深さを得ることを可能にすることにより、生産性の向上と、高強度化が期待できる窒化用鍛造部材及びその製造方法、並びに表面硬化鍛造部材の製造方法を提供しようとするものである。 The present invention has been made in view of this background, and after hot forging and before nitriding treatment, while ensuring machinability that does not cause manufacturing problems, deep hardening is achieved by nitriding treatment in a shorter time than before. An object of the present invention is to provide a nitriding forged member, a method for producing the same, and a method for producing a surface-hardened forged member, which can be expected to improve productivity and increase strength by making it possible to obtain depth.
本発明の一態様は、窒化処理を行う窒化用鍛造部材であって、
化学成分組成が、質量％で、Ｃ：０．０５～０．１５％、Ｓｉ：０．０５～０．５０％、Ｍｎ：０．５０～２．００％、Ｃｒ：０．５０～１．５０％、Ｍｏ：０．０５～０．３０％、Ａｌ：０．０２０％以下、Ｖ：０．１０～０．７０％を含有し、残部がＦｅ及び不可避的不純物よりなると共に、下記式１を満足し、
式１：７５≧３４×［Ｍｎ］＋５７×［Ｃｒ］－５３×［Ｖ］
（ここで、式１～３における［Ｘ］は、元素Ｘの含有率（質量％）の値を意味する。）
金属組織におけるベイナイトの面積率が８０％以上であり、
表面硬さが２８０ＨＶ以下であり、
窒化処理を行った場合の特性として、表面硬さが７００ＨＶ以上、芯部硬さが３００ＨＶ以上となり、かつ、硬さが４００ＨＶ以上となる表面からの硬化深さが、２時間の処理において０．２ｍｍ以上となることを達成可能である、窒化用鍛造部材にある。
One aspect of the present invention is a forged member for nitriding that performs nitriding treatment,
The chemical component composition is, in mass %, C: 0.05 to 0.15%, Si: 0.05 to 0.50%, Mn: 0.50 to 2.00%, Cr: 0.50 to 1.0%. 50%, Mo: 0.05 to 0.30%, Al: 0.020% or less, V: 0.10 to 0.70%, the balance being Fe and unavoidable impurities, and the following formula 1 satisfies the
Formula 1: 75≧34×[Mn]+57×[Cr]−53×[V]
(Here, [X] in Formulas 1 to 3 means the value of the content of element X (% by mass).)
The area ratio of bainite in the metal structure is 80% or more,
The surface hardness is 280 HV or less,
The characteristics of the nitriding treatment are that the surface hardness is 700 HV or more, the core hardness is 300 HV or more, and the depth of hardening from the surface where the hardness is 400 HV or more is 0.00 in 2 hours of treatment. The forged member for nitriding can achieve a thickness of 2 mm or more.
上記窒化用鍛造部材は熱間鍛造後窒化処理前の部材であって、上記の化学成分組成及び式１を具備し、かつ、金属組織の状態及び表面硬さが上記特定の状態にある。これにより、上記窒化用鍛造部材は、比較的軟らかく切削が容易であり、かつ、従来よりも短時間の窒化処理によって高硬度化が可能となる。 The above-mentioned forged member for nitriding is a member before nitriding treatment after hot forging, has the above-mentioned chemical composition and formula 1, and has the state of metal structure and surface hardness in the above-specified state. As a result, the forged member for nitriding is relatively soft and easy to cut, and can be hardened by nitriding in a shorter time than conventionally.
すなわち、上記窒化用鍛造部材は、上記化学成分組成及び式１を具備し、後述する特定の製造方法を採用することによって、ベイナイトの面積率が８０％以上であり、Ｖについては、切削性確保と後工程の窒化処理時における時効析出による強化に十分な量が固溶状態にある金属組織を有している。さらに、前記の通りＶを固溶させて、硬度を低下させることにより、表面硬さが２８０ＨＶ以下である。これらの条件を具備していることにより、上記窒化用鍛造部材は、熱間鍛造後所定形状に機械加工をする際に製造上問題のない切削性を確保することができる。なお、熱間鍛造後窒化処理前の上記窒化用鍛造部材においては、芯部硬さ（内部硬さ）と表面硬さがほぼ同等であり、上記表面硬さは、窒化用鍛造部材のほぼ全体の硬さ特性を示しているといえる。 That is, the above-mentioned forged member for nitriding has the above-mentioned chemical composition and formula 1, and by adopting a specific manufacturing method described later, the area ratio of bainite is 80% or more, and V ensures machinability. It has a metal structure in which a sufficient amount of steel is in a solid solution state for strengthening due to aging precipitation during the nitriding treatment in the post-process. Furthermore, as described above, the surface hardness is 280 HV or less by causing V to dissolve and lowering the hardness. Satisfying these conditions ensures that the above-mentioned forged member for nitriding is machined into a predetermined shape after hot forging and has machinability that does not pose any manufacturing problems. In the forged member for nitriding after hot forging and before nitriding treatment, the hardness of the core (internal hardness) and the surface hardness are substantially the same, and the surface hardness is substantially the same as that of the forged member for nitriding. It can be said that it shows the hardness characteristics of
また、上記窒化用鍛造部材は、上記化学成分組成及び式１を具備し、特に、Ａｌ含有率を０．０２０％以下に制限している。これらにより、窒化処理を施した場合において、Ｖ炭窒化物等の析出による時効硬化を促進させることができ、短時間で硬化深さを高めることが容易となる。そして、窒化処理を行った場合の特性として、上述した優れた硬化特性を得ることが可能となる。 Further, the forged member for nitriding has the above chemical composition and formula 1, and in particular, the Al content is limited to 0.020% or less. As a result, when nitriding treatment is performed, age hardening due to precipitation of V carbonitride and the like can be promoted, and it becomes easy to increase the hardening depth in a short time. Then, as a property when nitriding treatment is performed, it is possible to obtain the above-described excellent hardening property.
それ故、切削性を確保しつつ、従来鋼より短時間の窒化処理により深い硬化深さを得て、優れた強度を得ることができる窒化用鍛造部材を提供することができる。 Therefore, it is possible to provide a forged member for nitriding that can obtain a deeper hardening depth by nitriding treatment in a shorter time than conventional steel and obtain excellent strength while ensuring machinability.
上記窒化用鍛造部材は、前述したごとく、製造上問題のない切削性を確保しつつ、切削後の窒化処理による硬化を従来よりも短時間で行えるようしたものである。このような優れた特性を得るために発明者らが多くの実験の結果、着目した事項を以下に列挙する。 As described above, the above-described forged member for nitriding can be hardened by nitriding treatment after cutting in a shorter time than before while ensuring machinability that does not pose any problem in manufacturing. As a result of many experiments conducted by the inventors in order to obtain such excellent characteristics, the following items are noted.
（１）ベイナイト面積率が８０％以上であるベイナイト主体の組織とし、かつ、熱間鍛造時の加熱により適量のＶを固溶させ、材料を軟らかくすることにより、製造上問題のない切削性を確保することができる。
（２）ベイナイト主体であって、時効析出に必要な量のＶが固溶した金属組織を確実に得るために、Ｍｎ、Ｃｒ、Ｍｏ含有率を適切な範囲内に調整し、かつ、鍛造後の冷却速度を適正範囲に制御する（８００～５００℃の範囲の冷却速度を０．５℃／ｓ～５℃／ｓとする)ことが重要である。
（３）切削後の窒化処理時に、処理時の加熱を利用して、Ｖ炭窒化物等を時効析出させることにより、材料の芯部硬さを硬くし、強度を高めることができる。特に、Ｍｏ及びＶを同時に添加することにより、それぞれを単一で添加した場合よりも時効硬化量を増加させることができる。
（４）Ｍｎ、Ｃｒ、Ａｌは窒化物を形成して、窒化後の表面硬さを向上させる効果を発揮する一方で、硬化深さを減少させることに影響する。特にＡｌはこの影響が顕著である。この点に着目し、Ａｌの添加量を０．０２０％以下という極微量な範囲に制限する。これにより、従来提案されていた鋼と比較すると、より短時間で同じ硬化深さを得ることができる。前記した特許文献に記載の鋼を含め、従来提案されている鋼でも長時間処理を行えば、深い硬化深さを得ることは可能であるが、この場合、大幅に生産性が低下する。本発明を適用すれば、生産性を大きく低下させることなく、深い硬化深さを得て、高強度を得ることができる。また、Ａｌの添加量を極微量とすることにより、Ｖ炭窒化物の形成が容易となることを利用して、時効硬化の効果も高めることができる。
（５）Ａｌ含有率の制限は、上記のごとく効果的であるが、Ｍｎ、Ｃｒ及びＶの含有率の関係を適正に制御することが前提となり、式１の関係を具備することが重要である。
(1) A bainite-based structure with a bainite area ratio of 80% or more, and an appropriate amount of V dissolved by heating during hot forging to soften the material, so that machinability that does not cause manufacturing problems is obtained. can be secured.
(2) In order to reliably obtain a metal structure that is mainly bainite and in which the amount of V required for aging precipitation is solid-solved, the contents of Mn, Cr, and Mo are adjusted within an appropriate range, and after forging, It is important to control the cooling rate in the proper range (the cooling rate in the range of 800 to 500° C. is 0.5° C./s to 5° C./s).
(3) During the nitriding treatment after cutting, the heating during the treatment is used to cause aging precipitation of V carbonitride and the like, thereby increasing the core hardness of the material and increasing the strength. In particular, by adding Mo and V simultaneously, the amount of age hardening can be increased more than when each is added singly.
(4) Mn, Cr, and Al form nitrides, exhibiting the effect of improving the surface hardness after nitridation, but also reducing the hardening depth. In particular, this effect is remarkable for Al. Focusing on this point, the amount of Al added is limited to a very small range of 0.020% or less. This makes it possible to obtain the same hardening depth in a shorter period of time as compared with conventionally proposed steels. Although it is possible to obtain a deep hardening depth by long-time treatment even in conventionally proposed steels, including the steels described in the above-mentioned patent documents, productivity is greatly reduced in this case. By applying the present invention, it is possible to obtain a deep hardening depth and obtain high strength without significantly lowering productivity. In addition, by making the amount of Al to be added extremely small, the effect of age hardening can be enhanced by utilizing the fact that the formation of V carbonitride is facilitated.
(5) Limiting the Al content rate is effective as described above, but it is premised on properly controlling the relationship between the content rates of Mn, Cr, and V, and it is important to have the relationship of Formula 1. be.
次に、上記窒化用鍛造部材における化学成分組成の限定理由を説明する。 Next, reasons for limiting the chemical composition of the forged member for nitriding will be described.
Ｃ：０．０５～０．１５％、
Ｃ（炭素）は、焼入れ性を確保し、ベイナイト組織を得ると共に、Ｍｏ又はＶとの炭窒化物による時効析出を得るために重要な元素である。これらの効果を得るために、Ｃ含有率を０．０５％以上とする。一方、Ｃ含有率が高すぎる場合には被削性が低下するため、０．１５％以下とする。
C: 0.05 to 0.15%,
C (carbon) is an important element for ensuring hardenability, obtaining a bainite structure, and obtaining precipitation by carbonitride with Mo or V during aging. In order to obtain these effects, the C content is made 0.05% or more. On the other hand, if the C content is too high, the machinability will deteriorate, so the C content is made 0.15% or less.
Ｓｉ：０．０５～０．５０％、
Ｓｉ（ケイ素）は、固溶強化による強度向上に寄与し、脱酸処理に有効に寄与するためため、０．０５％以上含有させる。一方、Ｓｉ含有率が高すぎる場合には切削性が悪化するため０．５０％以下とする。
Si: 0.05 to 0.50%,
Si (silicon) contributes to strength improvement by solid-solution strengthening and effectively contributes to deoxidation treatment, so it is contained in an amount of 0.05% or more. On the other hand, when the Si content is too high, machinability deteriorates, so the Si content is made 0.50% or less.
Ｍｎ：０．５０～２．００％、
Ｍｎ（マンガン）は、焼入れ性を確保し、ベイナイト組織を得るために有効な元素である。これらの効果を得るために、Ｍｎ含有率は０．５０％以上とする。一方、Ｍｎ含有率が高すぎる場合には、組織がマルテンサイトとなりやすく、切削性を悪化させるおそれがあるため、２．００％以下とする。
Mn: 0.50-2.00%,
Mn (manganese) is an effective element for ensuring hardenability and obtaining a bainite structure. In order to obtain these effects, the Mn content should be 0.50% or more. On the other hand, when the Mn content is too high, the structure tends to become martensite, which may deteriorate the machinability.
Ｃｒ：０．５０～１．５０％、
Ｃｒ（クロム）は、焼入れ性を確保し、ベイナイト組織を得ると共に、窒化後の表面硬さ及び硬化深さを向上させるために有効である。これらの効果を得るために、Ｃｒ含有率は０．５０％以上とする。一方、Ｃｒ含有率が高すぎる場合には、窒化後の硬化深さの向上効果が得られなくなるため、１．５０％以下とする。
Cr: 0.50 to 1.50%,
Cr (chromium) is effective for securing hardenability, obtaining a bainite structure, and improving surface hardness and hardening depth after nitriding. In order to obtain these effects, the Cr content should be 0.50% or more. On the other hand, if the Cr content is too high, the effect of improving the hardening depth after nitriding cannot be obtained, so it is made 1.50% or less.
Ｍｏ：０．０５～０．３０％、
Ｍｏ（モリブデン）は、焼入れ性を確保し、ベイナイト組織を得ると共に、窒化時におけるＭｏ炭化物の析出による時効硬化を得るために有効である。これらの効果を得るために、Ｍｏ含有率は０．０５％以上とする。一方、Ｍｏ含有率が高すぎる場合には、組織がマルテンサイトとなりやすく、切削性を悪化させると共にコストが悪化するため、０．３０％以下とする。
Mo: 0.05-0.30%,
Mo (molybdenum) is effective for securing hardenability, obtaining a bainite structure, and obtaining age hardening due to precipitation of Mo carbide during nitriding. In order to obtain these effects, the Mo content should be 0.05% or more. On the other hand, if the Mo content is too high, the structure tends to become martensite, degrading the machinability and increasing the cost.
Ａｌ：０．０２０％以下、
Ａｌ（アルミニウム）は、製鋼時に脱酸に必要な元素であるため、少量の添加は必要であるが、本発明ではその含有率を低く抑えることにより、所定の硬化深さが得られることを見出したため、上限を低く抑え、窒化処理の処理時間を従来よりも短くすることを可能としている。この効果を得るために、Ａｌ含有率は、０．０２０％以下とする。
Al: 0.020% or less,
Al (aluminum) is an element necessary for deoxidation during steelmaking, so it must be added in a small amount. Therefore, it is possible to keep the upper limit low and shorten the processing time of the nitriding treatment. In order to obtain this effect, the Al content should be 0.020% or less.
Ｖ：０．１０～０．７０％、
Ｖ（バナジウム）は、窒化処理時の加熱を利用したＶ炭窒化物の時効析出により、芯部硬さを高め、強度向上に寄与するとともに、窒化処理後の表面硬さ及び硬化深さの向上に有効な元素である。この効果を得るために、Ｖ含有率は０．１０％以上とする。一方、Ｖ含有率を高くしすぎても上記効果が飽和すると共にコストが悪化するため、０．７０％以下とする。
V: 0.10 to 0.70%,
V (vanadium) increases the core hardness and contributes to strength improvement by aging precipitation of V carbonitride using heating during nitriding treatment, and also improves surface hardness and hardening depth after nitriding treatment. is an effective element for To obtain this effect, the V content should be 0.10% or more. On the other hand, if the V content is too high, the above effects will saturate and the cost will worsen.
次に、上記窒化用鍛造部材の化学成分組成は、より短時間の窒化処理で深い硬化深さを得るために、上述した各元素の含有範囲を規制した上で、さらに、式１を満足する必要がある。 Next, in order to obtain a deep hardening depth in a shorter nitriding treatment, the chemical component composition of the forged member for nitriding satisfies the formula 1 after restricting the content range of each element described above. There is a need.
式１：７５≧３４×［Ｍｎ］＋５７×［Ｃｒ］－５３×［Ｖ］ Formula 1: 75≧34×[Mn]+57×[Cr]−53×[V]
窒化処理により短時間での硬化深さの向上効果を得るためには、Ｖ含有率をＭｎ及びＣｒの含有率に応じて高めることが必要である。式１の関係を満たさない場合には、Ｖ含有率がＭｎとＣｒの含有率に関して十分ではなく、短時間での硬化深さ向上効果が得られない。 In order to obtain the effect of improving the hardening depth in a short time by nitriding treatment, it is necessary to increase the V content in accordance with the content of Mn and Cr. If the relationship of Formula 1 is not satisfied, the V content is insufficient with respect to the Mn and Cr content, and the effect of improving the hardening depth in a short time cannot be obtained.
また、上記窒化用鍛造部材は、金属組織におけるベイナイトの面積率が８０％以上である。この組織状態は、例えば後述する特定の製造方法を採用することによって実現でき、含有されるＶを後処理である窒化処理時の加熱を利用した析出強化による強度向上効果を得るのに十分な量を固溶させることができる。これにより、窒化処理前においては軟らかい状態となり、切削性に優れた状態を得ることができる。ベイナイトの面積率が８０％未満となり、フェライト・パーライト組織が増加した場合には、Ｖを十分に固溶させることが難しくなり、また、マルテンサイト組織の面積率が高くなった場合には、硬さが高くなり、切削性が低下するおそれがある。 Further, in the forged member for nitriding, the area ratio of bainite in the metal structure is 80% or more. This structural state can be realized, for example, by adopting a specific manufacturing method described later, and the amount of V contained is sufficient to obtain the effect of improving strength by precipitation strengthening using heating during nitriding treatment, which is a post-treatment. can be dissolved. As a result, before the nitriding treatment, the steel becomes soft and excellent in machinability. When the area ratio of bainite is less than 80% and the ferrite/pearlite structure increases, it becomes difficult to sufficiently dissolve V. On the other hand, when the area ratio of martensite structure increases, hardening occurs. There is a risk that the cutting performance will decrease due to the increase in hardness.
また、上記窒化用鍛造部材は、例えば後述する特定の製造方法を採用することによって、表面硬さ（及び芯部硬さ）が２８０ＨＶ以下の状態が実現されている。これにより、製造上問題のない切削性を確保することができる。 Further, the forged member for nitriding has a surface hardness (and core hardness) of 280 HV or less, for example, by adopting a specific manufacturing method to be described later. As a result, it is possible to ensure machinability that does not cause problems in manufacturing.
そして、上記窒化用鍛造部材は、窒化処理を行った場合の特性として、表面硬さが７００ＨＶ以上、芯部硬さが３００ＨＶ以上となり、かつ、硬さが４００ＨＶ以上となる表面からの硬化深さが、２時間の処理において０．２ｍｍ以上となることを達成可能という特性を有している。つまり、公知の窒化処理条件の範囲内で適正条件を選択することにより、処理前の表面硬さが２８０ＨＶ以下の場合であっても、少なくとも２時間（場合によっては２時間未満）の窒化処理により、表面硬さが７００ＨＶ以上、芯部硬さが３００ＨＶ以上となり、かつ、硬さが４００ＨＶ以上となる表面からの硬化深さ０．２ｍｍ以上という硬度特性を得ることが可能である。そのため、従来と比べて短時間で所望の表面硬化処理が可能となる。 The forged member for nitriding has characteristics when nitriding treatment is performed, such as a surface hardness of 700 HV or more, a core hardness of 300 HV or more, and a hardening depth from the surface where the hardness is 400 HV or more. has the property that it is possible to achieve a thickness of 0.2 mm or more in 2 hours of treatment. That is, by selecting appropriate conditions within the range of known nitriding conditions, even if the surface hardness before treatment is 280 HV or less, nitriding treatment for at least 2 hours (less than 2 hours in some cases) , surface hardness of 700 HV or more, core hardness of 300 HV or more, and hardness characteristics of 0.2 mm or more of hardening depth from the surface where hardness is 400 HV or more can be obtained. Therefore, the desired surface hardening treatment can be performed in a shorter time than conventionally.
また、上記特性を具備することにより、硬さが４００ＨＶ以上となる表面からの硬化深さについては、窒化処理の処理時間が４時間の処理において０．３ｍｍ以上、７時間の処理において０．４ｍｍ以上、１１時間の処理において０．５ｍｍ以上も達成できる場合がある。これは、後述する図１に示すように、従来鋼であるＳＣＭ４２０と比較すると、より短時間の処理で深い硬化深さが得られることを意味する。 In addition, due to the above characteristics, the hardening depth from the surface where the hardness is 400 HV or more is 0.3 mm or more when the nitriding treatment time is 4 hours, and 0.4 mm when the treatment time is 7 hours. As described above, a thickness of 0.5 mm or more may be achieved in 11 hours of treatment. This means that a deeper hardening depth can be obtained in a shorter treatment time than the conventional steel SCM420, as shown in FIG. 1, which will be described later.
このような短時間の窒化処理によって硬化深さを高める効果は、上記特定の製造方法によって窒化用鍛造部材を作製するだけでなく、上述した化学成分組成及び式１を満たし、特にＡｌ含有率を０．０２０％以下に制限することによって、初めて実現することができる。 The effect of increasing the hardening depth by such a short-time nitriding treatment is not only that the forged member for nitriding is produced by the specific manufacturing method described above, but also that the chemical composition and formula 1 described above are satisfied, and in particular, the Al content is It can be realized only by limiting the content to 0.020% or less.
次に、上述した優れた窒化用鍛造部材を製造する方法としては、上記化学成分組成を有すると共に上記式１を満足する鋼材に対して、１１００℃以上の熱間鍛造温度にて熱間鍛造を施し、その後８００～５００℃の範囲の冷却を０．５℃／秒～５℃／秒の冷却速度で行う、窒化用鍛造部材の製造方法がある。 Next, as a method for producing the excellent forged member for nitriding described above, hot forging is performed at a hot forging temperature of 1100 ° C. or higher for a steel material having the above chemical composition and satisfying the above formula 1. and then cooling in the range of 800 to 500° C. at a cooling rate of 0.5° C./sec to 5° C./sec.
この窒化用鍛造部材の製造方法によれば、熱間鍛造温度を１１００℃以上という温度に設定し、Ｖについて、熱間鍛造後の硬さを低下させ、かつ後工程である窒化処理時に得る析出強化を得るのに十分な量を固溶させた状態とする。そして、その後特定範囲の冷却速度に制限することにより、ベイナイトの面積率８０％以上の金属組織を得ることができる。 According to this method for producing a forged member for nitriding, the hot forging temperature is set to a temperature of 1100 ° C. or higher, the hardness of V after hot forging is reduced, and the precipitation obtained during the nitriding treatment in the subsequent process is It is in a solid solution state in an amount sufficient to obtain strengthening. After that, by limiting the cooling rate to a specific range, a metal structure having a bainite area ratio of 80% or more can be obtained.
熱間鍛造温度が１１００℃未満の場合には、Ｖの固溶量が不十分になり、熱間鍛造後の硬さ低下が不十分になって切削性が低下するとともに、熱間鍛造後の冷却時に８０％以上のベイナイト組織を得ることが困難となる。なお、熱間鍛造温度は、高くするほどＶの固溶量を高めることができるが、一方であまり高くしすぎると、多くのエネルギーを必要とし、省エネの点から問題が生じるだけでなく、結晶粒が粗大となって機械的特性が低下するおそれがあるため、上限は１３００℃程度とすることが好ましい。 When the hot forging temperature is less than 1100 ° C., the solid solution amount of V becomes insufficient, the hardness after hot forging is insufficient, and the machinability is reduced, and after hot forging It becomes difficult to obtain a bainite structure of 80% or more during cooling. The higher the hot forging temperature, the higher the solid solution amount of V. On the other hand, if the hot forging temperature is too high, a lot of energy is required, which poses a problem in terms of energy saving. The upper limit is preferably about 1300° C., because the grains become coarse and the mechanical properties may deteriorate.
また、熱間鍛造後の冷却時においては、上記のごとく、８００～５００℃の範囲における冷却を０．５℃／秒～５℃／秒の冷却速度で行う。この冷却速度よりも遅い場合には、フェライト-パーライト組織の生成が増加し、ベイナイト組織の面積率を８０％以上とすることが困難となる。一方、上記範囲よりも冷却速度が速い場合には、マルテンサイト組織が生成し、前記と同様にベイナイト組織の面積率を８０％以上とすることが困難となる。８００～５００℃の範囲で冷却速度を指定したのは、この範囲の温度の冷却速度で、冷却後の組織が決まるためである。 Further, during cooling after hot forging, as described above, cooling is performed in the range of 800 to 500° C. at a cooling rate of 0.5° C./second to 5° C./second. If the cooling rate is slower than this, the formation of ferrite-pearlite structure increases, making it difficult to increase the area ratio of bainite structure to 80% or more. On the other hand, if the cooling rate is faster than the above range, a martensite structure is formed, and it becomes difficult to increase the area ratio of the bainite structure to 80% or more as described above. The reason why the cooling rate is specified in the range of 800 to 500° C. is that the structure after cooling is determined by the cooling rate at temperatures within this range.
次に、表面硬化層を有する表面硬化鍛造部材を製造する方法としては、上記窒化用鍛造部材に対して、所定形状への切削加工を施し、その後、オーステナイト変態点温度よりも低い処理温度で窒化処理を行う方法がある。この方法によれば、上述した優れた特性を有する窒化用鍛造部材を用いるため、従来よりも短時間で窒化処理の効果を得ることができ、製造工程の合理化を図ることができる。 Next, as a method for producing a surface-hardened forged member having a surface-hardened layer, the forged member for nitriding is cut into a predetermined shape, and then nitrided at a treatment temperature lower than the austenite transformation temperature. There is a way to do things. According to this method, since the forged member for nitriding having the excellent properties described above is used, the effect of the nitriding treatment can be obtained in a shorter time than in the conventional method, and the manufacturing process can be streamlined.
上記窒化処理の方法は、公知の方法を採用することができる。例えば、オーステナイト変態温度よりも低い５００℃～６００℃の範囲で行うのが一般的である。また、窒素源としては、アンモニア（ＮＨ3）を用いる。そして、窒化処理としては、アンモニア（ＮＨ3）に窒素（Ｎ2）等を加えたガスを用い、Ｎのみの浸入を図る窒化処理と、アンモニア（ＮＨ3）にＲＸガス等を加えたガスを用い、Ｎだけでなく同時にＣの浸入も伴う軟窒化処理のいずれも採用可能である。 A known method can be adopted as the method of the nitriding treatment. For example, it is common to carry out in the range of 500° C. to 600° C., which is lower than the austenite transformation temperature. Ammonia (NH 3 ) is used as a nitrogen source. As the nitriding treatment, a gas obtained by adding nitrogen (N 2 ) or the like to ammonia (NH 3 ) is used, and a nitriding treatment for infiltrating only N or a gas obtained by adding RX gas or the like to ammonia (NH 3 ) is performed. It is possible to adopt any of the soft nitriding treatments accompanied by penetration of not only N but also C at the same time.
得られる表面硬化鍛造部品としては、例えば、次のものがある。
すなわち、表面硬化層を有する表面硬化鍛造部材であって、
化学成分組成が、質量％で、Ｃ：０．０５～０．１５％、Ｓｉ：０．０５～０．５０％、Ｍｎ：０．５０～２．００％、Ｃｒ：０．５０～１．５０％、Ｍｏ：０．０５～０．３０％、Ａｌ：０．０２０％以下、Ｖ：０．１０～０．７０％を含有し、残部がＦｅ及び不可避的不純物よりなると共に、下記式１を満足し、
式１：７５≧３４×［Ｍｎ］＋５７×［Ｃｒ］－５３×［Ｖ］
（ここで、式１～３における［Ｘ］は、元素Ｘの含有率（質量％）の値を意味する。）
表面硬さが７００ＨＶ以上、
芯部硬さが３００ＨＶ以上、かつ、
硬さが４００ＨＶ以上となる表面からの硬化深さが０．２ｍｍ以上である、表面硬化鍛造部材。
Examples of surface hardened forged parts that can be obtained include:
That is, a surface-hardened forged member having a surface-hardened layer,
The chemical component composition is, in mass %, C: 0.05 to 0.15%, Si: 0.05 to 0.50%, Mn: 0.50 to 2.00%, Cr: 0.50 to 1.0%. 50%, Mo: 0.05 to 0.30%, Al: 0.020% or less, V: 0.10 to 0.70%, the balance being Fe and unavoidable impurities, and the following formula 1 satisfies the
Formula 1: 75≧34×[Mn]+57×[Cr]−53×[V]
(Here, [X] in Formulas 1 to 3 means the value of the content of element X (% by mass).)
Surface hardness is 700HV or more,
The core hardness is 300HV or more, and
A surface-hardened forged member having a hardening depth of 0.2 mm or more from a surface having a hardness of 400 HV or more.
この表面硬化鋼部品は、窒化処理の時間を調整することによって、上記硬化深さを変化させることができる。具体的な処理時間は、特定の化学成分組成毎に若干異なってくるため、予備実験等を行って定めることができる。少なくとも、上述した窒化用鍛造部材を用いることにより、窒化処理を適切な条件で行えば、２時間の処理において０．２ｍｍ以上となることを達成可能である。さらには、４時間の処理において０．３ｍｍ以上、７時間の処理において０．４ｍｍ以上、１１時間の処理において０．５ｍｍ以上も達成できる場合がある The hardening depth of the hardened steel part can be changed by adjusting the nitriding time. Since the specific treatment time is slightly different depending on the specific chemical composition, it can be determined by performing a preliminary experiment or the like. At least, if the nitriding treatment is performed under appropriate conditions by using the forged member for nitriding described above, it is possible to achieve a thickness of 0.2 mm or more in two hours of treatment. Furthermore, in some cases, 0.3 mm or more can be achieved in 4 hours of treatment, 0.4 mm or more in 7 hours of treatment, and 0.5 mm or more in 11 hours of treatment.
（実験例１）
本例では、表１に示すごとく、化学成分組成が異なる複数種類の鋼材を準備して、窒化用鍛造部材を想定した試験材を作製し、各種評価を行った。表１に記載の鋼のうち、鋼種Ａ～Ｌは本発明で指定した成分や式１を満足する鋼であり、鋼種Ｍ～Ｕは、一部の成分又は式１を満足しない比較鋼であり、ＳＣＭ４２０は、従来から浸炭や窒化用として用いられている鋼であるＪＩＳ規格範囲内の鋼である。
(Experimental example 1)
In this example, as shown in Table 1, a plurality of types of steel materials with different chemical compositions were prepared to prepare test materials assuming nitriding forged members, and various evaluations were performed. Among the steels listed in Table 1, steel types A to L are steels that satisfy the composition specified in the present invention and formula 1, and steel types M to U are comparative steels that do not satisfy some of the compositions or formula 1. , SCM420 are steels within the range of JIS standards, which are steels conventionally used for carburizing and nitriding.
各試験材を得るに当たって、電気炉溶解によって鋳造した鋼材を用い、これを鍛伸によって、φ３２×３００ｍｍの丸棒に加工した。熱間鍛造を想定して、この丸棒を１２００℃に１時間保持する加熱をし、その後、８００～５００℃の温度範囲が０．７℃／ｓの冷却速度となるよう冷却を行ない試験材を得た。得られた試験材は、各評価試験毎に適した試験片に加工した。その後、各試験片に対して所定の窒化処理を施した。なお、従来鋼ＳＣＭ４２０については、他の鋼とは異なりＶを含有しておらず析出強化による強度向上効果が得られないため、他の鋼種と同じ処理では低い強度しか得られない。そのため、従来から高強度が要求される部品にＳＣＭ４２０を用いる場合には、焼入れ焼もどし処理がされていることに配慮し、８５０℃×１時間→油冷の焼入れ処理と６００℃×１００分の焼もどし処理を行った後に、後述の窒化処理を行った。そして、窒化処理前後において、各種評価試験を実施した。 In obtaining each test material, a steel material cast by electric furnace melting was used, and this was processed into a round bar of φ32×300 mm by forging. Assuming hot forging, the round bar is heated to 1200 ° C for 1 hour, and then cooled so that the temperature range from 800 to 500 ° C has a cooling rate of 0.7 ° C / s. got The obtained test materials were processed into test pieces suitable for each evaluation test. After that, each test piece was subjected to a predetermined nitriding treatment. In contrast to other steels, conventional steel SCM420 does not contain V and cannot obtain the effect of improving strength by precipitation strengthening. Therefore, when using SCM420 for parts that have traditionally required high strength, considering that quenching and tempering treatment is performed, 850 ° C x 1 hour → oil cooling quenching treatment and 600 ° C x 100 minutes After performing the tempering treatment, the nitriding treatment described later was performed. Various evaluation tests were conducted before and after the nitriding treatment.
＜窒化処理＞
各試験片に対し、５６０℃の処理温度で窒化処理を施した。窒化処理の種類は、鋼種Ｊ、Ｋ、Ｌ、Ｔ、Ｕについては、アンモニア（ＮＨ3）と窒素（Ｎ2）とを含む窒化ガスを用いたガス窒化処理とした。それ以外の鋼種については、アンモニア（ＮＨ3）とＲＸガスとを含む窒化ガスを用いたガス軟窒化処理とした。処理時間は、いずれも、２時間、４時間、７時間、１１時間の４種類とした。
<Nitriding treatment>
Each test piece was subjected to nitriding treatment at a treatment temperature of 560°C. As for the type of nitriding treatment, steel types J, K, L, T, and U were gas nitriding using a nitriding gas containing ammonia (NH 3 ) and nitrogen (N 2 ). Other steel types were subjected to gas nitrocarburizing using a nitriding gas containing ammonia (NH 3 ) and RX gas. The treatment time was set to 4 types of 2 hours, 4 hours, 7 hours and 11 hours.
＜窒化前後の芯部硬さ＞
ＪＩＳ Ｚ ２２４４（２０１７）のビッカース硬さ試験－試験方法に準拠して行った。試験荷重は９８Ｎとし、試験片の直径をＤとした場合（以下、同様。）、表面からＤ／４の深さ位置を芯部として、試験片の断面における芯部に相当する任意の５点について測定し、その算術平均を芯部硬さとした。なお、本例では、試験片が円柱であったため表面からＤ／４の深さ位置を芯部としたが、他の形状の場合には、試験片（部材）全体の中で十分に厚みのある部位の厚みをＴとして、表面からＴ／４深さの位置を芯部とすることができる。
<Core hardness before and after nitriding>
Vickers hardness test of JIS Z 2244 (2017) - Test method was performed. When the test load is 98 N and the diameter of the test piece is D (the same applies hereinafter), any 5 points corresponding to the core in the cross section of the test piece with the depth position of D / 4 from the surface as the core was measured, and the arithmetic average was taken as the core hardness. In this example, since the test piece was cylindrical, the depth position of D/4 from the surface was used as the core portion, but in the case of other shapes, the test piece (member) has a sufficient thickness in the entire test piece (member). Assuming that the thickness of a certain portion is T, the position of T/4 depth from the surface can be defined as the core portion.
＜窒化前後の表面硬さ＞
ＪＩＳ Ｚ ２２４４（２０１７）のビッカース硬さ試験－試験方法に準拠して行った。試験荷重は０．９８Ｎとし、試験片の表面から０．０５ｍｍの深さ位置を測定位置とし、試験片の断面において任意の５点について測定し、その算術平均を表面硬さとした。
<Surface hardness before and after nitriding>
Vickers hardness test of JIS Z 2244 (2017) - Test method was performed. The test load was set to 0.98 N, the depth position of 0.05 mm from the surface of the test piece was set as the measurement position, and five arbitrary points on the cross section of the test piece were measured, and the arithmetic average was taken as the surface hardness.
＜窒化後の硬化深さ＞
ＪＩＳ Ｚ ２２４４（２０１７）のビッカース硬さ試験－試験方法に準拠して行った。試験荷重は０．９８Ｎとし、試験片の断面において表面から中心に向かって所定の間隔で測定を行い、硬さ分布を求めた。硬さ分布より、硬さが４００ＨＶ以上の限界位置を硬化深さとした。
<Hardening depth after nitriding>
Vickers hardness test of JIS Z 2244 (2017) - Test method was performed. The test load was set to 0.98 N, and the hardness distribution was obtained by measuring the cross section of the test piece at predetermined intervals from the surface toward the center. From the hardness distribution, the limit position where the hardness is 400 HV or more was defined as the hardening depth.
＜ベイナイト面積率＞
試験片の表面からＤ／４の深さ位置の断面を撮影したミクロ組織写真を用い、画像解析によりベイナイト組織の面積率を算出した。この試験片の断面における芯部に相当する任意の５点について、ベイナイト面積率を算出し、その算術平均を求めた。
<Bainite area ratio>
The area ratio of the bainite structure was calculated by image analysis using a microstructure photograph of a cross section taken at a depth position of D/4 from the surface of the test piece. The bainite area ratio was calculated for arbitrary five points corresponding to the core portion in the cross section of this test piece, and the arithmetic mean was obtained.
上記評価結果を表２に示す。 Table 2 shows the above evaluation results.
表１及び２からわかるように、窒化処理、軟窒化処理のいずれの処理についても、化学成分組成が所望範囲にあり、式１を満足し、かつ、ベイナイト面積率が適正な場合（鋼種Ａ～Ｌ）、窒化前においては表面硬さが２８０ＨＶ以下という切削性を確保し得る状態を確保したうえで、窒化後において、表面硬さが７００ＨＶ以上、芯部硬さが３００ＨＶ以上となり、かつ、硬さが４００ＨＶ以上となる表面からの硬化深さが、２時間の処理において０．２ｍｍ以上、４時間の処理において０．３ｍｍ以上となり、７時間の処理において０．４ｍｍ以上となり、１１時間の処理において０．５ｍｍ以上となり、非常に優れた窒化特性を示すことがわかる。 As can be seen from Tables 1 and 2, in both the nitriding treatment and the soft nitriding treatment, when the chemical composition is within the desired range, the formula 1 is satisfied, and the bainite area ratio is appropriate (steel types A to L). Before nitriding, the surface hardness is 280 HV or less, which ensures machinability, and after nitriding, the surface hardness is 700 HV or more, the core hardness is 300 HV or more, and the hardness is The hardening depth from the surface where the hardness is 400 HV or more is 0.2 mm or more after 2 hours of treatment, 0.3 mm or more after 4 hours of treatment, 0.4 mm or more after 7 hours of treatment, and 11 hours of treatment. , it is 0.5 mm or more, and it can be seen that extremely excellent nitriding properties are exhibited.
一方、鋼種Ｍは、Ｍｎ含有率が低すぎたことにより、ベイナイト面積率が低くなってＶ固溶が十分に行われず、窒化後のＶ炭化物等の析出による時効硬化が十分に得られなかった。 On the other hand, in steel type M, since the Mn content was too low, the bainite area ratio was low and V solid solution was not sufficiently performed, and age hardening due to precipitation of V carbide and the like after nitriding was not sufficiently obtained. .
鋼種Ｎは、Ｃｒ含有率が低すぎたことにより、ベイナイト面積率が低くなってＶ固溶が十分に行われず、窒化後のＶ炭化物等の析出による時効硬化が十分に得られなかった。 In steel type N, since the Cr content was too low, the bainite area ratio was low, V solid solution was not sufficiently performed, and age hardening due to precipitation of V carbide and the like after nitriding was not sufficiently obtained.
鋼種Ｏ、Ｐ及びＴは、式１を満足していないため、鋼種Ａ～Ｌに比較して同じ処理時間で比較した場合に、浅い硬化深さしか得られなかった。 Steel grades O, P and T did not satisfy Equation 1, so only a shallow hardening depth was obtained when compared with steel grades A to L under the same treatment time.
鋼種Ｑ、Ｒ、Ｓ、Ｕは、Ａｌ含有率が高い影響で、鋼種Ｏ、Ｐ、Ｔと同様に、本発明鋼と比較すると、同じ処理時間で比較した場合に、より浅い硬化深さしか得られなかった。
また、従来鋼ＳＣＭ４２０は、Ａｌだけでなく他の成分も含めて、本発明で検討した成分の最適化が全く行われていないため、各処理時間における硬化深さが大きく劣るものである。
Steel grades Q, R, S, and U, like steel grades O, P, and T, have a shallower hardening depth when compared with the steel of the present invention when compared with the same treatment time due to the high Al content. I didn't get it.
In addition, the conventional steel SCM420, including not only Al but also other components, has not been optimized at all as studied in the present invention, so the hardening depth at each treatment time is greatly inferior.
窒化処理における処理時間と硬化深さとの関係を図１に示す。図１は、横軸に窒化時間（ｈ）を、縦軸に４００ＨＶ以上となる表面からの硬化深さ（ｍｍ）をとったものであり、鋼種Ａ、Ｏ、Ｒ及びＳＣＭ４２０の結果をプロットしたものである。この図１からも、化学成分組成、式１を具備する鋼種Ａが、他の鋼種に比べて短時間で硬化深さを高められることがわかる。 FIG. 1 shows the relationship between the treatment time and the hardening depth in the nitriding treatment. In FIG. 1, the horizontal axis is the nitriding time (h) and the vertical axis is the hardening depth (mm) from the surface at 400 HV or more, and the results of steel types A, O, R and SCM420 are plotted. It is. From FIG. 1 as well, it can be seen that the steel type A, which has the chemical composition of Formula 1, can increase the hardening depth in a shorter time than the other steel types.
また、図２には、横軸にＡｌ含有率を、縦軸に式１の右辺の値をとり、窒化後の４００ＨＶ以上の硬化深さが０．２ｍｍ以上を達成できた場合を合格（○）、達成できなかった場合と不合格（×）として、○及び×をプロットした。図２から、Ａｌ含有率０．０２０％以下と式１の両方を満たすことによって、短時間窒化での硬化深さ向上効果が得られることがわかる。 In addition, in FIG. 2, the horizontal axis represents the Al content rate and the vertical axis represents the value of the right side of Equation 1, and the case where the hardening depth of 400 HV or more after nitriding can achieve 0.2 mm or more is passed (○ ), ◯ and × were plotted as failure to achieve and failure (×). From FIG. 2, it can be seen that by satisfying both the Al content of 0.020% or less and Expression 1, an effect of improving the hardening depth in short-time nitriding can be obtained.
（実験例２）
本例では、上述した鋼種Ａ～Ｄ（表１）を用い、表３に示すごとく、鍛造温度に相当する加熱時間及びその後の冷却における冷却速度を変化させ、窒化前の状態での硬度、ベイナイト面積率、及び切削性への影響を調べる試験を行った。各試験材は、実験例１の製造方法を基本とし、熱間鍛造を想定した加熱温度（鍛造温度）及びその後の冷却速度を表３に記載の条件に変更した。
(Experimental example 2)
In this example, steel types A to D (Table 1) described above were used. A test was conducted to examine the influence on the area ratio and machinability. Each test material was based on the manufacturing method of Experimental Example 1, and the heating temperature (forging temperature) assuming hot forging and the subsequent cooling rate were changed to the conditions shown in Table 3.
芯部硬さの測定及びベイナイト面積率の測定は、実験例１の場合と同様に行った。また、本例では、窒化処理を行う前の状態の試験片を用いて、後述する切削性の評価を行った。この場合の基準鋼種として、実験例１で従来鋼として準備したＳＣＭ４２０を用いた。 Measurement of core hardness and measurement of bainite area ratio were carried out in the same manner as in Experimental Example 1. In addition, in this example, the test piece before nitriding was used to evaluate machinability, which will be described later. In this case, SCM420 prepared as conventional steel in Experimental Example 1 was used as the reference steel type.
＜切削性評価＞
＜切削性評価＞
切削性は、旋盤により切削する場合の切削工具の摩耗量によって評価した。上記旋盤としては、森精機製ＳＬ－２５旋盤を用い、切削工具としては、タンガロイ製ＳＮＭＧ１２０４０８－サーメットＮＳ５３０を用いた。切削条件は、切削速度：２００ｍ／ｍｉｎ、送り速度：０．３ｍｍ／ｒｅｖ、切り込み：１．５ｍｍとした。試験後に切削工具の摩耗量を測定し、その値がＳＣＭ４２０の焼入れ焼もどし後の試験片による切削性と比較して、同等以下であれば合格（○）、そうでない場合を不合格（×）とした。結果は表３に示す。
<Machinability evaluation>
<Machinability evaluation>
Machinability was evaluated by the amount of wear of the cutting tool when cutting with a lathe. SL-25 lathe manufactured by Mori Seiki was used as the lathe, and SNMG120408-Cermet NS530 manufactured by Tungaloy was used as the cutting tool. The cutting conditions were a cutting speed of 200 m/min, a feed rate of 0.3 mm/rev, and a depth of cut of 1.5 mm. After the test, the amount of wear of the cutting tool is measured, and if the value is equal to or less than the machinability of the test piece after quenching and tempering of SCM420, it passes (○), and if not, it fails (x). and The results are shown in Table 3.
表３からわかるように、鋼種Ａ～Ｄは、すべて、化学成分組成が適正で式１も満足するものの、鍛造温度及びその後の冷却条件が適正でない場合には、ベイナイト面積率が低下し、鍛造温度に相当する加熱処理を行った後の芯部硬さを２８０ＨＶ以下とすることができず、切削性が低下することがわかる。 As can be seen from Table 3, steel grades A to D all have appropriate chemical composition and satisfy formula 1, but when the forging temperature and subsequent cooling conditions are not appropriate, the bainite area ratio decreases and the forging It can be seen that the core hardness after the heat treatment corresponding to the temperature cannot be reduced to 280 HV or less, and the machinability deteriorates.
Claims (4)
化学成分組成が、質量％で、Ｃ：０．０５～０．１５％、Ｓｉ：０．０５～０．５０％、Ｍｎ：０．５０～２．００％、Ｃｒ：０．５０～１．５０％、Ｍｏ：０．０５～０．３０％、Ａｌ：０．０２０％以下、Ｖ：０．１０～０．７０％を含有し、残部がＦｅ及び不可避的不純物よりなると共に、下記式１を満足し、
式１：７５≧３４×［Ｍｎ］＋５７×［Ｃｒ］－５３×［Ｖ］
（ここで、式１～３における［Ｘ］は、元素Ｘの含有率（質量％）の値を意味する。）
金属組織におけるベイナイトの面積率が８０％以上であり、
表面硬さが２８０ＨＶ以下であり、
窒化処理を行った場合の特性として、表面硬さが７００ＨＶ以上、芯部硬さが３００ＨＶ以上となり、かつ、硬さが４００ＨＶ以上となる表面からの硬化深さが、２時間の処理において０．２ｍｍ以上となることを達成可能である、窒化用鍛造部材。 A forged member for nitriding that performs nitriding treatment,
The chemical component composition is, in mass %, C: 0.05 to 0.15%, Si: 0.05 to 0.50%, Mn: 0.50 to 2.00%, Cr: 0.50 to 1.0%. 50%, Mo: 0.05 to 0.30%, Al: 0.020% or less, V: 0.10 to 0.70%, the balance being Fe and unavoidable impurities, and the following formula 1 satisfies the
Formula 1: 75≧34×[Mn]+57×[Cr]−53×[V]
(Here, [X] in Formulas 1 to 3 means the value of the content of element X (% by mass).)
The area ratio of bainite in the metal structure is 80% or more,
The surface hardness is 280 HV or less,
The characteristics of the nitriding treatment are that the surface hardness is 700 HV or more, the core hardness is 300 HV or more, and the depth of hardening from the surface where the hardness is 400 HV or more is 0.00 in 2 hours of treatment. A forged member for nitriding, which can be achieved to be 2 mm or more.
上記化学成分組成を有すると共に上記式１を満足する鋼材に対して、１１００℃以上の熱間鍛造温度にて熱間鍛造を施し、その後８００～５００℃の範囲における冷却を０．５℃／秒～５℃／秒の冷却速度で行う、窒化用鍛造部材の製造方法。 A method for manufacturing a forged member for nitriding according to claim 1,
The steel material having the above chemical composition and satisfying the above formula 1 is hot forged at a hot forging temperature of 1100 ° C. or higher, and then cooled in the range of 800 to 500 ° C. at 0.5 ° C./sec. A method for manufacturing a forged member for nitriding at a cooling rate of ~5°C/sec.
化学成分組成が、質量％で、Ｃ：０．０５～０．１５％、Ｓｉ：０．０５～０．５０％、Ｍｎ：０．５０～２．００％、Ｃｒ：０．５０～１．５０％、Ｍｏ：０．０５～０．３０％、Ａｌ：０．０２０％以下、Ｖ：０．１０～０．７０％を含有し、残部がＦｅ及び不可避的不純物よりなると共に、下記式１を満足し、
式１：７５≧３４×［Ｍｎ］＋５７×［Ｃｒ］－５３×［Ｖ］
（ここで、式１～３における［Ｘ］は、元素Ｘの含有率（質量％）の値を意味する。）
表面硬さが７００ＨＶ以上、
芯部硬さが３００ＨＶ以上、かつ、
硬さが４００ＨＶ以上となる表面からの硬化深さが０．２ｍｍ以上である、表面硬化鍛造部材。 A surface-hardened forged member having a surface-hardened layer,
The chemical component composition is, in mass %, C: 0.05 to 0.15%, Si: 0.05 to 0.50%, Mn: 0.50 to 2.00%, Cr: 0.50 to 1.0%. 50%, Mo: 0.05 to 0.30%, Al: 0.020% or less, V: 0.10 to 0.70%, the balance being Fe and unavoidable impurities, and the following formula 1 satisfies the
Formula 1: 75≧34×[Mn]+57×[Cr]−53×[V]
(Here, [X] in Formulas 1 to 3 means the value of the content of element X (% by mass).)
Surface hardness is 700HV or more,
The core hardness is 300HV or more, and
A surface-hardened forged member having a hardening depth of 0.2 mm or more from a surface having a hardness of 400 HV or more.
上記化学成分組成を有すると共に上記式１を満足する鋼材に対して、１１００℃以上の熱間鍛造温度にて熱間鍛造を施し、その後８００～５００℃の範囲における冷却を０．５℃／秒～５℃／秒の冷却速度で行って、金属組織におけるベイナイトの面積率が８０％以上であり、表面硬さが２８０ＨＶ以下であり、窒化処理を行った場合の特性として、表面硬さが７００ＨＶ以上、芯部硬さが３００ＨＶ以上となり、かつ、硬さが４００ＨＶ以上となる表面からの硬化深さが、２時間の処理において０．２ｍｍ以上となることを達成可能である、窒化用鍛造部材を作製し、
該窒化用鍛造部材に対して、切削加工を施し、その後、窒化処理を行う、表面硬化鍛造部材の製造方法。 4. A method for manufacturing a hard case forged member according to claim 3, comprising:
The steel material having the above chemical composition and satisfying the above formula 1 is hot forged at a hot forging temperature of 1100 ° C. or higher, and then cooled in the range of 800 to 500 ° C. at 0.5 ° C./sec. At a cooling rate of ~5 ° C./sec, the area ratio of bainite in the metal structure is 80% or more, the surface hardness is 280 HV or less, and the surface hardness is 700 HV as a characteristic when nitriding is performed. As described above, the forged member for nitriding can achieve a core hardness of 300 HV or more and a hardening depth of 0.2 mm or more from the surface where the hardness is 400 HV or more in two hours of treatment. to create
A method for manufacturing a surface-hardened forged member, wherein the forged member for nitriding is cut and then nitrided.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2019049911A JP7196707B2 (en) | 2019-03-18 | 2019-03-18 | Forged member for nitriding and its manufacturing method, and surface hardened forged member and its manufacturing method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2019049911A JP7196707B2 (en) | 2019-03-18 | 2019-03-18 | Forged member for nitriding and its manufacturing method, and surface hardened forged member and its manufacturing method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2020152938A JP2020152938A (en) | 2020-09-24 |
| JP7196707B2 true JP7196707B2 (en) | 2022-12-27 |
Family
ID=72557883
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2019049911A Active JP7196707B2 (en) | 2019-03-18 | 2019-03-18 | Forged member for nitriding and its manufacturing method, and surface hardened forged member and its manufacturing method |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP7196707B2 (en) |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010147224A1 (en) | 2009-06-17 | 2010-12-23 | 新日本製鐵株式会社 | Steel for nitriding and nitrided steel components |
| CN102089452A (en) | 2009-05-15 | 2011-06-08 | 新日本制铁株式会社 | Steel for nitrocarburizing and nitrocarburized parts |
| WO2012067181A1 (en) | 2010-11-17 | 2012-05-24 | 新日本製鐵株式会社 | Steel for nitriding purposes, and nitrided member |
| WO2018101451A1 (en) | 2016-11-30 | 2018-06-07 | Ｊｆｅスチール株式会社 | Steel for soft nitriding, and component |
-
2019
- 2019-03-18 JP JP2019049911A patent/JP7196707B2/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102089452A (en) | 2009-05-15 | 2011-06-08 | 新日本制铁株式会社 | Steel for nitrocarburizing and nitrocarburized parts |
| WO2010147224A1 (en) | 2009-06-17 | 2010-12-23 | 新日本製鐵株式会社 | Steel for nitriding and nitrided steel components |
| WO2012067181A1 (en) | 2010-11-17 | 2012-05-24 | 新日本製鐵株式会社 | Steel for nitriding purposes, and nitrided member |
| WO2018101451A1 (en) | 2016-11-30 | 2018-06-07 | Ｊｆｅスチール株式会社 | Steel for soft nitriding, and component |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2020152938A (en) | 2020-09-24 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP4729135B2 (en) | Nitriding steel and nitriding parts | |
| JP4385019B2 (en) | Manufacturing method for steel nitrocarburized machine parts | |
| KR101726251B1 (en) | Steel for nitrocarburizing and nitrocarburized component, and methods for producing said steel for nitrocarburizing and said nitrocarburized component | |
| JP2006307273A (en) | Case hardening steel having excellent crystal grain coarsening resistance and cold workability and in which softening can be obviated, and method for producing the same | |
| JP4047499B2 (en) | Carbonitriding parts with excellent pitting resistance | |
| JP4737601B2 (en) | High temperature nitriding steel | |
| JP4448047B2 (en) | A steel for skin hardening that has excellent grain coarsening resistance and cold workability, and can omit softening annealing. | |
| JP2006307272A (en) | Case hardening steel having excellent crystal grain coarsening resistance and cold workability, and method for producing the same | |
| JP6477904B2 (en) | Crankshaft rough profile, nitrided crankshaft, and method of manufacturing the same | |
| JP5477248B2 (en) | Nitriding steel and nitriding parts with excellent machinability | |
| JPH09324241A (en) | Steel for sort-nitriding, soft-nitrided parts and its production | |
| JP4488228B2 (en) | Induction hardening steel | |
| JPH08176733A (en) | Steel for soft nitriding | |
| JP5999751B2 (en) | Manufacturing method of ferrous materials | |
| JPH10226817A (en) | Production of steel for soft-nitriding and soft-nitrided parts using this steel | |
| JP7196707B2 (en) | Forged member for nitriding and its manufacturing method, and surface hardened forged member and its manufacturing method | |
| JPH07157842A (en) | Steel for soft-nitriding | |
| JPH11229032A (en) | Production of steel for soft-nitriding and soft-nitrided parts using the steel | |
| JP7263796B2 (en) | RING GEAR FOR AUTOMOBILE TRANSMISSION AND MANUFACTURING METHOD THEREOF | |
| JPH10226818A (en) | Production of steel for soft-nitriding and soft-nitrided parts using this steel | |
| JP5582296B2 (en) | Iron-based material and manufacturing method thereof | |
| JP6477614B2 (en) | Steel for soft nitriding and parts and method for manufacturing them | |
| JP2006265703A (en) | Steel for case hardening having excellent crystal grain coarsening resistance and cold workability and method for producing the same | |
| JP2006249504A (en) | Material for nitriding part excellent in suitability to broaching and method for manufacturing the same | |
| JP2023144674A (en) | Steel for nitriding having excellent cold forging property and cold forged nitrided component |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20211126 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20221109 |
|
| TRDD | Decision of grant or rejection written | ||
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20221115 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20221128 |
|
| R150 | Certificate of patent or registration of utility model |
Ref document number: 7196707 Country of ref document: JP Free format text: JAPANESE INTERMEDIATE CODE: R150 |