JP5484103B2 - Steel plate for high-strength machine parts, method for producing the same, and method for producing high-strength machine parts - Google Patents
Steel plate for high-strength machine parts, method for producing the same, and method for producing high-strength machine parts Download PDFInfo
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本発明は、耐摩耗性および靭性に優れた高強度機械部品を製造するために、焼入れ焼戻し、オーステンパーなどの調質熱処理に供して使用される素材鋼板、およびその製造方法、並びにその素材鋼板を用いた高強度機械部品の製造方法に関する。 The present invention relates to a raw steel plate used for tempering heat treatment such as quenching and tempering and austemper in order to produce a high-strength mechanical part excellent in wear resistance and toughness, a manufacturing method thereof, and a raw steel plate thereof The present invention relates to a method for manufacturing a high-strength machine part using the above.
自動車部品、産業機械のチェーン部品、歯車などの動力伝達部材や、木材の切断・草刈等に使用する丸鋸、帯鋸などの刃物部材といった高強度機械部品には、長寿命化を目的とした「耐摩耗性」の向上が要求されている。一般に鋼材の耐摩耗性は、高硬度化することによって向上することが知られている。そのため、耐摩耗性を重視する部材には、焼入れ後に低めの温度で焼戻しを行ってより高い硬度に調質した鋼材や、炭素等の合金元素含有量の高い鋼材が使用されている。すなわち、鋼材の硬さと耐摩耗性は密接な関係にあり、マトリクスの硬さを高めることは耐摩耗性の向上に繋がることから、従来、鋼材に耐摩耗性を付与する手法としては硬さを増大させる手法を採用することが一般的である。 High-strength machine parts such as automobile parts, chain parts of industrial machines, power transmission members such as gears, and blade members such as circular saws and band saws used for cutting and mowing wood are aimed at extending the service life. Improvement of “abrasion resistance” is required. In general, it is known that the wear resistance of a steel material is improved by increasing the hardness. For this reason, steel materials that are tempered at a lower temperature after quenching and tempered to a higher hardness after hardening and steel materials with a high content of alloy elements such as carbon are used as members that place importance on wear resistance. In other words, the hardness and wear resistance of steel materials are closely related, and increasing the hardness of the matrix leads to an improvement in wear resistance. Therefore, conventionally, hardness has been used as a method for imparting wear resistance to steel materials. It is common to employ an increasing technique.
例えば特許文献１〜３には、Ｃ含有量が概ね０.２％以下の鋼において、合金元素の含有量を高めに設定し、固溶強化、析出強化等を利用して硬度を高めることによって耐摩耗性を向上させる技術が記載されている。しかし、昨今では耐摩耗性の要求レベルは従来にも増して厳しくなっており、単に硬度を高めただけでは十分満足できる耐摩耗性が得られない場合が多くなってきた。また特許文献１〜３のように合金元素の含有量を高めると、結果的に素材の製造性や加工性が低下し、製造コストが増大するという問題もある。 For example, in Patent Documents 1 to 3, in steel with a C content of approximately 0.2% or less, the alloy element content is set high, and the hardness is increased by using solid solution strengthening, precipitation strengthening, etc. A technique for improving wear resistance is described. However, nowadays, the required level of wear resistance has become stricter than ever, and there are many cases where sufficient wear resistance cannot be obtained simply by increasing the hardness. Moreover, when content of an alloy element is raised like patent documents 1-3, there exists a problem that the manufacturability and workability of a raw material will fall as a result, and manufacturing cost will increase.
一方、動力伝達部材や刃物部材は、安全上、使用中に折損しないことが重要である。折損を防止するためには部材に用いる鋼材の「靱性」を十分に確保する必要がある。一般に鋼材の靱性を向上させるには、調質硬さを低く抑えることが有効であるとされる。しかしながら、調質硬さを抑制すると、同時に耐摩耗性も低下してしまうのが通常である。すなわち、鋼材において「耐摩耗性」と「靱性」はトレードオフの関係にある。これまで、靱性をできるだけ阻害せずに耐摩耗性を改善する試みが種々なされてきた（特許文献４〜８）。 On the other hand, for safety reasons, it is important that the power transmission member and the blade member do not break during use. In order to prevent breakage, it is necessary to sufficiently secure the “toughness” of the steel used for the member. Generally, to improve the toughness of steel materials, it is considered effective to keep the tempering hardness low. However, when the tempering hardness is suppressed, the wear resistance is usually lowered at the same time. That is, “wear resistance” and “toughness” have a trade-off relationship in steel. Until now, various attempts have been made to improve wear resistance without impairing toughness as much as possible (Patent Documents 4 to 8).
特許文献９には、Ｎｂを大量に添加し、Ｎｂ系析出物を分散させることにより耐摩耗性を向上させる手法が記載されている。この手法は鋼材の耐摩耗性向上には有効であるが、「耐摩耗性」と「靱性」を高いレベルで両立させる手法については開示がない。特に、Ｃ含有量レベルが０.３２％以上の鋼については、特許文献９の開示に従っても安定して優れた靱性を実現することは困難である。 Patent Document 9 describes a technique for improving wear resistance by adding a large amount of Nb and dispersing Nb-based precipitates. Although this technique is effective for improving the wear resistance of steel materials, there is no disclosure of a technique for achieving both “wear resistance” and “toughness” at a high level. In particular, for steel having a C content level of 0.32% or more, it is difficult to achieve stable and excellent toughness even in accordance with the disclosure of Patent Document 9.
耐摩耗性改善によって部材の長寿命化を図るためには、アブレシブ摩耗についても配慮することが重要である。アブレシブ摩耗は、相手摩擦面の表面粗さや摩擦面に介在する異物によって材料表面が削り取られる摩耗形態である。特に刃物部材ではこの種の摩耗が主体となる。摩耗相手材の種類や使用環境によっては、摩擦面にアルミナや炭化ケイ素のような部材硬さに比べて遥かに硬質の異物が介在することがある。アブレシブ摩耗に対する抵抗力を付与するためには、部材を構成する鋼材のマトリクス中に粒子径数μｍのＮｂ、Ｔｉ、Ｖ等の炭化物を一定量以上分散させることが有効である。これらの炭化物の硬さは２０００ＨＶ以上に相当し、これはアルミナや炭化ケイ素とほぼ同等レベルの硬度である。鋼材マトリクス中に分散させた硬質粒子が摩耗に対する抵抗力として働くことで、アブレシブ摩耗による鋼材の摩耗量が大幅に低減される。 In order to extend the life of the member by improving the wear resistance, it is important to consider the abrasive wear. Abrasive wear is a form of wear in which the surface of a material is scraped off by the surface roughness of the mating friction surface and foreign matter present on the friction surface. In particular, this kind of wear is mainly used for blade members. Depending on the type of wear partner material and the usage environment, foreign matter that is much harder than the hardness of a member such as alumina or silicon carbide may be present on the friction surface. In order to impart resistance to abrasive wear, it is effective to disperse a certain amount or more of carbides such as Nb, Ti, and V having a particle diameter of several μm in the steel matrix constituting the member. The hardness of these carbides is equivalent to 2000 HV or more, which is almost the same level as that of alumina or silicon carbide. The hard particles dispersed in the steel matrix work as a resistance to wear, so that the amount of wear of the steel due to abrasive wear is greatly reduced.
従来検討されてきた鋼材の耐摩耗性改善手法は、「硬さ」を増大させる手段を用いて「耐摩耗性」を付与し、結晶粒の微細化などによって「靱性」の低下を抑制するという思想に基づくものが主流であった（例えば特許文献６〜８）。しかしこの場合、アブレシブ摩耗に対する抵抗力が十分ではなく、安定して部品の長寿命化を図ることは難しい。一方、Ｔｉ、Ｎｂ、Ｖ等の硬質な炭化物をマトリクス中に分散させてアブレシブ摩耗に対する抵抗力を向上させる技術（例えば特許文献４、５、９）を利用すれば、過度な硬質化を必要としないため靭性を確保する上でも有利であると考えられていた。しかしながら発明者らの調査によれば、Ｔｉ、Ｎｂ、Ｖ等の炭化物を分散させる手法を採用した場合、延性や靭性が逆に劣化することがあり、安定して良好な靭性を確保するためには更なる検討が望まれた。 The methods for improving the wear resistance of steel materials that have been studied in the past are to impart “wear resistance” by means of increasing the “hardness” and to suppress the decrease in “toughness” by refining crystal grains. Those based on the idea were mainstream (for example, Patent Documents 6 to 8). However, in this case, the resistance to abrasive wear is not sufficient, and it is difficult to stably extend the life of parts. On the other hand, if hard carbides such as Ti, Nb, and V are dispersed in the matrix to improve the resistance to abrasive wear (for example, Patent Documents 4, 5, and 9), excessive hardening is required. Therefore, it was considered advantageous for securing toughness. However, according to investigations by the inventors, when adopting a method of dispersing carbides such as Ti, Nb, V, etc., ductility and toughness may deteriorate on the contrary, in order to ensure stable good toughness Further study was desired.
本発明は、Ｃ含有量レベルが比較的高い亜共析鋼からなる鋼材において、「靭性」を十分に確保しながら、高強度機械部品の長寿命化にとって必要となる「耐摩耗性」を改善する技術を提供しようというものである。 The present invention improves the "wear resistance" necessary for extending the life of high-strength mechanical parts while ensuring sufficient "toughness" in steel materials made of hypoeutectoid steel with a relatively high C content level. Is to provide the technology to do.
発明者らの詳細な検討によれば、Ｔｉ、Ｎｂ、Ｖ等の炭化物を分散させた鋼材において靭性が劣化することがある原因として、鋳造時に粗大化したＴｉ系炭化物（ＴｉＣを主体とするもの）は、その後の工程で適正量にコントロールすることが必ずしも容易ではなく、部品中に過剰なＴｉ系炭化物が残留しやすいことが考えられた。そこで本発明者らは種々検討の結果、従来アブレシブ摩耗の改善に極めて有効であるとされていたＴｉ系炭化物を利用しなくても、Ｎｂ系炭化物（ＮｂＣを主体とするもの）の分散状態を適正化することによって、耐摩耗性を十分に付与することが可能であり、部材の長寿命化が可能になることを見出した。本発明はこのような知見に基づいて完成したものである。 According to the detailed examination by the inventors, as a cause of the deterioration of toughness in steel materials in which carbides such as Ti, Nb, and V are dispersed, Ti-based carbides coarsened during casting (mainly TiC) ) Was not always easy to control to an appropriate amount in the subsequent steps, and it was thought that excessive Ti-based carbides were likely to remain in the parts. Therefore, as a result of various studies, the present inventors have determined the dispersion state of Nb-based carbide (mainly NbC) without using Ti-based carbide, which has been considered to be extremely effective for improving abrasive wear. It has been found that, by optimizing, sufficient wear resistance can be imparted and the life of the member can be extended. The present invention has been completed based on such findings.
すなわち本発明では、質量％で、Ｃ：０.３２〜０.７０％好ましくは０.４５超え〜０.７０％、Ｓｉ：０.５％以下、Ｍｎ：０.１〜１.５％、Ｐ：０.０３％以下、Ｓ：０.０２％以下、Ｎｂ：０.１〜０.５％であり、必要に応じてＴｉ：０.１％未満を含有し、さらに必要に応じてＣｒ：１.５％以下、Ｍｏ：０.５％以下、Ｖ：０.５％以下、Ｎｉ：２％以下、Ｂ：０.００５％の１種以上を含有し、残部Ｆｅおよび不可避的不純物からなる化学組成を有し、Ｎｂを含有する粒子径１μｍ以上の炭化物が２００〜１０００個／ｍｍ2の密度でマトリクス中に存在する焼鈍組織を有する、機械部品用素材鋼板が提供される。鋼成分としてＴｉを含んでいる場合は、Ｎｂ、Ｔｉの１種以上を含有する粒子径１μｍ以上の炭化物が２００〜１０００個／ｍｍ2の密度でマトリクス中に存在する焼鈍組織を有するものが対象となる。 That is, in the present invention, by mass%, C: 0.32 to 0.70%, preferably more than 0.45 to 0.70%, Si: 0.5% or less, Mn: 0.1 to 1.5%, P: 0.03% or less, S: 0.02% or less, Nb: 0.1 to 0.5%, optionally containing Ti: less than 0.1%, and if necessary, Cr It contains at least one of 1.5% or less, Mo: 0.5% or less, V: 0.5% or less, Ni: 2% or less, B: 0.005%, and the balance from Fe and inevitable impurities There is provided a steel sheet for a machine part having an annealed structure in which a carbide having a chemical composition of Nb and having a particle diameter of 1 μm or more and having a particle diameter of 1 μm or more exists in a matrix at a density of 200 to 1000 pieces / mm 2 . When Ti is contained as a steel component, it has an annealing structure in which a carbide having a particle diameter of 1 μm or more containing one or more of Nb and Ti is present in a matrix at a density of 200 to 1000 pieces / mm 2. It becomes.
ここで、素材鋼板とは、まだ焼入れ焼戻しやオーステンパー等の調質熱処理を受ける前の段階にあるものを指す。この素材鋼板は部品形状への成形加工を経た後に調質熱処理に供される。上記の焼鈍組織は、マトリクスがフェライト相からなり、再結晶化されて軟質な状態となっている組織である。 Here, the material steel plate refers to a material in a stage before being subjected to a tempering heat treatment such as quenching and tempering or austempering. This material steel plate is subjected to a tempering heat treatment after forming into a part shape. The annealed structure is a structure in which the matrix is made of a ferrite phase and is recrystallized to be in a soft state.
また、上記の素材鋼板の製造方法として、
上記組成範囲に成分調整された鋼を鋳造後、冷却過程において１５００〜９００℃の温度領域の滞在時間を３０ｍｉｎ以上とすることによりＮｂあるいはＮｂ、Ｔｉの１種以上を含有する粗大炭化物を析出させる工程（鋳造工程）、
前記の粗大炭化物が存在する鋼を１１００〜１３５０℃の範囲かつ下記（１）式により定まるＡ値が０.０７７〜０.３８３となる温度Ｔ（℃）で加熱保持して、前記炭化物の一部を固溶化する工程（固溶化熱処理工程）、
前記固溶化熱処理を終えた鋼を熱間圧延して、ＮｂあるいはＮｂ、Ｔｉの１種以上を含有する粒子径１μｍ以上の炭化物が２００〜１０００個／ｍｍ2の密度でマトリクス中に存在する熱延鋼板を得る工程（熱延工程）、
Ａｃ1点未満の温度域に加熱する仕上焼鈍を施して焼鈍組織とする工程（仕上焼鈍工程）、
を有する製造方法が提供される。
Ａ＝Ｎｂ−１０x／Ｃ …（１）
たたし、ｘ＝３.４２−７９００／（Ｔ＋２７３）
（１）式のＮｂおよびＣの箇所にはそれぞれ質量％で表された当該鋼のＮｂおよびＣ含有量の値が代入される。
Moreover, as a manufacturing method of said raw material steel plate,
After casting the steel whose composition has been adjusted to the above composition range, the coarse carbide containing one or more of Nb, Nb, and Ti is precipitated by setting the residence time in the temperature range of 1500 to 900 ° C. to 30 min or more in the cooling process. Process (casting process),
The steel containing the coarse carbide is heated and held at a temperature T (° C.) in a range of 1100 to 1350 ° C. and an A value determined by the following formula (1) of 0.077 to 0.383, and Part solution process (solution heat treatment process),
The steel that has undergone the solution heat treatment is hot-rolled, and heat in which a carbide having a particle diameter of 1 μm or more containing one or more of Nb, Nb, or Ti is present in the matrix at a density of 200 to 1000 pieces / mm 2. A process of obtaining a rolled steel sheet (hot rolling process),
A process (finish annealing process) in which a finish annealing is performed by heating to a temperature range less than Ac 1 point to form an annealed structure,
A manufacturing method is provided.
A = Nb−10 x / C (1)
However, x = 3.42-7900 / (T + 273)
The values of Nb and C contents of the steel expressed in mass% are substituted for Nb and C in the formula (1), respectively.
熱延工程と仕上焼鈍工程の間においては、必要に応じてＡｃ1点未満の温度域に加熱する焼鈍および冷間圧延（焼鈍・冷間圧延工程）を１回以上行うことができる。 Between the hot rolling step and the finish annealing step, annealing and cold rolling (annealing / cold rolling step) for heating to a temperature range of less than Ac 1 point can be performed once or more as necessary.
また本発明では、上記の素材鋼板から成形加工した部材に対して、オーステナイト温度域での溶体化を１０００℃以下とする焼入れ焼戻し処理またはオーステンパー処理を施して５００〜６００ＨＶに調質する、耐摩耗性および靭性に優れた機械部品の製造方法が提供される。 Moreover, in this invention, with respect to the member shape | molded from said raw material steel plate, the quenching tempering process or austemper process which makes the solution treatment in an austenite temperature range 1000 degrees C or less is performed, and it heats to 500-600HV, Provided is a method for manufacturing a machine part having excellent wear and toughness.
本発明によれば、Ｃ含有量レベルが０.３２％以上あるいは更に０.４５％を超える亜共析鋼において「耐摩耗性」と「靱性」を高いレベルで両立させた鋼材（高強度機械部品）を、特段のコスト増を伴うことなく提供することが可能となった。この鋼材はアブレシブ摩耗に対する耐久性が高いことから、動力伝達部材の他、刃物部材に好適であり、これら各種用途において部品の長寿命化に寄与しうる。 According to the present invention, a steel material (high-strength machine) that achieves both high wear resistance and high toughness in hypoeutectoid steel having a C content level of 0.32% or more or more than 0.45%. Parts) can be provided without any particular increase in cost. Since this steel material has high durability against abrasive wear, it is suitable for a blade member in addition to a power transmission member, and can contribute to extending the life of parts in these various applications.
〔化学組成〕
本明細書において、鋼の成分元素に関する「％」は特に断らない限り「質量％」を意味する。
Ｃは、調質硬さや強度、耐摩耗性を確保するために重要な元素であり、本発明では０.０２％以上のＣを含有する鋼を対象とする。０.３２％を超えるＣ含有量、あるいは更に０.４５％を超えるＣ含有量を確保することがより望ましい。ただしＣ含有量が多くなると焼入れ焼戻しやオーステンパー等の調質熱処理時に未溶解セメンタイトが残留しやすくなる。また焼入れ時にはレンズ状マルテンサイトが生成しやすくなる。このような組織状態は靭性の低下を招くことがあるので好ましくない。種々検討の結果、本発明ではＣ含有量は０.７０％以下の範囲とする。０.６０％以下あるいは０.６０％未満とすることがより望ましい。
[Chemical composition]
In the present specification, “%” regarding the constituent elements of steel means “mass%” unless otherwise specified.
C is an important element for securing tempered hardness, strength, and wear resistance. In the present invention, steel containing 0.02% or more of C is targeted. It is more desirable to ensure a C content exceeding 0.32% or even a C content exceeding 0.45%. However, when the C content increases, undissolved cementite tends to remain during tempering heat treatment such as quenching and tempering or austempering. In addition, lenticular martensite is easily generated during quenching. Such a structural state is not preferable because it may cause a decrease in toughness. As a result of various studies, in the present invention, the C content is limited to 0.70% or less. It is more desirable to set it at 0.60% or less or less than 0.60%.
Ｓｉは、溶鋼の脱酸に有効であり、また焼戻し軟化抵抗を高める作用がある。それらの作用を十分に得るためには０.１％以上のＳｉ含有量を確保することがより効果的である。ただし過剰のＳｉ含有は熱延板、冷延板を硬質にし、製造性を阻害する要因となる。このためＳｉ含有量は０.５％以下の範囲とする。 Si is effective in deoxidizing molten steel and has the effect of increasing temper softening resistance. In order to sufficiently obtain these functions, it is more effective to secure a Si content of 0.1% or more. However, excessive Si content makes the hot-rolled sheet and cold-rolled sheet hard, and becomes a factor that hinders manufacturability. For this reason, Si content shall be 0.5% or less of range.
Ｍｎは、焼入れ性を向上させる元素であり、その作用を得るために０.１％以上の含有量を確保する。ただし過剰のＭｎ含有は靱性を著しく低下させる場合があるので、Ｍｎ含有量は１.５％以下に制限される。 Mn is an element that improves hardenability, and a content of 0.1% or more is ensured in order to obtain its effect. However, since excessive Mn content may significantly reduce toughness, the Mn content is limited to 1.5% or less.
Ｐは、焼入れ時にオーステナイト粒界に偏析して粒界強度を低下させ、疲労特性や靱性を低下させる要因となる。検討の結果、Ｐ含有量は０.０３％まで許容できる。 P segregates at the austenite grain boundaries during quenching, lowers the grain boundary strength, and causes fatigue characteristics and toughness. As a result of the study, the P content is acceptable up to 0.03%.
Ｓは、鋼中で衝撃破壊や疲労破壊の起点となるＭｎＳを形成し、疲労特性や靱性を低下させる要因となる。検討の結果、Ｓ含有量は０.０２％まで許容できる。 S forms MnS which is the starting point of impact fracture and fatigue fracture in steel, and becomes a factor of reducing fatigue characteristics and toughness. As a result of the study, the S content is acceptable up to 0.02%.
Ｎｂは、鋳造後の冷却過程で鋼中に非常に硬質なＮｂ含有炭化物として析出し、耐摩耗性、特に耐アブレシブ摩耗性の向上に寄与する。また、鋳造後の焼鈍工程で再固溶させたＮｂは焼入れ時の結晶粒を微細化させ、靱性の向上に寄与する。これらの作用を十分に引き出すためには、０.１％以上のＮｂ含有量を確保する必要があり、０.１５％以上とすることがより好ましい。一方、多量のＮｂ添加は、Ｎｂ含有炭化物を過剰に生成させ、それらが破壊の起点および亀裂伝播経路となり、靱性低下を招く。特に、Ｃ含有量レベルが比較的高い亜共析鋼において調質熱処理後の良好な靱性を確保するためにはＮｂ含有量は０.５０％以下に抑えることが肝要である。また、発明者らの検討によれば、Ｃ含有量が０.３２〜０.７０％レベルの鋼においては、Ｎｂ添加による耐摩耗性向上効果はＮｂ含有量０.５％程度で飽和する傾向にある。したがってＮｂは０.５％以下の範囲で含有させる。 Nb precipitates as a very hard Nb-containing carbide in the steel in the cooling process after casting, and contributes to improvement of wear resistance, particularly abrasive wear resistance. Moreover, Nb re-dissolved in the annealing process after casting refines the crystal grains at the time of quenching and contributes to the improvement of toughness. In order to sufficiently bring out these effects, it is necessary to secure an Nb content of 0.1% or more, and more preferably 0.15% or more. On the other hand, when a large amount of Nb is added, Nb-containing carbides are excessively generated, which become a starting point of fracture and a crack propagation path, leading to a decrease in toughness. In particular, in a hypoeutectoid steel having a relatively high C content level, it is important to suppress the Nb content to 0.50% or less in order to ensure good toughness after tempering heat treatment. In addition, according to the study by the inventors, in steel having a C content of 0.32 to 0.70%, the effect of improving wear resistance by adding Nb tends to saturate when the Nb content is about 0.5%. It is in. Therefore, Nb is contained in the range of 0.5% or less.
Ｃｒは、Ｍｎと同様に焼入れ性の向上に有効である。また、焼鈍時における炭化物の粗大化を抑制する作用を有し、衝撃値（靭性）の改善に有効である。このため必要に応じてＣｒを含有させることができる。上記各作用を十分に発揮させるためには０.１％以上のＣｒ含有量を確保することがより効果的である。ただし多量のＣｒを添加すると未溶解炭化物の生成量が増大し、靱性が著しく低下することがあるので、Ｃｒを添加する場合は１.５％以下の範囲で行う。 Cr is effective for improving the hardenability like Mn. Moreover, it has the effect | action which suppresses the coarsening of the carbide | carbonized_material at the time of annealing, and is effective in the improvement of an impact value (toughness). For this reason, Cr can be contained as needed. It is more effective to secure a Cr content of 0.1% or more in order to sufficiently exhibit the above-described functions. However, when a large amount of Cr is added, the amount of undissolved carbides generated increases and the toughness may be significantly reduced. Therefore, when Cr is added, it is performed within a range of 1.5% or less.
Ｔｉは、Ｎｂと同様、鋳造後の鋼中に非常に硬質なＴｉ含有炭化物を形成し、耐摩耗性の向上に寄与するとともに、鋳造後に再固溶させたＴｉは焼入れ時の結晶粒を微細化させ、靱性の向上に寄与する。またＴｉはＮとの結合力が強いため、Ｂを添加した場合にＢＮの生成を防止し、Ｂの焼入れ性向上作用を引き出す上で有利となる。このため本発明では必要に応じてＴｉを添加することができる。上記の各作用を十分に得るためには０.０１％以上のＴｉ含有量を確保することがより効果的である。しかしながら、発明者らの検討によれば、Ｔｉ系炭化物が部品中に多量に存在した場合には、靱性低下を招きやすいことがわかった。種々検討の結果、Ｔｉを添加する場合は０.１％未満の範囲で行うことが重要である。 Ti, like Nb, forms a very hard Ti-containing carbide in the steel after casting, contributing to the improvement of wear resistance, and Ti that has been re-dissolved after casting has fine grains during quenching. To contribute to improved toughness. Further, Ti has a strong bonding force with N. Therefore, when B is added, formation of BN is prevented, and it is advantageous in extracting the effect of improving the hardenability of B. For this reason, in this invention, Ti can be added as needed. In order to sufficiently obtain each of the above actions, it is more effective to secure a Ti content of 0.01% or more. However, according to the study by the inventors, it has been found that when a large amount of Ti-based carbide is present in the part, the toughness tends to be reduced. As a result of various investigations, when adding Ti, it is important to carry out within a range of less than 0.1%.
ＭｏおよびＶは、いずれも靱性の向上に有効な元素であり、必要に応じて添加することができる。Ｍｏの場合は０.１％以上の含有量を確保することがより効果的である。Ｖの場合も０.１％以上の含有量を確保することがより効果的である。ただしＭｏ、Ｖは高価な元素であり過剰添加はコスト増を招く。Ｍｏ、Ｖの１種または２種を添加する場合は、Ｍｏ、Ｖとも０.５％以下の含有量範囲とする。 Mo and V are both effective elements for improving toughness, and can be added as necessary. In the case of Mo, it is more effective to secure a content of 0.1% or more. In the case of V, it is more effective to secure a content of 0.1% or more. However, Mo and V are expensive elements, and excessive addition causes an increase in cost. When adding 1 type or 2 types of Mo and V, let Mo and V be 0.5% or less of content range.
Ｎｉは、焼入れ性の向上に有効であり、必要に応じて添加することができる。その場合、０.１％以上のＮｉ含有量を確保することがより効果的である。ただしＮｉの過剰添加は経済性を損ねる要因となるので、Ｎｉを添加する場合は２％以下の範囲で行う。 Ni is effective for improving hardenability and can be added as necessary. In that case, it is more effective to secure a Ni content of 0.1% or more. However, excessive addition of Ni is a factor that impairs economic efficiency. Therefore, when Ni is added, it is performed within a range of 2% or less.
Ｂは、焼入れ性の向上に有効な元素であり、必要に応じて添加することができる。焼入れ性向上作用を十分に発揮させるためには０.０００５％以上のＢ含有量を確保することがより効果的である。ただし、その作用は概ね０.００５％で飽和するので、Ｂを添加する場合は０.００５％以下の範囲で行う。 B is an element effective for improving the hardenability, and can be added as necessary. In order to sufficiently exhibit the hardenability improving effect, it is more effective to secure a B content of 0.0005% or more. However, since the action is saturated at about 0.005%, when B is added, it is performed within the range of 0.005% or less.
〔金属組織〕
本発明では耐摩耗性を顕著に向上させるためにＮｂを含有する硬質炭化物を利用する。Ｔｉを添加した鋼組成においてはＴｉを含有する硬質炭化物も有効となる。ただし、靱性を確保するために、その分散形態に配慮する必要がある。詳細な検討の結果、調質熱処理を終えた最終的な部品において、ＮｂあるいはＮｂ、Ｔｉの１種以上を含有する粒子径１μｍ以上の硬質炭化物が２００〜１０００個／ｍｍ2の密度でマトリクス中に存在する金属組織としたときに、耐摩耗性が顕著に向上し、かつ靱性を損なう弊害も回避されることがわかった。そして、そのような組織状態を実現するためには、調質熱処理前の素材鋼板の段階で上記の炭化物密度としておき、調質熱処理での溶体化温度を１０００℃以下に制限すればよいことが確認された。したがって本発明では、素材鋼板において、ＮｂあるいはＮｂ、Ｔｉの１種以上を含有する粒子径１μｍ以上の硬質炭化物が２００〜１０００個／ｍｍ2の密度でマトリクス中に存在する焼鈍組織を有するものを提供する。
[Metal structure]
In the present invention, a hard carbide containing Nb is used to remarkably improve the wear resistance. In steel compositions to which Ti is added, hard carbides containing Ti are also effective. However, in order to ensure toughness, it is necessary to consider the dispersion form. As a result of detailed examination, in the final part after the tempering heat treatment, in the matrix, a hard carbide having a particle diameter of 1 μm or more containing one or more of Nb, Nb, or Ti is 200 to 1000 pieces / mm 2. It has been found that when the metal structure is present in the steel, the wear resistance is remarkably improved and the adverse effect of impairing the toughness is avoided. And in order to realize such a structural state, the carbide density should be set at the stage of the raw steel plate before the tempering heat treatment, and the solution temperature in the tempering heat treatment should be limited to 1000 ° C. or less. confirmed. Therefore, in the present invention, the material steel plate has an annealed structure in which hard carbides having a particle diameter of 1 μm or more containing one or more of Nb, Nb, and Ti are present in the matrix at a density of 200 to 1000 pieces / mm 2. provide.
ここで、「Ｎｂを含有する炭化物」はＮｂＣを主成分とする硬質炭化物である。また「Ｎｂ、Ｔｉの１種以上を含有する炭化物」はＮｂＣ、ＴｉＣ、（Ｎｂ，Ｔｉ）Ｃなどを主成分とする硬質炭化物である。以下、これらの炭化物を単に「硬質炭化物」と呼ぶことがある。鋼中に含有される析出粒子がＮｂあるいはＮｂ、Ｔｉの１種以上を含有する炭化物に該当するかどうかは、ＥＤＸ等による微視的分析によって確かめることができる。個々の粒子の粒子径は、鋼材断面に観察される粒子の円相当径が採用される。すなわち、粒子の面積から同じ面積を有する真円の直径を算出し、この直径を当該粒子の粒子径とする。鋼材中に観察される硬質炭化物の最大粒子径は３０μｍ以下に調整されていることがより望ましい。粒子径１μｍ以上の硬質炭化物が２００個／ｍｍ2未満であると耐摩耗性向上効果が不十分となりやすい。４００個／ｍｍ2以上であることがより好ましい。ただし、１０００個／ｍｍ2を超えると靱性が不十分となりやすい。 Here, the “carbide containing Nb” is a hard carbide mainly composed of NbC. “Carbides containing one or more of Nb and Ti” are hard carbides mainly composed of NbC, TiC, (Nb, Ti) C, and the like. Hereinafter, these carbides may be simply referred to as “hard carbides”. Whether the precipitated particles contained in the steel correspond to carbides containing one or more of Nb, Nb, and Ti can be confirmed by microscopic analysis using EDX or the like. As the particle diameter of each particle, the equivalent circle diameter of the particle observed on the steel cross section is adopted. That is, the diameter of a perfect circle having the same area is calculated from the area of the particle, and this diameter is used as the particle diameter of the particle. It is more desirable that the maximum particle diameter of the hard carbide observed in the steel material is adjusted to 30 μm or less. When the number of hard carbides having a particle diameter of 1 μm or more is less than 200 / mm 2 , the effect of improving wear resistance tends to be insufficient. More preferably, it is 400 pieces / mm 2 or more. However, if it exceeds 1000 / mm 2 , the toughness tends to be insufficient.
なお、本発明の素材鋼板の焼鈍組織におけるマトリクスはフェライト相である。調質熱処理を終えた部品のマトリクスは、調質熱処理が焼入れ焼戻しである場合は焼戻しマルテンサイト相、オーステンパーである場合はベイナイト相である。 In addition, the matrix in the annealing structure | tissue of the raw material steel plate of this invention is a ferrite phase. The matrix of the parts after the tempering heat treatment is a tempered martensite phase when the tempering heat treatment is quenching and tempering, and a bainite phase when the tempering heat treatment is austempering.
上記のような金属組織を有する鋼材は、例えば以下のような製造工程によって得ることができる。
〔鋳造工程〕
まず、鋳造後の冷却過程を利用してＮｂあるいはＮｂ、Ｔｉの１種以上を含有する粗大炭化物を析出させる。具体的には、この種の硬質炭化物が成長しやすい１５００〜９００℃の温度領域の滞在時間が３０ｍｉｎ以上となるような冷却パターンとすることが効果的である。後述実施例のものはいずれもこの冷却パターンを満たしている。このような冷却パターンは、鋳造後に鋳片を放冷することによって実現できる他、連続鋳造においては各ロールの冷却条件や鋳片表面の冷却条件をコントロールすることによって実現できる。放冷とは鋳片を強制的に冷却することなく、自然冷却することをいう。「粗大炭化物」は、粒子径が概ね１μｍ以上の炭化物をいう。なお、本明細書でいう「鋳片」には造塊法におけるインゴットや、連続鋳造におけるスラブが含まれる。
The steel material having the metal structure as described above can be obtained by, for example, the following manufacturing process.
[Casting process]
First, a coarse carbide containing one or more of Nb, Nb, and Ti is deposited using a cooling process after casting. Specifically, it is effective to use a cooling pattern in which the residence time in the temperature region of 1500 to 900 ° C. at which this type of hard carbide is easy to grow is 30 minutes or more. All of the examples described later satisfy this cooling pattern. Such a cooling pattern can be realized by allowing the slab to cool after casting, and in continuous casting, it can be realized by controlling the cooling conditions of each roll and the slab surface. Allowing to cool refers to naturally cooling the slab without forcibly cooling it. “Coarse carbide” refers to a carbide having a particle size of approximately 1 μm or more. The “slab” in this specification includes ingots in the ingot-making method and slabs in continuous casting.
〔固溶化熱処理工程〕
前記の粗大炭化物が存在する鋼を１１００〜１３５０℃の範囲かつ下記（１）式により定まるＡ値が０.０７７〜０.３８３となる温度Ｔ（℃）で加熱保持する。加熱温度範囲は１１５０〜１３００℃とすることがより好ましい。
Ａ＝Ｎｂ−１０x／Ｃ …（１）
たたし、ｘ＝３.４２−７９００／（Ｔ＋２７３）
（１）式のＮｂおよびＣの箇所にはそれぞれ質量％で表された当該鋼のＮｂおよびＣ含有量の値が代入される。
[Solution heat treatment process]
The steel in which the coarse carbide is present is heated and held at a temperature T (° C.) in a range of 1100 to 1350 ° C. and an A value determined by the following formula (1) is 0.077 to 0.383. The heating temperature range is more preferably 1150 to 1300 ° C.
A = Nb−10 x / C (1)
However, x = 3.42-7900 / (T + 273)
The values of Nb and C contents of the steel expressed in mass% are substituted for Nb and C in the formula (1), respectively.
発明者らは種々検討の結果、耐摩耗性と靭性の両方を満足させるために必要なＮｂ含有炭化物の分布状態を精度良く実現するためには、予め十分な量のＮｂ含有粗大炭化物を過剰に析出させておき、その後、粗大炭化物の一部を再固溶させる過程を利用して適正な量にコントロールすることが簡便かつ極めて有効であることを見出した。再固溶後の硬質炭化物の量は、Ｎｂ含有量、Ｃ含有量、および保持温度Ｔ（℃）に依存する。上記（１）式は、Ｃ含有量が０.３〜０.６％である鋼において、再固溶後における粒子径１μｍ以上の硬質炭化物の存在量を表す指標である。発明者らによる数多くの実験の結果、Ａ値が０.０７７未満になる条件では、粒子径１μｍ以上の硬質炭化物の残存量が２００個／ｍｍ2未満となりやすく、耐摩耗性の改善効果を安定して得ることが難しくなる。Ａ値が０.３８３を超えると粒子径１μｍ以上の硬質炭化物の残存量が１０００個／ｍｍ2を超える状態となりやすく、靭性の改善効果を安定して得ることが難しくなる。なお、Ｔｉを含有する場合であっても、その含有量は０.１％未満と低いため、（１）式を満たす加熱条件を採用すればＴｉ含有炭化物が過剰に残存することによる弊害は回避される。 As a result of various studies, the inventors have excessively added a sufficient amount of Nb-containing coarse carbide in advance in order to accurately realize the distribution state of Nb-containing carbide necessary for satisfying both wear resistance and toughness. It has been found that it is simple and extremely effective to make it precipitate and then control to an appropriate amount by using a process of re-solidifying a part of the coarse carbide. The amount of hard carbide after re-dissolution depends on the Nb content, the C content, and the holding temperature T (° C.). The above formula (1) is an index representing the abundance of hard carbides having a particle diameter of 1 μm or more after re-solution in steel having a C content of 0.3 to 0.6%. As a result of many experiments by the inventors, under the condition that the A value is less than 0.077, the residual amount of hard carbide having a particle diameter of 1 μm or more tends to be less than 200 pieces / mm 2, and the effect of improving wear resistance is stabilized. And getting difficult. If the A value exceeds 0.383, the residual amount of hard carbide having a particle diameter of 1 μm or more tends to exceed 1000 pieces / mm 2 , and it becomes difficult to stably obtain the effect of improving toughness. Even when Ti is contained, the content is as low as less than 0.1%. Therefore, if heating conditions satisfying the formula (1) are adopted, adverse effects caused by excessive residual Ti-containing carbides can be avoided. Is done.
（１）式の条件を満たす温度域における保持時間は、温度や鋼材のサイズにもよるが、通常０.５〜１２ｈの範囲で最適保持時間を見出すことができる。実際には、使用する生産設備に対応した予備実験によって保持温度、保持時間を設定すればよい。 The holding time in the temperature range that satisfies the condition of formula (1) depends on the temperature and the size of the steel material, but the optimum holding time can usually be found in the range of 0.5 to 12 h. Actually, the holding temperature and holding time may be set by a preliminary experiment corresponding to the production equipment to be used.
なお、この固溶化熱処理工程は、熱間圧延時のスラブ加熱工程において実施することができる。造塊法の場合は分塊時の加熱工程、あるいは熱間圧延時のスラブ加熱工程の少なくとも一方おいて実施すればよい。 In addition, this solution heat treatment process can be implemented in the slab heating process at the time of hot rolling. In the case of the ingot-making method, it may be carried out in at least one of the heating process at the time of the ingoting or the slab heating process at the time of hot rolling.
〔熱延工程〕
上記の固溶化熱処理を終えた鋼を熱間圧延することにより、ＮｂあるいはＮｂ、Ｔｉの１種以上を含有する粒子径１μｍ以上の硬質炭化物が２００〜１０００個／ｍｍ2の密度でマトリクス中に存在する熱延鋼板を得ることができる。硬質炭化物のこのような分布形態は、通常の熱間圧延、熱延板焼鈍、冷間圧延、仕上焼鈍の各工程を経てもほぼ維持される。熱間圧延は例えば、加熱抽出温度１１００〜１３００℃、仕上圧延温度８００〜９００℃、巻取温度７５０℃以下の条件で行うことができる。
[Hot rolling process]
By hot rolling the steel after the solution heat treatment, hard carbides having a particle diameter of 1 μm or more containing one or more of Nb, Nb, and Ti are contained in the matrix at a density of 200 to 1000 pieces / mm 2. An existing hot-rolled steel sheet can be obtained. Such a distribution form of the hard carbide is substantially maintained even through each process of normal hot rolling, hot rolled sheet annealing, cold rolling, and finish annealing. Hot rolling can be performed, for example, under conditions of a heating extraction temperature of 1100 to 1300 ° C, a finish rolling temperature of 800 to 900 ° C, and a winding temperature of 750 ° C or less.
〔焼鈍・冷間圧延工程〕
必要に応じて熱延板焼鈍および冷間圧延を行い、目標板厚に調整する。熱延板焼鈍は、例えば６００℃以上Ａｃ1点未満の温度域に１０〜５０ｈ加熱保持する条件が採用できる。「焼鈍→冷間圧延」の工程を複数回行っても構わない。その場合、中間焼鈍も６００℃以上Ａｃ1点未満の温度域に加熱することが望ましい。
[Annealing and cold rolling process]
Perform hot-rolled sheet annealing and cold rolling as necessary to adjust to the target sheet thickness. For hot-rolled sheet annealing, for example, conditions of heating and holding for 10 to 50 hours in a temperature range of 600 ° C. or higher and less than Ac 1 point can be adopted. The step of “annealing → cold rolling” may be performed a plurality of times. In that case, it is desirable to heat the intermediate annealing to a temperature range of 600 ° C. or more and less than Ac 1 point.
〔仕上焼鈍工程〕
所定の板厚に調整された熱延鋼板または冷延鋼板に対して、仕上焼鈍を施し、軟質化された再結晶フェライト組織（焼鈍組織）を有する素材鋼板を得る。仕上焼鈍はＡｃ1点未満の温度域で行う必要がある。再結晶化を促進させるために、６００℃以上Ａｃ1点未満の温度域に加熱することが望ましい。保持時間は８〜４０ｈの範囲で最適条件を設定すればよい。前述の固溶化熱処理工程を経ることによって調整された熱延鋼板における硬質炭化物の分布状態（粒子径１μｍ以上の硬質炭化物の存在密度）は、この仕上焼鈍後もほぼ維持されることが確認されている。仕上焼鈍後の素材鋼板の断面硬さは概ね１５０〜２５０ＨＶの範囲にあり、部品形状への成形加工が十分可能である。
[Finish annealing process]
The hot-rolled steel sheet or cold-rolled steel sheet adjusted to a predetermined thickness is subjected to finish annealing to obtain a material steel sheet having a softened recrystallized ferrite structure (annealed structure). The finish annealing needs to be performed in a temperature range less than Ac 1 point. In order to promote recrystallization, it is desirable to heat to a temperature range of 600 ° C. or higher and lower than Ac 1 point. What is necessary is just to set optimal conditions in the range of 8-40h for holding time. It has been confirmed that the distribution state of hard carbides in the hot-rolled steel sheet adjusted by going through the above-described solution heat treatment step (the existence density of hard carbides having a particle diameter of 1 μm or more) is substantially maintained after this finish annealing. Yes. The cross-sectional hardness of the material steel plate after finish annealing is generally in the range of 150 to 250 HV, and can be sufficiently formed into a part shape.
〔調質熱処理工程〕
素材鋼板から部品形状に成形加工された部材は、焼入れ焼戻し、オーステンパー等の調質熱処理に供され、高強度化される。ただし、調質熱処理の溶体化温度はオーステナイト領域かつ１０００℃以下の範囲で行う必要がある。前記温度を超えると、前述の固溶加熱処理工程を経ることによって調整された硬質炭化物の分布形態が崩れるおそれがある。調質熱処理条件は、溶体化の上限温度を規制する他は、一般的な手法に従えばよい。本発明の素材鋼板を用いると、動力伝達部材や刃物部材に適する５００〜６００ＨＶに調質したとき、耐摩耗性および靭性を高いレベルで兼ね備えた高強度機械部品を得ることができる。
[Refining heat treatment process]
A member formed from a raw steel plate into a part shape is subjected to a tempering heat treatment such as quenching and tempering and austempering to increase the strength. However, the solution treatment temperature of the tempering heat treatment needs to be performed in the austenite region and in the range of 1000 ° C. or less. When the temperature is exceeded, there is a possibility that the distribution form of the hard carbide adjusted through the above-described solid solution heat treatment process may be destroyed. The tempering heat treatment conditions may follow a general method except that the upper limit temperature of solution treatment is regulated. When the raw steel plate of the present invention is used, a high-strength mechanical part having high wear resistance and toughness at a high level can be obtained when it is tempered to 500 to 600 HV suitable for a power transmission member and a blade member.
表１に示す化学組成の鋼を溶製し、鋳造後の冷却過程を放冷として鋳片を製造した。この放冷条件により、鋳造後の冷却過程において鋳片表面の温度が１５００〜９００℃の温度領域に滞在する時間は３０ｍｉｎ以上となることが確認されている。したがって、鋳片内部の全ての部位において１５００〜９００℃の温度領域の滞在時間は３０ｍｉｎ以上となる。得られた鋳片を１１５０〜１３５０℃の温度で１ｈの加熱（固溶化熱処理）に供した。加熱温度および前記（１）式から算出されるＡ値を表２中に示してある。その後、仕上圧延温度８５０℃、巻取温度５５０℃の条件で熱間圧延を行い、板厚３.５ｍｍの熱延鋼板を得た。次いで６９０℃×１５ｈの焼鈍を行い、酸洗後、冷間圧延にて板厚１.５ｍｍとし、６７０℃×１５ｈの仕上焼鈍を施すことにより、焼入れ焼戻し処理に供するための素材鋼板（板厚１.５ｍｍ）を得た。 Steel having the chemical composition shown in Table 1 was melted, and a slab was produced by allowing the cooling process after casting to cool. Under this cooling condition, it has been confirmed that the time during which the temperature of the slab surface stays in the temperature range of 1500 to 900 ° C. in the cooling process after casting is 30 min or more. Therefore, the residence time in the temperature region of 1500 to 900 ° C. is 30 min or more in all the parts inside the slab. The obtained slab was subjected to heating (solution heat treatment) for 1 h at a temperature of 1150 to 1350 ° C. Table 2 shows the heating temperature and the A value calculated from the equation (1). Thereafter, hot rolling was performed under conditions of a finish rolling temperature of 850 ° C. and a winding temperature of 550 ° C. to obtain a hot rolled steel plate having a thickness of 3.5 mm. Next, after annealing at 690 ° C. × 15 h, pickling, cold rolling to a plate thickness of 1.5 mm, and finish annealing at 670 ° C. × 15 h, a steel plate (plate thickness for use in quenching and tempering treatment) 1.5 mm) was obtained.
〔炭化物分布状態の調査〕
焼入れ処理に供する前の素材鋼板について、圧延方向および板厚方向に平行な断面（Ｌ断面）を分析走査型電子顕微鏡により観察し、観察面積６１×６１μｍ2×２０視野中に存在する「Ｎｂ、Ｔｉの少なくとも一方を含有する粒子径１μｍ以上の炭化物」の数をカウントし、その存在密度を算出した。粒子径は前述の円相当径であり、粒子径１μｍ以上の粒子を画像処理によってピックアップした。
[Investigation of carbide distribution state]
About the raw steel plate before being subjected to quenching treatment, a cross section (L cross section) parallel to the rolling direction and the plate thickness direction is observed with an analytical scanning electron microscope, and “Nb, which exists in the observation area 61 × 61 μm 2 × 20 field of view” The number of “carbides having a particle diameter of 1 μm or more containing at least one of Ti” was counted, and the existence density was calculated. The particle diameter was the aforementioned equivalent circle diameter, and particles having a particle diameter of 1 μm or more were picked up by image processing.
素材鋼板について下記条件の焼入れ焼戻し処理を施し、供試材を得た。
〔焼入れ焼戻し条件〕
８２０℃×１５ｍｉｎ→６０℃油焼入れ→Ｔｔ℃×３０ｍｉｎ焼戻し
焼戻し温度Ｔｔ（℃）は組成に応じて、断面硬さが５５０ＨＶの硬度レベルに調質される温度とした。得られた供試材のＬ断面について硬さを測定した結果、いずれも５５０ＨＶ±１０ＨＶの範囲に収まっていた。
The material steel plate was subjected to quenching and tempering treatment under the following conditions to obtain a test material.
[Quenching and tempering conditions]
820 ° C. × 15 min → 60 ° C. oil quenching → Tt ° C. × 30 min tempering The tempering temperature Tt (° C.) is a temperature at which the cross-sectional hardness is adjusted to a hardness level of 550 HV. As a result of measuring the hardness of the L cross section of the obtained test material, all were within the range of 550HV ± 10HV.
〔耐摩耗性試験〕
焼入れ焼戻し後の供試材から、摩擦面が１.５ｍｍ四方となる試験片を切り出し、ピンオンディスク型摩耗試験機を用いて試験を行った。摩耗相手材は、塩浴処理によりフラットな鋼板表面上に形成したＶＣ（バナジウムカーバイド）皮膜とした。この皮膜硬さは２４００ＨＶ程度に相当する。試験片を試料ホルダに固定して、回転する摩耗相手材に試験片表面を試験荷重Ｆ＝５００Ｎで押し付けながら、摩擦速度１ｍ／ｓｅｃ、摩擦距離Ｌ＝３６００ｍの条件で摩耗試験を行った。試験前後の試料板厚差から摩耗により消失した材料の体積を算出し、これを摩耗減量Ｗ（ｍｍ3）とした。そして、下記（２）式により比摩耗量Ｃ（ｍｍ3／Ｎｍ）を求めた。
比摩耗量Ｃ＝摩耗減量Ｗ／（試験荷重Ｆ×摩擦距離Ｌ） …（２）
調質硬さ５５０ＨＶの材料において、この比摩耗量Ｃが０.３５×１０-7ｍｍ3／Ｎｍ以下であれば、Ｃ含有量０.７０％以下の亜共析鋼を用いた動力伝達部材や刃物部材に使用されている現用鋼と比べ非常に優れた耐摩耗性を有すると判断される。
[Abrasion resistance test]
A test piece having a friction surface of 1.5 mm square was cut out from the specimen after quenching and tempering, and the test was performed using a pin-on-disk wear tester. The wear partner material was a VC (vanadium carbide) film formed on a flat steel plate surface by salt bath treatment. This film hardness corresponds to about 2400 HV. The test piece was fixed to the sample holder, and the wear test was performed under the conditions of a friction speed of 1 m / sec and a friction distance L = 3600 m while pressing the surface of the test piece against a rotating wear partner material with a test load F = 500 N. The volume of the material that disappeared due to wear was calculated from the difference in thickness of the sample plate before and after the test, and this was defined as wear loss W (mm 3 ). And specific abrasion amount C (mm < 3 > / Nm) was calculated | required by following (2) Formula.
Specific wear amount C = wear loss W / (test load F × friction distance L) (2)
If the specific wear amount C is 0.35 × 10 −7 mm 3 / Nm or less in a tempered hardness 550 HV material, a power transmission member using hypoeutectoid steel having a C content of 0.70% or less It is judged that it has very excellent wear resistance as compared to the steel used for cutting and blade members.
〔衝撃試験〕
焼入れ焼戻し後の供試材表面を研磨した板厚１.３５ｍｍの板材から、圧延方向を長手方向とし、ハンマー打撃方向が圧延方向と板厚方向に垂直な方向となる２ｍｍＶノッチ衝撃試験片（ノッチ先端半径は０.２５ｍｍ）を作製した。この試験片を用いて室温（２５℃±２℃）でのシャルピー衝撃試験を行った。
Ｃ含有量０.７０％以下の亜共析鋼の調質硬さ５５０ＨＶの材料において、この試験における衝撃値が２５Ｊ／ｃｍ2以上であれば、安全性の観点から十分な靱性を有すると判断される。
[Impact test]
A 2 mm V notch impact test piece (notch) in which the rolling direction is the longitudinal direction and the hammer striking direction is perpendicular to the rolling direction and the plate thickness direction from a plate material having a thickness of 1.35 mm polished on the surface of the specimen after quenching and tempering. The tip radius was 0.25 mm). A Charpy impact test at room temperature (25 ° C. ± 2 ° C.) was performed using this test piece.
In a material with a tempered hardness of 550 HV of hypoeutectoid steel with a C content of 0.70% or less, if the impact value in this test is 25 J / cm 2 or more, it is judged that the material has sufficient toughness from the viewpoint of safety. Is done.
これらの結果を表２に示す。上記の比摩耗量Ｃが０.３５×１０-7ｍｍ3／Ｎｍ以下、かつ上記の衝撃値が２５Ｊ／ｃｍ2以上である材料を、「耐摩耗性」と「靱性」が高レベル両立できた材料と判定し、評価○（合格）と表示した。それ以外の材料を評価×（不合格）と表示した。 These results are shown in Table 2. A material having the above specific wear amount C of 0.35 × 10 −7 mm 3 / Nm or less and the impact value of 25 J / cm 2 or more can achieve both high levels of “wear resistance” and “toughness”. It was determined that the material was evaluated, and the evaluation ○ (pass) was displayed. The other materials were indicated as evaluation x (failed).
表２からわかるように、本発明例のものは粒子径１μｍ以上の硬質炭化物が適正な密度で分布していることにより、Ｃ含有量が０.３２％以上である亜共析鋼、あるいは更に０.４５％を超える亜共析鋼において「耐摩耗性」と「靱性」が高レベルで両立できた。 As can be seen from Table 2, the examples of the present invention are hypoeutectoid steel having a C content of 0.32% or more because hard carbides having a particle diameter of 1 μm or more are distributed at an appropriate density, or “Abrasion resistance” and “toughness” were compatible at a high level in hypoeutectoid steel exceeding 0.45%.
これに対し、比較例であるＮｏ.１〜３はＣ含有量が高いため種々の条件で固溶化熱処理を行っても良好な靭性（衝撃値）は得られなかった。Ｎｏ.４はＣ含有量が不足しているため耐摩耗性に劣った。Ｎｏ.５はＮｂ含有量が過剰であるため硬質炭化物の量が多くなり、耐摩耗性には優れるものの、靭性に劣った。Ｎｏ.６、７はＮｂ含有量が不足するかあるいはＮｂ無添加であるため硬質炭化物の量を十分に確保することができず、耐摩耗性に劣った。Ｎｏ.８はＭｎ含有量が過剰であるため靭性に劣った。Ｎｏ.９はＴｉ含有量が過剰であるため粗大なＴｉ系硬質炭化物の量が多くなり、靭性に劣った。Ｎｏ.１２は固溶化熱処理の加熱温度が低すぎたので硬質炭化物の残存量が多くなり、靭性に劣った。Ｎｏ.１８は固溶化熱処理の加熱温度が高すぎたので硬質炭化物の残存量が少なくなり、耐摩耗性に劣った。Ｎｏ.１９、２０はＭｎ含有量およびＮｂ含有量が高いため耐摩耗性は良好であるものの、靱性が不十分である。 On the other hand, Nos. 1 to 3 as comparative examples have a high C content, and thus good toughness (impact value) was not obtained even when solution heat treatment was performed under various conditions. No. 4 was inferior in wear resistance due to insufficient C content. In No. 5, the Nb content was excessive, so that the amount of hard carbide was increased, and although the wear resistance was excellent, the toughness was inferior. Nos. 6 and 7 were inferior in wear resistance because the Nb content was insufficient or Nb was not added, so that the amount of hard carbide could not be secured sufficiently. No. 8 was inferior in toughness due to excessive Mn content. In No. 9, since the Ti content was excessive, the amount of coarse Ti-based hard carbide was increased and the toughness was inferior. No. 12 was inferior in toughness because the amount of residual hard carbide increased because the heating temperature of the solution heat treatment was too low. In No. 18, since the heating temperature of the solution heat treatment was too high, the residual amount of hard carbide was reduced and the wear resistance was inferior. Nos. 19 and 20 have high Mn content and Nb content, and thus wear resistance is good, but toughness is insufficient.
Claims (10)
前記の粗大炭化物が存在する鋼を１１００〜１３５０℃の範囲かつ下記（１）式により定まるＡ値が０.０７７〜０.３８３となる温度Ｔ（℃）で加熱保持して、前記炭化物の一部を固溶化する工程（固溶化熱処理工程）、
前記固溶加熱処理を終えた鋼を熱間圧延して、Ｎｂを含有する粒子径１μｍ以上の炭化物が２００〜１０００個／ｍｍ2の密度でマトリクス中に存在する熱延鋼板を得る工程（熱延工程）、
Ａｃ1点未満の温度域に加熱する仕上焼鈍を施して焼鈍組織とする工程（仕上焼鈍工程）、
を有する請求項１〜３のいずれかに記載の機械部品用素材鋼板の製造方法。
Ａ＝Ｎｂ−１０x／Ｃ …（１）
ただし、ｘ＝３.４２−７９００／（Ｔ＋２７３）
（１）式のＮｂおよびＣの箇所にはそれぞれ質量％で表された当該鋼のＮｂおよびＣ含有量の値が代入される。 After casting the component-adjusted steel, a step of depositing coarse carbide containing Nb by setting the residence time in the temperature range of 1500 to 900 ° C. to 30 min or more in the cooling process (casting step),
The steel containing the coarse carbide is heated and held at a temperature T (° C.) in a range of 1100 to 1350 ° C. and an A value determined by the following formula (1) of 0.077 to 0.383, and Part solution process (solution heat treatment process),
The step of hot rolling the steel after the solid solution heat treatment to obtain a hot-rolled steel plate in which Nb-containing carbides having a particle diameter of 1 μm or more are present in a matrix at a density of 200 to 1000 pieces / mm 2 (heat Extending process),
A process (finish annealing process) in which a finish annealing is performed by heating to a temperature range less than Ac 1 point to form an annealed structure,
The manufacturing method of the raw material steel plate for machine parts in any one of Claims 1-3 which has these.
A = Nb−10 x / C (1)
However, x = 3.42-7900 / (T + 273)
The values of Nb and C contents of the steel expressed in mass% are substituted for Nb and C in the formula (1), respectively.
前記の粗大炭化物が存在する鋼を１１００〜１３５０℃の範囲かつ下記（１）式により定まるＡ値が０.０７７〜０.３８３となる温度Ｔ（℃）で加熱保持して、前記炭化物の一部を固溶化する工程（固溶化熱処理工程）、
前記固溶化熱処理を終えた鋼を熱間圧延して、Ｎｂ、Ｔｉの１種以上を含有する粒子径１μｍ以上の炭化物が２００〜１０００個／ｍｍ2の密度でマトリクス中に存在する熱延鋼板を得る工程（熱延工程）、
Ａｃ1点未満の温度域に加熱する仕上焼鈍を施して焼鈍組織とする工程（仕上焼鈍工程）、
を有する請求項４〜６のいずれかに記載の機械部品用素材鋼板の製造方法。
Ａ＝Ｎｂ−１０x／Ｃ …（１）
ただし、ｘ＝３.４２−７９００／（Ｔ＋２７３）
（１）式のＮｂおよびＣの箇所にはそれぞれ質量％で表された当該鋼のＮｂおよびＣ含有量の値が代入される。 After casting the component-adjusted steel, a step (casting step) of precipitating coarse carbide containing one or more of Nb and Ti by setting the residence time in the temperature range of 1500 to 900 ° C. to 30 min or more in the cooling process,
The steel containing the coarse carbide is heated and held at a temperature T (° C.) in a range of 1100 to 1350 ° C. and an A value determined by the following formula (1) of 0.077 to 0.383, and Part solution process (solution heat treatment process),
The steel after the solution heat treatment is hot-rolled, and a hot-rolled steel sheet in which a carbide having a particle diameter of 1 μm or more containing one or more of Nb and Ti is present in a matrix at a density of 200 to 1000 pieces / mm 2. The process of obtaining (hot rolling process),
A process (finish annealing process) in which a finish annealing is performed by heating to a temperature range less than Ac 1 point to form an annealed structure,
The manufacturing method of the raw material steel plate for machine parts in any one of Claims 4-6 which has these.
A = Nb−10 x / C (1)
However, x = 3.42-7900 / (T + 273)
The values of Nb and C contents of the steel expressed in mass% are substituted for Nb and C in the formula (1), respectively.
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| JPH05239591A (en) * | 1992-02-27 | 1993-09-17 | Nkk Corp | Steel excellent in wear resistance |
| JPH05239590A (en) * | 1992-02-27 | 1993-09-17 | Nkk Corp | Steel excellent in wear resistance |
| JP3846008B2 (en) * | 1998-01-30 | 2006-11-15 | 大同特殊鋼株式会社 | Cold tool steel with excellent toughness and wear resistance and manufacturing method thereof |
| JP5217191B2 (en) * | 2007-03-08 | 2013-06-19 | Ｊｆｅスチール株式会社 | Wear-resistant steel plate with excellent workability and method for producing the same |
| JP5328331B2 (en) * | 2008-12-11 | 2013-10-30 | 日新製鋼株式会社 | Steel materials for wear-resistant quenched and tempered parts and manufacturing method |
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| EP3399067B1 (en) * | 2015-12-28 | 2021-07-14 | Posco | Steel sheet for tool and manufacturing method therefor |
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