JP4371072B2 - High carbon steel sheet - Google Patents
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本発明は、高炭素鋼板に関する。例えば、本発明は、熱処理後のビッカース硬度で６５０以上を要求されるような高強度鋼板部品の素材に供される高炭素鋼板に関するものであり、熱処理前においては軟質で良好な成形性を備え、かつ熱処理後においては硬度に比して優れた耐摩耗性を備える高炭素鋼板に関する。 The present invention relates to a high carbon steel sheet. For example, the present invention relates to a high-carbon steel sheet used for a material of a high-strength steel sheet part that requires a Vickers hardness of 650 or more after heat treatment, and is soft and has good formability before heat treatment. And after heat processing, it is related with the high carbon steel plate provided with the abrasion resistance outstanding compared with hardness.
自動車のミッション部品等には、その複雑な動きや耐久性の観点から、非常に高い強度と耐摩耗性とが要求される。
耐摩耗性を向上させる手段としてＣｒを添加する方法が一般に知られる。しかしながら、Ｃｒ等の合金元素を単に添加するのみで何ら工夫を施すことなく製造される鋼板は、合金元素の影響により硬化し、熱処理前の素材段階における成形性が劣化する。
From the viewpoint of complicated movement and durability, automobile parts and the like are required to have extremely high strength and wear resistance.
As a means for improving wear resistance, a method of adding Cr is generally known. However, a steel sheet manufactured without any contrivance by simply adding an alloy element such as Cr hardens due to the influence of the alloy element, and the formability at the material stage before heat treatment deteriorates.
一方、成形性と耐摩耗性とを具備する鋼板として、以下の技術が提案されている。
特許文献１には、成形性と耐摩耗性とに優れた熱処理用鋼板が開示されている。
特許文献２には、耐摩耗性に優れた加工面を有する加工部材の製造方法およびそれに供する加工部材用高強度鋼板が開示されている。
On the other hand, the following techniques have been proposed as steel sheets having formability and wear resistance.
Patent Document 1 discloses a steel sheet for heat treatment that is excellent in formability and wear resistance.
さらに、特許文献３には、耐摩耗性及び打抜き加工性に優れたオートマチックトランスミッションプレート用冷延鋼板が開示されている。
自動車のミッション用の部品等には、素材として供される鋼板を成形して鋼板部材とし、この鋼板部材に焼入れ焼戻しやオーステンパー等の熱処理を施すものがあり、熱処理前の素材段階における鋼板については軟質で良好な加工性を有することが、また熱処理後の鋼板部材については高い強度と耐摩耗性とを有することが、それぞれ要求される。 There are parts for automobile missions, etc., in which steel plates provided as raw materials are formed into steel plate members, and these steel plate members are subjected to heat treatment such as quenching and tempering and austemper. Are required to be soft and have good workability, and to have high strength and wear resistance for the steel plate member after the heat treatment.
熱処理後の鋼板部材について耐摩耗性を確保するには、ＣやＣｒ等の含有量が多いほうが有利であるが、これにより、熱処理前の素材段階における鋼板の成形性の劣化を招くことにつながる。 In order to ensure the wear resistance of the steel plate member after heat treatment, it is advantageous that the content of C, Cr, etc. is large, but this leads to deterioration of the formability of the steel plate in the material stage before heat treatment. .
一方、熱処理前の素材段階における鋼板を軟質化することにより良好な成形性を確保しようとしてＣやＣｒ等の含有量を減らすと、熱処理後の硬度が低下し、熱処理後の鋼板部材について必要な強度が確保できなくなったり耐摩耗性が劣化したりする。 On the other hand, if the content of C, Cr, etc. is reduced in order to ensure good formability by softening the steel plate in the material stage before heat treatment, the hardness after heat treatment will decrease, and it is necessary for the steel plate member after heat treatment Strength cannot be secured or wear resistance deteriorates.
特許文献１に開示されている熱処理用鋼板のＣ含有量は０．２５〜０．４０％（本明細書においては特にことわりがない限り「％」は「質量％」を意味するものとする）であり、しかも鋼中の炭化物としてグラファイトの含有をある程度許容するものである。鋼中の炭化物をグラファイト化させることは、鋼板の降伏点（ＹＰ）や引張強度（ＴＳ）を低下させることには有効な手段であるものの、グラファイト自体は延性に乏しいために曲げ加工等の際にその部分から亀裂を生じ易く、真に成形性に優れるとは云えない。また、この熱処理用鋼板は、Ｃ含有量が少ないために耐摩耗性も充分とは云えない。 C content of the steel sheet for heat treatment disclosed in Patent Document 1 is 0.25 to 0.40% (in this specification, “%” means “% by mass” unless otherwise specified). In addition, the inclusion of graphite as a carbide in steel is allowed to some extent. Graphitization of carbides in steel is an effective means for reducing the yield point (YP) and tensile strength (TS) of steel sheets, but graphite itself has poor ductility, so it is difficult to perform bending work. However, it is easy to form a crack from the part, and it cannot be said that it is truly excellent in formability. Moreover, this steel sheet for heat treatment cannot be said to have sufficient wear resistance because of its low C content.
特許文献２に開示されている加工部材用高強度鋼板のＣ含有量は０．０５〜０．２５％であり、しかも成形後に塗装焼付け処理程度の低温熱処理を施すものであり、本発明のように焼入れ等の高温熱処理を施すことを前提とするものとは用途が異なる。
The C content of the high-strength steel sheet for processing members disclosed in
さらに、特許文献３に開示されているオートマチックトランスミッションプレート用冷延鋼板のＣ含有量は０．１５〜０．２５％であり、かつ成形後に熱処理を施さないものであり、高温熱処理に供することを前提とするものとは用途が異なる。 Furthermore, the C content of the cold-rolled steel sheet for automatic transmission plates disclosed in Patent Document 3 is 0.15 to 0.25%, and is not subjected to heat treatment after forming, and is subjected to high-temperature heat treatment. Use is different from what is assumed.
これらの技術は、Ｃ含有量が少ないことからある程度良好な成形性を示すものの、耐摩耗性の点では充分であるとは云えない。 Although these techniques show good moldability to some extent because of their low C content, they cannot be said to be sufficient in terms of wear resistance.
本発明者は、上述した課題を解決するために、熱処理前の素材段階における高炭素鋼板の組成および組織について鋭意検討を行った結果、以下に列記する知見（１）及び（２）を得た。 In order to solve the above-described problems, the present inventor has earnestly studied the composition and structure of the high-carbon steel sheet in the material stage before the heat treatment, and as a result, obtained knowledge (1) and (2) listed below. .
（１）熱処理後の鋼板部材の耐摩耗性には、鋼板部材の硬度のみならず鋼板部材中の炭化物が重要な働きをする。すなわち、素材として供される高炭素鋼板は、一般に、鋼板部材に成形加工された後に焼入れ焼戻し等の熱処理が施されて使用されるが、この熱処理の際に、炭化物を総てオーステナイト中に固溶させるのではなく適度に未固溶炭化物として残留させることが有効である。そして、この未固溶炭化物の硬度が鋼板部材の耐摩耗性に大きく影響を及ぼす。この未固溶炭化物は、ＭｎとＣｒが溶け込み複炭化物となっており、高炭素鋼板におけるＭｎとＣｒとの原子数比｛（Ｍｎ／５５）／（Ｃｒ／５２）｝を特定の範囲内とすることにより耐摩耗性を著しく向上することができる。 (1) Not only the hardness of the steel plate member but also the carbide in the steel plate member plays an important role in the wear resistance of the steel plate member after the heat treatment. That is, a high carbon steel plate provided as a raw material is generally used after being formed into a steel plate member and then subjected to a heat treatment such as quenching and tempering. During this heat treatment, all carbides are solidified in austenite. It is effective to leave it as an undissolved carbide instead of dissolving it. The hardness of the insoluble carbide greatly affects the wear resistance of the steel plate member. This insoluble carbide is a double carbide in which Mn and Cr are mixed, and the atomic ratio of {Mn / 55) / (Cr / 52)} between Mn and Cr in the high carbon steel sheet is within a specific range. By doing so, the wear resistance can be remarkably improved.
（２）熱処理前の素材段階における鋼板を軟質にするには、Ｃ、Ｍｎ、Ｃｒ等の合金元素の含有量を低減することが有効であるが、鋼板部材の強度と耐摩耗性とを確保するためには、ある程度含有させることが必要となり、鋼組成のみで鋼板の軟質化を図ることには限界がある。そこで、フェライトの粒径および球状化炭化物の分布を特定の範囲内とすることにより、従来材よりも合金元素の含有量に比して軟質化することが可能となり、素材段階における鋼板について良好な加工性を実現することができる。 (2) To soften the steel sheet in the material stage before heat treatment, it is effective to reduce the content of alloy elements such as C, Mn, Cr, etc., but ensure the strength and wear resistance of the steel sheet member. In order to achieve this, it is necessary to contain a certain amount, and there is a limit to the softening of the steel sheet only by the steel composition. Therefore, by making the ferrite grain size and the distribution of spheroidized carbide within a specific range, it becomes possible to soften the alloy element content as compared with the conventional material, which is good for steel sheets in the material stage. Workability can be realized.
本発明は、これらの新規な知見（１）及び（２）に基づくものである。
本発明は、Ｃ：０．５０〜１．００％、Ｓｉ：０．３５％以下、Ｍｎ：０．６０〜０．９０％、Ｐ：０．０１５％以下、Ｓ：０．００３０％以下、Ｃｒ：０．３０〜０．６０％、ｓｏｌ．Ａｌ：０．００５〜０．０８０％、Ｎ：０．００５０％以下、残部Ｆｅおよび不純物からなり、さらに、Ｃｒ含有量およびＭｎ含有量が、（１）式：１．２≦（Ｍｎ／５５）／（Ｃｒ／５２）≦２．０を満足し、フェライトの平均結晶粒径が１０μｍ以上、望ましくは５０μｍ以下であるとともに、球状化炭化物のうち粒径が１．０μｍ以上であるものの個数比率が５０％以上であることを特徴とする高炭素鋼板である。ただし、（１）式における符号ＭｎおよびＣｒは、いずれも、鋼中における各元素の含有量（質量％）を示す。
The present invention is based on these novel findings (1) and (2).
The present invention, C: 0.50-1.00%, Si: 0.35% or less, Mn: 0.60-0.90%, P: 0.015% or less, S: 0.0030% or less, Cr: 0.30 to 0.60%, sol. Al: 0.005 to 0.080%, N: 0.0050% or less, remaining Fe and impurities, and further Cr content and Mn content are represented by the formula (1): 1.2 ≦ (Mn / 55 ) / (Cr / 52) ≦ 2.0, the average crystal grain size of ferrite is 10 μm or more, preferably 50 μm or less, and the number ratio of spheroidized carbides having a particle size of 1.0 μm or more. Is a high carbon steel sheet characterized by being 50% or more. However, the symbols Mn and Cr in the formula (1) both indicate the content (mass%) of each element in the steel.
本発明により、熱処理後のビッカース硬度で６５０以上を要求されるような高強度鋼板部品の素材に供される高炭素鋼板であって、熱処理前においては軟質で良好な成形性を備え、熱処理後においては硬度に比して優れた耐摩耗性を備える高炭素鋼板を得ることができる。 According to the present invention, a high-carbon steel sheet used for a material of a high-strength steel sheet component that requires a Vickers hardness of 650 or more after heat treatment, which is soft and has good formability before heat treatment, and after heat treatment Can provide a high carbon steel sheet having excellent wear resistance compared to the hardness.
より具体的には、本発明により、熱処理前の素材段階における鋼板の状態では、ビッカース硬度が１７０以下と非常に軟質でありながら、熱処理後の鋼板部材の状態では、ビッカース硬度が６５０以上と高い強度を備えるとともに優れた耐摩耗性を備える高炭素鋼板を得ることができる。 More specifically, according to the present invention, the Vickers hardness is as high as 170 or less in the state of the steel plate in the material stage before the heat treatment, while the Vickers hardness is as high as 650 or more in the state of the steel plate member after the heat treatment. A high carbon steel plate having strength and excellent wear resistance can be obtained.
このため、本発明は、自動車のミッション部品等の用途に利用価値の高い発明である。 For this reason, this invention is invention with high utility value for uses, such as a mission component of a motor vehicle.
以下、本発明に係る高炭素鋼板を実施するための最良の形態を、添付図面を参照しながら詳細に説明する。
本実施の形態の高炭素鋼板の限定理由を説明する。
Hereinafter, the best mode for carrying out the high carbon steel sheet according to the present invention will be described in detail with reference to the accompanying drawings.
The reason for limitation of the high carbon steel plate of this Embodiment is demonstrated.
Ｃ：０．５０〜１．００％
Ｃは、焼入れ焼戻しあるいはオーステンパー、さらには必要に応じて浸炭処理等の熱処理を施した後における、硬度、耐摩耗性さらには疲労強度を向上させる。本発明においては、熱処理後のビッカース硬度で６５０以上を確保するために、Ｃ含有量を０．５０％以上とする。一方、過剰に含有させると熱処理前の冷間加工性や熱処理後の靱性が劣化するため、Ｃ含有量を１．００％以下とする。好ましいＣ含有量は、０．６５％以上０．８０％以下である。
C: 0.50 to 1.00%
C improves the hardness, wear resistance, and fatigue strength after heat treatment such as quenching and tempering or austempering and, if necessary, carburizing treatment. In the present invention, in order to ensure a Vickers hardness of 650 or higher after heat treatment, the C content is set to 0.50% or higher. On the other hand, if contained excessively, cold workability before heat treatment and toughness after heat treatment deteriorate, so the C content is made 1.00% or less. The preferable C content is 0.65% or more and 0.80% or less.
Ｓｉ：０．３５％以下
Ｓｉは、多量に含有するとＳｉ酸化物を形成して熱処理後の鋼材の疲労強度の低下を招く。そこで、Ｓｉ含有量を０．３５％以下とする。好ましくは０．２０％以下である。
Si: 0.35% or less When Si is contained in a large amount, Si oxide is formed and the fatigue strength of the steel material after heat treatment is lowered. Therefore, the Si content is set to 0.35% or less. Preferably it is 0.20% or less.
Ｍｎ：０．６０〜０．９０％
Ｍｎは、本発明において重要な元素である。すなわち、Ｍｎは、セメンタイト中に固溶してセメンタイトの硬度を増加させることにより耐摩耗性を向上する。さらに、熱処理時の焼入性の確保を容易にしたり、あるいは靱性向上のための焼戻し温度およびオーステンパー温度を上昇させる。そこで、Ｍｎ含有量を０．６０％以上とする。しかし、０．９０％を超えて含有すると、熱延鋼板が過度に硬化するため、後続して行う酸洗や冷間圧延等を困難にするとともに、本発明の重要なポイントでもある熱処理前における鋼板の加工性の確保にも悪影響を及ぼす。このため、Ｍｎ含有量を０．６０％以上０．９０％以下とする。好ましくは、０．７０％以上０．８５％以下である。
Mn: 0.60 to 0.90%
Mn is an important element in the present invention. That is, Mn improves the wear resistance by dissolving in cementite and increasing the hardness of cementite. Furthermore, it is easy to ensure hardenability during heat treatment, or to raise the tempering temperature and austempering temperature for improving toughness. Therefore, the Mn content is set to 0.60% or more. However, if the content exceeds 0.90%, the hot-rolled steel sheet is excessively hardened, so that subsequent pickling, cold rolling, etc. are difficult, and before heat treatment, which is also an important point of the present invention. It also has an adverse effect on securing the workability of the steel sheet. For this reason, Mn content shall be 0.60% or more and 0.90% or less. Preferably, it is 0.70% or more and 0.85% or less.
Ｐ：０．０１５％以下
Ｐは、固溶強化元素であることから熱処理前の鋼板の加工性を劣化させる。また、靭性を劣化させる。したがって、Ｐはなるべく少ないほうがよく、Ｐ含有量を０．０１５％以下とする。好ましくは０．０１０％以下である。
P: 0.015% or less P is a solid solution strengthening element, and therefore deteriorates the workability of the steel sheet before heat treatment. In addition, the toughness is deteriorated. Therefore, P should be as small as possible, and the P content should be 0.015% or less. Preferably it is 0.010% or less.
Ｓ：０．００３０％以下
Ｓは、本発明の中で重要な位置を占める。すなわち、Ｓは介在物として存在し、鋼板の延性を低下させるばかりか、耐摩耗性を劣化させる。したがって、Ｓはなるべく少ないほうがよく、Ｓ含有量を０．００３０％以下とする。好ましくは０．００２０％以下である。
S: 0.0030% or less S occupies an important position in the present invention. That is, S exists as an inclusion and not only lowers the ductility of the steel sheet but also degrades the wear resistance. Therefore, S should be as small as possible, and the S content should be 0.0030% or less. Preferably it is 0.0020% or less.
Ｃｒ：０．３０〜０．６０％
Ｃｒは、本発明の中で耐摩耗性を確保する点で最も重要な元素である。Ｍｎと同様に、セメンタイト中に固溶してセメンタイトの硬度を増加させることにより耐摩耗性の向上に寄与する。さらに、熱処理時の焼入性の確保を容易にしたり、あるいは靱性向上のための焼戻し温度およびオーステンパー温度を上昇させる作用を有する。そこで、Ｃｒ含有量を０．３０％以上とする。しかし、０．６０％を超えて含有させると、熱延鋼板が過度に硬化するため、後続して行う酸洗や冷間圧延等を困難にするとともに、本発明の重要なポイントでもある熱処理前における鋼板の加工性の確保にも悪影響を及ぼす。このため、Ｃｒの含有量を０．３０％以上０．６０％以下とする。好ましくは、０．４５％以上０．５５％以下である。
Cr: 0.30-0.60%
Cr is the most important element in securing wear resistance in the present invention. Like Mn, it contributes to the improvement of wear resistance by increasing the hardness of cementite by dissolving in cementite. Furthermore, it has the effect of making it easy to ensure hardenability during heat treatment or increasing the tempering temperature and austempering temperature for improving toughness. Therefore, the Cr content is set to 0.30% or more. However, if the content exceeds 0.60%, the hot-rolled steel sheet is excessively hardened, so that subsequent pickling, cold rolling, etc. are difficult, and heat treatment is also an important point of the present invention. It also has an adverse effect on securing the workability of steel sheets. For this reason, content of Cr shall be 0.30% or more and 0.60% or less. Preferably, it is 0.45% or more and 0.55% or less.
ｓｏｌ．Ａｌ：０．００５〜０．０８０％
Ａｌは、鋼の溶製過程で脱酸剤として添加される。また、ＮをＡｌＮとして固定する作用も有する。Ａｌ含有量が０．００５％未満では脱酸作用が不十分であり、一方０．０８０％を超えると清浄度が低下して表面性状が劣化する。このため、Ａｌ含有量を０．００５％以上０．０８０％以下とする。好ましくは０．０２０％以上０．０４０％以下である。
sol. Al: 0.005-0.080%
Al is added as a deoxidizer in the melting process of steel. It also has the effect of fixing N as AlN. If the Al content is less than 0.005%, the deoxidation action is insufficient, while if it exceeds 0.080%, the cleanliness is lowered and the surface properties are deteriorated. For this reason, Al content shall be 0.005% or more and 0.080% or less. Preferably they are 0.020% or more and 0.040% or less.
Ｎ：０．００５０％以下
Ｎは、鋼中に不可避的に含有される不純物元素であり、Ａｌと結び付いてＡｌＮを形成し、フェライト粒径の粗大化を阻害することにより、熱処理前の鋼板の加工性が損なわれる。したがって、Ｎ含有量を０．００５０％以下とする。好ましくは０．００４０％以下である。
N: 0.0050% or less N is an impurity element inevitably contained in the steel, and is combined with Al to form AlN, thereby inhibiting the coarsening of the ferrite grain size. Workability is impaired. Therefore, the N content is 0.0050% or less. Preferably it is 0.0040% or less.
Ｃｒ含有量およびＭｎ含有量：１．２≦（Ｍｎ／５５）／（Ｃｒ／５２）≦２．０
Ｍｎ、Ｃｒはいずれも鉄炭化物に溶け易い元素である。セメンタイトにこれらの元素が固溶すると、一部のＦｅが置換されてＭ３Ｃと表される複炭化物になると考えられる。この際、鉄炭化物に溶ける元素の個数比が、耐摩耗性の確保に必要とされる炭化物の性質を決定する重要な因子である。すなわち、ＭｎとＣｒとの原子数比｛（Ｍｎ／５５）／（Ｃｒ／５２）｝が１．２≦（Ｍｎ／５５）／（Ｃｒ／５２）≦２．０の関係を満たすときに、炭化物が大きな耐摩耗性の向上効果を発揮する。好ましくは、１．４≦（Ｍｎ／５５）／（Ｃｒ／５２）≦１．８である。
Cr content and Mn content: 1.2 ≦ (Mn / 55) / (Cr / 52) ≦ 2.0
Both Mn and Cr are elements that are easily dissolved in iron carbide. When these elements are dissolved in cementite, it is considered that a part of Fe is substituted and a double carbide expressed as M 3 C is obtained. At this time, the number ratio of elements dissolved in the iron carbide is an important factor for determining the properties of the carbide required for ensuring the wear resistance. That is, when the atomic ratio of Mn to Cr {(Mn / 55) / (Cr / 52)} satisfies the relationship 1.2 ≦ (Mn / 55) / (Cr / 52) ≦ 2.0, Carbide exhibits a significant effect of improving wear resistance. Preferably, 1.4 ≦ (Mn / 55) / (Cr / 52) ≦ 1.8.
上記以外は、Ｆｅおよび不純物である。
また、熱処理前の素材段階における鋼板の組織は、素材としての加工性に重大な影響を及ぼすばかりか、熱処理そのものにも影響を与え、また、熱処理後の鋼板部材における耐摩耗性にも影響を及ぼす。このため、本実施の形態の高炭素鋼板の組織を説明する。
Other than the above are Fe and impurities.
In addition, the structure of the steel sheet in the material stage before heat treatment not only has a significant effect on the workability of the material, but also affects the heat treatment itself, and also affects the wear resistance of the steel sheet member after heat treatment. Effect. For this reason, the structure of the high carbon steel plate of the present embodiment will be described.
フェライトの平均結晶粒径：１０μｍ以上
フェライトの結晶粒径は、熱処理前の鋼板の軟質性に大きな影響を及ぼす。具体的には、フェライトの平均結晶粒径が１０μｍ未満では、熱処理前の鋼板を軟質化して成形性を確保することが困難になる。したがって、フェライトの平均結晶粒径を１０μｍ以上とする。フェライトの平均結晶粒径の上限は特に規定しないが、フェライトの平均結晶粒径が５０μｍ超であると、粒径を大きくすることに要する製造コストの増加が著しくなるので、フェライトの平均結晶粒径を５０μｍ以下とすることが好ましい。
Average crystal grain size of ferrite : 10 μm or more The crystal grain size of ferrite greatly affects the softness of the steel sheet before heat treatment. Specifically, if the average crystal grain size of ferrite is less than 10 μm, it becomes difficult to ensure the formability by softening the steel sheet before heat treatment. Therefore, the average crystal grain size of ferrite is 10 μm or more. The upper limit of the average crystal grain size of ferrite is not particularly specified, but if the average crystal grain size of ferrite exceeds 50 μm, the increase in manufacturing cost required to increase the grain size becomes significant. Is preferably 50 μm or less.
このフェライトの平均結晶粒径は、鋼板表面から板厚１／４深さの部位の領域で０．２
ｍｍ×０．２ｍｍの視野を５００倍で撮影した組織写真から観察されるフェライト粒径の平均値として、規定される。
The average crystal grain size of this ferrite is 0.2 in the region of the thickness 1/4 of the steel sheet surface.
It is defined as the average value of the ferrite particle diameter observed from a structure photograph obtained by photographing a field of view of mm × 0.2 mm at 500 times.
球状化炭化物のうち粒径が１．０μｍ以上であるものの個数比率：５０％以上
球状化炭化物の粒径は、熱処理前の鋼板の加工性に大きな影響を及ぼすのはもちろんのこと、本発明の重要なポイントである耐摩耗性に対しても大きな影響を及ぼす。すなわち、炭化物の粒径が大きいほうが熱処理前の素材段階における鋼板の加工性を確保することを容易にするとともに、熱処理中における炭化物の固溶を抑制して未固溶炭化物の残存させることを容易にして、耐摩耗に好影響を及ぼす。具体的には、球状化炭化物のうち粒径が１．０μｍ以上であるものの個数比率が５０％以上である状態が最も良好である。
Number ratio of spheroidized carbide having a particle size of 1.0 μm or more: 50% or more The particle size of the spheroidized carbide has a great influence on the workability of the steel sheet before heat treatment. It also has a significant effect on wear resistance, which is an important point. That is, the larger the particle size of the carbide, the easier it is to ensure the workability of the steel plate in the material stage before the heat treatment, and it is easier to suppress the solid solution of the carbide during the heat treatment and to leave the undissolved carbide. Thus, it has a positive effect on wear resistance. Specifically, the state in which the number ratio of spheroidized carbides having a particle size of 1.0 μm or more is 50% or more is the best.
球状化炭化物の粒径の測定は、ピクリン酸アルコールでエッチングしたミクロ組織を走査型電子顕微鏡によって観察し、さらに２０００倍で撮影した写真を画像解析して、個々の炭化物の面積を測定し、この測定値から個々の炭化物の円相当径を算出して、その大きさを測定することにより、行われる。 The particle size of the spheroidized carbide is measured by observing the microstructure etched with picric alcohol with a scanning electron microscope, analyzing the photograph taken at 2000 times, and measuring the area of each carbide. This is done by calculating the equivalent circle diameter of each carbide from the measured value and measuring its size.
このように、本実施の形態の高炭素鋼板は、ＭｎとＣｒとの原子数比｛（Ｍｎ／５５）／（Ｃｒ／５２）｝を所定の範囲内とすることによって成形加工された後に行われる焼入れ焼戻し等の熱処理の際に、炭化物を総てオーステナイト中に固溶させるのではなくＭｎとＣｒとが溶け込んだ未固溶炭化物として適度に残留させることができ、この未固溶炭化物の硬度により鋼板部材の耐摩耗性を大きく向上することができるとともに、フェライトの平均結晶粒径、および粒径が１．０μｍ以上である球状化炭化物の個数比率を、それぞれ１０μｍ以上５０μｍ以下、５０％以上とすることにより、従来材よりも合金元素の含有量に比較して軟質化することができ、熱処理前の素材段階における鋼板を軟質にして、良好な加工性を確保することができる。 As described above, the high carbon steel sheet of the present embodiment is formed after being formed by setting the atomic number ratio {(Mn / 55) / (Cr / 52)} between Mn and Cr within a predetermined range. During the heat treatment such as quenching and tempering, not all the carbides are dissolved in austenite, but can be appropriately left as undissolved carbides in which Mn and Cr are dissolved, and the hardness of the undissolved carbides Can greatly improve the wear resistance of the steel sheet member, and the average crystal grain size of ferrite and the number ratio of spheroidized carbides having a grain size of 1.0 μm or more are 10 μm or more and 50 μm or less and 50% or more, respectively. By doing so, it can be softened compared to the content of alloying elements than conventional materials, and the steel sheet in the material stage before heat treatment can be softened to ensure good workability. That.
このため、本実施の形態によれば、熱処理後のビッカース硬度で６５０以上を要求されるような高強度鋼板部品の素材に供される高炭素鋼板であって熱処理前においては軟質で良好な成形性を備え、さらに熱処理後においては硬度に比して優れた耐摩耗性を備える高炭素鋼板、より具体的には、熱処理前の素材段階における鋼板の状態ではビッカース硬度が１７０以下と非常に軟質でありながら熱処理後の鋼板部材の状態ではビッカース硬度が６５０以上と高い強度を備えるとともに優れた耐摩耗性を備える高炭素鋼板が提供される。このため、例えば自動車のミッション部品等の用途に利用価値が高い高炭素鋼板が提供される。 For this reason, according to the present embodiment, it is a high carbon steel plate used for a material of a high strength steel plate part that requires a Vickers hardness of 650 or more after the heat treatment, and is soft and good formed before the heat treatment. High carbon steel plate with high wear resistance compared to hardness after heat treatment, more specifically, Vickers hardness is 170 or less in the state of the steel plate in the raw material stage before heat treatment. However, in the state of the steel plate member after the heat treatment, a high carbon steel plate having a high Vickers hardness of 650 or more and an excellent wear resistance is provided. For this reason, for example, a high carbon steel plate having a high utility value for applications such as automobile mission parts is provided.
本発明を実施例に基づいて、さらに具体的に説明する。
表１−１、１−２に示す化学成分を有する鋼を溶製した。そして、表２−１、２−２に示すように、連続鋳造によりスラブとし、このスラブを１２５０℃に加熱してから、仕上げ温度８６０℃及び巻取温度５５０℃で３．６ｍｍ厚の熱延コイルを製造し、次いで、この熱延コイルを酸洗して黒皮スケールを除去した後、６９０〜７２０℃で２５時間、並びに７５０℃で６時間の炭化物球状化焼鈍（前焼鈍）を行い、中間処理として、冷間圧延機による２．０〜２．８ｍｍ厚までの冷間圧延（中間冷延１、２）と、バッチ焼鈍炉での７００℃で２０時間の焼鈍（中間焼鈍１、２）とを、１回ないし２回繰返して行った後、仕上げ処理として、１．８ｍｍまでの冷間圧延（仕上冷圧）と６９０℃で４時間の焼鈍（仕上焼鈍）とを行って、９０種の高炭素鋼板を製造した。
The present invention will be described more specifically based on examples.
Steels having chemical components shown in Tables 1-1 and 1-2 were melted. Then, as shown in Tables 2-1 and 2-2, a slab was formed by continuous casting, the slab was heated to 1250 ° C., and then hot-rolled to a thickness of 3.6 mm at a finishing temperature of 860 ° C. and a winding temperature of 550 ° C. A coil is manufactured, and then the hot rolled coil is pickled to remove the black scale, and then subjected to carbide spheroidizing annealing (pre-annealing) at 690 to 720 ° C. for 25 hours and 750 ° C. for 6 hours, As an intermediate treatment, cold rolling to 2.0 to 2.8 mm thickness (intermediate cold rolling 1, 2) by a cold rolling mill and annealing at 700 ° C. for 20 hours (intermediate annealing 1, 2) in a batch annealing furnace ) Is repeated once or twice, and as a finishing treatment, cold rolling up to 1.8 mm (finish cold pressure) and annealing at 690 ° C. for 4 hours (finish annealing) are performed. A seed high carbon steel plate was produced.
これらの高炭素鋼板について、上述した方法によってフェライトの平均結晶粒径、球状化炭化物のうち粒径が１．０μｍ以上であるものの個数比率、及びビッカース硬度を測定した。測定結果を表１−１、１−２に併せて示す。 About these high carbon steel plates, the average crystal grain diameter of ferrite, the number ratio of those having a grain diameter of 1.0 μm or more among the spheroidized carbides, and the Vickers hardness were measured by the method described above. The measurement results are shown in Tables 1-1 and 1-2.
次に、これらの高炭素鋼板から３ｃｍ×３ｃｍの試料を打抜き、この試料を８００℃で３０分間均熱した後、６０℃の油中へ焼入れを行い、その後１５０℃で３０分間焼戻す熱処理を行った。 Next, a sample of 3 cm × 3 cm is punched from these high-carbon steel sheets, and the sample is soaked at 800 ° C. for 30 minutes, then quenched into oil at 60 ° C., and then tempered at 150 ° C. for 30 minutes. went.
この後、表面研磨を行い、図１に概要を示す大越式摩耗試験機により表面の摩耗試験を行った。なお、図１における符号Ｐは摩耗試験時の負荷荷重を示し、符号Ｖは摩耗速度を示し、符号Ｌは摩耗距離（図示しない）を示し、符号ｂ０は摩耗痕の幅を示し、符号ｒは回転円板の半径を示し、さらに、符号Ｂは回転円板の厚さを示す。 Thereafter, surface polishing was performed, and a surface abrasion test was performed using an Ogoshi type abrasion tester schematically shown in FIG. 1 indicates the load applied during the wear test, V indicates the wear rate, L indicates the wear distance (not shown), b 0 indicates the width of the wear mark, and r Indicates the radius of the rotating disk, and symbol B indicates the thickness of the rotating disk.
本実施例では、Ｐ＝６７（Ｎ）、Ｖ＝０．７６（ｍ／ｓ）、Ｌ＝４００（ｍ）、ｒ＝３０（ｍｍ）、Ｂ＝３．０（ｍｍ）とするとともに、相手材としてＳＣＭ４１５を用いて、摩耗試験を行った。そして、摩耗量（ｍｍ３）を測定した。 In this embodiment, P = 67 (N), V = 0.76 (m / s), L = 400 (m), r = 30 (mm), B = 3.0 (mm), and the other party A wear test was performed using SCM415 as the material. And the amount of wear (mm < 3 >) was measured.
また、熱処理後のビッカース硬度も測定した。
摩耗試験の結果および熱処理後のビッカース硬度を表１に併せて示す。
また、図２は、各試料の摩耗量が１．５（ｍｍ３／（ｍｍ２・ｍｍ））未満である試料を●印（摩耗量小）として、摩耗量が１．５（ｍｍ３／（ｍｍ２・ｍｍ））以上１．６（ｍｍ３／（ｍｍ２・ｍｍ））未満である試料を▲印（摩耗量中）として、さらに摩耗量が１．６（ｍｍ３／（ｍｍ２・ｍｍ））以上である試料を×印（摩耗量大）として、各試料の母材である高炭素鋼板のＣｒ量及びＭｎ量をプロットして示すグラフである。なお、図２には、各試料の母材である高炭素鋼板のＭｎとＣｒとの原子数比｛（Ｍｎ／５５）／（Ｃｒ／５２）｝が、１．０、１．２、１．４、１．６、１．８、２．０及び２．２となる直線を併記してある。
Moreover, the Vickers hardness after heat processing was also measured.
The results of the abrasion test and the Vickers hardness after the heat treatment are also shown in Table 1.
In addition, FIG. 2 shows that the wear amount of each sample is less than 1.5 (mm 3 / (mm 2 · mm)), and the wear amount is 1.5 (mm 3 / mm). (Mm 2 · mm)) or more and less than 1.6 (mm 3 / (mm 2 · mm)) are marked with ▲ (in the wear amount), and the wear amount is further 1.6 (mm 3 / (mm 2 (Mm)) is a graph plotting the amount of Cr and the amount of Mn of a high-carbon steel sheet as a base material of each sample, with the samples having the above-mentioned x marks (large amount of wear). In FIG. 2, the atomic ratio {(Mn / 55) / (Cr / 52)} of Mn and Cr of the high-carbon steel plate that is the base material of each sample is 1.0, 1.2, 1 .4, 1.6, 1.8, 2.0 and 2.2 are also shown.
図２のグラフから理解されるように、ＭｎとＣｒとの原子数比｛（Ｍｎ／５５）／（Ｃｒ／５２）｝が１．２≦（Ｍｎ／５５）／（Ｃｒ／５２）≦２．０の関係を満たすときには、摩耗量小又は摩耗量中であり、炭化物が大きな耐摩耗性の向上効果を発揮することがわかるとともに、原子数比｛（Ｍｎ／５５）／（Ｃｒ／５２）｝が１．４≦（Ｍｎ／５５）／（Ｃｒ／５２）≦１．８の関係を満たすときには、摩耗量小であり、炭化物がさらに大きな耐摩耗性の向上効果を発揮することがわかる。 As understood from the graph of FIG. 2, the atomic ratio {(Mn / 55) / (Cr / 52)} between Mn and Cr is 1.2 ≦ (Mn / 55) / (Cr / 52) ≦ 2. 0.0 is satisfied, the wear amount is small or during wear, and it can be seen that the carbide exhibits a large effect of improving wear resistance, and the atomic ratio {(Mn / 55) / (Cr / 52) } Satisfies the relationship of 1.4 ≦ (Mn / 55) / (Cr / 52) ≦ 1.8, the wear amount is small, and it can be seen that the carbide exhibits a greater effect of improving wear resistance.
Claims (1)
１．２≦（Ｍｎ／５５）／（Ｃｒ／５２）≦２．０・・・・・・・（１）
ただし、（１）式における符号ＭｎおよびＣｒは、いずれも、鋼中における各元素の含有量（質量％）を示す。 In mass%, C: 0.50 to 1.00%, Si: 0.35% or less, Mn: 0.60 to 0.90%, P: 0.015% or less, S: 0.0030% or less, Cr: 0.30 to 0.60%, sol. Al: 0.005 to 0.080%, N: 0.0050% or less, balance Fe and impurities, Cr content and Mn content satisfy the following formula (1), and the average grain size of ferrite A high carbon steel sheet having a diameter of 10 μm or more and a number ratio of spheroidized carbides having a particle diameter of 1.0 μm or more of 50% or more.
1.2 ≦ (Mn / 55) / (Cr / 52) ≦ 2.0 (1)
However, the symbols Mn and Cr in the formula (1) both indicate the content (mass%) of each element in the steel.
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