JP6753226B2 - Hot-rolled steel and steel parts for steel parts with excellent fit and machinability between fracture surfaces after fracture separation - Google Patents
Hot-rolled steel and steel parts for steel parts with excellent fit and machinability between fracture surfaces after fracture separation Download PDFInfo
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Description
本発明は、破断分割した後に再び破断面同士を嵌合して使用する鋼部品およびその素材である熱間圧延鋼材に関わるものである。特に、熱間鍛造で部品成形した鋼部品用途に関わる。 The present invention relates to a steel part used by fitting the fractured surfaces together again after fracture division and a hot-rolled steel material as a material thereof. In particular, it is related to the use of steel parts formed by hot forging.
自動車エンジン用部品および足廻り用部品は、熱間鍛造で成形を行い、焼入れ焼き戻しといった熱処理（以降、調質とする）、あるいは、熱処理を適用せず（以降、非調質とする）のいずれかで、適用する部品に必要な機械特性を確保する。最近は製造工程における経済効率性の観点から、調質を省略した部品、すなわち、非調質部品が多く普及している。 Parts for automobile engines and suspension parts are formed by hot forging and heat-treated such as quenching and tempering (hereinafter referred to as tempering), or heat treatment is not applied (hereinafter referred to as non-tempering). In either case, ensure the mechanical properties required for the applicable part. Recently, from the viewpoint of economic efficiency in the manufacturing process, many parts without tempering, that is, non-conditioned parts have become widespread.
自動車エンジン用部品の事例としては、コネクティングロッド（以降、コンロッドとする）が挙げられる。この部品はエンジン内でピストン往復運動をクランクシャフトによる回転運動に変換する際に動力を伝達する部品である。コンロッドはクランクシャフトのピン部と称する偏芯部位にコンロッドのキャップ部とロッド部を挟み込んで締結し、ピン部と回転摺動する機構で動力を伝達する。このキャップ部とロッド部を締結するに際して、近年、破断分離型コンロッドが多く採用されている。 An example of a component for an automobile engine is a connecting rod (hereinafter referred to as a connecting rod). This part is a part that transmits power when converting the reciprocating motion of the piston into the rotary motion of the crankshaft in the engine. The connecting rod is fastened by sandwiching the cap portion and the rod portion of the connecting rod in an eccentric portion called the pin portion of the crankshaft, and power is transmitted by a mechanism that rotates and slides with the pin portion. In recent years, many break-separated connecting rods have been adopted for fastening the cap portion and the rod portion.
破断分離型コンロッドとは熱間鍛造等でキャップ部とロッド部が一体となった形状に成形した後、キャップ部とロッド部との境界に相当する部分に切欠きを入れて、破断分離する工法を採用したものである。この工法はキャップ部、ロッド部の合わせ面を破断分離した破面同士を嵌合させるため、合わせ面の機械加工が不要な上に、位置合わせのために施す加工も必要に応じて省略できる。これらから、部品の加工工程を大幅に削減でき、部品製造時の経済効率性は大幅に向上する。 What is a breaking separation type connecting rod? A method of forming a shape in which the cap part and the rod part are integrated by hot forging, etc., and then making a notch in the part corresponding to the boundary between the cap part and the rod part to break and separate. Is adopted. Since this method fits the fractured surfaces separated by breaking the mating surfaces of the cap portion and the rod portion, it is not necessary to machine the mating surfaces, and the processing performed for alignment can be omitted if necessary. From these, the processing process of parts can be significantly reduced, and the economic efficiency at the time of manufacturing parts is greatly improved.
破断分離型コンロッドに供する鋼材として、欧米で普及しているのは、ＤＩＮ規格のＣ７０Ｓ６である。これは０．７ｍａｓｓ％のＣを含む高炭素非調質鋼であり、破断分離時の寸法変化を抑えるため、延性、及び靭性の低いパーライト組織としたものである。Ｃ７０Ｓ６は破断時の破断面近傍の塑性変形量が小さいので破断分離性に優れる一方、現行のコンロッド用鋼である中炭素非調質鋼のフェライト−パーライト組織に比べて組織が粗大であるので、降伏比（降伏強さ／引張強さ）が低く、高い座屈強度が要求される高強度コンロッドには適用できないという問題がある。 The DIN standard C70S6 is widely used in Europe and the United States as a steel material to be used for a breaking separation type connecting rod. This is a high carbon non-treated steel containing 0.7 mass% C, and has a pearlite structure having low ductility and toughness in order to suppress dimensional changes during fracture separation. C70S6 has excellent fracture separability because the amount of plastic deformation near the fracture surface at the time of fracture is small, but it has a coarser structure than the ferrite-pearlite structure of medium carbon non-treated steel, which is the current steel for conrods. There is a problem that it cannot be applied to high-strength conrods that have a low yield ratio (yield strength / tensile strength) and require high buckling strength.
降伏比を高めるためには、炭素量を低く抑さえ、フェライト分率を増加させることが必要である。しかしながら、フェライト分率を増加させると延性が向上して、破断分離時に塑性変形量が大きくなり、クランクシャフトのピン部に締結されるコンロッド摺動部の形状変形が増大し、真円度が低下するといった部品性能上の問題が発生する。
また、近年は高出力ディーゼルエンジンあるいはターボエンジンの普及によるエンジン出力増大に伴い、コンロッドのキャップ部とロッド部のずれ防止、すなわち、嵌合性向上、締結力向上といったニーズがある。このうち、嵌合性向上については破断分離させた面の凹凸を顕著にする鋼材の組織制御が有効である。
In order to increase the yield ratio, it is necessary to keep the carbon content low and increase the ferrite fraction. However, increasing the ferrite fraction improves ductility, increases the amount of plastic deformation during fracture separation, increases the shape deformation of the connecting rod sliding portion fastened to the pin portion of the crankshaft, and reduces roundness. There is a problem with component performance such as
Further, in recent years, with the increase in engine output due to the spread of high-power diesel engines or turbo engines, there is a need to prevent the cap portion and the rod portion of the connecting rod from slipping, that is, to improve the fitting property and the fastening force. Of these, for improving the fitability, it is effective to control the structure of the steel material so that the unevenness of the surface separated by fracture becomes remarkable.
高強度の破断分離型コンロッドに好適な鋼材としていくつかの非調質鋼が提案されている。特許文献１および特許文献２には、ＳｉまたはＰのような脆化元素を多量に添加し、材料自体の延性及び靭性を低下させることによって破断分離性を改善する技術が記載されている。特許文献３および特許文献４には、第二相粒子の析出強化を利用してフェライトの延性および靭性を低下させることによって破断分離性を改善する技術が記載されている。さらに、特許文献５〜７には、Ｍｎ硫化物の形態を制御することによって破断分離性を改善する技術が記載されている。 Several non-microalloyed steels have been proposed as steel materials suitable for high-strength fracture-separated connecting rods. Patent Document 1 and Patent Document 2 describe a technique for improving breakability by adding a large amount of embrittlement element such as Si or P to reduce the ductility and toughness of the material itself. Patent Documents 3 and 4 describe techniques for improving fracture separability by reducing the ductility and toughness of ferrite by utilizing precipitation strengthening of second-phase particles. Further, Patent Documents 5 to 7 describe a technique for improving break separation by controlling the morphology of Mn sulfide.
これらの技術は破断分離した部位の変形量を小さくする一方で、材料を脆くするので、破断分離時、あるいは破断面同士を嵌合させたときに欠けが生じる。破断面の欠けが生じると、嵌合部の位置ずれが生じ、精度よく嵌合できないといった問題が発生する。特に破断面の凹凸を大きくすると、破断時に欠けやひびが発生する頻度が高くなるため、破断面の凹凸の確保と、破断時の欠け及びひびの発生防止との両立が求められていた。欠け、ひびの発生防止の解決策としては、特許文献８に示されるようにＶの偏析を低減することが挙げられる。なお、Ｖは高強度化を目的として添加する化学成分である。 While these techniques reduce the amount of deformation of the fracture-separated portion, they make the material brittle, so that chipping occurs at the time of fracture separation or when the fracture surfaces are fitted together. If the fracture surface is chipped, the fitting portion will be misaligned, causing a problem that accurate fitting cannot be performed. In particular, when the unevenness of the fracture surface is increased, the frequency of chipping and cracking at the time of fracture increases. Therefore, it has been required to secure the unevenness of the fracture surface and prevent the occurrence of chipping and cracking at the time of fracture. As a solution for preventing the occurrence of chipping and cracking, reduction of segregation of V can be mentioned as shown in Patent Document 8. V is a chemical component added for the purpose of increasing the strength.
しかしながら、Ｖの偏析の他にも欠け、ひびの原因がある。実際には、破断面の凹凸が過度に大きい場合、欠け、ひびの発生頻度が高くなる傾向にある。これは、破断面の引張方向の凹凸が形成されると同時に一部に破面方向にもき裂もしくは凹部が形成され、嵌合して破面同士を締結した際に、破面方向に応力印加され、き裂もしくは凹部が応力集中部となって、微細な破壊を起こすと考えられる。一方、破面同士の嵌合性を高めるためには、破断面の凹凸を大きくする必要がある。以上から、破断面の凹凸の顕著化と欠け及びひびの発生防止とは背反の関係があり、その両立は現行の工法では解決できなかった。 However, in addition to the segregation of V, there is a cause of chipping and cracking. In reality, when the unevenness of the fracture surface is excessively large, the frequency of chipping and cracking tends to increase. This is because unevenness in the tensile direction of the fracture surface is formed, and at the same time, cracks or recesses are also formed in a part in the fracture surface direction, and when they are fitted and the fracture surfaces are fastened to each other, stress is generated in the fracture surface direction. It is considered that when applied, the crack or recess becomes a stress concentration part and causes minute fracture. On the other hand, in order to improve the fitability between the fracture surfaces, it is necessary to increase the unevenness of the fracture surface. From the above, there is a contradictory relationship between the remarkable unevenness of the fracture surface and the prevention of chipping and cracking, and the compatibility could not be solved by the current construction method.
上記に加えて、コンロッド製造に際して、ドリルによる穴あけ加工等、切削加工性も重要視される。切削加工性を向上させることにより、作業が効率化され、生産性が向上することで多大な経済効果を生み出すためである。すなわち、機械特性を損なうことなく切削加工性を向上させる必要がある。 In addition to the above, cutting workability such as drilling with a drill is also important in manufacturing connecting rods. This is because the work efficiency is improved by improving the machinability, and the productivity is improved, which produces a great economic effect. That is, it is necessary to improve the machinability without impairing the mechanical properties.
本発明は上記の事情に鑑み、破断分離時の破断面近傍の変形量を小さくし、かつ、破断面の凹凸を大きくして嵌合性を高める一方で、破断面の欠けを抑制し、かつ被削性に優れた熱間圧延鋼材および鋼部品を提供することを目的とする。 In view of the above circumstances, the present invention reduces the amount of deformation in the vicinity of the fracture surface at the time of fracture separation, increases the unevenness of the fracture surface to improve the fit, and suppresses chipping of the fracture surface. An object of the present invention is to provide hot-rolled steel materials and steel parts having excellent machinability.
本発明者は、従来技術と比較して鋼中に存在するＭｎ硫化物の形状を制御することにより、破断時の破面の凹凸および欠けの防止を制御する点に特徴があることを知見した。 The present inventor has found that it is characterized in that it controls the prevention of unevenness and chipping of the fracture surface at the time of fracture by controlling the shape of Mn sulfide existing in the steel as compared with the prior art. ..
その具体的内容は以下のとおりである。
Ｍｎ硫化物は鋼材が棒材として熱間圧延で製造される際に圧延方向である長手方向に伸長化されて分布する。長手方向とほぼ垂直な方向に破断分離する際、この伸長化されたＭｎ硫化物にき裂が到達すると、き裂の方向は大きく変化し、Ｍｎ硫化物と母層の界面に沿って長手方向に伝播する。き裂がＭｎ硫化物端部を過ぎると応力方向に従って、再び長手方向とほぼ垂直な方向にき裂が伝播することにより破断分離が進む。この繰り返しにより破面に凹凸が形成される機構を知見した。
The specific contents are as follows.
The Mn sulfide is elongated and distributed in the longitudinal direction, which is the rolling direction, when the steel material is manufactured as a bar by hot rolling. When a crack reaches this elongated Mn sulfide during fracture separation in a direction substantially perpendicular to the longitudinal direction, the direction of the crack changes significantly, and the longitudinal direction is along the interface between the Mn sulfide and the mother layer. Propagate to. When the crack passes the end of Mn sulfide, the crack propagates again in the direction substantially perpendicular to the longitudinal direction according to the stress direction, so that the fracture separation proceeds. We have discovered the mechanism by which irregularities are formed on the fracture surface by repeating this process.
破面の凹凸形状はＭｎ硫化物の伸長化程度、分布頻度により変化し、破面同士の嵌合性へ影響を及ぼす。すなわち、Ｍｎ硫化物の伸長化が著しい場合は凹凸形状が顕著になることに加えて、過度に凹凸が著しくなると、欠けやひびが発生し、破面同士を嵌合する際に空隙が生じてかみ合わせ精度が低下する。また、伸長化されたＭｎ硫化物の分布頻度が増加すると、破面の凹凸の頻度が増加し、嵌合性が向上する。また、鋼中に微量のＢｉに加えて、Ｓｂ、ＳｎおよびＰｂからなる群から選択される１種または２種以上を含有すると、Ｂｉ、Ｓｂ、Ｓｎ、Ｐｂが結晶界面や母相と介在物との界面に偏析して、被削性が向上することを見出した。
以上の知見をもとに、本発明を完成させた。本発明の要旨は以下のとおりである。
The uneven shape of the fracture surface changes depending on the degree of elongation of Mn sulfide and the distribution frequency, and affects the fitability between the fracture surfaces. That is, when the elongation of Mn sulfide is remarkable, the uneven shape becomes remarkable, and when the unevenness becomes excessively large, chips and cracks occur, and voids are generated when the fractured surfaces are fitted to each other. Engagement accuracy is reduced. Further, when the distribution frequency of the elongated Mn sulfide increases, the frequency of the unevenness of the fracture surface increases, and the fitability is improved. Further, when one or more selected from the group consisting of Sb, Sn and Pb is contained in the steel in addition to a trace amount of Bi, Bi, Sb, Sn and Pb are contained in the crystal interface, the matrix and inclusions. It was found that the machinability was improved by segregation at the interface with.
Based on the above findings, the present invention has been completed. The gist of the present invention is as follows.
（１）化学成分が
Ｃ：０．３５−０．４５ｍａｓｓ％、
Ｓｉ：０．６−１．０ｍａｓｓ％、
Ｍｎ：０．６０−０．９０ｍａｓｓ％、
Ｐ：０．０１０−０．０３５ｍａｓｓ％、
Ｓ：０．０６−０．１０ｍａｓｓ％、
Ｃｒ：０．２５ｍａｓｓ％以下、
Ｖ：０．２０−０．４０ｍａｓｓ％、
Ｚｒ：０．００５０ｍａｓｓ％以下、
Ｎ：０．００６０−０．０１５０ｍａｓｓ％、
Ｂｉ：０．０００１−０．００５０ｍａｓｓ％
を含有し、残部がＦｅ及び不純物であり、更に、
Ｓｂ：０．０００１−０．００５０ｍａｓｓ％、
Ｓｎ：０．０００１−０．００５０ｍａｓｓ％および
Ｐｂ：０．０００１−０．００５０ｍａｓｓ％
からなる群から選択される１種または２種以上を含有することを特徴とする、破断分離後の破断面同士の嵌合性および被削性に優れた鋼部品用の熱間圧延鋼材。
（２）前記化学成分にさらに、
Ｔｉ：０．０５０ｍａｓｓ％以下、
Ｎｂ：０．０３０ｍａｓｓ％以下、
Ｍｇ：０．００５０ｍａｓｓ％以下および
ＲＥＭ：０．００１０ｍａｓｓ％以下
からなる群から選択される１種または２種以上を含有することを特徴とする上記（１）に記載の破断分離後の破断面同士の嵌合性および被削性に優れた鋼部品用の熱間圧延鋼材。
（３）上記（１）または（２）に記載された熱間圧延鋼材からなる鋼部品であり、
前記鋼部品を引張破断させた破面には、引張応力方向に向けて８０μｍ以上の高さで突出する凹凸が前記破面上の任意の方向長さ１０ｍｍあたり２箇所以上の比率で形成され、かつ、前記破面における脆性破壊破面が面積率にして９８％以上であり、更に、破面方向に沿って長さ８０μｍ以上に渡って形成されたき裂または凹部の数が、前記破面の任意の方向長さ１０ｍｍあたり３箇所未満であることを特徴とする破断分離後の破断面同士の嵌合性および被削性に優れた鋼部品。
(1) The chemical composition is C: 0.35-0.45 mass%,
Si: 0.6-1.0 mass%,
Mn: 0.60-0.90 mass%,
P: 0.010-0.035 mass%,
S: 0.06-0.10 mass%,
Cr: 0.25 mass% or less,
V: 0.20-0.40 mass%,
Zr: 0.0050 mass% or less,
N: 0.0060-0.0150 mass%,
Bi: 0.0001-0.0050 mass%
Is contained, the balance is Fe and impurities, and further
Sb: 0.0001-0.0050 mass%,
Sn: 0.0001-0.0050 mass% and Pb: 0.0001-0.0050 mass%
A hot-rolled steel material for steel parts having excellent fitability and machinability between fracture surfaces after fracture separation, which comprises one or more selected from the group consisting of.
(2) In addition to the chemical components
Ti: 0.050 mass% or less,
Nb: 0.030 mass% or less,
The fracture surface after fracture separation according to (1) above, which contains one or more selected from the group consisting of Mg: 0.0050 mass% or less and REM: 0.0010 mass% or less. Hot-rolled steel for steel parts with excellent fit and machinability.
(3) A steel part made of the hot-rolled steel material described in (1) or (2) above.
On the fracture surface obtained by tensile fracture of the steel part, irregularities protruding at a height of 80 μm or more in the tensile stress direction are formed at a ratio of two or more per 10 mm in any direction length on the fracture surface. Moreover, the brittle fracture surface of the fracture surface has an area ratio of 98% or more, and the number of cracks or recesses formed over a length of 80 μm or more along the fracture surface direction is the number of cracks or recesses of the fracture surface. A steel part having excellent fitability and machinability between fracture surfaces after fracture separation, characterized in that the number of locations is less than 3 per 10 mm in any direction.
本発明の熱間圧延鋼材及び鋼部品は、破断分離した際に、破断面近傍の塑性変形量が小さく、かつ、破断面の欠け発生が少なくなる。このため、破断面を嵌合させた場合、位置ずれが生じず、精度よく嵌合でき、鋼部品の精度向上、歩留向上を同時に実現できる。また、鋼中に微量のＢｉに加えて、微量のＳｂ、ＳｎおよびＰｂからなる群から選択される１種または２種以上を含有することにより、被削性を向上できる。また、本発明の熱間圧延鋼材及び鋼部品を用いることにより、欠けを振るい落とす工程を省略することができ、製造コストを低減でき、これにより、産業上の経済効率性の向上に大きな効果がある。 When the hot-rolled steel material and steel parts of the present invention are fractured and separated, the amount of plastic deformation in the vicinity of the fracture surface is small, and the occurrence of chipping of the fracture surface is reduced. Therefore, when the fracture surface is fitted, misalignment does not occur, the fitting can be performed accurately, and the accuracy and yield of steel parts can be improved at the same time. Further, the machinability can be improved by containing one or more selected from the group consisting of a trace amount of Sb, Sn and Pb in addition to a trace amount of Bi in the steel. Further, by using the hot-rolled steel material and steel parts of the present invention, the step of shaking off the chips can be omitted, the manufacturing cost can be reduced, and this has a great effect on the improvement of industrial economic efficiency. is there.
以下、本発明の実施形態である破断分離後の破断面同士の嵌合性および被削性に優れた鋼部品用の熱間圧延鋼材及び破断分離後の破断面同士の嵌合性および被削性に優れた鋼部品について説明する。 Hereinafter, hot-rolled steel materials for steel parts having excellent fitability and machinability between fracture surfaces after fracture separation and workability between fracture surfaces after fracture separation, which are embodiments of the present invention, and workability. Steel parts with excellent properties will be described.
本実施形態の熱間圧延鋼材は、化学成分として、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｃｒ、Ｖ、Ｚｒ、ＮおよびＢｉに加えて、Ｓｂ、ＳｎおよびＰｂからなる群から選択される１種または２種以上を所定の含有率で含む鋼材である。本実施形態の熱間圧延鋼材は、以下に説明する化学成分を含むことで、鋼の延性を低下させて引張破面における脆性破壊破面の割合を向上させ、かつ、ＭｎＳを析出させて破面の凹凸を大きくすることができ、破面同士の嵌合性を高めることができる。また、本実施形態の熱間圧延鋼材は、化学成分として更に、Ｔｉ、Ｎｂ、ＭｇおよびＲＥＭからなる群から選択される１種または２種以上を含有してもよい。
以下、本実施形態の熱間圧延鋼材の化学成分の限定理由について述べる。
The hot-rolled steel material of the present embodiment is selected from the group consisting of Sb, Sn and Pb in addition to C, Si, Mn, P, S, Cr, V, Zr, N and Bi as chemical components1 A steel material containing seeds or two or more seeds at a predetermined content. The hot-rolled steel material of the present embodiment contains the chemical components described below to reduce the ductility of the steel, improve the proportion of brittle fracture surface in the tensile fracture surface, and precipitate MnS to fracture. The unevenness of the surfaces can be increased, and the fitability between the fractured surfaces can be improved. Further, the hot-rolled steel material of the present embodiment may further contain one or more selected from the group consisting of Ti, Nb, Mg and REM as a chemical component.
Hereinafter, the reasons for limiting the chemical composition of the hot-rolled steel material of the present embodiment will be described.
Ｃ：０．３５−０．４５ｍａｓｓ％
Ｃは、本実施形態の熱間圧延鋼材及び鋼部品の引張強さを確保する効果、および、破断時の破断面近傍の塑性変形量を小さくして良好な破断分離性を実現する効果を有する。Ｃの増加に伴いパーライト組織の体積分率が上昇することにより、引張強さが上昇し延性および靭性が低下する。これらの効果を最大限に発揮させるため鋼中のＣ含有量の適正な範囲を０．３５−０．４５ｍａｓｓ％に設定した。この含有量の範囲の上限を超えるとパーライト分率が過大となり破断時の欠けの発生頻度が高くなる。また、含有量の下限に満たない場合は破断面近傍の塑性変形量が増加し嵌合性が低下する。なお、Ｃ含有量に関しては０．３５−０．３８ｍａｓｓ％であれば好ましい。
C: 0.35-0.45 mass%
C has the effect of ensuring the tensile strength of the hot-rolled steel material and the steel parts of the present embodiment, and the effect of reducing the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture to realize good fracture separability. .. As the volume fraction of the pearlite structure increases with the increase in C, the tensile strength increases and the ductility and toughness decrease. In order to maximize these effects, the appropriate range of C content in steel was set to 0.35-0.45 mass%. If the upper limit of this content range is exceeded, the pearlite fraction becomes excessive and the frequency of chipping at break increases. If the content is less than the lower limit, the amount of plastic deformation near the fracture surface increases and the fitability deteriorates. The C content is preferably 0.35-0.38 mass%.
Ｓｉ：０．６−１．０ｍａｓｓ％
Ｓｉは、固溶強化によってフェライトを強化させ延性及び靭性を低下させる。延性及び靭性の低下は破断時の破断面近傍の塑性変形量を小さくし破断分離性を向上させる。この効果を得るためにはＳｉ含有量の下限を０．６ｍａｓｓ％にする必要がある。他方、Ｓｉが過剰に含有すると破断面の欠けが発生する頻度が上昇するので、Ｓｉ含有量の上限を１．０ｍａｓｓ％とする。なお、Ｓｉ含有量に関しては０．７−０．９ｍａｓｓ％が好ましい。
Si: 0.6-1.0 mass%
Si strengthens ferrite by solid solution strengthening and lowers ductility and toughness. The decrease in ductility and toughness reduces the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture and improves fracture separability. In order to obtain this effect, it is necessary to set the lower limit of the Si content to 0.6 mass%. On the other hand, if the Si content is excessive, the frequency of chipping of the fracture surface increases, so the upper limit of the Si content is set to 1.0 mass%. The Si content is preferably 0.7-0.9 mass%.
Ｍｎ：０．６０−０．９０ｍａｓｓ％
Ｍｎは、固溶強化によってフェライトを強化し延性及び靭性を低下させる。延性及び靭性の低下は破断時の破断面近傍の塑性変形量を小さくし破断分離性を向上させる。また、Ｍｎは、Ｓと結合してＭｎ硫化物を形成する。本実施形態の熱間圧延鋼材からなる鋼部品を破断分割させる際に圧延方向に伸長したＭｎ硫化物に沿ってき裂が伝播するので、Ｍｎの含有は破断面の凹凸を大きくして破断面を嵌合する際に位置ずれを防止する効果がある。他方、Ｍｎを過剰に含有する場合、フェライトが硬くなりすぎて破断時の欠けが発生する頻度が増加する。これらを鑑みＭｎ含有量の範囲は０．６０−０９０ｍａｓｓ％である。なお、Ｍｎ含有量に関しては０．７５−０．８５ｍａｓｓ％が好ましい。
Mn: 0.60-0.90 mass%
Mn strengthens ferrite by solid solution strengthening and lowers ductility and toughness. The decrease in ductility and toughness reduces the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture and improves fracture separability. Further, Mn combines with S to form Mn sulfide. When the steel part made of the hot-rolled steel material of the present embodiment is fracture-divided, cracks propagate along the Mn sulfide extending in the rolling direction. Therefore, the inclusion of Mn increases the unevenness of the fracture surface to increase the fracture surface. It has the effect of preventing misalignment during mating. On the other hand, when Mn is excessively contained, the ferrite becomes too hard and the frequency of chipping at break increases. In view of these, the range of Mn content is 0.60-090 mass%. The Mn content is preferably 0.75-0.85 mass%.
Ｐ：０．０１０−０．０３５ｍａｓｓ％
Ｐは、フェライト及びパーライトの延性及び靭性を低下させる。延性及び靭性の低下は破断時の破断面近傍の塑性変形量を小さくし破断分離性を向上させる効果を有する。ただし、Ｐは、同時に結晶粒界の脆化を引き起こし破断面の欠けを発生しやすくする効果が顕著である。従って、Ｐの含有を利用して延性及び靭性を低下させる方法は欠け防止の観点から積極的に活用すべきではない。以上を考慮すればＰ含有量の範囲は０．０１０−０．０３５ｍａｓｓ％であり、さらに、０．０１０−０．０２５ｍａｓｓ％が好ましい。
P: 0.010-0.035 mass%
P reduces the ductility and toughness of ferrite and pearlite. The decrease in ductility and toughness has the effect of reducing the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture and improving the fracture separability. However, P has a remarkable effect of causing embrittlement of grain boundaries at the same time and easily causing chipping of the fracture surface. Therefore, the method of reducing ductility and toughness by utilizing the content of P should not be actively utilized from the viewpoint of preventing chipping. Considering the above, the range of P content is 0.010-0.035 mass%, and more preferably 0.010-0.025 mass%.
Ｓ：０．０６−０．１０ｍａｓｓ％
Ｓは、Ｍｎと結合してＭｎ硫化物を形成する。本実施形態の熱間圧延鋼材からなる鋼部品を破断分割させる際に、圧延方向に伸長したＭｎ硫化物に沿ってき裂が伝播するので、Ｓの含有は破断面の凹凸を大きくし破断面を嵌合する際に位置ずれを防止する効果がある。その効果を得るためにはＳ含有量の下限を０．０６ｍａｓｓ％にする必要がある。他方、Ｓが過剰に含有すると破断分割時の破断面近傍の塑性変形量が増大し破断分離性が低下する場合が発生することに加えて、破断面の欠けを助長することがある。以上から、Ｓ含有量の範囲を０．０６−０．１０ｍａｓｓ％とする。Ｓ含有量の好ましい範囲を０．０７−０．０９ｍａｓｓ％に限定する。
S: 0.06-0.10 mass%
S combines with Mn to form Mn sulfide. When the steel part made of the hot-rolled steel material of the present embodiment is fractured and divided, cracks propagate along the Mn sulfide extending in the rolling direction. Therefore, the inclusion of S increases the unevenness of the fracture surface and increases the fracture surface. It has the effect of preventing misalignment during mating. In order to obtain the effect, the lower limit of the S content needs to be 0.06 mass%. On the other hand, if S is excessively contained, the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture division may increase and the fracture separability may decrease, and in addition, chipping of the fracture surface may be promoted. From the above, the range of S content is 0.06-0.10 mass%. The preferred range of S content is limited to 0.07-0.09 mass%.
Ｃｒ：０．２５ｍａｓｓ％以下
Ｃｒは、Ｍｎと同様に固溶強化によってフェライトを強化し延性及び靭性を低下させる。延性及び靭性の低下は破断時の破断面近傍の塑性変形量を小さくし破断分離性を向上させる。しかし、Ｃｒを過剰に含有するとパーライトのラメラー間隔が小さくなり、かえってパーライトの延性及び靭性が高くなる。そのため、破断時の破断面近傍の塑性変形量が大きくなり破断分離性が低下する。さらに、Ｃｒを過剰に含有するとベイナイト組織が生成しやすくなり破断分離性が大幅に低下する場合がある。従って、Ｃｒを含有させる場合、その含有量を０．２５ｍａｓｓ％以下とする。上述の効果を鑑みた場合、好ましくはＣｒ含有量は０．１２ｍａｓｓ％以下である。
Cr: 0.25 mass% or less Cr strengthens ferrite by solid solution strengthening in the same manner as Mn, and lowers ductility and toughness. The decrease in ductility and toughness reduces the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture and improves fracture separability. However, if Cr is excessively contained, the lamellar interval of pearlite becomes small, and the ductility and toughness of pearlite become high. Therefore, the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture becomes large, and the fracture separability decreases. Further, if Cr is excessively contained, a bainite structure is likely to be formed, and the fracture separability may be significantly lowered. Therefore, when Cr is contained, the content thereof is set to 0.25 mass% or less. In view of the above effects, the Cr content is preferably 0.12 mass% or less.
Ｖ：０．２０−０．４０ｍａｓｓ％
Ｖは、熱間鍛造後の冷却時に主に炭化物又は炭窒化物を形成してフェライトを強化し延性及び靭性を低下させる。延性及び靭性の低下は破断時の破断面近傍の塑性変形量を小さくして熱間圧延鋼材からなる鋼部品の破断分離性を良好にする。また、Ｖは、炭化物又は炭窒化物の析出強化により熱間圧延鋼材の降伏比を高めるという効果がある。これら効果を得るためにはＶ含有量の下限を０．２０ｍａｓｓ％にする必要がある。Ｖ含有量の下限は好ましくは０．２３ｍａｓｓ％である。一方、Ｖを過剰に含有してもその効果は飽和するのでＶ含有量の上限は０．４０ｍａｓｓ％である。好ましくはＶ含有量の上限は０．３５ｍａｓｓ％である。
V: 0.20-0.40 mass%
V mainly forms carbides or carbonitrides during cooling after hot forging to strengthen ferrite and reduce ductility and toughness. The decrease in ductility and toughness reduces the amount of plastic deformation near the fracture surface at the time of fracture and improves the fracture separability of steel parts made of hot-rolled steel. Further, V has an effect of increasing the yield ratio of the hot-rolled steel material by strengthening the precipitation of carbides or carbonitrides. In order to obtain these effects, it is necessary to set the lower limit of the V content to 0.20 mass%. The lower limit of the V content is preferably 0.23 mass%. On the other hand, even if V is excessively contained, the effect is saturated, so the upper limit of the V content is 0.40 mass%. Preferably, the upper limit of the V content is 0.35 mass%.
Ｚｒ：０．００５０ｍａｓｓ％以下
Ｚｒは、酸化物を形成しＭｎ硫化物の晶出核または析出核となりＭｎ硫化物を均一に微細に分散させる。このＭｎ硫化物が破断分割時のき裂の伝播経路となり破断面近傍の塑性変形量を小さくし破断分離性を高める効果がある。ただし、Ｚｒを過剰に含有してもその効果は飽和するのでＺｒ含有量の上限を０．００５０ｍａｓｓ％とする。この効果を十分に発揮するためにはＺｒ含有量の下限を０．０００５ｍａｓｓ％とすることが好ましい。
Zr: 0.0050 mass% or less Zr forms an oxide to become crystallized nuclei or precipitated nuclei of Mn sulfide, and Mn sulfide is uniformly and finely dispersed. This Mn sulfide serves as a propagation path for cracks during fracture splitting, and has the effect of reducing the amount of plastic deformation in the vicinity of the fracture surface and improving fracture separability. However, even if Zr is excessively contained, the effect is saturated, so the upper limit of the Zr content is set to 0.0050 mass%. In order to fully exert this effect, the lower limit of the Zr content is preferably 0.0005 mass%.
Ｎ：０．００６０−０．０１５０ｍａｓｓ％
Ｎは、熱間鍛造後の冷却時に主にＶ窒化物又はＶ炭窒化物を形成してフェライトの変態核として働くことによってフェライト変態を促進する。これにより熱間圧延鋼材からなる鋼部品の破断分離性を大幅に損なうベイナイト組織の生成を抑制する効果がある。この効果を得るにはＮ含有量の下限を０．００６０ｍａｓｓ％とする。Ｎを過剰に含有すると熱間延性が低下し熱間加工時に割れ又は疵が発生しやすくなる場合があるため、Ｎ含有量の上限を０．０１５０ｍａｓｓ％とする。なお、Ｎ含有量に関しては０．００８０−０．０１２０ｍａｓｓ％が好ましい。
N: 0.0060-0.0150 mass%
N promotes ferrite transformation by mainly forming V-nitride or V-carbonitride during cooling after hot forging and acting as a transformation nucleus of ferrite. This has the effect of suppressing the formation of a bainite structure that significantly impairs the fracture separability of steel parts made of hot-rolled steel. To obtain this effect, the lower limit of the N content is set to 0.0060 mass%. If N is excessively contained, the hot ductility is lowered and cracks or defects may easily occur during hot working. Therefore, the upper limit of the N content is set to 0.0150 mass%. The N content is preferably 0.0080-0.0120 mass%.
Ｂｉ：０．０００１−０．００５０ｍａｓｓ％
Ｂｉは、結晶粒界、もしくは母相と介在物との界面に偏析し、界面の結合力を低下させることにより、微量の含有でも切削時の変形抵抗を低下させる効果がある。Ｂｉ含有量の下限を０．０００１ｍａｓｓ％としたが、効果を十分に発揮させるための好ましい範囲としては０．００１５ｍａｓｓ％以上とする。また、Ｂｉ含有量の上限については機械特性の観点から特に指定するものではないが、過剰の含有は鋼の熱間加工性を劣化させ、表面疵の多発等、熱間圧延が困難となる。従って、鋼材の製造性を考慮して０．００５０ｍａｓｓ％とした。さらに製造性を追究する場合、Ｂｉ含有量の上限を０．００３０ｍａｓｓ％とすることが好ましい。
Bi: 0.0001-0.0050 mass%
Bi segregates at the grain boundaries or at the interface between the matrix and inclusions and reduces the bonding force at the interface, so that even a small amount of Bi has the effect of reducing the deformation resistance during cutting. The lower limit of the Bi content is 0.0001 mass%, but the preferable range for fully exerting the effect is 0.0015 mass% or more. Further, the upper limit of the Bi content is not particularly specified from the viewpoint of mechanical properties, but an excessive content deteriorates the hot workability of the steel and makes hot rolling difficult due to frequent occurrence of surface defects. Therefore, it was set to 0.0050 mass% in consideration of the manufacturability of the steel material. Further, when pursuing manufacturability, it is preferable that the upper limit of the Bi content is 0.0030 mass%.
本発明は上記の成分に加えて、Ｓｂ、ＳｎおよびＰｂからなる群から選択される１種または２種以上をそれぞれ、０．０００１−０．００５０ｍａｓｓ％の範囲内で含有することが特徴である。これらの元素は結晶粒界、もしくは母相と介在物との界面に偏析し、界面の結合力を低下させることにより、微量の含有でも切削時の変形抵抗を低下させる効果がある。Ｓｂ、ＳｎおよびＰｂの含有量の下限を０．０００１ｍａｓｓ％としたが、効果を十分に発揮させるための好ましい範囲としては、Ｓｂ、ＳｎおよびＰｂの含有量の下限を０．００１５ｍａｓｓ％とする。また、Ｓｂ、ＳｎおよびＰｂの含有量の上限については機械特性の観点から特に指定するものではないが、過剰の含有は鋼の熱間加工性を劣化させ、表面疵の多発等、熱間圧延が困難となる。従って、鋼材の製造性を考慮して、Ｓｂ、ＳｎおよびＰｂの含有量の上限を０．００５０ｍａｓｓ％とした。製造性の観点から好ましくは、Ｂｉ、Ｓｂ、ＳｎおよびＰｂの合計含有量が０．０００１−０．００５０ｍａｓｓ％であればよい。さらに、製造性の観点から、Ｂｉ、Ｓｂ、ＳｎおよびＰｂの合計含有量の上限は０．００３０ｍａｓｓ％であることがより好ましい。 The present invention is characterized in that, in addition to the above-mentioned components, one or more selected from the group consisting of Sb, Sn and Pb are contained in the range of 0.0001-0.0050 mass%, respectively. .. These elements segregate at the grain boundaries or at the interface between the matrix and inclusions and reduce the bonding force at the interface, so that even a small amount of these elements has the effect of reducing the deformation resistance during cutting. The lower limit of the content of Sb, Sn and Pb is 0.0001 mass%, but the lower limit of the content of Sb, Sn and Pb is 0.0015 mass% as a preferable range for fully exerting the effect. Further, the upper limit of the contents of Sb, Sn and Pb is not particularly specified from the viewpoint of mechanical properties, but the excessive content deteriorates the hot workability of steel and causes hot rolling such as frequent occurrence of surface defects. Becomes difficult. Therefore, in consideration of the manufacturability of the steel material, the upper limit of the contents of Sb, Sn and Pb is set to 0.0050 mass%. From the viewpoint of manufacturability, the total content of Bi, Sb, Sn and Pb may be 0.0001-0.0050 mass%. Further, from the viewpoint of manufacturability, the upper limit of the total content of Bi, Sb, Sn and Pb is more preferably 0.0030 mass%.
本実施形態に係る熱間圧延鋼材は、発明の効果をさらに顕著にするために、更に、Ｔｉ：０．０５０ｍａｓｓ％以下、Ｎｂ：０．０３０ｍａｓｓ％以下、Ｍｇ：０．００５０ｍａｓｓ％以下およびＲＥＭ：０．００１０ｍａｓｓ％以下からなる群から選択される１種または２種以上を選択して含有することができる。 In the hot-rolled steel material according to the present embodiment, in order to further make the effect of the invention more remarkable, Ti: 0.050 mass% or less, Nb: 0.030 mass% or less, Mg: 0.0050 mass% or less and REM: One or more selected from the group consisting of 0.0010 mass% or less can be selected and contained.
Ｔｉ：０．０５０ｍａｓｓ％以下
Ｔｉは、熱間鍛造後の冷却時に主に炭化物又は炭窒化物を形成して析出強化によりフェライトを強化し延性及び靭性を低下させる。延性及び靭性の低下は破断時の破断面近傍の塑性変形量を小さくし破断分離性を向上させる効果がある。しかし、Ｔｉを過剰に含有するとその効果が飽和するので、上述の効果を得るためにＴｉを含有させる場合は、Ｔｉ含有量の上限を０．０５０ｍａｓｓ％とする。Ｔｉの効果を十分に発揮させるためには、Ｔｉ含有量の下限を０．００５ｍａｓｓ％とすることが好ましい。より好適なＴｉ含有量の範囲は０．０１５−０．０３０ｍａｓｓ％である。
Ti: 0.050 mass% or less Ti mainly forms carbides or carbonitrides during cooling after hot forging, strengthens ferrite by precipitation strengthening, and lowers ductility and toughness. The decrease in ductility and toughness has the effect of reducing the amount of plastic deformation near the fracture surface at the time of fracture and improving fracture separability. However, if Ti is contained in excess, the effect is saturated. Therefore, when Ti is contained in order to obtain the above-mentioned effect, the upper limit of the Ti content is set to 0.050 mass%. In order to fully exert the effect of Ti, the lower limit of the Ti content is preferably 0.005 mass%. A more preferred Ti content range is 0.015-0.030 mass%.
Ｎｂ：０．０３０ｍａｓｓ％以下
Ｎｂは、熱間鍛造後の冷却時に主に炭化物又は炭窒化物を形成して析出強化によりフェライトを強化し延性及び靭性を低下させる。延性及び靭性の低下は破断時の破断面近傍の塑性変形量を小さくし良好な破断分離性を得る効果がある。しかし、Ｎｂを過剰に含有するとその効果が飽和するので上述の効果を得るためにＮｂを含有させる場合、Ｎｂ含有量の上限を０．０３０ｍａｓｓ％とする。Ｎｂの効果を十分に発揮させるにためは、Ｎｂ含有量の下限を０．００５ｍａｓｓ％とすることが好ましい。より好適なＮｂ含有量の範囲は０．０１０−０．０３０ｍａｓｓ％である。
Nb: 0.030 mass% or less Nb mainly forms carbides or carbonitrides during cooling after hot forging, strengthens ferrite by precipitation strengthening, and lowers ductility and toughness. The decrease in ductility and toughness has the effect of reducing the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture and obtaining good fracture separability. However, if Nb is excessively contained, the effect is saturated. Therefore, when Nb is contained in order to obtain the above-mentioned effect, the upper limit of the Nb content is set to 0.030 mass%. In order to fully exert the effect of Nb, the lower limit of the Nb content is preferably 0.005 mass%. A more preferred range of Nb content is 0.010-0.030 mass%.
Ｍｇ：０．００５０ｍａｓｓ％以下
Ｍｇは、酸化物を形成しＭｎ硫化物の晶出核または析出核となりＭｎ硫化物を均一に微細に分散させる。このＭｎ硫化物が破断分割時のき裂の伝播経路となり破断面近傍の塑性変形量を小さくし破断分離性を高める効果がある。ただし、Ｍｇが過剰に含有してもその効果は飽和するのでＭｇ含有量の上限を０．００５０ｍａｓｓ％とする。この効果を十分に発揮するためには、Ｍｇ含有量の下限を０．０００５ｍａｓｓ％とすることが好ましい。
Mg: 0.0050 mass% or less Mg forms an oxide and becomes crystallized nuclei or precipitated nuclei of Mn sulfide, and Mn sulfide is uniformly and finely dispersed. This Mn sulfide serves as a propagation path for cracks during fracture splitting, and has the effect of reducing the amount of plastic deformation in the vicinity of the fracture surface and improving fracture separability. However, even if Mg is excessively contained, the effect is saturated, so the upper limit of the Mg content is set to 0.0050 mass%. In order to fully exert this effect, the lower limit of the Mg content is preferably 0.0005 mass%.
ＲＥＭ：０．００１０ｍａｓｓ％
ＲＥＭは、酸硫化物を形成し、Ｍｎ硫化物の晶出核または析出核となりＭｎ硫化物を均一に微細に分散させる。このＭｎ硫化物が破断分割時のき裂の伝播経路となり破断面近傍の塑性変形量を小さくし破断分離性を高める効果がある。ただし、ＲＥＭが過剰に含有すると鋼材製造段階において、鋳造工程でのノズル詰り等の不具合が生じるのでＲＥＭ含有量の上限を０．００１０ｍａｓｓ％とする。この効果を十分に発揮するためには、Ｍｇ含有量の下限を０．０００３ｍａｓｓ％とすることが好ましい。
REM: 0.0010 mass%
REM forms an acid sulfide and becomes a crystallized nucleus or a precipitated nucleus of Mn sulfide to uniformly and finely disperse Mn sulfide. This Mn sulfide serves as a propagation path for cracks during fracture splitting, and has the effect of reducing the amount of plastic deformation in the vicinity of the fracture surface and improving fracture separability. However, if the REM content is excessive, problems such as nozzle clogging in the casting process occur in the steel material manufacturing stage, so the upper limit of the REM content is set to 0.0010 mass%. In order to fully exert this effect, the lower limit of the Mg content is preferably 0.0003 mass%.
本実施形態に係る熱間圧延鋼材の残部は、鉄及び不純物である。不純物とは、鉱石やスクラップ等の原材料及び製造環境から混入するものをいう。さらに、本実施形態に係る熱間圧延鋼材は、上記成分の他、本実施形態に係る鋼の効果を損なわない範囲で、Ｔｅ、Ｚｎ等を含有することができる。 The balance of the hot-rolled steel material according to this embodiment is iron and impurities. Impurities are those that are mixed in from raw materials such as ore and scrap and the manufacturing environment. Further, the hot-rolled steel material according to the present embodiment may contain Te, Zn and the like in addition to the above components as long as the effects of the steel according to the present embodiment are not impaired.
また、本実施形態の熱間圧延鋼材には、鋼内部にＭｎＳが形成される。ＭｎＳは、熱間圧延鋼材の圧延方向に沿って伸長化していることが好ましい。伸長化されたＭｎＳは、鋼部品を引っ張り破断させた破面に凹凸形状を形成するために必須である。ＭｎＳの伸長化は、その実現方法として、鋼材を熱間圧延で製造する際のビレットから棒鋼までの圧延減面率を８０％以上にする必要がある。 Further, in the hot-rolled steel material of the present embodiment, MnS is formed inside the steel. It is preferable that MnS is elongated along the rolling direction of the hot-rolled steel material. The elongated MnS is indispensable for forming an uneven shape on the fracture surface obtained by pulling and breaking the steel part. As a method for realizing the extension of MnS, it is necessary to make the rolling surface reduction rate from the billet to the steel bar 80% or more when the steel material is manufactured by hot rolling.
鋼中のＭｎＳの伸長化の程度は、圧延方向を長軸側としてアスペクト比が１０以上の伸長化されたＭｎＳが１ｍｍ２あたり５０個以上分布することが望ましい。なお、伸長化されたＭｎＳのなかには分断されて圧延方向に列状に凝集して分布するものも観察されるが、それらも１つの伸長ＭｎＳとして計上する。 Regarding the degree of elongation of MnS in steel, it is desirable that 50 or more elongated MnS having an aspect ratio of 10 or more are distributed per 1 mm 2 with the rolling direction as the major axis side. It should be noted that some of the elongated Mns are divided and aggregated and distributed in a row in the rolling direction, but these are also counted as one elongated MnS.
次に、本実施形態の熱間圧延鋼材の製造方法について説明する。
上記の化学成分を有する鋼を転炉で溶製し、連続鋳造することによりブルームを製造する。得られたブルームを、更に分塊圧延工程等を経てビレットとする。得られたビレットをさらに熱間圧延によって丸棒とする。このようにして本実施形態の熱間圧延鋼材を製造する。なお、ビレットから丸棒形状までの圧延減面率は８０％以上とすることが好ましい。これにより、鋼中のＭｎＳを伸長化させることができる。
Next, a method for producing the hot-rolled steel material of the present embodiment will be described.
Bloom is produced by melting steel with the above chemical components in a converter and continuously casting it. The obtained bloom is further subjected to a bulk rolling process or the like to form a billet. The obtained billet is further hot-rolled into a round bar. In this way, the hot-rolled steel material of the present embodiment is manufactured. The rolling surface reduction rate from the billet to the round bar shape is preferably 80% or more. As a result, MnS in the steel can be elongated.
また、得られた熱間圧延鋼材から鋼部品を製造するには、熱間圧延鋼材を例えば１１５０〜１２８０℃に加熱して熱間鍛造し、空冷（大気中での放冷）もしくは衝風冷却（試験片へ風を送り冷却）によって室温まで冷却する。冷却後の鍛造材を切削加工することにより、所定の形状の鋼部品とする。熱間圧延鋼材を鍛造する際は、熱間鍛造に限らず、冷間鍛造してもよい。 Further, in order to manufacture steel parts from the obtained hot-rolled steel material, the hot-rolled steel material is heated to, for example, 1150 to 1280 ° C. and hot forged, and then air-cooled (cooling in the atmosphere) or impulse cooling. Cool to room temperature by (cooling by blowing air to the test piece). By cutting the cooled forged material, a steel part having a predetermined shape is obtained. When forging a hot-rolled steel material, the forging is not limited to hot forging, but cold forging may be used.
本実施形態の熱間圧延鋼材及び鋼部品は、引張破断させた際の破面に、引張応力方向に向けて８０μｍ以上の高さで突出する凹凸が破面上の任意の方向長さ１０ｍｍあたり２箇所以上の比率で形成される。また、破面における脆性破壊破面が面積率にして９８％以上になる。更に、破面方向に沿って長さ８０μｍ以上に渡って形成されたき裂または凹部の数が、破面の任意の方向長さ１０ｍｍあたり３箇所未満になる。 In the hot-rolled steel material and steel parts of the present embodiment, unevenness projecting at a height of 80 μm or more in the tensile stress direction on the fracture surface when tensilely fractured is per arbitrary length of 10 mm on the fracture surface. It is formed in a ratio of two or more places. In addition, the brittle fracture surface on the fracture surface has an area ratio of 98% or more. Further, the number of cracks or recesses formed over a length of 80 μm or more along the fracture surface direction is less than 3 per 10 mm in any direction length of the fracture surface.
破面の性状について規定した理由を述べる。引張破断により分離した破面同士を嵌合させ、破断面と水平方向に応力を加えると、その抵抗力は破面の凹凸により水平方向および２つの法線方向（面内で９０°の傾き方向、および、破断面と垂直方向）に３次元的に分散される。この場合、印加された応力は破面の凹凸が顕著であるほど分散される。また、破面の欠けが生じない前提条件で、破面の凹凸が顕著であることは応力印加時の位置ずれを防ぐ観点からも明らかである。 Describe the reasons for defining the properties of the fracture surface. When the fracture surfaces separated by tensile fracture are fitted to each other and stress is applied in the horizontal direction to the fracture surface, the resistance force is in the horizontal direction and in the two normal directions (in-plane tilt direction of 90 °) due to the unevenness of the fracture surface. , And perpendicular to the fracture surface) are three-dimensionally dispersed. In this case, the applied stress is dispersed so that the unevenness of the fracture surface is remarkable. Further, it is clear from the viewpoint of preventing the displacement when stress is applied that the unevenness of the fracture surface is remarkable under the precondition that the fracture surface is not chipped.
欠けを生じない範囲で破面の凹凸を最大化するためには、特にＭｎＳの形態および分散状態が破断面形状に大きな影響を及ぼすので、ＭｎＳの形態と分散状態を制御することが重要である。より具体的には、き裂伝播の経路となるＭｎＳを多量に分散させること、その一部が適正に伸長化されていることが、破断面の凹凸を顕著にさせることに寄与する。そこで、本発明では破断時に破断面の欠けを発生させない範囲で実験的に実現可能である顕著な破断面の凹凸形状を上記の通りに規定した。 In order to maximize the unevenness of the fracture surface within the range where chipping does not occur, it is important to control the morphology and dispersion state of MnS, since the morphology and dispersion state of MnS have a great influence on the fracture surface shape. .. More specifically, the fact that a large amount of MnS, which is a path for crack propagation, is dispersed and a part of the MnS is appropriately elongated contributes to making the unevenness of the fracture surface remarkable. Therefore, in the present invention, the remarkable uneven shape of the fracture surface, which can be experimentally realized within the range where the fracture surface is not chipped at the time of fracture, is defined as described above.
なお、引張応力方向の凹凸は、破面断面での段差の方向が引張方向に対して４５°以下の角度のものを対象とし、凹凸の長さは対象とする段差を引張方向に投影した長さとして定義する。また、破面方向のき裂または凹部は、破面断面でのき裂または凹部の方向が引張方向に対して４５°超の角度で内部に進展するものを対象とし、き裂または凹部の長さは開始点から、内部の終了点までの距離として定義する。
また、破面の凹凸形状の評価方法は、実施例において述べることとする。
The unevenness in the tensile stress direction is intended for the step direction in the fracture surface cross section at an angle of 45 ° or less with respect to the tensile direction, and the length of the unevenness is the length obtained by projecting the target step in the tensile direction. Defined as a dimension. The cracks or recesses in the fracture surface direction are those in which the direction of the cracks or recesses in the fracture surface cross section extends inward at an angle of more than 45 ° with respect to the tensile direction, and the length of the cracks or recesses. Sa is defined as the distance from the start point to the internal end point.
Further, the method for evaluating the uneven shape of the fracture surface will be described in the examples.
本実施形態の熱間圧延鋼材及び鋼部品は、破断分離した際に、破断面近傍の塑性変形量が小さく、かつ、破断面の欠け発生が少なくなる。このため、破断面を嵌合させた場合、位置ずれが生じず、精度よく嵌合でき、鋼部品の精度向上、歩留向上を同時に実現できる。また、鋼中に微量のＢｉに加えてＳｂ、ＳｎおよびＰｂからなる群から選択される１種または２種以上を含有することにより、被削性を向上できる。また、本実施形態の熱間圧延鋼材及び鋼部品を用いることにより、欠けを振るい落とす工程を省略することができ、製造コストを低減でき、これにより、産業上の経済効率性の向上に大きな効果がある。 When the hot-rolled steel material and steel parts of the present embodiment are fractured and separated, the amount of plastic deformation in the vicinity of the fracture surface is small, and the occurrence of chipping of the fracture surface is reduced. Therefore, when the fracture surface is fitted, misalignment does not occur, the fitting can be performed accurately, and the accuracy and yield of steel parts can be improved at the same time. Further, the machinability can be improved by containing one or more selected from the group consisting of Sb, Sn and Pb in addition to a small amount of Bi in the steel. Further, by using the hot-rolled steel material and steel parts of the present embodiment, the step of shaking off the chips can be omitted, the manufacturing cost can be reduced, and this has a great effect on improving the industrial economic efficiency. There is.
本発明を実施例によって以下に詳述する。なお、これら実施例は本発明の技術的意義、及び効果を説明するためのものであり、本発明の範囲を限定するものではない。 The present invention will be described in detail below by way of examples. It should be noted that these examples are for explaining the technical significance and effect of the present invention, and do not limit the scope of the present invention.
表１および表２に示す組成を有する、転炉で溶製した鋼を連続鋳造することによりブルームを製造し、このブルームを、分塊圧延工程を経て１６２ｍｍ角のビレットとし、さらに熱間圧延によって直径が５６ｍｍの丸棒形状とした。このときのビレットから丸棒形状までの圧延減面率は９０％である。なお、表中の「−」との記号は、記号が記載された箇所に係る元素の含有量が検出限界値以下であることを示している。分塊圧延前のブルームの加熱温度および加熱時間は、それぞれ１２７０℃、および１４０ｍｉｎであり、熱間圧延前のビレットの加熱温度および加熱時間は、それぞれ１２４０℃、および９０ｍｉｎであった。表２の比較鋼の下線部分は、本発明の範囲外であることを示す。 Bloom is produced by continuously casting molten steel having the compositions shown in Tables 1 and 2 in a converter, and this bloom is made into a 162 mm square billet through a slabbing rolling step, and further by hot rolling. It has a round bar shape with a diameter of 56 mm. At this time, the rolling surface reduction rate from the billet to the round bar shape is 90%. The symbol "-" in the table indicates that the content of the element related to the place where the symbol is described is not more than the detection limit value. The heating temperature and heating time of bloom before lump-rolling were 1270 ° C. and 140 min, respectively, and the heating temperature and heating time of billets before hot rolling were 1240 ° C. and 90 min, respectively. The underlined portion of the comparative steel in Table 2 indicates that it is outside the scope of the present invention.
次に、破断分離性を調べるために、鍛造コンロッド相当の試験片を熱間鍛造で作製した。具体的には、直径５６ｍｍ、長さ１００ｍｍの素材棒鋼を、１１５０〜１２８０℃に加熱後、棒鋼の長さ方向に垂直に鍛造して厚さ２０ｍｍとし、空冷（大気中での放冷）もしくは衝風冷却（試験片へ風を送り冷却）によって室温まで冷却した。冷却後の鍛造材から、ＪＩＳ４号引張試験片と、コンロッド大端部相当形状の破断分離性評価用試験片とを切削加工した。ＪＩＳ４号引張試験片は、鍛造材側面から３０ｍｍ位置で長手方向に沿って採取した。破断分離性評価用試験片は、図１に示すとおり、８０ｍｍ×８０ｍｍかつ厚さ１８ｍｍの板形状の中央部に、直径５０ｍｍの穴を開けたものであり、直径５０ｍｍの穴の内面上には、鍛造前の素材である棒鋼の長さ方向に対して±９０度の位置２ヶ所に、深さ１ｍｍかつ、先端曲率０．５ｍｍの４５度のＶノッチ加工を施した。更に、ボルト穴として直径８ｍｍの貫通穴を、その中心線がノッチ加工側の側面から８ｍｍの箇所に位置するように開けた。 Next, in order to investigate the fracture separability, a test piece equivalent to a forged connecting rod was produced by hot forging. Specifically, a material steel bar having a diameter of 56 mm and a length of 100 mm is heated to 1150 to 1280 ° C. and then forged perpendicularly to the length direction of the steel bar to a thickness of 20 mm, and is air-cooled (cooled in the atmosphere) or. It was cooled to room temperature by impulse cooling (cooling by sending air to the test piece). From the forged material after cooling, a JIS No. 4 tensile test piece and a test piece for evaluating fracture separability having a shape corresponding to the large end of the connecting rod were cut. The JIS No. 4 tensile test piece was collected along the longitudinal direction at a position 30 mm from the side surface of the forged material. As shown in FIG. 1, the test piece for evaluation of breakability has a hole with a diameter of 50 mm formed in the center of a plate shape of 80 mm × 80 mm and a thickness of 18 mm, and a hole having a diameter of 50 mm is formed on the inner surface of the hole. At two positions of ± 90 degrees with respect to the length direction of the steel bar, which is the material before forging, V-notch processing with a depth of 1 mm and a tip curvature of 0.5 mm was performed at 45 degrees. Further, a through hole having a diameter of 8 mm was formed as a bolt hole so that the center line was located at a position 8 mm from the side surface on the notch processing side.
破断分離性評価の試験装置は、割型と落錘試験機とから構成されている。割型は長方形の鋼材上に成型した直径４６．５ｍｍの円柱を中心線に沿って２分割した形状で、片方が固定され、片方がレール上を移動する。２つの半円柱の合わせ面にはくさび穴が加工されている。破断試験時には、試験片の直径５０ｍｍの穴をこの割型の直径４６．５ｍｍの円柱にはめ込み、くさびを入れて落錘の上に設置する。落錘は質量２００ｋｇであり、ガイドに沿って落下する仕組みである。落錘を落とすと、くさびが打ち込まれ、試験片は２つに引張破断される。なお、破断時に試験片が割型から遊離しないように、試験片は割型に押し付けられるように周囲を固定されている。 The test device for evaluating breakability is composed of a split mold and a drop weight tester. The split mold has a shape in which a cylinder having a diameter of 46.5 mm molded on a rectangular steel material is divided into two along the center line, one of which is fixed and the other of which moves on a rail. Wedge holes are machined on the mating surfaces of the two semi-cylinders. At the time of the fracture test, a hole having a diameter of 50 mm of the test piece is fitted into this split-shaped cylinder having a diameter of 46.5 mm, a wedge is inserted, and the test piece is placed on a drop weight. The drop weight has a mass of 200 kg and is a mechanism that falls along the guide. When the drop weight is dropped, a wedge is driven in and the test piece is pulled and broken in two. The circumference of the test piece is fixed so that it is pressed against the split mold so that the test piece does not release from the split mold at the time of breaking.
本試験では、落錘高さ１００ｍｍで破断を行い、破断後の試験片をつき合わせてボルト締めし、破断方向の内径と、破断方向に垂直な方向の内径との差を測定し、これを破断分割による変形量とした。その後、破断面をつき合わせて２０Ｎ・ｍのトルクでボルト締めして組み付ける作業とボルトを緩めて破断面を放す作業とを１０回繰り返し、これにより脱落した破片の総重量を破断面の欠け発生量と定義した。この欠け発生量は破断面の破面方向のき裂もしくは凹部の存在と相関がある。すなわち、ある一定の大きさ以上の破面方向のき裂もしくは凹部の箇所が多いほど、欠けの発生量が増加する。これらから、破断面を嵌合する際に破面方向のき裂もしくは凹部がボルト締結時に応力集中部として作用し微細に破断することにより欠けが発生すると考えられる。破断面の欠け発生量が１．０ｍｇを超えるものを不合格とした場合、破面方向のき裂もしくは凹部の箇所を最小限に抑えることが必要であることを知見し、その基準を８０μｍ以上のき裂または凹部の発生が破面方向に破面長さ１０ｍｍあたり３箇所未満であることとした。 In this test, fracture is performed at a height of 100 mm, the test pieces after fracture are put together and bolted, and the difference between the inner diameter in the fracture direction and the inner diameter in the direction perpendicular to the fracture direction is measured and measured. The amount of deformation due to fracture division was used. After that, the work of assembling the fractured surfaces together and tightening the bolts with a torque of 20 Nm and the work of loosening the bolts and releasing the fractured surface were repeated 10 times, and as a result, the total weight of the fallen fragments was chipped. Defined as quantity. The amount of this chipping correlates with the presence of cracks or recesses in the fracture surface direction of the fracture surface. That is, the more cracks or recesses in the fracture surface direction having a certain size or more, the more the amount of chips generated increases. From these, it is considered that a crack or a recess in the fracture surface direction acts as a stress concentration portion when the bolt is fastened when the fracture surface is fitted, and the fracture occurs finely. If a fracture surface with a chipping amount of more than 1.0 mg is rejected, it is found that it is necessary to minimize the cracks or recesses in the fracture surface direction, and the standard is 80 μm or more. It was decided that cracks or recesses were generated at less than 3 locations per 10 mm of fracture surface length in the fracture surface direction.
破断分離性については破断面の破壊形態が脆性的であること、および、破断分離による破面近傍の変形量が小さいことが望ましい。具体的には、破面形態に関して、へき開割れ、擬へき開割れもしくは粒界割れなどで構成される脆性破面の面積率が９８％以上となること、破面近傍の変形量が１００μｍ以下であることを良好な破断分離性を確保するための基準とした。
破面同士の嵌合性を高めるためには破断面の引張方向の凹凸が顕著となること、高い頻度で存在することが同時に達成されることが必要である。その基準として、破断面の長さ１０ｍｍあたり引張応力方向の凹凸が８０μｍ以上の凹凸が２箇所以上の比率で凹凸が形成されることを基準とした。
Regarding the fracture separability, it is desirable that the fracture shape of the fracture surface is brittle and that the amount of deformation in the vicinity of the fracture surface due to fracture separation is small. Specifically, regarding the fracture surface morphology, the area ratio of the brittle fracture surface composed of cleavage cracks, pseudo-cleavage cracks, grain boundary cracks, etc. is 98% or more, and the amount of deformation in the vicinity of the fracture surface is 100 μm or less. This was used as a standard for ensuring good break separation.
In order to improve the fitability between the fracture surfaces, it is necessary that the unevenness of the fracture surface in the tensile direction becomes remarkable and that it exists at a high frequency at the same time. As a standard, the unevenness in the tensile stress direction per 10 mm in the length of the fracture surface was 80 μm or more, and the unevenness was formed at a ratio of two or more.
破面の凹凸形状の測定は試験片を引張方向に切断し、破面断面を観察することにより引張方向の凹凸、破面方向の凹凸を測定した。なお、測定は任意の５視野で実施した。具体的には１０ｍｍあたりの引張方向の凹凸、破面方向の凹凸、き裂の大きさを測定し、それぞれ８０μｍ以上の凹凸もしくはき裂に関してはその測定された箇所数を数え、１０ｍｍあたりの発生頻度として各サンプルで平均値を求めた。上記に示す破断面の凹凸状況の評価に用いた断面観察写真の事例を図２に示す。 To measure the uneven shape of the fracture surface, the test piece was cut in the tensile direction, and the unevenness in the tensile direction and the unevenness in the fracture surface direction were measured by observing the cross section of the fracture surface. The measurement was carried out in any five visual fields. Specifically, the unevenness in the tensile direction, the unevenness in the fracture surface direction, and the size of the crack per 10 mm are measured, and for the unevenness or crack of 80 μm or more, the number of measured points is counted and the occurrence per 10 mm occurs. The average value was calculated for each sample as the frequency. FIG. 2 shows an example of a cross-section observation photograph used for evaluating the unevenness of the fracture surface shown above.
表３に示すように、製造Ｎｏ．１〜１７の本発明例はいずれも目標を達成しており、破断分離性に優れ、同時に嵌合性が良好であることがわかった。また、製造Ｎｏ．１〜２８については、鋼中のＭｎＳのうち、圧延方向を長軸側としてアスペクト比が１０以上の伸長化されたＭｎＳは、１ｍｍ２あたり５０個以上分布していた。
一方、表２に示すように、製造Ｎｏ．１８〜３８は、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｃｒ、Ｖ、Ｚｒ、Ｎ、ＢｉおよびＳｂ、Ｓｎ、Ｐｂの含有量のいずれかが本発明の範囲から外れている。これらは以下の理由により、表４に示すように、本発明の要件を満たしていない。
As shown in Table 3, Production No. It was found that all of the examples of the present invention 1 to 17 achieved the target, and were excellent in break separation and at the same time good fit. In addition, the production No. Regarding 1 to 28, among the MnS in the steel, 50 or more elongated MnS having an aspect ratio of 10 or more with the rolling direction as the major axis side were distributed per 1 mm 2 .
On the other hand, as shown in Table 2, the production No. In 18 to 38, any of the contents of C, Si, Mn, P, S, Cr, V, Zr, N, Bi and Sb, Sn, Pb is out of the scope of the present invention. These do not meet the requirements of the present invention, as shown in Table 4, for the following reasons.
製造Ｎｏ．１８、２０、２４、２９、３２はそれぞれＣ、Ｓｉ、Ｐ、Ｖ、Ｎの含有量が本発明の範囲の下限未満であり、破断分離時の塑性変形量が良好な破断分離性の条件である１００μｍを超える。
製造Ｎｏ．１９、２１、２３、２５はそれぞれＣ、Ｓｉ、Ｍｎ、Ｐの含有量が本発明の範囲の上限を超えており、破断時の欠け発生量が１．０ｍｇを超える。
製造Ｎｏ．２２はＭｎの含有量が本発明の範囲の下限未満であり、ＭｎＳの体積分率、伸長化度が不十分であり、破面の凹凸箇所数が本発明の要件に満たない。
Manufacturing No. The contents of C, Si, P, V, and N of 18, 20, 24, 29, and 32 are less than the lower limit of the range of the present invention, respectively, and the amount of plastic deformation at the time of fracture separation is good under the condition of fracture separability. It exceeds a certain 100 μm.
Manufacturing No. In 19, 21, 23, and 25, the contents of C, Si, Mn, and P each exceed the upper limit of the range of the present invention, and the amount of chipping at break exceeds 1.0 mg.
Manufacturing No. In No. 22, the Mn content is less than the lower limit of the range of the present invention, the volume fraction of MnS and the degree of elongation are insufficient, and the number of uneven portions on the fracture surface does not meet the requirements of the present invention.
製造Ｎｏ．２６はＳの含有量が本発明の範囲の上限を超えており、破断時の欠け発生量が１．０ｍｇを超えるとともに、破断分離時の塑性変形量が良好な破断分離性の条件である１００μｍを超える。
製造Ｎｏ．２７はＳの含有量が本発明の範囲の下限未満であり、ＭｎＳの体積分率、伸長化度が不十分であり、破面の凹凸箇所数が本発明の要件に満たない。
製造Ｎｏ．２８はＣｒの含有量が本発明の範囲の上限を超えており、破断分離時の塑性変形量が良好な破断分離性の条件である１００μｍを超える。
Manufacturing No. In No. 26, the content of S exceeds the upper limit of the range of the present invention, the amount of chipping at break exceeds 1.0 mg, and the amount of plastic deformation at break separation is 100 μm, which is a condition for good break separation. Exceed.
Manufacturing No. In No. 27, the content of S is less than the lower limit of the range of the present invention, the volume fraction of MnS and the degree of elongation are insufficient, and the number of uneven portions on the fracture surface does not meet the requirements of the present invention.
Manufacturing No. In No. 28, the Cr content exceeds the upper limit of the range of the present invention, and the amount of plastic deformation at the time of fracture separation exceeds 100 μm, which is a condition for good fracture separation.
製造Ｎｏ．３０はＺｒが含有されておらず、Ｍｎ硫化物の分布が粗に分散し、破面の凹凸箇所数が本発明の要件に満たないとともに、破断分離時の塑性変形量が良好な破断分離性の条件である１００μｍを超える。
製造Ｎｏ．３１はＮの含有量が本発明の範囲の上限を超えており、鋼材製造段階、すなわち、鋳造および熱間圧延段階で疵を多発させ、鋼部品に適用する素材として不適となる。
製造Ｎｏ．３３〜３６はＢｉおよびＳｂ、Ｓｎ、Ｐｂの含有量が本発明の上限を超えており、鋳造および熱間圧延段階で表面疵を多発させ、鋼部品に適用する素材として不適となる。
製造Ｎｏ．３７、３８はＢｉの含有量が本発明の下限未満であり、かつ、Ｓｂ、Ｓｎ、Ｐｂの含有量が本発明の範囲内であるが、Ｓｂ、ＳｎおよびＰｂの含有量の合計が本発明の好ましい範囲である０．００５０％を超えており、鋳造および熱間圧延段階で表面疵を多発させ、鋼部品に適用する素材として不適となる。
Manufacturing No. No. 30 does not contain Zr, the distribution of Mn sulfide is roughly dispersed, the number of uneven portions on the fracture surface does not meet the requirements of the present invention, and the amount of plastic deformation at the time of fracture separation is good. It exceeds 100 μm, which is the condition of.
Manufacturing No. In No. 31, the content of N exceeds the upper limit of the range of the present invention, which causes frequent defects in the steel material manufacturing stage, that is, in the casting and hot rolling stages, and is unsuitable as a material applied to steel parts.
Manufacturing No. The contents of Bi, Sb, Sn, and Pb of 33 to 36 exceed the upper limit of the present invention, which causes frequent surface defects in the casting and hot rolling stages, making them unsuitable as materials applied to steel parts.
Manufacturing No. In 37 and 38, the content of Bi is less than the lower limit of the present invention, and the content of Sb, Sn, Pb is within the range of the present invention, but the total content of Sb, Sn and Pb is the present invention. It exceeds 0.0050%, which is a preferable range of, and causes frequent surface defects in the casting and hot rolling stages, making it unsuitable as a material to be applied to steel parts.
被削性に関しては、先に述べた直径５６ｍｍの熱間圧延鋼材を直径２５ｍｍまで熱間鍛造した後、長さ５００ｍｍに切断し、ＮＣ旋盤を用いて、下記の条件で旋削加工し、被削性を調査した。 Regarding machinability, the hot-rolled steel material with a diameter of 56 mm mentioned above is hot-forged to a diameter of 25 mm, cut to a length of 500 mm, and turned under the following conditions using an NC lathe to be machined. I investigated the sex.
切りくず処理性は、以下の方法で評価した。
被削性試験中の１０秒間で排出された切りくずを回収した。回収された切りくずの長さを調べ、長いものから順に１０個の切りくずを選択した。選択された１０個の切りくずの総重量を「切りくず重量」と定義した。切りくずが長くつながった結果、切りくずの総数が１０個未満である場合、回収された切りくずの総重量を測定し、１０個の個数に換算した値を「切りくず重量」と定義した。例えば、切りくずの総数が７個であって、その総重量が１２ｇである場合、切りくず重量は、１２ｇ×１０個／７個、と計算した。被削性評価に用いたチップは、母材材質：超硬Ｐ２０種グレード、コーティング：なし、である。また、旋削加工条件は、周速：１５０ｍ／ｍｉｎ、送り：０．２ｍｍ／ｒｅｖ、切り込み：０．４ｍｍ、潤滑：水溶性切削油使用、である。各マークの切りくず重量が１５ｇ以下であれば、切りくず処理性が高いと判断した。切りくず重量が１５ｇを超える場合、切りくず処理性が低いと評価した。Ｂｉに加えて、Ｓｂ、ＳｎおよびＰｂからなる群から選択される１種または２種以上を含有する鋼についてはいずれも切りくず重量が１５ｇ以下であるのに対し、Ｂｉ、Ｓｂ、ＳｎおよびＰｂを含有しない製造Ｎｏ.１８〜２１は切りくず重量が１５ｇを超え、被削性に劣る。
The chip controllability was evaluated by the following method.
Chips discharged in 10 seconds during the machinability test were collected. The length of the collected chips was examined, and 10 chips were selected in order from the longest one. The total weight of the 10 selected chips was defined as "chip weight". When the total number of chips was less than 10 as a result of long-term connection of chips, the total weight of the collected chips was measured, and the value converted into the number of 10 pieces was defined as "chip weight". For example, when the total number of chips is 7, and the total weight thereof is 12 g, the chip weight is calculated to be 12 g × 10 pieces / 7 pieces. The insert used for the machinability evaluation is a base material: carbide P20 grade, coating: none. The turning conditions are peripheral speed: 150 m / min, feed: 0.2 mm / rev, depth of cut: 0.4 mm, and lubrication: use of water-soluble cutting oil. When the chip weight of each mark was 15 g or less, it was judged that the chip controllability was high. When the chip weight exceeded 15 g, it was evaluated that the chip controllability was low. In addition to Bi, steels containing one or more selected from the group consisting of Sb, Sn and Pb have a chip weight of 15 g or less, whereas Bi, Sb, Sn and Pb. Production Nos. 18 to 21 not containing the above have a chip weight of more than 15 g and are inferior in machinability.
実施例の鋼材は、熱間鍛造後に空冷または衝風冷却した後、破断分割を行った際に、破断面近傍の塑性変形量が小さく且つ破断面の欠け発生が少ない、優れた破断分離性を有する。また、実施例の鋼材は、破断面の塑性変形量が小さく、さらに欠け発生が少ないという特徴により、破断面の嵌合時に位置ずれが生じることなく精度良く破断面を嵌合させることができ、部品製造の歩留まりを向上させる。また、この特徴により、欠けを振るい落とす工程を省略することができ、製造コストの低減につながり、このことは産業上極めて効果が大きい。さらに、実施例の鋼材を熱間鍛造してなる部品は、被削性に優れているので、部品製造時の作業が効率化され、生産性を向上することができる。 The steel material of the example has excellent fracture separability, in which the amount of plastic deformation in the vicinity of the fracture surface is small and the fracture surface is less likely to be chipped when fracture splitting is performed after air cooling or impulse cooling after hot forging. Have. Further, the steel material of the example has a feature that the amount of plastic deformation of the fracture surface is small and the occurrence of chipping is small, so that the fracture surface can be fitted accurately without causing misalignment when fitting the fracture surface. Improve the yield of parts manufacturing. In addition, this feature makes it possible to omit the step of shaking off chips, which leads to a reduction in manufacturing cost, which is extremely effective in industry. Further, since the part obtained by hot forging the steel material of the embodiment has excellent machinability, the work at the time of manufacturing the part can be made more efficient and the productivity can be improved.
１・・・試験片、２・・・穴、３・・・Ｖノッチ、４・・・貫通穴。 1 ... test piece, 2 ... hole, 3 ... V notch, 4 ... through hole.
Claims (3)
Ｃ：０．３５−０．４５ｍａｓｓ％、
Ｓｉ：０．６−１．０ｍａｓｓ％、
Ｍｎ：０．６０−０．９０ｍａｓｓ％、
Ｐ：０．０１０−０．０３５ｍａｓｓ％、
Ｓ：０．０６−０．１０ｍａｓｓ％、
Ｃｒ：０．２５ｍａｓｓ％以下、
Ｖ：０．２０−０．４０ｍａｓｓ％、Ｚｒ：０．００５０ｍａｓｓ％以下、
Ｎ：０．００６０−０．０１５０ｍａｓｓ％、
Ｂｉ：０．０００１−０．００５０ｍａｓｓ％
を含有し、残部がＦｅ及び不純物であり、更に、
Ｓｂ：０．０００１−０．００５０ｍａｓｓ％、
Ｓｎ：０．０００１−０．００５０ｍａｓｓ％および
Ｐｂ：０．０００１−０．００５０ｍａｓｓ％
からなる群から選択される１種または２種以上を含有することを特徴とする、破断分離後の破断面同士の嵌合性および被削性に優れた鋼部品用の熱間圧延鋼材。 Chemical composition is C: 0.35-0.45 mass%,
Si: 0.6-1.0 mass%,
Mn: 0.60-0.90 mass%,
P: 0.010-0.035 mass%,
S: 0.06-0.10 mass%,
Cr: 0.25 mass% or less,
V: 0.20-0.40 mass%, Zr: 0.0050 mass% or less,
N: 0.0060-0.0150 mass%,
Bi: 0.0001-0.0050 mass%
Is contained, the balance is Fe and impurities, and further
Sb: 0.0001-0.0050 mass%,
Sn: 0.0001-0.0050 mass% and Pb: 0.0001-0.0050 mass%
A hot-rolled steel material for steel parts having excellent fitability and machinability between fracture surfaces after fracture separation, which comprises one or more selected from the group consisting of.
Ｔｉ：０．０５０ｍａｓｓ％以下、
Ｎｂ：０．０３０ｍａｓｓ％以下、Ｍｇ：０．００５０ｍａｓｓ％以下および
ＲＥＭ：０．００１０ｍａｓｓ％以下
からなる群から選択される１種または２種以上を含有することを特徴とする請求項１に記載の破断分離後の破断面同士の嵌合性および被削性に優れた鋼部品用の熱間圧延鋼材。 In addition to the chemical components
Ti: 0.050 mass% or less,
The first aspect of claim 1, wherein one or more selected from the group consisting of Nb: 0.030 mass% or less, Mg: 0.0050 mass% or less, and REM: 0.0010 mass% or less is contained. A hot-rolled steel material for steel parts that has excellent fitability and machinability between fracture surfaces after fracture separation.
前記鋼部品を引張破断させた破面には、引張応力方向に向けて８０μｍ以上の高さで突出する凹凸が前記破面上の任意の方向長さ１０ｍｍあたり２箇所以上の比率で形成され、かつ、前記破面における脆性破壊破面が面積率にして９８％以上であり、更に、破面方向に沿って長さ８０μｍ以上に渡って形成されたき裂または凹部の数が、前記破面の任意の方向長さ１０ｍｍあたり３箇所未満であることを特徴とする破断分離後の破断面同士の嵌合性および被削性に優れた鋼部品。 A steel part made of the hot-rolled steel material according to claim 1 or 2.
On the fracture surface obtained by tensile fracture of the steel part, irregularities protruding at a height of 80 μm or more in the tensile stress direction are formed at a ratio of two or more per 10 mm in any direction length on the fracture surface. Moreover, the brittle fracture surface of the fracture surface has an area ratio of 98% or more, and the number of cracks or recesses formed over a length of 80 μm or more along the fracture surface direction is the number of cracks or recesses of the fracture surface. A steel part having excellent fitability and machinability between fracture surfaces after fracture separation, characterized in that the number of locations is less than 3 per 10 mm in any direction.
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