JP6488774B2 - Hot rolled steel and steel parts for steel parts with excellent fit between fractured surfaces after fracture separation - Google Patents
Hot rolled steel and steel parts for steel parts with excellent fit between fractured 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 to be used by fitting the fractured surfaces again after the fracture division, and to a hot rolled steel material as a material thereof. In particular, it relates 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。 Car engine parts and undercarriage parts are molded by hot forging and either heat treatment such as quenching and tempering (hereinafter referred to as tempering) or no heat treatment is applied (hereinafter referred to as non-tempering). Either way, ensure the mechanical properties required for the part to be applied.
自動車エンジン用部品の事例として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 an automotive engine component is a connecting rod (hereinafter referred to as a connecting rod). This component is a component that transmits power when the piston reciprocating motion is converted into the rotational motion by the crankshaft in the engine. The connecting rod is fastened with a cap portion and a rod portion of the connecting rod sandwiched and fastened to an eccentric portion called a pin portion of the crankshaft, and transmits power by a mechanism that rotates and slides with the pin portion. In fastening the cap part and the rod part, in recent years, a fracture separation type connecting rod has been widely used.
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寮略できる。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。 A break-separated connecting rod is a method of forming a cap and rod part in an integrated shape by hot forging, etc., and then cutting and separating the part corresponding to the boundary between the cap part and the rod part. Is adopted. In this construction method, the fracture surfaces obtained by breaking and separating the mating surfaces of the cap part and the rod part are fitted to each other, so that machining of the mating surfaces is not required and processing for alignment can be omitted if necessary. . As a result, the machining process for the parts can be greatly reduced, and the economic efficiency during the production of the parts can be 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。 As a steel material to be used for the fracture separation type connecting rod, DIN standard C70S6 is widely used in Europe and the United States. This is a high carbon non-tempered steel containing 0.7 mass% C, and has a pearlite structure with low ductility and toughness in order to suppress dimensional changes during fracture separation. C70S6 is excellent in fracture separability because the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture is small, while the structure is coarse compared to the ferrite-pearlite structure of medium carbon non-tempered steel that is the current connecting rod steel, There is a problem that the yield ratio (yield strength / tensile strength) is low and it cannot be applied to high strength connecting rods that 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。 In order to increase the yield ratio, it is necessary to increase the ferrite fraction even if the carbon content is kept low. 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 decreases the roundness. This causes a problem in the performance of the parts.
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。 Further, in recent years, with the increase in engine output due to the widespread use of high-power diesel engines or turbo engines, there is a need for prevention of displacement between the cap portion and the rod portion of the connecting rod, that is, improved fitting and improved fastening force. Among these, for the improvement of the fitting property, it is effective to control the structure of the steel material that makes the unevenness of the fractured and separated surface 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硫化物の携帯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-tempered 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 fracture separation by adding a large amount of an embrittlement element such as Si or P and reducing the ductility and toughness of the material itself. Patent Document 3 and Patent Document 4 describe a technique for improving fracture separability by reducing precipitation ductility and toughness of ferrite by utilizing precipitation strengthening of second phase particles. Furthermore, Patent Documents 5 to 7 describe techniques for improving fracture separation by controlling the carrying 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。 These techniques make the material brittle while reducing the amount of deformation at the site of fracture separation, so that chipping occurs at the time of fracture separation or when fracture surfaces are fitted together. If the fracture surface is chipped, the position of the fitting portion is displaced, causing a problem that the fitting cannot be performed accurately. In particular, when the unevenness of the fracture surface is increased, the frequency of occurrence of cracks and cracks at the time of breakage increases. Therefore, it has been demanded to ensure the fracture surface irregularities and prevent the occurrence of cracks and cracks at the time of fracture. As a solution for preventing the occurrence of chipping and cracking, as shown in Patent Document 8, it is possible to reduce the segregation of V. 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 segregation of V, there are also causes of cracks and cracks. Actually, when the unevenness of the fracture surface is excessively large, the frequency of occurrence of chipping and cracking tends to increase. This is because when the irregularities in the tensile direction of the fracture surface are formed, cracks or recesses are also formed in part in the fracture surface direction, and when the fracture surfaces are fitted and fastened together, the stress in the fracture surface direction is It is considered that cracks or recesses are applied to the stress concentration part and cause fine fracture. On the other hand, in order to improve the fit 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 prominence of fractured surface irregularities and the prevention of chipping and cracking, and both of them cannot be solved by the current construction method.
本発明は上記の事情に鑑み、破断分離時の破断面近傍変形量を小さくし、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 deformation near the fractured surface during fracture separation, and increases the irregularities of the fractured surface to improve the fit, while hot rolling that suppresses fracture of the fractured surface It aims at providing steel materials and steel parts.
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、破断時の破断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 by controlling the shape of Mn sulfide present in steel as compared with the prior art, it is characterized by controlling the unevenness of the fracture surface and the prevention of chipping at the time of fracture . .
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断面に凹凸が形成される機構を知見した。 The specific contents are as follows. Mn sulfide is elongated and distributed in the longitudinal direction, which is the rolling direction, when the steel material is manufactured by hot rolling as a bar material. When the crack reaches the elongated Mn sulfide when breaking and separating in a direction substantially perpendicular to the longitudinal direction, the crack direction changes greatly, and the longitudinal direction along the interface between the Mn sulfide and the mother layer Propagate to. When the crack passes the end of the Mn sulfide, the crack propagates in the direction substantially perpendicular to the longitudinal direction again according to the stress direction, so that fracture separation proceeds. The mechanism by which irregularities are formed on the fracture surface by repeating this process has been found.
破断面の凹凸形状はＭｎ硫化物の伸長化程度、分布頻度により変化し、破断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、破断面同士を嵌合する際に空隙が生じて嵌合精度が低下する。また、伸長化されたＭｎ硫化物の分布頻度が増加すると破断面の凹凸の頻度が増加し、嵌合性が向上する。 Extension of approximately concave-convex shape is Mn sulfide of fracture surface, varies with the distribution frequency, it affects the fitting property of the fracture faces. That is, when the elongation of Mn sulfide is remarkable, the uneven shape becomes remarkable, and when the unevenness becomes excessively large, chipping and cracking occur, and voids are generated when fitting the fractured surfaces together. The fitting accuracy is reduced. Further, when the distribution frequency of the elongated Mn sulfide is increased, the frequency of unevenness of the fracture surface is increased, and the fitting property is improved.
他方、Ｍｎ硫化物の伸長化程度、分布頻度等の形態を制御するには、従来はＣａ、ＺｒあるいはＭｇを添加することが有効であるが、これらの元素を添加せずともＭｎ濃度を低減することにより、同様の形態に制御することが可能である。ただし、Ｍｎ濃度が低くなり、かつ、Ｓ濃度が高くなると高温域での割れが発生しやすくなり、特に連続鋳造で鋳片を製造する際に連続鋳造設備での湾曲部および曲げ戻し部で表面割れが高い頻度で発生する。このため、低Ｍｎ濃度、高Ｓ濃度の鋼材を製造するには、鋳片割れの防止策についても検討が必要であった。
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。
On the other hand, adding Ca, Zr, or Mg is effective for controlling the form of elongation, distribution frequency, etc. of Mn sulfide, but the Mn concentration is reduced without adding these elements. By doing so, it is possible to control to the same form. However, if the Mn concentration is low and the S concentration is high, cracks are likely to occur in the high temperature range, and particularly when the slab is produced by continuous casting, the surface is bent and bent back in the continuous casting equipment. Cracks occur frequently. For this reason, in order to manufacture a steel material having a low Mn concentration and a high S concentration, it has been necessary to study measures for preventing slab cracking.
Based on the above knowledge, 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：１．０〜１．９ｍａｓｓ％、
Ｍｎ：０．１０〜０．２０ｍａｓｓ％、
Ｐ：０．０１０〜０．０３５ｍａｓｓ％、
Ｓ：０．０６〜０．１０ｍａｓｓ％、
Ｃｒ：０．２５ｍａｓｓ％以下、
Ｖ：０．２０〜０．４０ｍａｓｓ％、
Ｎ：０．００６０〜０．０１５０ｍａｓｓ％、
Ｂ：０．００５０ｍａｓｓ％以下を含有し、
残部が鉄及び不純物からなる
ことを特徴とする、破断分離後の破断面同士の嵌合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
のうちの１種または２種を含有することを特徴とする上記（１）記載の破断分離後の破断面同士の嵌合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とともに、破断面を有する鋼部品であり、
前記破断面が、引張応力方向に向けて８０μｍの高さで突出する凹凸が前記破断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、前記破断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、破断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、前記破断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に優れた鋼部品。
(1) The chemical component is C: 0.35 to 0.45 mass%,
Si: 1.0 to 1.9 mass%,
Mn: 0.10 to 0.20 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%,
N: 0.0060-0.0150 mass%,
B: contains 0.0050 mass% or less ,
A hot-rolled steel material for steel parts excellent in fitting property between fractured surfaces after fracture separation, wherein the balance is made of iron and impurities .
(2) In addition to the chemical component,
Ti: 0.050 mass% or less,
Nb: Hot rolling for steel parts excellent in fitting property between fractured surfaces after fracture separation according to (1) above, containing one or two of 0.030 mass% or less Steel material.
(3) A steel part made of the hot-rolled steel described in (1) or (2) above and having a fracture surface ,
The fracture surface is uneven projecting in the 80μm toward the tensile stress direction height formed in any direction length ratio of the two or more positions per 10mm on the fracture surface, and broken brittle fracture in the fracture surface The surface area is 98% or more in terms of area ratio, and the number of cracks or recesses formed over the length of 80 μm or more along the fracture surface direction is 3 at every 10 mm in the length of the fracture surface. A steel part excellent in fitting property between fractured surfaces after fracture separation, characterized by being less than.
本発明の鋼材及び鋼部品は、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、破断面の嵌合をさせた場合、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、本発明の鋼材及び鋼部品を
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 steel material and steel part of the present invention are separated by fracture, the amount of plastic deformation in the vicinity of the fractured surface is small, and chipping of the fractured surface is reduced. For this reason, when the fractured surface is fitted, misalignment does not occur, the fitting can be performed with high accuracy, and the accuracy of steel parts and the yield can be improved at the same time. In addition, the presence of the steel material and steel parts of the present invention can eliminate the step of scraping off the chip and can reduce the manufacturing cost, which has a great effect on improving industrial economic efficiency.
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に優れた鋼部品について説明する。 Hereinafter, a hot-rolled steel material for steel parts excellent in fitting property between fractured surfaces after fracture separation and a steel part excellent in fitting property between fractured surfaces after fracture separation according to an embodiment of the present invention will be described. To do.
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、Ｎ及びＢ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を析出させて破断面の凹凸を大きくすることができ、破断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のうちの１種または２種を含有してもよい。 The hot-rolled steel material of the present embodiment is a steel material containing C, Si, Mn, P, S, Cr, V, N, and B as chemical components at a predetermined content rate. The hot-rolled steel material of the present embodiment includes the chemical components described below, thereby reducing the ductility of the steel and improving the ratio of the brittle fracture fracture surface in the tensile fracture surface, and depositing MnS to break the fracture. The unevenness of the cross section can be increased, and the fit between the fractured surfaces can be improved. Moreover, the hot-rolled steel material of the present embodiment may further contain one or two of Ti and Nb as chemical components.
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。
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り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濃度の適正な範囲を０．３５〜０．４５ｍａｓｓ％に設定した。この範囲の上限濃度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、下限濃度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濃度に関しては０．３５〜０．３８ｍａｓｓ％であればより好ましい。
Hereinafter, the reasons for limiting the chemical components of the hot rolled steel material of the present embodiment will be described.
C: 0.35-0.45 mass%
C has the effect of ensuring the tensile strength of the hot-rolled steel material and steel parts of the present embodiment, and the effect of realizing good fracture separation by reducing the amount of plastic deformation near the fracture surface at the time of fracture. As the volume fraction of the pearlite structure increases as C increases, the tensile strength increases and the ductility and toughness decrease. In order to maximize these effects, an appropriate range of C concentration in steel was set to 0.35 to 0.45 mass%. When the upper limit concentration in this range is exceeded, the pearlite fraction becomes excessive and the frequency of occurrence of chipping at the time of fracture increases. On the other hand, when the lower limit concentration is not reached, the amount of plastic deformation in the vicinity of the fracture surface increases and the fitting property decreases. In addition, regarding C density | concentration, if it is 0.35-0.38 mass%, it is more preferable.
Ｓｉ：１．０〜１．９ｍａｓｓ％
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１．０ｍａｓｓ％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、上限は１．９ｍａｓｓ％とする。なお、Ｓｉ濃度に関しては１．０〜１．４ｍａｓｓ％がより好ましい。
Si: 1.0-1.9 mass%
Si strengthens ferrite by solid solution strengthening and decreases 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 fracture separability. In order to obtain this effect, the lower limit of the Si content needs to be 1.0 mass%. On the other hand, if the Si content is excessive, the frequency of occurrence of chipping of the fracture surface increases, so the upper limit is 1.9 mass%. The Si concentration is more preferably 1.0 to 1.4 mass%.
Ｍｎ：０．１０〜０．２０ｍａｓｓ％
ＭｎはＳと結合してＭｎ硫化物を形成する。Ｍｎ濃度が０．１０〜０．２０ｍａｓｓ％の範囲であれば、Ｍｎ硫化物の大半が固相域で生成されるので、微細かつ高密度で分布する。他方、一部のＭｎ硫化物は鋼を鋳造で凝固させる際に固相と液相の界面で生成し、比較的大きなサイズとなる。このＭｎ硫化物は後続の熱間圧延で圧延方向に伸長化して鋼中に分布する。本実施形態の熱間圧延鋼材からなる鋼部品を破断させた場合にこれらの微細二分したＭｎ硫化物と伸長化したＭｎ硫化物に沿ってき裂が進展することになり、良好な破断分離性と顕著な破断面の凹凸形状の形成が実現する。本発明は、Ｚｒ、Ｃａ、Ｍｇ等のＭｎ硫化物の形態を制御する合金元素を添加することなく、上記に示すＭｎ硫化物の形態を制御するものである。Ｍｎ濃度が０．１０ｍａｓｓ％未満の場合は伸長化されたＭｎ硫化物の個数が減少し、破断面の凹凸形状を顕著にすることができない。また、Ｍｎ濃度が０．２０ｍａｓｓ％を超えると微細なＭｎ硫化物の個数が足らず、破断分離性が低下するとともに、破断面方向に欠け、ひびの発生が顕著となり、嵌合性が低下する。なお、より好ましいＭｎ濃度の範囲は０．１５〜０．２０ｍａｓｓ％である。
Mn: 0.10 to 0.20 mass%
Mn combines with S to form Mn sulfide. When the Mn concentration is in the range of 0.10 to 0.20 mass%, most of the Mn sulfide is generated in the solid phase region, so that it is finely and densely distributed. On the other hand, some Mn sulfides are formed at the interface between the solid phase and the liquid phase when the steel is solidified by casting, and have a relatively large size. This Mn sulfide is elongated in the rolling direction by subsequent hot rolling and distributed in the steel. When a steel part made of the hot-rolled steel material according to the present embodiment is broken, cracks develop along these finely divided Mn sulfides and elongated Mn sulfides. The formation of an uneven shape with a remarkable fracture surface is realized. The present invention controls the form of Mn sulfide shown above without adding an alloy element that controls the form of Mn sulfide such as Zr, Ca, and Mg. When the Mn concentration is less than 0.10 mass%, the number of elongated Mn sulfides decreases and the uneven shape of the fracture surface cannot be made remarkable. On the other hand, if the Mn concentration exceeds 0.20 mass%, the number of fine Mn sulfides is insufficient, and the fracture separability is lowered, cracking occurs in the direction of the fractured surface, cracks are prominent, and fitting properties are lowered. A more preferable range of Mn concentration is 0.15 to 0.20 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の添加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濃度の好適な範囲は０．０１０〜０．０３５ｍａｓｓ％であり、さらに、０．０１０〜０．０２５ｍａｓｓ％がより好ましい。
P: 0.010-0.035 mass%
P decreases the ductility and toughness of ferrite and pearlite. The reduction 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 fracture separation. However, P has a remarkable effect of causing embrittlement of the grain boundary and facilitating chipping of the fracture surface. Therefore, the method of reducing ductility and toughness using the addition of P should not be actively used from the viewpoint of chipping prevention. Considering the above, the preferable range of the P concentration is 0.010 to 0.035 mass%, and more preferably 0.010 to 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の好適な範囲を０．０６〜０．１０ｍａｓｓ％とする。さらにより好ましい範囲として０．０７〜０．０９ｍａｓｓ％の濃度に限定する。
S: 0.06-0.10 mass%
S combines with Mn to form Mn sulfide. Since cracks propagate along the Mn sulfide elongated in the rolling direction when the steel part made of the hot-rolled steel material of this embodiment is divided into fractures, the inclusion of S increases the irregularities of the fracture surface and fits the fracture surface. There is an effect of preventing misalignment when combining. In order to obtain the effect, the lower limit of the S content needs to be 0.06 mass%. On the other hand, when S is excessively contained, the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture division increases and the fracture separability may decrease, and in addition, the fracture of the fracture surface may be promoted. From the above, the preferable range of S is set to 0.06 to 0.10 mass%. As a still more preferable range, the concentration is limited to 0.07 to 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、その濃度を０．２５ｍａｓｓ％以下とする。上述の効果を鑑みた場合、より好ましくは０．１２ｍａｓｓ％以下である。
Cr: 0.25 mass% or less Cr, like Mn, strengthens ferrite by solid solution strengthening and decreases 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 fracture separability. However, when Cr is contained excessively, the lamellar spacing of pearlite is reduced, and on the contrary, the ductility and toughness of pearlite are increased. For this reason, the amount of plastic deformation in the vicinity of the fracture surface at the time of fracture increases and the fracture separability decreases. Further, when Cr is excessively contained, a bainite structure is likely to be generated, and the break separation property may be significantly reduced. Therefore, when it contains Cr, the density | concentration shall be 0.25 mass% or less. In view of the above effects, the content is more 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 lower 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 the fracture separability of steel parts made of hot-rolled steel. V has the effect of increasing the yield ratio of hot rolled steel by precipitation strengthening of carbides or carbonitrides. In order to obtain these effects, the lower limit of V content needs to be 0.20 mass%. The lower limit of the V content is preferably 0.23 mass%. On the other hand, since the effect is saturated even if V is contained excessively, the upper limit of V content is 0.40 mass%. Preferably, the upper limit of V content is 0.35 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濃度に関しては０．００８０〜０．０１２０ｍａｓｓ％がより好ましい。
N: 0.0060-0.0150 mass%
N promotes ferrite transformation by forming V nitride or V carbonitride mainly 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 separation of steel parts made of hot-rolled steel. In order to obtain this effect, the lower limit of the N content is set to 0.0060 mass%. If N is contained excessively, the hot ductility is lowered and cracking or flaws are likely to occur during hot working, so the upper limit of the N content is 0.0150 mass%. The N concentration is more preferably 0.0080 to 0.0120 mass%.
Ｂ：０．００５０ｍａｓｓ％以下
Ｂは焼入れ性を向上させる元素として代表的な化学成分である。本発明の特徴であるＭｎが低濃度であることに伴い、鋼材の焼入れ性が低下するがその低下代を補う元素として添加するものである。Ｂ相度に関して微量添加でも効果が認められるが好ましい下限は０．０００８ｍａｓｓ％以上である。また、Ｂによる焼入れ性向上効果は飽和するので上限については０．００５０ｍａｓｓ％とした。ただし、好ましい上限は０．００３５ｍａｓｓ％である。
B: 0.0050 mass% or less B is a typical chemical component as an element for improving hardenability. With the low concentration of Mn, which is a feature of the present invention, the hardenability of the steel material is reduced, but it is added as an element to compensate for the reduction allowance. Although an effect is recognized even if it is added in a small amount with respect to the B phase, a preferable lower limit is 0.0008 mass% or more. Moreover, since the hardenability improvement effect by B is saturated, the upper limit was set to 0.0050 mass%. However, a preferable upper limit is 0.0035 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、及び、Ｎｂ：０．０３０ｍａｓｓ％以下のうちの１種または２種を選択して含有することができる。 In order to make the effect of the invention more remarkable, the hot-rolled steel material according to the present embodiment further includes one or two of Ti: 0.050 mass% or less and Nb: 0.030 mass% or less. It 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、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 forms a carbide or carbonitride mainly during cooling after hot forging, strengthens ferrite by precipitation strengthening, and lowers ductility and toughness. The reduction 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 fracture separation. However, when Ti is contained excessively, the effect is saturated. Therefore, when Ti is contained to obtain the above-described effect, the upper limit of the Ti content is set to 0.050 mass%. In order to sufficiently exhibit the effect of Ti, the lower limit of the Ti content is preferably set to 0.005 mass%. A more preferable range of Ti content is 0.015 to 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 decreases ductility and toughness. The reduction 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 separation. However, when Nb is contained excessively, the effect is saturated. Therefore, when Nb is contained in order to obtain the above effect, the upper limit of the Nb content is set to 0.030 mass%. In order to fully exhibit the effect of Nb, the lower limit of the Nb content is preferably set to 0.005 mass%. A more preferable range of the Nb content is 0.010 to 0.030 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、及びＳｎ等を含有することができる。 The balance of the hot rolled steel material according to the present embodiment is iron and impurities. Impurities are those mixed from raw materials such as ores and scraps and the manufacturing environment. Furthermore, the hot-rolled steel material according to the present embodiment can contain Te, Zn, Sn, and the like as long as the effects of the steel according to the present embodiment are not impaired in addition to the above components.
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断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減面率を少なくとも８０％以上にする必要がある。 Moreover, MnS is formed in steel inside the hot rolled steel material of this embodiment. MnS is preferably elongated along the rolling direction of the hot-rolled steel material. Elongated MnS is indispensable for forming an uneven shape on a fractured surface obtained by pulling and breaking a steel part. As a method for realizing the elongation of MnS, it is necessary to make the area reduction rate from billet to steel bar at least 80% or more when manufacturing a steel material 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。 The degree of elongation of MnS in the steel is desirably such that 50 or more elongated MnS having an aspect ratio of 10 or more are distributed per mm 2 with the rolling direction as the major axis side. Although some elongated MnS are divided and aggregated and distributed in a row in the rolling direction, they 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、インゴットプロセスによって鋳造する。鋳造品は、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, the manufacturing method of the hot rolled steel material of this embodiment is demonstrated.
Steel having the above chemical components is melted in a converter and cast by an ingot process. The cast product is made into a billet through a block rolling process and the like. The obtained billet is further formed into a round bar by hot rolling. Thus, the hot rolled steel material of this embodiment is manufactured. The rolling area reduction rate from billet to round bar shape is preferably 80% or more. Thereby, MnS in steel can be extended.
インゴットプロセスは、連続鋳造プロセスとは異なり、通常採用される湾曲型連続鋳造機による鋳造時の曲げ応力等、高温割れの原因となる応力が発生しないので、高温割れ対策が不要になる。インゴットプロセスと同様に高温割れ対策が不要なプロセスとしては、垂直型連続鋳造機による鋳造が挙げられる。また、湾曲型連続鋳造機を使用する場合であっても、鋳片の表層部の化学成分を高温割れが抑制できるような成分とし、鋳片の内部の成分を本発明成分とする複層型鋳片とすれば、高温割れの抑制が可能になる。 Unlike the continuous casting process, the ingot process does not generate stress that causes hot cracking, such as bending stress during casting by a curved continuous casting machine that is normally employed, and therefore no countermeasures against hot cracking are required. As with the ingot process, a process that does not require countermeasures against hot cracking includes casting by a vertical continuous casting machine. In addition, even when a curved continuous casting machine is used, the chemical component of the surface layer portion of the slab is a component capable of suppressing high-temperature cracking, and the multi-layer type in which the component inside the slab is the present invention component If it is a slab, it becomes possible to suppress hot cracking.
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）もしくは一部もしくは衝風冷却（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。 Moreover, in order to manufacture a steel part 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 air-cooled (cooled in the atmosphere) or partially or Cool to room temperature by blast cooling (wind is sent to the test piece to cool it). By cutting the forged material after cooling, a steel part having a predetermined shape is obtained. When forging hot-rolled steel, it is not limited to hot forging, and 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断面に、引張応力方向に向けて８０μｍの高さで突出する凹凸が破断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、破断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、破断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、破断面の任意の方向長さ１０ｍｍあたり３箇所未満になる。 Hot rolled steel and steel parts of the present embodiment, the tensile rupture rupture surface when allowed per any direction length 10mm on irregularities projecting height of 80μm toward the tensile stress direction fracture surfaces 2 It is formed at a ratio that is greater than or equal to the location. Further, the brittle fracture fracture surface in the fracture surface becomes 98% or more in terms of area ratio. Furthermore, 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 .
破断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断面同士を嵌合させ、破断面と水平方向に応力を加えると、その抵抗力は破断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断面の凹凸が顕著であるほど分散される。また、破断面の欠けが生じない前提条件で、破断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。 The reason why the properties of the fracture surface are specified will be described. When fracture surfaces separated by tensile fracture are fitted to each other and stress is applied in the horizontal direction with the fracture surface, the resistance is in the horizontal direction and two normal directions (inclination direction of 90 ° in the plane) due to the unevenness of the fracture surface. , And in a direction perpendicular to the fracture surface). In this case, the applied stress is dispersed as the unevenness of the fracture surface becomes more prominent. Further, a prerequisite for chipping of fracture surface does not occur, that the unevenness of the fracture surface is remarkable is evident also from the viewpoint of preventing the positional deviation at the time of stress application.
欠けを生じない範囲で破断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凹凸形状を上記の通りに規定した。
In order to maximize the irregularities of the fractured surface within a range where no chipping occurs, it is important to control the morphology and the dispersed state of MnS, especially since the morphology and dispersion state of MnS greatly affect the fractured surface shape. . More specifically, a large amount of MnS serving as a crack propagation path and a part of the MnS being properly elongated contribute to making the fracture surface unevenness remarkable.
Accordingly, in the present invention, a remarkable fracture surface uneven shape that can be experimentally realized within a range in which no fracture of the fracture surface occurs at the time of fracture is defined as described above.
なお、引張応力方向の凹凸は、破断面の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、破断面方向のき裂または凹部は、破断面の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。 In addition, the unevenness in the tensile stress direction is intended for the case where the step direction in the cross section of the fracture surface is an angle of 45 ° or less with respect to the tensile direction, and the length of the unevenness is projected in the tensile direction. Define as length. Further, crack or recess in the fracture surface direction is directed to those that progress to the inside 45 ° greater angle direction with respect to the tensile direction of Crack or recess in the cross section of the fracture surfaces, crack or recess The length is defined as the distance from the start point to the internal end point.
また、破断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。 Moreover, the evaluation method of the uneven | corrugated shape of a torn surface shall be described in an Example.
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、破断面の嵌合をさせた場合、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、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 chipping of the fracture surface is reduced. For this reason, when the fractured surface is fitted, misalignment does not occur, the fitting can be performed with high accuracy, and the accuracy of steel parts and the yield can be improved at the same time. Further, by using the hot-rolled steel material and steel parts of the present embodiment, it is possible to omit the step of scraping off the chip, and to reduce the manufacturing cost, thereby greatly 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 invention is described in detail below by means of examples. These examples are for explaining the technical significance and effects of the present invention, and do not limit the scope of the present invention.
表１に示す組成を有する、転炉で溶製した鋼をインゴットプロセスで鋳造したのち、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の棒鋼形状とした。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。Ｘ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１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。 After steel melted in a converter having the composition shown in Table 1 was cast by an ingot process, it was made into a billet of 162 mm square through a block rolling process, and further formed into a steel bar shape having a diameter of 56 mm by hot rolling. The rolling area reduction rate from billet to round bar shape at this time is 90%. In addition, the symbol “-” in the table indicates that the content of the element related to the portion where the symbol is described is equal to or less than the detection limit value. The heating temperature and heating time of the bloom before X-slab rolling were 1270 ° C. and 140 min, respectively, and the heating temperature and heating time of the billet before hot rolling were 1240 ° C. and 90 min, respectively. The underlined portion of the comparative steel in Table 1 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成した。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、油焼入れ、衝風冷却（試験片へ風を送り冷却）、もしくは空冷（大気中での放冷）のいずれか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 separation, a test piece corresponding to a forged connecting rod was prepared by hot forging. Specifically, a steel bar having a diameter of 56 mm and a length of 100 mm is heated to 1150 to 1280 ° C., then forged perpendicularly to the length direction of the steel bar to a thickness of 20 mm, oil quenching, blast cooling (to the test piece) It was cooled to room temperature by either air cooling (air cooling) or air cooling (cooling in the air). From the forged material after cooling, a JIS No. 4 tensile test piece and a test piece for evaluation of fracture separation having a shape corresponding to the connecting rod large end were cut. A JIS No. 4 tensile test piece was sampled along the longitudinal direction at a position of 30 mm from the side surface of the forged material. As shown in FIG. 1, the test piece for fracture separation evaluation is a plate-shaped central portion of 80 mm × 80 mm and thickness 18 mm with a 50 mm diameter hole formed on the inner surface of the 50 mm diameter hole. Then, V-notch processing of 45 ° with a depth of 1 mm and a tip curvature of 0.5 mm was performed at two positions of ± 90 ° with respect to the length direction of the steel bar which is a material before forging. Further, a through hole having a diameter of 8 mm was opened as a bolt hole so that the center line thereof was located at a position of 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 apparatus for evaluation of breaking separation is composed of a split mold and a falling weight tester. The split mold is a shape in which a 46.5 mm diameter cylinder formed on a rectangular steel material is divided into two along the center line. One side is fixed and one side moves on the rail. Wedge holes are machined on the mating surfaces of the two semi-cylinders. At the time of the break test, a hole with a diameter of 50 mm of the test piece is fitted into this split mold with a diameter of 46.5 mm, and a wedge is placed on the falling weight. The falling weight has a mass of 200 kg and is a mechanism that falls along the guide. When the falling weight is dropped, a wedge is driven and the test piece is pulled and broken in two. Note that the periphery of the test piece is fixed so as to be pressed against the split mold so that the test piece is not released 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断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断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断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、破断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断面方向に破断面長さ１０ｍｍあたり３箇所未満であることとした。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。 In this test, the test piece was ruptured at a drop weight height of 100 mm, the test pieces after rupture were put together and bolted together, and the difference between the inner diameter in the rupture direction and the inner diameter in the direction perpendicular to the rupture direction was measured. The amount of deformation due to fracture splitting was used. After that, the process of attaching the broken surfaces together with bolts with a torque of 20 N · m and assembling them and the process of loosening the bolts and releasing the broken surfaces are repeated 10 times, and the total weight of the broken pieces is generated. Defined as quantity. This amount of chipping is correlated with the presence of cracks or recesses in the fracture surface direction of the fracture surface . That is, the larger the number of cracks or recesses in the direction of the fracture surface that is greater than a certain size, the greater the amount of chipping. From these, it is considered that when a fracture surface is fitted, a crack or a concave portion in the fracture surface direction acts as a stress concentration portion at the time of bolt fastening, and a chipping occurs due to fine fracture. Knowing that it is necessary to minimize the number of cracks or recesses in the direction of the fracture surface when the amount of cracks generated on the fracture surface exceeds 1.0 mg, the criterion is 80 μm or more. The number of occurrences of cracks or recesses in the fracture surface direction was less than 3 per 10 mm of the fracture surface length. The example of the cross-sectional observation photograph used for evaluation of the unevenness | corrugation state of the torn surface shown above is shown in FIG.
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、破断分離による破断面近傍の変形量が小さいことが望ましい。具体的には、破断面形態に関して、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％となること、破断面近傍の変形量は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。 Regarding the fracture separation, it is desirable that the fracture mode of the fracture surface is brittle and that the deformation near the fracture surface due to fracture separation is small. Specifically, regarding the fracture surface form, the area ratio of a brittle fracture surface composed of cleavage cracks, pseudo-cleavage cracks, or grain boundary cracks is 98%, and the deformation near the fracture surface is 100 μm or less. Was used as a standard for ensuring good break separation.
破断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。 In order to improve the fitting property between the fractured surfaces, it is necessary that the irregularities in the tensile direction of the fractured surfaces become prominent and that they exist at a high frequency at the same time. The criterion was that the irregularities with a tensile stress direction of 80 μm or more were formed at a ratio of 2 or more at a ratio of 2 or more per 10 mm of the fracture surface length.
破断面の凹凸形状の測定は試験片を引張方向に切断し、破断面の断面を観察することにより引張方向の凹凸、破断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、破断面方向の凹凸、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。
Measurements of the uneven shape of the fracture surface was cut a test piece in the tensile direction and the tensile direction of the irregularities by observing the cross-section of the fracture surface was measured unevenness of fracture surface direction. In addition, the measurement was implemented with arbitrary five visual fields. Specifically, the unevenness in the tensile direction per 10 mm, the unevenness in the direction of the fracture surface , and the size of the cracks were measured, and each unevenness or crack of 80 μm or more was counted and the number of occurrences per 10 mm was counted. The average value was obtained for each sample as the frequency.
表２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．１〜１７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。 As shown in Table 2, the production No. It was found that all of the inventive examples 1 to 17 achieved the target and were excellent in break separation property and at the same time good fitting property. In addition, production No. For 1 to 17, among the MnS in the steel, MnS aspect ratio is 10 or more extended the rolling direction as the long axis side, was distributed 1 mm 2 per 50 or more.
一方、製造Ｎｏ．１８〜３１は、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｃｒ、Ｖ、Ｎの濃度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、本発明の要件を満たしていない。 On the other hand, production No. As for 18-31, the density | concentration of C, Si, Mn, P, S, Cr, V, and N is outside the range of the present invention. These do not meet the requirements of the present invention for the following reasons.
製造Ｎｏ．１８、２０、２２、２４、２７、３１はそれぞれＣ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｎの濃度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、２６、２８はそれぞれＣ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｃｒの濃度が本発明の範囲の上限を超えており、破断時の欠け発生が１．０ｍｇを超える。
製造Ｎｏ．２９はＶの濃度が本発明の範囲の下限未満であり、脆性破壊面積率が９８％未満になる。
製造Ｎｏ．３０はＮの濃度が本発明の範囲の上限を超えており、製造時の鋼材疵が多発し、特性評価が行えなかった。
Production No. 18, 20, 22, 24, 27, and 31 each have a concentration of C, Si, Mn, P, S, and N that is less than the lower limit of the range of the present invention, and the amount of plastic deformation during break separation is good. This is over 100 μm.
Production No. Nos. 19, 21, 23, 25, 26 and 28 have C, Si, Mn, P, S and Cr concentrations exceeding the upper limit of the range of the present invention, and the occurrence of chipping at break exceeds 1.0 mg.
Production No. No. 29 has a V concentration below the lower limit of the range of the present invention, and a brittle fracture area ratio of less than 98%.
Production No. In No. 30, the concentration of N exceeded the upper limit of the range of the present invention, and many steel flaws were produced at the time of production, so that characteristic evaluation could not be performed.
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。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。 The steel materials of the examples have excellent fracture separability, in which the amount of plastic deformation in the vicinity of the fracture surface is small and chipping of the fracture surface is small when the fracture division is performed after air cooling or blast cooling after hot forging. . Due to the feature that the amount of plastic deformation of the fractured surface is small and the occurrence of chipping is small, it is possible to fit the fractured surface with high accuracy without causing displacement during fitting of the fractured surface, and to improve the yield of component manufacturing. In addition, this feature makes it possible to omit the step of scraping off chips, leading to a reduction in manufacturing costs, which is extremely effective in industry.
１…試験片、２…穴、３…Ｖノッチ、４…貫通穴。 DESCRIPTION OF SYMBOLS 1 ... Test piece, 2 ... Hole, 3 ... V notch, 4 ... Through-hole.
Claims (3)
Ｃ：０．３５〜０．４５ｍａｓｓ％、
Ｓｉ：１．０〜１．９ｍａｓｓ％、
Ｍｎ：０．１０〜０．２０ｍａｓｓ％、
Ｐ：０．０１０〜０．０３５ｍａｓｓ％、
Ｓ：０．０６〜０．１０ｍａｓｓ％、
Ｃｒ：０．２５ｍａｓｓ％以下、
Ｖ：０．２０〜０．４０ｍａｓｓ％、
Ｎ：０．００６０〜０．０１５０ｍａｓｓ％、
Ｂ：０．００５０ｍａｓｓ％以下を含有し、
残部が鉄及び不純物からなる
ことを特徴とする、破断分離後の破断面同士の嵌合性に優れた鋼部品用の熱間圧延鋼材。 Chemical component is C: 0.35-0.45 mass%,
Si: 1.0 to 1.9 mass%,
Mn: 0.10 to 0.20 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%,
N: 0.0060-0.0150 mass%,
B: contains 0.0050 mass% or less ,
A hot-rolled steel material for steel parts excellent in fitting property between fractured surfaces after fracture separation, wherein the balance is made of iron and impurities .
Ｔｉ：０．０５０ｍａｓｓ％以下、
Ｎｂ：０．０３０ｍａｓｓ％以下
のうちの１種または２種を含有することを特徴とする請求項１記載の破断分離後の破断面同士の嵌合性に優れた鋼部品用の熱間圧延鋼材。 In addition to the chemical component,
Ti: 0.050 mass% or less,
The hot-rolled steel material for steel parts having excellent fitting property between fractured surfaces after fracture separation according to claim 1, characterized in that it contains one or two of Nb: 0.030 mass% or less. .
前記破断面が、引張応力方向に向けて８０μｍの高さで突出する凹凸が前記破断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、前記破断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、破断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、前記破断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に優れた鋼部品。 A steel part comprising the hot-rolled steel according to claim 1 or 2 and having a fracture surface ,
The fracture surface is uneven projecting in the 80μm toward the tensile stress direction height formed in any direction length ratio of the two or more positions per 10mm on the fracture surface, and broken brittle fracture in the fracture surface The surface area is 98% or more in terms of area ratio, and the number of cracks or recesses formed over the length of 80 μm or more along the fracture surface direction is 3 at every 10 mm in the length of the fracture surface. A steel part excellent in fitting property between fractured surfaces after fracture separation, characterized by being less than.
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