JP5667502B2 - Friction welding machine structural steel and friction welding parts - Google Patents
Friction welding machine structural steel and friction welding parts Download PDFInfo
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本発明は、摩擦圧接される用途に適した機械構造用の鋼材および摩擦圧接された摩擦圧接部品に関する。 The present invention relates to a steel material for machine structure suitable for a friction welding application and a friction welding component subjected to friction welding.
例えば、自動車のエンジン、変速機、差動機などに用いられるピストンピンなどのエンジン部品、歯車、シャフト、コンロッドなどの鋼製の機械構造部品は、近年、省エネルギー化による車体重量の軽量化に伴い、小型化が追求されている。そして、自動車などのエンジンの高出力化に伴い、前記小型化との相乗作用で、これら機械構造部品への負荷は増大しつつある。このため、これらの機械構造部品には、基本的な要求特性である強度、靭性に加えて、衝撃特性、曲げ疲労特性、面圧疲労特性といった各種特性の向上がより求められている。 For example, engine parts such as piston pins used in automobile engines, transmissions, differentials, etc., and steel mechanical structural parts such as gears, shafts, connecting rods, etc. in recent years have been accompanied by a reduction in vehicle weight due to energy savings. Miniaturization is being pursued. And with the increase in the output of engines such as automobiles, the load on these mechanical structural parts is increasing due to the synergistic effect with the downsizing. For this reason, these mechanical structural parts are required to improve various characteristics such as impact characteristics, bending fatigue characteristics, and surface fatigue characteristics, in addition to basic required characteristics such as strength and toughness.
通常、これら機械構造部品の素材である鋼材には、加工性に優れた鋼材（肌焼き鋼、フェライトとパーライトとの混合組織）が用いられる。この鋼材は、通常、熱間圧延や熱間鍛造による棒材や線材などへの加工後に、冷間鍛造などの冷間加工が施された上で、機械構造部品形状に精密な切削・仕上げ加工が行われている。ここで、上記のように負荷増大に対応した機械構造部品の素材として、素材である機械構造用鋼材の強度、靭性を高くすると、前記冷間加工、精密な切削加工が著しく困難となる。したがって、前記高強度、高靭性と冷間加工性を兼備した鋼材が求められるが、強度と冷間加工性は相反する関係にあり、単一の機械構造用鋼材で、強度と冷間加工性とを両立させることは著しく困難である。 Usually, steel materials excellent in workability (hardened steel, mixed structure of ferrite and pearlite) are used for the steel materials that are the materials of these mechanical structural parts. This steel is usually processed into bars and wires by hot rolling or hot forging, and then subjected to cold processing such as cold forging, and then precision cutting and finishing to machine structural component shapes. Has been done. Here, when the strength and toughness of the mechanical structural steel material, which is the raw material, is increased as the material of the mechanical structural component corresponding to the increase in load as described above, the cold working and the precise cutting work become extremely difficult. Therefore, there is a need for a steel material that combines the high strength, high toughness, and cold workability, but the strength and cold workability are in a contradictory relationship. It is extremely difficult to achieve both.
このため、前記高強度、高靭性な部品特性と冷間加工性を両立させる方策の一つとして、強度、靭性などの前記部品特性が必要な部分に用いる鋼材と、冷間加工性が必要な部分に用いる鋼材とをそれぞれ別個に準備し、これら特性が各々異なる両鋼材を互いに接合することによって、複合鋼材あるいは複合鋼部品とし、前記部品特性と冷間加工性を両方達成する方法がある。 For this reason, as one of the measures for achieving both the high strength and high toughness of the component characteristics and the cold workability, the steel material used for the parts that require the component characteristics such as the strength and toughness, and the cold workability are required. There is a method of achieving both the component characteristics and the cold workability by preparing the steel materials used for the parts separately and joining the steel materials having different characteristics to each other to form a composite steel material or a composite steel part.
このような複合鋼材を作製するための、互いの鋼材間あるいは鋼部材間の接合方法としては、大きく分けて溶融接合法と固相接合法に分類される。このうち溶融接合では、互いの鋼材の接合部分が融点以上の高温状態となるため、接合部位で結晶粒の粗大化、気泡の発生など接合欠陥が発生しやすい。また、熱影響部が大きくなり、母材と熱影響部の界面で割れが発生しやすい問題も生じる。一方、固相接合は、互いの鋼材の接合面が固相面同士の接合方法のことであり、溶加材を用いることなく、母材の融点以下の温度で接合することができる。代表的な固相接合法としては摩擦圧接法がある。この摩擦圧接法は、２つの鋼材同士（鋼部材同士）を加圧・回転させながら、接触面（当接面）に摩擦熱を発生させることで、互いの鋼材の接合部分（以下、接合部とも言う）を加熱、軟化した後、この接合部に対するアップセット力（圧接力）を作用させて接合（溶着）する方法である。 Methods for joining such steel materials or steel members for producing such a composite steel material are roughly classified into a melt joining method and a solid phase joining method. Among these, in the fusion bonding, since the joining portions of the steel materials are in a high temperature state higher than the melting point, joining defects such as coarsening of crystal grains and generation of bubbles are likely to occur at the joining portions. In addition, the heat affected zone becomes large, and there is a problem that cracks are likely to occur at the interface between the base material and the heat affected zone. On the other hand, solid phase bonding is a method in which the bonding surfaces of the steel materials are solid surfaces, and can be bonded at a temperature below the melting point of the base material without using a filler material. As a typical solid phase bonding method, there is a friction welding method. This friction welding method generates frictional heat on the contact surface (contact surface) while pressurizing and rotating two steel materials (steel members) to each other, thereby joining each steel material (hereinafter referred to as a joint part). This is a method of joining (welding) by heating and softening, and then applying an upset force (pressure contact force) to the joint.
このような摩擦圧接法では、半溶融状態に加熱された部分がアップセット力の作用でバリとして接合面から排出されるため、清浄面同士が融点以下の温度で接合されることになる。このため、前記溶融接合法と比較して、接合部位で結晶粒の粗大化、気泡の発生、熱影響部の界面による割れなどが発生しにくい特徴がある。 In such a friction welding method, a portion heated to a semi-molten state is discharged from the joining surface as a burr by the action of the upset force, and the clean surfaces are joined at a temperature below the melting point. For this reason, compared with the said melt-bonding method, it has the characteristics that the coarsening of a crystal grain, the generation | occurrence | production of a bubble, the crack by the interface of a heat affected zone, etc. do not generate | occur | produce easily in a joining part.
この鋼材同士の摩擦圧接方法自体は従来から公知であって、例えば、特許文献１などで、この摩擦圧接方法の改良技術が提案されている。即ち、特許文献１では、摩擦圧接方法における、投入エネルギーおよび素材の無駄遣いを抑え、製品の寸法精度、接合強度、機械的性質のばらつきを抑えることが可能であることが開示されている。ただし、この特許文献１には、摩擦圧接方法に適した素材鋼材に関する記述はない。 The friction welding method itself between the steel materials is conventionally known. For example, Patent Document 1 discloses an improved technique for the friction welding method. That is, Patent Document 1 discloses that it is possible to suppress waste of input energy and materials in the friction welding method, and to suppress variations in product dimensional accuracy, bonding strength, and mechanical properties. However, this Patent Document 1 does not describe a material steel material suitable for the friction welding method.
一方、このような特徴を有する摩擦圧接法を鋼材同士の接合に適用した場合には、摩擦熱により熱影響を受ける部分（ＨＡＺ部）の強度低下や、逆に接合部分の強度増加が問題となる。この接合部分では、摩擦熱による加熱後、周りの母材によって急速に冷却されるため、マルテンサイト相となりやすく、強度が増加しやすいからである。そして、このような熱影響部の強度低下や接合部分の強度増加が大きいと、摩擦圧接された複合鋼材（複合鋼部品）の部位による強度変動が大きく、疲労強度、衝撃強度などの部品特性だけでなく、冷間加工性を低下させることとなる。 On the other hand, when the friction welding method having such characteristics is applied to the joining of steel materials, there is a problem in that the strength of the portion (HAZ portion) that is affected by frictional heat is reduced, and conversely, the strength of the joining portion is increased. Become. This is because the joint portion is rapidly cooled by the surrounding base material after being heated by frictional heat, so that it tends to become a martensite phase and the strength tends to increase. If the strength of the heat-affected zone is reduced or the strength of the joint is increased, the strength variation due to the friction-welded composite steel material (composite steel parts) is large, and only the component characteristics such as fatigue strength and impact strength. Instead, cold workability will be reduced.
このような課題に対して、前記熱影響部の強度低下だけ、あるいは前記接合部分の強度増加だけなど、個別の問題への対応でしかないが、従来から摩擦圧接用の素材鋼材側を改良した技術が種々提案されている。 For such a problem, only the strength reduction of the heat affected zone or only the strength increase of the joint portion can be dealt with individually, but the material steel side for friction welding has been improved conventionally. Various techniques have been proposed.
例えば、特許文献２には、前記熱影響部の強度低下を抑制した摩擦圧接用の高強度電縫鋼管の製造方法が提案されている。この特許文献２では、Ｃ：0.08〜0.23％、Si：0.5 質量％以下、Mn：1.8 ％以下、Nb：0.01〜0.1 ％、Mo：0.05〜0.60％を含有する鋼を、熱間圧延後、摩擦圧接時に析出するMo、Nbの炭窒化物を固溶状態に保つため、熱延鋼板の巻取り温度を450 ℃未満とする。そして、これら固溶状態としたNb、Moを摩擦圧接の際に、炭窒化物として析出させ、析出強化によって熱影響部の軟化を抑制している。 For example, Patent Document 2 proposes a method of manufacturing a high-strength ERW steel pipe for friction welding that suppresses the strength reduction of the heat-affected zone. In Patent Document 2, steel containing C: 0.08 to 0.23%, Si: 0.5% by mass or less, Mn: 1.8% or less, Nb: 0.01 to 0.1%, Mo: 0.05 to 0.60%, after hot rolling, In order to keep Mo and Nb carbonitrides precipitated during friction welding in a solid solution state, the coiling temperature of the hot-rolled steel sheet is set to less than 450 ° C. These Nb and Mo in a solid solution state are precipitated as carbonitrides during friction welding, and the softening of the heat affected zone is suppressed by precipitation strengthening.
しかし、前記した析出強化は、単に熱影響部だけでなく、通常は互いの鋼材の接合部分にまで及ぶ。この接合部分は、摩擦熱による加熱後、周りの母材によって急速に冷却されるため、マルテンサイト相となりやすく、元々強度が増加しやすい。更に、この析出強化も加わった場合は、前記マルテンサイト相化との相乗作用によって、逆に接合部分の強度は顕著に増加してしまう。このような接合部分の強度増加は、前記した衝撃、曲げ疲労、面圧疲労といった負荷が増大した機械構造部品では、使用中の接合部分の脆化を著しく促進させ、割れを発生しやすくする。このため、機械構造部品あるいは機械構造用鋼材としての信頼性を低下させる。 However, the precipitation strengthening described above extends not only to the heat-affected zone but also to the joint portion of the steel materials. Since this joined portion is rapidly cooled by the surrounding base material after being heated by frictional heat, it tends to become a martensite phase, and the strength tends to increase originally. Further, when this precipitation strengthening is also added, the strength of the joint portion increases conversely due to a synergistic effect with the martensite phase. Such an increase in the strength of the joint portion significantly accelerates the embrittlement of the joint portion in use and makes it easy to generate cracks in mechanical structural parts with increased loads such as impact, bending fatigue, and surface fatigue. For this reason, the reliability as a machine structural component or steel for machine structures is reduced.
特許文献３には、このような摩擦圧接による接合部分の強度増加を、素材である高炭素熱延鋼材側で抑制する技術が開示されている。この特許文献３では、微量の固溶Nbを含有させることによって、摩擦圧接の高圧力下での急速加熱における高炭素鋼材のオーステナイト結晶粒の粗大化を防止し、接合部分の硬さ増加と脆化を抑制している。この場合、固溶Nbは、摩擦圧接後に、NbCとして析出して結晶粒の粗大化防止に寄与している。 Patent Document 3 discloses a technique for suppressing an increase in strength of a joint portion due to such friction welding on the high carbon hot rolled steel material side that is a material. In Patent Document 3, by containing a small amount of solute Nb, the austenite crystal grains of the high carbon steel material are prevented from coarsening during rapid heating under high pressure of friction welding, and the hardness of the joint portion is increased and brittleness is increased. Is suppressed. In this case, solute Nb precipitates as NbC after friction welding and contributes to prevention of crystal grain coarsening.
本技術のような固溶Nbの利用は、予め焼入れ焼き戻しした鋼材同士を摩擦圧接した時の結晶粒の粗大化によるマルテンサイト変態を抑制する技術である。本技術では、硬さの変動による部品強度の劣化は抑制できるものの、組織は母材と同程度の結晶粒度であり、接合面の改善には十分でない。即ち、圧縮・引張といった単軸の負荷に対しては性能を発揮するものの、特に冷間鍛造のような多軸の負荷が与えられる冷間加工に対しては、摩擦圧接技術の性質上、接合面に沿って破壊が進行しやすいため、割れが発生しやすい問題が生じる。 The use of solute Nb as in the present technology is a technology that suppresses martensitic transformation due to the coarsening of crystal grains when steel materials that have been quenched and tempered in advance are friction welded. Although this technology can suppress the deterioration of the component strength due to the variation in hardness, the structure is a crystal grain size comparable to that of the base material and is not sufficient for improving the joint surface. In other words, it exhibits performance for uniaxial loads such as compression and tension, but especially for cold working where multiaxial loads such as cold forging are applied, due to the nature of friction welding technology, Since breakage easily proceeds along the surface, there is a problem that cracks are likely to occur.
前記した通り、通常の機械構造部品用の素材である鋼材において、摩擦圧接ままの状態で熱影響部の強度低下や接合部分の強度増加を同時に抑制して、母材、前記熱影響部、前記接合部分の各強度変動を最小限に抑え、複合鋼材の冷間加工性を維持または向上させる技術は、未だ提案されていない。 As described above, in steel materials that are materials for ordinary mechanical structural parts, the strength reduction of the heat-affected zone and the increase in strength of the joint are suppressed simultaneously in the state of friction welding, the base material, the heat-affected zone, No technology has yet been proposed for minimizing each strength fluctuation at the joint and maintaining or improving the cold workability of the composite steel material.
前記自動車などのエンジン部品用などの機械構造部品では、製造時のCO2排出量削減、あるいは、歩留まり向上のため、従来の熱間加工から冷間加工に置き換えることが求められている。したがって、摩擦圧接法による複合鋼材（複合鋼部品）をも、このような用途に適用するためは、当然これらの特性向上が求められる。この点、前記した従来技術が提案するような母材、前記熱影響部、前記接合部分の各強度変動を最小限に抑えるだけでなく、摩擦圧接前後における冷間加工性を向上させない限りは、摩擦圧接法による複合鋼材（複合鋼部品）は、前記自動車などのエンジン部品としては信頼性に欠け使用できない。 Mechanical structural parts such as those for engine parts such as automobiles are required to replace conventional hot working with cold working in order to reduce CO2 emissions during production or to improve yield. Accordingly, in order to apply a composite steel material (composite steel part) by the friction welding method to such applications, it is naturally required to improve these characteristics. In this respect, as long as not only the strength variation of the base material, the heat-affected zone, and the joint portion as proposed by the above-described conventional technology is minimized, but also the cold workability before and after the friction welding is improved, A composite steel material (composite steel part) obtained by the friction welding method lacks reliability and cannot be used as an engine part of the automobile or the like.
本発明はかかる問題に鑑みなされたもので、摩擦圧接前後の冷間鍛造性などの冷間加工性を向上させるとともに、摩擦圧接後の疲労強度および衝撃特性などの部品性能に優れた摩擦圧接用機械構造用鋼材および摩擦圧接部品（中間品を含む）を提供することをその目的（課題）とする。 The present invention has been made in view of such a problem, and improves the cold workability such as cold forgeability before and after friction welding and is excellent in parts performance such as fatigue strength and impact characteristics after friction welding. It is an object (problem) to provide a machine structural steel material and friction welded parts (including intermediate products).
本発明は上記課題を解決するための手段として、以下の内容を要旨とする摩擦圧接に適した機械構造用鋼材および摩擦圧接部品をここに提案する。 The present invention proposes, as means for solving the above-mentioned problems, a steel material for mechanical structure and a friction welding component suitable for friction welding, which are summarized as follows.
（１）C：0.001〜0.05質量％、Si：0.06〜2.0質量％、Mn：0.2〜3.0質量％、P：0.03質量％以下（0質量％を含まない）、S：0.002〜0.1質量％、Al：0.005〜0.1質量％、固溶N：0.008〜0.02質量％、残部はFeおよび不可避不純物からなり、鋼材組織中のフェライトの分率が95％以上、セメンタイトの分率が2％以下（0％を含む）で構成され、且つ前記フェライトの平均結晶粒径が10〜100μmであることを特徴とする摩擦圧接用機械構造用鋼材。 (1) C: 0.001 to 0.05 mass%, Si: 0.06 to 2.0 mass%, Mn: 0.2 to 3.0 mass%, P: 0.03 mass% or less (excluding 0 mass%), S: 0.002 to 0.1 mass%, Al: 0.005 to 0.1% by mass, solid solution N: 0.008 to 0.02% by mass, the balance consists of Fe and inevitable impurities, the ferrite fraction in the steel structure is 95% or more, and the cementite fraction is 2% or less (0 And the average crystal grain size of the ferrite is 10 to 100 μm.
（２）さらに他の元素として、Cr：2質量％以下（0％を含まない）またはMo：2質量％以下（0％を含まない）を含有する前記（1）に記載の摩擦圧接用機械構造用鋼材。 (2) The friction welding machine according to (1) above, which contains, as another element, Cr: 2% by mass or less (excluding 0%) or Mo: 2% by mass or less (not including 0%) Structural steel.
（３）さらに他の元素として、Ti：0.2質量％以下（0％を含まない）、Nb：0.2質量％以下（0％を含まない）、V：0.2質量％以下（0％を含まない）、B：0.01質量％以下（0％を含まない）より成る群から選ばれる少なくとも1種を含有することを特徴とする前記（1）または（2）に記載の摩擦圧接用機械構造用鋼材。 (3) Further, as other elements, Ti: 0.2% by mass or less (not including 0%), Nb: 0.2% by mass or less (not including 0%), V: 0.2% by mass or less (not including 0%) B: at least one selected from the group consisting of 0.01% by mass or less (not including 0%), the steel for friction welding according to (1) or (2) above.
（４）さらに他の元素として、Cu：5質量％以下（0％を含まない）またはNi：5質量％以下を含有する前記（1）〜（3）のいずれかに記載の摩擦圧接用機械構造用鋼材。 (4) The friction welding machine according to any one of (1) to (3), further containing Cu: 5% by mass or less (excluding 0%) or Ni: 5% by mass or less as another element Structural steel.
（５）前記（1）〜（4）のいずれかに記載の機械構造用鋼材が、相手側鋼材と摩擦圧接によって接合されてなる摩擦圧接部品。 (5) A friction welding component in which the machine structural steel according to any one of (1) to (4) is joined to a counterpart steel by friction welding.
（６）摩擦圧接による接合の前あるいは／および接合の後に冷間加工が施されてなる請求項５に記載の摩擦圧接部品。 (6) The friction-welded part according to claim 5, which is cold-worked before or / and after joining by friction welding.
本発明によれば、摩擦圧接前の冷間鍛造性などの冷間加工性は勿論のこと、摩擦圧接後における冷間加工性をも向上させることができるとともに、摩擦圧接後の疲労強度、衝撃特性などの優れた性能の部品を得ることが可能な摩擦圧接に適した機械構造用鋼材を提供することができる。 According to the present invention, not only cold workability such as cold forgeability before friction welding, but also cold workability after friction welding can be improved, and fatigue strength and impact after friction welding can be improved. It is possible to provide a steel material for machine structure suitable for friction welding capable of obtaining a component having excellent performance such as characteristics.
また、本発明によれば上記機械構造用鋼材を用いて他の相手側鋼材と摩擦圧接することにより、疲労強度、衝撃特性、さらに冷間加工性などに優れた摩擦圧接部品（中間品を含む）を提供することができる。 In addition, according to the present invention, friction welding components (including intermediate products) excellent in fatigue strength, impact characteristics, cold workability, etc. are obtained by friction welding with other counterpart steel materials using the steel for machine structure. ) Can be provided.
[本発明の特徴]
以下、本発明について詳述する。
先ず、本発明の摩擦圧接用機械構造用鋼材（以下、摩擦圧接用鋼材、本発明鋼材などと略称する場合がある）の主要な特徴について説明する。
[Features of the present invention]
Hereinafter, the present invention will be described in detail.
First, the main characteristics of the steel for machine structural use for friction welding of the present invention (hereinafter sometimes abbreviated as steel for friction welding, steel of the present invention, etc.) will be described.
本発明の摩擦圧接用鋼材は、（１）フェライト単一組織（フェライトが全体の95％以上）としていること、および（２）固溶N量を0.008質量％以上と一般の鋼材に比べて大幅に高めていること、を大きな特徴としている。
本発明では、上記（１）によって、摩擦圧接時の接合面近傍の組織を摩擦圧接前後で同一とすることができるため、母材そのままの靭性を維持することができ、且つ、冷間加工性を向上させることができ、また、上記（１）によって、摩擦圧接品の疲労強度を向上させることができる。
The steel for friction welding according to the present invention has (1) a ferrite single structure (95% or more of ferrite), and (2) a solid solution N content of 0.008% by mass or more compared to general steel materials. This is a major feature.
In the present invention, according to the above (1), the structure in the vicinity of the joint surface at the time of friction welding can be made the same before and after the friction welding, so that the toughness of the base material can be maintained and cold workability can be maintained. Further, the fatigue strength of the friction welded product can be improved by the above (1).
通常、摩擦圧接した鋼材の接合部は、一般の炭素鋼を用いた場合、急速加熱と冷却によって結晶粒の粗大化とマルテンサイト変態による硬さの急激な増加が生じる。そのため、接合部および接合部近傍が脆化し、疲労強度、衝撃特性（衝撃値）などの部品特性が満足できなくなる。前述の従来技術（特許文献２など）では、固溶Nbの活用によって結晶粒の粗大化を抑制しているが、通常のフェライト−パーライト組織鋼を使用すると部品強度を確保することができないため、予め焼入れ焼き戻しした鋼材を使用する必要がある。そのため、まず、鋼材自体の硬さが高くなっており、冷間加工性が劣化する問題がある。 Usually, when a general carbon steel is used for the joint portion of the steel material subjected to friction welding, rapid heating and cooling cause coarsening of crystal grains and a rapid increase in hardness due to martensitic transformation. Therefore, the joint portion and the vicinity of the joint portion become brittle, and the component characteristics such as fatigue strength and impact characteristics (impact value) cannot be satisfied. In the above-described conventional techniques (such as Patent Document 2), the coarsening of crystal grains is suppressed by utilizing solid solution Nb. However, if normal ferrite-pearlite structure steel is used, the strength of the parts cannot be ensured. It is necessary to use steel that has been pre-quenched and tempered. Therefore, first, the hardness of the steel material itself is high, and there is a problem that the cold workability deteriorates.
一方、本発明の技術では、組織をフェライト単一組織としており、摩擦圧接前後で組織変化が生じない。そのため、摩擦圧接による靭性の劣化がほとんど発生しない。ただし、フェライトは軟質であるため、強度が低いという問題がある。本発明においてはこの問題を解消して十分な強度を確保するため、固溶Nを増量し、摩擦圧接時の塑性ひずみと発熱を利用したひずみ時効による強度増加により、他方の鋼材（相手側鋼材）と強度を近接させることによって疲労特性を向上させることに成功した。この強度向上の具体的なメカニズムは以下のように推定される。 On the other hand, in the technique of the present invention, the structure is a single ferrite structure, and the structure does not change before and after friction welding. Therefore, the deterioration of toughness due to friction welding hardly occurs. However, since ferrite is soft, there is a problem that strength is low. In the present invention, in order to solve this problem and secure sufficient strength, the amount of solute N is increased, and the strength of the other steel material (the counterpart steel material is increased by strain aging using plastic strain and heat generation during friction welding. ) And strength were brought close to each other, and the fatigue characteristics were successfully improved. The specific mechanism of this strength improvement is estimated as follows.
まず、摩擦圧接によって圧接部およびその近傍には強い塑性ひずみが付与される。一般的な鋼材では、動的再結晶によって結晶粒が粗大化すると共に、マルテンサイト変態によって、脆性的な組織となるが、本発明鋼はフェライト単一組織鋼であるため、摩擦圧接時には非常に軟らかく、強い塑性ひずみが付与される部位は、バリとしてすぐに排出される。そのため、結晶粒径は摩擦圧接前後でほとんど変化しない。また、Cを十分低く制御しているため、摩擦圧接で生じる発熱と母材部分からの冷却速度では相変態が生じず、その結果、摩擦圧接前とほぼ同一の組織となり、摩擦圧接による急速加熱・冷却による脆化は発生しない。一方、フェライト単一組織では、部品として必要とされる強度とすることができないが、固溶N量を所定量以上とすることで強度を向上させることができる。 First, strong plastic strain is imparted to the pressure contact portion and its vicinity by friction welding. In general steel materials, crystal grains become coarse due to dynamic recrystallization and a brittle structure is formed by martensitic transformation.However, because the steel of the present invention is a ferritic single structure steel, The soft and strong plastic strained part is immediately discharged as a burr. Therefore, the crystal grain size hardly changes before and after friction welding. In addition, because C is controlled sufficiently low, phase transformation does not occur at the heat generated by friction welding and the cooling rate from the base metal part, resulting in almost the same structure as before friction welding and rapid heating by friction welding -No embrittlement due to cooling. On the other hand, in the ferrite single structure, the strength required as a component cannot be obtained, but the strength can be improved by setting the solid solution N amount to a predetermined amount or more.
固溶Nを所定量以上含有させることで、加工時に動的ひずみ時効が発生し、転位の増殖が顕著となる。一方、摩擦圧接後には摩擦圧接時に導入された転位が加工発熱によって動きやすくなった固溶Nによって固着されることで、静的ひずみ時効分の強化が付与され、加工硬化分以上に強度を増加させることができる。動的ひずみ時効によって疲労特性が劣化することが考えられたが、フェライト単相であれば、摩擦圧接部近傍が同時に硬化するため、硬さの不均一が発生せず、結果として、疲労特性は損なわれない。 When a predetermined amount or more of solute N is contained, dynamic strain aging occurs during processing, and dislocation growth becomes significant. On the other hand, after friction welding, dislocations introduced at the time of friction welding are fixed by solid solution N that has become easy to move due to processing heat generation, thereby strengthening static strain aging and increasing the strength beyond work hardening Can be made. It was thought that the fatigue characteristics deteriorated due to dynamic strain aging, but in the case of a ferrite single phase, the area near the friction weld was hardened at the same time, so there was no non-uniform hardness. Not damaged.
摩擦圧接によって上記のように接合部および接合部近傍を強化した本発明鋼材は、摩擦圧接ままの部品すなわち摩擦圧接後にさらに熱処理などの特性改善のための特別な処理を施さなくても、摩擦圧接したそのままの状態で靭性、疲労特性が向上した性能の優れた部品とすることができる。しかも、フェライト単一組織であるため、十分な変形能を有しており、摩擦圧接前後いずれにおいても冷間鍛造などの冷間加工で割れを発生させずに容易に所望の部品形状とすることができる。 The steel material of the present invention in which the joint portion and the vicinity of the joint portion are reinforced by friction welding as described above can be used for friction welding, even if a special treatment for improving the characteristics such as heat treatment is not performed after the friction welding component, that is, friction welding. In this state, it is possible to obtain a component with excellent performance with improved toughness and fatigue characteristics. Moreover, since it has a single ferrite structure, it has sufficient deformability and can easily be formed into the desired part shape without causing cracks in cold working such as cold forging before and after friction welding. Can do.
[本発明鋼材の化学成分]
次に、前記本発明鋼材の特徴を発揮させるための化学成分について、各主要元素の含有量の範囲とその限定理由を説明する。本発明鋼材の化学成分は前記した自動車のエンジン部品などの機械構造部品に要求される強度や靭性特性、これに加えた衝撃特性、曲げ疲労特性、面圧疲労特性、冷間加工性などの特性向上のためや、これらの特性向上のための前記本発明組織とするための前提条件となる。
[Chemical composition of the steel of the present invention]
Next, regarding the chemical components for exhibiting the characteristics of the steel material of the present invention, the range of the content of each main element and the reason for the limitation will be described. The chemical composition of the steel material of the present invention includes strength and toughness characteristics required for machine structural parts such as automobile engine parts described above, and characteristics such as impact characteristics, bending fatigue characteristics, surface fatigue characteristics, and cold workability. This is a precondition for improving the structure of the present invention for improving these characteristics.
（１）C：0.001〜0.05質量％
Cは、摩擦圧接時の組織変化抑制と冷間加工性に大きな影響を及ぼす元素である。C含有量は低ければ低いほど冷間加工性が向上するが、0.001質量％未満となると、溶製時にガスが発生し、欠陥が増えるため、疲労強度、靭性が劣化する。一方、Cが0.05質量％を超える場合、パーライトを形成しやすくなり、フェライト単一組織とすることが困難となり、疲労強度、靭性が劣化する。このため、C含有量は0.001〜0.05質量％の範囲とする。また、その下限については好ましくは0.005質量％、より好ましくは0.010質量％とし、その上限については好ましくは0.045質量％、より好ましくは0.040質量％とする。
(1) C: 0.001 to 0.05 mass%
C is an element that has a great influence on the suppression of structural changes and cold workability during friction welding. The lower the C content, the better the cold workability. However, if the C content is less than 0.001% by mass, gas is generated during melting and defects increase, so that fatigue strength and toughness deteriorate. On the other hand, when C exceeds 0.05% by mass, it becomes easy to form pearlite, making it difficult to form a ferrite single structure, and fatigue strength and toughness deteriorate. For this reason, C content shall be 0.001-0.05 mass%. The lower limit is preferably 0.005% by mass, more preferably 0.010% by mass, and the upper limit is preferably 0.045% by mass, more preferably 0.040% by mass.
（２）Si：0.001〜2.0質量％
Siは、固溶強化により母材強度を高める作用を有する。Si含有量を極端に低減することは製造上困難であり、コスト的にも見合わない。一方、Ｓｉを過剰に含有させると、変形抵抗の増大や変形能の低下を生じさせるため、冷間加工性が劣化する。この傾向はSi含有量が2.0質量％を超えると顕著に見られはじめる。このため、Si含有量は0.001〜2.0質量％の範囲とする。また、その下限については好ましくは0.005質量％、より好ましくは0.01質量％とし、その上限については好ましくは1.0質量％、より好ましくは0.5質量％とする。
(2) Si: 0.001 to 2.0 mass%
Si has the effect of increasing the strength of the base material by solid solution strengthening. Extremely reducing the Si content is difficult in production and is not cost effective. On the other hand, when Si is excessively contained, an increase in deformation resistance and a decrease in deformability are caused, so that cold workability is deteriorated. This tendency starts to be noticeable when the Si content exceeds 2.0 mass%. For this reason, Si content shall be the range of 0.001-2.0 mass%. The lower limit is preferably 0.005% by mass, more preferably 0.01% by mass, and the upper limit is preferably 1.0% by mass, more preferably 0.5% by mass.
（３）Mn：0.2〜3.0質量％
Mnは、溶製中の鋼の脱酸、脱硫元素として有効であり、また、鋼材への熱間加工時の加工性の劣化を抑制する効果を有する。更に、Sと結合することで鋼材の変形能、靭性を向上させることにも有効である。Mn含有量が少なすぎるとこれらの効果が得られず、靭性、疲労特性が劣化しやすくなる。一方で、Mnを過剰に含有させると、固溶強化による変形抵抗の増加と変形能の低下をもたらし、冷間加工性を劣化させる。また、Pの粒界への偏析を助長し、粒界強度の低下によって、靭性、疲労強度の低下を生じさせる。このため、Mn含有量は0.2〜3.0質量％の範囲とする。また、その下限については好ましくは0.25質量％、より好ましくは0.30質量％とし、その上限については好ましくは2.0質量％、より好ましくは1.5質量％とする。
(3) Mn: 0.2-3.0 mass%
Mn is effective as a deoxidizing and desulfurizing element for steel during melting, and has an effect of suppressing deterioration of workability during hot working on steel. Furthermore, it is effective to improve the deformability and toughness of the steel material by combining with S. If the Mn content is too small, these effects cannot be obtained, and the toughness and fatigue characteristics tend to deteriorate. On the other hand, when Mn is contained excessively, an increase in deformation resistance due to solid solution strengthening and a decrease in deformability are caused, and cold workability is deteriorated. In addition, segregation of P to grain boundaries is promoted, and a decrease in grain boundary strength causes a decrease in toughness and fatigue strength. For this reason, Mn content shall be the range of 0.2-3.0 mass%. The lower limit is preferably 0.25 mass%, more preferably 0.30 mass%, and the upper limit is preferably 2.0 mass%, more preferably 1.5 mass%.
（４）P：0.03質量％以下（0％を含まない）
Pは不可避的に混入し、不純物として含有する元素であり、フェライト粒界に偏析し、変形能、靭性、疲労特性を劣化させる。また、Pはフェライトを固溶強化させ、変形抵抗を増大させるため、この変形能の観点からは極力低減することが望ましいが、極端な低減は製鋼コストの増加を招く。したがって、P含有量は0.03質量％以下の低いほど良いが、0％とすることは製造上困難であるので、0.03質量％以下（但し0％を含まない）と規定する。また、その上限については好ましくは0.025質量％、より好ましくは0.02質量％とする。
(4) P: 0.03 mass% or less (excluding 0%)
P is an element that is inevitably mixed and contained as an impurity, segregates at the ferrite grain boundary, and deteriorates deformability, toughness, and fatigue characteristics. Further, since P strengthens ferrite in a solid solution and increases deformation resistance, it is desirable to reduce it as much as possible from the viewpoint of this deformability, but extreme reduction leads to an increase in steelmaking cost. Therefore, the lower the P content is, the better the content is 0.03% by mass or less, but it is difficult to make it 0%. The upper limit is preferably 0.025% by mass, more preferably 0.02% by mass.
（５）S：0.002〜0.1質量％
Sも不可避的に混入し、不純物として含有する元素であり、Feと結合すると、FeSとして粒界上に膜状に析出するため、変形能、靭性、疲労特性を劣化させる。したがって、Sは全量をMnと結合させ、MnSとして無害に析出させる必要がある。ただし、このMnSの析出量が増えると、やはり変形能、靭性、疲労特性が劣化する。一方で、Sは被削性向上効果があり、S含有量を極端に低減すると被削性を劣化させる。したがって、S含有量は部品特性と被削性のバランスを考慮して0.002〜0.1質量％の範囲とする。そして、その下限については好ましくは0.004質量％、より好ましくは0.006質量％とし、その上限については好ましくは0.07質量％、より好ましくは0.04％質量％とする。
(5) S: 0.002 to 0.1% by mass
S is an element that is inevitably mixed and contained as an impurity, and when combined with Fe, it precipitates in the form of a film on the grain boundary as FeS, which deteriorates deformability, toughness, and fatigue characteristics. Therefore, the entire amount of S needs to be combined with Mn and deposited harmlessly as MnS. However, as the amount of precipitation of MnS increases, the deformability, toughness, and fatigue characteristics deteriorate. On the other hand, S has an effect of improving machinability, and if the S content is extremely reduced, the machinability is deteriorated. Therefore, the S content is in the range of 0.002 to 0.1 mass% in consideration of the balance between the component characteristics and the machinability. The lower limit is preferably 0.004% by mass, more preferably 0.006% by mass, and the upper limit is preferably 0.07% by mass, more preferably 0.04% by mass.
（６）Al：0.005〜0.1質量％
Alは溶製中の鋼の脱酸元素として有効である。Al含有量が少なすぎると、溶製中の脱酸が不十分となり、ガス欠陥が生じやすくなるので、割れが生じやすくなり、変形能、靭性、疲労特性が劣化する。一方、Al含有量が過剰になると、酸化アルミ系の酸化物などの非金属介在物が生成し、変形能を劣化させる。したがって、Al含有量は0.005〜0.1質量％の範囲とした。また、その下限については好ましくは0.008質量％、より好ましくは0.01質量％とし、その上限については好ましくは0.08質量％、より好ましくは0.06％質量％とする。
(6) Al: 0.005 to 0.1% by mass
Al is effective as a deoxidizing element for steel during melting. If the Al content is too small, deoxidation during melting becomes insufficient and gas defects are likely to occur, so that cracking is likely to occur, and deformability, toughness, and fatigue characteristics deteriorate. On the other hand, when the Al content is excessive, non-metallic inclusions such as aluminum oxide-based oxides are generated, and the deformability is deteriorated. Therefore, the Al content is in the range of 0.005 to 0.1 mass%. The lower limit is preferably 0.008% by mass, more preferably 0.01% by mass, and the upper limit is preferably 0.08% by mass, more preferably 0.06% by mass.
（７）固溶N:0.008〜0.02質量％
固溶Nは本発明の特徴において述べたように疲労強度を確保する上で重要である。冷間鍛造などの冷間加工時に変形抵抗をあまり増加させずに摩擦圧接後に部品強度を大きく増加させ、所望の部品強度を得るためには固溶Nの含有量を0.008質量％以上とする必要がある。ただし、0.02質量％を超えると、動的ひずみ時効の影響が顕著となり、変形能が劣化し始めるため、冷間加工後に割れが生じやすくなる。したがって、本発明では、固溶Nの含有量を0.008〜0.02質量％に規定する。また、その下限については好ましくは0.0085質量％、より好ましくは0.0090質量％とし、その上限については好ましくは0.0180質量％、より好ましくは0.0150質量％とする。
(7) Solid solution N: 0.008 to 0.02 mass%
Solid solution N is important in securing fatigue strength as described in the features of the present invention. In order to greatly increase the strength of the parts after friction welding without significantly increasing deformation resistance during cold working such as cold forging, the content of solid solution N must be 0.008% by mass or more in order to obtain the desired part strength. There is. However, if it exceeds 0.02% by mass, the effect of dynamic strain aging becomes prominent and the deformability starts to deteriorate, so that cracking is likely to occur after cold working. Therefore, in the present invention, the content of solute N is specified to be 0.008 to 0.02 mass%. The lower limit is preferably 0.0085% by mass, more preferably 0.0090% by mass, and the upper limit is preferably 0.0180% by mass, more preferably 0.0150% by mass.
全Nについては本発明で特に規定しないものの、固溶Nが上記の範囲になるように調整された量とする。固溶Nは鋼中に添加されたTi、Nb、V 、B及びAlなどのN化合物形成元素により一部消費されて、減少するため、全Nの含有量はこれらの元素の種類や添加量に応じて固溶Nの減少分を見込んだ量を増加させる必要があるが、一般的には、0.008〜0.02質量％の範囲とすれば十分である。その下限については好ましくは0.0085質量％、より好ましくは0.009質量％とし、その上限については好ましくは0.0180質量％、より好ましくは0.0150質量％とする。 The total N is not particularly defined in the present invention, but is an amount adjusted so that the solid solution N is in the above range. Since solute N is partially consumed and reduced by N compound forming elements such as Ti, Nb, V, B and Al added to the steel, the total N content depends on the type and amount of these elements. In accordance with the above, it is necessary to increase the amount in consideration of the decrease in the solid solution N, but generally it is sufficient to be in the range of 0.008 to 0.02 mass%. The lower limit is preferably 0.0085 mass%, more preferably 0.009 mass%, and the upper limit is preferably 0.0180 mass%, more preferably 0.0150 mass%.
（８）Cr：2質量％以下（0％を含まない）またはMo：2質量％以下（0％を含まない）
Cr、Moは本発明鋼において必要に応じて含有される好適な選択元素であり、以下（９）〜（１０）に述べる他の元素も同様である。
Crは、摩擦圧接部品の強度を確保し、接合部の靭性を高めるのに有効な元素である。ただし、Cr含有量が過剰になると、固溶強化によって変形能が劣化する原因となる。したがって、Cr含有量は2％質量以下（0％を含まない）とする。また、その下限については好ましくは0.04質量％、より好ましくは0.08質量％とし、その上限については好ましくは1.5質量％、より好ましくは1.0質量％とする。
(8) Cr: 2% by mass or less (not including 0%) or Mo: 2% by mass or less (not including 0%)
Cr and Mo are suitable selective elements contained as necessary in the steel of the present invention, and the same applies to other elements described in (9) to (10) below.
Cr is an element effective for ensuring the strength of the friction welded part and increasing the toughness of the joint. However, when the Cr content is excessive, the deformability deteriorates due to solid solution strengthening. Therefore, the Cr content is 2% or less (excluding 0%). The lower limit is preferably 0.04 mass%, more preferably 0.08 mass%, and the upper limit is preferably 1.5 mass%, more preferably 1.0 mass%.
Moは、鋼材の靭性を向上させるのに有効な元素である。一方、Moの含有量が過剰になると、母材の硬度が必要以上に高くなって靭性、疲労特性が劣化するので、2質量％以下に限って添加することができる。また、その下限については好ましくは0.04質量％、より好ましくは0.08質量％とし、その上限については好ましくは1.5質量％、より好ましくは1.0質量％とする。 Mo is an element effective for improving the toughness of steel materials. On the other hand, if the Mo content is excessive, the hardness of the base material becomes higher than necessary and the toughness and fatigue characteristics deteriorate, so it can be added only to 2% by mass or less. The lower limit is preferably 0.04 mass%, more preferably 0.08 mass%, and the upper limit is preferably 1.5 mass%, more preferably 1.0 mass%.
（９）Ti：0.2質量％以下（但し0％を含まない）、Nb：0.2％質量以下（但し0％を含まない）、V：0.2質量％以下（但し0％を含まない）、B：0.01質量％以下（但し0％を含まない）の１種以上
Ti、Nb、V、Bは、いずれもN化合物などを形成し、摩擦圧接後の熱影響部における強度低下を抑制し、実質的に強度を向上させることができる。そこで、Ti：0.2％質量以下（但し0％を含まない）、Nb：0.2質量％以下（但し0％を含まない）、B：0.01質量％以下（但し0％を含まない）の１種以上を添加することができる。
(9) Ti: 0.2% by mass or less (excluding 0%), Nb: 0.2% by mass or less (excluding 0%), V: 0.2% by mass or less (excluding 0%), B: One or more of 0.01% by mass or less (excluding 0%)
Ti, Nb, V, and B all form an N compound and the like, can suppress a decrease in strength in the heat-affected zone after friction welding, and can substantially improve the strength. Therefore, Ti: 0.2% by mass or less (excluding 0%), Nb: 0.2% by mass or less (excluding 0%), B: 0.01% by mass or less (excluding 0%) Can be added.
Ti含有量の下限は0.005質量％とすることが好ましく、0.01質量％とすることがより好ましく、0.015質量％とすることが更に好ましい。一方、Ti含有量が多すぎるとTiNが多量に生成するため、逆に強度（疲労強度）が低下する。したがって、Ti含有量の上限は0.15質量％とすることが好ましく、0.1質量％とすることがより好ましい。 The lower limit of the Ti content is preferably 0.005% by mass, more preferably 0.01% by mass, and still more preferably 0.015% by mass. On the other hand, if the Ti content is too large, a large amount of TiN is generated, and the strength (fatigue strength) is conversely reduced. Therefore, the upper limit of the Ti content is preferably 0.15% by mass, and more preferably 0.1% by mass.
Nb含有量の下限は0.005質量％とすることが好ましく、0.01％質量とすることがより好ましく、0.015質量％とすることが更に好ましい。一方、Nb含有量が多すぎるとNbNが多量に生成するため、逆に強度（疲労強度）が低下する。したがって、Nb含有量の上限は0.15質量％とすることが好ましく、0.1質量％とすることがより好ましい。 The lower limit of the Nb content is preferably 0.005% by mass, more preferably 0.01% by mass, and still more preferably 0.015% by mass. On the other hand, if the Nb content is too large, a large amount of NbN is generated, and the strength (fatigue strength) is conversely reduced. Therefore, the upper limit of the Nb content is preferably 0.15% by mass, and more preferably 0.1% by mass.
V含有量の下限は0.005質量％とすることが好ましく、0.01質量％とすることがより好ましく、0.015質量％とすることが更に好ましい。一方、V含有量が多すぎるとVNが多量に生成するため、逆に強度（疲労強度）が低下する。したがって、V含有量の上限は0.15質量％とすることが好ましく、0.1質量％以下とすることがより好ましい。 The lower limit of the V content is preferably 0.005% by mass, more preferably 0.01% by mass, and still more preferably 0.015% by mass. On the other hand, if the V content is too large, a large amount of VN is generated, and the strength (fatigue strength) is conversely reduced. Therefore, the upper limit of the V content is preferably 0.15% by mass, and more preferably 0.1% by mass or less.
B含有量の下限は0.0005質量％とすることが好ましく、0.0010％質量とすることがより好ましい。一方、B含有量が多すぎるとBNが多量に生成するため、逆に強度（疲労強度）が低下する。したがって、B含有量の上限は0.008質量％とすることが好ましく、0.006％質量とすることがより好ましい。 The lower limit of the B content is preferably 0.0005% by mass, and more preferably 0.0010% by mass. On the other hand, if the B content is too large, a large amount of BN is generated, and conversely, the strength (fatigue strength) decreases. Therefore, the upper limit of the B content is preferably 0.008% by mass, and more preferably 0.006% by mass.
（１０）Cu：5質量％以下（0％を含まない）またはNi：5質量％以下（0％を含まない）
Cu、Niはいずれも鋼材をひずみ時効させ、母材や接合部分の強度、すなわち疲労強度を向上させるのに有効である。そこで、Cu：5質量％以下（但し0％を含まない）またはNi：5質量％（但し0％を含まない）を添加する。一方、Cu、Niの含有量が過剰になると熱間延性が劣化する。したがって、Cu、Niの含有量は各々5質量％以下とする。そして、これらの上限については好ましくは各々4質量％、より好ましくは各々3質量％とする。また、これらの下限については、添加による前記効果を有効に発揮させるために、0.1質量％が好ましく、より好ましくは各々0.2質量％、更に好ましくは各々0.3質量％とする。
(10) Cu: 5% by mass or less (not including 0%) or Ni: 5% by mass or less (not including 0%)
Both Cu and Ni are effective in strain aging steel materials and improving the strength of the base metal and the joint, that is, the fatigue strength. Therefore, Cu: 5% by mass or less (however, not including 0%) or Ni: 5% by mass (however, not including 0%) is added. On the other hand, when the Cu and Ni contents are excessive, hot ductility deteriorates. Therefore, the contents of Cu and Ni are each 5% by mass or less. And about these upper limits, Preferably each is 4 mass%, More preferably, you may be 3 mass% each. Moreover, about these minimums, in order to exhibit the said effect by addition effectively, 0.1 mass% is preferable, More preferably, it is 0.2 mass% respectively, More preferably, it is 0.3 mass% respectively.
[本発明鋼材の組織]
本発明鋼材の組織は前述の特徴のところで触れたように、摩擦圧接と冷間加工に適した組織とするために、フェライト相の分率が鋼組織全体の95％以上からなる実質的にフェライトの単一組織としなければならない。好ましくはフェライトの分率が95％以上、より好ましくは97％以上、さらに好ましくは99％以上とする。
したがって、5％未満であれば他の組織が混在してもかまわないが、セメンタイトについてはその分率を2％以下（0％を含む）する必要がある。セメンタイトは、冷間加工中の変形抵抗を増加させやすく、また、フェライトとセメンタイトの界面において、割れを生じさせるため、変形能、靭性、疲労特性を劣化させやすい。そのため、セメンタイトは極力低減することが必要であり、本発明においては鋼組織に含まれるセメンタイトの分率を2％以下に規定する。このセメンタイトの分率は好ましくは1.5％以下、特に好ましくは１％以下とするのが良い。
[Structure of the steel of the present invention]
As mentioned in the above characteristics, the steel structure of the present invention has a ferrite phase fraction of 95% or more of the entire steel structure in order to make the structure suitable for friction welding and cold working. Must be a single organization. Preferably, the ferrite fraction is 95% or more, more preferably 97% or more, and even more preferably 99% or more.
Therefore, if it is less than 5%, other tissues may be mixed, but for cementite, the fraction needs to be 2% or less (including 0%). Cementite tends to increase the deformation resistance during cold working, and also causes cracks at the interface between ferrite and cementite, and thus tends to deteriorate the deformability, toughness, and fatigue characteristics. For this reason, it is necessary to reduce cementite as much as possible. In the present invention, the fraction of cementite contained in the steel structure is specified to be 2% or less. The cementite fraction is preferably 1.5% or less, particularly preferably 1% or less.
上記セメンタイト以外のその他の組織は原則フェライトで構成されることが望ましいが、熱処理など製造工程によっては組織中にベイナイト、マルテンサイトなどが微量含まれる場合もあり、またこれらが含まれていても、その合計が3％未満の場合は靭性、疲労特性に影響を及ぼさないのでこれを許容する。 Other structures other than the above cementite are desirably composed of ferrite in principle, but depending on the manufacturing process such as heat treatment, bainite, martensite, etc. may be included in a small amount in the structure, and even if these are included, If the total is less than 3%, this is allowed because it does not affect toughness and fatigue properties.
[フェライトの結晶粒径]
また、本発明鋼材の上記フェライトの結晶粒径も変形抵抗と変形能に影響を及ぼす意味で重要であり、具体的にはその平均結晶粒径を10〜100μｍの範囲とすることが必要である。フェライト粒径を10μm以上とすることで変形能を劣化させずに変形抵抗を低減することができる。その効果は、フェライト粒径が100μmまで有効である。一方、フェライト粒径が100μmを超えると、変形能が低下し、粒界付近で割れが生じやすくなり、靭性、疲労特性が劣化する。また、フェライト粒径が10μm未満の場合は、冷間加工中に転位が増殖しやすくなり、固溶Nによる動的ひずみ時効の影響が顕著となり、変形抵抗が増加しやすく、靭性が劣化しやすい。したがって、フェライトの平均結晶粒径は10〜100μｍとするが、その下限については好ましくは15μｍ、より好ましくは20μmとし、またその上限については好ましくは90μｍ、より好ましくは80μmとする。
[Ferrite crystal grain size]
Further, the crystal grain size of the ferrite of the steel material of the present invention is also important in the sense that it affects the deformation resistance and the deformability. Specifically, the average crystal grain size must be in the range of 10 to 100 μm. . By setting the ferrite grain size to 10 μm or more, the deformation resistance can be reduced without deteriorating the deformability. The effect is effective up to a ferrite grain size of 100 μm. On the other hand, when the ferrite grain size exceeds 100 μm, the deformability is lowered, cracking is likely to occur near the grain boundary, and the toughness and fatigue characteristics are deteriorated. Also, when the ferrite grain size is less than 10 μm, dislocations tend to proliferate during cold working, the effect of dynamic strain aging due to solute N becomes prominent, deformation resistance tends to increase, and toughness tends to deteriorate. . Therefore, the average grain size of ferrite is 10 to 100 μm, but the lower limit is preferably 15 μm, more preferably 20 μm, and the upper limit is preferably 90 μm, more preferably 80 μm.
[本発明鋼材の製造方法]
次に、前記組織を有する本発明鋼材の製造方法について説明する。
まず、転炉、溶解炉、溶鋼処理炉などによって精錬、溶製され、前述の化学成分に成分調整がなされた溶鋼を、鋳造により鋼片（ビレット）となし、この鋼片に熱間加工を施す。この熱間加工として熱間圧延を採用する場合を例にとって詳説する。
すなわち、予め1100℃以上に前記鋼片を加熱後、900〜1100℃の温度で熱間圧延した後、0.5〜3℃/sの冷却速度で少なくとも600℃以下まで冷却することによって本発明鋼材を製造することができる。
本発明鋼材において規定する所定の固溶N、フェライト単一組織及びその結晶粒径を得るためには、前述の化学成分を前提とした上で、上記の熱間圧延時の加熱温度、圧延温度、圧延後の冷却速度などの熱処理条件を選定することが重要となる。
[Production method of the steel of the present invention]
Next, the manufacturing method of this invention steel material which has the said structure | tissue is demonstrated.
First, molten steel that has been refined and melted in a converter, melting furnace, molten steel processing furnace, etc., and whose components have been adjusted to the chemical components described above, is made into a billet by casting, and hot working is performed on this billet. Apply. The case where hot rolling is employed as the hot working will be described in detail as an example.
That is, after heating the steel slab to 1100 ° C or higher in advance, after hot rolling at a temperature of 900-1100 ° C, the steel material of the present invention is cooled to at least 600 ° C at a cooling rate of 0.5-3 ° C / s. Can be manufactured.
In order to obtain the prescribed solid solution N, ferrite single structure and crystal grain size thereof defined in the steel material of the present invention, on the premise of the above chemical components, the heating temperature during the above hot rolling, the rolling temperature It is important to select heat treatment conditions such as a cooling rate after rolling.
脱酸の目的で添加された鋼片中のAlは、固溶Nと結合したAlN の形態で存在するが、圧延前に1100℃以上の温度に加熱することでこのAlNが分解され、固溶N量を0.008質量％以上にすることができる。この加熱温度が1100℃未満の場合には、AlNを十分分解することができず、その後の熱処理工程によっても固溶Nを得ることができない。一方、温度が高ければ高いほど、AlNの分解が促進されるが、高すぎると、AlNの分解に対する効果が飽和するだけでなく、ビレットの端部が熱変形してしまう問題が生じることがあるため、この加熱温度は1250℃以下にすることが好ましい。 Al in the steel slab added for the purpose of deoxidation exists in the form of AlN combined with solute N. By heating to a temperature of 1100 ° C or higher before rolling, this AlN is decomposed and dissolved. N amount can be 0.008 mass% or more. When this heating temperature is less than 1100 ° C., AlN cannot be sufficiently decomposed, and solid solution N cannot be obtained even by a subsequent heat treatment step. On the other hand, the higher the temperature, the more the decomposition of AlN is promoted. However, if the temperature is too high, not only the effect on the decomposition of AlN will be saturated, but the billet end may be thermally deformed. Therefore, this heating temperature is preferably 1250 ° C. or lower.
また、熱間圧延中、AlNは析出しにくいが、圧延温度が900℃未満の低温となると、AlNが再び析出し始め、固溶Nを上記範囲とすることが困難になる。他方、1100℃を超える圧延温度では圧延時の加工熱によりビレットの高温化が極度に進み、その端部にダレが生じやすくなるなどの不具合を伴うため1100℃以下とする必要がある。 In addition, AlN hardly precipitates during hot rolling, but when the rolling temperature becomes a low temperature of less than 900 ° C., AlN begins to precipitate again, making it difficult to bring the solid solution N within the above range. On the other hand, when the rolling temperature exceeds 1100 ° C., the billet needs to be heated to 1100 ° C. or lower because the billet is extremely heated by the processing heat during rolling, and the end tends to sag.
さらに、加熱温度及び圧延温度を前記の範囲で実施した場合においても冷却条件を上記所定の範囲、すなわち0.5〜3℃/sの冷却速度で少なくとも600℃以下までで行なう必要がある。圧延後の冷却速度は、0.5℃/s未満となると、冷却中にAlNが再び析出し始め、固溶Nを所定範囲とすることが困難になるからである。一方、3℃/s以上となると、フェライトの結晶粒が微細化してその平均結晶粒径10μm未満になり易く、変形抵抗が増加することになる。 Furthermore, even when the heating temperature and the rolling temperature are performed within the above ranges, it is necessary to perform the cooling conditions within the above predetermined range, that is, at least 600 ° C. or less at a cooling rate of 0.5 to 3 ° C./s. This is because when the cooling rate after rolling is less than 0.5 ° C./s, AlN begins to precipitate again during cooling, and it becomes difficult to keep the solid solution N within a predetermined range. On the other hand, when the temperature is 3 ° C./s or more, the ferrite crystal grains become finer and the average crystal grain size tends to be less than 10 μm, and the deformation resistance increases.
また、この冷却速度の制御は、圧延後600℃までの温度域の範囲で行うことを必須とするものであり、さらに600℃未満の低温度域まで引き続き行っても勿論良いが、この低温度域での冷却速度は、組織変化およびAlNの析出には影響を与えないため、生産工程に合わせて適宜調整、変更することができる。 In addition, it is essential to control the cooling rate in the temperature range up to 600 ° C. after rolling, and it may of course be continued to a low temperature range below 600 ° C. Since the cooling rate in the region does not affect the structural change and the precipitation of AlN, it can be appropriately adjusted and changed according to the production process.
なお、上記の説明では、本発明鋼材の規定する固溶Nや組織を得る方法として熱間圧延時の熱処理条件について述べたが、熱間鍛造や熱間押出など他の熱間加工についても同様な条件を適用することで本発明鋼材を得ることが可能である。 In the above description, the heat treatment conditions at the time of hot rolling are described as a method for obtaining the solid solution N and the structure specified by the steel material of the present invention, but the same applies to other hot working such as hot forging and hot extrusion. The present steel material can be obtained by applying various conditions.
[本発明摩擦圧接部品の製造方法]
上述した本発明鋼材を用いて摩擦圧接部品を製造する方法について説明する。
本発明鋼材を摩擦圧接する際の相手側鋼材については、市販の摩擦圧接機により本発明鋼材と摩擦圧接が可能であれば、目的とする前記機械構造部品に応じて、種々の鋼種の相手鋼材が選択できる。また、本発明鋼材、相手側鋼材の形状も、目的とする前記機械構造部品に応じて種々の形状が選択できる。
[Production Method of Friction Welded Parts of the Present Invention]
A method for manufacturing a friction welded part using the above-described steel material of the present invention will be described.
With respect to the counterpart steel material when friction welding the steel material of the present invention, if it is possible to friction weld with the steel material of the present invention using a commercially available friction welding machine, depending on the intended mechanical structural parts, the counter steel material of various steel types Can be selected. Moreover, various shapes can be selected as the shapes of the steel material of the present invention and the counterpart steel material in accordance with the intended machine structural component.
例えば、相手側鋼材として本発明鋼材を選び、発明鋼材同士を摩擦圧接しても良く、また、相手側鋼材をＳ４５ＣやＳＣｒ４２０Ｈなどの機械構造用炭素鋼、合金鋼、Ｖ添加鋼、Ｂ添加鋼などとして、切削性や強度などの種々の特性を基準に選択して組み合わせても良い。また、形状も、摩擦圧接する鋼材同士の形状が異なっていても、同じあるいは類似であっても勿論良く、棒材同士の組み合わせ、頭部（円形材、角形材、傘状材、リング状材など）と軸となる棒材との組み合わせなど、自由に複合材形状が選定できる。 For example, the steel material of the present invention may be selected as the mating steel material, and the inventive steel materials may be friction-welded with each other. The mating steel material may be carbon steel for mechanical structures such as S45C and SCr420H, alloy steel, V-added steel, B-added steel. For example, various characteristics such as machinability and strength may be selected and combined. In addition, the shape of the steel materials to be friction welded may be different or the same or similar. Of course, a combination of bars, a head (round material, square material, umbrella material, ring material) Etc.) can be selected freely, such as a combination of shafts and rods.
本発明鋼材と上記種々の相手側鋼材を摩擦圧接して複合材とするが、所望の部品形状とするために摩擦圧接の前あるいは／および摩擦圧接後に冷間鍛造などの冷間加工を施す。すなわち、摩擦圧接前の本発明鋼材を冷間加工してこれを相手側鋼材を摩擦圧接してそのまま部品（本発明摩擦圧接部品）としても良いし、摩擦圧接後の複合材を冷間加工して部品としてもかまわないし、また、摩擦圧接前の本発明鋼材を一次の冷間鍛造を施してある程度部品形状に近い中間品とし、摩擦圧接を行った後、さらに二次の冷間加工を施してこれを部品としても良い。また、部品の最終形状を造りこむために上記冷間加工の後の切削などの仕上げ加工することも勿論良いものである。本発明鋼材との摩擦圧接される相手側鋼材についても、摩擦圧接に先立って必要な冷間加工を行って良いことは言うまでもない。 The steel material of the present invention and the above-mentioned various counterpart steel materials are friction welded to form a composite material, but cold working such as cold forging is performed before and / or after friction welding in order to obtain a desired part shape. That is, the steel material of the present invention before friction welding is cold worked, and the other steel material may be friction welded to make a part (the friction welding part of the present invention) as it is, or the composite material after friction welding is cold worked. The steel material of the present invention before friction welding is subjected to primary cold forging to an intermediate product that is close to the part shape to some extent, and after friction welding, secondary cold working is further performed. This may be used as a part. Of course, it is also good to perform finishing such as cutting after the cold working in order to create the final shape of the part. It goes without saying that the necessary cold working may be performed prior to the friction welding on the counterpart steel material to be friction welded with the steel of the present invention.
また、摩擦圧接、接合される鋼材が合金鋼の場合は、浸炭、窒化、浸炭窒化などの表面硬化処理を施され、次いで、合金鋼側だけが焼戻し処理されて、機械構造部品とされることも許容される。なお、機械構造部品としての用途に応じて、公知の防錆処理や防錆被覆などの適当な表面処理を施しても良い。 In addition, when the steel material to be joined by friction welding is alloy steel, surface hardening treatment such as carburizing, nitriding, carbonitriding, etc. is performed, and then only the alloy steel side is tempered to be machine structural parts. Is also acceptable. In addition, you may give appropriate surface treatments, such as a well-known antirust process and antirust coating, according to the use as a machine structural component.
（実施例）
以下、実施例を挙げて、本発明をより具体的に説明するとともにその優れた効果を実証するが、当然ながらこの実施例によって本発明が限定的に解釈されるものではない。
表1〜3に示す種々の化学成分（固溶N量も各表別欄に表示）の鋼材（供試材）を種々の方法で作り分けて製造した。そして、機械構造部品を模擬して、これら鋼材を、相手側鋼材であるS35Cおよび熱間鍛造非調質鋼と、各々摩擦圧接して複合材とした。そして、表4〜6に示す通り、これら複合材の衝撃特性、回転曲げ疲労特性、摩擦圧接前後の冷間鍛造性を各々評価した。なお、表１に本発明鋼材の化学成分の範囲を満たすものは○、満たさないものは×として成分判定の欄に示した。同表１の鋼材の製造条件の欄において示した冷却制御温度は、熱間圧延後に開始された、隣欄に表示の冷却速度による冷却制御がその温度まで継続して終了することを意味するものである。
また、表4〜6のミクロ組織の欄には、各鋼材の組織を構成するフェライト、セメンタイトの分率およびフェライトの平均結晶粒径示すともに、これらの組織が本発明鋼材の組織を満たすものは○、満たさないものは×として判定の欄に示した。
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, and the excellent effects thereof will be demonstrated. However, the present invention is not construed as being limited to the examples.
Steel materials (test materials) having various chemical components shown in Tables 1 to 3 (the amount of solute N is also displayed in each table) were produced by various methods. Then, by simulating machine structural parts, these steel materials were friction-welded with the counterpart steel material S35C and hot forged non-heat treated steel, respectively, to obtain composite materials. Then, as shown in Tables 4 to 6, the impact characteristics, rotational bending fatigue characteristics, and cold forgeability before and after friction welding of these composite materials were evaluated. In Table 1, those satisfying the chemical component range of the steel material of the present invention are shown in the column of component determination as ◯, and those not satisfying as x. The cooling control temperature shown in the column of manufacturing conditions for steel materials in Table 1 means that the cooling control based on the cooling rate indicated in the adjacent column, which has been started after hot rolling, continues to that temperature. It is.
In addition, in the columns of the microstructure in Tables 4 to 6, the ferrite constituting the structure of each steel material, the fraction of cementite and the average crystal grain size of ferrite are shown, and those structures satisfy the structure of the steel material of the present invention. ○, unsatisfied are indicated as “x” in the judgment column.
各鋼材の具体的な製造条件は下記の通りである。
[鋼材の製造条件１]
溶解・鋳造：供試鋼150kgを真空誘導炉で溶解し、上面：φ245mm×下面：φ210mm×長さ：480mmのインゴットに鋳造した。
ビレット鍛造：このインゴットを1200℃に加熱して、ビレット（155mm角）に熱間鍛造し、冷却した。
切断、溶接：この鍛造ビレットの端部を切断し、ダミービレット（１55mm角×9〜10m長さ）を溶接した。
熱間圧延：このダミービレット溶接後のビレットを900〜1200℃に加熱後、φ80ｍｍの丸棒を800〜1000℃で熱間圧延後、300〜700℃まで0.1〜50℃／sで冷却した。
なお、ダミービレットで溶接しているのは実機のラインで試験鋼材を圧延するためである。
この製造条件１による鋼材は表1、表2の鋼種No.の全てと、表3の鋼種No.2N〜2Zに該当する。
Specific production conditions for each steel material are as follows.
[Steel production conditions 1]
Melting and casting: 150 kg of the test steel was melted in a vacuum induction furnace and cast into an ingot having an upper surface of φ245 mm × lower surface of φ210 mm × length of 480 mm.
Billet forging: This ingot was heated to 1200 ° C., hot forged into billets (155 mm square), and cooled.
Cutting and welding: The end of this forged billet was cut and a dummy billet (155 mm square × 9 to 10 m length) was welded.
Hot rolling: The billet after the dummy billet welding was heated to 900 to 1200 ° C, and a φ80 mm round bar was hot rolled at 800 to 1000 ° C and then cooled to 300 to 700 ° C at 0.1 to 50 ° C / s.
The reason for welding with the dummy billet is to roll the test steel material on the actual machine line.
The steel materials according to this production condition 1 correspond to all the steel types Nos. 1 and 2 in Tables 1 and 2 and the steel types Nos. 2N to 2Z in Table 3.
[鋼材の製造条件２]
溶解・鋳造、ビレットの熱間鍛造は、上記製造条件１に示した熱間圧延材と同じ条件で製造し、上記熱間圧延を熱間鍛造に変更し、すなわちビレットを1100℃加熱後、φ80mmの丸棒に950℃で熱間鍛造を施し、500℃まで0.7℃／sで冷却した。この製造条件２による鋼材は表3の3A〜3Lに該当する。したがって、これら鋼種No.2N〜2Zにおける表3の鋼材の製造条件の欄の加熱温度は鍛造前の加熱温度、圧延温度は鍛造温度、冷却速度は鍛造後の冷却速度、冷却制御温度は鍛造後の冷却制御温度にそれぞれに読み替えるものとする。
[Steel production conditions 2]
Melting / casting and hot forging of billet are manufactured under the same conditions as the hot rolled material shown in manufacturing condition 1 above, and the hot rolling is changed to hot forging, that is, the billet is heated to 1100 ° C, then φ80mm The round bar was hot forged at 950 ° C and cooled to 500 ° C at 0.7 ° C / s. Steel materials according to production condition 2 correspond to 3A to 3L in Table 3. Therefore, the heating temperature in the column of the production conditions of Table 3 in these steel types No. 2N to 2Z is the heating temperature before forging, the rolling temperature is the forging temperature, the cooling rate is the cooling rate after forging, and the cooling control temperature is after forging. It shall be read as each cooling control temperature.
[固溶N量の特定方法]
本発明における固溶N量の値は、JIS G 1228に準拠し、鋼中の全N量から全N化合物を差し引くことで鋼中の固溶N量を算出する。全N量および全N化合物量の測定方法などは下記の通りである。
(a)鋼中の全N量は、不活性ガス融解法−熱伝導度法を用いる。供試鋼素材からサンプルを切り出し、サンプルをるつぼに入れ、不活性ガス気流中で融解してNを抽出し、熱伝導度セルに搬送して熱伝導度の変化を測定する。
(b)鋼中の全N化合物量は、アンモニア蒸留分離インドフェノール青吸光光度法を用いる。供試鋼素材からサンプルを切り出し、10%AA系電解液（鋼表面に不働態皮膜を生成させない非水溶媒系の電解液であり、具体的には10%アセチルアセトン、10%塩化テトラメチルアンモニウム、残部：メタノール）中で、定電流電解を行なう。約0.5gサンプルを溶解させ、不溶解残渣（N化合物）を穴サイズが0.1μmのポリカーボネート製のフィルタでろ過する。不溶解残渣を硫酸、硫酸カリウム及び純Cuチップ中で加熱して分解し、ろ液に合わせる。この溶液を水酸化ナトリウムでアルカリ性にした後、水蒸気蒸留を行い、留出したアンモニアを希硫酸に吸収させる。フェノール、次亜塩素酸ナトリウム及びペンタシアノニトロシル鉄（III）酸ナトリウムを加えて青色錯体を生成させ、光度計を用いて、その吸光度を測定する。
上記の方法によって求めた鋼中の全N量から全N化合物量を差し引くことで鋼中の固溶N量を算出する。
[Method for determining the amount of solute N]
The value of the solute N amount in the present invention is based on JIS G 1228, and the solute N amount in the steel is calculated by subtracting all N compounds from the total N amount in the steel. The method for measuring the total N amount and the total N compound amount is as follows.
(a) The total N amount in steel is determined by the inert gas melting method-thermal conductivity method. A sample is cut out from the test steel material, put in a crucible, melted in an inert gas stream to extract N, transported to a thermal conductivity cell, and the change in thermal conductivity is measured.
(b) The amount of total N compounds in steel is determined by ammonia distillation separation indophenol blue absorptiometry. A sample was cut out from the test steel material, and 10% AA electrolyte (non-aqueous solvent electrolyte that does not produce a passive film on the steel surface, specifically 10% acetylacetone, 10% tetramethylammonium chloride, Constant current electrolysis is performed in the remainder: methanol). About 0.5 g sample is dissolved, and the insoluble residue (N compound) is filtered through a polycarbonate filter having a hole size of 0.1 μm. The insoluble residue is decomposed by heating in sulfuric acid, potassium sulfate and pure Cu chips and combined with the filtrate. After making this solution alkaline with sodium hydroxide, steam distillation is performed, and the distilled ammonia is absorbed by dilute sulfuric acid. Phenol, sodium hypochlorite and sodium pentacyanonitrosyl iron (III) are added to form a blue complex, and its absorbance is measured using a photometer.
The solute N amount in the steel is calculated by subtracting the total N compound amount from the total N amount in the steel determined by the above method.
[フェライト、セメンタイト、その他の相の分率評価方法]
各鋼材のフェライト、セメンタイト、その他の相の分率は下記の手順で求めた。
(a) 各鋼材のサンプルを長手方向に対して垂直に切断
(b) 横断面が観察できるよう樹脂に埋め込む
(c) エメリー紙、ダイヤモンドバフで試料表面を鏡面研磨
(d) ナイタールで腐食
(e) D/4位置を光学顕微鏡の倍率100倍で観察し、5箇所写真撮影した。
(f) Image Pro Plusを用い、画像を2値化し、フェライトを白色、セメンタイトを黒色とし、どちらにも判定できない相をその他の相とし、それぞれの面積率を求め、5視野の平均値をそれぞれフェライト、セメンタイト、その他の相の面積率として算出し、これを各相の全組織中の分率とした。
[Fraction evaluation method for ferrite, cementite and other phases]
The fraction of ferrite, cementite, and other phases of each steel material was obtained by the following procedure.
(a) Cutting each steel sample perpendicular to the longitudinal direction
(b) Embed in resin so that cross section can be observed
(c) Mirror polishing of sample surface with emery paper and diamond buff
(d) Corrosion with nital
(e) The D / 4 position was observed at a magnification of 100 with an optical microscope, and five photographs were taken.
(f) Using Image Pro Plus, binarizing the image, setting ferrite as white, cementite as black, and determining the other area as the other phase, calculating the area ratio of each, and calculating the average value of the five fields of view. The area ratio of ferrite, cementite, and other phases was calculated and used as the fraction of the entire structure of each phase.
[フェライトの結晶粒径測定方法]
各鋼材のフェライトの平均結晶粒径は下記の手順で求めた。
(a) 圧延サンプルを長手方向に対して垂直に切断。
(b) 横断面が観察できるよう樹脂に埋め込む。
(c) エメリー紙、ダイヤモンドバフで試料表面を鏡面研磨。
(d) 表面のナイタールでエッチング。
(e) 光学顕微鏡を用い、D/4位置を撮影。
(f) 写真に線を引き、線と交差した結晶粒界の数をカウントし、結晶粒径を求めた。
(g) 5視野の平均値を平均結晶粒径とした。
[Method for measuring ferrite grain size]
The average crystal grain size of ferrite of each steel material was determined by the following procedure.
(a) Cutting a rolled sample perpendicular to the longitudinal direction.
(b) Embed in resin so that the cross section can be observed.
(c) The sample surface is mirror-polished with emery paper or diamond buff.
(d) Etching with nital on the surface.
(e) Photographed the D / 4 position using an optical microscope.
(f) A line was drawn on the photograph, and the number of crystal grain boundaries crossing the line was counted to obtain the crystal grain size.
(g) The average value of the five fields of view was defined as the average crystal grain size.
[摩擦圧接試験]
前記熱処理後の各丸棒の長手方向に沿って、D／4位置からφ20mm×１00mmLの棒材（試験片）を切出した。自動摩擦圧接機として日東制機（株）製の製品名FF-4511-Cを用い、ブレーキ法によって摩擦圧接した。即ち、前記切出した棒材同士、および前記切出した棒材の相手材をS35C、熱間鍛造非調質鋼として、各々長手方向に端部同士を突き合わせた丸棒複合鋼材（鋼部品）として、各々摩擦圧接した。摩擦圧接は、各例とも共通して以下の条件に従って行った。
摩擦圧力：80MPa
摩擦時間：7sec
アップセット圧力（接合部への丸棒両端部からの加圧力）：160MPa
アップセット時間（接合部への加圧時間）：7sec
回転数：1600rpm
全寄りしろ：5〜12mm（当初の丸棒長さからの縮み量）
[Friction welding test]
A bar (test piece) of φ20 mm × 100 mmL was cut out from the D / 4 position along the longitudinal direction of each round bar after the heat treatment. Nitto Seiki Co., Ltd. product name FF-4511-C was used as an automatic friction welding machine, and friction welding was performed by the brake method. That is, between the cut bar material, and the mated material of the cut bar material as S35C, hot forged non-heat treated steel, as a round bar composite steel material (steel parts) each end-to-end in the longitudinal direction, Each was friction welded. Friction welding was performed in accordance with the following conditions in common with each example.
Friction pressure: 80MPa
Friction time: 7sec
Upset pressure (pressure applied from both ends of the round bar to the joint): 160 MPa
Upset time (pressurization time to the joint): 7 sec
Rotation speed: 1600rpm
Total margin: 5-12mm (shrinkage from the original round bar length)
[衝撃特性の評価]
φ20mm×約200mmLの前記摩擦圧接品（丸棒複合鋼材）の中央位置から、接合部分がノッチ底となるように、JIS Z 2242に準拠し、1辺が10mmの正方形断面×55mmLのシャルピー試験片を作製した。なお、ノッチ形状は、Uノッチとし、ノッチ半径1mm、ノッチ深さ2mmとした。次いで、シャルピー衝撃試験機にて、試験片の衝撃特性評価を行った。試験条件は、室温、負荷速度5m／sの条件で、5回シャルピー衝撃試験を行い、シャルピー衝撃値（吸収エネルギー）を測定した。この測定値を表４〜６のシャルピー値の欄に、また５回の試験とも吸収エネルギーが15（ジュール）以上のものを合格（〇）とし、一方、1回の試験でも上記基準の吸収エネルギーを下回るものについては不合格（×）として、同表４〜６のシャルピー判定の欄に示した。
[Evaluation of impact properties]
Charpy test piece with a square cross section of 55mmL per 10mm side in accordance with JIS Z 2242 so that the joint is the bottom of the notch from the center of the friction welded product (round bar composite steel) of φ20mm x approx 200mmL Was made. The notch shape was a U notch, a notch radius of 1 mm and a notch depth of 2 mm. Subsequently, the impact characteristic evaluation of the test piece was performed with the Charpy impact tester. The test conditions were a room temperature, a load speed of 5 m / s, a Charpy impact test was performed 5 times, and a Charpy impact value (absorbed energy) was measured. The measured values are shown in the columns of Charpy values in Tables 4 to 6, and those with absorbed energy of 15 (Joule) or more in all five tests are accepted (O). Those less than 5 are shown as reject (x) in the column of Charpy determination in Tables 4-6.
[疲労特性の評価]
φ20mm×約200mmLの前記摩擦圧接品（丸棒複合鋼材）の中央位置から、JIS Z 2274に準拠し、標点間直径がφ6mmの1号試験片を作製した。次いで、回転曲げ疲労試験機にて、試験片の回転曲げ疲労特性評価を行った。試験条件は、周波数20Hzで負荷応力700MPaから200MPaの間で変化させ、10７回寿命に相当する応力（MPa）を求め、これを疲労強度の指標とした。表４〜６にこのようにして求められた疲労強度（疲労限応力）の値を表示するとともに、この値が245MPa以上となる複合鋼材を合格（〇）とし、一つの接合品でも300MPa未満があれば不合格（×）として疲労判定の欄に示した。
[Evaluation of fatigue properties]
From the center position of the friction welded product (round bar composite steel material) of φ20 mm × about 200 mmL, No. 1 test piece with a diameter between the gauges of φ6 mm was prepared according to JIS Z 2274. Subsequently, the rotating bending fatigue characteristic evaluation of the test piece was performed with the rotating bending fatigue testing machine. The test conditions were varied between 200MPa from the load stress 700MPa at frequency 20 Hz, calculated stress (MPa), which corresponds to 10 7 times life, which was used as an index of fatigue strength. The values of fatigue strength (fatigue limit stress) obtained in this way are displayed in Tables 4 to 6, and composite steel materials with this value of 245 MPa or more are accepted (◯), and even one bonded product is less than 300 MPa. If there is, it is shown as a failure (x) in the column of fatigue judgment.
[冷間鍛造性の評価]
φ20ｍｍ×約200ｍｍＬの摩擦圧接前の前記各鋼材と、同φ20ｍｍ×約200ｍｍＬの摩擦圧接後の前記各摩擦圧接品（丸棒複合鋼材）の中央位置から、圧縮方向と接合面が平行となり、接合面が試験片の中央になるようにして、φ10×15mmLの圧縮試験片を切り出した。これら試験片を、1600tプレスを用い、端面を拘束した状態で、室温で、ひずみ速度10／secの冷間鍛造により試験片の軸方向に圧縮率50％まで圧縮して、機械構造用部品の加工試験品（冷間鍛造材）を作製した。なお、加工ひずみ速度は、加工中（塑性変形中）のひずみ速度の平均値とした。なお、圧縮率は、機械構造用鋼の圧縮方向長をＨ0、圧縮後（機械構造用部品）の圧縮方向長をＨとして表したとき、（H0−H）/H0×100で算出される。試験後、実体顕微鏡を用い、20倍で表面状態を観察し、割れの有無をチェックし、割れの無かったものを合格（〇）とし、割れの有ったものの不合格（×）として表4〜6の冷鍛性（冷間鍛造性）の接合前（摩擦圧接前）と接合後（摩擦圧接後）の欄に示した。
[Evaluation of cold forgeability]
From the center position of each steel material before friction welding of φ20mm x approx. 200mmL and each friction welding product (round bar composite steel material) after friction welding of φ20mm x approx. 200mmL, the compression direction is parallel to the joining surface. A compression test piece of φ10 × 15 mmL was cut out so that the surface was at the center of the test piece. These test pieces were compressed to 50% in the axial direction of the test piece by cold forging at a room temperature at a strain rate of 10 / sec using a 1600t press with the end face constrained. A processed test product (cold forging material) was produced. The processing strain rate was an average value of strain rates during processing (plastic deformation). The compression ratio, when the compression direction length of the machine structural steel representing H 0, the compression direction length after compression (parts for machine structural) as H, calculated in (H0-H) / H 0 × 100 The After the test, using a stereomicroscope, observe the surface state at 20x, check for cracks, and pass (o) if there was no crack, and reject (x) if there was a crack. The cold forgeability (cold forgeability) of ~ 6 is shown in the columns before joining (before friction welding) and after joining (after friction welding).
以上の実施例に基づく、各鋼材の冷間鍛造性（冷鍛性）、摩擦圧接後の複合鋼材（摩擦圧接部品）の衝撃特性（シャルピー）、疲労強度および冷間鍛造性の評価を総合した判定した結果（表4〜6の右端欄に○、×で表示）から、本発明鋼材およびその摩擦圧接部品の実施例（鋼種No.1A〜1D-3、1D-5〜1D-6、1D-9〜1D11、1E、1G〜1Y、2A〜2Mおよび2Z〜3L）が比較鋼材およびその摩擦圧接部品の比較例（鋼種No.1D-4、1D-7〜1D-8、1D-12〜1D-13、2N〜2Y）に較べて優れた特性が得られていることが分かり、本発明の顕著な効果が実証されていることが明らかである。 Based on the above examples, the cold forgeability (cold forgeability) of each steel material, the impact properties (Charpy) of the composite steel material after friction welding (friction welding parts), fatigue strength, and evaluation of cold forgeability were integrated. From the judgment results (indicated by ○ and × in the right end column of Tables 4 to 6), examples of the steel material of the present invention and its friction welded parts (steel types No. 1A to 1D-3, 1D-5 to 1D-6, 1D -9 to 1D11 , 1E, 1G to 1Y, 2A to 2M, and 2Z to 3L ) are comparative steels and comparative examples of friction welding parts (steel grades No. 1D-4, 1D-7 to 1D-8, 1D-12 to 1D-13, 2N to 2Y), it is clear that excellent characteristics are obtained, and it is clear that the remarkable effects of the present invention have been demonstrated.
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| JP6165478B2 (en) * | 2013-03-21 | 2017-07-19 | 新日鐵住金株式会社 | Recessed steel pipe joint, bonded steel pipe, and method of joining steel pipes |
| CN113122771B (en) * | 2019-12-31 | 2022-01-14 | 中内凯思汽车新动力系统有限公司 | High-performance friction welding steel piston and preparation method thereof |
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| JP5194522B2 (en) * | 2007-03-30 | 2013-05-08 | Ｊｆｅスチール株式会社 | High-strength, high-workability hot-rolled steel sheet excellent in workability of the friction stir welding method and its production |
| JP5368830B2 (en) * | 2009-03-02 | 2013-12-18 | 株式会社神戸製鋼所 | Steel for machine structure, manufacturing method thereof and machine structure parts |
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| CN106133172A (en) * | 2014-04-08 | 2016-11-16 | 株式会社神户制钢所 | The steel plate of the HAZ tenacity excellent under extremely low temperature |
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