JPH11236644A - Steel for induction hardening excellent in high strength characteristic and low heat treating strain characteristic and its production - Google Patents
Steel for induction hardening excellent in high strength characteristic and low heat treating strain characteristic and its productionInfo
- Publication number
- JPH11236644A JPH11236644A JP5740498A JP5740498A JPH11236644A JP H11236644 A JPH11236644 A JP H11236644A JP 5740498 A JP5740498 A JP 5740498A JP 5740498 A JP5740498 A JP 5740498A JP H11236644 A JPH11236644 A JP H11236644A
- Authority
- JP
- Japan
- Prior art keywords
- ferrite
- steel
- induction hardening
- less
- low heat
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Heat Treatment Of Steel (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、高周波焼入れ用鋼
材に関わり、さらに詳しくは、特に５〜４０ｋＨｚの周
波数で高周波焼入れすることにより製造される各種歯車
類、ドライブシャフトや外輪のような各種シャフト類の
素材として好適な、高強度特性と低熱処理歪み特性に優
れた高周波焼入れ用鋼材とその製造方法に関するもので
ある。本発明で言う強度特性とは、主として捩り強度、
捩り疲労強度、曲げ疲労強度である。本鋼材の適用の対
象となる部品の成形加工工程は、焼鈍を行わずに直接冷
間鍛造を行う工程、冷間鍛造の前または中間に焼鈍を行
う工程、これらに切削工程を含んだ工程、または主とし
て切削により部品を成形加工する工程、一部焼鈍工程を
含んだ切削で部品を成形加工する工程、さらにこれらの
いずれかに転造加工を含む工程、あるいはこれらのいず
れかに温間鍛造を組み合わせた工程等である。なお、本
発明で対象としている部品はこのように切削や冷鍛等の
冷間加工により製造されるために、冷間加工性について
も留意されている。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel material for induction hardening, and more particularly, to various gears and various shafts such as drive shafts and outer rings manufactured by induction hardening at a frequency of 5 to 40 kHz. TECHNICAL FIELD The present invention relates to a steel material for induction hardening excellent in high strength characteristics and low heat treatment distortion characteristics, which is suitable as a kind of material, and a method for producing the same. The strength characteristics referred to in the present invention are mainly torsional strength,
They are torsional fatigue strength and bending fatigue strength. Forming process of parts to which the steel material is applied is a process of directly performing cold forging without performing annealing, a process of performing annealing before or during cold forging, a process including a cutting process in these processes, Alternatively, a process of forming a part mainly by cutting, a step of forming a part by cutting including a partial annealing step, a step including rolling in any of these, or warm forging in any of these These are combined steps. In addition, since the components targeted by the present invention are manufactured by cold working such as cutting and cold forging, the cold workability is also noted.
【０００２】[0002]
【従来の技術】高周波焼入れ工程で製造される各種歯車
類、シャフト類は、近年の自動車エンジンの高出力化あ
るいは環境規制対応にともない、高強度化の指向が強
い。また、研磨工程や矯正工程の省略を狙いとした高周
波焼入れ時に発生する熱処理歪みの低減の要求も強い。2. Description of the Related Art Various types of gears and shafts manufactured in an induction hardening process have a strong tendency to be strengthened in accordance with the recent increase in output of automobile engines or compliance with environmental regulations. There is also a strong demand for reduction of heat treatment distortion generated during induction hardening in order to omit the polishing step and the correction step.
【０００３】本発明では、５〜４０ｋＨｚの周波数で高
周波焼入れする製品を対象としている。従来の主流であ
る１００ｋＨｚ前後の周波数で高周波焼入れされる製品
は、そもそも硬化層深さが浅く（例えば、硬化層深さは
半径の４分の１程度）、耐摩耗性等の確保が主体であ
り、最表面の硬さの確保が重要な課題であった。これに
対して、本発明で対象とする、５〜４０ｋＨｚの周波数
で高周波焼入れする製品においては、捩り強度、捩り疲
労強度の確保が主たる狙いであり、硬化層深さを深くす
ることと硬化層の硬さムラを防ぐことが、高強度化のポ
イントである。また、硬化層の硬さムラを防ぐことによ
り、熱処理歪みは減少する。以上のためには、正味の高
周波焼入れ性を確保することが必須である。The present invention is directed to a product which is induction hardened at a frequency of 5 to 40 kHz. The products that are induction hardened at a frequency of around 100 kHz, which is the conventional mainstream, have a shallow hardened layer depth (for example, the hardened layer depth is about one-fourth of the radius), and mainly ensure wear resistance and the like. Therefore, securing the outermost surface hardness was an important issue. On the other hand, in the products subject to the present invention that are subjected to induction hardening at a frequency of 5 to 40 kHz, the main aim is to secure the torsional strength and the torsional fatigue strength. Preventing unevenness in hardness is the key to high strength. Further, by preventing the unevenness of the hardness of the cured layer, the heat treatment distortion is reduced. For the above reasons, it is essential to ensure a net induction hardening property.
【０００４】これに対して、特開平３−１７７５３７号
公報には、Ｃ：０．３８〜０．４５％、Ｓｉ：０．３５
％以下、Ｍｎ：０．３〜１．０％、Ｂ：０．０００５〜
０．００３５％、Ｔｉ：０．０１〜０．０５％、Ａｌ：
０．０１〜０．０６％、Ｎ：０．０１％以下、フェライ
ト結晶粒度番号：６以上、ミクロ組織：フェライトとパ
ーライト、硬さＨＲＢ８０〜９０、ＪＩＳ０５５８で規
定する脱炭深さ：ＤＭ−Ｔ０．２ｍｍ以下を有する直接
切削・高周波焼入れ用鋼材が示されている。該発明鋼材
はＢ鋼を適用し、脱炭深さを規定した点が特徴である。
該公報には、周波数１００ｋＨｚで高周波焼入れした場
合の特性は記載されているが、本発明で対象とする、５
〜４０ｋＨｚの周波数で高周波焼入れした場合の特性は
記載されていない。また、該公報には、そもそも、本発
明で着眼している静的捩り強度、捩り疲労強度、低熱処
理歪み特性については、全く言及されていない。即ち、
該公報記載の鋼材は高周波焼入れ性が不足するために、
高周波焼入れ部の硬さの不足や、硬さムラの発生が問題
となり、捩り強度等の強度特性は十分ではない場合が起
きると考えられる。On the other hand, JP-A-3-17737 discloses that C: 0.38 to 0.45% and Si: 0.35%.
% Or less, Mn: 0.3 to 1.0%, B: 0.0005 to
0.0035%, Ti: 0.01 to 0.05%, Al:
0.01 to 0.06%, N: 0.01% or less, ferrite crystal grain size number: 6 or more, microstructure: ferrite and pearlite, hardness HRB80 to 90, decarburization depth specified by JIS0558: DM-T0 A steel material for direct cutting and induction hardening having a diameter of 0.2 mm or less is shown. The invention steel material is characterized in that B steel is applied and the decarburization depth is defined.
Although the gazette describes the characteristics when induction hardening is performed at a frequency of 100 kHz, it is intended that the present invention be applied to 5
The characteristics when induction hardening is performed at a frequency of ４０40 kHz are not described. In addition, the publication does not mention at all the static torsional strength, torsional fatigue strength, and low heat treatment strain characteristics which are focused on in the present invention. That is,
Because the steel material described in the publication lacks induction hardening properties,
Insufficient hardness of the induction hardened part and unevenness in hardness may cause problems, and it is considered that strength characteristics such as torsional strength may not be sufficient.
【０００５】また、特開平５−１７９４００号公報に
は、Ｃ：０．３８〜０．４５％、Ｓｉ：０．３５％以
下、Ｍｎ：１．０％超〜１．５％、Ｂ：０．０００５〜
０．００３５％、Ｔｉ：０．０１〜０．０５％、Ａｌ：
０．０１〜０．０６％、Ｎ：０．０１％以下、フェライ
ト結晶粒度番号：６以上の細粒組織を有する直接切削・
高周波焼入れ用鋼材が示されている。該発明鋼材は特開
平３−１７７５３７号公報に対してＭｎ量を増加させた
鋼材である。該公報には、低熱処理歪み特性について
は、言及されていない。また、該公報には、捩り強度は
記載されているが、捩り疲労強度は記載されていない。
やはり、該鋼材も正味の高周波焼入れ性が不足し、高周
波焼入れ部の硬さの不足や、硬さムラの発生が問題とな
り、捩り疲労強度等は十分ではない場合が起きると考え
られる。また、Ｎ量またはＳｉ量が高いために、冷間加
工性が良くないと考えられる。Japanese Patent Application Laid-Open No. Hei 5-179400 discloses that C: 0.38 to 0.45%, Si: 0.35% or less, Mn: more than 1.0% to 1.5%, B: 0 .0005-
0.0035%, Ti: 0.01 to 0.05%, Al:
Direct cutting with a fine grain structure of 0.01 to 0.06%, N: 0.01% or less, ferrite grain size number: 6 or more
A steel for induction hardening is shown. The invention steel material is a steel material in which the amount of Mn is increased from that of JP-A-3-17737. The publication does not mention low heat treatment strain characteristics. In this publication, torsional strength is described, but torsional fatigue strength is not described.
Again, it is considered that the steel material also lacks the net induction hardening property, and the hardness of the induction hardened portion is insufficient, and the occurrence of hardness unevenness is a problem, and the case where the torsional fatigue strength or the like is not sufficient may occur. Further, it is considered that the cold workability is not good because the N amount or the Si amount is high.
【０００６】以上の経緯から、上記の鋼材は、必ずしも
幅広く適用されていないのが現状である。[0006] From the above circumstances, at present, the above steel materials are not always widely applied.
【０００７】[0007]
【発明が解決しようとする課題】上記のような開示され
た鋼材では、高周波焼入れ性は不十分であり、また高周
波焼入れ後の強度特性と低熱処理歪み特性が不足すると
考えられる。本発明はこのような問題を解決して、高強
度特性と低熱処理歪み特性に優れた高周波焼入れ用鋼材
とその製造方法を提供するものである。SUMMARY OF THE INVENTION It is considered that the steel materials disclosed above have insufficient induction hardening properties, and insufficient strength characteristics after induction hardening and low heat treatment distortion characteristics. The present invention solves such a problem and provides a steel material for induction hardening excellent in high strength characteristics and low heat treatment distortion characteristics, and a method of manufacturing the same.
【０００８】[0008]
【課題を解決するための手段】本発明者は、以下の手段
を用いて上記の課題を解決した。すなわち、本発明の請
求項１〜３の発明は、Ｃ：０．３８超〜０．５８％、Ｓ
ｉ：０．０１〜０．１５％、Ｍｎ：０．８５〜１．７
％、Ｓ：０．００５〜０．１５％、Ｃｒ：０．３５％以
下（０％を含む）、Ｂ：０．０００５〜０．００５％、
Ａｌ：０．０１５〜０．０５％、Ｎ：０．００７％未満
（０％を含む）を含有し、ＴｉをＮ含有量に応じて、
０．０１５〜３．４Ｎ＋０．０２％の範囲含有し、Ｐ：
０．０２５％以下（０％を含む）、Ｏ：０．００２５％
以下（０％を含む）に各々制限し、または必要に応じて
さらに、Ｍｏ：０．０２〜０．３％、Ｎｉ：０．０２〜
１．０％のうち１種または２種を含有し、または必要に
応じてさらに、Ｎｂ：０．００２〜０．０３５％、Ｖ：
０．０３〜０．４％のうち１種または２種を含有し、残
部が鉄および不可避的不純物からなり、かつ、ミクロ組
織は実質的にフェライト・パーライト組織であり、フェ
ライト結晶粒径が２５μｍ以下であり、熱間圧延方向に
平行な断面の組織のフェライトバンドの評点が１〜５で
あることを特徴とする高強度特性と低熱処理歪み特性に
優れた高周波焼入れ用鋼材である。The inventor has solved the above-mentioned problem by using the following means. That is, in the invention of claims 1 to 3 of the present invention, C: more than 0.38 to 0.58%,
i: 0.01 to 0.15%, Mn: 0.85 to 1.7
%, S: 0.005 to 0.15%, Cr: 0.35% or less (including 0%), B: 0.0005 to 0.005%,
Al: 0.015 to 0.05%, N: less than 0.007% (including 0%), and Ti according to the N content,
Containing 0.015 to 3.4N + 0.02%;
0.025% or less (including 0%), O: 0.0025%
Below (including 0%), or if necessary, further, Mo: 0.02 to 0.3%, Ni: 0.02 to
One or two of 1.0%, or if necessary, Nb: 0.002 to 0.035%, V:
One or two of 0.03 to 0.4%, the balance being iron and unavoidable impurities, and the microstructure is substantially a ferrite-pearlite structure, and the ferrite grain size is 25 μm. This is a steel material for induction hardening excellent in high strength characteristics and low heat treatment distortion characteristics, characterized in that a ferrite band having a cross section parallel to the hot rolling direction has a rating of 1 to 5.
【０００９】本発明の請求項４の発明は、上記に記載の
成分の鋼を、加熱温度を１０５０℃以上、熱間圧延の仕
上げ温度を７５０〜１０００℃、熱間圧延に引き続いて
７５０〜５００℃の温度範囲を１℃／秒以下の冷却速度
で徐冷する条件により線材または棒鋼に熱間加工し、熱
間加工後のミクロ組織が実質的にフェライト・パーライ
ト組織であり、フェライト結晶粒径が２５μｍ以下であ
り、熱間圧延方向に平行な断面の組織のフェライトバン
ドの評点が１〜５である鋼材となるようにすることを特
徴とする高強度特性と低熱処理歪み特性に優れた高周波
焼入れ用鋼材の製造方法である。According to a fourth aspect of the present invention, a steel having the above-mentioned composition is prepared by heating a steel at a heating temperature of 1050 ° C. or more, a finishing temperature of hot rolling at 750 to 1000 ° C. The steel is hot-worked into a wire or a steel bar under the condition that the temperature is slowly cooled at a cooling rate of 1 ° C./second or less in a temperature range of 1 ° C., and the microstructure after the hot working is substantially a ferrite-pearlite structure, and a ferrite crystal grain size. Is a high-frequency steel excellent in high-strength characteristics and low heat-treating distortion characteristics, characterized in that the steel material has a ferrite band rating of 1 to 5 having a structure of a cross section parallel to the hot rolling direction of 25 μm or less. This is a method for producing hardened steel.
【００１０】本発明の鋼材と製造方法を用いることによ
り、高周波焼入れ後に高強度特性と低熱処理歪み特性に
優れた製品得ることができる。[0010] By using the steel material and the manufacturing method of the present invention, it is possible to obtain a product excellent in high strength characteristics and low heat treatment distortion characteristics after induction hardening.
【００１１】[0011]
【発明の実施の形態】本発明者らは、高周波焼入れ部品
の製造において、高周波焼入れ後に優れた高強度特性と
低熱処理歪み特性を実現するために、鋭意調査し、次の
点を明らかにした。BEST MODE FOR CARRYING OUT THE INVENTION In the manufacture of induction hardened parts, the present inventors have conducted intensive studies to realize excellent high strength characteristics and low heat treatment distortion characteristics after induction hardening, and have clarified the following points. .
【００１２】優れた高強度特性と低熱処理歪み特性を実
現するためには、上記のように硬化層の硬さムラを低減
することがポイントであり、そのためには正味の高周波
焼入れ性を高くすることが重要である。通常の炉加熱の
場合の焼入れ性に比較して、高周波焼入れ性は急速加熱
のために、前組織の影響を大きく受ける。粗大なフェラ
イトがフェライトバンドとして列状に存在すると、炭化
物の溶体化が不十分であり、高周波焼入れ後、硬さ不足
や硬さムラを生じる。図１は、高周波焼入れ前の組織に
フェライトバンドが存在すると、高周波焼入れ後にどの
ような影響がでるかを模式的に表した図である。フェラ
イトバンドが顕著であると、図１に示したように、高周
波焼入れ後、元々パーライト組織の部分が高炭素マルテ
ンサイト、元々フェライトバンドの部分が低炭素マルテ
ンサイトとなり、硬い層と軟らかい層が軸方向に沿って
層状に存在することになる。このような鋼材に、捩り応
力を負荷した場合、軸方向が剪断応力最大の方向になる
ため、軟らかい低炭素マルテンサイト層にそって、剪断
き裂が発生・伝播し、低強度での破壊を招く。歯車のよ
うな曲げ応力が作用する場合も同様で、歯元において、
低炭素マルテンサイト層に沿って、曲げ応力によるき裂
が発生・伝播する。さらに、フェライト粒径が粗大なほ
ど炭素の拡散距離が長くなり、上記の硬さムラは顕著に
なるため、硬さムラの防止と硬化層深さを深くするため
には、フェライト粒径の微細化も重要である。以上か
ら、フェライトの結晶粒径をある値以下に制限し、フェ
ライトバンドを抑制することが必須である。従来技術の
項で示した特開平５−１７９４００号公報、特開平３−
１７７５３７号公報には、上記のようなフェライトバン
ドに関する規定がないために、高周波焼入れ部の硬さの
不足や、硬さムラの発生が問題となり、捩り疲労強度等
の強度特性は十分ではない場合が起きるものと考えられ
る。ここで、フェライトバンドの程度は、図２に示すよ
うに、昭和４５年社団法人日本金属学会発行「日本金属
学会誌第３４巻第９号第９６１頁」において１〜７の７
段階に評点化されている。すなわち、上記の日本金属学
会誌第３４巻第９号の第９５７頁〜９６２頁には、標題
のとおり「フェライト縞状組織におよぼすオーステナイ
ト結晶粒度と鍛造比の影響について」が記載されてお
り、第９６１頁左欄第７〜８行には「縞状組織の程度を
数量的に表示するために、Ｐｈｏｔｏ．４の基準写真を
作成した。」と記載されており、同頁の「Ｐｈｏｔｏ．
４Ｃｌａｓｓｉｆｉｃａｔｉｏｎｓ ｏｆ ｆｅｒｒｉ
ｔｅ ｂａｎｄｓ （×５０×２／３×５／６）」には
１〜７の基準写真が掲載されている。該評点では、評点
の番号が小さいほどフェライトバンドが軽微であり、評
点の番号が大きいほどフェライトバンドが顕著であるこ
とを示している。高周波焼入れ後の硬さムラを抑制する
ためには、熱間圧延方向に平行な断面の組織の、上記の
日本金属学会誌第３４巻第９６１頁で定義されたフェラ
イトバンドの評点が１〜５であることが必要である。In order to realize excellent high strength characteristics and low heat treatment distortion characteristics, the point is to reduce the hardness unevenness of the hardened layer as described above, and for that purpose, the net induction hardenability is increased. This is very important. Compared with the hardenability in the case of normal furnace heating, the induction hardenability is greatly affected by the prestructure due to rapid heating. If coarse ferrite exists in a row as a ferrite band, the solution of the carbide is insufficient, resulting in insufficient hardness or uneven hardness after induction hardening. FIG. 1 is a diagram schematically showing what effect is exerted after induction hardening when a ferrite band is present in the structure before induction hardening. When the ferrite band is remarkable, as shown in FIG. 1, after induction hardening, the part of the pearlite structure originally becomes high carbon martensite, the part of the ferrite band originally becomes low carbon martensite, and the hard layer and the soft layer form an axis. It will exist in layers along the direction. When a torsional stress is applied to such a steel material, the axial direction becomes the direction of the maximum shear stress, so that shear cracks are generated and propagate along the soft low-carbon martensite layer, and fracture at low strength is prevented. Invite. The same applies when bending stress acts like a gear.
Cracks due to bending stress are generated and propagate along the low carbon martensite layer. Furthermore, the larger the ferrite grain size is, the longer the carbon diffusion distance becomes, and the above hardness unevenness becomes remarkable. Therefore, in order to prevent the hardness unevenness and increase the depth of the hardened layer, it is necessary to use a fine ferrite grain size. Is also important. From the above, it is essential to limit the crystal grain size of ferrite to a certain value or less and suppress the ferrite band. JP-A-5-179400 and JP-A-3-179400 described in the section of the prior art.
Since there is no provision regarding the ferrite band as described above in JP-A No. 177537, insufficient hardness of the induction hardened portion and occurrence of uneven hardness are problematic, and strength characteristics such as torsional fatigue strength are not sufficient. Is thought to occur. Here, as shown in FIG. 2, the degree of the ferrite band is 1 to 7 in “The Journal of the Japan Institute of Metals, Vol. 34, No. 9, page 961” published in 1970.
It is graded on a scale. That is, in the above-mentioned Journal of the Japan Institute of Metals, Vol. 34, No. 9, pp. 957 to 962, as described in the title, "Influence of austenite grain size and forging ratio on ferrite stripe structure" is described. On page 961, the left column, lines 7 to 8, it states that "a reference photograph of Photo.4 was prepared in order to quantitatively display the degree of the striped structure."
4Classifications of ferri
In "te bands (x50x2 / 3x5 / 6)", reference photos 1 to 7 are published. In the rating, the smaller the rating number, the lighter the ferrite band, and the larger the rating number, the more prominent the ferrite band. In order to suppress unevenness in hardness after induction hardening, the ferrite band having a structure having a cross section parallel to the hot rolling direction as defined in the above-mentioned Journal of the Japan Institute of Metals, Vol. It is necessary to be.
【００１３】熱間加工後の鋼材のフェライトバンドの程
度を軽減するためには、熱間加工時の加熱温度を１０５
０℃以上と高めに設定し、圧延後の仕上げ温度・冷却条
件を最適化すれば良い。[0013] In order to reduce the degree of the ferrite band of the steel material after hot working, the heating temperature at the time of hot working is set at 105 ° C.
What is necessary is just to set it as high as 0 degreeC or more, and to optimize the finishing temperature and cooling conditions after rolling.
【００１４】上記の炭化物のとけ込み不良を防止し、硬
さムラを低減するためには、Ｃｒの含有量を低減し、Ｍ
ｎの含有量を高くして焼入れ性を確保するとさらに有効
である。In order to prevent the above-mentioned poor melting of carbides and to reduce unevenness in hardness, the content of Cr is reduced and M
It is more effective to increase the content of n to ensure hardenability.
【００１５】さらに、高周波焼入れ材の強度特性を向上
させるためには、旧オーステナイト粒界の粒界強化がポ
イントである。旧オーステナイト粒界の粒界強化には、
低Ｐ化、Ｂ添加が有効である。Further, in order to improve the strength characteristics of the induction hardened material, it is important to strengthen the former austenite grain boundary. For strengthening the grain boundary of the former austenite grain boundary,
It is effective to lower P and add B.
【００１６】次に、本発明で対象としている部品は切削
や冷鍛等の冷間加工により製造されるために、冷間加工
性の確保も重要な課題である。素材の段階で硬さの向上
を抑えて、高周波焼入れ性を向上させるためには、Ｓｉ
の低減とＢの添加が有効である。Ｂを焼入れ性に効かせ
るためには、固溶Ｎの固定が必要であり、そのために通
常Ｔｉを添加する。ここで、ＴｉＮ、Ｔｉ（ＣＮ）は、
冷間加工性を劣化させる。つまり、ＴｉＮ、Ｔｉ（Ｃ
Ｎ）による析出硬化により冷間変形抵抗がアップすると
ともに、冷鍛割れの原因となる。そのため、Ｎ量を０．
００７％以下に低減する。さらに、固溶Ｎを固定するた
めに添加するＴｉ量もＮ量に対応して、必要最小限とす
ることが必要である。また、酸化物系介在物は冷間鍛造
性を劣化させるので酸素量を特定量以下に制限する必要
がある。Next, since the parts targeted by the present invention are manufactured by cold working such as cutting or cold forging, securing cold workability is also an important issue. In order to suppress the improvement of hardness at the stage of material and improve the induction hardening,
And the addition of B are effective. In order to make B effective for hardenability, it is necessary to fix solid solution N. For this purpose, Ti is usually added. Here, TiN and Ti (CN) are:
Deteriorates cold workability. That is, TiN, Ti (C
The precipitation hardening by N) increases the cold deformation resistance and causes cold forging cracking. Therefore, the amount of N is set to 0.
007% or less. Further, the amount of Ti added to fix the solute N must be minimized in accordance with the amount of N. Further, since the oxide-based inclusions deteriorate the cold forgeability, it is necessary to limit the oxygen amount to a specific amount or less.
【００１７】素材の段階で硬さの向上を抑えて優れた冷
間加工性を確保するためには、圧延ままで、実質的にベ
イナイト組織を含まないフェライト・パーライト組織と
することが必要である。熱間加工後の鋼材にベイナイト
組織の生成を抑えて実質的にフェライト・パーライト組
織を得るためには、圧延後の仕上げ温度・冷却条件を最
適化する必要がある。In order to suppress the improvement in hardness at the stage of the raw material and to secure excellent cold workability, it is necessary to have a ferrite-pearlite structure which is as-rolled and substantially does not contain a bainite structure. . In order to suppress the formation of a bainite structure in a steel material after hot working and obtain a ferrite-pearlite structure substantially, it is necessary to optimize the finishing temperature and cooling conditions after rolling.
【００１８】本発明は以上の新規なる知見にもとづいて
なされたものである。The present invention has been made based on the above new findings.
【００１９】以下、本発明について詳細に説明する。Hereinafter, the present invention will be described in detail.
【００２０】まず、成分の限定理由について説明する。First, the reasons for limiting the components will be described.
【００２１】Ｃは鋼に必要な強度を与えるのに有効な元
素であるが、０．３８％以下では必要な強さを確保する
ことができず、０．５８％を越えると硬くなって冷間加
工性が劣化するので、０．３８超〜０．５８％の範囲内
にする必要がある。好適範囲は０．４〜０．５６％であ
る。C is an element effective for imparting necessary strength to steel, but if it is less than 0.38%, the required strength cannot be secured. If it exceeds 0.58%, it becomes hard and becomes cold. Since the interworkability deteriorates, it is necessary to be within the range of more than 0.38 to 0.58%. The preferred range is 0.4-0.56%.
【００２２】Ｓｉは鋼の脱酸に有効な元素であるととも
に、鋼に必要な強度、焼入れ性を与え、焼戻し軟化抵抗
を向上するのに有効な元素であるが、０．０１％未満で
はその効果は不十分である。一方、０．１５％を越える
と、硬さの上昇を招き冷間加工性が劣化する。以上の理
由から、その含有量を０．０１〜０．１５％の範囲内に
する必要がある。好適範囲は０．０３〜０．１％であ
る。Si is an element effective for deoxidizing steel, and is an element effective for imparting necessary strength and hardenability to steel and improving temper softening resistance. The effect is inadequate. On the other hand, when it exceeds 0.15%, the hardness is increased and the cold workability is deteriorated. For the above reasons, its content needs to be within the range of 0.01 to 0.15%. The preferred range is 0.03-0.1%.
【００２３】Ｍｎは、高周波焼入れ性の向上に有効な元
素である。高強度特性と低熱処理歪み特性を重視して、
十分な焼入れ性を確保するためには、０．８５％未満で
はその効果は不十分である。一方、１．７％を越える
と、硬さの顕著な上昇を招き冷間加工性が劣化するの
で、０．８５％〜１．７％の範囲内にする必要がある。
好適範囲は０．８５〜１．４％である。Mn is an element effective for improving induction hardening. Focusing on high strength characteristics and low heat treatment distortion characteristics,
In order to ensure sufficient hardenability, the effect is insufficient if less than 0.85%. On the other hand, when the content exceeds 1.7%, the hardness is significantly increased and the cold workability is deteriorated. Therefore, the content needs to be in the range of 0.85% to 1.7%.
The preferred range is 0.85 to 1.4%.
【００２４】Ｓは鋼中でＭｎＳを形成し、これによる被
削性の向上を目的として添加するが、０．００５％未満
ではその効果は不十分である。一方、０．１５％を超え
るとその効果は飽和し、むしろ粒界偏析を起こし粒界脆
化を招く。以上の理由から、Ｓの含有量を０．００５〜
０．１５％の範囲内にする必要がある。好適範囲は０．
００５〜０．０４％である。S forms MnS in the steel and is added for the purpose of improving the machinability. However, if the content is less than 0.005%, the effect is insufficient. On the other hand, if the content exceeds 0.15%, the effect is saturated, and rather, grain boundary segregation is caused to cause grain boundary embrittlement. For the above reasons, the content of S is 0.005 to
It must be within the range of 0.15%. The preferred range is 0.
005 to 0.04%.
【００２５】Ｃｒは焼入れ性の向上に有効な元素であ
る。但し、Ｃｒはセメンタイト中に固溶してセメンタイ
トを安定化する。そのために、高周波焼入れの短時間加
熱時にセメンタイトの溶け込み不良を起こしやすくな
り、硬さムラの原因となる。この挙動は、特に０．３５
％を超えると顕著になる。以上の理由から、その含有量
を０．３５％以下（０％を含む）に制限する必要があ
る。好適範囲は０．１５％以下である。Cr is an element effective for improving hardenability. However, Cr stabilizes cementite by forming a solid solution in cementite. For this reason, poor penetration of cementite is likely to occur during short-time heating in induction quenching, which causes uneven hardness. This behavior is particularly noticeable at 0.35
%, It becomes remarkable. For the above reasons, it is necessary to limit the content to 0.35% or less (including 0%). A preferred range is 0.15% or less.
【００２６】Ｂは次の３点を狙いとして添加する。棒
鋼・線材圧延において、圧延後の冷却過程でボロン鉄炭
化物を生成することにより、フェライトの成長速度を増
加させ、圧延ままでの軟質化を促進する。高周波焼入
れに際して、鋼に焼入れ性を付与する。高周波焼入れ
材の粒界強度を向上させることにより、機械部品として
の疲労強度・衝撃強度を向上させる。０．０００５％未
満の添加では、上記の効果は不十分であり、０．００５
％を超えるとその効果は飽和するので、その含有量を
０．０００５〜０．００５％の範囲内にする必要があ
る。好適範囲は０．００１〜０．００３％である。B is added aiming at the following three points. In steel bar and wire rod rolling, boron ferrous carbide is generated in a cooling process after rolling, thereby increasing the growth rate of ferrite and promoting softening as-rolled. At the time of induction hardening, steel is given hardenability. By improving the grain boundary strength of the induction hardened material, the fatigue strength and impact strength as mechanical parts are improved. If the addition is less than 0.0005%, the above effect is insufficient, and 0.005%
%, The effect saturates, so the content must be within the range of 0.0005 to 0.005%. A preferred range is 0.001 to 0.003%.
【００２７】Ａｌは脱酸剤として添加する。０．０１５
％未満ではその効果は不十分である。一方、０．０５％
を越えると、ＡｌＮが圧延加熱時に溶体化しないで残存
し、Ｔｉの析出物の析出サイトとなり、冷間加工性を劣
化させる。以上の理由から、その含有量を０．０１５〜
０．０５％の範囲内にする必要がある。好適範囲は０．
０２〜０．０４％である。Al is added as a deoxidizing agent. 0.015
%, The effect is insufficient. On the other hand, 0.05%
Is exceeded, AlN remains without solution during rolling and heating, and becomes a precipitation site of Ti precipitates, deteriorating cold workability. For the above reasons, the content is 0.015
Must be within the range of 0.05%. The preferred range is 0.
02 to 0.04%.
【００２８】Ｎは以下の２点の理由から極力制限するこ
とが望ましい。Ｂは上記のように焼入れ性向上、粒界
強化等を目的として添加するが、これらのＢの効果は鋼
中で固溶Ｂの状態で初めて効果を発現するため、Ｎ量を
低減してＢＮの生成を抑制することが必須である。ま
た、Ｎは鋼中のＴｉと結びつくと粗大なＴｉＮを生成
し、硬さを増加させるとともに、ＴｉＮが冷鍛割れの原
因となるため、冷間加工性が顕著に劣化する。上記の悪
影響はＮ量が０．００７％以上の場合特に顕著である。
以上の理由から、その含有量を０．００７％未満（０％
を含む）に制限する必要がある。好適範囲は０．００５
％以下である。It is desirable to limit N as much as possible for the following two reasons. B is added for the purpose of improving hardenability and strengthening the grain boundary as described above. However, since the effect of B is manifested only in the state of solid solution B in steel, the amount of N is reduced to reduce BN. It is essential to suppress the generation of. In addition, when N combines with Ti in steel, it generates coarse TiN and increases hardness, and at the same time, TiN causes cold forging cracking, so that cold workability is significantly deteriorated. The above adverse effects are particularly significant when the N content is 0.007% or more.
For the above reasons, the content is less than 0.007% (0%
). The preferred range is 0.005
% Or less.
【００２９】Ｔｉは鋼中でＮと結合してＴｉＮを生成す
るが、これによる固溶Ｎの固定によるＢＮの析出防止、
つまり固溶Ｂの確保を目的として添加する。しかしなが
ら、０．０１５％未満ではその効果は不十分である。一
方、ＴｉをＮ含有量に応じて、３．４Ｎ＋０．０２％を
超えて添加すると、ＴｉＣによる析出硬化が顕著にな
り、冷間加工性が顕著に劣化する。以上の理由から、そ
の含有量をＮ含有量に応じて、０．０１５〜３．４Ｎ＋
０．０２％の範囲内にする必要がある。好適範囲は、
０．０２〜３．４Ｎ＋０．０１５％である。Ti combines with N in the steel to form TiN, which prevents the precipitation of BN by fixing solid solution N,
That is, it is added for the purpose of securing solid solution B. However, if less than 0.015%, the effect is insufficient. On the other hand, when Ti is added in excess of 3.4N + 0.02% according to the N content, precipitation hardening due to TiC becomes remarkable, and the cold workability deteriorates remarkably. For the above reasons, the content is adjusted to 0.015 to 3.4 N + in accordance with the N content.
It must be within the range of 0.02%. The preferred range is
0.02 to 3.4N + 0.015%.
【００３０】Ｐは冷間鍛造時の変形抵抗を高め、靭性を
劣化させる元素であるため、冷間加工性が劣化する。ま
た、高周波焼入れ、焼戻し後の部品の結晶粒界を脆化さ
せることによって、最終製品の疲労強度を劣化させるの
でできるだけ低減することが望ましい。従ってその含有
量を０．０２５％（０％を含む）以下に制限する必要が
ある。好適範囲は０．０１５％以下である。Since P is an element that increases the deformation resistance during cold forging and deteriorates toughness, the cold workability deteriorates. In addition, the fatigue strength of the final product is degraded by embrittlement of the crystal grain boundaries of the component after induction hardening and tempering, so that it is desirable to reduce the fatigue strength as much as possible. Therefore, it is necessary to limit the content to 0.025% (including 0%) or less. A preferred range is 0.015% or less.
【００３１】また、Ｏは鋼中でＡｌ2Ｏ3のような酸化物
系介在物を形成する。酸化物系介在物が鋼中に多量に存
在すると、冷間加工性が劣化する。Ｏ含有量が０．００
２５％を超えると特にその傾向が顕著になる。以上の理
由から、その含有量を０．００２５％以下（０％を含
む）に制限する必要がある。好適範囲は０．００２％以
下である。O forms oxide inclusions such as Al 2 O 3 in steel. When a large amount of oxide-based inclusions is present in steel, the cold workability deteriorates. O content is 0.00
If it exceeds 25%, the tendency becomes particularly remarkable. For the above reasons, it is necessary to limit the content to 0.0025% or less (including 0%). A preferred range is 0.002% or less.
【００３２】次に、本発明第２請求項では、Ｍｏ、Ｎｉ
の１種又は２種を含有する。Next, in the second claim of the present invention, Mo, Ni
1 or 2 types.
【００３３】Ｍｏは鋼に強度、焼入れ性を与えるととも
に、高周波焼入れ後の粒界強度を向上させて強度特性を
増加させるのに有効な元素であるが、０．０２％未満で
はその効果は不十分であり、０．３％を越えて添加する
と硬さの上昇を招き冷間加工性が劣化する。以上の理由
から、その含有量を０．０２〜０．３％の範囲内にする
必要がある。Mo is an element effective for imparting strength and hardenability to steel and for improving the grain boundary strength after induction hardening to increase the strength characteristics. However, if less than 0.02%, the effect is ineffective. Sufficiently, if it exceeds 0.3%, the hardness is increased and the cold workability is deteriorated. For the above reasons, the content needs to be within the range of 0.02 to 0.3%.
【００３４】Ｎｉも鋼に強度、焼入れ性を与えるのに有
効な元素であるが、０．０２％未満ではその効果は不十
分であり、１．０％を越えて添加すると硬さの上昇を招
き冷間鍛造性が劣化する。以上の理由から、その含有量
を０．０２〜１．０％の範囲内にする必要がある。Ni is also an effective element for imparting strength and hardenability to steel, but its effect is insufficient if it is less than 0.02%, and if it exceeds 1.0%, the hardness increases. Invited cold forgeability deteriorates. For the above reasons, the content needs to be within the range of 0.02 to 1.0%.
【００３５】次に、本発明第３請求項では、Ｎｂ、Ｖの
１種又は２種を含有する。The third aspect of the present invention contains one or two of Nb and V.
【００３６】Ｎｂは鋼中のＣ、Ｎと結びついてＮｂ（Ｃ
Ｎ）を形成し、結晶粒の微細化および析出硬化による芯
部硬さの増加に有効な元素である。０．００２％未満で
はその効果は不十分である。一方、０．０３５％を超え
ると、素材の硬さが硬くなって冷間加工性が劣化すると
ともに、棒鋼・線材圧延加熱時の溶体化が困難になる。
以上の理由から、その含有量を０．００２〜０．０３５
％の範囲内にする必要がある。好適範囲は、０．００５
〜０．０３％である。Nb combines with C and N in the steel to form Nb (C
N) is an element effective for reducing the crystal grain size and increasing the core hardness by precipitation hardening. If it is less than 0.002%, the effect is insufficient. On the other hand, if the content exceeds 0.035%, the hardness of the material becomes hard and the cold workability deteriorates, and it becomes difficult to form a solution at the time of heating the bar and wire rod rolling.
For the above reasons, the content is 0.002 to 0.035
% Must be within the range. The preferred range is 0.005
~ 0.03%.
【００３７】ＶもＮｂと同様の効果を狙いとして添加す
る。０．０３％未満ではその効果は不十分である。一方
０．４％を超えると、素材の硬さが硬くなって冷間加工
性が劣化するとともに、棒鋼・線材圧延加熱時の溶体化
が困難になる。以上の理由から、その含有量を０．０３
〜０．４％の範囲内にする必要がある。好適範囲は、
０．０５〜０．３％である。V is also added for the same effect as Nb. If it is less than 0.03%, the effect is insufficient. On the other hand, when the content exceeds 0.4%, the hardness of the material becomes hard and the cold workability is deteriorated, and it becomes difficult to form a solution at the time of heating the bar and wire rod rolling. For the above reasons, the content is 0.03
It must be within the range of ~ 0.4%. The preferred range is
0.05-0.3%.
【００３８】次に、本発明では、熱間加工後のミクロ組
織が実質的にフェライト・パーライト組織であり、フェ
ライト結晶粒径を２５μｍ以下に制限し、かつ熱間圧延
方向に平行な断面の組織のフェライトバンドの評点が１
〜５の範囲に制限する。フェライトバンドの評点は、上
記のように日本金属学会誌第３４巻第９６１頁で定義さ
れた評点である。本発明において、組織因子をこのよう
に限定した理由を以下に述べる。Next, in the present invention, the microstructure after hot working is substantially a ferrite / pearlite structure, the ferrite crystal grain size is limited to 25 μm or less, and the structure of a cross section parallel to the hot rolling direction is provided. Of ferrite band of 1
Limited to the range of ~ 5. The score of the ferrite band is a score defined in the Journal of the Japan Institute of Metals, Vol. 34, page 961, as described above. In the present invention, the reason why the tissue factor is limited as described above will be described below.
【００３９】まず、ミクロ組織をフェライト・パーライ
ト組織としたのは、ミクロ組織にベイナイトやマルテン
サイト組織のような硬質組織が混入すると、冷間加工性
が顕著に劣化し、冷間鍛造や切削が困難になるためであ
る。First, the reason why the microstructure is a ferrite-pearlite structure is that if a hard structure such as bainite or martensite is mixed in the microstructure, the cold workability is remarkably deteriorated, and cold forging or cutting is difficult. Because it becomes difficult.
【００４０】次に、高周波焼入れは急速加熱であるため
に、高周波焼入れ前の組織のフェライトが粗大である
と、フェライトの部分は、オーステナイト化後、炭素の
拡散が不十分であり、炭素濃度が添加炭素濃度よりも低
くなり、焼入れ後、その位置での硬さが小さくなる。こ
こで、一般的に熱間圧延後の鋼材の圧延方向に平行な断
面ではフェライトバンドと呼ばれる縞状組織が認められ
る。粗大なフェライトがフェライトバンドとして列状に
連続して存在すると、図１に示したように、焼入れ後の
硬さムラが特に顕著になり、長手方向に元のフェライト
バンドに対応して硬さの軟らかいバンドを形成する。そ
のため、最終部品に捩りモーメントを負荷した時に、こ
の軟質なバンドに沿って剪断き裂力が生成し、低い強度
で破壊する。以上の現象は、フェライト粒径が２５μｍ
を超え、フェライトバンドの評点が５を超えると特に顕
著になる。以上の理由から、フェライト結晶粒径を２５
μｍ以下に制限し、かつ熱間圧延方向に平行な断面の組
織のフェライトバンドの評点が１〜５とした。好適範囲
は、フェライト結晶粒径を２０μｍ以下、熱間圧延方向
に平行な断面の組織のフェライトバンドの評点が１〜４
の範囲である。なお、本発明で言うフェライト粒径と
は、フェライトの形態が粒状の場合はその円相当径に相
当し、またフェライトの形態が板状の場合はその幅に相
当する。Next, since the induction hardening is rapid heating, if the ferrite in the structure before the induction hardening is coarse, the ferrite portion has insufficient carbon diffusion after austenitization and the carbon concentration is low. It becomes lower than the concentration of added carbon, and after quenching, the hardness at that position decreases. Here, a striped structure called a ferrite band is generally observed in a cross section parallel to the rolling direction of the steel material after hot rolling. When coarse ferrite exists continuously in a row as a ferrite band, as shown in FIG. 1, the hardness unevenness after quenching becomes particularly remarkable, and the hardness of the ferrite band in the longitudinal direction corresponds to the original ferrite band. Form a soft band. Therefore, when a torsional moment is applied to the final component, a shear crack force is generated along the soft band, and the component is broken with low strength. The above phenomenon is caused when the ferrite grain size is 25 μm
And when the rating of the ferrite band exceeds 5, it becomes particularly remarkable. For the above reasons, the ferrite grain size is 25
The rating of the ferrite band was restricted to 1 μm or less and the structure of the cross section parallel to the hot rolling direction was rated 1 to 5. The preferred range is a ferrite crystal grain size of 20 μm or less, and a score of a ferrite band having a structure of a cross section parallel to the hot rolling direction is 1 to 4
Range. The ferrite grain size referred to in the present invention corresponds to the circle equivalent diameter when the ferrite form is granular, and corresponds to the width when the ferrite form is plate-like.
【００４１】次に、本発明の請求項４は、加熱温度を１
０５０℃以上、熱間圧延の仕上げ温度を７５０〜１００
０℃、熱間圧延に引き続いて７５０〜５００℃の温度範
囲を１℃／秒以下の冷却速度で徐冷する条件で線材また
は棒鋼に熱間加工する。Next, a fourth aspect of the present invention is to set the heating temperature to 1
050 ° C or higher, hot rolling finish temperature 750-100
Subsequent to hot rolling at 0 ° C., the steel sheet is hot-worked into a wire or a bar under the condition of gradually cooling a temperature range of 750 to 500 ° C. at a cooling rate of 1 ° C./sec or less.
【００４２】まず、加熱温度を１０５０℃以上とするの
は、次の理由による。加熱温度が１０５０℃未満では、
フェライトバンドの評点が５を超えるほどにフェライト
バンドが顕著になり、その後の高周波焼入れ後の硬さム
ラが増大する。また、加熱温度が１０５０℃未満では、
加熱時にＴｉＣが溶体化できずＴｉ（ＣＮ）として粗大
化し、冷間加工性を劣化させる。そのため、熱間加工に
際して、１０５０℃以上の温度で加熱することが必要で
ある。好適範囲は１１００℃以上である。特に、Ｎｂ添
加鋼において、高周波焼入れ後のオーステナイト粒度を
１０番以上に微細化して高強度化を図るためには、加熱
温度を１１００℃以上とするのが望ましい。First, the heating temperature is set to 1050 ° C. or higher for the following reason. If the heating temperature is less than 1050 ° C,
As the rating of the ferrite band exceeds 5, the ferrite band becomes remarkable, and the hardness unevenness after the induction hardening increases. If the heating temperature is lower than 1050 ° C.,
At the time of heating, TiC cannot form a solution and coarsens as Ti (CN), deteriorating cold workability. Therefore, it is necessary to heat at a temperature of 1050 ° C. or more during hot working. A preferred range is 1100 ° C. or higher. Particularly, in the case of Nb-added steel, the heating temperature is desirably set to 1100 ° C. or higher in order to increase the austenitic grain size after induction hardening to 10 or more to achieve high strength.
【００４３】次に、熱間圧延の仕上げ温度を７５０〜１
０００℃とするのは次の理由による。仕上げ温度が７５
０℃未満では、フェライトバンドが評点５を超えるほど
に顕著になり、その後の高周波焼入れ後の硬さムラが増
大する。一方、仕上げ温度が１０００℃を超えると、圧
延材の硬さが硬くなって冷間加工性が劣化する。以上の
理由から、熱間圧延の仕上げ温度を７５０〜１０００℃
とする。好適範囲は８００〜９６０℃である。Next, the finishing temperature of the hot rolling is set to 750 to 1
The reason why the temperature is set to 000 ° C. is as follows. Finishing temperature is 75
If the temperature is lower than 0 ° C., the ferrite band becomes more remarkable as the rating exceeds 5, and the hardness unevenness after the induction hardening increases. On the other hand, when the finishing temperature exceeds 1000 ° C., the hardness of the rolled material becomes hard and the cold workability deteriorates. For the above reasons, the finishing temperature of hot rolling is set to 750 to 1000 ° C.
And The preferred range is 800-960 ° C.
【００４４】次に、熱間圧延に引き続いて７５０〜５０
０℃の温度範囲を１℃／秒以下の冷却速度で徐冷するの
は次の理由による。冷却速度が１℃／ｓを越えると、圧
延ままでの硬さの増加が顕著になり、冷間加工性が劣化
する。そのため、冷却速度１℃／秒以下に制限する。好
適範囲は０．７℃／ｓ以下である。なお、冷却速度を小
さくする方法としては、圧延ラインの後方に保温カバー
または熱源付き保温カバーを設置し、これにより、徐冷
を行う方法が挙げられる。Next, following the hot rolling, 750 to 50
The reason why the temperature range of 0 ° C. is gradually cooled at a cooling rate of 1 ° C./sec or less is as follows. When the cooling rate exceeds 1 ° C./s, the increase in hardness as it is rolled becomes remarkable, and the cold workability deteriorates. Therefore, the cooling rate is limited to 1 ° C./second or less. A preferred range is 0.7 ° C./s or less. In addition, as a method of reducing the cooling rate, there is a method of installing a heat insulating cover or a heat insulating cover with a heat source behind the rolling line, thereby performing slow cooling.
【００４５】本発明では、鋳片のサイズ、凝固時の冷却
速度、分塊圧延条件については特に限定するものではな
く、本発明の要件を満足すればいずれの条件でも良い。In the present invention, the size of the slab, the cooling rate at the time of solidification, and the conditions of the bulk rolling are not particularly limited, and any conditions may be used as long as the requirements of the present invention are satisfied.
【００４６】[0046]
【実施例】以下に、本発明の効果を実施例により、さら
に具体的に示す。EXAMPLES The effects of the present invention will be more specifically described below with reference to examples.
【００４７】表１に示す組成を有する転炉溶製鋼を連続
鋳造し、必要に応じて分塊圧延工程を経て１６２ｍｍ角
の圧延素材とした。比較鋼Ｎｏ．ｋはＪＩＳのＳ４０Ｃ
であり、Ｎｏ．ｌはＪＩＳのＳ５３Ｃである。続いて、
熱間加工により、直径３６〜４５ｍｍの棒鋼を製造し
た。熱間圧延後の冷却は、一部の材料は空冷、また一部
の材料は冷却床に設置した保温カバーを用いて冷却速度
を空冷よりも遅くした。Converter steelmaking compositions having the composition shown in Table 1 were continuously cast and, if necessary, were subjected to a slab rolling process to obtain a rolled material of 162 mm square. Comparative steel No. k is JIS S40C
No. 1 is JIS S53C. continue,
Bars having a diameter of 36 to 45 mm were manufactured by hot working. For cooling after hot rolling, some materials were air-cooled, and some materials were cooled at a lower cooling rate than air-cooling by using a heat insulating cover installed on a cooling floor.
【００４８】圧延後の棒鋼の組織観察を行い、フェライ
ト結晶粒度、圧延方向に平行な断面のフェライトバンド
の評点を求めた。The structure of the bar after rolling was observed, and the ferrite crystal grain size and the score of the ferrite band in a cross section parallel to the rolling direction were determined.
【００４９】また、圧延後の棒鋼のビッカース硬さを測
定した。切削性は硬さに比例することから、硬さを切削
性の指標とした。さらに、圧延ままの棒鋼から、据え込
み試験片を作成し、冷間加工性の指標として、冷間変形
抵抗と限界据え込み率を求めた。冷間変形抵抗は相当歪
み１．０における変形抵抗で代表させた。Further, the Vickers hardness of the bar after rolling was measured. Since machinability is proportional to hardness, hardness was used as an index of machinability. Further, an upsetting test piece was prepared from the as-rolled steel bar, and cold deformation resistance and a limit upsetting ratio were obtained as indices of cold workability. The cold deformation resistance was represented by the deformation resistance at an equivalent strain of 1.0.
【００５０】また、圧延ままの棒鋼を球状化焼鈍した材
料についても、上記の要領で硬さと冷鍛性の評価を行っ
た。The hardness and cold forgeability of the material obtained by spheroidizing an as-rolled steel bar were also evaluated in the manner described above.
【００５１】さらに、圧延材から平行部直径２０ｍｍの
静的捩り試験片、捩り疲労試験片を採取した。静的捩り
試験片、捩り疲労試験片について周波数８．５ｋＨｚ、
最高加熱温度９５０℃の条件で高周波焼入れを行い、そ
の後１７０℃×１時間の条件で焼戻しを行った。なお、
比較例３７、３８については、最高加熱温度１０３０℃
の条件で高周波焼入れを行った。その後、静的捩り試
験、捩り疲労試験を行った。捩り疲労特性は１×１０5
サイクルでの時間強度で評価した。Further, a static torsional test piece and a torsional fatigue test piece having a parallel portion diameter of 20 mm were sampled from the rolled material. The frequency of the static torsional test piece and the torsional fatigue test piece is 8.5 kHz,
Induction hardening was performed at a maximum heating temperature of 950 ° C., and then tempering was performed at 170 ° C. × 1 hour. In addition,
For Comparative Examples 37 and 38, the maximum heating temperature was 1030 ° C.
Induction hardening was performed under the following conditions. Thereafter, a static torsional test and a torsional fatigue test were performed. The torsional fatigue property is 1 × 10 5
Evaluated by the time intensity in the cycle.
【００５２】さらに、圧延材から直径２２ｍｍ×長さ２
００ｍｍの試験片を作成した。本試験片について、上記
の捩り試験片と同じ条件で高周波焼入れを行い、その後
１７０℃×１時間の条件で焼戻しを行った。その後、試
験片の中央部の振れ量を測定することにより、高周波焼
入れによる熱処理歪み量を測定した。Further, from the rolled material, a diameter 22 mm × length 2
A 00 mm test piece was prepared. This test piece was subjected to induction hardening under the same conditions as the above-mentioned torsion test piece, and then tempered at 170 ° C. × 1 hour. Then, the amount of distortion in the heat treatment due to induction hardening was measured by measuring the amount of deflection at the center of the test piece.
【００５３】これらの調査結果を熱間加工条件とあわせ
て表２、３に示す。高周波焼入れ材の硬化層深さは、Ｈ
Ｖ４５０の深さｔと半径ｒの比で表示した。Tables 2 and 3 show the results of these investigations together with the hot working conditions. The hardened layer depth of the induction hardened material is H
It is indicated by the ratio of the depth t to the radius r of V450.
【００５４】比較例３７はＪＩＳのＳ４０Ｃの特性、ま
た比較例３８はＪＩＳのＳ５３Ｃの特性である。本発明
例の０．４〜０．４２％Ｃ鋼については比較例３７と、
本発明例の０．４７〜０．５４％Ｃ鋼については比較例
３８と比較すると、本発明例の冷間変形抵抗は概ね小さ
く、限界据え込み率は概ね優れており、また硬さは概ね
小さい。つまり、本発明例の冷間加工性は、比較例３
７、３８に比較して優れている。球状化焼鈍材について
も同様のことが言える。一方、本発明例は、比較例３
７、３８に比較して高周波焼入れ時の最高加熱温度を低
めに設定しているが、それにもかかわらず、本発明例の
高周波焼入れ材の静的捩り強度、捩り疲労強度は比較例
３７、３８に比較してともに優れている。熱処理歪みも
小さい。Comparative Example 37 shows the characteristics of JIS S40C, and Comparative Example 38 shows the characteristics of JIS S53C. Comparative Example 37 for the 0.4 to 0.42% C steel of the present invention example,
As for the 0.47 to 0.54% C steel of the present invention, as compared with Comparative Example 38, the cold deformation resistance of the present invention example is generally small, the critical upsetting ratio is generally excellent, and the hardness is generally high. small. That is, the cold workability of the example of the present invention was higher than that of the comparative example
It is superior to 7, 38. The same can be said for the spheroidized annealing material. On the other hand, the present invention example is comparative example 3
Although the maximum heating temperature during induction hardening was set lower than in Examples 7 and 38, the static torsional strength and torsional fatigue strength of the induction hardened material of the present invention were nevertheless comparative examples 37 and 38. Are better than both. Heat treatment distortion is small.
【００５５】次に、表３において、比較例２７はＣの含
有量が本発明規定の範囲を下回った場合であり、高周波
焼入れ材の硬化層硬さが低く、強度特性が不足する。比
較例２８はＣの含有量が本発明規定の範囲を上回った場
合であり、比較例２９はＳｉの含有量が本発明規定の範
囲を上回った場合であり、本発明例に比較して、硬く、
冷間加工性が劣る。比較例３０はＭｎの含有量が本発明
規定の範囲を下回った場合であり、高周波焼入れ材の硬
化層深さが浅く、硬さムラも大きく、強度特性が不足す
る。比較例３１はＭｎの含有量が本発明規定の範囲を上
回った場合であり、本発明例に比較して、硬く、冷間加
工性が劣る。比較例３２はＣｒの含有量が本発明規定の
範囲を上回った場合であり、本発明例に比較して硬く、
また高周波焼入れ後の硬さムラも大きく、熱処理歪みも
大きい。Next, in Table 3, Comparative Example 27 is a case where the content of C is lower than the range specified in the present invention, and the hardened layer hardness of the induction hardened material is low and the strength characteristics are insufficient. Comparative Example 28 was a case where the content of C exceeded the range specified by the present invention, and Comparative Example 29 was a case where the content of Si exceeded the range specified by the present invention. Hard,
Poor cold workability. Comparative Example 30 is a case where the Mn content was below the range specified in the present invention, and the hardened layer depth of the induction hardened material was small, the hardness unevenness was large, and the strength characteristics were insufficient. Comparative Example 31 is a case where the Mn content exceeds the range specified in the present invention, and is harder and inferior in cold workability as compared with the present invention. Comparative Example 32 is a case where the content of Cr exceeds the range specified in the present invention, and is harder than that of the present invention.
In addition, hardness unevenness after induction hardening is large, and heat treatment distortion is large.
【００５６】比較例３３はＮの含有量が本発明規定の範
囲を上回った場合であり、冷鍛性の限界圧縮率が顕著に
劣る。比較例３１はＴｉの含有量が本発明規定の範囲を
上回った場合であり、硬く、冷間変形抵抗は高く、限界
圧縮率も顕著に劣る。In Comparative Example 33, the N content exceeded the range specified in the present invention, and the critical compressibility of cold forgeability was remarkably inferior. Comparative Example 31 is a case where the content of Ti exceeds the range specified in the present invention, and is hard, has a high cold deformation resistance, and is remarkably inferior in the critical compressibility.
【００５７】比較例３２はＰの含有量が本発明規定の範
囲を上回った場合であり、冷鍛性の限界圧縮率が劣化す
るとともに、高周波焼入れ後の強度特性が不足する。比
較例３６はＯの含有量が本発明規定の範囲を上回った場
合であり、冷鍛性の限界圧縮率が顕著に劣る。In Comparative Example 32, the content of P exceeds the range specified in the present invention, and the critical compressibility of cold forging deteriorates and the strength characteristics after induction hardening are insufficient. Comparative Example 36 is a case where the O content exceeds the range specified in the present invention, and the critical compressibility of cold forgeability is remarkably inferior.
【００５８】次に、比較例３９は、熱間圧延加熱温度が
本発明規定の範囲を下回り、圧延方向に平行な断面のフ
ェライトバンドの評点が本発明規定の範囲を上回った場
合であり、また、比較例４０は熱間圧延時の仕上げ温度
が本発明規定の範囲を下回り、圧延方向に平行な断面の
フェライトバンドの評点が本発明規定の範囲を上回った
場合であり、ともに高周波焼入れ材の硬化層の硬さムラ
が大きく、静的捩り強度、捩り疲労強度ともに顕著に劣
っている。比較例４１は、熱間圧延仕上げ温度が本発明
規定の範囲を上回った場合であり、比較例４２は熱間圧
延に引き続く冷却速度が本発明規定の範囲を上回った場
合であり、ともに、ベイナイトを生成し、冷間加工性が
顕著に劣る。比較例４３は、フェライト結晶粒径が本発
明規定の範囲を上回った場合であり、高周波焼入れ材の
硬化層の硬さムラが大きく、静的捩り強度、捩り疲労強
度ともに顕著に劣っている。Next, in Comparative Example 39, the hot rolling heating temperature was lower than the range specified in the present invention, and the score of the ferrite band having a cross section parallel to the rolling direction exceeded the range specified in the present invention. In Comparative Example 40, the finishing temperature during hot rolling was lower than the range specified in the present invention, and the rating of the ferrite band having a cross section parallel to the rolling direction was higher than the range specified in the present invention. The hardness unevenness of the hardened layer is large, and both the static torsional strength and the torsional fatigue strength are remarkably inferior. Comparative Example 41 is a case where the hot rolling finish temperature exceeds the range specified in the present invention, and Comparative Example 42 is a case where the cooling rate following hot rolling exceeds the range specified in the present invention. And the cold workability is remarkably inferior. Comparative Example 43 was a case where the ferrite crystal grain size exceeded the range specified in the present invention, and the hardness unevenness of the hardened layer of the induction hardened material was large, and both the static torsional strength and the torsional fatigue strength were remarkably inferior.
【００５９】[0059]
【表１】 [Table 1]
【００６０】[0060]
【表２】 [Table 2]
【００６１】[0061]
【表３】 [Table 3]
【００６２】[0062]
【発明の効果】本発明の高強度特性と低熱処理歪みに優
れた高周波焼入れ用鋼材とその製造方法を用いれば、高
強度高周波焼入れ部品の製造に際して、高周波焼入れ後
の硬さムラが低減でき、優れた強度特性と低熱処理歪み
特性を有する製品を得ることができる。本発明鋼を用い
ることによって、５〜４０ｋＨｚの周波数で高周波焼入
れすることにより製造される歯車類やシャフト類の高強
度化が可能になる。以上のように、本発明による産業上
の効果は極めて顕著なるものがある。The use of the steel material for induction hardening excellent in high strength characteristics and low heat treatment strain of the present invention and the method of manufacturing the same can reduce the hardness unevenness after induction hardening in the production of high strength induction hardened parts. A product having excellent strength characteristics and low heat treatment distortion characteristics can be obtained. By using the steel of the present invention, it is possible to increase the strength of gears and shafts manufactured by induction hardening at a frequency of 5 to 40 kHz. As described above, the industrial effects of the present invention are extremely remarkable.
【図１】高周波焼入れ前のフェライトバンド組織が高周
波焼入れ後に及ぼす影響を示す図である。FIG. 1 is a diagram showing the effect of a ferrite band structure before induction hardening on after induction hardening.
【図２】縞状組織の程度を数量的に表示する金属組織の
顕微鏡写真である（倍率：２８倍）。FIG. 2 is a micrograph of a metal structure that quantitatively indicates the degree of a striped structure (magnification: 28 times).
Claims (4)
％、Ｓｉ：０．０１〜０．１５％、Ｍｎ：０．８５〜
１．７％、Ｓ：０．００５〜０．１５％、Ｃｒ：０．３
５％以下（０％を含む）、Ｂ：０．０００５〜０．００
５％、Ａｌ：０．０１５〜０．０５％、Ｎ：０．００７
％未満（０％を含む）を含有し、ＴｉをＮ含有量に応じ
て、０．０１５〜３．４Ｎ＋０．０２％の範囲含有し、
Ｐ：０．０２５％以下（０％を含む）、Ｏ：０．００２
５％以下（０％を含む）に各々制限し、残部が鉄および
不可避的不純物からなり、かつ、ミクロ組織は実質的に
フェライト・パーライト組織であり、フェライト結晶粒
径が２５μｍ以下であり、熱間圧延方向に平行な断面の
組織のフェライトバンドの評点が１〜５であることを特
徴とする高強度特性と低熱処理歪み特性に優れた高周波
焼入れ用鋼材。1. C .: More than 0.38 to 0.58 by weight%
%, Si: 0.01-0.15%, Mn: 0.85-
1.7%, S: 0.005 to 0.15%, Cr: 0.3
5% or less (including 0%), B: 0.0005 to 0.00
5%, Al: 0.015 to 0.05%, N: 0.007
% (Including 0%), and contains Ti in a range of 0.015 to 3.4N + 0.02% depending on the N content;
P: 0.025% or less (including 0%), O: 0.002
5% or less (including 0%), the balance being iron and unavoidable impurities, and the microstructure is substantially a ferrite-pearlite structure, the ferrite crystal grain size is 25 µm or less, A ferrite band having a cross-section parallel to the hot rolling direction, wherein the ferrite band has a rating of 1 to 5, wherein the steel material for induction hardening is excellent in high strength characteristics and low heat treatment distortion characteristics.
０．３％、Ｎｉ：０．０２〜１．０％のうち１種または
２種を含有することを特徴とする請求項１記載の高強度
特性と低熱処理歪み特性に優れた高周波焼入れ用鋼材。2. In addition, Mo: 0.02 to 2% by weight.
The steel material for induction hardening excellent in high strength characteristics and low heat treatment distortion characteristics according to claim 1, characterized in that it contains one or two of 0.3% and Ni: 0.02 to 1.0%. .
０．０３５％、Ｖ：０．０３〜０．４％のうち１種また
は２種を含有することを特徴とする請求項１または請求
項２記載の高強度特性と低熱処理歪み特性に優れた高周
波焼入れ用鋼材。3. Nb: 0.002 to 2% by weight.
3. High strength characteristics and low heat treatment distortion characteristics according to claim 1 or 2, characterized by containing one or two of 0.035% and V: 0.03 to 0.4%. Steel material for induction hardening.
の成分の鋼を、加熱温度を１０５０℃以上、熱間圧延の
仕上げ温度を７５０〜１０００℃、熱間圧延に引き続い
て７５０〜５００℃の温度範囲を１℃／秒以下の冷却速
度で徐冷する条件により線材または棒鋼に熱間加工し、
熱間加工後のミクロ組織が実質的にフェライト・パーラ
イト組織であり、フェライト結晶粒径が２５μｍ以下で
あり、熱間圧延方向に平行な断面の組織のフェライトバ
ンドの評点が１〜５である鋼材となるようにすることを
特徴とする高強度特性と低熱処理歪み特性に優れた高周
波焼入れ用鋼材の製造方法。4. The steel according to claim 1, wherein the steel is heated at a temperature of at least 1050 ° C., a finishing temperature of the hot rolling is 750 to 1000 ° C., and 750 to 750 following the hot rolling. Hot working into a wire or steel bar under the condition of gradually cooling the temperature range of 500 ° C. at a cooling rate of 1 ° C./sec or less,
A steel material whose microstructure after hot working is substantially a ferrite-pearlite structure, a ferrite crystal grain size is 25 μm or less, and a ferrite band rating of a structure having a cross section parallel to the hot rolling direction is 1 to 5. A method for producing a steel material for induction hardening excellent in high strength characteristics and low heat treatment distortion characteristics, characterized in that:
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|---|---|---|---|
| JP05740498A JP3809004B2 (en) | 1998-02-24 | 1998-02-24 | Induction quenching steel with excellent high strength and low heat treatment strain characteristics and its manufacturing method |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP05740498A JP3809004B2 (en) | 1998-02-24 | 1998-02-24 | Induction quenching steel with excellent high strength and low heat treatment strain characteristics and its manufacturing method |
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| Publication Number | Publication Date |
|---|---|
| JPH11236644A true JPH11236644A (en) | 1999-08-31 |
| JP3809004B2 JP3809004B2 (en) | 2006-08-16 |
Family
ID=13054713
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|---|---|---|---|
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