JPH0967650A - Rod or wire rod of normalized hot rolled steel excellent in cold heading property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the deformation resistance at the time of cold working or the like such as bolt forming, etc., of a steel and to prolong the service life of a working tool and to improve the productive efficiency without executing heat treatment after cold rod drawing or cold wire drawing by specifying its compsn. and reducing the dislocation density of ferrite at the inside of the material represented by the half value width of an X-ray diffraction curve after hot rolling. SOLUTION: This steel has a compsn. contg., by weight, 0.10 to 0.35% C, 0.01 to 0.30% Si and 0.60 to 2.10% Mn, and in which the half value width of an X-ray diffraction after hot rolling is regulated to <2.3. As a means of regulating the above half value width, it is required that the ferritic fraction is made small as far as possible and the dislocation density is reduced, and for this purpose, it is preferable that its temp. at the time of hot rolling is set to a higher one or the cooling rate after the rolling is reduced. After the hot rolling, for obtaining the required shape, dimension and tensile strength, it is subjected to cold rod drawing or wire drawing and is subsequently subjected to cold forming into a normalized formed product.

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【発明の属する技術分野】本発明は、非調質でありなが
ら、ボルト成形等の冷間加工における変形抵抗が少な
く、従って該加工の為の工具について言えば、その寿命
の低下を招かない様な鋼材、殊に熱間圧延された棒また
は線材に関するものである。本発明の熱間圧延材は、一
般に冷間伸線加工を施した後、非調質のまま各種の冷間
加工に付されることを予定するものであるが、この冷間
加工における変形抵抗を低くすることを熱間加工鋼材と
して保証するものである。なお本発明の圧延鋼材は、冷
間伸線後の冷間加工の種類及び冷間加工によって製造さ
れる成形品の種類を一切制限するものではないが、以下
の説明においては、ボルト成形への適用例を代表的に取
り上げて説明することとする。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a low resistance to deformation in cold working such as bolt forming, although it is a non-heat treated material. Therefore, as for a tool for the working, the life of the tool is not shortened. Steel material, in particular hot rolled bar or wire. The hot-rolled material of the present invention is generally intended to be cold-drawn and then subjected to various cold-working in an untempered state. It is guaranteed as a hot-worked steel material that the temperature is low. Note that the rolled steel material of the present invention does not limit the types of cold working after cold drawing and the types of molded products produced by cold working at all, but in the following description, bolt forming An application example will be representatively described.

【０００２】[0002]

【従来の技術】引張強度６００〜８００Ｎ／ｍｍ² 級ボ
ルトは、中炭素鋼あるいは低合金鋼からなる線材や棒鋼
を用いて製造するが、その際通常のプロセスでは、球状
化焼きなまし処理、冷間伸線加工、冷間ボルト成形、ね
じ転造を経て、最後に焼入れ、焼戻し処理を行って所望
の特性に調整している。 ^2. Description of the Related Art Tensile strength 600 to 800 N / mm ² grade bolts are manufactured by using wire rods and bar steels made of medium carbon steel or low alloy steel, in which the usual process is spheroidizing annealing, cold working. After wire drawing, cold bolt forming and thread rolling, finally, quenching and tempering are performed to adjust to desired characteristics.

【０００３】これに対し近年の傾向として、省エネルギ
ーあるいは生産コストダウンの要求が強まり、球状化焼
きなましや焼入れ・焼戻し処理の省略が企図され、いわ
ゆる非調質ボルトへの指向が強まっている。On the other hand, as a tendency in recent years, there is an increasing demand for energy saving or production cost reduction, and it is attempted to omit the spheroidizing annealing and the quenching / tempering treatments, and the so-called non-heat treated bolts are becoming stronger.

【０００４】このような非調質ボルトでは、ボルト成形
の前の冷間伸線加工鋼線の段階で、ボルトとして要求さ
れる所定の引張強度を達成しておくことが必要であるた
め、従前の調質ボルト製造プロセスにおける球状化焼き
なまし材よりも引張強度において高めのものを使用する
ことになり、従ってボルト成形時の冷間圧造性がその分
悪くなるという共通の欠点が指摘されていた。In such a non-heat treated bolt, it is necessary to achieve a predetermined tensile strength required for the bolt at the stage of cold-drawn steel wire before bolt forming, so that it has been conventionally used. It has been pointed out that a common defect that the one having a higher tensile strength than that of the spheroidized annealed material in the tempered bolt manufacturing process is used, and thus the cold forging property at the time of bolt forming is deteriorated accordingly.

【０００５】そこで例えば特公昭６０−４０６号では、
ボルト成形の前に伸線加工を行うことにより（一種のバ
ウシンガー効果を利用することによって）変形抵抗を低
減させることが提案され、また特公昭５４−２０９３１
号では、Ｃを低下させると共に、Ｎｂ，Ｖなどの析出強
化型元素を添加することによって冷間圧造性を向上させ
ることが提案されている。しかしこれらの方法によって
も、従来の球状化焼きなまし材に比べると冷間圧造性の
改善は不十分で、ボルト成形時の工具寿命が短く、より
一層の改善が望まれている。Therefore, for example, in Japanese Examined Patent Publication No. 60-406,
It has been proposed to reduce the deformation resistance (by utilizing a type of Bauschinger effect) by drawing wire prior to bolt forming, and also in Japanese Examined Patent Publication No. 54-20931.
In No. 6, it is proposed to reduce C and improve cold forgeability by adding precipitation strengthening elements such as Nb and V. However, even by these methods, the improvement of the cold forging property is insufficient as compared with the conventional spheroidized annealed material, the tool life at the time of bolt forming is short, and further improvement is desired.

【０００６】一方特公平５−３０８８４では、上記バウ
シンガー効果を最大限に引出すという観点から、単なる
伸線加工の付加に止まらず、鋼の化学成分調整、組織制
御、圧延後の制御冷却などを総合的に組み合わせて実施
することが提案されている。この方法は相応の効果を発
揮するものであるが、全体的に見て複雑な制御を必要と
するので、必ずしも汎用性に富んでいるとは言い難い。On the other hand, in Japanese Examined Patent Publication No. 5-30884, from the viewpoint of maximizing the Bauschinger effect, not only the addition of wire drawing, but also the chemical composition adjustment of steel, the structure control, the controlled cooling after rolling, etc. It is proposed to carry out comprehensive combination. Although this method exhibits a corresponding effect, it is difficult to say that it is versatile because it requires complicated control as a whole.

【０００７】[0007]

【発明が解決しようとする課題】本発明は上記の様な事
情を考慮し、従来とは全く異なったアプローチからの検
討に基づいて為されたものであって、非調質且つ高強度
であっても、冷間伸線を施す前の段階、即ち熱間圧延材
の段階で、ボルト成形等の冷間加工における冷間圧造抵
抗を十分に低下させることができることを保証できる様
な鋼材、即ち冷間圧造性の良い熱間圧延材を提供するこ
とを目的としてなされたものである。換言すれば、本発
明の目的は、冷間加工時の変形抵抗が十分に低い非調質
高強度冷間加工材を製造することを保証できる様な熱間
圧延材の提供を目的とするものである。SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances and based on a study from an approach completely different from the conventional one, and it is non-tempered and has high strength. However, at the stage before cold drawing, that is, at the stage of hot-rolled material, it is possible to ensure that cold forging resistance in cold working such as bolt forming can be sufficiently reduced, that is, It was made for the purpose of providing a hot rolled material having good cold forging property. In other words, an object of the present invention is to provide a hot-rolled material capable of guaranteeing the production of a non-heat treated high-strength cold-worked material having sufficiently low deformation resistance during cold working. Is.

【０００８】[0008]

【課題を解決するための手段】上記課題を達成すること
のできた本発明とは、 Ｃ ：０．１０〜０．３５％ Ｓｉ：０．０１〜０．３０％ Ｍｎ：０．６０〜２．１０％ を含有する鋼の熱間圧延材であって、Ｘ線回折曲線の半
価幅が２．３未満であることを要旨とするものである。
即ちこの熱間圧延材を用いるならば、冷間圧造性の優れ
た非調質且つ高強度の冷間伸線棒または線材を製造でき
る旨保証されるのである。Means for Solving the Problems According to the present invention capable of achieving the above objects, C: 0.10 to 0.35% Si: 0.01 to 0.30% Mn: 0.60 to 2. It is a steel hot-rolled material containing 10%, and the gist is that the half-value width of the X-ray diffraction curve is less than 2.3.
That is, if this hot-rolled material is used, it is guaranteed that a cold-drawn bar or wire rod having excellent cold-formability and having no heat treatment and high strength can be manufactured.

【０００９】[0009]

【発明の実施の形態】まず本発明鋼を構成する化学成分
について説明する。 Ｃ：０．１０〜０．３５％ Ｃは固溶強化によって鋼に所望の強度を与える上で必要
な元素であり、とくに伸線加工後の引張強度を６００Ｎ
／ｍｍ² 以上とする為には、既に知られている様に０．
１０％以上の添加が必要である。しかし０．３５％を超
えると、靭性が低下すると共に冷間加工時の変形抵抗を
増大させ、成形品の割れや工具寿命の低下を招く。Ｃの
より好ましい添加範囲は０．１５〜３５％である。BEST MODE FOR CARRYING OUT THE INVENTION First, the chemical components constituting the steel of the present invention will be described. C: 0.10 to 0.35% C is an element necessary for giving the desired strength to the steel by solid solution strengthening, and especially the tensile strength after wire drawing is 600N.
/ Mm ² or more, it is 0.
It is necessary to add 10% or more. However, if it exceeds 0.35%, the toughness is lowered and the deformation resistance at the time of cold working is increased, resulting in cracking of the molded product and shortening of the tool life. The more preferable addition range of C is 0.15 to 35%.

【００１０】Ｓｉ：０．０１〜０．３０％ Ｓｉは鋼中において脱酸作用を発揮すると共に、固溶強
化によって強度向上に寄与する元素であるが、既に知ら
れている様に０．０１％以上の添加が必要である。しか
し０．３０％を超えると、靭性が低下すると共に冷間加
工時の変形抵抗を増大させ、成形品の割れや工具寿命の
低下を招く。なお本発明者等の研究によれば、同じく固
溶強化型元素であるＣに比べると、Ｓｉは変形抵抗を増
大させやすい元素であることが分かっており、本発明に
おいては、一般的にＳｉ添加量はＣ添加量より抑制する
ことが好ましいことが多い。Ｓｉのより好ましい添加範
囲は０．０５〜０．２５％である。Si: 0.01 to 0.30% Si is an element that exerts a deoxidizing action in steel and contributes to strength improvement by solid solution strengthening, but as already known, 0.01 % Or more must be added. However, if it exceeds 0.30%, the toughness decreases and the deformation resistance at the time of cold working increases, resulting in cracking of the molded product and shortening of the tool life. According to the research conducted by the present inventors, it has been found that Si is an element that easily increases the deformation resistance as compared with C, which is also a solid solution strengthening element, and in the present invention, Si is generally used. In many cases, it is preferable to suppress the addition amount from the C addition amount. The more preferable addition range of Si is 0.05 to 0.25%.

【００１１】Ｍｎ：０．６０〜２．１０％ Ｍｎは固溶強化元素であり、本発明では、Ｃによる固溶
強化作用を補充する。本発明では、Ｃの過剰添加による
変形抵抗の増大を避けることとしているので、Ｃを前記
の如く少なめの範囲に設定しており、これを補足すると
いう主旨から、既に知られている様に、少なくとも０．
６０％の添加を必須とするが、Ｍｎにおいても過剰添加
は靭性と変形抵抗の増大を招くので、２．１０％を超え
て添加させてはならない。より好ましい添加範囲は０．
７０〜２．００％、更に好ましい範囲は０．８０〜１．
６０％である。Mn: 0.60 to 2.10% Mn is a solid solution strengthening element, and in the present invention, the solid solution strengthening action of C is supplemented. In the present invention, since it is intended to avoid an increase in deformation resistance due to excessive addition of C, C is set in a small range as described above, and as is already known from the purpose of supplementing this, as already known, At least 0.
Although 60% of Mn is indispensable, excessive addition of Mn causes an increase in toughness and deformation resistance. Therefore, Mn should not be added in excess of 2.10%. A more preferable addition range is 0.
70 to 2.00%, more preferably 0.80 to 1.
60%.

【００１２】本発明鋼における必須元素は以上述べた通
りであり、他の元素の添加については格別制限されな
い。例えば析出強化型の元素であるＶ，Ｎｂ，Ｔｉ等を
添加することもできるが、最も通常の元素構成によれ
ば、残部は実質的にＦｅ及び不可避的元素である。この
ような不可避的元素としては、Ｐ，Ｓ，Ｃｒ，Ｎ，Ｏ等
が挙げられる。The essential elements in the steel of the present invention are as described above, and the addition of other elements is not particularly limited. For example, precipitation-strengthening elements such as V, Nb, and Ti may be added, but according to the most common elemental structure, the balance is substantially Fe and unavoidable elements. Examples of such inevitable elements include P, S, Cr, N and O.

【００１３】次に熱間圧延材のＸ線回折曲線の半価幅を
２．３未満と定めた理由について述べる。一般に冷間圧
造用工具の寿命は被加工材である鋼材の硬さ等によって
左右されるが、特にミクロ的な観点から見ると、フェラ
イト部の硬化度による影響が大きい。しかるにフェライ
ト部の硬化度は転位密度と深い関係を有しており、一方
転位密度の大きさは半価幅の大きさとして表すことがで
きる。本発明者等はこの様な観点から検討を行い、Ｘ線
回折曲線の半価幅が２．３未満になる様に制御された熱
間圧延線材では、これを一般的な伸線加工率（１０〜４
０％）で伸線したものを更に冷間圧造した時のフェライ
ト部の転位密度が比較的小さく、従って変形抵抗が少な
く工具寿命が長くなることを見出したのである。Next, the reason why the half width of the X-ray diffraction curve of the hot rolled material is set to less than 2.3 will be described. Generally, the life of a cold heading tool depends on the hardness of a steel material as a work material, etc., but from a microscopic point of view, the degree of hardening of a ferrite part has a large effect. However, the degree of hardening of the ferrite part has a deep relationship with the dislocation density, while the size of the dislocation density can be expressed as the size of the half-value width. The inventors of the present invention have studied from such a viewpoint, and in a hot-rolled wire controlled so that the half-value width of the X-ray diffraction curve is less than 2.3, this is a general wire drawing rate ( 10-4
It has been found that the dislocation density of the ferrite part is relatively small when the drawn wire is further cold forged at 0%), so that the deformation resistance is small and the tool life is long.

【００１４】Ｘ線回折曲線の半価幅を２．３未満とす為
の制御手段としては、上記したところから理解される様
に、フェライトの転位密度を小さくすることが必要であ
り、そのためにはフェライト分率をできる限り小さくす
ることが必要となる。従って例えば熱間圧延時の温度を
高めに設定したり、あるいは圧延後の冷却速度をできる
限り遅くすること等が望まれる。As will be understood from the above, it is necessary to reduce the dislocation density of ferrite as a control means for controlling the half width of the X-ray diffraction curve to less than 2.3. It is necessary to reduce the ferrite fraction as much as possible. Therefore, for example, it is desirable to set the temperature during hot rolling to be higher, or to lower the cooling rate after rolling as much as possible.

【００１５】[0015]

【実施例】表１に示す化学成分からなる鋼材を溶製して
得られる鋼塊を熱間圧延し、直径１０ｍｍの熱間圧延材
を製造した。Example A steel ingot obtained by melting a steel material having the chemical composition shown in Table 1 was hot-rolled to produce a hot-rolled material having a diameter of 10 mm.

【００１６】[0016]

【表１】 [Table 1]

【００１７】この熱間圧延材について、表面のスケール
を除去した後、最表面部について軸方向のＸ線回折曲線
［α鉄の（２１１面）］の半価幅を測定した。この時の
Ｘ線としてはＣｒ−Ｋα線を用い、ビーム径は２．０ｍ
ｍとした。After removing the scale on the surface of this hot rolled material, the half-value width of the X-ray diffraction curve [α iron (211 plane)] in the axial direction was measured for the outermost surface portion. At this time, Cr-Kα rays were used as X-rays, and the beam diameter was 2.0 m.
m.

【００１８】一方この熱間圧延材について、所望のサイ
ズ及び引張強度を得る為に伸線加工を施し、更に非調質
ボルトの成形加工を行った。熱間圧延材の半価幅、ボル
ト成形時の工具寿命は、表２に示す通りであった。On the other hand, this hot rolled material was subjected to wire drawing in order to obtain a desired size and tensile strength, and was further processed to form a non-heat treated bolt. The full width at half maximum of the hot rolled material and the tool life during bolt forming were as shown in Table 2.

【００１９】[0019]

【表２】 [Table 2]

【００２０】実験Ｎｏ．１〜４（実施例）は熱間圧延材
の半価幅が小さく、ボルト成形時の工具寿命は良好であ
ったが、実験Ｎｏ．５〜９（比較例）はいずれも熱間圧
延材の半価幅が大きく、ボルト成形時の工具寿命は短
い。特に実験Ｎｏ．３，４のものは、熱間圧延材の引張
強度が実験Ｎｏ．６〜９のものより大きいにもかかわら
ず、工具寿命において実験Ｎｏ．６〜９のものより良好
な成績を示していることは驚くべきことである。Experiment No. In Examples 1 to 4 (Examples), the half width of the hot-rolled material was small and the tool life during bolt forming was good, but Experiment No. In Examples 5 to 9 (Comparative Examples), the half-value width of the hot rolled material is large and the tool life during bolt forming is short. In particular, in Experiment No. In Nos. 3 and 4, the tensile strength of the hot-rolled material was No. Experiment No. 6 in tool life despite being larger than those of Nos. 6-9. It is surprising that they perform better than those of 6-9.

【００２１】[0021]

【発明の効果】本発明は上記の様に構成されているの
で、鋼材の化学成分及び熱間圧延材におけるＸ線回折曲
線の半価幅を規定することによって、冷間圧造時の変形
抵抗を低減することが可能となり、その結果加工工具の
寿命を延長し、生産コストの低減に寄与できることとな
った。EFFECTS OF THE INVENTION Since the present invention is constituted as described above, the deformation resistance during cold forging is determined by defining the chemical composition of steel and the half-value width of the X-ray diffraction curve in the hot rolled material. As a result, it is possible to extend the life of the machining tool and contribute to the reduction of production cost.

Claims (1)

【特許請求の範囲】[Claims] 【請求項１】Ｃ ：０．１０〜０．３５質量％（質量％
は以下単に％と表記する） Ｓｉ：０．０１〜０．３０％ Ｍｎ：０．６０〜２．１０％ を含有する鋼の熱間圧延材であって、Ｘ線回折曲線の半
価幅が２．３未満であることを特徴とする冷間圧造性の
優れた非調質熱間圧延鋼の棒または線材。1. C: 0.10 to 0.35 mass% (mass%
Is simply expressed as%) A hot rolled steel material containing Si: 0.01 to 0.30% Mn: 0.60 to 2.10% and having a half-value width of an X-ray diffraction curve. A bar or wire rod of non-tempered hot-rolled steel excellent in cold forging property, which is less than 2.3.