JPH08302447A - Case hardening steel excellent in cold workability and machinability - Google Patents

Abstract

PURPOSE: To provide a case hardening steel excellent in cold workability and machinability by preparing a steel having a specified componental compsn. in which the contents of Si, Mn, Cr and S are reduced and B is added. CONSTITUTION: A steel having a compsn. contg., by weight, 0.1 to 0.3% C, <0.15% Si, <=1.5% Mn, <=0.30% S, 0.003 to 0.005% B, 0.005 to 0.100% Nb, <=0.040% s-Al, <=0.10% Ti, and <=0.020% N, contg. one or >= two kinds selected from <=0.40% Pb, <=0.40% Bi, 0.001 to 0.050% Te, 0.0005 to 0.0030% Ca and 0.003 to 0.050% Se, and the balance Fe with impurities is prepd. Thus, the case hardening steel excellent in hot workability, machinability and cold forgeability can be obtd.

Description

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

【０００１】[0001]

【産業上の利用分野】本発明は冷間加工性および被削性
に優れた機械構造用鋼の製造方法に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a steel for machine structural use which is excellent in cold workability and machinability.

【０００２】[0002]

【従来の技術】歯車などの機械構造用鋼を製造する際に
は、クロム鋼等の綱材を溶解工程→熱間加工→球状化焼
なまし→冷間加工→焼ならし→浸炭焼入れ焼戻し→仕上
加工という工程からなる方法が適用されていた。ここで
いう熱間加工とは一般に行われている熱間圧延、熱間鍛
造を示すものである。2. Description of the Related Art When manufacturing steel for machine structures such as gears, melting process of steel such as chrome steel → hot working → spheroidizing annealing → cold working → normalizing → carburizing quenching and tempering → A method consisting of a finishing process was applied. The hot working referred to here means hot rolling and hot forging which are generally performed.

【０００３】上記工程において、球状化焼なまし工程
は、鋼材中に含有される炭化物を球状化して鋼材を軟化
させ、後段の冷間加工を容易にするために行われる。と
ころが球状化焼なまし工程は１０〜２０時間を要し、生
産性向上および省エネルギーの観点から球状化焼なまし
工程なしで冷間加工に供することのできる肌焼鋼の開発
が要望されていた。In the above process, the spheroidizing annealing process is carried out in order to make the carbide contained in the steel material spherical to soften the steel material and facilitate the subsequent cold working. However, the spheroidizing annealing process requires 10 to 20 hours, and there has been a demand for the development of case-hardening steel that can be subjected to cold working without the spheroidizing annealing process from the viewpoint of productivity improvement and energy saving. .

【０００４】上記問題点解決のために熱間仕上圧延条件
を規制した制御圧延によりオーステナイト粒の微細化お
よび変形帯の導入を図り，フェライト・パーライト変態
を促進させ熱間圧延ままで冷間加工性の優れた鋼材の製
造方法や、Ｂを添加することにより焼入性を変化させず
に冷鍛性を阻害するＳｉ，Ｃｒ，Ｍｎを低減させる肌焼
Ｂ綱などが提案されている。ところが肌焼Ｂ鋼は硬さが
低く延性が高いため、歯車などの切削加工を行ったとき
にバリが大きく出るという問題が生じている。In order to solve the above problems, fine rolling of austenite grains and introduction of a deformation zone are attempted by controlled rolling in which hot finish rolling conditions are regulated to promote ferrite-pearlite transformation and cold workability as hot rolling. Of the above-mentioned steel manufacturing method, and a case-hardening B steel that reduces Si, Cr, and Mn that inhibits cold forging without changing hardenability by adding B. However, since the case-hardening B steel has low hardness and high ductility, there arises a problem that large burrs are generated when cutting gears and the like.

【０００５】[0005]

【発明が解決しようとする課題】本発明は熱間加工まま
で優れた冷間加工性を持ち、なおかつ被削性にも優れた
肌焼鋼を提供することを目的とするものである。SUMMARY OF THE INVENTION It is an object of the present invention to provide a case-hardening steel which has excellent cold workability as it is while hot working and also has excellent machinability.

【０００６】[0006]

【課題を解決するための手段】本発明は上記問題点の解
決のために冷間加工性を阻害する元素であるＳを低減す
るとともに、変形抵抗を小さくするためにＳｉ，Ｃｒ，
Ｍｎを低減させた。また焼入性を確保するためＢを添
加、また結晶粒粗大化防止のため、Ｎｂを添加し、Ｎを
低減させた。そして切削時のバリを減少するために、Ｐ
ｂ，Ｂｉ，Ｔｅ，Ｃａ，Ｓｅの１種または２種以上を含
有した冷間加工性および被削性の優れた肌焼鋼を提供す
るものである。In order to solve the above problems, the present invention reduces S, which is an element that impairs cold workability, and reduces Si, Cr, and
Mn was reduced. Further, B was added to ensure hardenability, and Nb was added to prevent coarsening of crystal grains to reduce N. And in order to reduce the burr at the time of cutting, P
The present invention provides a case-hardening steel containing one or more of b, Bi, Te, Ca, and Se, which is excellent in cold workability and machinability.

【０００７】[0007]

【作用】本発明を以下に詳細に説明する。本発明の鋼材
において、Ｃは鋼材の心部の強度を確保する元素である
が、０．１％未満の含有量ではその効果は少なく、しか
し０．３％を超えて含まれると熱間加工後鋼材の硬さが
増大して球状化焼なまし行程を省略することが不可避と
なる。The present invention will be described in detail below. In the steel material of the present invention, C is an element that secures the strength of the core portion of the steel material, but if the content is less than 0.1%, its effect is small, but if it exceeds 0.3%, hot working occurs. Since the hardness of the rear steel material increases, it becomes unavoidable to omit the spheroidizing annealing process.

【０００８】Ｓｉはフェライト強化型元素であり０．１
５％以上含まれると変形抵抗が高くなり、冷間加工性を
悪化させるとともに、浸炭処理時の粒界酸化を助長して
破壊起点となりやすい。また硬さの上昇から被削性も悪
化する。Si is a ferrite strengthening element and is 0.1
If it is contained in an amount of 5% or more, the deformation resistance becomes high, the cold workability is deteriorated, and the grain boundary oxidation during the carburizing treatment is promoted, which easily becomes a fracture starting point. Further, the machinability is deteriorated due to the increase in hardness.

【０００９】Ｍｎは焼入れ性および鋼材心部の強度を向
上せしめる元素であるが、変形抵抗及び加工硬化率を高
くする元素であり、１．５０％を超えて含まれると冷間
加工性および被削性を悪化させる。Mn is an element that improves the hardenability and the strength of the steel core, but it is an element that increases the deformation resistance and the work hardening rate, and if it is contained in excess of 1.50%, the cold workability and the workability. Machinability deteriorates.

【００１０】Ｂは焼入性を向上せしめる元素であるが、
０．０００３％未満の含有量ではその効果は少なく、し
かし０．００５％を超えて含まれてもその効果は飽和
し、また赤熱脆性を起こす。B is an element that improves hardenability,
If the content is less than 0.0003%, the effect is small, but if the content is more than 0.005%, the effect is saturated and red hot brittleness occurs.

【００１１】Ｎｂはオーステナイト結晶粒を微細化する
元素であるが、０．００５％未満の含有量ではその効果
は少なく、しかし０．１００％を超えて含まれると製造
性が低下する。Nb is an element for refining austenite crystal grains, but if the content is less than 0.005%, its effect is small, but if it exceeds 0.100%, the manufacturability deteriorates.

【００１２】Ａｌは脱酸および冷間加工後の熱処理時に
おいてオーステナイト粒の粗大化を防止する効果を有し
ているが、０．０４０％を超えて含ませても効果が飽和
する。Al has the effect of preventing coarsening of austenite grains during heat treatment after deoxidation and cold working, but the effect is saturated even if it is contained in excess of 0.040%.

【００１３】ＴｉはＢが鋼材中でＢＮとなって焼入性向
上に寄与しなくなるのを防ぐ元素である。また０．１％
を超えて添加しても効果の向上度は少ない。ただしＴｉ
／Ｎ≧３．６でないとその効果は発揮されない。Ti is an element that prevents B from becoming BN in the steel material and not contributing to improving the hardenability. 0.1%
Even if added over the range, the degree of improvement in effect is small. However, Ti
The effect is not exhibited unless /N≧3.6.

【００１４】Ｎは鋼材中でＢＮとなり、Ｂの焼入性向上
効果を損なわせる元素である。また窒化物を生成し、限
界圧縮率への悪影響が大きいため０．０２０％以下とす
る。N is an element which becomes BN in the steel material and impairs the hardenability improving effect of B. Further, since nitride is generated and the adverse effect on the critical compressibility is large, the content is made 0.020% or less.

【００１５】Ｐｂ、Ｂｉ，Ｔｅ，Ｃａ，Ｓｅは切削加工
時のバリ生成を抑制する働きを持っており、それぞれＰ
ｂ≦０．４０％，Ｂｉ≦０．４０％，Ｔｅ：０．００１
％〜０．０５０％，Ｃａ：０．０００５％〜０．００３
０％，Ｓｅ：０．００３％〜０．０５０％の範囲とする
ことにより効果が現われる。各元素とも添加しすぎると
冷鍛性を悪化させる。Pb, Bi, Te, Ca and Se have the function of suppressing the formation of burrs during cutting, and P
b ≦ 0.40%, Bi ≦ 0.40%, Te: 0.001
% To 0.050%, Ca: 0.0005% to 0.003
The effect is exhibited by setting the range of 0% and Se: 0.003% to 0.050%. If each element is added too much, the cold forgeability deteriorates.

【００１６】Ｃｒ，Ｎｉ，Ｍｏは浸炭部およびそれより
内部の靭性向上に有効な元素であるが、請求項に記載し
た範囲を超えて含まれると熱間加工後の硬度が増大し球
状化焼なまし行程が不可避となり、また被削性も悪化さ
せる。Cr, Ni, and Mo are elements effective for improving the toughness of the carburized portion and the inside thereof. However, if they are contained beyond the range described in the claims, the hardness after hot working increases and spheroidized. The annealing process becomes unavoidable and the machinability deteriorates.

【００１７】ＳおよびＯは介在物を生成し冷間加工性、
特に変形能や疲れ強さを低下させる元素であるため、請
求項に記載した範囲以下とすることにより、大幅に鋼材
性能を向上させることになる。S and O form inclusions and cold workability,
In particular, since it is an element that lowers the deformability and the fatigue strength, the steel material performance is significantly improved by setting it within the range described in the claims.

【００１８】[0018]

【実施例】本発明による鋼材と比較鋼の化学成分を表１
に示す。これら鋼材は常法にて溶製され、その後ビレッ
ト段階を経て棒鋼に圧延した。[Examples] Table 1 shows the chemical composition of steel materials according to the present invention and comparative steel
Shown in These steel materials were melted by a conventional method, and then rolled into a steel bar through a billet stage.

【００１９】冷間加工性の評価は、圧延後の硬さおよび
冷間据込み性試験による割れ発生率により行い、また被
削性の評価は、旋削試験の工具寿命および歯切り試験時
に生じるバリ高さにより行った。冷間すえ込み試験に
は、１５Ｄ×２２．５Ｌの円柱試験片を用い端面拘束試
験により行った。圧縮率を６０，６５，７０，７５，８
０，８２．５％とし、各圧縮率で１０ヶ据え込み試験を
行い、一つでも割れが生じた圧縮率を限界圧縮率とし
た。歪速度は１〜３ｓ^−１である。The cold workability is evaluated by the hardness after rolling and the crack occurrence rate by the cold upsetting test, and the machinability is evaluated by the tool life in the turning test and the burrs generated during the gear cutting test. Made by height. The cold swaging test was conducted by an end face restraint test using a 15D × 22.5L cylindrical test piece. The compression rate is 60, 65, 70, 75, 8
The compression rate was set to 0,82.5%, 10 upsetting tests were performed at each compression rate, and the compression rate at which even one crack occurred was taken as the limit compression rate. The strain rate is ¹ to 3 s ^-1 .

【００２０】被削性の評価は、旋削試験を行い工具寿命
時間を測定した。切削条件は、切削速度：２００ｍ／ｍ
ｉｎ、送り：０．２０ｍｍ／ｒｐｍ、切込み：２ｍｍで
ある。工具寿命は境界摩耗が０．２ｍｍとなる時間であ
る。また切削時に生じるバリの測定は、歯切り試験を行
い、刃先に生じたバリの高さを光学顕微鏡を用いて測定
した。切削条件は、切削速度：１４８ｍ／ｍｉｎ、送
り：４ｍｍ／ｒｐｍ、切込み：５．４ｍｍである。For the evaluation of machinability, a turning test was conducted to measure the tool life time. Cutting conditions are cutting speed: 200m / m
in, feed: 0.20 mm / rpm, depth of cut: 2 mm. Tool life is the time when the boundary wear becomes 0.2 mm. For the measurement of burrs generated during cutting, a gear cutting test was performed, and the height of burrs formed on the cutting edge was measured using an optical microscope. The cutting conditions are: cutting speed: 148 m / min, feed: 4 mm / rpm, depth of cut: 5.4 mm.

【００２１】[0021]

【表１】 [Table 1]

【００２２】試験結果を表２に示す。The test results are shown in Table 2.

【００２３】[0023]

【表２】 [Table 2]

【００２４】本発明例は、Ｎｏ．１〜Ｎｏ．９である。
いずれも限界据え込み率は７５％以上であり、ＳＣｒ４
２０のＳＡ材並みの冷鍛性を有している。また旋削試験
による工具摩耗寿命は、硬さが低いこと及び快削元素を
添加していることからＳＣｒ４２０（Ｎｏ．１０）より
かなり高寿命となっている。問題の切削加工時に生じる
バリの高さは、すべて０．３ｍｍ以下であり、快削元素
を添加した効果が現われている。The example of the present invention is No. 1 to No. 9
In both cases, the critical upsetting rate is 75% or more, and SCr4
It has the cold forgeability equivalent to 20 SA material. Further, the tool wear life in the turning test is considerably longer than that of SCr420 (No. 10) due to its low hardness and addition of free-cutting elements. The height of burrs generated during the problematic cutting process is 0.3 mm or less, which shows the effect of adding the free-cutting element.

【００２５】それに対し、肌焼Ｂ綱であるＮｏ．１１
は、冷鍛性および工具摩耗寿命に優れているが、快削元
素を添加していないため切削時にかなりのバリを生じて
いる。On the other hand, no. 11
Has excellent cold forgeability and tool wear life, but since it does not contain a free-cutting element, considerable burr is generated during cutting.

【００２６】Ｎｏ．１２〜Ｎｏ．１７は、いずれも限界
圧縮率が低下している。Ｎｏ．１２はＣ、Ｎｏ．１３は
ＳＩ、Ｎｏ．１４はＭｎ、Ｎｏ．１６はＣｒ、Ｎｏ１７
はＭｏが請求項の上限を超えており、硬さが上昇し、延
性が低下したからである。Ｎｏ．１５はＳが０．０５０
％と高く鋼中のＭｎＳにより限界圧縮率が低下した場合
である。No. 12-No. In No. 17, the critical compression rate is lowered. No. No. 12 is C, No. No. 13 is SI, No. 14 is Mn, No. 16 is Cr, No17
Is because Mo exceeds the upper limit of the claims, hardness is increased, and ductility is decreased. No. 15 has S of 0.050
%, Which is high and the critical compressibility is lowered by MnS in the steel.

【００２７】Ｎｏ．１８〜Ｎｏ．２２は、バリ発生の抑
制のために添加した快削元素が請求項の上限を超えたた
め、限界圧縮率が低下した場合である。No. 18-No. No. 22 is the case where the free-cutting element added for suppressing the generation of burrs exceeded the upper limit of the claim, so that the critical compressibility was lowered.

【００２８】[0028]

【発明の効果】以上の実施例より本発明は、熱間加工ま
まで７５ＨＲＢ以下の硬さにすることができ、良好な被
削性と比較鋼のＳＡ材なみの冷鍛性を両立することがで
き、熱処理省略による生産性向上、省エネルギー化と産
業上の効果は極めて顕著なものがある。From the above examples, the present invention can achieve a hardness of 75 HRB or less as it is while hot working, and achieves both good machinability and cold forgeability similar to SA material of comparative steel. It is possible to improve productivity, save energy and industrial effects by omitting heat treatment.

Claims (3)

【特許請求の範囲】[Claims] 【請求項１】 Ｃ：０．１〜０．３％，Ｓｉ＜０．１５
％，Ｍｎ≦１．５％，Ｓ≦０．０３０％，Ｂ：０．００
０３％〜０．００５％，Ｎｂ：０．００５％〜０．１０
０％，ｓ−Å１≦０．０４０％，Ｔｉ≦０．１０％，Ｎ
≦０．０２０％およびＰｂ≦０．４０％，Ｂｉ≦０．４
０％，Ｔｅ：０．００１％〜０．０５０％，Ｃａ：０．
０００５％〜０．００３０％，Ｓｅ：０．００３％〜
０．０５０％から選ばれる１種または２種以上をを含
み、残部はＦｅおよび不純物よりなる冷間加工性および
被削性の優れた肌焼鋼。1. C: 0.1 to 0.3%, Si <0.15
%, Mn ≦ 1.5%, S ≦ 0.030%, B: 0.00
03% to 0.005%, Nb: 0.005% to 0.10.
0%, s-Å1 ≦ 0.040%, Ti ≦ 0.10%, N
≦ 0.020% and Pb ≦ 0.40%, Bi ≦ 0.4
0%, Te: 0.001% to 0.050%, Ca: 0.
0005% ~ 0.0030%, Se: 0.003% ~
A case-hardening steel containing one or more selected from 0.050% and the balance being Fe and impurities, which is excellent in cold workability and machinability. 【請求項２】 上記綱材にはさらにＣｒ≦１．５％，Ｎ
ｉ≦１．５％，Ｍｏ≦１．０％の１種または２種以上を
含有することを特徴とする請求項１に記載の冷間加工性
および被削性の優れた肌焼鋼。2. The steel material further comprises Cr ≦ 1.5%, N
The case-hardening steel excellent in cold workability and machinability according to claim 1, containing one or more of i ≦ 1.5% and Mo ≦ 1.0%. 【請求項３】 上記綱材にはさらにＳ＜０．００５％お
よび／またはＯ＜０．００１％に規制したことを特徴と
する請求項１または請求項２に記載の冷間加工性および
被削性の優れた肌焼綱。3. The cold workability and workability according to claim 1 or 2, wherein the steel material is further restricted to S <0.005% and / or O <0.001%. A case-hardening rope with excellent machinability.