JPH05339676A - Steel for machine structure excellent in cold workability and its manufacture - Google Patents

Steel for machine structure excellent in cold workability and its manufacture

Info

Publication number
JPH05339676A
JPH05339676A JP15249092A JP15249092A JPH05339676A JP H05339676 A JPH05339676 A JP H05339676A JP 15249092 A JP15249092 A JP 15249092A JP 15249092 A JP15249092 A JP 15249092A JP H05339676 A JPH05339676 A JP H05339676A
Authority
JP
Japan
Prior art keywords
ferrite
steel
less
pearlite
grains
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.)
Withdrawn
Application number
JP15249092A
Other languages
Japanese (ja)
Inventor
Toshizo Tarui
敏三 樽井
Hitoshi Tashiro
均 田代
Hiroshi Sato
洋 佐藤
Original Assignee
Nippon Steel Corp
新日本製鐵株式会社
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Nippon Steel Corp, 新日本製鐵株式会社 filed Critical Nippon Steel Corp
Priority to JP15249092A priority Critical patent/JPH05339676A/en
Publication of JPH05339676A publication Critical patent/JPH05339676A/en
Withdrawn legal-status Critical Current

Links

Abstract

PURPOSE:To obtain a steel having excellent cold workability as hot-rolled by specifying the contents of C, Si, Mn, Al, Ti and B in steel, subjecting it to finish rolling and cooling under prescribed conditions to regulate the size of ferritic grains and dispersing carbides therein. CONSTITUTION:Steel constituted of, by weight, 0.1 to 0.5% C, <=0.3% Si, 0.2 to 1.7% Mn, 0.01 to 0.1% Al, 0.002 to 0.03% Ti and 0.0003 to 0.007% B is melted. This steel is subjected to finish rolling at TC+30 deg.C to TC-30 deg.C (where TC( deg.C)=865-155XC%+11.5XSi%-33.8XMn%-8'Cr%+2.8XM%-21.8XNi%+13.7XV%) and at 70 to 95% total reduction of area. Next, it is gradually cooled in the temp. range from the start of ferritic transformation to the completion of pearlitic transformation at <=15 deg.C/min cooling rate. Then, the average grain size of ferritic grains and pearlitic grains over the wire size (mm)X0.1 to the wire size (mm)X0.3 from the surface layer is regulated to <=10mum, and carbides are dispersed in the ferritic grains.

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、ボルト、ナット、歯車
その他の機械部品を冷間鍛造、冷間圧造、冷間転造等の
冷間塑性加工によって製造する際に、熱処理を施すこと
なく熱間圧延ままで優れた冷間加工性を有する機械構造
用鋼材およびそ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 does not require heat treatment when manufacturing mechanical parts such as bolts, nuts, gears and the like by cold plastic working such as cold forging, cold forging and cold rolling. The present invention relates to a steel material for machine structure having excellent cold workability as hot rolled and a method for producing the same.
【0002】[0002]
【従来の技術】冷間加工は熱間加工、機械切削加工に比
べ、生産性が高く、製品の寸法精度が優れ、また鋼材の
歩留りがよいためにボルト、軸類、歯車その他の機械部
品の製造に広く応用されている。このような冷間加工で
使用される鋼材は冷間加工性が優れていること、即ち引
張強さが低く、延性(絞り)が高い必要がある。これは
鋼素材の引張強さが高いと冷間加工の工具寿命が低下
し、また延性が低いと冷間加工時に割れが発生しやすく
なり、経済性が悪くなるためである。そこで従来は鋼材
の引張強さを低下させ、延性を高めるために球状化焼鈍
処理を冷間加工前に実施しているのが一般的である。と
ころが球状化焼鈍処理は10〜20時間を要するため、
生産性の向上あるいは省エネルギーの観点から球状化焼
鈍処理の省略が可能な優れた冷間加工性を有する熱間圧
延材の開発が要望されていた。
2. Description of the Related Art Cold working has higher productivity than that of hot working and mechanical cutting, has excellent dimensional accuracy of products, and has a good yield of steel materials, so that cold working of bolts, shafts, gears and other mechanical parts Widely applied in manufacturing. The steel material used in such cold working needs to have excellent cold workability, that is, low tensile strength and high ductility (drawing). This is because if the tensile strength of the steel material is high, the tool life in cold working is shortened, and if the ductility is low, cracking is likely to occur during cold working, resulting in poor economic efficiency. Therefore, conventionally, spheroidizing annealing is generally performed before cold working in order to reduce the tensile strength of the steel material and enhance the ductility. However, since the spheroidizing annealing process requires 10 to 20 hours,
From the viewpoint of improving productivity or saving energy, there has been a demand for the development of a hot-rolled material having excellent cold workability capable of omitting the spheroidizing annealing treatment.
【0003】これに対して、従来の知見として例えば、
特公昭61−37333号公報、特公昭61−3733
4号公報、特開昭58−107416号公報、特公平1
−12815号公報には、いずれも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、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
が提案されている。これらの製造方法は、熱間圧延後の
冷却過程で生成する引張強さが高いベイナイト、あるい
はマルテンサイトの生成防止に対しては有効であるもの
の、球状化焼鈍処理材と比較すると冷間加工性が劣るた
め冷間加工度の厳しい機械部品に適用することは困難で
あり、満足すべき解決手段とは言い難かった。
On the other hand, as conventional knowledge, for example,
Japanese Patent Publication No. 61-37333, Japanese Patent Publication No. 61-3733
No. 4, JP-A-58-107416, JP-B-1
No. 12815 discloses that the controlled rolling in which the hot finish rolling conditions are regulated makes the austenite grains finer and introduces a deformation zone to promote the ferrite / pearlite transformation, and to improve the cold workability as it is in the hot rolling. An excellent method of manufacturing a steel material has been proposed. Although these manufacturing methods are effective in preventing the formation of bainite or martensite, which has a high tensile strength generated in the cooling process after hot rolling, it is cold workable in comparison with the spheroidized material. Since it is inferior, it is difficult to apply it to a machine part having a severe cold working degree, and it cannot be said to be a satisfactory solution.
【0004】[0004]
【発明が解決しようとする課題】本発明は上記の如き実
状に鑑みなされたものであって、熱間圧延ままで優れた
冷間加工性を有する機械構造用鋼材およびその製造方法
を提供することを目的とするものである。
SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and provides a steel material for machine structure having excellent cold workability as hot rolled and a method for producing the same. The purpose is.
【0005】[0005]
【課題を解決するための手段、作用】本発明者らは上記
問題点の解決のためにフェライト・パーライト組織とな
っている熱間圧延材の冷間加工性の支配因子について詳
細に解析し、Cの含有量が同一であれば表層のフェラ
イト・パーライト粒径とその表層からの幅が冷間加工性
に大きな影響を及ぼし、冷間加工性を向上させるために
は微細なフェライト・パーライト粒径にし、さらに微細
なフェライト・パーライト粒径を有する幅を最適にする
必要があること、さらに表層のフェライト中に炭化物
を分散させると冷間加工性が格段に向上することを確か
め、表層のフェライト・パーライト粒径を微細化すると
共に、フェライト粒内に炭化物を分散させるためには、
鋼材組成、熱間圧延仕上条件および熱間圧延後の冷却条
件を最適に選べば良いという全く新たな知見を得て本発
明を構成したものである。
[Means for Solving the Problems] In order to solve the above problems, the present inventors have analyzed in detail the controlling factors of the cold workability of a hot rolled material having a ferrite-pearlite structure, If the C content is the same, the ferrite / pearlite grain size of the surface layer and the width from the surface layer have a great influence on the cold workability, and in order to improve the cold workability, a fine ferrite / pearlite grain size is required. In addition, we confirmed that it is necessary to optimize the width with a finer ferrite / pearlite grain size, and that if the carbide is dispersed in the ferrite of the surface layer, the cold workability is significantly improved. In order to make the pearlite grain size finer and to disperse the carbide in the ferrite grains,
The present invention was constructed by obtaining completely new knowledge that the steel composition, hot rolling finishing conditions, and cooling conditions after hot rolling should be optimally selected.
【0006】すなわち、本発明は以上の知見に基づいて
なされるものであって、その要旨とするところは下記の
とおりである。 (1) 重量%で、C:0.10〜0.50%、Si:0.30%以
下、Mn:0.20〜1.70%、Al:0.01〜0.10%、Ti:
0.002 〜0.030 %、B:0.0003〜0.0070%を含み、残部
はFeおよび不可避不純物よりなり、表層から最小で線
径(mm)×0.1、最大で線径(mm)×0.3にわ
たってフェライト粒およびパーライト粒の平均粒径が1
0μm以下で且つフェライト粒内に炭化物が分散してい
ることを特徴とする冷間加工性の優れた機械構造用鋼
材。
That is, the present invention is based on the above findings, and the gist thereof is as follows. (1) C: 0.10 to 0.50%, Si: 0.30% or less, Mn: 0.20 to 1.70%, Al: 0.01 to 0.10%, Ti:
0.002 to 0.030%, B: 0.0003 to 0.0070%, the balance Fe and unavoidable impurities, ferrite from the surface layer over the minimum wire diameter (mm) × 0.1 and the maximum wire diameter (mm) × 0.3 The average grain size of grains and pearlite grains is 1
A steel material for machine structural use having excellent cold workability, characterized in that carbides are dispersed in ferrite grains of 0 μm or less.
【0007】(2) 重量%で、C:0.10〜0.50%、S
i:0.30%以下、Mn:0.20〜1.70%、Al:0.01〜0.
10%、Ti:0.002 〜0.030 %、B:0.0003〜0.0070%
を含み、さらにCr:0.10〜2.00%、Mo:0.05〜1.00
%、Ni:0.10〜2.00%、V:0.05〜1.00%、Nb:0.
005 〜0.10%の1種または2種以上を含有し、残部はF
eおよび不可避不純物よりなり、表層から最小で線径
(mm)×0.1、最大で線径(mm)×0.3にわた
ってフェライト粒およびパーライト粒の平均粒径が10
μm以下で且つフェライト粒内に炭化物が分散している
ことを特徴とする冷間加工性の優れた機械構造用鋼材。
(2) C: 0.10 to 0.50% by weight, S
i: 0.30% or less, Mn: 0.20 to 1.70%, Al: 0.01 to 0.
10%, Ti: 0.002-0.030%, B: 0.0003-0.0070%
In addition, Cr: 0.10 to 2.00%, Mo: 0.05 to 1.00
%, Ni: 0.10 to 2.00%, V: 0.05 to 1.00%, Nb: 0.
005 to 0.10% of 1 type or 2 types or more, and the balance is F
e and unavoidable impurities, and the average particle diameter of ferrite particles and pearlite particles is 10 from the surface layer to the minimum wire diameter (mm) × 0.1 and the maximum wire diameter (mm) × 0.3.
A steel material for machine structural use having excellent cold workability, which is characterized in that carbides are dispersed in ferrite grains having a size of not more than μm.
【0008】(3) 重量%で、C:0.10〜0.50%、S
i:0.30%以下、Mn:0.20〜1.70%、Al:0.01〜0.
10%、Ti:0.002 〜0.030 %、B:0.0003〜0.0070%
を含み、残部はFeおよび不可避不純物よりなる鋼を熱
間圧延するに際して、Tc+30℃〜Tc−30℃の温
度範囲において総減面率が70〜95%で仕上圧延を行
った後、少なくともフェライト変態開始からパーライト
変態終了までの温度範囲を15℃/分以下の冷却速度で
徐冷することを特徴とする冷間加工性の優れた機械構造
用鋼材の製造方法。
(3) C: 0.10 to 0.50% by weight, S by weight
i: 0.30% or less, Mn: 0.20 to 1.70%, Al: 0.01 to 0.
10%, Ti: 0.002-0.030%, B: 0.0003-0.0070%
When the steel containing Fe and the unavoidable impurities in the balance is hot-rolled, after finishing rolling with a total area reduction rate of 70 to 95% in the temperature range of Tc + 30 ° C. to Tc-30 ° C., at least ferrite transformation is performed. A method for producing a steel material for machine structural use having excellent cold workability, which comprises gradually cooling a temperature range from the start to the end of pearlite transformation at a cooling rate of 15 ° C./minute or less.
【0009】Tc(℃)=865 −155.0 × C%+11.5×
Si%−33.8×Mn%−8.0 ×Cr%+2.8 ×Mo%−21.8×Ni
%+13.7× V% (4) 重量%で、C:0.10〜0.50%、Si:0.30%以
下、Mn:0.20〜1.70%、Al:0.01〜0.10%、Ti:
0.002 〜0.030 %、B:0.0003〜0.0070%を含み、さら
にCr:0.10〜2.00%、Mo:0.05〜1.00%、Ni:0.
10〜2.00%、V:0.05〜1.00%、Nb:0.005 〜0.10%
の1種または2種以上を含有し、残部はFeおよび不可
避不純物よりなる鋼を熱間圧延するに際して、Tc+3
0℃〜Tc−30℃の温度範囲において総減面率が70
〜95%で仕上圧延を行った後、少なくともフェライト
変態開始からパーライト変態終了までの温度範囲を15
℃/分以下の冷却速度で徐冷することを特徴とする冷間
加工性の優れた機械構造用鋼材の製造方法。
Tc (° C.) = 865−155.0 × C% + 11.5 ×
Si% -33.8 x Mn% -8.0 x Cr% +2.8 x Mo% -21.8 x Ni
% + 13.7 x V% (4) Weight%, C: 0.10 to 0.50%, Si: 0.30% or less, Mn: 0.20 to 1.70%, Al: 0.01 to 0.10%, Ti:
0.002 to 0.030%, B: 0.0003 to 0.0070%, Cr: 0.10 to 2.00%, Mo: 0.05 to 1.00%, Ni: 0.
10-2.00%, V: 0.05-1.00%, Nb: 0.005-0.10%
1 or 2 or more of, and the balance Tc + 3 when hot rolling steel consisting of Fe and unavoidable impurities.
The total area reduction rate is 70 in the temperature range of 0 ° C to Tc-30 ° C.
After finishing rolling at ~ 95%, at least the temperature range from the start of ferrite transformation to the end of pearlite transformation is 15
A method for producing a steel material for machine structural use having excellent cold workability, which comprises gradually cooling at a cooling rate of not more than ° C / minute.
【0010】Tc(℃)=865 −155.0 × C%+11.5×
Si%−33.8×Mn%−8.0 ×Cr%+2.8 ×Mo%−21.8×Ni
%+13.7× V% 以下に本発明について詳細に説明する。まず本発明にお
いて冷間加工性の優れた鋼とは、熱間圧延ままでC含有
量によって決まる限界据込み率Hc(%)が下記の式で
表される値以上であることを意味している。
Tc (° C) = 865 -155.0 x C% +11.5 x
Si% -33.8 x Mn% -8.0 x Cr% +2.8 x Mo% -21.8 x Ni
% + 13.7 x V% The present invention will be described in detail below. First, in the present invention, steel having excellent cold workability means that the limit upsetting rate Hc (%) determined by the C content in the as-hot-rolled state is not less than the value represented by the following formula. There is.
【0011】Hc(%)=87.7−81.7× C(%)+62.7
× C(%)2 ここでHcが高いほど冷間加工性が良好であることを示
している。この式は、熱間圧延材の限界据込み率におよ
ぼすC量、合金元素の影響について解析した結果、熱間
圧延材の組織がフェライト・パーライト組織となってい
れば、限界据込み率はC含有量で一義的に決まり、S
i、Mn、Crなどの合金元素の種類および量には依存
しないことが明らかとなったためにC含有量で回帰した
ものである。なお限界据込み率は、日本塑性加工学会が
定めた冷間据込み性試験方法の基準に従って求めたもの
である。
Hc (%) = 87.7-81.7 × C (%) + 62.7
× C (%) 2 Here, it is shown that the higher the Hc, the better the cold workability. This formula shows that if the structure of the hot-rolled material is a ferrite-pearlite structure, the critical upsetting rate is C if the amount of C and the effect of alloying elements on the critical upsetting rate of the hot-rolled material are analyzed. Uniquely determined by the content, S
Since it became clear that it did not depend on the type and amount of alloying elements such as i, Mn, and Cr, it was regressed by the C content. The critical upsetting ratio is obtained according to the standard of cold upsetting test method established by the Japan Society for Plasticity Processing.
【0012】次に本発明の対象とする鋼の成分限定理由
について述べる。 C:Cは冷間加工後の焼入れ焼戻し処理において製品に
所要の引張強さを付与するために必須の元素であるが、
0.10%未満では所要の引張強さが得られず、一方 0.5
0%を超えると熱間圧延ままでは限界据込み率が低くな
り冷間加工が困難となるため、 0.10〜 0.50%の範囲
に制限した。
Next, the reasons for limiting the composition of the steel to which the present invention is applied will be described. C: C is an essential element for imparting the required tensile strength to the product in the quenching and tempering treatment after cold working,
If it is less than 0.10%, the required tensile strength cannot be obtained, while 0.5
If it exceeds 0%, the limit upsetting rate becomes low with hot rolling, which makes cold working difficult. Therefore, the content is limited to 0.10 to 0.50%.
【0013】Si:Siは固溶体硬化作用によって圧延
材の引張強さを高めるため、固溶体硬化作用の影響が少
ない 0.30%以下とした。好ましくは 0.10%以下とす
る。 Mn:Mnは脱酸、脱硫のために必要であるばかりでな
く冷間加工後の熱処理時の焼入性および焼戻し軟化抵抗
を向上させるために有効な元素であるが、 0.20%未満
では上記の効果が得られず、一方 1.70%を超えると熱
間圧延後のフェライトおよびパーライト成長速度が低下
してフェライト、パーライト変態終了温度が下がるため
に冷間加工性に有害なベイナイトが発生しやすくなると
ともに引張強さが高くなるため 0.20〜 1.70%の範囲
に制限した。
Si: Si enhances the tensile strength of the rolled material by the solid solution hardening action, so that the effect of the solid solution hardening action is less than 0.30%. Preferably it is 0.10% or less. Mn: Mn is an element effective not only for deoxidation and desulfurization but also for improving the hardenability during heat treatment after cold working and the temper softening resistance. On the other hand, if it exceeds 1.70%, the growth rate of ferrite and pearlite after hot rolling decreases, and the temperature at which ferrite and pearlite transformation ends are lowered, so bainite, which is harmful to cold workability, is likely to occur. However, the tensile strength is increased with the increase in temperature, so the range was limited to 0.20 to 1.70%.
【0014】B:Bは熱間圧延線材のフェライト粒内に
炭化物を析出させるために必須の元素であり、Bを利用
していることが本発明の特徴の一つである。即ち、本発
明者らにより、Bが添加されている鋼を通常行われてい
る条件で熱間圧延を行った後、冷却速度が15℃/分以
下の徐冷処理を行うと、フェライト/オーステナイト界
面に非常に微細なボロン炭化物(Fe23(CB)6 )が析出
し、フェライト変態およびパーライト変態が促進されて
引張強さを低下させる効果があるが、さらに熱間圧延の
仕上条件を最適に選択すると、ボロン炭化物の析出が促
進されるとともに、フェライト中の微細なボロン炭化物
が核となってBを含有したセメンタイト(Fe3(CB) )に
なることが新たに見出された。またフェライト粒内にセ
メンタイトが分散していると冷間鍛造性を格段に向上さ
せることが可能であることが新たな知見として明らかに
された。さらにBは冷間鍛造後の熱処理時の焼入性を向
上させる効果も有している。上記に示したBの効果は、
0.0003%未満ではその効果が発揮できず、一方0.0070%
を超えて添加しても効果が飽和するため、0.0003〜 0.0
07%の範囲に制限した。
B: B is an essential element for precipitating carbides in the ferrite grains of the hot rolled wire rod, and the use of B is one of the features of the present invention. That is, by the present inventors, when the steel containing B is hot-rolled under normal conditions and then subjected to a slow cooling treatment at a cooling rate of 15 ° C./min or less, ferrite / austenite is obtained. Very fine boron carbide (Fe 23 (CB) 6 ) precipitates at the interface, which promotes ferrite transformation and pearlite transformation, and has the effect of lowering tensile strength, but further optimizes the finishing conditions for hot rolling. It has been newly found that, when selected, the precipitation of boron carbide is promoted and at the same time, fine boron carbide in ferrite becomes nuclei and becomes cementite (Fe 3 (CB)) containing B. Further, it was revealed as a new finding that cold forgeability can be remarkably improved when cementite is dispersed in ferrite grains. Further, B also has an effect of improving hardenability during heat treatment after cold forging. The effect of B shown above is
If less than 0.0003%, the effect cannot be exhibited, while 0.0070%
The effect is saturated even if added in excess of 0.0003 to 0.0
Limited to the range of 07%.
【0015】Al:AlはNと結合してAlNを形成す
ることにより、BがNと反応して窒化物(BN)になる
ことを防ぐために添加される。BがNと反応すると固溶
Bが減少するために、上記に示したBの効果が減少す
る。さらに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も有して
いるが、0.01%未満ではこれらの効果が発揮されず、
0.10%を超えても効果が飽和するため0.01〜 0.10%
の範囲に限定した。
Al: Al is added to prevent B from reacting with N to form a nitride (BN) by forming AlN by combining with N. When B reacts with N, the solid solution B is reduced, so that the effect of B shown above is reduced. Furthermore, Al also has an effect of preventing coarsening of austenite grains during heat treatment after deoxidation and cold working, but if it is less than 0.01%, these effects are not exhibited,
Even if it exceeds 0.10%, the effect will be saturated, so 0.01 to 0.10%
Limited to.
【0016】Ti:TiはAlと同様にNと結合してT
i(CN)を形成することによりBが窒化物になること
を防ぐとともに熱間圧延後のオーステナイト結晶粒を微
細化させてフェライトおよびパーライトの核生成速度を
増加させ、圧延材の引張強さを低下させる作用があり、
さらに熱処理時のオーステナイト結晶粒の粗大化を防止
する効果を有しているが、 0.002%未満ではその効果が
不十分であり、一方0.030%を超えると冷間加工性に有
害である粗大なTi(CN)が生成するため、0.002〜
0.003%の範囲に制限した。
Ti: Ti, like Al, combines with N to form T
By forming i (CN), B is prevented from becoming a nitride and the austenite crystal grains after hot rolling are refined to increase the nucleation rate of ferrite and pearlite, thereby increasing the tensile strength of the rolled material. Has the effect of reducing
Further, it has an effect of preventing coarsening of austenite crystal grains during heat treatment, but if it is less than 0.002%, the effect is insufficient, while if it exceeds 0.030%, it is harmful to cold workability. Since Ti (CN) is generated, 0.002 ~
The range was limited to 0.003%.
【0017】以上が本発明の対象とする鋼の基本成分で
あるが、本発明においては、さらにこの鋼に Cr:0.10〜2.00% Mo:0.05〜1.00% Ni:0.10〜2.00% V:0.05〜1.00% Nb:0.005 〜0.10% の1種または2種以上を含有せしめることができる。
The above are the basic components of the steel to which the present invention is applied. In the present invention, however, Cr: 0.10-2.00% Mo: 0.05-1.00% Ni: 0.10-2.00% V: 0.05- 1.00% Nb: 0.005 to 0.10% of one kind or two or more kinds may be contained.
【0018】Cr:Crは高温でのフェライトおよびパ
ーライト成長速度を増加させるために有効な元素である
と共に、冷間鍛造後の熱処理時の焼入性および焼戻し軟
化抵抗の向上に極めて有効であるが、 0.10%未満では
その効果が十分に発揮できず、一方 2.00%を超えると
フェライト・パーライト成長速度が低下して、フェライ
トおよびパーライト変態終了温度が下がり、熱間圧延材
の引張強さが高くなるため 、0.10〜 2.00%に限定し
た。
Cr: Cr is an element effective for increasing the growth rate of ferrite and pearlite at high temperatures, and is extremely effective for improving the hardenability and the temper softening resistance during the heat treatment after cold forging. If less than 0.10%, the effect cannot be fully exerted, while if over 2.00%, the ferrite / pearlite growth rate decreases, the ferrite and pearlite transformation end temperature decreases, and the tensile strength of the hot rolled material decreases. Since it becomes higher, the content is limited to 0.10 to 2.00%.
【0019】Mo:Moは強い焼戻し軟化抵抗を有し、
熱処理後の引張強さを高めるために有効な元素である
が、0.05%未満ではその効果が少なく、一方 1.00%を
超えると熱間圧延後に徐冷処理を行っても引張強さが高
いベイナイトが発生しやすくなるため、これを上限とし
た。 Ni:Niは靱性を向上させると共に、熱処理時の焼入
性を向上させて引張強さを増加させるために添加される
が、 0.10%未満ではその効果が少なく、一方2.00%
を超えても添加量にみあう効果が発揮できないため、
0.10〜 2.00%の範囲に制限した。
Mo: Mo has a strong temper softening resistance,
It is an element effective for increasing the tensile strength after heat treatment, but if it is less than 0.05%, its effect is small, while if it exceeds 1.00%, bainite which has a high tensile strength even if annealed after hot rolling is applied. Since this is apt to occur, the upper limit is set. Ni: Ni is added to improve toughness and hardenability during heat treatment to increase tensile strength, but if less than 0.10%, its effect is small, while 2.00%
Even if it exceeds the above, the effect of matching the added amount cannot be exerted, so
The range was limited to 0.10 to 2.00%.
【0020】V:Vは焼戻し時の焼戻し軟化抵抗を増加
させる効果の他に熱間圧延後および熱処理時のオーステ
ナイト粒を微細化させる効果があるが、0.05%未満では
前記作用の効果が得られず、一方 1.00%を超えても効
果が飽和するため、0.05〜 1.00%に限定した。 Nb:NbもVと同様に熱間圧延後のオーステナイト粒
を微細化させるために有効な元素であるが、 0.005%未
満ではその効果が不十分であり、一方 0.10%を超える
と、この効果が飽和するため 0.005〜 0.10%に制限し
た。
V: V has the effect of increasing the temper softening resistance during tempering and the effect of refining the austenite grains after hot rolling and during heat treatment. However, if it is less than 0.05%, the above effect is obtained. On the other hand, the effect is saturated even if it exceeds 1.00%, so it was limited to 0.05 to 1.00%. Similar to V, Nb: Nb is also an effective element for refining austenite grains after hot rolling, but if it is less than 0.005%, its effect is insufficient, while if it exceeds 0.10%, this effect is obtained. Since it saturates, it was limited to 0.005 to 0.10%.
【0021】P、Sについては特に制限しないものの、
いずれの元素とも冷間加工性を劣化させるため、0.02%
以下にすることが好ましい。次に本発明の目的とする熱
間圧延ままでの冷間鍛造性の向上に対して重要な点であ
る鋼表層のフェライト・パーライト結晶粒径とその幅、
フェライト粒内の炭化物の分散の限定理由について述べ
る。
Although P and S are not particularly limited,
0.02% because all elements deteriorate cold workability.
The following is preferable. Next, the ferrite pearlite crystal grain size and its width of the steel surface layer which is an important point for improving the cold forging property in the as-hot-rolling as the object of the present invention,
The reasons for limiting the dispersion of carbide in ferrite grains will be described.
【0022】フェライト・パーライト粒径;鋼表層のフ
ェライト・パーライト粒径が10μmを超えると限界据
込み率が低下して冷間加工性が悪化するため、10μm
以下とした。図1に成分系が0.34%C −0.03%Si−0.38
%Mn−1.31%Cr−0.28%Mo−0.044%Al− 0.008%Ti−
0.0031%B で種々の熱間圧延条件で仕上げた線径が11
mmの熱間圧延線材のフェライト・パーライト粒径と限
界据込み率の関係について解析した一例を示す。ここで
フェライト・パーライト粒径は線材表層から2.2mm
の間の平均粒径であり、限界据込み率は日本塑性学会基
準に従って求めたものである。限界据込み率が高い方が
冷間加工性が良好であることを意味している。同図から
明らかなように、フェライト・パーライト粒径が10μ
mを超えると限界据込み率が急激に悪化していくことが
わかる。なお、通常の熱間圧延材のフェライト・パーラ
イト粒径は15〜25μm程度である。
Ferrite / pearlite grain size: When the ferrite / pearlite grain size of the steel surface layer exceeds 10 μm, the critical upsetting ratio is lowered and the cold workability is deteriorated.
Below. Fig. 1 shows that the composition system is 0.34% C-0.03% Si-0.38.
% Mn-1.31% Cr-0.28% Mo-0.044% Al- 0.008% Ti-
The wire diameter of 0.0031% B finished under various hot rolling conditions is 11
An example of analysis of the relationship between the ferrite / pearlite grain size and the critical upsetting ratio of a hot-rolled wire of mm is shown. Here, the particle size of ferrite / pearlite is 2.2 mm from the surface layer of the wire.
The average particle size is between the two, and the critical upsetting ratio is obtained according to the Japan Plastics Society standards. The higher the critical upsetting ratio, the better the cold workability. As is clear from the figure, the particle size of ferrite / pearlite is 10μ.
It can be seen that when the value exceeds m, the critical upsetting ratio deteriorates rapidly. The grain size of ferrite / pearlite of the usual hot rolled material is about 15 to 25 μm.
【0023】10μm以下のフェライト・パーライト粒
径の幅;10μm以下のフェライト・パーライト粒径の
幅が表層から線径×0.1未満では冷間加工性を向上す
る効果が少なく、一方表層から線径×0.3を超えても
冷間加工性の向上効果が飽和するばかりではなくフェラ
イト粒の細粒化効果によって引張強さが高くなり、冷間
加工時の冷間加工用工具寿命が低下するために、10μ
m以下のフェライト粒およびパーライト粒の幅を表層か
ら最小で線径×0.1、最大で線径×0.3とした。図
2に限界据込み率に及ぼすフェライト・パーライト粒径
が10μm以下である線材表層からの幅に対する線径の
比率の影響について解析した一例を示す。用いた鋼の成
分は0.34%C −0.03%Si−0.38%Mn−1.31%Cr−0.28%
Mo− 0.044%Al− 0.008%Ti−0.0031%B である。線径
に対する10μm以下のフェライト・パーライト粒の領
域の比率が0.1未満では限界据込み率を向上させる効
果が少なく、0.3を超えてもその効果が飽和すること
が明らかである。
Width of ferrite / pearlite grain size of 10 μm or less; if the width of ferrite / pearlite grain size of 10 μm or less from the surface layer is less than the wire diameter × 0.1, the effect of improving cold workability is small, while the line from the surface layer is small. Even if the diameter exceeds 0.3, not only is the effect of improving cold workability saturated, but the effect of refining the ferrite grains also increases tensile strength, reducing the tool life for cold work during cold work. 10μ to do
The width of ferrite particles and pearlite particles of m or less was set to a minimum wire diameter × 0.1 and a maximum wire diameter × 0.3 from the surface layer. FIG. 2 shows an example of analyzing the influence of the ratio of the wire diameter to the width from the surface layer of the wire having a ferrite / pearlite particle size of 10 μm or less on the critical upsetting ratio. The composition of the steel used is 0.34% C-0.03% Si-0.38% Mn-1.31% Cr-0.28%
Mo-0.044% Al-0.008% Ti-0.0031% B. It is clear that when the ratio of the ferrite / pearlite grain region of 10 μm or less to the wire diameter is less than 0.1, the effect of improving the critical upsetting ratio is small, and when it exceeds 0.3, the effect is saturated.
【0024】フェライト粒内の炭化物;通常の熱間圧延
材の組織は図3に示すようにフェライト粒内に炭化物は
析出していないが、図4に示すようにフェライト・パー
ライト粒径が10μm以下で且つフェライト粒内に炭化
物が分散している組織にすると冷間加工性が極めて向上
するため、フェライト粒内に炭化物が分散していること
を限定理由とした。図5に据込み率と割れ率の関係に及
ぼすフェライト粒内の炭化物の影響について解析した一
例を示す。フェライト・パーライト粒径と幅は同一の条
件で比較したものである。フェライト粒内に炭化物が分
散している鋼(図中●印)は分散していない鋼(図中○
印)に比べ高い据込み率でも冷間加工による割れが発生
しにくく、冷間加工性が向上していることが明らかであ
る。また図6に限界据込み率に及ぼすフェライト・パー
ライト粒径とフェライト粒内の炭化物の影響について、
従来の熱間圧延材と比較した一例を示す。鋼種はCおよ
び合金元素含有量を種々変化させたものである。フェラ
イト・パーライト粒径が10μm以下でフェライト粒内
に炭化物が分散している鋼(図中●印)は、フェライト
・パーライト粒径が10μm以下であるがフェライト粒
内に炭化物が分散していない鋼(図中○印)、従来方法
で製造したフェライト・パーライト粒径が20μm前後
でフェライト粒内に炭化物が分散していない鋼(図中□
印)に比べ限界据込み率が格段に向上していることがわ
かる。なお、フェライト粒内に炭化物を分散させるため
には、成分的にはBの添加が必須の条件である。
Carbides in ferrite grains: In the structure of a normal hot rolled material, carbides are not precipitated in ferrite grains as shown in FIG. 3, but as shown in FIG. 4, ferrite / pearlite grain size is 10 μm or less. In addition, since the cold workability is significantly improved when the structure is such that the carbides are dispersed in the ferrite grains, the reason why the carbides are dispersed in the ferrite grains is the limiting reason. FIG. 5 shows an example of analysis of the effect of carbide in ferrite grains on the relationship between the upsetting rate and the cracking rate. The particle size and width of ferrite / pearlite are compared under the same conditions. Steel in which carbide is dispersed in ferrite grains (marked with ● in the figure) is not dispersed in steel (○ in the figure)
It is clear that even when the upsetting rate is higher than that of (1), cracks are less likely to occur due to cold working and the cold workability is improved. Fig. 6 shows the effect of ferrite / pearlite grain size and carbide in the ferrite grain on the critical upsetting rate.
An example of comparison with a conventional hot rolled material is shown. The steel types are those in which the contents of C and alloy elements are variously changed. Steel with ferrite / pearlite grain size of 10 μm or less and carbide dispersed in ferrite grains (marked with ● in the figure) is a steel with ferrite / pearlite grain size of 10 μm or less but no carbide dispersed in ferrite grains. (○ in the figure), a steel manufactured by the conventional method with a ferrite / pearlite grain size of around 20 μm and no carbide dispersed in the ferrite grain (□ in the figure)
It can be seen that the marginal upsetting ratio is markedly higher than that of (). In addition, in order to disperse the carbide in the ferrite grains, the addition of B is essential as a component.
【0025】次に、表層から最小で線径(mm)×0.
1、最大で線径(mm)×0.3にわたってフェライト
粒およびパーライト粒の平均粒径が10μm以下で且つ
フェライト粒内に炭化物を分散させるための製造方法の
限定理由について述べる。 仕上圧延の温度範囲;仕上圧延の温度範囲は、フェライ
ト粒およびパーライト粒の粒径とその幅、並びにフェラ
イト粒内の炭化物の析出挙動に大きな影響を及ぼすた
め、仕上圧延の総減面率とともに重要な因子である。フ
ェライト・パーライト粒径とその幅、フェライト粒内の
炭化物の析出に及ぼす仕上圧延温度の影響を詳細に解析
した結果、総減面率が70〜95%の条件では仕上圧延
温度範囲をCと合金元素の種類と量で決まるTc±30
℃に設定すれば、冷間加工性に優れた10μm以下のフ
ェライト・パーライト粒径とフェライト粒内に炭化物が
分散した組織が得られることが明らかとなった。Tcは
鋼中のC含有量の他にSi、Mn、Cr、Mo、Ni、
V含有量(重量%)によって変化し、次式で表される。
Next, from the surface layer, the minimum wire diameter (mm) × 0.
1. The reasons for limiting the manufacturing method for dispersing the carbides in the ferrite grains in which the average grain size of the ferrite grains and the pearlite grains are 10 μm or less over the maximum wire diameter (mm) × 0.3 are described. Temperature range of finish rolling: The temperature range of finish rolling has a great influence on the grain size and width of ferrite grains and pearlite grains, and the precipitation behavior of carbides in ferrite grains, so it is important together with the total reduction rate of finish rolling. Is a factor. As a result of detailed analysis of the effect of the finish rolling temperature on the ferrite / pearlite grain size and its width, and the precipitation of carbides in the ferrite grains, under the condition that the total area reduction rate is 70 to 95%, the finish rolling temperature range is C and alloy. Tc ± 30 determined by the kind and amount of element
It was clarified that when the temperature was set to 0 ° C., a grain size of ferrite / pearlite of 10 μm or less excellent in cold workability and a structure in which carbide was dispersed in the ferrite grain were obtained. Tc is Si, Mn, Cr, Mo, Ni, in addition to the C content in steel.
It changes depending on the V content (% by weight) and is represented by the following formula.
【0026】Tc(℃)=865 −155.0 × C%+11.5×
Si%−33.8×Mn%−8.0 ×Cr%+2.8 ×Mo%−21.8×Ni
%+13.7× V% 上記の式は、表層から最小で線径(mm)×0.1、最
大で線径(mm)×0.3にわたってフェライト粒およ
びパーライト粒の平均粒径が10μm以下で且つフェラ
イト粒内に炭化物を分散するための合金元素の影響につ
いて詳細且つ広範囲にわたって解析した結果を重回帰分
析を行い求めたものである。仕上温度がTc+30℃よ
り高い場合は、フェライト粒内に炭化物が析出しない、
フェライト・パーライト粒径が10μmを超える、ある
いは粒径が10μm以下のフェライト・パーライト組織
の表層からの幅が線径×0.1未満となり、冷間加工性
に優れた組織を得ることが困難となる、等の理由で、仕
上温度の上限をTc+30℃に制限した。またTc−3
0℃未満の低温で仕上圧延を行うと、粒径が10μm以
下のフェライト・パーライト組織の幅が線径×0.3を
超えやすくなってフェライトの細粒化効果により引張強
さが上昇し、さらに圧延時の変形抵抗が増加するため圧
延が困難となるケースも生じてくるため、仕上温度の下
限をTc−30℃に制限した。
Tc (° C.) = 865−155.0 × C% + 11.5 ×
Si% -33.8 x Mn% -8.0 x Cr% +2.8 x Mo% -21.8 x Ni
% + 13.7 x V% The above formula shows that the average grain size of ferrite grains and pearlite grains is 10 μm or less from the surface layer to the minimum wire diameter (mm) x 0.1 and the maximum wire diameter (mm) x 0.3. In addition, the results of detailed and wide-range analysis of the influence of alloying elements for dispersing carbides in ferrite grains were obtained by performing multiple regression analysis. When the finishing temperature is higher than Tc + 30 ° C., carbide does not precipitate in the ferrite grains,
The width of the ferrite / pearlite structure having a ferrite / pearlite particle size of more than 10 μm or 10 μm or less from the surface layer is less than the wire diameter × 0.1, and it is difficult to obtain a structure excellent in cold workability. Therefore, the upper limit of the finishing temperature is limited to Tc + 30 ° C. Also Tc-3
When finish rolling is performed at a low temperature of less than 0 ° C., the width of the ferrite / pearlite structure having a grain size of 10 μm or less easily exceeds wire diameter × 0.3, and the tensile strength increases due to the grain refining effect of ferrite, Further, since the deformation resistance during rolling increases and there are cases where rolling becomes difficult, the lower limit of the finishing temperature is limited to Tc-30 ° C.
【0027】仕上圧延の総減面率;仕上圧延温度がTc
−30℃〜Tc+30℃の範囲での仕上圧延の総減面率
は、70%未満であるとフェライト・パーライト粒径が
10μmを超え、またフェライト粒内に炭化物が析出し
ないため、冷間加工性に優れた鋼にすることができず、
一方95%を超える総減面率の条件で仕上圧延を実施し
ても効果が飽和し、また10μm以下のフェライト・パ
ーライト粒径の幅が線径×0.3を超えやすくなり引張
強さが上昇するため、70〜95%の範囲に制限した。
Total reduction rate of finish rolling; finish rolling temperature is Tc
If the total area reduction rate of finish rolling in the range of -30 ° C to Tc + 30 ° C is less than 70%, the grain size of ferrite / pearlite exceeds 10 µm, and since carbides do not precipitate in the ferrite grains, cold workability is low. Cannot be made into excellent steel,
On the other hand, the effect is saturated even if the finish rolling is performed under the condition of the total area reduction ratio exceeding 95%, and the width of the ferrite / pearlite grain size of 10 μm or less easily exceeds the wire diameter × 0.3, and the tensile strength is increased. Due to the increase, the range was limited to 70 to 95%.
【0028】熱間圧延後の冷却条件;まず熱間圧延後の
冷却速度を15℃/分以下で徐冷する理由は、15℃/
分より速く冷却すると、フェライト変態およびパーライ
ト変態開始温度が低下するために、パーライト分率が増
加するとともにセメンタイト間隔が細かくなり圧延材の
引張強さが上昇することと、より引張強さが高く、延性
も低いベイナイトが生成する危険性があるためである。
冷却速度は遅い方が圧延材の引張強さの低下に対して有
利であるが、設備上、生産性上の実用的な点を考慮する
と、3〜10℃/分の冷却速度が圧延材の引張強さの低
下と生産を両立させる好ましい冷却速度範囲である。ま
た徐冷開始温度は熱間圧延後直ちに上記の冷却速度で徐
冷しても差し支えないが、生産性が極めて悪くなる。徐
冷開始温度はフェライト変態が生じる温度から徐冷すれ
ば十分なため、最低限の温度としてフェライト変態開始
温度とした。また徐冷停止温度は、パーライト変態終了
前に徐冷を停止すると、その後の放冷過程で引張強さが
高く、延性の低い低温変態パーライトもしくはベイナイ
トが生成するため、パーライト変態終了温度とした。
Cooling conditions after hot rolling: First, the cooling rate after hot rolling is 15 ° C./min.
If cooled faster than min, since the ferrite transformation and pearlite transformation start temperature decreases, the pearlite fraction increases and the cementite interval becomes finer and the tensile strength of the rolled material increases, and the tensile strength is higher, This is because there is a risk that bainite, which has low ductility, will be generated.
The slower the cooling rate, the more advantageous it is to reduce the tensile strength of the rolled material. However, considering the practical point in terms of equipment and productivity, the cooling rate of 3 to 10 ° C./min is lower than that of the rolled material. This is a preferable cooling rate range that achieves both reduction in tensile strength and production. Although the slow cooling start temperature may be slow cooled at the above cooling rate immediately after the hot rolling, the productivity is extremely deteriorated. Since the gradual cooling start temperature is sufficient if the gradual cooling is started from the temperature at which ferrite transformation occurs, the minimum temperature is set as the ferrite transformation start temperature. The gradual cooling stop temperature was set to the pearlite transformation end temperature because low temperature transformation pearlite or bainite having high tensile strength and low ductility is formed in the subsequent cooling process when gradual cooling is stopped before the pearlite transformation is completed.
【0029】次に本発明の効果を実施例によって、さら
に具体的に述べる。
Next, the effects of the present invention will be described more specifically by way of examples.
【0030】[0030]
【実施例】表1に供試材の化学成分を示す。これらの供
試材を用いて熱間圧延で線径8〜16mmに仕上げた。
仕上圧延温度、仕上圧延の総減面率、圧延後の冷却速度
の条件を表2、表3(表2のつづき)に示す。熱間圧延
材の評価はフェライト・パーライト粒径および線径に対
する10μm以下のフェライト・パーライト粒径の幅の
比率の測定、フェライト粒内の炭化物の組織観察(○印
は炭化物が分散していることを、×印は炭化物が分散し
ていないことを示す)、引張強さおよび絞りの機械的試
験、冷間据込み性試験について行った。これらの試験結
果を表2、表3に併記する。両表中試験No.の2、
8、11〜13、15〜20(印)が本発明例で、その
他は比較例である。両表から明らかなように本発明例は
いずれも10μm以下のフェライト・パーライト粒径の
幅が線径に対して0.1〜0.3の間にあり且つフェラ
イト粒内に炭化物が分散した組織となっている。この結
果、熱間圧延ままで引張強さを低く、絞りを高くするこ
とが可能となり、限界据込み率が目的とするHc(%)
以上の高いレベルとなっている。
[Examples] Table 1 shows the chemical components of the test materials. A wire diameter of 8 to 16 mm was finished by hot rolling using these test materials.
The conditions of finish rolling temperature, total area reduction of finish rolling, and cooling rate after rolling are shown in Tables 2 and 3 (continued from Table 2). The evaluation of the hot rolled material is carried out by measuring the ferrite / pearlite grain size and the ratio of the width of the ferrite / pearlite grain size of 10 μm or less to the wire diameter, and observing the structure of the carbide in the ferrite grain (the circle indicates that the carbide is dispersed. The symbol X indicates that the carbide is not dispersed), the mechanical test of tensile strength and drawing, and the cold upsetting test. The test results are also shown in Tables 2 and 3. Test No. in both tables 2,
8, 11 to 13, 15 to 20 (marks) are examples of the present invention, and others are comparative examples. As is clear from both tables, in all the examples of the present invention, the structure in which the width of the ferrite / pearlite grain size of 10 μm or less is between 0.1 and 0.3 with respect to the wire diameter and the carbide is dispersed in the ferrite grain Has become. As a result, the tensile strength can be lowered and the drawing can be increased with the hot rolling as it is, and the critical upsetting ratio is the target Hc (%).
The level is higher than the above.
【0031】これに対して、比較例であるNo.1は日
本工業規格のSWRCH35K、No.6はSCM42
0であるが、いずれもBを含有していないためにフェラ
イト粒内に炭化物が分散した組織にならず、限界据込み
率が目的とするレベルに到達していない。またNo.1
0はBを含有しているもののMnの含有量が多すぎるた
めにフェライト・パーライト変態が遅れ、引張強さが高
く延性の低いベイナイトが生成した例である。ベイナイ
トの生成は据込み限界率を低下させる。
On the other hand, in Comparative Example No. No. 1 is Japanese Industrial Standard SWRCH35K, No. 6 is SCM42
However, since neither of them contained B, carbides were not dispersed in the ferrite grains, and the critical upsetting ratio did not reach the target level. In addition, No. 1
No. 0 is an example in which bainite having a high tensile strength and a low ductility was formed because ferrite-pearlite transformation was delayed because the content of B was contained but the content of Mn was too large. The formation of bainite lowers the upset marginal rate.
【0032】比較例であるNo.5、7、21は従来方
法の熱間圧延条件で行ったものであり、仕上圧延温度が
Tc+30℃より高かった例である。仕上圧延温度が高
いと10μm以下のフェライト・パーライト粒径にする
ことが不可能であり、またフェライト粒内に炭化物を分
散した組織を得ることができない。この結果、限界据込
み率が目的とするHc未満となっている。逆にNo.3
は仕上圧延温度がTc−30℃未満の例である。仕上圧
延温度が低いために線径に対する10μm以下のフェラ
イト・パーライト粒径の幅の比率が0.3を超えてい
る。この結果、本発明例であるNo.2に比べ細粒化の
影響が大きくなり、引張強さが高くなっている。
No. which is a comparative example. Nos. 5, 7, and 21 were performed under the hot rolling conditions of the conventional method, and are examples in which the finish rolling temperature was higher than Tc + 30 ° C. If the finish rolling temperature is high, it is impossible to obtain a ferrite / pearlite grain size of 10 μm or less, and it is not possible to obtain a structure in which carbide is dispersed in the ferrite grain. As a result, the critical upsetting ratio is less than the target Hc. Conversely, No. Three
Is an example in which the finish rolling temperature is lower than Tc-30 ° C. Since the finish rolling temperature is low, the ratio of the width of the ferrite / pearlite grain size of 10 μm or less to the wire diameter exceeds 0.3. As a result, the No. Compared with No. 2, the effect of grain refinement was greater and the tensile strength was higher.
【0033】比較例であるNo.4、14は仕上圧延の
総減面率が70%未満の例である。総減面率が低いと線
径に対する粒径10μm以下の比率が0.1未満とな
り、またフェライト粒内に炭化物を分散した組織を得る
ことが困難となる。従って、限界据込み率も目的とする
Hc未満となっている。さらに比較例であるNo.9は
熱間圧延後の冷却速度が速いためベイナイトが生成し、
引張強さが高く、また絞りも低くなり、限界据込み率が
悪かった例である。
No. 3 which is a comparative example. Nos. 4 and 14 are examples in which the total area reduction rate of finish rolling is less than 70%. When the total area reduction rate is low, the ratio of the particle diameter of 10 μm or less to the wire diameter is less than 0.1, and it becomes difficult to obtain a structure in which carbides are dispersed in ferrite grains. Therefore, the critical upsetting ratio is also less than the target Hc. Furthermore, No. In No. 9, bainite was generated because the cooling rate after hot rolling was high,
In this example, the tensile uptake was high and the drawing was low, and the critical upsetting ratio was poor.
【0034】[0034]
【表1】 [Table 1]
【0035】[0035]
【表2】 [Table 2]
【0036】[0036]
【表3】 [Table 3]
【0037】[0037]
【発明の効果】以上の実施例からも明らかなごとく、本
発明は化学成分、仕上圧延の温度範囲、総減面率および
圧延後の冷却速度を最適に選択することにより、フェラ
イト・パーライト粒径が10μm以下で且つフェライト
粒内に炭化物が分散している限界据込み特性の良好な組
織にすることができ、熱間圧延ままで優れた冷間加工性
を有する鋼材およびその製造を可能にしたものであり、
産業上の効果は極めて顕著なものがある。
As is clear from the above examples, according to the present invention, the chemical composition, the temperature range of finish rolling, the total area reduction rate and the cooling rate after rolling are optimally selected to obtain the ferrite / pearlite grain size. Of 10 μm or less and carbides dispersed in the ferrite grains, and a structure with good critical upsetting characteristics can be obtained, and a steel material having excellent cold workability as hot-rolled and its production were made possible. Is something
The industrial effect is extremely remarkable.
【図面の簡単な説明】[Brief description of drawings]
【図1】フェライト・パーライト粒径と限界据込み率の
関係について解析した一例を示す図である。
FIG. 1 is a diagram showing an example of analysis of a relationship between a ferrite / pearlite grain size and a critical upsetting ratio.
【図2】限界据込み率と線径に対して粒径が10μm以
下のフェライト・パーライト組織の幅の比率の関係につ
いて解析した一例を示す図である。
FIG. 2 is a diagram showing an example of analysis of a relationship between a critical upsetting ratio and a ratio of a width of a ferrite-pearlite structure having a grain diameter of 10 μm or less to a wire diameter.
【図3】従来方法で製造した圧延材組織の一例を示す光
学顕微鏡金属組織写真図である。
FIG. 3 is an optical microscope metallographic photograph showing an example of a rolled material structure manufactured by a conventional method.
【図4】本発明方法で製造した圧延材組織の一例を示す
光学顕微鏡金属組織写真図である。
FIG. 4 is an optical microscope metallographic photograph showing an example of the structure of a rolled material produced by the method of the present invention.
【図5】冷間据込み特性に及ぼすフェライト粒内の炭化
物の影響について解析した一例を示す図である。
FIG. 5 is a diagram showing an example of analysis of influence of carbides in ferrite grains on cold upsetting characteristics.
【図6】限界据込み率に及ぼすフェライト・パーライト
粒径とフェライト粒内の炭化物の影響についてC量で整
理した一例を示す図である。
FIG. 6 is a diagram showing an example in which the effects of ferrite / pearlite grain size and carbides in ferrite grains on the critical upsetting rate are sorted by C content.

Claims (4)

    【特許請求の範囲】[Claims]
  1. 【請求項1】 重量%で、 C:0.10〜0.50%、 Si:0.30%以下、 Mn:0.20〜1.70%、 Al:0.01〜0.10%、 Ti:0.002 〜0.030 %、 B:0.0003〜0.0070% を含み、残部はFeおよび不可避不純物よりなり、表層
    から最小で線径(mm)×0.1、最大で線径(mm)
    ×0.3にわたってフェライト粒およびパーライト粒の
    平均粒径が10μm以下で且つフェライト粒内に炭化物
    が分散していることを特徴とする冷間加工性の優れた機
    械構造用鋼材。
    1. By weight%, C: 0.10 to 0.50%, Si: 0.30% or less, Mn: 0.20 to 1.70%, Al: 0.01 to 0.10%, Ti: 0.002 to 0.030%, B: 0.0003 to 0.0070%. Included, the balance consisting of Fe and unavoidable impurities, minimum wire diameter (mm) x 0.1 from the surface layer, maximum wire diameter (mm)
    A steel material for machine structural use having excellent cold workability, characterized in that the average grain size of ferrite grains and pearlite grains is 0.3 μm or less over 0.3 and carbides are dispersed in the ferrite grains.
  2. 【請求項2】 重量%で、 C:0.10〜0.50%、 Si:0.30%以下、 Mn:0.20〜1.70%、 Al:0.01〜0.10%、 Ti:0.002 〜0.030 %、 B:0.0003〜0.0070% を含み、さらに Cr:0.10〜2.00%、 Mo:0.05〜1.00%、 Ni:0.10〜2.00%、 V:0.05〜1.00%、 Nb:0.005 〜0.10% の1種または2種以上を含有し、残部はFeおよび不可
    避不純物よりなり、表層から最小で線径(mm)×0.
    1、最大で線径(mm)×0.3にわたってフェライト
    粒およびパーライト粒の平均粒径が10μm以下で且つ
    フェライト粒内に炭化物が分散していることを特徴とす
    る冷間加工性の優れた機械構造用鋼材。
    2. In% by weight, C: 0.10 to 0.50%, Si: 0.30% or less, Mn: 0.20 to 1.70%, Al: 0.01 to 0.10%, Ti: 0.002 to 0.030%, B: 0.0003 to 0.0070%. In addition, Cr: 0.10 to 2.00%, Mo: 0.05 to 1.00%, Ni: 0.10 to 2.00%, V: 0.05 to 1.00%, Nb: 0.005 to 0.10%, and one or more kinds, and the balance is Fe and unavoidable impurities, and the minimum wire diameter (mm) x 0.
    1. Excellent cold workability, characterized in that the average grain size of ferrite grains and pearlite grains was 10 μm or less over a maximum diameter (mm) × 0.3 and carbides were dispersed in the ferrite grains. Steel material for machine structure.
  3. 【請求項3】 重量%で、 C:0.10〜0.50%、 Si:0.30%以下、 Mn:0.20〜1.70%、 Al:0.01〜0.10%、 Ti:0.002 〜0.030 %、 B:0.0003〜0.0070% を含み、残部はFeおよび不可避不純物よりなる鋼を熱
    間圧延するに際して、Tc+30℃〜Tc−30℃の温
    度範囲において総減面率が70〜95%で仕上圧延を行
    った後、少なくともフェライト変態開始からパーライト
    変態終了までの温度範囲を15℃/分以下の冷却速度で
    徐冷することを特徴とする冷間加工性の優れた機械構造
    用鋼材の製造方法。 Tc(℃)=865 −155.0 × C%+11.5×Si%−33.8×
    Mn%−8.0 ×Cr%+2.8 ×Mo%−21.8×Ni%+13.7× V
    3. In weight%, C: 0.10 to 0.50%, Si: 0.30% or less, Mn: 0.20 to 1.70%, Al: 0.01 to 0.10%, Ti: 0.002 to 0.030%, B: 0.0003 to 0.0070%. At the time of hot-rolling steel consisting of Fe and unavoidable impurities, the balance of which is at least ferrite transformation after finishing rolling at a total area reduction of 70 to 95% in a temperature range of Tc + 30 ° C to Tc-30 ° C. A method for producing a steel material for machine structural use, which is excellent in cold workability, characterized by gradually cooling the temperature range from to the end of pearlite transformation at a cooling rate of 15 ° C./minute or less. Tc (° C) = 865 -155.0 x C% +11.5 x Si% -33.8 x
    Mn% −8.0 × Cr% + 2.8 × Mo% −21.8 × Ni% + 13.7 × V
    %
  4. 【請求項4】 重量%で、 C:0.10〜0.50%、 Si:0.30%以下、 Mn:0.20〜1.70%、 Al:0.01〜0.10%、 Ti:0.002 〜0.030 %、 B:0.0003〜0.0070% を含み、さらに Cr:0.10〜2.00%、 Mo:0.05〜1.00%、 Ni:0.10〜2.00%、 V:0.05〜1.00%、 Nb:0.005 〜0.10% の1種または2種以上を含有し、残部はFeおよび不可
    避不純物よりなる鋼を熱間圧延するに際して、Tc+3
    0℃〜Tc−30℃の温度範囲において総減面率が70
    〜95%で仕上圧延を行った後、少なくともフェライト
    変態開始からパーライト変態終了までの温度範囲を15
    ℃/分以下の冷却速度で徐冷することを特徴とする冷間
    加工性の優れた機械構造用鋼材の製造方法。 Tc(℃)=865 −155.0 × C%+11.5×Si%−33.8×
    Mn%−8.0 ×Cr%+2.8 ×Mo%−21.8×Ni%+13.7× V
    4. In weight%, C: 0.10 to 0.50%, Si: 0.30% or less, Mn: 0.20 to 1.70%, Al: 0.01 to 0.10%, Ti: 0.002 to 0.030%, B: 0.0003 to 0.0070%. In addition, Cr: 0.10 to 2.00%, Mo: 0.05 to 1.00%, Ni: 0.10 to 2.00%, V: 0.05 to 1.00%, Nb: 0.005 to 0.10%, and one or more kinds, and the balance is When hot rolling steel consisting of Fe and inevitable impurities, Tc + 3
    The total area reduction rate is 70 in the temperature range of 0 ° C to Tc-30 ° C.
    After finishing rolling at ~ 95%, at least the temperature range from the start of ferrite transformation to the end of pearlite transformation is 15
    A method for producing a steel material for machine structural use having excellent cold workability, which comprises gradually cooling at a cooling rate of not more than ° C / minute. Tc (° C) = 865 -155.0 x C% +11.5 x Si% -33.8 x
    Mn% −8.0 × Cr% + 2.8 × Mo% −21.8 × Ni% + 13.7 × V
    %
JP15249092A 1992-06-11 1992-06-11 Steel for machine structure excellent in cold workability and its manufacture Withdrawn JPH05339676A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP15249092A JPH05339676A (en) 1992-06-11 1992-06-11 Steel for machine structure excellent in cold workability and its manufacture

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP15249092A JPH05339676A (en) 1992-06-11 1992-06-11 Steel for machine structure excellent in cold workability and its manufacture

Publications (1)

Publication Number Publication Date
JPH05339676A true JPH05339676A (en) 1993-12-21

Family

ID=15541615

Family Applications (1)

Application Number Title Priority Date Filing Date
JP15249092A Withdrawn JPH05339676A (en) 1992-06-11 1992-06-11 Steel for machine structure excellent in cold workability and its manufacture

Country Status (1)

Country Link
JP (1) JPH05339676A (en)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6261388B1 (en) 1998-05-20 2001-07-17 Nippon Steel Corporation Cold forging steel having improved resistance to grain coarsening and delayed fracture and process for producing same
WO2007116599A1 (en) * 2006-03-31 2007-10-18 Jfe Steel Corporation Steel plate having excellent fine blanking processability and method for manufacture thereof
JP2009280893A (en) * 2008-05-26 2009-12-03 Jfe Steel Corp Steel for machine structure having excellent cold forgeability, and method for producing the same
KR100957319B1 (en) * 2007-12-11 2010-05-12 현대자동차주식회사 Composition for manufacturing gear
JP2014015664A (en) * 2012-07-09 2014-01-30 Kobe Steel Ltd Boron-added steel for high strength bolt having excellent delayed fracture resistance, and high strength bolt
WO2018061101A1 (en) 2016-09-28 2018-04-05 新日鐵住金株式会社 Steel

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6261388B1 (en) 1998-05-20 2001-07-17 Nippon Steel Corporation Cold forging steel having improved resistance to grain coarsening and delayed fracture and process for producing same
WO2007116599A1 (en) * 2006-03-31 2007-10-18 Jfe Steel Corporation Steel plate having excellent fine blanking processability and method for manufacture thereof
KR101024232B1 (en) * 2006-03-31 2011-03-29 제이에프이 스틸 가부시키가이샤 Steel plate having excellent fine blanking processability and method for manufacture thereof
KR100957319B1 (en) * 2007-12-11 2010-05-12 현대자동차주식회사 Composition for manufacturing gear
JP2009280893A (en) * 2008-05-26 2009-12-03 Jfe Steel Corp Steel for machine structure having excellent cold forgeability, and method for producing the same
JP2014015664A (en) * 2012-07-09 2014-01-30 Kobe Steel Ltd Boron-added steel for high strength bolt having excellent delayed fracture resistance, and high strength bolt
WO2018061101A1 (en) 2016-09-28 2018-04-05 新日鐵住金株式会社 Steel
KR20190041502A (en) 2016-09-28 2019-04-22 닛폰세이테츠 가부시키가이샤 River

Similar Documents

Publication Publication Date Title
JP4057930B2 (en) Machine structural steel excellent in cold workability and method for producing the same
JP3738004B2 (en) Case-hardening steel with excellent cold workability and prevention of coarse grains during carburizing, and its manufacturing method
EP0523375B1 (en) Process for producing steel bar wire rod for cold working
JP4629816B2 (en) High strength bolt excellent in delayed fracture resistance and method for producing the same
JP3485805B2 (en) Hot forged non-heat treated steel having high fatigue limit ratio and method for producing the same
JP3036416B2 (en) Hot forged non-heat treated steel having high fatigue strength and method for producing forged product
JP3606024B2 (en) Induction-hardened parts and manufacturing method thereof
JP3851147B2 (en) Non-tempered high strength and high toughness forged product and its manufacturing method
JP2004124190A (en) Induction-tempered steel having excellent twisting property
JPH08277437A (en) Production of high strength and high toughness non-heat treated steel for hot forging and forged product thereof
JPH05339676A (en) Steel for machine structure excellent in cold workability and its manufacture
JPH0643605B2 (en) Manufacturing method of non-heat treated steel for hot forging
JP4121416B2 (en) Non-tempered hot forged parts for machine structure and manufacturing method thereof
JP3644217B2 (en) Induction-hardened parts and manufacturing method thereof
JP3246993B2 (en) Method of manufacturing thick steel plate with excellent low temperature toughness
JP4116708B2 (en) Manufacturing method of fine grain structure steel
JP2618933B2 (en) Steel plate for heat treatment
JPH07116550B2 (en) Low alloy high speed tool steel and manufacturing method thereof
JP3419333B2 (en) Cold work steel excellent in induction hardenability, component for machine structure, and method of manufacturing the same
JP2002146480A (en) Wire rod/steel bar having excellent cold workability, and manufacturing method
JP3499425B2 (en) Manufacturing method of cold tool steel
JPH05339677A (en) Steel for machine structure excellent in cold workability and its manufacture
JPH07316720A (en) Non-heat treated steel having high durability ratio and high strength, and its production
JP4112676B2 (en) Manufacturing method of high strength steel wire
JP3823413B2 (en) Induction hardening component and manufacturing method thereof

Legal Events

Date Code Title Description
A300 Withdrawal of application because of no request for examination

Free format text: JAPANESE INTERMEDIATE CODE: A300

Effective date: 19990831