JPH11315349A - High strength wire rod excellent in delayed fracture resistance, its production, and high strength bolt - Google Patents
High strength wire rod excellent in delayed fracture resistance, its production, and high strength boltInfo
- Publication number
- JPH11315349A JPH11315349A JP12154298A JP12154298A JPH11315349A JP H11315349 A JPH11315349 A JP H11315349A JP 12154298 A JP12154298 A JP 12154298A JP 12154298 A JP12154298 A JP 12154298A JP H11315349 A JPH11315349 A JP H11315349A
- Authority
- JP
- Japan
- Prior art keywords
- strength
- wire
- delayed fracture
- fracture resistance
- temperature
- 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.)
- Pending
Links
Landscapes
- Heat Treatment Of Strip Materials And Filament Materials (AREA)
- Forging (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
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、自動車用や各種産
業機械用として使用されるボルト用として適した高強度
線材、およびその製造方法並びに高強度ボルト等に関す
るものであり、特に引張強度が1200N/mm2 以上
でありながら耐遅れ破壊性に優れた高強度線材、および
その様な高強度線材を製造する為の有用な方法、並びに
該高強度線材からなる高強度ボルト等に関するものであ
る。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength wire rod suitable for bolts used for automobiles and various industrial machines, a method for producing the same, a high-strength bolt, and the like. TECHNICAL FIELD The present invention relates to a high-strength wire rod which is not less than / mm 2 and excellent in delayed fracture resistance, a useful method for producing such a high-strength wire rod, and a high-strength bolt made of the high-strength wire rod.
【0002】[0002]
【従来の技術】一般の高強度ボルト用鋼としては、中炭
素合金鋼(SCM435、SCM440、SCr440
等)が使用されており、焼入れ・焼戻しによって必要な
強度を確保する様にしている。しかしながら、自動車用
や各種産業機械用として使用される一般の高強度ボルト
では、引張強さが約1200N/mm2 を超える領域に
なると、遅れ破壊が発生する危険があり、使用上の制約
がある。2. Description of the Related Art As a general high-strength bolt steel, a medium carbon alloy steel (SCM435, SCM440, SCr440) is used.
Etc.) are used, and the necessary strength is ensured by quenching and tempering. However, in general high-strength bolts used for automobiles and various industrial machines, when the tensile strength exceeds about 1200 N / mm 2 , there is a risk that delayed fracture occurs, and there are restrictions on use. .
【0003】遅れ破壊は、非腐食性環境下で起こるもの
と腐食性環境下で起こるものがあるが、その発生原因は
種々の要因が複雑にからみあっていると言われており、
一概に上記原因を特定することは困難である。上記の様
な遅れ破壊性を左右する制御因子としては、焼戻し温
度、組織、材料硬さ、結晶粒度、各種合金元素等の関与
が一応認められているものの、遅れ破壊を防止する為の
有効な手段が確立されている訳ではなく、試行錯誤的に
種々の方法が提案されているに過ぎないのが実状であ
る。[0003] Delayed destruction can occur in a non-corrosive environment or in a corrosive environment, and it is said that the cause of occurrence is complicated by various factors.
It is generally difficult to identify the above cause. As the control factors affecting the delayed fracture as described above, tempering temperature, structure, material hardness, crystal grain size, various alloying elements and the like have been recognized for some time, but they are effective for preventing delayed fracture. In fact, no means has been established, and only various methods have been proposed by trial and error.
【0004】耐遅れ破壊性を改善する為に、例えば特開
昭60−114551号、特開平2−267243号お
よび特開平3−243745号等の技術が提案されてい
る。これらの技術は、各種の主要な合金元素を調整する
ことによって、引張強さが1400N/mm2 以上でも
耐遅れ破壊性が優れた高強度ボルト用鋼の開発を目指し
てなされたものである。しかしながらこれらの技術によ
って、遅れ破壊発生の危険が完全に解消されたと言う訳
ではなく、それらの適用範囲はごく限られた範囲に止ま
っている。[0004] In order to improve the delayed fracture resistance, for example, Japanese Patent Application Laid-Open Nos. 60-114551, 2-267243 and 3-243745 have been proposed. These techniques are aimed at developing a high-strength bolt steel having excellent delayed fracture resistance even with a tensile strength of 1400 N / mm 2 or more by adjusting various main alloying elements. However, these techniques do not completely eliminate the danger of delayed fracture, but their application is limited.
【0005】[0005]
【発明が解決しようとする課題】本発明はこの様な事情
に着目してなされたものであって、その目的は、引張強
度が1200N/mm2 以上でありながら耐遅れ破壊性
に優れた高強度線材、およびその様な高強度線材を得る
為の有用な方法、並びに上記の特性を有する高強度ボル
トを提供することにある。SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to provide a high strength steel having excellent delayed fracture resistance while having a tensile strength of 1200 N / mm 2 or more. An object of the present invention is to provide a high-strength wire, a useful method for obtaining such a high-strength wire, and a high-strength bolt having the above characteristics.
【0006】[0006]
【課題を解決するための手段】上記目的を達成し得た高
強度線材とは、C:0.5〜1.0%を含む鋼からな
り、初析フェライト、初析セメンタイト、ベイナイトお
よびマルテンサイトの1種または2種以上の組織生成を
抑制し、パーライトノジュールサイズが粒度番号でN
o.7以上のパーライト組織の面積率を80%以上とし
たものであり、且つ強伸線加工によって1200N/m
m2 以上の強度にしたものである点に要旨を有するもの
である。ここでパーライトノジュールとは、パーライト
中のフェライトの結晶方位が揃った領域を意味する。The high-strength wire rod which has achieved the above object is composed of steel containing C: 0.5 to 1.0%, and comprises proeutectoid ferrite, proeutectoid cementite, bainite and martensite. Inhibits the formation of one or more types of tissues, and the pearlite nodule size is N
o. The area ratio of the pearlite structure of 7 or more is 80% or more, and 1200 N / m
The gist is that the strength is not less than m 2 . Here, the pearlite nodule means a region where the crystal orientation of ferrite in the pearlite is uniform.
【0007】また本発明の高強度線材には、必要に応じ
て(1)Si:2.0%以下(0%を含まない)および
/またはCo:0.5%以下(0%を含まない)、
(2)Cr,Mo,Ti,Nb,VおよびWよりなる群
から選択される1種以上を合計で0.01〜0.05
%、(3)Ai:0.01〜0.05%、等を含有させ
ることも有効である。The high-strength wire rod of the present invention may, if necessary, (1) Si: 2.0% or less (excluding 0%) and / or Co: 0.5% or less (excluding 0%). ),
(2) One or more selected from the group consisting of Cr, Mo, Ti, Nb, V and W in a total of 0.01 to 0.05.
%, (3) Ai: 0.01 to 0.05%, etc. is also effective.
【0008】上記の様な高強度線材を製造するに当たっ
ては、鋼材の圧延または鍛造終了温度が800〜100
0℃となる様に熱間圧延または熱間鍛造を行なった後、
平均冷却速度Vが下記(1)式を満足する様にして40
0℃まで冷却し、引き続き放冷することにより、初析フ
ェライト、初析セメンタイト、ベイナイトおよびマルテ
ンサイトの1種または2種以上の組織生成を抑制して、
パーライトノジュールサイズが粒度番号でNo.7以上
のパーライト組織の面積率を80%以上とし、その後強
伸線加工によって1200N/mm2 以上の強度にする
様にすれば良い。 166×(線径)-1.4≦V≦288×(線径)-1.4 …(1)[0008] In producing the high-strength wire as described above, the rolling or forging end temperature of the steel is 800 to 100.
After hot rolling or hot forging to 0 ° C,
The average cooling rate V is set to 40 so as to satisfy the following equation (1).
By cooling to 0 ° C. and subsequently allowing to cool, the formation of one or more types of proeutectoid ferrite, proeutectoid cementite, bainite and martensite is suppressed,
The pearlite nodule size is No. in the particle size number. The area ratio of the pearlite structure of 7 or more may be set to 80% or more, and then the strength may be increased to 1200 N / mm 2 or more by strong drawing. 166 × (wire diameter) -1.4 ≦ V ≦ 288 × (wire diameter) -1.4 … (1)
【0009】また本発明の高強度線材は、鋼材を800
〜1000℃に加熱した後、520〜650℃の温度ま
で急冷し、その温度で恒温保持することにより、初析フ
ェライト、初析セメンタイト、ベイナイトおよびマルテ
ンサイトの1種または2種以上の組織生成を抑制して、
パーライトノジュールサイズが粒度番号でNo.7以上
のパーライト組織の面積率を80%以上とし、その後強
伸線加工によって1200N/mm2 以上の強度にする
様にしても製造することができる。[0009] The high-strength wire of the present invention comprises a steel material of 800
After heating to about 1000 ° C., it is rapidly cooled to a temperature of 520 to 650 ° C. and maintained at that temperature to form one or more types of microstructures of proeutectoid ferrite, proeutectoid cementite, bainite and martensite. Restrain,
The pearlite nodule size is No. in the particle size number. It can also be manufactured by setting the area ratio of the pearlite structure of 7 or more to 80% or more, and thereafter making the strength of 1200 N / mm 2 or more by strong drawing.
【0010】更に、本発明の高強度線材は、鋼材の圧延
または鍛造終了温度が800〜1000℃となるように
熱間圧延または熱間鍛造を行なった後、5℃/秒以上の
平均冷却速度で520〜750℃の温度まで冷却し、そ
の温度で1.0℃/秒以下の平均冷却速度で200秒以
上保持し、引き続き放冷することにより、初析フェライ
ト、初析セメンタイト、ベイナイトおよびマルテンサイ
トの1種または2種以上の組織生成を抑制して、パーラ
イトノジュールサイズが粒度番号でNo.7以上のパー
ライト組織の面積率を80%以上とし、その後強伸線加
工によって1200N/mm2 以上の強度にする様にし
ても製造することができる。Further, the high-strength wire of the present invention is subjected to hot rolling or hot forging so that the rolling or forging end temperature of the steel is 800 to 1000 ° C., and then the average cooling rate of 5 ° C./sec or more. To a temperature of 520 to 750 ° C., holding at that temperature at an average cooling rate of 1.0 ° C./sec or less for 200 seconds or more, and then allowing to cool to obtain proeutectoid ferrite, proeutectoid cementite, bainite and martensite. The formation of one or more types of tissue at the site is suppressed, and the pearlite nodule size is No. in particle size number. It can also be manufactured by setting the area ratio of the pearlite structure of 7 or more to 80% or more, and thereafter making the strength of 1200 N / mm 2 or more by strong drawing.
【0011】一方、上記本発明の高強度線材を素材とし
て使用し、所定の長さに切断した後、(1)両端部をね
じ転造または切削によりねじ加工するか(スタッドボル
トにする)、または(2)温間鍛造によって一方端部に
ボルト頭部を形成し、温間鍛造の前または後に他方端部
をねじ転造または切削によりねじ加工すること、等によ
って優れた耐遅れ破壊性を発揮する高強度ボルトが得ら
れる。On the other hand, after using the high-strength wire of the present invention as a material and cutting it to a predetermined length, (1) threading or threading the both ends by threading or cutting (to form stud bolts); Or (2) forming a bolt head at one end by warm forging, and threading the other end before or after warm forging by thread rolling or cutting to provide excellent delayed fracture resistance. A high-strength bolt that can be used is obtained.
【0012】[0012]
【発明の実施の形態】本発明者らは、従来のボルト用高
強度鋼の耐遅れ破壊性が劣る原因について様々な角度か
ら検討した。その結果、従来の改善方法では、組織を焼
戻しマルテンサイトとして、焼戻脆性域の回避、粒界偏
析元素の低減、結晶粒微細化を図ることによって耐遅れ
破壊性を補ってきたが、こうした手段では高強度鋼の耐
遅れ破壊性を向上させるのには限界があることが判明し
た。BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have studied from various angles the cause of the inferior delayed fracture resistance of conventional high strength steel for bolts. As a result, in the conventional improvement method, the structure has been tempered martensite, and the delayed fracture resistance has been supplemented by avoiding the tempered embrittlement region, reducing the grain boundary segregation elements, and refining the crystal grains. It has been found that there is a limit in improving the delayed fracture resistance of high-strength steel.
【0013】そこで本発明者らは、耐遅れ破壊性を更に
向上させるために鋭意研究を重ねた結果、組織をある制
約をもったパーライト主体の組織とし、強伸線加工によ
り1200N/mm2 以上の強度とすれば、耐遅れ破壊
性が改善されることを見出し、本発明を完成した。The inventors of the present invention have conducted intensive studies to further improve the delayed fracture resistance. As a result, the structure was changed to a structure mainly composed of pearlite having a certain restriction, and 1200 N / mm 2 or more was formed by strong drawing. It has been found that if the strength is set as above, the delayed fracture resistance is improved, and the present invention has been completed.
【0014】本発明の高強度線材は、上述の如く初析フ
ェライト、初析セメンタイト、ベイナイトおよびマルテ
ンサイトの1種または2種以上の組織生成を抑制して、
パーライトノジュールサイズが粒度番号でNo.7以上
のパーライト組織の面積率を80%以上とする必要があ
る。上記組織のうち、初析フェライトと初析セメンタイ
トが多く生成すると、伸線時に縦割れを起こして伸線が
できなくなり、強伸線加工によって1200N/mm2
の強度を得ることができなくなる。また初析セメンタイ
トとマルテンサイトは、伸線時に断線を引き起こすので
少なくする必要がある。更に、ベイナイトはパーライト
に比べて加工硬化量が少なくなるので、強伸線加工によ
る強度上昇が望めないのでできるだけ少なくする必要が
ある。As described above, the high-strength wire of the present invention suppresses the formation of one or more types of pro-eutectoid ferrite, pro-eutectoid cementite, bainite and martensite,
The pearlite nodule size is No. in the particle size number. The area ratio of the pearlite structure of 7 or more needs to be 80% or more. When a large amount of pro-eutectoid ferrite and pro-eutectoid cementite is formed in the above-mentioned structure, longitudinal cracks are caused at the time of drawing and the drawing cannot be performed, and 1200 N / mm 2 is obtained by strong drawing.
Cannot be obtained. In addition, proeutectoid cementite and martensite cause disconnection during wire drawing, and thus need to be reduced. Further, since the amount of work hardening of bainite is smaller than that of pearlite, it is not possible to expect an increase in strength due to strong wire drawing.
【0015】一方、残部のパーライト組織は、セメンタ
イトとフェライトの界面で水素をトラップし、粒界に集
積する水素を低減させる効果があり、できるだけ多くす
る必要がある。こうしたことから、初析フェライト、初
析セメンタイト、ベイナイトおよびマルテンサイトの1
種または2種以上の組織生成をできるだけ抑制して(即
ち、20%未満にして)、パーライト組織の面積率を8
0%以上とする必要がある。尚パーライト組織の面積率
は、好ましくは90%以上とするのが良く、より好まし
くは100%パーライト組織とするのが良い。On the other hand, the remaining pearlite structure has the effect of trapping hydrogen at the interface between cementite and ferrite and reducing the amount of hydrogen accumulated at grain boundaries. From these facts, one of proeutectoid ferrite, proeutectoid cementite, bainite and martensite
The formation of the seed or two or more kinds of tissues is suppressed as much as possible (ie, less than 20%), and the area ratio of the pearlite structure is reduced to 8%.
Must be 0% or more. The area ratio of the pearlite structure is preferably 90% or more, and more preferably 100% pearlite structure.
【0016】また上記パーライト組織は、パーライトノ
ジュールサイズが粒度番号でNo.7以上であることが
必要である。パーライトノジュールサイズが粒度番号で
No.7未満では、破断絞り値が低くなり、その後の冷
間伸線が困難となり、必要な強度が得られない。これに
対してパーライトノジュールサイズを微細にすると、粒
界に負荷する応力が低減されると共に、粒界強度が上昇
する。これによって遅れ破壊発生時に見られる粒界破壊
が抑制され、耐遅れ破壊性が改善される。またパーライ
トノジュールサイズを微細化することによって、延性お
よび靭性が向上し、こうした観点からも耐遅れ破壊性が
改善される。即ち、初析フェライト、初析セメンタイ
ト、ベイナイトおよびマルテンサイト等の組織の少なく
とも1種をできるだけ少なくして、その合計の面積率が
20%未満となる様にしてパーライトノジュールサイズ
が粒度番号でNo.7以上であるパーライト組織の面積
率を80%以上にすることにより、優れた耐遅れ破壊性
が達成されるのである。尚パーライトノジュールサイズ
は、粒度番号でNo.8以上とするのが好ましく、より
好ましくはNo.10以上とするのがよい。The pearlite structure has a pearlite nodule size of No. in particle size number. It is necessary to be 7 or more. The pearlite nodule size is No. in the particle size number. If it is less than 7, the breaking reduction value becomes low, and subsequent cold drawing becomes difficult, and the required strength cannot be obtained. On the other hand, when the pearlite nodule size is reduced, the stress applied to the grain boundary is reduced, and the grain boundary strength is increased. As a result, grain boundary destruction observed when delayed fracture occurs is suppressed, and delayed fracture resistance is improved. Further, by reducing the pearlite nodule size, ductility and toughness are improved, and from this viewpoint, delayed fracture resistance is also improved. That is, at least one of the microstructures such as proeutectoid ferrite, proeutectoid cementite, bainite, and martensite is reduced as much as possible, and the total area ratio is less than 20%. By setting the area ratio of the pearlite structure of 7 or more to 80% or more, excellent delayed fracture resistance is achieved. The pearlite nodule size is No. in the particle size number. No. 8 or more, more preferably No. It is good to be 10 or more.
【0017】本発明の線材においては、圧延のままおよ
び鍛造ままでは必要な寸法精度が得られず、また120
0N/mm2 以上の強度を得ることが困難になるので、
強伸線加工が必要となる。また強伸線加工によって一部
のパーライト中のセメンタイトが微細に分散され、水素
トラップ能力を向上させると共に、伸線方向に沿って組
織が並ぶことによって亀裂の進展の抵抗になる(亀裂伝
播方向は伸線方向に垂直である)。In the wire rod of the present invention, required dimensional accuracy cannot be obtained as it is as rolled or forged.
Since it becomes difficult to obtain a strength of 0 N / mm 2 or more,
Strong wire drawing is required. In addition, cementite in some pearlite is finely dispersed by strong wire drawing to improve the hydrogen trapping ability, and the structure is arranged along the wire drawing direction to reduce the crack propagation resistance (the crack propagation direction is Perpendicular to the drawing direction).
【0018】本発明の高強度線材は、Cを0.5〜1.
0%含む中炭素鋼を想定したものであるが、C含有量の
範囲限定理由は、下記の通りである。In the high-strength wire rod of the present invention, C is set to 0.5 to 1.0.
The medium carbon steel containing 0% is assumed, but the reason for limiting the range of the C content is as follows.
【0019】C:0.5〜1.0% Cは鋼の強度確保の為に必要且つ経済的な元素であり、
C含有量を増加させるにつれて強度が増加する。目標強
度を確保する為には、Cは0.5%以上含有させる必要
がある。しかしながら、C含有量が1.0%を超える
と、初析セメンタイトの析出量が増加し、靭延性の低下
が顕著に現れ、伸線加工性を劣化させる。C含有量の好
ましい下限は、0.65%であり、より好ましくは0.
7%である。またC含有量の好ましい上限は、0.95
%であり、より好ましくは0.9%とするのが良い。 C: 0.5 to 1.0% C is a necessary and economical element for securing the strength of steel.
The strength increases as the C content increases. In order to secure the target strength, C needs to be contained at 0.5% or more. However, when the C content exceeds 1.0%, the precipitation amount of proeutectoid cementite increases, so that the toughness and ductility are significantly reduced and the wire drawing workability is deteriorated. A preferred lower limit of the C content is 0.65%, more preferably 0.1%.
7%. A preferable upper limit of the C content is 0.95.
%, More preferably 0.9%.
【0020】本発明の高強度線材は、通常添加される各
種元素(Si,Co,Mn,Cu,Ni,Cr,Mo,
Ti,Nb,V,W,Al,B等)を含有しても良いこ
とは勿論であるが、特に所定量のSiやCoを含有させ
ることは、初析セメンタイトの析出を抑制する上で有効
であり、またCr,Mo,Ti,Nb,V,W,Alは
結晶粒を微細化してパーライトノジュールサイズを微細
化するのに有効である。必要によって添加される各元素
の限定理由は下記の通りである。The high-strength wire of the present invention can be prepared by adding various elements (Si, Co, Mn, Cu, Ni, Cr, Mo,
Ti, Nb, V, W, Al, B, etc.) may of course be contained, but in particular, containing a predetermined amount of Si or Co is effective in suppressing the precipitation of proeutectoid cementite. In addition, Cr, Mo, Ti, Nb, V, W, and Al are effective for refining crystal grains to reduce the pearlite nodule size. The reasons for limiting each element to be added as necessary are as follows.
【0021】Si:2.0%以下(0%を含まない) Siは鋼線の焼入れ性を向上させて初析セメンタイトの
析出を抑える効果を発揮する。また脱酸剤としての作用
が期待され、しかもフェライトに固溶して顕著な固溶強
化作用も発揮する。これらの効果は、その含有量が増加
するにつれて増大するが、Si含有量が過剰になると伸
線後の鋼線の延性を低下させるので、2.0%を上限と
する。尚Si含有量の好ましい上限は、1.0%であ
り、より好ましくは0.5%である。 Si: 2.0% or less (excluding 0%) Si has the effect of improving the hardenability of steel wire and suppressing the precipitation of proeutectoid cementite. In addition, it is expected to act as a deoxidizing agent, and exhibits a remarkable solid solution strengthening effect by being dissolved in ferrite. These effects increase as the content increases, but an excessive Si content reduces the ductility of the drawn steel wire, so the upper limit is 2.0%. The preferred upper limit of the Si content is 1.0%, more preferably 0.5%.
【0022】Co:0.5%以下(0%を含まない) CoはSiと同様に初析セメンタイトの析出を抑制する
効果があり、初析セメンタイトの低減を図る本発明の高
強度における添加成分としては特に有効である。こうし
た効果は、含有量が増加すればするほど増大するが、
0.5%を超えて含有させてもその効果は飽和して不経
済となるので、その上限を0.5%とした。尚Co含有
量の好ましい範囲は0.05〜0.3%であり、更に好
ましくはその下限を0.1%、その上限を0.2%とす
るのが良い。 Co: 0.5% or less (excluding 0%) Co has the effect of suppressing the precipitation of pro-eutectoid cementite like Si, and the high-strength additive of the present invention for reducing pro-eutectoid cementite. This is particularly effective. These effects increase as the content increases,
If the content exceeds 0.5%, the effect is saturated and uneconomical, so the upper limit is made 0.5%. The preferred range of the Co content is 0.05 to 0.3%, and more preferably, the lower limit is 0.1% and the upper limit is 0.2%.
【0023】Cr,Mo,Ti,Nb,VおよびWより
なる群から選ばれる1種以上:合計で0.01〜0.5
% これらの元素は、微細な炭・窒化物を形成して耐遅れ破
壊性の向上に寄与する。またこれらの炭化物および窒化
物は、パーライトノジュールサイズを微細化する上でも
有効である。こうした効果を発揮させる為には合計で
0.01%以上含有させる必要があるが、過剰に含有さ
せると耐遅れ破壊性および靭性を阻害するので、合計で
0.5%以下にする必要がある。尚これらの元素含有量
の好ましい下限は合計で0.02%であり、より好まし
くは0.03%とするのが良い。また好ましい上限は合
計で0.3%であり、より好ましくは0.1%とするの
が良い。From Cr, Mo, Ti, Nb, V and W
One or more selected from the group consisting of: 0.01 to 0.5 in total
% These elements form fine carbon / nitride and contribute to the improvement of delayed fracture resistance. These carbides and nitrides are also effective in reducing the pearlite nodule size. In order to exert such effects, it is necessary to contain a total of 0.01% or more, but if it is contained excessively, the delayed fracture resistance and toughness are impaired, so it is necessary to make the total 0.5% or less. . The preferable lower limit of the content of these elements is 0.02% in total, and more preferably 0.03%. A preferable upper limit is 0.3% in total, and more preferably 0.1%.
【0024】Al:0.01〜0.05% Alは鋼中のNを捕捉してAlNを形成し、パーライト
ノジュールサイズを微細化することによって耐遅れ破壊
性の向上に寄与する。その為には、0.01%以上含有
させる必要があるが、0.05%を超えると窒化物系介
在物や酸化物系介在物が生成し、伸線性が低下するの
で、0.05%以下にする必要がある。尚Al含有量の
好ましい下限は0.025%であり、好ましい上限は
0.035%である。 Al: 0.01 to 0.05% Al captures N in steel to form AlN, and contributes to improvement in delayed fracture resistance by reducing the size of pearlite nodules. For this purpose, the content must be 0.01% or more. However, if it exceeds 0.05%, nitride-based inclusions or oxide-based inclusions are formed, and the wire drawing property is reduced. It must be: The preferred lower limit of the Al content is 0.025%, and the preferred upper limit is 0.035%.
【0025】Mn:0.2〜1.0% Mnは脱酸剤としての効果と、鋼線の焼入性を向上させ
て鋼線の組織の均一性を高める効果を発揮する。これら
の効果を発揮させる為には、0.2%以上含有させる必
要がある。しかしながらMn含有量が過剰になると、M
nの偏析部にマルテンサイトやベイナイトなどの過冷組
織が生成して伸線加工性を劣化させるので、1.0%を
上限とする。尚Mn含有量の好ましい下限は0.40%
であり、より好ましくは0.45%とするのが良い。ま
たMn含有量の好ましい上限は0.70%であり、より
好ましくは0.55%とするのが良い。 Mn: 0.2 to 1.0% Mn exerts an effect as a deoxidizing agent and an effect of improving the hardenability of the steel wire and improving the uniformity of the structure of the steel wire. In order to exert these effects, it is necessary to contain 0.2% or more. However, when the Mn content becomes excessive, M
Since a supercooled structure such as martensite or bainite is formed in the segregated portion of n to deteriorate the drawability, the upper limit is 1.0%. The preferred lower limit of the Mn content is 0.40%.
And more preferably 0.45%. Further, a preferable upper limit of the Mn content is 0.70%, and more preferably 0.55%.
【0026】Cu:0.5%以下(0%を含まない) Cuは析出硬化作用によって鋼線の高強度化に寄与する
元素である。しかしながら過剰に添加すると、粒界脆化
を起こして耐遅れ破壊性を劣化させる原因となるので、
0.5%を上限とする。尚Cu含有量の好ましい下限は
0.05%であり、より好ましくは0.1%とするのが
良い。またCu含有量の好ましい上限は0.3%であ
り、より好ましくは0.2%とするのが良い。 Cu: 0.5% or less (excluding 0%) Cu is an element that contributes to increasing the strength of a steel wire by a precipitation hardening action. However, if added excessively, it causes grain boundary embrittlement and deteriorates delayed fracture resistance.
The upper limit is 0.5%. The lower limit of the Cu content is preferably 0.05%, and more preferably 0.1%. The preferable upper limit of the Cu content is 0.3%, more preferably 0.2%.
【0027】Ni:1.0%以下(0%を含まない) Niは鋼線の強度上昇にはあまり寄与しないが、伸線材
の靭性を高める効果を有する。しかしながら、Ni含有
量が過剰になると、変態終了温度が長くなり過ぎて、設
備の大型過、生産性の劣化を来すため、1.0%を上限
とする。尚Ni含有量の好ましい下限は0.05%であ
り、より好ましくは0.1%とするのが良い。またNi
含有量の好ましい上限は0.5%であり、より好ましく
は0.3%とするのが良い。 Ni: 1.0% or less (excluding 0%) Ni does not significantly contribute to the increase in the strength of the steel wire, but has the effect of increasing the toughness of the drawn wire. However, if the Ni content is excessive, the transformation end temperature becomes too long, which leads to an excessively large facility and a deterioration in productivity. Therefore, the upper limit is 1.0%. The lower limit of the Ni content is preferably 0.05%, and more preferably 0.1%. Also Ni
A preferred upper limit of the content is 0.5%, and more preferably 0.3%.
【0028】B:0.0005〜0.003% Bは鋼の焼入れ性向上の為に添加されるが、その効果を
発揮するためには、0.0005%以上含有させる必要
がある。しかしながら、0.003%を超えて過剰に含
有すると却って靭性を阻害する。尚B含有量の好ましい
下限は0.0010%であり、好ましい上限は0.00
25%である。 B: 0.0005% to 0.003% B is added for improving the hardenability of steel, but in order to exhibit the effect, it is necessary to contain 0.0005% or more. However, if the content exceeds 0.003%, the toughness is rather hindered. The preferred lower limit of the B content is 0.0010%, and the preferred upper limit is 0.0010%.
25%.
【0029】N:0.015%以下(0%を含まない) NはAlNやTiN等の窒化物を形成することによっ
て、結晶粒の微細化ひいては耐遅れ破壊性の向上に好影
響を与える。しかしながら、過剰に含有すると窒化物が
増加し過ぎて伸線性に悪影響を及ぼすだけでなく、固溶
Nが伸線中の時効を促進することがあるので、0.01
5%以下にする必要がある。尚N含有量の好ましい上限
は0.007%であり、より好ましくは0.005%以
下にするのが良い。 N: 0.015% or less (excluding 0%) N forms a nitride such as AlN or TiN, and thereby has a favorable effect on the refinement of crystal grains and the improvement in delayed fracture resistance. However, if the N content is excessive, not only does the nitride excessively increase and adversely affect drawability, but also solute N promotes aging during drawing, so
Must be 5% or less. The upper limit of the N content is preferably 0.007%, and more preferably 0.005% or less.
【0030】本発明の高強度線材においては、上記成分
の他(残部)は基本的に鉄からなるものであるが、これ
ら以外にも微量成分を含み得るものでり、こうした成分
を含むものも本発明の技術的範囲に含まれるものであ
る。またその特性を更に良好にするという観点からし
て、P,SおよびOについては、下記の様に抑制するの
が良い。更に、本発明の高強度線材には、不可避的に不
純物が含まれることになるが、それらは本発明の効果を
損なわない限度で許容される。In the high-strength wire rod of the present invention, other than the above components (the rest) is basically made of iron, but may contain trace components in addition to these components. It is included in the technical scope of the present invention. From the viewpoint of further improving the characteristics, P, S and O are preferably suppressed as follows. Furthermore, although the high-strength wire of the present invention inevitably contains impurities, they are permissible as long as the effects of the present invention are not impaired.
【0031】P:0.03%以下(0%を含む) Pは粒界偏析を起こして、耐遅れ破壊性を劣化させる元
素である。そこでP含有量を0.03%以下とすること
により、耐遅れ破壊性の向上が図れる。尚P含有量は、
0.015%以下に低減するのが好ましく、より好まし
くは0.005%以下にするのが良い。 P: 0.03% or less (including 0%) P is an element that causes grain boundary segregation and deteriorates delayed fracture resistance. Therefore, by setting the P content to 0.03% or less, delayed fracture resistance can be improved. The P content is
It is preferably reduced to 0.015% or less, and more preferably 0.005% or less.
【0032】S:0.03%以下(0%を含む) Sは鋼中でMnSを形成し、応力が負荷されたときにM
nSが応力集中箇所となる。従って、耐遅れ破壊性の改
善にはS含有量をできるだけ減少させることが必要とな
り、0.03%以下にするのが良い。尚S含有量は、
0.01%以下に低減するのが好ましく、より好ましく
は0.005%以下にするのが良い。 S: 0.03% or less (including 0%) S forms MnS in steel, and when stress is applied, M
nS is the stress concentration point. Therefore, in order to improve the delayed fracture resistance, it is necessary to reduce the S content as much as possible, and the S content is preferably set to 0.03% or less. The S content is
It is preferably reduced to 0.01% or less, more preferably 0.005% or less.
【0033】O:0.005%以下(0%を含む) Oは常温では鋼にほとんど固溶せず、硬質の酸化物系介
在物として存在し、伸線時にカッピー断線を引き起こす
原因となる。従って、O含有量は極力少なくすべきであ
り、少なくとも0.005%以下に抑える必要がある。
尚O含有量は、0.003%以下に低減することが好ま
しく、より好ましくは0.002%以下に低減するのが
良い。 O: 0.005% or less (including 0%) O hardly forms a solid solution with steel at room temperature, exists as hard oxide-based inclusions, and causes wire breakage during drawing. Therefore, the O content should be as low as possible, and should be suppressed to at least 0.005% or less.
The O content is preferably reduced to 0.003% or less, and more preferably to 0.002% or less.
【0034】本発明の高強度線材は、上記した各製造方
法によって製造することができるが、各方法における作
用は下記の通りである。まず上記の様な化学成分組成を
有する鋼材を用い、鋼材の圧延または鍛造終了温度が8
00〜1000℃となる様にに熱間圧延または熱間鍛造
を行なった後、平均冷却速度Vが下記(1)式を満足す
る様にして400℃まで冷却し、引き続き放冷する。 166×(線径)-1.4≦V≦288×(線径)-1.4 …(1)The high-strength wire rod of the present invention can be manufactured by each of the above-mentioned manufacturing methods, and the operation of each method is as follows. First, a steel material having the above chemical composition is used, and the rolling or forging end temperature of the steel material is 8
After hot rolling or hot forging is performed so that the temperature becomes 00 to 1000 ° C., the temperature is cooled to 400 ° C. so that the average cooling rate V satisfies the following formula (1), and then the product is allowed to cool. 166 × (wire diameter) -1.4 ≦ V ≦ 288 × (wire diameter) -1.4 … (1)
【0035】この工程によって、通常の圧延材よりも均
質なパーライト組織が得られ、伸線前の強度上昇が図れ
る。圧延または鍛造終了温度が高過ぎると、オーステナ
イト粒径が粗大となり、パーライトノジュールサイズの
粗大化を招く。逆に、終了温度が低過ぎると、オーステ
ナイト化が不十分となり、均質なパーライト組織が得ら
れなくなる。こうした観点から、上記終了温度は800
〜1000℃とする必要がある。この加熱温度の好まし
い範囲は850〜950℃程度であり、更に好ましくは
850〜900℃程度である。By this step, a more uniform pearlite structure can be obtained than in a normal rolled material, and the strength before drawing can be increased. If the rolling or forging end temperature is too high, the austenite grain size becomes coarse, causing the pearlite nodule size to become coarse. Conversely, if the end temperature is too low, austenitization becomes insufficient and a homogeneous pearlite structure cannot be obtained. From such a viewpoint, the end temperature is 800
10001000 ° C. The preferred range of the heating temperature is about 850 to 950 ° C, more preferably about 850 to 900 ° C.
【0036】上記平均冷却速度Vが166×(線径)
-1.4よりも小さくなると、均質なパーライト組織が得ら
れなくなるばかりか、初析フェライトや初析セメンタイ
トが生成し易くなる。また平均冷却速度Vが288×
(線径)-1.4よりも大きくなると、ベイナイトやマルテ
ンサイトが生成し易くなる。The average cooling rate V is 166 × (wire diameter)
When it is smaller than -1.4, not only a homogeneous pearlite structure cannot be obtained, but also proeutectoid ferrite and proeutectoid cementite are easily formed. The average cooling rate V is 288 ×
(Wire diameter) When it is larger than -1.4 , bainite and martensite are easily generated.
【0037】また本発明の高強度線材は、上記の様な化
学成分組成を有する鋼材を用い、この鋼材を800〜1
000℃に加熱後、520〜650℃の温度まで急冷
し、その温度で恒温保持(パテンティング処理)するこ
とによっても、通常の圧延材より均質なパーライト組織
が得られ、伸線前の強度上昇が図れる。The high-strength wire of the present invention uses a steel having the chemical composition as described above,
After being heated to 000 ° C., it is rapidly cooled to a temperature of 520 to 650 ° C., and is kept at that temperature (patenting treatment) to obtain a pearlite structure that is more homogeneous than a normal rolled material, and to increase the strength before drawing. Can be achieved.
【0038】この方法において、鋼材加熱温度の規定範
囲については、上記圧延または鍛造終了温度と同じ理由
で800〜1000℃とする必要がある。この加熱温度
の好ましい範囲は、上記と同じである。パテンティング
処理は、ソルトバス、鉛、流動層等を利用し、加熱した
線材をできるだけ速い温度で急冷することが望ましい。
また均質なパーライト組織を得るには、520〜650
℃で恒温変態させることが必要である。この恒温変態温
度の好ましい温度範囲は、550〜600℃であり、最
も好ましい恒温保持温度はTTT線図のパーライトノー
ズ付近の温度である。In this method, the specified range of the steel material heating temperature must be 800 to 1000 ° C. for the same reason as the above-mentioned rolling or forging end temperature. The preferred range of the heating temperature is the same as described above. In the patenting process, it is desirable to use a salt bath, lead, a fluidized bed, or the like to rapidly cool the heated wire at a temperature as fast as possible.
In order to obtain a homogeneous pearlite structure, 520 to 650 is required.
It is necessary to carry out isothermal transformation at ℃. The preferred temperature range of the isothermal transformation temperature is 550 to 600 ° C., and the most preferred isothermal holding temperature is a temperature near the pearlite nose in the TTT diagram.
【0039】一方、鋼材の圧延または鍛造終了後温度が
800〜1000℃となる様に熱間圧延または熱間鍛造
した後、5℃/秒以上の平均冷却速度で520〜750
℃の温度まで冷却し、その温度から1℃/秒以下の平均
冷却速度で200秒以上保持し、引き続き放冷すること
によっても、通常の圧延材よりも均質なパーライト組織
が得られ、伸線前の強度上昇が図れる。こうした方法を
採用するときの各工程における作用は下記の通りであ
る。On the other hand, the steel material is hot-rolled or hot-forged so as to have a temperature of 800 to 1000 ° C. after completion of the rolling or forging, and then 520 to 750 at an average cooling rate of 5 ° C./sec or more.
C., cooled to a temperature of 1 ° C./second or less at an average cooling rate of 200 ° C. or more, and then allowed to cool to obtain a more uniform pearlite structure than a normal rolled material. The previous strength can be increased. The operation in each step when such a method is adopted is as follows.
【0040】まず圧延または鍛造終了後温度の規定範囲
については、上記鋼材加熱温度と同様の理由で800〜
1000℃と定めた。またこの温度の好ましい範囲は、
上記と同様である。熱間圧延後または熱間鍛造後の冷却
速度が遅過ぎると、冷却中にフェライト変態を引き起こ
す可能性があり、できるだけ速い冷却速度で冷却するこ
とが好ましい。そこでこのときの冷却速度は5℃/秒以
上と規定した。この冷却速度の好ましい範囲は、10℃
/秒以上であり、より好ましくは30℃/秒以上であ
る。この冷却によって520〜750℃まで冷却する必
要があるが、この冷却終了温度が520℃未満または7
50℃を超えると、その後の徐冷によってパーライト以
外の組織が生成し易くなる。First, the specified range of the temperature after the completion of rolling or forging is set to 800 to 800 for the same reason as the above-mentioned steel material heating temperature.
It was determined to be 1000 ° C. The preferred range of this temperature is
Same as above. If the cooling rate after hot rolling or hot forging is too slow, ferrite transformation may occur during cooling, and it is preferable to cool at a cooling rate as high as possible. Therefore, the cooling rate at this time was specified to be 5 ° C./sec or more. The preferred range of this cooling rate is 10 ° C.
/ Sec or more, more preferably 30 ° C / sec or more. It is necessary to cool down to 520 to 750 ° C. by this cooling.
If the temperature exceeds 50 ° C., a structure other than pearlite is likely to be generated by subsequent slow cooling.
【0041】上記で冷却した後は、均質なパーライト組
織を得るという観点から、その温度(520〜750℃
の温度:徐冷開始温度)から1℃/秒以下の平均冷却速
度でで冷却(徐冷)しつつ200秒以上保持する必要が
ある。このときの平均冷却速度が1℃/秒よりも速くな
ったり、保持時間が200秒未満になると、パーライト
組織に変態する前に放冷されて、ベイナイトやマルテン
サイトが生成し易くなる。尚この冷却速度の好ましい範
囲は、0.5℃/秒以下であり、より好ましくは0.2
℃/秒以下とするのが良い。また上記保持時間の好まし
い範囲は、300秒以上であり、より好ましくは600
秒以上とするのが良い。尚TTT線図のパーライトノー
ズ付近の温度に長く保持することが最も好ましい。After the above cooling, the temperature (520 to 750 ° C.) is obtained from the viewpoint of obtaining a homogeneous pearlite structure.
(Temperature: slow cooling start temperature), it is necessary to hold for 200 seconds or more while cooling (slow cooling) at an average cooling rate of 1 ° C./sec or less. If the average cooling rate at this time is higher than 1 ° C./sec or the holding time is less than 200 seconds, the material is left to cool before transforming to a pearlite structure, and bainite and martensite are easily generated. The preferred range of the cooling rate is 0.5 ° C./sec or less, more preferably 0.2 ° C./sec.
C./sec or less is preferable. A preferred range of the holding time is 300 seconds or more, more preferably 600 seconds.
It is good to be more than seconds. It is most preferable to keep the temperature near the pearlite nose in the TTT diagram for a long time.
【0042】上記の様にして得られた高強度線材を使用
し、所定の長さに切断した後、(1)両端部をねじ転造
または切削によりねじ加工するか(スタッドボルトにす
る)、或は(2)温間鍛造によりその一端部にボルト頭
部を形成し、温間鍛造前または後に他端部をねじ転造ま
たは切削によりねじ加工すること、等によって優れた耐
遅れ破壊特性および強度を発揮するボルトが得られる。
尚上記(2)の方法においてボルト頭部を形成する際に
温間鍛造法を採用するのは、線材の強度が高いため、通
常の冷間鍛造では所定のボルト形状に成形しにくいとい
う理由からである。After using the high-strength wire obtained as described above and cutting it to a predetermined length, (1) threading or thread-cutting both ends (to form stud bolts); Or (2) a bolt head is formed at one end by warm forging, and the other end is threaded by thread rolling or cutting before or after warm forging, and the like, so that excellent delayed fracture resistance and A bolt exhibiting strength is obtained.
In the above method (2), the use of the warm forging method when forming the bolt head is because the strength of the wire is high and it is difficult to form the bolt into a predetermined bolt shape by ordinary cold forging. It is.
【0043】以下本発明を実施例によって更に詳細に説
明するが、下記実施例は本発明を限定する性質のもので
はなく、前・後記の趣旨に徴して設計変更することはい
ずれも本発明の技術的範囲に含まれる。Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are not intended to limit the present invention. Included in the technical scope.
【0044】[0044]
【実施例】実施例1 下記表1に示す化学成分組成を有する供試鋼を用い、線
径:11mmφまたは14mmφまで圧延終了温度が約
930℃になる様に熱間圧延した後、平均冷却速度Vを
4.1〜12.3℃/秒(下記表2)の範囲として衝風
冷却した。その後、線径:7.06mmまで伸線した
(伸線率:59%.75%)。 Example 1 Using a test steel having the chemical composition shown in Table 1 below, hot rolling was performed to a wire diameter of 11 mm or 14 mm so that the rolling end temperature would be about 930 ° C., and then the average cooling rate V was subjected to blast cooling in a range of 4.1 to 12.3 ° C./sec (Table 2 below). Thereafter, the wire was drawn to a wire diameter of 7.06 mm (drawing ratio: 59% .75%).
【0045】[0045]
【表1】 [Table 1]
【0046】得られた各種線材を用い、図1に示すM8
×P1.25のスタッドボルトを作製し、遅れ破壊試験
を行なった。遅れ破壊試験は、ボルトを酸中に浸漬後
(15%HCl×30分)、水洗・乾燥して大気中で応
力負荷(負荷応力は引張り強さの90%)し、100時
間後の破断の有無で評価した。また初析フェライト、初
析セメンタイト、ベイナイト、マルテンサイトまたはパ
ーライト組織の分類を下記の方法で行ない、各組織の面
積率を求めた。更に、パーライトノジュールサイズを、
下記の方法で測定した。このとき比較の為に、一部のも
のについては、焼入れ・焼戻しを行って100%焼き戻
しマルテンサイト組織にしたものについても遅れ破壊試
験を行なった(後記表2のNo.19)。Using the obtained various wire rods, M8 shown in FIG.
A stud bolt of × P1.25 was prepared, and a delayed fracture test was performed. In the delayed fracture test, a bolt was immersed in an acid (15% HCl × 30 minutes), washed with water and dried, and subjected to a stress load in air (load stress was 90% of the tensile strength). The presence or absence was evaluated. In addition, pro-eutectoid ferrite, pro-eutectoid cementite, bainite, martensite or pearlite structures were classified by the following method to determine the area ratio of each structure. Furthermore, perlite nodule size,
It was measured by the following method. At this time, for the purpose of comparison, a delayed fracture test was performed on some of the alloys that had been quenched and tempered to have a 100% tempered martensite structure (No. 19 in Table 2 below).
【0047】(各組織の分類方法)線材の横断面を埋め
込み、研磨後、5%のピクリン酸アルコール液に15〜
30秒間浸漬して腐食させた後、走査型電子物顕微鏡
(SEM)によってD/4(Dは直径)部を組織観察し
た。1000〜3000倍で5〜10視野撮影し、パー
ライト組織部分を確定した後、画像解析装置によって各
組織の面積率を求めた。尚パーライト組織と区別がつき
にくい、ベイナイト組織や初析フェライト組織について
は、図2(図面代用顕微鏡写真)に示す様な組織をベイ
ナイト組織とし、図3(図面代用顕微鏡写真)に示す様
な組織を初析フェライト組織と判断した。これらの組織
の傾向として、初析フェライトと初析セメンタイトは、
旧オーステナイト結晶粒界に沿って針状に析出し、マル
テンサイトは塊状に析出していた。(Method of Classifying Each Tissue) The cross section of the wire is embedded, polished, and then immersed in a 5% alcoholic picric acid solution.
After immersion for 30 seconds to corrode, the structure of D / 4 (D: diameter) was observed by scanning electron microscope (SEM). After photographing 5 to 10 visual fields at 1000 to 3000 times and determining the pearlite tissue portion, the area ratio of each tissue was determined by an image analyzer. For the bainite structure and the proeutectoid ferrite structure, which are hard to distinguish from the pearlite structure, the structure shown in FIG. 2 (micrograph as a substitute for a drawing) is defined as a bainite structure, and the structure as shown in FIG. 3 (micrograph as a substitute for a drawing). Was determined to be a proeutectoid ferrite structure. As a tendency of these structures, proeutectoid ferrite and proeutectoid cementite are:
Needle-like precipitates were formed along the former austenite crystal grain boundaries, and martensite was precipitated in bulk.
【0048】(パーライトノジュールサイズの測定方
法)線材の横断面を埋め込み、研磨後、1〜2%のナイ
タール液に2〜10秒間浸漬した後、光学顕微鏡によっ
てD/4(Dは直径)部を組織観察した。パーライトノ
ジュールの粒度番号は、JIS G0551またはJI
S G0552のオーステナイト結晶粒度またはフェラ
イト結晶粒度と同じ単位(粒度番号)で規定した。(Measurement method of pearlite nodule size) After embedding the cross section of the wire, polishing and immersing it in a 1-2% nital solution for 2 to 10 seconds, the D / 4 (D is a diameter) portion was observed with an optical microscope. The tissue was observed. The particle size number of perlite nodule is JIS G0551 or JIS
It was defined in the same unit (grain number) as the austenite grain size or ferrite grain size of SG0552.
【0049】各線材の組織を平均冷却速度Vと共に下記
表2に、遅れ破壊試験結果を伸線条件および機械的特性
と共に下記表3に夫々示す。尚平均冷却速度Vの適正な
範囲[前記(1)式を満足する範囲]は、線径が14m
mのときに4.12≦V≦7.16(℃/秒)であり、
線径が11mmのときに5.78≦V≦10.03(℃
/秒)である。The structure of each wire is shown in Table 2 below together with the average cooling rate V, and the result of the delayed fracture test is shown in Table 3 below together with the drawing conditions and mechanical properties. The appropriate range of the average cooling rate V [the range satisfying the above equation (1)] is as follows.
4.12 ≦ V ≦ 7.16 (° C./sec) when m
When the wire diameter is 11 mm, 5.78 ≦ V ≦ 10.03 (° C.
/ Sec).
【0050】[0050]
【表2】 [Table 2]
【0051】[0051]
【表3】 [Table 3]
【0052】実施例2 前記表1に示した供試鋼Cを用い、線径:11mmφま
で圧延終了温度が約930℃になる様に熱間圧延した後
急冷し、下記表4に示す条件にてパテンティング処理
(加熱温度:750〜935℃、恒温変態:495〜6
65℃×4分)した。その後、線径:7.06mmまで
伸線した(伸線率:59%)。 Example 2 Using the test steel C shown in Table 1 above, hot rolling was performed so that the rolling end temperature was about 930 ° C. to a wire diameter of 11 mmφ, followed by rapid cooling. Patenting treatment (heating temperature: 750-935 ° C., constant temperature transformation: 495-6)
(65 ° C. × 4 minutes). Thereafter, the wire was drawn to a wire diameter of 7.06 mm (drawing ratio: 59%).
【0053】[0053]
【表4】 [Table 4]
【0054】得られた各種線材を用い、前記図1に示し
たM8×P1.25のスタッドボルトを作製し、遅れ破
壊試験を実施例1と同様にして行なった。各線材の組織
を前記表4に併記すると共に、遅れ破壊試験結果を伸線
条件および機械的特性と共に下記表5に夫々示す。Using the obtained various wire rods, an M8 × P1.25 stud bolt shown in FIG. 1 was prepared, and a delayed fracture test was performed in the same manner as in Example 1. The structure of each wire is also shown in Table 4 above, and the results of the delayed fracture test are shown in Table 5 below together with the drawing conditions and mechanical properties.
【0055】[0055]
【表5】 [Table 5]
【0056】実施例3 前記表1に示した供試鋼Cを用い、下記表6に示す圧延
条件にて線径:11mmφまで熱間圧延した。その後、
線径:7.06mmまで伸線した(伸線率:59%)。 Example 3 The test steel C shown in Table 1 was hot-rolled to a wire diameter of 11 mmφ under the rolling conditions shown in Table 6 below. afterwards,
The wire was drawn to a diameter of 7.06 mm (drawing ratio: 59%).
【0057】[0057]
【表6】 [Table 6]
【0058】得られた各種線材を用い、前記図1に示し
たM8×P1.25のスタッドボルトを作製し、遅れ破
壊試験を実施例1と同様にして行なった。各線材の組織
を下記表7に、遅れ破壊試験結果を伸線条件および機械
的特性と共に下記表8に夫々示す。Using the obtained various wire rods, M8 × P1.25 stud bolts shown in FIG. 1 were produced, and a delayed fracture test was performed in the same manner as in Example 1. The structure of each wire is shown in Table 7 below, and the results of the delayed fracture test are shown in Table 8 below together with the drawing conditions and mechanical properties.
【0059】[0059]
【表7】 [Table 7]
【0060】[0060]
【表8】 [Table 8]
【0061】これらの結果から明らかな様に、本発明鋼
の要件を満足するボルトは、引張り強度が1200N/
mm2 以上であっても、優れた耐遅れ破壊性を有してい
ることがわかる。As is apparent from these results, the bolt satisfying the requirements of the steel of the present invention has a tensile strength of 1200 N /
It can be seen that even if it is not less than mm 2 , it has excellent delayed fracture resistance.
【0062】[0062]
【発明の効果】本発明のボルト用鋼は以上の様に構成さ
れており、引張強度が1200N/mm2 以上でありな
がら耐遅れ破壊性に優れた高強度線材、およびその様な
高強度線材を得る為の有用な方法、並びに上記の特性を
有する高強度ボルトが実現できた。The steel for bolts according to the present invention is constituted as described above, and has a tensile strength of 1200 N / mm 2 or more and is excellent in delayed fracture resistance, and such a high-strength wire. And a high-strength bolt having the above-mentioned characteristics.
【図1】実施例において遅れ破壊試験に供したボルトの
形状を示す概略説明図である。FIG. 1 is a schematic explanatory view showing a shape of a bolt subjected to a delayed fracture test in an example.
【図2】ベイナイト組織を示す図面代用顕微鏡写真であ
る。FIG. 2 is a drawing-substituting micrograph showing a bainite structure.
【図3】初析フェライト組織を示す図面代用顕微鏡写真
である。FIG. 3 is a drawing-substituting micrograph showing a proeutectoid ferrite structure.
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.6 識別記号 FI C22C 38/10 C22C 38/10 38/30 38/30 F16B 35/00 F16B 35/00 J (72)発明者 家口 浩 神戸市西区高塚台1丁目5番5号 株式会 社神戸製鋼所神戸総合技術研究所内──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. 6 Identification code FI C22C 38/10 C22C 38/10 38/30 38/30 F16B 35/00 F16B 35/00 J (72) Inventor Hiroshi Ieguchi Kobe 1-5-5 Takatsukadai, Nishi-ku, Kobe Steel Works, Kobe Research Institute
Claims (9)
以下同じ)を含む鋼からなり、初析フェライト、初析セ
メンタイト、ベイナイトおよびマルテンサイトの1種ま
たは2種以上の組織生成を抑制し、パーライトノジュー
ルサイズが粒度番号でNo.7以上のパーライト組織の
面積率を80%以上としたものであり、且つ強伸線加工
によって1200N/mm2 以上の強度と優れた耐遅れ
破壊性を有する様にしたものであることを特徴とする耐
遅れ破壊性に優れた高強度線材。C: 0.5 to 1.0% (meaning by mass%,
The same shall apply hereinafter), which suppresses the formation of one or more types of pro-eutectoid ferrite, pro-eutectoid cementite, bainite and martensite, and has a pearlite nodule size of No. 1 in particle size number. The area ratio of the pearlite structure of 7 or more is 80% or more, and the strength is 1200 N / mm 2 or more and the delayed fracture resistance is excellent by strong drawing. High strength wire with excellent delayed fracture resistance.
および/またはCo:0.5%以下(0%を含まない)
を含有するものである請求項1に記載の高強度線材。2. Si: 2.0% or less (excluding 0%)
And / or Co: 0.5% or less (excluding 0%)
The high-strength wire according to claim 1, which comprises:
りなる群から選択される1種以上を合計で0.01〜
0.5%含有するものである請求項1または2に記載の
高強度線材。3. One or more kinds selected from the group consisting of Cr, Mo, Ti, Nb, V and W in a total amount of 0.01 to
The high-strength wire according to claim 1 or 2, which contains 0.5%.
ものである請求項1〜3のいずれかに記載の高強度線
材。4. The high-strength wire according to claim 1, which contains 0.01 to 0.05% of Al.
線材を製造するに当たり、鋼材の圧延または鍛造終了温
度が800〜1000℃となる様に熱間圧延または熱間
鍛造を行なった後、平均冷却速度Vが下記(1)式を満
足する様にして400℃まで冷却し、引き続き放冷する
ことにより、初析フェライト、初析セメンタイト、ベイ
ナイトおよびマルテンサイトの1種または2種以上の組
織生成を抑制して、パーライトノジュールサイズが粒度
番号でNo.7以上のパーライト組織の面積率を80%
以上とし、その後強伸線加工によって1200N/mm
2 以上の強度にすることを特徴とする耐遅れ破壊性に優
れた高強度線材の製造方法。 166×(線径)-1.4≦V≦288×(線径)-1.4 …(1)5. High strength according to claim 1.
In producing wire rods, the temperature at which steel is rolled or forged
Hot rolling or hot so that the temperature is 800-1000 ° C
After forging, the average cooling rate V satisfies the following formula (1).
Cool to 400 ° C and then allow to cool
Proeutectoid ferrite, proeutectoid cementite, bay
One or more sets of knight and martensite
Suppresses weaving and reduces perlite nodule size
No. by number. 80% area ratio of pearlite structure of 7 or more
After that, 1200 N / mm by strong wire drawing
Two Excellent in delayed fracture resistance characterized by having the above strength
Manufacturing method of high strength wire rod. 166 x (wire diameter)-1.4≦ V ≦ 288 × (wire diameter)-1.4 … (1)
線材を製造するに当たり、鋼材を800〜1000℃に
加熱した後、520〜650℃の温度まで急冷し、その
温度で恒温保持することにより、初析フェライト、初析
セメンタイト、ベイナイトおよびマルテンサイトの1種
または2種以上の組織生成を抑制して、パーライトノジ
ュールサイズが粒度番号でNo.7以上のパーライト組
織の面積率を80%以上とし、その後強伸線加工によっ
て1200N/mm2 以上の強度にすることを特徴とす
る耐遅れ破壊性に優れた高強度線材の製造方法。6. In producing the high-strength wire according to claim 1, the steel is heated to 800 to 1000 ° C., rapidly cooled to a temperature of 520 to 650 ° C., and kept at that temperature. By suppressing the formation of one or more types of proeutectoid ferrite, proeutectoid cementite, bainite and martensite, the pearlite nodule size becomes No. 1 in particle size number. A method for producing a high-strength wire excellent in delayed fracture resistance, characterized in that an area ratio of a pearlite structure of 7 or more is 80% or more, and thereafter, a strength of 1200 N / mm 2 or more is obtained by strong drawing.
線材を製造するに当たり、鋼材の圧延または鍛造終了温
度が800〜1000℃となる様に熱間圧延または熱間
鍛造を行なった後、5℃/秒以上の平均冷却速度で52
0〜750℃の温度まで冷却し、その温度で1.0℃/
秒以下の平均冷却速度で200秒以上保持し、引き続き
放冷することにより、初析フェライト、初析セメンタイ
ト、ベイナイトおよびマルテンサイトの1種または2種
以上の組織生成を抑制して、パーライトノジュールサイ
ズが粒度番号でNo.7以上のパーライト組織の面積率
を80%以上とし、その後強伸線加工によって1200
N/mm2 以上の強度にすることを特徴とする耐遅れ破
壊性に優れた高強度線材の製造方法。7. In producing the high-strength wire according to any one of claims 1 to 4, hot rolling or hot forging is performed so that the rolling or forging end temperature of the steel is 800 to 1000 ° C. Thereafter, at an average cooling rate of 5 ° C./sec or more, 52
It is cooled to a temperature of 0 to 750 ° C, and at that temperature, 1.0 ° C /
By holding for 200 seconds or more at an average cooling rate of 2 seconds or less, and then allowing to cool, the formation of one or more types of pro-eutectoid ferrite, pro-eutectoid cementite, bainite and martensite is suppressed, and the pearlite nodule size is reduced. Is the particle size number and No. The area ratio of the pearlite structure of 7 or more was set to 80% or more, and then 1200 mm by strong wire drawing.
A method for producing a high-strength wire excellent in delayed fracture resistance, characterized by having a strength of N / mm 2 or more.
線材を使用し、切断後に両端部をねじ転造または切削に
よりねじ加工したものである耐遅れ破壊性に優れた高強
度ボルト。8. A high-strength bolt excellent in delayed fracture resistance, obtained by using the high-strength wire rod according to claim 1 and cutting both ends by thread rolling or cutting after cutting. .
線材を使用し、切断後に温間鍛造によって一方端部にボ
ルト頭部を形成し、温間鍛造の前または後に他方端部を
ねじ転造または切削によりねじ加工したものである耐遅
れ破壊性に優れた高強度ボルト。9. A bolt head is formed at one end by warm forging after cutting using the high-strength wire rod according to claim 1, and the other end before or after warm forging. High-strength bolt with excellent delayed fracture resistance, which is made by thread rolling or cutting.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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JP12154298A JPH11315349A (en) | 1998-04-30 | 1998-04-30 | High strength wire rod excellent in delayed fracture resistance, its production, and high strength bolt |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP12154298A JPH11315349A (en) | 1998-04-30 | 1998-04-30 | High strength wire rod excellent in delayed fracture resistance, its production, and high strength bolt |
Related Child Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP2000107024A Division JP2000337333A (en) | 2000-01-01 | 2000-04-07 | High strength bolt excellent in delayed fracture resistance |
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Publication Number | Publication Date |
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JPH11315349A true JPH11315349A (en) | 1999-11-16 |
Family
ID=14813836
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WO2001079567A1 (en) * | 2000-04-07 | 2001-10-25 | Kabushiki Kaisha Kobe Seiko Sho | Method for manufacturing high strength bolt excellent in resistance to delayed fracture and to relaxation |
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1998
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