JP3490293B2 - Cold forging steel excellent in crystal grain coarsening prevention property and delayed fracture resistance, and its manufacturing method - Google Patents
Cold forging steel excellent in crystal grain coarsening prevention property and delayed fracture resistance, and its manufacturing methodInfo
- Publication number
- JP3490293B2 JP3490293B2 JP15367498A JP15367498A JP3490293B2 JP 3490293 B2 JP3490293 B2 JP 3490293B2 JP 15367498 A JP15367498 A JP 15367498A JP 15367498 A JP15367498 A JP 15367498A JP 3490293 B2 JP3490293 B2 JP 3490293B2
- Authority
- JP
- Japan
- Prior art keywords
- steel
- less
- delayed fracture
- particles
- tic
- 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.)
- Expired - Fee Related
Links
- 229910000831 Steel Inorganic materials 0.000 title claims description 55
- 230000003111 delayed effect Effects 0.000 title claims description 55
- 239000010959 steel Substances 0.000 title claims description 54
- 239000013078 crystal Substances 0.000 title claims description 50
- 238000010273 cold forging Methods 0.000 title claims description 20
- 238000004519 manufacturing process Methods 0.000 title claims description 11
- 230000002265 prevention Effects 0.000 title claims description 8
- 239000002245 particle Substances 0.000 claims description 34
- 229910052719 titanium Inorganic materials 0.000 claims description 29
- 229910052758 niobium Inorganic materials 0.000 claims description 22
- 239000011159 matrix material Substances 0.000 claims description 17
- 238000001816 cooling Methods 0.000 claims description 11
- 229910052799 carbon Inorganic materials 0.000 claims description 10
- 239000012535 impurity Substances 0.000 claims description 5
- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 229910052710 silicon Inorganic materials 0.000 claims description 4
- 229910052726 zirconium Inorganic materials 0.000 claims description 4
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- 229910052796 boron Inorganic materials 0.000 claims description 2
- 238000005242 forging Methods 0.000 claims description 2
- 238000010438 heat treatment Methods 0.000 description 25
- 230000000694 effects Effects 0.000 description 24
- 239000000463 material Substances 0.000 description 19
- 238000000034 method Methods 0.000 description 15
- 238000010791 quenching Methods 0.000 description 15
- 230000000171 quenching effect Effects 0.000 description 14
- 238000000137 annealing Methods 0.000 description 12
- 239000002244 precipitate Substances 0.000 description 12
- 238000012360 testing method Methods 0.000 description 12
- 229910000712 Boron steel Inorganic materials 0.000 description 10
- 238000005496 tempering Methods 0.000 description 8
- 229910001566 austenite Inorganic materials 0.000 description 6
- 229910052757 nitrogen Inorganic materials 0.000 description 6
- 238000001556 precipitation Methods 0.000 description 6
- 238000005096 rolling process Methods 0.000 description 6
- 229910000851 Alloy steel Inorganic materials 0.000 description 5
- 229920006395 saturated elastomer Polymers 0.000 description 5
- 239000011362 coarse particle Substances 0.000 description 4
- 239000006104 solid solution Substances 0.000 description 4
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 3
- PPWPWBNSKBDSPK-UHFFFAOYSA-N [B].[C] Chemical compound [B].[C] PPWPWBNSKBDSPK-UHFFFAOYSA-N 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 238000005275 alloying Methods 0.000 description 3
- 238000005260 corrosion Methods 0.000 description 3
- 230000006866 deterioration Effects 0.000 description 3
- 238000005098 hot rolling Methods 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 238000007670 refining Methods 0.000 description 3
- 239000002344 surface layer Substances 0.000 description 3
- 230000000007 visual effect Effects 0.000 description 3
- 229910000975 Carbon steel Inorganic materials 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- CREMABGTGYGIQB-UHFFFAOYSA-N carbon carbon Chemical compound C.C CREMABGTGYGIQB-UHFFFAOYSA-N 0.000 description 2
- 239000011203 carbon fibre reinforced carbon Substances 0.000 description 2
- 238000005255 carburizing Methods 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 230000001143 conditioned effect Effects 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 238000000465 moulding Methods 0.000 description 2
- 238000002791 soaking Methods 0.000 description 2
- 229910052720 vanadium Inorganic materials 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- 102220479482 Puromycin-sensitive aminopeptidase-like protein_C21D_mutation Human genes 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- FFBHFFJDDLITSX-UHFFFAOYSA-N benzyl N-[2-hydroxy-4-(3-oxomorpholin-4-yl)phenyl]carbamate Chemical compound OC1=C(NC(=O)OCC2=CC=CC=C2)C=CC(=C1)N1CCOCC1=O FFBHFFJDDLITSX-UHFFFAOYSA-N 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000010622 cold drawing Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Landscapes
- Heat Treatment Of Steel (AREA)
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、結晶粒粗大化防止
特性と耐遅れ破壊特性に優れた冷間鍛造用鋼とその製造
方法に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold forging steel having excellent grain coarsening prevention properties and delayed fracture resistance properties, and a method for producing the same.
【０００２】[0002]
【従来の技術】冷間鍛造（転造も含む）は製品の表面
肌、寸法精度が良く、熱間鍛造に比べて製造コストが低
く、歩留まりも良好であるためボルト、ギア部品、シャ
フトをはじめとする多くの分野に適用されている。これ
らの部品の冷間鍛造は、例えばＪＩＳ Ｇ ４０５１、
ＪＩＳ Ｇ ４０５２、ＪＩＳ Ｇ ４１０４、ＪＩＳ
Ｇ ４１０５、ＪＩＳ Ｇ ４１０６などに規定されて
いる中炭素の機械構造用炭素鋼、合金鋼を使用し、例え
ば熱間圧延−焼鈍−冷間鍛造−焼入れ−焼戻しのように
冷間鍛造前に焼鈍、あるいは球状化焼鈍工程を付加する
工程が一般的である。これは上記のような中炭素の炭素
鋼、合金鋼は圧延ままの硬度が高く、ボルト等の部品成
形時の冷間鍛造工具の消耗が著しくコスト高となった
り、素材の延性が不足しているため部品の成形時に割れ
を生じたり、等といった製造上の問題があるためであ
る。2. Description of the Related Art Cold forging (including rolling) has good surface texture and dimensional accuracy of products, lower manufacturing cost than hot forging, and good yield. Has been applied to many fields. Cold forging of these parts is performed, for example, according to JIS G4051,
JIS G 4052, JIS G 4104, JIS
Annealing before cold forging such as hot rolling-annealing-cold forging-quenching-tempering is performed using medium carbon carbon steel for machine structural use and alloy steel defined by G 4105, JIS G 4106, etc. Or, a step of adding a spheroidizing annealing step is generally used. This is because the above-mentioned medium carbon carbon steel and alloy steel have high hardness as they are rolled, the cost of the cold forging tool is extremely high during the molding of parts such as bolts, and the ductility of the material is insufficient. This is because there are manufacturing problems such as cracks occurring during the molding of parts.
【０００３】しかし、焼鈍にはエネルギー費、人件費、
設備費など多大なコストがかかるため、この工程を省略
しうる素材およびプロセスが求められてきた。そこで鋼
材のＣ量、合金元素量を低減することによって熱間圧延
ままの硬度を低減し、延性を向上して焼鈍工程を省略
し、Ｃｒ、Ｍｏ等の合金元素量の低減による焼入れ性の
低下を微量のＢを添加することによって補う、いわゆる
低炭素ボロン鋼が、例えば特開平５−３３９６７６、特
公平５−６３５２４、特開昭６１−２５３３４７のよう
に数多く提案されている。Ｂは微量の添加で焼入れ性を
向上できるが、鋼中に固溶Ｎが存在するとＢＮが生成
し、Ｂの持つ焼入れ性向上効果は失われてしまうため、
Ｔｉを添加して鋼中ＮをＴｉＮの形で固定し、ＢＮの生
成を抑制することが一般に行われている。However, annealing requires energy costs, labor costs,
Since a large cost such as equipment cost is required, a material and a process that can omit this step have been demanded. Therefore, by reducing the C content and alloying element content of the steel material, the hardness as hot-rolled is reduced, the ductility is improved, the annealing step is omitted, and the hardenability is reduced due to the reduction of the alloying element content such as Cr and Mo. Many so-called low-carbon boron steels have been proposed, which are supplemented by adding a small amount of B, such as JP-A-5-339676, JP-B-5-63524, and JP-A-61-253347. B can improve the hardenability by adding a small amount, but if solid solution N is present in the steel, BN is formed and the hardenability improving effect of B is lost.
It is generally practiced to add Ti to fix N in the steel in the form of TiN to suppress the formation of BN.
【０００４】部品の高強度化のニーズが強くなるに従
い、上記のような低炭素ボロン鋼をより高強度の部品に
適用する試みがなされている。しかし低炭素ボロン鋼は
Ｃ量、合金元素量を低減しているため、引張強さが１０
００ＭＰａ以上となるように熱処理を行うと遅れ破壊特
性が低下するという問題がある。高強度を得るために低
温の焼き戻しを行うと遅れ破壊強度が低下することが知
られているが、高温の焼き戻しでも高い強度を得て、遅
れ破壊強度を実用上問題ないレベルとするために、Ｃ量
の添加量を増加したり、ＳＣＲ、ＳＣＭなどの合金鋼を
使用すると、素材の強度が増加し、焼鈍が省略できなく
なる。焼鈍を省略できる低炭素ボロン鋼は経済的だが、
高強度を得るためには焼き戻しの温度を低くせざるを得
ず、その結果遅れ破壊強度が低下し、実用上の問題とな
るため、高強度部品への適用は難しかった。As the needs for higher strength of parts have become stronger, attempts have been made to apply the above low carbon boron steel to parts having higher strength. However, low carbon boron steel has reduced C content and alloying element content, so tensile strength is 10
If the heat treatment is performed so as to be 00 MPa or more, there is a problem that the delayed fracture characteristic is deteriorated. It is known that tempering at low temperature lowers delayed fracture strength to obtain high strength, but high strength is obtained even by tempering at high temperature so that delayed fracture strength is at a level where practically no problem occurs. In addition, when the amount of C added is increased or alloy steels such as SCR and SCM are used, the strength of the material increases and annealing cannot be omitted. Low carbon boron steel that can omit annealing is economical,
In order to obtain high strength, the tempering temperature must be lowered, and as a result, delayed fracture strength decreases, which poses a practical problem, making it difficult to apply to high strength parts.
【０００５】高強度部品へのボロン鋼適用の要求に応え
るため、不純物の量を低減し、遅れ破壊特性を合金鋼と
同等程度とした鋼が、例えば特開平８−６０２４５等の
ように提案されている。しかし上記のようなボロン鋼
は、切削肌の試験片での評価では合金鋼よりも優れた遅
れ破壊特性を示すが、実際の製造ラインで部品を作成
し、熱処理肌の状態で遅れ破壊特性の評価を行うと、ボ
ロン鋼の部品は合金鋼よりも遅れ破壊特性が悪くなると
いう問題が見出されている。したがって、上記のような
技術で部品の高強度化に対応するには限界がある。In order to meet the demand for the application of boron steel to high-strength parts, a steel in which the amount of impurities is reduced and the delayed fracture characteristics are comparable to those of alloy steel is proposed, for example, in Japanese Patent Laid-Open No. 60245/1996. ing. However, the boron steel as described above shows delayed fracture characteristics superior to alloy steel in the evaluation of the cut skin test piece, but when the parts are created on the actual production line, the delayed fracture characteristics of the heat treated skin are When evaluated, it has been found that boron steel parts have delayed fracture properties worse than alloy steels. Therefore, there is a limit to how high the strength of the component can be dealt with by the above-mentioned technique.
【０００６】また、上記の問題に加え、ボロン鋼は焼鈍
材に比べて焼入れ加熱時に特定のオーステナイト結晶粒
が異常に粗大化しやすくなるという問題がある。結晶粒
の粗大化が発生した部品は、焼入れ歪みによる寸法精度
の劣化、衝撃値、疲労寿命の低下、特に高強度部品にお
いて遅れ破壊特性の低下を招くため、ボロン鋼を高強度
部品に適用するには結晶粒の粗大化を抑制し、かつ結晶
粒を微細化しなければならない。この結晶粒の粗大化を
抑制するには結晶粒界の移動をピン止めする粒子を多
量、微細に分散させることが有効である。In addition to the above problems, boron steel has a problem that specific austenite crystal grains are likely to be abnormally coarsened during quenching and heating as compared with an annealed material. Parts with coarsening of crystal grains cause deterioration of dimensional accuracy due to quenching strain, decrease of impact value, fatigue life, and deterioration of delayed fracture property especially in high strength parts, so boron steel is applied to high strength parts. Therefore, it is necessary to suppress the coarsening of the crystal grains and to make the crystal grains finer. In order to suppress the coarsening of the crystal grains, it is effective to finely disperse a large amount of particles that pin the movement of the crystal grain boundaries.
【０００７】上記のようなボロン鋼の結晶粒粗大化を防
止するための技術が提案されている。例えば、特開昭６
１−２１７５５３はＴｉとＮの量を０．０２＜Ｔｉ−
３．４２ＮとすることによってＴｉＣを生成し、結晶粒
界をピン止めすることを目的としている。しかし、成分
を規定しただけではＴｉＣを微細に分散させることはで
きず、結晶粒の粗大化を防止できない。また例えば、特
公昭６３−６４４９５は０．００３５％以下の極低Ｎと
し、Ｔｉ量をＮ量に対して過剰とした成分を低温加熱圧
延を行うことによって結晶粒粗大化を防止することを目
的としている。しかし、焼入れ加熱前のＴｉＣ、Ｔｉ
（ＣＮ）の析出状態を最適化しない限り結晶粒の粗大化
を防止できない。Techniques have been proposed for preventing the crystal grain coarsening of boron steel as described above. For example, JP-A-6
1-217553, the amount of Ti and N is 0.02 <Ti-
The purpose is to generate TiC by setting it to 3.42 N and to pin the crystal grain boundaries. However, TiC cannot be finely dispersed only by defining the components, and coarsening of crystal grains cannot be prevented. Further, for example, Japanese Examined Patent Publication No. 63-64495 aims at preventing crystal grain coarsening by making extremely low N of 0.0035% or less and performing low temperature hot rolling of a component having an excessive Ti content relative to the N content. I am trying. However, TiC, Ti before quenching and heating
Unless the precipitation state of (CN) is optimized, coarsening of crystal grains cannot be prevented.
【０００８】また、例えは特開昭５２−１１４５４５は
素材段階でＴｉＣを固溶させ、焼入れ加熱時に初めてＴ
ｉＣを微細析出させることを目的としている。しかし焼
入れ加熱時にピン止め粒子を析出させる場合、ＴｉＣの
析出量は焼入れ加熱、または浸炭加熱時の加熱速度の影
響を受けるためピン止め効果の発現が不安定であり、同
じ素材を用いても部品のサイズや熱処理炉を変えただけ
で粗大化防止特性が劣化する可能性が高いため、実工程
での品質の安定性の点で課題を残している。Further, for example, in Japanese Unexamined Patent Publication No. 52-114545, TiC is solid-solved at the material stage, and T
The purpose is to finely precipitate iC. However, when pinning particles are precipitated during quenching heating, the amount of TiC precipitation is affected by the heating rate during quenching heating or carburizing heating, so the pinning effect is unstable, and even if the same material is used There is a high possibility that the coarsening prevention property will deteriorate just by changing the size and heat treatment furnace, so there remains a problem in terms of quality stability in the actual process.
【０００９】[0009]
【発明が解決しようとする課題】上記のような開示され
た方法では、冷間鍛造前の焼鈍、あるいは球状化焼鈍工
程を省略し、かつ高強度に熱処理を行った際の実部品で
の遅れ破壊特性を合金鋼と同等以上にすることができな
い。本発明はこのような問題を解決して、結晶粒粗大化
防止特性と耐遅れ破壊特性に優れた冷間鍛造用鋼とその
製造方法を提供するものである。SUMMARY OF THE INVENTION In the above-disclosed method, there is a delay in actual parts when annealing before cold forging or spheroidizing annealing is omitted and heat treatment is performed at high strength. The fracture characteristics cannot be made equal to or higher than that of alloy steel. The present invention solves such a problem and provides a steel for cold forging excellent in crystal grain coarsening prevention characteristics and delayed fracture resistance, and a manufacturing method thereof.
【００１０】[0010]
【課題を解決するための手段】本発明者らは、上記目的
を達成するために実部品の熱処理肌での遅れ破壊特性に
及ぼす諸因子の影響について鋭意調査し、
（ア）実部品での遅れ特性には、表面の性状が大きく影
響していること、すなわち、熱処理スケールが付着した
実ボルト（熱処理肌）と、表面層を切削・研削等によっ
て除去した試験片（切削肌）とでは同一条件で遅れ破壊
試験を行っても特性が大きく異なり、熱処理スケールが
付着した実部品の方が遅れ破壊特性が劣ること。
（イ）熱処理肌での遅れ破壊特性を改善するにはＣｒを
ある最適範囲で添加し、部品の熱処理時に生成されるス
ケールをＣｒの濃化した緻密なスケールとし、耐食性を
増すことでスケールおよびスケールの内側の鋼表面層が
腐食される過程で発生する水素量を低減させ、遅れ破壊
特性を向上することができること。
（ウ）ボロン鋼を引張強さ１０００ＭＰａ以上のボルト
等の高強度部品に適用する場合には、遅れ破壊特性の向
上のためＰ、Ｓ量を一定量以下に制限することが必要な
こと、および結晶粒の粗大化を防止することが必要なこ
と。
（エ）結晶粒の粗大化を防止するにはピン止め粒子とし
て微細なＴｉＣ、Ｔｉ（ＣＮ）、ＮｂＣ、Ｎｂ（Ｃ
Ｎ）、（Ｎｂ、Ｔｉ）（ＣＮ）粒子が有効であり、結晶
粒粗大化特性とこれらの析出物のサイズおよび分散状態
（析出粒子数）には極めて密接な関係があること、析出
物のピン止め効果を安定して発揮させるには、焼入れ加
熱前に一定量以上のＴｉＣ、Ｔｉ（ＣＮ）、ＮｂＣ、Ｎ
ｂ（ＣＮ）、（Ｎｂ、Ｔｉ）（ＣＮ）のうち１種以上の
粒子をあらかじめ微細析出させておくことが必要なこと
を見出し、本発明に至った。In order to achieve the above object, the inventors of the present invention have diligently investigated the effects of various factors on the delayed fracture characteristics of heat treated skin of actual parts, and (a) in actual parts The property of the surface has a great influence on the delay characteristics, that is, the actual bolt with the heat treatment scale (heat treated skin) and the test piece with the surface layer removed by cutting / grinding (cutting skin) are the same. Even if the delayed fracture test is performed under the conditions, the characteristics are significantly different, and the actual parts with the heat treatment scale attached have the delayed fracture characteristics inferior. (B) In order to improve the delayed fracture property in heat treated skin, Cr is added in an optimum range, and the scale generated during heat treatment of parts is a dense scale with Cr enriched to increase scale and corrosion resistance. It is possible to reduce the amount of hydrogen generated during the process in which the steel surface layer inside the scale is corroded and to improve delayed fracture characteristics. (C) When boron steel is applied to high strength parts such as bolts having a tensile strength of 1000 MPa or more, it is necessary to limit the amount of P and S to a certain amount or less in order to improve delayed fracture characteristics, and It is necessary to prevent coarsening of crystal grains. (D) In order to prevent coarsening of crystal grains, fine TiC, Ti (CN), NbC, Nb (C
N), (Nb, Ti) (CN) particles are effective, and the crystal grain coarsening property and the size and dispersion state (the number of precipitated particles) of these precipitates are extremely closely related. In order to stably exert the pinning effect, a certain amount or more of TiC, Ti (CN), NbC, N before quenching and heating is used.
The present inventors have found that it is necessary to finely precipitate at least one kind of particles of b (CN), (Nb, Ti) (CN) in advance, and have reached the present invention.
【００１１】本発明の特性は、（１）Ｃ：０．１０〜
０．４０％、Ｓｉ：０．１５％以下、Ｍｎ：０．３０〜
１．００％にすることにより焼入れ、焼戻し後の部品の
強度を確保し、Ｐ：０．０１５％以下（０％を含む）、
Ｓ：０．０１５％以下（０％を含む）に制限することに
よって遅れ破壊特性を改善し、Ｂ：０．０００３〜０．
００５０％に制限することによって焼入れ性を確保し、
Ｃｒ：０．５０〜１．２０％にすることによって熱処理
肌での遅れ破壊特性を改善し、実部品になった時の遅れ
破壊特性を顕著に改善することができる。さらに、Ｎ：
０．０１００％以下（０％を含む）に制限し、Ｔｉ：
０．０２０〜０．１００％にすることによってＴｉＣ、
Ｔｉ（ＣＮ）を生成し、結晶粒の粗大化を防止するため
のピン止め粒子として利用することができる。マトリッ
クス中に直径０．２μｍ以下のＴｉＣ、Ｔｉ（ＣＮ）の
うち１種または２種の粒子の総個数を２０個／１００μ
ｍ2 以上有することによってピン止め効果を最大限に発
揮させ、焼入れ加熱時の結晶粒の粗大化を防止するとと
もに旧オーステナイト結晶粒を微細化することができる
冷間鍛造用鋼である。The characteristics of the present invention are (1) C: 0.10 to
0.40%, Si: 0.15% or less, Mn: 0.30
By ensuring 1.00%, the strength of the parts after quenching and tempering is secured, and P: 0.015% or less (including 0%),
S: 0.015% or less (including 0%) is used to improve delayed fracture characteristics, and B: 0.0003 to 0.
The hardenability is secured by limiting to 0050%,
By setting Cr: 0.50 to 1.20%, the delayed fracture characteristic on the heat treated skin can be improved, and the delayed fracture characteristic when it becomes an actual part can be remarkably improved. Furthermore, N:
It is limited to 0.0100% or less (including 0%), and Ti:
TiC by adjusting 0.020 to 0.100%,
It can be used as pinning particles for producing Ti (CN) and preventing coarsening of crystal grains. The total number of one or two particles of TiC or Ti (CN) having a diameter of 0.2 μm or less in the matrix is 20 particles / 100 μ
By having m 2 or more, the pinning effect can be maximized, the coarsening of crystal grains at the time of quenching and heating can be prevented, and the former austenite crystal grains can be refined, which is a steel for cold forging.
【００１２】（２）また本発明の他の特徴は、上記成分
に加えて、Ｎｂ：０．００３〜０．１００％を含有し、
マトリックス中に直径０．２μｍ以下のＴｉＣ、Ｔｉ
（ＣＮ）、ＮｂＣ、Ｎｂ（ＣＮ）、（Ｎｂ、Ｔｉ）（Ｃ
Ｎ）のうち１種以上の粒子の総個数を２０個／１００μ
ｍ2 以上有することによって結晶粒の粗大化を防止する
ことができる冷間鍛造用鋼である。(2) Another feature of the present invention is that it contains Nb: 0.003 to 0.100% in addition to the above components,
TiC and Ti with a diameter of 0.2 μm or less in the matrix
(CN), NbC, Nb (CN), (Nb, Ti) (C
The total number of one or more particles in N) is 20 / 100μ
A steel for cold forging that can prevent the coarsening of crystal grains by having m 2 or more.
【００１３】（３）また本発明の他の特徴は、上記
（１）または（２）の成分に加えて、Ｖ：０．０５〜
０．３０％、Ｚｒ：０．００３〜０．１００％のうち１
種または２種を含有することによって旧オーステナイト
結晶粒をさらに微細化することができ、マトリックス中
に直径０．２μｍ以下のＴｉＣ、Ｔｉ（ＣＮ）、Ｎｂ
Ｃ、Ｎｂ（ＣＮ）、（Ｎｂ、Ｔｉ）（ＣＮ）のうち１種
以上の粒子の総個数を２０個／１００μｍ2 以上有する
ことによって結晶粒の粗大化を防止することができる冷
間鍛造用鋼である。(3) Another feature of the present invention is that, in addition to the above component (1) or (2), V: 0.05-
0.30%, Zr: 0.003 to 0.100% of 1
The former austenite crystal grains can be further refined by containing one or two kinds, and TiC, Ti (CN), Nb having a diameter of 0.2 μm or less in the matrix.
For cold forging that can prevent coarsening of crystal grains by having a total number of one or more particles of C, Nb (CN), (Nb, Ti) (CN) of 20 particles / 100 μm 2 or more. It is steel.
【００１４】（４）また本発明の他の特徴は、上記
（１）、（２）、（３）の成分よりなる鋼を１０５０℃
以上に加熱してＴｉＣ、Ｔｉ（ＣＮ）、ＮｂＣ、Ｎｂ
（ＣＮ）、（Ｎｂ、Ｔｉ）（ＣＮ）を一旦マトリックス
中に固溶させ、線材または棒鋼に熱間圧延した後、６０
０℃以下の温度まで冷却するに際して２℃／ｓ以下の冷
却速度で徐冷して軟質化するとともに、マトリックス中
に直径０．２μｍ以下の微細なＴｉＣ、Ｔｉ（ＣＮ）、
ＮｂＣ、Ｎｂ（ＣＮ）、（Ｎｂ、Ｔｉ）（ＣＮ）のうち
１種以上の粒子の総個数を２０個／１００μｍ2 以上分
散した鋼とする冷間鍛造用鋼の製造方法である。(4) Another feature of the present invention is that the steel containing the components of (1), (2) and (3) above is heated to 1050 ° C.
When heated to above, TiC, Ti (CN), NbC, Nb
(CN), (Nb, Ti) (CN) are once solid-solved in a matrix and hot-rolled into a wire rod or a steel bar.
When it is cooled to a temperature of 0 ° C. or lower, it is gradually cooled at a cooling rate of 2 ° C./s or lower to soften it, and fine TiC and Ti (CN) having a diameter of 0.2 μm or less in the matrix.
This is a method for producing a steel for cold forging, in which a total number of particles of one or more of NbC, Nb (CN), and (Nb, Ti) (CN) is dispersed into 20/100 μm 2 or more.
【００１５】[0015]
【発明の実施の形態】以下、本発明について詳細に説明
する。まず、成分の限定理由について説明する。Ｃは鋼
に必要な強度を与えるのに有効な元素であるが、０．１
０％未満では必要な引張強さを確保することができず、
０．４０％を超えると冷間鍛造性が低下し、冷間鍛造前
の焼鈍、あるいは球状化焼鈍工程を省略することができ
ない。また、部品の延性、靱性が劣化し、さらには遅れ
破壊特性も劣化する傾向があるので、０．１０〜０．４
０％の範囲内にする必要がある。好適範囲は０．２０〜
０．３０％である。BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. First, the reasons for limiting the components will be described. C is an element effective in giving the necessary strength to steel, but 0.1
If it is less than 0%, the required tensile strength cannot be secured,
If it exceeds 0.40%, the cold forgeability deteriorates, and the annealing before cold forging or the spheroidizing annealing step cannot be omitted. In addition, the ductility and toughness of parts tend to deteriorate, and the delayed fracture characteristics also tend to deteriorate.
It must be within the range of 0%. The preferred range is 0.20
It is 0.30%.
【００１６】Ｓｉは鋼の脱酸に有効な元素であるととも
に、鋼に必要な強度、焼入れ性を与え、焼戻し軟化抵抗
を向上するのに有効な元素であるが、０．１５％を超え
ると靱性、延性が劣化し、硬さの上昇を招き冷間鍛造性
が劣化するので、０．１５％以下の範囲内にする必要が
ある。好適範囲は０．１０％以下である。Si is an element effective for deoxidizing the steel, and is an element effective for imparting the necessary strength and hardenability to the steel and improving the temper softening resistance, but if it exceeds 0.15%. The toughness and ductility are deteriorated, the hardness is increased, and the cold forgeability is deteriorated. Therefore, it is necessary to set the content within the range of 0.15% or less. The preferred range is 0.10% or less.
【００１７】Ｍｎは鋼の脱酸に有効な元素であるととも
に、鋼に必要な強度、焼入れ性を与えるのに有効な元素
であるが、０．３０％未満では効果は不十分であり、
１．００％を超えると硬さの上昇を招き冷間鍛造性が劣
化するので、０．３０％〜１．００％の範囲にする必要
がある。好適範囲は０．４０〜０．７０％である。Mn is an element effective for deoxidizing the steel, and is an element effective for imparting the strength and hardenability required for the steel, but if it is less than 0.30%, the effect is insufficient.
If it exceeds 1.00%, the hardness is increased and the cold forgeability is deteriorated. Therefore, it is necessary to set it in the range of 0.30% to 1.00%. A suitable range is 0.40 to 0.70%.
【００１８】Ｐは冷間鍛造時の変形抵抗を高め、靱性を
劣化させる元素であるため、冷間鍛造性が劣化する。ま
た、焼入れ、焼戻し後の部品の結晶粒界を脆化させるこ
とによって遅れ破壊特性を劣化させるのでできるだけ低
減することが望ましい。したがって、その含有量を０．
０１５％以下に制限する必要がある。好適範囲は０．０
１０％以下である。Since P is an element that increases the deformation resistance during cold forging and deteriorates toughness, cold forgeability deteriorates. Further, the delayed fracture characteristics are deteriorated by embrittlement of the crystal grain boundaries of the parts after quenching and tempering, so it is desirable to reduce as much as possible. Therefore, its content should be 0.
It is necessary to limit it to 015% or less. The preferred range is 0.0
It is 10% or less.
【００１９】Ｓは冷間鍛造時に割れを生じやすくする元
素であるため、冷間鍛造性が劣化する。また、Ｐと同様
に焼入れ、焼戻し後の部品の結晶粒界を脆化させること
によって遅れ破壊特性を劣化させるのでできるだけ低減
することが望ましい。したがって、その含有量を０．０
１５％以下に制限する必要がある。好適範囲は０．０１
０％以下である。Since S is an element that easily causes cracking during cold forging, cold forgeability deteriorates. Further, as with P, the delayed fracture characteristics are deteriorated by embrittlement of the crystal grain boundaries of the part after quenching and tempering, so it is desirable to reduce it as much as possible. Therefore, its content is 0.0
It is necessary to limit it to 15% or less. The preferred range is 0.01
It is 0% or less.
【００２０】Ｃｒは鋼に強度、焼入れ性を与え、焼戻し
軟化抵抗を向上するのに有効な元素であるとともに特に
熱処理肌における遅れ破壊特性を顕著に改善する元素で
ある。Ｃｒは熱処理時に生成されるスケールをＣｒの濃
化した緻密なスケールとし、耐食性を増すことでスケー
ルが腐食される過程で発生する水素量を低減させ、遅れ
破壊特性を向上する効果がある。引張強さ１３５０ＭＰ
ａ近傍に調質したときの遅れ破壊特性に及ぼすＣｒ量の
影響を図１に示す。Cr is an element that imparts strength and hardenability to steel and is effective for improving the resistance to temper softening, and at the same time, it is an element that remarkably improves the delayed fracture property in the heat-treated skin. As for Cr, the scale generated during heat treatment is a dense Cr-rich scale, and by increasing the corrosion resistance, the amount of hydrogen generated in the process of corroding the scale is reduced and the delayed fracture characteristics are improved. Tensile strength 1350MP
FIG. 1 shows the effect of Cr content on the delayed fracture characteristics when tempered near a.
【００２１】図１は０．１Ｎ ＨＣｌ中での試験結果で
あるが、１％Ｈ2 ＳＯ4 中でもほぼ同様の傾向を示す。
図１から明らかなように、熱処理肌における遅れ破壊特
性にはＣｒ量の影響が大きく、０．５０％未満では充分
な遅れ破壊特性の向上効果を得ることができず、１．２
０％を超えて添加すると硬さの上昇を招き冷間鍛造性が
劣化するだけではなく、熱処理時に発生する表層の粒界
酸化の発生を助長し、遅れ破壊特性がかえって劣化す
る。この傾向は部品強度が高くなるほど顕著に現れる。
したがって、Ｃｒの添加量は、０．５０〜１．２０％の
範囲内にする必要がある。好適範囲は０．６０〜０．９
０％である。Although FIG. 1 shows the test results in 0.1N HCl, it shows almost the same tendency in 1% H 2 SO 4 .
As is clear from FIG. 1, the amount of Cr has a great influence on the delayed fracture characteristics of heat treated skin, and if it is less than 0.50%, a sufficient effect of improving the delayed fracture characteristics cannot be obtained.
If added in excess of 0%, not only does hardness increase and cold forgeability deteriorates, but it also promotes the generation of grain boundary oxidation of the surface layer that occurs during heat treatment, and the delayed fracture property deteriorates rather. This tendency becomes more remarkable as the strength of the component increases.
Therefore, the added amount of Cr needs to be within the range of 0.50 to 1.20%. The preferred range is 0.60 to 0.9
It is 0%.
【００２２】Ｂは微量の添加で鋼に焼入れ性を与えるの
に有効な元素であるが、０．０００３％未満ではその効
果は不十分であり、０．００５０％を超えると効果は飽
和するので、０．０００３〜０．００５０％の範囲内に
する必要がある。好適範囲は０．００１０〜０．００３
０％である。B is an element effective in imparting hardenability to steel with a small amount of addition, but if its content is less than 0.0003%, its effect is insufficient, and if it exceeds 0.0050%, the effect is saturated. , 0.0003 to 0.0050%. The preferred range is 0.0010 to 0.003
It is 0%.
【００２３】ＮはＢと結び付いてＢＮを生成し、Ｂの持
つ焼入れ性向上効果を低下させるため、本発明のような
Ｂ添加鋼では有害である。また、鋼中のＴｉと結び付く
とピン止めにほとんど寄与しない粗大なＴｉＮを生成
し、Ｔｉを含有する炭窒化物となりうるＴｉ量が減少
し、微細な析出物の量が減少するため、できるだけ低減
することが望ましい。したがって、その含有量をできる
だけ低く抑えることが結晶粒の粗大化抑制のポイントで
あり、また後述のようにＮ量が少なければＴｉの添加量
も少なくて済む。しかし実際の製造工程でＮを完全に除
くことは難しいため、その範囲を０．０１００％以下と
定めた。好適範囲は０．００５０％以下である。N is harmful in the B-added steel as in the present invention because N combines with B to form BN and reduces the hardenability improving effect of B. In addition, when combined with Ti in steel, coarse TiN that hardly contributes to pinning is generated, the amount of Ti that can become a carbonitride containing Ti is reduced, and the amount of fine precipitates is reduced. It is desirable to do. Therefore, it is a point to suppress the coarsening of the crystal grains by keeping the content thereof as low as possible, and the addition amount of Ti can be small if the amount of N is small as described later. However, it is difficult to completely remove N in the actual manufacturing process, so the range was set to 0.0100% or less. The preferred range is 0.0050% or less.
【００２４】Ｔｉは鋼中のＣ、Ｎと結び付いてＴｉＣ、
Ｔｉ（ＣＮ）を形成し、結晶粒の微細化、および結晶粒
の粗大化抑制に有効な元素である。また、Ｂとともに添
加した場合、鋼中の固溶ＮをＴｉＮ、Ｔｉ（ＣＮ）の形
で固定することによってＢＮの生成を抑制し、Ｂによる
焼入れ性向上効果を得るのに有効な元素であるが、０．
０２０％未満では効果は不十分であり、０．１００％を
超えるとその効果は飽和するのみならず硬さの上昇を招
き冷間鍛造性が劣化するので、０．０２０〜０．１００
％の範囲内にする必要がある。好適範囲は０．０２５〜
０．５０％である。もちろん、鋼中の固溶Ｎを全てＴｉ
Ｎの形で固定するためには、Ｎ量に応じてＴｉ量も増加
させる必要があるし、結晶粒界のピン止めに有効な微細
なＴｉＣ、Ｔｉ（ＣＮ）を十分な量確保するためにも、
Ｎ量に応じてＴｉ量も増加させる必要がある。少なくと
も、３．４Ｎ％を超えるＴｉの添加が必要である。Ti is tied with C and N in steel to form TiC,
It is an element that forms Ti (CN) and is effective in refining crystal grains and suppressing coarsening of crystal grains. Further, when added together with B, it is an element effective for suppressing the generation of BN by fixing the solid solution N in the steel in the form of TiN or Ti (CN) and for obtaining the hardenability improving effect of B. But 0.
If it is less than 020%, the effect is insufficient, and if it exceeds 0.100%, the effect is not only saturated, but also the hardness is increased and the cold forgeability is deteriorated, so 0.020 to 0.100.
Must be in the range of%. The preferred range is 0.025-
It is 0.50%. Of course, all the solid solution N in the steel is Ti
In order to fix in the form of N, it is necessary to increase the amount of Ti in accordance with the amount of N, and in order to secure a sufficient amount of fine TiC and Ti (CN) effective for pinning the crystal grain boundaries. Also,
It is necessary to increase the amount of Ti according to the amount of N. At least a Ti addition of more than 3.4 N% is required.
【００２５】Ｎｂは鋼中のＣ、Ｎと結び付いてＮｂＣ、
Ｎｂ（ＣＮ）、（Ｎｂ、Ｔｉ）（ＣＮ）を形成し、結晶
粒の微細化、および結晶粒の粗大化抑制に有効な元素で
ある。ＮｂはＴｉとともに添加された場合、そのほとん
どが安定な（Ｎｂ、Ｔｉ）（ＣＮ）を形成し、安定した
ピン止め効果を得ることができるが、０．００３％未満
では効果は不十分であり、０．１００％を超えるとその
効果は飽和するのみならず硬さの上昇を招き冷間鍛造性
が劣化するので、０．００３〜０．１００％の範囲内に
する必要がある。好適範囲は０．００５〜０．０３０％
である。Nb is combined with C and N in steel to form NbC,
It is an element that forms Nb (CN), (Nb, Ti) (CN), and is effective in refining crystal grains and suppressing coarsening of crystal grains. When Nb is added together with Ti, most of them form stable (Nb, Ti) (CN) and a stable pinning effect can be obtained, but if less than 0.003%, the effect is insufficient. , 0.100%, the effect is not only saturated, but also the hardness is increased and the cold forgeability is deteriorated. Therefore, it is necessary to set the content within the range of 0.003 to 0.100%. The preferred range is 0.005-0.030%
Is.
【００２６】Ｖは鋼中のＣ、Ｎと結び付いてＶＣ、ＶＮ
を形成し、結晶粒の微細化に有効な元素であるが、０．
０５％未満では効果は不十分であり、０．３０％を超え
るとその効果は飽和するのみならず硬さの上昇を招き冷
間鍛造性が劣化するので、０．０５〜０．３０％の範囲
内にする必要がある。好適範囲は０．１０〜０．２０％
である。V is associated with C and N in steel, and VC and VN
And is an element effective for making the crystal grains finer.
If it is less than 05%, the effect is insufficient, and if it exceeds 0.30%, the effect is not only saturated, but also the hardness is increased and the cold forgeability is deteriorated. Must be within range. The preferred range is 0.10 to 0.20%
Is.
【００２７】Ｚｒは鋼中のＣ、Ｎと結び付いてＺｒＣ、
ＺｒＮを形成し、結晶粒の微細化に有効な元素である
が、０．００３％未満では効果は不十分であり、０．１
００％を超えるとその効果は飽和するのみならず硬さの
上昇を招き冷間鍛造性が劣化するので、０．００３〜
０．１００％の範囲内にする必要がある。好適範囲は
０．００５〜０．０３０％である。Zr is combined with C and N in steel and ZrC,
It is an element that forms ZrN and is effective for making the crystal grains finer. However, if it is less than 0.003%, the effect is insufficient.
If it exceeds 00%, not only the effect is saturated, but also the hardness is increased and the cold forgeability is deteriorated.
It must be within the range of 0.100%. A suitable range is 0.005 to 0.030%.
【００２８】なお、Ｖ，Ｚｒは本発明において必須の元
素ではないが、結晶粒の微細化の目的のため必要に応じ
添加することができる。Although V and Zr are not essential elements in the present invention, they can be added as necessary for the purpose of refining the crystal grains.
【００２９】本発明はＡｌ添加量を規定していないが、
鋼の脱酸に有効な元素であるため、通常脱酸に使用され
るＡｌ量を含有してもよい。通常のＡｌ含有量は０．０
１０〜０．０５０％程度である。但し、Ａｌに代わる元
素（Ｓｉ、Ｍｎ、Ｔｉ、Ｚｒ等）を脱酸剤として用いる
場合は必ずしもＡｌを添加しなくとも良い。Although the present invention does not specify the amount of Al added,
Since it is an element effective for deoxidizing steel, it may contain an amount of Al usually used for deoxidation. Normal Al content is 0.0
It is about 10 to 0.050%. However, when an element (Si, Mn, Ti, Zr, etc.) that replaces Al is used as the deoxidizer, Al does not necessarily have to be added.
【００３０】次にマトリックス中のＴｉＣ、Ｔｉ（Ｃ
Ｎ）、ＮｂＣ、Ｎｂ（ＣＮ）、（Ｎｂ、Ｔｉ）（ＣＮ）
の分散状態について説明する。結晶粒の粗大化を抑制す
るには結晶粒界をピン止めする粒子を多量、微細に分散
させることが有効であり、粒子の直径が小さいほど、ま
た量が多いほどピン止め粒子の数が増加するため好まし
い。微細ＴｉＣ、Ｔｉ（ＣＮ）と結晶粒粗大化温度との
関係を図２に示す。なお、ＮｂＣ、Ｎｂ（ＣＮ）、（Ｎ
ｂ、Ｔｉ）（ＣＮ）についても同様の効果があり、図２
の関係に従う。Next, TiC and Ti (C
N), NbC, Nb (CN), (Nb, Ti) (CN)
The distributed state of will be described. In order to suppress the coarsening of crystal grains, it is effective to disperse a large number of particles that pin the crystal grain boundaries in a fine manner.The smaller the particle diameter and the larger the number, the larger the number of pinning particles. It is preferable because The relationship between fine TiC and Ti (CN) and the crystal grain coarsening temperature is shown in FIG. Note that NbC, Nb (CN), (N
b, Ti) (CN) has the same effect.
Obey the relationship.
【００３１】図２から明らかなように、結晶粒粗大化特
性と微細な析出粒子数には極めて密接な関連があり、マ
トリックス中に直径０．２μｍ以下のＴｉＣ、Ｔｉ（Ｃ
Ｎ）、ＮｂＣ、Ｎｂ（ＣＮ）、（Ｎｂ、Ｔｉ）（ＣＮ）
のうち１種以上の粒子の総個数を２０個／１００μｍ2
以上分散させると実用上の焼入れ加熱、あるいは浸炭加
熱温度域において結晶粒の粗大化が生じず、優れた結晶
粒粗大化防止特性が得られるため、マトリックス中に直
径０．２μｍ以下のＴｉＣ、Ｔｉ（ＣＮ）、ＮｂＣ、Ｎ
ｂ（ＣＮ）、（Ｎｂ、Ｔｉ）（ＣＮ）のうち１種以上の
粒子の総個数が２０個／１００μｍ2 以上分散している
ことが必要である。As is clear from FIG. 2, there is a very close relationship between the crystal grain coarsening property and the number of fine precipitated particles, and TiC and Ti (C (TiC) having a diameter of 0.2 μm or less are contained in the matrix.
N), NbC, Nb (CN), (Nb, Ti) (CN)
The total number of one or more particles is 20 particles / 100 μm 2
When dispersed as described above, crystal grains are not coarsened in the practical quenching heating or carburizing heating temperature range, and excellent grain coarsening prevention characteristics are obtained. Therefore, TiC, Ti having a diameter of 0.2 μm or less in the matrix (CN), NbC, N
It is necessary that the total number of particles of one or more of b (CN), (Nb, Ti) (CN) is 20 particles / 100 μm 2 or more.
【００３２】次に製造条件について説明する。上記の本
発明成分からなる鋼を、転炉、電気炉等の通常の方法に
よって溶製し、成分調整を行い、鋳造工程、必要に応じ
て分塊圧延工程を経て圧延素材とする。なお、分塊圧延
工程の前に鋳片を１２００〜１３５０℃程度の温度に数
時間保定する均熱拡散処理を行うと、Ｐ等の不純物元素
の偏析が軽減され、実部品での遅れ破壊特性が更に向上
するだけでなく、鋳造工程で析出する粗大な析出物が一
旦溶体化でき、次工程で析出物のマトリックスへの固溶
が容易になるため、この処理を行うとさらに特性が得ら
れる。Next, manufacturing conditions will be described. The steel comprising the above-described components of the present invention is melted by a usual method such as a converter or an electric furnace, the components are adjusted, a casting process and, if necessary, a slabbing process are performed to obtain a rolled material. If the slab is subjected to a soaking diffusion treatment in which the slab is held at a temperature of about 1200 to 1350 ° C. for several hours before the slab rolling process, segregation of impurity elements such as P is reduced, and delayed fracture characteristics in actual parts are reduced. Not only further improves, but also the coarse precipitates that precipitate in the casting process can be solutionized once and the precipitates can easily form a solid solution in the next process. .
【００３３】次に、圧延素材を１０５０℃以上の温度で
加熱する。加熱条件は、１０５０℃未満ではＴｉＣ、Ｔ
ｉ（ＣＮ）、ＮｂＣ、Ｎｂ（ＣＮ）、（Ｎｂ、Ｔｉ）
（ＣＮ）を一旦マトリックス中に固溶させることができ
ず、熱間圧延後にＴｉＣ、Ｔｉ（ＣＮ）、ＮｂＣ、Ｎｂ
（ＣＮ）、（Ｎｂ、Ｔｉ）（ＣＮ）のうち１種以上の粒
子を微細析出した鋼とすることができない。また固溶さ
せることができなかった粗大なＴｉＣ、Ｔｉ（ＣＮ）、
ＮｂＣ、Ｎｂ（ＣＮ）、（Ｎｂ、Ｔｉ）（ＣＮ）は、多
量に存在すると部品の延性を劣化させ、遅れ破壊特性に
も悪影響を及ぼす。更に、粗大な析出物が多く残存して
いると圧延後の冷却時に析出核として働き、さらに粗大
に成長するため、ピン止め粒子をマトリックス中に微細
に分散させることが困難になる。従って、加熱温度はで
きるだけ高温にすることが望ましい。好適範囲は１１５
０℃以上である。Next, the rolled material is heated at a temperature of 1050 ° C. or higher. The heating conditions are TiC and T at temperatures lower than 1050 ° C.
i (CN), NbC, Nb (CN), (Nb, Ti)
(CN) cannot be once solid-solved in the matrix, and after hot rolling TiC, Ti (CN), NbC, Nb
Steel cannot be obtained by finely depositing particles of one or more of (CN) and (Nb, Ti) (CN). In addition, coarse TiC, Ti (CN), which could not be dissolved,
If a large amount of NbC, Nb (CN), (Nb, Ti) (CN) is present, the ductility of the component is deteriorated and the delayed fracture characteristics are also adversely affected. Furthermore, if a large amount of coarse precipitates remain, they act as precipitation nuclei during cooling after rolling and grow coarser, making it difficult to finely disperse the pinning particles in the matrix. Therefore, it is desirable that the heating temperature be as high as possible. The preferred range is 115
It is 0 ° C or higher.
【００３４】次に、１０５０℃以上に加熱した圧延素材
を線材または棒鋼形状に熱間圧延した後、６００℃以下
の温度まで冷却するに際して２℃／ｓ以下の冷却速度で
徐冷する。冷却条件は、２℃／ｓを超えるとＴｉＣ、Ｔ
ｉ（ＣＮ）、ＮｂＣ、Ｎｂ（ＣＮ）、（Ｎｂ、Ｔｉ）
（ＣＮ）の析出温度域を短時間しか通過させることがで
きず、析出量が不十分となり、ピン止め粒子として有効
なＴｉＣ、Ｔｉ（ＣＮ）、ＮｂＣ、Ｎｂ（ＣＮ）、（Ｎ
ｂ、Ｔｉ）（ＣＮ）を多量・微細析出した鋼とすること
ができない。また、冷却速度が大きいと圧延材の硬さが
上昇し、冷間鍛造性が劣化するため、冷却速度はできる
だけ小さくするのが望ましい。好適範囲は１℃／ｓ以下
である。なお、熱間圧延後にさらに低い温度域（５００
℃以下）まで２℃／ｓの冷却速度で徐冷するのが好まし
い。低い温度域まで徐冷すると圧延材がさらに軟質化
し、冷間鍛造性が向上する。Next, after the rolled material heated to 1050 ° C. or higher is hot-rolled into the shape of a wire or bar, it is gradually cooled at a cooling rate of 2 ° C./s or less when it is cooled to a temperature of 600 ° C. or less. Cooling conditions are TiC and T when the temperature exceeds 2 ° C / s.
i (CN), NbC, Nb (CN), (Nb, Ti)
Since it can pass through the precipitation temperature range of (CN) only for a short time, the amount of precipitation becomes insufficient, and TiC, Ti (CN), NbC, Nb (CN), (N
b, Ti) (CN) cannot be obtained as a steel in which a large amount of fine precipitation is produced. Further, if the cooling rate is high, the hardness of the rolled material increases and the cold forgeability deteriorates. Therefore, it is desirable to make the cooling rate as low as possible. The preferred range is 1 ° C./s or less. In addition, the lower temperature range (500
It is preferable to gradually cool to a temperature of 2 ° C / s or less) at a cooling rate of 2 ° C / s. Slow cooling to a low temperature range further softens the rolled material and improves cold forgeability.
【００３５】[0035]
【実施例】以下に、実施例により本発明をさらに説明す
る。表１に示す組成を有する転炉溶製鋼を連続鋳造し、
必要に応じて均熱拡散処理工程、分塊圧延工程を経て１
６２ｍｍ角の圧延素材とした。続いて圧延素材を１０５
０℃以上の温度で加熱し、直径５〜５０ｍｍの棒鋼、線
材に熱間圧延した。一部は比較のために加熱温度を１０
５０℃以下とした。次に、圧延ラインの後方に設けた保
温カバーを使用し、徐冷を行った。一部は比較のために
徐冷を行わなかった。EXAMPLES The present invention will be further described below with reference to examples. Continuous casting of converter molten steel having the composition shown in Table 1,
If necessary, go through the soaking diffusion process and slabbing process 1
A 62 mm square rolled material was used. Then roll material 105
It was heated at a temperature of 0 ° C. or higher and hot-rolled into a steel bar and a wire rod having a diameter of 5 to 50 mm. For some, the heating temperature is 10 for comparison.
It was set to 50 ° C. or lower. Next, the heat insulation cover provided behind the rolling line was used to perform gradual cooling. Some were not annealed for comparison.
【００３６】[0036]
【表１】 [Table 1]
【００３７】ピン止め粒子として有効なＴｉＣ、Ｔｉ
（ＣＮ）、ＮｂＣ、Ｎｂ（ＣＮ）、（Ｎｂ、Ｔｉ）（Ｃ
Ｎ）の分散状態は、棒鋼、線材のマトリックス中に存在
する析出物を抽出レプリカ法によって採取し、透過型電
子顕微鏡で観察することによって測定した。観察方法は
１５０００倍で２０視野程度観察し、１視野中の直径
０．２μｍ以下のＴｉＣ、Ｔｉ（ＣＮ）、ＮｂＣ、Ｎｂ
（ＣＮ）、（Ｎｂ、Ｔｉ）（ＣＮ）の総数を数え、１０
０μｍ2 あたりの数に換算した。TiC, Ti effective as pinning particles
(CN), NbC, Nb (CN), (Nb, Ti) (C
The dispersed state of N) was measured by collecting the precipitates existing in the matrix of the steel bar and the wire rod by the extraction replica method and observing with a transmission electron microscope. The observation method was 15,000 times, and about 20 visual fields were observed. TiC, Ti (CN), NbC, Nb with a diameter of 0.2 μm or less in one visual field.
Count the total number of (CN), (Nb, Ti) (CN), and
It was converted to the number per 0 μm 2 .
【００３８】上記の工程で製造した線材または棒鋼の結
晶粒粗大化温度を測定した。圧延材に減面率７０％の冷
間引き抜き加工を行った後、８４０〜１２００℃に３０
分間加熱−水焼入れした。その後、切断面に研磨−腐食
を行い、旧オーステナイト粒径を観察して粗粒発生温度
（結晶粒粗大化温度）を求めた。The crystal grain coarsening temperature of the wire rod or steel bar manufactured in the above process was measured. After cold drawing with 70% reduction in area of the rolled material, 30 to 840-1200 ° C
Heated for minutes-water quenched. Then, the cut surface was subjected to polishing-corrosion, and the former austenite grain size was observed to determine the coarse grain generation temperature (grain coarsening temperature).
【００３９】ボルト等の実部品の焼入れ工程ではＡc3〜
９００℃の温度域で行われることが多いため、粗粒発生
温度が９００℃未満のものは結晶粒粗大化特性に劣ると
判定した。なお、旧オーステナイト粒度の測定はＪＩＳ
Ｇ ０５５１に準じて行い、４００倍で１０視野程度
観察し、粒度番号５番以下の粗粒が１つでも存在すれば
粗粒発生と判定した。In the quenching process of actual parts such as bolts, A c3
Since it is often carried out in the temperature range of 900 ° C., it was determined that those having a coarse particle generation temperature of less than 900 ° C. were inferior in crystal grain coarsening property. The former austenite grain size is measured according to JIS
The measurement was performed according to G 0551, and observation was performed at 400 times for about 10 fields of view, and if there was even one coarse particle having a particle size number of 5 or less, it was determined that coarse particles had occurred.
【００４０】次にこれらの材料の遅れ破壊特性を調査す
るため、７０％の冷間引き抜き加工を行った材料を環状
Ｖノッチ付きの遅れ破壊試験片に加工した。その後９０
０℃×３０分−焼入れ、その後焼戻しを行い、引張強さ
１３５０ＭＰａ級に調質し、実部品の表面肌に近い、熱
処理肌の遅れ破壊試験片を製作した。この遅れ破壊試験
片を０．１Ｎ ＨＣｌ中に浸漬し、負荷応力を変化させ
て破断までの時間を測定した。試験時間は最大２００時
間とし、２００時間破断しない最大の負荷応力を測定し
た。２００時間破断しない最大の負荷応力を大気中での
破断応力で割った値を「遅れ破壊強度比」と定義し、遅
れ破壊特性の指標とした。Next, in order to investigate the delayed fracture characteristics of these materials, 70% cold drawn materials were processed into delayed fracture test pieces with an annular V notch. Then 90
0 ° C x 30 minutes-Quenching, then tempering to prepare a delayed fracture test piece for heat-treated skin, which has a tensile strength of 1350 MPa and is close to the surface skin of an actual part. The delayed fracture test piece was dipped in 0.1N HCl, the load stress was changed, and the time until fracture was measured. The test time was 200 hours at maximum, and the maximum load stress without breaking for 200 hours was measured. The value obtained by dividing the maximum load stress that does not fracture for 200 hours by the fracture stress in the atmosphere was defined as the "delayed fracture strength ratio" and used as an index of the delayed fracture property.
【００４１】現在、引張強さが１０００〜１４００ＭＰ
ａ級の部品に多く使われているＳＣＭ４３５の遅れ破壊
強度比が０．５程度であることから、遅れ破壊強度比が
０．５未満のものは遅れ破壊特性に劣ると判断した。他
方で、遅れ破壊試験に供した試験片の結晶粒度を調査し
た。整粒の場合はマトリックスの平均粒度を測定し、混
粒の場合、あるいは粗大粒がある場合は観察視野中の最
大粒の粒度番号も測定した。なお、旧オーステナイト粒
度の測定は上記の結晶粒粗大化温度の調査と同じ方法で
行った。At present, the tensile strength is 1000 to 1400MP
Since the delayed fracture strength ratio of SCM435, which is often used for a-class parts, is about 0.5, it was judged that those with a delayed fracture strength ratio of less than 0.5 were inferior in delayed fracture characteristics. On the other hand, the grain size of the test pieces subjected to the delayed fracture test was investigated. In the case of sized particles, the average particle size of the matrix was measured, and in the case of mixed particles or when there were coarse particles, the particle size number of the largest particle in the observation visual field was also measured. The former austenite grain size was measured by the same method as the above-mentioned investigation of the crystal grain coarsening temperature.
【００４２】[0042]
【表２】 [Table 2]
【００４３】これらの各種試験結果を表２、表３、表４
に示す。表２の記号Ｎ、記号ＯはＴｉまたはＮ量が本発
明の範囲から外れているため、微細ＴｉＣ、Ｔｉ（Ｃ
Ｎ）、ＮｂＣ、Ｎｂ（ＣＮ）、（Ｎｂ、Ｔｉ）（ＣＮ）
の析出数が不足し、結晶粒粗大化特性が劣化している。
記号Ｖ、記号Ｘ、記号Ｙは圧延加熱温度が低いためＴｉ
Ｃ、Ｔｉ（ＣＮ）、ＮｂＣ、Ｎｂ（ＣＮ）、（Ｎｂ、Ｔ
ｉ）（ＣＮ）を一旦マトリックス中に固溶させることが
できず、熱間圧延後の冷却時に析出物を微細析出した鋼
とすることができないため、結晶粒粗大化特性が劣化し
ている。The results of these various tests are shown in Tables 2, 3 and 4.
Shown in. The symbols N and O in Table 2 are fine TiC, Ti (C
N), NbC, Nb (CN), (Nb, Ti) (CN)
The number of precipitates of is poor and the crystal grain coarsening property is deteriorated.
The symbols V, X, and Y are Ti because the rolling heating temperature is low.
C, Ti (CN), NbC, Nb (CN), (Nb, T
i) Since (CN) cannot be once solid-dissolved in the matrix and the precipitates cannot be finely precipitated steel during cooling after hot rolling, the crystal grain coarsening property is deteriorated.
【００４４】また、記号Ｗ、記号Ｚは圧延後の冷却速度
が大きすぎるため、微細析出物の析出量が不十分とな
り、結晶粒粗大化特性が劣化している。Further, in the symbols W and Z, since the cooling rate after rolling is too high, the amount of fine precipitates deposited becomes insufficient and the crystal grain coarsening characteristics deteriorate.
【００４５】[0045]
【表３】 [Table 3]
【００４６】[0046]
【表４】 [Table 4]
【００４７】表３は表２の圧延材を１３５０ＭＰａ程度
に、表４は１２００ＭＰａ程度に調質したときの遅れ破
壊特性を示したものである。表３の記号Ｐ、記号Ｑ、記
号ＴはＣｒ添加量が本発明の範囲から外れているため、
遅れ破壊特性が劣化している。記号Ｒ、記号ＳはＰ量ま
たはＳ量が本発明の範囲から外れているため、遅れ破壊
特性が劣化している。なお、結晶粒粗大化特性に劣るも
の（記号Ｎ、Ｏ、Ｖ、Ｗ、Ｘ、Ｙ、Ｚ）は遅れ破壊試験
片に粗大粒が発生しているため、遅れ破壊特性も劣化し
ている。表４は引張強さが１２００ＭＰａ程度であるた
め、表３よりも遅れ破壊特性が向上している。なお、表
１の成分番号２１、表２、表３の記号Ｕは現在多く使用
されている焼鈍を省略できない合金鋼の例である。これ
らの表から明らかなように、本発明で規定する条件を全
て満たすものは比較例に比べて結晶粒粗大化防止特性お
よび耐遅れ破壊特性ともに優れた特性を示している。Table 3 shows the delayed fracture characteristics when the rolled material of Table 2 was conditioned at about 1350 MPa and Table 4 was conditioned at about 1200 MPa. The symbols P, Q, and T in Table 3 indicate that the Cr addition amount is out of the range of the present invention.
Delayed fracture characteristics are degraded. In the symbols R and S, the P amount or the S amount is out of the range of the present invention, so that the delayed fracture characteristics are deteriorated. In addition, those having inferior crystal grain coarsening characteristics (symbols N, O, V, W, X, Y, and Z) have coarse grains generated in the delayed fracture test piece, and thus the delayed fracture characteristics are also deteriorated. In Table 4, since the tensile strength is about 1200 MPa, the delayed fracture characteristics are improved as compared with Table 3. In addition, the component number 21 in Table 1 and the symbol U in Table 2 and Table 3 are examples of alloy steels, which are often used at present and whose annealing cannot be omitted. As is clear from these tables, those satisfying all the conditions specified in the present invention exhibit excellent properties in terms of preventing coarsening of crystal grains and delayed fracture resistance as compared with Comparative Examples.
【００４８】[0048]
【発明の効果】本発明の冷間鍛造用鋼およびその製造方
法を用いれば、冷間鍛造前の焼鈍を省略でき、かつ熱処
理時の結晶粒粗大化による焼入れ歪みによる寸法精度の
劣化、衝撃値、疲労強度の低下が従来より少なく、しか
も熱処理肌で使用される実部品での遅れ破壊特性に特に
優れたボルト、ギア部品、シャフト等の素材を提供する
ことができる。EFFECTS OF THE INVENTION By using the steel for cold forging and the method for producing the same according to the present invention, annealing before cold forging can be omitted, and dimensional accuracy is deteriorated due to quenching strain due to coarsening of crystal grains during heat treatment and impact value. Further, it is possible to provide a material such as a bolt, a gear component, a shaft, which has less deterioration in fatigue strength than ever before and which is particularly excellent in delayed fracture characteristics in an actual component used for heat treatment.
【図１】熱処理肌での遅れ破壊特性に及ぼすＣｒ量の影
響について解析した一例を示す図FIG. 1 is a diagram showing an example of analysis of the effect of Cr content on delayed fracture characteristics of heat treated skin.
【図２】焼入れ加熱前の鋼のマトリックス中の微細Ｔｉ
Ｃ、Ｔｉ（ＣＮ）の総個数と結晶粗大化温度の関係につ
いて解析した一例を示す図FIG. 2 Fine Ti in matrix of steel before quenching and heating
The figure which shows an example which analyzed the relationship between the total number of C and Ti (CN), and the crystal coarsening temperature.
フロントページの続き (72)発明者 蟹澤 秀雄 北海道室蘭市仲町12番地 新日本製鐵株 式会社 室蘭製鐵所内 (72)発明者 村上 敦 埼玉県和光市中央一丁目４番１号 株式 会社本田技術研究所内 (72)発明者 石田 正雄 埼玉県和光市中央一丁目４番１号 株式 会社本田技術研究所内 (56)参考文献 特開 平10−130777（ＪＰ，Ａ) 特開 平10−36940（ＪＰ，Ａ) 特開 平９−268320（ＪＰ，Ａ) 特開 平８−295979（ＪＰ，Ａ) 特開 昭62−86149（ＪＰ，Ａ) 特開 平９−59745（ＪＰ，Ａ) 特開 平８−291360（ＪＰ，Ａ) 特開 平８−60245（ＪＰ，Ａ) (58)調査した分野(Int.Cl.7，ＤＢ名) C22C 38/00 C21D 8/00 Front page continuation (72) Hideo Kanizawa 12 Nakamachi, Muroran, Hokkaido Muroran Works (72) Nippon Steel Co., Ltd. In-lab (72) Inventor Masao Ishida 1-4-1 Chuo 1-4, Wako-shi, Saitama Incorporated in Honda R & D Co., Ltd. (56) References JP-A-10-130777 (JP, A) JP-A-10-36940 (JP , A) JP 9-268320 (JP, A) JP 8-295979 (JP, A) JP 62-86149 (JP, A) JP 9-59745 (JP, A) JP 8-291360 (JP, A) JP-A-8-60245 (JP, A) (58) Fields investigated (Int. Cl. 7 , DB name) C22C 38/00 C21D 8/00
Claims (4)
なり、かつ鋼のマトリックス中に直径０．２μｍ以下の
ＴｉＣ、Ｔｉ（ＣＮ）のうち１種または２種の粒子の総
個数を２０個／１００μｍ2 以上有することを特徴とす
る結晶粒粗大化防止特性と耐遅れ破壊特性に優れた冷間
鍛造用鋼。1. By weight%, C: 0.10 to 0.40%, Si: 0.15% or less, Mn: 0.30 to 1.00%, Cr: 0.50 to 1.20%, B: 0.0003 to 0.0050%, Ti: 0.020 to 0.100%, P: 0.015% or less (including 0%), S: 0.015% or less (0% , N: 0.0100% or less (including 0%), with the balance being Fe and inevitable impurities, and TiC, Ti (CN) having a diameter of 0.2 μm or less in the steel matrix. Among these, one or two types of particles have a total number of particles of 20/100 μm 2 or more, and a steel for cold forging excellent in grain coarsening prevention properties and delayed fracture resistance properties.
なり、かつ鋼のマトリックス中に直径０．２μｍ以下の
ＴｉＣ、Ｔｉ（ＣＮ）、ＮｂＣ、Ｎｂ（ＣＮ）、（Ｎ
ｂ、Ｔｉ）（ＣＮ）のうち１種以上の粒子の総個数を２
０個／１００μｍ2以上有することを特徴とする結晶粒
粗大化防止特性と耐遅れ破壊特性に優れた冷間鍛造用
鋼。2. By weight%, C: 0.10 to 0.40%, Si: 0.15% or less, Mn: 0.30 to 1.00%, Cr: 0.50% to 1.20% , B: 0.0003 to 0.0050%, Ti: 0.020 to 0.100%, Nb: 0.003 to 0.100%, and P: 0.015% or less ( 0% inclusive), S: 0.015% or less (inclusive of 0%), N: 0.0100% or less (inclusive of 0%), with the balance being Fe and inevitable impurities, and TiC, Ti (CN), NbC, Nb (CN), (N with a diameter of 0.2 μm or less in a steel matrix
b, Ti) (CN), the total number of one or more particles is 2
A steel for cold forging excellent in the property of preventing coarsening of crystal grains and the property of delayed fracture, which is characterized by having 0 pieces / 100 μm 2 or more.
可避的不純物よりなり、かつ鋼のマトリックス中に直径
０．２μｍ以下のＴｉＣ、Ｔｉ（ＣＮ）、ＮｂＣ、Ｎｂ
（ＣＮ）、（Ｎｂ、Ｔｉ）（ＣＮ）のうち１種以上の粒
子の総個数を２０個／１００μｍ2 以上有することを特
徴とする結晶粒粗大化防止特性と耐遅れ破壊特性に優れ
た冷間鍛造用鋼。3. In addition to the steel composition according to claim 1 or 2, V: 0.05 to 0.30%, Zr: 0.003 to 0.100%, containing one or two kinds, and the balance. Is Fe and inevitable impurities, and TiC, Ti (CN), NbC, Nb having a diameter of 0.2 μm or less in the steel matrix.
(CN), (Nb, Ti) (CN) having a total number of at least one kind of particles of 20/100 μm 2 or more, which is excellent in crystal grain coarsening prevention characteristics and delayed fracture resistance. Steel for forging.
０５０℃以上に加熱して線材または棒鋼に熱間圧延した
後、６００℃以下の温度まで冷却するに際して、２℃／
ｓ以下の冷却速度で徐冷し、マトリックス中に直径０．
２μｍ以下のＴｉＣ、Ｔｉ（ＣＮ）、ＮｂＣ、Ｎｂ（Ｃ
Ｎ）、（Ｎｂ、Ｔｉ）（ＣＮ）のうち１種以上の粒子の
総個数を２０個／１００μｍ2 以上分散した鋼とするこ
とを特徴とする結晶粒粗大化防止特性と耐遅れ破壊特性
に優れた冷間鍛造用鋼の製造方法。4. The steel composition according to claim 1 or 2 or 3
When heated to 050 ° C or higher and hot-rolled into a wire rod or steel bar, and then cooled to a temperature of 600 ° C or lower, 2 ° C /
Gradually cooled at a cooling rate of not more than s, and the diameter of the matrix was 0.
TiC, Ti (CN), NbC, Nb (C
N), (Nb, Ti), (CN), the total number of particles of one or more kinds is 20/100 μm 2 or more dispersed in steel, and is characterized by grain coarsening prevention characteristics and delayed fracture resistance characteristics. Excellent cold forging steel manufacturing method.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP15367498A JP3490293B2 (en) | 1997-07-23 | 1998-05-20 | Cold forging steel excellent in crystal grain coarsening prevention property and delayed fracture resistance, and its manufacturing method |
| US09/314,733 US6261388B1 (en) | 1998-05-20 | 1999-05-18 | Cold forging steel having improved resistance to grain coarsening and delayed fracture and process for producing same |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9-211251 | 1997-07-23 | ||
| JP21125197 | 1997-07-23 | ||
| JP15367498A JP3490293B2 (en) | 1997-07-23 | 1998-05-20 | Cold forging steel excellent in crystal grain coarsening prevention property and delayed fracture resistance, and its manufacturing method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH1192868A JPH1192868A (en) | 1999-04-06 |
| JP3490293B2 true JP3490293B2 (en) | 2004-01-26 |
Family
ID=26482226
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP15367498A Expired - Fee Related JP3490293B2 (en) | 1997-07-23 | 1998-05-20 | Cold forging steel excellent in crystal grain coarsening prevention property and delayed fracture resistance, and its manufacturing method |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3490293B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013145868A1 (en) | 2012-03-26 | 2013-10-03 | 株式会社神戸製鋼所 | Boron-added high strength bolt steel having excellent delayed fracture resistance and high strength bolt |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4964063B2 (en) * | 2006-08-28 | 2012-06-27 | 株式会社神戸製鋼所 | Case-hardened steel with excellent cold forgeability and grain coarsening prevention properties and machine parts obtained therefrom |
| JP5458048B2 (en) | 2011-03-29 | 2014-04-02 | 株式会社神戸製鋼所 | Case-hardened steel, its manufacturing method, and machine structural parts using case-hardened steel |
| JP6182489B2 (en) * | 2014-03-27 | 2017-08-16 | 株式会社神戸製鋼所 | Case-hardened steel that has excellent cold forgeability and can suppress abnormal grain generation during carburizing. |
| JP6427272B2 (en) | 2015-06-29 | 2018-11-21 | 新日鐵住金株式会社 | bolt |
| JP6601284B2 (en) * | 2016-03-11 | 2019-11-06 | 日本製鉄株式会社 | High strength bolt |
| US11098394B2 (en) * | 2016-07-05 | 2021-08-24 | Nippon Steel Corporation | Rolled wire rod |
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-
1998
- 1998-05-20 JP JP15367498A patent/JP3490293B2/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013145868A1 (en) | 2012-03-26 | 2013-10-03 | 株式会社神戸製鋼所 | Boron-added high strength bolt steel having excellent delayed fracture resistance and high strength bolt |
| US9845519B2 (en) | 2012-03-26 | 2017-12-19 | Kobe Steel, Ltd. | Boron-added high strength steel for bolt and high strength bolt having excellent delayed fracture resistance |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH1192868A (en) | 1999-04-06 |
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