JPH08176724A - High tensile steel having excellent welding cold crack resistance and production thereof - Google Patents
High tensile steel having excellent welding cold crack resistance and production thereofInfo
- Publication number
- JPH08176724A JPH08176724A JP32338994A JP32338994A JPH08176724A JP H08176724 A JPH08176724 A JP H08176724A JP 32338994 A JP32338994 A JP 32338994A JP 32338994 A JP32338994 A JP 32338994A JP H08176724 A JPH08176724 A JP H08176724A
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- Prior art keywords
- steel
- cold cracking
- transformation point
- welding
- strength
- Prior art date
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Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、橋梁・建築・ペンスト
ック・圧力容器などの分野に用いられる耐溶接低温割れ
性に優れた調質高張力鋼、特に引張り強さが６０ｋｇｆ
／ｍｍ2 以上の調質鋼およびその製造方法に関するもの
である。BACKGROUND OF THE INVENTION The present invention relates to a tempered high-strength steel excellent in weld cold-crack resistance used in the fields of bridges, construction, penstocks, pressure vessels, etc., and particularly has a tensile strength of 60 kgf.
/ Mm 2 or more, and to a method for producing the same.
【０００２】[0002]
【従来の技術】溶接構造物の大型化、省エネルギー化の
観点から、従来に比べて高張力鋼の使用が高まってい
る。高張力鋼の使用で最も重要な問題の一つは溶接低温
割れである。特に、低入熱溶接において水素量が高い溶
接材料で高張力鋼の溶接を行うと、溶接金属に固溶した
原子状の水素が溶接熱影響部（以下、ＨＡＺと記す）に
拡散し、溶接後数時間〜数日放置すると低温割れを発生
することがある。鋼材の強度が高くなるに従って合金元
素添加量が高くなると、ＨＡＺの硬化性が上昇するため
に、このような低温割れが助長される傾向にある。引張
り強さが６０ｋｇｆ／ｍｍ2 級以上の調質型高張力鋼に
おいては上記の傾向が著しく、溶接施工に当たっては溶
接前に予熱を行うことによりＨＡＺ硬化を抑えたり、水
素の拡散を容易にして低温割れを防止する対策がなされ
ている。2. Description of the Related Art The use of high-strength steel has been increasing compared with the conventional ones from the viewpoint of increasing the size of a welded structure and saving energy. One of the most important problems in the use of high strength steel is weld cold cracking. In particular, when welding high-strength steel with a welding material with a high hydrogen content in low heat input welding, atomic hydrogen dissolved in the weld metal diffuses into the weld heat affected zone (hereinafter referred to as HAZ), If left for a few hours to a few days after that, cold cracking may occur. When the amount of alloying elements added increases as the strength of the steel increases, the hardenability of the HAZ increases, and such low temperature cracking tends to be promoted. The above tendency is remarkable in the tempered high-strength steel with a tensile strength of 60 kgf / mm 2 or higher. In welding work, preheating before welding suppresses HAZ hardening and facilitates hydrogen diffusion. Measures are taken to prevent cold cracking.
【０００３】しかしながら、予熱は溶接施工時間が長く
なったり、その効果には限度があるため、有力な低温割
れ防止の手段とはなり得ていない。上記の問題を克服す
るために、これまでに種々の検討がなされてきた。特開
昭５３−１１５６１１号公報においては、Ｃａ／Ｓの比
が０．２〜２．０となるようにＣａを添加し、低融点の
硫化物であるＭｎＳの生成を抑制することにより、溶接
低温割れを低減できる技術が示されている。However, preheating cannot be an effective means for preventing cold cracking because it takes a long time for welding and its effect is limited. In order to overcome the above problems, various studies have been made so far. In Japanese Patent Laid-Open No. 53-115611, welding is performed by adding Ca so that the ratio of Ca / S is 0.2 to 2.0 and suppressing the formation of MnS which is a low-melting sulfide. Techniques that can reduce cold cracking have been shown.
【０００４】また、特開昭５６−１２３３５０号公報に
おいては、Ｃの添加量を下げ、かつ、ＶとＮの両方を多
量に含有することによりＶＮ析出物を生成させ、溶接低
温割れを低減できる技術が示されている。また、特開昭
５７−５１２１２号公報においては、鋼中のＳ、Ｏ量を
低下させた上で、Ｂ量を０．０００３０％以下とするこ
とにより、溶接低温割れを低減できることが示されてい
る。Further, in Japanese Patent Application Laid-Open No. 56-123350, by lowering the amount of C added and by containing a large amount of both V and N, VN precipitates can be formed and welding cold cracking can be reduced. Technology is shown. Further, Japanese Patent Application Laid-Open No. 57-51212 discloses that welding cold cracking can be reduced by reducing the amounts of S and O in steel and then setting the amount of B to 0.00030% or less. There is.
【０００５】さらに、特公平５−５５５８４号公報にお
いては、炭素当量値を０．４０％以下、およびＰｃｍ値
を０．２４％以下に制限することにより、溶接低温割れ
を起こさずにショートビード溶接を可能とする技術が示
されている。また、特開昭５９−１８５７６０号公報に
おいては、粒子径が０．１〜３．０μｍのＴｉ酸化物あ
るいはＴｉ酸化物と窒化物の複合体を鋼中に分散させ、
これらの酸化物・窒化物からフェライトを生成させ、γ
粒が粗大化する大入熱溶接ＨＡＺにおいて実質的に有効
結晶粒径を微細化し、ＨＡＺ靱性を向上させることが示
されている。Further, in Japanese Examined Patent Publication No. 5-55584, short bead welding is performed without causing cold cracking in the weld by limiting the carbon equivalent value to 0.40% or less and the Pcm value to 0.24% or less. The technology that enables is shown. Further, in JP-A-59-185760, a Ti oxide or a composite of a Ti oxide and a nitride having a particle diameter of 0.1 to 3.0 μm is dispersed in steel.
Ferrite is generated from these oxides and nitrides,
It has been shown that in the high heat input welding HAZ in which the grains become coarse, the effective grain size is substantially refined, and the HAZ toughness is improved.
【０００６】[0006]
【発明が解決しようとする課題】これらのうち、特開昭
５３−１１５６１１号公報は、Ｃａを添加することによ
りＭｎＳを減少させ、溶接低温割れを防止しようとする
ものであるが、ＭｎＳは主にラメラーティアの原因とな
るものであり、条件によってはＭｎＳが存在するほうが
ＨＡＺの硬化性が低下し、溶接低温割れをむしろ抑制す
る場合もあり、Ｃａ添加の効果は限られたものである。Of these, Japanese Patent Laid-Open No. 53-115611 aims to reduce MnS by adding Ca and prevent welding cold cracking, but MnS is mainly used. However, depending on the conditions, the presence of MnS lowers the HAZ hardenability and may rather suppress welding cold cracking, and the effect of Ca addition is limited.
【０００７】また、特開昭５６−１２３３５０号公報
は、ＶとＮの両者を同時に多量添加して低温割れを防止
するものであるが、ＶＮは熱的に不安定であり、高温に
加熱されるＨＡＺ部では固溶してしまうため効果がなく
なる上に、Ｎを多量に添加すると母材やＨＡＺの靱性が
著しく低下するために、溶接低温割れを防止できたとし
ても、厚鋼板としての基本特性である靱性の低下を来た
しやすく、実用的ではない。Further, Japanese Patent Application Laid-Open No. 56-123350 discloses that a large amount of both V and N are added at the same time to prevent cold cracking, but VN is thermally unstable and is heated to a high temperature. The effect is lost because it becomes a solid solution in the HAZ part, and the toughness of the base metal and HAZ is significantly reduced when a large amount of N is added. It is not practical because it tends to deteriorate the toughness that is a characteristic.
【０００８】また、特開昭５７−５１２４２号公報は、
Ｂ含有量を０．０００３０％以下とすることにより低温
割れを防止するものである。溶接割れ性を表す指標であ
る下記に示されるＰｃｍからも明らかなように、ＢはＨ
ＡＺの硬化性を著しく高め、溶接低温割れを助長する元
素であり、Ｂ添加量を低く抑えることは効果が大きい。Further, Japanese Patent Laid-Open No. 57-51242 discloses that
By setting the B content to 0.00030% or less, low temperature cracking is prevented. As is clear from Pcm shown below, which is an index showing weld crackability, B is H
It is an element that remarkably enhances the hardenability of AZ and promotes welding cold cracking, and it is very effective to suppress the addition amount of B to a low level.
【０００９】Ｐｃｍ＝Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋Ｃ
ｕ／２０＋Ｎｉ／６０＋Ｃｒ／２０＋Ｍｏ／１５＋Ｖ／
１０＋５Ｂ しかしながら、焼入れ焼戻し熱処理により母材の強度を
上昇させる調質型高張力鋼においては、Ｂは焼入れ性を
高めることにより母材強度上昇に極めて有用な元素であ
り、溶接低温割れを防止できても母材の強度確保に多大
な支障を来すことがある。Pcm = C + Si / 30 + Mn / 20 + C
u / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V /
10 + 5B However, in the tempered high-strength steel in which the strength of the base metal is increased by quenching and tempering heat treatment, B is an element that is extremely useful for increasing the strength of the base metal by increasing the hardenability, and it is possible to prevent welding cold cracking. However, this may greatly hinder the strength of the base metal.
【００１０】さらに、特公平５−５５５８４号公報は、
炭素当量値あるいはＰｃｍ値の上限値を設定することに
より溶接低温割れを防止するものであるが、上記と同様
に、炭素当量値あるいはＰｃｍ値を限定することにより
焼入れ性が低下し、母材製造時の焼入れ熱処理において
焼入れ組織が得られず、高張力鋼製造に支障を来すた
め、特に引張り強さが６０ｋｇｆ／ｍｍ2 級以上の調質
型高張力鋼には有効な手段ではない。Further, Japanese Patent Publication No. 5-55584 discloses
Although it is intended to prevent welding cold cracking by setting the upper limit of the carbon equivalent value or Pcm value, hardenability is lowered by limiting the carbon equivalent value or Pcm value in the same manner as described above, and the base metal production Since a quenching structure cannot be obtained in the quenching heat treatment at that time, which hinders the production of high-strength steel, it is not an effective means especially for tempered high-strength steel having a tensile strength of 60 kgf / mm 2 or higher.
【００１１】また、特開昭５９−１８５７６０号公報
は、Ｔｉ酸化物またはＴｉ酸化物と窒化物の複合体を鋼
中に微細分散させてＨＡＺの靱性を向上させるものであ
るが、本発明が対象とする合金元素含有量が高い調質高
張力鋼では、該析出物からのフェライト変態は期待でき
ない。また、溶接低温割れの防止を目的としたものでは
ない。Further, JP-A-59-185760 discloses a method in which a Ti oxide or a composite of a Ti oxide and a nitride is finely dispersed in steel to improve the toughness of HAZ. In the heat-treated high-strength steel with a high content of alloying elements, ferrite transformation from the precipitates cannot be expected. Further, it is not intended to prevent cold cracking in welding.
【００１２】本発明は、上記のような溶接低温割れの起
点となる介在物の低減や、溶接低温割れ性指標であるＰ
ｃｍ値を低下させることなく、調質型鋼張力鋼、特に引
張り強さが６０ｋｇｆ／ｍｍ2 以上の調質鋼において有
効に溶接低温割れを防止できる鋼板およびその製造方法
を提供することを目的とする。The present invention reduces the inclusions that are the origin of the above-described welding cold cracking and P, which is an index of the welding cold cracking property.
An object of the present invention is to provide a steel sheet capable of effectively preventing welding cold cracking in a tempered type tensile steel, particularly a tempered steel having a tensile strength of 60 kgf / mm 2 or more, and a method for producing the same, without lowering the cm value. .
【００１３】[0013]
【課題を解決するための手段】本発明者らは、溶接低温
割れを防止するためには、溶接金属からＨＡＺに拡散侵
入する水素を制御することが最も効果的であるとの考え
に基づき、鋼中にＴｉ酸化物を分散させ、この酸化物が
拡散性水素をガスとしてトラップすることにより溶接低
温割れを防止することが可能であることを知見した。In order to prevent welding cold cracking, the present inventors have found that it is most effective to control the hydrogen that diffuses and penetrates from the weld metal into the HAZ. It has been found that it is possible to prevent welding cold cracking by dispersing Ti oxide in steel and trapping diffusible hydrogen as a gas by this oxide.
【００１４】すなわち、本発明の要旨とするところは下
記のとおりである。 （１）重量％で、Ｃ：０．０３〜０．２０％、Ｓｉ：
０．１〜２．０％、Ｍｎ：０．５〜３．０％、Ｐ：０．
０３％以下、Ｓ：０．０１％以下、Ｃｒ：０．０５〜
２．０％、Ｍｏ：０．０２〜１．０％、Ａｌ：０．０１
％以下、Ｔｉ：０．００５〜０．０５０％、Ｏ：０．０
０１〜０．０１０％を含有し、残部Ｆｅおよび不可避的
不純物よりなることを特徴とする耐溶接低温割れ性に優
れた高張力鋼。That is, the gist of the present invention is as follows. (1) C: 0.03 to 0.20% by weight, Si:
0.1-2.0%, Mn: 0.5-3.0%, P: 0.
03% or less, S: 0.01% or less, Cr: 0.05 to
2.0%, Mo: 0.02-1.0%, Al: 0.01
% Or less, Ti: 0.005 to 0.050%, O: 0.0
A high-strength steel excellent in weld cold cracking resistance, characterized by containing 01 to 0.010%, and the balance being Fe and inevitable impurities.
【００１５】（２）重量％で、Ｎｂ：０．００５〜０．
２０％を含有することを特徴とする前記（１）記載の耐
溶接低温割れ性に優れた高張力鋼。 （３）重量％で、Ｖ：０．００５〜０．２０％を含有す
ることを特徴とする前記（１）または（２）記載の耐溶
接低温割れ性に優れた高張力鋼。(2) Nb: 0.005 to 0.
20% is contained, The high-strength steel excellent in weld cold cracking resistance according to the above (1). (3) The high-strength steel excellent in welding cold crack resistance according to the above (1) or (2), characterized by containing V: 0.005 to 0.20% by weight.
【００１６】（４）重量％で、Ｃｕ：０．０５〜２．０
％、Ｎｉ：０．０５〜２．０％の１種または２種を含有
することを特徴とする前記（１）〜（３）のいづれか１
項に記載の耐溶接低温割れ性に優れた高張力鋼。(4) Cu: 0.05-2.0 by weight
%, Ni: 0.05 to 2.0% of 1 type or 2 types, any one of (1) to (3) above
High-strength steel excellent in weld cold cracking resistance according to the item.
【００１７】（５）重量％で、Ｂ：０．０００１〜０．
００３０％を含有することを特徴とする前記（１）〜
（４）のいづれか１項に記載の耐溶接低温割れ性に優れ
た高張力鋼。 （６）重量％で、Ｃａ：０．０００３〜０．００２５
％、ＲＥＭ：０．０００３〜０．００２５％の１種また
は２種を含有することを特徴とする前記（１）〜（５）
のいづれか１項に記載の耐溶接低温割れ性に優れた高張
力鋼。(5) B: 0.0001 to 0.
0030% is contained in the above (1)-
High-strength steel excellent in weld cold cracking resistance according to any one of (4). (6)% by weight, Ca: 0.0003 to 0.0025
%, REM: 0.0003 to 0.0025% of 1 type or 2 types, (1) to (5) above
High-strength steel excellent in welding cold crack resistance as described in any one of 1 above.
【００１８】（７）前記（１）〜（６）のいづれか１項
に記載の化学成分を有する鋼塊を、Ａｃ3 変態点〜１２
５０℃に加熱して再結晶温度域において累積圧下率で４
０〜９０％の熱間圧延を施し、常温〜３００℃まで０．
１〜１００℃／秒の冷却速度で冷却した後、Ａｃ3 変態
点〜１０００℃に再加熱し、５〜１００℃／秒の冷却速
度で常温〜３００℃まで冷却し、さらに３００℃〜Ａｃ
1 変態点に焼戻しすることを特徴とする耐溶接低温割れ
性に優れた高張力鋼の製造方法。(7) A steel ingot having the chemical composition described in any one of (1) to (6) above is converted into an Ac 3 transformation point to 12
It is heated to 50 ℃ and the cumulative rolling reduction is 4 in the recrystallization temperature range.
Hot rolling of 0 to 90% is performed, and room temperature to 300 ° C.
After cooling at a cooling rate of 1 to 100 ° C./sec, it is reheated to an Ac 3 transformation point to 1000 ° C., cooled to room temperature to 300 ° C. at a cooling rate of 5 to 100 ° C./sec, and further 300 ° C. to Ac.
1. A method for producing high-strength steel excellent in welding cold crack resistance, which is characterized by tempering to a transformation point.
【００１９】（８）前記（１）〜（６）のいづれか１項
に記載の化学成分を有する鋼塊を、Ａｃ3 変態点〜１２
５０℃に加熱して再結晶温度域において累積圧下率で４
０〜９０％の熱間圧延を施し、Ａｒ3 変態点以上の温度
から５〜１００℃／秒の冷却速度で常温〜３００℃まで
冷却し、さらに３００℃〜Ａｃ1 変態点に焼戻しするこ
とを特徴とする耐溶接低温割れ性に優れた高張力鋼の製
造方法。(8) A steel ingot having the chemical composition described in any one of (1) to (6) above is converted into an Ac 3 transformation point to 12
It is heated to 50 ℃ and the cumulative rolling reduction is 4 in the recrystallization temperature range.
Hot rolling of 0 to 90%, cooling from a temperature of Ar 3 transformation point or higher to room temperature to 300 ° C. at a cooling rate of 5 to 100 ° C./sec, and further tempering to 300 ° C. to Ac 1 transformation point. A method for producing high-strength steel having excellent weld cold-crack resistance.
【００２０】（９）前記（１）〜（６）のいづれか１項
に記載の化学成分を有する鋼塊を、Ａｃ3 変態点〜１２
５０℃に加熱して再結晶温度域において累積圧下率で４
０〜９０％の熱間圧延を施し、引き続き未再結晶温度域
において累積圧下率で４０〜９０％の圧延を施した後、
Ａｒ3 変態点以上の温度から５〜１００℃／秒の冷却速
度で常温〜３００℃まで冷却し、さらに３００℃〜Ａｃ
1 変態点に焼戻しすることを特徴とする耐溶接低温割れ
性に優れた高張力鋼の製造方法。(9) A steel ingot having the chemical composition described in any one of (1) to (6) above is converted into an Ac 3 transformation point to 12
It is heated to 50 ℃ and the cumulative rolling reduction is 4 in the recrystallization temperature range.
After hot rolling of 0 to 90% and then rolling of 40 to 90% in cumulative rolling reduction in the non-recrystallization temperature range,
From the temperature above the Ar 3 transformation point to a room temperature to 300 ° C at a cooling rate of 5 to 100 ° C / sec, and further 300 ° C to Ac.
1. A method for producing high-strength steel excellent in welding cold crack resistance, which is characterized by tempering to a transformation point.
【００２１】[0021]
【作用】本発明者らは、溶接低温割れ感受性を高める合
金元素の添加量を制限することは溶接低温割れ防止に有
効であるが、これらの元素は同時に母材の焼入れ熱処理
時の焼入れ硬化性を高め、母材の強度上昇に必要である
ことから、引張り強さが６０ｋｇｆ／ｍｍ2 級以上の調
質高張力鋼においては合金元素量の制限には限度がある
との認識に基づき、溶接低温割れの原因の根幹である拡
散性水素を制御することが最も普遍的かつ有効であると
考えた。The present inventors have found that limiting the amount of alloying elements that increase the susceptibility to cold cracking in welding is effective in preventing cold cracking in welding. However, at the same time, these elements simultaneously suppress the quench hardening during quenching heat treatment of the base metal. Therefore, it is necessary to increase the strength of the base metal and to improve the strength of the base metal. Therefore, in the case of tempered high-strength steel with a tensile strength of 60 kgf / mm 2 or higher, there is a limit to the amount of alloying elements We thought that controlling the diffusible hydrogen, which is the root cause of cold cracking, was the most universal and effective.
【００２２】溶接低温割れに必要な条件とは、（１）拡
散性水素、（２）ＨＡＺ硬化組織、および（３）引張り
応力が同時に存在することである。上記のとおり、溶接
により、大気中あるいは溶接材料中の水分がＨとＯに分
解し、Ｈが溶接金属中に拡散性水素として固溶する。溶
接後、時間が経過すると、この拡散性水素はＨＡＺに拡
散、移動し、硬化したＨＡＺ組織の拡散性水素濃度が上
昇し、同時に残留応力が作用することにより、硬化した
ＨＡＺ組織に割れを発生する。上記のように、合金元素
添加量を制限することは、ＨＡＺの硬化性を低下させて
割れを防止するものであり、これには限度があることは
既に述べたとおりである。また、残留応力は凝固した溶
接金属の熱収縮により不可避的に存在するものであり、
これをなくすことはできない。The conditions necessary for welding cold cracking are that (1) diffusible hydrogen, (2) HAZ hardening structure, and (3) tensile stress are present at the same time. As described above, by welding, water in the atmosphere or in the welding material is decomposed into H and O, and H is solid-dissolved in the weld metal as diffusible hydrogen. After a lapse of time after welding, this diffusible hydrogen diffuses and migrates into the HAZ, the concentration of diffusible hydrogen in the hardened HAZ structure rises, and at the same time residual stress acts, causing cracking in the hardened HAZ structure. To do. As described above, limiting the addition amount of the alloying element lowers the hardenability of the HAZ to prevent cracking, and it has been already described that there is a limit. Residual stress is inevitably present due to thermal contraction of the solidified weld metal,
It cannot be eliminated.
【００２３】本発明者らは、拡散性水素量を低下させる
方法を種々検討した結果、ある種の酸化物が拡散性水素
をガスとしてトラップし、割れに有害な拡散性水素濃度
を低下させることができるものと考えた。酸化物に限ら
ず、一般に、鋼中の介在物は鋼とは異なった熱膨張係数
を有するため、相変態によりＨＡＺ組織が生成された後
の冷却過程で介在物周辺に内部応力を生成することにな
る。介在物の熱膨張係数が鋼（変態後を問題とするの
で、フェライト相とする）のそれより大きい場合、介在
物の熱収縮のほうが大きいために、介在物と鋼の界面に
は引張りの内部応力が作用することになる。水素が拡散
してくると、引張りの内部応力のために介在物と鋼の界
面に拡散性水素がガスとして集積することが容易とな
る。このようにして、熱膨張係数が鋼より大きい介在物
は水素をガスとしてトラップし、低温割れに影響する拡
散性水素濃度を低下させ得ることを知見した。As a result of various studies on the method for reducing the amount of diffusible hydrogen, the present inventors found that certain oxides trap diffusible hydrogen as a gas and reduce the concentration of diffusible hydrogen harmful to cracking. I thought that I could do it. Not only oxides, but inclusions in steel generally have different coefficients of thermal expansion from steel, so that internal stress is generated around inclusions in the cooling process after the HAZ structure is formed by phase transformation. become. If the thermal expansion coefficient of the inclusions is larger than that of steel (ferrite phase because it is a problem after transformation), the thermal contraction of the inclusions is larger, so the interface between the inclusions and the steel has internal tension. The stress will act. When hydrogen diffuses, it becomes easy for diffusible hydrogen to accumulate as a gas at the interface between the inclusions and the steel due to the internal tensile stress. In this way, it was found that inclusions having a coefficient of thermal expansion larger than that of steel can trap hydrogen as a gas and reduce the concentration of diffusible hydrogen that affects cold cracking.
【００２４】種々の酸化物の熱膨張係数を検討した結
果、殆どの酸化物の熱膨張係数は室温から６００℃の平
均で１０×１０-6℃-1以下であり、鋼（フェライト相）
の熱膨張係数の約１３×１０-6℃-1より小さい。これに
対して、Ｔｉ2 Ｏ3 としてのＴｉ酸化物は特異的に高い
熱膨張係数を有し、上記の観点から水素のトラップサイ
トとして最も有効であることが明らかとなった。すなわ
ち、Ｔｉ2 Ｏ3 は六方晶構造を有し、そのｃ軸方向の熱
膨張係数は６５×１０-6℃-1であり、鋼のそれよりはる
かに大きく、変態後、ｃ軸方向に非常に大きな引張り応
力が鋼との界面に作用し、水素ガスが集積しやすいこと
を見出した。As a result of examining the thermal expansion coefficients of various oxides, most of the oxides have a thermal expansion coefficient of 10 × 10 -6 ° C. -1 or less on average from room temperature to 600 ° C.
The thermal expansion coefficient is less than about 13 × 10 -6 ° C -1 . On the other hand, Ti oxide as Ti 2 O 3 has a specific high thermal expansion coefficient, and it has been clarified that it is most effective as a hydrogen trap site from the above viewpoint. That is, Ti 2 O 3 has a hexagonal crystal structure, and its coefficient of thermal expansion in the c-axis direction is 65 × 10 −6 ° C. −1, which is much larger than that of steel, and is extremely high in the c-axis direction after transformation. It was found that a large tensile stress acts on the interface with steel and hydrogen gas is easily accumulated.
【００２５】これを確認するために、表１および表２
（表１のつづき）に示す化学成分を有する鋼に溶接再現
熱サイクルを与えて、ＨＡＺ組織を再現した試料につい
て水素を侵入させ、水素濃度を測定した。すなわち、最
高加熱温度が１４００℃、８００〜５００℃の冷却時間
が８秒の熱サイクルを与えた再現ＨＡＺ材を硫化水素飽
和酸性溶液（ＮＡＣＥ液）中に４８時間浸漬した後、Ｊ
ＩＳ Ｚ３１１３に記載のグリセン法により拡散性水素
濃度を測定した。結果を表３に示す。To confirm this, Table 1 and Table 2
A steel having the chemical composition shown in (Continued in Table 1) was subjected to a welding reproducible heat cycle, and hydrogen was allowed to penetrate into a sample in which the HAZ structure was reproduced, and the hydrogen concentration was measured. That is, the reproduced HAZ material subjected to a thermal cycle of a maximum heating temperature of 1400 ° C. and a cooling time of 800 to 500 ° C. of 8 seconds was immersed in a hydrogen sulfide saturated acidic solution (NACE solution) for 48 hours, and then J
The diffusible hydrogen concentration was measured by the glycene method described in IS Z3113. The results are shown in Table 3.
【００２６】[0026]
【表１】 [Table 1]
【００２７】[0027]
【表２】 [Table 2]
【００２８】[0028]
【表３】 [Table 3]
【００２９】鋼１の本発明鋼はＴｉ脱酸により鋼中にＴ
ｉ2 Ｏ3 粒子を含有する鋼である。１０００倍の光学顕
微鏡で測定したＴｉ酸化物の個数は３２個／ｍｍ2 、サ
イズは３μｍ以下である。合金元素添加量は鋼１とほぼ
同じでＡｌ脱酸鋼である鋼２に比べ、鋼１の拡散性水素
濃度が著しく低下することが確認された。水素侵入環境
およびＨＡＺ組織は同一であり、鋼中に侵入した全水素
量は両鋼で同じであるにもかかわらず、測定された拡散
性水素濃度に上記のような差が生じたのは、鋼１におい
てＴｉ2 Ｏ3 と地鉄の界面で水素をガスとしてトラップ
したためである。The steel of the present invention, Steel 1, is made of T by deoxidizing Ti.
Steel containing i 2 O 3 particles. The number of Ti oxides measured with an optical microscope of 1000 magnifications is 32 / mm 2 , and the size is 3 μm or less. It was confirmed that the amount of alloying elements added was almost the same as that of Steel 1 and that the diffusible hydrogen concentration of Steel 1 was significantly reduced as compared with Steel 2 which is an Al deoxidized steel. The hydrogen penetration environment and HAZ structure are the same, and although the total amount of hydrogen that penetrated into the steel was the same in both steels, the difference in the diffusible hydrogen concentration measured was as follows. This is because hydrogen was trapped as a gas at the interface between Ti 2 O 3 and the base steel in Steel 1.
【００３０】本来、Ｔｉは水素と親和力が強い元素であ
り、このこともＴｉ2 Ｏ3 が水素をトラップしやすいこ
とに寄与している可能性もある。鋼中にＴｉ2 Ｏ3 を多
量に分散させておけば、溶接金属から拡散してきた水素
をガスとしてトラップすることができる。ガスとしてト
ラップされた水素はもはや拡散性水素として鋼中に拡散
することは殆どなく、溶接低温割れに関与しなくなる。Originally, Ti is an element having a strong affinity for hydrogen, which may also contribute to Ti 2 O 3 being able to easily trap hydrogen. If a large amount of Ti 2 O 3 is dispersed in the steel, hydrogen diffused from the weld metal can be trapped as a gas. The hydrogen trapped as a gas hardly diffuses into the steel as diffusible hydrogen any longer and does not participate in welding cold cracking.
【００３１】鋼中にＴｉ2 Ｏ3 を分散させる方法はＴｉ
2 Ｏ3 の微粉末を溶鋼中に投入する方法が直接的である
が、これ以外の製鋼上最も簡便な方法は、Ｔｉ脱酸によ
るものである。すなわち、ＡｌをはじめとするＴｉより
もＯと親和力が強い元素の量をできる限り低くしてＴｉ
で脱酸することにより、凝固過程でＴｉ2 Ｏ3 が晶出
し、これにより容易にＴｉ2 Ｏ3 を鋼中に分散すること
が可能である。The method of dispersing Ti 2 O 3 in steel is Ti
The method of introducing fine powder of 2 O 3 into molten steel is direct, but the other simplest method for steelmaking is by Ti deoxidation. That is, the amount of elements having a stronger affinity for O than Ti such as Al should be kept as low as possible.
In by deoxidation, in the solidification process Ti 2 O 3 is crystallized out, thereby it is possible to easily disperse the Ti 2 O 3 in the steel.
【００３２】水素をガスとしてトラップする能力はＴｉ
2 Ｏ3 の全量およびＴｉ2 Ｏ3 と鋼界面の総面積に依存
する。従って、ＴｉとＯの量が多いほど溶接低温割れ抑
制の効果が大きくなるばかりでなく、同一のＴｉとＯの
量でも、Ｔｉ2 Ｏ3 の粒子が微細なほど表面積が増える
ので、より顕著な効果が得られる。また、粗大なＴｉ 2
Ｏ3 は破壊の起点となりやすいため、できるだけ微細に
分散させたほうが鋼材の延性・靱性特性の上からも優れ
る。このような観点から、Ｔｉ2 Ｏ3 粒子の個数は１０
００倍の光学顕微鏡による測定で１０個／ｍｍ2 以上、
サイズは５μｍ以下とすることが望ましい。The ability to trap hydrogen as a gas is Ti
2O3Of Ti and Ti2O3And the total area of the steel interface
I do. Therefore, the higher the amounts of Ti and O, the lower the weld cold cracking suppression.
Not only the effect of the control increases, but the same Ti and O
Ti in quantity2O3The finer the particles, the larger the surface area
Therefore, a more remarkable effect can be obtained. Also, coarse Ti 2
O3Is a starting point of destruction, so make it as fine as possible.
Dispersion is superior in terms of ductility and toughness of steel materials
It From such a viewpoint, Ti2O3The number of particles is 10
10 / mm when measured with a 00x optical microscope2that's all,
The size is preferably 5 μm or less.
【００３３】以上が本発明の基本的な考えであるが、各
合金元素添加量を限定した理由を以下に述べる。Ｃは母
材の強度を高めるのに最も有効な元素である。Ｃ添加量
が０．０３％未満では充分な母材強度が得られないの
で、下限を０．０３％とした。逆に、０．２０％を超え
てＣを添加すると、ＨＡＺ硬化性が上昇し、溶接低温割
れを助長し、さらに靱性低下が著しくなる。従って、上
限値を０．２０％とした。The above is the basic idea of the present invention, but the reason why the addition amount of each alloying element is limited will be described below. C is the most effective element for increasing the strength of the base material. If the amount of C added is less than 0.03%, sufficient base metal strength cannot be obtained, so the lower limit was made 0.03%. On the contrary, when C is added in an amount of more than 0.20%, the HAZ hardenability is increased, the welding cold cracking is promoted, and the toughness is significantly lowered. Therefore, the upper limit is set to 0.20%.
【００３４】Ｓｉは脱酸剤として有用な元素である。Ｓ
ｉの脱酸能力はＴｉよりやや低いため、Ｓｉを含有して
もＴｉ2 Ｏ3 生成に及ぼす影響は比較的少ない。ただ
し、２．０％超添加すると、Ｔｉ2 Ｏ3 生成量が低下す
るとともに、母材靱性の低下が著しくなる。従って、上
限値を２．０％とした。逆に、０．１％未満となると、
不要な介在物が増加し、靱性・延性を低下させる。従っ
て、下限値を０．１％とした。Si is an element useful as a deoxidizing agent. S
Since the deoxidizing ability of i is slightly lower than that of Ti, even if Si is contained, the effect on Ti 2 O 3 production is relatively small. However, if over 2.0% is added, the amount of Ti 2 O 3 produced will be reduced and the toughness of the base material will be significantly reduced. Therefore, the upper limit is set to 2.0%. On the contrary, when it is less than 0.1%,
Unnecessary inclusions increase, reducing toughness and ductility. Therefore, the lower limit is set to 0.1%.
【００３５】Ｍｎは焼入れ性を上げ、母材強度上昇に効
果を有する。０．５％未満では母材強度上昇に効果を発
揮しないので、下限値を０．５％とした。逆に、３．０
％を超えて添加するとＨＡＺ硬化性が上昇し、溶接低温
割れを生じやすくなる。従って、上限値を３．０％とし
た。Ｐは靱性に有害な不純物元素であり、低いほうが好
ましい。０．０３％を超えて含有するとＨＡＺにおける
粒界破壊を生じやすくなるので、上限値を０．０３％と
した。Mn has the effect of increasing the hardenability and increasing the strength of the base material. If it is less than 0.5%, the effect of increasing the strength of the base material is not exhibited, so the lower limit was made 0.5%. Conversely, 3.0
%, The HAZ hardenability is increased and weld cold cracking is likely to occur. Therefore, the upper limit is set to 3.0%. P is an impurity element which is harmful to toughness, and its lower content is preferable. If the content exceeds 0.03%, grain boundary fracture in the HAZ is likely to occur, so the upper limit was made 0.03%.
【００３６】ＳはＭｎＳを生成し、ラメラーティアをは
じめとする割れに有害であり、低いほうが好ましい。
０．０１％を超えて含有すると割れが著しくなるので、
上限値を０．０１％とした。Ｃｒは焼入れ性を上げ、焼
入れ熱処理による母材強度上昇に寄与する。０．０５％
未満の添加では焼入れ性上昇効果が少ないので、下限値
を０．０５％とした。逆に、２．０％超添加すると、母
材強度は上昇するが、ＨＡＺ硬化性が高くなり過ぎて溶
接低温割れが生じやすくなる。従って、上限値２．０％
とした。S forms MnS and is harmful to cracks such as lamellar tears, and a lower amount is preferable.
If the content exceeds 0.01%, cracking will be significant, so
The upper limit value was 0.01%. Cr enhances hardenability and contributes to an increase in base metal strength due to quenching heat treatment. 0.05%
If it is added in an amount of less than 5, the effect of increasing the hardenability is small, so the lower limit was made 0.05%. On the other hand, when the content exceeds 2.0%, the base metal strength increases, but the HAZ hardenability becomes too high, and weld cold cracking easily occurs. Therefore, the upper limit value is 2.0%
And
【００３７】Ｍｏは焼入れ性を上げ、焼入れ熱処理によ
る母材強度上昇に寄与する。０．０２％未満の添加では
焼入れ性上昇効果が少ないので、下限値を０．０２％と
した。逆に、１．０％超添加すると母材強度は上昇する
が、ＨＡＺ硬化性が高くなり過ぎて溶接低温割れが生じ
やすくなる。従って、上限値１．０％とした。ＡｌはＴ
ｉよりＯとの親和性が強く、多量に含有するとＴｉ2 Ｏ
3 生成を阻害するので、低いほうが好ましい。０．０１
％超含有すると、Ａｌ酸化物が生成してＴｉ2 Ｏ3 量が
低下する。従って、Ａｌの上限値を０．０１％とした。Mo enhances the hardenability and contributes to the strength increase of the base material due to the quenching heat treatment. The addition of less than 0.02% has little effect of increasing the hardenability, so the lower limit was made 0.02%. On the contrary, if the content exceeds 1.0%, the base metal strength increases, but the HAZ hardenability becomes too high, and welding cold cracking is likely to occur. Therefore, the upper limit value is set to 1.0%. Al is T
i has a stronger affinity for O than i, and if contained in a large amount, Ti 2 O
3 It inhibits the production, so a lower value is preferable. 0.01
If it is contained in excess of%, Al oxide is generated and the amount of Ti 2 O 3 is reduced. Therefore, the upper limit of Al is set to 0.01%.
【００３８】Ｔｉは本発明では必須元素である。Ｔｉ2
Ｏ3 生成の観点からは多量に含有することが望ましい。
０．００５％未満の添加ではＴｉ2 Ｏ3 生成量が少ない
ので、下限値を０．００５％とした。一方、０．０５０
％超添加するとＴｉ2 Ｏ3 以外にＴｉＣを多量に析出す
るようになり、母材・ＨＡＺの靱性を著しく低下させ
る。従って、上限値を０．０５０％とした。Ti is an essential element in the present invention. Ti 2
From the viewpoint of O 3 production, it is desirable to contain a large amount.
If the addition amount is less than 0.005%, the amount of Ti 2 O 3 produced is small, so the lower limit value was made 0.005%. On the other hand, 0.050
If it is added in excess of%, a large amount of TiC will be precipitated in addition to Ti 2 O 3 , and the toughness of the base metal / HAZ will be significantly reduced. Therefore, the upper limit is set to 0.050%.
【００３９】Ｏは本発明では必須元素である。Ｔｉ2 Ｏ
3 生成の観点からは多量に含有することが望ましい。
０．００１％未満の添加ではＴｉ2 Ｏ3 生成量が少ない
ので、下限値を０．００１％とした。逆に、０．０１０
％超添加するとＴｉ2 Ｏ3 以外の酸化物が多量に生成し
て鋼の清浄度を低下させ、母材の靱性・延性を低下させ
る。従って、上限値を０．０１０％とした。Ｔｉ2 Ｏ3
におけるＴｉとＯの化学当量比は約２．０である。従っ
て、Ｔｉ2 Ｏ3 を生成し、これ以外の有害な酸化物生成
を最小限とするためにはＴｉ／Ｏを２．０以上とするこ
とが望ましい。O is an essential element in the present invention. Ti 2 O
3 From the viewpoint of generation, it is desirable to contain a large amount.
The addition amount of less than 0.001% produces a small amount of Ti 2 O 3, so the lower limit was made 0.001%. Conversely, 0.010
If it is added in excess of%, a large amount of oxides other than Ti 2 O 3 are produced and the cleanliness of the steel is lowered, and the toughness and ductility of the base material are lowered. Therefore, the upper limit is set to 0.010%. Ti 2 O 3
The chemical equivalent ratio of Ti to O in is about 2.0. Therefore, it is desirable to set Ti / O to 2.0 or more in order to generate Ti 2 O 3 and to minimize the generation of other harmful oxides.
【００４０】さらに、選択元素として含有する元素の添
加量範囲を以下の理由で限定した。Ｎｂは母材焼入れ熱
処理における焼入れ性を上昇させ、母材強度向上に効果
があるだけでなく、特に直接焼入れ処理において焼入れ
前のオーステナイト粒を微細化し、母材靱性の向上にも
効果がある。Ｎｂ量が０．００５％未満ではこの効果が
少ないので、下限値を０．００５％とした。逆に、０．
２０％超添加すると、Ｎｂの炭窒化物を多量に生成して
靱性を低下させるので、上限値を０．２０％とした。Further, the addition amount range of the element contained as the selective element is limited for the following reason. Nb not only has the effect of increasing the hardenability in the base material quenching heat treatment and improving the base material strength, but also has the effect of improving the base material toughness by refining the austenite grains before quenching especially in the direct quenching process. Since this effect is small when the amount of Nb is less than 0.005%, the lower limit was made 0.005%. Conversely, 0.
If added in excess of 20%, a large amount of Nb carbonitride is generated and the toughness is reduced, so the upper limit was made 0.20%.
【００４１】Ｖは母材焼入れ熱処理における焼入れ性を
上昇させ、母材強度向上に効果があるだけでなく、特に
焼入れ処理において焼入れ前のオーステナイト粒を微細
化し、母材靱性の向上にも効果がある。Ｖ量が０．００
５％未満ではこの効果が少ないので、下限値を０．００
５％とした。逆に、０．２０％超添加すると、ＨＡＺ硬
化性が高くなり過ぎて溶接低温割れを助長し、さらにＶ
の炭窒化物を多量に生成して靱性を低下させる。従っ
て、上限値を０．２０％とした。V not only has the effect of enhancing the hardenability in the base material quenching heat treatment and improving the strength of the base material, but also has the effect of improving the base material toughness by refining the austenite grains before quenching especially in the quenching treatment. is there. V amount is 0.00
If less than 5%, this effect is small, so the lower limit is set to 0.00
It was set to 5%. On the other hand, if over 0.20% is added, the HAZ hardenability becomes too high, which promotes welding cold cracking, and further V
To produce a large amount of carbonitrides and reduce the toughness. Therefore, the upper limit is set to 0.20%.
【００４２】Ｃｕは焼入れ性を上昇させ、母材強度上昇
に効果を有する。Ｃｕ量が０．０５％未満ではその効果
が少ないので、下限値を０．０５％とした。逆に、２．
０％超添加するとＨＡＺ硬化性が高くなり過ぎて溶接低
温割れを助長する。従って、上限値を２．０％とした。
ＮｉはＣｕと同様に焼入れ性を上昇させ、母材強度上昇
に効果を有する。Ｎｉ量が０．０５％未満ではその効果
が少ないので、下限値を０．０５％とした。逆に、２．
０％超添加するとＨＡＺ硬化性が高くなり過ぎて溶接低
温割れを助長する。従って、上限値を２．０％とした。Cu has the effect of increasing hardenability and increasing the strength of the base material. If the Cu content is less than 0.05%, the effect is small, so the lower limit was made 0.05%. Conversely, 2.
If added in excess of 0%, the HAZ hardenability will be too high and promotes welding cold cracking. Therefore, the upper limit is set to 2.0%.
Similar to Cu, Ni increases the hardenability and is effective in increasing the strength of the base material. If the Ni content is less than 0.05%, the effect is small, so the lower limit was made 0.05%. Conversely, 2.
If added in excess of 0%, the HAZ hardenability will be too high and promotes welding cold cracking. Therefore, the upper limit is set to 2.0%.
【００４３】Ｂは焼入れ性を上昇させ、焼入れ熱処理に
より製造する母材の強度上昇に極めて効果を有する元素
である。Ｂ量が０．０００１％未満ではこの効果が少な
いので、下限値を０．０００１％とした。逆に、０．０
０３０％超添加するとＨＡＺ硬化性が高くなり過ぎて溶
接低温割れを助長し、また硼炭化物を生成して靱性を低
下させる。従って、上限値を０．００３０％とした。B is an element which enhances the hardenability and is extremely effective in increasing the strength of the base material produced by the quenching heat treatment. This effect is small when the amount of B is less than 0.0001%, so the lower limit was made 0.0001%. Conversely, 0.0
If added in excess of 030%, the HAZ hardenability becomes too high, which promotes welding cold cracking and also forms borocarbides to reduce toughness. Therefore, the upper limit is set to 0.0030%.
【００４４】ＣａはＭｎＳ生成を減少させ、割れ低減に
寄与する。Ｃａ量が０．０００３％未満ではその効果が
少ないので、下限値を０．０００３％とした。逆に、
０．００２５％超添加すると、Ｃａ酸化物を生成してＴ
ｉ2 Ｏ3 生成量を低下させる。従って、上限値を０．０
０２５％とした。ＲＥＭはＣａと同様にＭｎＳ生成を減
少させ、割れ低減に寄与する。ＲＥＭ量が０．０００３
％未満ではその効果が少ないので、下限値を０．０００
３％とした。逆に、０．００２５％超添加すると、ＲＥ
Ｍ酸化物を生成して、Ｔｉ2 Ｏ3生成量を低下させる。
従って、上限値を０．００２５％とした。ＲＥＭとして
はＹ、アクチノイド系、ランタノイド系の元素を含み、
その内どれを使用しても差し支えないが、その中でも代
表的なものはＬａおよびＣｅである。Ca reduces MnS production and contributes to crack reduction. If the amount of Ca is less than 0.0003%, the effect is small, so the lower limit was made 0.0003%. vice versa,
When added over 0.0025%, Ca oxides are formed and T
i 2 O 3 production is reduced. Therefore, the upper limit is 0.0
It was set to 025%. Similar to Ca, REM reduces MnS production and contributes to crack reduction. REM amount is 0.0003
%, The effect is small, so the lower limit is 0.000.
It was 3%. Conversely, if over 0.0025% is added, RE
It produces M oxide and reduces the amount of Ti 2 O 3 produced.
Therefore, the upper limit is set to 0.0025%. REM includes Y, actinide-based and lanthanoid-based elements,
Any of them may be used, but typical ones thereof are La and Ce.
【００４５】本発明によるＴｉ酸化物による拡散性水素
量低減効果は引張り強さが６０ｋｇｆ／ｍｍ2 級以上の
高張力鋼でけだなく、軟鋼、および引張り強さが５０ｋ
ｇｆ／ｍｍ2 級の高張力鋼でも作用を有する。しかしな
がら、軟鋼、および引張り強さが５０ｋｇｆ／ｍｍ2 級
の高張力鋼では容易に炭素当量値あるいはＰｃｍ値を低
下させることができるため、本発明のようなＴｉ酸化物
を利用しなくても溶接低温割れを防止することは容易で
ある。本発明は、炭素当量値あるいはＰｃｍ値を低下さ
せることが困難である引張り強さが６０ｋｇｆ／ｍｍ2
級以上の高張力鋼に特に効果を発揮する。これらの高張
力鋼は、焼入れ焼戻し（請求項７）、直接焼入れ焼戻し
（請求項８）、あるいは制御圧延後直接焼入れ焼戻し
（請求項９）処理により製造される。The effect of reducing the amount of diffusible hydrogen by the Ti oxide according to the present invention is not only high tensile steel having a tensile strength of 60 kgf / mm 2 or higher, but also mild steel and a tensile strength of 50 k.
It has an effect even on high-strength steel of gf / mm 2 class. However, mild steel and high-strength steel with a tensile strength of 50 kgf / mm 2 grade can easily lower the carbon equivalent value or Pcm value, so that welding without using the Ti oxide as in the present invention is possible. It is easy to prevent cold cracking. The present invention has a tensile strength of 60 kgf / mm 2 which makes it difficult to reduce the carbon equivalent value or Pcm value.
Particularly effective for high-strength steel of grade or higher. These high-strength steels are manufactured by quenching and tempering (Claim 7), direct quenching and tempering (Claim 8), or direct rolling after control rolling (Claim 9).
【００４６】母材の製造条件を限定した理由を以下に述
べる。焼入れ焼戻し処理においては熱間圧延に先立ち鋼
塊を１００％オーステナイト化することが必須である。
このために鋼塊の加熱温度の下限をＡｃ3 変態点とし
た。また、１２５０℃を超えて加熱するとオーステナイ
トの粒成長が著しくなるため、上限を１２５０℃とし
た。The reasons for limiting the manufacturing conditions of the base material will be described below. In the quenching and tempering treatment, it is essential to convert the steel ingot to 100% austenite prior to hot rolling.
Therefore, the lower limit of the heating temperature of the steel ingot is set to the Ac 3 transformation point. Moreover, since the grain growth of austenite becomes remarkable when heated above 1250 ° C., the upper limit was made 1250 ° C.
【００４７】再結晶温度域の圧延は、再結晶によりオー
ステナイト粒を微細化し、最終的に得られる母材組織を
微細化するのが目的である。累積圧下率が４０％未満で
は再結晶が充分に進行しないので、下限を４０％とし
た。逆に、９０％超の圧下率とすると圧延パス回数が増
加し、圧延温度が低下して未再結晶域温度域となってし
まうので、上限を９０％とした。The purpose of rolling in the recrystallization temperature range is to refine the austenite grains by recrystallization and to refine the finally obtained base material structure. If the cumulative rolling reduction is less than 40%, recrystallization does not proceed sufficiently, so the lower limit was made 40%. On the other hand, if the rolling reduction is more than 90%, the number of rolling passes increases and the rolling temperature lowers to the non-recrystallized region temperature region. Therefore, the upper limit was set to 90%.
【００４８】また、請求項９の制御圧延後直接焼入れ焼
戻し処理において、未再結晶域圧延を行う場合、累積圧
下率が４０％未満ではオーステナイト粒内に充分な変形
帯が導入されず、制御圧延の効果が得られないので、下
限を４０％とした。逆に、９０％超の圧下率とすると、
圧延パス数が増加して圧延温度が低下し、フェライト変
態を生じる可能性があること、ならびに圧延荷重が上昇
し、実質的に圧延ができなくなるので、上限を９０％と
した。In the direct quenching and tempering treatment after controlled rolling according to claim 9, when the unrecrystallized region rolling is performed, if the cumulative rolling reduction is less than 40%, a sufficient deformation zone is not introduced into the austenite grains and the controlled rolling is performed. Therefore, the lower limit was set to 40%. On the contrary, if the reduction ratio is over 90%,
The upper limit was set to 90% because the number of rolling passes increases, the rolling temperature decreases, ferrite transformation may occur, and the rolling load increases, which makes rolling substantially impossible.
【００４９】請求項７では圧延後再加熱により１００％
オーステナイト化した後に焼入れすることが必要であ
り、このために再加熱温度の下限をＡｃ3 変態点とし
た。逆に、再加熱温度を１０００℃超とすると、粒成長
が著しくなるので、上限を１０００℃とした。また、圧
延後の冷却は空冷、強制冷却のいづれでもよい。０．１
℃／秒未満では冷却途中で変態するフェライト・ベイナ
イト組織が粗大化して再加熱時の組織が粗大化し、最終
的に得られる組織も粗大化するので好ましくない。従っ
て、下限値を０．１℃／秒とした。逆に、１００℃／秒
超とすると鋼板の変形を生じやすくなる。従って、上限
を１００℃／秒とした。In claim 7, 100% is obtained by reheating after rolling.
It is necessary to quench after austenitizing. For this reason, the lower limit of the reheating temperature was set to the Ac 3 transformation point. On the contrary, if the reheating temperature exceeds 1000 ° C., grain growth becomes remarkable, so the upper limit was made 1000 ° C. Further, cooling after rolling may be either air cooling or forced cooling. 0.1
If it is less than ° C / sec, the ferrite / bainite structure transformed during cooling becomes coarse, the structure at the time of reheating becomes coarse, and the finally obtained structure also becomes coarse, which is not preferable. Therefore, the lower limit value is set to 0.1 ° C./second. On the contrary, if it exceeds 100 ° C./sec, the steel sheet is likely to be deformed. Therefore, the upper limit is set to 100 ° C./second.
【００５０】請求項７、８、および９いづれの製造方法
においても、焼入れ熱処理の冷却速度は５℃／秒以上と
することが必要である。５℃／秒未満の冷却速度では高
温変態組織が生成し、十分な強度が得られない。逆に、
１００℃／秒超とすると、焼入れ時の変形と残留応力の
上昇を来すので、上限を１００℃／秒とした。また、焼
入れ終了温度は３００℃以下とすることが必要である。
これを超える温度で冷却を停止すると、変態が完全に終
了しないために、十分な強度が得られない。In any of the manufacturing methods of claims 7, 8 and 9, it is necessary that the cooling rate of the quenching heat treatment is 5 ° C./sec or more. At a cooling rate of less than 5 ° C./sec, a high temperature transformation structure is generated and sufficient strength cannot be obtained. vice versa,
If it exceeds 100 ° C / sec, deformation during quenching and an increase in residual stress occur, so the upper limit was made 100 ° C / sec. Further, the quenching end temperature needs to be 300 ° C. or lower.
If the cooling is stopped at a temperature higher than this, sufficient strength cannot be obtained because the transformation is not completely completed.
【００５１】請求項７、８、および９いづれの製造方法
においても、焼入れ後に焼戻し処理をすることが必要で
ある。３００℃未満の温度では回復が生じないため、焼
戻しの効果が得られない。また、焼戻しはオーステナイ
ト逆変態を生じない温度で行う必要がある。このため
に、焼戻し温度の範囲を３００℃〜Ａｃ1 変態点とし
た。In any of the manufacturing methods of claims 7, 8 and 9, it is necessary to perform tempering treatment after quenching. Since the recovery does not occur at a temperature lower than 300 ° C, the effect of tempering cannot be obtained. Further, tempering must be performed at a temperature at which austenite reverse transformation does not occur. Therefore, the tempering temperature range is set to 300 ° C. to Ac 1 transformation point.
【００５２】[0052]
【実施例】以下に、実施例を示す。表４および表５（表
４のつづき）に本発明鋼および比較鋼の化学成分を示
す。転炉で溶製した溶鋼を連続鋳造により鋼塊とした。
表６および表７（表６のつづき）に母材の製造条件と引
張り特性を示す。板厚は全て３５ｍｍである。EXAMPLES Examples will be shown below. Tables 4 and 5 (continued from Table 4) show the chemical compositions of the steels of the present invention and comparative steels. Molten steel produced in a converter was cast into a steel ingot.
Table 6 and Table 7 (continued from Table 6) show the manufacturing conditions and tensile properties of the base material. The plate thicknesses are all 35 mm.
【００５３】ＪＩＳ Ｚ３１５８に従って溶接低温割れ
試験を実施し、ＨＡＺに割れが生じなくなる予熱温度
（割れ停止温度）を求めた。低水素系の８０ｋｇｆ／ｍ
ｍ2 級被覆溶接棒を用いた。溶接入熱は１７ｋＪ／ｃｍ
とした。同一条件で溶接した溶着金属の拡散性水素濃度
（ＪＩＳ Ｚ３１１３に記載のグリセリン法による）は
溶着金属１００ｇあたり２．８〜３．２ｃｃであった。
表８に得られた割れ停止温度を示す。また、図１にＰｃ
ｍに対して割れ停止温度をプロットした結果を示す。割
れ停止温度はＰｃｍに依存するが、同一のＰｃｍ値で比
較すると、本発明鋼は比較鋼に比べて割れ停止温度が低
く、溶接低温割れ感受性が低いことが確認された。A welding low temperature cracking test was carried out in accordance with JIS Z3158, and a preheating temperature (cracking stop temperature) at which cracking did not occur in the HAZ was determined. Low hydrogen type 80kgf / m
An m 2 grade coated welding rod was used. Welding heat input is 17 kJ / cm
And The diffusible hydrogen concentration of the weld metal welded under the same conditions (according to the glycerin method described in JIS Z3113) was 2.8 to 3.2 cc per 100 g of the weld metal.
Table 8 shows the crack stop temperatures obtained. In addition, in FIG.
The result which plotted the crack stop temperature with respect to m is shown. Although the crack stop temperature depends on Pcm, when compared at the same Pcm value, it was confirmed that the steel of the present invention had a lower crack stop temperature and a lower cold-susceptibility to cold welding than the comparative steel.
【００５４】[0054]
【表４】 [Table 4]
【００５５】[0055]
【表５】 [Table 5]
【００５６】[0056]
【表６】 [Table 6]
【００５７】[0057]
【表７】 [Table 7]
【００５８】[0058]
【表８】 [Table 8]
【００５９】[0059]
【発明の効果】以上説明したように、本発明鋼はＴｉ酸
化物により水素をガスとしてトラップさせることによ
り、ＨＡＺ中の拡散性水素濃度を実質的に低下させるこ
とにより溶接低温割れを防止できる。本発明は引張り強
さが６０ｋｇｆ／ｍｍ2 級以上の高張力鋼で合金元素低
減によるＨＡＺ硬化性低下が困難な鋼において特に効果
を発揮するものである。As described above, the steel of the present invention can prevent welding cold cracking by trapping hydrogen as a gas by Ti oxide and substantially reducing the concentration of diffusible hydrogen in the HAZ. The present invention is particularly effective for high-tensile steel having a tensile strength of 60 kgf / mm 2 grade or more and in which it is difficult to reduce the HAZ hardenability by reducing alloy elements.
【図１】ｙ割れ試験における割れ停止温度をＰｃｍに対
してプロットした図である。FIG. 1 is a diagram in which a crack stop temperature in a y crack test is plotted against Pcm.
Claims (9)
を特徴とする耐溶接低温割れ性に優れた高張力鋼。1. By weight%, C: 0.03 to 0.20%, Si: 0.1 to 2.0%, Mn: 0.5 to 3.0%, P: 0.03% or less, S: 0.01% or less, Cr: 0.05 to 2.0%, Mo: 0.02 to 1.0%, Al: 0.01% or less, Ti: 0.005 to 0.050%, O : High-strength steel excellent in weld cold cracking resistance, containing 0.001 to 0.010%, and the balance Fe and unavoidable impurities.
割れ性に優れた高張力鋼。2. The high-strength steel excellent in weld cold cracking resistance according to claim 1, characterized by containing Nb: 0.005 to 0.20% by weight.
溶接低温割れ性に優れた高張力鋼。3. The high-strength steel excellent in weld cold cracking resistance according to claim 1 or 2, characterized by containing V: 0.005 to 0.20% by weight.
〜３のいづれか１項に記載の耐溶接低温割れ性に優れた
高張力鋼。4. The composition according to claim 1, wherein the content is 1% or 2% by weight of Cu: 0.05 to 2.0% and Ni: 0.05 to 2.0%.
High-strength steel excellent in weld cold cracking resistance according to any one of 1 to 3 above.
項に記載の耐溶接低温割れ性に優れた高張力鋼。5. The composition according to claim 1, wherein B: 0.0001 to 0.0030% by weight is contained.
High-strength steel excellent in weld cold cracking resistance according to the item.
〜５のいづれか１項に記載の耐溶接低温割れ性に優れた
高張力鋼。6. The composition according to claim 1, which comprises, by weight, one or two of Ca: 0.0003 to 0.0025% and REM: 0.0003 to 0.0025%.
High-strength steel excellent in weld cold cracking resistance according to any one of 1 to 5 above.
学成分を有する鋼塊を、Ａｃ3 変態点〜１２５０℃に加
熱して再結晶温度域において累積圧下率で４０〜９０％
の熱間圧延を施し、常温〜３００℃まで０．１〜１００
℃／秒の冷却速度で冷却した後、Ａｃ3 変態点〜１００
０℃に再加熱し、５〜１００℃／秒の冷却速度で常温〜
３００℃まで冷却し、さらに３００℃〜Ａｃ1 変態点に
焼戻しすることを特徴とする耐溶接低温割れ性に優れた
高張力鋼の製造方法。7. A steel ingot having the chemical composition according to any one of claims 1 to 6 is heated to an Ac 3 transformation point to 1250 ° C., and a cumulative rolling reduction is 40 to 90% in a recrystallization temperature range.
Hot rolling is performed at room temperature to 300 ° C for 0.1 to 100
After cooling at a cooling rate of ° C / sec, the Ac 3 transformation point to 100
Reheat to 0 ° C and cool at a cooling rate of 5 to 100 ° C / sec.
A method for producing a high-strength steel excellent in welding cold cracking resistance, which comprises cooling to 300 ° C. and further tempering to 300 ° C. to an Ac 1 transformation point.
学成分を有する鋼塊を、Ａｃ3 変態点〜１２５０℃に加
熱して再結晶温度域において累積圧下率で４０〜９０％
の熱間圧延を施し、Ａｒ3 変態点以上の温度から５〜１
００℃／秒の冷却速度で常温〜３００℃まで冷却し、さ
らに３００℃〜Ａｃ1 変態点に焼戻しすることを特徴と
する耐溶接低温割れ性に優れた高張力鋼の製造方法。8. A steel ingot having the chemical composition according to any one of claims 1 to 6 is heated to an Ac 3 transformation point to 1250 ° C. and a cumulative rolling reduction of 40 to 90% in a recrystallization temperature range.
Hot-rolling is performed, and the temperature from the Ar 3 transformation point or higher to 5-1
A method for producing a high-strength steel excellent in welding cold cracking resistance, which comprises cooling from room temperature to 300 ° C. at a cooling rate of 00 ° C./second, and further tempering to 300 ° C. to Ac 1 transformation point.
学成分を有する鋼塊を、Ａｃ3 変態点〜１２５０℃に加
熱して再結晶温度域において累積圧下率で４０〜９０％
の熱間圧延を施し、引き続き未再結晶温度域において累
積圧下率で４０〜９０％の圧延を施した後、Ａｒ3 変態
点以上の温度から５〜１００℃／秒の冷却速度で常温〜
３００℃まで冷却し、さらに３００℃〜Ａｃ1 変態点に
焼戻しすることを特徴とする耐溶接低温割れ性に優れた
高張力鋼の製造方法。9. A steel ingot having the chemical composition according to any one of claims 1 to 6 is heated to an Ac 3 transformation point to 1250 ° C. and a cumulative rolling reduction is 40 to 90% in a recrystallization temperature range.
Hot rolling, followed by rolling at a cumulative rolling reduction of 40 to 90% in the non-recrystallization temperature range, and then from the temperature of the Ar 3 transformation point or higher to a cooling rate of 5 to 100 ° C./room temperature to room temperature to
A method for producing a high-strength steel excellent in welding cold cracking resistance, which comprises cooling to 300 ° C. and further tempering to 300 ° C. to an Ac 1 transformation point.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP32338994A JPH08176724A (en) | 1994-12-26 | 1994-12-26 | High tensile steel having excellent welding cold crack resistance and production thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP32338994A JPH08176724A (en) | 1994-12-26 | 1994-12-26 | High tensile steel having excellent welding cold crack resistance and production thereof |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH08176724A true JPH08176724A (en) | 1996-07-09 |
Family
ID=18154198
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP32338994A Withdrawn JPH08176724A (en) | 1994-12-26 | 1994-12-26 | High tensile steel having excellent welding cold crack resistance and production thereof |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH08176724A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9945015B2 (en) | 2011-10-03 | 2018-04-17 | Jfe Steel Corporation | High-tensile steel plate giving welding heat-affected zone with excellent low-temperature toughness, and process for producing same |
| JP2020204073A (en) * | 2019-06-17 | 2020-12-24 | 日本製鉄株式会社 | High strength steel sheet for high heat input welding |
-
1994
- 1994-12-26 JP JP32338994A patent/JPH08176724A/en not_active Withdrawn
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9945015B2 (en) | 2011-10-03 | 2018-04-17 | Jfe Steel Corporation | High-tensile steel plate giving welding heat-affected zone with excellent low-temperature toughness, and process for producing same |
| EP2765210B1 (en) * | 2011-10-03 | 2018-12-19 | JFE Steel Corporation | High-tensile steel plate giving welding heat-affected zone with excellent low-temperature toughness, and process for producing same |
| JP2020204073A (en) * | 2019-06-17 | 2020-12-24 | 日本製鉄株式会社 | High strength steel sheet for high heat input welding |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A300 | Withdrawal of application because of no request for examination |
Free format text: JAPANESE INTERMEDIATE CODE: A300 Effective date: 20020305 |