JPH07138639A - Production of low yield ratio steel tube excellent in low temp. toughness - Google Patents
Production of low yield ratio steel tube excellent in low temp. toughnessInfo
- Publication number
- JPH07138639A JPH07138639A JP28695993A JP28695993A JPH07138639A JP H07138639 A JPH07138639 A JP H07138639A JP 28695993 A JP28695993 A JP 28695993A JP 28695993 A JP28695993 A JP 28695993A JP H07138639 A JPH07138639 A JP H07138639A
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- steel
- quenching
- yield ratio
- steel sheet
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Abstract
Description
【0001】[0001]
【産業上の利用分野】本発明は、建造物、橋梁、タンク
等の鋼構造物の建築材料として使用するのに好適な低降
伏比高張力鋼管の製造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a low yield ratio high tensile steel pipe suitable for use as a building material for steel structures such as buildings, bridges and tanks.
【0002】[0002]
【従来の技術】従来より、建造物、橋梁、タンク等の鋼
構造物は徐々に大型化される傾向にあり、かかる大型化
に対応するため、鋼構造物の建築材料である鋼材には、
高強度化および厚肉化が求められている。求められる強
度のレベルは引張強さ:590N/mm2以上である。2. Description of the Related Art Conventionally, steel structures such as buildings, bridges, and tanks have been gradually increased in size.
Higher strength and thicker wall are required. The required strength level is a tensile strength of 590 N / mm 2 or more.
【0003】また、鋼構造物に生じる脆性破壊を防止す
るため、上記の鋼材には降伏比が低いこと、つまり、引
張強さに対する降伏強さ (降伏点または耐力) の割合が
低いことも要求されている。求められる降伏比のレベル
は降伏比で80%以下である。このような低降伏比高張力
鋼材を製造する方法が、従来より種々提案されている。Further, in order to prevent brittle fracture occurring in a steel structure, the above steel materials are required to have a low yield ratio, that is, a low ratio of yield strength (yield point or proof stress) to tensile strength. Has been done. The required yield ratio level is 80% or less. Various methods for producing such a low-yield-ratio high-strength steel material have been conventionally proposed.
【0004】特開平2−205626号公報には、C:0.02〜
0.20%、Si:0.02〜0.50%、Mn:0.20〜2.00%およびA
l:0.010 〜0.100 %と、さらにCu:0.10〜2.00%、N
b:0.005 〜0.10%、V:0.005 〜0.10%、Ti:0.005
〜0.10%のうちの1種または2種以上、さらに必要に応
じて、Ni:0.10〜2.00%、Cr:0.10〜1.00%、Mo:0.05
〜0.50%およびB:0.0003〜0.0030%のうちの1種また
は2種以上を、次式 DI = (17−0.1Nr)×8√C×(0.7Si+1) ×(3.3Mn+1) ×(0.4Cu+1) × ( 0.4Ni +1) ×(2.2Cr+1) ×(3.0Mo+1) ×(1.8V+1) ×(200B+1) ≦ex p(0.015t+2.0) ただし、Nr:焼入れ時のASTMオーステナイト粒度番号 t:板厚(mm) を満たすように含有し、残部Feおよび不可避的不純物か
らなる鋼片に熱間圧延を行った後、焼入れ焼戻し処理ま
たは直接焼入れ焼戻し処理を行うことにより、タンクや
ペンストック等の溶接構造物用材料に適した低降伏比高
張力鋼板を製造する方法が提案されている。Japanese Unexamined Patent Publication No. 2-205626 discloses C: 0.02 to
0.20%, Si: 0.02-0.50%, Mn: 0.20-2.00% and A
l: 0.010 to 0.100%, Cu: 0.10 to 2.00%, N
b: 0.005 to 0.10%, V: 0.005 to 0.10%, Ti: 0.005
~ 0.10% of 1 or 2 or more, if necessary, Ni: 0.10 ~ 2.00%, Cr: 0.10 ~ 1.00%, Mo: 0.05
To 0.50% and B: 0.0003 to 0.0030%, one or more of them are expressed by the following formula D I = (17−0.1Nr) × 8√C × (0.7Si + 1) × (3.3Mn + 1) × (0.4Cu + 1) ) × (0.4Ni +1) × (2.2Cr + 1) × (3.0Mo + 1) × (1.8V + 1) × (200B + 1) ≦ ex p (0.015t + 2.0) where Nr: ASTM austenite grain size number during quenching t: Plate thickness (mm) is contained in the steel, and the steel slab consisting of the balance Fe and unavoidable impurities is hot-rolled, and then subjected to quenching and tempering treatment or direct quenching and tempering treatment. There has been proposed a method of producing a high yield steel plate having a low yield ratio suitable for a material for materials.
【0005】この方法は、略述すれば、DI で表わされ
る焼入性を特定のレベルに抑え、その一方で鋼板にCu、
Nb、V、Ti等の析出強化元素を添加してQ−TまたはD
Q−T (ただし、Q:オーステナイト域焼入れ、DQ:
オーステナイト域直接焼入れ、T:焼戻し) を行うこと
により、低降伏比でかつ所定の高強度(引張強さ:588N
/mm2(60kgf/mm2) 級以上)を有し、さらに溶接性も優れ
た低降伏比高張力鋼板を製造する方法である。In short, this method suppresses the hardenability represented by D I to a specific level, while at the same time Cu,
QT or D by adding precipitation strengthening elements such as Nb, V, Ti
Q-T (however, Q: austenite quenching, DQ:
By performing direct quenching in the austenite region and T: tempering, it has a low yield ratio and a specified high strength (tensile strength: 588N).
/ mm 2 (60 kgf / mm 2 ) grade or higher) and a low yield ratio high tensile steel sheet with excellent weldability.
【0006】また、特開平3−219012号公報には、C:
0.03〜0.10%、Si:0.05〜0.60%、Mn:0.60〜2.00%、
Mo:0.10〜0.50%、P:0.030 %以下、S:0.020 %以
下を含み、さらにNi:1.00%以下、Cr:0.70%以下、C
u:0.70%以下、V:0.06%以下、Nb:0.05%以下およ
びB:0.0050%以下のうちから選ばれた一種以上、必要
に応じてTi:0.003 〜0.05%、残部Feおよび不可避的不
純物からなり、かつ溶接割れ感受性指標PCM (%) =C
+Si/30 +Mn/20 +Ni/60 +Cr/20 +Cu/20+Mo/15 +
V/10 +5Bが0.16〜0.21%である鋼を熱間圧延後、直
ちに300 〜550 ℃まで急冷するか、もしくは空冷後Ac3
点以上の温度に再加熱した後300 〜550 ℃まで急冷した
のち、室温まで空冷し、さらにAc1 〜Ac3 変態点間の2
相域温度に加熱保持した後、空冷以上の冷却速度で焼入
れを行い、その後450 〜600 ℃の温度で焼戻しを行うこ
とにより、溶接割れ感受性が小さく予熱が不要で、降伏
比が80%以下、引張強さが588N/mm2(60kgf/mm2) 以上の
低降伏比高張力鋼板を製造する方法が提案されている。Further, in Japanese Patent Laid-Open No. 3-219012, C:
0.03 to 0.10%, Si: 0.05 to 0.60%, Mn: 0.60 to 2.00%,
Mo: 0.10 to 0.50%, P: 0.030% or less, S: 0.020% or less, Ni: 1.00% or less, Cr: 0.70% or less, C
u: 0.70% or less, V: 0.06% or less, Nb: 0.05% or less and B: 0.0050% or less, if necessary, Ti: 0.003 to 0.05%, balance Fe and unavoidable impurities And weld crack susceptibility index P CM (%) = C
+ Si / 30 + Mn / 20 + Ni / 60 + Cr / 20 + Cu / 20 + Mo / 15 +
Steel with V / 10 + 5B of 0.16 to 0.21% is hot-rolled and then immediately quenched to 300 to 550 ° C or air-cooled to Ac 3
After being reheated to a temperature above the point, it is rapidly cooled to 300-550 ° C, then air-cooled to room temperature, and further between the Ac 1 -Ac 3 transformation points.
After heating and holding at the phase region temperature, quenching is performed at a cooling rate of air cooling or higher, and then tempering is performed at a temperature of 450 to 600 ° C, which reduces weld cracking susceptibility, requires no preheating, and has a yield ratio of 80% or less. A method for producing a high-strength steel sheet having a low yield ratio and a tensile strength of 588 N / mm 2 (60 kgf / mm 2 ) or more has been proposed.
【0007】すなわち、この方法は、C含有量を0.10%
以下に低減し合金元素を添加した上記の組成を有する鋼
で、2相焼入れ前の組織を若干粗い組織として焼入れ焼
戻し処理を施す方法である。That is, this method has a C content of 0.10%.
This is a method of performing quenching and tempering treatment on the steel having the above-described composition with the alloying elements reduced and having the above-described composition, with the structure before two-phase quenching being made a slightly rough structure.
【0008】さらに、特開昭61−288018号公報には、熱
間圧延後あるいは高温度に再加熱された鋼管を高温度か
ら急冷した後、高周波加熱法で鋼管の表面硬化層のみに
局部焼戻し処理あるいは局部焼戻し急冷処理を行うこと
により、高強度でかつ低降伏比鋼管 (引張強さ:634N/m
m2以上、降伏比:83.0%以下) を製造する方法が提案さ
れている。Further, in Japanese Patent Laid-Open No. 61-288018, a steel pipe that has been hot-rolled or reheated to a high temperature is rapidly cooled from a high temperature, and then locally tempered to a surface hardened layer of the steel pipe by a high frequency heating method. Steel pipe with high strength and low yield ratio (tensile strength: 634 N / m
m 2 or more, a yield ratio: 83.0% or less) A method for producing have been proposed.
【0009】特開平2−205626号公報または特開平3−
219012号公報により提案された方法によれば、鋼板とし
ては目標とする引張強度および降伏比を達成することは
できる。しかし、鋼管を製造すると製管加工によって鋼
管の降伏比が80%超となり、降伏比が80%以下である58
8N/mm2以上の低降伏比高張力鋼管を製造することはでき
ない。JP-A-2-205626 or JP-A-3-205626
According to the method proposed by Japanese Patent No. 219012, it is possible to achieve the target tensile strength and yield ratio for a steel sheet. However, when steel pipes are manufactured, the yield ratio of steel pipes exceeds 80% due to pipe manufacturing, and the yield ratio is 80% or less.
It is not possible to manufacture high-strength steel pipes with a low yield ratio of 8 N / mm 2 or more.
【0010】一方、特開昭61−288018号公報により提案
された方法によれば、確かに降伏比を低減することは可
能であるが、製管加工後の鋼管に急冷、焼戻しという2
度にわたる熱処理を行うため新たに鋼管用の加熱、急冷
設備の新設とそのための日程の確保が必要となり、コス
トおよび鋼管の納期の点で問題である。On the other hand, according to the method proposed in Japanese Patent Laid-Open No. 61-288018, although it is possible to surely reduce the yield ratio, it is necessary to perform quenching and tempering on the steel pipe after pipe forming.
In order to carry out heat treatment over a period of time, it is necessary to newly install heating and quenching equipment for steel pipes and secure schedules for that, which is a problem in terms of cost and delivery time of steel pipes.
【0011】[0011]
【発明が解決しようとする課題】これらを踏まえ、本発
明者らは、以前、特願平5−130682号において、Ceq
(%) =C+Si/24 +Mn/6+Ni/40 +Mo/4+V/14 +Cr/
5で示される炭素当量Ceqを0.38〜0.45%に規定すると
ともに、熱間圧延条件をも所定範囲に規定することによ
り鋼板表面の硬度をコントロールし、製管加工による耐
力の上昇を予め見込んで熱間圧延後の熱延鋼板の耐力、
引張強さ、降伏比等を目標値の下限付近に抑制し、製管
加工後に目標値を満足させる方法を提案した。Based on the above, the present inventors have previously proposed in Japanese Patent Application No. 5-130682, Ceq.
(%) = C + Si / 24 + Mn / 6 + Ni / 40 + Mo / 4 + V / 14 + Cr /
The carbon equivalent Ceq shown in 5 is specified to 0.38 to 0.45%, and the hot rolling conditions are also specified to a predetermined range to control the hardness of the steel sheet surface, and to increase the proof stress due to the pipe forming process in advance. Yield strength of hot rolled steel sheet after hot rolling,
We proposed a method to suppress the tensile strength, yield ratio, etc. near the lower limit of the target values and satisfy the target values after pipe manufacturing.
【0012】しかし、この方法においても製管加工後の
表面の硬化は避けられず、鋼管の表面から厚みの1/4 の
位置(t/4位置) での靱性は0℃でのシャルピー吸収エネ
ルギー vE0≧27J を保証するにとどまっている。However, even with this method, hardening of the surface after pipe forming is unavoidable, and the toughness at the position 1/4 of the thickness (t / 4 position) from the surface of the steel pipe is the Charpy absorbed energy at 0 ° C. It only guarantees vE 0 ≧ 27J.
【0013】今後の寒冷地での使用、破壊に対する安全
性の向上を考えた場合、さらなる低温靱性の向上が必要
である。また、Ceqを0.38〜0.45%にコントロールする
ことも現状の製造法では工程、製造コストの面で問題で
ある。Considering future use in cold regions and improvement in safety against fracture, further improvement in low temperature toughness is required. Controlling Ceq to 0.38 to 0.45% is also a problem in terms of steps and manufacturing costs in the current manufacturing method.
【0014】ここに、本発明の目的は、建造物、橋梁、
タンク等の鋼構造物の建築材料として使用するのに好適
な、降伏比:80%以下、引張強さ:590N/mm2以上の低降
伏比高張力鋼管の製造方法を提供することである。Here, an object of the present invention is to construct a building, a bridge,
It is to provide a method for producing a high-strength steel pipe having a low yield ratio and a yield ratio of 80% or less and a tensile strength of 590 N / mm 2 or more, which is suitable for use as a building material for a steel structure such as a tank.
【0015】より特定的には、本発明の目的は、耐力
(0.2%YS) ≧440N/mm2、引張強さ(TS):590 〜740N/m
m2、降伏比(YR)≦80%、伸び(El)≧20%、−20℃のシャ
ルピー吸収エネルギーvE-20 ≧27Jの機械的特性を備え
た低温靱性に優れた低降伏比高張力鋼管の製造方法を提
供することにある。More specifically, the object of the present invention is to
(0.2% YS) ≧ 440N / mm 2 , Tensile strength (TS): 590〜740N / m
m 2, the yield ratio (YR) ≦ 80%, elongation (El) ≧ 20%, - 20 ℃ low yield ratio high-strength steel pipe excellent in low temperature toughness having the mechanical properties of the Charpy absorbed energy vE -20 ≧ 27 J of It is to provide a manufacturing method of.
【0016】さらに本発明の別の目的は、前述の特願平
5−130682号で提案した方法に必要であったCeqおよび
熱間圧延条件についての制約なしで、安価に上記の目的
に合った鋼管を製造し、しかも鋼管の表面から厚みの1/
4 の位置での靱性を向上させる低降伏比高張力鋼管の製
造方法を提供することである。Still another object of the present invention is to meet the above-mentioned object at a low cost without the restrictions on the Ceq and hot rolling conditions required for the method proposed in the above-mentioned Japanese Patent Application No. 5-130682. Manufactures steel pipes, and 1 / thick of the thickness from the surface of the steel pipe
It is an object of the present invention to provide a method for manufacturing a low yield ratio high strength steel pipe that improves the toughness at position 4.
【0017】[0017]
【課題を解決するための手段】焼入れまま(as quenche
d) の表面におけるオーステナイト結晶粒度と表面硬度
との間には、従来から知られているように、一定の相関
関係がある。鋼板の表裏面では加熱によりオーステナイ
ト結晶粒が粗大化するが、焼入れままではそのような粗
大結晶粒のため、焼きが入り易くなり、表裏面の硬度が
著しく高まってしまい、後続して行われる熱処理 (2相
域焼入れ、焼戻し) によっても焼き入れままによる高硬
度が解消されずに残り、さらに製管加工時の加工硬化に
より表裏面の硬度が著しく高まり、降伏比(YR)の上昇を
もたらしてしまう。したがって、鋼管の降伏比を80%以
下に抑制するには、表裏面のオーステナイト結晶粒の粗
大化を防止し、鋼管表面のビッカース硬さ(Hv 10kgf)を
200 以下に抑制する必要がある。[Means for solving the problems] As quenching
As is conventionally known, there is a certain correlation between the austenite grain size on the surface of d) and the surface hardness. On the front and back of the steel sheet, the austenite crystal grains become coarse by heating, but if they are just quenched, such coarse crystal grains make it easy to quench, and the hardness of the front and back surfaces increases significantly. The high hardness due to as-quenching remains unresolved even by (two-phase region quenching and tempering), and the hardness of the front and back surfaces is significantly increased due to work hardening during pipe manufacturing, resulting in an increase in the yield ratio (YR). I will end up. Therefore, in order to suppress the yield ratio of the steel pipe to 80% or less, coarsening of the austenite crystal grains on the front and back surfaces and the Vickers hardness (Hv 10kgf) on the surface of the steel pipe are prevented.
It should be kept below 200.
【0018】本発明者らはさらに鋭意検討した結果、表
裏面のオーステナイト結晶粒の粗大化防止には、2相域
焼入れ、焼戻しに先立って行う、第1回目の焼入れを表
裏面の加熱温度をAc3 点未満にし、中心部だけをAc3 以
上にすることが有効であることを知見した。このような
表面、中心部の温度差のある加熱は、通常の方法では不
可能だが、本発明者らは、通電加熱装置を用いることに
より、中心を高温(Ac3以上) に保ちながら表面を水冷な
どで強制冷却することで可能となることを見い出した。As a result of further diligent studies, the present inventors have found that the first quenching, which is carried out prior to the two-phase region quenching and tempering, is performed to prevent the austenite crystal grains on the front and back surfaces from coarsening by changing the heating temperature of the front and back surfaces. It was found that it is effective to set the Ac to less than 3 points and to set only the central part to Ac 3 or more. Such surface and center heating with a temperature difference is not possible by a normal method, but the present inventors have used an electric heating device to maintain the surface at a high temperature (Ac 3 or more) while maintaining the center at a high temperature. We found that it is possible by forced cooling with water.
【0019】ここに、本発明は、重量%で、C:0.02 〜
0.20%、Si:0.02 〜0.50%、Mn:0.50 〜2.00%を含有
し、さらにCu:0.10 〜1.5 %、Ni:0.10 〜0.50%、Nb:
0.005〜0.10%、およびV:0.005〜0.10%からなる群か
ら選ばれた1種または2種以上、残部Feおよび不可避的
不純物から成る鋼組成を有する鋼片を、熱間圧延後、鋼
板に直接通電することにより、鋼板中心を1〜25℃/秒
の速度で昇温させ、同時に表裏面を強制冷却し、鋼板中
心がAc3 点以上、表裏面がAc3 点未満の温度域から焼入
れを行い、引き続いてAc1 点以上、Ac3 点以下の2相温
度域に再加熱し焼入れを行い、さらに焼戻しを行ってか
ら製管加工を行うことを特徴とする低温靱性に優れた低
降伏比鋼管の製造法である。In the present invention, C: 0.02% by weight is used.
0.20%, Si: 0.02-0.50%, Mn: 0.50-2.00%, Cu: 0.10-1.5%, Ni: 0.10-0.50%, Nb:
A steel slab having a steel composition consisting of 0.005 to 0.10% and V: 0.005 to 0.10%, one or more selected from the group consisting of the balance Fe and unavoidable impurities is directly applied to a steel sheet after hot rolling. By energizing, the temperature of the steel sheet center is raised at a rate of 1 to 25 ° C / sec, and at the same time the front and back surfaces are forcibly cooled, and quenching is performed from a temperature range where the steel sheet center is at least Ac 3 points and the front and back surfaces are less than Ac 3 points. Low yield ratio excellent in low temperature toughness, characterized by performing reheating to a two-phase temperature range of Ac 1 point or more and Ac 3 point or less, quenching, and then tempering before pipe forming. It is a method of manufacturing steel pipes.
【0020】[0020]
【作用】本発明にかかる製造方法の大きな特徴は、鋼板
中心をAc3 点以上に、表裏面をAc3 点未満に加熱するこ
とであり、具体的には第1回目の加熱、焼き入れにおい
て、鋼板に直接電流を通じることにより鋼板自体の抵抗
発熱により加熱を行う直接通電加熱法を採用したことで
ある。そのような直接通電加熱の利用により上述したよ
うに鋼板表面を強制冷却、例えば水冷するだけで、鋼板
表裏面の温度を低下させた状態での焼入れが可能とな
る。A major feature of the manufacturing method according to the present invention is that the center of the steel sheet is heated to the Ac 3 point or more and the front and back surfaces are heated to the Ac 3 point or less. Specifically, in the first heating and quenching That is, the direct current heating method in which heating is performed by resistance heating of the steel sheet itself by directly passing an electric current through the steel sheet is adopted. By utilizing such direct electric heating, quenching can be performed in a state in which the temperature of the front and back surfaces of the steel sheet is lowered only by forcedly cooling the steel sheet surface as described above, for example, water cooling.
【0021】また、直接通電加熱法の作用としてさら
に、従来の炉では実現できない設定温度近傍での昇温速
度の制御が可能となり、設定温度まで一定速度で加熱が
行え、加熱時間の短縮および温度管理が簡単に行うこと
ができることが挙げられる。なお、直接通電加熱の操作
自体は以上の説明から当業者には自明と考えられるの
で、これ以上の説明を略す。Further, as a function of the direct current heating method, it becomes possible to control the rate of temperature rise near the set temperature, which cannot be realized by the conventional furnace, and heating can be performed up to the set temperature at a constant rate, thus shortening the heating time and the temperature. It is possible to manage easily. The operation itself of direct electric heating is considered to be obvious to those skilled in the art from the above description, and therefore further description is omitted.
【0022】このようにして直接通電により加熱された
鋼板のうち、表裏面は水冷などの強制冷却によって焼入
れ温度を調整してから焼入れ処理を行うことで、表面の
γ粒の粗大化をおさえ、鋼板での表面硬度を低く (Hv=
150 以下に) コントロールすることが可能となる。これ
により、製管による加工硬化で表面が硬化しても安定し
て−20℃のシャルピー吸収エネルギーvE-20 ≧27J が保
証でき、さらに急速加熱を行うため中心部のオーステナ
イト粒の成長も小さく、炭素当量Ceqの制約なしで製管
後の降伏比(YR)のコントロールも可能となる。これによ
り低温靱性に優れた低降伏比鋼管の製造が可能となる。Among the steel sheets thus heated by direct energization, the front and back surfaces of the steel sheet are subjected to quenching treatment by adjusting the quenching temperature by forced cooling such as water cooling to suppress the coarsening of γ grains on the surface. Low surface hardness on steel plate (Hv =
It will be possible to control (below 150). As a result, the Charpy absorbed energy vE -20 ≧ 27J at −20 ° C. can be stably guaranteed even if the surface is hardened by work hardening by pipe manufacturing, and since the rapid heating is performed, the growth of austenite grains in the central part is also small, It is also possible to control the yield ratio (YR) after pipe production without restriction of the carbon equivalent Ceq. This makes it possible to manufacture a low yield ratio steel pipe excellent in low temperature toughness.
【0023】図1に、この時の鋼板温度変化をグラフに
示した。図中、上側の線として示した通電加熱による中
心部の加熱は昇温速度が問題となる。加熱速度が1℃/
秒未満だと熱間圧延によって得られた転位等が消失し、
25℃/秒より速いと鋼板の加熱が不均一となるため、鋼
板中心の加熱速度を1 〜25℃/秒に制限した。この加熱
により添加元素の固溶を行う。このようにして板中心部
はAc3 点以上にまで加熱され、表裏面は図中、下側の線
として示したが、例えば水冷によってAc3 点未満にまで
加熱されるようにする。それは水量調節などの強制冷却
の程度を調節することで行なえばよい。なお、その後の
熱処理については後述する。次に、本発明において鋼組
成および熱処理条件を前述のように限定する理由を説明
する。FIG. 1 is a graph showing changes in the steel plate temperature at this time. In the heating of the central portion by electric heating shown as the upper line in the figure, the rate of temperature rise becomes a problem. Heating rate is 1 ℃ /
If it is less than a second, dislocations etc. obtained by hot rolling disappear,
If the heating rate is higher than 25 ° C / sec, the heating of the steel sheet becomes uneven, so the heating rate at the center of the steel sheet was limited to 1 to 25 ° C / sec. This heating causes the additional element to form a solid solution. In this way, the central part of the plate is heated to the Ac 3 point or higher, and the front and back surfaces are shown as the lower line in the figure, but are heated to less than the Ac 3 point by, for example, water cooling. It may be performed by adjusting the degree of forced cooling such as water amount adjustment. The subsequent heat treatment will be described later. Next, the reasons for limiting the steel composition and heat treatment conditions in the present invention as described above will be explained.
【0024】C:0.02〜0.20% Cは、強度確保のために0.02%以上の添加が必要である
が、0.20%を超えて過剰に添加すると溶接性を損なう。
そこで、本発明では、C含有量は0.02%以上0.20%以下
と限定する。 C: 0.02 to 0.20% C needs to be added in an amount of 0.02% or more to secure the strength, but if added in excess of 0.20%, the weldability is impaired.
Therefore, in the present invention, the C content is limited to 0.02% or more and 0.20% or less.
【0025】Si:0.02〜0.50% Siは、主に鋼の脱酸のために添加され、通常その添加量
は0.02%以上であり、また降伏比の低減にも有効であ
る。しかし、0.50%を超えて過剰に添加すると靱性を劣
化させるので好ましくない。そこで、本発明では、Si含
有量は0.02%以上0.50%以下と限定する。 Si: 0.02 to 0.50% Si is added mainly for deoxidizing steel, and the addition amount is usually 0.02% or more, and it is also effective for reducing the yield ratio. However, if added in excess of 0.50%, the toughness deteriorates, which is not preferable. Therefore, in the present invention, the Si content is limited to 0.02% or more and 0.50% or less.
【0026】Mn:0.50〜2.00% Mnは、強度確保のために0.50%以上の添加が必要である
が、2.00%を超えて過剰に添加すると溶接性を損なう。
そこで、本発明では、Mn含有量は0.50%以上2.00%以下
と限定する。 Mn: 0.50 to 2.00% Mn needs to be added in an amount of 0.50% or more to secure the strength, but if added in excess of 2.00%, the weldability is impaired.
Therefore, in the present invention, the Mn content is limited to 0.50% or more and 2.00% or less.
【0027】さらに、本発明では、高強度化を図るため
に、Cu:0.10〜1.5 %、Ni:0.10〜0.50%、Nb:0.005
〜0.10%およびV:0.005 〜0.10%からなる群から選ば
れた1種または2種以上を含有する。以下、これらの元
素についても組成の限定理由を説明する。Further, in the present invention, in order to increase the strength, Cu: 0.10 to 1.5%, Ni: 0.10 to 0.50%, Nb: 0.005.
.About.0.10% and V: 0.005 to 0.10%, and one or more kinds selected from the group consisting of. The reasons for limiting the composition of these elements will be described below.
【0028】Cu:0.10〜1.5 % Cuは、0.10%以上の添加により高強度化に有効である
が、1.5 %を超えて過剰に添加すると溶接性を損なうと
ともに熱間割れも生ずる。そこで、Cuを添加する場合に
は、その含有量は0.10%以上1.5 %以下と限定すること
が望ましい。 Cu: 0.10 to 1.5% Cu is effective in increasing the strength by adding 0.10% or more, but if added in excess of 1.5%, the weldability is impaired and hot cracking occurs. Therefore, when Cu is added, its content is preferably limited to 0.10% or more and 1.5% or less.
【0029】Ni:0.10〜0.50% Niは、0.10%以上の添加により強度上昇に有効である
が、過剰に添加すると溶接性および低温靱性がともに劣
化する。特に、Niは高価な元素であり0.50%を超えて添
加すると経済性の点でも問題がある。そこで、Niを添加
する場合には、その含有量は0.10%以上0.50%以下と限
定することが望ましい。 Ni: 0.10 to 0.50% Ni is effective in increasing the strength by adding 0.10% or more, but if added excessively, both weldability and low temperature toughness deteriorate. In particular, Ni is an expensive element, and if added in excess of 0.50%, there is a problem in terms of economy. Therefore, when Ni is added, its content is preferably limited to 0.10% or more and 0.50% or less.
【0030】Nb:0.005 〜0.10% Nbは、0.005 %以上の添加により特に直接焼入れ焼戻し
法において高強度化に有効であるが、0.10%を超えて過
剰に添加すると靱性および溶接性がともに劣化する。そ
こで、Nbを添加する場合には、その含有量は0.005 %以
上0.10%以下と限定することが望ましい。 Nb: 0.005 to 0.10% Nb is effective for increasing the strength particularly in the direct quenching and tempering method by adding 0.005% or more, but if added in excess of 0.10%, both toughness and weldability deteriorate. . Therefore, when Nb is added, its content is preferably limited to 0.005% or more and 0.10% or less.
【0031】V:0.005 〜0.10% Vは、0.005 %以上の添加で鋼の強度を高めるが、0.10
%を超えて過剰に添加すると効果が飽和するばかりでな
く、溶接性を劣化させる。本発明にあって、Vを添加す
る場合には、その含有量は0.005 %以上0.10%以下と限
定することが望ましい。上記以外の組成は、Feおよび不
可避的不純物である。 V: 0.005 to 0.10% V increases the strength of steel by adding 0.005% or more, but 0.10% to 0.10%
If it is added excessively in excess of%, not only the effect is saturated, but also the weldability is deteriorated. In the present invention, when V is added, its content is preferably limited to 0.005% or more and 0.10% or less. Compositions other than the above are Fe and inevitable impurities.
【0032】本発明によれば、上述のような鋼組成を有
する鋼片に熱間加工を行うが、本発明の場合、熱間圧延
条件は特に制限されない。熱間圧延の開始温度は1100〜
1000℃程度、仕上温度は 800〜700 ℃程度、熱間圧延時
の総圧下率は66〜96%程度を例示することができる。According to the present invention, the steel slab having the above-mentioned steel composition is subjected to hot working, but in the case of the present invention, hot rolling conditions are not particularly limited. Hot rolling start temperature is 1100 ~
For example, about 1000 ° C, the finishing temperature is about 800 to 700 ° C, and the total rolling reduction during hot rolling is about 66 to 96%.
【0033】中心部のAc3 点以上からの焼入れ、Ac1 点
〜Ac3 点の2相域からの焼入れ、焼戻し 本発明では、熱間圧延を終了した熱延鋼板の強度を確保
するため、鋼板中心部はAc3 点以上の温度域からの焼入
れを行う。中心部の焼入れ温度がAc3 点未満であると、
所望の強度を確保することができないからである。な
お、この時、鋼板表裏面はAc3 点未満から急冷されるこ
とになるのは前述のとおりである。焼入れの態様は特に
限定を要さない。水焼入れ、油焼入れ等を適宜行えばよ
い。 Quenching from the center Ac 3 points or more, Ac 1 point
Quenching from 2 phase region to Ac 3 point, tempering in the present invention, in order to ensure the strength of the hot rolled steel sheet finished hot-rolled steel sheet center performs quenching from a temperature range of not lower than 3 points Ac. If the quenching temperature of the center is less than Ac 3 points,
This is because the desired strength cannot be secured. At this time, the front and back surfaces of the steel sheet are rapidly cooled from less than Ac 3 point, as described above. The mode of quenching is not particularly limited. Water quenching, oil quenching, etc. may be appropriately performed.
【0034】次に、本発明では、Ac1 点〜Ac3 点の2相
域からの焼入れを行い、軟質フェライト相および硬質ベ
イナイト相を析出して低降伏比化を図るとともに、軟質
フェライト相および硬質ベイナイト相の析出に起因した
靱性劣化を防止するため、焼戻しを行う。焼戻しは、通
常の温度 (500 〜600 ℃程度) で行えばよい。Next, in the present invention, quenching is carried out from the two-phase region of Ac 1 point to Ac 3 point to precipitate the soft ferrite phase and the hard bainite phase to achieve a low yield ratio, and the soft ferrite phase and Tempering is performed to prevent deterioration of toughness due to precipitation of hard bainite phase. Tempering may be performed at a normal temperature (500 to 600 ° C).
【0035】本発明では、このようにして熱処理を終え
た熱延鋼板を素材として製管加工を行い、鋼管を製造す
る。製管加工の方法は特定の手段には限定されない。例
えば、電縫鋼管、鍛接鋼管さらにはUOE鋼管等の溶接
鋼管の製管加工法を適用できる。In the present invention, the hot-rolled steel sheet thus heat-treated is used as a raw material for pipe manufacturing to manufacture a steel pipe. The pipe manufacturing method is not limited to a particular means. For example, a method for producing a welded steel pipe such as an electric resistance welded pipe, a forged steel pipe, and a UOE steel pipe can be applied.
【0036】このようにして、本発明により、0.2 %YS
≧440N/mm2、TS:590 〜740N/mm2、YR≦80%、El≧20
%、vE-20 ≧27Jの機械的特性を有し、建造物、橋梁、
タンク等の鋼構造物の建築材料として使用するのに好適
な低降伏比高張力鋼管を製造することが可能となった。
さらに、本発明を実施例を参照しながら詳述するが、こ
れは本発明の例示であり、これにより本発明が限定され
るものではない。Thus, according to the present invention, 0.2% YS
≧ 440N / mm 2 , TS: 590 to 740N / mm 2 , YR ≦ 80%, El ≧ 20
%, VE -20 ≧ 27J mechanical properties, structures, bridges,
It has become possible to manufacture low yield ratio high tensile steel pipes suitable for use as building materials for steel structures such as tanks.
Further, the present invention will be described in detail with reference to examples, but this is an example of the present invention and the present invention is not limited thereto.
【0037】[0037]
【実施例】表1に鋼管製造条件、表2にその鋼管の寸法
と特性値の測定結果を示した。表1、2共に、上段の1
〜8は本発明例、下段の9〜19は比較例である。以下、
本発明例に沿って説明する。EXAMPLES Table 1 shows the conditions for producing steel pipes, and Table 2 shows the results of measuring the dimensions and characteristic values of the steel pipes. Both Tables 1 and 2 are the top 1
8 to 8 are examples of the present invention, and lower 9 to 19 are comparative examples. Less than,
An example of the present invention will be described.
【0038】表1に示す鋼組成、Ac1 点 (℃) および、
Ac3 点 (℃) を有する鋼片に、通電加熱しながら表裏面
を水冷し、鋼板中心がAc3 点以上、表裏面がAc3 点以下
の温度域から第1回目の焼入れ (Q) を行った。引き続
いてAc1 点以上、Ac3 点以下の2相温度域に再加熱し第
2回目の焼入れ (Q')を行い、さらに焼戻し (T) を行
ってから製管加工を行い、表2記載の板厚、外径の鋼管
を製造した。The steel compositions shown in Table 1, Ac 1 point (° C.), and
A steel piece with an Ac 3 point (° C) is water-cooled on the front and back sides while being electrically heated, and the first quenching (Q) is performed from the temperature range where the steel plate center is at or above the Ac 3 point and the front and back sides are at or below the Ac 3 point. went. Next, reheat to a two-phase temperature range of Ac 1 point or more and Ac 3 point or less, perform the second quenching (Q '), and further temper (T), and then perform pipe forming processing, and describe in Table 2. A steel pipe with a plate thickness and outer diameter of
【0039】[0039]
【表1】 [Table 1]
【0040】[0040]
【表2】 [Table 2]
【0041】これらの電縫鋼管から、長さ方向について
JIS 4号試験片を切り出して、耐力(0.2%YS) 、引張強
さ(TS)、降伏比(YR)および伸び(El)を測定するととも
に、鋼管の表面から厚みの1/4 の位置部分から長さ方向
についてJIS 4号試験片を切り出して、−20℃でのシャ
ルピー吸収エネルギーvE-20(J)を測定した。結果を同
じく表2にまとめて示す。From these ERW pipes, in the longitudinal direction
A JIS No. 4 test piece is cut out and the yield strength (0.2% YS), tensile strength (TS), yield ratio (YR) and elongation (El) are measured, and at a position 1/4 of the thickness from the surface of the steel pipe. A JIS No. 4 test piece was cut out in the longitudinal direction from the sample, and the Charpy absorbed energy vE- 20 (J) at -20 ° C was measured. The results are also summarized in Table 2.
【0042】表2における鋼種No.1〜No.8は、本発明で
規定する条件を全て満足するため、0.2 %YS≧440N/m
m2、TS:590 〜740N/mm2、YR≦80%、El≧20%、vE-20
≧27Jという本発明の目標値を全て満足している。Since the steel types No. 1 to No. 8 in Table 2 satisfy all the conditions specified in the present invention, 0.2% YS ≧ 440 N / m
m 2 , TS: 590 to 740 N / mm 2 , YR ≤ 80%, El ≥ 20%, vE -20
All of the target values of the present invention of ≧ 27 J are satisfied.
【0043】これに対し、鋼種No.9は、C含有量が本発
明の範囲を下回っているため、0.2%YSが低下した。鋼
種No.10 は、Si含有量が本発明の範囲の上限を上回って
いるため、vE-20 が低下した。On the other hand, in the steel type No. 9, the C content was below the range of the present invention, so that 0.2% YS was reduced. Steel type No. 10 had a Si content above the upper limit of the range of the present invention, and thus had a decreased vE- 20 .
【0044】鋼種No.11 は、Mn含有量が本発明の範囲の
下限を下回っているため、TSとvE-20 が低下した。鋼種
No.12 は、NbおよびV含有量が本発明の範囲の上限を上
回っているためvE-20 が低下した。In steel type No. 11, since the Mn content was below the lower limit of the range of the present invention, TS and vE- 20 were lowered. Steel grade
In No. 12, since the Nb and V contents exceeded the upper limit of the range of the present invention, vE- 20 was lowered.
【0045】鋼種No.13 は、CuおよびNi含有量が本発明
の範囲の上限を上回っているためvE-20 が低下した。鋼
種No.14 および15は、第1回焼入れ時の表面/裏面温度
が、Ac3 点を上回っているため、vE-20 が低下した。In steel type No. 13, the Cu and Ni contents were above the upper limit of the range of the present invention, so vE -20 was lowered. Steel types No. 14 and 15 had vE- 20 lowered because the front / back surface temperature during the first quenching exceeded the Ac 3 point.
【0046】鋼種No.16 は、第1回焼入れ時の鋼板中心
温度が、Ac3 点を下回っているため、0.2 %YS、TSが低
下した。鋼種No.17 は、2相域からの焼入れ(第2回目
の焼入れ、Q')温度が本発明の範囲の上限を上回ってい
るため、YRが高くなった。In steel type No. 16, the center temperature of the steel sheet during the first quenching was below the Ac 3 point, so 0.2% YS and TS decreased. Steel type No. 17 had a higher YR because the quenching temperature from the two-phase region (second quenching, Q ') was above the upper limit of the range of the present invention.
【0047】鋼種No.18 および19は、第1回目の焼入れ
(Q) において通電加熱をせず、通常加熱炉を用いたの
で、表面/裏面温度が、鋼板中心温度と同じくAc3 点を
上回っているため、vE-20 が低下した。Since the steel types No. 18 and 19 did not conduct electric heating in the first quenching (Q) and used a normal heating furnace, the front surface / back surface temperature exceeded the Ac 3 point like the steel plate center temperature. Therefore, vE -20 has decreased.
【0048】[0048]
【発明の効果】以上詳述したように、本発明により、0.
2 %YS≧440N/mm2、TS:590 〜740N/mm2、YR≦80%、El
≧20%、vE-20 ≧27Jの機械的特性を有し、建造物、橋
梁、タンク等の鋼構造物の建築材料として使用するのに
好適な低降伏比高張力鋼管を製造することが可能となっ
た。As described above in detail, according to the present invention,
2% YS ≧ 440N / mm 2 , TS: 590 ~740N / mm 2, YR ≦ 80%, El
It has mechanical properties of ≧ 20% and vE -20 ≧ 27J, and it is possible to manufacture high-strength steel pipe with low yield ratio suitable for use as a building material for steel structures such as buildings, bridges and tanks. Became.
【図1】本発明の第1回目の加熱および焼き入れの際の
鋼板中心部および表裏面の温度変化を説明するグラフで
ある。FIG. 1 is a graph illustrating temperature changes of a central portion of a steel plate and front and back surfaces during the first heating and quenching of the present invention.
Claims (1)
%を含有し、さらにCu:0.10 〜1.5 %、Ni:0.10 〜0.50
%、Nb:0.005〜0.10%、およびV:0.005〜0.10%からな
る群から選ばれた1種または2種以上、 残部Feおよび不可避的不純物から成る鋼組成を有する鋼
片を、熱間圧延後、鋼板に直接通電することにより、鋼
板中心を1〜25℃/秒の速度で昇温させ、同時に表裏面
を強制冷却し、鋼板中心がAc3 点以上、表裏面がAc3 点
未満となるように加熱し、そのときの温度域から焼入れ
を行い、引き続いてAc1 点以上、Ac3 点以下の2相温度
域に再加熱し焼入れを行い、さらに焼戻しを行ってから
製管加工を行うことを特徴とする低温靱性に優れた低降
伏比鋼管の製造法。1. By weight%, C: 0.02 to 0.20%, Si: 0.02 to 0.50%, Mn: 0.50 to 2.00.
%, Cu: 0.10 to 1.5%, Ni: 0.10 to 0.50
%, Nb: 0.005 to 0.10%, and V: 0.005 to 0.10%, one or two or more selected from the group consisting of the balance Fe and unavoidable impurities. , By directly energizing the steel sheet, the center of the steel sheet is heated at a rate of 1 to 25 ° C / second, and at the same time, the front and back surfaces are forcibly cooled, and the center of the steel sheet becomes Ac 3 points or more and the front and back surfaces become less than Ac 3 points. Like above, quenching from the temperature range at that time, then reheating to a two-phase temperature range of Ac 1 point or more and Ac 3 point or less, quenching, and further tempering before pipe making A method for producing a low yield ratio steel pipe excellent in low temperature toughness, which is characterized by the following.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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JP28695993A JPH07138639A (en) | 1993-11-16 | 1993-11-16 | Production of low yield ratio steel tube excellent in low temp. toughness |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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JP28695993A JPH07138639A (en) | 1993-11-16 | 1993-11-16 | Production of low yield ratio steel tube excellent in low temp. toughness |
Publications (1)
Publication Number | Publication Date |
---|---|
JPH07138639A true JPH07138639A (en) | 1995-05-30 |
Family
ID=17711174
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Country | Link |
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JP (1) | JPH07138639A (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
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JP2016079449A (en) * | 2014-10-15 | 2016-05-16 | 新日鐵住金株式会社 | Production method of steel pipe and steel pipe |
-
1993
- 1993-11-16 JP JP28695993A patent/JPH07138639A/en not_active Withdrawn
Cited By (1)
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JP2016079449A (en) * | 2014-10-15 | 2016-05-16 | 新日鐵住金株式会社 | Production method of steel pipe and steel pipe |
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