JP5151693B2 - Manufacturing method of high-strength steel - Google Patents

Manufacturing method of high-strength steel Download PDF

Info

Publication number
JP5151693B2
JP5151693B2 JP2008140327A JP2008140327A JP5151693B2 JP 5151693 B2 JP5151693 B2 JP 5151693B2 JP 2008140327 A JP2008140327 A JP 2008140327A JP 2008140327 A JP2008140327 A JP 2008140327A JP 5151693 B2 JP5151693 B2 JP 5151693B2
Authority
JP
Japan
Prior art keywords
less
steel
strength
content
addition
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
Application number
JP2008140327A
Other languages
Japanese (ja)
Other versions
JP2009287081A (en
Inventor
大 西尾
知哉 藤原
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Corp
Original Assignee
Nippon Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Steel Corp filed Critical Nippon Steel Corp
Priority to JP2008140327A priority Critical patent/JP5151693B2/en
Publication of JP2009287081A publication Critical patent/JP2009287081A/en
Application granted granted Critical
Publication of JP5151693B2 publication Critical patent/JP5151693B2/en
Expired - Fee Related legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Description

本発明は、建築、産業機械、建設機械、さらには圧力容器等の産業分野で利用可能な、厚鋼板などの高張力鋼の製造方法に関する。
The present invention relates to a method for producing high-strength steel such as thick steel plates that can be used in industrial fields such as construction, industrial machinery, construction machinery, and pressure vessels.

構造物の高性能化および大型化が進展するのに伴って、高強度鋼板の開発の重要性が高まっている。鋼板強度は添加する合金元素の添加量を増加させることにより達成することができるが、合金元素の増加は一般に溶接施工時の耐溶接割れ性を低下させる。このため、合金元素の添加量を増加させることなく高強度を得ることができる化学組成を有する鋼材およびその製造法について、種々の検討がなされてきた。   As the performance and size of structures increase, the importance of developing high-strength steel sheets is increasing. The strength of the steel sheet can be achieved by increasing the amount of the alloying element to be added. However, the increase in the alloying element generally reduces the weld crack resistance during welding. For this reason, various investigations have been made on steel materials having a chemical composition capable of obtaining high strength without increasing the amount of alloying elements added and methods for producing the same.

たとえば、0.0003〜0.0025%程度の微量のB添加により、鋼の焼入性が著しく向上することから、耐溶接割れ性の極端な劣化を生じさせることなく、780MPa(780N/mm)以上の引張強さを有する高張力鋼を製造できることが明らかにされている。 For example, the addition of a small amount of B of about 0.0003 to 0.0025% significantly improves the hardenability of the steel, so that 780 MPa (780 N / mm 2) is obtained without causing extreme deterioration of the weld crack resistance. It has been clarified that high strength steel having the above tensile strength can be produced.

例えば、下記の特許文献1にはB含有鋼に関して圧延終了温度温度を上げて焼入性を高めるものが、特許文献2にはB含有鋼に関して化学組成をMn、Cr、Mo、N、Ti、Zr、Hf含有率からなる式で規定するものが、特許文献3にはB含有鋼に関して化学成分をNb、V含有率からなる式で規定するものが、そして、特許文献4にはB含有鋼に関してB炭窒化物の含有量上限を規定するものが、それぞれ、開示されている。   For example, Patent Document 1 listed below increases the rolling end temperature for B-containing steel to improve hardenability, and Patent Document 2 describes the chemical composition of B-containing steel with Mn, Cr, Mo, N, Ti, What is defined by the formula consisting of the Zr and Hf contents is Patent Document 3 that specifies the chemical composition of the B-containing steel by the formula consisting of Nb and V contents, and Patent Document 4 is the B-containing steel. Each of those specifying the upper limit of the content of B carbonitride is disclosed.

また、特許文献5には化学組成をMn、Ni、Cu、Mo、Nb、V含有率からなる式で規定するものが、そして、特許文献6には化学組成をC、Mn、Cu、Ni含有率からなる式で規定するものが、それぞれ、開示されている。   Patent Document 5 defines the chemical composition by a formula comprising Mn, Ni, Cu, Mo, Nb, and V contents, and Patent Document 6 includes the chemical composition containing C, Mn, Cu, and Ni. Each of those defined by a formula consisting of a rate is disclosed.

特開平9-256049号公報Japanese Patent Laid-Open No. 9-256049 特開2000-160281号公報Japanese Unexamined Patent Publication No. 2000-160281 特開2003-160833号公報Japanese Patent Laid-Open No. 2003-160833 特開2004-156095号公報Japanese Patent Laid-Open No. 2004-156095 特開2004-323917号公報JP 2004-323917 特開2004-312916号公報Japanese Patent Laid-Open No. 2004-312916

しかしながら、上述した特許文献で開示されている高張力鋼は、いずれも合金元素の添加量を減らして焼入性を減少させた場合に、溶接継手強度に及ぼす影響についての配慮がない。   However, any of the high-tensile steels disclosed in the above-mentioned patent documents has no consideration on the effect on weld joint strength when the addition amount of alloy elements is reduced to reduce the hardenability.

さらに、特許文献1では未再結晶域の圧下による組織微細化による靭性向上が不十分である。特許文献2では焼入性に有効なCu、Niへの配慮が不十分である。特許文献4ではB炭窒化物の含有量を抑制することを開示するのみであり、有効B量へ掘り下げての検討がなされていない。そして、特許文献5および6では、CuおよびNiへの依存度が高いため、コスト高となる。   Furthermore, in Patent Document 1, the improvement in toughness due to the refinement of the structure due to the reduction of the unrecrystallized region is insufficient. In Patent Document 2, consideration for Cu and Ni effective for hardenability is insufficient. Patent Document 4 only discloses that the content of B carbonitride is suppressed, and no investigation has been made to dig into the effective B amount. And in patent document 5 and 6, since the dependence to Cu and Ni is high, it becomes high cost.

本発明の目的は、高価な合金元素の添加量を抑制し、安定かつ大量に生産することが可能であり、そして、優れた母材特性と耐溶接割れ感受性を備えるとともに、良好な溶接継手特性を示す、780MPa以上の引張強さを有する高張力鋼の製造方法を提供することにある。
The object of the present invention is to suppress the amount of expensive alloy elements added, enable stable and large-scale production, and have excellent base material characteristics and resistance to weld cracking, as well as good weld joint characteristics. An object of the present invention is to provide a method for producing a high-tensile steel having a tensile strength of 780 MPa or more.

本発明者らは、高張力鋼の母材特性と耐溶接割れ性を劣化させることなく、溶接熱影響部靭性を向上させる方法について、合金成分および製造方法を含めた種々の観点から、鋭意研究を行った。   The present inventors have intensively studied from various viewpoints including alloy components and production methods on the method of improving the weld heat affected zone toughness without degrading the base metal properties and weld crack resistance of high-strength steel. Went.

まず、780MPa以上の引張強さを有する高張力鋼の合金元素の種類とその含有量を種々に変化させて、溶接入熱量40kJ/cmの多層溶接を行い、その溶接継手部の靭性、強度及び断面硬度を調査した。その結果、溶接部において靭性が最も低下するのは溶融線近傍であった。また、溶融線近傍では硬度が大きく低下していた。そして、硬度の低下が著しい、または硬度の低下域が広い場合には、得られる溶接継手は780MPaを下回る引張強さであった。これは、溶融線近傍では焼入性が低下し、強度及び靭性に劣る上部ベイナイト組織が生成するためであると思われる。   First, various types of alloy elements of high-strength steel having a tensile strength of 780 MPa or more and the content thereof are changed, and multilayer welding with a welding heat input of 40 kJ / cm is performed. The toughness, strength, and The cross-sectional hardness was investigated. As a result, it was in the vicinity of the melting line that the toughness was most reduced in the weld zone. Further, the hardness was greatly reduced in the vicinity of the melting line. And when the fall of hardness was remarkable or the fall range of hardness was wide, the obtained welded joint was the tensile strength less than 780 Mpa. This is presumably because hardenability decreases in the vicinity of the melting line, and an upper bainite structure inferior in strength and toughness is generated.

次に、含有量を変化させた合金元素の種類とその含有量及び溶接継手部の特性の関係を鋭意調査した結果、溶融線近傍での焼入性の低下を抑制し、優れた溶接継手特性を得るためには、焼入性の指数である焼入性指数DIを高めることに加えて、Nb添加量および有効B量を調整することで、所望の引張強さ及び溶接継手引張強さを得ることができ、さらに、C量、S量及びNb量を調整することで所望の溶接継手靭性を得ることができるとの知見を得た。   Next, as a result of intensive investigations on the relationship between the type of alloy element whose content was changed, its content, and the characteristics of the welded joint, it was possible to suppress the deterioration of hardenability near the melting line and to achieve excellent welded joint properties. In order to obtain the desired tensile strength and weld joint tensile strength by adjusting the Nb addition amount and the effective B amount in addition to increasing the hardenability index DI, which is an index of hardenability. Further, it was found that the desired weld joint toughness can be obtained by adjusting the amount of C, S and Nb.

すなわち、(a) 焼入性指数DIを高めることに加え、適量のNbを添加し、有効B量を確保することで、母材強度が高まる。(b) 焼入性指数DIを高めることに加え、適量のNbを添加することで、継手引張強度が高まる。(c) 焼入性指数DIを高めることに加え、C量及びS量を抑制し、Nb量を調整することで、溶融線位置での靭性が高まる。   That is, (a) In addition to increasing the hardenability index DI, adding an appropriate amount of Nb and securing an effective B amount increases the strength of the base material. (b) In addition to increasing the hardenability index DI, adding a suitable amount of Nb increases the joint tensile strength. (c) In addition to increasing the hardenability index DI, suppressing the C content and S content and adjusting the Nb content increases the toughness at the position of the melt line.

ここで、これらの知見を、それぞれ詳細に考察してみる。   Let us now consider each of these findings in detail.

(a) 焼入性指数DIを高めることに加え、適量のNbを添加し、有効B量を確保することで、母材強度が高まることについて
焼入性指数DIは理想臨界直径の近似式の一つでありこれを高めることにより、熱間圧延後の直接焼入れにおいて焼入性を高める。Nbは特に熱間圧延後の直接焼入れにおいて変態点を下げ、焼入性を高める効果があり、焼入性指数DIが不足する場合にこれを補うことが出来る。なお、有効BとはNと結合していない固溶Bを指しており、熱間圧延後の直接焼入れにおける焼入性の向上に有効である。
(a) In addition to increasing the hardenability index DI, adding an appropriate amount of Nb and securing the effective B amount increases the strength of the base metal. The hardenability index DI is an approximation of the ideal critical diameter. By increasing this, it is possible to improve the hardenability in direct quenching after hot rolling. Nb has the effect of lowering the transformation point and improving hardenability, particularly in direct quenching after hot rolling, and this can be compensated when the hardenability index DI is insufficient. Effective B refers to solid solution B that is not bonded to N, and is effective in improving the hardenability in direct quenching after hot rolling.

(b) 焼入性指数DIを高めることに加え、適量のNbを添加することで、継手引張強度が高まることについて
焼入性指数DIとNbについては、母材強度に関して述べた効果に加え、下記の作用がある。
(b) In addition to increasing the hardenability index DI, adding an appropriate amount of Nb increases the joint tensile strength. For the hardenability index DI and Nb, in addition to the effects described for the base metal strength, Has the following effects.

焼入性指数DIを高めることにより、溶融線や溶接熱影響部で比較的冷却速度の小さい場合にも焼入性向上に有効である。Nbは回復・再結晶遅滞効果により溶接熱影響部の軟化抵抗を高めるのに有効であり、焼入性指数DIが不足する場合にこれを補うことができる。   Increasing the hardenability index DI is effective in improving the hardenability even when the cooling rate is relatively low in the melted line or weld heat affected zone. Nb is effective in increasing the softening resistance of the weld heat affected zone by the recovery / recrystallization delay effect, and can compensate for the lack of the hardenability index DI.

(c) 焼入性指数DIを高めることに加え、C量及びS量を抑制し、Nb量を調整することで、溶融線位置での靭性が高まることについて
継手引張強度の向上の場合と同じく、焼入性指数DIを高め焼入性を高めることで、靭性の劣化を抑制することができる。C、Sは靭性を劣化させる元素であり、特に溶融線位置での靭性を高めるためには、C量、S量を抑制するのがよい。Nbは回復・再結晶遅滞効果により、結晶粒が粗大化し靭性が劣化することを抑制する効果があるが、過剰な添加は結晶粒界へ炭化物として析出し靭性を劣化させるため、適宜添加量を調整するのがよい。ここで有効Bによる焼入性向上が有効でないのは、溶融線では溶接時にTiNの再固溶が起こり、その結果、有効Bが喪失され焼入性が低下するためである。
(c) In addition to increasing the hardenability index DI, suppressing the amount of C and S and adjusting the amount of Nb to increase the toughness at the position of the melt line is the same as in the case of improving the joint tensile strength The deterioration of toughness can be suppressed by increasing the hardenability index DI and increasing the hardenability. C and S are elements that deteriorate toughness. In particular, in order to increase toughness at the position of the melting line, it is preferable to suppress the amounts of C and S. Nb has the effect of suppressing coarsening and deterioration of toughness due to the recovery and recrystallization delay effect, but excessive addition precipitates as carbide on the grain boundary and deteriorates toughness. It is good to adjust. Here, the reason why the hardenability improvement by the effective B is not effective is that TiN is re-dissolved during welding in the melting line, and as a result, the effective B is lost and the hardenability is lowered.

本発明は、これらの知見に基づいて、完成したものであるが、その目標特性は780MPa以上の引張強さを有する高張力鋼である。具体的には、鋼材の1/4板厚位置から圧延方向に平行に採取した2mmVノッチシャルピー衝撃試験片による-20℃でのシャルピー吸収エネルギーが70J以上、溶接入熱量40kJ/cmの多層突き合わせ溶接を行って得た継手から採取した、JIS Z 3121に規定される1号引張試験片による継手引張強さが780MPa以上、継手の1/4板厚から2mmVノッチシャルピー衝撃試験片をそのノッチ位置を溶融線に合わせて採取して得た0℃でのシャルピー吸収エネルギーが70J以上とした。   The present invention has been completed based on these findings, but the target characteristic is a high-tensile steel having a tensile strength of 780 MPa or more. Specifically, multilayer butt welding with a Charpy absorbed energy at -20 ° C of 70 J or more and a welding heat input of 40 kJ / cm using a 2 mm V-notch Charpy impact test specimen taken in parallel to the rolling direction from a 1/4 thickness position of steel. The joint tensile strength of the No. 1 tensile test piece specified in JIS Z 3121, taken from the joint obtained by JIS Z 3121, is 780 MPa or more. The Charpy absorbed energy at 0 ° C. obtained by sampling according to the melting line was 70 J or more.

そして、後述するとおり、この目標特性を有する高張力鋼は、質量%で、C:0.03〜0.1%、Si:0.5%以下、Mn:0.4〜2.5%、P:0.03%以下、S:0.008%以下、Cr:0.1〜2%、Nb:0.005〜0.06%、Ti:0.005〜0.03%、B:0.0003〜0.0025%、Al:0.005〜0.08%、N:0.006%以下並びに残部Feおよび不純物を含有し、溶接割れ感受性を示す指数である溶接割れ感受性指数Pcmが0.23以下であり、かつ、次の(1)式〜(3)式のいずれをも満足させることによって得られることが分かった。
680×Nb(%)+12000×[B(%)−10.8/14.1×(N(%)−Ti(%)/3.4)]+DI≧82・・・(1)式
3390×Nb(%)+DI≧125・・・(2)式
5800×C(%)+76400×S(%)+3190×|Nb(%)−0.013|−DI≦410・・・(3)式
ただし、(1)式の計算に際して、(N(%)−Ti(%)/3.4)の数値が負となる場合にはその負の値ではなくゼロを代入し、そして、[B(%)−10.8/14.1×(N(%)−Ti(%)/3.4)]の数値が負となる場合にはその負の値ではなくゼロを代入する。
And as will be described later, the high-tensile steel having this target property is in mass%, C: 0.03 to 0.1%, Si: 0.5% or less, Mn: 0.4 to 2.5%, P: 0.03% or less, S: 0.008% or less, Cr: 0.1-2%, Nb: 0.005-0.06%, Ti: 0.005-0.03%, B: 0 .0003 to 0.0025%, Al: 0.005 to 0.08%, N: 0.006% or less, and the balance Fe and impurities are included, and the weld crack sensitivity index Pcm, which is an index indicating weld crack sensitivity, is 0. It was found that it was obtained by satisfying any of the following formulas (1) to (3).
680 × Nb (%) + 12000 × [B (%)-10.8 / 14.1 × (N (%) − Ti (%) / 3.4)] + DI ≧ 82 (1)
3390 × Nb (%) + DI ≧ 125 (2) formula
5800 × C (%) + 76400 × S (%) + 3190 × | Nb (%) − 0.013 | −DI ≦ 410 (3) However, when calculating (1), (N (%) − Ti If the value of (%) / 3.4) is negative, substitute zero instead of the negative value, and [B (%)-10.8 / 14.1 × (N (%)-Ti (%) / 3.4 If the value of]) is negative, substitute zero instead of the negative value.

なお、DIとPcmはそれぞれ、次の(4)式および(5)式で定義される。
DI=0.311×√C(%)×[1+0.64×Si(%)]×[1+4.1×Mn(%)]×[1+0.27Cu(%)]×[1+0.52×Ni(%)]×[1+2.33×Cr(%)]×[1+3.14×Mo(%)]×25.4・・・(4)式
Pcm=C(%)+Si(%)/30+Mn(%)/20+Cu(%)/20+Ni(%)/60+Cr(%)/20+Mo(%)/15+V(%)/10+5×B(%)・・・(5)式
また、(1)式〜(5)式の中の各元素記号(%)は各元素の含有量(質量%)を示す。
DI and Pcm are defined by the following equations (4) and (5), respectively.
DI = 0.311 x √C (%) x [1 + 0.64 x Si (%)] x [1 + 4.1 x Mn (%)] x [1 + 0.27 Cu (%)] x [1 + 0.52 x Ni (%) ] X [1 + 2.33 x Cr (%)] x [1 + 3.14 x Mo (%)] x 25.4 (4)
Pcm = C (%) + Si (%) / 30 + Mn (%) / 20 + Cu (%) / 20 + Ni (%) / 60 + Cr (%) / 20 + Mo (%) / 15 + V (%) / 10 + 5 × B (%) (5) Formula Moreover, each element symbol (%) in Formula (1)-Formula (5) shows content (mass%) of each element.

なお、この高張力鋼は、質量%で、さらに、Ni:2%以下、Cu:0.6%以下、Zr:0.05%以下、Mo:1%以下、V:0.1%以下、Ca:0.004%以下、Mg:0.002%以下およびREM:0.002%以下のうちの1種又は2種以上の成分を含有してもよい。   In addition, this high-tensile steel is mass%, and further, Ni: 2% or less, Cu: 0.6% or less, Zr: 0.05% or less, Mo: 1% or less, V: 0.1% or less, One or more components of Ca: 0.004% or less, Mg: 0.002% or less, and REM: 0.002% or less may be contained.

次に、この目標特性を有する高張力鋼は、上記の化学組成を有する鋼片を、1000〜1200℃に加熱し、900℃以下の温度域での累積圧下率が50%以上となるように熱間圧延した後熱間多段拘束ローラにて平坦矯正を行って直ちに急冷し、表面温度が300℃以下に達した時点で急冷を停止し、以後室温まで放冷することによって、製造することができる。あるいは、室温まで放冷した後、さらに600℃以下の温度で焼戻してもよい。焼入性指数DIを高めることに加えて、含有成分を調整した鋼片を用い、一定の条件下において熱間圧延後、焼入れを行うことで組織制御を行い、必要な引張強度を得ることができる。   Next, in the high-tensile steel having this target characteristic, the steel slab having the above chemical composition is heated to 1000 to 1200 ° C. so that the cumulative rolling reduction in the temperature range of 900 ° C. or less is 50% or more. After hot rolling, flattening is performed with a hot multistage constraining roller and immediately cooled rapidly. When the surface temperature reaches 300 ° C. or lower, the rapid cooling is stopped, and then the product is allowed to cool to room temperature. it can. Or after standing to cool to room temperature, you may further temper at the temperature of 600 degrees C or less. In addition to increasing the hardenability index DI, using steel slabs with adjusted ingredients, it is possible to obtain the necessary tensile strength by controlling the structure by performing quenching after hot rolling under certain conditions. it can.

本発明は、これらの知見に基づいて、完成したものであり、その要旨は次の(1)〜(6)の780MPa以上の引張強度を有する高張力鋼の製造方法にある。
The present invention has been completed based on these findings. The gist of the present invention is the following (1) to (6) of a method for producing a high-strength steel having a tensile strength of 780 MPa or more.

(1)質量%で、C:0.03〜0.1%、Si:0.5%以下、Mn:0.4〜2.5%、P:0.03%以下、S:0.008%以下、Cr:0.1〜2%、Nb:0.005〜0.06%、Ti:0.005〜0.03%、B:0.0003〜0.0025%、Al:0.005〜0.08%、N:0.006%以下残部Feおよび不純物を含有し、溶接割れ感受性指数Pcmが0.23以下であり、かつ次の(1)式〜(3)式のいずれをも満足する化学組成の鋼片を、1000〜1200℃に加熱し、900℃以下の温度域での累積圧下率が50%以上となるように熱間圧延した後熱間多段拘束ローラにて平坦矯正を行って直ちに急冷し、表面温度が300℃以下に達した時点で急冷を停止し、以後室温まで放冷することを特徴とする、780MPa以上の引張強度を有する高張力鋼の製造方法。
680×Nb(%)+12000×[B(%)−10.8/14.1×(N(%)−Ti(%)/3.4)]+DI≧82・・・(1)式
3390×Nb(%)+DI≧125・・・(2)式
5800×C(%)+76400×S(%)+3190×|Nb(%)−0.013|−DI≦410・・・(3)式
ただし、(1)式の計算に際して、(N(%)−Ti(%)/3.4)の数値が負となる場合にはその負の値ではなくゼロを代入し、そして、[B(%)−10.8/14.1×(N(%)−Ti(%)/3.4)]の数値が負となる場合にはその負の値ではなくゼロを代入する。
なお、DIとPcmはそれぞれ、次の(4)式および(5)式で定義される。
DI=0.311×√C(%)×[1+0.64×Si(%)]×[1+4.1×Mn(%)]×[1+0.27Cu(%)]×[1+0.52×Ni(%)]×[1+2.33×Cr(%)]×[1+3.14×Mo(%)]×25.4・・・(4)式
Pcm=C(%)+Si(%)/30+Mn(%)/20+Cu(%)/20+Ni(%)/60+Cr(%)/20+Mo(%)/15+V(%)/10+5×B(%)・・・(5)式
また、(1)式〜(5)式の中の各元素記号(%)は各元素の含有量(質量%)を示す。
(1) By mass%, C: 0.03-0.1%, Si: 0.5% or less, Mn: 0.4-2.5%, P: 0.03% or less, S: 0.008 %: Cr: 0.1-2%, Nb: 0.005-0.06%, Ti: 0.005-0.03%, B: 0.0003-0.0025%, Al: 0.005 ~ 0.08%, N: 0.006% or less Remaining Fe and impurities are included, weld cracking sensitivity index Pcm is 0.23 or less, and any of the following formulas (1) to (3) Steel strip with a satisfactory chemical composition is heated to 1000-1200 ° C, hot-rolled so that the cumulative reduction in the temperature range of 900 ° C or lower is 50% or more, and then flattened with a hot multistage constraining roller , Immediately quenching, stopping rapid cooling when the surface temperature reaches 300 ° C. or lower, and then allowing to cool to room temperature, 780 Method for producing a high tensile steel having a tensile strength of at least Pa.
680 × Nb (%) + 12000 × [B (%)-10.8 / 14.1 × (N (%) − Ti (%) / 3.4)] + DI ≧ 82 (1)
3390 × Nb (%) + DI ≧ 125 (2) formula
5800 × C (%) + 76400 × S (%) + 3190 × | Nb (%) − 0.013 | −DI ≦ 410 (3) However, when calculating (1), (N (%) − Ti If the value of (%) / 3.4) is negative, substitute zero instead of the negative value, and [B (%)-10.8 / 14.1 × (N (%)-Ti (%) / 3.4 If the value of]) is negative, substitute zero instead of the negative value.
DI and Pcm are defined by the following equations (4) and (5), respectively.
DI = 0.311 x √C (%) x [1 + 0.64 x Si (%)] x [1 + 4.1 x Mn (%)] x [1 + 0.27 Cu (%)] x [1 + 0.52 x Ni (%) ] X [1 + 2.33 x Cr (%)] x [1 + 3.14 x Mo (%)] x 25.4 (4)
Pcm = C (%) + Si (%) / 30 + Mn (%) / 20 + Cu (%) / 20 + Ni (%) / 60 + Cr (%) / 20 + Mo (%) / 15 + V (%) / 10 + 5 × B (%) (5) Formula Moreover, each element symbol (%) in Formula (1)-Formula (5) shows content (mass%) of each element.

(2)上記(1)に規定する成分に加えて、質量%で、さらにNi:2%以下を含有する鋼片を用いることを特徴とする、上記(1)の780MPa以上の引張強度を有する高張力鋼の製造方法。   (2) In addition to the component specified in (1) above, a steel piece containing Ni: 2% or less in mass% is used, and the tensile strength of 780 MPa or more of (1) above is used. Manufacturing method of high-strength steel.

(3)上記(1)または(2)に規定する成分に加えて、質量%で、さらにCu:0.6%以下およびZr:0.05%以下のうちの1種又は2種の成分を含有する鋼片を用いることを特徴とする、上記(1)または(2)の780MPa以上の引張強度を有する高張力鋼の製造方法。   (3) In addition to the component specified in the above (1) or (2), by mass%, further, one or two of Cu: 0.6% or less and Zr: 0.05% or less A method for producing high-tensile steel having a tensile strength of 780 MPa or more as described in (1) or (2) above, wherein the steel piece is contained.

(4)上記(1)〜(3)のいずれかに規定する成分に加えて、質量%で、さらにMo:1%以下およびV:0.1%以下のうちの1種又は2種の成分を含有する鋼片を用いることを特徴とする、上記(1)〜(3)のいずれかの780MPa以上の引張強度を有する高張力鋼の製造方法。   (4) In addition to the component specified in any one of the above (1) to (3), in mass%, Mo: 1% or less and V: 0.1% or less of one or two components A method for producing a high-tensile steel having a tensile strength of 780 MPa or more according to any one of the above (1) to (3), characterized by using a steel slab containing bismuth.

(5)上記(1)〜(4)のいずれかに規定する成分に加えて、質量%で、さらにCa:0.004%以下、Mg:0.002%以下およびREM:0.002%以下のうちの1種又は2種以上の成分を含有する鋼片を用いることを特徴とする、上記(1)〜(4)のいずれかの780MPa以上の引張強度を有する高張力鋼の製造方法。   (5) In addition to the components specified in any one of (1) to (4) above, in mass%, Ca: 0.004% or less, Mg: 0.002% or less, and REM: 0.002% or less A method for producing a high-strength steel having a tensile strength of 780 MPa or more according to any one of (1) to (4), wherein a steel piece containing one or more components is used.

(6)室温まで放冷した後、さらに600℃以下の温度で焼戻すことを特徴とする、上記(1)〜(5)のいずれかの780MPa以上の引張強度を有する高張力鋼の製造方法。   (6) The method for producing high-tensile steel having a tensile strength of 780 MPa or more according to any one of (1) to (5) above, wherein the steel is allowed to cool to room temperature and then tempered at a temperature of 600 ° C. or lower. .

本発明によれば、優れた母材特性と耐溶接割れ感受性を備えるとともに、良好な溶接継手特性を示す、780MPa以上の引張強さを有する高張力鋼を、高価な合金元素の添加量を抑制して、安定かつ大量に生産することが可能となる。   According to the present invention, a high strength steel having a tensile strength of 780 MPa or more, which has excellent base material characteristics and resistance to weld cracking, and exhibits good weld joint characteristics, suppresses the addition amount of expensive alloy elements. Thus, stable and mass production is possible.

(A)高張力鋼の化学組成について
以下に、本発明に係る高張力鋼の各化学組成およびそれぞれの含有量並びにPcmおよび(1)式〜(3)式の規定理由をその作用効果とともに説明する。なお、含有量に関する「%」は「質量%」を意味する。
(A) Chemical composition of high-strength steel Below, the chemical composition and content of the high-strength steel according to the present invention, Pcm, and the reasons for defining the expressions (1) to (3) are explained together with their effects. To do. In addition, "%" regarding content means "mass%".

C:0.03〜0.1%
Cは、鋼板の強度を確保する目的で添加する。その含有量が0.03%未満では焼入性が不足して所望の780MPaの引張強度(TS)を確保するのが困難であり、また靱性も劣化する。TSが780MPa以上、2mmVノッチシャルピー衝撃試験片を用いた-20℃での衝撃試験における吸収エネルギーが70J以上という、強度と靱性を確保する上で、Cは0.03%以上含有させることが必要である。一方、その含有量が0.1%を超えると、母材の靱性が低下するだけでなく、溶接熱影響部の硬度が上昇して溶接割れ感受性が高くなる。したがって、Cの含有量を0.03〜0.1%とした。なお、C含有量の上限は0.07%とすることが望ましい。また、C含有量の下限は0.05%とすることが望ましい。
C: 0.03-0.1%
C is added for the purpose of securing the strength of the steel sheet. If the content is less than 0.03%, hardenability is insufficient, and it is difficult to secure a desired tensile strength (TS) of 780 MPa, and toughness is also deteriorated. In order to secure strength and toughness with TS of 780 MPa or more and absorbed energy of 70 J or more in an impact test at −20 ° C. using a 2 mm V notch Charpy impact test piece, C needs to be contained by 0.03% or more. It is. On the other hand, if the content exceeds 0.1%, not only the toughness of the base material is lowered, but also the hardness of the weld heat affected zone is increased, and the weld crack sensitivity is increased. Therefore, the content of C is set to 0.03 to 0.1%. Note that the upper limit of the C content is preferably 0.07%. The lower limit of the C content is desirably 0.05%.

Si:0.5%以下
Siは添加しなくてもよい。ただし、添加すれば鋼を脱酸する効果がある。しかし、その含有量が0.5%を超えると、母材及び溶接熱影響部の硬度を著しく上昇させる島状マルテンサイトの局所的な生成を誘発して靱性の劣化を招く。したがって、Siの含有量の上限を0.5%とする必要がある。Si含有量の上限は0.3%とすることが望ましい。なお、この効果を確実に得るには、Siは0.01%以上の含有量とすることが好ましい。より好ましくは、0.03%以上である。
Si: 0.5% or less Si may not be added. However, if added, it has the effect of deoxidizing the steel. However, when its content exceeds 0.5%, local formation of island martensite that significantly increases the hardness of the base metal and the weld heat affected zone is induced, leading to deterioration of toughness. Therefore, the upper limit of the Si content needs to be 0.5%. The upper limit of the Si content is desirably 0.3%. In addition, in order to acquire this effect reliably, it is preferable to make Si content 0.01% or more. More preferably, it is 0.03% or more.

Mn:0.4〜2.5%
Mnは、鋼板の焼入性を向上させ、強度を高めるために添加する元素であり、その含有量が0.4%未満では所望の強度を確保することが困難となる。一方、2.5%を超えて含有させると、溶接低温割れの発生頻度が高くなる。したがって、Mnの含有量を0.4〜2.5%とした。なお、Mnの含有量は0.7〜2%とすることが好ましい。
Mn: 0.4 to 2.5%
Mn is an element added to improve the hardenability of the steel sheet and increase the strength. If the content is less than 0.4%, it is difficult to ensure the desired strength. On the other hand, if the content exceeds 2.5%, the frequency of occurrence of welding cold cracks increases. Therefore, the Mn content is set to 0.4 to 2.5%. The Mn content is preferably 0.7-2%.

P:0.03%以下
Pは、不純物として鋼中に不可避的に存在する。0.03%を超えると、粒界に偏析して靭性を低下させるのみならず、溶接時に高温割れを招くため0.03%以下とする必要がある。
P: 0.03% or less P is unavoidably present in steel as an impurity. If it exceeds 0.03%, not only does it segregate at the grain boundary to lower the toughness, but also cause hot cracking during welding, so it is necessary to make it 0.03% or less.

S:0.008%以下
Sは、不純物として鋼中に不可避的に存在する。多すぎると中心偏析を助長したり、延伸したMnSが多量に生成したりするため、母材およびHAZの機械的性質が劣化する。このため、上限を0.008%とする。Sは少ないほど好ましいため、下限は特に規定するものではない。
S: 0.008% or less S is unavoidably present in steel as an impurity. If the amount is too large, center segregation is promoted or stretched MnS is produced in a large amount, so that the mechanical properties of the base material and the HAZ are deteriorated. For this reason, the upper limit is made 0.008%. Since the smaller S is, the lower limit is not particularly specified.

Cr:0.1〜2%
Crは、主として焼入性の向上を通じて鋼板の強度を高める作用を有する。この効果を得るためには、Crは0.1%以上の含有量とする必要がある。しかし、その含有量が2%を超えると母材靱性や溶接性の劣化を招く。したがって、Crの含有量を0.1〜2%とした。
Cr: 0.1 to 2%
Cr has the effect of increasing the strength of the steel sheet mainly through improving hardenability. In order to acquire this effect, it is necessary to make Cr content 0.1% or more. However, if the content exceeds 2%, the base metal toughness and weldability are deteriorated. Therefore, the content of Cr is set to 0.1 to 2%.

Nb:0.005〜0.06%
Nbは、オーステナイトの低温域で微細なNb炭窒化物を形成することによりオーステナイト粒を微細化する。更に、析出したNb炭窒化物は圧延によって加工を受けた未再結晶オーステナイト粒の回復、再結晶を抑制する効果を有しており、母材靱性の確保に有効である。その含有量が0.005%未満ではこれらの効果が十分に得られない。一方、0.06%を超えて含有させると、溶接時の割れ性が劣化してしまうので、Nbの含有量の上限は0.06%とする必要がある。Nb含有量の上限は0.03%とすることが望ましい。したがって、Nbの含有量を0.005〜0.06%とした。
Nb: 0.005 to 0.06%
Nb refines austenite grains by forming fine Nb carbonitrides in the low temperature region of austenite. Further, the precipitated Nb carbonitride has an effect of suppressing the recovery and recrystallization of unrecrystallized austenite grains that have been processed by rolling, and is effective in securing the base material toughness. If the content is less than 0.005%, these effects cannot be obtained sufficiently. On the other hand, if the content exceeds 0.06%, the cracking property during welding deteriorates, so the upper limit of the Nb content needs to be 0.06%. The upper limit of the Nb content is preferably 0.03%. Therefore, the Nb content is set to 0.005 to 0.06%.

Ti:0.005〜0.03%
Tiは、オーステナイト粒の微細化、固溶Nの固定による有効B量確保のために不可欠な元素である。また、連続鋳造鋳片の横ひび割れを防止する上でもその添加が不可欠である。しかし、その含有量が0.005%未満では添加効果が不十分となる。一方、0.03%を超えて含有させると、母材靱性や溶接熱影響部の靱性が著しく損なわれる。したがって、Tiの含有量を0.005〜0.03%とした。
Ti: 0.005 to 0.03%
Ti is an indispensable element for securing an effective B amount by refining austenite grains and fixing solute N. Moreover, the addition is indispensable also in preventing the lateral crack of a continuous cast slab. However, if the content is less than 0.005%, the effect of addition becomes insufficient. On the other hand, if the content exceeds 0.03%, the base material toughness and the toughness of the weld heat affected zone are significantly impaired. Therefore, the content of Ti is set to 0.005 to 0.03%.

B:0.0003〜0.0025%
Bは、鋼に微量固溶することで焼入性を向上させるので、板厚中心部まで十分な強度を確保することが可能になる。しかし、その含有量が0.0003%未満ではこの効果が十分には得られず、0.0025%を超えると母材靱性及び溶接熱影響部靱性の大幅な劣化を招く。したがって、Bの含有量を0.0003〜0.0025%とした。
B: 0.0003 to 0.0025%
Since B improves hardenability by dissolving in a small amount in steel, it is possible to ensure sufficient strength up to the center of the plate thickness. However, if the content is less than 0.0003%, this effect cannot be sufficiently obtained, and if it exceeds 0.0025%, the base material toughness and the weld heat affected zone toughness are significantly deteriorated. Therefore, the content of B is set to 0.0003 to 0.0025%.

Al:0.005〜0.08%
Alは脱酸及び組織微細化の作用を有する。この効果を得るためには、Alは0.005%以上の含有量とする必要がある。しかし、その含有量が0.08%を超えると溶接熱影響部の靱性が劣化することに加えて、熱処理を行って組織を微細化させても靱性の低下を招く。したがって、Alの含有量を0.005〜0.08%とした。なお、Alの含有量は0.03〜0.06%とすることが望ましい。ここで、本発明でいう「Al」量とは、いわゆる「sol.Al(酸可溶Al)」量を指す。
Al: 0.005 to 0.08%
Al has an action of deoxidation and fine structure. In order to acquire this effect, it is necessary to make Al content 0.005% or more. However, if its content exceeds 0.08%, the toughness of the weld heat-affected zone deteriorates, and even if the structure is refined by heat treatment, the toughness is reduced. Therefore, the content of Al is set to 0.005 to 0.08%. The Al content is preferably 0.03 to 0.06%. Here, the “Al” amount in the present invention refers to a so-called “sol.Al (acid-soluble Al)” amount.

N:0.006%以下
Nは鋼中に不可避的不純物として存在し、母材及び溶接熱影響部の靱性を低下させてしまう。特にその含有量が0.006%を超えると、母材及び溶接熱影響部の靱性低下が著しい。したがって、Nの含有量を0.006%以下とした。
N: 0.006% or less N is present as an inevitable impurity in steel, and reduces the toughness of the base metal and the weld heat affected zone. In particular, when the content exceeds 0.006%, the toughness of the base metal and the weld heat affected zone is significantly reduced. Therefore, the N content is set to 0.006% or less.

Pcm:0.23%以下
Pcmは、溶接割れ感受性を示す指数であり、(5)式で示される。この値が低いほど、溶接予熱温度を低くして割れを生じさせることなく溶接を行うことができる。一般に、鉄骨建築構造物の施工現場での溶接による組立の際に、予熱処理を行うことは実際上不可能である。Pcmを0.23%以下に抑えておけば、予熱なしでも溶接割れを生じさせることなく溶接することができる。
Pcm=C(%)+Si(%)/30+Mn(%)/20+Cu(%)/20+Ni(%)/60+Cr(%)/20+Mo(%)/15+V(%)/10+5×B(%)・・・(5)式
なお、(5)式中の各元素記号(%)は各元素の含有量(質量%)を示す。
Pcm: 0.23% or less
Pcm is an index indicating weld cracking sensitivity and is expressed by equation (5). The lower this value is, the lower the welding preheating temperature is, and welding can be performed without causing cracks. In general, it is practically impossible to perform preheating when assembling a steel building structure by welding at a construction site. If Pcm is suppressed to 0.23% or less, welding can be performed without causing weld cracking even without preheating.
Pcm = C (%) + Si (%) / 30 + Mn (%) / 20 + Cu (%) / 20 + Ni (%) / 60 + Cr (%) / 20 + Mo (%) / 15 + V (%) / 10 + 5 × B (%) (5) Formula In addition, each element symbol (%) in Formula (5) shows content (mass%) of each element.

(1)式: 82以上
下記に示す(1)式は、鋼材の母材強度を発現する効果について、各合金元素の寄与を総合的に調査して決定した式であり、この値が82以上のときに母材強度及び継手強度が780MPa以上となる。ここで、Bの関わる項は、B窒化物として結合していない量を算出することで有効B量を導き、これによる母材強度への寄与度を具体的に示している。
680×Nb(%)+12000×[B(%)−10.8/14.1×(N(%)−Ti(%)/3.4)]+DI≧82・・・(1)式
ただし、(1)式の計算に際して、(N(%)−Ti(%)/3.4)の数値が負となる場合にはその負の値ではなくゼロを代入し、そして、[B(%)−10.8/14.1×(N(%)−Ti(%)/3.4)]の数値が負となる場合にはその負の値ではなくゼロを代入する。
なお、(1)式中の各元素記号(%)は各元素の含有量(質量%)を示す。
Equation (1): 82 or more Equation (1) shown below is an equation determined by comprehensively investigating the contribution of each alloy element with respect to the effect of developing the strength of the base material of the steel. In this case, the base material strength and joint strength are 780 MPa or more. Here, the term related to B specifically shows the degree of contribution to the base material strength by deriving an effective amount of B by calculating the amount not bonded as B nitride.
680 x Nb (%) + 12000 x [B (%)-10.8 / 14.1 x (N (%)-Ti (%) / 3.4)] + DI ≥ 82 (1) However, calculation of formula (1) At this time, if the value of (N (%) − Ti (%) / 3.4) is negative, substitute zero instead of the negative value, and [B (%) − 10.8 / 14.1 × (N ( %) − Ti (%) / 3.4)] is negative, substitute zero instead of the negative value.
In addition, each element symbol (%) in the formula (1) indicates the content (% by mass) of each element.

(2)式: 125以上
下記に示す(2)式は、鋼材に所定の溶接を行った継手の溶接熱影響部の軟化を抑制して継手強度を発現する効果について、各合金元素の寄与を総合的に調査して決定した式であり、この値が125以上のときに母材強度及び継手強度が780MPa以上となる。
3390×Nb(%)+DI≧125・・・(2)式
ここで、DIは次の(4)式で定義される。
DI=0.311×√C(%)×[1+0.64×Si(%)]×[1+4.1×Mn(%)]×[1+0.27Cu(%)]×[1+0.52×Ni(%)]×[1+2.33×Cr(%)]×[1+3.14×Mo(%)]×25.4・・・(4)式
なお、(2)式および(4)式の中の各元素記号(%)は各元素の含有量(質量%)を示す。
Formula (2): 125 or more Formula (2) below shows the contribution of each alloying element to the effect of suppressing the softening of the weld heat affected zone of the joint that has been welded to the steel material and expressing the joint strength. The formula is determined by comprehensive investigation, and when this value is 125 or more, the base material strength and joint strength are 780 MPa or more.
3390 × Nb (%) + DI ≧ 125 (2) Formula Here, DI is defined by the following formula (4).
DI = 0.311 x √C (%) x [1 + 0.64 x Si (%)] x [1 + 4.1 x Mn (%)] x [1 + 0.27 Cu (%)] x [1 + 0.52 x Ni (%) ] X [1 + 2.33 x Cr (%)] x [1 + 3.14 x Mo (%)] x 25.4 (4) Equations (2) and (4) %) Indicates the content (mass%) of each element.

(3)式: 410以下
下記に示す(3)式は、鋼材に所定の溶接を行った継手の溶融線上より採取した2mmVノッチシャルピー衝撃試験片の0℃での衝撃吸収エネルギーについて、各合金元素の寄与を総合的に調査して決定した式であり、この値が410以下のときに衝撃吸収エネルギーが70J以上となる。
5800×C(%)+76400×S(%)+3190×|Nb(%)−0.013|−DI≦410・・・(3)式
ここで、DIは次の(4)式で定義される。
DI=0.311×√C(%)×[1+0.64×Si(%)]×[1+4.1×Mn(%)]×[1+0.27Cu(%)]×[1+0.52×Ni(%)]×[1+2.33×Cr(%)]×[1+3.14×Mo(%)]×25.4・・・(4)式
なお、(3)式および(4)式の中の各元素記号(%)は各元素の含有量(質量%)を示す。
Equation (3): 410 or less Equation (3) shown below is for each of the alloy elements in terms of impact absorption energy at 0 ° C. of a 2 mm V notch Charpy impact specimen taken from the melting line of a joint that has been welded to steel. Is determined by comprehensively investigating the contribution, and when this value is 410 or less, the impact absorption energy is 70 J or more.
5800 × C (%) + 76400 × S (%) + 3190 × | Nb (%) − 0.013 | −DI ≦ 410 (3) Here, DI is defined by the following equation (4).
DI = 0.311 x √C (%) x [1 + 0.64 x Si (%)] x [1 + 4.1 x Mn (%)] x [1 + 0.27 Cu (%)] x [1 + 0.52 x Ni (%) ] X [1 + 2.33 x Cr (%)] x [1 + 3.14 x Mo (%)] x 25.4 (4) Equations (3) and (4) %) Indicates the content (mass%) of each element.

本発明に係る高張力鋼は、必要に応じて、上記の合金成分のほか、Ni、Cu、Zr、Mo、V、Ca、MgおよびREMの中から選んだ1種以上をさらに含有してもよい。   The high-tensile steel according to the present invention may further contain one or more selected from Ni, Cu, Zr, Mo, V, Ca, Mg, and REM in addition to the above alloy components as necessary. Good.

Ni:2%以下
Niは任意添加元素である。添加すれば、溶接性や靱性を高める効果がある。したがって、これらの効果を得たい場合には、必要に応じて、Niを添加してもよい。しかし、Niは高価な元素であり、添加することによって鋼板価格の上昇を招くため、経済性の観点から、低く抑えることが好ましく、その含有量を2%以下とする。経済性の観点からは、Ni含有量の上限は0.6%とすることが望ましく、0.4%とすれば一層好ましい。なお、Niの添加効果を確実に得るためには、Niは0.1%以上の含有量とすることが好ましい。
Ni: 2% or less Ni is an optional additive element. If added, it has the effect of improving weldability and toughness. Therefore, when it is desired to obtain these effects, Ni may be added as necessary. However, since Ni is an expensive element and adding it causes an increase in the price of the steel sheet, it is preferable to keep it low from the viewpoint of economy, and its content is set to 2% or less. From the economical point of view, the upper limit of the Ni content is desirably 0.6%, more preferably 0.4%. In addition, in order to acquire the addition effect of Ni reliably, it is preferable to make content of Ni 0.1% or more.

Cu: 0.6%以下
Cuは任意添加元素である。添加すれば、焼入性を向上させて強度を高める効果がある。したがって、この効果を得たい場合には、必要に応じて、Cuを添加してもよい。しかし、その含有量が0.6%を超えると、強度上昇効果よりも靱性や溶接性を劣化させる効果の方が著しくなってしまうので、Cuの含有量の上限は0.6%とする必要がある。Cu含有量の上限は0.4%とすることが望ましい。なお、Cuの添加効果を確実に得るためには、Cuの含有量は0.15%以上とすることが望ましい。
Cu: 0.6% or less Cu is an optional additive element. If added, it has the effect of improving hardenability and increasing strength. Therefore, when it is desired to obtain this effect, Cu may be added as necessary. However, if the content exceeds 0.6%, the effect of degrading toughness and weldability becomes more significant than the effect of increasing strength, so the upper limit of the Cu content needs to be 0.6%. There is. The upper limit of the Cu content is desirably 0.4%. In addition, in order to acquire the addition effect of Cu reliably, it is desirable that content of Cu shall be 0.15% or more.

Zr: 0.05%以下
Zrは任意添加元素である。添加すれば、鋼中で微細窒化物を分散析出し、強度を向上させる効果がある。したがって、この効果を得たい場合には、必要に応じて、Zrを添加してもよい。しかし、その含有量が0.05%を超えると、粗大析出物を形成し、靭性を劣化させるので、Zrの含有量の上限は0.05%とする必要がある。なお、Zrの添加効果を確実に得るためには、Zrの含有量は0.0005%以上とすることが望ましい。
Zr: 0.05% or less Zr is an optional additive element. If added, fine nitride is dispersed and precipitated in the steel, and the strength is improved. Therefore, in order to obtain this effect, Zr may be added as necessary. However, if its content exceeds 0.05%, coarse precipitates are formed and toughness is deteriorated, so the upper limit of the Zr content needs to be 0.05%. In order to reliably obtain the effect of adding Zr, the content of Zr is preferably set to 0.0005% or more.

Mo: 1%以下
Moは任意添加元素である。添加すれば、焼入性及び焼戻し軟化抵抗を向上させる効果がある。したがって、この効果を得たい場合には、必要に応じて、Moを添加してもよい。しかし、その含有量が1%を超えると、強度が高くなりすぎて母材靱性が低下するし、溶接性の著しい劣化も招くので、Moの含有量の上限は1%とする必要がある。なお、Moの添加効果を確実に得るためには、Moの含有量は0.2%以上とすることが望ましい。
Mo: 1% or less Mo is an optional additive element. If added, there is an effect of improving hardenability and temper softening resistance. Therefore, when it is desired to obtain this effect, Mo may be added as necessary. However, if the content exceeds 1%, the strength becomes too high, the base material toughness decreases, and the weldability is significantly deteriorated. Therefore, the upper limit of the Mo content needs to be 1%. In addition, in order to acquire the addition effect of Mo reliably, it is desirable that content of Mo shall be 0.2% or more.

V:0.1%以下
Vは任意添加元素である。添加すれば、焼戻し軟化抵抗を増大させて、高温での焼戻しを可能とすることにより、強度及び靱性の向上に寄与する効果がある。したがって、この効果を得たい場合には、必要に応じて、Vを添加してもよい。しかし、その含有量が0.1%を超えると靱性が劣化するので、Vの含有量の上限は0.1%とする必要がある。Vの含有量の上限は0.05%とすることが望ましい。なお、Vの添加効果を確実に得るためには、Vの含有量は0.01%以上とすることが望ましい。
V: 0.1% or less V is an optional additive element. If added, the temper softening resistance is increased to enable tempering at a high temperature, thereby contributing to improvement of strength and toughness. Therefore, if this effect is desired, V may be added as necessary. However, since the toughness deteriorates when the content exceeds 0.1%, the upper limit of the V content needs to be 0.1%. The upper limit of the V content is preferably 0.05%. In order to surely obtain the effect of addition of V, the V content is preferably 0.01% or more.

Ca: 0.004%以下
Caは任意添加元素である。添加すれば、Caは鋼中のSと反応して溶鋼中で酸・硫化物(オキシサルファイド)を形成し、この酸・硫化物はMnSなどと異なって圧延加工で圧延方向に伸びることがなく圧延後も球状であるため、延伸した介在物の先端などを割れの起点とする溶接割れや水素誘起割れを抑制する効果がある。したがって、これらの効果を得たい場合には、必要に応じて、Caを添加してもよい。しかし、その含有量が0.004%を超えると靱性の劣化を招くことがあるので、Caの含有量の上限は0.004%とする必要がある。なお、Caの添加効果を確実に得るためには、Caの含有量は0.0005%以上とすることが望ましい。
Ca: 0.004% or less Ca is an optional additive element. If added, Ca reacts with S in the steel to form acid / sulfide (oxysulfide) in the molten steel, and this acid / sulfide does not extend in the rolling direction during rolling unlike MnS. Since it is spherical after rolling, it has the effect of suppressing weld cracks and hydrogen-induced cracks starting from the ends of the stretched inclusions. Therefore, in order to obtain these effects, Ca may be added as necessary. However, if the content exceeds 0.004%, the toughness may be deteriorated, so the upper limit of the Ca content needs to be 0.004%. In addition, in order to acquire the addition effect of Ca reliably, it is desirable to make content of Ca 0.0005% or more.

Mg: 0.002%以下
Mgは任意添加元素である。添加すれば、MgはMg含有酸化物を生成し、TiNの発生核となり、TiNを微細分散させる効果を持つ。したがって、これらの効果を得たい場合には、必要に応じて、Mgを添加してもよい。しかし、その含有量が0.002%を超えると、酸化物が多くなりすぎて延性低下をもたらすので、Mgの含有量の上限は0.002%とする必要がある。なお、Mgの添加効果を確実に得るためには、Mgの含有量は0.0005%以上とすることが望ましい。
Mg: 0.002% or less Mg is an optional additive element. When added, Mg forms an Mg-containing oxide, serves as a TiN generation nucleus, and has the effect of finely dispersing TiN. Therefore, when it is desired to obtain these effects, Mg may be added as necessary. However, if the content exceeds 0.002%, the amount of oxides increases and ductility is reduced, so the upper limit of the Mg content needs to be 0.002%. In order to reliably obtain the effect of adding Mg, the Mg content is desirably 0.0005% or more.

REM: 0.002%以下
REM(希土類元素)は任意添加元素である。添加すれば、REMは溶接熱影響部の組織の微細化や、Sの固定に寄与する効果がある。したがって、これらの効果を得たい場合には、必要に応じて、REMを添加してもよい。REMは、反面、介在物となって清浄度を低下させる作用を有するが、REMの添加によって形成される介在物は、比較的靱性劣化への影響が小さいため、0.002%以下であれば含有させても母材の靱性の低下は許容できるので、REMの含有量の上限は0.002%とする。なお、REEMの添加効果を確実に得るためには、REMの含有量は0.0005%以上とすることが望ましい。
REM: 0.002% or less REM (rare earth element) is an optional additive element. If added, REM has the effect of contributing to refinement of the structure of the weld heat affected zone and fixation of S. Therefore, when it is desired to obtain these effects, REM may be added as necessary. REM, on the other hand, has the effect of reducing the cleanliness as an inclusion, but the inclusion formed by the addition of REM has a relatively small influence on toughness deterioration. Even if it is contained, the lowering of the toughness of the base material is acceptable, so the upper limit of the content of REM is made 0.002%. In order to surely obtain the effect of adding REEM, the content of REM is preferably 0.0005% or more.

ここで、本発明でいう「REM」は、Sc、Yおよびランタノイドの合計17元素の総称であり、REMの含有量は上記元素の合計含有量を指す。   Here, “REM” as used in the present invention is a general term for a total of 17 elements of Sc, Y and lanthanoid, and the content of REM indicates the total content of the above elements.

(B)高張力鋼の製造条件について
以下に、本発明に係る高張力鋼の製造条件を上記のように規定する理由を作用効果とともに説明する。
(B) About the manufacturing conditions of high-tensile steel Below, the reason which prescribes | regulates the manufacturing conditions of the high-tensile steel which concerns on this invention as mentioned above is demonstrated with an effect.

(B−1)鋼片の加熱温度について
鋼片の加熱温度は1000〜1200℃とする。これは、鋼片全体の組織を均一にオーステナイト化するために必要な温度であり、1000℃未満では加熱時に均一なオーステナイト粒を得ることができない。しかし、1200℃を超えて加熱するとオーステナイト粒が著しく大きくなって母材靱性が劣化するため、加熱温度は1200℃以下とする必要がある。
(B-1) About the heating temperature of a steel piece The heating temperature of a steel piece shall be 1000-1200 degreeC. This is a temperature necessary for uniformly austenitizing the structure of the entire steel slab, and if it is less than 1000 ° C., uniform austenite grains cannot be obtained during heating. However, when heated above 1200 ° C, the austenite grains become extremely large and the base material toughness deteriorates, so the heating temperature needs to be 1200 ° C or lower.

(B−2)熱間圧延について
「圧延後直接焼入れ」して組織を微細化するためには未再結晶温度域で適正量の圧下(加工)を加える必要がある。これは、オーステナイトの再結晶温度域で圧下してもオーステナイト粒内に格子欠陥が蓄積されないので、圧延後に急冷しても組織の微細化が生じないからである。又、未再結晶温度域で圧下してもその累積圧下量が少ないと、オーステナイト粒内に蓄積される格子欠陥が少なくなるので、圧延後に急冷しても組織の微細化が生じないからである。
(B-2) About hot rolling In order to refine the structure by “direct quenching after rolling”, it is necessary to apply an appropriate amount of reduction (processing) in the non-recrystallization temperature range. This is because no lattice defects are accumulated in the austenite grains even when the austenite is recrystallized in the recrystallization temperature range, so that the structure is not refined even if quenched after rolling. In addition, if the cumulative reduction amount is small even if the reduction is performed in the non-recrystallization temperature range, the lattice defects accumulated in the austenite grains are reduced, so that the structure is not refined even if rapidly cooled after rolling. .

本発明が対象とする前記(A)項に記載の化学組成を有する鋼の場合、その未再結晶温度域は900℃以下であり、この温度域で累積圧下率が50%以上となる圧下を行った場合に初めて「圧延後直接焼入れ」した組織を微細化できる。したがって、上記(B−1)項に記載の温度域の温度に加熱した鋼片を熱間圧延して鋼板にするに際して、900℃以下の温度域での累積圧下率を50%以上とした。50%以上の累積圧下を加える未再結晶温度域の下限の温度は、圧延後の急冷で強度を確保する観点から750℃とするのがよい。なお、900℃以下の温度域での累積圧下率が50%以上でありさえすればよいので、900℃を超える再結晶温度域での圧下率については特に規定しなくても良い。   In the case of the steel having the chemical composition described in the item (A), which is the subject of the present invention, the non-recrystallization temperature range is 900 ° C. or less, and the reduction at which the cumulative reduction rate is 50% or more in this temperature range. When this is done, the structure that has been “hardened directly after rolling” can be refined for the first time. Therefore, when the steel slab heated to the temperature range described in the above (B-1) section is hot-rolled into a steel sheet, the cumulative rolling reduction in the temperature range of 900 ° C. or lower is set to 50% or more. The lower limit temperature of the non-recrystallization temperature range to which the cumulative reduction of 50% or more is applied is preferably 750 ° C. from the viewpoint of securing strength by rapid cooling after rolling. In addition, since it is only necessary that the cumulative rolling reduction in the temperature range of 900 ° C. or less is 50% or more, the rolling reduction in the recrystallization temperature range exceeding 900 ° C. does not have to be specified.

本発明でその後に続く「圧延後直接焼入れ」の前に熱間多段拘束ローラにて平坦矯正を行う。このような工程を行うのは、この温度域でひずみを加えることで熱間圧延直後の過剰に扁平な結晶粒を整粒化し、その後の「直接焼入れ」での焼入性を高めるためであり、また、高強度鋼であるために、熱間圧延直後の鋼材が高い温度を保っているうちの方が、その後の「圧延後直接焼入れ」後の室温あるいは更にその後の「焼戻し」時より、機械荷重を著しく抑制することができ、極めて効率的であるためである。   In the present invention, flattening is performed with a hot multistage constraining roller before the subsequent “direct quenching after rolling”. The reason why such a process is performed is to increase the hardenability in the subsequent “direct quenching” by applying strain in this temperature range to regulate excessively flat crystal grains immediately after hot rolling. In addition, because it is a high-strength steel, the steel material immediately after hot rolling is kept at a higher temperature than the room temperature after the subsequent “direct quenching after rolling” or further “tempering” after that, This is because the mechanical load can be remarkably suppressed and is extremely efficient.

(B−3)「圧延後直接焼入れ」のための急冷について
熱間圧延後は直ちに急冷を行うが、その急冷の停止温度を適正に制御することが極めて重要である。急冷を停止する被処理材の表面温度が300℃を超える場合には強度確保に必要なマルテンサイト変態が不十分となり強度が低下すると同時に靱性も劣化してしまう。したがって、被処理材の表面温度が300℃以下の温度域の温度に達した時点で急冷を停止し、以後室温まで放冷することとした。
(B-3) About rapid cooling for “direct quenching after rolling” Immediately after hot rolling, rapid cooling is performed, but it is extremely important to appropriately control the quenching stop temperature. When the surface temperature of the material to be treated that stops the rapid cooling exceeds 300 ° C., the martensitic transformation necessary for securing the strength is insufficient and the strength is lowered and the toughness is also deteriorated. Accordingly, the rapid cooling is stopped when the surface temperature of the material to be treated reaches a temperature in the temperature range of 300 ° C. or less, and then it is allowed to cool to room temperature.

なお、熱間圧延後「直ちに」鋼板を急冷するとは、圧延後の鋼板を再加熱することなく水や油などの冷媒によって「圧延後直接焼入れ」することをいう。又、「放冷」とは、大気中での自然冷却を指す。   It should be noted that “immediately cooling the steel sheet after hot rolling” means “direct quenching after rolling” with a coolant such as water or oil without reheating the steel sheet after rolling. Further, “cooling” refers to natural cooling in the atmosphere.

(B−4)焼戻しについて
「圧延後直接焼入れ」後、必要に応じて鋼板に焼戻しを施すことで、優れた強度と靱性のバランスを確保してもよい。ただし、この焼戻し温度が600℃を超えると強度が著しく低下し、引張強度780MPa以上という所望の強度を確保することが困難となる。したがって、鋼板に焼戻しを施す際の焼戻し温度は600℃以下とした。
(B-4) Tempering After “direct quenching after rolling”, the steel sheet may be tempered as necessary to ensure a good balance between strength and toughness. However, when the tempering temperature exceeds 600 ° C., the strength is remarkably lowered, and it becomes difficult to secure a desired strength of a tensile strength of 780 MPa or more. Therefore, the tempering temperature when tempering the steel sheet was set to 600 ° C. or lower.

表1に示す化学組成の鋼片を溶製し、熱間鍛造および制御圧延を行って、160mm幅、1000mm長の鋼板を作製し、一部の鋼種については焼戻しを行った。なお、鋼片の加熱温度、900℃以下の累積圧下率、仕上げ板厚、直接焼入れ停止温度および焼戻し温度は表2に示した。   Steel pieces having the chemical composition shown in Table 1 were melted and subjected to hot forging and controlled rolling to produce a steel plate having a width of 160 mm and a length of 1000 mm, and some steel types were tempered. Table 2 shows the heating temperature of the steel slab, the cumulative reduction ratio of 900 ° C. or less, the finished plate thickness, the direct quenching stop temperature, and the tempering temperature.

各鋼板それぞれついて、平行部直径14mm標点距離50mmの丸棒引張試験片を、板厚25mmの供試鋼は1/2板厚位置から、板厚60mmの供試鋼(試験No.28)は1/4板厚位置から、2mmVノッチシャルピー衝撃試験片を1/4板厚位置から、それぞれ圧延方向に平行に採取し、母材の機械的性質を調査した。   For each steel plate, a round bar tensile test piece with a parallel part diameter of 14 mm and a mark distance of 50 mm, a test steel with a plate thickness of 25 mm, from a 1/2 plate thickness position, a test steel with a plate thickness of 60 mm (Test No. 28) , 2mmV notch Charpy impact test specimens were taken from the 1/4 thickness position in parallel to the rolling direction from the 1/4 thickness position, and the mechanical properties of the base metal were investigated.

さらに、一部の供試鋼について、表3の条件で多層突き合わせ溶接を行い、JIS Z 3121に規定される1号引張試験片、溶接金属からJIS Z 2111に規定されるA2号引張試験片、1/4板厚から2mmVノッチシャルピー衝撃試験片をそのノッチ位置を溶融線に合わせて採取し、継手の機械的性質を調査した。なお、溶接条件を表3に示す。   In addition, for some of the test steels, multilayer butt welding was performed under the conditions shown in Table 3, and No. 1 tensile test piece specified in JIS Z 3121, A2 tensile test piece specified in JIS Z 2111 from weld metal, A 1 / 4mm thickness 2mmV notch Charpy impact test piece was taken with its notch position aligned with the melt line, and the mechanical properties of the joint were investigated. Table 3 shows the welding conditions.

母材、継手の機械的性質を調査した結果を表4に示す。   Table 4 shows the results of investigating the mechanical properties of the base metal and the joint.

表4に示す結果から分かる通り、化学組成が本発明で規定する条件から外れると、母材強度、継手強度および継手靭性のうち、少なくとも一つは目標特性を満足しない。特に、鋼Gは目標母材強度780MPaを満足するにも拘わらず目標継手強度780MPaを満足しないが、このときの溶接金属の強度は目標継手強度780MPaを十分満足しており、母材が溶接熱影響により軟化したために継手強度を満足できないことを示すものである。   As can be seen from the results shown in Table 4, when the chemical composition deviates from the conditions defined in the present invention, at least one of the base material strength, joint strength, and joint toughness does not satisfy the target characteristics. In particular, steel G does not satisfy the target joint strength of 780 MPa even though it satisfies the target base material strength of 780 MPa, but the strength of the weld metal at this time sufficiently satisfies the target joint strength of 780 MPa, and the base metal is welded heat. This shows that the joint strength cannot be satisfied because it is softened by the influence.

本発明に係る高張力鋼は、優れた母材特性と耐溶接割れ感受性を備えるとともに、良好な溶接継手特性を示すだけでなく、780MPa以上の引張強さを有する。   The high-tensile steel according to the present invention has excellent base material characteristics and resistance to weld cracking, and not only exhibits good weld joint characteristics, but also has a tensile strength of 780 MPa or more.

Claims (6)

質量%で、C:0.03〜0.1%、Si:0.5%以下、Mn:0.4〜2.5%、P:0.03%以下、S:0.008%以下、Cr:0.1〜2%、Nb:0.005〜0.06%、Ti:0.005〜0.03%、B:0.0003〜0.0025%、Al:0.005〜0.08%、N:0.006%以下、残部Feおよび不純物を含有し、溶接割れ感受性指数Pcmが0.23以下であり、かつ次の(1)式〜(3)式のいずれをも満足する化学組成の鋼片を、1000〜1200℃に加熱し、900℃以下の温度域での累積圧下率が50%以上となるように熱間圧延した後熱間多段拘束ローラにて平坦矯正を行って直ちに急冷し、表面温度が300℃以下に達した時点で急冷を停止し、以後室温まで放冷することを特徴とする、780MPa以上の引張強度を有する高張力鋼の製造方法。
680×Nb(%)+12000×[B(%)−10.8/14.1×(N(%)−Ti(%)/3.4)]+DI≧82・・・(1)式
3390×Nb(%)+DI≧125・・・(2)式
5800×C(%)+76400×S(%)+3190×|Nb(%)−0.013|−DI≦410・・・(3)式
ただし、(1)式の計算に際して、(N(%)−Ti(%)/3.4)の数値が負となる場合にはその負の値ではなくゼロを代入し、そして、[B(%)−10.8/14.1×(N(%)−Ti(%)/3.4)]の数値が負となる場合にはその負の値ではなくゼロを代入する。
なお、DIとPcmはそれぞれ、次の(4)式および(5)式で定義される。
DI=0.311×√C(%)×[1+0.64×Si(%)]×[1+4.1×Mn(%)]×[1+0.27Cu(%)]×[1+0.52×Ni(%)]×[1+2.33×Cr(%)]×[1+3.14×Mo(%)]×25.4・・・(4)式
Pcm=C(%)+Si(%)/30+Mn(%)/20+Cu(%)/20+Ni(%)/60+Cr(%)/20+Mo(%)/15+V(%)/10+5×B(%)・・・(5)式
また、(1)式〜(5)式の中の各元素記号(%)は各元素の含有量(質量%)を示す。
In mass%, C: 0.03-0.1%, Si: 0.5% or less, Mn: 0.4-2.5%, P: 0.03% or less, S: 0.008% or less, Cr: 0.1-2%, Nb: 0.005-0.06%, Ti: 0.005-0.03%, B: 0.0003-0.0025%, Al: 0.005-0. 08%, N: 0.006% or less, remaining Fe and impurities, weld cracking sensitivity index Pcm is 0.23 or less, and satisfies any of the following formulas (1) to (3) A steel slab having a chemical composition is heated to 1000 to 1200 ° C., hot-rolled so that the cumulative rolling reduction in a temperature range of 900 ° C. or less is 50% or more, and then flattened with a hot multistage constraining roller. 780MP, characterized by immediately cooling immediately, stopping the rapid cooling when the surface temperature reaches 300 ° C or lower, and then allowing to cool to room temperature. Method for producing a high tensile steel having a tensile strength of at least.
680 × Nb (%) + 12000 × [B (%)-10.8 / 14.1 × (N (%) − Ti (%) / 3.4)] + DI ≧ 82 (1)
3390 × Nb (%) + DI ≧ 125 (2) formula
5800 × C (%) + 76400 × S (%) + 3190 × | Nb (%) − 0.013 | −DI ≦ 410 (3) However, when calculating (1), (N (%) − Ti If the value of (%) / 3.4) is negative, substitute zero instead of the negative value, and [B (%)-10.8 / 14.1 × (N (%)-Ti (%) / 3.4 If the value of]) is negative, substitute zero instead of the negative value.
DI and Pcm are defined by the following equations (4) and (5), respectively.
DI = 0.311 x √C (%) x [1 + 0.64 x Si (%)] x [1 + 4.1 x Mn (%)] x [1 + 0.27 Cu (%)] x [1 + 0.52 x Ni (%) ] X [1 + 2.33 x Cr (%)] x [1 + 3.14 x Mo (%)] x 25.4 (4)
Pcm = C (%) + Si (%) / 30 + Mn (%) / 20 + Cu (%) / 20 + Ni (%) / 60 + Cr (%) / 20 + Mo (%) / 15 + V (%) / 10 + 5 × B (%) (5) Formula Moreover, each element symbol (%) in Formula (1)-Formula (5) shows content (mass%) of each element.
請求項1に規定する成分に加えて、質量%で、さらにNi:2%以下含有する鋼片を用いることを特徴とする、請求項1に記載の780MPa以上の引張強度を有する高張力鋼の製造方法。   The high tensile steel having a tensile strength of 780 MPa or more according to claim 1, wherein a steel piece containing, in addition to the components defined in claim 1, mass% and further containing Ni: 2% or less is used. Production method. 請求項1または2に規定する成分に加えて、質量%で、さらにCu:0.6%以下およびZr:0.05%以下のうちの1種又は2種の成分を含有する鋼片を用いることを特徴とする、請求項1または2に記載の780MPa以上の引張強度を有する高張力鋼の製造方法。   In addition to the components defined in claim 1 or 2, a steel slab containing, in mass%, one or two of Cu: 0.6% or less and Zr: 0.05% or less is used. The manufacturing method of the high strength steel which has the tensile strength of 780 Mpa or more of Claim 1 or 2 characterized by the above-mentioned. 請求項1から3までのいずれかに規定する成分に加えて、質量%で、さらにMo:1%以下およびV:0.1%以下のうちの1種又は2種の成分を含有する鋼片を用いることを特徴とする、請求項1または2に記載の780MPa以上の引張強度を有する高張力鋼の製造方法。   A steel slab containing, in addition to the components defined in any one of claims 1 to 3, by mass%, and further containing one or two components of Mo: 1% or less and V: 0.1% or less. The method for producing a high-strength steel having a tensile strength of 780 MPa or more according to claim 1 or 2, wherein: 請求項1から4までのいずれかに規定する成分に加えて、質量%で、さらにCa:0.004%以下、Mg:0.002%以下およびREM:0.002%以下のうちの1種又は2種以上の成分を含有する鋼片を用いることを特徴とする、請求項1または2に記載の780MPa以上の引張強度を有する高張力鋼の製造方法。   In addition to the components specified in any one of claims 1 to 4, in mass%, Ca: 0.004% or less, Mg: 0.002% or less, and REM: 0.002% or less Or the steel slab containing 2 or more types of components is used, The manufacturing method of the high strength steel which has the tensile strength of 780 Mpa or more of Claim 1 or 2 characterized by the above-mentioned. 室温まで放冷した後、さらに600℃以下の温度で焼戻すことを特徴とする、請求項1から5までのいずれかに記載の780MPa以上の引張強度を有する高張力鋼の製造方法。
The method for producing high-tensile steel having a tensile strength of 780 MPa or more according to any one of claims 1 to 5, wherein the steel is further cooled to room temperature and further tempered at a temperature of 600 ° C or lower.
JP2008140327A 2008-05-29 2008-05-29 Manufacturing method of high-strength steel Expired - Fee Related JP5151693B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2008140327A JP5151693B2 (en) 2008-05-29 2008-05-29 Manufacturing method of high-strength steel

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2008140327A JP5151693B2 (en) 2008-05-29 2008-05-29 Manufacturing method of high-strength steel

Publications (2)

Publication Number Publication Date
JP2009287081A JP2009287081A (en) 2009-12-10
JP5151693B2 true JP5151693B2 (en) 2013-02-27

Family

ID=41456580

Family Applications (1)

Application Number Title Priority Date Filing Date
JP2008140327A Expired - Fee Related JP5151693B2 (en) 2008-05-29 2008-05-29 Manufacturing method of high-strength steel

Country Status (1)

Country Link
JP (1) JP5151693B2 (en)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP5458923B2 (en) * 2010-02-04 2014-04-02 新日鐵住金株式会社 Welded joint with excellent brittle fracture resistance
JP5630322B2 (en) * 2011-02-24 2014-11-26 Jfeスチール株式会社 High-tensile steel plate with excellent toughness and manufacturing method thereof
JP5630321B2 (en) * 2011-02-24 2014-11-26 Jfeスチール株式会社 High-tensile steel plate with excellent toughness and manufacturing method thereof
JP5833966B2 (en) * 2012-04-20 2015-12-16 株式会社神戸製鋼所 Welded joint with excellent fatigue characteristics
CN105200329A (en) * 2015-09-11 2015-12-30 武汉钢铁(集团)公司 Tensile strength-700MPa level easy-to-weld low-internal-stress structural steel plate and manufacturing method thereof
JP6501042B2 (en) 2016-07-29 2019-04-17 日本製鉄株式会社 High strength steel plate

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2604518B2 (en) * 1992-06-26 1997-04-30 新日本製鐵株式会社 Steel plate straightening method
JPH11267755A (en) * 1998-03-18 1999-10-05 Nkk Corp Manufacture of thick steel plate and straightening device used in it
JP4478083B2 (en) * 2005-07-29 2010-06-09 新日本製鐵株式会社 Steel plate top and bottom uniform cooling system
JP4427522B2 (en) * 2006-04-05 2010-03-10 新日本製鐵株式会社 Method for producing high strength thick steel plate with tensile strength of 780 MPa excellent in weldability and low temperature toughness
JP4714628B2 (en) * 2006-04-14 2011-06-29 新日本製鐵株式会社 Thick steel plate cooling equipment row and cooling method

Also Published As

Publication number Publication date
JP2009287081A (en) 2009-12-10

Similar Documents

Publication Publication Date Title
EP2272994A1 (en) High-tensile strength steel and manufacturing method thereof
JP5476763B2 (en) High tensile steel plate with excellent ductility and method for producing the same
JP4547944B2 (en) Manufacturing method of high strength and high toughness thick steel plate
JP4096839B2 (en) Manufacturing method of high yield thick steel plate with low yield ratio and excellent toughness of heat affected zone
JP5439973B2 (en) High-strength thick steel plate having excellent productivity and weldability and excellent drop weight characteristics after PWHT, and method for producing the same
JP5846311B2 (en) Thick high-strength steel excellent in welding heat affected zone CTOD characteristics and method for producing the same
JP2008208454A (en) High-strength steel excellent in delayed fracture resistance and its production method
JP5407478B2 (en) High-strength thick steel plate with excellent toughness of heat-affected zone of single layer large heat input welding and method for producing the same
JP5034290B2 (en) Low yield ratio high strength thick steel plate and method for producing the same
JP5151693B2 (en) Manufacturing method of high-strength steel
JP2013104124A (en) Directly quenched and tempered high tensile strength steel sheet having excellent bendability and method for producing the same
JP2012122111A (en) Method for producing tmcp and tempering process type high-strength thick steel plate having both excellent productivity and weldability, and excellent in drop-weight characteristic after pwht
JP3045856B2 (en) Method for producing high toughness Cu-containing high tensile steel
JP2004091916A (en) Wear-resisting steel
JP4998708B2 (en) Steel material with small material anisotropy and excellent fatigue crack propagation characteristics and method for producing the same
JP4770415B2 (en) High tensile steel plate excellent in weldability and method for producing the same
JP5151034B2 (en) Manufacturing method of steel plate for high tension line pipe and steel plate for high tension line pipe
JP5515954B2 (en) Low yield ratio high-tensile steel plate with excellent weld crack resistance and weld heat-affected zone toughness
JP2005272854A (en) Method for producing high-tensile steel excellent in refractoriness and toughness in welded heat affected part
JP2012188749A (en) Thick steel plate with high toughness in multi-pass welded part and multi-pass welded joint
JP2019199649A (en) Non-tempered low yield ratio high tensile thick steel sheet and its production method
JP5151510B2 (en) Manufacturing method of high strength steel with excellent low temperature toughness and crack propagation stop properties
JP4434029B2 (en) High-tensile steel with excellent weldability and joint toughness
JP2000104116A (en) Production of steel excellent in strength and toughness
JP6579135B2 (en) Low yield ratio steel sheet for construction and manufacturing method thereof

Legal Events

Date Code Title Description
A621 Written request for application examination

Free format text: JAPANESE INTERMEDIATE CODE: A621

Effective date: 20100525

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20120904

A711 Notification of change in applicant

Free format text: JAPANESE INTERMEDIATE CODE: A712

Effective date: 20121011

A521 Written amendment

Free format text: JAPANESE INTERMEDIATE CODE: A523

Effective date: 20121011

A521 Written amendment

Free format text: JAPANESE INTERMEDIATE CODE: A523

Effective date: 20121017

TRDD Decision of grant or rejection written
A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

Effective date: 20121106

A61 First payment of annual fees (during grant procedure)

Free format text: JAPANESE INTERMEDIATE CODE: A61

Effective date: 20121119

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20151214

Year of fee payment: 3

R151 Written notification of patent or utility model registration

Ref document number: 5151693

Country of ref document: JP

Free format text: JAPANESE INTERMEDIATE CODE: R151

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20151214

Year of fee payment: 3

S533 Written request for registration of change of name

Free format text: JAPANESE INTERMEDIATE CODE: R313533

R350 Written notification of registration of transfer

Free format text: JAPANESE INTERMEDIATE CODE: R350

LAPS Cancellation because of no payment of annual fees