JPH0670250B2 - Manufacturing method of tempered high strength steel sheet with excellent toughness - Google Patents
Manufacturing method of tempered high strength steel sheet with excellent toughnessInfo
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- JPH0670250B2 JPH0670250B2 JP63293343A JP29334388A JPH0670250B2 JP H0670250 B2 JPH0670250 B2 JP H0670250B2 JP 63293343 A JP63293343 A JP 63293343A JP 29334388 A JP29334388 A JP 29334388A JP H0670250 B2 JPH0670250 B2 JP H0670250B2
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- temperature
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Description
【発明の詳細な説明】 ＜産業上の利用分野＞ この発明は、降伏強度:90kgf/mm2，引張強度:97kgf/mm2
以上並びに衝撃遷移温度：−60℃以下の性能を有する高
張力鋼板の製造方法に係り、特に、板厚が100mm以上の
極厚材を対象とした場合にも上記性能を安定して付与す
ることができる調質型高張力鋼板の製造方法に関するも
のである。DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> This invention has a yield strength of 90 kgf / mm 2 and a tensile strength of 97 kgf / mm 2.
The above and impact transition temperature: related to a method for producing a high-strength steel sheet having a performance of −60 ° C. or less, and particularly, to provide the above-mentioned performance in a stable manner even when an extremely thick material having a sheet thickness of 100 mm or more is targeted. The present invention relates to a method for producing a heat-treated high-strength steel sheet that can be manufactured.
＜従来技術とその課題＞ 近年、溶接構造物の大型化傾向は益々著しくなってお
り、これらに使用される構造用鋼板はより一層のハイテ
ン化並びに極厚化の一途をたどっている。例えば、揚水
発電所の水圧鉄管に180mm厚の80kgf/mm2級高張力鋼板が
使用されたり、ジャキアップ型石油掘削リグのラック材
に100〜150mm厚の80kgf/mm2級高張力鋼板が使用される
に至っている。<Prior Art and Its Problems> In recent years, the tendency toward large-sized welded structures has become more and more remarkable, and the structural steel sheets used for these have become even higher in tensile strength and extremely thicker. For example, a 180 mm thick 80 kgf / mm 2 class high-strength steel sheet is used for a penstock of a pumped storage power plant, and a 100-150 mm thick 80 kgf / mm 2 class high-strength steel sheet is used for a rack material of a jack-up type oil drilling rig. Has been done.
ところが、従来よりこの種の用途に供する高張力鋼板に
はHT60やHT80クラスの鋼種が当てられてきたが、上述し
たような大型化が著しい近年の溶接構造物に対しては降
伏強度:90kgf/mm2以上という高強度を有するHT100クラ
スの、しかも100mm厚以上の極厚高張力鋼板の適用が望
まれるようになった。However, the HT60 and HT80 class steel grades have hitherto been applied to the high-strength steel sheets used for this type of application, but the yield strength: 90 kgf / The application of HT100 class, which has high strength of mm 2 or more, and extremely thick high-strength steel sheet of 100 mm or more has been desired.
しかしながら、降伏強度:90kgf/mm2以上で引張強度:97k
gf/mm2以上と言うHT100クラスの高強度を100mm厚を超え
る極厚鋼板に安定して確保することは工業上極めて難し
く、また例えこのような高強度を付与し得たとしても同
時に十分な靭性をも確保することはより一層困難である
ため、上記極厚高張力鋼板の安定多量供給体制が確立さ
れていないのが現状であった。However, yield strength: 90 kgf / mm 2 and above, tensile strength: 97 k
It is industrially extremely difficult to stably secure the high strength of gf / mm 2 or higher in the HT100 class for extra-thick steel sheets exceeding 100 mm thickness, and even if such high strength can be imparted, it is sufficient at the same time. Since it is even more difficult to secure toughness, the present situation is that a stable large-volume supply system for the above-mentioned ultra-thick high-strength steel sheet has not been established.
つまり、100mm厚を超える板厚の100kgf/mm2級高張力極
厚鋼板を製造するに当っては、板厚中心部の強度確保を
図るために焼入れ性が非常に高い成分設計を行う必要が
あるが、極厚材のため焼入れに際しての表層部と中心部
との冷却速度に大きな差があり、中心部の強度を確保し
ようとすると表層部の強度が高くなり過ぎて低温靭性が
中止部より著しく劣化する結果となる。そのため、板厚
方向に亘って優れた強度・靭性バランスを有する鋼板を
安定して得ることが“100mm厚を超える100kgf/mm2級高
張力極厚鋼板”の製造において最大の難関となるが、未
だこの問題を十分に克服するには至らなかった。In other words, when manufacturing a 100 kgf / mm 2 class high-strength extra-thick steel plate with a plate thickness exceeding 100 mm, it is necessary to design a component with extremely high hardenability in order to secure the strength of the center part of the plate thickness. However, since it is an extremely thick material, there is a large difference in the cooling rate between the surface layer part and the center part during quenching, and when trying to secure the strength of the center part, the strength of the surface layer part becomes too high and the low temperature toughness is higher than the discontinued part. This will result in significant deterioration. Therefore, stable production of a steel sheet having an excellent balance of strength and toughness in the thickness direction is the biggest challenge in the production of "100 kgf / mm 2 class high-strength extra-thick steel sheet exceeding 100 mm thickness". We have not yet been able to fully overcome this problem.
＜課題を解決するための手段＞ そこで、本発明者等は上述のような観点から、降伏強
度:90kgf/mm2，引張強度:97kgf/mm2以上及び衝撃遷移温
度：−60℃以下の性能を有し、特に板厚が100mmを超え
る場合にも前記性能を安定して付与することができる極
厚高張力鋼板の製造手段を提供すべく鋭意研究を重ねた
結果、次に示す如き知見を得るに至った。即ち、 （ａ）所望の溶接性を確保した上でコスト的にも実用的
な100kgf/mm2級の高張力鋼を得るには強化元素の多量添
加手段等は不適当であり、焼入れによる鋼材組織をマル
テンサイト組織化が欠かせないこと， （ｂ）しかし、極厚鋼板を焼入れする場合には板厚中心
部と表面部とで冷却速度にどうしても大きな差が生じて
しまうため、中心部での十分な強度確保を図ると表面部
では焼きが入りすぎて極端に低温靭性が劣化するが、こ
の際、焼入れ時のγ粒径を極力小さくすることによって
細粒のマルテンサイト組織が得られるような手立てを講
じると、焼きが過度になりがちな鋼材表面部においても
十分に満足できる低温靭性が維持されること， （ｃ）そして、焼入れ時に所望の細粒γ粒を実現するた
めには、Nb添加によって鋼材加熱時におけるγ粒の成長
を抑制すると同時に、事前に一旦焼入れ処理を施して加
熱前組織（γ化前の組織）の微細化を図っておくのが極
めて有効であり、このNb添加と二回焼入れによる相乗効
果を活用すれば、細粒のγ粒を経て極めて微細なマルテ
ンサイト組織の確保が安定して可能となること， （ｄ）ただ、この場合、第二回目焼入れ前のγ粒を微細
に保つため第二回目焼入れは比較的低温のγ域から行う
必要があり、焼入れの効果が不十分となる懸念もある
が、この問題は焼入れ性向上元素であるＢの添加により
極めて効果的に解消されること， （ｅ）また、熱間圧延によって特定量以上の圧下を受け
た所定成分組成鋼であれば、前記第一回目の焼入れ処理
に代えて熱延に続く直接焼入れを採用しても同等の効果
が確保されること。<Means for Solving the Problems> Therefore, from the viewpoints described above, the present inventors have evaluated the yield strength: 90 kgf / mm 2 , tensile strength: 97 kgf / mm 2 or more and impact transition temperature: −60 ° C. or less. As a result of extensive research to provide a manufacturing method of an extra-thick high-strength steel sheet capable of stably imparting the above performance even when the sheet thickness exceeds 100 mm, the following findings are obtained. I got it. That is, (a) In order to obtain a high-strength steel of 100 kgf / mm 2 class, which is practical and cost-effective, while ensuring the desired weldability, the means for adding a large amount of strengthening elements, etc. are unsuitable. It is essential that the structure be martensite structured, (b) However, when quenching an extremely thick steel plate, a large difference in cooling rate is inevitably generated between the center part and the surface part of the plate thickness, so that at the center part. If sufficient strength is secured, the surface will be excessively quenched and the low temperature toughness will be extremely deteriorated.At this time, by minimizing the γ grain size during quenching, a fine grain martensite structure can be obtained. If sufficient measures are taken, sufficient satisfactory low temperature toughness is maintained even on the surface of the steel material that tends to be excessively quenched, (c) and in order to achieve the desired fine γ grains during quenching, Addition of Nb makes it easier to heat steel materials. It is extremely effective to suppress the growth of γ-grains and to make the structure before heating (structure before γ-ization) finer at the same time as suppressing the growth of γ grains. By utilizing the synergistic effect, it is possible to stably secure an extremely fine martensite structure via fine γ grains, (d) However, in this case, the γ grains before the second quenching are made finer. The second quenching must be performed from the relatively low temperature γ region to maintain the temperature, and there is a concern that the quenching effect may be insufficient, but this problem is extremely effectively eliminated by the addition of B, which is a quenchability improving element. (E) In addition, if the steel has a predetermined composition that has been subjected to reduction of a specific amount or more by hot rolling, direct quenching subsequent to hot rolling may be adopted instead of the first quenching treatment. The same effect should be secured.
本発明は、「100kgf/mm2級高張力鋼板にて優れた低温靭
性を実現するためには細粒なオーステナイト（γ）粒か
ら変態したマルテンサイト組織を得ることが開発のポイ
ントとなる」との観点からの研究により得られた上記知
見等に基づいてなされたものであり、 「C:0.10〜0.20％（以降、成分割合を表わす％は重量％
とする）， Si:0.30％以下、 Mn:0.40〜1.20％， Cu:0.5％以下， Ni:3.5超〜4.5％， Cr:0.10〜1.20％， Mo:0.05〜0.80％， V:0.005〜0.1％， Nb:0.005〜0.03％， sol.Al:0.015〜0.10％， B:0.0003〜0.0030％， P:0.010％以下， S:0.005％以下， N:0.004％以下 で、残部が実質的にFeから成る鋼を、第１図で示すよう
に1000℃以上に加熱して熱間圧延した後、Ac3点〜1050
℃の温度域に再加熱して焼入れし、その後更に「Ac3点
〜950℃の温度域でかつ第一回目の焼入れ温度以下の温
度に加熱して再度の焼入れを行うか、或いは第２図で示
すように前記“熱間圧延−焼入れ処理”に代え“900℃
以上の温度域にて30％以上の累積圧下を与えると共に仕
上圧延を800℃以上で終了した後そのまま水冷する処
理”を行い、続いてAc1点以下の温度で焼戻しして水冷
することにより、板厚が100mm厚を超えるものであって
も降伏強度:90kgf/mm2，引張強度:97kgf/mm2以上並びに
衝撃遷移温度：−60℃以下の性能を安定して示す高張力
鋼板を工業的規模で量産し得るようにした点」を特徴と
している。According to the present invention, "the point of development is to obtain a martensite structure transformed from fine austenite (γ) grains in order to realize excellent low temperature toughness in a 100 kgf / mm 2 class high strength steel plate". It was made based on the above findings obtained from research from the viewpoint of “C: 0.10 to 0.20% (hereinafter,% representing the component ratio is% by weight.
, Si: 0.30% or less, Mn: 0.40 to 1.20%, Cu: 0.5% or less, Ni: more than 3.5 to 4.5%, Cr: 0.10 to 1.20%, Mo: 0.05 to 0.80%, V: 0.005 to 0.1 %, Nb: 0.005 to 0.03%, sol.Al: 0.015 to 0.10%, B: 0.0003 to 0.0030%, P: 0.010% or less, S: 0.005% or less, N: 0.004% or less, and the balance is substantially Fe. the steel consisting of, after hot rolling is heated above 1000 ° C. as shown in FIG. 1, Ac 3 point to 1050
Reheat to the temperature range of ℃, and then quench, and then further "heat in the temperature range of Ac 3 point to 950 ℃ and below the first quenching temperature and perform quenching again, or As shown in, replace the above "hot rolling-quenching treatment" with "900 ° C.
By giving a cumulative reduction of 30% or more in the above temperature range and performing water cooling as it is after finishing rolling at 800 ° C. or more ”, followed by tempering at a temperature of Ac 1 point or less and water cooling, Even if the plate thickness exceeds 100 mm, the high strength steel plate that stably shows the performance of yield strength: 90 kgf / mm 2 , tensile strength: 97 kgf / mm 2 or more and impact transition temperature: -60 ° C or less is industrially available. It is characterized in that it can be mass-produced on a scale. "
次に、本発明において高張力鋼板の製造条件を前記の如
くに限定した理由を、その裏付けとなった作用と共に説
明する。Next, the reason why the manufacturing conditions for the high-strength steel sheet are limited as described above in the present invention will be explained together with the action that supports them.
＜作用＞ Ａ）素材鋼の成分組成 ａ）Ｃ Ｃは鋼板の強度を確保する上で必要な元素であるが、そ
の含有量が0.10％未満では100kgf/mm2級高張力鋼板とし
ての必要強度を確保することができず、（この傾向は、
特に100mm厚以上の極厚鋼板の場合に一層著しい）、一
方、0.20％を超えて含有させると溶接低温割れ感受性が
高くなる等の問題を生じることから、Ｃ含有量は0.10〜
0.20％と定めた。<Action> A) Composition of raw material steel a) C C is an element necessary to secure the strength of the steel sheet, but if its content is less than 0.10%, the required strength as a 100 kgf / mm 2 class high strength steel sheet. Can not be secured, (This tendency is
In particular, it is more remarkable in the case of an extremely thick steel plate having a thickness of 100 mm or more). On the other hand, if the content exceeds 0.20%, problems such as high weld cold cracking susceptibility occur, so the C content is 0.10-
It was set at 0.20%.
ｂ）Si 通常、Siは鋼の脱酸と強度確保のために添加される元素
であるが、Siを低減することによって溶接継手部や溶接
熱影響部の靭性を向上することができる。これは、低Si
化によって冷却速度の比較的速い溶接継手部においても
靭性に悪影響を及ぼす島状マルテンサイトの生成を抑制
できるためでる。そして、上記効果を十分に確保するた
めにはSi含有量を0.30％以下にする必要があり、従って
Si含有量を0.30％以下と限定したが、好ましくは0.15％
以下にすることにより更に優れた効果が得られる。b) Si Normally, Si is an element added for deoxidizing steel and securing strength, but by reducing Si, the toughness of the welded joint and the weld heat affected zone can be improved. This is low Si
This is because the formation of island martensite that adversely affects toughness can be suppressed even in a welded joint portion having a relatively high cooling rate. And, in order to sufficiently secure the above effect, it is necessary to set the Si content to 0.30% or less.
The Si content was limited to 0.30% or less, but preferably 0.15%
Further excellent effects can be obtained by the following.
ｃ）Mn Mn成分には鋼の脱酸剤としての作用のほか、焼入性を確
保する作用があるが、その含有量が0.40％未満では前記
作用による所望の効果が得られず、一方、1.20％を超え
て含有させると溶接性及び母材靭性の劣化を招くことか
ら、Mn含有量を0.40〜1.20％と定めた。c) Mn Mn component not only acts as a deoxidizing agent for steel, but also acts to secure hardenability, but if its content is less than 0.40%, the desired effect due to the above action cannot be obtained. If the content exceeds 1.20%, the weldability and the toughness of the base material are deteriorated, so the Mn content was set to 0.40 to 1.20%.
ｄ）Cu Cuは靭性を損なうことなく強度を高めるのに有効な元素
であり、微量の添加によっても該効果が確認できるが、
0.5％を超えて添加してもコストアップに見合うだけの
強度上昇効果が得られないばかりか、高温延性に悪影響
を及ぼすようになることから、Cu含有量は0.5％以下と
定めた。d) Cu Cu is an element effective for increasing the strength without impairing the toughness, and the effect can be confirmed even by adding a small amount,
The Cu content is specified to be 0.5% or less because not only the effect of increasing the strength commensurate with the cost increase cannot be obtained even if added over 0.5%, but also the hot ductility is adversely affected.
ｅ）Ni Ni成分には鋼の焼入れ性確保と低温靭性の改善作用があ
るが、その含有量が3.5％以下では100mm厚を超える100k
gf/mm2級高張力鋼板に必要強度を確保することができ
ず、一方、4.5％を超えて添加してもその効果が飽和す
るばかりかコストアップにつながるため、Ni含有量は3.
5％を超えかつ4.5％以下の範囲と定めた。e) Ni The Ni component has the effects of ensuring the hardenability of steel and improving the low temperature toughness, but if its content is 3.5% or less, 100k exceeding 100mm thickness
The necessary strength cannot be ensured for gf / mm 2 class high-strength steel sheets, while on the other hand, addition of more than 4.5% not only saturates the effect but also leads to cost increase, so the Ni content is 3.
The range is defined as more than 5% and less than 4.5%.
ｆ）Cr Cr成分には鋼の焼入性と強度を確保する作用があるが、
その含有量が0.1％未満では前記作用による所望の効果
が得られず、一方、1.2％を超えて含有させると溶接性
及び母材性能を劣化するようになることから、Cr含有量
は0.1〜1.2％と定めた。f) Cr The Cr component has the function of ensuring the hardenability and strength of steel,
If the content is less than 0.1%, the desired effect due to the above action cannot be obtained, while if it exceeds 1.2%, the weldability and base metal performance deteriorate, so the Cr content is 0.1 to It was set at 1.2%.
ｇ）Mo Moは鋼の焼入性を増加させると共に、焼戻し軟化抵抗を
高めて所望強度を確保する上で有効な元素であるが、そ
の含有量が0.05％未満では十分な前記効果が得られず、
一方、0.80％を超えて含有させると溶接性を著しく劣化
させることから、Mo含有量は0.05〜0.80％と定めた。g) Mo Mo is an element effective in increasing the hardenability of steel and increasing the temper softening resistance to secure the desired strength. However, if the content is less than 0.05%, the above-mentioned effect is sufficiently obtained. No
On the other hand, when the content exceeds 0.80%, the weldability is significantly deteriorated, so the Mo content was set to 0.05 to 0.80%.
ｈ）Ｖ Ｖは鋼に強度を確保のために添加される元素であるが、
その含有量が0.005％未満では所望強度の確保が困難で
あり、一方、0.10％を超えて含有させると母材靭性及び
溶接性を著しく劣化させることから、Ｖ含有量は0.005
〜0.10％と定めた。h) V V is an element added to steel to secure strength,
If the content is less than 0.005%, it is difficult to secure the desired strength, while if it exceeds 0.10%, the toughness and weldability of the base metal are significantly deteriorated, so the V content is 0.005%.
It was set at ~ 0.10%.
ｉ）Nb Nb成分には、微細析出物としてオーステナイト（γ）領
域に存在することにより、そのピン止め効果によってオ
ーステナイト粒の成長を抑制しオーステナイト粒を細粒
化する作用があるが、Nb含有量が0.005％未満では前記
作用による所望の効果が得られず、一方、0.03％を超え
て含有させると溶接性を損なうようになることから、Nb
含有量は0.005〜0.30％と定めた。i) Nb Nb component exists as a fine precipitate in the austenite (γ) region, and its pinning effect suppresses the growth of austenite grains and reduces the austenite grains. If less than 0.005%, the desired effect due to the above action cannot be obtained, while if it exceeds 0.03%, the weldability is impaired, so Nb
The content was set to 0.005 to 0.30%.
ｊ）sol.Al Al成分には鋼の脱酸作用と共にオーステナイト結晶粒を
微細化して靭性を向上させる作用があるが、その含有量
が0.015％未満では前記作用による所望の効果が得られ
ず、一方、0.10％を超えて含有させると逆のアルミナ等
の脱酸生成物増加により靭性が損なわれるようになるこ
とから、sol.Al含有量を0.015〜0.10％と定めた。j) sol.Al Al component has a deoxidizing effect of steel and an effect of refining austenite crystal grains to improve toughness, but if the content is less than 0.015%, the desired effect due to the above effect cannot be obtained, On the other hand, if the content exceeds 0.10%, the toughness will be impaired due to an increase in deoxidation products such as alumina, which is the reverse. Therefore, the sol.Al content was set to 0.015 to 0.10%.
ｋ）Ｂ Ｂは微量添加で大幅に鋼の焼入性を向上させる元素であ
り、鋼の強度・靭性を向上させるのに非常に有効な成分
であるが、その含有量が0.0003％未満では鋼に所望の強
度・靭性を確保することができず、一方、0.003％を超
えて含有させてもその効果が飽和することから、Ｂ含有
量は0.0003〜0.003％と定めた。k) BB B is an element that significantly improves the hardenability of steel with a small amount of addition, and is a very effective component for improving the strength and toughness of steel, but if its content is less than 0.0003%, it is steel. In addition, the desired strength and toughness cannot be ensured, and even if the content exceeds 0.003%, the effect is saturated, so the B content was set to 0.0003 to 0.003%.
１）Ｐ Ｐは鋼の焼戻し脆性を促進して靭性を劣化させる不純物
元素である。特に100kgf/mm2級高張力鋼板ではその影響
を受けやすい。ただ、Ｐ含有量を0.01％以下に抑えるこ
とによって前記悪影響が容認し得る程度に抑制されるこ
とから、Ｐ含有量は0.01％以下と限定した。1) P P is an impurity element that promotes temper embrittlement of steel and deteriorates toughness. Especially, 100kgf / mm 2 class high-strength steel sheet is easily affected by this. However, since the adverse effect is suppressed to an acceptable level by controlling the P content to 0.01% or less, the P content is limited to 0.01% or less.
ｍ）Ｓ Ｓは、通常、鋼中においてMnSの形態で存在し、圧延に
より展伸される靭性の異方性を生じる不純物元素であ
る。そして、高強度鋼においては特に展伸した介在物が
著しい靭性劣化の原因となるが、Ｓ含有量を0.005％以
下に抑えることによって該悪影響を容認し得る程度に抑
制されることから、Ｓ含有量は0.005％以下と限定し
た。m) S S is an impurity element that usually exists in the form of MnS in steel and causes anisotropy of toughness that is expanded by rolling. In high-strength steel, in particular, expanded inclusions cause significant deterioration in toughness, but by suppressing the S content to 0.005% or less, the adverse effect can be suppressed to an acceptable level. The amount was limited to 0.005% or less.
ｎ）Ｎ Ｎを0.004％以下にすることは、鋼の焼入性を高め母材
の強度と靭性向上に極めて有効な手段である。即ち、Ｎ
含有量を0.004％以下にすると共にsol.Al含有量を0.015
〜0.10％に調整することによって固溶Ｂ量を0.0003％以
上とすることができ、焼入性の著しい向上が達成され
る。また、Ｎ量を0.004％以下に低減するとAlNの粗大化
が抑制され、靭性も向上する。更に、低Ｎ化によってVN
の生成が抑制されるので通常のオーステナイト化温度で
Ｖが均一固溶するようになり、従ってＶの添加量を削減
できる効果も確保できる。このようなことから、Ｎ含有
量は0.004％以下と限定した。n) Setting N N to 0.004% or less is an extremely effective means for enhancing the hardenability of steel and improving the strength and toughness of the base material. That is, N
Content of 0.004% or less and sol.Al content of 0.015
By adjusting the content to 0.10%, the amount of solid solution B can be made 0.0003% or more, and the hardenability is remarkably improved. Further, when the N content is reduced to 0.004% or less, coarsening of AlN is suppressed and toughness is also improved. Furthermore, due to the low N, VN
Since the formation of V is suppressed, V becomes a solid solution at a normal austenitizing temperature, so that the effect of reducing the amount of V added can be secured. For this reason, the N content is limited to 0.004% or less.
Ｂ）圧延・熱処理条件 圧延−二回焼入れ・焼戻しの場合 ａ）圧延加熱温度 圧延に際してはＶ炭窒化物やBN等の固溶を図るために高
温加熱することが望まれるが、該加熱温度が1000℃未満
では上記析出物の十分な固溶がなされないことから、圧
延加熱温度は1000℃以上と定めた。B) Rolling / heat treatment conditions Rolling-double quenching / tempering a) Rolling heating temperature At the time of rolling, it is desirable to heat at a high temperature in order to form a solid solution of V carbonitride, BN, etc. If the temperature is less than 1000 ° C, the above precipitates are not sufficiently solid-dissolved, so the rolling heating temperature is set to 1000 ° C or higher.
ｂ）第一回目焼入れ温度 第一回目の焼入れは、次のことを目的として実施される
ものである。即ち、 （イ）前組織を焼入れ組織としておくことにより第二回
目焼入の際の加熱時におけるγ粒径を細粒にする， （ロ）100mm厚を超える極厚材を製造する場合には圧延
後の徐冷時にBNやNb（CN）の粗大析出が生じるが、これ
ら析出物の固溶を図り、Ｂによる焼入性向上効果の改善
やNbによるγ粒細粒化効果の改善を図る。b) First quenching temperature The first quenching temperature is carried out for the following purposes. That is, (a) by making the preceding structure a quenched structure, the γ grain size during heating during the second hardening is made finer, (b) when manufacturing an extremely thick material exceeding 100 mm thickness, Coarse precipitation of BN and Nb (CN) occurs during gradual cooling after rolling, but the solid solution of these precipitates is aimed to improve the hardenability improving effect of B and the γ grain refining effect of Nb. .
そして、そのためには少なくともAc3点以上のγ域に加
熱する必要があるが、1050℃を超える温度域に加熱する
と、逆にγ粒の成長が著しくなって次工程である第二回
目焼入時にも細粒γ粒を確保できなくなることから、第
一回目焼入れ温度やAc3〜1050℃と定めた。And for that purpose, it is necessary to heat at least the Ac 3 point or higher γ range, but when heated to a temperature range higher than 1050 ° C, the γ grains grow remarkably and the next step, the second quenching Since it is not possible to secure fine γ grains even at times, the first quenching temperature and Ac 3 to 1050 ° C were set.
ｃ）第二回目焼入れ温度 第二回目の焼入れは、細粒γからの焼入れで細粒なマル
テンサイト変態組織を得ることを狙いとしてしている。
そして、第二回目の焼入れ時に急冷前組織を細粒γ組織
に維持しておくためには、Nbのピンニング効果を活用す
ることのできる低温γ域からの焼入とする必要がある。
しかし、焼入れ温度が低すぎると（Ac3点の温度未満で
あると）固溶Ｂ量が確保できず、Ｂが有する焼入れ性向
上作用を活用することができない。一方、950℃を超え
る高温に加熱するとBNやAlNの分解が生じるためにフリ
ーＮが増加し、これが焼入れ時に固溶Ｂと結合してＢの
焼入れ性向上効果を失わしめる。このようなことから、
第二回目焼入れ温度はAc3〜950℃と定めた。c) Second quenching temperature The second quenching is aimed at obtaining a fine grain martensitic transformation structure by quenching from fine grain γ.
Then, in order to maintain the structure before quenching in the fine grain γ structure during the second quenching, it is necessary to quench from the low temperature γ region where the pinning effect of Nb can be utilized.
However, if the quenching temperature is too low (below the temperature of the Ac 3 point), the amount of solid solution B cannot be secured, and the quenching property improving effect of B cannot be utilized. On the other hand, when heated to a temperature higher than 950 ° C., BN and AlN are decomposed, so that free N increases, and this is combined with solid solution B during quenching, and the effect of improving hardenability of B is lost. From such a thing,
The second quenching temperature was set to Ac 3 to 950 ° C.
ｄ）焼戻し処理条件 焼戻し処理は、焼入れによって導入された歪みを除去
し、かつ炭化物を微細に析出させることにより強度−靭
性バランスを改善するために実施される。そして、この
焼戻しは一般にAc1点以下の温度域で行われるのが常で
あり、この温度にて十分な効果が得られることから、本
発明においても焼戻し温度をAc1点以下の温度と定め
た。d) Tempering treatment conditions The tempering treatment is carried out to remove the strain introduced by quenching and to improve the strength-toughness balance by finely precipitating carbides. Then, this tempering is generally performed in a temperature range of Ac 1 point or lower, and since a sufficient effect can be obtained at this temperature, the tempering temperature is set to a temperature of Ac 1 point or lower in the present invention. It was
なお、本発明においては焼戻し温度に加熱・保持した後
水冷することも主要条件としている。これは、製造する
鋼板（100kgf/mm2級高張力鋼板）が100mm厚を超えるよ
うな場合には、焼戻し後の冷却を水冷としなければ冷却
速度が著しく遅くなり、そのため焼戻し脆性の感受性が
高まって靭性の劣化を招くためである。In the present invention, heating and holding at the tempering temperature and then water cooling are the main conditions. This is because if the steel sheet to be manufactured (100 kgf / mm 2 class high-strength steel sheet) exceeds 100 mm thick, the cooling rate will be significantly slower unless water cooling is used after tempering, which increases the susceptibility to temper brittleness. This causes deterioration of toughness.
圧延・直接焼入れ−焼入れ・焼戻しの場合 この場合における圧延加熱温度，第二回目焼入れ温度並
びに焼戻し処理条件を限定した理由は、上述した“圧延
−二回焼入れ・焼戻し”の場合におけるのと同じである
が、圧延加熱温度を除いた圧延・直接焼入れの条件を前
述したように限定したのは次の理由による。In the case of rolling / direct quenching-quenching / tempering The reason for limiting the rolling heating temperature, the second quenching temperature and the tempering treatment conditions in this case is the same as in the case of "rolling-double quenching / tempering" described above. However, the reason for limiting the rolling / direct quenching conditions excluding the rolling heating temperature as described above is as follows.
ａ）圧延圧下量 100mm厚を超える高靭性極厚高張力鋼板をも安定して製
造できるようにするのが本発明の目的とするところであ
るが、極厚鋼板の場合には連続鋳造スラブ等の如き比較
的薄い鋼片を出発素材とすると、鍛練比不足から板厚中
心部組織の細粒化が図れないことがある。本発明では、
細粒のマルテンサイト組織を得ることを最終的な狙いと
しているため、先にも述べたようにその前組織をできる
だけ細粒にしておく必要がある。そして、このためには
900℃以上の温度域で30％以上の圧下を加える必要があ
り、従って直接焼入れを適用する場合は900℃以上の温
度域で30％以上の累積圧下を与えることと定めた。a) The object of the present invention is to enable stable production of a high-toughness extra-thickness high-strength steel sheet having a rolling reduction of more than 100 mm. However, in the case of extra-thickness steel sheet, a continuous cast slab or the like is used. When such a relatively thin steel slab is used as a starting material, it may not be possible to achieve a fine grain structure in the central portion of the plate thickness due to a lack of a forging ratio. In the present invention,
Since the ultimate aim is to obtain a fine-grained martensite structure, it is necessary to make the preceding structure as fine grain as possible, as described above. And for this
It is necessary to apply a reduction of 30% or more in a temperature range of 900 ° C or higher, and therefore, it is specified that a cumulative reduction of 30% or more is applied in a temperature range of 900 ° C or higher when direct quenching is applied.
ｂ）圧延仕上温度 直接焼入れは、前述した二回焼入れの場合における第一
回目焼入れに代替するものである。従って、直接焼入れ
の直前にはBNやNb（CN）を固溶状態としておかねばなら
ないが、そのためには圧延を800℃以上で仕上げる必要
がある。このようなことから、圧延仕上温度は800℃以
上と定めた。b) Rolling finishing temperature The direct quenching is an alternative to the first quenching in the case of the double quenching described above. Therefore, BN and Nb (CN) must be in solid solution immediately before direct quenching, but for that purpose, rolling must be finished at 800 ° C or higher. For this reason, the rolling finishing temperature was set to 800 ° C or higher.
ｃ）直接焼入 直接焼入れは二回焼入れの場合における第一回目焼入れ
に代替するものであるので、仕上圧延後の鋼板はそのま
ま直ちに水冷される。c) Direct quenching Direct quenching is an alternative to the first quenching in the case of double quenching, so the steel sheet after finish rolling is immediately water cooled.
続いて、本発明の実施例によって更に具体的に説明す
る。Then, it demonstrates still more concretely by the Example of this invention.
＜実施例＞ まず、常法に従って第１表に示される成分組成のスラブ
をを得た後、これらを第２表に示す条件で処理し、板
厚:150mmの極厚鋼板を製造した。<Examples> First, slabs having the component compositions shown in Table 1 were obtained according to a conventional method, and then treated under the conditions shown in Table 2 to produce an extremely thick steel plate having a plate thickness of 150 mm.
次に、得られた各鋼板から試験片を切り出して機械的性
質及び溶接性の評価を行い、その結果を第２表に併せて
示した。Next, a test piece was cut out from each of the obtained steel plates and evaluated for mechanical properties and weldability, and the results are also shown in Table 2.
なお、溶接性の評価はｙ開先拘束割れ試験によって行っ
たが、ｙ開先拘束割れ試験は、各鋼板より採取した斜め
ｙ開先拘束割れ試験片（板厚50mm）を125℃に予熱後、
入熱量:17kJ/cmで手溶接し（電流:170A,電圧:25V,速度:
15 cm/min）、この際の表面割れ、ルート割れ及び断面割れ
の有無を調べる条件の下で実施した。The weldability was evaluated by the y-groove constrained cracking test. The y-groove constrained cracking test was conducted after preheating the oblique y-groove constrained cracking test pieces (plate thickness 50 mm) collected from each steel plate to 125 ° C. ,
Heat input: 17kJ / cm, hand welded (current: 170A, voltage: 25V, speed:
15 cm / min), and the conditions under which the presence of surface cracks, root cracks, and cross-section cracks were checked.
第２表に示される結果からも明らかなように、本発明で
規定する条件通りに製造された極厚鋼板は良好な溶接性
を示し、かつ所望の強度（降伏強度:90kgf/mm2以上，引
張強度:97kgf/mm2以上）及び靭性（衝撃遷移温度：−60
℃以下）が共に表面から中心に亘って全て満足している
ことが分かる。As is clear from the results shown in Table 2, the extra-thick steel sheet manufactured under the conditions specified in the present invention exhibits good weldability and has a desired strength (yield strength: 90 kgf / mm 2 or more, Tensile strength: 97 kgf / mm 2 or more) and toughness (impact transition temperature: −60)
It can be seen that all of the values (below ° C) are satisfied from the surface to the center.
これに対して、同様成分組成鋼を用いたとしても処理方
法が本発明の規定から外れると目標性能が達成できなく
なる。On the other hand, even if the same composition steel is used, if the treatment method deviates from the regulation of the present invention, the target performance cannot be achieved.
例えば、試験番号５のように焼戻し後の冷却を空冷にす
ると強度を満足しても所望靭性が確保できない。また、
試験番号６のように第二回目の焼入れを第一回目の焼入
温度り高い温度で行うと細粒のマルテンサイト組織が得
られないため、やはり所望靭性を確保することができな
い。更に、試験番号７のようにAc1点を超える高い温度
で焼戻しを行うと強度を確保できないばかりでなく、靭
性の確保もできない。そして、試験番号８は仕上圧延温
度が低くなったため直接焼入れ温度を確保できなかった
例であるが、直接焼入によりマルテンサイト組織とする
ことができなかったことに起因して引き続く焼入時に細
粒マルテンサイトが得られず、靭性を確保することがで
きなかった。For example, if the cooling after tempering is air-cooled as in Test No. 5, the desired toughness cannot be secured even if the strength is satisfied. Also,
When the second quenching is performed at a temperature higher than the first quenching temperature as in Test No. 6, a fine-grained martensite structure cannot be obtained, and thus the desired toughness cannot be secured. Further, as in Test No. 7, when tempering is performed at a high temperature exceeding Ac 1 point, not only the strength cannot be secured, but also the toughness cannot be secured. And, test number 8 is an example in which the direct quenching temperature could not be secured because the finish rolling temperature became low, but due to the fact that the martensite structure could not be formed by direct quenching, the fine quenching during the subsequent quenching was performed. Grain martensite was not obtained, and toughness could not be secured.
一方、試験番号９〜12は素材鋼の成分組成が本発明で規
定する範囲を外れている場合の例であるが、試験番号９
及び11の結果からも分かるように、焼入性向上のため単
にCeqの高い成分系にして強度を確保したとしても所望
靭性が確保できない。また、試験番号10はSi,Cu及びＳ
が本発明での規定範囲を超える成分系の鋼を素材とした
ものであるが、母材の強度及び靭性は目標値に近いもの
の溶接性に劣っており、実用材とはならない。更に、試
験番号12は、Ni以外の元素で強度を確保しようとする成
分系の鋼を素材としたものであるが、やはり所定量のNi
添加を行わないと目標強度が確保できない。On the other hand, Test Nos. 9 to 12 are examples in which the composition of the raw material steel is out of the range specified in the present invention.
As can be seen from the results of Nos. 11 and 11, the desired toughness cannot be ensured even if the strength is secured simply by using a component system having a high Ceq to improve the hardenability. Test number 10 is Si, Cu and S
Is made of a steel having a chemical composition exceeding the specified range in the present invention, but the strength and toughness of the base material are close to the target values but are poor in weldability, and are not practical materials. Furthermore, Test No. 12 is made of a steel of a composition system that is intended to secure strength with an element other than Ni, but it is still a prescribed amount of Ni.
If it is not added, the target strength cannot be secured.
＜効果の総括＞ 以上に説明した如く、この発明によれば、板厚100mm以
上で、降伏強度:90kgf/mm2以上，引張強度:97kgf/mm2並
びに衝撃遷移温度：−60℃以下の優れた性能を有する極
厚高張力鋼板をも安定して製造することが可能となるな
ど、産業上極めて有用な効果をもたらされる。As described above <Summary of Effects> According to the present invention, in the plate thickness 100mm or more, the yield strength: 90 kgf / mm 2 or more, a tensile strength: 97kgf / mm 2 and the impact transition temperature: -60 ° C. Excellent follows It is possible to produce extremely thick high-strength steel sheets with excellent performance in a stable manner, which is extremely useful in industry.
第１図は、本発明に係る高張力鋼板製造条件の説明図で
ある。 第２図は、本発明に係る別の高張力鋼板製造条件の説明
図である。FIG. 1 is an explanatory view of high-tensile steel plate manufacturing conditions according to the present invention. FIG. 2 is an explanatory view of another high-tensile steel plate manufacturing condition according to the present invention.
Claims (2)
て熱間圧延した後、Ac3点〜1050℃の温度域に再加熱し
て焼入れし、その後更にAc3点〜950℃の温度域でかつ第
一回目の焼入れ温度以下の温度に加熱して再度の焼入れ
を行い、続いてAc1点以下の温度で焼戻しして水冷する
ことを特徴とする、靭性の優れた調質型高張力鋼板の製
造方法。1. By weight ratio, C: 0.10 to 0.20%, Si: 0.30% or less, Mn: 0.40 to 1.20%, Cu: 0.5% or less, Ni: more than 3.5 to 4.5%, Cr: 0.10 to 1.20%, Mo: 0.05 to 0.80%, V: 0.005 to 0.1%, Nb: 0.005 to 0.03%, so1.Al:0.015 to 0.10%, B: 0.0003 to 0.0030%, P: 0.010% or less, S: 0.005% or less, N : 0.004% or less, the balance of which consists essentially of Fe is heated to 1000 ℃ or more and hot-rolled, and then reheated to a temperature range of Ac 3 points to 1050 ℃ and quenched, and then Ac 3 In the temperature range of the point to 950 ° C. and at a temperature not higher than the first quenching temperature, quenching is performed again, followed by tempering at a temperature not higher than the Ac 1 point and water cooling. A method for manufacturing an excellent tempered high-strength steel sheet.
熱間圧延し、900℃以上の温度域にて30％以上の累積圧
下を与えると共に仕上圧延を800℃以上で終了した後そ
のまま水冷し、次いでAc3点〜950℃の温度域に再加熱し
て焼入れを行い、引き続いてAc1点以下の温度で焼戻し
して水冷することを特徴とする、靭性の優れた調質型高
張力鋼板の製造方法。2. By weight ratio, C: 0.10 to 0.20%, Si: 0.30% or less, Mn: 0.40 to 1.20%, Cu: 0.5% or less, Ni: more than 3.5 to 4.5%, Cr: 0.10 to 1.20%, Mo: 0.05 to 0.80%, V: 0.005 to 0.1%, Nb: 0.005 to 0.03%, so1.Al:0.015 to 0.10%, B: 0.0003 to 0.0030%, P: 0.010% or less, S: 0.005% or less, N : 0.004% or less of steel, the balance of which is essentially Fe, is heated to 1000 ° C or higher and hot-rolled to give a cumulative reduction of 30% or more in the temperature range of 900 ° C or higher and finish rolling of 800 ° C or higher. After that, it is water-cooled as it is, then reheated to a temperature range of Ac 3 point to 950 ° C to perform quenching, and subsequently tempered at a temperature of Ac 1 point or less and water-cooled, which is excellent in toughness. Method for manufacturing tempered high-strength steel sheet.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP63293343A JPH0670250B2 (en) | 1988-11-19 | 1988-11-19 | Manufacturing method of tempered high strength steel sheet with excellent toughness |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP63293343A JPH0670250B2 (en) | 1988-11-19 | 1988-11-19 | Manufacturing method of tempered high strength steel sheet with excellent toughness |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH02141528A JPH02141528A (en) | 1990-05-30 |
| JPH0670250B2 true JPH0670250B2 (en) | 1994-09-07 |
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| KR100957929B1 (en) * | 2002-12-18 | 2010-05-13 | 주식회사 포스코 | Method for manufacturing high-tensile steel sheets having excellent low temperature toughness |
| KR101028613B1 (en) | 2008-11-11 | 2011-04-11 | 신닛뽄세이테쯔 카부시키카이샤 | High strength thick steel sheet and its manufacturing method |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61127813A (en) * | 1984-11-22 | 1986-06-16 | Nippon Steel Corp | Production of high arrest refined steel containing ni |
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1988
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|---|---|---|---|---|
| JPS61127813A (en) * | 1984-11-22 | 1986-06-16 | Nippon Steel Corp | Production of high arrest refined steel containing ni |
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