JP2652538B2 - Method for producing high-strength steel with excellent weldability and low-temperature toughness - Google Patents
Method for producing high-strength steel with excellent weldability and low-temperature toughnessInfo
- Publication number
- JP2652538B2 JP2652538B2 JP19943687A JP19943687A JP2652538B2 JP 2652538 B2 JP2652538 B2 JP 2652538B2 JP 19943687 A JP19943687 A JP 19943687A JP 19943687 A JP19943687 A JP 19943687A JP 2652538 B2 JP2652538 B2 JP 2652538B2
- Authority
- JP
- Japan
- Prior art keywords
- temperature
- steel
- cooling
- toughness
- strength
- 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 - Lifetime
Links
Landscapes
- Heat Treatment Of Steel (AREA)
Description
【発明の詳細な説明】 産業上の利用分野 本発明は、溶接性及び低温靭性にすぐれる引張強さ54
kgf/mm2以上の高強度鋼の製造方法に関し、詳しくは、
船舶、海洋構造物、LPGタンク等に好適に用いることが
できる高強度鋼の製造方法に関する。DETAILED DESCRIPTION OF THE INVENTION INDUSTRIAL APPLICATION The present invention relates to a tensile strength 54 having excellent weldability and low-temperature toughness.
relates to a manufacturing method of kgf / mm 2 or more high-strength steels, particularly,
The present invention relates to a method for producing high-strength steel that can be suitably used for ships, marine structures, LPG tanks, and the like.
従来の技術 船舶や海洋構造物に用いられる鋼板には、構造物の軽
量化及び溶接施工コストの低減を目的として、溶接性に
すぐれる凍強度鋼が要求されている。2. Description of the Related Art For steel plates used in ships and marine structures, frost-strength steels having excellent weldability are required for the purpose of reducing the weight of the structures and reducing welding work costs.
かかる要望に応えるために、例えば、特開昭58−9681
7号公報、特開昭59−13641号公報、特開昭60−174820号
公報等に記載されているように、Nb及びTiを含有する鋼
片を圧延し、圧延終了後、200℃以下の温度まで直接焼
入れし、次いで、Ac1点以下の温度で焼戻しすることに
よつて、高強度鋼を製造する方法が既に多数提案されて
いる。しかし、このように、圧延終了後に200℃以下の
温度まで直接焼入れする方法によれば、直接焼入れ後、
水素が鋼板内に残存し、水素性欠陥が発生しやすい問題
がある。To meet such a demand, for example, Japanese Patent Application Laid-Open No. 58-9681
No. 7, JP-A-59-13641, JP-A-60-174820, as described in JP-A-60-174820, and rolled a steel slab containing Nb and Ti, after the completion of rolling, 200 ℃ or less Many methods have already been proposed for producing high-strength steel by directly quenching to a temperature and then tempering at a temperature of 1 point or less of Ac. However, according to the method of directly quenching to a temperature of 200 ° C. or less after the end of rolling, after direct quenching,
There is a problem that hydrogen remains in the steel sheet and hydrogen defects are likely to occur.
他方、低温靭性を高めるために、特開昭59−100214号
公報や特開昭61−143517号公報に記載されていれよう
に、Niを多量に添加する方法や、或いは特開昭60−5901
8号公報、「鉄と鋼」1985年S1507頁等に記載されている
ように、Cuを1.0％以上添加して、その析出強化作用を
利用する方法も提案されている。しかし、このようなNi
やCuを多量に添加する方法によるときは、製造費用が非
常に高くなり、他方、溶接も低下する問題がある。On the other hand, as described in JP-A-59-100214 and JP-A-61-143517, in order to enhance low-temperature toughness, a method of adding a large amount of Ni, or JP-A-60-5901
As described in No. 8, "Iron and Steel", 1985, p. S1507, a method of adding 1.0% or more of Cu and utilizing its precipitation strengthening action has been proposed. But such Ni
When a method of adding a large amount of Cu or Cu is used, the production cost becomes extremely high, and on the other hand, there is a problem that welding is reduced.
発明が解決しようとする問題点 本発明者らは、従来の高強度鋼の製造における上記し
た問題を解決するために鋭意研究した結果、ＣとNbの添
加量を最適に規制した鋼片をNbが固溶する温度に加熱
し、制御圧延にて結晶粒を微細にした後、300℃以上の
温度まで水冷し、その後、空冷又は徐冷することによつ
て水素を放出させ、更に、最適な温度で再加熱すること
によつて、水素性欠陥が少なく、且つ、溶接性及び低温
靭性にすぐれる高強度鋼を得ることができることを見出
して本発明に至つたものである。Problems to be Solved by the Invention The present inventors have conducted intensive studies to solve the above-described problems in the production of conventional high-strength steel, and as a result, have obtained a steel slab in which the amounts of C and Nb added are optimally regulated. Is heated to a temperature at which the solid solution is dissolved, the crystal grains are refined by controlled rolling, water-cooled to a temperature of 300 ° C. or more, and then hydrogen is released by air cooling or slow cooling, and then the optimal The present inventors have found that reheating at a temperature can provide a high-strength steel with few hydrogen defects and excellent weldability and low-temperature toughness.
問題点を解決するための手段 本発明による溶接性及び低温靭性にすぐれる高強度鋼
の製造方法の第１は、重量％で Ｃ 0.01〜0.15％、 Si 0.05〜0.50％、 Mn 0.80〜2.00％、 Al 0.01〜0.10％ Nb 0.01〜0.10％、 Ti 0.005〜0.020％、 Ｎ 0.0020〜0.0080％、 残部鉄及び不可避的不純物よりなり、且つ、 とするとき、 Ceq≦0.38％、且つ、 0.10≦Ｃ＋2.5Nb≦0.18（％） （但し、元素記号は当該元素の鋼中の添加量（重量％）
を示す。） を満たす鋼片を1150〜1250℃の温度に加熱し、未再結晶
域における累積圧下率が50％以上となるように熱間圧延
し、（Ar3−40）〜（Ar3＋60）℃の温度にて圧延を終了
し、２℃／秒以上の冷却速度にて300〜550℃の範囲の温
度まで加速冷却し、次いで、空冷又は徐冷にて室温まで
冷却した後、550〜650℃の範囲の温度に再加熱すること
を特徴とする。Means for Solving the Problems The first method for producing a high-strength steel having excellent weldability and low-temperature toughness according to the present invention is as follows: C 0.01 to 0.15%, Si 0.05 to 0.50%, Mn 0.80 to 2.00% by weight. , Al 0.01 to 0.10% Nb 0.01 to 0.10%, Ti 0.005 to 0.020%, N 0.0020 to 0.0080%, balance iron and unavoidable impurities, and Where, Ceq ≦ 0.38% and 0.10 ≦ C + 2.5Nb ≦ 0.18 (%) (However, the element symbol indicates the amount of the element added in steel (% by weight)
Is shown. ) Heating billet to a temperature of 1150 to 1250 ° C. satisfying the cumulative rolling reduction is hot rolled so as to be 50% or more in the pre-recrystallization region, (Ar 3 -40) ~ ( Ar 3 +60) ℃ Rolling is completed at a temperature of 3 ° C., accelerated cooling to a temperature in the range of 300 to 550 ° C. at a cooling rate of 2 ° C./sec or more, and then cooled to room temperature by air cooling or slow cooling, and then 550 to 650 ° C. It is characterized by reheating to a temperature in the range of
本発明による溶接性及び低温靭性にすぐれる高強度鋼
の製造方法の第２は、上記（ａ）として規定した元素に
加えて、下記（ｂ）として規定するように、 （ｂ）Cu 0.05〜0.70％、 Ni 0.05〜0.70％、 Cr 0.05〜0.50％、 Mo 0.05〜0.50％ Ｖ 0.01〜0.10％、 Ca 0.0005〜0.0040％、及び REM0.005〜0.03％ よりなる群から選ばれる少なくとも１種の元素を含有
し、残部鉄及び不可避的不純物よりなり、且つ、 とするとき、 Ceq≦0.38％、且つ、 0.10≦Ｃ＋2.5Nb≦0.18（％） （但し、元素記号は当該元素の鋼中の添加量（重量％）
を示す。） を満たす鋼片を前記第１の方法と同様に処理することを
特徴とするものである。The second method of producing a high-strength steel having excellent weldability and low-temperature toughness according to the present invention is as follows: (b) Cu 0.05 to At least one element selected from the group consisting of 0.70%, Ni 0.05 to 0.70%, Cr 0.05 to 0.50%, Mo 0.05 to 0.50%, V 0.01 to 0.10%, Ca 0.0005 to 0.0040%, and REM 0.005 to 0.03% Containing the balance iron and unavoidable impurities, and Where, Ceq ≦ 0.38% and 0.10 ≦ C + 2.5Nb ≦ 0.18 (%) (However, the element symbol indicates the amount of the element added in steel (% by weight)
Is shown. ) Is treated in the same manner as in the first method.
先ず、本発明において用いる鋼片の化学成分について
説明する。First, the chemical composition of the billet used in the present invention will be described.
Ｃは、鋼強度54kgf/mm2以上を確保するために、0.01
％以上を添加することが必要である。しかし、過多に添
加するときは、耐溶接割れ性の劣化や、溶接熱影響部
（HAZ）の靭性劣化を招くので、添加量は0.15％以下と
する。C, in order to secure the steel strength 54kgf / mm 2 or more, 0.01
% Or more must be added. However, excessive addition causes deterioration of welding crack resistance and deterioration of the toughness of the heat affected zone (HAZ). Therefore, the addition amount is set to 0.15% or less.
Siは、鋼の脱酸及び強度上昇に効果を有し、かかる効
果を有効に得るためには、0.05％以上を添加する必要が
ある。しかし、過多に添加するときは、溶接性を劣化せ
るので、添加量の上限は0.50％とする。Si has an effect on deoxidation and strength increase of steel, and it is necessary to add 0.05% or more to effectively obtain such an effect. However, excessive addition deteriorates the weldability, so the upper limit of the addition amount is 0.50%.
Mnは、鋼の強度を上昇させるために、0.80％以上を添
加する。しかし、2.00％を越える過多量の添加は、溶接
性を劣化させる。Mn is added in an amount of 0.80% or more to increase the strength of the steel. However, an excessive addition exceeding 2.00% deteriorates weldability.
Alは、鋼の脱酸と共に、AlNとして結晶粒の微細化に
効果を有する。これらの効果を有効に得るためには、少
なくとも0.01％を添加することが必要であるが、0.10％
を越えて過多に添加するときは、靭性を害する。Al has the effect of deoxidizing steel and also as AlN to refine crystal grains. In order to obtain these effects effectively, it is necessary to add at least 0.01%, but 0.10%
If added in excess of, the toughness is impaired.
Nbは、本発明において最も重要な元素である。即ち、
Nbは、加熱圧延時には、オーステナイトの再結晶を抑制
し、仕上温度の低下によつて、微細なオーステナイト粒
を生成させ、延いては靭性を向上させる。更に、加速冷
却後に固溶したままであるNbは、再加熱時に炭窒化物と
して析出し、強度を上昇させる。これらの効果を有効に
得るためには、本発明においては、Nbを少なくとも0.01
％添加することが必要である。しかし、過多に添加する
ときは、溶接性を劣化させることとなるので、添加量は
0.10％以下とする。Nb is the most important element in the present invention. That is,
Nb suppresses austenite recrystallization during hot rolling, and generates fine austenite grains by lowering the finishing temperature, thereby improving toughness. Further, Nb which remains in a solid solution after accelerated cooling precipitates as carbonitride upon reheating and increases the strength. In order to effectively obtain these effects, in the present invention, Nb should be at least 0.01%.
% Must be added. However, adding too much will degrade weldability, so the amount added is
0.10% or less.
Tiは、母材靭性及びHAZ靭性を確保するために必須の
元素である。圧延加熱時にTiは難固溶のTiNとして析出
しているため、オーステナイト結晶粒の粗大化を防止
し、延いては母材靭性を向上させる。また、溶接時にお
いても、微細分散したTiN粒子がHAZの結晶粒粗大化を防
止し、HAZ靭性を向上させる。これらの効果を有効に発
現させるために、最適の添加量範囲は、本発明において
は、0005〜0.020％とする。Ti is an element essential for ensuring base metal toughness and HAZ toughness. Since Ti is precipitated as hardly soluble TiN at the time of rolling and heating, coarsening of austenite crystal grains is prevented, and the base material toughness is further improved. Also, at the time of welding, the finely dispersed TiN particles prevent the crystal grains of the HAZ from becoming coarse and improve the HAZ toughness. In order to effectively exhibit these effects, the optimum addition amount range is set to 0005 to 0.020% in the present invention.
Ｎは、上記したように、Tiと結合して、TiN粒子とし
て、母材靭性及びHAZ靭性を向上させる。Ｎ量が余り少
ないときは、靭性を向上に寄与するTiN量も過小となる
ため、Ｎは少なくとも0.0020％が必要である。しかし、
Ｎ量が過多であるときは、靭性に有害な遊離Ｎが増加す
るので、含有量の上限は0.0080％に規制される。As described above, N combines with Ti to improve base material toughness and HAZ toughness as TiN particles. When the amount of N is too small, the amount of TiN contributing to the improvement of toughness becomes too small, so that N needs to be at least 0.0020%. But,
When the amount of N is excessive, free N which is harmful to toughness increases, so that the upper limit of the content is restricted to 0.0080%.
本発明においては、前述した合金元素のうち、ＣとNb
については、その添加量が 0.10≦Ｃ＋2.5Nb≦0.18（％） （但し、元素記号は、当該元素の鋼中において添加量
（重量％）を示す。） なる関係を満たすことが必要である。ＣとNbとを前述し
た範囲でそれぞれ添加しても、Ｃ＋0.25Nbが0.10％より
も少ないときは、引張強さ54kgf/mm2以上を得ることが
できず、他方、Ｃ＋0.25Nbが0.18％を越えるときは、溶
接性及びHAZ靭性が劣化するからである。即ち、本発明
によれば、ＣとNbの添加量を上記のように最適に規制す
ることによつて、所期の引張強さを確保しつつ、同時に
すぐれた溶接性を確保することができる。In the present invention, among the above-mentioned alloy elements, C and Nb
It is necessary that the addition amount satisfies the following relationship: 0.10 ≦ C + 2.5Nb ≦ 0.18 (%) (where the element symbol indicates the addition amount (% by weight) in the steel of the element). Even if C and Nb are added in the above-mentioned ranges, respectively, when C + 0.25Nb is less than 0.10%, a tensile strength of 54 kgf / mm 2 or more cannot be obtained, while C + 0.25Nb has 0.18% This is because, when it exceeds, weldability and HAZ toughness deteriorate. That is, according to the present invention, by controlling the addition amounts of C and Nb optimally as described above, it is possible to secure the desired tensile strength and at the same time secure excellent weldability. .
更に、本発明においては、 とするとき、Ceq≦0.38％ 0.10≦Ｃ＋2.5Nb≦0.18（％）であることが必要であ
る。Ceqが0.38％を越えるときは、少入熱溶接時に溶接
部の硬化性が増し、溶接割れが生じやすくなるために、
溶接時の予熱が必要となり、更に、HAZ靭性の劣化も大
きくなる。Further, in the present invention, In this case, it is necessary that Ceq ≦ 0.38% 0.10 ≦ C + 2.5Nb ≦ 0.18 (%). When Ceq exceeds 0.38%, the hardening of the welded portion increases during low heat input welding, and welding cracks are likely to occur.
Preheating at the time of welding is required, and the deterioration of HAZ toughness also increases.
本発明による高強度鋼の製造方法においては、用いる
鋼片は、前記した元素に加えて、Cu、Ni、Cr、Mo、Ｖ、
Ca及びREMよりなる群から選ばれる少なくとも１種の元
素を含有することができる。In the method for producing a high-strength steel according to the present invention, the billet used is, in addition to the above-described elements, Cu, Ni, Cr, Mo, V,
It can contain at least one element selected from the group consisting of Ca and REM.
Cuは、強度上昇に有効な元素であつて、この効果を有
効に得るためには、0.05％以上を添加する必要がある
が、0.70％を越えて過多に添加するときは、熱間割れが
生じやすくなり、溶接性が劣化する。Cu is an element effective for increasing the strength. To obtain this effect effectively, it is necessary to add 0.05% or more. However, if it is added excessively exceeding 0.70%, hot cracking may occur. This easily occurs and the weldability deteriorates.
Niは、HAZ靭性を劣化させることなく、強度を上昇さ
せる効果を有する。この効果を有効に得るためには、0.
05％以上を添加する必要があるが、0.70％を越えて過多
に添加するときは、溶接性の劣化を招くのみならず、Ni
は高価な元素であるので、添加量の上限を0.70％とす
る。Ni has the effect of increasing strength without deteriorating HAZ toughness. To obtain this effect effectively, 0.
It is necessary to add not less than 05%, but if added over 0.70%, not only will the weldability deteriorate, but also Ni
Is an expensive element, so the upper limit of the addition amount is set to 0.70%.
Cr及びMoは、いずれも鋼の強度を高める元素である
が、添加量がそれぞれ0.05％よりも少ないときは、上記
効果が十分に発現されない。しかし、いずれの元素も0.
50％を越えて過多に添加するときは、溶接性及びHAZ靭
性の劣化を招来する。従つて、Cr及びMoのいずれの元素
についても、その添加量は0.05〜0.50％の範囲とする。Both Cr and Mo are elements that increase the strength of the steel, but when the added amount is less than 0.05%, the above effects are not sufficiently exhibited. However, all elements are 0.
Excessive addition exceeding 50% causes deterioration of weldability and HAZ toughness. Therefore, the addition amount of any of the elements Cr and Mo is in the range of 0.05 to 0.50%.
Ｖは、強度上昇を目的として添加されるが、0.01％よ
りも少ないときは、上記効果が乏しく、他方、0.10％を
越えるときは、溶接性を阻害する。V is added for the purpose of increasing the strength. When V is less than 0.01%, the above effect is poor. On the other hand, when V exceeds 0.10%, the weldability is impaired.
Caは、異方性の改善及び耐ラメラテイア特性の向上に
効果を有するが、0.0005％よりも少ない添加量では上記
効果に乏しく、他方、0.0040％を越えて過多に添加して
も、その効果が飽和するので、経済的ではない。Ca has an effect of improving anisotropy and improving lamella tear resistance. However, the effect is poor at an addition amount of less than 0.0005%. On the other hand, even if it is added excessively exceeding 0.0040%, the effect is not improved. It is not economical because it saturates.
REMも、Caと同様の効果を有し、0.005％以上の添加が
有効である。しかし、0.030％を越えるときは、大型の
介在物が生成するので、添加量の上限を0.030％とす
る。REM also has the same effect as Ca, and the addition of 0.005% or more is effective. However, when the content exceeds 0.030%, large inclusions are generated, so the upper limit of the addition amount is set to 0.030%.
本発明による第２の製造方法においても、 とするとき、Ceq≦0.38％、且つ、 0.10≦Ｃ＋2.5Nb≦0.18（％）であることが必要であ
る。Ceqが0.38％を越えるときは、少入熱溶接時に溶接
部の硬化性が増し、溶接割れが生じやすくなるために、
溶接時の予熱が必要となり、更に、HAZ靭性の劣化も大
きくなるからである。In the second manufacturing method according to the present invention, In this case, it is necessary that Ceq ≦ 0.38% and 0.10 ≦ C + 2.5Nb ≦ 0.18 (%). When Ceq exceeds 0.38%, the hardening of the welded portion increases during low heat input welding, and welding cracks are likely to occur.
This is because preheating at the time of welding is required, and the deterioration of HAZ toughness also increases.
次に、本発明における製造方法について説明する。 Next, the manufacturing method in the present invention will be described.
鋼片の加熱温度は、Nbの析出強化による強度上昇を最
大限に発揮させるために、添加したNbがすべて固溶する
温度以上とすることが重要である。しかし、加熱温度が
高すぎる場合は、オーステナイト粒が粗大化し、靭性の
劣化を招く。従つて、本発明におては、鋼片加熱温度を
1150〜1250℃の範囲とする。It is important that the heating temperature of the steel slab be equal to or higher than the temperature at which all the added Nb forms a solid solution in order to maximize the strength increase due to the precipitation strengthening of Nb. However, if the heating temperature is too high, the austenite grains become coarse and the toughness deteriorates. Therefore, in the present invention, the billet heating temperature is
The range is 1150 to 1250 ° C.
本発明においては、鋼片を上記温度に加熱した後、未
再結晶域においてオーステナイト粒内に変形帯を多く導
入し、フエライト変態の核として最終的にフエライト結
晶粒を微細化して、靭性をすぐれたものとするために、
未再結晶化域における累積圧下率50％以上とすると共
に、圧延終了温度を（Ar3−40）〜（Ar3＋60）℃として
熱間圧延を終了する。In the present invention, after heating the steel slab to the above temperature, a large number of deformation zones are introduced into the austenite grains in the non-recrystallized region, and finally the ferrite crystal grains are refined as nuclei of the ferrite transformation to improve the toughness. In order to
The hot rolling is completed by setting the cumulative rolling reduction in the non-recrystallized region to 50% or more, and setting the rolling end temperature to (Ar 3 −40) to (Ar 3 +60) ° C.
更に、加速冷却によつてNb炭窒化物の析出を抑制し、
再加熱後の析出強化を有効に確保するために、上記圧延
終了後に、できる限りに速やかに加速冷却を開始し、且
つ、この加速冷却においては、２℃／秒以上の冷却速度
にて水冷することが必要である。Further, the precipitation of Nb carbonitride is suppressed by accelerated cooling,
In order to effectively ensure precipitation strengthening after reheating, accelerated cooling is started as soon as possible after the end of the rolling, and water is cooled at a cooling rate of 2 ° C./sec or more in this accelerated cooling. It is necessary.
上記加速冷却の停止温度は、水素性欠陥の発生を抑制
するために、300〜550℃の範囲の温度である。室温まで
冷却した場合は、水素が冷却後の鋼板に残存したままと
なるため、水素に起因する欠陥や割れが発生しやすくな
る。The stop temperature of the accelerated cooling is a temperature in the range of 300 to 550 ° C. in order to suppress the generation of hydrogen defects. When cooled to room temperature, hydrogen remains in the steel sheet after cooling, so that defects and cracks due to hydrogen are likely to occur.
従来、直接焼入れは、圧延後、組織をマルテンサイト
又は下部ベイナイト主体の組織とするために、室温まで
水冷して、変態を完了させることを目的としており、HT
−80クラスの高強度鋼の場合は、このように、室温まで
焼入れることが必要である。Conventionally, direct quenching, after rolling, in order to make the structure martensite or lower bainite-based structure, water cooling to room temperature, the purpose is to complete the transformation, HT
In the case of a −80 class high-strength steel, it is necessary to harden to room temperature.
しかし、本発明による鋼は、引張強さ54kgf/mm2以上
であるHT−60クラスの強度レベルを対象としており、本
発明においては、低温靭性の向上の観点から圧延仕上温
度を低下させているため、水冷後の組織は、フエライト
−ベイナイト又はフエライト−ベイナイト−マルテンサ
イト又はアシキユラーフエライト主体の組織となる。即
ち、本発明の方法においては、水冷は、焼入れではな
く、フエライト粒の微細化、ベイナイト分率の増大、或
いはNb炭窒化物の析出抑制のために行なうのであり、Ms
点以下の室温まで冷却する必要はない。また、圧延、冷
却後、再加熱した鋼の強度は、本発明に従つて製造した
ものと、室温まで冷却したものと同じである。従つて、
本発明の方法においては、室温まで水冷せず、水素を鋼
板外に放出させるために、300〜550℃の範囲の温度まで
水冷し、その後は空冷又は徐冷によつて室温まで冷却す
る。However, the steel according to the present invention is intended for the strength level of the HT-60 class having a tensile strength of 54 kgf / mm 2 or more, and in the present invention, the rolling finish temperature is lowered from the viewpoint of improving the low-temperature toughness. Therefore, the structure after water cooling is a structure mainly composed of ferrite-bainite, ferrite-bainite-martensite, or acidular ferrite. That is, in the method of the present invention, water cooling is performed not for quenching but for refining ferrite grains, increasing the bainite fraction, or suppressing the precipitation of Nb carbonitride.
There is no need to cool to room temperature below the point. Also, the strength of the steel re-heated after rolling and cooling is the same as that produced according to the invention and that cooled to room temperature. Therefore,
In the method of the present invention, water is not cooled to room temperature, but is cooled to a temperature in the range of 300 to 550 ° C. in order to release hydrogen out of the steel sheet, and then cooled to room temperature by air cooling or slow cooling.
本発明の方法によれば、上記のようにして、加速冷却
後、室温まで空冷又は徐冷して得た鋼板を、550〜650℃
の範囲の温度に再加熱することによつて、Nb炭窒化物が
析出し、靭性の劣化が殆どなしに、高強度化が達成れ
る。更に、この再加熱は、加速冷却後の残留応力の低減
にも有効である。上述の加速冷却後、室温まで冷却した
ままでは、Nb炭窒化物が析出せず、Nbの効果が有効に活
用されない。According to the method of the present invention, as described above, after accelerated cooling, the steel sheet obtained by air cooling or slow cooling to room temperature, 550 ~ 650 ℃
By reheating to a temperature in the range, Nb carbonitride is precipitated, and high strength is achieved with almost no deterioration in toughness. Further, this reheating is also effective in reducing residual stress after accelerated cooling. After cooling to room temperature after the above-described accelerated cooling, Nb carbonitride does not precipitate, and the effect of Nb is not effectively utilized.
発明の効果 以上のように、本発明によれば、ＣとNbの添加量を最
適に規制した鋼片をNbが固溶する温度に加熱し、制御圧
延にて結晶粒を微細にした後、300℃以上の温度まで水
冷し、その後、空冷又は徐冷することによつて水素を放
出させ、更に、最適な温度で再加熱し、Nb炭窒化物を析
出させて高強度化を図るので、水素性欠陥が少なく、且
つ、溶接時に予熱の必要なしに、母材及びHAZの靭性に
すぐれる高強度鋼を得ることができる。Effects of the Invention As described above, according to the present invention, a steel slab in which the addition amounts of C and Nb are optimally controlled is heated to a temperature at which Nb forms a solid solution, and crystal grains are refined by controlled rolling. Water is cooled to a temperature of 300 ° C or higher, and then hydrogen is released by air cooling or slow cooling, and further reheating is performed at an optimum temperature to precipitate Nb carbonitride to increase the strength. It is possible to obtain a high-strength steel having few hydrogen defects and excellent toughness of the base material and the HAZ without requiring preheating at the time of welding.
実施例 以下に実施例を挙げて本発明を説明するが、本発明は
これらの実施例により何ら限定されるものではない。EXAMPLES Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.
第１表に示す化学成分を有する本発明鋼Ａ〜Ｅ及び比
較鋼Ｇ〜Ｊを第２表に示す温度に加熱し、熱間圧延した
後、所定の冷却速度にて所定の温度まで加速冷却し、次
いで、室温まで空冷し、更に、この後、600℃又は680℃
に再加熱した。このようにして得たそれぞれの鋼板につ
いて、その水素性欠陥を有無、母材特性、溶接部靭性及
び溶接性を第２表に示す。The present invention steels A to E and the comparative steels G to J having the chemical components shown in Table 1 were heated to the temperatures shown in Table 2, hot rolled, and then accelerated to a predetermined temperature at a predetermined cooling rate. And then air-cooled to room temperature and then 600 ° C or 680 ° C
Was reheated. Table 2 shows the presence / absence of hydrogen defects, base metal properties, weld toughness, and weldability of each of the steel sheets thus obtained.
この結果から明らかなように、本発明鋼は、水素性欠
陥による割れがなく、引張強さ54kgf/mm2以上の強度を
有し、更に、母材のvTrsが−80℃以下、溶接継手ボンド
部のvE-40が4.0kgf・ｍ以上の高靭性を有しており、斜
めＹ形溶接割れ試験における割れ防止予熱温度が25℃以
下であつて、すぐれた溶接性を有することが明らがであ
る。As is clear from these results, the present invention steel, no cracking due to hydrogen defects have a tensile strength of 54kgf / mm 2 or more strength, further, vTrs of the base material is -80 ° C. or less, welded joint bond VE- 40 has high toughness of 4.0 kgf ・ m or more, and the crack prevention preheating temperature in the oblique Y-shaped weld cracking test is 25 ° C or less, indicating that it has excellent weldability. It is.
比較鋼２は、加熱温度が低すぎ、比較鋼３は、冷却温
度が遅く、比較鋼４は、冷却後の再加熱温度が高すぎる
ために、いずれも強度が低い。比較鋼６は仕上温度が高
すぎ、未再結晶域では圧下率が小さいために、母材靭性
が悪く、また、比較鋼７は圧延終了後、室温まで水冷し
たために、水素性欠陥による割れが発生している。Comparative steel 2 has a too low heating temperature, comparative steel 3 has a low cooling temperature, and comparative steel 4 has a low strength because the reheating temperature after cooling is too high. In Comparative Steel 6, the finishing temperature was too high, and in the unrecrystallized region, the rolling reduction was small, so that the base material toughness was poor. In addition, Comparative Steel 7 was water-cooled to room temperature after the completion of rolling, so that cracks due to hydrogen defects were generated. It has occurred.
比較鋼Ｇは、Ｃ＋2.5Nbが0.10％よりも少 なく、従つて、これより得られた比較鋼12は、強度が不
足している。他方、比較鋼ＨはＣ＋2.5Nbが0.18％を越
えており、従つて、これより得られた比較鋼13は、割れ
防止予熱温度が高く、溶接部靭性も悪い。Tiを含有して
いな比較鋼Ｉから得られた比較鋼14は、母材靭性及び溶
接部靭性が悪く、また、Nbを含有していない比較鋼Ｊか
ら得られた比較鋼15は、強度が低い。Comparative steel G has C + 2.5Nb less than 0.10% Therefore, the comparative steel 12 obtained therefrom lacks strength. On the other hand, the comparative steel H has a C + 2.5Nb content exceeding 0.18%, and thus the comparative steel 13 obtained therefrom has a high crack prevention preheating temperature and poor weld toughness. Comparative steel 14 obtained from comparative steel I not containing Ti had poor base metal toughness and weld toughness, and comparative steel 15 obtained from comparative steel J not containing Nb had a strength. Low.
本発明鋼Ｃについて、第２表において、加速冷却後、
室温まで空冷して得た鋼板の再加熱温度と、強度及び靭
性との関係を第１図に示す。再加熱によつて、低温靭性
には実質的に変化なしに、引張強さ及び降伏強さが高め
られることが明らかである。In the steel C of the present invention, in Table 2, after accelerated cooling,
FIG. 1 shows the relationship between the reheating temperature, strength, and toughness of the steel sheet obtained by air cooling to room temperature. It is evident that the reheating increases the tensile and yield strength with substantially no change in low temperature toughness.
第１図は、強度と靭性に及ぼす加速冷却後の再加熱温度
の影響を示すグラフである。FIG. 1 is a graph showing the effect of reheating temperature after accelerated cooling on strength and toughness.
───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 昭63−38519（ＪＰ，Ａ) 特開 昭62−103347（ＪＰ，Ａ) 特開 昭63−153217（ＪＰ，Ａ) ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-38519 (JP, A) JP-A-62-103347 (JP, A) JP-A-63-153217 (JP, A)
Claims (2)
を示す。） を満たす鋼片を1150〜1250℃の温度に加熱し、未再結晶
域における累積圧下率が50％以上となるように熱間圧延
し、（Ar3−40）〜（Ar3＋60）℃の温度にて圧延を終了
し、２℃／秒以上の冷却速度にて300〜550℃の範囲の温
度まで加速冷却し、次いで、空冷又は徐冷にて温室まで
冷却した後、550〜650℃の範囲の温度に再加熱すること
を特徴する引張強さ54kgf/mm2以上の溶接性及び低温靭
性にすぐれる高強度鋼の製造方法。[Claim 1] In terms of% by weight, C is 0.01 to 0.15%, Si is 0.05 to 0.50%, Mn is 0.80 to 2.00%, Al is 0.01 to 0.10%, Nb is 0.01 to 0.10%, Ti is 0.005 to 0.020%, N is 0.0020 to 0.0080%, and the remainder. Consisting of iron and unavoidable impurities, and Where, Ceq ≦ 0.38% and 0.10 ≦ C + 2.5Nb ≦ 0.18 (%) (However, the element symbol indicates the amount of the element added in steel (% by weight)
Is shown. ) Heating billet to a temperature of 1150 to 1250 ° C. satisfying the cumulative rolling reduction is hot rolled so as to be 50% or more in the pre-recrystallization region, (Ar 3 -40) ~ ( Ar 3 +60) ℃ Rolling is completed at a temperature of 3 ° C., accelerated cooling to a temperature in the range of 300 to 550 ° C. at a cooling rate of 2 ° C./sec or more, and then cooled to a greenhouse by air cooling or slow cooling. A method for producing a high-strength steel excellent in weldability and low-temperature toughness with a tensile strength of 54 kgf / mm 2 or more, characterized by reheating to a temperature in the range of
し、 残部鉄及び不可避的不純物よりなり、且つ、 とするとき、 Ceq≦0.38％、且つ、 0.10≦Ｃ＋2.5Nb≦0.18（％） （但し、元素記号は当該元素の鋼中の添加量（重量％）
を示す。） を満たす鋼片を1150〜1250℃の温度に加熱し、未再結晶
域における累積圧下率が50％以上となるように熱間圧延
し、（Ar3−40）〜（Ar3＋60）℃の温度にて圧延を終了
し、２℃／秒以上の冷却速度にて300〜550℃の範囲の温
度まで加速冷却し、次いで、空冷又は徐冷にて室温まで
冷却した後、550〜650℃の範囲の温度に再加熱すること
を特徴する引張強さ54kgf/mm2以上の溶接性及び低温靭
性にすぐれる高強度鋼の製造方法。2. In weight%: (a) C 0.01 to 0.15%, Si 0.05 to 0.50%, Mn 0.80 to 2.00%, Al 0.01 to 0.10% Nb 0.01 to 0.10%, Ti 0.005 to 0.020%, and N 0.0020 to (B) Cu 0.05-0.70%, Ni 0.05-0.70%, Cr 0.05-0.50%, Mo 0.05-0.50% V 0.01-0.10%, Ca 0.0005-0.040%, and REM0.005 Containing at least one element selected from the group consisting of -0.03%, the balance being iron and unavoidable impurities, and Where, Ceq ≦ 0.38% and 0.10 ≦ C + 2.5Nb ≦ 0.18 (%) (However, the element symbol indicates the amount of the element added in steel (% by weight)
Is shown. ) Heating billet to a temperature of 1150 to 1250 ° C. satisfying the cumulative rolling reduction is hot rolled so as to be 50% or more in the pre-recrystallization region, (Ar 3 -40) ~ ( Ar 3 +60) ℃ Rolling is completed at a temperature of 3 ° C., accelerated cooling to a temperature in the range of 300 to 550 ° C. at a cooling rate of 2 ° C./sec or more, and then cooled to room temperature by air cooling or slow cooling, and then 550 to 650 ° C. A method for producing a high-strength steel excellent in weldability and low-temperature toughness with a tensile strength of 54 kgf / mm 2 or more, characterized by reheating to a temperature in the range of
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP19943687A JP2652538B2 (en) | 1987-08-10 | 1987-08-10 | Method for producing high-strength steel with excellent weldability and low-temperature toughness |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP19943687A JP2652538B2 (en) | 1987-08-10 | 1987-08-10 | Method for producing high-strength steel with excellent weldability and low-temperature toughness |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS6442526A JPS6442526A (en) | 1989-02-14 |
| JP2652538B2 true JP2652538B2 (en) | 1997-09-10 |
Family
ID=16407789
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP19943687A Expired - Lifetime JP2652538B2 (en) | 1987-08-10 | 1987-08-10 | Method for producing high-strength steel with excellent weldability and low-temperature toughness |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2652538B2 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH02126219A (en) * | 1988-11-04 | 1990-05-15 | Fuji Elelctrochem Co Ltd | Optical isolator |
| JP4904774B2 (en) * | 2005-10-31 | 2012-03-28 | Ｊｆｅスチール株式会社 | Manufacturing method of high-strength, high-toughness steel with excellent strength in the medium temperature range |
| JP4904806B2 (en) * | 2005-12-26 | 2012-03-28 | Ｊｆｅスチール株式会社 | Manufacturing method of high-strength, high-toughness steel sheet with excellent strength and deformability in the middle temperature range |
-
1987
- 1987-08-10 JP JP19943687A patent/JP2652538B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6442526A (en) | 1989-02-14 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP4344073B2 (en) | High strength steel excellent in high temperature strength and method for producing the same | |
| JPH10306316A (en) | Production of low yield ratio high tensile-strength steel excellent in low temperature toughness | |
| JP4362219B2 (en) | Steel excellent in high temperature strength and method for producing the same | |
| JP3255790B2 (en) | Method for producing thick steel sheet with excellent brittle crack arrestability and low temperature toughness | |
| JPH0541683B2 (en) | ||
| JPH0781164B2 (en) | Method for manufacturing high-strength and high-toughness steel sheet | |
| JPH09256037A (en) | Production of thick high tensile strength steel plate for stress relieving annealing treatment | |
| JPS6352090B2 (en) | ||
| JP2652538B2 (en) | Method for producing high-strength steel with excellent weldability and low-temperature toughness | |
| KR102400036B1 (en) | Steel sheet having excellent low temperature toughness and low yield ratio and method of manufacturing the same | |
| JPS6167717A (en) | Manufacture of high tension steel plate having superior strength and toughness in its weld heat-affected zone | |
| JP3212344B2 (en) | Manufacturing method of structural steel plate for welding with excellent toughness at low temperature | |
| JPH083636A (en) | Production of low yield ratio high toughness steel | |
| JP2671732B2 (en) | Manufacturing method of high strength steel with excellent weldability | |
| JPH0277521A (en) | Production of ultra-high-tension steel sheet for welding having excellent homogeneity in thickness direction | |
| JPH09256038A (en) | Heat treatment before stress relieving annealing treatment for thick steel plate | |
| JPS6289815A (en) | Manufacture of high yield point steel for low temperature | |
| JP2626421B2 (en) | Manufacturing method of high strength steel with excellent weldability | |
| JP3848415B2 (en) | Method for producing low yield ratio high strength steel with excellent weldability and low temperature toughness | |
| JP3217111B2 (en) | Manufacturing method of high strength and high toughness structural steel plate | |
| JPS62158817A (en) | Manufacture of thick steel plate having high strength and high toughness | |
| JPS6367524B2 (en) | ||
| JPH08225883A (en) | Production of high tensile strength steel plate excellent in strength and toughness | |
| JPH0247525B2 (en) | ||
| JPH08143955A (en) | Production of thick-walled high tensile strength steel uniformized in strength in plate thickness direction |