JP3399983B2 - Method for producing high-strength steel sheet with excellent weldability and low yield ratio of 570 N / mm2 or more - Google Patents
Method for producing high-strength steel sheet with excellent weldability and low yield ratio of 570 N / mm2 or moreInfo
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- JP3399983B2 JP3399983B2 JP22609192A JP22609192A JP3399983B2 JP 3399983 B2 JP3399983 B2 JP 3399983B2 JP 22609192 A JP22609192 A JP 22609192A JP 22609192 A JP22609192 A JP 22609192A JP 3399983 B2 JP3399983 B2 JP 3399983B2
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Description
【0001】[0001]
【産業上の利用分野】本発明は、主として建築構造物に
使用される570N/mm2級以上の調質高張力鋼板に関し、詳
しくは、溶接性の優れた降伏比の低い570N/mm2級以上の
高張力鋼板の製造方法に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tempered high-strength steel sheet of 570 N / mm 2 grade or higher, which is mainly used for building structures, and more specifically, 570 N / mm 2 grade with excellent weldability and low yield ratio. The present invention relates to the method for manufacturing a high-strength steel plate described above.
【0002】[0002]
【従来の技術】引張強さ570N/mm2級以上の調質高張力鋼
板は、タンク、橋梁、ペンストックなどに使用されてき
たが、焼入れ焼もどしによってマルテンサイトやベイナ
イトなどの高硬度のミクロ組織の生成を利用しているた
め、降伏比(降伏強さ/引張強さ)が通常90%以上と高
く、塑性変形能が十分でなく、大地震時に十分な安全性
を確保できないため、建築用としてはほとんど用いられ
なかった。 2. Description of the Related Art Heat-treated high-strength steel sheets with a tensile strength of 570 N / mm 2 grade or higher have been used for tanks, bridges, penstocks, etc., but by quenching and tempering, high hardness micro steel such as martensite and bainite. Since the generation of structure is used, the yield ratio (yield strength / tensile strength) is usually as high as 90% or more, the plastic deformability is not sufficient, and sufficient safety cannot be ensured in the event of a large earthquake. It was rarely used for business.
【0003】近年、建築構造物に対しては高層化、大ス
パン化の要求が強まり従来の 490N/mm2 級鋼板から、よ
り強度の高い570N/mm2級以上の高張力鋼板を使用しよう
とする動きが強まり、降伏比を85%程度以下に低減した
高張力鋼板が要求されるようになった。In recent years, there has been an increasing demand for building structures to have a higher layer and a larger span, and it has been attempted to use high-strength steel plates of 570 N / mm 2 class or higher, which are stronger than the conventional 490 N / mm 2 class steel plate. This has led to the demand for high-strength steel sheets with a yield ratio reduced to around 85% or less.
【0004】この要求を満足する鋼板として、Ac3点以
上の温度からの再加熱焼入れ(Q)〔あるいはAr3点以
上の温度からの直接焼入れ(DQ)〕とAc1点未満の温
度での焼もどし(T)との組み合せからなる従来の熱処
理方法と異なり、この二つの熱処理の中間に、二相域温
度(Ac1点以上Ac3点未満)からの焼入れ(Q’)を施
す新たな熱処理方法(Q−Q’−TおよびDQ−Q’−
T法)が開発された。この方法によれば、Q’によって
低硬度で延性に優れるフェライトが組織中に生成するた
め、低い降伏比が得られるのである。As a steel sheet satisfying this requirement, reheating quenching (Q) from a temperature of Ac 3 point or higher (or direct quenching from a temperature of Ar 3 point or higher (DQ)) and a temperature of less than Ac 1 point Different from the conventional heat treatment method consisting of a combination with tempering (T), a new quenching (Q ') from the two-phase region temperature (Ac 1 point or more and Ac 3 points or less) is performed between these two heat treatments. Heat treatment method (Q-Q'-T and DQ-Q'-
T method) was developed. According to this method, a low yield ratio is obtained because ferrite having low hardness and excellent ductility is generated in the structure due to Q '.
【0005】このような、熱処理によって得られる低降
伏比の570N/mm2級鋼板は、高層建築用として使用される
ようになったが、フェライトの生成を利用しているた
め、所定の強度を確保するためには従来の570N/mm2級鋼
板よりも炭素当量を高くする必要があり、溶接性がやや
劣るという問題があり、その改善が求められている。The low yield ratio 570N / mm 2 class steel sheet obtained by such heat treatment has come to be used for high-rise buildings, but since it utilizes the formation of ferrite, it has a predetermined strength. In order to secure it, it is necessary to make the carbon equivalent higher than that of the conventional 570N / mm 2 grade steel sheet, and there is a problem that the weldability is slightly inferior, and improvement is required.
【0006】一方、建築物がさらに高層化するにともな
い、溶接施工量が増大するという問題が生じ、これを防
ぐ目的から、鋼板の板厚減少を達成するために、より高
強度鋼板の使用が検討されている。すなわち、引張強さ
780N/mm2級以上で低降伏比の鋼板への開発要求が強まっ
ている。[0006] On the other hand, as the number of buildings increases, the amount of welding work increases, and in order to prevent this, it is necessary to use higher strength steel sheets in order to reduce the thickness of the steel sheets. Is being considered. That is, tensile strength
There is an increasing demand for development of steel plates with a high yield ratio of 780 N / mm 2 or higher.
【0007】しかしながら、前述のQ−Q’−T法によ
っても、780N/mm2級鋼板の場合には、高い強度と低降伏
比を確保するためには、フェライトを生成させると同時
に、マルテンサイトやベイナイトの硬度や分率を高めね
ばならないため、その炭素当量は従来型の780N/mm2級鋼
板よりも高める必要があり、溶接性が劣るという問題が
あった。However, even in the case of the 780 N / mm 2 grade steel sheet, in order to secure high strength and low yield ratio, the above-mentioned Q-Q'-T method also produces ferrite and at the same time produces martensite. Since the hardness and the fraction of bainite must be increased, the carbon equivalent must be higher than that of the conventional 780N / mm 2 grade steel sheet, and there was the problem of poor weldability.
【0008】[0008]
【発明が解決しようとする課題】本発明は、引張強さ57
0N/mm2級以上の調質高張力鋼板において、85%以下の低
い降伏比を確保すると同時に、従来のQ−T法による高
降伏比型高張力鋼板と同等以上の溶接性の優れた降伏比
の低い570N/mm2級以上の高張力鋼板の製造方法を提供す
ることを目的とするものである。The present invention has a tensile strength of 57.
For tempered high-strength steel sheets of 0 N / mm 2 grade or higher, while maintaining a low yield ratio of 85% or less, yield yielding excellent weldability equivalent to or higher than the high yield ratio type high-strength steel sheets by the conventional QT method. It is an object of the present invention to provide a method for producing a high-strength steel sheet having a low ratio of 570 N / mm 2 or higher.
【0009】[0009]
【課題を解決するための手段】本発明者らは、引張強さ
570N/mm2級以上の高強度を確保しつつ、85%以下の低降
伏比と良好な溶接性を確保するために、鋭意研究を行っ
た。その結果、低降伏比を実現する上で重要なQ’(二
相域からの焼入れ)に替えてModifiedQ’(二相域温度
に加熱後、所定の温度まで空冷した後、焼入れ)とする
新型熱処理の適用により、低降伏比を維持したまま、Q
−Q’−T法の場合よりも高強度を実現し得るという知
見を得て本発明に至ったものである。The present inventors have found that the tensile strength
In order to secure a high strength of 570 N / mm 2 class or higher, a low yield ratio of 85% or less and a good weldability, intensive research was conducted. As a result, a new type that replaces Q '(quenching from the two-phase region), which is important for realizing a low yield ratio, with Modified Q' (heats to the two-phase region temperature and then air-cools to a predetermined temperature, then quenches) By applying heat treatment, while maintaining a low yield ratio, Q
The present invention has been completed based on the finding that higher strength can be realized than in the case of the -Q'-T method.
【0010】このQ−ModifiedQ’−T法の活用によ
り、高強度化が可能な分だけ鋼板の炭素当量を低減する
ことができるため、低降伏比型高張力鋼板の溶接性の改
善が可能となるのである。By utilizing the Q-Modified Q'-T method, it is possible to reduce the carbon equivalent of the steel sheet by an amount capable of increasing the strength, so that it is possible to improve the weldability of the low yield ratio type high strength steel sheet. It will be.
【0011】その第1発明は、C:0.05〜0.20%、 Si:0.
05〜0.50%、 Mn:0.30〜1.80%、Al:0.005〜0.10%を含
有し、残部Feおよび不可避的不純物からなる鋼片を熱間
圧延した後、下記の熱処理を施す溶接性の優れた降伏比
の低い570N/mm2級以上の高張力鋼板の製造方法である。
熱処理方法:焼入れ(Q)+特殊焼入れ(Modified
Q’)+焼もどし(T)
ただし、焼入れ温度:Ac3点以上 980℃以下
特殊焼入れ:Ac1点以上Ac3点未満に加熱し、 400〜70
0 ℃の間の所定の温度まで空冷した後、焼入れを行う
焼もどし温度:400 ℃点以上Ac1点未満The first invention is that C: 0.05 to 0.20%, Si: 0.
05-0.50%, Mn: 0.30-1.80%, Al: 0.005-0.10%, hot-rolled steel slab consisting of balance Fe and unavoidable impurities, and then heat-treated as follows. This is a method for producing high-strength steel sheets with a low ratio of 570 N / mm 2 or higher. Heat treatment method: Quenching (Q) + Special quenching (Modified
Q ') + tempering (T) However, quenching temperature: Ac 3 points or more and 980 ° C or less Special quenching: Ac 1 point or more and less than Ac 3 points, 400 to 70
After air cooling to a specified temperature between 0 ° C, quenching Tempering temperature: 400 ° C or more and less than Ac 1 point
【0012】第2発明は、C:0.05〜0.20%、 Si:0.05〜
0.50%、 Mn:0.30〜1.80%、Al:0.005〜0.10%を含有
し、残部Feおよび不可避的不純物からなる鋼片を圧延仕
上温度がAr3点以上の温度で熱間圧延し直接焼入れを行
った後、下記の熱処理を施す溶接性の優れた降伏比の低
い570N/mm2級以上の高張力鋼板の製造方法である。
熱処理方法:特殊焼入れ(ModifiedQ’)+焼もどし
(T)
ただし、特殊焼入れ:Ac1点以上Ac3点未満に加熱し、
400〜700 ℃間の所定の温度まで空冷した後、焼入れを
行う
焼もどし温度:400 ℃点以上Ac1点未満The second invention is C: 0.05-0.20%, Si: 0.05-
Direct quenching is performed by hot rolling a steel slab containing 0.50%, Mn: 0.30 to 1.80%, Al: 0.005 to 0.10% and the balance Fe and unavoidable impurities at a rolling finish temperature of Ar 3 points or higher. After that, the following heat treatment is performed, which is a method for producing a high-strength steel sheet having a high yield ratio of 570 N / mm 2 or higher and excellent weldability. Heat treatment method: Special quenching (Modified Q ') + tempering (T) However, special quenching: Heating at Ac 1 point or more and less than Ac 3 points,
After air cooling to a specified temperature between 400 and 700 ° C, quenching Tempering temperature: 400 ° C or higher and less than Ac 1 point
【0013】第3発明は、化学成分として、さらに Cu:
0.05〜1.20%、 Ni:0.05〜3.00%、Cr: 0.05〜1.20%、
Mo:0.05〜1.00%、 V:0.005〜0.08%、Nb:0.005〜0.05
%、B:0.0003〜0.0025%、Ti:0.005〜0.025 %、Ca:0.0
01〜0.010 %の内から選んだ1種または2種以上を含有
する請求項1または2記載の溶接性の優れた降伏比の低
い570N/mm2級以上の高張力鋼板の製造方法である。A third aspect of the present invention further comprises Cu:
0.05 to 1.20%, Ni: 0.05 to 3.00%, Cr: 0.05 to 1.20%,
Mo: 0.05-1.00%, V: 0.005-0.08%, Nb: 0.005-0.05
%, B: 0.0003 to 0.0025%, Ti: 0.005 to 0.025%, Ca: 0.0
The method for producing a high-strength steel sheet having a high yield ratio of 570 N / mm 2 or more, which has excellent weldability and contains at least one selected from the range of 01 to 0.010%.
【0014】[0014]
【作用】以下に、本発明の製造条件について説明する。
まず、熱処理方法の限定理由について説明する。本発明
者らは表1に示す化学成分を有する鋼板を用い、いく種
類かの熱処理を施し、強度、降伏比に及ぼす熱処理方法
の影響について調べた。熱処理としては、従来の780N/m
m2級鋼板に適用されているQ−T法、二相域熱処理であ
るQ’を含むQ−Q’−T法、これを改良したQ−Modi
fiedQ’−T法の3種類である。熱処理条件を図1に示
す。The manufacturing conditions of the present invention will be described below.
First, the reasons for limiting the heat treatment method will be described. The inventors of the present invention used a steel sheet having the chemical composition shown in Table 1 and performed some kinds of heat treatments to investigate the influence of the heat treatment method on the strength and the yield ratio. The conventional heat treatment is 780 N / m
Q-T method applied to m 2 grade steel sheets, Q-Q'-T method including Q'which is a two-phase heat treatment, and improved Q-Modi
There are three types of fied Q'-T method. The heat treatment conditions are shown in FIG.
【0015】ここで、Q:Ac3点以上の温度からの再加
熱焼入れ、
Q’:二相域温度(Ac1点以上Ac3点未満)からの再加
熱焼入れ、
ModifiedQ’:二相域温度に加熱後、所定の温度まで空
冷した後、焼入れ、
T:Ac1点未満の温度からの焼もどしである。
なお、ModifiedQ’熱処理における焼入れ開始温度は 7
00〜280 ℃の範囲で変化させた。Here, Q: reheating and quenching from a temperature of Ac 3 points or more, Q ': reheating and quenching from a two-phase region temperature (Ac 1 point or more and less than Ac 3 points), Modified Q': two-phase region temperature After heating to T, the material is air-cooled to a predetermined temperature, then quenched, and tempered from a temperature of T: Ac less than 1 point. The tempering start temperature in Modified Q'heat treatment is 7
It was changed in the range of 00 to 280 ° C.
【0016】熱処理後の引張試験結果を図2に示す。図
から従来型のQ−T法では、降伏比は90%以上であるの
に比べ、二相域熱処理を含む他の2種類の方法では、い
ずれも85%以下の低降伏比が得られること、これらの二
相域熱処理法の中でも、ModifiedQ’の焼入れ開始温度
が 400〜700 ℃のQ−ModifiedQ’−T法の場合には、
Q−Q’−T法の場合よりも高い引張強さが得られてい
ることがわかる。The results of the tensile test after the heat treatment are shown in FIG. From the figure, the conventional Q-T method has a yield ratio of 90% or more, while the other two methods including the two-phase heat treatment can obtain a low yield ratio of 85% or less. Among these two-phase heat treatment methods, in the case of the Q-Modified Q'-T method in which the quenching start temperature of Modified Q'is 400 to 700 ° C,
It can be seen that higher tensile strength is obtained than in the case of QQ'-T method.
【0017】このように、Q−ModifiedQ’−T法とい
う新規な熱処理は、低い降伏比を確保しながら高強度化
する上で非常に有効である。As described above, the new heat treatment called the Q-Modified Q'-T method is very effective in increasing the strength while ensuring a low yield ratio.
【0018】この理由は、図3に模式的に示すようなミ
クロ組織の相違によるものと考えられる。すなわち、第
1段の熱処理Qに引き続き二相域に加熱した段階では、
マルテンサイトや下部ベイナイトの前組織は部分的にオ
ーステナイトに逆変態する。その後の冷却においては、
Q’熱処理ではただちに焼入れを行うため、オーステナ
イトは硬さの高いマルテンサイトや下部ベイナイトに変
態する。The reason for this is considered to be due to the difference in microstructure as schematically shown in FIG. That is, at the stage where the first-stage heat treatment Q is followed by heating in the two-phase region,
The pre-structure of martensite and lower bainite partially reverse transforms to austenite. In the subsequent cooling,
In the Q'heat treatment, quenching is performed immediately, so that austenite transforms to high hardness martensite or lower bainite.
【0019】これに対し、ModifiedQ’熱処理では、初
期の空冷時に少量のフェライトが生成するとともにオー
ステナイト中へのC の濃縮が生じ、この段階から焼入れ
を行うため、C の濃縮したオーステナイトからはC 濃度
が高くより高硬度のマルテンサイトが生成するものと考
えられる。したがって、Q−ModifiedQ’−T法の方が
Q−Q’−T法の場合よりも高い強度が得られるのであ
る。なお、この場合にも軟質のフェライトが硬質層中に
分散するため低い降伏比が得られるのである。On the other hand, in the Modified Q'heat treatment, a small amount of ferrite is generated during the initial air cooling, and C is concentrated in austenite. Since quenching is performed from this stage, the C concentration is increased from the austenite enriched with C. It is considered that martensite with high hardness and higher hardness is generated. Therefore, the Q-Modified Q'-T method can obtain higher strength than the Q-Q'-T method. In this case as well, since the soft ferrite is dispersed in the hard layer, a low yield ratio can be obtained.
【0020】[0020]
【表1】 [Table 1]
【0021】以上の新知見を活用することにより、本発
明者らは570N/mm2級以上の低降伏比型高張力鋼板の溶接
性の改善を試みた。表2に示すように、従来のQ−Q’
−T法による低降伏比型570N/mm2級鋼板の炭素当量約0.
44%に対し、炭素当量を0.39%にまで低減した鋼に、Q
−ModifiedQ’−T法とQ−Q’−T法を適用した。そ
の機械的性質を表2に併記する。By utilizing the above new knowledge, the present inventors have tried to improve the weldability of a high yield strength steel sheet with a low yield ratio of 570 N / mm 2 or higher. As shown in Table 2, the conventional Q-Q '
Carbon equivalent of about 0 low yield ratio 570N / mm 2 class steel sheet by -T method.
For steel with carbon equivalent reduced to 0.39% against 44%, Q
-Modified Q'-T method and Q-Q'-T method were applied. Its mechanical properties are also shown in Table 2.
【0022】表2から明らかなように、Q−Modified
Q’−T法を適用した場合には、低い炭素当量であるに
もかかわらず十分な強度と低い降伏比が得られている。
これに対し、Q−Q’−T法を適用すると、炭素当量が
低いため、十分な強度が確保できなかった。As is clear from Table 2, Q-Modified
When the Q'-T method is applied, sufficient strength and low yield ratio are obtained despite the low carbon equivalent.
On the other hand, when the QQ'-T method is applied, sufficient strength cannot be secured because the carbon equivalent is low.
【0023】以上の理由から、本発明においては熱処理
方法として、Q−ModifiedQ’−T法に限定する。な
お、Q熱処理については、完全なオーステナイト域から
の焼入れという意味では同等である圧延後の直接焼入れ
によってもよい。For the above reasons, in the present invention, the heat treatment method is limited to the Q-Modified Q'-T method. The Q heat treatment may be direct quenching after rolling, which is equivalent in terms of quenching from a complete austenite region.
【0024】[0024]
【表2】 [Table 2]
【0025】つぎに、上記の各熱処理における温度範囲
の限定理由について説明する。焼入れ温度については、
マルテンサイトやベイナイトなどの高硬度のミクロ組織
を生成させ、十分な強度を確保するために、完全なオー
ステナイト域とする必要があり、Ac3点以上とする。し
かし、あまりに高い温度であると組織が粗大化し、延
性、靱性が劣化するため、上限を980 ℃とする。Next, the reason for limiting the temperature range in each of the above heat treatments will be described. For the quenching temperature,
In order to generate a high-hardness microstructure such as martensite and bainite and secure sufficient strength, it is necessary to make it a complete austenite region, and Ac is set to 3 or more. However, if the temperature is too high, the structure becomes coarse and the ductility and toughness deteriorate, so the upper limit is made 980 ° C.
【0026】また、直接焼入れを行う場合の圧延仕上温
度をAr3点以上とする理由は、これよりも圧延仕上温度
が低下すると、二相域熱処理の前に十分に焼きの入った
マルテンサイトやベイナイト相を確保することができず
強度確保が困難となるためである。Further, the reason why the rolling finishing temperature in the case of direct quenching is set to Ar 3 point or higher is that when the rolling finishing temperature is lower than this, the martensite and the fully tempered before the two-phase region heat treatment are This is because the bainite phase cannot be secured and it becomes difficult to secure the strength.
【0027】ModifiedQ’の焼入れ開始温度について
は、フェライトの生成にともなうオーステナイトへのC
の濃縮を利用して高C マルテンサイトを生成させ、高強
度化を図るためには、前述の図2に示されるように、焼
入れ開始温度を 400〜700 ℃の範囲とする必要がある。Regarding the quenching start temperature of Modified Q ', C in austenite accompanying the formation of ferrite
In order to generate high-C martensite by utilizing the above-mentioned concentration and achieve high strength, it is necessary to set the quenching start temperature in the range of 400 to 700 ° C as shown in Fig. 2 described above.
【0028】焼もどし温度に関しては、靱性を向上させ
構造物の安全性を確保する上では、あまり低い温度では
好ましくないため、400 ℃以上とする。一方、Ac1点を
超えると強度の低下を生じるため、Ac1点未満とする。The tempering temperature is set to 400 ° C. or higher because it is not preferable at a too low temperature for improving the toughness and ensuring the safety of the structure. On the other hand, if it exceeds the Ac 1 point, the strength is lowered, so the value is set to less than the Ac 1 point.
【0029】つぎに、本発明における化学成分の限定理
由について説明する。C は高張力鋼板としての強度を確
保するために必要な元素であり、含有量が0.05%未満で
は引張強さ570N/mm2級以上の強度が得がたい。また、0.
20%を超えて添加すると耐溶接割れ性を害するので好ま
しくない。したがって、C 含有量は0.05〜0.20%の範囲
とする。Next, the reasons for limiting the chemical components in the present invention will be explained. C is an element necessary to secure the strength as a high-strength steel sheet, and if the content is less than 0.05%, it is difficult to obtain a tensile strength of 570 N / mm 2 grade or higher. Also, 0.
If it is added in excess of 20%, the weld crack resistance is impaired, which is not preferable. Therefore, the C content is in the range of 0.05 to 0.20%.
【0030】Siは脱酸に必要な元素であるが、含有量が
0.05%未満ではこの効果は少なく、また、0.50%を超え
て過多に添加すると、溶接性、靱性を劣化させるので好
ましくない。したがって、Si含有量は0.05〜0.50%の範
囲とする。Si is an element necessary for deoxidation, but its content is
If it is less than 0.05%, this effect is small, and if it is added in excess of 0.50%, the weldability and toughness are deteriorated, which is not preferable. Therefore, the Si content is set to the range of 0.05 to 0.50%.
【0031】Mnは焼入れ性を向上させ、板厚内部の強度
を確保するために必要な元素であるが、含有量が0.30%
未満ではこのような効果が十分に得られず、また、1.80
%を超えて過多に添加すると、溶接性、靱性を劣化させ
るので好ましくない。したがって、Mn含有量は0.30〜1.
80%の範囲とする。Mn is an element necessary for improving the hardenability and ensuring the strength inside the plate thickness, but its content is 0.30%.
If it is less than 1, this effect is not sufficiently obtained, and 1.80
If it is added in excess, the weldability and toughness are deteriorated, which is not preferable. Therefore, the Mn content is 0.30 to 1.
The range is 80%.
【0032】Alは脱酸元素であり、含有量が 0.005%未
満ではそのような効果は少なく、また、0.10%を超えて
添加すると、靱性の劣化をもたらす。したがって、Al含
有量は 0.005〜0.10%の範囲とする。Al is a deoxidizing element, and if the content is less than 0.005%, such an effect is small, and if it exceeds 0.10%, toughness is deteriorated. Therefore, the Al content should be in the range of 0.005 to 0.10%.
【0033】この他に、Cu、Ni、Cr、Mo、V 、Nb、B 、
Ti、Caなどを板厚、目標靱性レベルに応じて1種または
2種以上添加するものとする。Besides this, Cu, Ni, Cr, Mo, V, Nb, B,
Ti, Ca, etc. are added in one kind or two or more kinds depending on the plate thickness and the target toughness level.
【0034】Cuは固溶強化、析出強化により強度上昇に
有効な元素であるが、含有量が0.05%未満ではこのよう
な効果を十分に発揮することができず、また、1.20%を
超えて添加すると熱間加工性が劣化し鋼板表面に割れが
生じやすい。したがって、Cu含有量は0.05〜1.20%の範
囲とする。Cu is an element effective for increasing strength by solid solution strengthening and precipitation strengthening, but if the content is less than 0.05%, such effects cannot be sufficiently exhibited, and if it exceeds 1.20%. If added, hot workability deteriorates and cracks easily occur on the steel sheet surface. Therefore, the Cu content is in the range of 0.05 to 1.20%.
【0035】Niは靱性を向上させる効果があるが、含有
量が0.05%未満ではその十分な効果が得られず、また、
3.00%を超えて添加するとスケール疵が発生しやすくな
り、またコストアップにもなる。したがって、Ni含有量
は0.05〜3.00%の範囲とする。Ni has an effect of improving the toughness, but if the content is less than 0.05%, the sufficient effect cannot be obtained.
If added in excess of 3.00%, scale defects are likely to occur and the cost will increase. Therefore, the Ni content is in the range of 0.05 to 3.00%.
【0036】Crは焼入れ性向上に有効な元素であるが、
含有量が0.05%未満ではこのような効果は十分に発揮さ
れず、また、1.20%を超えて添加すると溶接性を害す
る。したがって、Cr含有量は0.05〜1.20%の範囲とす
る。Although Cr is an element effective for improving hardenability,
If the content is less than 0.05%, such an effect is not sufficiently exhibited, and if it exceeds 1.20%, the weldability is impaired. Therefore, the Cr content is in the range of 0.05 to 1.20%.
【0037】Moは焼入れ性を高め、焼もどし軟化抵抗を
増す元素であるが、含有量が0.05%未満では十分な効果
が得られず、また、1.00%を超えて過剰に添加すると、
溶接性を劣化させ、コストアップにもなる。したがっ
て、Mo含有量は0.05〜1.00%の範囲とする。Mo is an element that enhances the hardenability and increases the resistance to temper softening, but if the content is less than 0.05%, a sufficient effect cannot be obtained, and if it is added in excess of 1.00%,
It also deteriorates the weldability and increases the cost. Therefore, the Mo content is set to 0.05 to 1.00%.
【0038】V は少量の添加により、焼入れ性を増し、
焼もどし軟化抵抗を高める元素であり、その効果を得る
ためには、 0.005%以上の添加が必要であるが、0.08%
を超えて添加すると溶接性を害する。したがって、V 含
有量は 0.005〜0.08%の範囲とする。By adding a small amount of V, the hardenability is increased,
It is an element that enhances temper softening resistance. To obtain its effect, it is necessary to add 0.005% or more, but 0.08%
If added in excess of 1, the weldability will be impaired. Therefore, the V content should be in the range of 0.005 to 0.08%.
【0039】Nbは結晶粒微細化作用を有し、また直接焼
入れ・焼もどしを行う場合には析出強化作用をもたらす
元素である。その効果を得るためには、 0.005%以上の
添加が必要であり、また、0.05%を超えて添加すると溶
接性、靱性を劣化させる傾向にある。したがって、Nb含
有量は 0.005〜0.05%の範囲とする。Nb is an element which has a crystal grain refining action, and also exerts a precipitation strengthening action when directly quenching and tempering. To obtain this effect, addition of 0.005% or more is necessary, and addition in excess of 0.05% tends to deteriorate weldability and toughness. Therefore, the Nb content should be in the range of 0.005 to 0.05%.
【0040】B は微量で焼入れ性の向上をもたらす元素
であるが、含有量が0.0003%未満ではその効果が得られ
ず、また、0.0025%を超えて添加すると靱性が劣化す
る。したがって、B 含有量は0.0003〜0.0025%の範囲と
する。Although B is an element that improves the hardenability in a small amount, its effect cannot be obtained if the content is less than 0.0003%, and the toughness deteriorates if it is added in excess of 0.0025%. Therefore, the B content should be in the range of 0.0003 to 0.0025%.
【0041】Tiは脱酸作用、 Nの固定化による Bの焼入
れ性向上効果の促進作用を有するが、含有量が 0.005%
未満ではこれらの効果が得られず、また、 0.025%を超
えて添加すると介在物の増加により靱性が劣化する。し
たがって、Ti含有量は 0.005〜0.025 %の範囲とする。Ti has a deoxidizing effect and an effect of promoting the hardenability improving effect of B by immobilizing N, but the content is 0.005%.
If it is less than 0.025%, these effects cannot be obtained, and if it exceeds 0.025%, the toughness deteriorates due to the increase of inclusions. Therefore, the Ti content should be in the range of 0.005 to 0.025%.
【0042】Caは非金属介在物の球状化作用を有し、異
方性の低減に有効であるが、含有量が0.001 %未満では
その十分な効果が得られず、また、0.010 %を超えて添
加すると介在物の増加により靱性が劣化する。したがっ
て、Ca含有量は 0.001〜0.010 %の範囲とする。Ca has a spheroidizing action of non-metallic inclusions and is effective in reducing anisotropy, but if the content is less than 0.001%, the sufficient effect cannot be obtained, and if it exceeds 0.010%. If added as an additive, the toughness deteriorates due to the increase of inclusions. Therefore, the Ca content should be in the range of 0.001 to 0.010%.
【0043】[0043]
【実施例】以下に、本発明に係わる溶接性の優れた降伏
比の低い570N/mm2級以上の高張力鋼板の製造方法の実施
例について説明するが、本発明は本実施例のみに限定さ
れるものではない。[Examples] Hereinafter, examples of a method for producing a high-strength steel sheet having a high yield ratio and a low yield ratio of 570 N / mm 2 or more according to the present invention will be described, but the present invention is limited to the present embodiment. It is not something that will be done.
【0044】供試鋼板は表3に示す化学成分を有する鋼
片を、表4に示す板厚25〜80mmの鋼板に圧延した後、表
4に示す熱処理条件で熱処理したものである。これらの
鋼板から試験片を採取し、母材の引張試験を行った。そ
の結果を熱処理条件とともに表4に併記する。The test steel sheet is obtained by rolling a steel piece having the chemical composition shown in Table 3 into a steel sheet having a plate thickness of 25 to 80 mm shown in Table 4 and then heat treating it under the heat treatment conditions shown in Table 4. Test pieces were sampled from these steel plates and a tensile test of the base material was performed. The results are also shown in Table 4 together with the heat treatment conditions.
【0045】表4から明らかなように、本発明法A〜I
は、いずれも570N/mm2級以上の引張強さと85%未満の低
降伏比を有している。As is clear from Table 4, the present invention methods A to I
Have a tensile strength of 570 N / mm 2 or higher and a low yield ratio of less than 85%.
【0046】これに対して、比較例J〜Nは熱処理方法
がQ−ModifiedQ’−T法でないため強度が低すぎる
か、降伏比が高すぎる。On the other hand, in Comparative Examples J to N, since the heat treatment method is not the Q-Modified Q'-T method, the strength is too low or the yield ratio is too high.
【0047】[0047]
【表3】 [Table 3]
【0048】[0048]
【表4】 [Table 4]
【0049】[0049]
【発明の効果】以上説明したように、本発明の溶接性の
優れた降伏比の低い570N/mm2級以上の高張力鋼板の製造
方法は、化学成分を制御し、圧延後、焼入れし、さらに
二相域温度に加熱後、所定の温度まで空冷した後、焼入
れし、その後、焼もどしを行う熱処理を行っているた
め、良好な溶接性を有し、85%以下の低い降伏比を有す
る570N/mm2級以上の鋼板の製造が可能であるという優れ
た効果を有するものである。As described above, the method for producing a high-strength steel sheet having a low yield ratio of 570 N / mm 2 or more, which has excellent weldability according to the present invention, controls the chemical composition, and after rolling, quenching, After further heating to the two-phase region temperature, air cooling to a predetermined temperature, quenching, and then tempering are performed, so good weldability and low yield ratio of 85% or less are obtained. It has an excellent effect that a steel sheet of 570 N / mm 2 grade or more can be manufactured.
【図1】熱処理条件を示す図である。FIG. 1 is a diagram showing heat treatment conditions.
【図2】熱処理後の引張試験結果を示す図である。FIG. 2 is a diagram showing a tensile test result after heat treatment.
【図3】熱処理段階ごとのミクロ組織の相違を模式的に
示す図である。FIG. 3 is a diagram schematically showing a difference in microstructure at each heat treatment stage.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 岡野 重雄 兵庫県加古川市金沢町1番地 株式会社 神戸製鋼所 加古川製鉄所内 (56)参考文献 特開 昭63−286517(JP,A) 特開 昭64−55335(JP,A) 特開 平4−110423(JP,A) 特開 平4−318(JP,A) (58)調査した分野(Int.Cl.7,DB名) C21D 8/02 C22C 38/00 301 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shigeo Okano 1 Kanazawa-machi, Kakogawa-shi, Hyogo Kobe Steel Works Kakogawa Steel Works (56) Reference JP-A-63-286517 (JP, A) JP-A-64 -55335 (JP, A) JP 4-110423 (JP, A) JP 4-318 (JP, A) (58) Fields investigated (Int.Cl. 7 , DB name) C21D 8/02 C22C 38/00 301
Claims (3)
n:0.30〜1.80%、Al:0.005〜0.10%を含有し、残部Feお
よび不可避的不純物からなる鋼片を熱間圧延した後、下
記の熱処理を施すことを特徴とする溶接性の優れた降伏
比の低い570N/mm2級以上の高張力鋼板の製造方法。 熱処理方法:焼入れ(Q)+特殊焼入れ(Modified
Q’)+焼もどし(T) ただし、焼入れ温度:Ac3点以上 980℃以下 特殊焼入れ:Ac1点以上Ac3点未満に加熱し、 400〜70
0 ℃の間の所定の温度まで空冷した後、焼入れを行う 焼もどし温度:400 ℃点以上Ac1点未満1. C: 0.05 to 0.20%, Si: 0.05 to 0.50%, M
n: 0.30 to 1.80%, Al: 0.005 to 0.10%, hot-rolled steel slab consisting of the balance Fe and unavoidable impurities, and then subjected to the following heat treatment yielding excellent weldability A method for manufacturing high-strength steel sheets with a low ratio of 570 N / mm 2 or higher. Heat treatment method: Quenching (Q) + Special quenching (Modified
Q ') + tempering (T) However, quenching temperature: Ac 3 points or more and 980 ° C or less Special quenching: Ac 1 point or more and less than Ac 3 points, 400 to 70
After air cooling to a specified temperature between 0 ° C, quenching Tempering temperature: 400 ° C or more and less than Ac 1 point
n:0.30〜1.80%、Al:0.005〜0.10%を含有し、残部Feお
よび不可避的不純物からなる鋼片を圧延仕上温度がAr3
点以上の温度で熱間圧延し直接焼入れを行った後、下記
の熱処理を施すことを特徴とする溶接性の優れた降伏比
の低い570N/mm2級以上の高張力鋼板の製造方法。 熱処理方法:特殊焼入れ(ModifiedQ’)+焼もどし
(T) ただし、特殊焼入れ:Ac1点以上Ac3点未満に加熱し、
400〜700 ℃間の所定の温度まで空冷した後、焼入れを
行う 焼もどし温度:400 ℃点以上Ac1点未満2. C: 0.05 to 0.20%, Si: 0.05 to 0.50%, M
A steel slab containing n: 0.30 to 1.80% and Al: 0.005 to 0.10% and the balance Fe and unavoidable impurities has a rolling finish temperature of Ar 3
A method for producing a high-strength steel sheet having a high yield ratio of 570 N / mm 2 or higher, which is excellent in weldability, which is obtained by hot rolling at a temperature equal to or higher than a point, direct quenching, and then performing the heat treatment described below. Heat treatment method: Special quenching (Modified Q ') + tempering (T) However, special quenching: Heating at Ac 1 point or more and less than Ac 3 points,
After air cooling to a specified temperature between 400 and 700 ° C, quenching Tempering temperature: 400 ° C or higher and less than Ac 1 point
%、 Ni:0.05〜3.00%、Cr: 0.05〜1.20%、 Mo:0.05〜
1.00%、 V:0.005〜0.08%、Nb:0.005〜0.05%、B:0.00
03〜0.0025%、Ti:0.005〜0.025 %、Ca:0.001〜0.010
%の内から選んだ1種または2種以上を含有する請求項
1または2記載の溶接性の優れた降伏比の低い570N/mm2
級以上の高張力鋼板の製造方法。3. The chemical composition further contains Cu: 0.05 to 1.20.
%, Ni: 0.05 to 3.00%, Cr: 0.05 to 1.20%, Mo: 0.05 to
1.00%, V: 0.005-0.08%, Nb: 0.005-0.05%, B: 0.00
03-0.0025%, Ti: 0.005-0.025%, Ca: 0.001-0.010
%, 570 N / mm 2 with excellent weldability and low yield ratio, containing one or more selected from the group
High-strength steel sheet of higher grade or higher.
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JP22609192A JP3399983B2 (en) | 1992-08-25 | 1992-08-25 | Method for producing high-strength steel sheet with excellent weldability and low yield ratio of 570 N / mm2 or more |
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JPH0665636A JPH0665636A (en) | 1994-03-08 |
JP3399983B2 true JP3399983B2 (en) | 2003-04-28 |
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ID=16839686
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JP4710488B2 (en) * | 2005-08-30 | 2011-06-29 | Jfeスチール株式会社 | Method for producing 9% Ni steel with excellent low temperature toughness |
CN102618799B (en) * | 2012-03-22 | 2014-07-23 | 宝山钢铁股份有限公司 | High-performance quenched and tempered steel plate with 80 kg carbon equivalent and manufacturing method of high-performance quenched and tempered steel plate |
CN103695782B (en) * | 2013-12-16 | 2016-03-09 | 武汉钢铁(集团)公司 | Tensile strength 630MPa level transportable pressure vessel steel and production method thereof |
KR101449511B1 (en) * | 2014-07-29 | 2014-10-13 | 한국기계연구원 | Work hardenable yield ratio control steel and method for manufacturing the same |
CN108950380A (en) * | 2018-06-11 | 2018-12-07 | 南京钢铁股份有限公司 | A kind of Q690GJ building sheet and preparation method thereof |
CN111441000A (en) * | 2020-03-30 | 2020-07-24 | 江阴兴澄特种钢铁有限公司 | 690 MPa-yield-strength low-yield-ratio high-strength steel plate and manufacturing method thereof |
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