【発明の詳細な説明】[Detailed description of the invention]
本発明は耐溶接割れ性のすぐれた溶接構造用高
張力鋼に関する。
溶接構造物は最近、海洋構造物、ペンストツク
等、鋼材の板厚が厚くなり、しかも構造物の拘束
度の大きいものが増えており、その場合、鋼の溶
接割れの発生の危険が高くなつている。その解決
法として、溶接時に鋼を予熱して拡散性水素を軽
減する方法、拘束度をできるだけ少なくする構造
物にする方法がある。しかし前者では溶接作業に
手間を多く要するし、予熱温度にも留意しなけれ
ばならず好ましくない。又後者では、構造物自体
の機能をもたせるためには構造物の拘束度を下げ
るには限度があり本質的な問題解決とならない。
又、溶接割れの発生しにくい鋼の検討がこれま
でもなされ、溶接割れを改善するにはC含有量を
下げることが知られているが、溶接構造用鋼には
耐溶接割れ性のみでなく、強度が高いことも要求
される。また板厚も例えば100mm程度と厚みの大
なることも要求されている。
これらの要求に対して、満足し得る溶接構造用
鋼が十分でないのが実情である。
本発明はかかる実情に鑑みて種々検討したとこ
ろ、Cの含有量を下げ、かつVとNの両方の含有
量を多くすると、溶接時に鋼の予熱を施さずとも
溶接割れが発生せず、母材強度も50キロ級の高強
度で、さらに板厚が例えば100mm程度と大であつ
ても前記の耐溶接割れ性と強度を有することを見
出し、耐溶接割れ性のすぐれた溶接構造用高張力
鋼を提供するものである。
そしてその要旨は、
C:0.04〜0.12%
Si:0.1〜1.0%
Mn:0.5〜1.8%
P:0.03%以下
S:0.01%以下
Al:0.006〜0.060%
V:0.08%を越え0.20%以下
N:0.010〜0.030%
Cu:0.1〜0.5%に
Ni:0.1〜0.5%、Cr:0.1〜0.5%の少なくとも1
種
さらにCa:0.0005〜0.0070%、Mg:0.0005〜
0.0070%の少なくとも1種
を含有し、残部鉄よりなる耐溶接割れ性のすぐれ
た溶接構造用鋼にある。
次に本発明について詳細に述べる。
以下に成分範囲を決めた理由を説明する。
Cは、溶接割れ防止のため0.12%以下が望まし
く、また、溶接割れ防止には少ない程よいけれど
も、0.04%以下では母材強度上問題があるので
0.04〜0.12%とする。
Siは製鋼上0.1%以上は添加されるが、1.0%上
では母材靭性が劣化する。
Mnは、0.5%以上、母材の強度と靭性上必要で
あるが1.8%以上では溶接割れに好ましくないの
で0.5〜1.8%とする。
P、Sも各々0.03%以上、0.01%以上になる
と、母材靭性を劣化させる。
Alは、製鋼上0.006%以上のキルド鋼のため必
要であり、一方AlはNとの親和力が強いので、
この含有量が多くなると後記するVNの生成を阻
害するのと、母材靭性を劣化させるので0.060%
以下とする。
Vは、Nとともに本発明の基本となるもので、
VNの析出を有効に作用させるため0.08%を越え
るVは必要で、0.20%以上では強度上飽和して必
要としない。
Nは、VNの有効析出のため0.010%以上必要
で、0.030%以上では、製鋼上健全な鋼塊を作る
ことがむずかしい。
Cuは、固溶強化等を通じて母材の強度上昇に
有効であるが、さらに耐溶接割れ性に対しても、
少量の添加であれば大きな影響を与えない。また
耐食性にも有効である。母材の強度を確保するた
めには、最低0.1%は必要で、0.5%より大になる
と、コスト上昇及び靭性劣化を招く。
Ni、Crは、Cu同様母材の強度上昇に有効であ
るがその量は、Ni0.1%、Cr0.1%各々以下では効
果がなく、Ni0.5%、Cr0.5%各々以上ではコスト
上昇のため問題がある。
これらの成分は選択的に1種または2種含有さ
れる。
Ca、MgはともにNによる歪時効の防止と介在
物コントロールによる母材靭性の向上があり、
0.0005%以下では効果なく、0.0070%以上ではむ
しろ劣化させる。このCaとMgはいずれか1種を
含有させれば前記の作用があり、また両方を含有
させてもよい。
本発明鋼は転炉あるいは電気炉などで溶製さ
れ、分塊圧延あるいは連続鋳造された後、熱間圧
延により製造され、圧延まま、又は焼準などの熱
処理が施されて製品となる。
図面に本発明鋼と比較鋼の耐溶接割れ性(Y開
先拘束割れ試験によるN量と割れ防止予熱温度の
開係板厚:50mm)の試験結果を示す。この試験で
の溶接法は被覆アーク溶接であり、縦軸は溶接割
れ発生を防止するため、溶接割れ防止の予熱温度
で、横軸はN含有量である。この図より明らかな
ように、本発明鋼(C:0.05%、Si:0.35%、
Mn:1.70%、P:0.010%、S:0.003%、Cu:
0.2%、Ni:0.2%、Cr:0.2%、V:0.10%、
Al:0.025%、Ca:0.0015%、N:0.0180%、残
部Fe)1は常温に相当する25℃でも溶接割れは
発生せず、予熱不要である。これに対して比較鋼
(C:0.16%、Mn:1.4%、V:0.02%、Ca:
0.0030%、残部Fe)2は予熱を必要とすること
が認められる。
以下実施例を示す。
第1表に化学成分を、第2表に母材の機械的性
能および溶接割れ防止予熱温度を示す。
The present invention relates to high-strength steel for welded structures with excellent weld cracking resistance. Recently, there has been an increase in the number of welded structures, such as offshore structures and pen stocks, where the steel plate thickness is thicker and the structure is more constrained, and in such cases, there is a high risk of weld cracking occurring in the steel. There is. As a solution, there are methods to preheat the steel during welding to reduce diffusible hydrogen, and methods to create a structure that minimizes the degree of restraint. However, in the former case, the welding operation requires a lot of effort, and the preheating temperature must also be taken into consideration, which is not preferable. Furthermore, in the latter case, there is a limit to how much the degree of restraint of the structure can be lowered in order to provide the structure with its own functions, and this does not essentially solve the problem. In addition, studies have been made to find steels that are less likely to cause weld cracking, and it is known that lowering the C content is a way to improve weld cracking. , high strength is also required. Additionally, the board is required to be as thick as, for example, about 100 mm. The reality is that there are not enough welded structural steels to meet these demands. The present invention has been developed based on various studies in view of the above circumstances, and it has been found that by lowering the C content and increasing the V and N contents, weld cracking will not occur even without preheating the steel during welding, and We have discovered that the material has a high strength of 50 kg class, and that it has the above-mentioned weld cracking resistance and strength even when the plate thickness is as large as, for example, 100 mm. It provides steel. And the gist is as follows: C: 0.04-0.12% Si: 0.1-1.0% Mn: 0.5-1.8% P: 0.03% or less S: 0.01% or less Al: 0.006-0.060% V: More than 0.08% and 0.20% or less N: At least 1 of 0.010~0.030% Cu: 0.1~0.5%, Ni: 0.1~0.5%, Cr: 0.1~0.5%
Seeds Also Ca: 0.0005~0.0070%, Mg: 0.0005~
It is a welded structural steel with excellent weld cracking resistance, containing 0.0070% of at least one kind, with the remainder being iron. Next, the present invention will be described in detail. The reasons for determining the component ranges are explained below. It is desirable for C to be 0.12% or less to prevent weld cracking.Although less is better to prevent weld cracking, if it is 0.04% or less, there will be problems with the strength of the base material.
Set at 0.04-0.12%. Si is added in an amount of 0.1% or more for steelmaking purposes, but if it exceeds 1.0%, the toughness of the base material deteriorates. Mn is 0.5% or more, which is necessary for the strength and toughness of the base metal, but 1.8% or more is unfavorable for weld cracking, so it is set at 0.5 to 1.8%. When P and S exceed 0.03% and 0.01%, respectively, the toughness of the base material deteriorates. Al is necessary for killed steel with a content of 0.006% or more in steelmaking, and on the other hand, Al has a strong affinity with N, so
If this content increases, it will inhibit the generation of VN described later and deteriorate the toughness of the base material, so 0.060%
The following shall apply. V is the basis of the present invention together with N,
More than 0.08% of V is necessary for effective VN precipitation, and if it is more than 0.20%, the strength is saturated and is not necessary. N is required to be 0.010% or more for effective precipitation of VN, and if it is 0.030% or more, it is difficult to produce a sound steel ingot. Cu is effective in increasing the strength of the base metal through solid solution strengthening, etc., but it also improves weld cracking resistance.
If added in small amounts, it will not have a large effect. It is also effective for corrosion resistance. In order to ensure the strength of the base metal, a minimum content of 0.1% is necessary; if it exceeds 0.5%, it will increase cost and deteriorate toughness. Ni and Cr, like Cu, are effective in increasing the strength of the base material, but their amounts are less than 0.1% Ni and 0.1% Cr, respectively, and are not effective, and more than 0.5% Ni and 0.5% Cr, respectively, are costly. There is a problem because of the rise. One or two types of these components are selectively contained. Both Ca and Mg prevent strain aging due to N and improve base material toughness by controlling inclusions.
If it is less than 0.0005%, it will have no effect, and if it is more than 0.0070%, it will actually deteriorate. If either one of Ca and Mg is contained, the above-mentioned effect can be obtained, or both may be contained. The steel of the present invention is produced by melting in a converter or electric furnace, followed by blooming or continuous casting, followed by hot rolling, and is made into a product either as rolled or subjected to heat treatment such as normalizing. The drawings show test results for weld cracking resistance (difference between N content and cracking prevention preheating temperature plate thickness: 50 mm in a Y-groove restraint cracking test) of the steel of the present invention and comparative steel. The welding method used in this test was covered arc welding, and the vertical axis represents the preheating temperature to prevent weld cracking, and the horizontal axis represents the N content. As is clear from this figure, the present invention steel (C: 0.05%, Si: 0.35%,
Mn: 1.70%, P: 0.010%, S: 0.003%, Cu:
0.2%, Ni: 0.2%, Cr: 0.2%, V: 0.10%,
Al: 0.025%, Ca: 0.0015%, N: 0.0180%, balance Fe) 1 does not cause weld cracking even at 25°C, which corresponds to room temperature, and does not require preheating. In contrast, comparative steel (C: 0.16%, Mn: 1.4%, V: 0.02%, Ca:
It is recognized that 0.0030%, balance Fe)2 requires preheating. Examples are shown below. Table 1 shows the chemical composition, and Table 2 shows the mechanical performance of the base metal and the preheating temperature to prevent weld cracking.
【表】【table】
【表】
ここで溶接割れ防止温度はすべて、Y開先拘束
割れ試験によるものである。
また、サンプルA−1、A−2、A−5、A−
6、A−7、A−8、およびA−9は本発明鋼
で、A−3、A−4は比較鋼である。
第2表から明らかなように、本発明鋼は強度
(引張り強さσB)が50キロ級であつて、溶接割れ
防止の予熱温度が常温に相当する30℃または25℃
以下であり、比較鋼に比較して低く、溶接時に割
れ防止のため予熱を必要としない。
即ち耐溶接割れ性がすぐれている。[Table] All welding crack prevention temperatures here are based on the Y-groove restraint cracking test. In addition, samples A-1, A-2, A-5, A-
Steels No. 6, A-7, A-8, and A-9 are inventive steels, and A-3 and A-4 are comparative steels. As is clear from Table 2, the steel of the present invention has a strength (tensile strength σ B ) of 50 kg, and the preheating temperature for preventing weld cracking is 30°C or 25°C, which is equivalent to room temperature.
It is lower than that of comparative steel, and does not require preheating to prevent cracking during welding. That is, it has excellent weld cracking resistance.
【図面の簡単な説明】[Brief explanation of the drawing]
図面は本発明鋼と比較鋼の耐溶接割れ性を示す
図である。
The drawing shows the weld cracking resistance of the steel of the present invention and comparative steel.