Metal treatment – Stock – Ferrous
Patent
1996-03-20
1998-02-17
Yee, Deborah
Metal treatment
Stock
Ferrous
148654, 148648, 420123, 420127, 219137WM, 2191461, 21914623, 21912133, C22C 3812, C21D 802, B23K 900
Patent
active
057187762
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a steel plate, which is less susceptible to welding distortion and highly deformable by lineal heating, for use in shipbuilding, offshore structures, buildings, bridges, civil engineering and the like, a process for producing the steel plate, a welding material for use in welding of the steel plate, and a method for welding the steel plate.
BACKGROUND ART
In various steel structures, at the time of welding of steel products, shrinkage on solidification of a molten metal and shrinkage and expansion on subsequent cooling and phase transformation result in an out-of-plane distortion called "angular distortion," for example, in the case of joints model by fillet welding. Such residual deformation causes a lowering in structural strength, that is, a lowering in buckling resistance, for example, when a compressive load is applied. An attempt to forcibly prevent such distortion by means of a welding jig results in the creation of excessive residual stress. Further, this results in unsatisfactory dimensional accuracy and, hence, poses a problem, associated with the production of structures, resulting in deteriorated appearance. For this reason, various proposals on straightening by local heating of residual deformation created at the time of welding, such as described in "Yosetu Henkei No Hassei To Sono Boshi (Occurrence of Distortion in Welding and Its Prevention)" in Journal of Japan Welding Society (J.W.S.), Vol. 52, Nos. 4-9, 1983, have been made based on experience. Reheating a weld, however, unavoidably leads to deteriorated quality. In addition, the time and cost necessary for the straightening work pose a serious problem. Therefore, the development of a welding method which can reduce or eliminate the straightening work, has been desired in the art.
Meanwhile, steel products used in upper structures of shipbuilding should be as thin as possible from the viewpoint of a reduction in weight. Regarding other structures as well, the use of a thin steel sheet has been desired with a view to reducing the weight. Reducing the plate thickness, however, causes the welding distortion to become significant, necessitating a great deal of labor in a work, prior to welding, for preventing creating a strain or repair of distortion created in welding (straightening).
A measure taken up to now has been mainly based on an improvement in a welding process and straightening as described in "Yosetu Henkei No Hassei To Sono Boshi (Occurrence of Distortion in Welding and Its Prevention)" in Journal of Japan Welding Society (J.W.S.), Vol. 52, Nos. 4-9, 1988. Such techniques, however, need additional work and apparatuses and, hence, unavoidably cause an increase in cost. Therefore, the development of a steel product in which welding distortion can be universally reduced has been desired in the art. Up to now, however, no useful technique for reducing welding distortion through an improvement in a steel product has been reported in the art.
Mechanisms for the creation of residual stress and distortion in a weld are described in detail in Sato, "Yosetu Kozo Binran," 1988, Kuroki Shuppan and K. Masubuchi, "Analysis of Welded Structures" 1980 PERGAMON PRESS. These publications describe that the distortion in welding is determined mainly by the geometry of the member with respect to welding heat input. That is, they do not focus on detailed properties of the welding material used. That the phase transformation temperature of a weld in a steel structure is a factor which affects the residual stress and distortion is described in the above publications. However, no study is specifically made on the quantification of influence and components with respect to a welding material contemplated for steel structures.
Sato shows in Journal of Japan Welding Society (J.W.S.), Vol. 45, No. 7, 1976 that, even in the case of an identical Q/h.sup.2, wherein h represents plate thickness and Q represents welding heat input, the welding distortion can be reduced when steel products are different from eac
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Fujita Takashi
Horii Yukihiko
Kasuya Tadashi
Kawashima Yokimi
Kojima Kazuhiro
Nippon Steel Corporation
Yee Deborah
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