構造用高張力鋼（５０，６０および８０キロ級）の電子ビーム溶接性に関する研究 ＶＩＩ

Abstract

From a viewpoint of the practical use for electron beam (EB) welding, the penetration characteristics and the occurring region for weld defects were studied in various welding conditions for thick plate (50-100 mm) of the structural high strength steels, and nextly some mechanical and metallurgical characteristics of the deep-penetrated weld metal were made clear in this investigation. Moreover some problems of the EB-welding procedure in practical use were investigated by using 25 mm thick plate of SM50A. The remarkable conclusions are as follows;(1) The weld defects occurred in the thicker materials were divided into two main classes, that is, the vertical crack-like center and bottom defects in the stand point of the occurred location in the deeppenetrated weld metals. The former often occurred nearly in ab; 1.0, and the latter occurred in ab>1.3 or <0.5. Besides the crack-like center defect sometimes switched over to the cavern-like defect in case of the weld bead in a large weld heat input.(2) It was found that the sound weld metal without defect, the penetration depth of which is 7577 mm, was obtained nearly for ab; 0.7 in case of 27KW beam power. The regions for the sound weld metal obtained tended to be expanded with a decrease of the beam power.(3) There is no obvious variation in the oxygen and nitrogen contents between the base and weld metals, or between the face and bottom parts of deep-penetrated weld metal. Furthermore the Mn content in weld metal is decreased 10 % less than that in base metal according to the EPMA-analysis. The degree of the decrease tends to be decreased with an increase of the penetration depth for the analized location.(4) The impact strength of the deep-penetrated weld metal tends to be lowered in general with an increase of weld heat input, and the strength of the bottom part in the penetration showed higher value than that of the face part. Moreover the impact strength of EB-weld metal had a tendency to be increased with an increase of the hardness of it in general.(5) It was comfirmed to be possible to enlarge the allowable limit for groove opening and to improve the impact characteristics for EB-weld metal by using the cut wire as an insert material. Furthermore the allowable limits for groove condition in L joint were respectively clarified against the three levels of welding condition, the bead shape of which makes the wedge, well and wine-cup types.