高炭素鋼の電弧熔接に於ける熱影響に關する研究  [in Japanese] Effects of Welding Heat to High Carbon Steel in Are Welding  [in Japanese]

Not only the hardened zone is detected in the welded part of high carbon steel, but sometimes also the welding crack appears in them. In this research the author has studied to find the welding condition that is to mitigate hardening or to prevent weld crack. Three kinds of high carbon steel contained : C 0.40%, 0.55% and 0.76% respectively, has been applied to various tests. The weld hardening and the crack generation are mainly affected by the carbon content and cooling velocity. The more the carbon content in steel, the more the number of crack or the length of crack on bead. The cooling velocity, in welding practice, has two important factors that is to say electric current and welding speed. The author has found two kinds of crack or fissure on bead. The former is generated by shrinkage stress, transformation stress etc. and the latter is mainly caused by transformation stress as due to the local formation of martensite at comparative low temperature. From the result of various tests it is corcluded for prevention of crack generation that is to apply such a welding condition as slow speed and low current as possible. Preheating is also effective on the above purpose. As an example of practical application of the above tests, building up of worn tyres has been excuted as well as in the test condition and this repair practice has proved the superior results in the both side of theoretical tests and practical uses. Since at the point of welding all temperatures may be present from that of liquid metal to steel at normal temperature, these effects may be quite complicated. As one of the fundamental researches on the effect of welding heat, the hardness distributions, produced in high carbon steel specimens by short time heating in lead bath and quenching in water or air cooling have been determined. From these results, the heat effects in welded part may be approximately considered in the relation between the maximum heated temperature and hardness or microstructure.