Abstract
In the previous work, it was clarified that the decrease of tensile impact value of the heat affected zone of welded part corresponds to the hardening of that zone by rapid cooling after the welding. So, in this study, it was tried to increase the decreased impact values in the heat affected zone by post heating of the welded plates. In this preliminary study welded plates were heated at 20°C lower than A1 transformation temperature or at 20°C higher than A3 transformation temperature of each steels. As the results of the experiment the following facts were obtained.
1. On mild steel, 55 kg/mm2 and 60 kg/mm2 high tension steel, Mn-Si fine grained steel and 2.5% Ni steel, the distributions of Vickers hardness and tensile impact value of the heat affected zone were little changed by the post heating.
2. On 80 kg/mm2 high tension steel, the maximum hardness of the heat afiected zone was decreased nearly to the hardness of unaffected base metal by post heating, but impact values of that zone was increased. The hardness of base metal was also decreased, and its impact value was increased by post heating.
3. On the three kinds of steels for machine parts, ed. 0.45% C plain carbon steel, chromiummolybdenum and chromium steels, the heat affected zones were softened by post heating. Weld metal and base metal were also softened, and the hardness distribution in welded part became uniform. By means of post heating, impact value of the heat affected zone was also increased.
