高マンガン鋼のガスシールドアーク溶接(第2報)

Abstract

In previous report, various properties of weld metals with 16 Mn-16 Cr welding wire were investigated, which were deposited automatically by gas shielded arc welding process.The automatic welding being characterized by large heat input, the weld heat-affected zone (HAZ) extends over a wide area and, in the case of austenitic manganese steel, the embrittlement of weld HAZ is likely to aggravate on account of carbide precipitation.The following experiments, in this study, were made to reveal the deterioration of toughness as a part of the study on gas shielded arc welding.The thermal cycles in various parts of the weld were measured in single bead welding of austenitic manganese steel plates and continuous automatic welding (electrogas welding) of austenitic manganese steel rails. Based on the data obtained 15 simple thermal cycles (5 peak temperatures ×3 thermal cycle speeds) were selected, which were similar to those produced in actual weld. Austenitic manganese steel specimens were subjected to the above thermal cycles reproduced by synthetic thermal cycle apparatus, and to impact test as well as microscopic inspection.Deterioration of toughness in synthetic HAZ takes place around 650°C of peak temperature and it becomes heavy at low speed of thermal cycle. In that case, precipitations of carbides appear at intercrystalline boundaries.At over 1300°C of peak temperature, the toughness of synthetic HAZ decreases remarkably regardless of the speed of thermal cycle; this is due to the presence of intercrystalline cracks or cavities caused through heating.The toughness of synthetic HAZ at 650°C of peak temperature tends to be somewhat low when the impact test temperature is low (-40-20°C).Finally the decrease of toughness in weld HAZ was discussed from the standpoint of carbide-preciptation temperature-range in thermal cycles measured. Mention was also made of high temperature cracks observed.