The microstructural characteristics of the local brittle layer (LBL) reported to be formed at the weld center of tandem electro-gas (EG) weld made with EG70T-G wire have been investigated to identify the critical factors causing its brittleness and thus facilitate the development of welds free from the local brittle layer. The results showed that in addition to the directional characteristics of columnar grain structures, the proportion of grain boundary ferrite played an important role in LBL formation and in controlling the impact toughness of electro-gas welds at the weld center. These results led to investigate the additional electro-gas welds containing less amounts of grain boundary ferrite with an aim to improve the toughness at weld center. In addition, the relative brittleness of the local brittle layer was evaluated in terms of Charpy V-notch ductile-brittle transition curves and a stepwise transition unusually obtained from local brittle layer was discussed from the perspective of the microstructural characteristics of LBL.

研究了用EG70T-G焊丝在串联电气（EG）焊缝的焊接中心处形成的局部脆性层（LBL）的微观结构特征，以确定导致其脆性的关键因素，从而促进了开发没有局部脆性层的焊缝。结果表明，除了柱状晶粒结构的定向特性外，晶界铁素体的比例在LBL的形成和控制焊接中心电热焊缝的冲击韧性方面也起着重要作用。这些结果导致研究了另外的包含较少量的晶界铁素体的电焊缝，目的是提高焊接中心的韧性。此外，