1996 年 14 巻 1 号 p. 27-32
Large heat-input welding is increasingly employed because of its high productivity. For this welding, titanium and boron (Ti-B) bearing welding materials are suitable in acquiring high toughness at low temperatures. However, their properties at high temperatures have not been known. Preferable ductility at high temperatures is required when they are applied to the welding of fire-resistant steels. The present study examines the mechanical properties of Ti-B bearing welding materials for fire-resistant steels in large heat-input welding.
Submerged arc welding with two electrodes in tandem was conducted with the heat-input of 13 kJ/mm. The mechanical and metallurgical investigation were v-notch Charpy tests, weld metal tensile tests, chemical analyses, and metallographic observation on ruptured surfaces.
It was found that the addition of titanium and/or boron lowers the high temperature elongation. This reduction was caused by grain boundary fracture at the prior-austenite grain boundaries of the weld metal with titanium and boron. However, the high temperature properties were recovered in the weld metal with titanium as low as 30 ppm and nil boron, and this weld metal fractured in an intragranular mode with enough toughness.
