Metallurgical Factor Controlling Notch Toughness of Multipass Weld Metal

Study on Notch Toughness of Weld Metal in Large Current MIG Arc Welding

Abstract

In previous papers, the authors demonstrated that the addition of Ti and B are extremely effective to improve the notch toughness of weld metal and verified the inherent and complex effects of Ti, B and oxygen on the refinement of microstructure.
This paper deals with the notch toughness of weld metal produced by the multipass large current MIG arc welding. Attention was focused on the effects of alloying elements such as Ti, B, oxygen, nitrogen and post weld heat treatments on the notch toughness of weld metal. The results obtained were as follows:
(1) Ti-B weld metal consisting predominantly of acicular ferrite structures gives the optimum toughness at Ti content of 0.02%. The oxygen content ranging from 300 to 500 ppm has little influence on its toughness.
(2) Nitrogen deteriorates the notch toughness of Si-Mn-Mo weld metal significantly, whereas Ti-B weld metal shows highly tolerance to it.
(3) The deleterious effect of stress relieved heat treatment on the notch toughness of Ti-B weld metal is due to temper embrittlement phenomenon which occurs during the cooling stage after heat treatment.
(4) The toughness of quenched and tempered weld metal made by Si-Mn-Ni-Cr containing consumable wires gives good correlation with tensile strength and oxygen content, and the transition temperatures of Charpy impact test are lowered by decreasing oxygen content within the tensile strength range of 60-65 kg/mm².