Effects of Ti and N on Notch Toughness of Synthetic Weld Heat Affected Zone

Abstract

Effects of microstructures, prior austenite grain size, soluble Ti, soluble N and insoluble Ti on the notch toughness of the synthetic weld heat affected zone have been investigated using mild steels with a microalloyelement Ti. The results obtained are as follows: (1) The austenite grains are refined by increase of Ti and N contents. Especially, the grain refinement occurs remarkably in specimens with less than 0.0060 wt% N. (2) The microstructures are changed by Ti and N contents and when Ti and N contents are optimum the finest ferrite-pearlite structures are obtained. (3) The notch toughness strongly depends on the quantities of a soluble N and Ti even if the microstructures are the most favorable. (4) Optimum Ti content to improve the notch toughness is given by following Eq. Optimum Ti=-1070N³+1.09N+ 0.0137 (wt%). (5) The summation of soluble Ti and soluble N should be considered as a important factor affecting the notch toughness.