Effect of Titanium and Nitrogen on Toughness of Heat-Affected Zone of Steel Plate with Tensile Strength of 50kg/mm² in High Heat Input Welding

Abstract

A study has been made of the effect of titanium and nitrogen on heat-affected zone (HAZ) toughness in one-sided submerged arc welding by using 30 mm thick steel plate with tensile strength of 50kg/mm². The distribution of TiN particles in the steel plates and welding thermal cycle specimens simulated the HAZ, was observed in relation to the toughness.
The HAZ toughness exhibits the highest value at approximately 0.015% titanium, which also gives the finest distribution of TiN particles in the HAZ regardless nitrogen content. The optimum nitrogen content for the toughness is about 0.0050%, although the number of TiN particles increases with increasing nitrogen. The degradation of the toughness in the range of more than about 0.0050% nitrogen can be explained by the increase of free nitrogen harmful to toughness. By means of controlling the amounts of titanium and nitrogen in the optimum range, the fine distribution of TiN particles can be attained, which enables the production of steel plates for high heat input welding in conventional steel making process without special precaution.