Effect of nitrogen content on simulated heat affected zone toughness of titanium containing thermomechanically controlled rolled steel

Abstract

The variation of simulated heat affected zone (HAZ) toughness with nitrogen content in titanium containing thermomechanically controlled rolledsteelwas investigated andinterpreted in termsof its microstructure and the amount of free nitrogen present. Measurement of the amounts of titanium and aluminium in precipitates extracted from the HAZ showed that 13–45%TiN and 72–79%AlN were dissolved at 1400°C peak temperature. The measured amount of titanium was in good agreement with the amount calculated by means of thermodynamic analysis, indicating that such analysis canbe used toestimate the amounts ofTiN and free nitrogen inthe HAZ at a given peak temperature. Simulated HAZ toughness was influenced notonly by the microstructure, in turn influenced by the amount of undissolved TiN at the peak temperature, but also by the amount of free nitrogen present after the formation of BN during the cooling cycle. Multiple regression analysis of the simulated HAZ toughness showed that the detrimental effect of free nitrogen was much greater than the beneficial effect of TiN in this experimental condition.