Effects of weld thermal cycles and post-welding tempering on second phase particles in 2·25Cr–1Mo–0·25V steels

Abstract

The solution and precipitation behaviours of second phase particles in the heat affected zone of 2·25Cr–1Mo–0·25V steels were investigated using a Gleeble-3500 thermal simulator and A-TEM. The results show that the mean size and the dimensional range of the second phase particles undergoing one weld thermal cycle decrease to 37·3 and 100 nm respectively. With increasing the number of weld thermal cycle and decreasing peak temperature of the second weld thermal cycles, the number of the precipitates increases. For the typical carbonitride formed in one and two weld thermal cycle, the composition of its centre is rich in titanium and the edge is rich in niobium and vanadium. In addition, after going through two weld thermal cycle, many strip particles are found in the bainitic ferrite laths and the composition is rich in niobium. After going through post-welding tempering, the particle dimensional range is about 200–300 nm and its shape became regular. The number of precipitate increases with increasing tempering holding time. The precipitates distribute along the grain boundary are rich in chromium, vanadium, iron and manganese.