Austenitization Behaviors of X80 Pipeline Steel With High Nb and Trace Ti Treatment

The austenitization behaviors of two high niobium-containing X80 pipeline steels with different titanium contents, including the dissolution of microalloying precipitates and the austenite grain growth, were investigated by using physical-chemical phase analysis method and microstructural observation. The results illustrated that most niobium could be dissolved into austenite during soaking at 1 180 °C, whereas little amount of titanium could be dissolved. It was found that during soaking, the austenite grain growth rate was initially high, and then decreased after soaking for 1 h; moreover, the austenite grains grew up more rapidly at temperatures above 1 180 °C than below 1 180 °C. The results show that the steel with titanium content of 0. 016% has a larger austenite grain size than that with titanium content of 0. 012% under the same soaking conditions, which is explained by considering the particle size distribution.