Grain growth behaviour on reheating Al-Nb containing HSLA steel in the homogenised condition

Grain size development during reheating is important to the mechanical properties of steels, and non-uniform grain growth including abnormal and bimodal grain growth is undesirable for steel manufacturing. In this paper, reheating treatments for Al-Nb containing steel (0.057 wt% Al and 0.019 wt% Nb) were selected based on ThermoCalc predictions for the dissolution temperatures of precipitates in the steel for a fully homogenised condition. Abnormal grain growth occurred in the homogenised Al-Nb sample when reheated at 1170 ºC, associated with random dissolution of the grain boundary pinning AlN precipitates; whilst the bimodal grain growth was not observed. Abnormal grain growth was associated with dissolution of the (more stable) AlN precipitates and grain size distributions developed during reheating schedules (1070 – 1200 ºC and 1– 3 hours) have been related to the dissolution rate of AlN.