Site-specific analysis of precipitates during the coiling of an HSLA steel containing V and Nb

Precipitation in a high-strength low-alloy steel containing V and Nb additions during coiling at 500 degrees C, was investigated by advanced characterization techniques including electron backscattered diffraction, focused ion beam, transmission electron microscopy and atom probe tomography. During coiling, nano precipitates were preferentially formed around dislocations and grain/sub-grain boundaries in the high Kernel Average Misorientation (KAM) areas associated with bainite. Precipitates were frequently observed around cementite in the low KAM areas with cementite which were identified as granular bainite. Interphase clusters were found in the low KAM areas associated with ferrite. The site-specific methods reveal the co-existence of different kinds of precipitates. Analysis of the results indicates that the precipitation of microalloy particles close to cementite could lower the precipitation hardening contribution that could be achieved through microalloying.