Prior austenite grain size and tempering effects on the dislocation density of low-C Nb-Ti microalloyed lath martensite

The dislocation density of two as-quenched and quenched and tempered low-C Nb-Ti microalloyed martensitic steels was measured with X-ray diffraction for a range of prior austenite grain sizes. The dislocation density decreases with increasing prior austenite grain size in the as-quenched condition but the opposite occurs after high temperature tempering. The flow strength of all conditions is a function of dislocation density and follows a Taylor hardening model. The properties are insensitive to Nb microalloying for the two alloys assessed. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.