An ultrafine grained microstructure was produced in a Nb microalloyed steel by cold rolling ofmartensite followed by an annealing heat treatment. Different hold times were used to determine the effectof annealing at 550°C on the microstructure and mechanical behaviour of the ultrafine grained steel. Theresults have shown that with increasing annealing time, both the ductility and strength decrease. Thisbehaviour has been attributed to the relaxation of long range stress field within ultrafine grains/subgrainsand carbide particle growth.
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