Achieving ultrafine dual-phase structure with superior mechanical property in friction stir processed plain low carbon steel

Ultrafine dual-phase structure was successfully prepared in a plain low carbon steel via friction stir processing (FSP) at a tool rotation rate of 400 rpm and a travel speed of 50 mm/min under rapid water cooling. Ultrafine polygonal ferrite grains (similar to 1 mu m) were distributed around the martensite phase consisting of nanostructured laths with a width of similar to 200 nm. FSP steel exhibited a good combination of ultrahigh yield strength of similar to 1100 MPa and large uniform elongation of similar to 7%. This work provides an effective strategy to prepare high strength low carbon steels. (C) 2013 Elsevier B.V. All rights reserved.