Cold-rolled steel sheet having ultrafine grain structure and method for manufacturing the same

摘要

A cold-rolled steel sheet having an ultrafine grain structure including a ferrite phase is provided. The cold-rolled steel sheet contains C, Si, Mn, Ni, Ti, Nb, Al, P, S, N and Fe and incidental impurities. The ferrite phase has a content of 65 percent by volume or more and an average grain size of 3.5 mu m or less.