HOT ROLLED STEEL SHEET HAVING AN ULTRAFINE GRAIN STRUCTURE AND PROCESS FOR PRODUCING STEEL SHEET

摘要

PURPOSE: A hot rolled steel sheet has an ultra fine grain structure, superior mechanical characteristics, reduced anisotropy in its mechanical characteristics and high formability. CONSTITUTION: A hot rolled steel sheet comprises ultrafine ferrite grains as a main phase and fine second phase particles. The ferrite grains have an average grain size of not less than 2 micrometer but less than 4 micrometer. The second phase has an average particle size of not more than 8 micrometer and in not less than 80% of the second phase, the spacing of the second phase particle with the closest second phase particle is not less than the second phase particle size.