Patent ID: 6719860
Filing Date: 2004-04-13
Classification: C21D

Abstract:
A method of producing ultra-fine grain structure for an unalloyed or low-alloyed hypoeutectoid or eutectoid steel, comprising:heating the steel to a temperature above the Ac3 temperature for transforming the structure of the steel into fully austenitic structure, while constraining the temperature T1 and the holding time at the temperature T1 for hindering the grain growth of the austenite so that the mean grain size is not more than 15 &mgr;m prior to rolling of the steel; cooling the steel below the Tnr temperature without working the steel, starting rolling of the steel below the Tnr temperature and continuing rolling of the steel in a region below the Tnr temperature and no more than the Ar3 temperature where the structure of the steel is essentially austenitic but no recrystallization of the austenite occurs; and cooling the steel further below the Ar3 and Ar1 temperatures, wherein the mean grain size of a resulting microstructure of the steel is not more than 3 &mgr;m after cooling of the steel further below the Ar3 and Ar1 temperatures.