| 摘要 |
A method of producing ultra-fine grain structure for an unalloyed or low-alloyed steel is characterized in that it includes as a combination steps wherein the steel is heated (1, 2) to a temperature (T1) above Ac3 temperature for transforming the structure thereof completely austenitic whereby both temperature level (T1) and holding time (d1) at the temperature (T1) are restricted for hindering austenitic grain growth, the steel is cooled (3) without any deformation below Tnr temperature, rolling (4a, 4b) is started below Tnr temperature and is continued within the temperature range between Tnr and Ac3 in which the structure of the steel is essentially austenitic but with no recrystallization of austenite, and the steel is cooled further (5) below Ar3 and Ar1 temperatures. The method of the invention is suitable to be used at the final storage of production, especially, for improving some properties, like hardness, tensile strength and impact toughness, of a steel. |
