Hereditary feature of original coarse grain of steel OOCrl INil IMoTi rolled at 1 150 °C and solid-solution treated at 780 ~900 °C has been studied. Results show that there is a critical temperature Ac for the steel
at which the austenite renews nucleation and the heredity of coarse grain do not carried out; the Ac of steel OOCrllNillMoTi is 870 ~ 900 °C and higher than transformation point A
f
and with heating at A
f
~ Ac
the heredity of original coarse grain occurs. With pre-heat-treating in two-phase region As (630 °C) - A
f
( 730 °C )
the critical temperature Ac to renew nucleation of austenite decreases
but it is not available to refine grain with pre-heat-treating at temperature higher than Ac.