The test steel Mn18Cr18N (0.03C

19.25Cr

17.96Mn

0.59N) is melted by an 100 kg pressured vacuum induction furnace

forged breakdown and rolled to 12mm plate. With using Gleeble 3800 thermal simulation machine the effect of temperature (750-1150 ℃) and deformation (15%-60%) on microhardness and structure of high nitrogen steel Mnl8Crl8N is studied to get a recrystallization diagram of the high nitrogen steel. Test results show that in non-crystallization region with increasing temperature at definite strain

the microhardness of high nitrogen steel Mn18Cr18N decreases slowly

but decreases quickly in part-recrystallization region

finally again decreases slowly in complete recrystallization region ； in complete recrystallization region the main strengthening mechanism is grain refining strengthening and the microhardness value and average grain size are in accordance with Hall-Petch experienced formula ； in non-recrystallization region the strain strengthening is major strengthening mechanism ； and the effect of strain strengthening in non-crystallization region is higher than that in recrystallization region.