Abstract: To control the microstructure and properties of retaining ring steel after hot forging,the dynamic behavior of Mn18Cr18N retaining ring steel was investigated by thermomechanical compression test under the conditions of experimental temperature from 900℃ to 1 200℃,strain rate from 0.001 s-1 to 0.1 s-1 and initial grain size from 48 μm to 230 μm.The hyperbolic constitutive model was established.Based on the hyperbolic constitutive model and dynamic material model,the iso-efficiency map was constructed.Through power dissipation map and microstructure analysis,the deformation temperature and deformation rate duing casting were studied.The results show that the power dissipation rate ηJ increased with the decrease of strain rate and the increase of temperature when the deformation temperature was not higher than 1 100℃,however,changes were opposite when higher than 1 100℃.The fine homogenized and completely dynamic recrystallization could be obtained when the ηJ was not smaller than 0.2.