The hot deformation behavior of PH13-8Mo stainless steel was investigated by Gleeble thermal simulation machine at deformation temperature in range of 900 ℃ to 1 150 ℃ and strain rate in range of 0.1 s

-1

to 10 s

-1

.The results show that with strain increase

the flow stress is increased dramatically to a peak value

and then it is decreased continuously（900～1 050 ℃）or tended a steady value（1 100℃and 1 150℃）.The flow stress is decreased with the increase of deformation temperature and the decrease of strain rate.Based on the Arrhenius equation

the hot deformation constitutive relationship of the peak flow stress was established

and the hot deformation activation energy Qis calculated as 567.32 kJ/mol.The error analysis shows that the relative error between calculated value and experimental value is lower than 1.3%

presenting the higher precision.Microstructure analysis indicates that increasing deformation temperature and decreasing strain rate are beneficial for dynamic recrystallization

while its grain size is easier to be coarsened.