Wall thickness asymmetry is a common problem for cross wedge rolling( CWR) hollow shafts,which is especially usual in the CWR process of hollow shafts of small diameter and large height-diameter ratio. In this paper,the constitutive equation of hot deformation of 5Cr21Mn9Ni4 N heat resistant steel was investigated by the thermocompression experiment on the Gleeble-1500 D thermo-simulation machine. The law for the variation of wall thickness during forming 5Cr21Mn9Ni4 hollow valve with CWR was presented,whic...