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In this work, the static softening behaviour of GH4500 superalloy during the two-pass thermal deformation was investigated via thermal-simulation compression experiments at the temperature range of 1293 K to 1373 K, strain rate range of 0.01 s−1 to 1 s−1 and interval time range of 0 s to 180 s. The metallographic structure acquired from optical microscope (OM) indicated that both static recovery (SRV) and post dynamic recrystallization (PDRX) would occur during the holding stage. Meanwhile, the influence of interval time, deformation temperatures and strain rates on static softening behaviour were revealed. The results showed that the softening effects principally induced by PDRX strengthened with the increase of the interval time, deformation temperatures and strain rates. To quantitatively describe the PDRX kinetic process of GH4500 superalloy, a model on grounds of Avrami kinetics was established to predict the PDRX softening fraction via eliminating the effect of static recovery. The predicted data of the PDRX softening fraction were well consistent with the experimental data, manifesting that the model could precisely evaluate the PDRX softening behaviour in the stage of inter-pass holding.