Abstract: The high temperature mechanical tests of X12CrMoWVNbN10-1-1 heat-resistant steel were carried out with the different testing temperature in the range of 300~600℃. The microstructure and fracture morphology of the samples at different temperature tests were analyzed using OM， SEM and TEM. Effect of temperature on the microstructure and high temperature mechanical properties was studied. The results showed that when the testing temperature increased in the range of 300~400℃， the quantity and size of brittle M₃C carbides gradually increased and the segregation became more significant， resulting in an increase of precipitation strengthening and work hardening. For plastic deformation stage， the stress concentration and cracks were more prone to appear around M₃C carbides during deformation. The plasticity slowly decreased with temperature. When the temperature increased between 400℃ and 600℃， it was found that the carbides started to transform， M₃C carbides decomposed rapidly， M₇C₃ and M₂₃C₆ carbides gradually precipitated and the quantity of precipitations began to decrease， which resulted in a decrease of strengthening ability. Meanwhile，dynamic recovery became more significant and led to a dramatic decrease of strength and rapid increase of plasticity.

Key words: X12CrMoWVNbN10-1-1 steel, mechanical properties, microstructure, precipitated phase, in-situ transformation mechanism