The new ductile fracture criterion for 30Cr2Ni4MoV ultra-super-critical rotor steel at elevated temperatures

In this paper a new ductile fracture criterion was derived by taking into account the plastic deformation capacity of material and stress states, which can be used to describe fracture behavior and critical rupture conditions of 30Cr2Ni4MoV ultra-super-critical rotor steel during hot forging process. In order to establish this criterion, the tensile tests at different temperatures and strain rates were firstly conducted on Gleeble-1500 thermo-mechanical simulator, and then a measurement and conversion method was applied to estimate the equivalent fracture strain image that represents the deformation capacity of material in ductile fracture process. Experimental results indicated that image greatly depends on the temperature and strain rate. A model of image as a function of the temperature and strain rate was also established. To validate the proposed fracture criterion, additionally, the simulation of tensile test and the fractographic observation of the tensile specimen were conducted. The upsetting tests that possess different stress states and the corresponding numerical simulations were also performed. These results show that the developed criterion can accurately predict the cracks initiation and the location of the cracks at elevated temperatures.