Investigation of Grain Misorientation on Creep Void Nucleation in P91 Heat-Resistant Steel by Experimentation and Crystal Plasticity Simulation

Heat-resistant steels are candidates for pipes under high-temperature corrosion conditions owing to their good high-temperature thermal strength, oxidation resistance, corrosion resistance and creep properties. Normally, the failure of heat-resistant steel originates from the nucleation of creep voids at grain boundaries. Hence, a mesoscopic approach was adopted in this paper to study the local stress distributions of two adjacent grains. This approach incorporates the elasticity, plasticity and viscosity characteristics of P91 heat-resistant steel crystals. Simulations were performed at a series of misorientation angles between the two grains (e.g., 8.4 degrees, 16.9 degrees, 33.6 degrees, 50 degrees, 65.8 degrees and 77.1 degrees) at 600 degrees C and 110 MPa. Complementary experimental work was conducted to verify the simulation results. The simulation revealed that a high stress was generated at the grain boundary with grain misorientation angles ranging from 33.6 degrees to 50 degrees, which was supported by EBSD observations. The stress concentration at the grain boundary due to the misorientation between neighboring grains could facilitate the nucleation of creep voids, and its variation in magnitude confirmed that creep void nucleation was dependent on spatial orientation. The results were useful for better understanding the creep void nucleation mechanism in P91 heat-resistant steel at high temperatures.