In-situ investigation of tensile deformation and fracture mechanism of 12Cr1MoV steel after long-term service

The deformation behavior and fracture mechanism of 12Cr1MoV steel after 20,000 and 200,000 operation hours were investigated by in-situ scanning electron microscope (SEM) tensile testing. The microstructure of the steel after 200,000 operation hours is comprised of ferrite and sphere-shaped carbides distributing along the grain boundaries instead of that of ferrite and pearlite after 20,000 operation hours. With increase of the strain, deformation begins in ferrite matrix at the initial stage of plastic deformation and subsequently slip lines coarsen and cross-slip becomes predominant regardless of microstructure. Crack initiation and propagation behavior are different in the two types of samples due to difference in microstructure. Crack initiates at the position where two slip bands interconnected each other and transgranularly propagates in the sample after 20,000 h operation. However, in the sample after 200,000 h operation, crack initiates near the carbides and both transgranular and intergranular propagation of crack can be observed.