Analysis of creep deformation process of heat resistant steels using positron annihilation lifetime

Creep deformation mechanism of the steels with a different matrix, alpha (ferrite), alpha' (martensite) and gamma (austenite), and precipitates such as MX and M23C6 has been analyzed using positron annihilation lifetime measurement. The positron annihilation lifetime has been found to be a very useful tool for evaluating the characteristic creep damage of the steels with different microstructure and the corresponding microstructural evolution during creep deformation. The creep deformation process of the alpha steel is heterogeneous, while the alpha'+M23C6 steel exhibits gradual changes in the creep rate in both transient and acceleration creep regions with the largest off-set strain, implying the homogeneous creep deformation. The alpha'+M23C6+MX steel is in between the alpha and alpha'+M23C6 steels. The homogeneous creep deformation takes place in the 7 steel.