Magnetic evaluation of accelerated aging degradation on 2.25Cr-1Mo steel with martensitic and bainitic microstructure

Abstract

Accelerated aging-induced microstructure, mechanical properties, and magnetic properties were evaluated on martensitic and bainitic 2.25Cr-1Mo steel to correlate the properties for magnetic non-destructive evaluation (NDE) of aged Cr-Mo steel components. Decline in hardness and coercive force was observed with the increase in aging time for the microstructural modifications as the pinning of dislocations and magnetic domain wall corresponds to the mechanical and magnetic hardening. Although high hardness and coercive force was found for the martensitic steel compared to the bainitic steel due to its metastable microstructure with large amount of compressive residual stress, in longer periods of ageing the hardness and coercive force was found to be lower for the martensitic steel for its faster degradation. Strong correlations were found among the coercive force and microhardness in both the martensitic and bainitic steels, indicating a possibility of precise NDE of ageing degradation in Cr-Mo steel components by magnetic hysteresis loop measurement through a portable magnetic NDE device.