Correlation between magnetic hysteresis Properties and Vickers hardness in cladded reactor pressure vessel steel

We investigated the microstructure, magnetic hysteresis properties, and micro Vickers hardness of nuclear reactor pressure vessel(RPV) steel cladded with austenitic stainless steel. Characterization of the crystalline structure by electron backscatter diffraction revealed the existence of a delta ferrite phase in the austenitic cladding, and the formation of coarse and fine grain microstructures in the heat affected zone(HAZ)of the RPV steel. The block specimen was cut into small pieces and magnetic hysteresis loops were measured with a vibrating sample magnetometer. Although the saturation magnetization of the RPV steel was constant, the coercivity in the HAZ region decreased gradually as a function of distance from the weld fusion boundary. A linear correlation was confirmed between the coercivity and hardness. This study demonstrates the feasibility of a magnetic evaluation of hardness and microstructures in RPV steel.