Degradation Evaluation of HK40 Steel Using Magnetic Properties

The effect of isothermal heat treatments, which simulate the microstructural changes observed in furnace heater tube steel at the service temperature, on the magnetic properties was investigated. HK40 steel specimens with five different periods of aging were prepared by an isothermal heat treatment at 1050°C. Magnetic properties such as susceptibility were measured. The magnetic susceptibility at room temperature monotonously increased with the extent of degradation of the material. The Vickers hardness also increased with the extent of degradation. The correlation between the measured magnetic susceptibility and the Vickers hardness was studied. In addition, the applicability of magnetic susceptibility measurements to the evaluation of degraded HK40 steel was discussed. As result, the magnetic susceptibility method could predict the thermal degradation of HK40 steel with high reliability.