Effect of Tempering on the Saturation Magnetization of Martensitic Steels Containing Carbon

In steels with low Ms temperature, austenite cannot transform to martensite completely and untransformed austenite retains within martensite matrix. Since the value of saturation magnetization (SM) is very sensitive against the existence of non-magnetic phases, the measurement of SM was applied on the quantitative evaluation of small amount of austenite that has retained within martensite matrix. The SM-method was also applied to 90% cold rolled pure iron and it was confirmed that dislocation does not give any influence on the SM values. During tempering of martensite containing carbon, complicated carbide reactions occur but no change was found on the SM values of tempered martensite. As a result, in steels with bcc structure, the SM value J* is not dependent of microstructure but depends on only the amount of alloying element X (mass%) in steels, as expressed by the following equation: