The operation of some early-generation light water reactors may be limited by the irradiation-induced embrittlement of their reactor vessels. Additional nondestructive methods of measuring the actual embrittlement are desirable to support limits placed on the operation of these vessels. Previous studies have indicated that the increase in microhardness with irradiation may correlate with shifts in the ductile-to-brittle transition temperature. However, the previous research did not consider variations in the test temperature to determine whether it affects the correlation with transition temperature or whether microhardness may correlate with the fracture energy outside the transition region. The Vickers microhardness measurements were made at eight temperatures from -195 to 90°C (-320 to 200°F) by holding the samples in a liquid bath during the application of the test load. Both unirradiated and irradiated samples were evaluated for the three A533-B steels. These tests indicate that the Vickers hardness may correlate with the strength and ductility of unirradiated steels. In addition, both the change in microhardness and the shift in test temperature at a constant hardness may correlate with the shift in transition temperature caused by irradiation.