This report details the investigations conducted by Bethlehem-Lukens Plate into the behavior of ASTM A516 Grade 70 steel plate subjected to post-weld heat treatment (PWHT). Those studies, conducted under PVRC Project No. 98-TME-01, were initiated to characterize the effects of PWHT on hardness and notch toughness of welded joints. Inherent in the scope of these efforts was some work on the behavior of the base metal. However, the reports generated from those studies in­cluded little definitive discussion on the effects of PWHT on base metal properties. They further suggested that the amount of scatter in the limited amount of data made it difficult to establish trends, especially pertaining to any parametric analysis such as correlation with Larson-Miller Parameter (LMP). The results of earlier internal work by Lukens Steel demonstrated a well-defined correlation between base metal strength, toughness and time-temperature relationships. Additional investigations have been continued by Bethlehem-Lukens Plate to improve normalized base metal toughness and improve internal guidelines for predicting properties of post-weld heat-treated material conforming to A516 Grade 70. These new data reinforce previous conclusions that PWHT has a detrimental and predictable effect on base metal properties that needs to be considered when evaluating application of PWHT.