A 0.3C-CrMoV(ESR) steel is being developed primarily for making pressure vessels used for aerospace applications. Since it is important to understand the range of microstructures and mechanical properties that will be obtained in the heat affected zone of welds, the steel has been subjected to different austenitizing treatments (temperatures ranging from 925 degrees C to 1250 degrees C) followed by cooling at various rates to room temperature. It has been shown that the austenite grain size increased from about 10 to 250 mu m as the austenitizing temperature is increased from 925 degrees C to 1250 degrees C (1 hr) and that the hardness, YS, UTS,% elongation and% reduction in area as well as CVN energy for 450 degrees C tempered condition decrease as the austenitizing temperature is increased for all cooling rates (furnace cooling, air cooling, oil quenching, quenching and tempering at 450 degrees C). This is attributed mainly to the increase in austenitic grain size. The ranges of microstructures that can be obtained in the heat-affected zone are massive ferrite, fine pearlite, upper as well as lower bainite and martensite. The Charpy impact energy for the oil-quenched steel tempered at 200 degrees C, however, did not vary significantly with austenitizing temperature.