Structural variations in heat treated low alloy steel forgings

A study has been made of the microstructures of two low alloy Cr–Mo–Ni–V steel forgings in the quenched and tempered condition. Optical metallography of variously etched specimens, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) and X-ray diffraction were used to characterize the tempered martensite microstructures. Variations in prior austenite grain size and martensite lath structure have been related to the observed different carbide distributions. These arise from small differences in composition, mainly vanadium content, and the consequent response to heat treatment. The metallographic results can account for the differences in tensile and fracture toughness properties observed between the two materials as well as between the two ends of the same forging.