Effects of heat treatment on structure and properties of 12%Cr steels

Abstract

Studies have been made of the effects ofaustenitizing and tempering heat treatments on the microstructures and mechanical properties of three 12% Cr steels. The effects of heat treatment on the constitution are shown to be in agreement with previously published data. In addition, the grain-refining actions of niobium carbonitride particles and delta ferrite have been demonstrated. Investigations of the tempering characteristics of the steels have shown that molybdenum, vanadium, and niobium accentuate secondary hardening and retard overaging primarily by inhibiting the annealing out of dislocations. Detailed descriptions of the tempering sequences have been given. Structure-property relationships have been investigated and the prior austenite grain size has been related to the Charpy impact transition temperature. Furthermore, the separate contribution of the strength of the material to the impact transition temperature has been established, together with the effect of the strength on the impact upper shelf energy value. Room-temperature tensile properties and stress-rupture data at 550°C have also been evaluated. Finally, the anisotropies of both upper shelf energy and tensile ductility values in the longitudinal and transverse directions are shown to result from the presence of elongated manganese sulphide inclusions, which produce 'woody' or fibrous fractures in transversely tested specimens.