Microalloyed Pearlite Steels for the Wire Industry – Mechanisms of Alloy Element Redistribution and Strengthening Processes in Chromium-Vanadium Eutectoid Steels
The strength of continuously cooled pearlitic steel rod can be increased by up to 200MN/m2 by small additions of chromium and vanadium. We report here a detailed investigation of the microstructure and properties of a range of such steels. In addition to conventional mechanical property and microscopical studies, the techniques of field emission STEM X-ray analysis and atom probe microanalysis have been used to examine the redistribution of alloying elements during heat treatment. Both chromium and vanadium have a strong tendency to redistribute to the cementite phase by short-circuit diffusion along the austenite-pearlite interface. Under rapid transformation conditions, however, this redistribution process is incomplete, and secondary carbonitride precipitation can occur within the pearlitic ferrite. An unusual feature of vanadium additions is their tendency to produce grain boundary ferrite films, even in steels of eutectoid composition. This effect is believed to be due to nucleation of vanadium carbide particles in austenite grain boundaries, prior to pearlite formation. Nucleation of pearlitic cementite is consequently inhibited, allowing a continuous ferrite film to develop. Fortunately, the presence of such films does not adversely effect subsequent cold drawing properties, which are fully comparable to those of lead patented plain carbon steels.
chromium-vanadium eutectoid steels, pearlitic steel rod, transformation, vanadium carbide, pearlitic cementite, secondary carbonitride precipitation, boundary ferrite.
T. D. Mottishaw and G.D.W. Smith
Department of Metallurgy and Science of Materials, Oxford University, Parks Road, Oxford OX1 3PH, England
HSLA Steels, Technology and Applications; Philadelphia, Pa, U.S.A, 3-6 Oct. 1983, pp.163-175 (Vanitec Publication - V0385)