Effect of molybdenum on the kinetics of phase transformation of undercooled austenite in high-speed steels under continuous cooling

Abstract

The aim of these investigations was to determine the effect of the ratio % Mo to % W in the austenite of high‐speed steels on the kinetics of its transformation under continuous cooling. The investigations were carried out on model alloys. Three CCT curves were drawn. Also the influence of cooling velocity on the volume fraction of retained austenite in high‐speed steels was evaluated. It was determined that with the increase of the Mo content in the high‐speed steel matrix the MS temperature decreases and the fraction of retained austenite increases, the development of the bainite transformation decreases and the stability of austenite increases in the range of diffusion transformations. With an increased cooling rate, the volume fraction of retained austenite decreases at first and then it increases. These changes are caused by the precipitation of carbides from undercooled austenite and can give rise to the differences in the content of retained austenite on the cross‐section of quenched tools.

Hardenability of Steel

“…Woodhead has reported that if the vanadium concentration is sufficient and if the austenitizing temperature is high enough, the presence of vanadium may exhibit a marked inhibition in pearlite formation (35). Pacyna et al showed that up to 0.14%, vanadium increases the hardness and hardenability slightly by decreasing slightly the onset temperature of ferrite precipitation and increasing the time for pearlite transformation (36). This is important since vanadium carbides, which may be present in the steel, do not readily dissolve at most standard austenitization temperatures and thus do not affect the kinetics of phase transformation.…”