High speed steels - A tribute of microalloyed steels

Abstract

: High speed steels (HSS) have been an alloy steel based on strategies of precipitation in microalloyed steel. Tendency of carbide formation has been utilized for producing a hard, wear resistant and chemically stable product after increasing alloy contents in addition to carbon. Precipitation has been a key term to study its genesis (i) at start of solidification, (ii) during heat-treatment, (iii) effects of retained austenite on fracture toughness, (iv) dissolution tendency of precipitates in austenite in heat treatment, (v) resistance of precipitates to thermalization effects and (vi) favourable effects of precipitates from view points of size, shape and distribution in matrix. Chromium, vanadium, niobium, titanium, cobalt, molybdenum and tungsten are considered as primary and secondary carbide forming elements for acceptable performance, e.g. high temperature wear resistance. Fracture in these alloy steels are initiated by carbides, which have been formed at high temperature and retained as such in heat treatment and likely to coarsen on later courses of lower temperatures. Finer precipitates have been more acceptable and produced by vanadium carbides. Ti, Nb, Mo and W have formed high temperature carbides. Cast route has formed low ductile skeleton of precipitates after solidification, which can not be deformed by hot working, however ferro-vanadium inoculation has changed morphology of carbides for equi-distribution after heat treatment. Controlled atmosphere - powder metallurgy has been route for fabrication of HSS, where ductility is required. Centrifugal casting has rendered successful process for HSS roll manufacture.