Pearlite phase transformation in Si and V steel
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I.
INTRODUCTION
A number of investigations of carbon steels have considered the effect of ternary alloys additions on the decomposition of austenite to pearlite. Mainly, the influence on decomposition kinetics has been considered. Thus, the effects of the customary steel additions, such as manganese, nickel chromium, or molybdenum, on pearlite growth rate and the corresponding influence on interlamellar spacing were well documented in earlier work. j~ 6[ More recently, there have been a number of studies concentrating more on alterations to the overall microstructure caused by alloying additions. It has been realized that additions that are strong carbide formers, e.g., chromium and vanadium, can both influence the nature of the pearlitic carbide and form additional carbide dispersions in the microstructure. In certain cases, for example, in steels with moderately high chromium contents of about 5 wt pct, pearlitic cementite can be replaced by chromium carbide, [7-~u giving rise to the term "alloy pearlite." Separate regions containing dense dispersions of uniaxially aligned fibrous alloy carbides are characteristically observed in steels containing additions of vanadium, molybdenum, or chromium.t"~'~e'~3r In addition, parallel layers of small alloy carbide particles (typically vanadium carbide), termed "interphase precipitation, "l~~ have also been found in pearlitic ferrite, tl6aT] These latter fine dispersions of alloy carbide give a useful strength increment and are currently being exploited in medium- and high-carbon steels with a significant pearlite component in the microstructure, t~8,~9,2~ It has also been recognized that the presence of minor K. HAN, formerly Graduate Student, Department of Materials, Oxford University, is with the Department of Metallurgy, Delft University of Technology, Delft, The Netherlands. G.D.W. SMITH, Reader in Metallurgy, is with the Department of Materials, Oxford University, Oxford, United Kingdom. D.V. EDMONDS, formerly University Lecturer, Department of Materials, Oxford University, is Professor, the School of Materials, University of Leeds, Leeds, United Kingdom. Manuscript submitted August 8, 1994. METALLURGICAL AND MATERIALSTRANSACTIONS A
amounts of ternary alloying elements can have more subtle effects on pearlitic microstructures. It was reported as early as 1937 that the addition of a small amount of vanadium to steel of eutectoid composition resulted in the occurrence of ferrite at the prior austenite grain boundariesJ 2u Vanadium should lower the eutectoid carbon content, t22,23,2< and, if anything, hypereutectoid rather than hypoeutectoid reaction products might have been expected. This anomalous behavior passed virtually unnoticed until recently, when it has been confirmed by other investigators. 125,26.27]Furthermore, recent work has shown that vanadium suppresses the growth of cementite on the prior austenite grain boundaries in eutectoid steels.128 321 Previously, the suppression of carbide formation in steels by substitutionally alloying elements was well kno
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