Some observations have been made on the formatioll of austenite graills from ferrite-jJearlite and martensite structures heated at 2°G/mill and 2°G/sec, using a low carbon chromium steel. I t is foun d that heating of ferri te-pearlite at either heating rate gives rise to nucleation of austellite at ferrite-IJearlite interfaces and IJearlite colony boundaries and its granular growth and finally the granular allstenite goes into an initial allstenite grain after the completion of traniformatioll. I t is also indicated that heating of martensite at 2°G/sec 1)1"O(/uces a small amount of acicular austellite and a large amount qf granular austenite at IJrior austenite grain boundaries and grain interior which grows integrating acicular o/u and goes into initial austenite grains (ifter the completion of the traniformation. Slow heating of martellsite at 2°Cjmin, however, brings the differellt process of the formation of initial austenite grains, Ihat is, a large amount of acicular austenite is created in the prior austenile grain interior along with granular one at the boundaries, which comes to compose a lamellar structure of austellite and acicular ferri te. Vanishing of acicular ferrite by completion of the transformation results in acicular subgra;ns of austenite which are Vel)' unstable owing to the high grain boundmy area and thus a subgrain acquiring enough energy grows rapidly, sweeping the other Sllbgrain boundaries, resulting in granular austenite grain. A1igration of austenite-ferrite intelface is found to be inhibited at ferrite boundaries and thus it is proposed that the growth of granular austenite in martensite may proceed with s),mpathetic nucleation of austenite.
Effecls of chro mium, moly'bdenum and vanadium on slJheroidi z alion of carbides in 0.8 0 a carbon sleel b)' slow cooling annealing have been invesligaled. An addilion of chromium remarkably accelerales spheroidiz alion of carbides, while addilions of molybdenum and vanadium do a lillie. X-ray' anal ,),sis of carbides indicates lhal M 3C and M,C 3 are only carbides observed lhrouglzoul lhe annealing IJrocess ill 2 0 0 and 5 '-;' chromium sleels, respeclively.. In molybdenum and vanadium sleels, however, carbides formed b), lhe eu lecloid reaction are proved 10 differ from lhose surviving in auslenile on annealing, i.e., M 23 C. and M 3C are euleeloid carbides in moly'bdenum and vanadium sleels respectively, while tvlo 2 C and VC survive in auslenile in lhe sleels respeclively. Although lhe addilion of airy of lhese el~men ls results in increasing amounls of undissolved carbides in auslenite, the facl thaI chromium has a marked effect on spheroidization of carbides strongly suggesls thaI an undissolved parlicle of carbides in au slenite of chromium sleels act as a cenler for the precipilalion of eulecloid carbides since undissolved carbides coincide with eulectoid carbides. Thu s il is concluded thaI coincidence of carbide precipilaling during eulectoid reaction with lhal surviving in auslenile will be of a primary importance in slJheroidiz alion of wlecloid carbides b), slow cooling annealing.
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