Splitting phenomena occurring in the martensitic transformation of Cr13 and CrMoV14 stainless steels in the absence of c
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I.
INTRODUCTION
VARIOUS investigations conducted over the last 2 decades have sought an explanation for certain uncommon types of behavior observed during the martensitic transformation of alloyed steels with carbide-forming elements such as chromium, molybdenum, vanadium, and tungsten. In these steels, the nonisothermal austenite-martensite transformation does not occur continuously and in one single stage throughout a certain range of temperatures, M s - My. Under certain conditions, this transformation splits into different, successive stages limited by different points M s . In theory, the most coherent explanation for this splitting phenomena is the break down of austenites that coexist with different chemical compositions. According to Kulmburg and Korntheuerm and Maratray, and Poulationt2] the martensitic transformation splitting results from carbide precipitation and/or the growth of some existing carbides. It is likely that these processes would cause concentration gradients inside the austenite, which could produce the splitting. Vaugeois t31 attributes the splitting phenomenon to the existence of dual, intra-, and intergranular precipitation leading to different concentrations in the areas of austenite located inside and near the grain boundaries. According to Freire Vieirat4] and Silcock and Denham,tS] in order for the splitting phenomenon to appear, carbide precipitation must occur during cooling, the presence of intergranular carbides being the common factor in all the cases in which said splitting arises. It is important to note that both Vaugeois[3] and Freire Vieira t4] only refer to splitting stages occurring at temperatures above the principal stage temperature at which the massive austenite is transformed. In other words, these authors consider that the splitting is always caused by the
C. GARCiA DE ANDRES, Senior Research Scientist, and L.F. ~.LVAREZ, Research Scientist, are with the Centro Nacional de Investigaciones Metalflrgicas (CENIM), C.S.I.C., Avda. Gregorio del Amo 8, 28040 Madrid, Spain. J.A. JIMENEZ, Postdoctoral Fellow, formerly with the Centro Nacional de Investigaciones Metalrrgicas (CENIM), C.S.I.C., is with the Max Planck Institut flir Eisenforschung, 4000 Diisseldorf 1, Max Planck str 1, Germany. Manuscript submitted October 15, 1993. METALLURGICALAND MATERIALSTRANSACTIONS A
transformation of areas of austenite with a smaller concentration of carbon and carbide-forming elements than the massive austenite. The majority of the articles cited have focused attention on high-speed steels, steels for tools, cold- and hot-working steels, and certain types of martensitic stainless steels. Generally speaking, these articles explain the martensitic splitting phenomena exclusively in terms of carbide precipitation during cooling. In the stainless steels used in this article (Table I), however, splitting phenomena were detected experimentally in the absence of carbide precipitation during cooling. The four martensitic stainless steels listed in Table I were made by arc melting. The X60C
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