Obrabotka Metallov 2013 No. 4

ОБРАБОТКА МЕТАЛЛОВ № 4 (61) 2013 70 МАТЕРИАЛОВЕДЕНИЕ Abstract Morphology of hypereutectoid cementite is essential for mechanical properties of ultra-high carbon steels. The influence of cooling rate of hypereutectoid steel on morphology of -hypereutectoid cementite is studied. Using results of dilatometric experiment the diagram “time – temperature – transformation” (TTT-diagram) was plotted for hypereutectoid ultra-high carbon steel containing 1.56%C. Cooling of samples with rates of 0.1 to 30 ºC/s from 1150 ºC was carried out in quenching dilatometer Linseis L78 R.I.T.A. The critical points of steel are: M s = 138 °C; A с1 = 742 °C; A сm = 960 °C. Metallographic studies of cooled dilatometric samples showed that an increase in the rate of cooling leads to changes of cementite morphology. Widmanstatten cementite precipitates at cooling rates faster than 1 ÷ 3 ºC/s while net-shape cementite is typical for slow cooling. Accelerated cooling does not completely prevent the formation of cementite network at the grain boundaries. Morphology of hypereutectoid cementite is in dependence on the grain size of austenite. Increasing of the austenite grain size produces needle of widmanstatten cementite at lower cooling rates. Keywords: hypereutectoid steel, ultrahigh carbon steel, widmanstatten cementite, austenite, cementite network, TTT- diagram. References 1. Plotnikova N.V. Rol’ morfologii cementita v obespechenii konstruktivnoj prochnosti uglerodistyh zajevtektoidnyh stalej. Diss. kand. tehn. nauk [The role of the morphology of the cementite in providing structural strength carbon hypereutectoid steels. Cand. tech. sci. diss. ]. Novosibirsk, 2004. 193 p. 2. Sherby O.D., Wadsworth J. Damascus Steels. Scientific American. 1985, Vol. 252, pp. 112-120. 3. Verhoeven J.D., Pendray A.H., Dauksch W.E. The Key Role of Impurities in Аncient Damascus Steel Blades. JOM. 1998, № 50 (9), pp. 58-64. 4. Burov S.V., Hudorozhkova Yu.V., Plotnikova N.V. Jevoljucija raspredelenija izbytochnogo cementita v processe deformirovanija zajevtektoidnyh stalej [The evolution of the distribution of excess cementite in the process of deformation of steel hypereutectoid]. Sbornik dokladov i materialov I Mezhdunarodnogo nauchno-prakticheskogo seminara: “Damasskaja stal’. Bulat. Metallicheskie kompozity. Teorija i praktika” [The collection of reports and materials I International scientific-practical seminar “Damascus steel. Bulat. Metal Composites. Theory and Practice”]. Moscow, BMSTU, 2012, pp. 105-109. 5. Ryzhkov M.A., Popov A.A. Metodicheskie voprosy postroenija termokineticheskih diagramm prevrashhenija pereohlazhdennogo austenita v nizkolegirovannyh staljah [Methodological aspects of plotting of thermokinetic diagrams of transformation of supercooled austenite in low-alloy steels]. Metallovedenie i termicheskaja obrabotka metallov - Metal Science and Heat Treatmen t, 2010, no. 12, pp. 37-41. 6. Popov A.A., Popova L.E. Spravochnik termista. Izotermicheskie i termokineticheskie diagrammy raspada pereohlazhdjonnogo austenite [Heat Treater’s Guide. Isothermal and thermokinetic diagrams of decomposition of supercooled austenite]. Moscow, Mashgiz, 1961. 430 p. 7. Kral M.V., Spanos G. Three Dimensional Analysis of Proeutectoid Cementite Precipitates. Acta Metallurgica. 1999, № 47 (2), pp. 711-724.