Effect of the ratio Mo/Cr in the precipitation and distribution of carbides in alloyed nodular iron

Abstract

ABSTRACTThis investigation deals with the effect of 2/0, 1/1 and 1/0.5 Cr/Mo ratios on the local fraction, distribution and the comparative size of carbides precipitated in cast nodular iron. “Y” block castings with a thickness of 1.5 cm are cast in green sand molds. Two samples are cut from each casting, one located on the center and another on the wall. The carbide volume fraction is evaluated by a digital analysis system. Each sample is analyzed in three zones: bottom, middle and top. Carbide mappings are generated according to the average local carbide fraction in order to get the distribution of carbides on the casting. Results show that higher volume fractions of carbides precipitate for the ratio 2/0 of Cr/Mo with values between 28.5 and 19.5%. The lowest fraction of carbides is presented in nodular iron alloyed with a Cr/Mo ratio of 1/1 between 6.5 and 4.6%. Also a very heterogeneous distribution of the carbides is observed in the three alloys and massive carbides are observed in the last freezing zone of the castings.