Effect of cooling rate on the formation and distribution of carbides in nodular iron alloyed with Cr

R. HERNÁNDEZ; J. HINOJOSA; A TAMAYO; BASSO, ALEJANDRO DANIEL; J . SIKORA

Cancún

Congreso; XXI International Materials Research Congress (IMRC) 2012; 2012

Sociedad Mexicana de Materiales

In this work was studied the effect of cooling rate on the formation of carbide nodular iron alloyed with 2.2 % Cr and equivalent carbon near to 4.3%. In the experimental stage three Y-blocks of 1.5, 3 and 5.5 cm thickness were poured in green sand mold. Castings were sectioned in two positions (wall and center samples) in order to determine the characteristics of the precipitated carbides (fraction, distribution and relative size) from surface to center and from the bottom to the top of the castings applying quantitative analysis of digital processing image. The results obtained showed the presence of carbides in all of the casting. Finer carbides were obtained in the thin casting but a high variation between the samples located in the wall and center. All the casting presented massive carbides in the last freezing zone (LFZ). Therefore the cooling rate associated with casting thick has important effect on the fraction and distribution of carbides. These microstructural characteristics are important, because this iron is the material for the manufacturing of Carbide Austempered Ductile Iron (CADI) and the carbides may be preferentially dissolve during the austenizing step of the isothermal process.