Computational modeling of austempering heat treatment of a nodular cast iron

ADRIÁN D. BOCCARDO; PATRICIA M. DARDATI; DIEGO J. CELENTANO; LUIS A. GODOY

Puerto Iguazú

Congreso; 13er SAM-CONAMET, Congreso Internacional en Ciencia y Tecnología de Metalurgia y Materiales; 2013

The nodular cast iron is an alloy of iron, carbon and silicon, in which the graphite have nodules shaped. Its mechanical properties are determined by the microstructure formed during cooling of the casting or during subsequent thermal treatments. The nodular cast austempered (ADI) is obtained taking a conventional ductile iron and treat it thermally. As a result can be obtained a stronger material than the pearlitic nodular cast iron, keeping suitable levels of ductility and elongation, with increased wear resistance and improved fatigue behavior. The transformations that occur during the heat treatment of austempering are: i) stage I formation of acicular ferrite and stabilized austenite ii) step II in which the volume fractions of acicular ferrite and stabilized austenite remain practically constant and iii) step III in which the stabilized austenite decomposes into ferrite and carbide. In this paper, the evolution of the volume fraction of stabilized austenite of stage I is simulated, using the element finite program of general purpose, ABAQUS. Through of user subroutines we implemented a solidification model according to plurinodular theory and a simulation model for the development of stabilized austenite volume fraction using Avrami ́s equation. The solidification model was used to simulate cooling of a Y standard block, while the computational analysis of the variation in time of the stabilized austenite volume fraction of stage I, was performed for a specimen of size 55x10x10mm obtained from the Y block. The numerical results obtained were compared with experimental measurements.