Effect of the Starting Microstructure in the Formation of Austenite at the Intercritical Range in Ductile Iron Alloyed with Nickel and Copper

Abstract

Intercritical austenitizing is a key step on the production of dual-phase austempered ductile iron. Therefore, understanding the formation of austenite at the intercritical range should provide critical information for the future development of this family of alloys. In this work, a ductile iron alloyed with copper and nickel (3.4 C, 2.6 Si, 0.9 Ni, 0.6 Cu, wt%) was studied. The as-cast alloy was submitted to ferritic annealing and normalizing in order to obtain fully ferritic and fully pearlitic microstructures, respectively. The effect of microsegregation, initial microstructure (ferrite or pearlite) and nodule count on the formation of austenite in the intercritical range under continuous heating was studied using electron probe micro-analyzer-EPMA-high-resolution dilatometry, optical microscopy and scanning electron microscope-SEM-. The results showed that silicon, copper and nickel segregate around the graphite nodules and manganese segregates to the last freezing zones. Also as nodule count increases the segregation level decreased. Regarding the rate of austenite formation, the results showed that it increases as nodule count increases. Additionally, austenite formation is faster when the starting microstructure is pearlitic and it increases as the pearlite interlaminar spacing decreases. Finally, the results showed that the critical temperatures for austenite formation depend mainly on the starting microstructure (ferrite or pearlite).

Study of the effects of vanadium and molybdenum on the microstructure of ductile iron (DI) and austempered ductile iron (ADI) and their corrosion resistance

“…Intercritical heat treatments can also be performed on DI to increase the mechanical properties. Intercritical heat treatments can be applied to obtain microstructures of graphite nodules in a matrix of ferrite and austenite particles or graphite nodules in a matrix of ferrite and tempered martensite (Aristizabal et al, 2012;Machado et al, 2020). Corrosion behavior, like mechanical properties, is related to the alloy microstructure.…”

Effect of Austempering Times on the Microstructures and Mechanical Properties of Dual-Matrix Structure Austempered Ductile Iron (DMS-ADI)

“…[1][2][3][4][5][6][7][8] In previous studies, DMS-ADI was named as dual-phase austempered ductile iron (DP-ADI) [9][10][11][12][13][14][15][16] , austempered ductile iron with dualmatrix structure (ADI with DMS) 1-3, 7, 8, 17, 18 , ductile cast iron with dual-matrix structure (DMS) 19,20 , dual-phase matrix austempered ductile iron (DPM-ADI) 21 , dual-matrix ductile iron (DM-DI) 22 , and intercritically austempered ductile iron (IADI). [23][24][25][26][27][28][29][30][31][32] The term dual-matrix structure was used first by Voigt et al in their study. 33 However, Wade&Ueada 34 first produced the dual-matrix structure in ductile irons and they had named it ductile cast iron with duplex matrix.…”

“…[1][2][3]9,10,[35][36][37] Ausferrite has been defined as a mixture of bainitic ferrite (a b ) and high-carbon stabilized austenite (c HC ) in austempered ductile irons. 1,9,26,[38][39][40] The ausferritic structure provides a good combination of tensile strength, ductility, and impact toughness in the ADIs. 9,24,26,[41][42][43][44][45][46][47][48][49] Moreover, the ausferritic structures significantly improve the tribological properties of the ADIs.…”

“…1,9,26,[38][39][40] The ausferritic structure provides a good combination of tensile strength, ductility, and impact toughness in the ADIs. 9,24,26,[41][42][43][44][45][46][47][48][49] Moreover, the ausferritic structures significantly improve the tribological properties of the ADIs. 17,18,47,[50][51][52] Researchers have tried to develop the mechanical properties and ductility of the ADIs by controlling the starting microstructures 26 , austenitizing temperatures 1,2 , partitioning treatments 53 , and temperature and time of austempering.…”

The Effect of Cryogenic Treatment on Hardness, Toughness, and Tribological Properties of Austempered Ductile Iron with Different Nickel Contents

“…They reported that austenite formation is related to starting microstructure and austenite formation is faster with a starting microstructure of pearlite and it increases with the decreasing interlaminar spacing. 11 One of the most promising usage areas of ADI is in high load contact cases, with a number of studies having reported the wear and friction properties of DI under different conditions. Wen et al investigated the wear behavior of ADI using a ball on disk wear test setup.…”