The objective in producing spheroidal graphite cast iron (SGI) is to secure the formation of graphite nodules with the proper matrix and hardness. However, sometimes, the use of bad quality charge materials and bad melting practices result in liquid conditions so poor that even the usual alloy additions do not work [1,2]. In this context, preconditioner alloys have been developed to improve the system response to alloy addition.

The use of preconditioners remains a challenge in some markets, where the effectiveness of these alloys is not observed. Therefore, the preconditioner's effect on the matrix microstructural characteristics and graphite nodules was evaluated.

For this purpose, different melts of SGI were produced with the addition of 0.15% (Al,Zr,Ca)–FeSi alloy as a preconditioner and of (Ca,Al)–FeSi alloy as an inoculant. Preconditioning treatment was applied in different occasions: at the cold charge, on top of the furnace with the last cold charge, and at tapping from the furnace to the Mg-treatment ladle.

Microstructural characterization was performed through optical microscopy (OM), scanning electron microscopy (SEM) with (EDS) and electron backscatter diffraction (EBSD). Different EBSD maps were performed to evaluate the grain size of the matrix, the misorientation, phase analysis and crystallographic orientation. The hardness distribution of the samples was evaluated with Vickers microhardness maps with 98 mN of load.

OM characterization suggests that preconditioning treatment slightly improves graphite nodularity without increasing graphite nodule density. The different treatment of precondition has an effect of the microstructure of the matrix, revealed by EBSD analysis.

References

[1] Hossain, Md. Sojib S., A.K.M. Bazlur B. Rashid. Archives of Foundry Engineering, 2020, Volume 20, Issue 1, 61 – 66

[2] Juretzko, F.R., L.P. Dix, R. Ruxanda, D.M. Stefanescu. Transactions of the American Foundry Society, 2004, Volume 112, 04-014