TITLE:
Evaluation of the Influence of Bainitic Transformation on some Mechanical Properties of Calcium Treated Cast iron
AUTHORS:
L.E. aUmoru, J.A. Ali, A.A. Afonja
KEYWORDS:
Austempering, cast iron, calcium, austenitizing, isothermal, transformation, bainites, strength, elongation
JOURNAL NAME:
Journal of Minerals and Materials Characterization and Engineering,
Vol.6 No.2,
October
20,
2007
ABSTRACT: This work has investigated the effect of austempering variables on hardness,
strength and toughness of 0.48wt. % calcium treated cast iron. The iron was subjected to
varying austenitizing and isothermal transformation temperatures and times. Samples
were austenitized for 15, 30, 45 and 60 minutes at each of the temperatures 850, 875,
900, 925 and 950 degrees centigrade. Also for 950℃ and 60 minutes of austenitizing
conditions, samples of the 0.48wt. % calcium treated irons were isothermally transformed
at 300 330, 360 and 420℃ for 2 hours each.
The results of this work show that austenitizing temperature enhances the
hardness property of the austempered iron. The Brinell hardness values of austempered
iron increased from 275 BHN to368 BHN after austenitizing for an hour between 850 and
950℃ respectively. The austenitizing time does not show any significant influence in the
same temperature range. The tensile strength increased from 277.5MPa at the
transformation temperature 300℃ to a maximum of about 430MPa at 374℃ and
decreased afterwards. The percentage elongation on the other hand, reduced to a
minimum of 2.7% at 360℃ and increased thereafter with increase in transformation
temperature. The austempered microstructures were the accicular lower bainites that are
fine for isothermal temperatures below 374℃ and coarse upper bainites for higher
isothermal transformation temperatures.