Evaluation of the Influence of Bainitic Transformation on some Mechanical Properties of Calcium Treated Cast iron
- 1 Department of Metallurgical and Materials Engineering,Obafemi Awolowo University, Ile-Ife, Nigeria.
- 2 Nigeria Building and Road Research Institute (NIBRRI)Garki, Abuja
- 3 Department of Metallurgical and Materials Engineering,Obafemi Awolowo University, Ile-Ife, Nigeria.
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.
- Dorazil, E. (1982) Influence of heat treatment conditions and chemical composition on the mechanical properties of Low Alloyed Austempered Nodular Cast iron, Giesserei – Praxis, No 19, 303 – 310.
- Gulaev , A (1980). Physical Metallurgy, Vol. 1. 5 th Edition MIR Publishers Moscow.
- Harding. R.A. (1986). Effect of metallurgical variables on austempered ductile irons, Metals and Materials, 65-70.
- Imasogie, B.I., Afonja, A.A. and Ali, J.A. (2000). Properties of ductile cast iron nodularized with multiple calcium-magnesium based master alloy, Materials Science and Technology, 16, 194-201
- Pickering, F.B (1967) Mechanism of Bainite Formation in the Low Alloy Steel containing up to 0.40 wt. % Carbon, Transformation and Hardenability in Steels, Climax Molybdenum Co. Ann. Arbor Michigan
- Rajan , T.V; Sharma C.P. ; Sharma, Ashok (1988), Heat Treatment –Principles and Techniques Prentice – Hall of India Private Limited,
- Rossi, T.S and Gupta, B.K (1981) Austempering of nodular cast iron Automobile component: Metal Progress Vol. 119, No 5, 25 – 31
- Rundman, K.B. and Klurg, R.C (1982) An X-ray and Metallographic study of an Autempered Ductile cast Iron Transaction of the American Foundrymen’s Society, Vol. 90, 499 – 508.
- Umoru, L.E.; Ali, J.A.; and Afonja, A.A. (2005) Effect of calcium on the degree of nodularisation of graphite in cast iron, NSE Technical Transactions, 40,.2, 33-42.
- Warrick, R.J.; Althoff, P.; Druschitz, A.P.; Lemke, J.P.; Zimmerman, K.; Mami, P.H. and Rackers, M.L.(2000) Austempered Ductile Iron castings for Chasis Applications. Society of Automotive Engineers Inc.