Effect of Initial Microstructure on the Activation Energy of Second Stage During Austempering of Ductile Iron

• Published in: Scripta materialia Vol. 38; no. 8; pp. 1281 - 1287
• Main Authors: Campos-Cambranis, R.E, Narváez Hernández, L, Cisneros-Guerrero, M.M, Pérez-López, M.J
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Ltd 13.03.1998; Elsevier Science
• Subjects: Applied sciences; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Metals. Metallurgy; Physics; Treatment of materials and its effects on microstructure and properties; Austempering; Austenite transformation; Alloy cast iron; Phase transformations; Malleable cast iron; Cast iron; Experimental study; Heat treatments; Thermal expansion; Austenitizing; Property structure relationship; Microstructure; Activation energy
• ISSN: 1359-6462; 1872-8456
• DOI: 10.1016/S1359-6462(98)00036-0

The empirical activation energy for the reaction ( gamma )+( alpha )- > alpha +carbides on a Ni-Mo alloyed ductile iron was experimentally determined. When the iron was austempered at 573 and 593K, an activation energy of 279.9 kJ/mol was calculated; for the irons treated at 643 or 673K a value of 193.9 kJ/mol was determined. The initial ausferrite structure has a significant influence on the activation energy of stage II. Low temperature ausferrite requires activation energies higher than those required by high temperature ausferrite. Non-isothermal dilatometry resulted a successful technique in determining the activation energy of stage II of the austempering treatment of ductile iron.