TESTING 1-2-3
New As-Cast Ductile Iron Raises Bar for Properties
Researchers are developing ductile iron that features properties similar to ADI, without heat treatment.
SUSANA MENDEZ, U. DE LA TORRE, PELLO LARRANAGA, IK4-AZTERLAN, DURANGO, SPAIN; RAMON SUAREZ, VEIGALAN ESTUDIO 2010, DURANGO, SPAIN;
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DORU M. STEFANESCU, OHIO STATE UNIVERSITY, COLUMBUS, OHIO, AND UNIVERSITY OF ALABAMA, TUSCALOOSA, ALA.
uctile iron has a wide range of mechanical properties, depending on its metallic matrix. T e material can replace cast and forged steel in a large number of applications due to its combina- tion of high strength and toughness, in addition to lower density. Because of this, the search for new ductile
iron alloys with improved mechanical properties and lowered production costs is an important
ADDING IT ALL UP
Breaking down the latest research is as easy as 1-2-3. “Processing Thickness Window for As-cast Ausferritic Castings,” Susana Mendez, U. de la Torre, and Pello Larranaga, IK4-Azterlan, Durango, Spain; Ra- mon Suarez, Veigalan Estudio 2010, Durango, Spain; Doru M. Stefanescu, Ohio State Univ., Columbus, Ohio, and Univ. of Alabama, Tuscaloosa, Alabama
Background—One of the key points to achieve as-cast ausferritic microstructures is to defi ne the minimum cooling rate. The goal of the research was to develop an experimental model able to defi ne the thickness window where the as-cast ausferritic microstructures can be guaranteed.
Procedure—To obtain different cooling rates, castings with different thermal moduli (thicknesses) and several geometries were poured and studied to build data for the model. Results and Conclusions—Based on the results of the experi- ment, an Excel spreadsheet model was developed to establish if a specifi c casting, with specifi c thickness differences, can be produced through engineered cooling and exhibit fully ausferritic microstructures on all sections. The experimental model has been validated with different geometries in a defi ned range of thermal moduli (0.4-1.5 cm) and for specifi c range of chemical composition (3-5%Ni; 0-0.2%Mo; 0.1-1%Cu by weight). ■
research fi eld. T e ductile iron with the highest resistance/ductility rate is austempered ductile iron (ADI), which gets its superior proper- ties from its microstructure. T is microstructure, called “ausferritic,” is diff erent than that of conventional irons. Fine grains of ferrite yield high strength, and the distribution of austenite and ferrite together make ADI more ductile and tougher than conventional irons. ADI achieves its microstructure
through a heat treatment process called austempering. T is is a well- established method, and ADI parts have replaced hundreds of steel forg- ings and fabrications in production volume levels. As a secondary operation, austem-
pering adds cost and time to casting production. Researchers are investi- gating a new process to achieve cast- ings with the same microstructure as ADI (ausferritic) without heat treatment. In this process, engineered cooling is used to coerce the metal to form the desirable ausferritic mi- crostructure. For end-users, it could mean lower cost, high strength parts with shorter lead times. T e process variables that must
be controlled to achieve the as-cast ausferritic microstructure include the chemical composition of the metal and the cooling rate of the diff erent
Sept/Oct 2015 | METAL CASTING DESIGN & PURCHASING | 39
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