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FEATURE A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 1 8 4 4 12 poised to satisfy weight-related obstacles. The one remain- ing issue with austempering—the “Holy Grail of bainite”—is hardness. Additional research in microalloying ADI and steel would solve that major hurdle. ~HTPro For more information: Jack Titus, AFC-Holcroft LLC,49630 Pontiac Trail, Wixom, MI 48393, 248.231.3950, jtitus@ afc-holcroft.com , www.afc-holcroft.com. References 1. Global Fuel Economy Initiative (GFEI), www. globalfueleconomy.org . 2. T. Bell, How Is Magnesium Metal Produced?, Commod- ities: Metals, www.thebalance.com , updated Sept. 2017. 3. G. Gardiner, Recycled Carbon Fiber Update: Closing the CFRP Lifecycle Loop, Composites World, Nov. 2014. 4. Z. Lawrynowicz, Ausferritic or Bainitic Transformation in ADI, University of Technology and Life Sciences, Dept. Matls. Sci. and Engrg., Bydgoszcz, Poland. 5. V. Zanardi, ADI for Lightweight Suspension Compo- nents in Light Commercial Vehicles, Ductile Iron Soc. 2016 World Conf. on ADI, Oct. 2016. 6. Test from ASME Gear Research Institute Report A 4001. Austenite is not retained as some have indicated, be- cause the parts would never have cooled below the M s tem- perature. Carbon in the austenite is high enough to lower the M s temperature well below room temperature. Some proposed that this microstructure contributes to the hard- ening effect when the part is subjected to strain or stress, producing the shear or deformation required to change from face centered cubic (fcc) austenitic lattice to body centered tetragonal (bct) martensitic lattice. Zanardi Fonderie S.p.A. [5] compared the properties of cast iron and ADI parts treated in a universal batch quench austemper (UBQA) furnace (Fig. 2). Fig. 3 shows a suspen- sion arm made of austempered ductile iron compared to a pearlitic-ferritic cast iron version. Both weight savings and strength are gained by using austempered ductile iron ver- sus pearlitic-ferritic cast iron. In addition to strength, DI is in- herently quieter than steel alternatives due to the presence of graphite. Fig. 4 shows the relative damping of ductile iron and steel [6] . CONCLUSION Several weight reduction options exist when it comes to the materials and processes available to designers and heat treaters for automotive applications. However, remain- ing challenges include whether the choice for weight reduc- tion can be cost effective in vehicle pricing, and whether the selected process can be integrated cost effectively into the predictive process automation methodology of the manufacturer. From a heat treating perspective, controlling distortion is a primary goal in reducing manufacturing cost. Because steel and ductile iron offer the greatest potential for achiev- ing an appropriate strength and wear resistance parameter, austempering with its predictable, uniform growth seems Fig. 2 — Universal batch quench austemper furnace (914 × 1829 × 1422 mm) used at Zanardi Fonderie S.p.A. to study heat treated properties of cast iron and austempered ductile iron. Three chambers enable transferring product to a salt-quench tank under a protective atmosphere. Fig. 3 — (a) Austempered ductile iron (ISO 17804/JS/900-S) suspension armprovides weight savings (5.9 kg machined weight versus 8 kg) and strength (600 MPa yield, 900 MPa tensile, 8% elong. versus 370 MPa, 590 tensile, and 10% elong.) over the (b) GH 60-38-10 pearlitic-ferritic cast iron version. Fig. 4 — Relative damping of ductile iron and steel. (a) (b)