Evaluation of CADI Low Alloyed with Chromium for Camshafts Application

Abstract

Different processing routes have been developed to increase the strength and hardness of camshafts for automotive applications. In this work, two carbidic austempered ductile irons (CADIs), alloyed with 0.2 and 0.4 wt% Cr, were evaluated to determine their suitability in the camshaft production by microscopy techniques and mechanical tests. The CADIs were produced at austempering temperatures of 265 and 305 °C, during 30, 60, 90, and 120 min. The microstructural characterization was carried out by optical microscopy, while Rockwell C Hardness, tensile, Charpy impact, and block-on-ring wear loss tests were evaluated for mechanical characterization from the camshaft and standard keel block. The volume fraction of high-carbon austenite was determined for the heat treatment conditions by X-ray diffraction measurements. The process window was found in the range from 60 to 120 min, for both austempering temperatures, while the highest amount of ausferrite was obtained at 90 min. The formation of carbides was increased as the chromium content was increased. The highest hardness (49 HRC) and wear resistance (0.252 mm3) were obtained for the lower austempering temperature (265 °C, 90 min) and higher chromium content (0.4%). The highest austempering temperature (305 °C, 90 min) and lowest chromium content (0.2%) allow for obtaining the highest toughness (22.91 J) and elongation (4.2%), while the highest tensile strength (1027 MPa) was obtained for the CADI containing 0.2% Cr heat-treated to 265 °C.

Statistical Data-Driven Model for Hardness Prediction in Austempered Ductile Irons

“…The microstructures obtained under all treatment conditions are shown in Figure A1 in Appendix A, demonstrating an increase in the presence and size of γhC blocks caused by an increment in TA. This behavior has been also documented in several investigations and is attributed to carbon atoms diffusing longer distances and stabilizing a greater amount of austenite, resulting in lower nucleation of αac needles [45][46][47]. The TA effect is also evidenced by this figure as it is possible to observe the enlargement and thickening of αac needles as time elapses, with a redistribution of carbon and achieving a transformation of γhC into αac [19,48,49].…”

“…Such a transition in ausferritic morphology is primarily influenced by T A and occurs because at temperatures around T Ms the transformation is dominated by α ac needle nucleation, and at higher temperatures the transformation is dominated by their growth, as reported by [19,45,50]. αac needle nucleation, and at higher temperatures the transformation is dominated by their growth, as reported by [19,45,50]. Throughout the austempering process, cooling is performed from Tγ to TA with its impact being observed in terms of αac needle nucleation.…”

“…At a temperature of 290 • C (Figure 5a) the presence of lower ausferrite indicated by red circles is evident, at 320 • C (Figure 5b) a combination of lower and upper ausferrite can be observed and finally at temperatures of 350 and 380 • C (Figure 5c,d) an all upper ausferritic morphology is indicated by yellow circles. Such a transition in ausferritic morphology is primarily influenced by T A and occurs because at temperatures around T Ms the transformation is dominated by α ac needle nucleation, and at higher temperatures the transformation is dominated by their growth, as reported by [19,45,50]. αac needle nucleation, and at higher temperatures the transformation is dominated by their growth, as reported by [19,45,50].…”

Comparison of the surface morphologies of ceramic reinforced metal matrix composite cams after wear tests under dry and wet conditions

“…11 Improving the wear response of the wear cams is attempted through various surface-and through-treatments. 12 Utilization of chills to acquire ledeburitic structure on the surface, 6 induction hardening, 13 carbidic austempering of the ductile irons, 14 carburizing and induction flame quenching of low/middle steels and cathodic electrolytic plasma hardening (CEPH) 15 of cast iron and steels can be given as examples. Only recently, there has been meaningful research on exploring the usability of the ceramic reinforced metal matrix composites (MMCs) as camshafts or cams.…”

Microstructure and Dry/Wet Tribological Behaviors of 1% Cu-Alloyed Austempered Ductile Iron

“…Furthermore, heat treatment is a crucial technology for most cast irons used in practical applications [ 5 ]. For instance, the austempering treatment of DI can significantly improve its mechanical properties, resulting in austempered ductile iron (ADI) with improved hardness, toughness, and fatigue properties [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. Because of these advantages, ADI is often used in gears, suspension brackets, rails, brake blocks, and other materials requiring high contact stress.…”