Ductile iron camshafts low alloyed with 0.2 and 0.3 wt % vanadium were produced by one of the largest manufacturers of the ductile iron camshafts in México “ARBOMEX S.A de C.V” by a phenolic urethane no-bake sand mold casting method. During functioning, camshafts are subject to bending and torsional stresses, and the lobe surfaces are highly loaded. Thus, high toughness and wear resistance are essential for this component. In this work, two austempering ductile iron heat treatments were evaluated to increase the mechanical properties of tensile strength, hardness, and toughness of the ductile iron camshaft low alloyed with vanadium. The austempering process was held at 265 and 305 °C and austempering times of 30, 60, 90, and 120 min. The volume fraction of high-carbon austenite was determined for the heat treatment conditions by XRD measurements. The ausferritic matrix was determined in 90 min for both austempering temperatures, having a good agreement with the microstructural and hardness evolution as the austempering time increased. The mechanical properties of tensile strength, hardness, and toughness were evaluated from samples obtained from the camshaft and the standard Keel block. The highest mechanical properties were obtained for the austempering heat treatment of 265 °C for 90 min for the ADI containing 0.3 wt % V. The tensile and yield strength were 1200 and 1051 MPa, respectively, while the hardness and the energy impact values were of 47 HRC and 26 J; these values are in the range expected for an ADI grade 3.
In the present study, ductile iron camshafts low alloyed with 0.2 and 0.3 wt % vanadium were produced to study the microstructural and mechanical evaluation of lobes and camshaft. For this purpose, camshafts were produced in one of the largest manufacturers of the ductile iron camshaft in México by the phenolic urethane no-bake sand mold casting method. The microstructure of the lobes was studied in three zones located at the top, middle, and bottom of the lobes by optical microscopy, and mechanical tests were performed on lobes and camshafts. A homogeneous distribution of spheroidal graphite with high nodularity for both castings was obtained from the regions of the lobes analyzed. The high cooling rate on the lobe surfaces enabled us to obtain a high nodule count of a smaller size instead of the middle region where big nodules with a low nodule count are presented. An inverse chill behavior was found in the middle region of the lobes where there is an increase in the concentration of carbide-forming elements, leading to the highest micro-hardness values in this region. The tensile properties were increased when the vanadium contents were increased; however, the toughness and ductility of the as-cast alloys were decreased as a result of the increase of the volume fraction of carbide particles.
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