Abstract
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.
Highlights
Austempered ductile iron or austempered ductile iron (ADI) is a family of ductile iron (DI) that has been treated by austempering [1] that results in nodules immerses in an ausferritic matrix composed of acicular ferrite and high-carbon austenite [2]
Two hyper-eutectic ductile irons containing 0.2% and 0.3 wt % V were produced in an Induction Furnace of medium frequency (300 Hz), Inductotherm of 3500 kW potency capacity, and 6 tons per hour of furnace capacity by ARBOMEX S.A de C.V., which is a Mexican company located at Celaya and Apaseo el Grande Guanajuato, México that specializes in camshafts manufacturing
A microstructure constituted by fine acicular ferrite and a few blocks of high-carbon austenite was obtained for both ADIs austempered to 265 ◦C, while coarse ausferrite was obtained when the austempering temperature was increased to 305 ◦C
Summary
Austempered ductile iron or ADI is a family of ductile iron (DI) that has been treated by austempering (isothermal heat treatment) [1] that results in nodules immerses in an ausferritic matrix composed of acicular ferrite (αAc) and high-carbon austenite (γHC) [2]. The complete austempered heat treatment is a set of processes used to obtain ADIs. The heat treatment starts with the austenitizing step of ductile iron in the range of temperatures of 850–950 ◦C for 1 h, or longer residence times to ensure transformation from the as-cast matrix to austenite [4]. In the ADI process, two stages of austempering have been identified; in the first stage represented by reaction (1), the austenite unstable (γ) transforms into acicular ferrite (αAc) and high-carbon austenite (γHC)
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