Effects of Tempering Temperature on Mechanical and Tribological Behavior of Ductile Iron

The mechanical properties and tribological behavior of ductile iron tempered at different temperatures were investigated. The tempered sample was composed of spheroidal graphite, alpha phase, and carbides. The strength and hardness decreased near-linearly but the plasticity increased with the increase of tempering temperature, which was mainly because carbon atoms precipitated from martensite and thus reduced the distortion of martensite. Wear tests indicated that the friction coefficient of the sample tempered at 420 degrees C decreased first and then increased with the increasing loads and exhibited the lowest friction coefficient of 0.37. No obvious change was detected for the friction coefficient of the sample tempered at 500 degrees C at different loads. The friction coefficient of the sample tempered at 580 degrees C increased to a stable value with the increase of loads. The wear rate of tempered ductile iron was increased with the increase of tempering temperature, which indicated that hardness was the critical factor for wear properties of ductile iron. The main wear mechanisms of tempered ductile iron were adhesive and abrasive wear. Adhesive wear was predominant for the sample tempered at low temperature but was gradually replaced by abrasive wear with the increase of tempering temperature and normal loads.