The Influence of Austempering Temperature on the Wear Resistance of Ductile Iron under Two Different Tribosystems

Abstract

This paper reports the results obtained in a research conducted to evaluate austempered ductile iron (ADI) as a wear resistant material for the production of machine parts processed at intermediate and high austempering temperatures (Ta). Severe abrasion in actual service performance trials and low stress abrasion laboratory tests (ASTM G-65) were carried out along with microstructural characterization by optical microscopy and X-ray diffraction. The results derived show that ADI yields excellent abrasion resistance under the operating conditions resulting from the field tests when Ta is raised. Nevertheless, ADI show an opposite trend under the low stress abrasion conditions imposed by the dry sand/rubber wheel abrasion apparatus (ASTM G-65). The presence of a metastable and ductile ausferrite phase (reacted and unreacted austenite+ferrite) in ADI microstructure appears to be the most relevant factor influencing the performance observed. In addition to a high deformation capability detected at the wear surfaces, an austenite to martensite transformation took place as determined by X-ray diffraction. These two factors combined make the ausferritic microstructure overcome hardness reduction when the austempering temperature is raised, improving or sustaining the resistance to severe abrasive wear but, at the same time, increasing impact toughness.