• Seabra, Jorge
• Santos, H.
• Duarte, A.

Abstract

In order to austemper a CuMn ductile iron, a new approach was adopted, consisting of a two-step isothermal process imposed on the austenitised material. During the first step, martensite forms and austenite is preserved in the martensitic domain; during the second step, martensite is tempered and austenite is transformed into ausferrite. In this way, an ADI with tempered martensite in its microstructure is obtained. The degree of undercooling (relative to Ms temperature) in the first step controls the martensite fraction. The temperature used in the second step controls the intensity of the martensite tempering and the nature of the ausferrite. Tests were performed in a quenching dilatometer to determine the processing conditions of the ductile iron (temperature and duration of each isothermal stage). Tensile and contact fatigue tests were run to evaluate the mechanical properties of the material after heat treatment. The results show that high tensile strength may be obtained for ADI after a two-step treatment at intermediate temperatures in the bainitic domain (340degreesC) with considerable reduction of processing time and increased contact fatigue life.

Topics

• impedance spectroscopy
• microstructure
• strength
• fatigue
• mass spectrometry
• iron
• tensile strength
• quenching
• tempering