Influence of the heat treatment on the fatigue behaviour of spheroidal graphite irons

The use of ductile irons for structural applications is increasing thanks to their interesting mechanical properties combined with the casting technology, which allows to manufacture components having complex geometries. Mechanical properties can be adjusted by varying the chemical composition and the heat treatment parameters (temperatures and holding times). As an example, best high cycle fatigue performances or best wear resistance performances can be achieved. In this paper the fatigue behaviour of some ductile irons in the as-cast as well as in the austempered conditions was investigated. Push-pull, strain-controlled fatigue tests were carried out on ferritic, pearlitic, isothermed and austempered ductile irons covering a range of tensile strengths from about 400 MPa to 1300 MPa. For comparison purposes an alloy steel was also fatigue tested. Material parameters of the strain-life and the cyclic stress-strain curves were fitted on experimental results in order to assure compatibility. Finally the fatigue behaviour of the different ductile irons was analysed on the basis of the plastic strain hysteresis energy.