Resistência à propagação de trinca de fadiga em ferros fundidos nodulares austemperados.

Abstract

Austempered ductile cast irons have waked to a great interest. The possibility of an excellent combination of toughness and fatigue strength .makes this material very attractive. In this work the fatigue crack growth resistance of two austempered ductile cast irons was determined: molybdenum alloyed nodular cast iron (0.2% Mo) and another unalloyed iron. Both austempered ductile cast irons were inoculate with 0.5, 0.7 and 0.9% FeSi75A. The fatigue tests were carried in room temperature, ambient atmosphere and in a servohydraulic Material Test System (MTS 810) test machine under load control mode. The load ratio, R, was kept constant at 0.10. The results obtained showed that the unalloyed austempered ductile cast iron, for all situations and independent of FeSi75A content, always presented the most fatigue crack growth resistance. This behavior was explained with basis in the silicon effect, present within inoculante, on the microstructure characteristics to the ausferritic matrix. The fracture surfaces presented a mixed mechanism fracture with a flat fracture, cleavage-like regions within which regular parallel arrest lines were observed.