The purpose of this study is to investigate the fatigue crack growth (FCG) behavior of austempered ductile irons (ADIs) in different environments. In particular, the FCG rates in several aqueous environments and lubrication oil were made a comparison for various heat treatment conditions and loading frequencies. Experimental results show that austempering heat treatment did not improve the corrosion resistance of ductile iron in the given corrosive environments. In various room-temperature aqueous environments, all the austempered ductile irons exhibited lower FCG rates at 20 Hz than those in air due to the crack closure effect induced by corrosion products. By subtracting the crack closure effect, the given room-temperature corrosive environments did not exert any detrimental effects on the FCG behavior at 20 Hz for the given ductile irons as the effective FCG curves of each iron in these corrosive environments were close to that in air. In other words, the FCG behavior of the given ductile irons at 20 Hz was not sensitive to the environmental effects at room temperature. The SAE 10W40 lubrication oil provided an inert environment to reduce the FCG rates for the given ductile irons as compared to atmospheric environment. An increase in the temperature of salt water from room temperature to 80℃ caused a remarkable increase in FCG rate for ADI due to the enhanced diffusion rate and hydrogen embrittlement (HE) effect at the crack tip. As the cyclic loading frequency was reduced, more time was available in each cycle for the corrosive environments to interact with the crack tip and enhance the HE effect. As a result, the FCG rates at a lower frequency (1 Hz) were greater than those at a higher frequency (20 Hz) in corrosive environments.
Austempered ductile iron Corrosion fatigue crack growth Crack closure effect