FATIGUE AND FRACTURE-BEHAVIOR OF A NICKEL-CHROMIUM FREE AUSTENITIC STEEL

The austenitic steels based on the Fe-Mn-Al-C system are relatively le ss expensive than those from the Fe-Cr-Ni-C system due to their being nickel-chromium free stainless steels. The fatigue crack growth (FCG) behavior and elastic-plastic fracture toughness (J-integral) of an all oy of the Fe-Mn-Al-C system have been studied at room temperature. Thi s fatigue crack growth study revealed a bilinear form of behavior in r elation to the Paris approach. Fractographic studies confirmed that th e crack growth micromechanism changes from being microstructure-sensit ive to being structure-insensitive when the reversed plastic zone size exceeds the grain size of the material. This change is accompanied by a change in crack closure mechanism from a roughness-induced to a pla sticity-induced one. The Ni-Cr free austenitic steel offers better fat igue crack growth resistance as compared to that for the conventional 304L type stainless steel containing Ni-Cr. It also is found to posses s a high fracture toughness (J(Ic)) value of 187 kJ/m2 comparable with other grades of stainless steel containing nickel and chromium.