Deformation and Cracking Behavior of Iron-Manganese-Aluminum Alloys in Sodium Chloride Solution

Five Fe-Mn-Al (Femnal) alloys with ferrite contents from 0.5% to 98% were tested in air and deaerated 3.5% sodium chloride (NaCl) solution at room temperature to examine their sensitivities to environmentally assisted cracking (EAC). Smooth and notched tensile specimens were chosen for tensile testing at slow extension rates. Notched specimens were more sensitive to EAC. The fully austenitic alloy was more resistant. The fully ferritic alloy showed less susceptibility, presumably because the plasticity intrinsically was too limited. For the two-phase alloys (≤ 65% ferrite) studied, susceptibility to EAC increased with increasing ferrite. Fractographical observation showed the ferritic phase was more susceptible to EAC than the austenitic phase. Secondary cracks grew only in the ferrite grains or along the ferrite/austenite boundaries.