Grain refinement and hydrogen embrittlement in iron aluminide alloy FA129

Abstract

Iron aluminides are susceptible to hydrogen cold cracking during gas tungsten arc welding. Fine grained base materials have been shown to be more resistant to environmental embrittlement when tested in the presence of water vapour than coarse grained base materials. To study the effect of fusion zone grain size on cold cracking susceptibility, welds were produced using magnetic arc oscillation to refine the fusion zone grain structures. Tensile tests were conducted in varying water vapour atmospheres, on weldments with average fusion zone grain sizes ranging between 115 and 530 μm. Fracture strength data followed Hall–Petch behaviour and the effect of water vapour concentration was also incorporated into the traditional plot. The results of the tensile tests showed the finer grain size fusion zones were less susceptible to hydrogen cracking and more tolerant of high hydrogen concentration than coarse fusion zone grain structures.