Solidification microstructure and creep rupture behaviour of electron beam welded austenitic Fe-28Mn-6Al-1C alloy

Austenitic Fe-28Mn-6Al-1C alloy was welded using the electron beam (EB) welding technique. After EB welding, fully austenitic microstructure was observed in the weld. Moreover, the entire weld consisted mainly of columnar dendrites with a preferred orientation. The growth and convergence of these columnar dendrites led to the formation of an apparent 'parting' in the weld centreline. The parting exhibited a lower hardness value while a peak hardness was observed in the heat affected zone (HAZ) of the weld. The higher hardness value in the HAZ was associated with the strain induced twinning caused by EB welding. Creep rupture tests of the weldment and the base metal were conducted at 873 K over a stress range of 225-350 MPa. Creep fracture of the weldments was observed to occur in the region of the parting. The rupture life and rupture ductility of the weldments were considerably lower than those of the base metal. (C) 1997 The Institute of Materials.