PM synthesis and properties of steel foams

Steel foam steel was synthesized by a powder metallurgical route, resulting in densities less than half that of steel. Process parameters for foam synthesis were investigated, and two standard powder formulations were selected consisting of Fe–2.5%C and 0.2 wt.% foaming agent (either MgCO3 or SrCO3). Using the PM approach, foams with relative density ranging between 0.38 and 0.64 were obtained. Compression tests were performed on annealed and pre-annealed foam samples of different density to determine mechanical response and energy absorption behavior. The stress–strain response was strongly affected by annealing, which reduced the carbon content and converted much of the pearlitic structure to ferrite. These microstructural changes led to a more ductile response during compressive loading, in which a long stress plateau typically occurred after initial yielding. In fact, annealed steel foams behaved much like aluminum foams under compressive loading, despite pore structures that were considerably more coarse than those reported for aluminum foams.