Mechanical properties of low alloy steel foams: Dependency on porosity and pore size

Steel foams can be used as lightweight and high-functional materials in applications such as transport vehicles, machines and structural parts due to their low cost, high strength, high heat resistance and good weldability. In this paper, low alloy steel foams (Fe–1.75Ni–1.5Cu–0.5Mo–0.6C) having porosities in the range of 47.8–70.9% with different pore sizes were produced by the space holder-water leaching technique in powder metallurgy. The structural and mechanical property variations resulting from the use of spacer particles having different amounts and sizes were investigated. Irregular carbamide particles were used as spacer. The porosity and pore size of steel foams replicated the initial amount and size of the spacer. Visual inspections were performed for the coated spacers having different sizes and amounts with steel powders after the final mixing. The amount and size of spacer determined the coatability of the mixtures. A decrease in pore size improves the strength of the steel foams by sharing the load with more and smaller pores; however, small pores having the highest porosity can impair the strength because no enough metals hold the integrity of the new pore walls. The influence of pore size on stress drop ratio of steel foams was also studied. The stress drop ratio decreased with decreasing porosity of steel foams. In addition, an increase in pore size caused a bigger stress drop ratio. However, the highest stress drop ratio was determined for small pores having the highest porosity due to the interconnection of macropores in the foam structure.