The room temperature mechanical behavior of particulate composites made from pure iron and white cast iron powders was investigated. These particulate composites can be made by pressure sintering at warm temperatures without a protective atmosphere. The compacts produced by this process were more than 97% of theoretical density and the structure of the powders is retained in the compact; that is, there is little long-range diffusion of carbon during the warm pressing operation. These particulate composites can then be given a heat treatment that allows selective hardening of the white cast iron constituent while the iron matrix is relatively unaffected. A great variety of mechanical properties and microstructures can be developed with this selective heat treatment by controlling the amount of interdiffusion and tempering. The role of interdiffusion during selective heat treatment is assessed and evaluated.