Impact Fracture Behaviour of Powder Metallurgy Steels Sintered at Different Temperatures

For powder metallurgy steels prepared through the press-and-sinter route, interparticle bonding is the most decisive feature defining the mechanical properties. It depends on the compacting pressure, but predominantly on the sintering conditions, mainly the sintering temperature. In the present contribution, the progressive strengthening of the sintering necks with increasing temperature is shown by fractography for plain carbon steels as well as alloyed grades. For sintered steels, in contrast to wrought steels, the appearance of cleavage fracture is rather a positive sign, indicating pronounced interparticle strength as attained at high sintering temperatures. At lower temperatures, in contrast, localised failure of the sintering necks typically occurs as ductile rupture, but with rather low consumed energy. Alloy elements with a high oxygen affinity introduced by prealloying retard formation of sound sintering bridges up to temperatures at which carbothermal reduction of the surface oxides becomes possible, while admixing such elements through suitable masteralloys yields attractive interparticle strength already at standard belt furnace temperatures of 1120 °C.