SINTERED IRON-BASE ALLOYS WITH HIGH STRENGTH USING SELECTED NITRIDES AND SILICIDES *

Abstract

The techniques used in alloying in iron powder metallurgy have been extended by employing special compounds. The introduction of the alloying elements in this form and the decomposition of selected nitrides and silicides are described. Elements that oxidize readily at high temperatures (e.g. Cr, Si) can be added in a relatively pure and homogeneous state. These elements stabilize the α phase and thus improve the sintering behaviour.

The paper deals mainly with the preparation of binary Fe-Cr, Fe-Si, and also ternary Fe-Cr-Si alloys obtained by ‘in situ’ decomposition of Si₃N₄, Cr₂N, and CrSi₂ in an iron matrix (WP-150).

The study covers the properties of the powders and their mixtures, the pressing and sintering conditions, the sintering behaviour in the range 1000–1300°C with varying alloying additions, for different sintering times and atmospheres. The tensile strengths observed are ∼525 N/mm² at a densityof 6·7 g/cm³, with ∼3% elongation at fracture. With respect to the low density and the carbon free state of the alloys, the strength values may be considered as rather high. A study of the homogenization process is being carried out.