Powder metallurgy (P/M) constitutes a growing metal-forming technology with many favourable attributes. Ferrous materials provide the largest class of P/M alloys. The sintering of iron is examined in this review to establish the fundamental behaviour and to determine possible successes through enhanced sintering treatments. Within the scope of enhanced sintering, both activated and liquid-phase treatments are considered. The available data are collected to determine the effects of various additions on the sintering of iron. It is believed that small additions of elements like phosphorus, boron, carbon, and nitrogen provide for rapid densification and strengthening. However, the benefits are often offset by degradation of other properties such as ductility. These effects, as well as dimensional changes, are documented for several systems. Emphasis is given to describing the atomic processes responsible for the observed changes. There is considerable room for further progress in this area, including...

Enhanced sintering treatments for ferrous powders

(1974). PROPERTIES OF STRUCTURAL POWDER-METAL PARTS—OVER-RATED OR UNDER-ESTIMATED? Powder Metallurgy: Vol. 17, No. 33, pp. 103-125.

Properties of structural powder-metal parts—over-rated or under-estimated?

In this discussion, the concern is with the properties of systems with high volume fractions of solid (typically over 50% solid at the sintering temperature), which includes most practical materials processed by liquid phase sintering techniques. There is a diversity of final microstructures possible by liquid phase sintering. The microstructure carries over to affect the properties, especially mechanical behavior. However, microstructure is not the only factor affecting the properties of liquid phase sintered materials (1,2). Table 9.1 lists the specific factors by categories of powder characteristics, sintering cycle, alloy composition, post-sintering heat treatment, sintered microstructure, and testing conditions. In light of such diversity, it is difficult to make specific statements about optimal conditions. However, there are some general results which provide insight to the links between composition, processing, microstructure, and properties.

Properties of Liquid Phase Sintered Materials

A study of the sintering behaviour of iron compacts containing additions of tin up to 1 wt.-% has been made. A tensile strength of 234 MN/m2 (34 x 103 lbf/in2) has been achieved with an optimum tin addition of 0·5 wt.-%, sintering being carried out for 10 min at 1100°C (1373 K) in a reactive halide atmosphere. Combination of the two ‘activating’ techniques (addition of tin and sintering in a reactive atmosphere) permits current properties to be attained at considerably lower sintering temperatures or sintered densities, and is much more effective than when they are applied individually. A tensile strength of 165·3 MN/m2 (24 x 103lbf/in2), achieved by sintering at 1200°C (1473 K) for 10 min with an addition of 0·5 wt.-% tin can be obtained by reactive-sintering the same composition at 900°C (1173 K) for 10 min. Alternatively, the density of the part can be reduced from 6·7 to 6·2 g/cm3 with no loss of strength or elongation. Tin in excess of 0·5 wt.-% causes deterioration in properties under the si...

C. A. Calow

Papers

Studies on the activation-sintering of iron powder