II. Report on Austenitic Cast Irons

Abstract

Austenitic cast irons may be regarded as bearing the same relation to ordinary cast irons as some of the stainless steels bear to the ordinary steels. Although more expensive, both in raw materials and manufacture, the austenitic cast irons have properties which mark them off as different from all other cast irons, particularly in their softness and ductility; high resistance to wear, erosion, corrosion and heat; non-magnetism and relatively high electrical resistance; low thermal conductivity and high thermal expansion. Their mechanical properties compare with those of a good engineering cast iron, but their softness and toughness make them readily machinable. They are readily welded. They are not susceptible to ordinary heat treatment, i.e. quenching and tempering, but nevertheless can be annealed at low temperatures with advantage. They can be cast white if required, and a simple thermal treatment such as annealing at 950 deg. C. for 30 minutes yields a metal with 2–3 per cent elongation in the cold. While the founding of these irons presents special problems, these can be overcome and the smallest castings can be, and are, successfully made in austenitic irons, down to -inch section; but if thin sections should be hard, they can be softened by the treatment given above. They melt at about 1,150 deg. C., a figure similar to that of the non-phosphoric cast irons, and have a specific gravity of 7·2–7·6. The present report is intended primarily as a guide to the engineering properties of the austenitic cast irons, in order that engineers may use them to the fullest extent justified by their properties. The data presented are drawn from authoritative sources, and a list of the papers and reports consulted is given at the end. In general, the data are those of interest to the user rather than the maker, to the engineer rather than the metallurgist.