GB623360A - Alloy iron castings and method of producing the same - Google Patents

Abstract

An alloy cast iron contains the following elements with the percentage ranges stated: total carbon 2.5 to 3.5, silicon 1.5 to 3, manganese 0.5 to 1.5, chromium 0.2 to 1.5, vanadium 0.2 to 1.25, aluminium 0.2 to 0.75, iron the balance. The proportions of the constituents are such that, for the section and rate of cooling of a casting the alloy iron structure would, in the "as cast" condition, be similar to that of a fine-grained white cast iron, the alloy iron having been heat treated to a temperature above the critical range until the cementite has been partially broken down into small particles of non-acicular form and even distribution and then cooled slowly through the critical range to produce a casting which is machinable. The alloy cast iron may also contain zirconium and/or tellurium up to 0.05 per cent. The cast iron may contain other elements as impurities, such as the following, up to the percentage ranges stated: nickel 0.75, tungsten 0.25, cobalt 0.25, titanium 0.4, boron 0.1, molybdenum 0.25, phosphorus 0.5, sulphur 0.1. Preferably the cementite particles in the alloy iron casting, e.g. a piston ring, after heat treatment, have an apparent size which does not exceed 1/8 inch in any direction when the specimen is examined under a microscope at a magnification of 100 diameters. To produce such a microstructure, in an example wherein the metal is approximately 5/8 inch thick as cast, it is reheated to 1000 DEG C and cooled down at a rate of 2 DEG C to 3 DEG C per minute through the critical range. Reference has been directed by the Comptroller to Specification 390,687.