GB478127A - Process for improving the machining qualities of iron-nickel-aluminium-copper alloys - Google Patents

Abstract

The machining qualities of an iron-nickel-aluminium-copper alloy containing 7-35 per cent of nickel, 5-20 of aluminium, 0,01-40 of copper and at least 30 of iron are improved by bringing the alloy to a temperature between 700 DEG C. and its melting point and then cooling so that the mean rate of cooling between the a -g transformation temperature and 500 DEG C. amounts to less than 10 DEG per minute and preferably between 1 and 2 DEG per minute. The alloy may be kept at the temperature above 700 DEG C. for 15 minutes to 24 hours and this temperature may be below the transformation temperature. The alloy may be cast, e.g. in a sand mould, and cooled before being heated or after casting may be cooled as stated above. The alloy after the treatment described above is machined and may then be hardened by heating to 1000-1350 DEG C. and cooling to temperatures below 500 DEG C. with or without a tempering at 500-700 DEG C. The cooling between the a -g transformation point and 500 DEG C. may be carried out in stages. Alloys containing at least 25 per cent of iron, 5-20 of aluminium and 7-35 of nickel may also contain 0,5-25 of cobalt. The alloys may also contain one or more of the elements chromium, manganese, molybdenum, silicon, uranium, titanium, vanadium or tungsten in a total amount of not more than 5 per cent. Specification 478,126 is referred to. The Specification as open to inspection under Sect. 91 also contained the subject-matter of Specification 478,126, but this subject-matter does not appear in the Specification as accepted.