GB601975A - Improvements in the production of high strength malleable iron alloy castings - Google Patents

Abstract

In a process for producing malleable iron alloy castings from low alloy white cast iron containing one or more metals capable of inhibiting carbide decomposition viz:- chromium, manganese, molybdenum, nickel, vanadium, tungsten, the total carbon content is reduced by a decarburizing heat-treatment to an amount which if uniformly distributed would give a carbon content in any part of the casting equal to that required in a low alloy wrought steel, the casting then being submitted to a deep diffusion annealing under non-oxidising conditions within the temperature limits for solid solution i.e., between Ac3 and the solidus line-until a homogeneous structure with uniform carbide distribution is attained. The temperature for the diffusion annealing is preferably higher than that for decarburizing, and a normalising treatment may follow. The products of the treatment may be hardened, tempered or austempered. In an example, a low alloy cast iron containing 2.7 per cent C, 0.6 per cent Si, 1.5 per cent Mn, 0.06 per cent P, 0.03 per cent S, 0.9 per cent Cr, 0.4 per cent Mo was decarburized at 1,000 DEG C in an oxidising atmosphere until the carbon content was reduced to 0.4 per cent, followed by annealing in a neutral atmosphere at 1,150 DEG C. After normalising, hardening at 850 DEG C, and tempering at 650 DEG C, for 3 hours mechanical properties comparable to those of a low alloy steel of the same composition were attained.