GB1232491A - - Google Patents

Abstract

1,232,491. Casting processes; mould materials. GENERAL ELECTRIC CO. 10 May, 1968 [11 May, 1967; 3 April, 1968], No. 22417/68. Heading B3F. [Also in Division C7] Ferrous metal containing at least 50% of iron and more carbon than is soluble in the matrix phase is pressure die cast, at the least the interior surfaces of the die being made from molybdenum, tungsten, or a refractory alloy containing at least 50% of one or both of these metals, such an alloy having at the average operating temperature a thermal diffusivity of at least 1 foot<SP>2</SP>/hour, a heat diffusivity of at least 40 BTU/foot<SP>2</SP>/<SP>‹</SP> F./hour¢, and a melting point above 3000‹ F.; the dies are operated at an elevated temperature to prevent surface irregularities in the casting, which is subsequently heat treated for less than four hours to precipitate carbon from solution in the form of dispersed nodules. The dies may be made entirely of refractory metal or alloy, but preferably consist of massive inserts of such material in a steel backing, although thinner layers such as produced by cladding may be employed. Where inserts are used it is essential that they are thermally bonded to a heat sink as particularly described the die blocks incorporate heating elements. Suitable die-face alloys are molybdenum precipitation strengthened with titanium, zirconium or hafnium and carbon, nitrogen or boron, and tungsten alloyed with rhenium or containing 2% thoria; also tungsten or molybdenum liquid-phase sintered with nickel or iron, or sintered tungsten infiltrated with copper or silver. As exemplified iron containing 3.5% carbon, 2.2% silicon and 0.7% manganese was cast to provide a gray iron core with outer layers of white iron; the latter were converted to malleable iron by annealing for 2 hours at 1650‹ F. Also a casting containing 2.5% carbon, 1.5% silicon, 0.45% manganese, 0.6% molybdenum which solidified as white iron was converted to malleable iron in 2 hours at 1650‹ F., while iron having 3.6% carbon, 2.1% silicon and low manganese and treated with magnesium, which solidified white, was converted to nodular iron in 30 minutes at 1700‹ F.