Machinery's Handbook, 31st Edition
MATERIALS FOR IRON AND STEEL CASTING 1481 or heat resistance. Alloy cast irons are used extensively for such parts as automotive cylin ders, pistons, piston rings, crankcases, and brake drums; for certain machine tool castings; for certain types of dies; for parts of crushing and grinding machinery; and for applications where the casting must resist scaling at high temperatures. Machinable alloy cast irons hav- ing tensile strengths up to 70,000 psi (483 MPa) or even higher may be produced. Malleable-Iron Castings.— Malleable iron is produced by the annealing or graphitization of white iron castings. The graphitization in this case produces temper carbon which is graphite in the form of compact rounded aggregates. Malleable castings are used for many industrial applications where strength, ductility, machinability, and resistance to shock are important factors. In manufacturing these castings, the usual procedure is to first produce a hard, brittle white iron from a charge of pig iron and scrap. These hard white-iron castings are then placed in stationary batch-type furnaces or car-bottom furnaces and the graphiti zation (malleablizing) of the castings is accomplished by means of a suitable annealing heat treatment. During this annealing period the temperature is slowly (50 hours) increased to as much as 1650 or 1700 ° F (899 or 927 ° C), after which time it is slowly (60 hours) cooled. The American National Standard Specifications for Malleable Iron Castings—ANSI/ASTM A47-77 specifies the following grades and their properties: No. 32520, having a minimum tensile strength of 50,000 psi (345 MPa), a minimum yield strength of 32,500 psi (224 MPa), and a minimum elongation in 2 inches (50.8 mm) of 10 percent; and No. 35018, having a minimum tensile strength of 53,000 psi (365 MPa), a minimum yield strength of 35,000 psi (241 MPa), and a minimum elongation in 2 inches of 18 percent. Cupola Malleable Iron: Another method of producing malleable iron involves initially the use of a cupola or a cupola in conjunction with an air furnace. This type of malleable iron, called cupola malleable iron, exhibits good fluidity and will produce sound castings. It is used in the making of pipe fittings, valves, and similar parts and possesses the useful property of being well suited to galvanizing. The American National Standard Specifications for Cupola Malleable Iron — ANSI/ASTM 197-79 calls for a minimum tensile strength of 40,000 pounds per square inch (276 MPa); a minimum yield strength of 30,000 psi (207 MPa); and a minimum elongation in 2 inches of 5 percent. Pearlitic Malleable Iron: This type of malleable iron contains some combined carbon in various forms. It may be produced either by stopping the heat treatment of regular malleable iron during production before the combined carbon contained therein has all been trans- formed to graphite or by reheating regular malleable iron above the transformation range. Pearlitic malleable irons exhibit a wide range of properties and are used in place of steel castings or forgings or to replace malleable iron when a greater strength or wear resistance is required. Some forms are made rigid to resist deformation while others will undergo considerable deformation before breaking. This material has been used in axle housings, differential housings, camshafts, and crankshafts for automobiles; machine parts; ord- nance equipment; and tools. Tension test requirements of pearlitic malleable iron castings called for in ASTM Standard A220-99 (R2018) are given in the accompanying table. Tension Test Requirements of Pearlitic Malleable Iron Castings ASTM A220-99 (R2018) Casting Grade Numbers 40010 45008 45006 50005 60004 70003 80002 90001 Min. Tensile Strength psi 60000 65000 65000 70000 80000 85000 95000 105000 MPa 414 448 448 483 552 586 655 724 Min. Yield Strength psi 40000 45000 45000 50000 60000 70000 80000 90000 MPa 276 310 310 345 414 483 552 621 Min. Elongation in 2 Inch, % 10 8 6 5 4 3 2 1 Ductile Cast Iron.— A distinguishing feature of this widely used type of cast iron, also known as spheroidal graphite iron or nodular iron, is that the graphite is present in ball- like form instead of in flakes as in ordinary gray cast iron. The addition of small amounts of magnesium- or cerium-bearing alloys together with special processing produces this spheroidal graphite structure and results in a casting of high strength and appreciable
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