Material Properties of Iron and Steel Castings

Steel castings are especially adapted for machine parts that must withstand shocks or heavy loads. They are stronger than wrought iron, cast iron, or malleable iron, and are very tough. The steel used for making steel castings may be produced either by the open-hearth, electric arc, side-blow converter, or electric induction methods. The raw materials used are steel scrap, pig iron, and iron ore, the materials and their proportions varying according to the process and the type of furnace used. The open-hearth method is used when large tonnages are continually required, while a small electric furnace might be used for steels of widely differing analyses, which are required in small lot production. The high-frequency induction furnace is used for small quantity production of expensive steels of special composition such as high-alloy steels. Steel castings are used for such parts as hydroelectric turbine wheels, forging presses, gears, railroad car frames, valve bodies, pump casings, mining machinery, marine equipment, engine casings, etc.

Steel castings can generally be made from any of the many types of carbon and alloy steels produced in wrought form and respond similarly to heat treatment; they also do not exhibit directionality effects that are typical of wrought steel. Steel castings are classified into two general groups: carbon steel and alloy steel.

Carbon Steel Castings

Carbon steel castings may be designated as low-carbon, medium-carbon, and high-carbon. Low-carbon steel castings have a carbon content of less than 0.20 percent (most are produced in the 0.16 to 0.19 percent range). Other elements present are: manganese, 0.50 to 0.85 percent; silicon, 0.25 to 0.70 percent; phosphorus, 0.05 percent max.; and sulfur, 0.06 percent max. Their tensile strengths (annealed condition) range from 40,000 to 70,000 pounds per square inch (276-483 MPa). Medium-carbon steel castings have a carbon content of from 0.20 to 0.50 percent. Other elements present are: manganese, 0.50 to 1.00 percent; silicon, 0.20 to 0.80 percent; phosphorus, 0.05 percent max.; and sulfur, 0.06 percent max. Their tensile strengths range from 65,000 to 105,000 pounds per square inch (448-724 MPa) depending, in part, upon heat treatment. High-carbon steel castings have a carbon content of more than 0.50 percent and also contain: manganese, 0.50 to 1.00 percent; silicon, 0.20 to 0.70 percent; and phosphorus and sulfur, 0.05 percent max. each. Fully annealed high-carbon steel castings exhibit tensile strengths of from 95,000 to 125,000 pounds per square inch (655-125 MPa). See Table 1 for grades and properties of carbon steel castings.

Table 1. Mechanical Properties of Steel Castings

Alloy Steel Castings

Alloy cast steels are those in which special alloying elements such as manganese, chromium, nickel, molybdenum, or vanadium have been added in sufficient quantities to obtain or increase certain desirable properties. Alloy cast steels are comprised of two groups-the low-alloy steels with their alloy content totaling less than 8 percent and the high-alloy steels with their alloy content totaling 8 percent or more. The addition of these various alloying elements in conjunction with suitable heat-treatments, makes it possible to secure steel castings having a wide range of properties. The three accompanying tables give information on these steels. The lower portion of Table 1 gives the engineering grades of low-alloy cast steels grouped according to tensile strengths and gives properties normally expected in the production of steel castings. Tables 2 and 3 give the standard designations and nominal chemical composition ranges of high-alloy castings which may be classified according to heat or corrosion resistance. The grades given in these tables are recognized in whole or in part by the Alloy Casting Institute (ACI), the American Society for Testing and Materials (ASTM), and the Society of Automotive Engineers (SAE).

Table 2. Nominal Chemical Composition and Mechanical Properties
of Heat-Resistant Steel Castings ASTM A297-81

The specifications committee of the Steel Founders Society issues a Steel Castings Handbook with supplements. Supplement 1 provides design rules and data based on the fluidity and solidification of steel, mechanical principles involved in production of molds and cores, cleaning of castings, machining, and functionality and weight aspects. Data and examples are included to show how these rules are applied. Supplement 2 summarizes the standard steel castings specification issued by the ASTM SAE, Assoc. of Am. Railroads (AAR), Am. Bur of Shipping (ABS), and Federal authorities, and provides guidance as to their applications. Information is included for carbon and alloy cast steels, high alloy cast steels, and centrifugally cast steel pipe. Details are also given of standard test methods for steel castings, including mechanical, non-destructive (visual, liquid penetrant, magnetic particle, radiographic, and ultrasonic), and testing of qualifications of welding procedures and personnel. Other supplements cover such subjects as tolerances, drafting practices, properties, repair and fabrication welding, of carbon, low alloy and high alloy castings, foundry terms, and hardenability and heat treatment.

Austenitic Manganese Cast Steel: Austenitic manganese cast steel is an important high-alloy cast steel which provides a high degree of shock and wear resistance. Its composition normally falls within the following ranges: carbon, 1.00 to 1.40 percent; manganese, 10.00 to 14.00 percent; silicon, 0.30 to 1.00 percent; sulfur, 0.06 percent max.; phosphorus, 0.10 percent, max. In the as-cast condition, austenitic manganese steel is quite brittle. In order to strengthen and toughen the steel, it is heated to between 1830 and 1940°F (999 and 1060°C) and quenched in cold water. Physical properties of quenched austenitic manganese steel that has been cast to size are as follows: tensile strength, 80,000-100,000 psi (552–689 MPa); shear strength (single shear), 84,000 psi(579 MPa); elongation in 2 inches(50.8 mm), 15 to 35 percent; reduction in area, 15 to 35 percent; and Brinell hardness number, 180 to 220. When cold worked, the surface of such a casting increases to a Brinell hardness of from 450 to 550. In many cases the surfaces are cold worked to maximum hardness to assure immediate hardness in use. Heat-treated austenitic manganese steel is machined only with great difficulty since it hardens at and slightly ahead of the point of contact of the cutting tool.

Table 3. Nominal Chemical Composition and Mechanical Properties
of Corrosion-Resistant Steel Castings ASTM A743-81a