CAST STEEL-Low-carbon cast steels-medium-carbon cast steels
Low-carbon (less than 0.20%), medium-carbon (0.20 to 0.50), high-carbon (more than 0.5), and low-alloy (less than 8 total alloy content) steels that have been cast in sand, graphite, metal, ceramic, or other molds to produce finished or semifinished products. Steel castings having greater alloy content are commonly identified by other terms, such as heat-resistant castings or corrosion-resistant castings. Cast and wrought steels of equivalent composition respond similarly to heat treatment and have fairly similar properties. A major difference, however, is that cast steels are more isotropic in mechanical properties because, for wrought steels, these properties generally vary with respect to grain direction, that is, the direction of hot or cold working. For example, the impact strength of wrought steels is typically greater than that of cast steels, but the values reported for the wrought steels usually pertain only to the longitudinal grain direction. Values transverse to grain are lower. Impact strength of cast steels is generally intermediate to that of wrought steels in the longitudinal and transverse directions.
Low-carbon cast steels and medium-carbon cast steels generally contain 0.5 to 1.20% manganese, as much as 0.8 silicon, and small amounts of phosphorus and sulfur. Low-carbon grades used for electrical equipment are restricted to 0.20% manganese to enhance magnetic properties. As-cast, tensile properties of a 0.19% carbon, 0.74% manganese grade are about 64,000 lb/in2 (441 MPa) ultimate strength, 35,000 lb/in2 (241 MPa) yield strength, and 33% elongation. Annealing markedly improves impact strength without appreciably affecting tensile properties. Surface-hardening methods, such as car-burizing, are often used to increase wear resistance. Besides electrical equipment, low-carbon cast steels are used for railroad components, auto and truck parts, and heat-treating equipment. Medium-carbon grades, the most widely used, are almost always heat-treated by annealing, normalizing, normalizing and tempering, or quenching
and tempering after casting. Depending on the grade, tensile properties range from 65,000 to 175,000 lb/in2 (448 to 1,207 MPa) ultimate strength, 35,000 to 145,000 lb/in2 (241 to 1,000 MPa) yield strength, and 24 to 6% elongation. High-carbon cast steels are less frequently used, and tensile properties are markedly influenced by carbon content. The ultimate tensile strength of one annealed grade, for example, ranges from about 94,000 lb/in2 (648 MPa) to 126,000 lb/in2 (869 MPa) as carbon content increases from 0.50 to 1.00%. The steels also may be normalized and tempered or quenched and tempered.
Low-alloy cast steels are generally medium-carbon grades containing chromium, nickel, molybdenum, and vanadium. Compared with the plain-carbon cast steels, they provide better hardenability, toughness (at greater strength levels), wear resistance, and/or heat and corrosion resistance. For example, the cast grades similar to wrought grades 41XX, 43XX, and 86XX can provide 50% greater tensile yield strength and equivalent impact strength to plain-carbon cast steels. Although they can provide ultimate tensile strengths exceeding 200,000 lb/in2 (1,379 MPa), specified strength levels are generally less. ASTM A487 cast steels, for example, are normally specified for ultimate strengths of 70,000 to 145,000 lb/in2 (483 to 1,000 MPa) and yield strengths of 30,000 to 100,000 lb/in2 (207 to 690 MPa) in the normalized and tempered or quenched and tempered conditions. Corresponding elongations range from 24 to 14%. Applications include auto, truck, steam-turbine, and earthmoving equipment parts, machine tools, valves, marine hardware, and processing equipment of many kinds.

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