Classification of steel and cast iron and their classification and their properties and application
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1. Iron – carbon equilibrium diagram, Classification of steel and cast Iron microstructure, properties and application.
2. Types of Metal Alloys • Metal alloys, by virtue of composition, are often grouped into two classes—ferrous and nonferrous. • Ferrous alloys, those in which iron is the principal constituent, include steels and cast irons. FERROUS ALLOYS Ferrous alloys—those of which iron is the prime constituent—are produced in larger quantities than any other metal type.
3. Steels • Steels are iron–carbon alloys that may contain appreciable concentrations of other alloying elements; there are thousands of alloys that have different compositions and/or heat treatments. • The mechanical properties are sensitive to the content of carbon, which is normally less than 1.0 wt%. Some of the more common steels are • classified according to carbon concentration—namely, into low-, medium-, and high carbon types. • Plain carbon steels contain only residual concentrations of impurities other than carbon and a little manganese. For alloy steels, more alloying elements are intentionally added in specific concentrations.
4. Low-Carbon Steels • These generally contain less than about 0.25 wt% C and are unresponsive to heat treatments intended to form martensite; strengthening is accomplished by cold work. • Microstructures consist of ferrite and pearlite constituents. • These alloys are relatively soft and weak but have outstanding ductility and toughness; in addition, they are machinable, weldable, and, of all steels, are the least expensive to produce • Typical applications include automobile body components, structural shapes (I-beams, channel and angle iron), and sheets that are used in pipelines, buildings, bridges, and tin cans
5. CODES USED • American Iron And Steel Institute (AISI). • The Society Of Automotive Engineers (SAE). • The American Society For Testing And Materials (ASTM). • The Uniform Numbering System (UNS).
6. Medium-Carbon Steels • The medium-carbon steels have carbon concentrations between about 0.25 and 0.60 wt%. •Microstructures consist of tempered martensite . • These alloys may be heat treated by austenitizing, quenching, and then tempering to improve their mechanical properties. • The plain medium-carbon steels have low hardenabilities and can be successfully heat treated only in very thin sections and with very rapid quenching rates.
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