SUMMARY OF CHAPTER 11

Ferrous Alloys Ferrous alloys (steels and cast irons) are those in which iron is the prime constituent. The most common types of steels are plain low-carbon, high-strength low-alloy, medium-carbon, tool, and stainless. Stainless steels are classified according to the main microstructural constituent. The three classes are ferritic, austenitic, and martensitic. Gray, ductile (or nodular), malleable, and compacted graphite irons are the four most widely used cast irons; the latter three are reasonably ductile. Nonferrous Alloys All other alloys fall within the nonferrous category, which is further subdivided according to base metal or some distinctive characteristic that is shared by a group of alloys. Nonferrous alloys may be further subclassified as either wrought or cast. Alloys that are amenable to forming by deformation are classified as wrought. Cast alloys are relatively brittle, and therefore fabrication by casting is most expedient. Seven classifications of nonferrous alloys were discussedcopper, aluminum, magnesium, titanium, the refractory metals, the superalloys, and the noble metals, as well as miscellaneous (nickel, lead, tin, zinc, and zirconium). Forming Operations Forming operations are those in which a metal piece is shaped by plastic deformation. When deformation is carried out above the recrystallization temperature, it is termed hot working; otherwise, it is cold working. Forging, rolling, extrusion, and drawing are four of the more common forming techniques Casting Depending on the properties and shape of the finished piece, casting may be the most desirable and economical fabrication process.

The most common casting techniques are sand, die, investment, lost foam, and continuous Miscellaneous Techniques Powder metallurgy involves compacting powder metal particles into a desired shape, which is then densified by heat treatment. P/M is used primarily for metals that have low ductilities and/or high melting temperatures. Welding is used to join together two or more workpieces; a fusion bond forms by melting portions of the workpieces and, in some instances, a filler material. Annealing Processes Exposure of a material to an elevated temperature for an extended time period followed by cooling to room temperature at a relatively slow rate is termed annealing. During process annealing, a cold-worked piece is rendered softer yet more ductile as a consequence of recrystallization. Internal residual stresses that have been introduced are eliminated during a stress relief anneal. For ferrous alloys, normalizing is used to refine and improve the grain structure. Heat Treatment of Steels Hardenability is a parameter used to ascertain the influence of composition on the susceptibility to the formation of a predominantly martensitic structure for some specific heat treatment. Martensite content is determined using hardness measurements. Precipitation Hardening Some alloys are amenable to precipitation hardeningthat is, to strengthening by the formation of very small particles of a second, or precipitate, phase.