Plasticity Plasticity  is  the  ability  of  a  material  to  deform permanently without breaking or rupturing. This prop- erty is the opposite of strength. By careful alloying of metals, the combination of plasticity and strength is used to  manufacture  large  structural  members.  For  example, should a member of a bridge structure become over- loaded,  plasticity  allows  the  overloaded  member  to  flow allowing the distribution of the load to other parts of the bridge  structure. Brittleness Brittleness is the opposite of the property of plastic- ity. A brittle metal is one that breaks or shatters before it deforms. White cast iron and glass are good examples of brittle material. Generally, brittle metals are high in compressive strength but low in tensile strength. As an example, you would not choose cast iron for fabricating support beams in a bridge. Ductility  and  Malleability Ductility is the property that enables a material to stretch, bend, or twist without cracking or breaking. This property makes it possible for a material to be drawn out into  a  thin  wire.  In  comparison,  malleability  is  the property  that  enables  a  material  to  deform  by  compres- sive forces without developing defects. A malleable material is one that can be stamped, hammered, forged, pressed, or rolled into thin sheets. CORROSION  RESISTANCE Corrosion resistance, although not a mechanical property, is important in the discussion of metals. Cor- rosion resistance is the property of a metal that gives it the  ability  to  withstand  attacks  from  atmospheric, chemical,  or  electrochemical  conditions.  Corrosion, sometimes  called  oxidation,  is  illustrated  by  the  rusting of iron. Table 1-2 lists four mechanical properties and the corrosion resistance of various metals or alloys. The first metal or alloy in each column exhibits the best charac- teristics of that property. The last metal or alloy in each column exhibits the least. In the column labeled “Tough- ness,” note that iron is not as tough as copper or nickel; however, it is tougher than magnesium, zinc, and alumi- num. In the column labeled “Ductility,” iron exhibits a reasonable amount of ductility; however, in the columns labeled “Malleability” and “Brittleness,” it is last. 1-4 METAL TYPES The metals that Steelworkers work with are divided into  two  general  classifications:  ferrous  and  nonferrous. Ferrous metals are those composed primarily of iron and iron alloys. Nonferrous metals are those composed pri- marily of some element or elements other than iron. Nonferrous metals or alloys sometimes contain a small amount of iron as an alloying element or as an impurity. FERROUS METALS Ferrous  metals  include  all  forms  of  iron  and  steel alloys. A few examples include wrought iron, cast iron, carbon  steels,  alloy  steels,  and  tool  steels.  Ferrous  met- als are iron-base alloys with small percentages of carbon and other elements added to achieve desirable proper- ties. Normally, ferrous metals are magnetic and nonfer- rous  metals  are  nonmagnetic. Iron Pure iron rarely exists outside of the laboratory. Iron is produced by reducing iron ore to pig iron through the use of a blast furnace. From pig iron many other types of iron and steel are produced by the addition or deletion of carbon and alloys. The following paragraphs discuss the different types of iron and steel that can be made from iron ore. PIG IRON.— Pig iron is composed of about 93% iron, from 3% to 5% carbon, and various amounts of other elements. Pig iron is comparatively weak and brittle; therefore, it has a limited use and approximately ninety percent produced is refined to produce steel. Cast-iron pipe and some fittings and valves are manu- factured from pig iron. WROUGHT IRON.— Wrought iron is made from pig iron with some slag mixed in during manufacture. Almost pure iron, the presence of slag enables wrought iron to resist corrosion and oxidation. The chemical analyses of wrought iron and mild steel are just about the same. The difference comes from the properties controlled during the manufacturing process. Wrought iron can be gas and arc welded, machined, plated, and easily formed; however, it has a low hardness and a low-fatigue   strength. CAST IRON.— Cast iron is any iron containing greater than 2% carbon alloy. Cast iron has a high-com- pressive  strength  and  good  wear  resistance;  however,  it lacks  ductility,  malleability,  and  impact  strength.  Alloy- ing  it  with  nickel,  chromium,  molybdenum,  silicon,  or vanadium improves toughness, tensile strength, and