Normalizing is a type of heat treatment applicableto ferrous metals only. It differs from annealing in thatthe metal is heated to a higher temperature and thenremoved from the furnace for air cooling.The purpose of normalizing is to remove the internalstresses induced by heat treating, welding, casting, forg-ing, forming, or machining. Stress, if not controlled,leads to metal failure; therefore, before hardening steel,you should normalize it first to ensure the maximumdesired results. Usually, low-carbon steels do not re-quire normalizing; however, if these steels are normal-ized, no harmful effects result. Castings are usuallyannealed, rather than normalized; however, some cast-ings require the normalizing treatment. Table 2-2 showsthe approximate soaking periods for normalizing steel.Note that the soaking time varies with the thickness ofthe metal.Normalized steels are harder and stronger than an-nealed steels. In the normalized condition, steel is muchtougher than in any other structural condition. Partssubjected to impact and those that require maximumtoughness with resistance to external stress are usuallynormalized. In normalizing, the mass of metal has aninfluence on the cooling rate and on the resulting struc-ture. Thin pieces cool faster and are harder after normal-izing than thick ones. In annealing (furnace cooling), thehardness of the two are about the same