It has long been known that the homes of some metals could be altered by heat treating. Grains in metals tend to grow larger as the metal is warmed. A grain can grow larger by atoms moving from another grain that may ultimately disappear. Dislocations can not cross grain borders quickly, so the size of grains determines how quickly the dislocations can move. As expected, metals with little grains are stronger but they are less ductile. Figure 5 reveals an example of the grain structure of metals. Quenching and Solidifying: There are numerous methods which metals can be heat treated. Annealing is a softening process in which metals are heated and after that allowed to cool gradually. Many steels might be solidified by heating and quenching (cooling rapidly). This procedure was used rather early in the history of processing steel. In fact, it was believed that biological fluids made the very best quenching liquids and urine was in some cases utilized. In some ancient civilizations, the red hot sword blades were in some cases plunged into the bodies of hapless detainees! Today metals are quenched in water or oil. In fact, quenching in seawater solutions is much faster, so the ancients welded steel pipe were not completely wrong.Quenching lead to a metal that is extremely hard however likewise fragile. Carefully heating up a solidified metal and enabling it to cool slowly will produce a metal that is still difficult but likewise less brittle. This procedure is known as tempering. (See Processing Metals Activity). It leads to many little Fe3C precipitates in the steel, which obstruct dislocation motion which consequently provide the strengthening.Cold Working: Due to the fact that plastic deformation arises from the movement of dislocations, metals can be reinforced by preventing this movement. When a metal is bent or shaped, dislocations are generated and move. As the variety of dislocations in the crystal increases, they will get tangled or pinned and will not have the ability to move. This will strengthen the metal, making it more difficult to deform. This procedure is known as cold working. At greater temperatures the dislocations can reorganize, so little strengthening occurs.You can attempt this with a paper clip. Unbend the paper clip and flex one of the straight areas back and forth numerous times. Imagine what is taking place on the atomic level. Notice that it is harder to bend the metal at the exact same place. Dislocations have actually formed and ended up being tangled, increasing the strength. The paper clip will ultimately break at the bend. Cold working certainly just works to a certain level! Too much contortion results in a tangle of dislocations that are unable to move, so the metal breaks instead.Heating gets rid of the impacts of cold-working. When cold worked metals are warmed, recrystallization occurs. New grains form and grow to take in the cold worked portion. The brand-new grains have less dislocations and the original homes are restored.