It has long been known that the properties of some metals could be altered by heat treating. Grains in metals tend to grow larger as the metal is heated. A grain can grow larger by atoms moving from another grain that may ultimately disappear. Dislocations can not cross grain boundaries quickly, so the size of grains determines how quickly the dislocations can move. As expected, metals with small grains are more powerful but they are less ductile. Figure 5 reveals an example of the grain structure of metals. Quenching and Solidifying: There are numerous ways in which metals can be heat dealt with. Annealing is a softening process in which metals are heated and after that enabled to cool gradually. A lot of steels may be solidified by heating and quenching (cooling rapidly). This procedure was used rather early in the history of processing steel. In fact, it was thought that biological fluids made the very best quenching liquids and urine was often utilized. In some ancient civilizations, the red hot sword blades were sometimes plunged into the bodies of unlucky prisoners! Today metals are satiated in water or oil. Really, satiating in seawater solutions is quicker, so the ancients were not entirely wrong.Quenching lead to a metal that is very tough but likewise fragile. Carefully heating up a solidified metal and enabling it to cool gradually 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 higher temperature levels the dislocations can rearrange, so little reinforcing occurs.You can try this with a paper clip. Unbend the paper clip and flex one of the straight areas back and forth numerous times. Imagine what welded steel pipe is happening on the atomic level. Notice that it is harder to bend the metal at the exact same location. Dislocations have formed and ended up being tangled, increasing the strength. The paper clip will ultimately break at the bend. Cold working obviously just works to a certain degree! Excessive deformation leads to a tangle of dislocations that are unable to move, so the metal breaks instead.Heating gets rid of the effects of cold-working. When cold worked metals are heated up, recrystallization occurs. New grains form and grow to consume the cold worked part. The new grains have less dislocations and the original residential or commercial properties are restored.