It has actually long been understood that the residential or commercial properties of some metals could be changed by heat dealing with. 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 vanish. Dislocations can not cross grain boundaries 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 many methods which metals can be heat treated. Annealing is a softening procedure in which metals are heated and then permitted to cool slowly. Most steels might be hardened by heating and quenching (cooling quickly). This process was utilized quite early in the history of processing steel. In fact, it was thought that biological fluids made the best quenching liquids and urine was often used. In some ancient civilizations, the red hot sword blades were often plunged into the bodies of hapless detainees! Today metals are quenched in water or oil. In fact, quenching in seawater services is much faster, so the ancients were not completely wrong.Quenching lead to a metal that is extremely hard but likewise fragile. Gently heating up a hardened metal and enabling it to cool gradually will produce a metal that is still difficult however also less breakable. This process is called tempering. (See Processing Metals Activity). It results in lots of small Fe3C speeds up in the steel, which block dislocation movement which thus supply the strengthening.Cold Working: Because plastic contortion results from the motion of dislocations, metals can be strengthened by avoiding this motion. When a metal is bent or shaped, dislocations are produced 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 enhance the metal, making it more difficult to deform. This procedure is known as cold working. At greater temperatures the dislocations can reorganize, 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 a number of times. Imagine what is happening on the atomic level. Notification that it is more difficult to flex the metal GI Pipe at the same location. Dislocations have formed and become twisted, increasing the strength. The paper clip will eventually break at the bend. Cold working undoubtedly only works to a specific level! Too much contortion results in a tangle of dislocations that are not able to move, so the metal breaks instead.Heating removes 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 new grains have less dislocations and the original homes are restored.