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 warmed. A grain can grow larger by atoms migrating from another grain that may ultimately disappear. Dislocations can not cross grain borders easily, so the size of grains figures out how easily the dislocations can move. As expected, metals with little grains are stronger however they are less ductile. Figure 5 shows an example of the grain structure of metals. Satiating and Hardening: There are lots of ways in which metals can be heat dealt with. Annealing is a softening procedure in which metals are heated and then enabled to cool slowly. The majority 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 believed that biological fluids made the very best quenching liquids and urine was in some cases used. 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 were not entirely wrong.Quenching lead to a metal that is very tough but likewise brittle. Carefully heating up a solidified 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 thereby offer the strengthening.Cold Working: Because plastic contortion results from the motion of dislocations, metals can be strengthened by avoiding this movement. 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 strengthen the metal, making it more difficult to deform. This procedure is known as cold working. At greater temperatures 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 a number of times. Envision what is happening on the atomic level. Notification that it is more difficult to flex the metal 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 Steel Pipe 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.