It has actually long been understood that the homes of some metals could be changed 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 might 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 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 gradually. 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 believed that biological fluids made the very best quenching liquids and urine was sometimes 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 salt water solutions is quicker, 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 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: Since plastic deformation arises from the movement of dislocations, metals can be enhanced 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 process is called cold working. At higher temperature levels the dislocations can rearrange, so little reinforcing occurs.You can try this with a paper Steel Pipes clip. Unbend the paper clip and flex one of the straight areas back and forth numerous times. Imagine what is happening on the atomic level. Notice that it is harder to flex 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.