8/18/2019 Precipitation Because the is Very Slow

1/1

precipitation because the diffusion rate is very slow. Here the rate of the reaction is controlledby the rate at which atoms can migrate. The rate of precipitation is also very slowat temperatures just below the solvus line (point e, Fig. 16.1). In this case, the solution isonly slightly oversaturated and the free-energy decrease resulting from precipitation isvery small. Nucleation is, accordingly, slow, and precipitation is controlled by the rate atwhich nuclei can form. The high diffusion rates that exist at these temperatures can do littleif nuclei do not form. At intermediate temperatures, between the two abovementionedextremes, the precipitation rate increases to a maximum, so that the time tocomplete the precipitation is very short. In this range, the combination

include: aluminum, copper, silicon, phosphorus, nickel, and zirconium. Other elementsare found in both the ferrite and the carbides. A number of these elements in theorder of their tendency to form carbides (manganese having the least and titanium thegreatest) are: manganese, chromium, tungsten, molybdenum, vanadium, and titanium.Most alloying elements in steels tend to increase the resistance of the steel to softeningwhen it is heated, which means that for a given time and temperature of tempering,an alloy steel will possess a greater hardness after tempering