**4. Effect of alloying element on tempering**

In the case of the tempering of the plain carbon steels, when the temperature is increased, then the hardness value is decreased; thus hardened steels are softened. At the same time, the hardness drops continuously. Some alloying elements play an important role in retarding the softening effect of the hardened steel at elevated temperature. When tempering is done at elevated temperature, then the steel may soften. Usually the elements that remain dissolved in ferrite, such as Ni, Si, and Mn, have very little effect in the retardation of the softening of steels at elevated temperature.

The complex carbide-forming elements such as Cr, W, Mo, and V retard the softening at elevated temperature while tempering. Besides, they do not only retard the softening effect but also improve the hardness of the plain carbon steels to some aspects.
