These steels possess the best compromise between mechanical strength and toughness. The use of these steels is mainly reserved to special mechanical parts which need high resistance to shocks and vibrations (for example rods, pins, shafts, levers, etc.). In the market there are many grades available, with only carbon (eg. C45E-R) or with alloying elements in greater or lesser quantity (Ni, Cr, Mo, Mn); generally the percentage of carbon varies between 0,21% and 0,60%.
The alloying elements can decrease the carbon concentration at which there is the highest toughness, and have the following purposes :
These steels are usually treated with the process of quenching in water or in oil, and tempering at 620° C approx..
Examples of steels for quenching and tempering C45E-C45R, 25CrMoS4, 39NiCrMo3, 42CrMoS4