It is suitable to withstand high loads, impacts and especially to withstand fatigue. It possesses the best compromise between resilience and toughness. It has a carbon concentration of between 0.21% and 0.45%.

The alloying elements, in addition to allowing to decrease the carbon concentration at which there is the greatest toughness, have the following functions:

  • Nickel: promotes hardenability and toughness;
  • Chromium: favors the hardenability;
  • Molybdenum: work against the development of disease Krupp (to tempering fragility);
  • Manganese: improves hardenability;
  • Vanadiumo: refines the crystal grain.