Strength, yield strength and tensile strength
The yield strength indicates the maximum load a component can be subjected to without permanent deformation. The tensile strength defines the maximum load a component or structure can withstand before it breaks completely.
Generally, both yield strength and tensile strength increase with higher carbon content. At a certain carbon content, certain alloying elements—particularly micro-alloying additives like niobium and vanadium in very small amounts (<0.1%)—can improve yield strength through strong precipitation hardening. For example, the steel grade S355J2 (SS 2172), with 0.15% carbon and 1.5% manganese, has a yield strength comparable to that of C45E (SS 1672), which contains 0.45% carbon.
Yield and tensile strength can also be increased through heat treatment, particularly quenching and tempering, which involves hardening followed by tempering at a high temperature. Maximum strength in quenching and tempering is achieved by combining carbon with alloying elements such as chromium (Cr), nickel (Ni), and molybdenum (Mo) in amounts between 0.2 and 2%, or sometimes even higher.
Strength is also affected by the dimension of the component; thicker dimensions generally result in lower strength than thinner ones. Therefore, it may be necessary to select a steel with a higher alloy content to maintain the same strength in larger components as in smaller ones.