Sometimes the physical properties of hardness and hardenability are confused. Hardness represents an existing condition after processing by heat treatment. It is a direct indicator of the mechanical strength of the steel. Hardenability denotes the potential of a steel to develop a particular value of hardness after a particular heat treatment. Hardenability is primarily dependent on the chemical composition of the steel. Hardenability is associated with a steel's ability to develop hardness to a given desired depth in thickness of the finished product. Developing high hardness throughout thick cross sections is usually more difficult to attain without adding expensive elements (compared to carbon) to the composition.
Often when engineers consider mechanical fatigue they envision cyclic, reversing stresses in a spinning shaft or possibly the up and down flex of aircraft wings. Rolling contact fatigue (RCF) or the associated mechanical wear is an important, closely related process to the traditional mechanism of fatigue but with distinct differences. RCF is also often known as spalling.
Creep of a metal or alloy is defined as its time-dependent deformation under constant stress at a given temperature, and is associated with elevated temperatures, usually defined as any temperature above 1/2 the melting point (in absolute degrees).