What is it?

Yield strength is the maximum stress that steel can sustain before its shape is altered permanently; the approximate elastic limit of the steel. When stress is applied, but does not reach the yield point, the steel will revert back to its original shape once stress is relieved. However, if the stress applied is above the yield point, the steel will not be able to return to its former shape. Yield strength represents the highest limit of stress that can be safely applied to the steel, which is an important measurement to know when designing components.

Yield Strength