How is Fy defined for heat-treated steel?

The definition of Fy, or yield strength, for heat-treated steel is accurately described as the stress corresponding to a 0.2% deviation from the perfectly elastic line. This measure is critical in the context of structural engineering, as it indicates the point at which the material begins to undergo plastic deformation.

In practical terms, the 0.2% offset method is a standard approach used to define yield strength for materials that do not show a clear yield point. It provides a consistent way to determine Fy, ensuring that engineers have a reliable value for design and analysis when working with heat-treated steels, which display enhanced properties like increased strength and ductility as a result of their treatment.

When heat-treated, the steel's microstructure is altered to improve its mechanical properties, leading to a well-defined region of elastic behavior followed by yielding at the specified offset. This characteristic helps in ensuring that structures can be designed safely within elastic limits before any permanent deformation occurs.

The alternative definitions provided for the other choices do not align with the commonly accepted definition of Fy in the context of heat-treated steel. For instance, the idea of maximum stress before failure pertains more to ultimate tensile strength, not yield strength. Similarly, while yield strength at room temperature may be