Why ferritic and austenitic stainless steel are not heat treatable?

Answer 1

Ferritic and austenitic stainless steels are not heat treatable since "heat

treatable" is taken to mean that martensite may be made to form with relative ease upon

quenching austenite from an elevated temperature.

For ferritic stainless steels, austenite does not form upon heating, and, therefore, the

austenite-to-martensite transformation is not possible.

For austenitic stainless steels, the austenite phase field extends to such low temperatures

that the martensitic transformation does not occur.

Answer 2

Ferritic and austenitic stainless steels are not heat treatable because they do not undergo a phase change during heating and cooling, which is required for heat treatment to modify their mechanical properties. Their microstructure remains stable at high temperatures, unlike martensitic stainless steels that can be hardened through heat treatment.