Q. Mechanical Properties of high temperature strength of metals?

The high temperature strength of metals is related to their melting points, but many other factors limit the practicality of using higher melting point metals.

Carbon steels in pressure retaining services are usually limited to a maximum operating temperature of 750°F (400°C) where its elastic properties predominate. Above this temperature, graphitization of the carbon and excessive oxidation may occur over time, resulting in significantly reduced mechanical strength.

For temperatures between 750° and 950°F (400°-510°C). Above 950°F (510°C), the addition of chromium to steel assists in the prevention of oxidation and scaling. The addition of molybdenum (Mo) is the most effective alloying element for increasing the creep strength of steel. Up to 1000°F (540°C), designs may be based on the material's short time high temperature properties.

For temperatures above 1000°F (540°C), creep becomes the controlling factor and must be considered in the design. Under these conditions or for somewhat more rigorous service, austenitic stainless steels and nickel alloys have much higher creep strength than carbon steel or other ferritic alloys.