Q. Material selection by temperature range 750° to 1100°F (400° to 600°C) ?

Plain carbon steels are usually limited to a maximum operating temperature of 750°F (400°C).  There are some instances where carbon steels can be used for elevated temperatures, however graphitization may occur over long periods of time.

Low-alloy ferritic steels are commonly used in this slightly higher temperature range.  Alloy additions increase creep and corrosion resistance. Cr-Mo and Cr-Mo-V steels may be used up to 930°F (500°C).  These alloys and C-½Mo steels have higher elevated temperature strengths than the carbon steels of similar content.

For medium and high-pressure turbine rotors, 0.2C-1Cr-1Mo-¼-V steel is commonly used.  For high-pressure steam or where resistance to hydrogen attack is necessary, 2 ¼Cr-1Mo steel and Class II Super 12% Cr steels (high strength), are often used.  The Class I super 12% Cr steels are regularly used as pressure vessel linings having operating temperatures of 500° - 900°F (260° - 480°C).

The stainless steels are used frequently in this temperature range.  The 400 series (ferritic) stainless steels may be subject to 885°F (475°C) embrittlement, if the chromium content exceeds 13%.  Type 410 is used up to 1000°F (540°C) and has moderate strength and good corrosion resistance.  Type 403 is used for steam turbine rotor and gas turbine compressor blades up to 900°F (480°C).  Tempering at 1100°F (595°C) removes the possibility of 885°F (475°C) embrittlement.