ATI 321™ (UNS S32100), ATI 347™ (UNS S34700), and ATI 348™(UNS S34800) alloys are stabilized stainless steels which offer as their main advantage an excellent resistance to intergranular corrosion following exposure to temperatures in the chromium carbide precipitation range from 800 to 1500°F (427 to 816°C). ATI 321 alloy is stabilized against chromium carbide formation by the addition of titanium. ATI 347 and ATI 348 alloys are stabilized by the addition of columbium and tantalum. ATI 348 alloy has restricted cobalt and tantalum content for nuclear applications.

While ATI 321, ATI 347 and ATI 348 alloy continue to be employed for prolonged service in the 800 to 1500°F (427 to 816°C) temperature range, ATI 304L™alloy has supplanted these stabilized grades for applications involving only welding or short time heating. (For information on ATI 304L alloy, consult the Technical Data Sheet for ATI 304L™ alloy.)

ATI 321, ATI 347 and ATI 348 stainless steels are also advantageous for high temperature service because of their good mechanical properties. ATI 321, ATI 347 and ATI 348 stainless steels offer higher creep and stress rupture properties than ATI 304 alloy and, particularly, ATI 304L stainless which might also be considered for exposures where sensitization and intergranular corrosion are concerns. This results in higher elevated temperature allowable stresses for these stabilized alloys for ASME Boiler and Pressure Vessel Code applications. The ATI 321, ATI 347 and ATI 348 alloys have maximum use temperatures of 1500°F (816°C) for code applications as does ATI 304™ stainless, whereas ATI T304L™stainless is limited to 800°F (426°C).

The properties of ATI 348 stainless are similar to the properties of ATI 347 alloy, and according to ASTM A240 their chemical compositions are the same except for tantalum and cobalt contents.

High carbon versions of all three alloys are available. These grades have UNS designations S32109, S34709, and S34809.