Stainless Steel 321 grade is an alloy made of chromium, nickel, iron, etc. Stainless Steel 321 is a general-purpose austenitic stainless steel stabilized against carbide precipitation. The alloy works within the carbide precipitation at various temperature ranges. Stainless Steel 321H can be stabilized further by Titanium or Niobium additions. Due to this, Stainless Steel 321H Pipes show excellent oxidation resistance and low-temperature toughness.

Type 321 is a standard austenitic 18/8 chromium nickel alloy with the addition of Titanium making it an excellent choice in elevated temperature environments. The titanium stabilises the material removing its susceptibility to the effects of intergranular corrosion. 321 is therefore the stainless steel material of choice for applications in working environments up to 9000 C. A drawback of Type 321 is that the titanium does not transfer well across a high temperature arc, so it is not recommended as a welding consumable.

Corrosion Resistance of 321 Stainless Steel Pipes

equivalent to Grade 304 in the annealed condition and superior if a weldment in these grades has not been post-weld annealed or if the application involves service in the 425-9000C range. Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 600C. Considered resistant to potable water with up to about 200mg/L chlorides at ambient temperatures, reducing to about 150mg/L at 600C.

Heat Treatment of 321 Stainless Steel Pipes

Solution Treatment (Annealing) - heat to 950-11200C and cool rapidly for maximum corrosion resistance.

Stabilising - heat to 870-9000C for 1 hour per 25mm of thickness and air cool. Stabilisation is recommended for most severe service conditions (above 4250C) and particularly for material annealed at the upper side of the annealing temperature range.

Stress Relief - Heat to 7000C for 1 to 2 hours and air cool. These grades cannot be hardened by thermal treatment.

Grades 321 and 347 are the basic austenitic 18/8 steel (Grade 304) stabilized by Titanium (321) or Niobium (347) additions. These grades are used because they are not sensitive to intergranular corrosion after heating within the carbide precipitation range of 425-8500C. Grade 321 is the grade of choice for applications in the temperature range of up to about 9000C, combining high strength, resistance to scaling and phase stability with resistance to subsequent aqueous corrosion.