Type 321 is an austenitic stainless steel stabilized by additions of titanium to reduce or prevent carbide precipitation during welding and in service at 800/1650ºF (430/900ºC.) The titanium addition also improves high temperature properties. The grade has good resistance to corrosion and oxidation and good creep strength. Type 321 is good for applications at temperatures where carbide precipitation occurs in non – stabilized grades. These high temperature applications include aircraft applications such as exhaust manifolds and expansion joints.
Carbon .08 max
Manganese 2.00 max
Phosphorus .045 max
Sulfur .030 max
Silicon 1.00 max
Chromium 17.00 – 19.00
Nickel 9.00 – 12.00
Nitrogen 0.10 max
Titanium 5 x (C + N) min
Type 321 is used in jet aircraft components, oil refinery equipment, diesel and heavy duty auto exhaust systems and high temperature chemical process equipment.
Type 321 has good inherent forgeability, but its differences from carbon and alloy steels must be taken into account. Type 321 has higher hot strength than carbon, alloy, even martensitic stainless steels, hence much higher forging pressures or more hammer blows are required to forge it – and other austenitic stainless steels. In fact two to three times as much energy is required to forge 300 series stainless steels as is required for carbon and alloy steels.
Type 321 is forged between 2300/1700ºF (1260/930ºC,) and air cooled, but to be more specific, a forging temperature coincident with forging conditions might be used.
Type 321 stainless steel cannot be hardened by heat treatment, in fact the only heat treat operation that is performed on it is that of annealing, at around 1950ºF (1065ºC,) followed by a water quench. This treatment gives maximum corrosion resistance for type 321 forgings.
Type 321, like all austenitic stainless steels, machines to give tough, stringy chips. Chip breakers are recommended and since the alloy has a rapid work hardening rate, positive feeds are recommended.
Type 321 may be welded by shielded fusion and resistance welding operations. Austenitic stainless steel welds do not harden on cooling, hence the welds will show good toughness.
Oxyacetylene welding is not recommended due to the possibility of carbon pick up in the weld area.
The alloy can be welded without loss of corrosion resistance due to carbide precipitation and the steel can be used in the as-welded condition. For use at elevated temperatures however, a post-weld stabilizing heat treatment at 1550/1650ºF (840/900ºC) is recommended.