Characterised by high corrosion resistance in general atmospheric corrosive environments it exhibits excellent resistance to most oxidizing agents, general foodstuffs, sterilizing solutions, dyestuffs, most organic chemicals plus a wide variety of inorganic chemicals, also hot petroleum gases, steam combustion gases, nitric acid, and to a lesser extent sulphuric acid. It displays good oxidation resistance at elevated temperatures has excellent resistance to intergranular corrosion and has excellent weldability.

321 cannot be hardened by thermal treatment, but strength and hardness can be increased substantially by cold working, with subsequent reduction in ductility.

Used extensively for applications where the addition of titanium and its stabilizing effect as a carbide forming element allows it to be welded and/or used within the carbide precipitation range 430 ^oC - 870 ^oC without the risk of intergranular corrosion. These include Food Processing, Dairy Equipment, Chemical, Petrochemical, Transport and associated industries etc.

Material non magnetic in the annealed condition, but can become mildly magnetic following heavy cold working.
Annealing is required to rectify if necessary.

N.B. Optimum corrosion resistance is achieved in the annealed condition.

It can also be used within the carbide precipitation range 430 ^oC - 870 ^oC without the risk of intergranular corrosion.

Mechanical properties are reduced as temperature increases.

N.B. 321 even when cold worked will still have good high strength and ductility at sub-zero temperature.

N.B. It is most important that oxygen is always allowed to circulate freely on all stainless steel surfaces to ensure that a chrome oxide film is always present to protect it. If this is not the case, rusting will occur as with other types of non stainless steels.

For optimum corrosive resistance, surfaces must be free of scale and foreign particles.
Finished parts should be passivated.

Do not forge below 900 ^oC

Finished forgings should be air cooled.

Finally forgings will require to be annealed in order to obtain optimum corrosion resistance.

*Actual soaking time should be long enough to ensure that the part is heated thoroughly throughout its section to the required temperature, 30 minutes per 25 mm of section may be used as a guide.

Please consult your heat treater for best results.

Due to the high work hardening rate of this grade, cutting or drilling tools etc. must be kept sharp at all times and not cause unnecessary work hardening of the surface etc..

All machining should be carried out as per machine manufacturers recommendations for suitable tool type, feeds and speeds.

Oxyacetylene welding is not recommended due to possible carbon pick up in the weld area.

It can be welded without loss of corrosion resistance due to intergranular carbide precipitation, and post-weld annealing is not generally required, except for service in the more extreme conditions.

A post weld stabilizing treatment however, is recommended when being used at elevated temperature.

*Please consult your welding consumables supplier.

The resultant austenitic structure at room temperature has optimum corrosion resistance containing as it does all of the chromium in solution. If subsequently used in service at room temperature while some slight precipitation of chromium carbide can occur over an extended period this will generally have little affect on corrosion resistance.

This situation changes drastically when heat is applied either in service, or during welding, especially when heating through the range 430 ^oC - 850 ^oC, then the carbon and chromium atoms will move (precipitate) coming together to form chromium carbide (Cr²³ C⁶), depleting the structure of chromium and its corrosion resistance.

To overcome this problem, two methods have been adopted:
1) Use a low carbon grade - 304L or 316L etc.
2) Use a titanium stabilized grade - 321 etc.

Low carbon grades have insufficient carbon to deplete the chromium content generally throughout the structure, However local depletion within the weld area can still be a problem leading to some intergranular corrosion if later exposed to severe corrosive conditions.

Titanium acts as a stabilizer because the carbon has more affinity to it than it has to the chromium, thus titanium carbide is formed instead and the chromium is unaffected giving the material optimum corrosion resistance.