Description

Alloy 321 (UNS S32100) is a titanium stabilized austenitic stainless steel with good general corrosion resistance. It has excellent resistance to intergranular corrosion after exposure to temperatures in the chromium carbide precipitation range of 800 – 1500°F (427 – 816°C). The alloy resists oxidation to 1500°F (816°C) and has higher creep and stress rupture properties than alloys 304 and 304L. It also possesses good low temperature toughness.

High carbon steels prone more to intercrystalline attack in weld zones and slower cooling sections. This steel avoids such attacks through its stabilization with Ti. The corrosion behaviour of this alloy in natural environments is very similar to the TP 304/304L alloys. Architecturally, it may not be adequate for near industrial or onshore locations in Europe. Satisfactory in many low-chloride waters, it is prone to pitting or crevice corrosion in seawater. Water treatment, galvanic protection and deaeration can influence the performance.
The annealing temperature range for Type 321 is 1800 to 2000° F (928 to 1093° C). While the primary purpose of annealing is to obtain softness and high ductility, this steel may also be stress relief annealed within the carbide precipitation range 800 to 1500° F (427 to 816° C), without any danger of subsequent intergranular corrosion. Relieving strains be annealing for only a few hours in the 800 to 1500°F (427 to 816° C) range will not cause any noticeable lowering in the general corrosion resistance, although prolonged heating within this range does tend to lower the general corrosion resistance to some extent. As emphasized, however, annealing in the 800 to 1500° F (427 to 816° C) temperature range does not result in a susceptibility to intergranular attack.

For maximum ductility, the higher annealing range of 1800 to 2000° F (928 to 1093° C) is recommended.

When fabrication chromium-nickel stainless steel into equipment requiring the maximum protection against carbide precipitation obtainable through use of a stabilized grade, it is essential to recognize that there is a difference between the stabilizing ability of columbium and titanium. For these reasons the degree of stabilization and of resulting protection may be less pronounced when Type 321 is employed.

When maximum corrosion resistance is called for, it may be necessary with Type 321 to employ a corrective remedy which is known as a stabilizing anneal. It consists of heating to 1550 to 1650° F (843 to 899° C) for up to 5 hours depending on thickness. This range is above that within which chromium carbides are formed and is sufficiently high to cause dissociation and solution of any that may have been previously developed. Furthermore, it is the temperature at which titanium combines with carbon to form harmless titanium carbides. The result is that the chromium is restored to solid solution and carbon is forced into combination with titanium as harmless carbides.

When heat treatments are done in an oxidizing atmosphere the oxide should be removed after annealing in a descaling solution such as a mixture of nitric and hydrofluoric acids. These acids should be thoroughly rinsed off the surface after cleaning.

Chemical composition (%)

Mechanical Properties:

Convert ksi to Mpa Formula:  ksi/0.1450377