An Expert Guide To Stainless Steel 321

Key Properties of 321 Stainless Steel

Stainless steel 321 is a titanium stabilized chromium nickel austenitic stainless steel with corrosion resistance similar to 304/304L. This grade is typically used in the 800-1500˚F temperature range where it is stabilized against chromium carbide precipitation by the addition of titanium, which results in the precipitation of titanium carbides. Type 321 has excellent intergranular corrosion resistance after exposure to this temperature range, and this grade resists oxidation up to 1500˚F and has higher creep and stress rupture properties than 304/304L. It also possesses good low temperature toughness and is non-magnetic in the annealed condition.

Grades 321 is the basic austenitic 18/8 steel stabilized by Titanium or Niobium additions. These grades are used because they are not sensitive to intergranular corrosion after heating within the carbide precipitation range of 425-850 °C. Grade 321 is the grade of choice for applications in the temperature range of up to about 900 °C, combining high strength, resistance to scaling and phase stability with resistance to subsequent aqueous corrosion.

321 stainless steel (UNS S32100) is a titanium stabilized austenitic stainless steel that features improved resistance to intergranular corrosion. This grade is suitable for high-temperature applications up to 1500°F (815°C), where the addition of titanium stabilizes the material against chromium carbide formation. Since titanium has a stronger affinity for carbon than chromium, titanium carbide precipitates within the grain instead of forming at the grain boundaries. While corrosion resistance is similar to 304 and 304L in the annealed condition, it features higher creep and stress rupture properties. These properties make it ideal for pressure vessels and boiler applications. 321 stainless steel is non-magnetic and heat resistant for continuous service at elevated temperatures.

321 stainless materials cannot be hardened through heat treatment, only cold working. It is easily welded by all standard methods, and post-weld annealing is not required. This product is ductile and can be formed with ease. While corrosion resistance is generally excellent, especially against dilute organic acids, 321 SS is not suitable for chloride solutions, where it is susceptible to pitting and crevice corrosion.

The main chemical composition of stainless steel 321

Type 321 finds application in heavy welding components, along with dynamic environments that are subject to changes. However, the addition of titanium limits the application of 321 in terms of working. The metal is not recommended for certain welding techniques as it is not consumable. Beyond this, stainless steel 321 has excellent forming characteristics, does not require annealing after being welded, and displays toughness in a range of temperatures. The metal shows strength even when exposed to cryogenic temperatures. Additionally, it is often chosen over Type 304 for its increased resistance to creep and rupture. Both metals may be susceptible to stress corrosion cracking.

321 stainless steel is manufactured with titanium but based on 304 stainless steel. The added titanium enhances its corrosion and heat resistance, among othe rproperties. Stainless steel 321 is high chromium- high nickel stainless steel with the presence of titanium. Titanium content is at least five times the carbon content. Chromium content is in the range of 17-19% with a nickel content of 9-12%.

Stainless steel 321 physical properties

Stainless steel Grade 321 attains a metric density of 0.29 g/cm3.

The modulus of elasticity is 193 Gpa.

Electrical resistivity is 72 Microhm-cm.

The melting point range is 1371- 1399°C

Thermal properties

Thermal expansion coefficient is 16.6 µm/m° at 1-100°C and

Thermal conductivity is 16.1 W/mK at 100°C and 22.2 W/mK at 500°C.

Mechanical properties

Stainless steel 321 attains a tensile strength of 515 Mpa and yield strength of 205 Mpa. Hardness is 70B. Elongation is 40% in 50mm.

Why choose Stainless Steel 321 over other grades of stainless steel

HEAT TREATMENT

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 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.

WELDING

Austenitic stainless steels are considered to be the most weldable of the high-alloy steels and can be welded by all fusion and resistance welding processes. It is important to maintain the level of stabilizing element present in Type 321 during welding. Type 321 is more prone to loss of titanium. Care needs to be exercised to avoid pickup of carbon from oils and other sources and nitrogen from air. Weld practices which include attention to cleanliness and good inert gas shielding are recommended for these stabilized grades as well as other non-stabilized austenitic alloys.

Weld metal with a fully austenitic structure is more susceptible to cracking during the welding operation. For this reason, Type 321 is designed to resolidify with a small amount of ferrite to minimize cracking susceptibility. Columbium stabilized stainless steels are more prone to hot cracking than titanium stabilized stainless steels. Matching filler metals are available for welding Type 321 stabilized stainless steel. Stabilized alloys may be joined to other stainless steels or carbon steels.

Applications of 321 Stainless Steel

321 stainless steel is used in so many different applications because of its resistance to corrosion and ability to withstand high temperatures in harsh environments. They are used to manufacture a range of components in the transportation industries and are frequently used in equipment that handles corrosive or harmful chemicals. Below, we outline a few key applications of 321 stainless steel.

Aerospace industry: To manufacture exhaust systems and heat exchangers.

Automotive industry: In catalytic converters and exhaust systems.

Chemical processing industry: For pipes, tanks and valves in chemical handling.

Food processing industry: To manufacture food processing equipment.

Medical industry: In medical equipment like dental tools and surgical implants.

Petrochemical industry: In boilers, heat exchangers, and pipes.