Stainless Steel 321 is a titanium-stabilized austenitic stainless steel with superior intergranular corrosion resistance. Including titanium stabilizes the material against chromium carbide formation, making it acceptable for high-temperature applications up to 815°C. Titanium carbide forms within the grain rather than at the grain boundaries because titanium has a greater affinity for carbon than chromium. While it has equal corrosion resistance as 304 and 304L when annealed, it has better creep and stress rupture qualities, making it appropriate for pressure vessels and boilers. In addition, SS 321 is nonmagnetic and heat resistant for sustained use at high temperatures.
Type 321 is a stabilized stainless steel with exceptional intergranular corrosion resistance when exposed to chromium carbide precipitation temperatures ranging from 800° to 1500° F. The addition of titanium to Type 321 prevents the production of chromium carbide.
BENEFITS OF STAINLESS STEEL 321
Resistance to Corrosion
If a weldment has not been post-weld annealed or the application involves service in the 797°-1652 °F range, it is superior to Grade 304 in the annealed condition. However, warm chloride conditions are prone to pitting, crevice corrosion, and stress corrosion cracking above 60 °C. Potable water resistance is estimated to be around 200 mg/L at ambient temperatures, falling to about 150 mg/L at 60 °C.
Resistance to Heat
SS 321 covers exceptional oxidation resistance in intermittent service up to 900°C and continuous service up to 925°C. These grades function effectively at temperatures between 425 and 900°F, especially when aqueous corrosive conditions are present. The increased hot strength of 321H makes it ideal for high-temperature structural applications.
Because of the identical chromium concentration, the stabilized Type 321 alloy resists pitting and crevice corrosion in the presence of chloride ions, similarly to Type 304 or Type 304L stainless steels. In most aquatic settings, 100 ppm chloride is considered the limit for both unstabilized and stabilized alloys, especially if fissures are present. Higher chloride ion concentrations may cause crevice corrosion and pit. Alloys having molybdenum, such as Type 316, should be considered for more harsh conditions such as greater chloride levels, lower pH, and higher temperature. The stabilized Type 321 alloy passes the ASTM-B-117 100-hour, 5% neutral salt spray test with no rusting or discoloration of samples.
Heat to 950° to 1120°C for solution treatment (annealing) and cool quickly for optimal corrosion resistance. Type 321 annealing temperatures range from 1800° to 2000°F (928 to 1093 degrees Celsius). While the primary goal of annealing is to achieve softness and ductility, this steel can be stress relieved annealed in the carbide precipitation; within a range of 800° to 1500° F without risk of intergranular corrosion. Reducing stresses by annealing for a few hours at 800° to 1500°F may not result in a noticeable reduction in general corrosion resistance, while prolonged heating within this range will.
The preservation of corrosion resistance and avoidance of cracking are two significant factors for constructing weld joints in austenitic stainless steel. During welding, it is critical to maintain the degree of stabilization present in SS 321. In addition, stainless steel 321 is prone to titanium loss. Therefore, it’s essential to prevent picking up carbon from lubricants and sources and nitrogen from the air. For stabilized grades and non-stabilized alloys, weld techniques involve attention to cleanliness, and appropriate inert gas shielding is suggested.
Weld metal is prone to cracking during welding. SS 321 is designed to resolidify with a small quantity of ferrite to reduce the risk of cracking. Hot cracking is common in column stabilized stainless steel and titanium stabilized stainless steel. Welding stainless steel 321 requires matching filler metals. Any other stainless steel or carbon steel can be linked to stabilized alloys.
APPLICATIONS OF STAINLESS STEEL 321
Some of the typical applications of stainless steel 321 include:
- Aircraft exhaust manifolds
- Expansion joints
- Aircraft exhaust stacks
- Furnace parts
- Heating element tubing
- Heat Exchangers
- Welded equipment
- Woven or welded screens for high-temperature mineral processing
- Jet engine parts
- Spiral Welded tube for burner pipes
- Useful for chromium carbide precipitation range
- Chemical processing equipment
The steel possesses special forming and welding properties and excellent toughness even at cryogenic temperatures. If you need stainless steel to withstand intergranular corrosion, 304L is the most typical choice because it is the most widely used and supplied steel.
Stainless steel 321, on the other hand, is a considerably superior solution in operating temperatures above 500° C and has its virtues. However, because SS 321 does not polish well, it is not suitable for use as a decorative architectural component.
Because of its superior mechanical qualities, 321 stainless steel provides advantages in high-temperature environments and offers excellent ductility and stress fracture resistance. In continuous use up to 930°C and intermittent service up to 870°C, 321 has good oxidation resistance. It can also be utilized without intergranular corrosion within the carbide precipitation range of 430°C to 870°C. As the temperature rises, mechanical characteristics decrease.