Alloy 321 (UNS S32100) is a titanium stabilized austenitic stainless steel with good general corrosion resistance.
Type 321 is basic type 304 modified by adding titanium in an amount at least 5 times the carbon plus nitrogen contents.
These titanium bearing stainless steels are stabilized against carbide precipitation and designed for eperation within the damaging temperature range where carbide precipitation develops. In this type of steel, the carbon combines preferentially with titanium to form a harmless titanium carbide, leaving the chromium in solution ot maintain full corrosion resistance.
Common Applications
- Aerospace – piston engine manifolds
- Chemical Processing
- Expansion Joints
- Food Processing – equipment and storage
- Petroleum Refining – polythionic acid service
- Waste Treatment – thermal oxidizers
- ASTM:A312, A403, A182
- ASME: SA312, SA403, SA182
Chemical Composition - 321/321H Stainless steel
| Grade | 321 | 321H |
| UNS Designation | S210000 | S32109 |
| Carbon (C) Max. | 0.08 | 0.04 – 0.10 |
| Manganese (Mn) Max. | 2.00 | 2.00 |
| Phosphorous (P) Max. | 0.040 | 0.040 |
| Sulphur (S) Max. | 0.030 | 0.030 |
| Silicon (Si) Max. | 0.75 | 0.75 |
| Chromium (Cr) | 17.0 – 20.0 | 17.0 – 20..0 |
| Nickel (Ni) | 9.0 – 12.0 | 9.0 – 12.0 |
| Molybdenum (Mo) | — | — |
| Nitrogen (N) | 0.1 Max. | 0.1 Max. |
| Iron (Fe) | Bal. | Bal. |
| Other Elements | Ti=5(C) to 0.70% | Ti=5(C) to 0.60% |
*The titanium content shall not be less than 5 times the carbon content and not more than 0.60%. 321H requires the titanium content to be not less than 4 times the carbon content and not more than 0.60%.
Typical Mechanical Properties
| Material | Tensile Strength Rm, N/mm² | Yield Strength Rp 0.2, N/mm² | % Elongation |
| Alloy 321 Tube | 500-730 | 200 | 35 |
Design Features - 321/321H Stainless Steel
- Immune to intergranular corrosion when heated within the carbide precipitation range.
- Titanium addition eliminates the formation of chromium carbides at the grain boundaries by tying up the carbon and nitrogen as titanium carbides or nitrides.
- Better high temperature properties than 304 or 304L. Generally used for parts which are intermittently heated up to 1500°F. For continuous service the alloy is good to 1650°F.
- May be susceptible to chloride stress cracking.
- Excellent weldability in field.
- Type 321H has high carbon (.04 to .10) for better high temperature creep properties.
Typical Applications - 321/321H Stainless Steel
- High temperature chemical process heat exchanger tubes
- Refineries
- High temperature steam service
Tensile Requirements - 321/321H Stainless Steel
- Tensile Strength (KSI): 75
- Yield Strength (KSI): 30
Proces：
Alloy 321/H can be easily welded and processed by standard shop fabrication practices.
Hot Forming
- Working temperatures of 2100 – 2300°F (1149 – 1260°C) are recommended for forging, upsetting and other hot working processes.
- Alloy not suitable for work at temperatures below 1700°F (927°C).
- Material must be water quenched or fully annealed after working to re-attain maximum corrosion resistance.
Cold Forming
- Quite ductile and forms easily.
Welding
- Readily welded by most standard processes.
- Post weld heat treatment is not necessary
Machining
- Hardening rate of 321 makes it less machinable than 410 stainless steel, but similar to 304
Corrosion Resistance
- exhibits good general corrosion resistance that is comparable to 304.
- developed for use in the chromium carbide precipitation range of 1800 – 1500°F (427 – 816°C) .
- can be used in most diluted organic acids at moderate temperatures .
- can be used in pure phosphoric acid at lower temperatures.
- can be used in up to 10% diluted solutions at elevated temperatures.
- resists polythionic acid stress corrosion cracking in hydrocarbon service.
- utilized in chloride or fluoride free caustic solutions at moderate temperatures.
- does not perform well in chloride solutions, even in small concentrations, or in sulfuric acid service.
