321 stainless steel – UNS S32100
Titanium-stabilized Cr-Ni austenitic stainless steel
18-10 stainless stabilized with titanium, which prevents chromium carbide precipitation in the 425 – 815 °C range. Indicated for continuous or intermittent high-temperature service and welded parts that cannot be solution annealed.
Designations and equivalents
| System | Designation |
|---|---|
| UNS | S32100 (321H: S32109) |
| W.Nr./EN | 1.4541 (X6CrNiTi18-10); 1.4878 is the heat-resisting version |
| DIN | X6CrNiTi18-10 |
| JIS | SUS321 |
| Trade names | AISI 321 |
Standards by product form
| Form | Standard |
|---|---|
| Bar | ASTM A479 / A276 |
| Forging/flange | ASTM A182 F321 |
| Plate | ASTM A240 |
| Tube | ASTM A312 / A213 TP321 |
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7222.30.00 | 7222.30 | 7222.30.0024 | 7222 30 51 |
| Hot-rolled bar | 7222.11.00 | 7222.11 | 7222.11.0059 | 7222 11 11 |
| Plate (> 10 mm, width ≥ 600 mm) | 7219.21.00 | 7219.21 | 7219.21.0020 | 7219 21 10 |
| Seamless pipe | 7304.41.90 | 7304.41 | 7304.41.6045 | 7304 41 00 |
| Welded pipe | 7306.40.00 | 7306.40 | 7306.40.5085 | 7306 40 80 |
| Flange and fitting | 7307.21.00 | 7307.21 | 7307.21.5000 | 7307 21 00 |
Tariff class: stainless steel (by chemical composition, under the Chapter 72 Notes and Section XV Note 5).
*: US and EU codes for reference. NCM per current legislation (General Rules of Interpretation, Notes to Chapters 72, 74 and 75 and Section XV Note 5). Confirm the final code with your customs broker according to the item size and finish. HS = first 6 digits of the NCM.
Chemical composition (%)
ASTM A479 / A182 F321 (A240: Si ≤ 0.75%)
| Element | Range (%) |
|---|---|
| C | ≤ 0.08 |
| Mn | ≤ 2.00 |
| P | ≤ 0.045 |
| S | ≤ 0.030 |
| Si | ≤ 1.00 |
| Cr | 17.0 – 19.0 |
| Ni | 9.0 – 12.0 |
| N | ≤ 0.10 |
| Ti | 5×(C+N) – 0.70 |
| Fe | balance |
Mechanical properties
Solution annealed (ASTM A479; A240 in parentheses)
| Property | Value |
|---|---|
| Yield strength (0.2%) | ≥ 205 MPa |
| Tensile strength | ≥ 515 MPa |
| Elongation | ≥ 30% (A240: ≥ 40%) |
| Reduction of area | ≥ 40% (A182: ≥ 50%) |
| Hardness | ≤ 217 HB (A240) |
Typical physical properties
| Property | Value |
|---|---|
| Density | 7.92 g/cm³ |
| Melting range | 1,398 – 1,446 °C |
| Modulus of elasticity | 193 GPa |
| Thermal conductivity (20–100 °C) | 16.3 W/m·K |
| Thermal expansion (20–100 °C) | 16.6 µm/m·K |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | Up to 816 °C in code applications (ASME); oxidation ≈ 900 °C. For creep above ≈ 540 °C, 321H. |
| Heat treatment | Solution annealing at a minimum of 1,040 °C (usual range 1,040 – 1,120 °C) with rapid cooling. Stabilizing anneal 845 – 900 °C for up to 5 h. Stress relief 425 – 815 °C without risk of sensitization. |
| Welding | Good. Use ER347 / E347 (Nb transfers across the arc, Ti does not); ER309L for joining to carbon steel. |
| Machining | Machinability lower than carbon steel: it work hardens quickly; use sharp tools, positive rake, constant feed without 'rubbing' and abundant coolant. Ti carbonitrides are abrasive. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- Engine and turbine exhaust manifolds and ducts
- Expansion joints and bellows
- Furnace and heater parts
- Heat exchangers and boiler tubes
- Refining and petrochemicals at intermediate temperature
Alternatives: 347 when the part will be welded with many passes or requires better creep resistance; 304H for high temperature without the need for stabilization; 310S above ≈ 900 °C.
321 stainless steel: complete guide
What 321 stainless steel is
321 belongs to the family of austenitic stainless steels. It is 304 with a titanium addition, an element with greater affinity for carbon than chromium: it forms titanium carbides and leaves the chromium in solution. That is why 321 does not suffer intergranular corrosion after exposure to the 450 – 800 °C range, where plain 304 precipitates chromium carbides at the grain boundaries.
Chemical composition and role of the elements
Chromium (17 – 19%) and nickel (9 – 12%) are those of 304. Titanium is added in an amount of at least five times the sum of carbon and nitrogen, up to 0.70%. The 321H version, with carbon controlled between 0.04 and 0.10%, is the choice for creep design above 540 °C.
Mechanical properties
Solution annealed, it meets a minimum yield strength of 205 MPa, minimum tensile strength of 515 MPa, minimum elongation of 30% in bar and forgings (40% in plate) and minimum reduction of area of 50% in forgings (40% in bar), with a maximum hardness of 217 HBW.
Service temperature and corrosion
Aqueous corrosion resistance is that of 304, with a PREN of 17 to 20: good in atmosphere and fresh water, limited in chlorides. For chlorides with temperature, 316Ti.
Applications
Exhaust manifolds and pipes, bellows and expansion joints, heat exchangers, furnace and boiler components, hot process piping in refineries and petrochemical plants, thick welded parts that cannot be solution annealed after welding.
Supply forms and Dustre services
Round bars and blocks forged in open die, cut to size on a band saw, with rough or finish machining, solution annealing in our own furnaces and hardness, tensile and impact testing. All material is supplied with a 3.1 inspection certificate and heat traceability.
Frequently asked questions
What is the chemical composition of 321 stainless steel?
Per ASTM A479 / A182 F321 (A240: Si ≤ 0.75%): C ≤ 0.08; Mn ≤ 2.00; P ≤ 0.045; S ≤ 0.030; Si ≤ 1.00; Cr 17.0 – 19.0.
Which standards cover 321 stainless steel?
Bar: ASTM A479 / A276. Forging/flange: ASTM A182 F321. Plate: ASTM A240. Tube: ASTM A312 / A213 TP321.
Up to what temperature can 321 stainless steel be used?
Up to 816 °C in code applications (ASME); oxidation ≈ 900 °C. For creep above ≈ 540 °C, 321H.
Which materials can replace 321 stainless steel?
347 when the part will be welded with many passes or requires better creep resistance; 304H for high temperature without the need for stabilization; 310S above ≈ 900 °C.
