SECTION 01321 or 321H: Which Carbon Range to Order
The two grades share the same chromium and nickel base and the same titanium stabilising principle. The difference is the carbon window, and that difference decides the service temperature at which the part can carry load. Ordering plain 321 for a component that will sit above 537 C under stress gives away creep strength that the H grade would have provided.
| Characteristic | Grade 321 (S32100) | Grade 321H (S32109) |
|---|---|---|
| Carbon | 0.08 % max | 0.04 to 0.10 % |
| Titanium stabilising rule | 5 × (C + N) min, 0.70 % max | 4 × (C + N) min, 0.70 % max |
| EN material number | 1.4541, X6CrNiTi18-10 | 1.4878, X8CrNiTi18-10 |
| Reason for the grade | Intergranular corrosion resistance after thermal exposure | Creep and stress rupture strength above about 537 C |
| Hardenable by heat treatment | No, cold work only | No, cold work only |
In many heats the carbon lands inside both windows, which is why 321 and 321H plate and bar are frequently dual certified. If your specification demands the H grade for code work, say so on the enquiry: dual certification is a convenience, not a guarantee that any 321 heat will qualify.
SECTION 02Designations and International Equivalents
Any of the following designations is understood on an enquiry as 321H material. Note that the plain 321 numbers are listed separately in section 01 and are not interchangeable where the H grade is specified.
EN 1.4878 is classified as an austenitic heat resisting steel and appears in EN 10095, the standard for heat resisting steels and nickel alloys, with a quoted density of 7.9 g/cm³.
SECTION 03Chemical Composition
| Element | 321H limits | Role in the alloy |
|---|---|---|
| Carbon, C | 0.04 - 0.10 | Raised deliberately for creep and stress rupture strength |
| Chromium, Cr | 17.00 - 19.00 | Oxidation and general corrosion resistance |
| Nickel, Ni | 9.00 - 12.00 | Stabilises the austenitic structure |
| Titanium, Ti | 4 × (C + N) min, 0.70 max | Ties up carbon as titanium carbide, preventing chromium carbide at grain boundaries |
| Manganese, Mn | 2.00 | Deoxidiser, austenite former |
| Silicon, Si | 0.75 | Deoxidiser |
| Nitrogen, N | 0.10 | Counted with carbon in the titanium stabilising ratio |
| Phosphorus, P | 0.045 | Residual |
| Sulfur, S | 0.030 | Residual |
| Iron, Fe | Balance | Base |
Some general reference tables list titanium for 321H as a single figure of 0.35 percent rather than as a ratio to carbon plus nitrogen. The ratio form is what the product specifications impose, so it is the controlling requirement on a mill certificate.
SECTION 04Mechanical Properties
Two sets of figures circulate for this grade because plate and bar are specified differently. Both are given below with the product form named, so you can match the right set to your drawing.
| Property | Plate, typical minima | General 321H values |
|---|---|---|
| Tensile strength, Rm | 515 MPa (75,000 psi) min | 480 MPa |
| 0.2 % proof stress, Rp0.2 | 205 MPa (30,000 psi) min | 205 MPa |
| Elongation | 40 % min in 50 mm | 29 % |
| Hardness | 217 HB max | 187 HB max |
| Elastic modulus | 193 GPa (28.0 × 106 psi) | 200 GPa |
The property that actually justifies the H grade does not appear in a room temperature table. 321 and 321H offer higher creep and stress rupture strength than 304 and particularly 304L, and the raised carbon of 321H was introduced to extend that advantage above about 537 C. The grade also keeps useful low temperature toughness, which matters for equipment that cycles from ambient to operating temperature.
Because the alloy cannot be hardened by heat treatment, there is no quenched and tempered condition to specify. Strength above the annealed minima can only be obtained by cold work, which is rarely appropriate for a forging and reduces the corrosion performance that the grade was chosen for.
SECTION 05Physical Properties
| Property | Metric | Imperial |
|---|---|---|
| Density | 7.92 g/cm³ | 0.286 lb/in³ |
| Modulus of elasticity | 193 GPa | 28.0 × 106 psi |
| Specific heat, 0 to 100 C | 444 J/kg·K | 0.12 BTU/lb·°F |
| Thermal conductivity at 100 C | 16.0 W/m·K | 9.3 BTU/hr/ft²/ft/°F |
| Melting range | 1398 to 1446 C | 2550 to 2635 °F |
| Electrical resistivity | 72 microhm·cm | 72 microhm·cm |
Mean coefficient of thermal expansion
| Temperature range | µm/m·C | in/in · °F |
|---|---|---|
| 20 to 100 C (68 to 212 °F) | 16.0 | 9.2 × 10-6 |
| 20 to 600 C (68 to 1112 °F) | 18.9 | 10.5 × 10-6 |
| 20 to 1000 C (68 to 1832 °F) | 20.5 | 11.4 × 10-6 |
Expansion of this order is a design issue rather than a footnote. An austenitic stainless section expands roughly half again as much as a ferritic steel over the same temperature rise, so expansion joints, bellows and bolted flange connections in 321H service need that movement designed in rather than restrained.
SECTION 06Forging, Hot Working and Annealing
6.1 Forging window at our works
The alloy is not suitable for working below about 927 C. Our open-die practice therefore keeps the whole forging sequence above that figure, reheating rather than finishing cold, and the piece is water quenched or fully annealed after working so that maximum corrosion resistance is restored. Finishing a stabilised austenitic grade below its working limit is the classic route to a part that passes dimensional inspection and then fails a corrosion test.
6.2 Solution annealing and stabilising
Austenitic grades are solution annealed well above 1040 C, and for H grades used in code work the specified minimum solution treatment temperature is higher than for the plain grade, with mill practice reported around 1093 C for 321H. A separate stabilising anneal is sometimes applied to titanium stabilised 321 material, heating to roughly 870 to 900 C for one hour per 25 mm of section, which deliberately forms titanium carbide and leaves chromium in solution. Specify which of the two treatments your drawing requires, because they are not interchangeable.
6.3 Welding and machining
321H welds readily by most standard processes and a post weld heat treatment is not necessary, which is a significant practical advantage over the martensitic grades. Clean the weld zone properly and use matching or over alloyed filler. On machining, the cold work hardening rate makes the alloy less machinable than 410 but comparable to 304: expect turning speeds in the region of 12 to 28 m/min with high speed steel tooling and cutting oil, rising to roughly 67 to 108 m/min with carbide, lighter depths of cut taking the higher speeds.
SECTION 07Corrosion and Oxidation Behaviour
General corrosion resistance is comparable to grade 304. The reason to choose 321H instead is what happens after the metal has spent time between 427 and 816 C: an unstabilised grade such as 304 precipitates chromium carbide at the grain boundaries in that window and becomes vulnerable to intergranular attack, whereas the titanium in 321H ties up the carbon first.
Where it performs
The alloy is serviceable in most diluted organic acids at moderate temperature, in pure phosphoric acid at lower temperatures and in diluted solutions up to about 10 percent at elevated temperature, and in chloride free and fluoride free caustic solutions at moderate temperature. It resists polythionic acid stress corrosion cracking in hydrocarbon service, which is why refinery operators specify it for units that are shut down and exposed to air and moisture. Oxidation resistance extends to about 816 C, and 816 C is also the maximum use temperature applied to grade 321 in code applications.
Where it does not
It does not perform well in chloride solutions even at small concentrations, and it is not suitable for sulfuric acid service. If the process stream carries chlorides at temperature, this is the wrong grade and the enquiry should move to a molybdenum bearing or nickel alloy option.
SECTION 08321H Forged Products We Manufacture
| Forged form | Scope | Typical destination |
|---|---|---|
| Forged bars | Round, square, rectangular, flat and hexagonal bars and billets | Machining stock, stud and bolt stock, tube sheet studs |
| Hollow bars and sleeves | Forged sleeves, bushes, pipes, tubes, barrels, casings, shells, cylinders, hubs, housings | Furnace rolls, burner sleeves, thermowells |
| Seamless rolled rings | Ring rolled forgings, plain or profiled, wide diameter range | Flange blanks, expansion joint rings, retaining rings |
| Discs, blocks and plates | Forged discs, disks, blocks, slabs and plate forgings | Tube sheets, closure plates, blind blanks |
| Shafting and rods | Forged shafts, stepped shafts, spindles, piston rods | Furnace and kiln shafting, high temperature drive components |
| Flange and valve blanks | Near net shape forgings to A182 F321H geometry | Weld neck, slip-on and blind flange blanks, valve bodies and bonnets |
Applicable delivery standards are ASTM A182 / A182M F321H for forged or rolled flanges, forged fittings and valve parts, ASTM A473 for stainless steel forgings covering austenitic, austenitic-ferritic, ferritic and martensitic forgings for general use and for low or high temperature service, and EN 10250-4 for open die stainless steel forgings for general engineering purposes, including forged bars and products pre-forged and finished in ring rolling mills. Plate grades are covered by ASTM A240 and ASME SA 240, with AMS 5510 also cited for this alloy. EN 10204 3.1 inspection certificates are issued with each heat.
SECTION 09Typical Applications
321H goes where the metal must stay sound after long exposure in the carbide precipitation range. Documented applications include aircraft exhaust stacks and manifolds, jet engine parts, aerospace engine manifolds, expansion joints, welding equipment, chemical processing equipment, petroleum refining service including polythionic acid exposure, thermal oxidisers and waste treatment plant, food and beverage processing, and pharmaceutical manufacturing equipment.
Related grades in our stainless programme
For a martensitic grade with high torque strength for shafting, see AISI 431 / 1.4057. Where precipitation hardening strength is wanted instead, see 15-5PH, 17-7PH and PH13-8Mo. For service above the oxidation limit of 321H, or in chloride bearing streams at temperature, our nickel alloy forgings are the usual next step.
SECTION 10Questions and Answers
What is AISI 321H stainless steel?
A titanium stabilised austenitic stainless steel with 17 to 19 percent chromium, 9 to 12 percent nickel and carbon controlled to 0.04 to 0.10 percent. The titanium suppresses grain boundary chromium carbide precipitation, which is what gives resistance to intergranular corrosion after exposure between 427 and 816 C. It is non magnetic when annealed and can be hardened only by cold working.
What is the difference between 321 and 321H?
Carbon. Grade 321 allows up to 0.08 percent; 321H is held between 0.04 and 0.10 percent to raise creep and stress rupture strength above about 537 C. The titanium stabilising minimum also changes, from five times carbon plus nitrogen for 321 to four times for 321H, both capped at 0.70 percent.
What is the equivalent grade of AISI 321H?
UNS S32109, EN 1.4878, X8CrNiTi18-10, and the forging grade ASTM A182 F321H. Plain 321 is UNS S32100 and EN 1.4541, X6CrNiTi18-10, and should not be substituted where the H grade is specified.
What is the maximum service temperature?
Oxidation resistance runs to about 816 C, and 816 C is the maximum use temperature applied to grade 321 in code applications. The H grade exists to carry load above roughly 537 C, where its creep and stress rupture strength exceed those of 304 and 304L.
Can AISI 321H be forged?
Yes, provided the work stays above about 927 C. Below that temperature the alloy is not suitable for working. After hot working the forging is water quenched or fully annealed to restore corrosion resistance.
Is AISI 321H magnetic?
No, not in the annealed condition. It can become slightly magnetic after significant cold working, which is a useful clue that a part has been cold formed when it should not have been.
Does 321H need post weld heat treatment?
It can be readily welded by most standard processes and a post weld heat treatment is not necessary. Clean the weld area properly and use matching or over alloyed filler for best corrosion performance.
Can Jiangyin Jiangnan Metal supply 321H to ASTM A182 F321H?
Yes. We forge 321H bars, hollow bars, seamless rolled rings, discs, blocks, shafts and flange and valve blanks to ASTM A182 F321H, ASTM A473 and EN 10250-4, with EN 10204 3.1 certificates. Send the drawing, the governing specification and edition, the required condition and the quantity to sales@steelforgepieces.com.
SECTION 11The Works
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. We produce open-die forgings, forged bars, seamless rolled rings, forged hollow bars, discs, blocks and shafting in carbon steel, alloy steel, tool steel, stainless steel and nickel alloys, including AISI 321H, 1.4878 and F321H. Telephone +86-189-2135-9659, email sales@steelforgepieces.com, or use the contact page.
Standards referenced on this page
ASTM A182 / A182M, forged or rolled alloy and stainless steel pipe flanges, forged fittings and valves and parts for high temperature service, grade F321H. ASTM A473, stainless steel forgings. ASTM A240 and ASME SA 240, chromium and chromium-nickel stainless steel plate, sheet and strip for pressure vessels. ASTM A479, stainless steel bars and shapes for use in boilers and other pressure vessels. EN 10250-4, open die steel forgings for general engineering purposes, part 4, stainless steels. EN 10095, heat resisting steels and nickel alloys. AMS 5510. EN 10204, inspection documents for metallic products.
Technical data compiled October 2026 from published grade datasheets and specification summaries. Figures are typical reference values for 321/321H product and are not a guarantee of properties for any specific order. The governing values are those of the applicable specification edition and of the mill certificate issued with the heat. A plain text version of this page is available at AISI-321H.md.