SUS321 Stainless Steel Sheet Specifications: JIS G4304/G4305 and ASTM A240

SUS321 Sheet and Plate: Grade Overview

SUS321 sheet and plate is the titanium-stabilised austenitic stainless steel (06Cr18Ni11Ti) specified for high-temperature service, resistance to intergranular corrosion and stable mechanical performance. The grade is widely used in chemical, petrochemical, automotive exhaust and food processing equipment, and it is supplied as cold-rolled sheet, hot-rolled sheet, plate and coil.

This specification guide summarises chemical composition, mechanical properties, dimensional ranges and fabrication practice with reference to the JIS and ASTM standards that actually govern flat-rolled product.

Which Standard Applies to SUS321 Sheet?

Two families of standard are normally quoted on a SUS321 sheet purchase order, and they are not interchangeable by title alone:

JIS G4304 – hot-rolled stainless steel plate, sheet and strip. This is the Japanese standard that covers SUS321 sheet and plate in the hot-rolled condition.

JIS G4305 – cold-rolled stainless steel plate, sheet and strip, covering SUS321 cold-rolled sheet.

JIS G4303 – stainless steel bars. This standard applies to round, square and hexagonal bar, not to sheet; it is frequently mis-quoted when flat product is required.

ASTM A240 – chromium and chromium-nickel stainless steel plate, sheet and strip for pressure vessels and for general applications, in which the grade appears as Type 321 (UNS S32100). General requirements such as tolerances and permissible variations are covered by ASTM A480.

Composition and mechanical requirements are effectively equivalent between the JIS and ASTM systems for SUS321 / Type 321, but the dimensional tolerances, the permitted silicon and nickel ranges and the marking requirements differ in detail. The invoked edition of the standard, not the grade name alone, governs acceptance.

Chemical Composition

Element	Typical requirement	Notes
Carbon (C)	≤ 0.08%	Kept low to limit carbide formation
Manganese (Mn)	≤ 2.00%	Austenite stability
Silicon (Si)	≤ 1.00% (ASTM A240 caps at 0.75%)	Deoxidation
Phosphorus (P)	≤ 0.045%	Residual element
Sulfur (S)	≤ 0.030%	Residual element
Chromium (Cr)	17.0–19.0%	Passive film and oxidation resistance
Nickel (Ni)	9.0–12.0% (JIS allows up to 13.00%)	Austenite former
Titanium (Ti)	≥ 5 × C%, maximum 0.70%	Stabilising element
Nitrogen (N)	≤ 0.10%	Strength contribution

The titanium-to-carbon relationship is the defining feature of the grade. Titanium must be present at not less than five times the carbon content, with a ceiling of 0.70%, so that titanium carbide forms in preference to chromium carbide and the sheet keeps its intergranular corrosion resistance after welding or long exposure in the 425–850 °C sensitisation band.

Mechanical Properties

Property	Metric	Imperial
Tensile strength (min)	515 MPa	74.7 ksi
Yield strength, 0.2% offset (min)	205 MPa	29.7 ksi
Elongation (min)	40%	40%
Hardness (max, annealed)	217 HB	-
Density	7.93 g/cm³	0.286 lb/in³
Maximum continuous service temperature	870 °C	1600 °F

Values are typical minimum requirements for annealed flat product; heavier plate may be supplied to slightly adjusted limits, and the mill certificate for the actual heat should always be checked against the specification invoked.

Dimensional Ranges and Surface Finish

Cold-rolled sheet: approximately 0.3–6.0 mm thick, supplied in coil or cut-to-length.

Hot-rolled sheet and plate: approximately 3.0–150 mm thick, in cut-to-length or coiled form depending on thickness.

Width: typically 1000–2000 mm, with 1219 mm and 1500 mm the most common stock widths.

Length: cut-to-length to order, or continuous coil.

Finishes: No.1 (hot-rolled, annealed and pickled), 2B (cold-rolled, annealed and skin-passed), BA (bright annealed), No.4 brushed and mirror-polished on request.

Thickness tolerance is the specification point most often overlooked at enquiry stage. Tolerances for cold-rolled sheet are tighter than for hot-rolled plate, and both vary with width, so the permissible variation table of the governing standard should be quoted explicitly rather than assumed.

Fabrication, Cutting and Welding

Forming: SUS321 sheet has good cold formability; a bending radius of roughly 1.5–2 times the sheet thickness is normal practice for a 90° bend across the rolling direction.

Welding: a stabilised filler of the ER347 type matches the base metal and preserves intergranular corrosion resistance in the heat-affected zone.

Heat treatment: preheating is not required, and post-weld heat treatment is normally unnecessary because titanium stabilisation prevents chromium depletion.

Cutting: shearing, plasma, laser and waterjet cutting are all used; thermally cut edges should be dressed before service in corrosive media.

Pickling and passivation: recommended after welding or heat exposure to restore a uniform passive film.

Frequently Asked Questions

Q: Is JIS G4303 the correct standard for SUS321 sheet?
No. JIS G4303 covers stainless steel bars. Flat-rolled SUS321 sheet and plate are specified under JIS G4304 for hot-rolled product and JIS G4305 for cold-rolled product.

Q: Are JIS SUS321 and ASTM A240 Type 321 equivalent?
They are equivalent in engineering terms and their composition and mechanical requirements overlap closely, but permitted ranges for silicon and nickel and the dimensional tolerance tables differ, so the specification invoked on the order governs.

Q: Why is titanium added to SUS321 sheet?
Titanium is added at a minimum of five times the carbon content so that titanium carbide, rather than chromium carbide, forms during welding or elevated-temperature service. Chromium stays in solution and the sheet remains resistant to intergranular corrosion.

Q: Is SUS321 sheet better than SUS304 for high-temperature applications?
Yes. SUS321 is titanium stabilised, which suppresses carbide precipitation at grain boundaries during exposure in the sensitisation range, whereas SUS304 relies on low carbon content or post-weld heat treatment for the same protection.

Q: Can SUS321 sheet be welded without post-weld heat treatment?
In most cases yes. Titanium stabilisation minimises the risk of intergranular corrosion in the heat-affected zone, so welded sheet and plate are usually put into service in the as-welded condition.

Q: Which industries commonly use SUS321 sheet and plate?
Petrochemical and chemical processing, food and beverage processing, automotive exhaust systems, furnace and heat-treatment equipment, and high-temperature processing plants.