SUS321 vs SUS201 Stainless Steel: Key Differences in Composition and Performance

Two Austenitic Families at Opposite Ends of the Cost Curve

SUS321 and SUS201 are both austenitic stainless steels, yet they occupy very different positions in the alloying and price spectrum. SUS321 (AISI 321 / UNS S32100, EN 1.4541) is a nickel-rich grade stabilised with titanium, developed for welded equipment that must resist intergranular corrosion and serve at high temperature. SUS201 (AISI 201 / UNS S20100, EN 1.4372) belongs to the 200 series, in which manganese and nitrogen replace part of the nickel to bring material cost down. Understanding how that substitution changes corrosion behaviour, heat resistance, mechanical response and weldability is the key to specifying the right one.

Chemical Composition Compared

Element (wt%)	SUS321	SUS201
C	0.08 max	0.15 max
Si	1.00 max	1.00 max
Mn	2.00 max	5.50-7.50
P	0.045 max	0.060 max
S	0.030 max	0.030 max
Cr	17.0-19.0	16.0-18.0
Ni	9.0-12.0	3.5-5.5
N	-	0.25 max
Ti	5 x C min	-

The titanium figure is the important one for SUS321: it precipitates carbon as titanium carbide, leaving chromium free to form the passive film. In SUS201 the manganese and nitrogen additions stabilise the austenitic structure despite the low nickel level, which is what allows the alloy to exist at all at this price point.

Corrosion and High-Temperature Resistance

Performance index	SUS321	SUS201
General corrosion	Excellent, including welded zones	Moderate
Intergranular corrosion	Excellent, titanium stabilised	Risk after welding if not properly treated
Chloride pitting	Good in mildly chloride-bearing service	Susceptible
High-temperature service	Continuous to about 900 C; long-term design often capped near 850 C where creep governs	Not recommended much above 300 C
Oxidation	Strong, suitable for heat-treatment equipment	Weak, discolours readily

SUS321 is the clear choice wherever the part runs hot or where welds must stay corrosion resistant for years. SUS201 performs acceptably in indoor, decorative and lightly corrosive conditions, but it should not be substituted into a high-temperature line simply because the two steels look identical on delivery.

Mechanical and Fabrication Properties

Property	SUS321	SUS201
Tensile strength (Rm)	520 MPa min	520 MPa min
0.2% proof strength (Rp0.2)	205 MPa min	275 MPa min as supplied, higher after cold work
Elongation (A)	40% min	40% min
Magnetic response	Non-magnetic when annealed	Becomes noticeably magnetic after cold work
Formability	Excellent, suited to deep drawing and complex shapes	Good, but work hardens quickly
Weldability	Good with stabilised filler	Average, intergranular attack possible at welds

Cost, Supply, Applications and Selection Guidance

The cost difference comes almost entirely from nickel. SUS321 carries 9-12% nickel plus titanium, so its price tracks the nickel market closely and machinability is moderate. SUS201 holds only 3.5-5.5% nickel and offsets that with 5.5-7.5% manganese, giving a lower and more stable input cost, though scrap value and corrosion margin are correspondingly smaller. SUS321 is therefore found in exhaust systems, heat exchangers, boiler internals, expansion joints and aerospace components, while SUS201 is common in kitchenware, elevator and escalator panels, doors, window frames, handrails and general hardware where appearance and price dominate the specification.

Specify SUS321 when service temperature exceeds roughly 400 C, when the part is welded and must resist intergranular corrosion, or when the environment carries chlorides, acids or process chemicals.

Specify SUS201 when the duty is decorative or lightly corrosive, when temperature stays below about 300 C, and when cost control is the governing constraint.

Do not swap SUS201 into an existing SUS321 drawing: the lower nickel content changes heat resistance, weld corrosion behaviour and the magnetic response after forming.

Where weight matters, both grades are austenitic and dense; if mass is the main driver, a different material family should be evaluated instead.

Frequently Asked Questions

Q: Are SUS321 and SUS201 interchangeable?
No. They share an austenitic structure but differ sharply in nickel and chromium content, so corrosion resistance, heat resistance and weld behaviour are not equivalent and substitution should be reviewed by an engineer.

Q: Why does SUS201 contain manganese?
Manganese, together with nitrogen, stabilises the austenitic structure when nickel is reduced to 3.5-5.5%. This lowers alloy cost, but the resulting film is less protective than the chromium-rich film on a high-nickel grade.

Q: Which grade should be used for welded high-temperature piping?
SUS321, welded with a titanium- or niobium-stabilised filler. Its titanium content prevents chromium carbide precipitation in the heat-affected zone, which is exactly the failure mode SUS201 is prone to.

Q: Up to what temperature can SUS201 be used?
Service much above 300 C is not recommended. Oxidation and loss of strength become significant, and the grade offers no stabilisation against sensitisation.

Q: Does cold working change the properties?
Yes, particularly for SUS201, which work hardens rapidly and becomes partly magnetic. SUS321 also work hardens but keeps a non-magnetic annealed structure and better ductility in service.

Q: How can the two be told apart in the warehouse?
By the mill test certificate and heat number rather than by appearance. Chemical analysis, or a grade-identification test on the delivered material, is the reliable check.