What is the difference between AISI 321 and 321H?

When it comes to high-temperature resistant stainless steel, AISI 321 and AISI 321H are two of the most commonly used grades in industries such as petrochemicals, aerospace, power generation, and heat exchangers. Both are titanium-stabilized austenitic stainless steels designed to prevent carbide precipitation and intergranular corrosion.

However, their carbon content differs significantly, affecting their temperature resistance, strength, and weldability. We will now compare these two materials in detail, exploring their advantages and how to choose the right steel for your project.

 

What material is equivalent to AISI 321?
AISI 321 is equivalent to UNS S32100 (ASTM) and 1.4541 (European EN) stainless steel. Other equivalent materials include SUS321 (Japanese JIS standard) and 321S31 (British BS).

What material is equivalent to AISI 321H?
Equivalent materials to AISI 321H include the European standard 1.4878, the European designation X8CrNiTi18-10, and the UNS designation S32109. While AISI 321 and 321H are very similar, the 'H' designation indicates a slightly different carbon content, providing improved high-temperature strength, and the European 1.4878 is the direct equivalent for 321H.

 

AISI 321H vs. AISI 321：Chemical Composition 

AISI 321H contains higher carbon content (0.04–0.10%), which provides better creep strength and high-temperature performance than AISI 321.

Element	AISI 321 (%)	AISI 321H (%)
Carbon (C)	≤ 0.08	0.04 – 0.10
Chromium (Cr)	17.0 – 19.0	17.0 – 19.0
Nickel (Ni)	9.0 – 12.0	9.0 – 12.0
Titanium (Ti)	≥ 5 × C min	≥ 5 × C min
Manganese (Mn)	≤ 2.0	≤ 2.0
Silicon (Si)	≤ 0.75	≤ 0.75
Phosphorus (P)	≤ 0.045	≤ 0.045
Sulfur (S)	≤ 0.03	≤ 0.03
Iron (Fe)	Balance	Balance

 

AISI 321H vs. AISI 321：Mechanical Properties  (Annealed Condition)

 

321H performs better under long-term exposure above 500°C, making it ideal for superheaters, heat exchangers, and reformer tubes.321 is preferred in applications below 500°C, or where welding and formability are key considerations.

Property	AISI 321	AISI 321H
Tensile Strength (MPa)	≥ 515	≥ 515
Yield Strength (MPa)	≥ 205	≥ 205
Elongation (%)	≥ 40	≥ 35
Hardness (HB)	≤ 217	≤ 217
Maximum Service Temperature (°C)	~870°C	~900°C

 

AISI 321H vs. AISI 321：Corrosion and Heat Resistance

Feature	AISI 321	AISI 321H
Corrosion Resistance	Excellent in oxidizing environments	Excellent in oxidizing environments
Intergranular Corrosion Resistance	Excellent (due to Ti stabilization)	Excellent
Creep Strength	Moderate	Higher
Weldability	Very good	Slightly reduced due to higher carbon
Oxidation Resistance	Up to 870°C	Up to 900°C

 

Can AISI 321 and 321H be used interchangeably?
Sometimes. However, for temperatures above 500°C, 321H is the preferred grade due to its higher carbon content and better creep strength.

 

Is 321H harder to weld than 321?
Yes, slightly. The higher carbon content can increase the risk of carbide precipitation if not properly heat-treated, but post-weld annealing solves this issue.

 

Are 321 and 321H magnetic?
No, both are non-magnetic in annealed condition and slightly magnetic when cold worked.

 

What is the equivalent of 321H in EN standards?
EN 1.4878 (X8CrNiTi18-10) is equivalent to AISI 321H.

 

AISI 321/321H Stainless Steel price per kg:

The price of 321H stainless steel is about 8-12% higher than that of 321 stainless steel, mainly due to its more stringent production control and higher carbon content.

 

If you are looking for AISI 321 or 321H stainless steel in stock, Gnee offers full-range solutions for your industrial and high-temperature applications:

✅ Wide supply range: ASTM A213 / A312 seamless pipes, A240 plates, A276 bars

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✅ Dimensional range: OD 6mm–630mm, thickness 0.5–50mm, length up to 12 meters.

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✅ Fast global delivery: Lead time 7–15 days for most sizes, competitive pricing for bulk orders.