Comparison Of SUS316 And SUS316H: Standard Molybdenum-Containing Vs High-Carbon High-Temperature Molybdenum-Containing Austenitic Stainless Steel

Among the molybdenum-bearing 316 family, SUS316 and SUS316H look almost identical on paper. The decisive difference is carbon: SUS316 limits carbon to 0.08% maximum, while SUS316H is a controlled high-carbon variant with 0.04-0.10% carbon (UNS S31609). That single change raises creep strength at 600-870 C without giving up the chloride-resisting molybdenum content that defines the 316 series.

Chemical Composition

The table below compares composition limits per JIS G4304 (SUS316 plate) and ASTM A240 (UNS S31609).

Element (wt%)	SUS316 (JIS G4304)	SUS316H (ASTM A240, UNS S31609)
C	≤0.08	0.04-0.10
Si	≤1.00	≤0.75
Mn	≤2.00	≤2.00
P	≤0.045	≤0.045
S	≤0.030	≤0.030
Cr	16.00-18.00	16.0-18.0
Ni	10.00-14.00	10.0-14.0
Mo	2.00-3.00	2.0-3.0

Room-Temperature Mechanical Properties

In the annealed condition the two grades are practically equal in strength. Values below are per JIS G4304 and ASTM A240.

Property	SUS316	SUS316H
Tensile strength (MPa)	≥520 (JIS) / ≥515 (ASTM)	≥515
Yield strength (MPa)	≥205	≥205
Elongation (%)	≥40	≥40
Hardness	≤217 HB (ASTM A240)	≤217 HB (ASTM A240)

High-Temperature Behaviour: Why Carbon Is Controlled

Creep strength

Above about 600 C, time-dependent deformation governs design. The 0.04% carbon minimum in 316H guarantees enough carbide precipitation to pin dislocations and slow creep. Typical reported 1000-hour creep rupture strength at 700 C is about 60 MPa for standard 316 and about 80 MPa for 316H; these are typical published design data, not specification minimums.

Intergranular corrosion after welding

The trade-off is sensitization. The higher carbon makes 316H more susceptible to chromium-carbide precipitation at grain boundaries in the weld heat-affected zone. Where welded components also face corrosive media, a post-weld solution anneal is normally required.

Weldability and Post-Weld Heat Treatment

316H is welded with molybdenum-bearing austenitic filler of the AWS ER316H or ER316L type. Heat input should be kept moderate to limit grain growth. Where post-weld treatment is required, stress relief around 850-900 C followed by air cooling is a common shop practice; a full solution anneal at 1010-1120 C restores optimum corrosion resistance.

Designations and Selection

SUS316 is designated UNS S31600, AISI 316 and EN 1.4401. SUS316H is UNS S31609, ordered to ASTM A240 (plate), A213 (tube) or A312 (pipe). There is no direct EN 10088 designation for the H variant, so cross-border orders should reference UNS S31609 or the ASTM specification. In mill quotations, 316H typically carries a premium of about 8-12% over standard 316 (market data).

FAQ

1. What is the real difference between SUS316 and SUS316H?

Carbon content. SUS316 is limited to 0.08% maximum; SUS316H is controlled at 0.04-0.10%. The higher minimum carbon gives 316H substantially better creep strength for stressed service at 600-870 C.

2. Can SUS316 replace SUS316H above 600 C?

No. Above about 600 C the creep resistance of standard 316 is insufficient, and stressed components deform progressively with time. SUS316H is the preferred material for load-bearing parts in that range.

3. Why is the carbon lower limit set at 0.04%?

The 0.04% floor ensures enough carbide forms to sustain creep strength; the 0.10% ceiling avoids excessive carbide precipitation, which would degrade corrosion resistance and toughness.

4. Is 316H more difficult to weld than 316?

Not inherently, but it needs tighter control: lower heat input to limit grain growth, and post-weld annealing where the welded component will face corrosive media.

5. How do I choose between them?

Use SUS316 for service up to about 600 C in moderately corrosive media. Use SUS316H for stressed components at 600-870 C, such as boiler superheater tubing, high-temperature flanges and gas-turbine fuel-system parts.