SUS316H Stainless Steel: High-Carbon Austenitic Grade for High-Temperature Service

What Is SUS316H Stainless Steel?

SUS316H is the high-carbon version of the standard molybdenum-bearing 18-8 austenitic grade. Its carbon range of 0.04–0.10% is deliberately higher than that of ordinary SUS316, which lifts both short-term and long-term elevated-temperature strength while keeping the chloride resistance that made the 316 family a workhorse of the chemical and power industries. The grade is designated SUS316H in JIS G4303 (bars) and JIS G4304/G4305 (plate, sheet and strip), Type 316H in ASTM A240, and UNS S31609 in the unified numbering system.

Because the higher carbon level increases the risk of sensitisation in the heat-affected zone, SUS316H is normally chosen for heavy-section or high-temperature components where creep and stress-rupture strength matter more than as-welded corrosion resistance in severe halide service.

Chemical Composition of SUS316H

Element	Requirement (wt%)	Function
Carbon (C)	0.04–0.10	Raises high-temperature strength and creep resistance
Silicon (Si)	≤ 1.00	Deoxidation; ASTM A240 restricts Type 316H to ≤ 0.75
Manganese (Mn)	≤ 2.00	Austenite stability, nitrogen solubility
Phosphorus (P)	≤ 0.045	Residual, controlled for toughness
Sulfur (S)	≤ 0.030	Residual, controlled for weldability
Chromium (Cr)	16.00–18.00	Passive film, oxidation resistance
Nickel (Ni)	10.00–14.00	Stabilises the austenitic structure
Molybdenum (Mo)	2.00–3.00	Pitting and crevice corrosion resistance
Iron (Fe)	Balance	Matrix

The chemical balance is what separates SUS316H from SUS316L: the low-carbon grade is specified where welding without post-weld heat treatment is required, while SUS316H is specified where the design temperature is high enough that carbon becomes a strengthening element rather than a liability.

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 in 50 mm (min)	40%	40%
Hardness (max)	217 HB	-
Density	8.00 g/cm³	0.289 lb/in³

High-Temperature Behaviour: Creep and Oxidation

Creep and stress rupture: the 0.04–0.10% carbon level promotes fine carbide precipitation that pins grain boundaries, giving useful creep strength for continuous service in roughly the 500–800 °C band.

Oxidation resistance: the 16–18% chromium content forms a dense, self-healing oxide scale that protects the base metal in air and combustion atmospheres up to about 800 °C.

Chloride performance: molybdenum additions give SUS316H clearly better resistance to pitting and crevice attack than the molybdenum-free 304H grade.

Structural stability: the fully austenitic face-centred cubic matrix keeps ductility and toughness high, so the material tolerates thermal cycling without brittle fracture.

Post-service behaviour: components that have operated in the sensitisation range should be assessed for grain-boundary carbide precipitation before being returned to aggressive wet service.

Welding and Fabrication

Use matching 316H or 16-8-2 type filler metal; for dissimilar or high-restraint joints an austenitic filler with higher ferrite or a nickel-bearing filler may be considered.

Preheat is normally unnecessary. For heavy sections or severe restraint, a solution anneal at approximately 1040–1120 °C followed by rapid cooling restores optimum corrosion resistance.

Cold forming is readily achievable; the grade work-hardens quickly, so inter-pass annealing is advisable for deep-drawn parts.

Machining is comparable to SUS316, using positive rake tooling and generous coolant because of the gummy austenitic chip.

Typical Applications

High-temperature chemical reactor tubes and internal components

Boiler superheater and reheater tubing in coastal power plants

Furnace parts exposed to chloride-rich combustion products

Gas turbine and exhaust system components

Heavy-wall pressure vessels and thick-section flanges for elevated-temperature service

Frequently Asked Questions

Q: What is the difference between SUS316H and SUS316?
SUS316H has a controlled carbon range of 0.04–0.10%, whereas standard SUS316 is capped at 0.08%. The higher minimum carbon gives SUS316H greater creep strength and allows it to be used at higher design temperatures.

Q: Is SUS316H the same as 316L?
No. 316L is the extra-low-carbon grade (maximum 0.030%), chosen for as-welded corrosion resistance. SUS316H is the high-carbon grade chosen for elevated-temperature strength.

Q: What is the maximum service temperature of SUS316H?
Load-controlled designs are typically limited by creep data rather than oxidation. In air, continuous service to about 800 °C is practical, with the exact limit depending on stress, atmosphere and section thickness.

Q: Can SUS316H be welded without post-weld heat treatment?
For most low-corrosion, high-temperature applications it can. Where the weld will be exposed to aggressive wet chloride service, a solution anneal is recommended because the carbon content makes the grade more prone to sensitisation.

Q: How does SUS316H compare with SUS304H?
Both are high-carbon austenitic grades, but SUS316H contains 2–3% molybdenum. That addition gives it noticeably better pitting and crevice corrosion resistance in chloride-bearing environments.

Q: Which product forms are available in this grade?
Plate, sheet, strip, bar, seamless and welded tube, pipe, forgings and fittings can all be produced to the appropriate JIS or ASTM product specification.