The basic performance parameters of Hastelloy alloy C276

author: Qishine Industry

2024-12-28

Hastelloy C276 (UNS N10276, W.Nr. 2.4819) is a nickel-molybdenum-chromium alloy supplied in the solution-annealed condition for aggressive media in chemical, petrochemical and oil and gas service. Low carbon and silicon keep carbides from precipitating in the heat-affected zone, so the alloy holds up in oxidizing and reducing media where standard austenitic grades fail. Parts that touch chlorides, such as flange gaskets, are a typical case.

Grade Designations and Chemical Composition

One alloy can carry several designations, so a purchase specification may name it three ways. Confirm the UNS number on the material certificate.

NAS NW276 — also written NW 276 in material tables.
UNS N10276 — unified numbering system entry.
W.Nr. 2.4819 — European material number.
JIS NW0276 — Japanese industrial designation.

Carbon and silicon are held to tight limits, while molybdenum and tungsten carry the resistance to reducing acids.

Element	Min, %	Max, %
C	—	0.01
Si	—	0.08
Mn	—	1.0
P	—	0.04
S	—	0.03
Cr	14.5	16.5
Mo	15	17
Fe	4	7
W	3	4.5
Co	—	2.5
V	—	0.35
Ni	balance	balance

Composition in percent by mass; nickel forms the balance.

Physical Properties

These values go into the thermal and stress calculations for process equipment.

Property	Value
Density ρ	8.9 g/cm³
Specific heat	436 J/(kg·K)
Electrical resistivity	130 μΩ·cm
Thermal conductivity λ	10.8 W/(m·K)
Thermal diffusivity α	2.8×10⁻⁶ m²/s
Mean CTE 20–100 °C	12.2×10⁻⁶ 1/°C
Mean CTE 20–200 °C	12.5×10⁻⁶ 1/°C
Mean CTE 20–300 °C	12.9×10⁻⁶ 1/°C
Mean CTE 20–400 °C	13.2×10⁻⁶ 1/°C
Mean CTE 20–500 °C	13.6×10⁻⁶ 1/°C
Elastic modulus E	21.1×10⁴ MPa
Melting range	1325–1370 °C
Magnetism	essentially non-magnetic

Mean coefficient of thermal expansion, 10⁻⁶ per °C, over the range shown.

Mechanical Properties and Heat Treatment

Minimum mechanical values apply to solution-annealed material at room temperature.

Property	Minimum
0.2% proof strength YS	≥283 N/mm²
Tensile strength TS	≥690 N/mm²
Elongation	≥40%
Hardness	≤100 HRB

Minimum values for solution-annealed product; 1 N/mm² equals 1 MPa.

Solution annealing at 1150–1170 °C followed by rapid cooling.
Holding the heated part at the right temperature limits carbide precipitation in the heat-affected zone.
Cold work raises strength and lowers elongation, so heavy forming calls for re-annealing.

Corrosion Resistance

Pitting resistance is ranked in ferric chloride solution; crevice and intergranular attack are checked with the methods listed below.

Alloy	CPT 6% FeCl₃ + 1% HCl	Green death
NAS NW276	>120 °C	>120 °C
NAS 254N	80 °C	80 °C
NAS 329J3L	50 °C	45 °C
SUS 316L	10 °C	25 °C

Critical pitting temperature per ASTM G48 Method C; green death is 7% H₂SO₄ + 3% HCl + 1% FeCl₃ + 1% CuCl₂.

ASTM G48 Method C — 72 h in ferric chloride solution.
ASTM G48 Method D — 72 h with multi-toothed clamps that form the crevice.
Green death immersion — 24 h.
ASTM G28 Method A — 24 h in boiling 50% H₂SO₄-Fe₂(SO₄)₃ solution, for intergranular corrosion.

Corrosion rates in dilute sulfuric and hydrochloric acid stay low for C276 at 80 °C, while SUS 316L rises quickly as the concentration increases. Rates can be converted from g/m²·h to mm/year with mm/year = g/m²·h × 8.76 / d, where d is density in g/cm³.

Molybdenum, tungsten and low carbon together explain why the alloy is specified for pipe flanges, valve trim and bolting in hydrochloric acid, sulfuric acid and chloride-bearing process streams.