Invar 36

metal

iron-nickel low-expansion alloy

FeNi36Nilo 36Pernifer 36UNS K93600DIN 1.3912Alloy 36Invar

Density

8.11 g/cm³

YS (LPBF as-built (XY))

280–370 MPa

UTS (LPBF as-built (XY))

430–520 MPa

Elongation (LPBF as-built (XY))

20.0–40.0 %

Elastic modulus

140–155 GPa

Thermal conductivity

12.0–14.5 W/m·K

Melting point

1420–1450 °C

Composition — UNS K93600 / ASTM F1684

Element	Min %	Max %	Notes
Fe	bal.		balance
Ni	35.00	37.000	36% Ni is the critical inflection point for minimum CTE; deviations of ±1% change CTE significantly
Mn	—	0.600	Improves hot workability; minor solid-solution strengthener
Si	—	0.350
C	—	0.050	Low carbon avoids carbide precipitation which degrades CTE stability

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Mechanical & thermal properties — 2 conditions

Property	LPBF as-built (XY)	LPBF stress-relieved (850°C / 1h / furnace cool)
Elastic modulus	140–155 GPa	—
Yield strength (0.2%)	280–370 MPa	250–330 MPa
Ultimate tensile strength	430–520 MPa	400–480 MPa
Elongation at break	20.0–40.0 %	25.0–45.0 %
Hardness (HV)	160–200 HV10	—
Density	8.11 g/cm³	—
Relative density	99.0–99.9 %	—
Thermal conductivity	12.0–14.5 W/m·K	—
CTE	0.9–1.8 µm/m·K	0.9–1.8 µm/m·K
Melting / solidus point	1420–1450 °C	—
As-built surface Ra	7.0–18.0 µm	—

Values shown as min–max where a spread is reported, otherwise as typical ± unit. Ranges reflect inter-source variation, not single-sample scatter. All values are for AM-processed specimens unless noted.

Engineering considerations

CTE must be confirmed by measurement on the final LPBF part — do not rely solely on powder composition certificates
Stress relief at 850°C/1h before final machining is the industry-standard post-process for LPBF Invar tooling
Design autoclave tooling with the coefficient mismatch between Invar (1.3 µm/m·°C) and composite mandrel in mind — typical CFRP CTE is 0–2 µm/m·°C in-plane
Confirm magnetic behaviour is acceptable for the application — Invar 36 is ferromagnetic at RT and becomes paramagnetic above ~277°C
Minimum wall thickness: ~0.4 mm achievable but thicker walls (>1.5 mm) recommended for tooling structural integrity
Residual oxygen in build chamber must be <50 ppm to prevent oxidation of the nickel-rich alloy
Creep at elevated temperatures (>200°C) is a design consideration for long autoclave cycles — refer to pröbstle-2018-invar-creep for data
Powder reuse: characterise CTE of recycled powder batches — oxidation can shift Ni/Fe ratio and alter CTE

Advantages

Lowest CTE of any commercial LPBF metal (~1.3 µm/m·°C) — 7× lower than stainless steel
Dimensional stability across temperature cycles — essential for composite tooling in autoclaves (up to 180°C)
Good ductility (elongation ≥30%) — complex thin-walled tooling features are feasible
LPBF allows integration of complex cooling/venting channels not achievable in wrought Invar
Near-wrought CTE maintained in LPBF condition when composition is well controlled
No phase transformation between room temperature and autoclave service temperatures

Limitations

Extremely high raw material cost — Ni content makes Invar powder 3–5× more expensive than stainless steel powder per kg
High residual stress in as-built LPBF condition — stress relief before final machining is mandatory
Magnetic at room temperature — cannot be used in MRI environments or near magnetically sensitive equipment below Curie temperature (~277°C)
Low hardness (~180 HV) — not suitable for wear surfaces without hard coating
Low thermal conductivity (13 W/m·K) — residual stress accumulates rapidly; requires preheat and optimised scan strategy
Limited published LPBF parameter databases compared to Ti-6Al-4V or 316L — expect parameter development effort
CTE is highly sensitive to Ni content — powder composition control to ±0.5% Ni is essential
Susceptible to hot cracking in LPBF if scan strategy and parameters are not optimised

Typical applications

Composite lay-up jigs and fixtures for aerospace (CFRP, GFRP structures)Autoclave tooling masters and mandrels for composite structuresMetrological tooling and precision gauges requiring dimensional stabilitySatellite and space optical bench structuresLaser and interferometric equipment framesBimetallic thermostat elements and temperature-compensating devicesPrecision mould tooling inserts for optics manufacturingShadow masks for cathode ray tube and display manufacturing (legacy)

Invar 36

Composition — UNS K93600 / ASTM F1684

Mechanical & thermal properties — 2 conditions

Engineering considerations

Advantages

Limitations

Typical applications

Industries

Compatible AM processes (2)

Other metal materials

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