Nickel-iron alloy, INVAR, soft (annealed)

INVAR Designation, soft (annealed)

INVAR
Condition	Soft (annealed)
UNS number	K93600, K93601, K93603
US name	ASTM Alloy T36
EN name	FeNi36
EN number	1.3912

INVAR Tradenames, soft (annealed)

INVAR	ArcelorMittal (FRANCE)
INVAR 36	ArcelorMittal (FRANCE)
NILO 36	Special Metals Corp. (USA)

Typical uses, soft (annealed)

Absolute standards of length measurement

Clock and watch mechanisms

Bimetallic thermostatic strips

Containers for transporting liquefied natural gas

Superconducting systems

Electronic components

INVAR Composition detail, soft (annealed)

C (carbon)	0	–	0.1	%
Fe (iron)	62	–	65	%
Mn (manganese)	0	–	0.6	%
Ni (nickel)	35	–	37	%
Si (silicon)	0	–	0.35	%

INVAR Physical properties, soft (annealed)

Density

8.1

–

8.2

g/cm³

INVAR Mechanical properties, soft (annealed)

Young’s modulus	137	–	145	GPa
Specific stiffness	16.8	–	17.8	MN.m/kg
Yield strength (elastic limit)	240	–	315	MPa
Tensile strength	445	–	555	MPa
Specific strength	29.4	–	38.7	kN.m/kg
Elongation	30	–	45	% strain
Compressive strength	240	–	315	MPa
Flexural modulus	137	–	145	GPa
Flexural strength (modulus of rupture)	240	–	315	MPa
Shear modulus	54	–	58	GPa
Bulk modulus	106	–	112	GPa
Poisson’s ratio	0.28	–	0.3
Shape factor	27
Hardness – Vickers	120	–	180	HV
Hardness – Rockwell B	68	–	87	HRB
Hardness – Rockwell C	0	–	6	HRC
Hardness – Brinell	121	–	172	HB
Elastic stored energy (springs)	207	–	347	kJ/m³
Fatigue strength at 10^7 cycles	185	–	280	MPa
Fatigue strength model (stress range) Parameters: Stress Ratio = -1, Number of Cycles = 1e7cycles	170	–	304	MPa

INVAR Impact & fracture properties, soft (annealed)

Fracture toughness	215	–	239	MPa.m^0.5
Toughness (G)	327	–	404	kJ/m²

INVAR Thermal properties, soft (annealed)

Melting point	1420	–	1440	°C
Maximum service temperature	300	–	400	°C
Minimum service temperature	-273			°C
Thermal conductivity	12	–	15	W/m.°C
Specific heat capacity	505	–	525	J/kg.°C
Thermal expansion coefficient	1.25	–	2	µstrain/°C
Thermal shock resistance	946	–	1610	°C
Thermal distortion resistance	6.58	–	10.9	MW/m
Latent heat of fusion	270	–	290	kJ/kg

INVAR Electrical properties, soft (annealed)

Electrical resistivity	75	–	85	µohm.cm
Electrical conductivity	2.03	–	2.3	%IACS
Galvanic potential	-0.46	–	-0.38	V

INVAR Magnetic properties, soft (annealed)

Magnetic type

Magnetic

INVAR Optical, aesthetic and acoustic properties, soft (annealed)

Transparency	Opaque
Acoustic velocity	4100	–	4220	m/s
Mechanical loss coefficient (tan delta)	7e-4	–	0.0011

INVAR Processing properties, soft (annealed)

Metal casting	Acceptable
Metal cold forming	Excellent
Metal hot forming	Excellent
Metal press forming	Excellent
Metal deep drawing	Unsuitable
Machining speed	17.7 m/min
Weldability Notes: _{Preheating is not required, post weld heat treatment is required}	Good

INVAR Durability, soft (annealed)

Water (fresh)	Excellent
Water (salt)	Excellent
Weak acids	Excellent
Strong acids	Acceptable
Weak alkalis	Excellent
Strong alkalis	Excellent
Organic solvents	Excellent
Oxidation at 500C	Excellent
UV radiation (sunlight)	Excellent
Galling resistance (adhesive wear) _{Notes Bronze or zinc alloy dies should be used to minimize galling.}	Limited use
Flammability	Non-flammable

INVAR Corrosion resistance, soft (annealed)

Pitting resistance equivalent number (PREN)	0
Pitting and crevice corrosion	Low (<20)
Stress corrosion cracking Note: Rated in chloride; Other susceptible environments: Hydroxide	Not susceptible

INVAR Notes, soft (annealed)

Warning

INVAR is easy to weld to other metals, but designers must be aware that INVAR’s exceptionally low thermal expansion coefficient may cause problems, if a good match with the thermal properties of the other metal is required.

Other notes

INVAR is a trademark of Societe Creusot-Loire (METALIMPHY), France. It is sold by other companies under several other tradenames, e.g. NILVAR. At temperatures above 400C, its thermal expansion coeff. is comparable to other Ni alloys. Ferromagnetic

INVAR Standards with similar compositions, soft (annealed)

India: IS 12836 to IS 12836, IS 12881 to IS 12881

Tradenames: ALLOY 36, AMETEK 936, BETHLEHEM NO. 6 NICKEL STEEL, DILATHERM 15, EN36, ERGILOY 3912 HP, INVAR, KRUPP NI 36, MAGNIFER 36, NAS 36, NAS 36LG, PERMANT, PERNIFER 36-ALLOY 36, RODSEAL 36, SUPRA 36, TECHALLOY 36 (INVAR), UNILOY 36, UNISPAN 36