What is invar alloy?

INVAR alloy, the abbreviation of Invariability, composed of64% Fe, 36% Ni and little other elements such as S, P, and C, has a very low linear expansion coefficient under 100 ℃, also known as low expansion steel, it’s firstly found by French physicist C.E.GuialmeI by 1896. The NVAR trademark was originally held by the French elfin alloy company and conformed to AFNOR NF A54, DIN 17745, ASTM F1684 and ASTM B753.

Most metals expand in volume when heated and contract when cooled, but for invar alloy, because of its ferromagnetism and the invar effect over a certain temperature range, has an extremely low coefficient of expansion, sometimes even zero or negative. Invar alloy is indispensable for manufacturing precision instrument due to the advantages of low expansion, has been widely used in the electronics industry and precision instrument industry and other areas where required special size like double metal materials, magnetic materials, such as measuring instruments with a fixture, astronomical telescope components, optical instruments, liquid, gas storage containers, antenna parts, FPD shielding frame, high precision printing with the framework, such as laser gyroscope.

 

Commercial brands for Invar alloy

French	Aperam Alloys Imphy(Imphy Alloys)	Invar®
American	CARPENTER	Invar 36® Alloy
	ATI	ATI 36™
	Special Metals	NILO alloy 36
German	VDM Metals	Pernifer® 36
	VAC	VACODIL 36
Japan	NIPPON YAKIN	NAS 36
Italy	Valbruna AG	SG5

 

Standards for Invar alloy

Country	French	German	American	China
Standards	AFNOR NF A54-301, Fe-Ni36	DIN 17745 Ni36，1.3912	ASTM F1684 UNS K93603ASTM B753 T-36	YB/T 5241 4J36

 

Perm invar alloy composition

Grades	Fe	Ni	C	Si	Mn	P,max	S,max	Cr	Co
1.3912	R	35.0~37.0	≤0.05	≤0.3	≤0.5	/	/	/	/
K93603	R	36.0	≤0.05	≤0.4	≤0.6	0.015b	0.015b	≤0.25	≤0.5
T-36	R	36.0	≤0.15	≤0.4	≤0.6	0.025	0.025	≤0.25	≤0.5
4J36	R	35.0~37.0	≤0.05	≤0.3	0.2~0.6	0.02	≤0.02	/	/

 

Physical property

Density, g/cm3: 8.12

Hardness, HV: 140

Tensile strength, MPa: 500

Elongation, %: 30~45%

Modulus of elasticity, MPa: 134000

Cupping test value, mm: 9.8

Thermal conductivity, W·(m·K)-1:  0.109~0.134

Magnetoconductivity, mH·m-1: 2.04

 

Invar alloy coefficient of linear expansion（4J36）

The ratio of the length of metal at 0 ° c to its length at 1 ° c for each change in temperature is called the linear expansion coefficient.:

Temperature	The average coefficient of linear expansion, ā，10-6/℃
20℃~50℃	0.6
20℃~100℃	0.8
20℃~200℃	2.0
20℃~300℃	5.1
20℃~400℃	8.0
20℃~500℃	10.0

 

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