Austenitic alloys — Kanthal®

Categories: Heating materials , Resistance materials

Nickel-chrome (NiCr), also called nichrome, alloys have a high mechanical strength, which is retained even at high temperatures. This makes them suitable as heat-resistant material in industrial processes. Kanthal’s NiCr alloy products, Nikrothal®, are also used as resistive heating elements in electric grills, tumble dryers and blow-dryers.

Content:
Nikrothal® advantages
Physical and mechanical properties
Kanthal® resistance heating alloys - summary

NICKEL-IRON ALLOYS (NiFe)
Up to 600°C (1110°F): Nifethal® 70 and Nifethal® 52 are alloys with low resistivity and high temperature coefficient of resistance. The positive temperature coefficient allows heating elements to reduce power as temperature increases. Typical applications are in low temperature tubular elements with self-regulating features.

AUSTENITIC ALLOYS (NiCr, NiCrFe)
Up to 1200°C (2190°F): Nikrothal® 80 is the austenitic alloy with the highest nickel content. Because of its good workability and high-temperature strength, Nikrothal® 80 is widely used for demanding applications in the electric appliance industry.

Up to 1200°C (2190°F): Nikrothal® TE has been developed for use in metal sheathed tubular elements operating at red hot temperatures. Suitable electrical properties and a relatively low nickel content makes Nikrothal® TE an attractive alternative to alloys of higher nickel content, such as Nikrothal® 80.

Up to 1250°C (2280°F): Nikrothal® 70 is normally used in furnace applications.

Up to 1150°C (2100°F): Nikrothal® 60 has good corrosion resistance, good oxidation properties and very good form stability. The corrosion resistance is good except in sulfur containing atmospheres. Typical applications for Nikrothal® 60 are in tubular heating elements and as suspended coils.

Up to 1100 °C (2010°F): Nikrothal® 40 is used as electric heating element material in domestic appliances and other electric heating equipment.

Up to 1050°C (1920°F): Nikrothal® 20 will be produced on volume based request.

NIKROTHAL® ADVANTAGES

Higher hot and creep strength

Nikrothal® alloys have higher hot and creep strength than Kanthal® alloys. Kanthal® APM, Kanthal® AF and Kanthal® AE are better in this respect than the other Kanthal® grades and have a very good form stability, however, not as good as that of Nikrothal®.

Better ductility after use

Nikrothal® alloys remain ductile after long use.

Higher emissivity

Fully oxidized Nikrothal® alloys have a higher emissivity than Kanthal® alloys. Thus, at the same surface load the element temperature of Nikrothal® is somewhat lower.

Non-magnetic

In certain low-temperature applications a non-magnetic material is preferred. Nikrothal® alloys are non-magnetic (except Nikrothal® 60 at low temperatures). Kanthal® alloys are non-magnetic above 600°C (1100°F).

Better wet corrosion resistance

Nikrothal® alloys generally have better corrosion resistance at room temperature than non-oxidized Kanthal® alloys. (Exceptions: atmospheres containing sulphur and certain controlled atmospheres).

Physical and mechanical properties

		Nikrothal® 80	Nikrothal® TE	Nikrothal® 70	Nikrothal® 60	Nikrothal® 40	Nikrothal® 20
Max continuous operating temp.	°C	1200	1200	1250	1150	1100	1050
(element temperature in air)	°F	2190	2190	2280	2100	2010	1920
Nominal composition (See Note), %	Cr	20	22	30	16	20	24
	Al	–	–	–	–	–	–
	Fe	–	9	–	balance	balance	balance
	Ni	80	balance	70	60	35	20
Density ρ	g/cm³	8.30	8.10	8.10	8.20	7.90	7.80
Density ρ	Ib/in³	0.300	0.293	0.293	0.296	0.285	0.281
Resistivity at 20°C	Ω mm²/m	1.09	1.19	1.18	1.11	1.04	0.95
at 68°F	Ω/cmf	655	716	709	668	626	572
Temperature factor of the resistivity, Ct
250°C (480°F)		1.02	1.04	1.02	1.04	1.08	1.12
500°C (930°F)		1.05	1.06	1.05	1.08	1.15	1.21
800°C (1470°F)		1.04	1.06	1.04	1.10	1.21	1.28
1000°C (1830°F)		1.05	1.07	1.05	1.11	1.23	1.32
1200°C (2190°F)		1.07	1.07	1.06	–	–	–
Linear thermal expansion coefficient α, × 10-6/K
20 – 100°C (68 – 210°F)		–	–	–	–	–	–
20 – 250°C (68 – 480°F)		15	14	14	16	16	16
20 – 500°C (68 – 930°F)		16	15	15	17	17	17
20 – 750°C (68 – 1380°F)		17	16	16	18	18	18
20 – 1000°C (68 – 1840°F)		18	17	17	18	19	19
Thermal conductivity λ at 50°C	W/m K	15	14	14	14	13	13
at 122°F	Btu in/ft2 h °F	104	97	97	97	90	90
Specific heat capacity at 20°C	kJ/kg K	0.46	0.46	0.46	0.46	0.50	0.50
at 68°F	Btu/lb °F	0.110	0.110	0.110	0.110	0.119	0.119
Melting point (approx.)	°C	1400	1380	1380	1390	1390	1380
Melting point (approx.)	°F	2550	2515	2515	2535	2535	2515
Mechanical properties^* (approx.)
Tensile strength	N/mm²	810	800	820	730	675	675
Tensile strength	psi	117500	116000	118900	105900	97900	97500
Yield point	N/mm²	420	390	430	370	340	335
Yield point	psi	60900	56600	62400	53700	49300	48600
Hardness	Hv	180	190	185	180	180	160
Elongation at rupture	%	30	30	30	35	35	30
Tensile strength at 900°C	N/mm²	100	–	120	100	120	120
at 1650°F	psi	14500	–	17400	14500	17400	17400
Creep strength^***
at 800°C	N/mm²	15	15	–	15	20	20
at 1470°F	psi	2160	2160	–	2160	2900	2900
at 1000°C	N/mm²	4	4	–	4	4	4
at 1830°F	psi	560	560	–	560	560	560
at 1100°C	N/mm²	–	–	–	–	–	–
at 2010°F	psi	–	–	–	–	–	–
at 1200°C	N/mm²	–	–	–	–	–	–
at 2190°F	psi	–	–	–	–	–	–
Magnetic properties		2)	2)	2)	3)	2)	2)
Emissivity, fully oxidized condition		0.88	0.88	0.88	0.88	0.88	0.88

1) Magnetic (Curie point approx. 600°C (1100°F))
2) Non-magnetic
3) Slightly magnetic
4) Magnetic up to 610°C (1130°F) (Curie point)
5) Magnetic up to 530°C (990°F) (Curie point)
6) ± 10%

Note: Composition listed is nominal. Actual composition may vary to meet standard electrical resistance and dimensional tolerances.

* The values given apply for sizes of approx. 1.0 mm diameter (0.039 in)

** 4.0 mm (0.157 in) Thinner gauges have higher strength and hardness values while the corresponding values are lower for thicker gauge

*** Calculated from observed elongation in a Kanthal standard furnace test. 1% elongation after 1000 hours

**** Composition listed is nominal. Actual composition may vary to meet standard electrical resistance and dimensional tolerances.