Nickel-chromium alloys

The material. Nickel forms a wide range of alloys, valued by the chemi­cal engineering and food-processing industries for their resistance to cor­rosion and by the makers of furnaces and high temperature equipment for their ability to retain useful strength at temperatures up to 1200° C. Typical of these are the nickel-chromium (Ni-Cr) alloys, often containing some iron (Fe) as well. The chromium increases the already good resistance to corrosion and oxidation by creating a surface film of Cr2O3, the same film that makes stainless steel stainless. The data given here is for nickel – chromium alloys. There are separate records for stainless steel and nickel – based superalloys.

Composition

Ni + 10 to 30% Cr + 0 to 10% Fe.

General properties

Density

8300 –

8500

kg/m3

Price

*34.5 –

37.9

USD/kg

Mechanical properties

Young’s modulus

200 –

220

GPa

Yield strength (elastic limit)

365 –

460

MPa

Tensile strength

615 –

760

MPa

Elongation

20 –

35

%

Hardness—Vickers

160 –

200

HV

Fatigue strength at 107 cycles

*245 –

380

MPa

Fracture toughness

*80 –

110

MPa. m1/2

Thermal properties

Melting point

1350 –

1430

°C

Maximum service temperature

*900 –

1000

°C

Thermal conductor or insulator?

Poor conductor

Thermal conductivity

9 –

15

W/m. K

Specific heat capacity

430 –

450

J/kg. K

Thermal expansion coefficient

12 –

14

p, strain/°C

Electrical properties

Electrical conductor or insulator?

Good conductor

Electrical resistivity

102 –

114

puhm. cm

The heating elements of the dryer and toaster are Nichrome, an alloy of nickel and chromium that resists oxidation well.

Ecoproperties: material

Annual world production

1.5 X 106 –

1.6 X 106

tonne/yr

Reserves

63 X 106 –

65 X 106

tonne

Embodied energy, primary production

127 –

140

MJ/kg

CO2 footprint, primary production

*7.89 –

8.82

Water usage

*134 –

512

l/kg

Eco-indicator

4900 –

5500

millipoints/kg

Ecoproperties: processing

Casting energy

*3.68 –

4.06

MJ/kg

Casting CO2

*0.221 –

0.243

kg/kg

Forging, rolling energy

*2.52 –

2.78

MJ/kg

Forging, rolling CO2

*0.202 –

0.222

kg/kg

Recycling

Embodied energy, recycling

31.8 –

35

MJ/kg

CO2 footprint, recycling

*1.97 –

2.21

kg/kg

Recycle fraction in current supply

22 –

26

%

Typical uses. Heating elements and furnace windings; bimetallic strips; thermocouples; springs; food-processing equipment; chemical engineering equipment.