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┃ Material
Alloy 902, UNS N09902, Ni-Span-C Alloy 902, 3J53
NI-SPAN-C is a trademark of the Special Metals Corporation group of companies
┃ Overview
Alloy 902 is a Nickel-Iron-Chrome elastic alloy with controllable thermoelastic coefficient. The desired thermoelastic coefficient is then obtained by using cold working and appropriate heat treatment. Cold working will create internal strain, making the coefficient more negative. Heat treatment, in a lower temperature range, reduces strain. They also cause complex ordering phenomena that make the coefficients correct. Heating at temperatures higher than about 900°F causes the intermetallic compounds of titanium and nickel to precipitate, extracting nickel from the matrix and moving the coefficients further in a positive direction
┃ Characteristics
Alloy 902 is melted to the close compositional ranges. The desired thermoelastic coefficient is obtained by using cold work and the proper thermal treatment. Cold work produces internal strains, making the coefficient more negative. Thermal treatments, in the lower temperature ranges, relieve strain. They also cause complex ordering phenomena which make the coefficient more positive. Heating at temperatures above about 900°F causes the precipitation of an intermetallic compound of titanium and nickel, withdrawing nickel from the matrix and moving the coefficient further in the positive direction.
┃ Application
Typical applications as below
(1) Low frequency devices. These include springs, Bourdon tubes, aneroid capsules, etc.
(2) High frequency devices. Tuning forks, vibrating reeds, mechanical filters and similar instrumentation fall in this category.
┃ Chemical composition (wt%)
Table 1
|
Material |
Ni |
Fe |
Cr |
Ti |
Al |
|
Alloy 902 |
41.0~43.5 |
balance |
4.90-5.75 |
2.20-2.75 |
0.30-0.80 |
|
Material |
C |
Mn |
Si |
P |
S |
|
Alloy 902 |
≤0.06 |
≤0.80 |
≤1.00 |
≤0.040 |
≤0.040 |
┃ Modulus of elasticity
The tensile modulus of elasticity ranges between about 24 to 29 x 103 ksi, depending on the processing. Torsional modulus range is about 9 to 10 x 103 ksi.
Cold work causes an increase in the modulus. Raising the temperature of heat treatment also causes an increase.
┃ Magnetostrictive properties
The alloy has low magnetostrictive properties. However, they are quite adequate for some applications, such as delay lines.
┃ Magnetic properties
The saturation magnetization at room temperature is approximately 5000 gauss. Permeability is affected by cold work and heat treatment but no extensive investigation has been made to establish values.
┃ Corrosion resistance
Alloy 902 is not “stainless”, as it will acquire an adherent red-brown oxide film when exposed to outdoor environments. Tests in industrial and marine atmospheres have shown corrosion rates of less than 0.001 inch per year.
┃ Available Process
(1) Hot formed, annealed, descaled
(2) Cold worked and bright annealed
(3) Cold worked, bright annealed, polished (MP etc.)
┃ Common Tests
Chemical composition
Tension
Hardness
Flaring
Flange
Flattening
Micro structure
Hydrostatic
NDT
Intergranular Corrosion
Surface condition
Shape and dimension
Positive Material Identification
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