|
NASA
engineers originally specified a heat-treated AISI 8640 or equivalent
steel alloy as
having sufficient mechanical properties for long life.
AISI 8640 is a high strength,
high hardenability oil quench steel
alloy.
(The 8640 composition is 0.38-0.43C,
0.75-1.00 Mn, 0.15-0.30 Si, 040-0.60Cr, 0.40-0.70 Ni. 0.15-0.25 Mo.)
|
|
With
the heavy cross-section of the shoe, a rapid water quench was required for the 8640
alloy to produce the required
strength and hardness. But during water quench of the first prototype,
the
AISI 8640 alloy shoe cracked severely in areas
that could not be repaired.
|
 |
Hot
Track Shoe Ready to Quench |
| An
alternate alloy had to be found that would give the required
strength, microstructure, and hardness with a suitable
heat-treatment, but could also be water quenched without cracking
in the heavy cross-sections. |
|
