Page 108 - MY STORY
P. 108
The alloy we chose to evaluate was 18% nickel, 7%
cobalt, 5% molybdenum, .5% Titanium, balance iron
(called 18-7-5 Maraging Steel). The thermal treatments
required to reach high strength levels was inexpensive
and simple. However, little was known about its fracture
toughness and weldability, critical for this application.
The issue of doing this at Douglas Aircraft was manifold.
At the expected strength levels, internal tank pressure,
and diameter the tank wall thickness would be about ¾”.
There were few steel companies that could manufacture
plate of this thickness in the sizes required to build
something this large, and the weights of the fabricated
hardware were well beyond the crane and handling
capacity of Douglas’ shops.
For the first problem solution, we made contact with U.S.
Steel research people in Pittsburgh to inquire if they’d be
willing to engage in cooperative development of this alloy.
Our plan was to obtain enough plate material (about
1,000 pounds) to develop mechanical design properties
and begin work on developing welding techniques (and
properties) that met the requirements for the large booster
rockets.