Published: Jan 1965
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Cold-rolled stainless steel sheet possesses combinations of properties and characteristics which make it suitable for use as cyrogenic propellant tankage for large missiles and spacecraft. While extra cold-rolled Type 301 is used in both the Atlas and Centaur vehicles, other alloys including Types 304 L and 310 have also been evaluated for these applications by screening tests including tension, notched-tension, crack propagation, cross-tension, and shear tests on resistance spot welded joints, and static tension and cyclic fatigue tests of large complex weld joint specimens. Data are presented on the properties of the three alloys in base metal and weld joint configurations.
Type 301 stainless steel can be cold rolled to the highest tensile strength of the three alloys because of its lowest austenite stability, resulting in considerable transformation to martensite upon cold rolling. This factor is also responsible for embrittlement which is particularly manifested in reduced strength and fatigue resistance of welded joints tested at liquid hydrogen temperature. Use of more highly alloyed and more stable stainless steel such as Type 310 eliminates low-temperature embrittlement but at sacrifice in payload potential because of reduced strength.
Low-temperature embrittlement of cold-rolled Type 301 was overcome by incorporating sheet of nickel foil between two sheets of stainless steel to be resistance welded. The nickel alloys into the weld nugget and produces completely stable austenitic nuggets which are tough and ductile at −423 F. Both the strength and fatigue resistance of missile weld joints are markedly increased by the nickel foil, permitting reliable use of Type 301 in cryogenic tankage down to −423 F. Nickel also greatly increases the ability of radiography to detect weld defects in nickel enriched spot welds and has resulted in improvement in welding procedures and quality control.
Manager, Materials and Processes, General Dynamics/Astronautics, San Diego, Calif.
Scheck, W. G.
Narmco Research and Development Div., Whittaker Corp., San Diego, Calif.