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National Advisory Committee for Aeronautics, Technical Notes - Welding of High Chromium Steels

The high chromium steels designed to resist various forms
of corrosion are generally known under a large variety of trade
names. Each name may apply to a group of alloys in which the
percentage content of some element or elements varies according
to the specific properties desired. The element chromium is
the most important of the corrosion—resisting group. The other
constituents such as nickel, silicon, manganese and carbon play
an important part in this class of alloys, especially with re—
gard to the welding problem. No attempt will be made to clas—
sify the different alloys according to their trade names as such
a classification would require needless repetition and would be
confusing. A brief description will be given of the different
groups according to their composition and more generally accept—
ed names. The welding procedure.for a given group will there—
fore be much the same regardless of the slight Variations in
chemical composition which may exist within a certain group.

Rustless iron is considered here as that group of alloys
containing between 12% and 80% chromium with less than .lSfi
carbon, the balance being chiefly iron with normal amounts of
manganese and silicon. Within this composition range there are
two classes of alloys which are commercially available, the class
N.A.C.A. Technical Note No. 890 8
being determined by the chromium content. The alloys containing
12e14% chromium constitute one type, and those with 14—20% chrom—
ium, the other type. Alloys containing 12—14% chromium are more
susceptible to heat treatment than those containing 18—30% chrom—
ium. The resistance to corrosion increases with the chromium
content.

Stainless steel belongs to the group containing 12—14%
chromium with upwards of .8% carbon. The difference between
rustless iron and stainless steel lies in the carbon content.
Stainless steel is very susceptible to heat treatment, its cor—
rosion resistance depending on its heat treatment and surface
finish. On account of the air—hardening properties of the alloy,
welds and metal adjacent to the weld in stainless steel will be
hard and brittle. This brittle condition may be remedied some—
what by annealing followed by slow furnace cooling. After this
treatment the metal will not have its maximum stainless proper—
ties which are developed only by quenching and drawfhg operations
followed by proper surface finishing. On account of the hard—
ness and brittleness of welds in stainless steel and the diffi—
culty of properly heat treating and surface finishing the mater—
ial after welding, stainless steel is unsuitable for welded
parts subjected to corrosion, stress and vibration unless sup—
ported by other metals.