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portation industry. Automobiles used
more trim and trucks were lined to carry
milk, food, and acid. However, the most
interesting use was on trains. Budd Man-
ufacturing Co. designed the Zephyr, a
passenger train made of stainless steel.
It consisted of a locomotive, baggage car,
and two passenger cars. From 1935 to
the start of WWII, 47 stainless steel trains
were manufactured using aircraft con-
struction methods. The original Zephyr
is now on display at the Museum of Sci-
ence and Industry in Chicago. During the
war, stainless steel was used extensively
for aircraft exhaust systems and engine
valves, ship galleys, and hardware wher-
ever corrosion was a problem.
Alloy development
Following WWII, several stainless
steel producers developed alloys that
respond well to precipitation harden-
ing. Success was first achieved by The
American Rolling Mill Co. (Armco). They
kept the chromium content at 17%, but
reduced the nickel to 4% and added
3.5% copper (17-4 PH) or 7% nickel with
1%aluminum (17-7 PH) and, a third alloy
with 7% nickel, 2.5% molybdenum, and
1% aluminum. These alloys have design
strengths of 200,000 to 220,000 psi after
heat treatment. Another alloy system
in development during this time was
duplex stainless steels, which feature a
microstructure of roughly 50% austenite
and 50% ferrite to improve strength and
corrosion resistance.
AOD process
The major problem in ferritic and
austenitic stainless steels productionwas
the requirement for very low carbon con-
tent to avoid precipitation of chromium
carbides, which lower the chromiumcon-
tent needed for corrosion resistance. This
was a particular problem during welding,
where a region in the heat-affected zone
sits at the ideal temperature for carbide
formation. Union Carbide Corp. (UCC)
tried using an oxygen lance to reduce the
carbon level, but was unsuccessful due to
theuncontrolled temperatureof thebath.
They hired a recent MIT graduate named
William A. Krivsky to work on improving
the oxygen process. Krivsky tried adding
the inert gas argon with the oxygen to
control the bath temperature and carbon
reaction. He successfully decreased the
carbon to very low levels without exces-
sive chromium loss. Following his labo-
ratory success, UCC looked for a stainless
producer to scale up the process to pro-
duction levels. Only one company was in-
terested—Joslyn Steel, a small producer
in Fort Wayne, Ind.
Over many years and many heats
of steel, Joslyn was unable to produce a
satisfactory result. They had tried intro-
ducing oxygen and argon into the elec-
tric arc furnace using lances coated with
ceramics. Joslyn and UCC finally realized
that the refining was going to need a
separate vessel where argon was blown
through the bottom, but oxygen was still
introduced with a lance. The new vessel
was similar to the oldBessemer converter
and the technique became the success-
ful argon oxygen decarburization (AOD)
process. Union Carbide started offering
licenses in 1970. As industry began to
learn about the new process, more than
100 vessels were installed within a dozen
years with 75%of world production even-
tually using AOD. This was the greatest
technological advance in the history of
processing stainless steel.
Newandnovel
applications
A major use for stainless steel after
WWII was for the exterior walls of high-
rise buildings. The austenitic grade with
18%chromiumand 8%nickel was select-
ed for its corrosion resistance, formabili-
ty, and added strength when cold rolled.
The first design was the Socony-Mobil
Building in New York. Within a few years,
it was common practice to clad skyscrap-
er buildings with stainless steel.
It was also used for kitchen sinks
in the late 1930s, later expanding to the
exteriors of refrigerators, stoves, dish-
washers, and other appliances. Although
stainless has largely disappeared as auto
trimand hubcaps, its current automotive
use is for exhaust systems with catalytic
converters and fuel injection systems.
The chemical, pharmaceutical, and elec-
trical power industries also use large
amounts of stainless in piping, tanks,
pumps, and other equipment. Stainless
steel is the ideal metal alloy for designs
requiring steel that does not rust. ~AM&P
For more information: Charles R. Sim-
coe can be reached at
For more metallurgical history, visit
.
The argonoxygen
decarburization
(AOD) process
was the greatest
technological
advance in
the historyof
processing
stainless steel.
Walt Disney Concert Hall, Los Angeles,
designed by architect Frank Gehry. Public
domain image.
Socony-Mobil Building, the first high-rise
to use a stainless steel exterior. Courtesy
of SebasTorrente at en.wikipedia.
Modern kitchen with stainless steel
appliances. Public domain image.
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