STAINLESS STEEL OVERVIEW: TUTORIAL
How is it made?
Stainless steel is produced in an electric arc furnace where carbon electrodes contact recycled stainless scrap and various alloys of chromium (and nickel, molybdenum etc. depending on the stainless type). A current is passed through the electrode and the temperature increases to a point where the scrap and alloys melt. The molten material from the electric furnace is then transferred into an AOD (Argon Oxygen Decarbonization) vessel, where the carbon levels are reduced (remember stainless has a much lower carbon level than mild steel) and the final alloy additions are made to make the exact chemistry. Exhibit 1 shows the process from melting and casting either into ingots or continually cast into a slab or billet form. Then the material is hot rolled or forged into its final form. Some material receives cold rolling to further reduce the thickness as in sheets or drawn into smaller diameters as in rods and wire.
Most stainless steels receive a final annealing (a heat treatment that softens the structure) and pickling (an acid wash that removes furnace scale from annealing and helps promote the passive surface film that naturally occurs).
LIFE CYCLE
The fact that stainless steel has a great resistance to corrosion means that
using stainless will result in a very long life compared to mild steel.
Structures made from stainless steel will last many times the normal life
(well over 100 years in most cases). So, while stainless steel is probably
more expensive to buy in the beginning -- because it lasts a long time,
it is usually cheaper in the long run because there is little or no maintenance
and repair costs. AND, once the useful life is over, stainless steel is
100% RECYCLABLE. Scrap stainless steel is recharged into the electric furnaces
for re-melting back into stainless steel. Stainless steel is a true "full
life cycle" material.
Mechanical Properties |
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(Annealed condition) |
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|
Tensile Strength |
Yield Strength |
Elongation |
Hardness |
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Stainless |
ksi |
MPa |
ksi |
MPa |
|
|
410 |
70 |
483 |
45 |
310 |
25 |
B80 |
430 |
75 |
517 |
50 |
345 |
25 |
B85 |
304 |
84 |
579 |
42 |
290 |
55 |
B80 |
316 |
84 |
579 |
42 |
290 |
50 |
B79 |
Elongation in 2" (50.80 mm) |
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Hardness in Rockwell B |
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