|
|
Argon-Oxygen Decarburization (AOD)
WHAT A process for
further refinement of stainless steel through reduction of carbon
content.
WHY
The amount of carbon in stainless steel must be lower than that in
carbon steel or lower alloy steel (i.e., steel with alloying element
content below 5%). While electric arc furnaces (EAF) are the
conventional means of melting and refining stainless steel, AOD is an
economical supplement, as operating time is shorter and temperatures
are lower than in EAF steelmaking. Additionally, using AOD for
refining stainless steel increases the availability of the EAF for
melting purposes.
HOW
Molten, unrefined steel is transferred from the EAF into a separate
vessel. A mixture of argon and oxygen is blown from the bottom of the
vessel through the melted steel. Cleaning agents are added to the
vessel along with these gases to eliminate impurities, while the
oxygen combines with carbon in the unrefined steel to reduce the
carbon level. The presence of argon enhances the affinity of carbon for oxygen and thus facilitates the removal of
carbon.
Attrition
WHAT A natural reduction in work force as a result of
resignations, retirements,
or
death.
WHY
Most unionized companies cannot unilaterally reduce their employment
levels to cut costs, so management must rely on attrition to provide
openings that they, in turn, do not fill. Because the median ages of work
forces at the integrated mills may be more than 50, an increasing number of
retirements may provide these companies with added flexibility to
improve their competitiveness. |
|
Austenitic
The largest category
of stainless steel, accounting for about 70% of all production. The austenitic
class offers the most resistance to corrosion
in the stainless group, owing to its substantial nickel content and
higher levels of chromium. Austenitic stainless steels are hardened
and strengthened through cold working (changing the structure and shape of
steel by applying stress at low temperature) instead of by heat
treatment. Ductility (ability to change shape without fracture) is
exceptional for
the austenitic stainless steels. Excellent weldability and superior
performance in very low-temperature services are additional features
of this class. Applications include cooking utensils, food processing
equipment, exterior architecture, equipment for the chemical industry, truck trailers, and
kitchen sinks. The two most common grades are type 304 (the most
widely specified stainless steel, providing corrosion
resistance in numerous standard services) and type 316 (similar to 304
with molybdenum added, to increase opposition to various forms of
deterioration).
Automatic Gauge Control
Using hydraulic roll force
systems, steelmakers have the ability to control precisely their steel
sheet's gauge (thickness) while it is traveling at more than 50 miles
per hour through the cold mill. Using feedback or feed-forward
systems, a computer's gap sensor
adjusts the distance between the reduction rolls of the mill 50-60
times per second. These adjustments prevent the processing of any
off-gauge steel sheet.
<<BACK
|
|
