AGGLOMERATING PROCESSES Fine particles of limestone (flux) and iron ore are difficult to handle and transport because of dusting and decomposition. The powdery material is therefore usually processed into larger pieces. The raw material’s properties determine the technique that is used by mills.
Sinter Baked particles that stick together in roughly one-inch chunks. Normally used for iron ore dust collected from the blast furnaces.
Pellets Iron ore or limestone particles are rolled into little balls in a balling drum and hardened by heat.
Briquettes Small lumps are formed by pressing material together. Hot Briquetted Iron (HBI) is a concentrated iron ore substitute for scrap for use in electric furnaces. ****
AGING A change in the properties of certain metal and alloys (such as steel) that occurs at ambient or moderately elevated temperatures after a hot working heat treatment or cold working operation. Typical properties impacted are: hardness, yield strength, tensile strength, ductility, impact value, formability, magnetic properties, etc. ****
AISI (AMERICAN IRON AND STEEL INSTITUTE) An association of North American companies that mine iron ore and produce steel products. There are 31 member companies and 118 associate members, which include both suppliers and customers that distribute, process, or consume steel. The AISI represents the interests of Canada, Mexico, and the United States. ****
ALLOYING ELEMENT Any metallic element added during the melting of steel or aluminum for the purpose of increasing corrosion resistance, hardness, or strength. The metals used most commonly as alloying elements in stainless steel include chromium, nickel, and molybdenum. ****
ALLOY STEEL An iron-based mixture is considered to be an alloy steel when manganese is greater than 1.65%, silicon over 0.5%, copper above 0.6%, or other minimum quantities of alloying elements such as chromium, nickel, molybdenum, or tungsten are present. An enormous variety of distinct properties can be created for the steel by substituting these elements in the recipe. ****
ALUMINUM KILLED STEEL (SPECIAL KILLED) 1 Steel deoxidized with aluminum in order to reduce the oxygen content to a minimum so that no reaction occurs between carbon and oxygen during solidification. ****
What? A heat or thermal treatment process by which a previously cold-rolled steel coil is made more suitable for forming and bending. The steel sheet is heated to a designated temperature for a sufficient amount of time and then cooled.
Why? The bonds between the grains of the metal are stretched when a coil is cold-rolled, leaving the steel brittle and breakable. Annealing “recrystallizes” the grain structure of steel by allowing for new bonds to be formed at the higher temperature.
How? There are two ways to anneal cold-rolled steel coils: batch and continuous.
1 Batch (Box) Three to four coils are stacked on top of each other, and a cover is placed on top for up to 3 days, then heated in a non-oxygen atmosphere (to prevent rust) and slowly cooled.
2 Continuous. Normally part of a coating line, the steel is uncoiled and run through a series of vertical loops within a heater. The temperature and cooling rates are controlled to obtain the desired mechanical properties for the steel. ****
APPARENT SUPPLY Derived demand for steel using AISI reported steel mill shipments plus Census Bureau reported imports, less Census Bureau reported exports. Domestic market share percentages are based on this figure, which does not take into account any changes in inventory. ****
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. In addition, 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. ****
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 it, in turn, does 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). ****
AUTO STAMPING PLANT A facility that presses a steel blank into the desired form of a car door or hood, for example, with a powerful die (pattern). The steel used must be ductile (malleable) enough to bend into shape without breaking. ****
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. ****