Steel Production And Forming Methods Flashcards
What are the main methods of steel production?
How is steel made?
The open-hearth furnace
The basic oxygen furnace (B.O.F)
The electric furnace
The bessemer converter
Steel is produced by refining pig iron, usually 40% or more scrap steel is added to the refining furnace with the remaining comprised of pig iron
How does the open hearth furnace work? how much steel can be produced in a day? Although less efficient than other furnaces why is the open-hearth furnace more versatile?
Hot air from one checker chamber on one side is blown across the surface of the molten charge and fuel is fed in to produce large sheets of flame that cover the surface of the metal. The hot air passes through a second checker chamber and the direction of the air flow is reversed.
The open-hearth furnace requires 6 to 12 hours to completely refine the contents of steel. These furnaces are usually capable of producing several hundred tons of steel per day.
Although the process is less efficient than the B.O.F or the bessemer converter, it is more versatile on that most grades of steel can be produced
How does a basic oxygen furnace work and how much steel can be produced an hour? What percent of pig iron is used to make steel in the B.O.F.
The furnace is mounted on trunnions and can be rotated through a ful circle. The furnace is titled and the charge is loaded. After its loaded its titled back up and a water cooled oxygen lance is lowered. Oxygen is blown onto the surface of the molten metal at high speeds. The oxygen rapidly combines with carbon and other impurities in the molten charge. Like another materials are added as fluxes to help carry off the oxidized impurities. After refined the furnace is titled and pours the molten steel into a label through a top hole. Alloys are added to give the steel the precise chemistry required.
Molten pig iron from the blast furnaces comprise 80% of the metallic charge. The other 20% is comprised of scrap steel
The B.O.F. has a production rate of about 250 tons an hour
Explain how the electric furnace works and what it’s used for
Electric furnaces are usually reserved for production of alloy, stainless, tool and specialty steels. The hear within the furnace can be precisely controlled and there is no contamination from fuel oil or the combustion of gasses.
The heat of an electric furnace is produced as the electric current arcs from one electrode (of the three inserted into the furnaces roof) to the metallic charge and back to another electrode. The charge is usually carefully selected scrap steel and pure iron.
Explain the Bessemer converter and how much steel it can produce
Similar in design of the B.O.F. and operation. The process is fast and relatively inexpensive, producing up to 20 tons of steel in
10 to 15 minutes, but the product is not as pure as that produced by other processes.
The use of the Bessemer converter has declined. Today its uses is largely confined to the production of pipe, easily machinable steel and wire
What happens to the molten steel after its poured into the ladle from the furnaces
It follows on of the 2 major routes to the rolling mills that shape most of the finished products. The traditional method involved pouring the molten steel from the ladle into ingot moulds. When the steel has solidified sufficiently, the moulds are removed and ingots are taken to the furnaces called “soaking pits”. There, they are “soaked” in heat until they reach a uniform temperature
What are the 3 types of ingots
Rimmed
Semi-killed
Killed
Explain rimmed steel ingots
In rimmed steel, no action has been taken go rid the metal of gases or during the time it is poured into ingot moulds. The gases bubbles up on the outer edges as it starts to solidify or are entrapped in the central core. Rimmed steel is always characterized by an outer skin about 75mm (3in.) thick that is pure iron and a central core area into which trapped gases have segregated. These gases result in the formation of blow holes.
Rimmed steel is the least expensive and most common grade. It is relatively soft, containing about 0.15% carbon and practically no silicon. During welding the impurities may cause porosity or other weld defects, especially in butt joints
Explain how killed steel is identified
Killed steel is fully deoxidized during the refining process. No gas evolution occurs when the ingot is poured. The ingotnis uniform in composition without the segregation that occurs in rimmed steel. Because there are no blowholes caused by gas formation, shrinkage results and killed steel ingots are characterized by a cavity or “pipe” that forms at the top of the ingot. This pipe is usually sheared off before further processing.
Explain how semi-killed steel is identified
A small amount of deoxidizing material (usually ferro-silicon) is added to the melt. This reduces the oxygen content, reducing the gas evolution in the solidifying ingot. There is, however, sufficient gas formation to compensate for the shrinkage during solidification, and blowholes are generally confined to the upper half of the ingot. Welding semi-killed steel generally presents few problems.
What is the process called that skips the ingots sequence and how does it work?
Continuous casting is used to turn molten steel into blooms, bullets or slabs. The ladle of molten steel is lifted to the top of the strand caster. Steel ows from the bottom of the ladle into a reservoir called the “tundish” and from their into copper molds. The molds are internally cooled with water. This causes a thin skin to form on the outside of the liquid metal. It is then run through pinch rolls that form the shape of the metal and are sprayed with water. After the metal is solid throughout it is cut to size by a torch
What is steel shaped into after it has been cast into ingots? And what are these different shapes used for?
Blooms, slabs and Billets
Blooms are square and oblong, with a minimum cross-sectional area of 3m2 (36 in.2). They are finished into structural-steel shapes such as S-beams, channels, angle and rails
Billets are more often square in cross section. They are usually produced from blooms and are smaller and usually longer. Bars, piping, tubing and wire are made from Billets
Slabs are wider and thinner than Billets and are rolled into plate, sheet and strip steel.
What are some differences in hot and cold rolling?
Hot rolled steel features slightly rounded edges, while cold-rolled products with the higher dimensional controls have squared edges.
During hot rolling, steel is kept at a temperature between 500C and 1333C (900F to 2400F). Hot rolling produces a residue of grey or black mill scale caused by the oxidation of the metals surface at these temperatures.
What is the name of flat-rolled steel used in the butt-welded pipe manufacturing?
Skelp
What does forging do to steel? What are the 2 major classes of forges?
Forging “kneads” the original steel into a denser structure, which greatly adds to its mechanical properties. It is widely used for parts that sill be subjected to high stress.
Open-die forging uses hydraulic presses to work heated steal into its desired shape
Closed-die forging uses the impact of hammers rather than the squeezes of hydraulics to work the heated steel into its desired shape
