is made up of iron, coal, and limestone. Alloy of iron and carbon to about 2% or less. Owes it
diverse properties to allotropy, or changeable crystalline structure of iron. As iron cools below the melting
temp. of 1538 c. (2800 f.) its atoms align themselves into a body-centered cubic structure. They form
cubes with an atom at each corner and one in the center. Iron Ferrite. When iron cools below 2541f. it
becomes austenite, which is face centered, atom at each corner and one in center of face. Carbon remains
dissolved more readily in austenite than in ferrite because there is more room bt. Atoms.
In principle steel making is a melting, purifying (refining), and alloying process carried out at 1600 C.
(2900 f.) under molten conditions. Comes from pig iron or scrap metal, refined in basic oxygen or open
hearth, electric arc used for scrap metal. When refined alloys are added.
– Molten steel can be poured into molds for solidification, these can later be reheated and rolled
into semi finished shapes such as blooms or slabs.
– molten steel is tapped from a ladle into a mold, extracted as a long strand,
and immediately cut, worked, and treated in one continuous operation.
Carbon steels – most widely used 90% of worlds production
Low alloy – exceptionally strong and used for machine parts, bridges etc.
High alloy – more than 8% alloy elements
mined in open pits, shipped from the Lake Superior region
– coke what is left over after gases, hydrocarbons have been removed, very hard and does
not crush under iron, burns evenly, coke ovens coke coal – no oxygen, remove brick dose with water to
take blast furnace
– serve as a flux, impurity magnet liberated in the blast furnace, melts in furnace,
combines with unwanted materials and then floats to the top – Slag
– White hot liquid iron, vertical steel cylander lined with heat resistant refractory brick in
which materials are melted down by blast of hot gas.
- lined with ganister, a silica, air was blown from the bottom through a charge of
molton pig iron, Bessemer realized that the subsequent oxidation of the silicon and carbon in the iron
would release heat and that, if a large enough vessel were used, the heat generated would offset the heat
lost. 15 minutes of 1650cf. heat could charge a ½ ton.
– reduce amount of carbon in iron, Bessemer, open hearth to the Blast Oven Furnace, 300
tons in 45 min. vs 5 in 8 hours in open hearth.
Oxygen combines with all the undesirable elements to make steel pear-shaped vessel lined with refractory
material. Blow oxygen over molten metal, add flux, 3000 d.f. pour out steel
Alloys then added, tungsten-heat resistant, chromium/nickel-stainless steel, molybdenum – hardenability
– consists primarily of hammering, pressing, rolling, and extruding under high heat.