Steel Flashcards
What is steel?
an alloy containing Iron and Carbon (not a chemical compound)
how is it steel manufactured?
Smelting / blast furnace
Raw iron ore is quarried (oxides)
Blast Furnace produce cooks the iron ore with coke (coal heated to 2000c absent of oxygen)
Iron ore has oxygen removed and is now pig iron
oxygen is then passed through the motlen iron creating co2
Limestone is used as a flux (cleaning agent to remove impurities creating GGBS
Electric arc furnace
creates steel from scrap collected
What are the classifications of steel according to carbon content and what are its uses?
0.1-0.25% low carbon/ mild steel - civil engineering
0.2-0.5% medium carbon - car gears and machinery
0.5-1.5% high carbon - used for tools and machining
Legacy materials
Wrought Iron 0.1% carbon and 1- 2% slag ( see the grain)
Cast iron 2-4% Cabon very hard but brittle
Stainless Steel 10% chromium
what is hot rolling?
hot rolling used for most construction steel
cheaper
shirks
oxidizes on the surface
what is cold rolling?
more expensive
more accurate but harder to do
cleaner surface
greater strength due to strain hardening/ cold working
how much of the uks rebar is made from recycled steel?
100%
what determines steels mechanical properties?
chemical composition (carbon content e.t.c.)
heat treatment (quenching)
Manufacturing (hot or cold rolling)
What effect does cooling have on metals?
The slower the cooling the more ductile they are,
the faster the cooling the stronger they are but less ductility
what effect does Strain hardening or work hardening have?
Working the metal and increasing plastic strain dislocates the crytal lattice causing hardning and less ductility.
What is annealing?
Annealing is bringing metal to 0.6 of melting point
recrystalises and resets it to its original dislocation density.
makes it more ductile
What is quenching and tempering?
Steel is heated until glowing, quenched in water making it incredible hard but brittle.
it is then tempered (heated to a relativly low temp to soften it slightly but increase toughness
what is rebar?
Reinforcing bars for concrete
what is the typical compitsition of uk rebar?
CARES typical compisition is
0.2 Carbon
0.8 manganese
Silicon nickle and chromium
How is rebar made?
molten steel is poured into a billet (a long ingot)
This is then hot rolled back and forth through rollers until its the right diameter 10-50mm
on the final pass ribs are embossed onto it
hot bars are then quenched to make a hard outer layer with a ductile core. the inner core then self tempers the outer layer QST
Grading of rebar?
B500A where 500 is the tensile yield
A-C represents ductility class
A - ribs go in the same direction
B - ribs alternat on either side
C - ribs at diference angles creating V’s
