18MTY – 4 ENMaterials
Steel and cast iron, structures and phases, thermal processing
Quenching, tempering and annealing,
thermo-mechanical processing of steels
Steel – alloy of Fe and C
Polymorphic alloy
E
E´
P
FerriteBCC
AusteniteFCC
Binary diagram Fe-C
steels Cast iron
Microstructures created during cooling
Alloying elementsSteel is an alloy of iron, carbon and other alloying elements containing less than 2.14 wt % of carbon and iron is prevailing element
Alloying elementsAustenitotvorné – Ni, Mn, CoFeritotvorné – Cr, W, Mo, P, V
Alloying element
har
dn
ess
Structure
PropertiesProcessing
Thermal processing - quenching
Binary diagram Fe-C
steels Cast iron
Microstructures created during cooling
Continuous cooling diagram
Bainite carbides
<20 HRC
30-40 HRC
40-45 HRC
50-60 HRC
~65 HRC
Isothermal cooling diagrams
Isothermal cooling diagram – true time scale
Austenite (FCC) Martensite(BCT –TetragonalLattice)
Quenching types and temperatures
Quenchinga-directb-brokenc-thermal
ab
c
Quenchingtemperatures
Continuous cooling diagram
Influence of composition on hardenability
Jominiend-quench test
General scheme of thermal processing of steel
time
tem
per
atu
re
I..…heatingII.…constant temperatureIII…cooling
Annealing
Relation between annealing and microstructure
Other types of steel processing
• Induction Hardening
• Thermo-chemical processing• Carburizing (800-900°C, thickness 1 mm)
• Nitriding (450-580°C, thickness 0.2 mm)
• Carbonitriding, ferritic nitrocarburizing
Cast iron structures