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