1. IE210 Production Engineering Heat Treatment n Annealing n Martensite Formation in Steel – Time-Temperature-Transformation Curve – Heat Treatment Process – Hardenability n Precipitation Hardening n Surface Hardening n Heat Treatment Methods Outline

2. IE210 Production Engineering Heat Treatment Annealing n Heat, Soak and Cool slowly to – reduce hardness and brittleness – alter microstructure – reduce residual stresses – recrystallise (original grain structure) and – soften n Full annealing and Normalising of Ferrite Metals creates course and fine pearlite n Recovey anneal is partial annealing

3. IE210 Production Engineering Heat Treatment Martensite Formation in Steel n Equilibrium diagram assumes slow cooling n Austenite -> Ferrite and Cementite (Fe 3 C) n Rapid cooling causes non-equilibrium n Austenite -> Martensite n Martensite formation described through: – Time-Temperature-Transformation Curve n Hardness is a function of Carbon content – Martensite – Pearlite

4. IE210 Production Engineering Heat Treatment TTT Curve

5. IE210 Production Engineering Heat Treatment Heat Treatment Process n Austenitising – Raise temp. into Austenite region n Quenching – Rapid cooling in oil or water n Tempering – Reduces brittleness – Increases toughness

6. IE210 Production Engineering Heat Treatment Hardenability n Capacity to transform to martensite over a certain depth n Harness is function of carbon and alloys – chromium, manganese, molybdenum and nickle n TTT curve is moved to right n Jominy end-quench test

7. IE210 Production Engineering Heat Treatment Precipitation Hardening n Fine particals block movement of dislocations – Aluminium, Copper – Magnesium, Nickel etc. n Solvus line must be present n Three step process n Aging dictates degree of precipitation (hardness)