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Heat Treatment

Heat Treatment. Outline. Annealing Martensite Formation in Steel Time-Temperature-Transformation Curve Heat Treatment Process Hardenability Precipitation Hardening Surface Hardening Heat Treatment Methods. Annealing. Heat, Soak and Cool slowly to reduce hardness and brittleness

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Heat Treatment

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  1. Heat Treatment Outline • Annealing • Martensite Formation in Steel • Time-Temperature-Transformation Curve • Heat Treatment Process • Hardenability • Precipitation Hardening • Surface Hardening • Heat Treatment Methods

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

  3. Martensite Formation in Steel • Equilibrium diagram assumes slow cooling • Austenite -> Ferrite and Cementite (Fe3C) • Rapid cooling causes non-equilibrium • Austenite -> Martensite • Martensite formation described through: • Time-Temperature-Transformation Curve • Hardness is a function of Carbon content • Martensite • Pearlite

  4. TTT Curve

  5. Heat Treatment Process • Austenitising • Raise temp. into Austenite region • Quenching • Rapid cooling in oil or water • Tempering • Reduces brittleness • Increases toughness

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

  7. Precipitation Hardening • Fine particals block movement of dislocations • Aluminium, Copper • Magnesium, Nickel etc. • Solvus line must be present • Three step process • Aging dictates degree of precipitation (hardness)

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