01-04-2014, 12:53 PM
Heat Treatment
[attachment=60734]
Heat Treatment is the controlled heating and cooling of metals to alter their physical and mechanical properties without changing the product shape.
Why heat treatment is required
Manipulating properties such as hardness, strength, toughness,ductility and elasticity .
PURPOSE OF HEAT TREATMENT
To remove strain hardening of a cold worked steel component.
To improve the ductility of metals.
Soften a metal to improve its machinabillity.
Improves hardness of steel.
Improves wear resistance.
Refine the grain structure.
ANNEALING
Slowly heated to 25° C to 30° C above the upper critical temperature.
Soaked at that temperature for some predetermined time ( according to thickness).
Cooling at room temperature (switch off Furnacce).
Austenite ( γ) Ferrite (α) Cementite
0.8% C 0.02 % C 6.67% C
FCC BCC Orthorhombic
NORMALIZING
Heated up to 50 ° C- 60 ° C above the critical temperature.
Soaked at this temperature for sufficient time (depend on thickness).
Cooled at room temperature in still air.
HARDENING
Heated slowly to a temperature of 50 ° C – 60 ° C above the upper critical temperature.
Components are hold at this temperature for complete austenization.
Cooled by quenching in a water bath or oil bath to the room temperature.
Austenite (γ) rapid cool martensite
FCC body centered tetragonal
0.8% C 0.8% C
AUSTEMPERING
Steel component is heated slightly above the austenitic temp. till the entire component becomes austenite.
Quenching austenite temp. to a temp. above the Ms temp. by dipping them in oil bath maintained at 350 to 400 °C.
Soaking at this temp to see the austenite transforms.
Slow cooling to room temp.
Improves the toughness of steel.
[attachment=60734]
Heat Treatment is the controlled heating and cooling of metals to alter their physical and mechanical properties without changing the product shape.
Why heat treatment is required
Manipulating properties such as hardness, strength, toughness,ductility and elasticity .
PURPOSE OF HEAT TREATMENT
To remove strain hardening of a cold worked steel component.
To improve the ductility of metals.
Soften a metal to improve its machinabillity.
Improves hardness of steel.
Improves wear resistance.
Refine the grain structure.
ANNEALING
Slowly heated to 25° C to 30° C above the upper critical temperature.
Soaked at that temperature for some predetermined time ( according to thickness).
Cooling at room temperature (switch off Furnacce).
Austenite ( γ) Ferrite (α) Cementite
0.8% C 0.02 % C 6.67% C
FCC BCC Orthorhombic
NORMALIZING
Heated up to 50 ° C- 60 ° C above the critical temperature.
Soaked at this temperature for sufficient time (depend on thickness).
Cooled at room temperature in still air.
HARDENING
Heated slowly to a temperature of 50 ° C – 60 ° C above the upper critical temperature.
Components are hold at this temperature for complete austenization.
Cooled by quenching in a water bath or oil bath to the room temperature.
Austenite (γ) rapid cool martensite
FCC body centered tetragonal
0.8% C 0.8% C
AUSTEMPERING
Steel component is heated slightly above the austenitic temp. till the entire component becomes austenite.
Quenching austenite temp. to a temp. above the Ms temp. by dipping them in oil bath maintained at 350 to 400 °C.
Soaking at this temp to see the austenite transforms.
Slow cooling to room temp.
Improves the toughness of steel.