Heat treatment processes and types .pptx

Heat treatment

1. Heat treatment processes Presented by: b.Srinivas 23rs5a 0312

2. introduction HEAT TREATMENT Heat treatment of metals may be defined as an operation or a combination of operations involving the heating and cooling of metals or alloys in the solid state to produce certain desired properties. Its purpose is to change a mechanical property or combination of mechanical properties so that the metal will be more useful,serviceable,and safe for definite purpose . By heat treating, a metal can be made harder, stronger,and more resistant to impact, heat treatment can also make a metal softer and more ductile .

3. TYPES OF HEAT TREATMENT ANNEALING NORMALIZING HARDENING TEMPERING SPHEROIDISING

4. ANNEALING Annealing may be defined as the softening process, in which steels are heated to above the transformation range and holding the steel at this temperature for certain time,then allowed the steel to cool slowly in the furnance. (OR) Annealing is the process for softening materials or to bring about required changes in properties ,such as machinability, mechanical or electrical properties,or dimensional stability.

5. PURPOSE OF ANNEALING To soften the steel To improve machinability To refine grain size To remove internal stresses To increase ductility and toughness To imrove mechanical properties

6. Classification of annealing processes FULL ANNEALING PROCESS ANNEALING SPHEROIDISE ANNEALING ISOTHERMAL ANNEALING

7. 1. FULL ANNEALING In the full annealing process , it consists of heating the steel to austenite phase, holding there for a proper time and allowing it to cool slowly in the “ furnace ” itself. PROCESS : Full annealing consists of 1. Heating the hypo eutectoid steel to a temperature of 30º to 50º C above upper critical point 910º C(A3) and 30º to 50º C above the lower critical point 723º C (A1,3) in the case of hyper eutectoid steel.

8. 2.Holding at this temperature for sufficient time so as to attain internal structural changes. 3.Slow cooling on the furnace .

9. 2. PROCESS ANNEALING Process annealing is a subcritical annealing operation. A subcritical operation takes below the lower critical temperature (A1) PROCESS : Heating the steel to a temperature of 600-700º C Holding at this temperature for a prolonged time “ Slow cooling”

10. PURPOSE OF PROCESS ANNEALING: To reduce crystal distortions resulting from cold working. To remove strain hardening. To relieve internal stresses. To get homogenous fine grained structure.

11. 3. Spheroidise annealing In spheroidise annealing,lamellar pearlite will be transformed into granules or spheroids. PROCESS: Heting the steel above the lower critical temperature (730-770º C). Holding at this temperature for a prolonged time . Slow cooling in furnace upto 600º C followed by air cooling

12. PURPOSE OF SPHEROIDISE ANNEALING: To improve machinability of medium and high carbon steels. To improve ductility and toughness. To reduce strength sand hardness.

13. 4. Isothermal annealing “In isothermal annealing the process is same as the full annealing except the cooling rate(rapid cooling)”. PROCESS: Heating the hypo eutectoid steel to a temperature of 30º to 50º C above upper critical point 910º C(A3) and 30º to 50º C above the lower critical point 723º C (A1,3) in the case of hyper eutectoid steel. Holding at this temperature for certain time to form austenite. Then steel is suddenly cooled to a temperature of50-100º C below lower critical temperature.

14. PURPOSE OF ISOTHERMAL ANNEALING: To reduce the hardness of the alloy steels. To reduce internal stresses . To improve machinability. To improve ductility and toughness.

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