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Write short note on i)Tempering ii) Ausforming iii)Normalizing.
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i) Tempering:

  • Tempering is a process done subsequent to quench hardening.

  • Quench-hardened parts are often too brittle. This brittleness is caused by a due to formation of Martensite.

  • This brittleness is removed by tempering. Tempering results in a desired combination of hardness, ductility, toughness, strength, and structural stability.

ii) Ausforming:

  • In this process, the deformation over 50% of metastable austenite in done in metastable bay between the pearlite and bainite noses of the pertinent TTT diagram (i.e., in range 600-400°C) and is then quenched to martensite.

  • Temperature should be low as possible such that carbides should be dissolved without grain growth.

  • The cooling rate from austinizing temperature to deformation temperature should be very low as to form ferritie and to avoid formation of bainite.

  • Deformation temperature also should be low enough to stop recovery and recrystallization. It has high dislocation density which is desirable.

iii) Normalizing:

  • Normalization is an annealing process in which a metal is cooled in air after heating in order to relieve stress.

  • It can also be referred to as heating a ferrous alloy to a suitable temperature above the transformation temperature range and cooling in air to a temperature substantially below the transformation range.

  • This process is typically confined to hardenable steel.

  • It is used to refine grains which have been deformed through cold work, and can improve ductility and toughness of the steel.

  • It involves heating the steel to just above its upper critical point. It is soaked for a short period then allowed to cool in air.

  • Small grains are formed which give a much harder and tougher metal with normal tensile strength and not the maximum ductility achieved by annealing.

  • It eliminates columnar grains and dendritic segregation that sometimes occurs during casting.

  • Normalizing improves machinability of a component and provides dimensional stability if subjected to further heat treatment processes.

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