Friday, 4 March 2016

Hardening methods

          The most extensively used method is conventional hardening or quenching in a single medium. The disadvantage of this method, however, is that the cooling rate in the martensitic transformation range will be very high. It will differ only slightly from the rate on the upper zone of super-cooled austenite of low stability and, therefore, cracks, distortion and other defects may occur in this method. Other hardening methods, which shall be briefly described, are generally employed to avoid these defects and to obtain the required properties.
          The various hardening methods are:
  • Quenching in two media.
  • Hardening with self tempering.
  • Stepped quenching or martempering.
  • Isothermal quenching or austempering.

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