Tuesday, June 25, 2013

FACTORS FOR HEAT TREAT RELATED ISSUES PART I BY TRINITY NDT

Heat treatment Hardness Related Issues - Part I

WHEN NEUTRAL HARDENING (i.e., QUENCH & TEMPER)

Low Hardness


  • Variation in steel chemistry (e.g., % carbon at the low end of the specification).
  • Surface De-carburization in the furnace. (i.e., low carbon potential)
  • Delay quench (i.e., excessive hold time between austenizing furnace and quench).
  • Insufficient quench time
  • Quench media temperature (high)
  • Quench media agitation (insufficient)
  • Tempering furnace temperature (high)

High Hardness 


  • Variation in steel chemistry (e.g., % carbon at the high end of the specification).
  • Improper austenizing furnace atmosphere (i.e., high carbon potential)
  • Quench media temperature (low)
  • Tempering furnace temperature (low)
  • Insufficient tempering (i.e., time/temperature relationship).

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