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).