Tool Steel Heat Treatment

Tool Steel Hardening for Enhanced Strength, Corrosion Resistance & Temperature Stability

Hardening processes of tool steels in a vacuum furnace are highly dependent on alloy.  That said there is a basic template that is common to all, that is:

  • 1 or 2 preheat steps.
  • An austenitizing step.
  • A quench step.

Temperatures and times will vary for the pre-heat and austenitizing steps depending on alloy and geometry of the parts being heat treated.  Quench rates and thus quench pressures will also vary with material and geometry.  Distortion concerns will also be a factor in regard to selecting the proper quench pressure.


ThermTech has vacuum furnaces up to 72” in length and 10,000 lbs. maximum load capacity.  Our largest vacuum furnace has 15 bar maximum quench pressure and we are Ford and GM approved for aluminum die cast dies.   All vacuum furnaces are certified to AMS2750 for pyrometry.  Therm Tech staff is well versed in heat treating to NADCA specifications.  


The critical variables for hardening tool steels are time and temperature.  Each type of steel has prescribed temperatures which the steels must be heated to so that full hardness is reached.  The time at this temperature is an important variable and varies with section size.  If the steel is not at the hardening temperature for a long enough time the result will be incomplete transformation which manifests itself in the form of low hardness and poor wear properties.
Once the time at temperature criteria has been met the steel must be quenched at the proper rate which will yield a martensitic microstructure.  Too slow a quench rate will result in low hardness, too fast a quench rate will maximizing hardness can result in excessive distortion and possible cracking.


The process of hardening tool steel can appear mundane when only looking at the prescribed process given by the steel company.   The final success of the process is dependent on three parties, the steel supplier, the tool maker and the heat treater.  Good lines of communication must be established to provide feedback on distortion and performance so that the hardening process can be tailored to be optimal.