Oil Quench Hardening

Oil quench hardening is the preferred method for hardening for most steel grades of investment castings. It’s preferred because it enables the casting to achieve its required strength and hardness properties while posing less risk of distortion than water or polymer quench processes.


Oil hardening for investment castings is performed in our numerous batch-type internal quench atmosphere furnaces, which are exceptional for their process and lot control capabilities. All of these furnaces are certified to the temperature uniformity requirements of  AMS 2750 , and our largest furnace capable of performing oil quench hardening has internal working dimensions of 36”W x 72”L x 42”H and can handle weights of up to 7000 pounds.


The process of oil quench hardening for investment castings is performed by first fully austenitizing the steel in the temperature range of 1500°F – 1650°F depending on the steel grade.  It is held at this temperature for a time proportionate with the part cross-section.
The entire austenitizing process is carried out under a protective carbon-controlled atmosphere that protects the surface quality of the parts under high temperature.  Once soaked at the austenitizing temperature for the appropriate amount of time, the load is quenched in agitated oil to produce a fully hardened martensitic microstructure. From this point, the parts are tempered down to the specified hardness range to improve toughness while reducing overall strength.
In cases where parts are especially distortion sensitive, ThermTech will modify the oil quench process to minimize or eliminate these problems completely while still achieving the required material properties. For extreme distortion tolerances, take a look at our marquench hardening or austempering services.


Please be aware that lower final hardness ranges that require tempering above 900°F will result in temper oxide formation on most steel grades. Because of this, ThermTech offers blasting services to remove that oxide formation and improve the surface finish.  Alternatively, we also offer vacuum oil hardening, which can result in a bright surface finish after hardening (depending on the tempering temperature employed)

ThermTech offers oil hardening processes of investment castings for many low-alloy steel grades. Some of the most common materials we offer this process for include:

  • Oil hardening 4140 steel
  • Oil hardening 4145 steel
  • Oil hardening 4150 steel
  • Oil hardening 4340 steel

For distortion sensitive parts we recommend our marquench process. We also routinely carbon-restore investment castings prior to the hardening operation. 

To learn more about how our oil hardening process can benefit your Investment Casting products please contact our sales staff for a formal quote today!