Oil Hardening

Oil quench hardening is the most common method used to harden gear products, as it will achieve required strength and hardness properties while minimizing the risk of distortion.


ThermTech offers two types of oil hardening processes for gears.  First, gears can be either carburized or direct hardened in batch atmosphere furnaces depending on the material selection.  The maximum working dimensions of these furnaces are 36”W x 72”L x 42”H or 70000 pounds.

Second, ThermTech operates a vacuum furnace equipped with oil quench to vacuum carburize or direct harden gear.  Vacuum Carburizing can be advantageous because it allows for greater case depth control, repeatability, uniformity of depth around a gear tooth, and also part cleanliness.  This furnace has internal working dimensions of 30”W x 48”L x 30”H, and can handle weights of up to 2500 pounds.


The process of oil quench hardening for gears 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 determined in relation to the part cross-section.

The entire austenitizing process is carried out under a protective carbon-controlled atmosphere or vacuum, 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.  The parts are then tempered down to the specified hardness range to improve toughness.

In cases where parts are especially distortion sensitive, ThermTech will customize our oil quench process to minimize or eliminate these problems completely while still achieving the required material properties. If the gear products have more stringent distortion requirements, consider our marquench hardening or flame hardening 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 suitable for removing that oxide formation from gears as well as improving the surface finish of such products.

ThermTech offers oil hardening processes for several alloys used in gear fabrication. The grades we possess the most experience with include:

  • Oil hardening 4320 steel
  • Oil hardening 8620 steel
  • Oil hardening 9310 steel

For large volumes of gears, or to learn more about how our oil hardening process can benefit them please contact our sales staff for a formal quote today!