Oil Quenching

Oil Quench Steel Forgings

Oil quenching is a common method for hardening alloy steel forgings. It’s ideal for achieving the required strength and hardness properties on many alloys.

When you oil quench steel forgings there’s also less risk of cracking compared to water quenching or polymer quenching


ThermTech offers oil quench hardening for forgings that are made from any of several low-alloy steel grades.

We oil quench steel of the following grades:

  • 4140
  • 4142
  • 4145
  • 4150
  • 4340

As a leading commercial heat treating company, we oil quench steel forgings in our numerous batch-type internal quench atmosphere furnaces. These furnaces are engineered for optimal process & lot control.

All of our furnaces are certified to meet temperature uniformity & accuracy requirements of AMS 2750.

Our largest furnace is capable of performing oil quench hardening with internal working dimensions of 36”W x 72”L x 42”H. It can also handle weights of up to 7,000 lbs.


When we oil quench steel forgings we start by fully austenitizing the steel in the temperature range of 1500°F – 1650°F, depending on the steel grade. It’s held at this temperature for a time proportionate with the part cross-section.

The initial austenitizing process is typically carried out under a protective carbon-controlled atmosphere. This atmosphere prevents excessive scale formation on the forged surface.

Once soaked at the austenitizing temperature for the appropriate amount of time, the forgings are quenched in agitated oil. This produces a fully hardened martensitic microstructure, the depth of which is dependent on the alloy grade and section thickness.

At this point, the parts are tempered down to the specified hardness range for improved toughness.


Eliminate Temper Oxide or Light Scale

Most forgings are tempered in excess of 1,000°F. This results in formation of temper oxide or light scale after tempering. 

To eliminate temper oxide or light scale, ThermTech offers forging blasting services to remove oxide formation & improve surface finish.

Heavier Cross-Section Forgings or Forgings Made from Lower Grade Alloys

For heavier cross-section forgings or for forgings made from lower alloy grades that require a more rapid quenching process due to mechanical requirements, we recommend polymer quenching or water quench hardening.

Distortion Sensitive or Crack Prone

If your parts are especially distortion-sensitive or crack-prone, ThermTech will custom-tailor an oil quench process to minimize or eliminate these problems completely while still achieving the required material properties.

Extreme Distortion Tolerances or Unique Property Requirements

For extreme distortion tolerances or unique property requirements, take a look at our marquench hardening or austempering services.

Contact ThermTech for large volumes of forged parts and/or to learn more about how our oil hardening process can benefit your products!