The Science, Benefits, and Advantages of Oil Quenching Steel

Oil quenching is an indispensable technique in the realm of heat treatment. Its prominence isn’t just rooted in its application for altering steel properties but also in its widespread use for hardening alloy steel forgings. Here’s an in-depth look at the process, its science, and its undeniable advantages, especially when dealing with steel forgings, machined parts, gears, and tooling.

Understanding the Science of Oil Quenching

Heat treatment is fundamentally about modifying the properties of steel. Quenching, which encompasses the rapid cooling of steel from high temperatures, plays a pivotal role in this. The choice of quenching medium influences the steel’s final characteristics profoundly. Oil, among its counterparts like water or brine, cools steel moderately. This controlled rate of cooling facilitates the evolution of a blend of martensitic and other microstructures, leading to a composite of mechanical properties that’s often optimal for many applications.

Advantages of Oil Quenching Steel Forgings, Machined Parts, Gears, and Tooling

  • Ideal Hardening for Many Alloys: Oil quenching is optimal for bestowing the necessary strength and hardness traits on a multitude of alloys.
  • Reduced Crack Risk: When you opt to quench steel forgings in oil, you mitigate the risks associated with cracking – a common issue with water or polymer quenching.
  • Specialized Capabilities: At ThermTech, our expertise extends to quenching steel grades including 4140, 4142, 4145, 4150, 4340, 1045, 52100, O-1 Tool steel, O-6 Tool Steel, and S-5 Tool Steel. Our furnaces, compliant with AMS 2750 standards, ensure temperature uniformity and precision. Our largest furnace, featuring dimensions of 36”W x 72”L x 42”H, can bear up to 7,000 lbs.

Diving into the Process at ThermTech

  • Austenitizing Phase: We initiate by fully austenitizing the steel, with the temperature oscillating between 1500°F – 1650°F based on the steel’s grade. The steel remains at this temperature for a period corresponding to its part cross-section. Notably, this phase usually occurs under a carbon-controlled environment to prevent excessive scale formation.
  • Quenching: After adequate soaking, the parts undergo quenching in agitated oil, resulting in a hardened martensitic microstructure. The depth of this transformation depends on the alloy’s grade and thickness.
  • Tempering: Lastly, the parts are tempered to align with the specified hardness range, enhancing toughness in the process.

Expert Recommendations from ThermTech:

  • For Oxide Elimination: We understand that many forgings undergo tempering beyond 900°F, which can lead to temper oxide or light scale formation. To address this, ThermTech offers forging blasting services, ensuring oxide removal and surface finish improvement.
  • For Heavier or Lower-Grade Alloys: In scenarios where you’re dealing with hefty forgings or those made from lesser alloy grades needing rapid quenching, we advocate for polymer quenching or water quench hardening.
  • For Sensitive Parts: If your components are susceptible to distortion or cracking, ThermTech has expertise in designing an oil quench technique that alleviates these concerns while still adhering to material property requirements.
  • For Specific Needs: For those with stringent distortion tolerances or unique requirements, consider our marquench hardening or austempering services.

In summation, the science and benefits of oil quenching steel underscore its importance in heat treatment. This method leverages the unique attributes of oil to craft steel with the ideal amalgamation of strength, malleability, and durability.

ThermTech—Experts in Austempering Stampings, Machined Parts, and Investment Castings

ThermTech, Inc. offers both small and large batch capabilities for austempering steel and iron investment castings. Between our neutral salt bath furnaces and our larger austempering furnaces, we have the capabilities to austemper a wide variety of stamping, machined components, and investment castings. We have run austempering on alloys from 1060 through 4340 to ductile iron machined parts.

Our dedicated team works with you to ensure we meet your specifications. Count on our decades of experience with hardening, tempering, surface heat treatments, vacuum treatments, and annealing. To learn more about our services, please contact us today.


ThermTech’s quality policy is ZERO DEFECTS for all customer products and in all quality management system activities. Through our efforts to continually improve the quality of the work we offer, we’ve been recognized as being able to meet the rigorous quality standards required by several of our major customers. ThermTech is certified for ISO 9001 and AS9100 in both Metal Heat Treat and Metal Finishing.