February 2021 Volume 3

EQUIPMENT & TECHNOLOGY MATERIALS

It must also be noted that quench oils carry a significant safety hazard in that they can flash if overheated. Flashing can lead to horrific fires if not properly and swiftly suppressed. For this reason, it is increasingly rare to see large open tanks of quench oil in heat treating shops and they are usually confined to integral quench furnaces that are purged of oxygen. Any open pits that remain in use should employ capable fire suppression systems. Polymer Polymer quenchants are provided as a bulk concentrate liquid that can be added to a water quench bath at a desired concentration. Thus, these quenchants can provide a variety of speeds from faster than water to an approximation of oil. They are a great choice for a flexible quenching system that can be used to harden a variety of alloys and cross-sections. Some systems can also be set up to run a variety of different concentrations via holding tanks and pumps. In practice, it is not nearly descriptive enough to simply state “polymer quench” as many heat treating specifications do. While these products have gained popularity as a replacement for open oil tanks with zero fire hazard, it is critical that the end user understands their cooling behavior. The combination of product selected, concentration, and tank agitation design can provide a great variety of cooling behaviors that must be kept under tight control. Polymers must be frequently tested for tank concentration (preferably daily) as

repeated quenching will drag out polymer concentrate. They must also be routinely tested for quality in a lab setting as they degrade over time, which can severely alter performance. Water Water is considered the most aggressive quench media available. It is typically used for low hardenability alloys such as 1045 or 4130 that other quench media will be incapable of quenching fast enough to attain maximum hardness. Because water does not have any wetting agents, it is especially critical for water tanks to have strong agitation or quench performance will be lagging. Additionally, water quench systems are much more effective at cold temperatures and begin to degrade once the bath temperature gets over ~90°F. Therefore, water quench systems usually need to be connected to a refrigerant chiller system to provide repeat performance at lower temperatures. ■

Chuck Hartwig is the Director of Operations for Carburizing and Batch Hardening at ThermTech in Waukesha, WI. He holds a B.S. in Metallurgical Engineering from Colorado School of Mines. Email: chuck.hartwig@thermtech.net

FIA MAGAZINE | FEBRUARY 2021 51