Quenching has been used for hundreds of years to harden steel and was one of the first thermal processing techniques to be developed, but modern quenching techniques are very different than the dip in water or oil that medieval blacksmiths used to rely on. Today's quenching techniques involve vacuum chambers, special formula baths, and even gases in place of the usual liquids. Discover how gas quenching improves the hardening process in five distinct ways.
Quenching in a liquid involves immersing a very hot piece of metal into a liquid at room temperature or below, so naturally the contact between the hot surface and the cooler liquid leads to rapid boiling and vaporization. This means that the metal is not cooled evenly, even with advanced circulation of the fluids. Since gasses are swirled around the piece being processed in a vacuum chamber, the resulting quenching is as even as possible when you pinpoint the right combination of air speed and pressure. This leads to reduced distortion, which is crucial for parts like gears that must fit tightly.
If you're handling the quenching process in your own facility to cut down on secondary manufacturing costs, you and your employees will both appreciate that using gas for quenching is remarkably safer than relying on liquids. All of the gasses used for this kind of quenching, such as helium, are non-toxic and won't hurt anyone if there's a sudden leak that sends gas into the rest of the work area. In contrast, the oils and salt water bath formulas used for liquid quenching are often so dangerous that employees need to wear costly full body suits to protect themselves from serious damage.
Aside from being safer for humans, these cooling gasses are also better for the environment. Helium, nitrogen, and other pure gasses can be released into the environment without any impact, which is definitely not the case for quenching liquids that require special and costly recycling treatments.
Lower Finishing Costs
Since the efficiency of gas quenching results in fewer distortions, it stands to reason that this results in lower costs by reducing expensive finishing techniques like
- Clamping and straightening processes to undo curvatures and distortions caused by the heat treatment
- Grinding to create a smoother surface and increase hardness
- Machining to restore tight tolerances that were lost during heat treatment or quenching.
Aside from lowering finishing costs, gas quenching can also replace expensive press quenching, a process in which parts are kept from distorting by being dipped into a liquid bath while clamped in a mold.
Tired of having to clean stubborn residue deposits off of the inside of your hardening furnaces after a certain number of pieces are treated? Inert gases like helium and nitrogen don't deposit anything on the surface of a piece of treated metal, so there's nothing to burn off and stick to the furnace. Aside from saving time on cleaning furnaces with caustic chemicals to cut through the deposits, you'll also spend less time and money on cleaning the metal parts themselves. Oil quenching formulas are particularly bad at leaving parts coated with a layer of residue that interferes with finishing and causes corrosion if not completely removed, so gas quenching can make it easier to get pieces out quickly and with more reliable cleanliness.
Finally, the vacuum chamber system used for gas quenching offers surprisingly fine control over the entire process. By making tiny changes to the amount of pressure inside the chamber or the air circulation speed, you can pinpoint the precise settings that produce the most hardening and least distortion for each alloy mixture and part shape. You can adjust liquid quenching baths in the same way, but the adjustments are not as fine and take longer to implement and test.