We’ve come a long way from the days of early blacksmithing, when quench tempering simply meant dipping steel into water to rapidly cool it. Today, we’re able to utilize a myriad of different quenchants in different tempering applications and rely on the different properties of these liquids to ensure the right outcome for the metal being treated. Take a look at just some of the properties that are prized in different quenchants and what roles they play during a quench temper in Gastonia, NC:
Cooling rate and quenching speed
Simply put, this is the rate at which a quenchant is able to completely cool a work piece. This can vary depending on the type of metal being treated and the reactivity point of the metal itself. Generally, the cooling rate and quenching speed is determined via the nickel ball test, wherein a solid nickel ball is heated and dropped into the quenchant—the time it takes for the nickel to become magnetized is a determination of the cooling rate.
Thermal conductivity
Thermal conductivity is the measure of a quenchant’s ability to transfer heat. This differs from the cooling rate in that it’s not measuring the rate at which an object is cooled, but rather the rate at which the quenchant is able to relieve the work piece of its retained heat.
Viscosity
Often measured in centistokes (cSt), viscosity is the thickness of a liquid. Heat transfer rate is directly proportionate to viscosity in a quenchant, increasing with lower viscosities and decreasing with higher viscosities.
Water content
It’s important to measure the water content within a quenchant because depending on the level, a higher rate of soft spots, uneven hardness or staining may occur. It’s best to utilize quenchants with water contents that are below .1 percent, to alleviate any interference the water may have during the quenching process.
Sludge content
This is the amount of sludge and varnish that’s present in the quenchant as a result of thermal and oxidative degradation. Sludge byproducts are generally not adsorbed uniformly on a metal’s surface while it’s being quenched, which results in sporadic heat transfer that presents in increased thermal gradients, cracking and sometimes even distortion. Sludge unfortunately also clogs filters and heat-exchanger surfaces, resulting in overheating, dangerous foaming and sometimes fires.
There are also a number of secondary properties that come into account when picking a quenchant, including operating temperature, pour point and flash point. In coupling these variables with those listed above, metallurgists can achieve quench perfection and in turn, amiable properties for whatever they’re treating. Every variable must be considered equally when picking a quenchant and not every fluid will be right for the job at hand—it takes a seasoned metallurgist to understand how each property comes into play and how it will impact the overall quenching process, as well as the metal being treated during that process.