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What Is Quenching?

August 1st, 2021

Before steel products are ready for application, they need to be treated with heat to increase their strength. Learn about how our professionals at Specialty Steel Treating handle the quenching, or cooling, process and what types of media are used for different applications and products. 

Different Media for Quenching Steel

Most manufacturers use oil as the medium for steel quenching process. There are many kinds of oil, allowing for the process to be modified to suit the type of steel and treatment requirements. For example, when treating steel with a low carbon content, using a fast oil, or one that cools quickly, is better than using a slow oil, or one that stays hot for long periods of time. Additionally, oil boils slowly, so the treated steel has longer to adjust to the heating process.

Some of our clients prefer to use gas for the steel quenching process if they need to maintain an exact cooling rate or prevent their parts from getting dirty. Gas quenching always takes place in a vacuum and usually involves nonflammable nitrogen, but argon and helium are also possibilities. This medium is ideal for steel that cannot risk the distortion that is possible with oil quenching but still needs to be extremely hard.

The simplest and cheapest version of quenching uses air as its medium. The most precise form of air quenching involves blowing compressed air onto heated steel until it has cooled to the right degree. This process can involve simply heating steel and letting it cool in a normal environment, though. Air quenching is only possible if the steel equipment does not need to become drastically harder because its cooling process is so uncontrolled.

Choosing the right medium depends on the carbon content of the steel in question, its desired softness, its cost, and the amount of time available. For example, vacuum quenching is expensive, but it may be necessary for a hyper-controlled cooling process.

Steel Quenching Process

Regardless of the medium used to cool steel, all quenching processes begin with the application of heat. First, the steel is heated until it’s hotter than its upper critical temperature, which is between 1333 and 1670 degrees Fahrenheit. Then, the piece is moved to the quenching medium, whether that is an oil bath, water tank, or gas vacuum chamber.

The temperature of the cooling medium depends on how hard the finished product should be. Generally, the more quickly a batch of steel is cooled, the more severe the quench is and the harder the steel becomes. For example, to make steel with a high concentration of alloys slightly harder, we use a medium that isn’t very severe. A high-temperature oil bath is a good option.

There are several major safety concerns when completing the steel quenching process, so it must be completed carefully and with proper personal protective equipment. First, because it involves using steel that has been heated to very high temperatures, the chances of burns and equipment breakdowns increase. Secondly, using oil as a quenching agent increases the risk of a fire, particularly if some of the hot oil spills during the work. Finally, while some of the other options for quenching are not flammable, they can pose health risks to workers, including melted salt and caustic liquids.   

Work with SST today!

Although steel quenching can be a dangerous process, it’s necessary for making sure steel is strong enough for use in manufacturing, medicine, construction, and research. By choosing the proper cooling medium and handling the process carefully and safely, Specialty Steel Treating produces heat-treated steel that has the proper hardness and carbon content for its designated purpose.