One of the most common forms of heat treating, quenching has enjoyed popularity as a way to change the physical properties of metals for centuries. Today, manufacturers still employ this process widely.
During quenching, a manufacturer immerses very hot metal in a cooling medium in order to obtain a sudden rapid drop in temperature. This fast temperature transition prevents most metals from undergoing softening changes which occur during more gradual cooling. The precise quenching effects vary based upon the properties of the constituent metals and their alloys. Quenching hardens most steels and ferrous alloys.
The Quenching Process
The process of quenching occurs after a manufacturer heats metal to a point above its re-crystallization temperature. The application of intense heat causes the solid material to begin liquefying. Applying intense heat helps refine the internal grain structure of many steels and ferrous alloys, for instance. Raising the temperature of a ferrous metal object above the critical point disrupts the symmetrical latticed arrangement of its constituent atoms.
For instance, by heating most carbon steel alloys above the 1,674 degree Fahrenheit temperature level, a manufacturer causes thermal expansion and enables the iron atoms in the metal to break free from a latticed, solid formation. They begin moving more freely. In this condition, iron atoms often form bonds with carbon, another element present in the metal. Rapid quenching helps preserve these high-temperature changes in the newly re-solidified steel.
By quenching a ferrous object in a cooling media quickly, the manufacturer prevents the hot metal from melting into a liquid shape and completely losing its solid structure. Importantly, this process also enables the steel to retain the benefits of the finer internal grain restructuring which occurs at high temperatures. Quenching helps preserve molecular changes which contribute to harder steels.
In order to produce desired changes, quenching in high volume production settings must occur within very specific parameters. Both the temperature levels and the speed of re-heating and quenching play important roles in the creation of hardened steels meeting customer specifications. Manufacturers must pay close attention to the composition of the metal alloys involved in determining the best quenching protocols to use to achieve desired results.
Quenching a metal item too rapidly causes cracking or even fracturing, for example. It may contribute to the creation of internal stresses within the object due to the development of excessive exterior brittleness. Alternatively, quenching at too slow a pace also sometimes inadvertently results in slower-than-optimal cooling of hot metals. Fabrication companies performing quenching benefit by implementing robust quality control measures.
In the past, blacksmiths performed quenching by submerging hot metal parts extracted from the fire into buckets of cold water. Modern quenching has become far more sophisticated. It occurs within diverse fabrication settings. The facilities used to implement this hardening process range from comparatively low-tech blacksmith studios to specialized modern plants equipped with a variety of quenching media and temperature control options.
Most high volume steel mills and metal parts production plants have automated this process, for instance. Additionally, depending upon the metal and the production specifications, manufacturers sometimes select from a variety of available quenching media. Substances used for quenching in these settings frequently include water, oil, specialized polymers, salt brine or gases. Each of these popular quenching mediums offers advantages and disadvantages:
Water, the traditional substance for quenching hot metals, still performs a valuable role today. Some manufacturers employ fresh water during the quenching process.
Oil baths serve as quenching media for certain steel alloys, especially some high tensile varieties. This process often occurs in conjunction with carburizing, a process used by some manufacturers to obtain case hardening.
Certain manufacturers have developed specialized polymers for specific quenching uses during metal parts fabrication. Many of these chemicals fall within the scope of proprietary formulations.
In some locations, manufacturers utilize salt brine baths to quench certain categories of steel alloys. The composition of the salts in the brine may vary, depending upon manufacturing specifications.
Forced air gases also provide a quenching medium in modern industrial parts fabrication settings. Manufacturers frequently use nitrogen, for instance. A quenching process involving nitrogen gas or ammonia gas sometimes occurs in conjunction with nitriding, a process widely used to harden the surfaces of some specialized high-carbon steels.
Since quenching remains a popular process for hardening many steel items and it enjoys a long history, it has obtained numerous applications. For instance, this method of hardening ferrous metals during former centuries often played a part in the production of fine steel swords and sabres.
Quenching may offer a highly cost-effective way to harden a variety of other metal products, too. For instance, in some places manufacturers harden certain small engine components, tools and consumer items entirely (or in part) through quenching.
Key Advantages of Quenching
Quenching offers some important advantages as a process for hardening ferrous metal products. First, this process sometimes occurs within very "low tech" settings. Even comparatively small enterprises may discover this process provides an accessible way to harden steel items in fabrication environments.
Second, quenching as a process works well in conjunction with some other widespread heat treating processes, such as carburizing, nitriding, annealing and normalizing. It offers a way to make a steel object more wear resistant and, potentially, longer lasting. Some metal parts manufacturers today include quenching as a routine automated step during finishing.
Third, quenching potentially accommodates a variety of differently sized products. This process works well to harden both small and large items.