Heat Treat Today's Technical Tuesday feature provides an overview of the heat treatment process and the benefits wrought from heat treating in salt baths. The article also illuminates details to understand part composition and the austempering and quenching process as a whole. Salt Bath Hardening: This process involves heating the workpiece to a high temperature, followed by rapid quenching in a salt bath.
It results in increased hardness and improved wear resistance. At the turn of the 20th century, the use of molten salt as a heating and quenching medium for steels was developed in England. It rapidly came into use in Europe as a low-cost method of heat treating.
Equipment was inexpensive, and molten salt provided a reproducible method of heat treatment. In this short article I will review the types of salts used for heat treating and some hazards. Using salt baths also helps with controlled cooling conditions during quenching.
In conventional quenching operations, either water or oil is used as the quenching media, and the high cooling rate provided by water/oil may cause cracks and distortions. The term "quenching" is a heat treatment process for ferrous materials that improves their physical and mechanical properties by altering their crystalline structure. It involves heating the ferrous workpiece to a high temperature, then quickly cooling it.
The quenching or cooling medium is typically oil or water. However, the Salt Quenching process uses various mixtures of salt bath mediums. A work part immersed into a molten salt is heated by heat transferred by conduction (combined with convection) through the liquid media (salt bath).
The heat transfer rate in a liquid media is much greater than that in other heating mechanisms: radiation, convection through a gas (e.g., air). Controlled cooling conditions during quenching. Salt Pots and What I Used "Salt bath" or "salt pot" heat treating refers to the use of molten salts for heating steel.
Specific salts are used for different temperature ranges, so that they melt under the necessary temperature without certain bad things happening by overheating them. For these experiments I used "Neutral Salt B" by Hubbard. The Benefits of Salt Quenching for Alloy Steel Many of the same benefits derived by heat-treating HSS in molten salts apply to processing tool steel and alloy steel products in salts.
For example, increased toughness can be obtained by quenching into salt, rather than oil. Quenching in molten salt offers many benefits, including reduced distortion, and the ability to austemper suitable steel parts. However, many of the beneficial characteristics of salt baths can make fires difficult to contain and extinguish.