The Operating Principles of Salt Pot and How It is Used in Heat Treatment

01 December 2022

Ferrous and non-ferrous metals are materials often maximised by industries in creating a wide array of products.

Ferrous metals, for instance, are primarily used to make automotive components, industrial piping systems, railroad tracks, shipping containers, and other domestic and commercial tools. Non-ferrous metals, on the other hand, are utilised in producing aircraft frames, gold clubs, gears, electrical hardware, and many more.

One key difference between these two metal types is that the ferrous ones contain a huge amount of iron. The presence of this element makes ferrous metals prone to rust. Both metal types, however, can be heat treated effectively through salt pots.

The Essence of Heat Treatment

Heat treatment is a group of metalworking processes that can change the physical properties of a material. Processes of heat treatment can also sometimes alter the chemical characteristics of a material, ensuring that it can generate products needed by various industries. The basic steps of heat treatment, however, involve the heating of the workpiece without reaching its melting temperature and subsequently cooling it in a controlled way to acquire the desired properties.

The metalworking processes involved in heat treatment include heating, annealing, holding, normalising, hardening, ageing, stress relieving, and cooling. Many more processes can be carried out for metals and alloys with the help of the right tools and equipment. One of the tools that can be used in carrying out metalworking processes is a salt pot.

Salt Pot’s Operating Principles

A salt pot is a tool used by metallurgists in heat-treating ferrous and non-ferrous materials. It is often made from high-alloyed stainless steel, which contains around 20% of nickel. Some heat treatment processes that can be carried out with a salt pot are annealing, hardening, stress relieving, and case hardening.

When carrying out heat treatment processes with a salt pot, metallurgists would often heat the salt until it reaches its molten stage. The workpieces that will be heat treated are subsequently lowered into the molten salt, ensuring that the heat treatment processes can be carried out optimally. The salt used during these processes can be chloride or cyanide.

As the molten salt interacts with an alloy workpiece, the former would often attack the latter and its protective layer. The molten salt will then alter the content of the workpiece, leading to the exposure of alloy grain boundaries. The salt will further penetrate the grain boundaries to create holes. To reduce the corrosiveness of the salt, it must be paired with additives like silica, ferrosilicon, and methyl chlorides.

Benefits of Maximising Salt Pot

Tons of benefits are associated with maximising salt pot for heat treatment processes.

For one, a salt pot can ensure that distortion and quench cracking to workpieces can be prevented. Compared to other quench media, molten salt has a slower and more controlled cooling rate. This quality allows treated parts to be free from distortion and quench cracking, making the salt pot great for workpieces with tight tolerances.

Heating is also elevated with a salt pot. When immersed with molten salt, workpieces can be heated more quickly, making heat treatment processes be carried out faster than heating by convection or radiation. The risk of surface oxidation and decarburisation is, ultimately, minimised with parts immersed in the molten salt due to minimal contact with the atmosphere.

If you require heat treatment with a salt pot, you can contact us at Alpha Detroit Heat Treatment.

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