Salt Bath hardening 


Martempering involves austenitisation followed by step quenching, at a rate fast enough to avoid the formation of ferrite, pearlite or bainite. Soaking must be long enough to avoid the formation of bainite.

The advantage of martempering is the reduction of thermal stresses compared to normal quenching. This prevents cracking and minimises distortion.

Martempering is used to produce martensite without developing the high stresses that usually accompany its formation. It is similar to conventional hardening except that distortion is minimized - the process is frequently used on Tool Steels particularly prone to cracking due to severe changes in section size or sharp corners.

Neutral Hardening

Neutral Hardening can offer advantages over alternative hardening and tempering methods.

Molten salt is often considered the ‘ideal’ heat treating medium. When parts are immersed in the molten salt, heat is transferred by direct contact to the surface. Since the parts are immersed in the salt, air cannot contact the work piece and scaling, oxidation and decarburisation are avoided.

Heat transfer into components is very rapid - much faster than with radiation or convection methods. Additionally, the uniform rate of heat transfer permits components having complex geometries and diverse cross-sections to be heat treated and quenched with minimal distortion.

Salt Bath Hardening is ideal for Tool Steels.


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Cyanide Case Hardening

Cyanide Case Hardening offers the same advantages as the Neutral method, just in a different salt composition for case hardening, rather than through hardening, steels. 

The process used to be very common amongst subcontract and, particularly, captive heat treaters but is now very uncommon due to high running costs driven by health, safety and environmental controls and is normally only required for some very old and outdated Aerospace specifications (which we continue to support).

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Registered Address.: Aalberts Surface Technologies Heat Ltd, Blackhorse Road, Letchworth. SG6 1HD 

Tel: 01462 472147