Hardening & Tempering
This process is used to increase the hardness (and therefore the strength) of steels. Heat treatment processes are also used to increase fatigue life, wear resistance and, in some cases, corrosion properties.
It should be noted that Hardening means to fully Through Harden a material, not surface hardening or precipitation hardening.
Hardening is carried out by heating the work to elevated temperatures (over 780°C), followed by quenching, or cooling at a controlled rate. This rapid cooling transforms the steel structure and is done for example by quenching in oil or gas. Because of the temperatures involved, there will inevitably be some degree of distortion.
After hardening, the work will be in its strongest possible condition, but unfortunately its most brittle condition. Consequently, it must be tempered. This increases the toughness whilst optimising the required hardness. It is important that this process is done within a short time after Hardening otherwise cracking may occur due to the high stresses within the part.
Most of the processes are performed in highly sophisticated vacuum furnace equipment, specially designed to give the best results possible.
Hardening is a very broad subject and there are many different routes which can be used for different materials. If you are in any doubt about the best process for your purpose, we would advise that speak to one of our experienced metallurgists prior to specifying treatments. For details of the best person to speak to within your area refer to your nearest plant site for contact information.
Hardening is commonly carried out under controlled atmosphere sealed quench furnaces to medium carbon steels. Certain steels such as tool steels however benefit from hardening in vacuum.