Heat Treatment of Tool Steels
This treatment in case of tool steels in a significant step before actually employing the tool. Most properties are attained after heat treatment. There are specific special but essential precautions to be seemed in heat treating tool steels. That type of precautions may be clear knowing of austenising temperature that is affected greatly by addition of alloying elements.
Normalizing and Annealing
Normalizing becomes essential in case of forged tools. Forging induces unneeded residual stresses, non-uniform and coarse grains structure. These defects are eliminated by normalizing treatment. The normalized tools are machined to accurate dimensions. That machining increases the hardness due to strain hardening.
The middle annealing from simply below A1 temperature is applied upon the tool to eliminate the effects of strain hardening.
The tools steels comprise lower thermal conductivity and whether the tool is heated on a faster rate distortion and cracking may arise. To ignore such cracking and distortion the tool before any of treatment is preheated slowly to temperature in between 600 to 800oC. The tool is held on the preheat temperature adequately long to permit entire body to come to uniform temperature and after that heat to needed temperature for any of treatment.
Given preheat the tool is austenised via heating to correct austenising temperature to acquire fine grained austenite whether carbides are dissolved.
The austenised tool is quenched in air, water, brine, oil or molten salt bath depending on the harden-ability and thickness of cross-section. The cooling correct rate will choose the quenching media and cooling faster than the correct rate will consequence in beneath stresses.
The distortion of tool in extremely conveniently avoided via austempering or martempering.