HEAVY SECTION TEMPERING RECOMMENDATIONS
This pertains to cross sections of A-2, D-2 and S-7 tool steel (over 2 ½” thick). If these pieces are to be EDM machined, after heat treatment it is important to note that it is highly recommended that these tools have a minimum high double temper prior to the EDM process. Depending on the grade involved and required business, the higher the better.
A variation of 1 or 2 Rockwell points should not affect the performance of the tool. The higher tempering will add to the matrix toughness and its ability to absorb input and stress variations of the EDM process.
The safest way to minimize residual stress and eventual cracking in the steel is to ensure thorough tempering at a high enough temperature to condition the matrix, and with air hardening grades, that require a double temper.
One other suggestion that can help to eliminate premature failure in service is to re-temper the tool at 25 to 50 degrees Fahrenheit below the last tempering temperature after the EDM machining. This will relieve any internal stress that was created during the EDM process.
Plates/Flats