D2 tool steel is a well-known cold-work tool steel that has secondary-hardening values during high-temperature tempering. Generally, the steel will require at least a double temper in order for the tool to have dimensional stability during application. This type of tool steel (D series) is considered by AISI to be a “dimensionally stable” tool steel. This means that it is relatively dimensionally stable (providing that it has been machined and appropriately stress relieved).
That is not to say that no distortion will occur. Distortion will always occur in terms of movement depending on:
- How the steel chemistry was controlled
- How the steel was cut prior to final heat treatment (grain direction, grain flow, grain size)
- How the steel was machined
- Intermediate heat treatment (stress relieve)
- If a surface-treatment operation was performed
Applications and Suggested Hardness Values After Temper for D2 Tool Steel
- Cutting tools: 58-60 HRC
- Fine blanking tools: 58-60 HRC
- Shearing tools: 58-60 HRC
- Broaches and reamers: 58-60 HRC
- Thread rollers: 58-60 HRC
Heat Treatment after Hardening
It is recommended that the D2 tool steel be cryogenically treated to remove the risk of any retained austenite transforming to untempered martensite. Additionally, it is recommended that a minimum of a double temper procedure is given.
It is strongly recommended that if the process of EDM is used for cavities or holes sinking into the die, that the die is tempered immediately. The reason for this is that EDM will produce a brittle, hard surface layer of untempered martensite and a strong probability of forming large globular carbides. This is because of the elevated temperatures that the steel will experience when removing stock by the EDM. Because of the high chromium and carbon content of the steel chemistry, the probability of forming large globular carbides in the immediate surface is very high based on the EDM process temperature.
The only conclusion that can be reached when treating D2 is to handle the steel very carefully and preheat the tool thoroughly for heat treatment before attempting any of the high-temperature hardening procedures.