475 International Circle
   Summerville, South Carolina 29483
Phone: 1 888 928 9927
1 843 871 2157
1528 St. Paul Avenue
Gurnee, Illinois 60031
Phone: 1 888 928 9927
1 843 871 2157


SERIES I: Introducing the Concept of Tool Steel Microstructure

SERIES II: Typical Failure Modes for Cold Work Tooling and Their Association with Microstructure

SERIES III: Basics of Heat Treatment • Part 1

SERIES III: Basics of Heat Treatment • Part 2

SERIES III: Basics of Heat Treatment • Part 3

SERIES III: Basics of Heat Treatment • Part 4

SERIES III: Basics of Heat Treatment • Part 5

SERIES III: Basics of Heat Treatment • Part 6


Z-A11 PM
Z-420 PM

Z-T15 PM
Z-M48 PM



SERIES III: Basics of Heat Treatment • Part 6

Figure 1

Figure 1: Example of how salt bath remains an important method for certain tooling applications especially long parts, which require hot straightening.

Effectively managing the heat treat function requires a high level of involvement with the process. Simply calling out a Rockwell hardness and sending the parts out in the first truck to arrive at the dock is not generally a recipe for success. Granted that heat treat is an inconvenient, but vital process, that occurs in the middle of the often complex steps involved in the manufacture of tooling. It is amazing, from the tool steel supplier's perspective, how often the focus becomes logistics, turnaround time, and cost with little regard for the actual metallurgy necessary for a sound heat treatment process. While one might get away with this in the case of simple components and basic commodity tool steels, it is a sure fire recipe for downstream problems for tough applications involving highly alloy, high performance grades such as powder metals. A more involved, proactive approach will result not only in more consistent results, but can also differentiate the performance of your tooling relative to competitors who may be less concerned with the heat treatment process.

Figure 2

Figure 2: Example of how some delicate tooling components (Z M4PM) require special handling and creative fixturing to prevent warping and damage to sharp cutting edges

The first step to ensure quality heat treatment involves careful selection of a capable heat treat source. We would offer the following five questions to ask as one attempts to qualify a vendor to provide this service.

  1. What is their primary business focus? Granted many heat treat shops tend to be a jack of all trades, but one should be aware of the philosophical differences between production heat treat (high volume, repetitive parts, nuts and bolts heat teat) as compared to the care and attention required for tooling components. It is important to determine the dedication that a heat treater has to the heat treatment of tool steels. If possible consideration needs to be given to heat treaters who specialize at running tool steel and who maintain a broad array of capabilities developed specifically for this type of work. Is heat treatment of tool steels one of their core capabilities?
  2. Have they made investment in new equipment dedicated to tooling work? State of the art vacuum furnace technology represents a huge improvement (especially in regard to quench performance) over older equipment. Although heat treated parts may look the same after being run, those done in the more recent equipment will have much better metallurgical structure.
  3. Do they have capability for electronic data collection and process documentation? Control technology is another area where significant gains have been made in recent years, and information of this type can be hugely beneficial when attempting to deal with tooling issues and make improvements in tool life.
  4. Do they have a basic met lab? Running a heat teat without lab capability is like driving a car without a speedometer! Zapp's tech series has highlighted the matter of metallurgical structure, and a basic lab with metallographic capability is the means by which this critical aspect can be controlled.
  5. How do the intangibles compare? There are many factors to consider in qualifying a heat treat source including some that can provide a basic indication as to how they run their business. This would include housekeeping, lighting, organization, fixturing capability, etc. While not rocket science by any stretch of the imagination, the heat treatment of tooling is less forgiving and often does require extra care and attention along the way.

Figure 3

Figure 3: Another example of how salt bath can be extremely effective method for niche grades and large parts that would be difficult to batch.

Given the appropriate choice of a well-qualified heat treat vendor, the following list of five suggestions can be offered as steps toward maintaining close control of quality as parts go through the process.

  1. Work with the heat treater (and steel supplier) to develop a written specification for the common materials being run. Specifications do NOT have to be so stringent that it backs the heat treater into the corner. It is always possible to design specifications such that parts can be effectively batched and still obtain desired results from a metallurgical stand point.
  2. Require certification for each job run. This sends a strong message that you are keeping an eye on the process. Measuring the process always improves the process.
  3. Inspect work when received from heat treat. This should include a quick hardness check as well as a visual examination looking for anything out of the ordinary. It is far better to identify concerns early as opposed later after incurring more costs in downstream operations.
  4. Periodically visit and audit the heat treat shop. This can be more for the purpose of maintaining an open dialogue and communication, but it is smart to ensure procedures are being followed as specified.
  5. Periodically run a sample through a lab to verify metallurgical structure. This entails having a sample sectioned, mounted and polished. This is the only way to absolutely judge the quality of heat treat and is certainly worth the effort in the case of critical components which get run through heat treat on a regular basis.

Figure 4

Figure 4: State of the art digital control which alloys process display and electronic data collection.

Final comments are in fact an impassioned defense for tool steel heat treaters who take this work seriously. The first would be to allow them the time to do perform the process correctly. A typical hardening cycle in a vacuum furnace can take 4 to 6 hours, and a triple temper cycle with a thorough cool down between each can take upwards of 12 hours or more. If your expectation is the heat treater should pick up your parts up in the afternoon and return them first thing the following day, you are indicating it is acceptable for some corners to be cut in the process. Proper heat treatment takes time. Along similar lines the matter of cost needs careful consideration. Heat treat expense in most cases is a relatively small percentage of the overall cost of tooling manufacture and given the importance for tool performance, it is not an area to cut corners in order to shave a few cents off the bill. In some cases, heat treat services are where one gets what they pay for. Finally, heat treaters who have invested in new equipment and technology need a fair return on their investment and deserve the support of customers who value good, quality heat treatment.

Hopefully this has provided some food for thought for toolmakers working with outside heat treat sources. Quality heat treatment is a valuable asset for your business.

We hope you find this heat treatment series informative. Should you have any questions or comments, please send them directly to

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