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Phone: 1 888 928 9927
1 843 871 2157
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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 I: Introducing the Concept of Tool Steel Microstructure

A basic tenant of metallurgy is that the properties of a metal are a function of its microstructure. Consequently, further understanding of tool steel requires an appreciation for the type of microstructure offered by each grade. This may seem a bit abstract to some, but is not difficult even from a layman’s point of view. Microstructure tells a more complete story in that it reflects not only the composition of the grade, but also the way the material was manufactured and the thermal history of the article in question.

The constituents of tool steel microstructure primarily involve alloy carbide in a hardened martensitic matrix. The type, size, and distribution of the carbides largely determine the wear and toughness characteristics of each particular grade. This attributes are tied to the method for melting the alloy, as well as, the amount of hot working involved in the production process. Conventional melt processes utilize ingot casting of materials which leads to non-uniform structures. As cost pressures continue, mill producers have introduced larger ingots into the process to reduce overall costs which can be detrimental to the tool steel structure. Particle metallurgy (PM) melt practices involved the atomization of metals which leads to uniform carbide distribution and structure.

Differences can be readily seen when examining cold work grades such as Z-Wear PM and conventionally produced D2 (figure 1). While both grades can offer similar wear performance, the large, banded carbides of the D2 result in potential for cracking and a greater tendency to chip in finished tools. The Z-Wear PM is produced by particle metallurgy methods which result in a microstructure with fine uniformly distributed chrome and vanadium carbide. This provides better toughness and higher hardness capability which together facilitate more versatile and consistent tool performance.

PM Microstructures

Within the Zapp Tooling Alloys series of PM alloys, grades are differentiated by the type and volume of carbide that is present in the heat treated microstructure. The Z-Wear PM offers the highest toughness and impact strength while maintaining good wear performance at a typical working hardness in the range of RC 58-62. The Z-M4 PM high speed steel offers increased wear resistance and attainable hardness (up to RC 64-66) while maintaining an intermediate level toughness. The Z-A11 PM has a high volume of vanadium carbide which offers exceptional wear and abrasion resistance (at RC 58&-62) while toughness will be somewhat less by comparison with the other 2 grades (figure 2).

Tool Steel Selection on The Basis of Microstructure

The difference in the microstructures of these grades allows them to cover a broad range of application requirements. Depending on factors such as type of part material, stock thickness, die design, desired tool life, etc. it should be possible to find a grade which fits the bill. The uniform microstructure of the PM grades can provide significant benefits in regard to predictable and consistent tool performance.

Gary Maddock, Technical Manager, Zapp Tooling Alloys, Inc.

The “Tool Steel Training” Series is meant as an educational and technical tool for Zapp’s customer and will be a regular part of the marketing efforts. Look for future discussing other areas of interest relating to tooling performance improvements. If you have a subject suggestion, please feel free to submit a request to Gary Maddock at or Harry O’Brien at

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