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Phone: 1 888 928 9927
1 843 871 2157
ztasales@zapp.com

TOOL STEEL
TECHNICAL LIBRARY

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
 

ZAPP HIGH-PERFORMANCE
STEEL GRADES:

TOOL STEELS
Z-TUFF PM
Z-WEAR PM
Z-A11 PM
Z-A11LV PM
Z-420 PM

HIGH SPEED STEELS
Z-M4 PM
Z-T15 PM
Z-M48 PM
Z-MAX PM
Z-M2
 

ZAPP PERFORMANCE PRODUCTS:
ZDM BLANKS
 

TOOL STEEL TECHNICAL TRAINING

SERIES III: Basics of Heat Treatment • Part 1

It is the heat treat process that essentially “pulls the trigger” to unlock the strength‚ wear resistance‚ and toughness capabilities of the alloy being treated. Yet despite the well recognized importance, heat treat related issues remain commonplace much because of the difficulty involved in determining if the job was done correctly (unless something REALLY bad happened‚ a poorly heat treated tool looks the same as a good one). We rely day to day on the good old hardness test as the simple to perform measurement by which we gage the success of the heat treat operation. Unfortunately‚ the hardness test just doesn’t tell the whole story. It is not unlike attempting to build a die to extremely close tolerances with nothing but a yard stick to measure your work.

From a metallurgical perspective‚ the heat treat process actually involves a number of specific and fairly complex changes in the metallurgical structure of the materials. This is where we talk about topics like austenite transforming to martensite‚ etc. These changes can be easily observed under a microscope using a polished and etched sample which makes analysis of microstructure the best method by which to judge the outcome of the heat treat process. Consider the following example as a case in point.

Comparison of Z-Wear PM Heat Treated Microstructures

These photos were taken from a pair Z–Wear PM fine blanking punches which both checked RC 60–62‚ but were found to exhibit microstructures which appear very different. The sample shown in figure 1 came from a punch which failed (cracked) prematurely after only 6000 hits, and a number of problems are clearly evident. The pronounced grain boundaries indicate the tool had been overheated (2100°F) during hardening and was poorly quenched. The light etching matrix (background) indicates the tool was also poorly tempered and contains retained austenite and untempered martensite. These factors together resulted in a near total loss of toughness. The structure shown in figure 2 came from a new tool which was correctly hardened at 1950°F‚ 6 bar quenched‚ and triple tempered. It went on to run 25‚000 hits. Remember that both punches checked at the specified hardness of Rc 60–62.

Full coverage of all the ins and outs concerning the proper heat treatment of tool steel obviously is beyond the scope of this short article. However, future installments will continue to take a look at some of the common issues and will attempt to answer some of the most frequently asked questions concerning the heat treatment of the Zapp Tooling Alloys line of PM grades. Along the way we will also provide some practical advice in regard to working with your heat treat source and how heat treatment can be used as a means to optimize the performance of high alloy tool materials.

Subsequent releases from Zapp’s heat treatment series will be released shortly and address: 1) Austenitizing Temperatures and Quench Rates, 2) Proper Tempering Procedures, and 3) Cryogenic Treatments.

Questions or comments may be sent to Gary Maddock at gmaddock@zapp.com.

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