May 2021 Volume 3

MATERIALS

What can be done to prevent heat checks? Again we come back to the subject of die temperature. Keeping the die surfaces within a temperature range without excessive high and low swings is the best remedy for preventing heat checks or at least extending the time before they develop. This requires a disciplined approach to minimizing the time hot billet material is in contact as well as a measured method of applying die lubricant or coolant so as to not overcool the die surfaces. Not an easy or repeatable task in a manual forge operation. Highly automated forge setups are more controllable for these conditions.

the forge shop to determine by trials if the coating is economically worth it to add to a die design specification. This article focused on steel alloys for dies. However, for special high temperature or exotic material forging, higher performance materials such as nickel based superalloys, molybdenum, or a combination of die materials may be required to withstand the rigors of the forging process. ■

Richard Polenick is the Technical Manager for Ellwood Specialty Steel in New Castle, PA. He has over thirty years of experience in manufacturing including positions with General Motors and Delphi Corp. in materials, product design, and tool engineering. In his current position he oversees the application and technical support for the tool steel products that ESS markets to its customers. He holds degrees in Metallurgical Engineering and Manufacturing Management. Phone: 800-932-2188 Email: rpolenick@elwd.com

Should a forging die be surface hardened or coated? This is a question that is difficult to answer and the writer normally chooses to not commit to a response. The reason being that when a forging process is being developed and a die is designed, built, and validated; that is done with minimal production time and parts. It is only after extended production can it be determined that a certain area of the die is not holding up and part dimensions are out-of-spec due to a steel wear condition. There are many surface altering processes to enhance the properties of a die, mostly by increasing the hardness to resist wear forces. Most popular of these processes is likely nitriding. Nitriding is a relatively low temperature heat treating process whereby the steel is exposed to a nitrogen rich atmosphere that allows the nitrogen atoms to diffuse into the steel surface and form hard particles that raise the hardness level. This nitride layer is normally shallow (< .020”) with hardness in the high HRC 60’s to low 70’s. The low temperature application prevents any softening of the base steel and there is no quenching required that could cause cracks or distortion. Other surface enhancements are commercially available to achieve the same surface improvements. The hesitancy to prescribe a surface hardened coating is that one cannot predict the benefit of the added expense and time element involved for applying a coating. The thin layers may or may not add production life to a die set. However, if a given die design experiences the same wear pattern and that is the primary reason for removing the tool from production a coating may be the solution. It is up to

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FIA MAGAZINE | MAY 2021