Quenching metal parts after heat treating increases hardness, but can sometimes lead to quench cracking…and scrapped parts. Why does this happen?
When parts are rapidly cooled, they expand, and the outer layer of the material locks into place first since it makes contact with the quench first. As the core cools and expands, it exerts pressure on the outer layer of the material. In this Metallurgy Minute, Paulo metallurgist Rob Simons explains this “balloon effect,” along with the design characteristics that can make parts especially vulnerable to quench cracking.

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