Total Case Depth with Induction Hardening – One Way We Measure

It is important when discussing how we measure total case depth to first state that the only way that we (Zion) heat parts to austenitizing temperatures is through the use of induction coils.

The methodology outlined below is SOP for Zion Industries unless instructed otherwise by our customers or a part specific specification.

  1. We take the induction hardened part and section it in a manner to expose the area that we need to measure the total case depth in.
  2. The next step is for the part to be sandblasted in the area that we need to measure the case depth in.
  3. Using a 10X eye loupe we then measure the total case depth by going in from the surface at 90° and measuring how deep the “shinny” portion of the part is. Note that the induction hardened depth will remain “shinny” while the soft area of the part will turn a matt grey.

It is our experience that the portion of the case that is at or above HRC 40 (approximate) will remain shinny when the sectioned part is sandblasted.

Why do we use this approach?

In induction hardening steel parts, heating the parts to the correct depth is only ½ of the job. The other half of the job is to ensure that the properly heated parts are quenched correctly. It is common to have induction hardened parts that, depending on alloy, required case depth, and part geometry, display a significant difference between the “heat effected zone” and the hardened zone.

Note that many specifications define a total case depth as “total heat effected” which is what you would typically see, using a macro approach, if you prepare a sectioned part for total case depth measurement using an acid wash. However, once again that only qualifies how deep you heated the part, not neither necessarily how deep you hardened it nor how effective you’re quenching systems are.

We at Zion, through many years of experience, are confident that in using the method of sandblasting to qualify total case depth we have a methodology that is an accurate and cost effective approach to measuring the effectiveness of our induction hardening process.
Should you have any concerns or questions please do not hesitate to contact us.

Ken Feuerstein
Quality Manager
Zion Industries, Inc.

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