Calculate effective case depth from two hardness-traverse readings at the ISO 2639 550 HV limit or your own, or estimate depth or time from k√t.

Prefilled with the ISO 2639 limit of 550 HV; enter 50 for SAE J423 at 50 HRC. Use one hardness scale for all three values.

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Effective Case Depth Formula

Estimate the threshold crossing by interpolating between two adjacent measured hardness-depth points that bracket the specified hardness. The full traverse and applicable test specification determine effective case depth; a whole-layer linear assumption is not a substitute for those measurements.

xe = x1 + (x2 − x1) · (H1 − He) / (H1 − H2)

Variables:

  • De is the effective case depth
  • x1 and x2 are the adjacent shallower and deeper measured depths
  • H1 is hardness at the shallower point
  • H2 is hardness at the deeper point
  • He is the effective hardness criterion (the hardness value used to define “effective case depth,” such as 50 HRC or 550 HV, depending on the specification)

The threshold must lie between the two measured hardness values, on the same scale and under compatible test conditions. The alternative scenario modes use d = k√t and t = (d/k)² with hours and a process-calibrated depth factor k; k is not a diffusion coefficient, and these scenarios do not certify a treatment.

What is Effective Case Depth?

Effective case depth is the depth from a hardened surface at which the material’s hardness reaches a specified criterion (a specified hardness value or other requirement set by a standard or engineering specification). It is used to ensure that the hardened layer is deep enough to provide wear resistance and fatigue strength while the core remains tougher to better resist impact and cracking. In practice, effective case depth is determined from a hardness traverse and interpolation to the specified criterion (for example, many carburized steel specifications use a criterion such as a specified HRC value or a specified HV value; do not assume those scales are interchangeable, but the exact value depends on the standard and application).

How to Calculate Effective Case Depth?

The following steps outline how to calculate the Effective Case Depth.

  1. First, identify adjacent measured depths x1 and x2 that bracket the required hardness.
  2. Next, enter H1 at x1.
  3. Next, enter H2 at x2 on the same hardness scale.
  4. Next, choose the effective hardness criterion (He) specified by your standard or design requirement.
  5. Finally, interpolate xe = x1 + (x2 − x1) × (H1 − He) / (H1 − H2).
  6. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Adjacent measured depths x1 = 0.8 mm and x2 = 1.2 mm

Hardness H1 = 58 HRC

Hardness H2 = 46 HRC

Specified threshold He = 50 HRC; interpolated crossing is approximately 1.066667 mm.