Calculate effective case depth from hardness-profile interpolation, estimate diffusion depth, or reverse-solve process time in millimeters or inches.

Method and solve target
Use the two adjacent measured profile points that bracket the threshold.
Use one hardness scale consistently (for example, HRC or HV).

Related Calculators

Effective Case Depth Formula

The following formula estimates effective case depth by assuming the hardness drops linearly from the surface hardness to the core hardness across the total case depth (a common simplification when you do not have a full hardness traverse).

Dₑ = Dₜ × (Hₛ - Hₑ) / (Hₛ - H_c)

Variables:

  • D_e is the effective case depth
  • D_t is the total case depth
  • H_s is the surface hardness
  • H_c is the core hardness
  • H_e 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)

To estimate the effective case depth under the linear-profile assumption, multiply the total case depth by the fraction of the hardness drop from surface to the effective criterion relative to the total hardness drop from surface to core.

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 50 HRC or approximately 550 HV, 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, determine the total case depth (D_t).
  2. Next, determine the surface hardness (H_s).
  3. Next, determine the core hardness (H_c).
  4. Next, choose the effective hardness criterion (H_e) specified by your standard or design requirement.
  5. Finally, calculate the Effective Case Depth using the formula D_e = D_t × (H_s − H_e) / (H_s − H_c) (linear-profile estimate).
  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.

Total Case Depth (D_t) = 5 mm

Surface Hardness (H_s) = 700 HV

Core Hardness (H_c) = 300 HV

Effective Hardness Criterion (H_e) = 550 HV