Total vs. Effective Case Depth

One of the benefits of induction hardening is the ability to selectively apply a surface hardness or case hardness to steel materials. The case hardness will allow the piece to have superior wear and strength characteristics at the surface, but allow the interior of the piece to remain flexible.

Case hardness is defined as the outer surface that has been made harder than the interior, or core. The term case depth refers to the depth of the case, or hardened layer of a piece of material. Case depth is typically measured as “total” or “effective”. The two terms are sometimes misunderstood, but are different and it is important to understand those differences.

The term total case depth refers to the depth of hardness where the hardened layer reaches the same hardness and properties as the base or core material. Total case depth is typically measured by sectioning the work piece and polishing and etching with an acid solution to reveal the depth of the hardened layer. The measurements can then be taken visually and measured using a calibrated eyepiece or scale to qualify the total depth.

The total case depth definition refers to the depth where a hardness measurement drops below a specified point. The hardness will then continue to decline until the “total” case depth is reached. The hardness at the effective depth is specified based on the characteristics required and the hardenabiltiy of the material. For example, high carbon steel that may have a minimum surface hardness of 60 HRc may call for an effective case depth of 0.120” at 50 HRc. The method of determining effective case depth involves sectioning the piece and polishing the surface. Measurements of the hardness are then taken at regular depth intervals until the hardness drops to the specified range. This distance from the surface is then measured to determine the effective depth.

At Zion Industries we work with our customers to make sure that we understand their requirements, and when necessary can help clarify the requirements that may be on a third party print. It is important to understand that the measurement method called for on the print was established at the engineering stage, and the design intent must be followed as the method of measurement is determined.

Lou Ghinga
Estimator
Zion Industries, Inc.