ISO 2639 — determination of effective case depth after carburizing
Effective versus total case depth, the 550 HV 1 default limit hardness, where on a fastener the traverse is taken, and the exact wording that makes a case-depth requirement unambiguous.
| Related service | Heat Treatment |
|---|---|
| Testing and measurement | ISO 2639 |
| Also written as | ISO 2639:2002, DIN 50190-1, SAE J423, ASTM E384 (microhardness) |
| Updated |
Scope — and what it does not cover
ISO 2639 defines how the effective depth of hardening of carburized and hardened steel is measured: a microhardness traverse on a prepared cross-section, from the surface inwards, with the effective case depth (CHD) reported as the distance at which the hardness falls to a defined limit hardness — 550 HV 1 by default. It is a MEASUREMENT standard. It does NOT tell you what case depth your part needs, does not carry the same limit hardness across to nitrided layers, and does not replace the drawing, which must state the depth, the limit hardness if it differs, and where on the part the measurement is taken.
Standards are copyrighted documents. We explain scope, intent and practical application in our own words; obtain the current edition from ISO, ASTM, DIN or your national standards body.
What actually bites in production
- 1Effective case depth and total case depth are different numbers. Effective depth stops at the limit hardness, total depth runs to the unaffected core. "Case depth 0.3 mm" without saying which is ambiguous.
- 2The default limit hardness is 550 HV 1. When the core is hard — roughly 450 HV and above — the default stops being meaningful and a different limit hardness has to be agreed and written down.
- 3Measurement position matters on a fastener. Case depth at a thread crest, at the root and on the shank genuinely differ, because carbon diffuses from every exposed face.
- 4Preparation is part of the result: the section must be perpendicular, mounted and polished without rounding the edge, and the indentation spacing rules of the hardness standard still apply.
- 5The traverse is destructive, so case depth is a lot-sampled property, verified on sacrificial parts or on process coupons that ran with the load.
- 6Deeper is not better. On a small fastener an excessive case reduces core toughness and raises the risk of brittle failure.
Reference tables
Scroll the table sideways on a narrow screen.
Effective case depth — reference values
| Item | Reference value |
|---|---|
| Default limit hardness | 550 HV 1 |
| Test force for the traverse | HV 1 (9.807 N) |
| Typical indentation spacing | ≈ 0.1 mm |
| Designation written on a drawing | CHD 550 HV 1 = 0.20–0.35 mm |
When the core hardness approaches or exceeds the default limit hardness (roughly 450 HV and above), a different limit hardness must be agreed and written on the drawing.
Values on this page are typical industry figures that depend on the part, the coating system and the governing specification. They are not guarantees. Always confirm against the edition in force and the customer drawing — this page does not replace either.
What to write on the drawing or PO
- The effective case depth range in mm with the limit hardness — "CHD 550 HV 1 = 0.20–0.35 mm" is unambiguous.
- Where it is measured: thread flank, root, crest, shank or coupon, with a sketch if the geometry is awkward.
- The required surface hardness and core hardness, separately from the case depth.
- Sample size per lot and whether a hardness traverse report is required with the delivery.
What goes wrong when it is cited loosely
- "Case depth 0.2–0.4" with no limit hardness and no location. Three suppliers will report three different numbers, all of them correctly.
- Applying the 550 HV 1 default to a part whose core is already above it.
- Measuring at a thread crest and comparing the result against a specification written for the root.
- Assuming a deeper case is always safer.
Defects this standard gets cited on
Steel grades where this decision is made
Part types we process to this
Frequently asked questions
What case depth is normal for small carburized fasteners?+
Typical effective case depths on small parts run from roughly 0.1 mm on thin self-tapping screws to around 1.0 mm on larger case-hardened items, but the number belongs to the part and its drawing, not to a general table. Send the drawing and we will confirm what is achievable.
Do you provide a hardness traverse report?+
Our laboratory measures hardness and case depth by microhardness traverse. Where the order calls for it, results are reported per lot with the test conditions stated.
Effective or total case depth — which does my customer mean?+
Ask, and get it in writing. In most automotive and fastener drawings it is effective case depth at 550 HV 1, but that assumption is exactly the kind that produces a rejected first article.
Values on this page are typical industry figures that depend on the part, the coating system and the governing specification. They are not guarantees. Always confirm against the edition in force and the customer drawing — this page does not replace either.
Related standards
Other standards in this reference
Send the drawing and let us check it against this standard
Send the drawing or the specification line as it is written today, the property class or coating requirement, the thread and tolerance class, and the part itself if you have one. We will tell you which lines are processable as written, which are arithmetically impossible on that thread, and what has to be added before the requirement can be quoted, inspected and defended.
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