SAE J423
Methods of Measuring Case Depth
Recommended practice defining total and effective case depth for carburized, carbonitrided, cyanided, nitrided, induction- and flame-hardened steel parts and describing the chemical, mechanical (hardness traverse), visual and metallographic methods for measuring them.
What SAE J423 specifies
SAE J423 is the North American reference for what "case depth" means and how it is measured. It defines total case depth as the distance from the surface to where the case can no longer be distinguished from the core and effective case depth as the distance to a specified hardness — 50 HRC (about 513 HV / 542 HK500) for carburized and carbonitrided cases, and for induction- or flame-hardened parts a hardness that depends on the steel's carbon content: 35 HRC for 0.28–0.32 % C, 40 HRC for 0.33–0.42 % C, 45 HRC for 0.43–0.52 % C and 50 HRC for 0.53 % C and over. Measurement methods are the chemical method (incremental turning and carbon analysis), the mechanical method (Knoop or Vickers microhardness traverse, or superficial Rockwell on a taper section, on a perpendicular cross-section), the visual method (macro-etch of a fractured or polished section for shop control) and the microscopic method (etched metallographic section).
Tests and the drawing call-out
Tests the document imposes
- Mechanical method: microhardness traverse (ASTM E384, HK or HV, typically 500 gf) at fixed increments on a perpendicular section
- Mechanical method: superficial Rockwell (HR15N / HR30N) traverse on a taper-ground section
- Chemical method: carbon gradient by machining successive layers and combustion analysis
- Visual method: fractured or macro-etched cross-section (shop check of total case)
- Microscopic method: etched metallographic section (ASTM E3 / E407) at known magnification
How to cite it
Drawing call-out
EFFECTIVE CASE DEPTH 0.030–0.045 IN (TO 50 HRC) PER SAE J423 MECHANICAL METHOD, MEASURED AT LOCATION SHOWNAngle brackets mark the choices the drawing must make; every finish page shows a completed example.
Heat treatments specified to SAE J423
| Treatment | Role | Cost |
|---|---|---|
Carbonitriding diffuses both carbon and nitrogen into low-carbon steel in the austenitic range, then quenches and tempers the surface to martensite. | Test method | $$ |
Carburizing diffuses carbon into low-carbon steel at austenitizing temperature, then quenches and tempers the enriched surface into a hard martensitic case. | Test method | $$$ |
Flame hardening rapidly austenitizes selected steel surfaces with an oxy-fuel flame and immediately quenches them to martensite. | Test method | $$ |
Gas nitriding diffuses nitrogen into finished ferrous parts below the transformation temperature, producing a hard compound layer and diffusion zone without quenching. | Test method | $$$$ |
Induction hardening uses an alternating magnetic field to austenitize selected steel surfaces, followed immediately by quenching. | Test method | $$ |
Plasma nitriding uses a glow discharge to clean, heat, and diffuse nitrogen into ferrous surfaces. | Test method | $$$$ |
SAE J423 — frequently asked
Effective or total case depth — which should I specify?
Effective depth (to 50 HRC for carburized parts) is what carries load and what a hardness traverse measures repeatably; total depth includes the low-carbon tail and is useful mainly for process control or for nitrided cases. Most drawings specify effective depth after finish grinding.
Why different hardness thresholds for induction hardening?
A 1045 surface hardened by induction reaches 58–62 HRC but its core carbon is about 0.45 %, so the case–core transition is defined at 45 HRC; a 4140 part (0.40 % C) uses 40 HRC. Using 50 HRC for every steel would understate the depth on medium-carbon grades.
How is the traverse done?
The part or a coupon is sectioned perpendicular to the surface, mounted and polished; Knoop or Vickers indentations at 500 gf are placed at steps of about 0.05–0.1 mm from just below the surface into the core, and the depth where the curve crosses the threshold is the effective case depth. Taper sections with superficial Rockwell are used on thicker cases.
Does J423 cover nitrided cases?
It includes nitrided cases in its definitions and methods, but nitrided depth is normally measured by traverse to a hardness a fixed amount above the core (ISO 18203 uses core plus 50 HV 0.5 for NHD) rather than to 50 HRC; state the threshold explicitly on nitrided drawings.
SAE J423 is copyrighted by SAE International. This page explains the document so a drawing can be read; it does not reproduce the standard. Purchase the current edition from the publisher. Official source ↗