IH Induction hardening
Induction hardening · Tratamiento térmico · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Induction harden 55-60 HRC · toothed area” states a induction hardening requirement.
What controls
Localized surface hardening: an induction coil heats only the area of interest to transformation temperature, which is then rapidly quenched, leaving that area hard over an untreated core. The drawing must define the hardened zone, the required hardness and the case depth. It is a highly repeatable process once set up, but heavily dependent on tooling: the coil and its path are specific to each part.
How to verify
Surface hardness with a hardness tester at several points along the hardened zone, including the ends, which is where it usually drops. The actual depth and extent of the case are determined by metallographic sectioning of a part from the run, or by macro-etching the section, which visually reveals how far the hardening reached. Subsequent parts are controlled by machine parameters and surface hardness.
Workshop guideline values
- General
- Case depths on the order of 1–3 mm on raceways and bearing areas of machine parts.
- Accuracy
- Case depths on the order of 1–2 mm with hardness and zone extent controlled part by part.
- High precision
- Case profile verified by macro-etch and hardness in a narrow range, with dedicated tooling.
Guidance only: the drawing's value always wins.
Common mistakes when interpreting it
- Assuming the hardened zone has a sharp edge: the transition is gradual and the drawing must state where it may fall.
- Grinding afterward without accounting for the abrasive removing part of the case.
- Checking hardness only in the middle of the treated zone, which is exactly where it never fails.
How to get it in the workshop / if it comes out of tolerance
Widely used on bearing raceways, gear teeth, cams and bearing areas. Because only one area is heated, the part distorts less than with through-hardening, but it does distort: leave grinding stock in the treated zone. The transition between hard and soft zones is gradual and the drawing usually limits where it may fall: it is not a clean boundary. Any subsequent machining in the treated zone is done with abrasives, not with a cutting edge.
Low hardness at the ends of the treated zone: this is the typical defect, corrected by adjusting the coil, the scan speed or the overlap. Quench cracks: overly severe quench or geometry with stress raisers (keyways, holes) inside the treated zone. Hardened zone shorter or longer than specified: tooling or program, not material. Distortion: grind afterward, leaving enough stock without eating through the case.
Related symbols
Other symbols in Heat treatment
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