Flame and induction hardening have significant advantages over heat treatment methods involving through hardening because only the specific area requiring hardening is affected – general problems of distortion are minimized and design restrictions apply only to the heat-affected zone.
Designing for flame or induction hardening is similar to designing for other heat treatment processes. The ideal shape is one where heat is absorbed (during the heating cycle) and transmitted (during the quenching cycle) at the same rate across the entire surface being hardened. This may be difficult to achieve in practice but these simple guidelines may help (these apply only in the heat affected zone).
- Avoid large differences in section thickness.
- Avoid sharp corners that may create notch effects – use fillet radii and chamfer holes.
- Keep the shape simple, uniform and symmetrical.
- Do not place holes too close to the hardened surface (about 20mm min) – drill after hardening if in doubt.
- Allow for grinding or final machining of bores in components where the bore is large relative to the OD.
It is always advisable, when making large batches, to produce, harden and test a small sample batches.