SH Surface hardening (general)
Surface hardening (general) · Tratamiento térmico · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Surface harden per procedure P-042” states a surface hardening (general) requirement.
What controls
Generic label covering treatments whose purpose is to harden only the outer layer of the part while leaving the core tough: carburizing, nitriding, nitrocarburizing, induction hardening and flame hardening. When a drawing uses this term on its own, it is not specifying anything verifiable: you need to know which process, what surface hardness, what case depth and to which hardness criterion that depth is measured. The processes are not interchangeable: they differ in distortion, case thickness, whether they allow subsequent machining and which steels they work on.
How to verify
Verification depends on the specific process, but the scheme is always the same: surface hardness with a hardness tester using a load suited to the case, case depth by metallography or macro-etching on a witness coupon from the batch, and core hardness on the cross-section. All of it backed by the heat treatment certificate, which must identify the process, the batch and the results obtained.
Common mistakes when interpreting it
- Taking “surface hardening” as a complete specification: without process, hardness and depth there is nothing to verify.
- Substituting one process for another because the shop has it more readily available: distortion and case thickness change completely.
- Applying the same hardness measurement method to a carburized case and to a nitrided layer.
How to get it in the workshop / if it comes out of tolerance
If you receive a drawing that just says “surface hardening”, get it clarified before planning: the choice determines the order of operations, the stock allowance and whether the part can be finished before or after heat treatment. Nitriding is done on a finished part and does not allow grinding; carburizing requires stock and subsequent grinding. Also check which areas are excluded and how they are masked.
The first step with a nonconformance is to confirm which process was actually applied and which method was used to measure: a large share of rejections on hardened cases are measurement errors, mostly from using high loads on thin cases. If the chosen process is not compatible with the material or the manufacturing sequence, the problem is one of definition and must be resolved by engineering, not by repeating the treatment.
Other symbols in Heat treatment
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