H Hardening / quenching
Hardening / quenching · Tratamiento térmico · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Harden to 58-62 HRC · oil quench” states a hardening / quenching requirement.
What controls
Cycle of heating above the transformation temperature followed by rapid cooling in a quenchant (water, oil, polymer, gas or salts) to obtain a hard structure in steel. On the drawing it usually appears as a process note accompanied by an enforceable result: the hardness range. The two must be kept separate: the heat treater carries out the process, but what is accepted or rejected at receiving inspection is the result (hardness and, where applicable, depth), measured in the area indicated on the drawing. A low-carbon steel will not harden no matter how much the drawing asks for it: hardenability comes from the composition, not from the note.
How to verify
Hardness tester on the scale specified on the drawing, on a clean, flat surface with the part firmly supported; several indentations in the functional area, not just one. If decarburization or scale must be removed before measuring, it is done with light grinding that does not heat the area. On parts that cannot be marked, witness coupons treated in the same load are used, and the result is backed by the heat treatment certificate, which must identify the load and the cycle.
Workshop guideline values
- General
- On the order of 45–55 HRC in commonly used tool and hardenable steels.
- Accuracy
- On the order of 58–62 HRC in wear parts and tools, with a tight range and subsequent grinding.
- High precision
- Narrow ranges, 2–3 HRC points wide, with load control, witness coupon and certificate.
Guidance only: the drawing's value always wins.
Common mistakes when interpreting it
- Reading the hardening note as the requirement and forgetting that what can be verified is the resulting hardness in the indicated area.
- Specifying hardening for a steel whose composition does not allow it and expecting tool-steel hardness.
- Finishing before heat treatment and discovering the part has distorted with no stock left to correct it.
How to get it in the workshop / if it comes out of tolerance
Hardening moves the part: it distorts, grows and can crack if it has sharp corners or abrupt section changes. Plan machining in two stages, leaving grinding stock on the tight dimensions and heat treating before finishing. After hardening the part is hard to machine: any forgotten operation (a hole, a thread, a chamfer) becomes expensive or impossible. Also check that the drawing specifies the quenchant, because distortion and cracking risk depend on it.
Hardness below range: first check the material (heat and composition) and then the cycle; in thick sections it is common for the core not to reach hardness even though the surface does. Cracks after quenching: almost always geometric stress raisers (sharp corners, abrupt section changes, holes close to an edge) or an overly severe quenchant. Excessive distortion: split the machining, stress relieve before hardening, and leave enough stock to correct by grinding.
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