T Tempering
Tempering · Tratamiento térmico · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Temper 180 °C · 58-62 HRC” states a tempering requirement.
What controls
Heating after hardening, below the transformation temperature, that reduces the brittleness and stresses of the hardened structure at the cost of some hardness. It is the operation that sets the final hardness of the part: hardening gives the maximum possible and tempering brings it down to the drawing range. A hardened, untempered steel is brittle and can break from an impact; that is why tempering is not optional even if the drawing only cites the final hardness.
How to verify
Hardness tester on the finished part or on a witness coupon from the same load, with several indentations spread out. The heat treatment certificate must record tempering temperature and time along with the hardness obtained. If the drawing also requires mechanical properties (tensile strength, yield strength, impact toughness), those come from coupon tests, not from the hardness tester.
Workshop guideline values
- General
- Low-temperature tempers that keep hardness high, typical of tools and wear parts.
- Accuracy
- Intermediate tempers to balance hardness and toughness in machine parts.
- High precision
- Double tempering with a narrow hardness range and per-load certification on critical parts.
Guidance only: the drawing's value always wins.
Common mistakes when interpreting it
- Believing tempering is an optional step because the drawing only mentions hardening.
- Trying to raise a low hardness with more tempering: tempering can only lower it.
- Measuring hardness immediately after quenching and drawing conclusions before tempering.
How to get it in the workshop / if it comes out of tolerance
When the drawing gives a hardness range after hardening, what is actually being controlled is the tempering. Higher tempering temperatures lower hardness and raise toughness, and that trade-off is what the heat treater works with to hit the range. If the part must withstand impact, a high hardness range is not always better. After tempering, the part is dimensionally stable for grinding.
Hardness above range: insufficient tempering or the temperature was too low; the part can be retempered at a somewhat higher temperature. Hardness below range: it cannot be recovered by tempering; the part must be re-hardened and tempered from scratch. If the part fails in a brittle manner despite being on hardness, check whether tempering was done in a temperature range unfavorable for that steel, which is the heat treater's decision and must be recorded on the certificate.
Related symbols
Other symbols in Heat treatment
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