Embrittlement of quenched-and-tempered alloy steels, especially nickel-chromium grades, caused by phosphorus, antimony, tin and arsenic segregating to prior austenite grain boundaries during exposure around 375 to 575 °C. Hardness is unchanged, but Charpy impact energy falls and the transition temperature rises. It is avoided by tempering above the range and cooling fast, and by molybdenum additions. A separate problem, tempered martensite embrittlement, hits around 260 to 370 °C.
Charpy values collapsed but hardness is dead on, smells like temper embrittlement, find out how slow they cooled after temper.
When a part passes hardness and fails Charpy, the first question is what temperature it was tempered at and how it cooled.
Also heard as
- temper brittleness
- reversible temper embrittlement
- two-step temper embrittlement
Related terms
Tempering
Reheating hardened steel below its lower critical temperature to trade some hardness for toughness.
Q&T
Quench and temper: hardening steel by quenching, then tempering it back to a set strength and toughness.
Grain size
The average size of the crystals in a metal, usually reported as an ASTM number where higher means finer.