Summary
Temper embrittlement is a loss of low temperature ductility after prolonged exposure to high temperatures exhibited by specific low alloy ferritic steels, containing high levels of residual elements. Temper embrittlement particularly affects 2.25Cr-1Mo and 3Cr-1Mo steels. More highly alloyed (e.g., 5Cr-0.5Mo and 9Cr-1Mo) and less highly alloyed (e.g., 1Cr-0.5Mo and 1.25Cr-0.5Mo) steels are less susceptible to temper embrittlement.
The loss in ductility due to temper embrittlement is apparent only at temperatures below approximately 150°C (300°F).