Temper Embrittlement
A loss of impact toughness in low-alloy steels caused by prolonged exposure to or slow cooling through temperatures between 350 °C and 550 °C.
Temper embrittlement occurs in alloy steels when they remain in the critical temperature range for a longer time after welding or heat treatment. Impurity elements migrate to the grain boundaries and the material becomes brittle, even though there are no external signs. The problem only shows up under load or during subsequent machining – the structure then breaks without warning. When welding, you have to keep an eye on the cooling rate in the critical range and control the heat input so that the component passes through this range quickly. If you have the choice, use a steel that is less susceptible to this. For already welded parts, often only a heat treatment helps to get rid of the brittleness.