Which type of steel is susceptible to temper embrittlement?

Temper embrittlement primarily affects low alloy steels, especially those that contain certain elements such as chromium and molybdenum. This phenomenon typically occurs when these steels are exposed to elevated temperatures for extended periods, particularly during processes like tempering after hardening.

During the tempering process, the steel's microstructure changes, and certain atom diffusion occurs which can lead to the segregation of these alloying elements at grain boundaries. This segregation results in embrittlement, making the steel less ductile and more susceptible to cracking under stress, especially in the heat-affected zones of welds or in service conditions.

Understanding that higher chromium and molybdenum content increases the risk, low alloy steels are particularly vulnerable compared to other steel types, such as stainless steels and tool steels. Stainless steels often have better corrosion resistance and typically do not exhibit the same level of susceptibility to temper embrittlement due to their composition, while tool steels are designed to maintain high hardness and toughness, making them less prone to such embrittlement at standard operating temperatures and conditions.