API 571 Certification (Corrosion & Materials) Practice Test

Which material is primarily affected by temper embrittlement?

1. Stainless steel

2. 2.25Cr-1Mo steel

3. High-strength low-alloy steels

4. Carbon steels

The correct answer is: 2.25Cr-1Mo steel

Temper embrittlement is a phenomenon that primarily affects certain alloy steels, particularly those with a composition that includes chromium and molybdenum. 2.25Cr-1Mo steel, which is a low-alloy steel known for its high strength and toughness at elevated temperatures, is specifically susceptible to temper embrittlement under certain conditions, such as prolonged exposure to elevated temperatures. This susceptibility arises from the formation of embrittling microstructures as a result of the diffusion of certain elements (like phosphorus and some other impurities) during the tempering process. In 2.25Cr-1Mo steel, this results in a decrease in ductility and toughness, making the steel more prone to brittle fracture, particularly at lower temperatures. In contrast, while stainless steels, high-strength low-alloy steels, and carbon steels may experience other types of embrittlement or issues with temperature and processing, they are not as prone to temper embrittlement as 2.25Cr-1Mo steel. Thus, understanding the unique properties and behaviors of 2.25Cr-1Mo steel helps clarify why it is the choice that aligns with the question about materials affected by temper embrittlement.