API 571 Certification (Corrosion & Materials) Practice Test

Which of the following is susceptible to brittle fracture?

1. New Carbon Steel

2. 400 series Stainless Steel

3. Stainless Steel with high nickel content

4. Nickel Based Alloys

The correct answer is: 400 series Stainless Steel

Brittle fracture is a failure mode characterized by a sudden, catastrophic break with little to no plastic deformation occurring before the failure. It typically occurs in materials that have limited ductility and a tendency to fracture under stress, especially at lower temperatures. The 400 series stainless steels are primarily ferritic and martensitic stainless steels. These materials can exhibit brittle fracture especially in conditions of low temperature or when subjected to stress. The microstructure of 400 series stainless steels contributes to this susceptibility because they are often hardened through martensitic transformations, which can create residual stresses that make them more prone to brittle failure. In contrast, new carbon steels usually have better ductility and toughness when compared to high-carbon materials that are specifically treated for hardness. Stainless steels with high nickel content are designed to enhance toughness and corrosion resistance and typically exhibit more ductile behavior, especially at lower temperatures. Nickel-based alloys are also known for their toughness and resilience against brittle fracture due to their face-centered cubic (FCC) structure, which provides enhanced ductility. Thus, among the options, 400 series stainless steel is most susceptible to brittle fracture, particularly under specific environmental conditions of temperature and stress, making it the correct choice.