API 571 Certification (Corrosion & Materials) Practice Test

What aspect of carbon steels increases susceptibility to environmental stress cracking?

1. Higher chromium content

2. Low carbon levels

3. Heat treatment history

4. Presence of welds

The correct answer is: Heat treatment history

The susceptibility of carbon steels to environmental stress cracking is significantly influenced by their heat treatment history. The heat treatment processes can alter the microstructure of the steel, which in turn has a direct impact on the material's mechanical properties, including strength and ductility. For instance, different heat treatment methods such as quenching and tempering can create residual stresses within the material, leading to increased brittleness and a reduced ability to withstand stress in corrosive environments. Additionally, various cooling rates and subsequent tempering can lead to the formation of different phases within the steel, some of which may be more prone to cracking when exposed to specific environments. On the other hand, options like higher chromium content and low carbon levels generally relate more to corrosion resistance rather than specifically increasing susceptibility to stress cracking. While the presence of welds can introduce local stress concentrations and potential corrosive environments, heat treatment history remains a more direct influencing factor on susceptibility to stress corrosion cracking in carbon steels.