Stress corrosion cracking is most likely to occur in which scenario?

• A. In any metal component that is completely free of tensile stress.
• B. Only in magnesium parts.
• C. Only in castings with no holes.
• D. In any metal component that is continually under tensile stress; especially near holes in castings with pressed-in bushings.

Answer: (D)

Stress corrosion cracking happens when a metal is simultaneously exposed to a corrosive environment and subjected to tensile stress. The crack can grow slowly under that sustained load, especially where the metal experiences a local concentration of stress or a crevice.

The most likely scenario is a component that is continually under tensile stress, with a stress concentrator such as a hole in a casting that has a pressed-in bushing. The hole concentrates stress and the area around the bushing can trap corrosive solutions, creating a crevice environment that promotes crack initiation and propagation under the tensile load.

If there’s no tensile stress, SCC doesn’t occur; restricting factors like using magnesium alone or castings with no holes remove the primary conditions that accelerate SCC, even though any metal under corrosive conditions and tensile stress can be susceptible in the appropriate environment.