Which type of environmental cracking involves crack growth due to corrosion and cyclic loading?

• A. Stress corrosion cracking
• B. Hydrogen embrittlement
• C. Corrosion fatigue (CF)
• D. Hydrogen-induced cracking

Answer: (C)

The main concept is that crack growth driven by both a corrosive environment and cyclic loading is corrosion fatigue. In this mechanism, the repeated opening and closing of the crack under fluctuating stress continually exposes fresh metal to the environment, and the environment accelerates material removal or hydrogen interactions at the crack tip during each tensile peak. This combination speeds up crack propagation beyond what either corrosion or fatigue would cause alone, so failure occurs under cyclic loading in a corrosive setting.

Stressing that this differs from stress corrosion cracking, which can progress under a sustained, static tensile load in a corrosive environment, helps separate the ideas. Hydrogen embrittlement and hydrogen-induced cracking involve hydrogen effects on the metal's lattice or microstructure, often under hydrogen exposure, and are not defined by the necessity of cyclic loading.