In nitrated parts, the origins of the fatigue cracks will occur at

Answer: Option B

Nitriding is a surface-hardening process that diffuses nitrogen into the surface, creating a hard, wear-resistant case with compressive residual stresses.

Fatigue crack initiation: Due to the compressive stresses at the surface, fatigue cracks are generally suppressed at the outer layer. Instead, they tend to originate just below the surface, where the protective effect of compressive stress is lower.

Why not surface: Although surface imperfections can sometimes cause cracks in practice, the theoretical and exam-oriented answer is that cracks start just beneath the hardened case.

Conclusion: From an exam perspective, the correct answer is Option B: Just below the surface.