Mode of cracking in martensitic stainless steels under hot caustic: which mode?

• A. Intergranular
• B. Transgranular
• C. Transcrystalline
• D. Mixed

Answer: (B)

Cracking in martensitic stainless steels under hot caustic tends to be transgranular because the brittle martensitic matrix, when exposed to hydrogen from the caustic environment, breaks within the grains rather than along grain boundaries. Hydrogen embrittlement reduces the lattice cohesion, so cracks propagate through crystallographic planes inside the grains, producing a transgranular (cleavage-like) fracture path. Intergranular cracking would require grain boundary weakening conditions (like sensitization in some stainless steels), which are not the typical driver for martensitic types in hot caustic. So the crack path is through the grains, i.e., transgranular.