Mechanism for welding liquation cracking in a boron containing 9% Cr martensitic stainless steel

In the present study, welding thermal simulation was carried out on a boron containing 9% Cr martensitic stainless steel and a liquation cracking tendency was found. The steel fractured intergranularly at 1350 ℃ with tension strain 0.5%, and a large number of eutectic microstructures were found on the fracture surface. Constitutional liquation of large sized interdendritic Laves phase, which had already existed in as received condition, was responsible for the liquation cracking. Welding provided a non-equilibrium heating process in which the released alloy atoms such as Mo by dissolving Laves phase at rapid heating rates could not diffuse sufficiently in the matrix γ-Fe. Matrix adjacent Laves phase became enriched in Mo, and eutectic reaction occurred between Laves phase and matrix, leading to localized liquation. Liquation cracking occurred by the combination of liquid and tension strain at high temperatures. Moreover, a large number of boron atoms released by dissolving Laves phase might also contribute to the liquation cracking tendency.