Anisotropy of micro-evolution and spall behavior of free-cutting steel containing bismuth under shock loading

Based on non-equilibrium molecular dynamics (NEMD) simulation, the effect of Bi in free-cutting steel containing bismuth on the overall mechanical properties of steel under high pressure was studied by piston shock method. Considering the complexity of real crystals, four different crystal orientations were selected. The results show that the peak impact stress in the Bi-containing model is the same as that in the perfect single-crystal Fe, but its strength is significantly lower than that of the perfect single crystal. Under shockwave loading, the (001) orientation exhibits a single-wave structure, while the (110), (111), and (112) orientations exhibit multi-wave structures. Analysis shows that elastic waves are reflected at the surface of the Bi particles, and the resulting shear stress activates the {112} <111> slip system around the Bi particles, leading to premature phase changes. During the fracture failure phase, the strength of the (001) crystal orientation is the highest. Regardless of the crystal orientation, cavities and defects always preferentially form inside the Bi particles. This study provides important insights for exploring the performance of Bi-containing free-cutting steel under extreme conditions and has significant implications for related production practices.

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