Understanding the surface grain refinement mechanisms for type 316L stainless steel during machining process via advanced microstructure characterization

Microstructural investigation of the surface machined zone of a type 316 L stainless steel was performed via complementary techniques to understand the associated microstructure formation and grain refinement mech-anisms. The results show that the surface machined zone of 316 L has a gradient microstructure. The topmost thin region has a nano-crystalline microstructure with dislocations, nano-twins and stacking faults. The fine -grains are preferentially [101]-orientated along the machining direction. The nano-crystalline region is sug-gested to be formed as a result of temperature promoted slip and lattice rotation rather than recrystallization. The region beneath the nano-crystalline layer has large amount of mechanical twins and twin intersections. Martensite was not identified in the machined layer. The grain refinement mechanisms during machining process for 316 L are discussed.