Evaluation of Dislocation Density and Dislocation Strengthening Mechanism in Ultra Low-Carbon Martensitic Steel

In ultra low-carbon Fe-18%Ni alloy with a lath martensitic structure, the effects of microstructure and dislocation density on the yielding and deformation behavior were investigated. The microstructure of the matrix became finer with decreasing austenite grain size but no difference was found in the yielding behavior up to 2% deformation. Dislocation density was constant independent of the microstructure and was estimated to be about 1.5 × 1015/m2. The dislocations that had been introduced by martensitic transformation formed a tangled dislocation cell structure within a lath and the amount of dislocation strengthening was determined by a critical stress that was required to make the tangled dislocations bow out. As a result, it was confirmed that the 2% proof stress of the steel used can be evaluated by adding the amount of dislocation strengthening to the friction stress. © 2024 The Society of Materials Science, Japan.