Microstructural features of cold-rolled carbon steel evaluated by X-ray diffraction line profile analysis and their correlation with mechanical properties

Abstract

Line profile analyses of cold-rolled carbon steels were conducted to evaluate microstructural features such as dislocation density, crystallite size, and M values. After the samples were subjected to 40% coldrolling, dislocation density increased from 7 × 1013 m-2 to 2 × 1015 m-2 and crystallite size decreased from 155 nm to 35 nm. The component ratio of screw and edge dislocations was approximately 1:1, as determined from the evaluation of the q values. The M value that indicated interaction of dislocations substantially decreased during the initial stage of cold-rolling, which means interaction of dislocations becomes strong. Proof stress, hardness, and tensile strength were increased by the cold-rolling process. Furthermore, the ratios between proof stress and hardness were initially 2 and increased to approximately 3. The correlation between the microstructures and the mechanical properties was demonstrated according to the Bailey-Hirsch relationship between flow shear stress and dislocation density. Variations in the proof stress and hardness as a function of the square root of dislocation density indicated that the work-hardening of the material is affected by not only the total amount of dislocations but also other factors, such as crystallite size and arrangement of dislocations. © 2014 ISIJ.