Abstract: Dislocation densities in 20CrMnTi steel under different sizes of strain were determined exactly by X-ray diffraction method and a new profile analysis theory. The relation of strain and dislocation densities was analyzed. The results show that the increase of dislocation density is accompanied by the increase of deformation amount. The dislocation density has lower value when the steel is annealed. TEM tests prove that 20CrMnTi become ferrite and pearlite after annealing. Intragranular dislocation appears as zigzag dislocation line and comes into being cell structure with the appearance of twin crystals after deformation. Cell structure improves the strength of steel greatly.

Key words: 20CrMnTi steel, X-ray diffraction, dislocation densities, crystal structure, dislocation mode