Evaluation of Dislocation Accumulation and Work Hardening in Ferritic Steels Containing Plastically Deformable Soft Particles

Abstract

The work hardening behavior and the change in dislocation density during tensile deformation were investigated in ferritic steels containing hard carbide/oxide particles or soft Cu particles with different volume fraction and particle diameter. The magnitude of work hardening were significantly different between both types of steels. In the hard particle dispersion steels, the results of dislocation density measurements agreed well with the theory estimating GN dislocation density proposed by Ashby. On the other hand, in soft Cu particle dispersion steels, the increase in dislocation density during tensile deformation was relatively small compared with the hard particle dispersion steels, resulting in the smaller work hardening rate. This is due to the plastic deformation of Cu particle itself leading to the partial accommodation of the shear strain given in the existence area of particle. A quantitative evaluation of accumulation of GN dislocations was attempted in the soft Cu particle dispersion steels by modifying Ashby's theory using ‘particle plastic accommodation parameter’. With this modification, it was found the work hardening behavior in the early stage of tensile deformation of ferritic steels could be systematically explained by the accumulation of GN dislocations regardless of the stiffness of dispersion particles.