Study on the formation of micro-voids during ductile fracture

In this work, the formation of micro-voids for ductile fracture has been discussed with regards to the classical nucleation theory from the phase transformation in 20CrNi2Mo steel. The differences in them were determined based upon the driving force and the resistance. In terms of tensile load, the driving force was the energy of tensile load before necking, while the resistance was the surface energy from the formation of mass of micro-voids, as determined by the fracture toughness instead of the phase transformation. Finally, the relationship between the formation of micro-voids and the macroscopic properties was discussed. The results illustrated that the formation of micro-voids depended on the elastic-plastic energy and on the yield strength represented by r* (the critical formation radius) and $\Delta G^{\ast }$ (the critical formation energy). These results were confirmed from r ₁* (with the experiment) and r ₂* (with the calculation). The work provided a novel way to study the relationship of micro-parameters and macro-properties. In addition, it was found that the critical formation diameter (2r*) of micro-voids was close to the width of martensite lath (d _l). (paper)