Segregation and precipitation of carbon in the vicinity of dislocations during strain aging in low carbon steels

Segregation and precipitation behaviour of solute C in the vicinity of dislocations during strain aging was investigated by internal friction (IF) measurements, 3-dimensional atom probe (3D-AP) analysis, and TEM observations. IF measurement has indicated that approximately 3-6 C atoms per atom plane segregated along dislocation after straining. On the other hand, smaller amount of C segregation, 1.3 atoms per atom plane, along a dislocation after aging at 17O0C was found by 3D-AP analysis. The distribution of C atoms after aging appears to show C atoms has segregated to dislocation core with strong interaction, whereas C atoms interact weakly with dislocations before aging. It was confirmed that iron carbide plays an important role on strain aging behaviour in low carbon (LC) steels containing more than several wt. ppm of initial solute C. During a strain aging at 170"deg;C, the nucleation kinetics and distribution of iron carbides were observed to be affected by an initial dislocation density, due to the preferential precipitation of the carbides on dislocations. The reason for the pre-strain dependence on strain aging behaviour in the LC steels seems to be well explained as the effect of dislocations on nucleation kinetics and distribution of iron carbides.