Effect of Dislocation Density on σ Phase Precipitation Behavior in KA-SUS304J1HTB

The effect of dislocation density on the σ phase precipitation behavior in KA-SUS304J1HTB was investigated. The specimen was pre-strained by room-temperature uniaxial tensile test and subjected to ageing at 700℃. The number density and area fraction of the σ phase after ageing increased with the amount of pre-strain. On the other hand, the pre-strain had no significant effect on the average σ phase diameter. Electron backscatter diffraction (EBSD) analysis revealed that the geometrically necessary dislocation (GND) density was increased with the amount of pre-strain. Moreover, the GND density of the pre-strained specimens showed little change after the ageing. The EBSD analysis also revealed that the GND density was significantly higher around the grain boundaries compared to the grain interior. Using the GND density around the grain boundaries in the pre-strained specimens, the change in the number density of the σ phase during ageing was calculated based on the classical nucleation theory. The calculated number density of the σ phase showed good agreement with the experimental results. This result implies that the effect of the pre-strain on the number density of the σ phase after ageing can be explained by the change in GND density around the grain boundaries.