Morphology of cu particle during higherature deformation in cu-added ferritic stainless steels

In this study, Cu-added ferritic stainless steel sheets were investigated to understand the influences of Cu contents on the higherature strength during the higherature deformation. Higherature proof stress at 700∼900°C was improved greatly by addition of more than 1% of Cu. In the case of static aging at 900°C, the rod-shaped e-Cu particles satisfed the K-S orientation relationship with the a matrix, but spherical-shaped e-Cu particles without specifc orientation relationship started appearing during the tensile deformation at 900°C. Similarly, the spherical-shaped and fne e-Cu particles were observed during the thermal fatigue process in the temperature range from 200°C to 700°C with a 50% restriction ratio. During the observation using the higherature in-situ TEM straining, it was clarifed that the e-Cu particles were divided by dislocation shearing and parts of them were found dissolved. According to the LSW theory, it was suggested that the microstructure with fne and spherical-shaped e-Cu particles was formed by the repetition of dissolution and precipitation during the higherature deformation.