Effect of Chromium Addition on the Coarsening of Cu-particle in Ferritic Stainless Steels

摘要

Coarsening of Cu-particles in 11.4%Cr-1.48%Cu (11Cr steel) and 23.7%Cr-1.48%Cu (24Cr steel) ferritic stainless steels were investigated mainly using transmission electron microscopy and energy dispersive X-ray spectrometry. The samples were solution-treated at 1250 degrees C and then isothermally aged at 800 degrees C for up to 604.8 ks. Precipitation hardening in steels occurred due to precipitation of Cu-particles during aging. Decrease of hardness of 24Cr steel associated with coarsening of Cu-particles occurred slower than that of 11Cr steel during aging. The normalized standard deviation of the size distribution of Cu-particles increased and reached saturation at a certain value during aging. The kinetic analysis for coarsening of Cu-particles showed that the interfacial energy of Cu-particles/matrix of 24Cr steel was lower than that of 11Cr steel, while diffusion coefficient of the steels did not depend on chromium concentration. The segregation of chromium formed at the interface of Cu-particles/matrix may decrease interfacial energy of Cu-particles resulting in retardation of coarsening of Cu particles.