Effect of carbon and nitrogen on grain boundary segregation in irradiated stainless steels

A systematic approach for the study of radiation-induced segregation/depletion at grain boundaries in steels

“…The present results obtained at relatively high fluence (8 dpa) show that carbon segregation may play a role in retaining Cr at the grain boundary thereby slowing down the depletion phenomenon associated with point defect gradients. This is also consistent with previous results on austenitic steels where additions of minor elements such as carbon, nitrogen or hafnium were used to mitigate RIS [24,27,37]. While the role of large atoms such as Hf is to reduce the number of migrating vacancy available for Cr diffusion away from grain boundaries, the positive binding energy between carbon and chromium is more likely to act towards a pinning mechanism slowing down Cr depletion.…”

“…On the other hand, the formation of Cr rich carbides below 700°C can also lead to the depletion of Cr at grain boundaries in austenitic steels (sensitization effect) [25,26], which could bias the observation of Cr at grain boundaries during irradiation. Finally it has been suggested that carbon segregation at grain boundaries could retard Cr depletion in the austenitic steels [27,28].…”

Experimental and theoretical evidence for carbon-vacancy binding in austenite

“…Indeed, one can see apparent effects of carbon on susceptibility, as in the work of Kano et al [30] on radiation-induced segregation of substitutional solutes to grain boundaries in 304 and 316L stainless steels irradiated with 12 MeV nickel ions at 300°C. These investigators observed systematic changes in the depth and width of the concentration profiles of chromium, nickel, silicon, and molybdenum at grain boundaries as a function of carbon or nitrogen content in the range 0 to 0.1 wt pct.…”

A Multicomponent Model of Radiation-induced Segregation for Commercial Stainless Steels

“…The previous studies showed that RIS in stainless steels depended on the amount of other minor elements such as C, N, and P, and that a higher amount of these elements resulted in a lower RIS. 21,27) This is likely due to lower effective mobility of vacancies and interstitials in steels containing higher levels of impurities that trap point defects. The migration energies of vacancies and interstitials were expected to be higher than the often-used values of 1.3 and 0.9 eV 16,17) and were assumed to be 1.4-1.5 eV and 1.0-1.1 eV, respectively.…”

“…1,3,19,20) Ternary Fe-Cr-Ni and binary Fe-Si models have been separately used to predict RIS in stainless steels using different physical parameters. RIS in the Fe-CrNi system is known to be suppressed by adding other elements such as interstitial C and N, 21) undersized Si and P, 22) and oversized elements such as Hf and Zr. 23) The effects of additional elements were also modeled by modifying the ternary models.…”