Model of vacancy diffusion-assisted intergranular corrosion in low-alloy steel

A model is presented for intergranular corrosion (IGC) of nonsensitized low-carbon pipeline steels, in which enhanced grain boundary (GB) oxidation is enhanced by vacancies produced by oxidation of re-active Si atoms. Evidence for vacancy injection at corroding GBs had been provided by recent nanoin-dentation measurements. Model calculations of IGC evolution controlled by lattice vacancy diffusion are compared to experimental measurements. Realistic dihedral angles of corroded GB grooves are predicted based on a vacancy diffusivity within the range of values expected for bcc iron. The calculations ratio-nalize observations of sharpening of GB grooves with time during corrosion exposures, and show that vacancy diffusion quantitatively accounts for enhancement of IGC by reactive solute atoms, without in-voking solute segregation or precipitation at GBs. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The paper presents a model for intergranular corrosion of nonsensitized low-carbon pipeline steels, where enhanced grain boundary oxidation is explained by vacancies produced by reactive Si atoms. Experimental evidence supports the role of vacancy diffusion in the evolution of IGC, with calculations showing agreement with experimental measurements. The rationalization of sharpening of GB grooves over time during corrosion exposures and the quantitative explanation of IGC enhancement by vacancy diffusion without solute segregation or precipitation at GBs are key findings.