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Sensitisation behaviour of grain boundary engineered austenitic stainless steel
Materials Science and Engineering: A, Volume: 527, Issue: 16-17, Pages: 4275 - 4280
Swansea University Author: Valerie Randle
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Thermo-mechanical processes involving both single and multiple cycles of low level (5%) strain and annealing were applied to specimens of a type 304 austenitic stainless steel in order to encourage grain boundary engineering (GBE). As a result of the GBE processing the total length proportion of Σ3n...
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Thermo-mechanical processes involving both single and multiple cycles of low level (5%) strain and annealing were applied to specimens of a type 304 austenitic stainless steel in order to encourage grain boundary engineering (GBE). As a result of the GBE processing the total length proportion of Σ3n coincidence site lattice (CSL) boundaries was increased from 43% up to a maximum of 75% in conjunction with moderate grain growth. The increases in Σ3 and Σ9 boundaries resulted in significant decreases in the degree of sensitisation following exposure at 650 °C for up to 4 h and assessment through Double Loop-Electrochemical Potentiokinetic Reactivation (DL-EPR) tests. Over 97% of Σ3 boundaries were immune to sensitisation and approximately 80% of Σ9 boundaries were either immune or partially resistant to sensitisation, whereas all other CSL boundaries and general boundaries did not resist sensitisation. Therefore, only Σ3 and Σ9 boundaries were ‘special’. Deformation applied by cold rolling was more effective than tensile deformation in bringing about GBE. In summary, the results presented here show that increasing the fraction of Σ3 and Σ9 boundaries through GBE processing, accompanied by only moderate grain growth, provides an effective route to protection from sensitisation and intergranular corrosion.
This work arose from a £88,493 grant awarded from Rolls Royce Marine for a project ‘Mitigation of intergranular degradation in austenitic stainless steels’. This paper, in a journal with a five-year IF 2.22 and having 11 citations, reports how intergranular corrosion (sensitization) is reduced by custom-designed grain boundary engineering (GBE). The data provided unequivocal support for GBE: after processing 97% of Σ3 boundaries were sensitization immune and 80% of Σ9 boundaries were immune or partially immune. These improvements were achieved using small strains and short annealing times, which is an attraction for future scale-up of this work for commercial purposes.
•Intergranular corrosion; •Grain boundary type; •Grain boundary engineering; •Sensitisation; •Austenitic stainless steel
Faculty of Science and Engineering