Effects of iron oxidation state and chromium distribution on the corrosion resistance of high interstitial stainless steel for down-hole application

Abstract

The corrosion properties of Fe-Cr-Mn-C-N high interstitial austenitic stainless cast steels were investigated for down-hole application in sour environments. The two cast alloys contained 0.66% and 0.71% of total nitrogen and carbon. The corrosion properties of the alloys that were solution-treated and fast-cooled were directly responsible for high corrosion resistance in NaCl solution, including resistance to pitting corrosion resulting from a better distribution of chromium chemical compound in the high interstitial stainless cast steel. However, the sour corrosion resistance of the alloys decreased with the fast cooling rate, which can be attributed to the increased amount of ferrite containing Fe2+, which causes iron sulfide precipitate formation in H2S.