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Abstract

The intergranular corrosion resistance of a range of experimental ferritic stainless steels containing 40% Cr and low levels of the interstitial elements carbon and nitrogen was assessed by means of total immersion and electrochemical potentiokinetic reactivation testing. Despite the low interstitial element levels, these alloys can be susceptible to severe intergranular corrosion in the. solution annealed condition. Sensitisation was mainly related to grain boundary precipitation of chromium rich M²³(C, N)₆ with associated chromium depleted zones. This undesirable precipitation is the result of the low carbon and nitrogen solubility at a level of 40% Cr. Total immunity to intergranular attack in solution annealed Fe-40Cr alloys was only observed at stabiliser/(C+ N) ratios>20. A 4 h isothermal annealing heat treatment at 621°C restores the intergranular corrosion resistance, similarly to the behaviour of lower chromium alloys.

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Intergranular Corrosion in Low Interstitial 40%Cr Ferritic Stainless Steels

Abstract

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References