Atomic scale understanding of the interaction between alloying copper and MnS inclusions in stainless steels in NaCl electrolyte

• The detailed reaction mechanisms between the alloying Cu and the MnS inclusions in a stainless steel are investigated by advanced TEM techniques.
• Cu concentrates in the skin layer of MnS before MnS dissolution occurs.
• The structure of the layer where Cu enriched and the reaction mechanism were revealed at an atomic scale.
• Alloying Cu is beneficial to stabilize the harmful sulphur species (released from the dissolved MnS) in NaCl solution by forming Cu2S depositions.

The effect of alloying copper on the dissolution of manganese sulphide which triggers the pitting corrosion of stainless steels was studied by in-situ ex-environment transmission electron microscopy (TEM) with an atomic resolution. It was found that the benefits of Cu addition act in two ways: Cu ions replace the Mn ions in the surface layer of MnS and insoluble copper sulphide compound forms; on the other hand, Cu ions could stabilize harmful surphur species released from dissolved MnS. The two processes are supposed to be helpful to reduce the detrimental effect of MnS on the corrosion resistance of stainless steels.

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