Effect of SO42− on the corrosion of 316L stainless steel in molten FLiNaK salt

Highlights: • High temperature corrosion of 316 L stainless steel in molten FLiNaK salt. • Effect of SO₄²⁻ on the corrosion of 316 L stainless steel in molten FLiNaK salt. • The SO₄²⁻ in the FLiNaK salt remarkably accelerates the corrosion of 316 L stainless steel. • The SO₄²⁻ can react with Mn in the 316 L stainless steel to form MnS at the high temperature molten FLiNaK salt. • The galvanic couple between MnS and matrix can accelerate the corrosion of 316 L stainless steel in molten fluoride salts. - Abstract: The effect of SO₄²⁻ on the corrosion behavior of 316 L stainless steel (SS) in molten FLiNaK (LiF-NaF-KF: 46.5–11.5–42 mol.%) salt was studied. Results reveal that the SO₄²⁻ in the salt remarkably accelerates the corrosion of 316 L SS by promoting the dissolution of Cr, leading to increasing intergranular corrosion of the alloy. On the other hand, the results of structural characterization indicate that the SO₄²⁻ can react with Mn to form MnS at the grain boundaries of the alloy. The galvanic couple between MnS and steel matrix could further accelerate the intergranular corrosion of 316 L SS in molten fluoride salt environments.