[SMM Stainless Steel Market Flash] Tohoku Study Ties Grinding-Induced Pitting in 304 Stainless to Damaged MnS Inclusions

Published: Jul 28, 2026 09:22

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Researchers at Japan's Tohoku University have identified why ground stainless steel surfaces corrode more readily in chloride environments, a question long unresolved despite the known link between surface roughness and localised corrosion. Working with Type 304 in saltwater, the team found grinding leaves fine scratches that cut into manganese sulphide inclusions in the steel, deforming and cracking them and partly embedding them in the matrix. Pitting occurred only where scratches intersected MnS particles; roughness alone did not trigger it. Professor Masashi Nishimoto said damage to MnS inclusions, rather than disruption of the passive film, was the dominant factor. The findings, published in npj Materials Degradation, point toward revised grinding and surface-treatment guidance.

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