Preparation and strengthening of stainless steel passive films: Methods, latest developments, and challenges

Stainless steel corrosion resistance is governed by an ultrathin, chemically graded passive film, whose protectiveness depends on composition, defect chemistry, electronic structure, and ion transport. This structured critical review examined literature published primarily during 2015–2025, while retaining seminal studies needed to compare the point defect, place exchange, and high-field models. The reviewed evidence showed that selective Fe dissolution and Cr enrichment constructed a Cr-rich inner barrier and a Fe-rich outer layer, whereas localized corrosion originated from the competition among film dissolution, defect accumulation, and repassivation. Across representative studies, optimized chemical, electrochemical, plasma, and laser-assisted treatments reduced corrosion or passive current density by approximately 1–5 orders of magnitude, increased pitting potential by about 100–500 mV in a strong-field laser system under specific test conditions, and sustained protection for more than 6500 h. Unlike method-centered reviews, this work linked preparation routes to five strengthening pathways—composition regulation, thickness/architecture control, defect-chemistry regulation, semiconductor modulation, and suppression of ion transport—and critically compared their environmental impact, characterization requirements, and industrial applicability. The resulting framework supports mechanism-guided passive-film design for marine, nuclear, hydrogen-energy, biomedical, and food-processing applications, while identifying operando characterization, physics-informed modeling, high-throughput screening, and machine-learning-assisted prediction as priority directions.