초고강도 철강소재 내 미량 첨가된 합금원소 (Cr 및 Si)가 제조공정 중 표층 산화물 형성과 3.5% NaCl 수용액 내 부식거동에 미치는 영향

Abstract

This study investigated the impact of microalloying with chromium (Cr) and silicon (Si), along with shot blasting, on the formation of surface oxides and the long-term corrosion behavior of ultra-high-strength steel in saline environments. X-ray photoelectron spectroscopy revealed that the combined addition of Cr and Si promotes the development of stable oxides, such as Cr2O3 and SiO2. In contrast, Si-only alloys, despite having a higher Si content, formed less stable oxides like SiOx during the high-temperature anneal- ing process. Electrochemical tests indicated that the Cr-Si-bearing samples exhibited the highest polariza- tion resistance and the lowest corrosion current density, although some fluctuations were noted. This is closely linked to the stable formation of adherent (Fe,Cr)-enriched corrosion products, which can inhibit the penetration of corrosive species. Although the shot-blasting process initially compromised the stability of the surface oxide layer, increasing electrochemical reactivity, corrosion resistance gradually improved over immersion time. In contrast, Si-only samples demonstrated relatively higher electrochemical reactiv- ity due to the formation of unstable Si-containing Fe oxides, characterized by higher defect levels and weaker interfacial adhesion to the steel substrate. These findings offer valuable insights into alloy design strategies for ultra-high-strength steel aimed at enhancing surface stability and long-term corrosion resis- tance in chloride-rich environments.