Materials and Corrosion. 2020;1–12. www.matcorr.com © 2020 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim | 1 Received: 17 February 2020 | Accepted: 2 March 2020 DOI: 10.1002/maco.202011596 ARTICLE Influence of cathodic polarity during electrocleaning process on the brown stain defect formation after skin pass on cold‐rolled close annealed steel Subho Chakraborty 1 | Ashwin Pandit 2 | Kuntal Sarkar 1 | Nitu Rani 1 1 Research and Development Division, Tata Steel Limited, Jamshedpur, India 2 Quality Assurance Division, Tata Steel Limited, Jamshedpur, India Correspondence Subho Chakraborty, Research and Development Department, Tata Steel Limited, Jamshedpur 831001, India. Email: subho.chakraborty@tatasteel.com Abstract Skin pass rolling is considered as the final forming stage in cold‐rolled close annealed steel. Surface properties and flatness are the key attributes for au- tomotive customers. Efficient skin pass rolling overcomes surface defects that lead to material rejection. This study portrays a brown stain defect with higher defect severity. The brown stain defect is observed in a few coils that are processed through alkaline electrocleaning (ECL). Coils bypassing ECL do not show such defect. Defect characterization through scanning electron micro- scopy, Fourier transform infrared spectroscopy, and Raman spectroscopy shows initiation of oxidation of steel substrate. The presence of skin pass fluid residues in the defected area is the root cause for the stain formation. Techniques such as glow discharge optical emission spectroscopy, Kelvin probe, Raman spectroscopy, and electrochemical tests emphasize the role of final electrode polarity in ECL with the nature of passive oxide film formed when skin pass fluid is applied on the steel surface. This study reveals that skin pass fluid applied on anodically cleaned coils provides a uniform passive surface that restricts the defect formation. KEYWORDS brown stain, CRCA, electrocleaning, scanning Kelvin probe, skin pass rolling 1 | INTRODUCTION Steel is one of the most important material for automotive industry. Among steel flat products, the cold‐rolled close annealed (CRCA) steel sheet is widely used to make different components of automobiles. Generally, CRCA is skin passed to provide smooth and clean surface finish, which enhances the flexibility during the forming operations carried out at the automobiles' customer end. [1] After cold rolling, steel is subjected to batch annealing furnace (BAF) where microstructure gets adjusted and the rolling oil residues are burnt off. Critical automotive grade CRCA coils are subjected to electrocleaning (ECL) before batch annealing, to ensure cleaner surface with higher reflectivity. [2] After BAF, the CRCA coils are subjected to wet skin pass application. During wet skin pass application, coils are passed through light rolling in the presence of skin pass fluid to transfer desired roughness and prevent formation of Luders band. [1,3] A little elongation, approxi- mately 0.5–1.0%, can also be expected during skin pass rolling. After skin pass rolling, rust preventative oil is applied on steel before packaging and dispatching to customer. The schematic diagram starting from pickling to packaging of CRCA steel sheet is provided in Figure 1. During skin pass rolling, the skin pass fluid is applied at a concentration of 3–4% solution in demineralized