Inhibition of Temper Patch on Automotive Steel Coils by Nitrite‐Based Wet Temper Fluid

This study evaluates the temper patch protection of a novel nitrite‐based wet temper fluid on three CRCA (cold rolled closed annealed) steel substrates: anodic cleaned, cathodic cleaned, and non‐ECL (electrolytic cleaning line). Findings indicate that anodic cleaning is the most effective, producing a uniform silicate layer coupled with nitrite ion adsorption leading to the highest charge transfer resistance ( R ct = 1.7 × 10 7 Ω), signifying exceptional corrosion resistance. In contrast, cathodic cleaning resulted in non‐uniform carbonaceous and silicate deposits, leading to the lowest R ct (2.8 × 10 5 Ω) and higher corrosion susceptibility. Scanning Kelvin probe studies confirmed more negative Volta potential for cathodic substrates, making them less noble. Raman spectroscopy identified protective iron oxides like hematite and goethite, which are more prevalent and stable on anodic substrates due to their low solubility products. Ultimately, the study concludes that anodic cleaning promotes a superior kinetic barrier at the metal‐electrolyte interface, offering robust protection against temper patch compared to cathodic and non‐ECL alternatives.