Taguchi method and Box-Behnken design approach for process parameter optimization of magnetite (Fe 3 O 4 ) coating developed on stainless steel 410 grade by hot alkaline treatment

The blackening of materials is widely used in the automobile industry, defense applications, aerospace applications, and solar applications. Methods such as electroless chemical process, conversion coating, physical vapor deposition, chemical vapor deposition, and diamond-like carbon are some of the commonly employed techniques to produce black coatings on various metals. Hot aqueous alkaline treatment is a chemical conversion coating process. In this study, hot alkaline treatment is used to blacken surgical equipment made of stainless steel 410, which is a novel approach. The effect of process variables such as immersion time, salt solution temperature, and wt% of sodium dichromate on the anti-reflective property of ferrous ferric oxide (magnetite, Fe₃O₄) coating has been optimized using the Taguchi method and response surface methodology. The experiments were designed using a Taguchi orthogonal array and a Box-Behnken design. The influences of coating parameters on average percentage reflectance were quantified by the signal-to-noise ratio, main effect plot, analysis of variance, and two-dimensional and three-dimensional plots. The comparison of experimental and confirmatory tests shows that both procedures optimized the parameters successfully. The lowest average percentage reflectance value of 8.013% was obtained at 56.976 min immersion time, 124.998°C salt solution temperature, and 348.689 g/l wt% of sodium dichromate in the composition by Box-Behnken design methodology.