Cold rolled black annealed coils (CRBA), inozivikanwawo se "Blue Steel".CRBA iriinotonhora yakakungurutswa simbi coilsizvo zvakave ne oxidized ne annealing mune yakakosha kuisirwa kuitira kuti ibudise yakanyanya kutetepa magnetite layer (Fe304) pamusoro (isingasviki 1 μm gobvu) kuti iwedzere kuchengetedzwa.