Cold rolled black annealed coils (CRBA), wanda kuma aka sani da "Blue Steel".CRBA asanyi birgima karfe coilswanda aka sanya oxidized ta annealing a cikin wani musamman shigarwa domin samar da wani bakin ciki magnetite Layer (Fe304) a saman (kasa da 1 μm kauri) don ƙarin kariya.