Cold Rolled Black Annealed Coils (CRBA), makwaara dị ka "Blue Steel".CRBA bụ aoyi akpọrepu ígwè eriri igwenke ejirila oxidized site na nchichi na nrụnye pụrụ iche iji mepụta akwa magnetite dị gịrịgịrị (Fe304) n'elu (ihe na-erughị 1 μm oke) maka nchebe ọzọ.