1.blue tempered spring for rolling shutter 2.CK67,AISI 1065,1070,CS70 3.0.15~ ... .round, slit Blue Tempered spring steel strip for rolling shutter doorHeat treatment is carried out mainly for reducing sheet thickness, improving surface finishing ... EK2, EK4Finishes: Nature, Polished bright, grey blue, polished blue, yellowEdge: Mill, Slit, Round, sheared/millTensile strength: 1405-1577 kg/mm2 (137 ...