Corrosion resistance of chromium-coated 20895 electrical steel

• Published in: Metal science and heat treatment 1991-11, Vol.33 (11-12), p.807-809
• Main Authors: BABICH, S. G, ZYABREV, A. A, SKIBINA, G. B, VAVILOVA, N. V
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Heat treatment; Metals. Metallurgy; Production techniques; Thermochemical treatment and diffusion treatment
• ISSN: 0026-0673; 1573-8973
• DOI: 10.1007/BF00811057

Previously abstracted from original as item 9208-58-1165. A circulation method of chromizing 20895 transformer steel (0.035 carbon, 0.30 manganese, 0.30 silicon, 0.20 phosphorus, 0.020 sulfur and 0.030% copper) in a chloride gas medium at 950-1000 deg C for 1-9 h was developed to raise corrosion resistance. Metallography and X-ray structural analysis of chromized samples indicated that the surface was composed of an alpha -solid solution of chromium in iron, traces of carbides based on Cr of the M sub 23 C sub 6 and M sub 7 C sub 3 type, and sigma -phase (FeCr). Anodic polarization studies in a 3% NaCl solution and in a 1N solution of H sub 2 SO sub 4 at 20 deg C indicated that the threshold corrosion potential (E sub cor ) was significantly higher with the Cr coating on the steel. As chromizing time increased from 0 to 9 h, E sub corr increased from --0.35 to +0.18 V in the 3% NaCl solution. In the H sub 2 SO sub 4 solution, the corrosion resistance of the chromized 20895 steel was three to four times greater than Kh18 steel in the passive region at 0.5 V potential. The coercive force of 20895 transformer steel decreased from 95 to 78 A/m after chromizing.