ABSTRACT
According to data gathered in the last Metal Foundry Industrial Production Survey [1[1] MODERN CASTING STAFF, “49th Census of world casting production”, Modern Casting, v. 103, n. 12, pp. 26-31, Dic. 1996.], approximately 46% of the industrial production of ferrous alloys is gray-iron. In this context the study of the atmospheric corrosion resistance of gray-iron becomes interesting to asset its useful life when subject to weathering conditions. The studies of gray-iron atmospheric corrosion behavior are scarce due to the fact that it takes long periods of time for its real-time characterization.
In order to validate an accelerated atmospheric corrosion test, a gray cast iron [2[2] ASTM Standard A48/A48M - 03 (Reapproved 2012), 2012, “ Standard Specification for Gray Iron Castings”, ASTM International, West Conshohocken, PA, 10.1520/A0048_A0048M-03R12, http://www.astm.org.
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] and a carbon steel [3[3] ASTM Standard A36/A36M-14, 2014, “Standard Specification for Carbon Structural Steel”, ASTM International, West Conshohocken, PA, DOI: 10.1520/A0036_A0036M-14, http://www.astm.org.
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] were subjected to a 40 days accelerated testing, that includes wetting in a saline fog chamber, washing and drying [4[4] ARTIGAS, A., MONSALVE, A., SIPOS, K., et al., “Development of accelerated wet–dry cycle corrosion test in marine environment for weathering steels”, Corrosion Engineering, Science and Technology”, v. 50, n. 8, pp. 628-632, Feb. 2015.], measuring the corroded thickness at each exposure time. These results were then compared with those obtained by Southwell et al [5[5] SOUTHWELL, C., BULTMAN, J., ALEXANDER, A., “The corrosion rates of structural metals in sea-water, fresh water and tropical atmospheres: Summary of a sixteen-year exposure study”, Modern Casting, v. 19, n. 3, pp. 179-183, Mar. 1969.] after 16 years of exposure in a marine environment (Panamá Canal). The result analysis reveals that both materials show a bimodal behavior, in accordance with those results reported by Melchers et al [6[6] MELCHERS, R., “Long-term corrosion of cast irons and steel in marine and atmospheric environments”, Corrosion Science, v. 68, n. 1, pp. 186-194, Mar. 2013., 7[7] MELCHERS, R., JEFFREY, R. “The critical involvement of anaerobic bacterial activity in modelling the corrosion behaviour of mild steel in marine environments”, Electrochimica Acta, v. 54, n. 1, pp. 80-85, Mar. 2008., 8[8] MELCHERS, R., “Microbiological and abiotic processes in modelling longer-term marine corrosion of steel”, Bioelectrochemistry, v. 97, n. 1, pp. 186-194, Jun. 2014.]. This behavior is characterized by an inflection point in the kinetic curve of corrosion, meanly related to the presence of bacteria in the interphase metal-corrosion products. The fact that the kinetic curve of corroded thickness shows an inflection point, allows the validation of the proposed methodology as a path to evaluate the atmospheric corrosion resistance in a short time test.
Keywords:
atmospheric corrosion; iron; weight loss; bacterial corrosion
