Corrosão nas soldas do aço ASTM A 285 grau C empregados na obtenção de celulose pelo método Kraft

Abstract

In this work samples of ASTM A 285 Grade C class steel, welded with covered electrodes AWS E7018 and AWS E6013, and with variations in the welding energy, were tested electrochemically, immersed in alkaline liquor, which is used in Kraft batch digesters. Workpieces were cut by electroerosion process from base metal (MB), heat affected zone (ZTA) and weld metal (MS), and submitted to metallographic characterization. A perlitic and ferritic microstructure was observed, with acicular ferrite surrounded by grain boundary ferrite and formation of Widmanstätten ferrite. Samples welded with AWS E7018 electrodes show microhardness profiles higher than AWS E6013 electrodes due to higher contents of manganese and silicon. Corrosion rates of MB, ZTA and MS regions increase with liquor temperature, and MS regions show corrosion rates higher than ZTA and MB, without heat treatment, for both electrodes. Values calculated were 0,30 mm/year for MB, 1,49 mm/year for ZTA and 2,63 mm/ano for MS with AWS E7018 electrode, without heat treatment, high energy, and for AWS E6013 electrode, in the same conditions, 1,24 mm/year for ZTA and 1,65 mm/year for weld metal.