The influences of microstructure and composition on the electrochemical behavior of a516 steel weldment

ASTM-A516 (Grade 70) low carbon steel weldments have been characterized in terms of the effect of metallurgical stimuli on electrochemical behavior. Potentiodynamic polarization measurement and electrochemical impedance spectroscopy (EIS) were made for the specimens, prepared with three different welding heat input conditions (15, 30 and 45 kJ cm^-1) either by submerged arc welding or by weld thermal simulation with a Gleeble machine, in NACE solution (5 wt% NaCl + 0.5 wt% CH₃ COOH) of pH 2.8 at 25°C. The polarization resistances of the base metal, thermal simulated heat-affected zone and weld metal obtained using linear polarization method and EIS were compared. The results show that weld metal is distinguished in having the greatest polarization resistance. Furthermore, the polarization resistances of the weld metal and simulated grain-coarsened HAZ increased with increasing welding heat input. The electrochemical behavior of the weld metal is dependent upon the volume fraction ratio of grain boundary ferrite (GF) to acicular ferrite (AF), while that of the thermal simulated grain-coarsened HAZ is associated with the coarsening of Widmanstätten ferrite (WF).