Investigation of galvanic corrosion in laser-welded stainless steel sheets

In the present study, bead-on-plate specimens of 1-mm sheets of austenitic and duplex stainless steels were fabricated by laser penetration welding with a 2.5-kW CW Nd:YAG laser. The galvanic corrosion behavior of laser-weldment (LW) against as-received (AR) specimens with an area ratio of 1:1 in 3.5% NaCl solution was studied by means of a zero-resistance ammeter. The free corrosion potentials of as-received specimens were found to be considerably higher than those of laser weldments, indicating that the weldments are more active and always act as anodes. The ranking of galvanic current densities (I-G) of the couples in ascending order is : AR S31603-LW S31603 < AR S31803-LW S31803 < AR S32760-LW S32760 < AR S30400-LW S30400. For the galvanic couple between AR S30400 and LW S30400, the I-G is the highest (78.6 nA/cm(2)) because large amount of delta-ferrite in the weld zone acts as active sites. On the other hand, the I-G of the galvanic couple between AR S31603 and LW S31603 is the lowest (-26 nA/cm(2)) because no delta-ferrite is present after laser welding. The recorded I-G of all couples revealed constantly low values (in the range of nA/cm(2)) and sometimes stayed negative, which indicated polarity reversal.