Influence of welding current intensity on pitting corrosion resistance in welded joint of stainless steel X5CrNi18-10

Abstract

The effect of welding current on the pitting corrosion resistance in the welded joint of austenitic stainless steel X5CrNi18-10 was tested. Welding was carried out using three different current intensity (110 A, 130 A and 150 A). Testing of pitting corrosion resistance was performed by electrochemical potentiodynamic method on the base metal, in the heat affected zone (HAZ) and in the weld metal. Values of pitting corrosion resistance indicators for the base metal are similar to values of the indicators for the weld metal, regardless of the applied welding current. The values of indicators for pitting corrosion resistance in the HAZ are less than the values of these indicators for the base metal and for the weld metal. This is caused by the precipitation of chromium carbides at grain boundaries and by partial formation of chromium depleted areas along the grain boundaries in the HAZ. HAZ that was formed at welding current of 150 A shows the smallest pitting corrosion resistance. This can be explained by the largest depletion in chromium of grain boundary areas at welding current of 150 A. The sensitization degree in the HAZ to intergranular corrosion is also the greatest, in this case. With increase of the sensitization degree to intergranular corrosion the value of metastable pitting potential linearly decreases, which means that pitting corrosion resistance in the HAZ is reduced.

Ispitan je uticaj jačine struje zavarivanja na otpornost prema piting koroziji zavarenog spoja austenitnog nerđajućeg čelika X5CrNi18-10. Zavarivanje austenitnog nerđajućeg čelika je izvršeno primenom tri različite jačine struje (110 A, 130 A i 150 A). Ispitivanja otpornosti prema piting koroziji su izvršena elektrohemijskom potenciodinamičkom metodom na osnovnom metalu, u zoni uticaja toplote (ZUT) i u metalu šava zavarenog spoja. Vrednosti pokazatelja piting korozije za osnovni metal su bliske vrednostima odgovarajućih pokazatelja za metal šava, nezavisno od primenjene jačine struje pri zavarivanju. Vrednosti pokazatelja piting korozije u ZUT-u su manje od vrednosti odgovarajućih pokazatelja za osnovni metal i metal šava. To je posledica delimičnog izdvajanja hrom-karbida po granicama zrna i obrazovanja hromom osiromašenih oblasti uz granicu zrna u ZUT-u. ZUT formiran pri jačini struje zavarivanja od 150 A pokazuje najmanju otpornost prema piting koroziji, što se može objasniti najvećim osiromašenjem prigraničnih oblasti zrna hromom pri ovoj jačini struje zavarivanja. Tada je i sklonost ZUT-a prema interkristalnoj koroziji najveća. Povećanjem stepena senzibilizacije ZUT-a prema interkristalnoj koroziji vrednost potencijala metastabilnog pitinga se linearno smanjuje, što znači da se smanjuje otpornost ZUT-a prema piting koroziji.