SURFACE STATE EFFECT OF WELDED STAINLESS STEELS ON CORROSION BEHAVIOR

Abstract

Welding joints of stainless steels are in practice very sensitive places attacked by local corrosion, such as pitting and crevice corrosion, mostly in chloride containing oxidizing environments. It is caused by different oxidation products created on the surface by welding. Corrosion resistance of stainless steels is affected by quality of passive layer (Cr2O3) which created at normal conditions on air. After welding the steels are heated and on the surface are originated different types of oxides which have not the same protective properties. Resistances to intercrystalline and pitting corrosion of two type of welded stainless steel with different surface finishing were tested. Experimental materials are the austenitic stainless steel AISI 316L (welded by the TIG method in inert Ar atmosphere with filler) and the ferritic stainless steel AISI CA6-NM (welded by the WPS method in inert Ar atmosphere with filler and after welding heat treated). Character of the surface after welding and after mechanical finishing by grinding was evaluated by SEM microscopy, EDX analysis. Corrosion resistance to local forms of corrosion was tested by electrochemical potentiodynamic test and by exposure tests in chloride solutions. The steel AISI CA6-NM was tested in fluvial water to simulate real operation environment. The evaluation is supported by microscopic analysis. Susceptibility to intergranular corrosion was tested too and results detect the dangerous localities for corrosion attack and show increasing of corrosion resistance by surface treatment.