Prevention of crevice corrosion of AISI 304 stainless steel in sea water by local laser surface cladding

AISI 304 stainless steels suffer severe crevice corrosion, within the crevices under bolt and rivet heads and other shielded areas caused by holes, gasket surfaces, lap joints and surface deposit, in the sea water. To prevent this kind of corrosion, Fe-30Cr-4Mo and Fe-19Cr-18Ni- 6Mo-0.2N coatings were deposited on these areas on the steels by laser surface cladding. The microstructure and chemical composition of the coatings were studied with optical and electron microscopy, x-ray diffraction and electron probe microanalysis. Fe-30Cr-4Mo coating consists of ferrite fine dendrites with slight segregation of Cr and Mo at dendrite boundaries and Fe-19Cr-18Ni-6Mo-0.2N coating consists of austenite fine dendrites also with slight segregation of Cr and Mo at dendrite boundaries. Crevice corrosion resistance of the coatings was evaluated with electrochemical method (Wilde’s method) and free immersion tests in artificial sea water and 10wt% FeCl₃. Results of electrochemical tests show that Fe-30Cr-4Mo and Fe-19Cr-18Ni- 6Mo-0.2N coatings have much better crevice corrosion resistance than commercial AISI 304 stainless steel. After immersed in artificial sea water for 2 months, laser surface cladded samples did not suffer any crevice corrosion whereas untreated samples suffered severe crevice corrosion. After immersed in 10wt% FeCl₃ for 2 months, crevice corrosion started on both Fe- 30Cr-4Mo and Fe-19Cr-18Ni-6Mo-0.2N coatings.