PITTING CORROSION RESISTANCE OF AISI TYPE 316 (N) SS WELD AFTER VARIOUS SURFACE TREATMENTS AND THERMAL AGING

摘要

Pitting corrosion resistance of AISI type 316 (N) stainless steel (SS) weld, in neutral sodium chloride environment was investigated after various surface treatments (mechanical and chemical) and thermal aging. Mechanical treatment included lathe turning and wet polishing up to 320-grit emery, and diamond polishing. Chemical treatments included pickling and pickling followed by passivation for the lathe turned surface. The treated specimens were subsequently examined for its pitting corrosion resistance in 0.5M NaCl solution by potentiodynamic anodic polarization method. It was observed that the pitting corrosion resistance was dependant on the surface finish of the material. Chemical treatments like pickling and passivation were found to significantly enhance the pitting corrosion resistance. The weld metal was thermally aged at 1023 K and 1123 K for 100 h each, and evaluated for its pitting corrosion resistance in 0.5M NaCl solution and the results were correlated to the microstructural changes that occurred on thermal aging. The pitting corrosion resistance for the aged weld was found to be much less than that for the as-welded, as a result of transformation of delta ferrite in the weld metal into secondary precipitates. No discernable difference in the pitting corrosion resistance was observed among the thermally aged welds.