Investigation into the influence of laser melting on the sulphide inclusions in AISI 416 stainless steel

AISI 416 is a high sulphur martensitic stainless steel with elliptical shaped sulphide inclusions over 2 μm in length. After laser melting the sulphide inclusions became spherical and reduced in size to below 0.5 μm in diameter. SEM investigations showed that the total number of inclusions increased dramatically and it was calculated that the total volume of sulphur in the stainless steel had not changed during the laser treatment. The pitting potential was increased by over 200 mV with an inverse linear dependency on the average inclusion size. The frequency of metastable pitting events decreased by a factor of 100.

► Laser surface treatment reduces sulphide inclusion size from over 2 μm to below 0.5 μm.
► Total volume of sulphur in stainless steel not reduced by laser surface treatment.
► Pitting potential in 500 ppm chloride increases by more than 200 mV.
► Inverse linear relationship between pitting potential and size sulphide inclusions.
► No Influence of Ar or N2 shielding gas on pitting behavior.