Product Code: ICA10_1703

Effect of Laser Surface Melting on Corrosion Behavior of Aged Duplex Stainless Steel
Authors:
K.H. Lo, Department of Electromechanical Engineering, University of Macau; Macau Peoples Republic of China
W.K. Chan, Department of Electromechanical Engineering, University of Macau; Macau Peoples Republic of China
C.T. Kwok, Department of Electromechanical Engineering, University of Macau; Macau Peoples Republic of China
Presented at ICALEO 2010

Duplex stainless steels (DSSs) have been widely used as the structural components for chemical industries, oil and gas production and offshore applications due to its outstanding corrosion resistance in chloride-containing environments. However, depletion of chromium and molybdenum is a well-known problem in DSSs, especially in welded assemblies, hot-worked and improperly heat-treated parts heated at temperatures ranging from 500 to 900°C. As the sigma phase form, it depletes the neighboring regions of Cr and Mo, thereby lowering the Cr and Mo contents of the surface oxides over these regions. Then the DSSs become susceptible to corrosion attack. Laser surface melting (LSM) is a possible route to restore the corrosion resistance of DSSs by melting the surface with a laser beam followed by rapid solidification for homogenizing chemical compositions. Different laser parameters will cause different phase distributions for duplex stainless steels, and hence various corrosion properties are resulted. In present study, the corrosion behavior and microstructure of aged DSS 7MoPlus (UNS S32950) were investigated in 3.5% NaCl solution at 25 °C before and after LSM by a Nd:YAG laser. By LSM, the corrosion resistance of aged 7MoPlus was found to be significantly enhanced as reflected by the increase in the pitting potential and decrease in passive current density. The improvement of corrosion resistance of the laser surface melted 7MoPlus is attributed to the refinement of the microstructure and re-dissolution and removal of the sigma phase.