Investigation of Corrosion Properties of Welded and Laser-Surface Melted SUS 304 in Nuclear Power Operating Conditions

Welded SUS 304 stainless steel surface was melted using an Nd:YAG laser beam in order to increase its corrosion resistance in operating conditions of nuclear power plants. The optimum process conditions for laser-surface melting of welded SUS 304 stainless steel were determined by measuring the depth melted by the laser beam of welded regions through an optical microscope, observing the microstructures of the laser-melted surface, and measuring the double-loop electrochemical potentio-dynamic reactivation (DL-EPR) curves in a 1L aqueous solution of 0.5M H₂SO₄ and 0.01M KSCN. From the test results, the optimum laser-surface melting process conditions were as follows; a laser power of 170W, a N₂ gas flow rate of 20L/min, a beam scan rate of 600mm/min, and laser power density of 20J/mm². The microstructure of the laser-surface melted (LSM) region was observed to be very fine and homogenous, and of cellular structure. Grain growth in the LSM region from the substrate occurred epitaxially. No Cr depletion along the grain boundary in the LSM region was detected, which would result in increasing the corrosion, specially intergranular corrosion (IGC) including intergranular stress corrosion resistance (IGSCC) of the welded SUS 304.