A Study on the Microstructure and Mechanical Properties of SA508 Gr.3 Cl.1 Steel Cladded by a Laser Beam using Alloy 82 and 308L Powders for Small Modular Reactor

Abstract

Laser cladding is an innovative welding method for application to small modular reactors (SMRs). Therefore, the characteristics of laser cladding were studied. A low alloy steel SA508 Gr.3 Cl.1 was used as the substrate, and powder-type Alloy 82 and STS 308L were used as the cladding materials. Although certain differences existed depending on the cladding materials, the tendencies of laser cladding were similar as a whole. The heat-affected region near the fusion line of Alloy 82 had a coarsened structure consisting mainly of lower bainite. The heat affected zone (HAZ) had a higher hardness value than the base material. The hardness of the HAZ was higher for Alloy 82 than for 308L. The 308L cladding had a carbide as a precipitate that was dispersed in the fusion line and cladding grain boundary. The dilution rates of Alloy 82 and 308L cladding within 1.5 mm from the fusion line were low levels of 3-6%. Dilution rates increased as heat input increased, but hardness values did not differ. δ-ferrite values of 308L were satisfactory, that is, more than 5 FN. Intergranular corrosion testing of the 308L cladding did not reveal any cracks. In conclusion, laser cladding could be applied to SMR manufacturing.