Microstructural Investigation And Thermal Aging Behavior Of Ni-201 Weld Cladding Onto Stainless Steel

Molten salt reactor is the most promising reactor for the fourth-generation reactors.The nickel-base alloy N10003,a candidate structural material,has good high-temperature mechanical properties,resistance to molten salt corrosion,and radiation resistance.However,it is very difficult to use N10003 alloy to make large-scale equipment.Its high-temperature data is incomplete and it is expensive.In order to solve the above problems,the ERNi-1 welding wire was deposited on a 304stainless steel substrate by gas tungsten-arc welding?GTAW?.This provides another idea for the structural material of the molten salt reactor.The welding process parameters,the microstructure and mechanical properties of the cladding layers under as-welded and high-temperature aged were studied.In this paper,the effects of welding current and wire feed speed on weld formation and element distribution were studied firstly,and the optimized parameters of welding process were as follows:peak welding current 200A-220A,wire feed speed 1.5m/min.Based on the optimized process parameters,the microstructure,elemental segregation,phase composition,hardness and bending properties of the weld overlay were studied.The results showed that there was a good metallurgical bond between the cladding layer and the base metal.The hardness of the cladding layer after thermal aged at 700^oC for 1h to 2000h were tested.The results showed that the first layer and the second layer had different hardening behavior,while the hardness of the third layer remained basically unchanged.The grain boundary and intragranular precipitation phases of the cladding layer aged at 700^oC for 1h to 2000h were systematically characterized.During the aging,adjacent distributions of M₂₃C₆ and TiC carbides were formed on the grain boundaries in the first cladding layer and TiC carbides were formed in the second layer.The?Ti,Cr?C carbides coarsening process in dendrite and interdendrites of the first layer conforms to the LSW theory,the coarsening rates K were 0.067×10^-27 m³/s and0.072×10^-27 m3/s,respectively.The coarsening rate K of the?Ti,Cr?C carbide in the second layer was 0.136 x 10^-27 m³/s.The third cladding layer was very stable in the aging process and no precipitate was found.