Microstructural characterization and mechanical behavior of Cr25Ni35NbM alloy dissimilar weld joint for application in a hydrogen reformer furnace

The microstructural characterization and mechanical behavior of Cr25Ni35NbM/15CrMo and Cr25Ni35NbM/SUS321 dissimilar weld joints were studied in this paper. The microstructure, room temperature and high temperature (1173 K) tensile strength of dissimilar weld joints were analyzed through optical microscopy (OM), scanning electron microscopy (SEM) and electronic universal tensile testing machine. The microstructure of HAZ in 15CrMo steel of Cr25Ni35NbM/15CrMo dissimilar weld joint transformed from ferrite-pearlite into ferrite-martensite. A large volume fraction of α phase was found to have precipitated in the HAZ of SUS321 austenitic stainless steel for Cr25Ni35NbM/SUS321 dissimilar weld joint. At room temperature, the tensile strength and yield strength of these two type dissimilar weld joints is less than Cr25Ni35NbM alloy similar weld joint. The high temperature tensile strength of these two type dissimilar weld joints is less than Cr25Ni35NbM alloy similar weld joint. Both at room and high temperature, the fracture locations of two types dissimilar weld joints are the HAZ of the base metal 15CrMo and SUS321 stainless steel, respectively. It indicates that the weak part of the Cr25Ni35NbM alloy dissimilar weld joints is the low-performance base metals 15CrMo and SUS321 stainless steel.