Characterization and analysis of diffusion bonding process in a Cr25Ni7Mo4MnSi duplex stainless steel

Similar diffusion bonding of a duplex stainless steel (Cr25Ni7Mo4MnSi) was performed using a Gleeble 3500 thermo-mechanical simulator. Isostatic diffusion bonding was carried out at 1100 °C. The effect of surface condition, cold rolling, holding time and pressure was systematically studied. Microstructures along bonding interface were characterized using scanning electron microscopy and electron backscattering diffraction. The mechanisms of diffusion bonding were analyzed in terms of plastic deformation, diffusion, and rotation and migration of grain boundaries. Small surface roughness and large cold rolling were beneficial for bonding process while increasing holding time and pressure first greatly and then slowly increased the joint shear strength. Holding for 5 min at a pressure of 10 MPa obtained the joint shear strength of 407 MPa, which is comparable to 420 MPa of the base material. The influence of superplastic deformation was also analyzed, indicating a larger deformation (20% to 50%) led to a larger joint shear strength (395 to 418 MPa). These demonstrate the feasibility of this steel for superplastic forming and diffusion bonding technique.