Isostatic diffusion bonding and post-solution treatment between Cr22Ni5Mo3MnSi and Cr30Ni7Mo3MnSi duplex stainless steels

In order to satisfy the requirement of different corrosion resistances in the same application, superplastic diffusion bonding at 1100 °C between expensive Cr30Ni7Mo3MnSi (SAE 2906, having higher corrosion resistance) and cheap Cr22Ni5Mo3MnSi (SAE 2205, having lower corrosion resistance) duplex stainless steels was systematically studied using a Gleeble-1500 thermo-mechanical simulator. The joint shear strength rapidly increased with an increase in holding time and pressure and then slowly increased when the holding time and pressure reached 5 min and 10 MPa, respectively. This increased strength was due to the void shrinkage and grain boundary migration across bonding interface. Post-solution at 1100 °C for 10 min significantly increased the joint shear strength up to 808 MPa, which was higher than 740 MPa of the base steel. It was ascribed to the dissolution of σ phase and further void shrinkage by volume diffusion. However, post-solution at 1050 °C deteriorated the bonding strength due to σ phase precipitation, while post-solution above 1100 °C also slowly reduced the bonding strength predominantly because of a decrease in the austenite fraction.