Diffusion Bonding by Hot Extrusion of Incoloy 825 and Duplex 2205 to a Low Alloy Steel

AISI 4130 low alloy steel has been diffusion bonded to an Incoloy 825 and a Duplex 2205 stainless steel by an industrial hot extrusion process, the final product being a seamless clad tube with an internal lining of these corrosion resistant alloys. The microstructures of the as-extruded products have been analysed using optical metallography, SEM and STEM techniques. The interdiffusion of the different elements through the interface has been determined using EDS microanalysis both in SEM and STEM. For the combinations AISI 4130-Incoloy825 a region close to the original interface on the Incoloy side is observed, where a deformation substructure with subgrains, dislocations and an important amount of carbides M23C6 type are found. Different layers of austenite, martensite and ferrite-pearlite are observed on the steel side. In the case of the combinations AISI 4130-Duplex 2205 and close to the interface, a region with a low amount of ferrite with a big profussion of M23C6 carbides precipitated at the grain boundaries is observed, followed by regions with a higher amount of ferrite at grain boundaries to reach the original structure of the Duplex. The influence of several heat treatments consisting in quenching plus tempering in the region around the bonding have also been analysed.