Austenitic Stainless Steel Cladding Interface Microstructures Evaluated for Petrochemical Applications

Low-carbon steel was clad with austenitic stainless steel using three different processes: fusion welding, hot roll bonding, and inertia friction welding. Systematic metallurgical characterization was performed for the etching response, microhardness, compositional mixing, constituent phases, and morphology to evaluate their advantages and limitations. The composition across the transition region was used as the input into the Gooch equation for calculation of marten site start temperature to estimate the thickness of the martensite region. The E309L stainless steel fusion weld cladding exhibited a >100-mu m-thick, continuous region of interfacial martensite due to partial mixing with the base 1018 steel and subsequent phase transformation during cooling. In addition, the fusion weld exhibited large austenite grains. The combination of a continuous martensite layer and large austenite grains has been demonstrated to be detrimental in claddings for petrochemical applications. In comparison, solid-state joining methods suppressed the formation of martensite to different extents. For instance, hot roll bond cladding of 304L stainless steel on low-carbon steel precluded martensite layer formation due to the relatively low amount of total deformation, but the austenite grains were enlarged due to long holding times at an elevated temperature. On the other hand, friction welding produced thin (similar to 1 mu m) and discontinuous martensite interlayers and thin (similar to 5 mu m) austenite grains at the dissimilar interface, indicating good potential for cladding applications in petrochemical processing piping and equipment.