Evaluation of High Temperature Oxidation Behavior and Adhesion of Heat-Resistant Ferritic Steel Claddings on Austenitic Stainless Steel Produced by GTAW Process

In the present paper, in order to improve the high temperature oxidation resistance of 316 AISI stainless steel, claddings of ER446 and ER446 + 4 wt. % Al filler wires were deposited on this steel using GTAW process. The chemical composition, phase types and microstructure of the claddings were determined by light microscopy (OM), electron microscopy (FESEM-EDS) and X-ray diffraction (XRD). The oxidation behavior of the cladded samples was evaluated and compared using isothermal oxidation test in air (at 1000 °C) and air + 1.5% SO2 (at 800 °C) environments. The adhesion of the interface between the claddings and the substrate was measured by shear strength test before and after oxidation according to ASTM A264 standard. Microstructural observations from the cross section showed that both claddings had excellent adhesion to the substrate and no cavities and discontinuities were observed in the interface between the claddings and the substrate. The results of shear strength test showed that both claddings before and after high temperature oxidation have higher shear strength than the minimum value specified (140 MPa) in the ASTM A264 standard. l Evaluation of the oxidation behavior of the base metal before and after the exert of the coating showed that the claddings (especially with present 4% Al) strongly reduced the oxidation rate (improving the oxidation resistance) in both oxidizing environments. In the early stages of oxidation, chemical reactions at the interface between the oxide scale and the metal controlled the oxidation reaction, and after primarily stages until the end of examination, the diffusion and transfer of oxygen and aggressive ions through the oxide scale toward the interface controlled the oxidation process. It was found that the oxidation kinetics of both claddings follow the parabollic law of oxidation and the cladding containing 4% Al had a constant oxidation rate (kp) 16 times lower than the coating without aluminum. The results showed that the presence of SO2 gas increased the oxidation rate of both claddings.