Long-term oxidation behaviour and thermal stability of heat-resistant stainless steel claddings deposited on AISI 316 stainless steel by the GTAW process

Abstract

In the present study, the microstructure, oxidation behaviour, and thermal stability of the ER310 and ER446 weld overlay claddings deposited on AISI 316 stainless steel by the gas tungsten arc welding (GTAW) process were investigated. In this regard, the chemical composition, microstructure, and phase composition of the weld metals were characterized by optical microscopy (OM), field-emission scanning electron microscopy (FESEM-EDS), and X-ray diffraction (XRD) analysis. The oxidation behaviour and the bonding state of the clad plates were evaluated and compared after 1500 h of oxidation at 1000 °C using the isothermal oxidation and shear strength tests. Cross-sectional microstructural observations revealed that the substrates and weld overlay claddings were well bonded, and dense and uniform cladding layers without pores, cracks, or discontinuities were achieved. The weld metal produced by ER310 filler wire exhibited a completely austenitic microstructure, while the weld overlay produced by ER446 filler wire showed a ferritic-martensitic two-phase microstructure. The shear strength test results indicated that the bond strength of the ER446/AISI 316 and ER310/AISI 316 interfaces in the as-welded and oxidized conditions was higher than the minimum value (140 MPa) stated in the ASTM A264 standard. It was found that the oxidation process did not significantly reduce the bond strength of the interfaces. The weight gain data showed that both weld overlay claddings follow the parabolic rate law of oxidation, improving the oxidation behaviour of the AISI 316. The ER446 weld overlay had a lower parabolic rate constant (k p ) than the ER310 weld overlay. The SEM images showed that the oxide scales formed on the weld overlay claddings mainly consisted of three layers; Si-rich oxide at the innermost layer, Cr-rich oxide in the middle layer, and spinel oxide at the outer part of the scale. The oxidation behaviour of the clad samples was explained by the diffusion coefficients of elements, thermal stresses, and growth stresses, which are all associated with the matrix structure. • Heat-resistant stainless steel claddings were deposited on the surface of AISI 316 stainless steel using the GTAW process. • Thermal stability and oxidation behavior of the claddings after 1500 h of isothermal oxidation at 1000 °C were investigated. • The ER446 overlay displayed a ferritic-martensitic, while the ER310 overlay exhibited a fully austenitic microstructure. • The clad plates in the as-welded and oxidized conditions had a strength higher than the minimum value stated in ASTM A264. • Both ER446 and ER310 weld overlay claddings were improved the oxidation behaviour of the substrate.