Effects of radial bending stress on hot corrosion behaviour of dissimilar martensitic heat-resistant steel weldments in ultra-supercritical unit

The influences of the applied radial bending stresses on the corrosion behaviour of dissimilar weldments of two types of martensitic heat-resistant steel (F92/Co3W2) are investigated with NaCl-Na2SO4 deposited salts at 620 °C and 24 hours employing a four-point bending jig. The applied external stress exhibits no obvious influence on corrosion products, which mainly consist of Fe2O3, Fe3O4, and FeCr2O4. However, the stress tends to aggravate the corrosion degree, and the weldments with stress addition yield more mass gain and greater corrosion scale thickness. Such phenomenon is more serious in the parent F92, implying F92 is more sensitive to the corrosion environment with stress. The corrosion scale of weldments without stress shows typical double-layer structure: outer Fe-O layer and inner Fe-Cr-O layer, while the weldments with bending stresses show interesting multi-layers (10 or more layers) with Fe-oxide and Fe, Cr-oxide alternately appearing. The mechanism for hot corrosion behaviour and the influence of hot corrosion on the local mechanical properties of different welding zones with and without stresses are further discussed.