• Increasing impurity content significantly reduces the hot corrosion resistance of DD98M alloy at 950 °C in Na2SO4+NaCl salt.
• Nitrogen impurities increase alloy porosity, facilitating rapid diffusion of molten salt and oxygen into the alloy.
• Bilateral diffusion of oxygen and sulfur leads to accumulation at the oxide-matrix interface, promoting interfacial crack formation and propagation.
• A growth model for hot corrosion products was developed, accounting for varying impurity levels.