The significant roles of Nb and Mo on enhancement of high temperature urea corrosion resistance in ferritic stainless steel

Abstract The significant roles of Nb and Mo on enhancing high temperature urea corrosion (HTUC) resistance of ferritic stainless steels applied in selective catalytic reduction (SCR) system of commercial vehicle were investigated. By slightly increasing of Nb or Mo, the reactivation rate (Ra) of ferritic stainless steels was significantly reduced, indicating an improvement in HTUC resistance. High temperature nitriding induced by the decomposition of urea resulted in precipitation of chromium nitride particles, which caused chromium depletion in the matrix and resultant deterioration of corrosion resistance. Moreover, the high temperature oxidation accompanied by thermal fatigue further accelerates the formation and exfoliation of oxide layer, showing detrimental consequences on service life of materials for commercial vehicle.