From Fossil‐Fueled to Hydrogen‐Fueled Annealing Furnaces: Effects on the Oxidation of Stainless Steels

Abstract

The possibility of replacing methane with hydrogen as the fuel gas in an annealing furnace is studied regarding the oxidation of ferritic AISI 441 and austenitic AISI 304 stainless steels during simulated short‐term annealing. Oxide‐scale formation using the simulated atmospheres based on methane–air, methane–oxygen, and hydrogen–oxygen combustions with different oxidant gas excesses is compared at steel grades’ furnace temperature ranges in an annealing process. Thermogravimetry is used to determine variations of weight gain during oxidation, and field‐emission scanning electron microscopy and glow discharge optical emission spectroscopy are used to characterize oxide scales. The transition to H2 as the fuel gas is more suitable for the ferritic grade than the austenitic grade at the studied temperatures. High water vapor content in hydrogen– and methane–oxygen combustion atmospheres promotes breakaway oxidation for both steel grades. Nodule formation is significantly observed under the most demanding annealing conditions for the ferritic grade, while only the lightest conditions remain without the signs of breakaway oxidation for the austenitic grade. Changes in the oxide‐scale structures produced in both hydrogen–oxygen and methane–oxygen atmospheres are in significant, which can facilitate the exchanges between these atmospheres in relation to methane–air combustion.