The Atmosphere’s Effect on Stainless Steel Slabs’ Oxide Formation in a CH4-Fuelled Reheating Furnace

Abstract

Utilising the oxyfuel practice for CH4-fuelled combustion has positive effects on the emissions, efficiency and cost of high temperature furnace practices. However, especially in older installations, oxyfuel usage requires retrofitting and alters the atmosphere in which the oxidation of the steel occurs, when compared to using air as the oxidiser. Stainless steel slab oxide growth during reheating was studied in different atmospheres. The simulated post-burn atmospheres from oxyfuel, lean oxyfuel and air-fuel practices were used to compare oxide-scale layer growth and morphology during simulated typical AISI 304 stainless steel slab reheating prior to hot rolling. Thermogravimetric measurements, glow discharge optical emission spectrometer (GDOES) and field-emission scanning electron microscope energy dispersive X-ray (FESEM-EDS) methodology were applied to discern differences between oxide growth and inner oxide layer morphology between the three practices. Switching from air to oxyfuel practice at a single temperature had the same increasing effect on the scale formation amount as a 25 °C temperature increase in air atmosphere. Inner oxide layer depth profiling revealed C, Si and Ni to be the main elements that differed between temperatures and atmospheres. A morphology study showed Si and Ni behaviour to be linked to breakaway oxidation.

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

“…Similar observations of the formed oxide scale's composition have also been made at 1120 °C using an atmosphere based on methane–air burning that contained 0% oxygen [ 1 ] and also for longer oxidation times at 1275 °C in an atmosphere based on CH 4 –oxygen burning with 0% oxygen. [ 39 ] In this study, the composition and the structure of AISI 304 oxide scale formed using the 1O 2 atmosphere studied with 1 min of annealing at 1200 °C, and the GDOES elemental profile showed a chromium peak in the oxide layer with an increase of iron toward the oxide–metal interface (as seen in Figure 13 a). However, this profile does not differ from the profile produced by the 5O 2 atmosphere (see Figure 13b), which represents the distribution of elements in a thin layer of chromium‐rich oxide.…”

Oxide Scale Formation of Stainless Steels with Different Heating Methods – Effect of Hydrogen as Fuel

“…Another potential method to reduce material losses from hydrogen-fueled heating could be to minimize the amount of free oxygen in the post-burn atmosphere, which on laboratory scale showed the potential to decrease the oxidation rate of AISI 304 when using a lean oxyfuel method for methane. [29] Furthermore, the studied oxyfuel simulations revealed the worst-case scenario of oxidation, because the oxyfuel method allows for a shorter exposure time in the furnace than the air-fuel method due to a higher heating rate. [8] The faster heating of oxyfuel methods could affect the difference between the oxide scales of air-fuel and oxyfuel methods.…”

“…Weight gain as a function of time for simulations of different combustion methods in a reheating furnace is presented in Figure 2, and the total weight gain values of all methods and comparison to values obtained in a previous study [29] are shown in Table 3.…”

“…For the ferritic AISI 444, a thin oxide scale layer covered the surface after all heating methods, as shown in Figure 5. [29] 17.7 [29] 18.2 19.1 1275 4.1 0.4 20.0 [29] 22.7 [29] 33.0 Induction simulation produced a layer consisting of smaller oxide scale pieces, while after combustion simulations, oxide scale layers were more uniform.…”

“…[28] In addition, the lean oxyfuel method (no free O 2 ) produces significantly less oxide scale than a 3% free oxygencontaining air-fuel and oxyfuel methods of methane combustions for austenitic AISI 304 in simulating slab reheating. [29] The proportion of water vapor in the furnace atmosphere has an increasing effect on the oxide scale formation of stainless steels. [30,31] In reheating conditions, oxide scale growth in atmospheres containing water vapor has been generally studied using simulated methane combustion with air [32][33][34][35] or humid air atmospheres.…”