Reheat furnace atmospheres

Oxidation of iron and some commercial steels in reheat furnace atmospheres was extensively studied by the GKN group from the late 1950s to the early 1970s [33,54] and was reviewed by Sachs and Tuck [25] and by Ajersch... 

Summarizing the above studies on iron and steel oxidation in reheat furnace atmospheres, it can be concluded that ... 

Oxidation of iron and steel in reheat furnace atmospheres initially follows the linear rate law. The initial period can be very long when the free oxygen concentration is low or absent. 

Oxidation in reheat furnace atmospheres follows the linear law initially and may become parabolic at the later stage if the furnace atmosphere contains a sufficient amount of free oxygen. 

In the presence of free oxygen, the dominant oxidizing species in the reheat furnace atmosphere is oxygen. 

M. Odgers and C. W. Tuck, Scaling of mild steel and pure iron in simulated reheating furnace atmospheres . Internal Report No. 947, GKN Group Research Centre, August 1967. 

Table 5-4 summarizes the types of high-temperature corrosion which occur in various industrial processes (Lai et al., 1985). As can be inferred from this table, many high-temperature processes involve atmospheres which contain oxidants in addition to O2, H2O, or CO2 the most prevalent of these are sulfur, carbon, nitrogen, and chlorine. The corrosive effects of these additional oxidants depend on the oxygen potential in the atmosphere, which is measured by the equilibrium Pq. In relatively high- multi-oxidant atmospheres, such as those resulting from the combustion of hydrocarbon fuels with excess air, the corrosive effects tend to be minimal or even beneficial. An example of a beneficial effect is that of traces of sulfur in the combustion environment of a reheat furnace which acts to slow the oxidation rate of steel as a result of a surface-poisoning effect (Lee, 1997). 

As discussed earlier, slab reheating in the conventional strip process route is achieved by burning natural gas or other fuels in a reheat furnace. In the thin slab casting route, equalization of slab temperature is usually achieved in a natural-gas-combusted tunnel furnace. The common feature in these processes is that the slab is oxidizing in an atmosphere containing a mixture of several gas species. Normally, the furnaces are operated under air-rich combustion conditions, i.e. more than sufficient amounts of air are used to react with the fuels introduced to the furnaces, and therefore, when in equilibrium, the... 

At temperatures in excess of 750°C the addition of water vapour accelerates the rate of growth of FeO (Fig. 7.10) by producing large pores in the FeO" . At much higher temperatures (1 200°C) Sheasby et have found that addition of steam to Oj-Nj, Oj-HjO-Nj and HjO-Nj, in a simulated reheating atmosphere furnace, caused increases in scale growth due to improved adhesion at the scale/metal interface. They concluded that water vapour enhances scale creep as previously reported by Tuck et... 

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