Abstract: High-temperature flue gas is a significant by-product during the rotary hearth furnace (RHF) smelting process. Its acidic components, especially hydrogen chloride (HCl), easily cause pipeline corrosion, thereby seriously endangering the safe and stable operation of the smelting system. Currently, although the studies on the chlorine-induced corrosion of steel under the scenarios of seawater, industrial pollution, and fused salt have been extensively conducted, they have relatively little reference value for understanding the HCl gas corrosion behavior of RHF flue gas, due to its typical characteristics such as large emission volume, high temperature (700-900 ℃), and complex gas and dust compositions. The typical materials of RHF flue gas pipeline (Q245R and 15CrMo) were selected as the objects, and the effects of HCl gas concentration and temperature on the corrosion behavior of the pipeline under simulated RHF flue gas conditions were experimentally studied. Simultaneously, the underlying corrosion mechanisms were clarified. The results showed that the corrosion of both materials is significantly aggravated with increasing temperature and HCl concentration. With the temperature rising from 700 to 900 ℃, the increased weight per unit surface area (IWPSA) of Q245R and 15CrMo under 0.4% HCl is increased from 1.89 and 2.38 to 3.56 and 4.47 mg cm^-2, respectively. Furthermore, at 900 ℃, increasing the HCl concentration from 0.1% to 0.5% leads to an increase in the IWPSA from 2.93 to 4.34 mg cm^-2 for Q245R and from 3.47 to 5.06 mg cm^-2 for 15CrMo. Moreover, compared with 15CrMo, Q245R exhibits better corrosion resistance in the oxygen-deficient environment, since the chromium content, which can facilitate the progress of corrosion reaction, of Q245R is low. Mechanism analysis of the corrosion process reveals that HCl molecules first penetrate the surface oxide layer to reach the interface between the oxide layer and substrate. Subsequently, HCl reacts with the base metal to form FeCl₂, which can be melted and volatilized, destroying the integrity of oxide layer and inducing its severe spallation.