Abstract: Due to high content of alkali metals such as Na and K in Zhundong coal and biomass,there will be related problems of ash in the combustion process,and it is easy to slag and deposit on the heating surfaces in the combustion process,resulting in high-temperature corrosion of metal tube,which will affect the heat exchange efficiency and use safety of metal tube bundles.In serious cases,it can lead to tube explosion and threaten the normal and safe operation of the boiler.In this paper,the high-temperature corrosion test under simulated flue gas was conducted on metal materials of 15 CrMoG and T91 and the deposition corrosion of alkali metal salt on the surface of heating surface was simulated by KCl coating method. The morphology and composition of corrosion products were analyzed by SEM,EDS and XRD,and the effects of metal materials,corrosion time and reaction temperature on the high temperature corrosion of alkali metal chloride were studied.The results show that the KCl coating on the metal surface aggravates the high-temperature corrosion,and the alkali metal chloride can effectively intensify the high-temperature corrosion of the metal materials.Under various corrosion time and reaction temperature,the weight gain and thickness of corrosion layer of metal material 15 CrMoG are greater than that of T91,indicating that the corrosion resistance of T91 is greater than that of 15 CrMoG.With the increase of reaction time,the weight and thickness of corrosion increase gradually,while the corrosion rate decreases gradually. Compared with the corrosion time between 20-48 h,the corrosion rate is faster when the corrosion time is less than 20 h and the corrosion curve generally conformes to the parabolic law. The main reason for the decrease of corrosion rate in the later stage of corrosion is that high-temperature corrosion will lead to the formation of dense oxide film covering the metal substrate surface,which has a protective effect on the metal and slows down the occurrence of corrosion.With the increase of reaction temperature,the corrosion is intensified.When the temperature is lower than 500 ℃,the slope of the curve is smaller and the corrosion rate is lower; when the temperature is higher than 500 ℃,the slope of the curve is obviously increased and the corrosion rate is faster.The trend of temperature corrosion thickening curve is basically the same as that of weight increase curve and the corrosion curve is in accordance with parabola law.With the increase of temperature,the chemical reaction rate of alkali metal corrosion has an exponential relationship with the temperature.With the increase of temperature,the number of active molecules participating in the corrosion reaction increase,and the corrosion reaction rate is accelerated rapidly.It can be seen from the corrosion micrograph that before corrosion,the metal matrix structure is complete and the surface is smooth.After corrosion,the contact surface between the metal and the corrosion layer appeares uneven structure.With the increase of corrosion time,the thickness of the corrosion layer increases gradually. According to the results of SEM-EDS,the main components of the corrosion products of the two kinds of metal materials are Fe and O.Combined with XRD peak spectrum identification,the corrosion products of the metal materials are mainly in the form of Fe_2O_3.