Microstructure Characteristics of 12Cr1MoV Heat Pipes with the Combined Effects of Compression Creep and Molten Alkali Salts Corrosion

12Cr1MoV is one of the low alloy steels which is widely applied in heat pipes of biomass fired boilers. But with the combined effects of molten alkali salts corrosion caused from combustion of biomass and creep deformation which is resulted by the high temperature stress as well as steam pressure, they bring negative influence on the mechanical properties. Based on the fact, the present work mainly focuses on studying the microstructure deformation of samples after compression creep in different molten alkali salts. 12Cr1MoV steels chosen as candidate materials are first cut by EDM. Molten salts conditions are described as NaCl-40%KCl, NaCl-70%KCl and NaCl-40%Na2SO4. Creep properties of 12Cr1MoV in molten salts were obtained by the creep test at 150 MPa. Experiments were tested on RDL05 electronic creep fatigue test machine after reformation to create a condition of hot corrosion. The results showed that different creep deformation was generated by different salt mixtures. When the temperature was set at 650°C, sample in molten NaCl-70%KCl showed the severest destruction than other samples on surfaces and cross sections. In these areas, the applied stress played a synergic role with corrosion leading to the progressive loss of material load-bearing capacity. On the substrate, spheroidization of cementites and precipitation of carbides along grain boundaries were clearly detected, which is also the reason to lower the strength of 12Cr1MoV. It is interesting to note that creep deformation of microstructures in NaCl-40%Na2SO4 was the weakest, indicating that sulfates can suppress corrosion effects of molten chlorides.