Influence Of Si And Mn Contents On Microstructure And Tensile Properties Of In625 Alloy

Under the background of energy crisis and environmental problems,it is imperative that further improve the efficiency of coal-fired power plants to achieve energy-saving emission reduction.The development of advanced ultra-supercritical（A-USC）with steam temperature of up to 700℃ become urgent.Alloy In625 is a Ni-Cr-Mo based alloy to achieve a unique combination of mechanical strength,fabricability,weldability and corrosion resistance under aggressive environments,which has been designed for use as air cylinder and valve casing materials for boilers in 700℃ advanced ultra-supercritical（A-USC）coal-fired power plants.The current domestic large superalloy casting technology is basically blank,Si and Mn element of trace element have important influence on the microstructure and service performance of cast superalloy.This paper manufacture small furnace with nine different Si and Mn content of alloys,the microstructure of solidification,solid solution and long-term thermal exposure were analyzed,and combined with the tensile properties of room temperature and 700℃.The experimental basis and theoretical basis for the optimization of Si and Mn contents were carried out,while further revealing the role of Si and Mn in alloy casting mechanism.The research conclusions are as follows:Alloy In625 only MC carbides present when it without addition Si and Mn elements.Si is a strong Laves phases forming element,which promotes the formation of γ/Laves eutectic structure in the alloy solidification structure.With the addition of Si content,Laves phases,MC carbides and γ significantly lower melting temperature,γ / Laves eutectic microstructure by a mesh-like shape to the petals,massive Laves phase evolution,but also a significant increase in the content of Laves phase and MC carbide content decreasing.Mn content on the precipitation of alloy solidification organizations had no obvious effect,but its promote dendritic segregation is aggravating,so that combined additions of Si and Mn alloy compared to the same amount of added Si content of the alloy alone,Laves phase morphology and its contents have a certain change.Si and Mn element can promote alloy increase secondary dendrite.After the solid solution treatment at 1200 ℃/1h/WQ,which γ / Laves eutectic into a massive Laves phase of of Si-containing alloys.The addition of Si and Mn had little effect on the yield strength at 700℃ and plasticity of the alloy,but significantly deterioration in the alloy yield,ultimate tensile strength at room temperature and ultimate tensile strength at 700 ℃,especially in Si and Mn content is higher,or combined additions of Si and Mn,the tensile strength decreased significantly.All alloys after long-term aging at 700℃ for 5000 h,γ" phase apparent coarsening,MC carbides small amount of degradation of M₂₃C₆ carbides.Meanwhile,Laves phases can also degenerate into M₂₃C₆ carbides of Si-containing alloys.The grain boundaries of the alloys that not additioned Si element are continuous M₂₃C₆ carbide film,while the Si element promotes the precipitation of M6 C carbides,which makes the grain boundary of Si-containing alloys is mainly M6 C carbide film.In addition,Si elements promote that the alloys precipitated η-M6 C carbides after thermal exposure,and with Si content increased η-M6 C carbides content increased.The Mn element has no obvious effect on the long-term aging microstructure of the alloy.The tensile test at 700℃ of all alloys after long-term aging at 700℃ for 5000h: when Si or Mn content is 1.5 wt.%,the tensile strength and ductility of the alloy are obviously deteriorated.In conclusion,in cast In625 alloys,Si element has a great influence on the microstructure evolution of the alloy,while the Mn element has no obvious effect on the microstructure of the alloy.Considering the microstructure and tensile properties of the alloy,the content of Si or Mn need be strictly control less than 1.0wt.%.