The Research Of Effect Of Temperature On Microstructure And Properties Of X12CrMoWVNbN10-1-1 Steel

X12CrMoWVNbN10-1-1 steel(X12 steel for short)are widely used to manufacture castings and forgings like turbine disk,rotor and valve-body of ultra-supercritical steam turbines,due to its desirable properties including low coefficient of thermal expansion and high thermal conductivity,good corrosion and oxidation resistance,excellent elevated temperature strength and creep resistance.The current research focus on phase transformation,heat treatment process,elevated temperature creep behavior and so on.But few researches focuses on high temperature mechanical properties,it is not clear how the mechanical properties and microstructure of materials change with temperature.This paper try to find out how the temperature effect on microstructure and mechanical properties of X12 steel by tensile test at room temperature,300?,350?,400?,450?,500?,600?,analyze of microstructure,facture surface through optical microscopy,scanning electron microscopy,transmission electron microscopy.The follow facts are discovered:(1)Tensile test results showed that the strength of X12 steel decreased with temperature,but the elongation of materials firstly decreased and then increased rapidly with the increased of temperature,the lowest interval elongation was occurred at 400?,it was 14.2%.During experimental temperature,the dimples were firstly shallow,smaller and then been deepen,bigger.The smallest and shallowest dimples was also occurred at 400?.(2)During 300?-400?,the main precipitation in matrix were M3C carbides,the quantity and size of brittle M3C carbides gradually increased,the segregation also been more significantly with the increased of temperature.M7C3 carbides precipitated at 400?.A large amount of M7C3 carbides was precipitated in martrix after holding at 500?.M23C6 carbides became the main precipitation of X12 steel after holding at 600?.(3)Between 300? and 400?,continuously increased and segregated M3C carbides which results increase of precipitation strengthening and work hardening ability,the stress concentration and cracks were more prone to appear,propagate,accelerate the fracture of materials at around M3C carbides during deformation.The plasticity and strength slowly decreased with temperature.Above 400?,the precipitation began to transform.With the increased of temperature,M3C carbides decomposed rapidly and M7C3 carbides gradually generated on the ferrite surface.Continued to raise temperature,M7C3 carbides transform to M23C6 carbides by in-situ transformation.From 400? to 600?,with the increase of temperature,carbide transformation make the quantity of precipitations decreased which results decrease of strengthening ability,simultaneously,dynamic recovery play a major role,leading to dramatic decrease of strength,fast increase of plasticity.