Investigation Of Microstructure And Properties Of Blades Steel 10Cr12Ni3Mo2VN For USC Unites

In order to reduce fuel consumption and environmental pollution,Ultra supercritical(USC)unites have been developed and used in worldwide.The materials used for USC unites must have higher properties.Last stage blades are key component of USC unites,which are mainly produced by martensitic heat-resistant steels.Now,our nation still cannot produce high quality martensitic heat-resistant steels used for USC unites last stage blades.Some technologies are still not mastered,such as forging,heat treatment,elimination of mechanical properties anisotropy and 8 ferrite,and improvement of low-temperature toughness.That hinders the development of domestic USC unites.Based on the background,development of martensitic heat-resistant steels used for USC unites last stage blades is included into the 863 Program.In order to promote the development of domestic martensitic heat-resistant steels,in this paper,several common scientific problems of steel 10Cr12Ni3Mo2VN used for 600?USC unites last stage blades were systematically studied by investigating the relationship between microstructure and mechanical properties and the production technology.The phase transformation of steel 10Cr12Ni3Mo2VN was researched to provide theoretical basis for optimization design of forging and heat treatment.The austenite transformation temperature Ac1 and AC3 are 750?and 925?respectively.Generally,the equilibrium precipitation temperature of?ferrites is about 1200?.Under a cooling rate of 0.05?/s or above,only martensitic transformation occurs during the cooling process after austenitizing.The influence of quenching and tempering on mechanical properties of steel 10Cr12Ni3Mo2VN was studied.And the heat treatment technology was optimized.There is some irreversible temper embrittlement when tempered at 625?.The temper embrittlement can be overcame by re-tempering at higher temperature.In addition,the precipitation of precipitates during tempering and the influence of precipitates on mechanical properties were investigated.The tempered embrittlement at 625?is attributed to the precipitation of M23C6 along martensite lath and grain boundaries.The low-temperature toughness of steel 10Cr12Ni3Mo2VN are mainly influenced by grain size,large size M23C6(bigger than 500nm)and tempering temperature.Refining grains and increasing tempering temperature can significantly improve the low-temperature toughness.The large size M23C6 have an extremely adverse effect on the low-temperature toughness.The effect mechanism of grain size and large size M23C6 on low-temperature toughness was investigated.In order to meet the requirement FATT50?-35?,the optimum microstructure was proposed.The mechanical properties anisotropy of steel 10Cr12Ni3Mo2VN is caused by banded 8 ferrites and unrelated with other precipitates.Heat treatment has a little influence on anisotropy.The effect mechanism of 8 ferrites on mechanical properties anisotropy was studied.The 8 ferrites damage transverse toughness by promoting the formation of brittle pre-cracks.In order to get high mechanical properties isotropy,8 ferrites in forging bars must be eliminated.The high-temperature deformation behavior of steel 10Cr12Ni3Mo2VN was studied by thermal simulation experiment.Completely dynamic recrystallization occurs at 1100?and above.High-temperature deformation has a significant influence on heat treatment microstructure due to microstructure heredity.The tensile embrittlement mechanism at about 800?was investigated.The embrittlement is attributed to intergranular cracks.Refining garins can improve the high-temperature plasticity.The technology of refining and homogenizing microstructure by high-temperature large deformation was put forth.At room temperature,the 8 ferrite is nonequilibrium phase and caused by the microsegregation of electroslag remelting ingot.The?ferrites in forging bars are difficult to be eliminated by quenching and tempering.The?ferrites in electroslag remelting ingot can be reduced by high-temperature solution,but the solution rate is low.High-temperature deformation can markedly promote the solution of 8 ferrites by increasing the interface area and interior grain boundaries.The technology of improving solution rate of 8 ferrites by large deformation and the forging technology of eliminating 8 ferrites were put forth.According to the basic-characteristic and relationship between microstructure and properties,the integrated quality control technology containing forging,heat treatment and microstructure and properties controlling was put forth and applied to industrial production.Domestic steel 10Cr12Ni3Mo2VN with no?ferrites,no mechanical properties anisotropy and excellent low-temperature toughness has been massively and stably produced and supplied for blades production.