Microstructure Evolution Mechanism During Tempering Prosess Of X12CrMoWVNbN10₁Thermal Power Steel

For X12steel the most important mechanism of strengthening is strengtheningprecipitates. So the research on phase transition precipitated of X12steel is important.The current research focuses on the types of precipitates on high temperature.However, in practice due to the large size of the workpiece cause uneven cooling rateof inside and outside, so there is the phenomenon of self-tempering. Therefore, thispaper use Vickers hardness tester, optical microscopy, scanning electron microscopy,transmission electron microscopy to study microstructure and mechanical prope rtiesof X12steel under low-temperature tempering and analysis precipitation changes inthe microscopic.The results show that X12steel hardness began to decline in the400-550℃tempering in1h,tempering4h the hardness increased, this is because the martensitelath generated a lot of carbides. However, when tempered at600℃, the hardnessdecrease with prolonged tempering because the tempering temperature cause a largeincrease in the ferrite grains.650to700℃tempering hardness with temperingtemperature decreases, prolonged heat hardness unchanged.The study found that observed macroscopically, X12steel in the400-550℃tempering, tempering with the extension of time, the martensite lath width wider,narrower lengt h, In this temperature region tempe ring, with the extension of theholding time does not change the type of organizational structure.600℃tempering,X12organizational transformation into tempered steel troostite.700℃tempering,the organization into sorbite.X12steel at450℃tempering appeared only needle M3C precipitates,500℃start generating rod M7C3carbides,600℃tempering still find two carbideprecipitation phase precipitates in the martensite lath matrix.From the microscopic observation, X12steel in the450-600℃tempereing, Withthe extension of tempering time, the carbides begin decomposition During500-600℃tempering, With the extension of tempering time, the needle-like carbides decomposefaster than carbide rod, changing the tempering time has no effect on the shift ofcarbide type. Also found tempering temperature at550℃, with increasing annealingtime, the carbide on the substrate α-phase disappears,but tempering at600℃, Withthe extension time of tempering, carbides begin to precipitate in the α-phase matrix,some carbide nucleation occurs independently. With the increase of tempering temperature of two carbide size appeared adecreasing trend. Tempering temperature at650℃, ins ulation1h, the micros tructurehas no needles M3C carbide, but also retain a little rod M7C3precipitates.Whenholding time to8h, the organization is no longer found in the M7C3phase, replaced bya lump of M23C6carbides and MX tiny spherical precipitates. Tempering at700℃,the organization only MX type precipitates and M23C6phase.Mechanism for the observed changes in precipitation phase is formed in situmechanisms carbide concrete transition process is as follows:M3C→M3C+M7C3→M7C3→M7C3+M23C6→M23C6...