A Of .1 Cr20co6ni2wmov Steel Flow Stress Model Of Heat Treatment On Microstructure,

Under the isothermal hot compression, the flow stress model and microstructure evolvement of 1Cr20Co6Ni2WMoV martensitic heat-resistant steel were researched using Gleeble-2000. The effects of the heat treatment on the microstructures were also investigated systematically by means of optical metallography, SEM, TEM, XRD and chemistry quantitative analysis. According to the above results, the strengthening mechanism of the heat- resistant steel was also discussed. Summing the paper, the main results are as follows.Under different hot deformation temperatures, dynamic recrystallization occurs obviously in steel 1Cr20Co6Ni2WMoV during hot compression at low strain rate. Only dynamic recovery occurs when the strain rate over 10s^-1. The size of dynamic recrystallization grain decreases obviously with the decreasing of deformation temperature and increasing of strain rate. The critical deformation amount for recrystallization and complete recrystallization amount both increase with the increasing of Z parameter, i.e., with the decreasing of deformation temperature and increasing of strain rate. Especially critical deformation amount of the complete recrystallization has been changed obviously.The hot deformation activation energy of steel 1Cr20Co6Ni2WMoV during hot compression is 508.137 kJ/mol. The peak stress expression is:Martensite lath width of the steel 1Cr20Ni2Co6WMoV is about 0.15～0.5μm under different heat treatment. There is a well relationship between martensite lath width and mechanical properties of the steel. The martensite lath break up partly and the lath boundary become blurred with the reducing of cold treatment temperature and rising of tempering temperature.The results of TEM and XRD showed that there is only M₂₃C₆ carbide in steel 1Cr20Ni2Co6WMoV. The M₂₃C₆ carbides are distributed in the steel by two different means. First, carbides are distributed at the ferrite boundary,ferrite grain inner and the martensite lath inner under the shape of dark strip and chain. The size of these carbides is changed from several nanometer to more than ten nanometer. These carbides play animportant role in strengthing the steel. Second, the bigger M₂₃C₆ carbides formed during metallurgy are distributed at the grain inner and boundary under the shape of dark ellipse and globosity, which size can reach to about 1μm. The amount of M₂₃C₆ increases with decreasing of cold treatment temperature. With tempering temperature increasing, the M₂₃C₆ carbides in the martensite lath become coarsen, getting together and growing up. And there are secondary M₂₃C₆ carbides precipitated on dislocation line during low tempering temperature.There are 60.48% residual austenite in the quenched steel 1Cr20Ni2Co6WMoV. The residual austenite content changes with the changing of cold-treatment temperature, the cold-treatment temperature lower, the residual austenite content fewer. The residual austenite content of the steel is 3.88% after treatment: 1060℃ × 1h+(-70℃)×2h+ 640℃ ×2h.The main strength mechanism of the steel is composed of the martensite phase transformation, carbide precipitation and solid solution, especially by Co solid solution.