Study On Thermal Deformation Behavior Of New Type 9Cr And 12Cr Heat-resisting Steels

Thermal power generation is the main force of Chinese power industry.Therefore,it is necessary to improve the efficiency of thermal power generation as well as reduce energy consumption and greenhouse gas emissions,In order to meet the ever-increasing demands of power plant steam parameters,9%-12%Cr heat-resistant steels have been widely applied to the key components such as rotors and vanes in power station units.This kind of heat-resistant steels have excellent high temperature creep strength and good steam oxidation resistance.13Cr9 Co VNi Nb NB and 11Cr12Ni3Mo2 VN heat-resistant steels belong to martensitic steels,being suitable for key components of ultra-supercritical thermal power generating units.Gleeble-3500 thermo-mechanical simulator was used in this paper.Then the stress-strain curves of 13Cr9 Co VNi Nb NB and 11Cr12Ni3Mo2 VN at different temperatures from 900? to 1050? and strain rates from 0.001s-1 to 10s-1 were drawn out.By analyzing the flow stress under different conditions,the variation of flow stress with temperatures and strain rates was studied.By introducing the Zener-Hollomon parameter,the flow stress constitutive equations of 13Cr9 Co VNi Nb NB and 11Cr12Ni3Mo2 VN were established.Then the accuracy and error of the constitutive equation was verified and analyzed.The results confirmed that the proposed equations can be used to describe the hot deformation behavior of 13Cr9 Co VNi Nb NB and 11Cr12Ni3Mo2 VN steels.Microstructure of the materials after hot deformation also studied in this paper.The result shows: The temperatures and strain rates have great impacts on the microstructure of the materials after hot deformation.At low temperatures,dynamical recovery dominates and dynamic recrystallization is difficult to occur.At high temperatures,dynamical recrystallization tends to occur.In addition,the strain rates have a great influence on the size of the dynamical recrystallized grains.At high strain rates,the dynamic recrystallization process is inadequate due to the short time of hot deformation.Relatively speaking,low strain rates can create better conditions for the dynamical recrystallization.Then the TEM photos of 13Cr9 Co VNi Nb NB heat-resisting steel were studied.It is understood that the density of dislocations,the number and size of dislocation cells contained in the grains are affected by temperatures and strain rates.In addition,the study also found that the temperature have a great impacts on the way of dynamical recrystallization grain nucleation.In order to determine the hot deformation processing parameters of 13Cr9 Co VNi Nb NB and 11Cr12Ni3Mo2 VN heat-resistant steels,two heat-resisting steels' hot processing maps has established in this paper.The analysis of the 13Cr9 Co VNi Nb NB heat-resistant steel found that the power dissipation parameter was less affected by the strain.But the strain has a great influence on instability maps.As for the 11Cr12Ni3Mo2 VN heat-resistant steel,the power dissipation parameter was very low at ?=0.2.And at ? = 0.5 and 0.7,the greater power dissipation parameter occurs.Therefore,in the determination of the hot deformation process of 13Cr9 Co VNi Nb NB and 11Cr12Ni3Mo2 VN heat-resistant steels,the effects of strain,temperature and strain rate should be comprehensively considered.