Hot compression experiments conducted on a Gleeble-3500thermo-mechanical simulator and metallographic observation tests were employed to study the critical conditions of dynamic recrystallization(DRX)of 316 LN auste...Hot compression experiments conducted on a Gleeble-3500thermo-mechanical simulator and metallographic observation tests were employed to study the critical conditions of dynamic recrystallization(DRX)of 316 LN austenitic stainless steel.The true stress-true strain curves of 316 LN were obtained at deformation temperatures ranging from 900℃to 1 200℃and strain rates ranging from 0.001s-1 to 10s-1.Based on the above tests,the critical conditions of DRX were determined and compared with those obtained from work-hardening theory and the Cingara-McQueen flow stress model.Furthermore,the microstructure was observed to validate the calculated results.The ratio of critical strain to peak strain(εc/εp)for 316 LN was determined,and the quantitative relationship between the critical strain and the deformation parameters of 316 LN was elucidated.The results demonstrated that the onset of DRX corresponds to the constant normalized strain hardening rate(Γ),namely,the critical strain hardening rateΓcfor316LN is equal to 0.65.展开更多
The compressive deformation behaviors of 300M high strength steel were investigated over a wide range of temperatures (850- 1200 C) and strain rates (0. 001- 10 s^- 1 ) on a Gleeble-3800 thermo-mechanical simulato...The compressive deformation behaviors of 300M high strength steel were investigated over a wide range of temperatures (850- 1200 C) and strain rates (0. 001- 10 s^- 1 ) on a Gleeble-3800 thermo-mechanical simulator. The measured flow stress was modified by the corrections of the friction and the temperature compensations, which nicely reflect negative effects of the friction and temperature on the flow stress. The corrected stress-strain curves were the dynamic recrystallization type on the conditions of higher deformation temperature and lower strain rate. Flow stress increases with the increase of strain rate at the same deformation temperature and strain. By contrast, flow stress decreases with the increase of temperature at the same strain rate and strain. Dependence of the peak stress on temperature and strain rate for 300M steel is described by means of the conventional hyperbolic sine equation. By re gression analysis, the activation energy (Q) in the whole range of deformation temperature is determined to be 367. 562 kJ/mol. The effects of the temperature and the strain rate on mierostructural evolution are obvious. With the increase of the deformation temperature and the decrease of the strain rate, the original austenite grain sizes of 300M steel increase. At the same time, the corrected flow stress curves more accurately determine the evolution of the microstrueture.展开更多
The influence of the MnS plastic inclusion on the accumulation of internal damage was considered, and the Gurson– Tvergaard–Needleman (GTN) model was calibrated based on the finite element inverse method and image a...The influence of the MnS plastic inclusion on the accumulation of internal damage was considered, and the Gurson– Tvergaard–Needleman (GTN) model was calibrated based on the finite element inverse method and image analysis method using ABAQUS and GTN models. The modified GTN damage model was used to simulate the initiation and propagation of cracks in an as-cast 304 stainless steel with MnS inclusions at 900 C. The simulation results agreed well with the experimental results, indicating that the model can be effectively applied to examine the high-temperature fracture behavior of MnS inclusions. The simulation and high-temperature tensile test results revealed that MnS inclusions increased the number of holes initiation and the probability of hole polymerization, reduced the crack propagation resistance, accelerated the occurrence of material fracture behavior, and were closely related to the stress state at high temperatures. When the stress triaxiality was low, the plastic strain in the metal matrix was high, and the MnS plastic inclusions accelerated the polymerization of the pores, making metal fracture failure more likely. On the other hand, when the stress triaxiality was high, the stress state in the metal matrix was biased to the tensile state, the plastic strain in the metal matrix was low, and the influence of MnS plastic inclusions on the fracture behavior was not evident.展开更多
Effect of aging heat treatment on the grain boundary microstructure and creep properties of a cast Ni-based superalloy was investigated. With increasing aging temperature from 750 to 1000 ℃, M_(23)C_6 carbides along ...Effect of aging heat treatment on the grain boundary microstructure and creep properties of a cast Ni-based superalloy was investigated. With increasing aging temperature from 750 to 1000 ℃, M_(23)C_6 carbides along the grain boundaries evolve from fine distributed block, continuous film into the coarse discrete block. Moreover, the M_(23)C_6 carbides are mainly enveloped within γ’ layers along grain boundaries during 1000 ℃ aging. Creep rupture lifetime and elongation at 760 ℃ and 645 MPa are improved with increasing the aging temperature. In particular, the creep rupture lifetime of the specimens aging at 1000 ℃ is one order of magnitude higher than that of the specimens aging at 750 ℃. The enhancement of ductility induced by the γ’ envelopes plays a significant role in the improvement of creep rupture lifetime.展开更多
The temperature changes at the rim,1/2 radius,and bore of the turbine disk during the solution treatment were measured.Based on the measured temperature data,solution treatment experiments with different cooling rates...The temperature changes at the rim,1/2 radius,and bore of the turbine disk during the solution treatment were measured.Based on the measured temperature data,solution treatment experiments with different cooling rates(14,51,and 93℃/min)were performed,and the solution temperatures were 1120 and 1080℃.At all three cooling rates,the multimodal size distribution of γ' precipitates was detected,and the size of γ' precipitates is inversely related to the cooling rate.Only the secondary and tertiary γ' precipitates were found at a solution temperature of 1120℃,and the secondary γ' precipitates progressed from spherical(93 and 51℃/min)to flower-like(14℃/min)shape,with the flower-like γ' precipitates regulated by aggregation.At a solution temperature of 1080℃,the γ' precipitates evolve from cuboids(93 and 51℃/min)to irregular shapes(14℃/min).Irregular γ' precipitates are affected by the lattice mismatch between the matrix and the γ' precipitates.展开更多
Nonmetallic inclusions mixed into large forged metal objects destroy the continuity in the metal and affect the quality of the forged product.Research on how inclusions affect the plastic deformation of a matrix shows...Nonmetallic inclusions mixed into large forged metal objects destroy the continuity in the metal and affect the quality of the forged product.Research on how inclusions affect the plastic deformation of a matrix shows the significance of the formation mechanism of inclusion defects.For upset forging,the nonlinear finite element model was shown to be appropriate for the ingot hot-forging process by comparing the results with experiments involving plastic and hard inclusions inserted into the forged piece.The high-temperature stress-strain curves of MnS plastic inclusions were obtained experimentally.The results show how,during upsetting,the morphology of MnS plastic inclusions varies from spherical to ellipsoidal,until finally becoming flat in shape.The larger the inclusion is,the larger the degree of deformation of the inclusion is,and large inclusions enhance the risk of the final product failing to pass inspection for inclusion flaws.Strain significantly concentrates in the matrix near a hard inclusion.When the hard inclusion reaches a certain size,conical fractures form on both sides of the inclusion.To pass inclusion-flaw inspection and close hole defects to the extent possible,the flat-anvil upsetting is recommended.Finally,the inclusiondeformation state obtained by finite element simulation is verified experimentally.展开更多
基金Item Sponsored by National Natural Science Foundation of China(51101136)Scientific and Technological Research Foundation for Outstanding Young Talents of Hebei Provincial Universities of China(Y2012034)College Innovation Team Leader Training Program of Hebei Province of China(LJRC012)
文摘Hot compression experiments conducted on a Gleeble-3500thermo-mechanical simulator and metallographic observation tests were employed to study the critical conditions of dynamic recrystallization(DRX)of 316 LN austenitic stainless steel.The true stress-true strain curves of 316 LN were obtained at deformation temperatures ranging from 900℃to 1 200℃and strain rates ranging from 0.001s-1 to 10s-1.Based on the above tests,the critical conditions of DRX were determined and compared with those obtained from work-hardening theory and the Cingara-McQueen flow stress model.Furthermore,the microstructure was observed to validate the calculated results.The ratio of critical strain to peak strain(εc/εp)for 316 LN was determined,and the quantitative relationship between the critical strain and the deformation parameters of 316 LN was elucidated.The results demonstrated that the onset of DRX corresponds to the constant normalized strain hardening rate(Γ),namely,the critical strain hardening rateΓcfor316LN is equal to 0.65.
基金Sponsored by Technology Major Projects of "High-end CNC Machine Tools and Basic Manufacturing Equipment"(2012ZX04010081)Natural Science Research Foundation Program for Distinguished Young Scholars in Higher EducationInstitutions of Hebei Province of China(Y2012034)
文摘The compressive deformation behaviors of 300M high strength steel were investigated over a wide range of temperatures (850- 1200 C) and strain rates (0. 001- 10 s^- 1 ) on a Gleeble-3800 thermo-mechanical simulator. The measured flow stress was modified by the corrections of the friction and the temperature compensations, which nicely reflect negative effects of the friction and temperature on the flow stress. The corrected stress-strain curves were the dynamic recrystallization type on the conditions of higher deformation temperature and lower strain rate. Flow stress increases with the increase of strain rate at the same deformation temperature and strain. By contrast, flow stress decreases with the increase of temperature at the same strain rate and strain. Dependence of the peak stress on temperature and strain rate for 300M steel is described by means of the conventional hyperbolic sine equation. By re gression analysis, the activation energy (Q) in the whole range of deformation temperature is determined to be 367. 562 kJ/mol. The effects of the temperature and the strain rate on mierostructural evolution are obvious. With the increase of the deformation temperature and the decrease of the strain rate, the original austenite grain sizes of 300M steel increase. At the same time, the corrected flow stress curves more accurately determine the evolution of the microstrueture.
基金This research was supported by the National Natural Science Foundation of China (Grant Nos. 51575475 and 51675465).
文摘The influence of the MnS plastic inclusion on the accumulation of internal damage was considered, and the Gurson– Tvergaard–Needleman (GTN) model was calibrated based on the finite element inverse method and image analysis method using ABAQUS and GTN models. The modified GTN damage model was used to simulate the initiation and propagation of cracks in an as-cast 304 stainless steel with MnS inclusions at 900 C. The simulation results agreed well with the experimental results, indicating that the model can be effectively applied to examine the high-temperature fracture behavior of MnS inclusions. The simulation and high-temperature tensile test results revealed that MnS inclusions increased the number of holes initiation and the probability of hole polymerization, reduced the crack propagation resistance, accelerated the occurrence of material fracture behavior, and were closely related to the stress state at high temperatures. When the stress triaxiality was low, the plastic strain in the metal matrix was high, and the MnS plastic inclusions accelerated the polymerization of the pores, making metal fracture failure more likely. On the other hand, when the stress triaxiality was high, the stress state in the metal matrix was biased to the tensile state, the plastic strain in the metal matrix was low, and the influence of MnS plastic inclusions on the fracture behavior was not evident.
基金financially supported by the National Key Research and Development Program of China (No. 2016YFB0701403)the National Natural Science Foundation of China (Nos. 51701220, 51631008, 51671196 and 51871210)
文摘Effect of aging heat treatment on the grain boundary microstructure and creep properties of a cast Ni-based superalloy was investigated. With increasing aging temperature from 750 to 1000 ℃, M_(23)C_6 carbides along the grain boundaries evolve from fine distributed block, continuous film into the coarse discrete block. Moreover, the M_(23)C_6 carbides are mainly enveloped within γ’ layers along grain boundaries during 1000 ℃ aging. Creep rupture lifetime and elongation at 760 ℃ and 645 MPa are improved with increasing the aging temperature. In particular, the creep rupture lifetime of the specimens aging at 1000 ℃ is one order of magnitude higher than that of the specimens aging at 750 ℃. The enhancement of ductility induced by the γ’ envelopes plays a significant role in the improvement of creep rupture lifetime.
基金supported by the National Science and Technology Major Project(2017-VI-0018-0090).
文摘The temperature changes at the rim,1/2 radius,and bore of the turbine disk during the solution treatment were measured.Based on the measured temperature data,solution treatment experiments with different cooling rates(14,51,and 93℃/min)were performed,and the solution temperatures were 1120 and 1080℃.At all three cooling rates,the multimodal size distribution of γ' precipitates was detected,and the size of γ' precipitates is inversely related to the cooling rate.Only the secondary and tertiary γ' precipitates were found at a solution temperature of 1120℃,and the secondary γ' precipitates progressed from spherical(93 and 51℃/min)to flower-like(14℃/min)shape,with the flower-like γ' precipitates regulated by aggregation.At a solution temperature of 1080℃,the γ' precipitates evolve from cuboids(93 and 51℃/min)to irregular shapes(14℃/min).Irregular γ' precipitates are affected by the lattice mismatch between the matrix and the γ' precipitates.
基金Item Sponsored by National Natural Science Foundation of China(51575475)College Innovation Team Leader Training Program of Hebei Province of China(LJRC012)
文摘Nonmetallic inclusions mixed into large forged metal objects destroy the continuity in the metal and affect the quality of the forged product.Research on how inclusions affect the plastic deformation of a matrix shows the significance of the formation mechanism of inclusion defects.For upset forging,the nonlinear finite element model was shown to be appropriate for the ingot hot-forging process by comparing the results with experiments involving plastic and hard inclusions inserted into the forged piece.The high-temperature stress-strain curves of MnS plastic inclusions were obtained experimentally.The results show how,during upsetting,the morphology of MnS plastic inclusions varies from spherical to ellipsoidal,until finally becoming flat in shape.The larger the inclusion is,the larger the degree of deformation of the inclusion is,and large inclusions enhance the risk of the final product failing to pass inspection for inclusion flaws.Strain significantly concentrates in the matrix near a hard inclusion.When the hard inclusion reaches a certain size,conical fractures form on both sides of the inclusion.To pass inclusion-flaw inspection and close hole defects to the extent possible,the flat-anvil upsetting is recommended.Finally,the inclusiondeformation state obtained by finite element simulation is verified experimentally.