The dynamic recrystallization behavior of microalloyed forged steel was investigated with a compression test in the temperature range of 1 223-1 473 K and a strain rate of 0. 01-5 s^-1. Activation energy was calculate...The dynamic recrystallization behavior of microalloyed forged steel was investigated with a compression test in the temperature range of 1 223-1 473 K and a strain rate of 0. 01-5 s^-1. Activation energy was calculated to be 305.9 kJ/mol by regression analysis. Modeling equations were developed to represent the dynamic recrystallization volume fraction and grain size. Parameters of the modeling equations were determined as a function of the Zener-Hollomon parameter. The developed modeling equation will be combined with finite element modeling to predict microstructural change during the hot forging processing.展开更多
The cracking morphology of the hardfacing specimens taken from steel 5CrNiMo was observed. Meanwhile, the residual stress fields were measured and simulated. Based on experiment mentioned above, the improved structure...The cracking morphology of the hardfacing specimens taken from steel 5CrNiMo was observed. Meanwhile, the residual stress fields were measured and simulated. Based on experiment mentioned above, the improved structure and modified inclusion in hardfacing metal with rare earth （RE） oxide were analyzed. The results show that, the hardfacing crack is initiated from the coarse dendritic crystal grain boundary, inclusions and coarse austenite grain boundary in the HAZ and propagated by the residual stress existing in the center of the hardfacing metal and HAZ. The primary columnar grain structure can be refined by adding RE oxide in the coating of the electrode. The inclusion in the hardfacing metal can be modified as well. Meanwhile, if the martensite transformation temperature is decreased, the largest value of the residual tensile stress in the dangerous region can be reduced.展开更多
With a focus on the backup roll, a rolling-contact-fatigue experiment was performed on samples of 5% Cr forged steel. The P-S-N fatigue curves were determined and the fatigue strength was calculated. The emergence of ...With a focus on the backup roll, a rolling-contact-fatigue experiment was performed on samples of 5% Cr forged steel. The P-S-N fatigue curves were determined and the fatigue strength was calculated. The emergence of cracks on the test-sample surfaces was observed at different fatigue cycles. A micro-hardness tester was used to measure the hardness of the subsurface fatigue layer. The microstructures were analyzed at various magnifications with an optical microscope, scanning electron microscope, and transmission electron microscope. Based on these tests, the rolling-contact-fatigue mechanism of the large forged steel backup roll was also considered. The results showed that the contact-fatigue strength of the tested backup roll steel was 1 249 MPa;the surface fatigue crack lengthened continuously as the number of cycles increased and followed an S-shaped curve; the subsurface fatigue hardness reached its highest value at about 90 （HV） increment from the matrix hardness of 540 （HV） in the backup roll; the subsurface martensite/bainite microstructure was crushed and the dislocation density was greatly increased. Under alternating contact stresses,the surface/subsurface material was damaged and exhibited many microdefects. At the least, the surface fatigue layer on backup rolls should be fully removed before the microcracks enter a period of rapid propagation.展开更多
Transmission electron microscopy(TEM),scanning electron microscopy(SEM),hardness tests and tensile tests were performed to investigate the effect of aging on microstructure and mechanical properties of forged Al-4.4Cu...Transmission electron microscopy(TEM),scanning electron microscopy(SEM),hardness tests and tensile tests were performed to investigate the effect of aging on microstructure and mechanical properties of forged Al-4.4Cu-0.7Mg-0.6Si alloy.The results show that the alloy exhibits splendid mechanical properties with an ultimate tensile strength of504MPa and an elongation of10.1%after aging at170°C for16h.With tensile testing temperature increasing to150°C,the strength of the alloy declines slightly to483MPa.Then,the strength drops quickly when temperature reaches over200°C.The high strength of the alloy in peak-aged condition is caused by a considerable amount ofθ'and AlMgSiCu(Q)precipitates.The relatively stable mechanical properties tested below150°C are mainly ascribed to the stability ofθ'precipitates.The growth ofθ'and Q precipitates and the generation ofθphase lead to a rapid drop of the strength when temperature is over150°C.展开更多
At the request of the Chinese Embassy in Namibia,the Nanjing Municipal Government invited the Namibian Table Tennis Association to send a delegation to visit the city.Led by association President Ramon Hansen,the Nami...At the request of the Chinese Embassy in Namibia,the Nanjing Municipal Government invited the Namibian Table Tennis Association to send a delegation to visit the city.Led by association President Ramon Hansen,the Namibian players received table tennis training from Aug 23 to Sept 5,2016.The delegation’s展开更多
基金National Natural Science Foundation of China (50275094)
文摘The dynamic recrystallization behavior of microalloyed forged steel was investigated with a compression test in the temperature range of 1 223-1 473 K and a strain rate of 0. 01-5 s^-1. Activation energy was calculated to be 305.9 kJ/mol by regression analysis. Modeling equations were developed to represent the dynamic recrystallization volume fraction and grain size. Parameters of the modeling equations were determined as a function of the Zener-Hollomon parameter. The developed modeling equation will be combined with finite element modeling to predict microstructural change during the hot forging processing.
基金Project supported by Key Project of Science and Technology of Hebei Province (04212201D) and Research Foundationfor theReturned Overseas Chinese Scholars of State Education Ministry
文摘The cracking morphology of the hardfacing specimens taken from steel 5CrNiMo was observed. Meanwhile, the residual stress fields were measured and simulated. Based on experiment mentioned above, the improved structure and modified inclusion in hardfacing metal with rare earth （RE） oxide were analyzed. The results show that, the hardfacing crack is initiated from the coarse dendritic crystal grain boundary, inclusions and coarse austenite grain boundary in the HAZ and propagated by the residual stress existing in the center of the hardfacing metal and HAZ. The primary columnar grain structure can be refined by adding RE oxide in the coating of the electrode. The inclusion in the hardfacing metal can be modified as well. Meanwhile, if the martensite transformation temperature is decreased, the largest value of the residual tensile stress in the dangerous region can be reduced.
文摘With a focus on the backup roll, a rolling-contact-fatigue experiment was performed on samples of 5% Cr forged steel. The P-S-N fatigue curves were determined and the fatigue strength was calculated. The emergence of cracks on the test-sample surfaces was observed at different fatigue cycles. A micro-hardness tester was used to measure the hardness of the subsurface fatigue layer. The microstructures were analyzed at various magnifications with an optical microscope, scanning electron microscope, and transmission electron microscope. Based on these tests, the rolling-contact-fatigue mechanism of the large forged steel backup roll was also considered. The results showed that the contact-fatigue strength of the tested backup roll steel was 1 249 MPa;the surface fatigue crack lengthened continuously as the number of cycles increased and followed an S-shaped curve; the subsurface fatigue hardness reached its highest value at about 90 （HV） increment from the matrix hardness of 540 （HV） in the backup roll; the subsurface martensite/bainite microstructure was crushed and the dislocation density was greatly increased. Under alternating contact stresses,the surface/subsurface material was damaged and exhibited many microdefects. At the least, the surface fatigue layer on backup rolls should be fully removed before the microcracks enter a period of rapid propagation.
基金Project(51301209)supported by the National Natural Science Foundation of China
文摘Transmission electron microscopy(TEM),scanning electron microscopy(SEM),hardness tests and tensile tests were performed to investigate the effect of aging on microstructure and mechanical properties of forged Al-4.4Cu-0.7Mg-0.6Si alloy.The results show that the alloy exhibits splendid mechanical properties with an ultimate tensile strength of504MPa and an elongation of10.1%after aging at170°C for16h.With tensile testing temperature increasing to150°C,the strength of the alloy declines slightly to483MPa.Then,the strength drops quickly when temperature reaches over200°C.The high strength of the alloy in peak-aged condition is caused by a considerable amount ofθ'and AlMgSiCu(Q)precipitates.The relatively stable mechanical properties tested below150°C are mainly ascribed to the stability ofθ'precipitates.The growth ofθ'and Q precipitates and the generation ofθphase lead to a rapid drop of the strength when temperature is over150°C.
文摘At the request of the Chinese Embassy in Namibia,the Nanjing Municipal Government invited the Namibian Table Tennis Association to send a delegation to visit the city.Led by association President Ramon Hansen,the Namibian players received table tennis training from Aug 23 to Sept 5,2016.The delegation’s
