The continuous cooling transformation (CCT) diagrams of 86CrMoV7 steel samples including hot deformed and not hot deformed were constructed by dilatometry, metallography and transmission electron microscopy (TEM). The...The continuous cooling transformation (CCT) diagrams of 86CrMoV7 steel samples including hot deformed and not hot deformed were constructed by dilatometry, metallography and transmission electron microscopy (TEM). The results showed that hot deformation accelerated pearlite transformation and fine pearlite microstructure. Moreover, the undissolved carbides became the nucleating sites of pearlite, accelerated pearlite formation and fine pearlite if the steel had been deformed at high temperature. In contrast, undissolved carbides did not make any influence on pearlite transformation if the steel had not been deformed at high temperature.展开更多
The influences of hot deformation parameters on pearlite grain nucleation and growth during austenite-pearlite phase transformation in a steel wire rod have been investigated through quantitative analysis of microstru...The influences of hot deformation parameters on pearlite grain nucleation and growth during austenite-pearlite phase transformation in a steel wire rod have been investigated through quantitative analysis of microstructure parameters such as austenite grain size,ferrite grain size,pearlite colony size,and lamellar spacing.During hot deformation,the austenite grain size decreases due to recrystallization,providing extra nucleation sites for pearlite phase transformation,which decreases the ferrite grain size and pearlite colony size.Moreover,the stored strain energy in undercooled austenite accelerates carbon diffusion during pearlite phase transformation,which facilitates ferrite grain growth and increases pearlite colony size.Consequently,the competing influence of recrystallization and strain energy provides flexibility in adjusting ferrite grain size and colony size by hot deformation.This study highlights the critical role of hot deformation in determining the microstructure of pearlitic steel.展开更多
The true stress–true strain curves of 25Cr2Ni4MoVA steel were obtained by uniaxial compression experiments at 850–1200℃ in the strain rate range of 0.001–10.0 s^(−1).And the dynamic continuous cooling transformati...The true stress–true strain curves of 25Cr2Ni4MoVA steel were obtained by uniaxial compression experiments at 850–1200℃ in the strain rate range of 0.001–10.0 s^(−1).And the dynamic continuous cooling transformation curves were obtained at the cooling rate range of 0.5–15.0℃ s^(−1) from the austenitization temperature of 1000℃ to the room temperature by pre-strain of 0.2 as well.The power dissipation map and the dynamic continuous cooling transformation diagram were constructed based on the data provided by these curves.Compared with the optical micrographs of the compressed samples,the full dynamic recrystallization region is located between 1000 and 1200℃ and at the strain rate range from 0.01 to 10.0 s^(−1) with the power dissipation efficiency not less than 0.33.In the full dynamic recrystallization region,the power dissipation efficiency increases and the dynamic recrystallization activation energy decreases with the temperature increasing.With the strain rate decreasing,the power dissipation efficiency increases firstly and then starts to decrease as the strain rate is less than 0.1 s^(−1),and dynamic recrystallization activation energy changes on the contrary.According to the dynamic continuous cooling transformation diagram,slow cooling is a better way for the hot-deformed piece with large size or complex shape to avoid cracking as the temperature of the piece is lower than 400℃,and different cooling ways can be used for the hot-deformed piece with small size and simple shapes to obtain certain microstructure and meet good compressive properties.展开更多
文摘The continuous cooling transformation (CCT) diagrams of 86CrMoV7 steel samples including hot deformed and not hot deformed were constructed by dilatometry, metallography and transmission electron microscopy (TEM). The results showed that hot deformation accelerated pearlite transformation and fine pearlite microstructure. Moreover, the undissolved carbides became the nucleating sites of pearlite, accelerated pearlite formation and fine pearlite if the steel had been deformed at high temperature. In contrast, undissolved carbides did not make any influence on pearlite transformation if the steel had not been deformed at high temperature.
基金supported by the National Natural Science Foundation(Grant No.52031013).
文摘The influences of hot deformation parameters on pearlite grain nucleation and growth during austenite-pearlite phase transformation in a steel wire rod have been investigated through quantitative analysis of microstructure parameters such as austenite grain size,ferrite grain size,pearlite colony size,and lamellar spacing.During hot deformation,the austenite grain size decreases due to recrystallization,providing extra nucleation sites for pearlite phase transformation,which decreases the ferrite grain size and pearlite colony size.Moreover,the stored strain energy in undercooled austenite accelerates carbon diffusion during pearlite phase transformation,which facilitates ferrite grain growth and increases pearlite colony size.Consequently,the competing influence of recrystallization and strain energy provides flexibility in adjusting ferrite grain size and colony size by hot deformation.This study highlights the critical role of hot deformation in determining the microstructure of pearlitic steel.
基金The authors are grateful for the financial support from the National Natural Science Foundation of China(General Project,Grant No.51674004).
文摘The true stress–true strain curves of 25Cr2Ni4MoVA steel were obtained by uniaxial compression experiments at 850–1200℃ in the strain rate range of 0.001–10.0 s^(−1).And the dynamic continuous cooling transformation curves were obtained at the cooling rate range of 0.5–15.0℃ s^(−1) from the austenitization temperature of 1000℃ to the room temperature by pre-strain of 0.2 as well.The power dissipation map and the dynamic continuous cooling transformation diagram were constructed based on the data provided by these curves.Compared with the optical micrographs of the compressed samples,the full dynamic recrystallization region is located between 1000 and 1200℃ and at the strain rate range from 0.01 to 10.0 s^(−1) with the power dissipation efficiency not less than 0.33.In the full dynamic recrystallization region,the power dissipation efficiency increases and the dynamic recrystallization activation energy decreases with the temperature increasing.With the strain rate decreasing,the power dissipation efficiency increases firstly and then starts to decrease as the strain rate is less than 0.1 s^(−1),and dynamic recrystallization activation energy changes on the contrary.According to the dynamic continuous cooling transformation diagram,slow cooling is a better way for the hot-deformed piece with large size or complex shape to avoid cracking as the temperature of the piece is lower than 400℃,and different cooling ways can be used for the hot-deformed piece with small size and simple shapes to obtain certain microstructure and meet good compressive properties.
