Dynamic strain-induced transformation of the low carbon steel Q（235） at 770℃ and 850℃ leads to fine ferrite grains. The microstructure characterization and mechanism of the fine ferrite grain were studied by scann...Dynamic strain-induced transformation of the low carbon steel Q（235） at 770℃ and 850℃ leads to fine ferrite grains. The microstructure characterization and mechanism of the fine ferrite grain were studied by scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electron backscattered diffraction （EBSD） technique. The results show that strain-induced microstructure is the mixed microstructure of ferrite and pearlite, with cementite randomly distributed on ferrite grain boundaries and the grains interiors. EBSD images of grain boundaries demonstrate that high angle grain boundaries （HAGBs） are dominant in both of the deformation induced microstructures occurring below and above A（e3） , with only a few low angle grain boundaries （LAGBs） existing in the grain interiors. It implies that the dynamic strain-induced transformation （DSIT） happens above and below A（e3） temperature and has the same phase transition mechanisms. The refinement of ferrite is the cooperative effect of DSIT and continuous dynamic recrystallization （CDRX） of ferrite. Besides, DSIT is deemed as an incomplete carbon diffusion phase transition through the analysis of microstructure and the previous simulated results. The strengths of the Q（235） steel with refined ferrite and pearlite structure get doubled than the initial state without treated by DSIT and the residual stress in the refined structure is partly responsible for the ductility loss.展开更多
X65, X70, and X80 belong to high grade pipeline steels. Toughness is one of the most important properties of pipeline steels when the pipeline transports the gas or oil, and the means to control toughness is very impo...X65, X70, and X80 belong to high grade pipeline steels. Toughness is one of the most important properties of pipeline steels when the pipeline transports the gas or oil, and the means to control toughness is very important for exploring even higher grade pipeline steels. We established the relationship between toughness and crystallographic parameters of high grade pipeline steels by studying the crystallographic parameters of X65, X70, and X80 using EBSD and analyzing Charpy CVN of X65, X70 and X80. The results show that the effective grain size, the frequency distribution of grain boundary misorientation and the ratio of high angle grain boundary to small angle grain boundary are important parameters. The finer the effective grain size, and the higher the frequency distribution of grain boundaries （〉 50~）, the more excellent toughness of high grade pipeline steels will be.展开更多
基金support from the National Natural Science Foundation of China (NSFC) under Grantb No. 50871109
文摘Dynamic strain-induced transformation of the low carbon steel Q（235） at 770℃ and 850℃ leads to fine ferrite grains. The microstructure characterization and mechanism of the fine ferrite grain were studied by scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electron backscattered diffraction （EBSD） technique. The results show that strain-induced microstructure is the mixed microstructure of ferrite and pearlite, with cementite randomly distributed on ferrite grain boundaries and the grains interiors. EBSD images of grain boundaries demonstrate that high angle grain boundaries （HAGBs） are dominant in both of the deformation induced microstructures occurring below and above A（e3） , with only a few low angle grain boundaries （LAGBs） existing in the grain interiors. It implies that the dynamic strain-induced transformation （DSIT） happens above and below A（e3） temperature and has the same phase transition mechanisms. The refinement of ferrite is the cooperative effect of DSIT and continuous dynamic recrystallization （CDRX） of ferrite. Besides, DSIT is deemed as an incomplete carbon diffusion phase transition through the analysis of microstructure and the previous simulated results. The strengths of the Q（235） steel with refined ferrite and pearlite structure get doubled than the initial state without treated by DSIT and the residual stress in the refined structure is partly responsible for the ductility loss.
基金Funded by China Postdoctoral Science Foundation(No.20060390319)
文摘X65, X70, and X80 belong to high grade pipeline steels. Toughness is one of the most important properties of pipeline steels when the pipeline transports the gas or oil, and the means to control toughness is very important for exploring even higher grade pipeline steels. We established the relationship between toughness and crystallographic parameters of high grade pipeline steels by studying the crystallographic parameters of X65, X70, and X80 using EBSD and analyzing Charpy CVN of X65, X70 and X80. The results show that the effective grain size, the frequency distribution of grain boundary misorientation and the ratio of high angle grain boundary to small angle grain boundary are important parameters. The finer the effective grain size, and the higher the frequency distribution of grain boundaries （〉 50~）, the more excellent toughness of high grade pipeline steels will be.
