The quantitative analysis of substructure in the martensite/bainite mixed structure, which is obtained from low-carbon NiCrMoV steels under different cooling conditions, was made by means of optical microscope （OM）,...The quantitative analysis of substructure in the martensite/bainite mixed structure, which is obtained from low-carbon NiCrMoV steels under different cooling conditions, was made by means of optical microscope （OM）, scanning electron microscope （SEM）, electron backscatter diffraction （EBSD）, and transmission electron microscope （TEM）, in order to research the effect on toughness. The test results indicate that the toughness of the steel is en- hanced with the decrease in the packet and block size under the condition of the same prior austenite grain size mixed with different ratios of martensite and bainite while the lath width is about 0.38μm. The calculation shows that both the packet and block boundaries have the same hindering effect on crack extension. Furthermore, the effect of the block width on impact energy is much larger than that of the packet. Therefore, the block can be used as microstruc- tural substructure to affect the toughness in low-carbon martensite steels, suggesting that the block size is ＂the effective grain size＂ for controlling toughness.展开更多
A new ultrahigh strength pipeline steel with high yield strength and high impact toughness was fabricated in this work, and mechanical properties and microstructure of the steel were investigated. The steel exhibited ...A new ultrahigh strength pipeline steel with high yield strength and high impact toughness was fabricated in this work, and mechanical properties and microstructure of the steel were investigated. The steel exhibited out- standing mechanical properties with yield strength levels of up to 951 MPa and tensile strength levels up to 1023 MPa. The sharp notch toughness with absorbed energy values of 227 J/cm2 at -30℃ and shear area of up to 95% in drop weight tear test （DWTT） at temperature of --20℃ were achieved. It was found that microstructure of the steel com- prises a majority of low-carbon lath bainite with different sublaths and sub-sublaths, meanwhile there is a high density of dislocation between laths and the dispersed film-like martensite-austenite （M-A） constituents. Most of the precipi- tates in this steel are duplex type containing Nb and Ti with characterized morphology of cap with the range of precipitation size from a few to tens nanometers.展开更多
Dynamic CCT （continuous cooling transformation） curves and effects of microstructures and M/A islands of X100 hot rolled strip on mechanical properties were studied by means of a thermal simulator, a scanning electr...Dynamic CCT （continuous cooling transformation） curves and effects of microstructures and M/A islands of X100 hot rolled strip on mechanical properties were studied by means of a thermal simulator, a scanning electron mi- croscope （SEM）, a transmission electron microscope （TEM）, a digital micro-hardness tester and Image-Pro Plus analysis software. The results show that high contents of C and Mo can make transformation lines of acicular ferrite and bain- ite shift rightward. High Mo tested strip has higher strength and micro-hardness and lower toughness than the other one because lath bainite appears instead of quasi-polygonal ferrite. Tested strip with granular bainite, lath bainite and M/A islands has better mechanical properties and in the microstructures lath bainite content is around 36.50% and M/A islands are fine and disperse in the matrix.展开更多
文摘The quantitative analysis of substructure in the martensite/bainite mixed structure, which is obtained from low-carbon NiCrMoV steels under different cooling conditions, was made by means of optical microscope （OM）, scanning electron microscope （SEM）, electron backscatter diffraction （EBSD）, and transmission electron microscope （TEM）, in order to research the effect on toughness. The test results indicate that the toughness of the steel is en- hanced with the decrease in the packet and block size under the condition of the same prior austenite grain size mixed with different ratios of martensite and bainite while the lath width is about 0.38μm. The calculation shows that both the packet and block boundaries have the same hindering effect on crack extension. Furthermore, the effect of the block width on impact energy is much larger than that of the packet. Therefore, the block can be used as microstruc- tural substructure to affect the toughness in low-carbon martensite steels, suggesting that the block size is ＂the effective grain size＂ for controlling toughness.
文摘A new ultrahigh strength pipeline steel with high yield strength and high impact toughness was fabricated in this work, and mechanical properties and microstructure of the steel were investigated. The steel exhibited out- standing mechanical properties with yield strength levels of up to 951 MPa and tensile strength levels up to 1023 MPa. The sharp notch toughness with absorbed energy values of 227 J/cm2 at -30℃ and shear area of up to 95% in drop weight tear test （DWTT） at temperature of --20℃ were achieved. It was found that microstructure of the steel com- prises a majority of low-carbon lath bainite with different sublaths and sub-sublaths, meanwhile there is a high density of dislocation between laths and the dispersed film-like martensite-austenite （M-A） constituents. Most of the precipi- tates in this steel are duplex type containing Nb and Ti with characterized morphology of cap with the range of precipitation size from a few to tens nanometers.
基金Item Sponsored by National Key Technology Research and Development Program in 12th Five-year Plan of China(2011BAE35B01)
文摘Dynamic CCT （continuous cooling transformation） curves and effects of microstructures and M/A islands of X100 hot rolled strip on mechanical properties were studied by means of a thermal simulator, a scanning electron mi- croscope （SEM）, a transmission electron microscope （TEM）, a digital micro-hardness tester and Image-Pro Plus analysis software. The results show that high contents of C and Mo can make transformation lines of acicular ferrite and bain- ite shift rightward. High Mo tested strip has higher strength and micro-hardness and lower toughness than the other one because lath bainite appears instead of quasi-polygonal ferrite. Tested strip with granular bainite, lath bainite and M/A islands has better mechanical properties and in the microstructures lath bainite content is around 36.50% and M/A islands are fine and disperse in the matrix.
