The morphology and characteristics of granular bainite (GB) in pipeline steels at different continuous cooling rates were investigated by scanning electron microscopy, transmission electron microscopy and electron bac...The morphology and characteristics of granular bainite (GB) in pipeline steels at different continuous cooling rates were investigated by scanning electron microscopy, transmission electron microscopy and electron back-scattered diffraction (EBSD). The results show that the morphology of ferrite matrix in GB turned from the lath sheaf structure into the nearly equiaxed large grain with the cooling rate decreasing from high (60℃/s) to low (5-10℃/s). At the medium cooling rate (20-40℃/s), GB consisted of the irregular ferrite matrix, the granular martensite/austenite (M/A) constituents and abundant substructures inside. The formation of the irregular ferrite and substructure was attributed to the high-temperature recovery which occurred at relatively high-temperature stage before phase transformation. The granular morphology of M/A constitu-ents was formed from the carbon-rich triple junctions which were produced by the multidirectional substructure interfaces converged with each other. Particularly, some martensite in M/A constituents was misoriented from the adjacent ferrite by very small misorientation angle, which could be characterized by the mean band contrast function of EBSD qualitatively or semiquantitatively.展开更多
The relationship between micro structure and corrosion behavior of high-grade pipeline steel under low-temperature conditions was comparatively investigated by the potentiodynamic polarization and electrochemical impe...The relationship between micro structure and corrosion behavior of high-grade pipeline steel under low-temperature conditions was comparatively investigated by the potentiodynamic polarization and electrochemical impedance spec-troscopy test combining with optical micrographs,scanning electron microscopy,transmission electron microscopy and electron back-scattered diffraction.The results showed that,compared with room and high temperature,low temperature could influence the corrosion behavior of high-grade pipeline steel,which means that the corrosion potential and current density decreased and the corrosion resistance increased significantly.Moreover,double layer structures of the interface became thicker and more compact.Under low-temperature environment,acicular ferrite had the martensite/austenite constituents with less amount and smaller size,a higher density of low angle grain boundaries and smaller effective grain sizes compared with granular bainite,which demonstrated higher corrosion resistance.展开更多
The mechanical properties,microstructure and second phase precipitation behavior of flange forgings for high-pressure hydrogen storage vessels at different tempering temperatures(620–700℃)were studied.The results sh...The mechanical properties,microstructure and second phase precipitation behavior of flange forgings for high-pressure hydrogen storage vessels at different tempering temperatures(620–700℃)were studied.The results showed that when tempered at 620–680°C,the main microstructure of the test steel was tempered sorbite,and the main microstructure of tempered steel changed to martensite at 700℃.At 700℃,the dislocation density increased and some retained austenite existed.With the tempering temperature increasing,the yield strength showed a decreasing trend,the formation of fresh martensite made the tensile strength first decrease and then increase slightly,the impact energy at−40℃increased first and then decreased,and the impact energy at 660℃had the maximum value.The precipitates of MC type were mainly(Mo,V,Ti)C.The test steel had excellent strength and toughness matching at 660℃tempering,the tensile strength at different cross section locations was above 750 MPa,the impact energy was above 200 J at−40℃,and the relative percentage reduction of area(ZH2/ZN2)was above 75%at hydrogen environment of 6.3 MPa.展开更多
目的:对比2011 Kwak版甲状腺影像报告和数据系统(Thyroid Imaging Reporting and Data System by Kwak,Kwak TI-RADS)、2015 ATA《成人甲状腺结节与分化型甲状腺癌指南》(ATA指南)及2017 ACR版甲状腺影像报告和数据系统(American Colleg...目的:对比2011 Kwak版甲状腺影像报告和数据系统(Thyroid Imaging Reporting and Data System by Kwak,Kwak TI-RADS)、2015 ATA《成人甲状腺结节与分化型甲状腺癌指南》(ATA指南)及2017 ACR版甲状腺影像报告和数据系统(American College of Radiology Thyroid Imaging Reporting and Data System,ACR TI-RADS)3种方法对甲状腺良恶性结节的诊断效能。方法:回顾性分析265个甲状腺结节的超声特征,应用以上3种方法对结节进行诊断分级,以病理结果为金标准,构建受试者工作特征曲线(receiver operating characteristic,ROC)。结果:Kwak TI-RADS、ATA指南与ACR TIRADS的ROC曲线下面积(the area under the ROC curve,AUC)分别为0.914、0.829、0.910,三者对甲状腺结节均具有较高的诊断效能,其中Kwak TI-RADS与ACR TI-RADS诊断效能更高于ATA指南方法(P<0.05),Kwak TI-RADS与ACR TI-RADS分级方法的诊断效能间无显著差异(P>0.05);三者的最佳诊断值分别为Kwak TI-RADS 4c,高度可疑恶性,ACR TI-RADS 5。Kwak TI-RADS诊断恶性结节的准确率高于另外2种方法(P<0.05),ACR TI-RADS的特异度及阳性预测值较高、敏感度及阴性预测值较低,ATA指南对部分甲状腺结节无法进行明确分类。结论:Kwak TI-RADS、ATA指南及ACR TI-RADS对甲状腺结节的诊断均具有较好的诊断效能,其中Kwak TI-RADS与ACR TI-RADS诊断效能更高于ATA指南。展开更多
文摘The morphology and characteristics of granular bainite (GB) in pipeline steels at different continuous cooling rates were investigated by scanning electron microscopy, transmission electron microscopy and electron back-scattered diffraction (EBSD). The results show that the morphology of ferrite matrix in GB turned from the lath sheaf structure into the nearly equiaxed large grain with the cooling rate decreasing from high (60℃/s) to low (5-10℃/s). At the medium cooling rate (20-40℃/s), GB consisted of the irregular ferrite matrix, the granular martensite/austenite (M/A) constituents and abundant substructures inside. The formation of the irregular ferrite and substructure was attributed to the high-temperature recovery which occurred at relatively high-temperature stage before phase transformation. The granular morphology of M/A constitu-ents was formed from the carbon-rich triple junctions which were produced by the multidirectional substructure interfaces converged with each other. Particularly, some martensite in M/A constituents was misoriented from the adjacent ferrite by very small misorientation angle, which could be characterized by the mean band contrast function of EBSD qualitatively or semiquantitatively.
基金supported by the National Key Research and Development Program of China(Grant No.2017YFB0304900)the National Natural Science Foundation of China(Grant No.51911530129).
文摘The relationship between micro structure and corrosion behavior of high-grade pipeline steel under low-temperature conditions was comparatively investigated by the potentiodynamic polarization and electrochemical impedance spec-troscopy test combining with optical micrographs,scanning electron microscopy,transmission electron microscopy and electron back-scattered diffraction.The results showed that,compared with room and high temperature,low temperature could influence the corrosion behavior of high-grade pipeline steel,which means that the corrosion potential and current density decreased and the corrosion resistance increased significantly.Moreover,double layer structures of the interface became thicker and more compact.Under low-temperature environment,acicular ferrite had the martensite/austenite constituents with less amount and smaller size,a higher density of low angle grain boundaries and smaller effective grain sizes compared with granular bainite,which demonstrated higher corrosion resistance.
基金supported by the National Key research and Development Program of China(No.2022YFB4003001).
文摘The mechanical properties,microstructure and second phase precipitation behavior of flange forgings for high-pressure hydrogen storage vessels at different tempering temperatures(620–700℃)were studied.The results showed that when tempered at 620–680°C,the main microstructure of the test steel was tempered sorbite,and the main microstructure of tempered steel changed to martensite at 700℃.At 700℃,the dislocation density increased and some retained austenite existed.With the tempering temperature increasing,the yield strength showed a decreasing trend,the formation of fresh martensite made the tensile strength first decrease and then increase slightly,the impact energy at−40℃increased first and then decreased,and the impact energy at 660℃had the maximum value.The precipitates of MC type were mainly(Mo,V,Ti)C.The test steel had excellent strength and toughness matching at 660℃tempering,the tensile strength at different cross section locations was above 750 MPa,the impact energy was above 200 J at−40℃,and the relative percentage reduction of area(ZH2/ZN2)was above 75%at hydrogen environment of 6.3 MPa.
文摘目的:对比2011 Kwak版甲状腺影像报告和数据系统(Thyroid Imaging Reporting and Data System by Kwak,Kwak TI-RADS)、2015 ATA《成人甲状腺结节与分化型甲状腺癌指南》(ATA指南)及2017 ACR版甲状腺影像报告和数据系统(American College of Radiology Thyroid Imaging Reporting and Data System,ACR TI-RADS)3种方法对甲状腺良恶性结节的诊断效能。方法:回顾性分析265个甲状腺结节的超声特征,应用以上3种方法对结节进行诊断分级,以病理结果为金标准,构建受试者工作特征曲线(receiver operating characteristic,ROC)。结果:Kwak TI-RADS、ATA指南与ACR TIRADS的ROC曲线下面积(the area under the ROC curve,AUC)分别为0.914、0.829、0.910,三者对甲状腺结节均具有较高的诊断效能,其中Kwak TI-RADS与ACR TI-RADS诊断效能更高于ATA指南方法(P<0.05),Kwak TI-RADS与ACR TI-RADS分级方法的诊断效能间无显著差异(P>0.05);三者的最佳诊断值分别为Kwak TI-RADS 4c,高度可疑恶性,ACR TI-RADS 5。Kwak TI-RADS诊断恶性结节的准确率高于另外2种方法(P<0.05),ACR TI-RADS的特异度及阳性预测值较高、敏感度及阴性预测值较低,ATA指南对部分甲状腺结节无法进行明确分类。结论:Kwak TI-RADS、ATA指南及ACR TI-RADS对甲状腺结节的诊断均具有较好的诊断效能,其中Kwak TI-RADS与ACR TI-RADS诊断效能更高于ATA指南。
