The martensitic microstructures in two high-carbon low alloy steels have been investigated by classical and automated crystallographic analysis under a transmission electron microscope. It is found that the martensiti...The martensitic microstructures in two high-carbon low alloy steels have been investigated by classical and automated crystallographic analysis under a transmission electron microscope. It is found that the martensitic substructure changes from consisting mostly of transformation twins for 1.20 mass% carbon （C） steel to both transformation twins and planar defects on {101}M for 1.67 mass% C steel. In the 1.67 mass% C steel it is further found that small martensite units have a rather homogeneous substructure, while large martensite units are more inhomogeneous. In addition, the martensite units in both steels are frequently found to be of zigzag patterns and have distinct crystallographic relationships with neighboring martensite units, e.g. kink or wedge couplings. Based on the present findings the development of martensite in high-carbon low alloy steels is discussed and a schematic of the martensite formation is presented. Moreover, whether the schematic view can be applied to plate martensite formation in general, is discussed.展开更多
The 1.1C-1.5Si-1.1Mn1.4Cr-0.5Mo-0.6Al-0.6Co （in wt%） steel was treated, respectively, by isothermal austempering process and newly developed austempering-partitioning-tempering process （A-P-T）. After austempering ...The 1.1C-1.5Si-1.1Mn1.4Cr-0.5Mo-0.6Al-0.6Co （in wt%） steel was treated, respectively, by isothermal austempering process and newly developed austempering-partitioning-tempering process （A-P-T）. After austempering at 250, 280 and 300 ℃ for 38, 20 and 10 h, respectively, the sample microstructures were composed of bainitic ferrite plates and film-like retained austenite with thicknesses between 60 and 150 nm. The highest tensile strength of 2003 MPa and hardness value of 53.9 HRC were obtained for the steel after austempering at 250 ℃ for 38 h, resulting from the combining effect of super-saturated martensite decarburization and stabilization of bainitic formation. After A-P-T treating （heated at 300 ℃ for 8 h following water cooling, and then heated at 300 ℃ for 2 h following air cooling）, bamboo leaf-like martensite, primary and secondary bainites and retained austenite were observed. The thickness of the secondary bainitic ferrite plates formed during partitioning is much smaller than that of the primary bainite formed during 300 ℃ austempering. Samples subjected to A-P-T treatment showed improvement in ductility compared to that subjected to austempering.展开更多
基金performed within the VINN Excellence Center Hero-m,financed by VINNOVA,the Swedish Governmental Agency for Innovation Systems,Swedish Industry,KTH Royal Institute of Technology
文摘The martensitic microstructures in two high-carbon low alloy steels have been investigated by classical and automated crystallographic analysis under a transmission electron microscope. It is found that the martensitic substructure changes from consisting mostly of transformation twins for 1.20 mass% carbon （C） steel to both transformation twins and planar defects on {101}M for 1.67 mass% C steel. In the 1.67 mass% C steel it is further found that small martensite units have a rather homogeneous substructure, while large martensite units are more inhomogeneous. In addition, the martensite units in both steels are frequently found to be of zigzag patterns and have distinct crystallographic relationships with neighboring martensite units, e.g. kink or wedge couplings. Based on the present findings the development of martensite in high-carbon low alloy steels is discussed and a schematic of the martensite formation is presented. Moreover, whether the schematic view can be applied to plate martensite formation in general, is discussed.
文摘The 1.1C-1.5Si-1.1Mn1.4Cr-0.5Mo-0.6Al-0.6Co （in wt%） steel was treated, respectively, by isothermal austempering process and newly developed austempering-partitioning-tempering process （A-P-T）. After austempering at 250, 280 and 300 ℃ for 38, 20 and 10 h, respectively, the sample microstructures were composed of bainitic ferrite plates and film-like retained austenite with thicknesses between 60 and 150 nm. The highest tensile strength of 2003 MPa and hardness value of 53.9 HRC were obtained for the steel after austempering at 250 ℃ for 38 h, resulting from the combining effect of super-saturated martensite decarburization and stabilization of bainitic formation. After A-P-T treating （heated at 300 ℃ for 8 h following water cooling, and then heated at 300 ℃ for 2 h following air cooling）, bamboo leaf-like martensite, primary and secondary bainites and retained austenite were observed. The thickness of the secondary bainitic ferrite plates formed during partitioning is much smaller than that of the primary bainite formed during 300 ℃ austempering. Samples subjected to A-P-T treatment showed improvement in ductility compared to that subjected to austempering.
