The influence of soaking time in deep cryogenic treatment on the tensile and impact properties of low-alloy medium-carbon HY-TUF steel was investigated in this study. Microstructural studies based on phase distributio...The influence of soaking time in deep cryogenic treatment on the tensile and impact properties of low-alloy medium-carbon HY-TUF steel was investigated in this study. Microstructural studies based on phase distribution mapping by electron backscatter diffraction show that the deep cryogenic process causes a decrease in the content of retained austenite and an increase in the volume fraction of η-carbide with increasing soaking time up to 48 h. The decrease in the content of retained austenite from ~1.23vol% to 0.48vol% suggests an isothermal martensitic transformation at 77 K. The η-type precipitates formed in deep cryogenic-treated martensite over 48 h have the Hirotsu and Nagakura orientation relation with the martensitic matrix. Furthermore, a high coherency between η-carbide and the martensitic matrix is observed by high-resolution transmission electron microscopy. The variations in macrohardness, yield strength, ultimate tensile strength, and ductility with soaking time in the deep cryogenic process show a peak/plateau trend.展开更多
The lath-or plate-shaped bainitic ferrite of low and medium carbon alloy steels consists of packets of ferrite sublaths which are composed of many finer and regular ferrite blocks.They are uniform shear growth units o...The lath-or plate-shaped bainitic ferrite of low and medium carbon alloy steels consists of packets of ferrite sublaths which are composed of many finer and regular ferrite blocks.They are uniform shear growth units of bainitic phase transformation.No carbide is precipitated from them.The bainitic O-carbides are precipitated from γ-α interface or carbon-rich austenite.The mode of arrangement of the units in ferrite sublath packet is in uni-or bi-di- rection.Single surface relief is produced by the accumulation of uniform shear strains with all the ferrite units arranged unidirectionally in a sublath packet,while tent-shaped surface relief is formed by the integration of the uniform shear strains of two groups with ferrite units piling up in two directions and growing face to face;whereas if they grow back to back,the integra- tion will be responsible for invert-tent-shaped surface relief.The interface trace between two groups of ferrite units in a sublath packet is shown as“midrib”.展开更多
文摘The influence of soaking time in deep cryogenic treatment on the tensile and impact properties of low-alloy medium-carbon HY-TUF steel was investigated in this study. Microstructural studies based on phase distribution mapping by electron backscatter diffraction show that the deep cryogenic process causes a decrease in the content of retained austenite and an increase in the volume fraction of η-carbide with increasing soaking time up to 48 h. The decrease in the content of retained austenite from ~1.23vol% to 0.48vol% suggests an isothermal martensitic transformation at 77 K. The η-type precipitates formed in deep cryogenic-treated martensite over 48 h have the Hirotsu and Nagakura orientation relation with the martensitic matrix. Furthermore, a high coherency between η-carbide and the martensitic matrix is observed by high-resolution transmission electron microscopy. The variations in macrohardness, yield strength, ultimate tensile strength, and ductility with soaking time in the deep cryogenic process show a peak/plateau trend.
文摘The lath-or plate-shaped bainitic ferrite of low and medium carbon alloy steels consists of packets of ferrite sublaths which are composed of many finer and regular ferrite blocks.They are uniform shear growth units of bainitic phase transformation.No carbide is precipitated from them.The bainitic O-carbides are precipitated from γ-α interface or carbon-rich austenite.The mode of arrangement of the units in ferrite sublath packet is in uni-or bi-di- rection.Single surface relief is produced by the accumulation of uniform shear strains with all the ferrite units arranged unidirectionally in a sublath packet,while tent-shaped surface relief is formed by the integration of the uniform shear strains of two groups with ferrite units piling up in two directions and growing face to face;whereas if they grow back to back,the integra- tion will be responsible for invert-tent-shaped surface relief.The interface trace between two groups of ferrite units in a sublath packet is shown as“midrib”.
