The dislocation pipe diffusion of Mn during annealing of 5Mn steel was experimentally investigated using transmission electron microscopy （TEM）. Many dislocations existed inside the ferrite and terminated at the α/...The dislocation pipe diffusion of Mn during annealing of 5Mn steel was experimentally investigated using transmission electron microscopy （TEM）. Many dislocations existed inside the ferrite and terminated at the α/γin- terface of the sample after intercritieal annealing at 650 ℃ for 1 min. Line scans of Mn distribution demonstrated a high Mn concentration in austenite and Mn enrichment at dislocations, indicating that the dislocation pipe diffusion of Mn during intercritical annealing occurred in addition to the γ/α interface diffusion. In-situ TEM observations at 500 ℃revealed that due to Ostwald ripening, large cementite precipitates grew while small cementite precipitates dissolved via Mn diffusion along the dislocations between them.展开更多
The cementite formation and coarsening behaviors of 0. 2 mass% C-5 mass% Mn steel during tempering at 500℃ were investigated by in-situ transmission electron microscope（ TEM）. In-situ TEM observation showed uniform...The cementite formation and coarsening behaviors of 0. 2 mass% C-5 mass% Mn steel during tempering at 500℃ were investigated by in-situ transmission electron microscope（ TEM）. In-situ TEM observation showed uniform distribution of cementite particles at the early stage of tempering in the rapidly heated（ 500 ℃ / s） sample. Elemental analysis confirmed that the cementite growth was dominated by Mn diffusion. During the cementite growth,the coarsening behavior of intragranular cementite was significantly controlled by the matrix diffusion,while that of the intergranular cementite was mainly governed by the boundary diffusion. The in-situ TEM observation revealed that the dislocation pipe diffusion of Mn took place during tempering,which accelerated the Mn diffusion between cementite particles. The coarsening rates of individual cementite particles were calculated based on the in-situ TEM observation.展开更多
The microstructural evolutions of 5Mn steel during various heat treatments have been investiga- ted by in-situ transmission electron microscopy （TEM）. The specimen of 5Mn steel was pre- pared using focused ion beam ...The microstructural evolutions of 5Mn steel during various heat treatments have been investiga- ted by in-situ transmission electron microscopy （TEM）. The specimen of 5Mn steel was pre- pared using focused ion beam （FIB） milling, which allowed the selection of specific morphology of interest prior to the in-situ observation, The complete austenization at 800 ℃ was verified at the atomic scale by minimizing thermal expansion and sample drift in a heating holder based on micro-electro-mechanical-systems. During annealing at 650 ℃, the formation of reverted austen- ite was dynamically observed, while the morphologies of austenite laths of 5Mn steel after in-situ heating were quite similar to that after ex-situ intereritical annealing. During annealing at 500 ℃, the morphological evolution of cementite and associated Mn diffusion were investigated. It was demonstrated that a combination of FIB sampling and high temperature in-situ TEM enables us to probe the morphological evolution and elemental diffusion of specific areas of interest in steel at high spatial resolution.展开更多
Due to traffic and wave actions, cast steel joints are subjected to variable-amplitude fatigue loading, which may cause fatigue problems. The ratio of the minimum strain to the maximum strain(strain ratio)can be emplo...Due to traffic and wave actions, cast steel joints are subjected to variable-amplitude fatigue loading, which may cause fatigue problems. The ratio of the minimum strain to the maximum strain(strain ratio)can be employed to analyze the influence of variable-amplitude fatigue both in the elastic and plastic ranges. To evaluate the effect of the strain ratio on G20Mn5 QT cast steel, the fatigue tests of smooth specimens were carried out at the strain ratio of 0.1. The cyclic deformation and the relationships between the strain amplitude, the stress amplitude, the Smith, Watson and Topper(SWT)parameter and fatigue life were studied and compared with those at the strain ratio of-1. Compared with other methods, Basquin formula and Solonberg formula provide reliable and appropriate ranges of S-N curve and fatigue limit at different strain ratios respectively. The SWT parameter can be used to predict the fatigue life at other strain ratios accurately.展开更多
The microstructure, composition and shape of precipitated phase under as-cast and finished product state of 5Cr21Mn9Ni4N steel with different rare earth （RE） amount were studied. Mechanical properties of 5Cr21Mn9Ni4...The microstructure, composition and shape of precipitated phase under as-cast and finished product state of 5Cr21Mn9Ni4N steel with different rare earth （RE） amount were studied. Mechanical properties of 5Cr21Mn9Ni4N steels withont RE addition and with RE added by 0. 2% in mass percent were tested respectively. The results indicate that the solid solution amount of RE is about 10^-6 -10^-5 order of magnitude in 5Cr21Mn9Ni4N steel. Dendrite of as-cast condition is refined obviously and dimension of interstitial phase is shortened when RE is added by 0.10%-0.20%. But the microstructure will be coarser if surplus RE is added. Precipitated phase under finished product state distributes evenly in nearly same size with RE added by 0. 2% which leads to a largely improved high temperature mechanical property.展开更多
The oxidation resistance of 5Cr21Mn9Ni4N steel micro-alloying by RE at 700 - 900 ℃ was investigated. The results indicate that oxidation exponent n and oxidation activation energy are increased, and oxidation velocit...The oxidation resistance of 5Cr21Mn9Ni4N steel micro-alloying by RE at 700 - 900 ℃ was investigated. The results indicate that oxidation exponent n and oxidation activation energy are increased, and oxidation velocity constant kp is decreased when 0.2% RE is added in 5Cr21Mn9Ni4N steel. The addition of RE elements does not alter phase constitution of oxidation scale, however it improves the configuration of oxidation scale, and increases thermal stability and adhesivity of oxidation scale, which results in the raise of oxidation resistance of 5Cr21Mn9Ni4N steel at high temperature. The oxidation scale constitutes of refractory steel transfer from manganic oxide mostly to ferric oxide mostly with the increase of temperature, which leads to descend of compactness and desquamation resistance of oxidation scale. The mass increase of ferric oxide in the oxidation scale and the looseness of oxidation scale are the main reason to descend the oxidation resistance of refractory steel.展开更多
Owing to the remarkable advantages in mechanical behavior,cast steel nodes have been widely used in static structures.Nowadays,cast steel nodes also gain increasing popularity due to the superior fatigue performance i...Owing to the remarkable advantages in mechanical behavior,cast steel nodes have been widely used in static structures.Nowadays,cast steel nodes also gain increasing popularity due to the superior fatigue performance in dynamic structures,but they are not yet widely used because the fatigue properties of cast steel are not well understood.In this paper,the fatigue test of cast steel GS20Mn5V commonly used in steel castings is carried out.The strength of medium and low cycle fatigue and the fatigue limit are obtained.The feasibility of the estimated S-N(fatigue stress versus life)curve is tested.The double logarithmic linear model(DLLM)and the reversed generalized Pareto model(RGPM)are used to fit the experimental data,and the comparison is made.The P-S-N(the relationship between fatigue stress and life at different survival rates)curve obtained by the RGPM is proposed.The results show that the estimated S-N curve is not suitable for low cycle fatigue life,fitting the experimental data with the RGPM is the best,and obtaining the P-S-N curve from the RGPM is feasible.展开更多
基金Item Sponsored by National Key Research and Development Program of China(2016YFB0700402)National Basic Research Program of China(2010CB630800,2015CB921700)+1 种基金National Natural Science Foundation of China(51671112,51471096,51390471,11374174)Tsinghua University Initiative Scientific Research Program(20141081200,20131089311)
文摘The dislocation pipe diffusion of Mn during annealing of 5Mn steel was experimentally investigated using transmission electron microscopy （TEM）. Many dislocations existed inside the ferrite and terminated at the α/γin- terface of the sample after intercritieal annealing at 650 ℃ for 1 min. Line scans of Mn distribution demonstrated a high Mn concentration in austenite and Mn enrichment at dislocations, indicating that the dislocation pipe diffusion of Mn during intercritical annealing occurred in addition to the γ/α interface diffusion. In-situ TEM observations at 500 ℃revealed that due to Ostwald ripening, large cementite precipitates grew while small cementite precipitates dissolved via Mn diffusion along the dislocations between them.
基金Item Sponsored by National Basic Research Program of China(2010CB630800,2015CB921700)National Natural Science Foundation of China(51471096,51001064)Specialized Research Fund for the Dectoral Program of Higher Education of China(20100002120047)
文摘The cementite formation and coarsening behaviors of 0. 2 mass% C-5 mass% Mn steel during tempering at 500℃ were investigated by in-situ transmission electron microscope（ TEM）. In-situ TEM observation showed uniform distribution of cementite particles at the early stage of tempering in the rapidly heated（ 500 ℃ / s） sample. Elemental analysis confirmed that the cementite growth was dominated by Mn diffusion. During the cementite growth,the coarsening behavior of intragranular cementite was significantly controlled by the matrix diffusion,while that of the intergranular cementite was mainly governed by the boundary diffusion. The in-situ TEM observation revealed that the dislocation pipe diffusion of Mn took place during tempering,which accelerated the Mn diffusion between cementite particles. The coarsening rates of individual cementite particles were calculated based on the in-situ TEM observation.
基金funded by National Basic Research Program of China(2010CB630800,2015CB921700)National Natural Science Foundation of China(51671112,51471096,51390471,11374174)+2 种基金National Key Research and Development Program(2016YFB0700402)National Key Scientific Instruments and Equipment Development Project(2013YQ120353)Tsinghua University(20141081200)
文摘The microstructural evolutions of 5Mn steel during various heat treatments have been investiga- ted by in-situ transmission electron microscopy （TEM）. The specimen of 5Mn steel was pre- pared using focused ion beam （FIB） milling, which allowed the selection of specific morphology of interest prior to the in-situ observation, The complete austenization at 800 ℃ was verified at the atomic scale by minimizing thermal expansion and sample drift in a heating holder based on micro-electro-mechanical-systems. During annealing at 650 ℃, the formation of reverted austen- ite was dynamically observed, while the morphologies of austenite laths of 5Mn steel after in-situ heating were quite similar to that after ex-situ intereritical annealing. During annealing at 500 ℃, the morphological evolution of cementite and associated Mn diffusion were investigated. It was demonstrated that a combination of FIB sampling and high temperature in-situ TEM enables us to probe the morphological evolution and elemental diffusion of specific areas of interest in steel at high spatial resolution.
基金Supported by the National Natural Science Foundation of China(No.51178307 and No.51525803)
文摘Due to traffic and wave actions, cast steel joints are subjected to variable-amplitude fatigue loading, which may cause fatigue problems. The ratio of the minimum strain to the maximum strain(strain ratio)can be employed to analyze the influence of variable-amplitude fatigue both in the elastic and plastic ranges. To evaluate the effect of the strain ratio on G20Mn5 QT cast steel, the fatigue tests of smooth specimens were carried out at the strain ratio of 0.1. The cyclic deformation and the relationships between the strain amplitude, the stress amplitude, the Smith, Watson and Topper(SWT)parameter and fatigue life were studied and compared with those at the strain ratio of-1. Compared with other methods, Basquin formula and Solonberg formula provide reliable and appropriate ranges of S-N curve and fatigue limit at different strain ratios respectively. The SWT parameter can be used to predict the fatigue life at other strain ratios accurately.
文摘The microstructure, composition and shape of precipitated phase under as-cast and finished product state of 5Cr21Mn9Ni4N steel with different rare earth （RE） amount were studied. Mechanical properties of 5Cr21Mn9Ni4N steels withont RE addition and with RE added by 0. 2% in mass percent were tested respectively. The results indicate that the solid solution amount of RE is about 10^-6 -10^-5 order of magnitude in 5Cr21Mn9Ni4N steel. Dendrite of as-cast condition is refined obviously and dimension of interstitial phase is shortened when RE is added by 0.10%-0.20%. But the microstructure will be coarser if surplus RE is added. Precipitated phase under finished product state distributes evenly in nearly same size with RE added by 0. 2% which leads to a largely improved high temperature mechanical property.
文摘The oxidation resistance of 5Cr21Mn9Ni4N steel micro-alloying by RE at 700 - 900 ℃ was investigated. The results indicate that oxidation exponent n and oxidation activation energy are increased, and oxidation velocity constant kp is decreased when 0.2% RE is added in 5Cr21Mn9Ni4N steel. The addition of RE elements does not alter phase constitution of oxidation scale, however it improves the configuration of oxidation scale, and increases thermal stability and adhesivity of oxidation scale, which results in the raise of oxidation resistance of 5Cr21Mn9Ni4N steel at high temperature. The oxidation scale constitutes of refractory steel transfer from manganic oxide mostly to ferric oxide mostly with the increase of temperature, which leads to descend of compactness and desquamation resistance of oxidation scale. The mass increase of ferric oxide in the oxidation scale and the looseness of oxidation scale are the main reason to descend the oxidation resistance of refractory steel.
基金the National Key Research and Development Program of China(No.2017YFC0805100)the National Natural Science Foundation of China(No.51578137)+1 种基金the Priority Academic Program Development of the Jiangsu Higher Education Institutionsthe Open Research Fund Program of Jiangsu Key Laboratory of Engineering Mechanics。
文摘Owing to the remarkable advantages in mechanical behavior,cast steel nodes have been widely used in static structures.Nowadays,cast steel nodes also gain increasing popularity due to the superior fatigue performance in dynamic structures,but they are not yet widely used because the fatigue properties of cast steel are not well understood.In this paper,the fatigue test of cast steel GS20Mn5V commonly used in steel castings is carried out.The strength of medium and low cycle fatigue and the fatigue limit are obtained.The feasibility of the estimated S-N(fatigue stress versus life)curve is tested.The double logarithmic linear model(DLLM)and the reversed generalized Pareto model(RGPM)are used to fit the experimental data,and the comparison is made.The P-S-N(the relationship between fatigue stress and life at different survival rates)curve obtained by the RGPM is proposed.The results show that the estimated S-N curve is not suitable for low cycle fatigue life,fitting the experimental data with the RGPM is the best,and obtaining the P-S-N curve from the RGPM is feasible.
