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建立了考虑δ/γ相变的GCr15轴承钢大方坯连铸凝固两相区溶质微观偏析模型,并应用于220 mm ×260 mm铸坯的凝固传热。结果表明:通过模型可以获得高碳钢精确的固液相线温度,以及温度与固相率的关系;GCr15轴承钢大方坯凝固过程仅析出γ相,凝固末期S、P和C元素的偏析严重;固相率越大,冷却速率对偏析度的影响更明显;S和P元素含量以及冷却速率对零塑性温度(ZDT)影响较大;采用基于凝固传热模型优化的连铸工艺后,铸坯中心碳偏析指数控制在0.961.05,且铸坯未产生内裂纹。 相似文献
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板坯连铸实时跟踪动态控制模型的开发与应用 总被引:1,自引:0,他引:1
基于耦合多元合金两相区凝固计算的板坯连铸凝固传热数学模型,并采用以恒定间距方式进行离散化的切片单元法开发了板坯连铸实时跟踪动态控制模型CCPS ONLINE.可根据合理的冶金准则并结合铸坯的在线跟踪信息对板坯连铸浇铸过程中的关键工艺参数(二冷水量、扇形段辊缝)进行动态调整,以获得稳定可靠的浇铸工艺条件和良好的铸坯质量.模型已投入工业应用,现场工作表明,其控制算法合理、仿真精度良好,具有较好的可靠性和实用性. 相似文献
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《冶金设备》2017,(3)
基于ANSYS软件建立了310mm×360mm断面大方坯连铸过程二维凝固传热数学模型,通过窄面射钉试验及铸坯表面测温对模型的准确性进行了验证,模拟了不同碳含量的高碳耐磨球钢大方坯宽面和窄面凝固坯壳的生长。结果表明模型能精确地获得不同工况下任意位置凝固坯壳的厚度分布、凝固终点位置及铸坯中心固相率;发现不同碳含量的高碳耐磨球钢具有相同的凝固规律:结晶器弯月面至二冷区出口,相应的铸坯柱状晶区凝固坯壳厚度与凝固时间的平方根呈线性关系,符合平方根定律,并对平方根定律进行了修正,修正项与过热度有关;二冷区出口至凝固终点,相应的铸坯等轴晶区凝固坯壳厚度与凝固时间的平方根呈非线性关系,不再符合平方根定律。 相似文献
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以某钢厂GCr15钢大方坯为研究对象,采用ProCAST软件建立凝固数学模型,研究了过热度、拉速和比水量对大方坯凝固过程的影响,并通过对铸坯中心固相率及液芯长度的分析,确定了最佳末端电磁搅拌位置,并优化了拉速。研究结果表明:过热度对铸坯凝固影响最小,随着过热度增加,铸坯表面温度升高,铸坯液芯长度和液相区长度均随之增加,而两相区长度则随之减小;拉速对铸坯凝固影响最大,拉速提高,铸坯表面温度、液芯长度、两相区长度、液相区长度均增大;比水量增加,铸坯表面温度降低,液芯长度减小;当比水量为0.29 L/kg时,过热度应控制在15~35℃,拉速需控制在0.46~0.49m/min,且最佳拉速为0.48 m/min。 相似文献
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The low-temperature creep behavior of carburized 4320 steel with retained austenite contents of 35 and 14 pct and two uncarburized
4320 steels was investigated. The temperature range in the experiments was from 70 °C to 195 °C. The creep rate obeyed a logarithmic
law when the stress level was below or near the proportional limit. A kinetic model is presented which de-scribes the low-temperature
creep behavior of this steel under different stress and temperature conditions. The techniques for determining the constants
in the model are given.
Formerly Visiting Assistant Professor, Department of Mechanical and Industrial Engineering, University of Illinois 相似文献
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Based on the assumption that the transverse cross‐section of dendrites is a regular hexagon, a coupled macro‐heat transfer and solute diffusion model was developed to describe micro‐segregation behavior of solute elements in the mushy zone during wide‐thick slab continuous casting. The heat transfer model and the micro‐segregation model were validated by the industrial tests and the experiment measurements in literatures, respectively. The results show that the cooling rate decreases from 51.1°C s?1 at the surface to 0.13°C s?1 at the center of the wide‐thick slab of peritectic steel continuous casting. The effective cooling rate equaling to 1.78°C s?1 mainly depends on mold cooling and varies little with casting speed. The micro‐segregation behavior of solute elements in the mushy zone depends on back diffusion ability and local equilibrium at interfaces. Compared with other elements in the steel, phosphorus, and sulfur elements exhibit a much higher segregation ratio at the end of the solidification and are more significantly affected by the initial carbon content. 相似文献
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Assessment of Creep Deformation,Damage, and Rupture Life of 304HCu Austenitic Stainless Steel Under Multiaxial State of Stress 总被引:1,自引:0,他引:1
K. C. Sahoo Sunil Goyal P. Parameswaran S. Ravi K. Laha 《Metallurgical and Materials Transactions A》2018,49(3):881-898
The role of the multiaxial state of stress on creep deformation and rupture behavior of 304HCu austenitic stainless steel was assessed by performing creep rupture tests on both smooth and notched specimens of the steel. The multiaxial state of stress was introduced by incorporating circumferential U-notches of different root radii ranging from 0.25 to 5.00 mm on the smooth specimens of the steel. Creep tests were carried out at 973 K over the stress range of 140 to 220 MPa. In the presence of notch, the creep rupture strength of the steel was found to increase with the associated decrease in rupture ductility. Over the investigated stress range and notch sharpness, the strengthening was found to increase drastically with notch sharpness and tended toward saturation. The fractographic studies revealed the mixed mode of failure consisting of transgranular dimples and intergranular creep cavitation for shallow notches, whereas the failure was predominantly intergranular for relatively sharper notches. Detailed finite element analysis of stress distribution across the notch throat plane on creep exposure was carried out to assess the creep failure of the material in the presence of notch. The reduction in von-Mises stress across the notch throat plane, which was greater for sharper notches, increased the creep rupture strength of the material. The variation in fracture behavior of the material in the presence of notch was elucidated based on the von-Mises, maximum principal, and hydrostatic stresses. Electron backscatter diffraction analysis of creep strain distribution across the notch revealed localized creep straining at the notch root for sharper notches. A master curve for predicting creep rupture life under the multiaxial state of stress was generated considering the representative stress having contributions from both the von-Mises and principal stress components of the stress field in the notch throat plane. Rupture ductility was also predicted based on the multiaxial state of stress. 相似文献
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In the present study a simple model is proposed to assess creep behavior. The model is applied to experimental results performed on austenitic steel X8 CrNiMoNb 16 16. The model is based on a modification of the Levy‐Mises equation for plasticity to consider creep time effects, introducing as a parameter the intrinsic creep resistance. The assessment of creep behavior applied for monotonic and two stages loading data is good. The model could assess negative creep strain rates as well as damage accumulation observed as an increase of the minimum creep rate after each reloading at the same stress level in two stages tests. 相似文献
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Characterization of Models for Time-Dependent Behavior of Soils 总被引:5,自引:0,他引:5
Different classes of constitutive models have been developed to capture the time-dependent viscous phenomena (creep, stress relaxation, and rate effects) observed in soils. Models based on empirical, rheological, and general stress-strain-time concepts have been studied. The first part is a review of the empirical relations, which apply only to problems of specific boundary conditions and frequently involve natural time alone. The second part deals with different rheological models used for describing the viscous effects in the field of solid mechanics. The rheological models are typically developed for metals and steel but are, to some extent, used to characterize time effects in geomaterials. The third part is a review of constitutive laws that describe not only viscous effects but also the inviscid (rate-independent) behavior of soils, in principle, under any possible loading condition. Special attention is paid to elastoviscoplastic models that combine inviscid elastic and time-dependent plastic behavior. Various general elastoviscoplastic models can roughly be divided into two categories: Models based on the concept of overstress and models based on nonstationary flow surface theory. Although general in structure, both have shortcomings when used for modeling of soils. 相似文献
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Akira Matsushita Ryosuke Takai Hideaki Ezaki Toshimitsu Okane Makoto Yoshida 《Metallurgical and Materials Transactions A》2017,48(4):1701-1707
This paper proposes a new method for obtaining the rheological properties of solidifying alloys in the brittle temperature range (BTR). In that range, alloys show not only rheological, but also brittle behavior. Conventional methods to obtain rheological properties require steady state stress with ductility. Therefore, rheological properties of BTR alloys are unobtainable, or are otherwise including the effects of microscopic damage. The method proposed in this paper uses the stress–strain relation derived from the Maxwell model assuming that strain hardening is negligible in solid-liquid coexistence states. By removing the plastic strain term, the creep strain rate in Norton’s law is derived by the total strain rate and stress rate without the steady state stress condition. Consequently, the stress exponent n and material constant A of Norton’s law can be obtained even for alloys in the BTR. We applied this method to both tensile process before crack initiation and stress relaxation process. According to the Maxwell model, couples of the properties (n and A) obtained in both processes must be equal. Therefore, the difference can validate the obtained properties. From tensile and stress relaxation tests, we obtained the properties of solidifying Al-5 wt pct Mg alloy. We validated results by examining the difference. This report is the first to provide a method to obtain the rheological properties of BTR alloy without damage. 相似文献
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Avoiding particle entrapment into the solidifying shell of a steel continuous caster is important to improve the quality of the continuous cast product. Therefore, the fluid flow dynamics in the steel melt and mushy zone, heat transfer and solidification of the steel shell, as well as the motion and entrapment of inclusion particles during the casting process were investigated using computational models. Solidification of the strand shell is modelled with an enthalpy‐formulation by assuming a columnar morphology in the mushy zone. The motion of particles is tracked with a Lagrangian approach. When the particles reach the solidification front, they can be entrapped/engulfed into the solid shell or pushed away from the solidification front, depending on the mushy zone morphology and the forces acting on them. The current paper focuses on the mould region at a steel continuous caster, including the submerged entry nozzle (SEN) and 1.2 m length of the strand. The results are validated with plant measurements and demonstrate the potential of the model to predict fluid flow, shell growth and the positions and the amount of entrapped/engulfed particles in the solidifying strand. 相似文献
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Kyoung-Kyu Choi Mahmoud M. Reda Taha Mark J. Masia Penelope L. Shrive Nigel G. Shrive 《Canadian Metallurgical Quarterly》2010,14(6):812-822
Numerical analysis using a finite-element model was performed to simulate and investigate the long-term behavior of two RC beams with similar steel reinforcement, cast from the same batch of concrete. One beam was a plain RC beam and the other beam was strengthened using carbon fiber-reinforced polymer (FRP) strips. The deflections of both beams have been monitored for 5 years after loading. The finite-element model included both creep of concrete and viscoelasticity of the epoxy adhesive at the concrete-carbon FRP (CFRP) interface. The results of the finite-element analysis are compared to experimental observations of the two beams. The finite-element analysis was found to be able to simulate the long-term behavior of the CFRP-strengthened beam and help us understand the complex changes in the stress state that occur over time. 相似文献
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Alexandre Kepler Soares Dídia I. C. Covas Luisa Fernanda R. Reis 《Canadian Metallurgical Quarterly》2008,134(9):1389-1394
This research work focuses on the analysis of hydraulic transients in polyvinyl chloride (PVC) pipes, which are characterized by a viscoelastic rheological behavior. Transient pressure data were collected in a pipe rig consisting of a set of PVC pipes. The creep function of the PVC pipes was determined by using an inverse transient model based on collected transient pressure data and compared with that obtained by carrying out mechanical tensile tests of PVC pipe specimens. The numerical results obtained from the transient solver have shown that the attenuation, dispersion, and shape of transient pressures were well described. The incorporation of the viscoelastic mechanical behavior in the hydraulic transient model has provided an excellent fitting between numerical results and observed data. Calibrated creep function based on inverse analysis fit the one determined by mechanical tests well, which emphasized the importance of pipe-wall viscoelasticity in hydraulic transients in PVC pipes. 相似文献