Founded in 1895 as Peiyang University,Tianjin University is the oldest institution of higher education in modern Chinese history.After 130 years of growth and development,it has now become one of the leading research and teaching univer-sities,pioneering various aspects of engineering education and applications.As an integral part of the university,the Department of Mechanics has grown from a mechanics lab-oratory in the 1920s to its current status as one of the leading research and teaching departments,covering solid mechan-ics,fluid mechanics,engineering mechanics,and dynamics and control.Its distinctive research in solid mechanics and interdisciplinary fields ranges from elastic waves and con-trol,experimental mechanics,nonlinear dynamics,contact mechanics and tribology to nanomechanics,contributing both to the fundamental understanding of nature and to engi-neering applications.
The high-temperature corrosion behaviors of an as-rolled Fe-17.4Cr-12.4Ni-2.63Mo-1.57Mn-0.044C (in wt.%) austenitic stainless steel in nuclear-grade helium environments containing with 10, 100 and 1000 magnification impurity tolerance concentrations at 550 degrees C were investigated and compared. Based on the quantitative relationship between mass gain and corrosion time, the high-temperature corrosion kinetics curves of the alloy in different helium environments were determined. The results demonstrated that for different samples, their mass gains exhibited a parabolic increase over the corrosion time. Raman spectroscopy and GIXRD analyses revealed that the high-temperature corrosion mechanisms of different samples are similar and the formed surface oxide layers were primarily composed of Fe2O3, Cr2O3, Fe3O4 and NiFe2O4. Under the equivalent corrosion damage and mass gain conditions in helium containing with 10, 100 and 1000 magnification impurity tolerance concentrations, the corresponding corrosion time required to achieve a mass gain of 0.5 mg/cm2 were determined to be 200, 600 and 1000 h, respectively. Based on the principle of same damage mechanism and equal damage degree, an acceleration testing method was proposed and the corresponding empirical formulas were established for evaluating the long-term high-temperature corrosion extent of austenitic stainless steels in nuclear-grade helium environments.
Currently, the supply of high Fe grade and low gangue pellet feeds has become increasingly tight due to yearly large-scale consumption of iron ores worldwide, which will inevitably restrict the development of iron ore pelletizing process and carbon dioxide emissions mitigation of the steel industry. To promote utilization of high silica pellet feeds, the roasting behavior of high silica acid pellets with varying binary basicity (w(CaO)/w(SiO2) = 0.01, 0.20, 0.35, 0.50) through the straight-grate process was examined, and its metallurgical performance in blast furnace and gas-based shaft furnace was also evaluated. The results show that all fired pellets achieved optimal strength by roasting at 1225 °C for 10 min at basicity of 0.35. The metallurgical performance tests under blast furnace and Midrex direct reduction conditions indicate that the addition of a proper quantity of calcium flux improves the pellet reducibility and low-temperature reduction degradation performance, decreases the reduction swelling index and narrows the softening and melting range with better bed permeability at desirable basicity of 0.20 and 0.35. However, further increasing the basicity to 0.50 presents negative impacts on the pellet induration characteristics and metallurgical properties due to excessive formation of liquid phase inhibiting interconnection of hematite particles. Thus, the fired pellets exhibit poorer resistance and structural stability to the mechanical stress and lattice transformation during reduction and cooling process.
A coupled numerical model integrating molten steel flow, solidification behavior, matrix deformation behavior, and surface crack tip extension was developed. Following validation of temperature evolution and strain–stress curve, the model was used to investigate slab crack propagation with various strip feeding ratios during continuous casting, accounting for variations in crack positions and types. The results show that the “double roll” flow is formed under the limitations of the mold narrow surface, meniscus, and submerged entry nozzle, inducing an easier propagation of crack at the slab narrow surface where the S32654 matrix exhibits higher temperature and lower yield strength. The feeding strip prevents the jet from washing on the slab narrow surface, significantly reducing the temperature and increasing the yield strength there. As the strip feeding ratio increases, crack propagation becomes more difficult, while surface crack area gradually decreases. Moreover, longitudinal crack propagation occurs most easily, followed by 45° oblique crack propagation, while transverse crack propagation is the most difficult, due to the increasing angle between the directions of stress release and slab casting. The optimal strip feeding ratio should be around 0.75
The influence of Mn/Cr ratio variation in the Mn–Cr-rich body-centered cubic matrix phase on the high-temperature oxidation resistance and mechanical properties of L21-strengthened Al20Fe50CrxMn25−xTi5 (x = 15, 25 at.
