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[en] In this study, a series of fatigue tests were conducted on C45 steel specimens with local surface cracks. The effects of carburizing treatment with different case depths were discussed under cyclic tensile and torsional loading. Moreover, the surface crack extension paths and crack propagation rates were discussed. In addition, the effects of additional static torsion under cyclic tensile loading and additional static tension under cyclic torsional loading were analyzed, and comparisons were made between the results of the carburized materials and those of the uncarburized materials. Some conclusions show that carburization can effectively retard crack extension and improve fatigue life. However, the improvement provided by the case depth on the fatigue life is limited to a certain range, and extensive case depths might decrease the fatigue strengths of materials. For the studied material, carburization had a more direct influence on the crack growth under cyclic tensile loading than cyclic torsional loading.
[en] Quenching is one of the most important processes, which is least understood, in heat reacting. This article provides key-points in quench-system design and how to control quenchant flow velocity, turbulence and directionality of flow which, in turn, influence the uniformity of the quenching media. Cooling must be monitored to ensure the formation of desired transformation-products and to minimize distortion, residual stresses and cracking. It is important that heat-treaters should select both the best quenching and optimum design of the quench-system for the job. (author)
[en] The hot deformation behavior of as-cast hypoeutectic Al-Si-Mg alloy has been investigated through hot compression tests at temperatures between 573 and 773 K and the strain rate of 0.001-1 s−1. A modified Hansel-Spittel constitutive model is proposed, which takes the effect of strain rate on strain hardening into account. The processing maps are established based on the dynamic material model and the Murty criterion. Microstructure observations show that dynamic recovery dominates the dynamic softening behavior, and recrystallized grains are found in the sample tested at 773 K with strain rate of 0.01 and 0.001 s−1. The size of Si particles decreases by about 64.73% with the effective strain increasing from 0 to 1.2. The optimal hot processing parameters of as-cast hypoeutectic Al-Si-Mg alloy are established based on the processing maps.
[en] A closed-form solution is presented for the small deformation analysis of a straight thin-walled circular cylinder. Dimensionless interaction curves and charts which relate the variables, bending moment, curvature, maximum effective strain, twisting moment, and shear strain are also provided for engineering practice convenience. The average stress-strain diagram of the cylinder is described by two straight lines. The result is not only a good approximation of a wide class of piping materials, but also provides a standard tool for estimating the accuracy of different direct schemes such as numerical integration, finite-difference, and finite-element methods
[en] Replication metallography test on reformer catalyst tube for octanol production process has been carried out. Those tubes have been operated for 4 years. The testing results show that several tubes are in carburized condition, blister, creep, micro and macro crack. According to damage rank macro cracks occurred around 42% from all tubes. In spite of tubes are planned to be operated around 100,000 hours or 11 years, but tubes that have macro have the remaining life of 1.5 months up to 3.5 years. (author)