Advanced Materials Research Vols. 287-290

Abstract: 55NiCrMoV7 steel is extensively used as mould steel. However, how to obtain a product combined with both high strength and good toughness is still a problem in the heat treatment process. In current study, a series of 55NiCrMoV7 steel specimens were quenched with different cooling rates to obtain martensite, lower bainite and upper bainite, then tempered at 600°C, 620°C and 650°C, respectively. The micrographs show the evolution of microstructure with the variation of cooling rates and tempering temperature. Mechanical properties test has revealed that, 1) at the same tempering temperature, the tempered martensite has the highest strength and hardness, while the tempered lower bainite has the best impact toughness; 2) at the same ratio of yield strength to tensile strength (YS/TS), the ductility and toughness of martensite are better than that of bainite. Furthermore, fractographs of impact specimens show the ductile and brittle fracture behavior for martensite and upper bainite respectively.

Abstract: The mechanical properties and microstructure of high boron alloy (HBA) with different content of boron and carbon were investigated using Taguchi method for obtaining the optimized composition. In addition, the effect of modification with different RE content and the effect of heat treatment on the alloy were studied as well. Results show that the optimized chemical compositions of the HBA are as follows: 0.5% C、3.0% B、1.0% Si、1.0% Mn、1.0% Cu、1.5% Cr、0.5% V and the rest is Fe, and the best content of the RE are 0.8%-1.0%. After the modification and the heat treatment, the mechanical properties of alloy improve significantly. This is because that the matrix of alloy is changed from pearlite to martensite, and the network of boride is broken up and distributed more evenly to form an isolated and discontinuous distribution. The alloy with this composition has been successfully used for anode claw in aluminum smelter, which greatly improves the wear resistance.

Abstract: Aiming at the characteristics of pavement rutting damage of test road under the condition of heavy load and abrupt slope, an overlay design scheme and a new overlay material with high performance was proposed. The new material is PG82 modified asphalt SMA-13 added polyester fibre which can significantly improve the high temperature performance of asphalt mixture under severe environment, and its strength and crack resistance are superior to normal SMA-13. Tracking survey of test road shows that the pavement performances keeps good and rutting is under good control. Therefore those measurements are successful and can be a reference to similar projects.

Abstract: In this article, some empirical and theoretical models accounting the relationship between the strength and pore structure of cement-based materials is reviewed and analyzed. From the literature review and analysis, it can be found that the total porosity can be singly used to characterize the relationship between compressive strength and pore structure, but can not be applied into describe the relationship between pore structure and tensile strength. Another major parameter of pore structure - pore size distribution, will have a major impact on strength; the relationship between pore structure and tensile strength is for most models of cement paste, without the consideration of aggregate, and the application of the model must comply with the relevant assumptions. The research on the relationship between the tensile strength of concrete is still at a preliminary stage, requiring more theoretical and experimental study.

Abstract: The microstructure of Cu-37%Zn-2%Mn-1.6%Al-0.7%Fe-0.7%Si (mass fraction)alloy was studied by scan electron microscopy, X-ray and optical microscopy. The α phase ratio and micro-hardness of this alloy after aging treatment were investigated. The results show that three kinds of phases, such as α phase, β phase and hexagonal club-shape Mn₅Si₃ phase were observed. The needle α phase ratio increases with aging temperature under 420°C and reach peak value 25 percent after aging at 420°C×1h. The α phase ratio begin decreases when the aging temperature over 420°C. The micro-hardness varying with aging temperature is the opposite.

Abstract: We report on a novel method for preparation of high purity Sm₂Fe₁₇ phase by removing the liquid impurity phase from the Sm-rich precursor at high temperatures. With decreasing Sm addition, the percentage of liquid phase left as impurity is decreasing. Nitrogen absorption to the Sm₂Fe₁₇ powders results in a complete formation of Sm₂Fe₁₇N₃, which shows a weak disproportionation reaction at 773 K. The magnetic performance of the Sm₂Fe₁₇N₃ from precursors with different Sm content is improving with decreasing Sm content.

Abstract: In this study, scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) are used to measure the inclusion size and identify the inclusion type respectively. The evaluated maximum nonmetallic inclusion size of bearing steel has been obtained using statistics of extreme values (SEV), and the influence of oxygen content on the maximum nonmetallic inclusion size and the fatigue life of bearing steel have also been discussed. By adopting the criterion of return period (T) at 200, the serial analyses show that the predicted inclusion size for_max is proportional to the oxygen content of steel, but the relation between fatigue life and oxygen content of steel is inverse proportion. This results from the defragment of hard inclusion during rolling process, and the decrease of concentration of stress around the inclusion.

Abstract: In order to identify the influence of solid solution, aging and solid solution plus aging treatments on the low-cycle fatigue behavior of the extruded AZ61 magnesium alloy, the low-cycle fatigue tests were performed at room temperature for the extruded AZ61 magnesium alloy with different treating states. The results indicate that the cyclic stress response behavior of the extruded AZ61 magnesium alloy exhibits both cyclic strain hardening and stability. The solid solution, aging and solid solution plus aging treatments tend to decrease the cyclic deformation resistance of the extruded AZ61 alloy in most conditions. The solid solution treatment can enhance the fatigue lives of the extruded AZ61 alloy at medium total strain amplitudes. In addition, the aging treatment can prolong the low-cycle fatigue lives of the AZ61 alloy at most total strain amplitudes, while the case for the solid solution plus aging treatment is just contrary. For the extruded AZ61 alloy with different treating states, a linear relationship between cyclic stress amplitude and plastic strain amplitude is noted.

Abstract: In this paper, a new insulation system of polyurethane foam and moulding board with glazed-hollow-bead mortar is designed. According to the principle of the temperature gradient and the spreading and releasing stress in different layers, the fire prevention and aging resistance performance of polystyrene board in external insulation system are improved. Performances of fireproofing and insulation motor of different ingredients, such as glazed hollow bead, fly ash, polymer emulsion powder, quicklime and fiber were tested in the lab, and the reasonable mix ratio of the mortar was obtained. Moulding board of glazed-hollow-bead mortar was deigned and manufactured. To quickly construct and improve quality of the new insulation system, fixed moulding board system was manufactured, board of glazed-hollow mortar and fixed board system were gained.

Abstract: The influence of Al₂O₃ on alkali content in concrete pore solution was investigated, Al₂O₃ was added into concrete by bauxite. The quartz glass as active aggregate was dipped in the NaOH solution with Al³⁺ and without Al³⁺ respectively. The morphology of the products was observed by scanning electron microscope, the element composition was analyzed by Energy analyzer and the mineral composition was measured by X-ray diffractometer. The results showed that alkali content in pore solution can be reduced effectively by Al₂O₃. The more content of Al₂O₃, the lower alkali content in pore solution. The existence of Al³⁺ changed the ASR products. The products inclined to crystal rather than gel and zeolite was formed. Therefore, the decrease of alkali content in pore solution and transformation of ASR products were the reasons of the substance containing aluminum inhibition ASR.