Applied Mechanics and Materials Vols. 423-426

Abstract: The oxidation behavior of Fe-Cr-Ni-Mo-Ti maraging steel was investigated within an intermediate temperature range of 450-600°C. Analysis of oxidation kinetics demonstrated excellent oxidation resistance after exposure in air for 100 h; the oxide layer formed was protective and can resist further oxidation. Surface morphology evolution and oxidized surface hardness were characterized by scanning electron microscope and nanoindentation test. The surface oxidation film was rather smooth with Cr enriched at 450°C, appeared a needle-like structure at 500°C together with a few nodule protrusions enriched in O but absent in Fe and Cr; and then transformed to a smooth and compact oxide surface with some protrusion emerged on the original grain boundaries of austenite at 550°C; finally a Fe₂O₃ phase particle structure appeared at 600°C. The oxidation layer formed on substrate of Fe-Cr-Ni-Co-MoTi was harder than the substrate when oxidation temperature was lower than 550°C.

Abstract: 211Z is a new type of high strength and toughness Al-Cu-Mn casting aluminum alloy. With the aid of GPS-100 high-cycle fatigue testing machine and DDL100 multifunction tensile testing machine, conventional mechanics performance tests and high-cycle fatigue tests were carried out in this paper. The conventional mechanical property results show that the tensile strength is 477.5 MPa, the theory yield strength is 397.5 MPa and the elongation is 6.625%. Fatigue experiments were performed with load control at room temperature and R =-1 in ambient air. The tensile and compression fatigue strength is 130 MPa under ten million times fatigue test, and S-N fatigue life curve of this alloy was also given in the investigations. 211Z casting aluminum alloy possessing high fatigue strength can be attributed to the fact that it owns high strength and good plasticity simultaneously. The microstructure analysis of fatigue fracture appearance shows that, the fatigue crack initiation behavior of this aluminium alloys depends mainly on the region possessing defects under the surface, there has only one crack source, which means it is belongs to low nominal stress unidirectional bending. In the crack growth stage, the width of fatigue striations decreases with the increase of stress, and a few secondary cracks were found in this stage. When cracks finally losed stability, an instantaneous fracture occured in the investigated samples. Shear lips and dimples were found in the fracture appearance and the final fracture is belongs to ductile fracture.

Abstract: Some problems have seriously affected the implementation of smelting ferrochromium in the argon-oxygen furnace. This paper discussed reducing chromium loss and controlling excessively high bath temperature by thermodynamic analysis. The results show that the process is divided into two stages and the critical carbon concentration of its switchover point is controlled in the range of 1.5%-2% to reduce chromium loss; dynamic control of oxygen and argon supply by theoretical calculation and AI(Artificial Intelligence) technology and carbon dioxide blown by a lance with double channel as coolant instead of steel scrap and chrome ore can flexibly control furnace temperature.

Abstract: this Paper studies the influence of Gd, a rare-earth element, on AM60B Mg cast alloys structures and, after the analysis of scanning electron microscope (SEM) and energy spectrum analysis, as well as the observation and analysis of XRD, demonstrates Gd could change the precipitates and precipitated phases of Mg cast alloys. The result shows that the adding of Gd to AM60B alloys may effectively refine the alloys structures and the generation of rare-earth compounds, and be conducive to improving the fracture ways of magnesium alloys.

Abstract: The carbon steel/stainless steel composite pipe was prepared by centrifugal compound casting-hot extrusion-cold rolling. SEM was employed in detecting the microstructure and alloy element distribution maps in stainless steel of composite pipe. The mechanical properties were measured through tensile test. The corrosion resistance of the composite pipe was detected in acid, alkali and salt solutions. The results show that the outer and inner layers are integrated with good metallurgical behavior, and the mechanical properties of the composite pipe are satisfactory, the chemical compositions are well-distributed. The grain-boundary corrosion test is qualified. This composite pipe has better corrosion resistance in 10%H₂SO₄ and 10%NaOH solution than in FeCl₃ solution at room temperature.

Abstract: Ti₃Al based alloy has performed a comprehensive properties of low density, high tensile strength and excellent oxidation resistant at high temperature, which results in a good potential application in aerospace areas. In this paper, technologies relevant to preparation of Ti-23Al-17Nb expansion part for nozzle have been studied, and main properties of the part have been test and evaluated. The result revealed that Ti₃Al based alloy prepared by powder metallurgy can replace nickel based alloy to be a candidate materials for high temperature structures.

Abstract: A physical model was established according to the similarity theory to simulate the real 175t RH-TB vacuum refining device. Liquid steel is simulated by Nacl solution, the air is approximate argon and polypropylene simulate inclusions. The influence regularity of treatment time ,lift gas flow rate and submersion depth of snorkels on the inclusions removal rate have been discussed, the optimal values for each influence factor have been found and can be used in optimizing the refining technology.

Abstract: Novel two-stage solution heat treatments were applied to Cu-Cr-Zr alloy to improve its properties. The influences of these treatments on the microstructures and properties of the alloy were investigated by TEM, SEM, tensile testing and electrical conductivity test. The investigation showed that with the proposed solution treatments, it was possible to obtain better properties than the properties obtained by conventional single-stage solution treatment. For example, in the case of an alloy of Cu-0.4wt.%Cr-0.1wt.%Zr, it was found that a two-stage solution treatment system (8 h at 920 °C followed by 1 h at 1010 °C) produced better combination property than the conventional single-stage solution system (1 h at 950 °C) applied by other researchers. The first stage solution treatment is crucial to the dissolution of CuZr precipitates, dissolved CuZr phase completely, at the same time precipitated Cr phase. Subsequently, excess Cr precipitates all dissolved at the second stage solution treatment. As a result, a pure matrix is obtained after such two-stage solution heat treatments.

Abstract: An initial thermodynamic modeling of the Cu-Ni-Si-Co system was built using CALPHAD approach. The liquid phase and terminal solid solutions were described by substitutional solution model, the nonlinear compounds used sublattice model and the other binary compounds were treated to be stoichiometric compounds. Based on the experimental conditions, the thermodynamic calculations were done to predict the stable precipitates of the alloys and investigated the effect of Co on the phase transitions. The experimental results showed an acceptable agreement with the calculation and verified the reliability of the Cu-Ni-Si-Co thermodynamic modeling.

Abstract: The behavior evolvement of Mg-7.22Gd-4.84Y-1.26Nd-0.58Zr (EW75) magnesium alloy during the hot deformation process was discussed. The flow stress behavior of magnesium alloy over the strain rate range 0.002s^-1 to 2s^-1and the temperature range 623K to 773K had been researched on Gleeble-1500D hot simulator under the maximum deformation degree 60%. A mathematical model was established to predict the stress-strain curves of this alloy during deformation. The experimental results showed that the stress-strain curves were obviously affected by the strain rates and deformation temperatures. The mathematical model could predict the stress-strain curves when the strain rates were under 0.2^-1, but there was significant error in some of stress-strain curves when the strain-rate was 2^-1 by the reason of deformation temperature rising.