Advanced Materials Research Vols. 311-313

Abstract: The static constant corrosion tests on Fe-B eutectic alloy are investigated in liquid zinc at 500°C. The systematic observation and research of the corrosion layer are performed using SEM, TEM, XRD. The results show that corrosion resistance of Fe-B eutectic alloy in liquid zinc is perfect. Corrosion products are Fe3B and FeZn7. The corrosion layer is regular, the structure of which is hollow dendritic skeleton and the thickness of which increases with the corrosion time extending. Corrosion process is that the interdiffusion of ferro and zinc atomic results in corrosion layer formation and the corrosion layer ruptures and dissolves under the action of thermal stress and impact stress of liquid zinc. The process repeating leads to the failure of the matrix eventually.

Abstract: This paper investigates the simulation technique for analyzing the distortion behavior induced by welding process on welded plate which was clamped on one side. This clamping method is intended to enable the investigation of the maximum distortion on the other side. FEA software SYSWELD was employed to predict multipassed butt weld distortion of low carbon steel with thicknesses of 6 mm and 9 mm. The simulation begins with the development of model geometry and meshing type followed by suitable selection of heat source model represented by the Goldak’s double ellipsoid model. Other parameters such as travel speed, heat input, clamping method etc. were determined. The model is dedicated for multipass welding techniques using Gas Metal Arc Welding (GMAW). The experimental works were conducted by using Robotic welding process.

Abstract: The microstructure and precipitate of the two kinds of medium-carbon vanadium microalloyed steels whose nitrogen contents were 0.0035% and 0.012% respectively, were studied by image analysis and transmission electron microscope (TEM). The results show there are the large amount of 10~20nm dispersion distribution irregular flake VC precipitates within the ferrite, the part of clustered fibrous VC precipitates with the diameter of 4~13nm that grow toward to ferrite intracrystalline along the grain boundary with some angle in the local area, and only a very small amount of 20 ~ 50nm spherical particles V (C, N) in the low-nitrogen steel. However, in the high-nitrogen steel, the precipitates are divided into two stages: the first stage is the part of 30~80nm spherical particles V(C, N) which precipitation in austenite, the second stage is flakiness VC which precipitation in ferrite during the following γ → α phase transformation and cooling process. Compared with the low-nitrogen steel, the number of precipitates in decreased significantly and the size increased obviously in the high-nitrogen steel. The substantial increase of nitrogen content leads to the rapid increase of driving force that V (C, N) precipitation in austenite. A lot of V (C, N) that precipitation before phase transformation results in the significant increase of ferrite nucleation rate, which leads to the microstructure of high-nitrogen steel fined obviously.

Abstract: According to standard test method for fatigue crack growth rates of metallic materials, the crack growth rate of 30NCD16 at three stress ratio (R=0.1, 0.3 and 0.5) were measured. Based on linear elasticity fracture mechanics theory, the fatigue crack growth rate was studied through the nonlinear least squares fitting method. The Paris model parameters at steady growth region and near threshold growth region and NASGRO model parameters were obtained. The effective stress intensity factors versus curves at three stress ratios were determined by crack closure effect. The results show that the Paris equation can preferably describe relations at steady growth region. At this region the model parameter m lies 2.5-4. This result is consistent with the known statistical facts of most metallic materials. NASGRO equation can preferably describe relations from near threshold growth region to high values region. all the test data at three stress ratio was able to correlate and . Crack closure was the major factor in correlating stress ratio and crack growth rate, the degree of crack closure weaken with increasing stress ratio.

Abstract: For the international New invention, that orbital lumbar joint puncture unique technology, Studied and developed intelligent detection and control system of the needle production process based on machine vision. Through the high speed camera gain image of work piece , uses the multi-wavelet transform pre-and double-cubic interpolation to enlarge the image, using least squares support vector machine workpiece quality intelligent detection and identification, according to the process parameters to obtain real-time control of the production process. Experiments show that this system can meet technical requirements, good stability, high efficiency, has a higher value.

Abstract: Improper heat treatment may result in unsatisfactory microstructure and mechanical properties for P91 steel. In this work, the effect of abnormal heat treatment on microstructure and properties of P91 steel were studied. Results showed that with the normalization temperature increased from 860°C to 1000°C, the microstructures of P91 steel are ferrite, mixture of ferrite and martensite, and tempered martensite correspondingly. Cooling rate after austenization has important influence on microstructure and properties. The tempered microstructure has a gradual transition from coarse inhomogeneous ferrite to finer martensite when the cooling rate increased from 1 to 3°C/min. The reduced temperature normalization has no significant effect on hardness even as low as 860°C under aircooling condition, whereas the hareness is inadequate when the cooling rate is too slow. Incomplete austenization and transformation in dual phase zone may account for the phenomenon.

Abstract: Effects of rare earth elements (RE) on modification of inclusions, the corrosion dynamic laws and the electrochemical properties of low carbon steel in Compact strip production (CSP) technology have been investigated with SEM, EDS and polarization curve measurements. The results show that the RE elements play an important role on the morphology and type control of inclusions and also reduce their size in low carbon steel. The corrosion is mitigated due to relatively compact corrosion products and the dispersion spherical RE oxides and/or oxy-sulfides inclusions with the addition of RE. Meanwhile, the electrochemical measurements show that the corrosion current density of low carbon steel with RE is lower than that of steel without RE. The corrosion resistance is improved to a certain extent by RE.

Abstract: It is impossible to keep pipelines free from defects in the manufacturing, installation and servicing processes. In this paper, pre-tension deformation was used to imitate the defects of the part of material and the U-notch specimens were used to investigate the fatigue crack initiation life of X60 pipeline steel after pre-tension straining with ductile deformation of 0,5%,10% and 15%. Test results show that the prestrain had apparent straining hardening effects, but decreased the plasticity of pipeline steel. The prestrain prolonged the fatigue crack initiation life, and increased resistance coefficient and equivalent stress threshold of the fatigue crack initiation.

Abstract: Annealing process with different rapid cooling temperatures of a hot-dip galvanized high Al dual phase steel was simulated by hot-dip process simulator (HDPS). The results indicated that the tensile strength of the samples increased and the elongation decreased slightly with the increase of rapid cooling temperature from 460 °C to 520 °C. When the rapid cooling temperature was higher than 500 °C, the tensile strength was more than 605MPa, and the elongation rate reached to 32%, the samples was found to have better mechanical properties. It was found by transmission electron microscope (TEM JEM2100F) that the microstructures of the samples were mainly composed of ferrite, island martensite and retained austenite when the rapid cooling temperature was higher than 500 °C, and when this temperature was lower than 480 °C, some island martensites were tempered and carbide was appeared in the island phase.

Abstract: The effects of different TiO2-containing ore’s allocated proportion on quality, mineral structure and sintering process of Xuan steel sinter were studied in this paper. The results showed that the increasing of the TiO2-containing ore’s allocated proportion was disadvantageous to the sinter sample’s anti-compressive strength, and the yield and tumbler strength of sinter were decreased although the velocity of sintering was improved. The tumbler strength decreased from 68.67% to 63.33%, and the main reason is that the content of perovskite increases and the content of calcium ferrite decreases with the increasing of TiO2-content in the sinter. The TiO2-content in the sinter should be controlled less than 1.3% considering effect of TiO2-content on sintering process, burdening and iron making of blast furnace in all.