Materials Science Forum Vol. 850

Abstract: 0Cr17Ni7Al is a precipitation hardening stainless steel, which combines the advantages of austenitic stainless steel and martensitic stainless steel. 0Cr17Ni7Al shows good corrosion resistance, excellent processability and high strength. This paper is mainly focused on the fracture morphology of 0Cr17Ni7Al wire during torsional deformation. Cracking mechanism and torsion failure reason is analyzed in detail. The results show that AlN inclusions are observed both in raw steel wire and fracture, the micro-cracks appear along the axial direction of the steel wire. The torsion strength is normally 2958MPa. but, the local stress of steel wire reaches up to5295MPa when a 0.4mm deep micro-crack locates on the surface of steel wire, and the local stress is obtained to 2953MPa around a 10μm AlN inclusion. Stress concentrating is caused by inclusions and micro-cracks, and the crack propagation lead to the torsion failure of steel wire when the local stress is beyond the torsion limit.

Abstract: A method for the determination of seven hazardous elements in Non-stick Pan Materials in five food simulants by inductively coupled plasma mass spectrometry (ICP-MS) was established. Using this method, the experiments were carried out on the samples of imitated migratory elements (Cr、Mn、Ni、Cu、As、Pb、Cd) in food simulants of water, 4%(W/V) acetic acid solution, 10%(V/V) ethanol solution, 2g/L sodium chloride solution and olive oil. The sample preparation method of five food simulants was confirmed through experiment. Experiments by resolution, stability, sensitivity and other parameters were adjusted tuning instrument to determine the instrument to achieve the best working condition. The linear range of this methods was 0.1~50ng/ml. For all elements, the correlation coefficient of the calibration curves was above 0.9990 and the detection limits were within the range of 0.008~0.12ng/ml. Most of the recoveries at 1ng/ml concentration level was from 85.34%~112.3%, while the RSD was from 0.37%~4.1%.

Abstract: The corrosion behaviors of austenitic stainless steels, 304 and 316L as a contrast material, are investigated in hydrochloric acid corrosion under different conditions including immersion corrosion, single-phase flow and two-phase flow, respectively. The corrosion mass loss test and electrochemical test were carried out to evaluate the influence of medium temperature and concentration. The specimen surface morphologies and chemical compositions were obtained using scanning electron microscope to analyze the corrosion mechanism. The results show that the static corrosion rates of 304 and 316L steels and erosion corrosion rates of 304 steel increase obviously with the medium temperature increasing, but, the effect of hydrochloric acid concentration on their corrosion rate is less than that of the temperature. The corrosion current density values of 304 stainless steel increase and its passivation region of the polarization curve becomes narrowing and disappeared as the medium temperature increase. Uniform corrosion is the main way found on the surfaces of the stainless steels at room temperature in the hydrochloric acid solution. However, the selective corrosion occurs on their surface with the medium temperature increasing, and the higher temperature and concentration of corrosion medium, the more serious selective corrosion.

Abstract: The flexural performance, 24 h creep-24 h recovery of the Populus alba wood fiber reinforced high-density polyethylene composites prepared by forming mat-compression molding method is investigated. Two-parameter power law model, Findley’s power law model and Burgers model are used to describe the 24 h creep curve of wood fiber reinforced polymer composite. Through model testing and parameter testing, and comparing the sum squared error of three models found that four elements Burgers model is successfully simulated with the creep resistance performances of resulted wood fiber reinforced polymer composites, and the two-parameter power law model is the worst. In summary, the four elements Burgers model is suitable for describing the creep performances of wood fiber reinforced polymer composites and predicting the safety and stability during application.

Abstract: In order to optimize the size of wood fiber reinforced polymer, and extend the application field of wood fiber reinforced polymer composites and improve the safety of their use, four size of wood fiber reinforced high-density polyethylene (HDPE) composites were prepared by forming mat-compression molding. The four kinds of fibers of different size include 80-120 mesh, 40-80 mesh, 20-40 mesh and 10-20 mesh fibers. The flexural performance, impact resistance performance and 24 hours creep - 24 hours recovery of the composites are studied. Fiber of 20-40 mesh presents the best flexural and impact resistance performance. The flexural strength, the elastic modulus and the impact strength reach 26.71MPa, 2.73Gpa and 6.88 KJ/m² respectively. The impact performance of wood fiber/HDPE composites do not change a lot, while the fiber size increases from 10 to 80 mesh. However, the composites containing 80-120 mesh fibers has minimum impact performance. The creep performance of the wood fiber/HDPE composites with 80-120 mesh is the worst. After 24h creep test, the strain of the other three groups is almost the same. Creep recovery of the composites reinforced with 40-80 mesh fiber is the worst (61.74%). The creep recovery of the other three is above seven percent. Therefore, excessively large or small fiber size proves to be negative to improve the mechanical and creep performance, and polymer composites reinforced by them are not suitable for work under long-term load.

Abstract: In this work, impact toughness and tensile properties of valve stem used in NPP are obtained. Combining with microstructure analysis of fracture morphology and metallurgical structure, the thermal aging behavior of the martensitic stainless steel is studied. The results show that the thermal aging embrittlement is significant when the valve stem serves in high temperature for a long time. The ductile to brittle transition temperature (DBTT) and the hardness increase, and the upper platform energy decreases.

Abstract: Premature fracture of an axle under torsional load occurred after a tracked military tank had experienced field testing for only 80 kilometers. Visual metallographic examinations were performed with optical microscope (OM) and scanning electron microscope (SEM). The investigation demonstrates that the premature fracture is caused by metallurgical problems inside the axle where the primary and secondary cracks originate, propagate, and eventually result in final catastrophic rupture through torsional fatigue. The failure mechanism is summarized and improvement of the fatigue lifetime for the axle is recommended.

Abstract: Eddy current testing and metal magnetic memory testing, cooperated with special testing devices, were applied to detect the superficial defects of old cylinder barrel. It was indicated that there were three types of the signals, which were non-defect signals, discontinuous peak signals and continuous peak signals. Non-defect signals indicated that there was no defect in cylinder barrel, and the discontinuous peak signals denoted that there was circumferential cracking, and the continuous peak signals showed that there was longitudinal cracking in the surface of cylinder barrel. The amplitude of eddy current testing signals characterizes the depth of cracking, and the gradient of magnetic signals descript the degree of stress concentration. The method mentioned above detects the cracking and stress concentration in the superficial coat of old cylinder barrel, which effectively guarantee the quality of automobile cylinder.

Abstract: The influence of surface conditions on the fatigue behavior A357 aluminum alloy was studied in this paper. Four-point bending fatigue tests method were performed to obtain the fatigue strength of A357 cast aluminum alloy specimens with different surface conditions. A joint bearing rig was designed to minimize the experimental error caused by the misalignment associated with a four-point bend test. The results showed that the fatigue strength of specimens with as-cast surfaces was higher those with machined surface roughness of Ra=1.6μm and 3.2μm, while lower than that with Ra=0.4μm. Optical microscope (OM) and scanning electron microscope (SEM) observations, indicating that the fatigue cracks initiate from machined grooves for specimens with roughness of Ra=1.6μm and 3.2μm, while subsurface crack initiates from cast defects inside the specimen with roughness of Ra=0.4. For specimens with as-cast surface, the fatigue cracks initiate from the surface irregularities or cast defects near the surface.

Abstract: The cupping tests under different rate demonstrated that there was a correlation between the plastic deformation and shaping time of transformation induced plasticity (TRIP) steel, illustrating that there was also the rheology in the process of plastic forming for solid metal materials. The creep experiments were carried out by Gleeble 3500 thermal simulated test machine, and Mises yield rule was used to verify the creep experiments satisfying the visco-plastic conditions when the load was greater than yield strength. The visco-plastic deformation rate of creep experiments was obtained based on Bingham model. The viscous correlation coefficient (γ) was deduced, reaching that the viscosity of TRIP steel shows deformation resistance in the process of plastic shaping. These results provide the theoretical basis for increasing the plate yield and controlling the forming rate.