Applied Mechanics and Materials Vols. 395-396

Abstract: Kinetics and products of oxidation behavior of binary Co-10Al, Co-10Si and Co-10Cr alloys at 0.1Mpa oxygen at 973 and 1073K were analyzed and compared. The investigations show that CoO doesn't provide protective properties at high temperatures. Among the three alloy components, Co-10Cr has better oxidation resistance at 973K, while Co-10Al has at 1073K, and the causes are given. In addition, the schematic model of scale growth process is presented.

Abstract: The α + β dual-phase titanium alloy, Ti-6Al-4V, was thermohydrogen processed with 0.1, 0.3 and 0.5 wt% hydrogen. Hydrogen was removed from the hydrogenated titanium alloy by vacuum annealing. Microstructure and mechanical properties of the hydrogenated and dehydrogenated titanium alloy were investigated. Effect of hydrogen as a temporary alloying element on the microstructure and mechanical properties of Ti-6Al-4V titanium alloy was systematically discussed. It was found that hydrogen stabled the β phase and leaded to the formation of α martensite as well as δ hydride in the hydrogenated titanium alloy. Mechanical properties of hydrogenated titanium alloy deteriorated with increasing hydrogenation content. The α martensite and δ hydride decomposed during the dehydrogenation and the dehydrogenated titanium alloy only consisted of α and β phases. The mechanical properties of hydrogenated titanium alloy with different hydrogen content were recovered and were tend to be consistent after dehydrogenation.

Abstract: Nickel-base alloys with different boron contents were prepared by vacuum arc furnace. The effect of the boron contents to metallography was characterized simultaneously by XRD and SEM with EDS part. The thermal behavior was analyzed by DSC curves which mainly represents the eutectic temperature of alloys. The Vickers hardness and ball-on-flat wear test were carried out to reveal the relationship between metallographic phase formation and wear resistance. The results indicated that main composites are eutectic Ni-Cr as matrix and CrB, Ni₃B as precipitated phase. A considerable amount of dislocation and stacking faults exist in the specific orientation (200) of Ni₃B. 2.0~4.0%B alloys melt at 1060oC, while the boride-poor alloy melts at 1085oC. 3.0~4.0%B alloys performed the best on wear resistance. Wear volume reduces along with increasing hardness at the beginning, and then keeps invariant. Borides are main reinforcing phases, which affects hardness and wear resistance greatly.

Abstract: An Fe-1.7wt% Ti alloy was prepared and the electron energy loss spectroscopy (EELS) of iron was collected. The d-electron occupancy of Fe is measured from the white-line intensity of EELS. It was found that relative to pure iron the d-electron occupancy of Fe in Fe-1.7wt% Ti alloy increased.

Abstract: A Monte Carlo Potts model coupled with sintering pressure for the sintering process of nanocomposite ceramic tool materials is proposed, the relation between grain growth and sintering pressure is presented. The grain growth process at different sintering pressure is investigated in this model, and the effect of sintering pressure on microstructure evolution is discussed, it is found that the mean grain size increases with the increase of sintering pressure during simulation. The results from this simulation are shown to correlate well with the experimental observations.

Abstract: Vehicle weight reduction has become the development trend of the automotive industry, lightweight magnesium alloy as the material can be applied to automobile parts to achieve more substantial weight loss results. This paper adopts a car seat frame, refer to the regulations for strength of seat system, finite element software ANSYS, the static strength analysis of magnesium alloy seat frame. And further on carbon steel material for static strength analysis, conclusions and magnesium alloys were compared, from lightweight, economy and other aspects show the superiority of magnesium alloys.

Abstract: Oxidation characteristics of a microalloyed low carbon steel were investigated by a hot rolling mill combined with acceleration cooling system over the cooling rate range from 20 to 70°C/s. The effects of cooling rate after hot rolling on microstructure and phase composition of oxide scale were examined. The results showed that the increase of the cooling rate has a significant influence on the decrease of the grain size and surface roughness of oxide scale. A higher cooling rate promotes the formation of retain wustite and primary magnetite precipitation while suppression of eutectoid α-iron precipitates. This provides the possibility to enhance potential contribution of magnetite precipitates with preferable ductility, and hence fabricates a desired oxide-scale structure under continuous post cooling conditions considering a suitable cooling rate.

Abstract: In order to improve the toughness of oil casing steel N80 without the sacrifice of its original high strength, an intercritical quenching treatment was conducted under the temperature determined by a differential scanning calorimetry (DSC) analysis. Effects of intercritical quenching on the microstructure of oil casing steel N80 were characterized by means of optical microscope (OM) and scanning electron microscope (SEM). Tensile strength, reduction of cross-sectional area and microhardness were measured to evaluate the mechanical property of oil casing steel N80 after intercritical quenching treatment. The study results show that the tensile strength and microhardness of intercritical quenched oil casing steel N80 consisting of ferrite (F) and martensite (M) is slightly lower than that of tempered oil casing steel N80 composing of sorbite (S), yet which is still higher than that of full annealled oil casing steel N80 composing of pearlite (P) and a little amount of ferrite (F). In particular, the reduction of cross-sectional area of oil casing steel N80 intercritical quenched at 740°C is higher than those of tempered and full annealled. Additionally, both dimple and cleavage can be found on the impact fracture surface of N80 steel after intercritical quenching at 740°C. The toughness of oil casing steel N80 can be obviously improved by the intercritical quenching treatment at 740°C due to the formation of ferrite (F).

Abstract: This paper investigates the effects of aging precipitates on the mechanical and corrosion resistance properties of 18Cr-18Mn-2Mo-0.96N super high nitrogen austenitic stainless steel (HNS) through Vickers hardness, Charpy impact, tensile and electrical chemical methods. The probable affected mechanism is discussed by optical microscope (OM) and transmission electron microscopy (TEM). The results are presented as follow: the initial TTP curve with 0.05% precipitates volume fraction presents C type which has a nose temperature at 850°C with an incubation period for 60s. The precipitates increase with prolonging aging time to 40%. The HV results of aged HNS present firstly decrease then increase, the relevant yield strength firstly increase then decrease with increasing the aging time. Meanwhile, the impact energy, ultimate tensile strength and elongation are deteriorated significantly because of the formation and growth of cellular Cr₂N and χ phase with concomitant increased amount of intergranular Cr₂N. The IGC susceptibility increases and the pitting corrosion potentials decrease because of the Cr, N and Mo depletion through the formation of intergranular, cellular Cr₂N and intermetallic χ precipitates by aging treatments.

Abstract: Nanometer calcium and magnesium oxides were added into molten steel by the carrier method in the experiment. The experiment takes the X80 pipeline steel as the research object and analyses the effect of nanometer calcium and magnesium oxides addition on the inclusions in the cast microstructure of the X80 pipeline steel. The scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were used to analyze the composition of the inclusions in the cast microstructure of the X80 pipeline steel. The result reveals that when no addition of nanooxides, the inclusions in the cast microstructure are the C-Fe-Si-Al-Mn-based inclusions. When adding nanoMgO, the inclusions are mainly the composite oxides of Fe-Mg-Si-O, Fe-Mg-Si-Mn-O and Mg-Si-Mn-Al-O. When adding nanoCaO, the inclusions are mainly the composite oxides of Fe-Ca-Al-O, Fe-Ca-Si-O, Fe-Ca-Si-Mn-O and the composite oxides or sulfides of Fe-Ca-Si-Mn-O-S. There is more Fe in some inclusions and Fe is not uniformly dispersed in the molten steel. As the result, some certain segregation phenomenon takes place.