The effect of V and Si on the microstructure and mechanical properties of medium-carbon pearlitic steels for wheel was studied by means of OM、SEM and TEM, as well as tensile and impact tests. The results showed that the austenite grain size, the pearlite colony size and interlamellar spacing were significantly refined by increasing V content, which also led to an increase in the volume fraction of proeutectoid ferrite of the steels. With the increasing of V content, the yield strength at room temperature and the impact toughness at -20℃were enhanced due to precipitation strengthening and grain refinement effects of VC. However, the tensile strength at room temperature was decreased due to the increasing of the soft phase, i.e., proeutectoid ferrite. The increase of Si content resulted in the great decrease of proeutectoid ferrite and the significant refinement of pearlite interlamellar spacing but the slight refinement of austenite grain size. Si addition also promoted the VC precipitation but had only a little influence. The yield- and tensile-strength were enhanced mainly by the effect of solid solution strengthening and the refinement of pearlite interlamellar spacing due to Si addition. The balance of strength and toughness in medium-carbon pearlite steels could be effectively optimized by microalloying with the combination of medium 0.07%-0.08%V(mass fraction) and relatively high 0.8%-0.9%Si (mass fraction).
Five ferrite/bainite (F/B) multi-phase steels with different volume fractions of bainite were obtained by TMCP process. The strain hardening behavior of high deformability pipeline steel with F/B multi-phase was studied by the analysis of longitudinal mechanical properties and modified C-J analysis. The relationships between volume fraction of bainite and stress ratio as well as yield ratio were analyzed, and relevant mechanisms were illustrated by modified C-J analysis. The results show that the stage of elastic deformation of high deformability pipeline steel mainly corresponds to stage I in modified C-J analysis, and the stage of plastic deformation consists of stage II and stage III; and the stage near yield point (0.5% strain) can go across stage I and stage II. However, the strain hardening capability of each stage is obviously different from each other, and the strain hardening behavior is closely related to the volume fraction of bainite in F/B multi-phase steel. The optimal matching between strength and plasticity of pipeline steel can be achieved by controlling the microstructure suitably. The stress ratio of Rt1.5/Rt0.5 is appropriate to describe the strain hardening capability near the yield point, and the stress ratios of Rt2/Rt1 and Rt5/Rt1 are appropriate to represent the strain hardening capability of plastic deformation stage in X70 grade pipeline steel. The stress ratio of Rt2/Rt1 is suitable to characterize the strain hardening capability of plastic deformation stage in X80 grade pipeline steel.
Microcapsules of phase change- and humidity-controlling material were synthesized by sol-gel method with hexadecanol-palmitic acid-lauric acid as core, SiO2 as shell and silaneas coupling agent. Then their performance of humidity controlling and temperature controlling, particle size distribution, composition and structure, surface morphology and thermal properties were characterized by isothermal sorption method, cooling curve measurement, laser particle analyzer (LPSA), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) respectively. The results show that the amount of deionizedwater, absolute alcohol, hexadecanol-palmitic acid-lauric acid and silane coupling agent had great effect on the properties of the prepared phase change- and humidity-controlling materials. The phase change- and humidity-controlling material of good performance as spherical particles with smooth surface, homogeneous size distribution in a range of 1680.60~1735.35 nm and excellent dispersibility may be synthesized by the following optimal processing parameters: the mole ratio of deionized water totetraethyl orthosilicateis 9, the mole ratio of absolute alcohol totetraethyl orthosilicate 5, the mole ratio of hexadecanol-palmitic acid-lauric acid to tetraethyl orthosilicate 0.5, and the mole ratio of silane coupling agent totetraethyl orthosilicate 0.1.
Polytetrafluoroethylene (PTFE) composites filled with mullite were prepared by mechanical blending, heat compression and then sintering at elevated temperature. The mechanical properties, crystal structure and thermal properties were characterized by universal material testing machine, X-ray diffraction (XRD) and thermal mechanical analysis (TMA), respectively. The friction coefficient and wear rate of the prepared PTFE composites were tested by an MRH-3 high speed friction and wear tester, and the surface morphologies of the composites after friction test were analyzed by a field-emitting scanning electron microscope. It was found that mullite fillings were well dispersed in PTFE, and the thermal and mechanical properties of the composites were enhanced, such as modulus of elasticity, glass transition temperature and average linear expansion coefficient. The friction coefficients of the prepared composites with mullite fillings less than 10% (mass fraction) were smaller than that of pure PTFE, and the larger friction coefficient was found for those with higher among of mullite fillings. It was more important to find that the wear rate of the composites filled with 40% (mass fraction) of mullite fillings decreased to 1/530 of that for the pure PTFE.
The influence of C content on the glass forming ability, thermal stability and corrosion resistance of Ni68.6Cr8.7Nb3P(16.5-x)B3.2Cx (x=0, 0.1, 0.3, 0.5, 0.7, 1, %) alloy was studied. The results show that an amorphous rod of 2 mm in diameter could be made for the alloy with 0.5 % C; a certain among of C addition can improve the thermal stability of the Ni-based amorphous alloy; with the increase of C amount, the corrosion resistance of amorphous ribbon in 1 mol/L H2SO4 solution is enhanced gradually.
It is well known that the increasing dosage of high Mg-containing V-bearing titanomagnetite, the iron ore was adopted for the iron works at Panxi area of the Southwest China and correspondingly the MgO content (%mass fraction) increased gradually in the blast furnace slag. In view of the above fact, it is meaningful to investigate the influence of MgO content on the viscous flow property of high-Ti blast furnace slag containing high melting point material, such as TiC, TiN, Ti(C, N) etc. Results show that the blast furnace slag containing 20% TiO2 and 14% A12O3 presents the so call "short slag" characteristic with binary basicity R2 in a range of 1.0~1.2, of which the melting temperature increases from 1332℃ to 1364℃ with the increasing MgO content from 8% to 12% . At temperatures above 1450℃, the slag viscosity is lower than 0.3 Pas with a good liquidity, which can meet the requirements for the smooth operation of blast furnace.
The carbonization in a tube bomb of medium-temperature coal tar pitch and the purified coal tar pitch, of which quinoline insoluble (QI) had been removed by anti-solvent method, was comparatively studied. The results show that coal tar pitch with high QI contents could not be suitable for preparation of needle coke of high quality. However, the coke which was obtained through carbonization under 0.2 MPa at 500℃ for 10 h had a relatively lower coefficient of thermal expansion (CTE). The QI could be removed effectively by anti-solvent method when kerosene and wash oil were mixed as solvents. By a precipitation process at 100℃ and precipitation time for 4 h with the ratio of wash oil to kerosene was 0.4 and stirring for 0.5 h, the QI contents of the refined coal tar pitch could be reduced to 0.0914% and 0.0695% for the ratios of solvents to coal tar pitch as 1.8 and 2 respectively. The needle coke which were prepared by such refined coal tar pitch showed lower CTE after being carbonized at 500℃, by 0.2 MPa and for 10 h.
Two types of magneto-active elastomers (MAEs) with fillers of NdFeB powder and powder mixture of carbonyl iron and NdFeB are prepared respectively, and then they were all magnetized by different magnetization intensities. The microstructure of MAEs is characterized by KEYENCE VHX-600 digital microscope. The magnetization characteristic curves and the mechanical properties of MAEs weremeasured by VSM and MCR-301 rheometer respectively. The influence of the fraction and magnetic remanence intensity of the hard magnetic fillers on the magneto-control mechanical behavior of the MAEs was carefully examined.The results demonstrated that the mechanical properties of MAEs filled with NdFeB powder were affected strongly by the intensity of magnetic field adoped for magnetization treatments. An appropriate amount of the hard magnetic fillers and the magnetization by higher magnetic field intensity are beneficial to the improvement of the shear storage modulus of the MAEs.
The effect of alloying element V on the microstructure and high temperature creep properties of a diretional solidified nickel-base superalloy was researched by varying the amount of V addition. The alloy composition was set in a controlled fixedness except for element V, and then the effect of V can be assessed. The alloys were directionally solidified by utilizing Bridgeman casting process and followed by appropriate post heat treatment. The microstructure and high temperature creep properties of the prepared alloys were then characterized. The results shown that, with lower amount of V addition, the alloying V existed mainly in acicular type carbides rather than in blocky type carbides; while for the higher addition of V, the shape of vanadium carbides in the alloys transition from acicular type to blocky type. When the V content reaches 1.04 % in the alloy, the shape of carbides has been transformed into blocky type completely. After solid solution treatment, the carbides in the alloy were dissolved partly, and the acicular carbides in the alloy with lower V content dissolved much more than the blocky carbides in high V content alloy. Under the condition of 980℃/216 MPa and 760℃/725 MPa, the stress rupture life is shorter for the alloy with lower V content, but loger for that with higher V content. The amount of M23C6 type carbide precipitated at grain boundaries in the alloy with higher V content is less than that with lower V content during creep test and aging heat treatment. During creep test, cracks initiate and grow mainly at the MC type carbide within grains or the M23C6 type carbides precipitated at the grain boundaries. Therefore, the increase of V content is of benefit for the improvement of creep life of the alloy.
Cavitation erosion of 304 stainless steel was studied by means of caviting water jet (CWJ) with varying stress and time. By tracking the surface morphology change with scanning electron microscope after the CWJ treatment, the process and mechanism of cavitation erosion were analyzed and the microstructure evolution of the surface and the relevant deformation mechanism were investigated as well. The results are as follows: according to the difference in damage rate and mechanism, the cavitation damage zone can be divided into jet impact zone, transition zone and turbulent zone from the center to the periphery, among them, the damage degree of jet impact zone was the worst, transition zone was the weakest. The damage of jet impact zone was accelerated by the jet pressure 35 MPa for 40 min, and it presented clear characteristics of fatigue damage, the initiation and propagation of fatigue crack in the area of slip band and grain boundary is one of the important reasons leading to the spalling damage; The twin layer of the transition zone and turbulent zone were thicker than that of the jet impact zone in the cross-sectional microstructure, and the thickness of the twin layer in turbulent zone was 140 μm; Under the conditions of this experiment, the main deformation mode of 304 stainless steel is slip deformation, the second is twin deformation. There are two kinds of mechanism of cavitation erosion induced by the cavitating water jet, one is fatigue failure under cyclic loading, the other is arc-shaped pit caused by plastic deformation, necking and spalling.
