Effect of Cyclic Annealing on Microstructure and Mechanical Properties of Medium Carbon Steel

The microstructure and mechanical properties of medium carbon steel after cyclic heat treatment were in-vestigated.The effects of cyclic numbers and long time annealing on the microstructure and mechanical properties of the experimental steel were compared.A short-duration (5 min)holding at 1 023 K (above A1 temperature)and a short-duration (3 min)holding at 893 K are adopted in each cyclic heat treatment.The spheroidization is accelerated during cyclic heat treatment,and the spheroidizing ratio grows with cyclic numbers.After 1 2-cycle heat treatments, there are few incompletely spheroidized regions in the specimens,and cementite lamellae mostly change into cement-ite particles.The morphological character of cementite for 12 cycles is similar to that undergoing annealing for 10 h at 973 K.The strength of the experimental steel after 5-cycle heat treatment is the lowest in the following cyclic heat treatment,but it is still higher than that of specimens with subcritical annealing over a long period (10 h).After 12-cycle heat treatment,the strength of the experimental steel is close to that of the normalized steel,and the plasticity is the best in all heat-treated specimens.     

Effect of Ce^＋ Ion Implantation upon Oxidation Resistance of Superalloy K38G

The addition of small quantities of reactive ele ments (RE) or other elements with high oxygen affini ty, usually in the order of 0 1%~0 2% mass frac tion, will result in a beneficial effect on the oxidationresistance to superalloys[1~4].A number of mechanisms have been proposed toexplain the beneficial effect of RE additions on theCr2O3 forming alloys, including physical blocking byRE ions or second phase particles at grain boundaries,pegging effect between the oxide and the …     

310S耐热不锈钢高温循环氧化性能

研究了310S耐热不锈钢在800、900、1000、1100、1200℃时高温循环氧化性能,采用SEM、XRD、EDS对高温循环氧化生成物进行分析。实验结果表明:1000℃以下时,钢的氧化速率较为缓慢,当温度达到1200℃时其氧化速率急剧增加。310S耐热不锈钢高温循环氧化产物分为3层,外层是FeO·Cr2O3和尖晶石结构的MnCr2O4,中间为Cr2O3,内层为SiO2氧化膜,这种结构是其具有良好耐高温氧化性能的主要原因。     

High-temperature low-cycle fatigue behavior of K40S cobalt-base superalloy

An investigation was made on the strain-controlled low-cycle fatigue (LCF) of K40S cobalt-base superalloy at 900 °C in ambient atmosphere. The results show that K40S alloy possesses high LCF resistance in comparison with X-40 alloy. Under the testing conditions in this study, K40S alloy exhibits a cyclic stress response of initial hardening followed by softening. The cyclic stress response behavior has been attributed to dislocation-dislocation interactions and dislocation-precipitate interactions. The high response stress can lead to a large stress concentration at locations where inelastic strains of high amplitude accumulate, which account for the decreasing fatigue life with increasing strain rate. The well-distributed carbide particles are the “secondary” crack initiation sites. The secondary crack initiation relaxes the stress concentration at the crack tip, reducing the driving force of crack propagation. High-temperature LCF failure of K40S alloy results from the interaction of the mechanical fatigue and environmental oxidation.     

Low cycle fatigue behavior of inconel 718 at 298 K and 823 K

The cyclic stress-strain response and the low cycle fatigue life of conventionally heat treated Inconel 718 were studied. Fully reversed strain-controlled tests were performed at room temperature and at 823 K. Optical and electron microscopy were used to study the development of deformation and cracking during cycling. A power-law relationship between life-time and plastic strain amplitude was obtained. A substantial decrease in fatigue life occurred as the temperature was increased from 298 to 823 K and as the cycling frequency was lowered from 3 cyclesJmin to 0.3 cyclesJmin at 823 K. At 298 K, for all the strain amplitudes investigated, an initial rapid hardening was followed by softening, while at 823 K only softening occurred. Electron microscopy showed that the precipitates were sheared in the course of cyclic straining and that plastic deformation proceeded by the propagation of planar bands. These bands were identified as twins. Twinning was found to be more abundant at elevated temperatures than at room temperature, especially at lower frequencies. Cracking was generally initiated along the interfaces between these twin bands and the matrix but, at elevated temperatures and low strain rates, intercrystalline cracking took place, as well. The influence of particles shearing and twinning on the cyclic stress-strain response of the material are discussed. The importance of planar deformation and twinning on intergranular cracking is emphasized. Formerly with Centre des Matériaux     

以铀矿渣为载体联合PEG2000的细菌固定化培养

以铀矿渣为载体,采用逐次降低接种率循环培养的方法,开展了氧化亚铁硫杆菌的固定化培养试验,研究了聚乙二醇2000（PEG2000）对游离细菌和铀矿渣载体柱中固定化细菌生长的影响。试验结果表明：90 mg/L PEG2000对游离细菌的生长促进作用最大。铀矿渣和K3环材料均可作为载体进行细菌固定化培养。固定化完成时,其亚铁离子的平均氧化速率分别稳定在0.6和0.5 g/(L?h)附近。90 mg/L PEG2000对循环培养和连续培养阶段的固定化细菌生长均具有促进作用。循环培养阶段,可使Fe2+氧化为Fe3+的时间缩短约1/3。连续培养阶段,PEG2000能够促进固定化细菌对亚铁离子的氧化速率,在0.5 L/h进液流量时,未加PEG2000的亚铁离子氧化速率为7.04 g/(L?h),而加PEG2000的,达到了8.18 g/(L?h),亚铁离子氧化效率提高了16.2%。     

Internal oxidation and mechanical properties of TZM-Mo alloy

The internal oxidation behavior of the bcc alloy TZM-Mo (Mo-0.5 wt pct Ti-0.08 wt pct Zr-0.02 wt pet C) was investigated in low-pressure O₂, CO, and H₂O environments at 1098 and 1273 K. The results indicate that a diffusion process controls the kinetics of the oxygen absorption at 1098 K, while bulk diffusion and gas-metal interaction at the specimen surface both affect the rate at 1273 K. The carbon content of TZM in these experiments increased initially and then decreased. Decarburization became significant only after extended exposure at 1273 K. The deformation and fracture behavior of both oxidized and heat-treated TZM specimens were studied at temperatures to 1589 K. TZM specimens showed an increase in strength and a linear decrease in ductility with oxygen content. Oxidized TZM lost its ductility completely at an oxygen level of 300 ppm at room temperature, 1366, and 1589 K, but 500 ppm was required at 1098 K. The ductility of embrittled TZM was increased significantly with heat treatment at high temperatures and was almost completely restored after annealing at 1973 K. The change in mechanical properties is discussed in terms of internal oxidation and precipitation of oxides.     

循环应变-高温退火制备Al-Cu-Li合金单晶

通过循环预拉伸应变-高温退火制备Al-Cu-Li合金单晶,同时探讨循环预拉伸应变-高温退火过程中预拉伸应变量、循环应变退火次数、应变退火温度对Al-Cu-Li合金晶粒长大的影响以及晶粒长大的过程与机制.研究结果表明,通过循环预拉伸应变退火可以使得合金晶粒异常长大,并且成功制备出厘米级别的宏观粗大晶粒,其长大机理主要为应...     

Evolution of Relationships Between Dislocation Microstructures and Internal Stresses of AISI 316L During Cyclic Loading at 293 K and 573 K (20 °C and 300 °C)

The evolution of dislocation densities and of dislocation microstructures during cyclic loading of AISI 316L is systematically evaluated. In addition, internal stresses are also measured for every cycle and comprehensively analyzed. These observations are made in order to establish relationships between the evolution of dislocation condition and internal stresses, and ultimately to obtain a thorough insight into the complex cyclic response of AISI 316L. Moreover, the dependencies of established relationships on the variation of temperature and strain amplitude are investigated. The back stresses (long-range stresses associated with the presence of collective dislocations over different length scales) are mainly responsible for the cyclic deformation response at high strain amplitudes where dislocations tend to move more quickly in a wavy manner. In contrast, the effective stress, coupling with short-range dislocation interactions, plays an insignificant role on the material cyclic response for wavy slip conditions, but increasingly becomes more important for planar slip conditions. The additionally strong short-range interactions between dislocations and point defects (initially with solute atoms and later in life with corduroy structure) at 573 K (300 °C) cause dislocations to move in more planar ways, resulting in a significant increase in effective stress, leading to their influential role on the material cyclic response.     

Convection during thermally unstable solidification of Pb-Sn in a magnetic field

Convection and macrosegregation in directionally solidified hypoeutectic Pb-38 wt pct Sn and hypereutectic Pb-64.5 wt pct Sn have been examined during upward and downward growth. Temperature fluctuations are observed along the length of the melt column during downward growth. With increasing Rayleigh number, these fluctuations change from none, to cyclic, to time periodic having multiple harmonics, and finally to random. At the higher convective driving force of 350 K temperature inversion, the transverse magnetic field decreased convective levels, strong random temperature fluctuations (flows) becoming smaller and periodic. The maximum field of 0.45 T was unable to completely eliminate convection. For the lower convective driving force of 150 K temperature inversion, the 0.05 T magnetic field decreased flows, and at 0.15 T, the field caused a dramatic decrease in the characteristic frequency of the temperature fluctuations, indicating a change in the nature of the flow, the waveform of the temperature fluctuations changing from sinusoidal to a pulsed wave. Temperature fluctuations and time delays between thermocouples were used to estimate flow velocities. Irrespective of the convection in the bulk melt (ahead of the mushy zone), longitudinal macrosegregation occurs only if the interdendritic melt mixes with the bulk melt.     

Cyclic work hardening and formation of dislocation substructures during low-cycle fatigue of tempered dual-phase steels

A C-Mn-Si dual-phase steel, containing 33.8% lath martensite of 0.45% C content (called steel 1), was tempered at 200, 460 and 650°C and designated steels J, K and L, respectively. Sheet specimens of 3 mm thickness and 10 mm gauge length pertaining to steels I, J, K and L were subjected to tensile and low cycle fatigue testing at room temperature. The steels I, K and L show cyclic softening while the steel J exhibits a small cyclic hardening. The cyclic stress response varies significantly at higher and lower applied strain amplitudes for each of the steels which has been discussed in terms of competing processes of hardening and softening during strain cycling. The value of the cyclic strain hardening exponent decreases continuously in the order steels I>J>K>L. Varied dislocation substructures form at higher and lower strain amplitudes during cyclic deformation.     

Methods of Protecting VKh-2K Alloy from High-Temperature Gas and Salt Corrosion

Heat resistance (1173-1573 K, 10-1000 h) has been examined for VKh-2K alloy together with the resistance to high-temperature sulfide and chloride corrosion (873-1273 K, 1-30 h). The alloy has high heat resistance up to 1473 K, but it falls substantially at higher temperatures. The alloy has higher resistance to sulfide corrosion than do high-chromium nickel alloys. In chloride melts, the alloy is subject to rapid corrosion. A two-layer YCrO₃ – ZrO₂ protective coating improves the resistance to oxidation and high-temperature corrosion in all media by more than two orders of magnitude.     

The nitriding of Fe-V alloys

Fe-V alloys containing 1.06 wt pct V, 5.23 wt pct V and 15.55 wt pct V, have been nitrided in purified NH₃ gas in temperatures ranging between 773 K and 1173 K. The nitriding kinetics of all these alloys in this temperature range obey a parabolic rate law. The comparison of the nitriding rate constants evaluated from experimental results and from the calculations based on Wagner's internal oxidation model show a deviation which is explained in terms of the effect of the lattice strains on the solubility and diffusivity of nitrogen in the Fe matrix. The hardness of the nitrided zone increases with the vanadium content in solution and reaches a saturation value of about 1300 VHN (12.75 GNm⁻²) which corresponds to about 4 wt pct V. The hardening in the nitrided region is cuased by the precipitation of VN which cannot be observed on specimens nitrided at the lower limits of the temperature range. Precipitates grown in size can be seen on specimens nitrided at 1073 K and 1173 K.     

The oxidation behavior of Ni-Cr-Al-2ThO2 alloys at 1093° and 1204°C

A pack diffusion process has been developed which permits the introduction of nearly 6 wt pct Al into solid solution in the near surface region of TDNiCr (Ni-20 wt pct Cr-2 vol pct ThO₂) and Ni-20Cr. Alumina scales, adherent under cyclic heating and cooling conditions, were produced on TDNiCr-5.86A1 upon exposure to an environment of 1.33 × 10³N/m² (10 torr) or 1.01 × 10⁵N/m² (760 torr) air at temperatures of 1093° and 1204°C. While the same oxidation kinetics were observed in isothermal tests for Ni-14.6Cr-5.86Al as were obtained for the TDNiCr-5.86A1, the dispersion strengthened alloy exhibited superior oxide scale adhesion during cyclic testing. At 1204°C continuous weight gains were observed under all test conditions for TDNiCr-5.86A1, in contrast to the weight loss with time which occurred several hours after exposure of TDNiCr to an oxidizing environment. TDNiCr with an initial aluminum surface concentration of 4.95 wt pct has nearly comparable oxidation resistance to the TDNiCr-5.86Al alloy. Specimens with 4.3 wt pct Al at the surface have inadequate aluminum to form Al₂O₃ scales, and weight losses are observed after 40 h upon exposure of these specimens to 1.01 × 10⁵N/m² (760 torr) air at 1204°C.     

High-Temperature Oxidation Behavior of Vanadium, Titanium-Bearing Magnetite Pellet

 By means of isothermal oxidation and chemical analysis, great importance was attached to the parameters that made effects on the oxidation degree of vanadium, titanium-bearing magnetite pellet in high-temperature processing (1073-1323 K). Based on the experimental data, oxidation kinetics of pellet was analyzed according to shrinking unreacted-core model subsequently. Experiment results display that the oxidation degree of pellet increases with increasing of oxidation time, oxidation temperature and oxygen content, as well as shrinking of pellet diameter. Under the condition of oxidation time 20 min, oxidation temperature 1223 K, oxygen content 15%, and pellet diameter 12 mm, oxidation degree of pellet reaches 92.92%. The analysis of oxidation kinetics indicates that oxidation process of pellet is controlled by chemical reaction with activation energy 68.64 kJ/mol at a relatively lower temperature (1073-1173 K). Oxidation process of pellet is mixed-controlled by chemistry reaction and diffusion with activation energy 39.66 kJ/mol in the temperature range of 1173-1273 K. When oxidation temperature is higher than 1273 K, the limited link of oxidation reaction is the diffusion control with the activation energy 20.85 kJ/mol. These results can serve as a reference to the production of vanadium, titanium-bearing magnetite pellet.     

Effect of yttrium addition on water-gas shift reaction over CuO/CeO2 catalysts

This paper presented a study on the role of yttrium addition to CuO/CeO2 catalyst for water-gas shift reaction. A single-step co-precipitation method was used for preparation of a series of yttrium doped CuO/CeO2 catalysts with yttrium content in the range of 0-5wt.%. Properties of the obtained samples were characterized and analyzed by X-ray diffraction (XRD), Raman spectroscopy, H2-TPR, cyclic voltammetry (CV) and the BET method. The results revealed that catalytic activity was increased with the yttrium content at first, but then decreased with the further increase of yttrium content. Herein, CuO/CeO2 catalyst doped with 2wt.% of yttrium showed the highest catalytic activity (CO conversion reaches 93.4% at 250℃) and thermal stability for WGS reaction. The catalytic activity was correlated with the surface area, the area of peak y of H2-TPR profile (I.e., the reduction of surface copper oxide (crystalline forms) interacted with surface oxygen vacancies on ceria), and the area of peak C2 and A1 (Cu0→Cu2+ in cyclic voltammetry process), respectively. Besides, Raman spectra provided evidences for a synergistic Cu-Ovacancy interaction, and it was indicated that doping yttrium may facilitate the formation of oxygen vacancies on ceria.     

Oxidation Kinetics of an Al–6 wt % Li Alloy Modified by Cerium

The oxidation kinetics of an Al–6 wt % Li alloy modified by ≤0.5 wt % Ce is studied by thermogravimetry. The oxidation rate of the initial alloy is shown to increase with addition of cerium to the alloy or with temperature. Herewith, the apparent activation energy decreases from 35.2 kJ/mol for the initial alloy to 27.7 kJ/mol for the alloy with 0.5 wt % Ce. The oxidation of the alloys is found to occur according to a hyperbolic mechanism.     

双相变回温温度对钢组织及其热塑性的影响

含铌钢连铸过程极易产生铸坯角部横裂纹。对连铸坯角部实施γ→α→γ双相变控冷工艺,可提高其组织的高温热塑性而减少裂纹产生。其中,α→γ相变阶段的回温温度是影响双相变控冷工艺实施效果的重要参数。通过Gleeble热模拟与金相观察、析出物透射以及断口扫描相结合的检测手段,研究分析了双相变过程回温温度对Q345D-Nb钢组织演变及其热塑性的影响规律。结果表明,回温温度为850℃时的奥氏体晶粒相比传统冷却工艺下的晶粒尺寸未产生细化,平均晶粒尺寸为502.2μm;回温温度升至900℃时,回温奥氏体出现了明显的混晶现象;当回温温度达到950℃时,晶粒细化至61.2μm;当回温温度达到1 000℃时,回温奥氏体晶粒出现了一定程度粗化,相比950℃回温温度下的奥氏体平均晶粒尺寸增加了38.07%。传统冷却工艺和不同回温温度时的双相变控冷工艺(回温温度为850、900、950、1 000℃),钢组织在700～900℃温度区内的断面收缩率最低值分别为29.6%、45.0%、56.3%、68.2%、63.2%。在传统冷却工艺下,钢组织在750℃时晶界铁素体膜的厚度为20～25μm,且碳氮化物呈大尺寸链状分布,...     

Effect of annealing temperature on microstructure and electrochemical performance of La0.75Mg0.25Ni3.5Co0.2 hydrogen storage electrode alloy

To improve the cyclic stability of La-Mg-Ni system alloy, as-cast La0.75Mg0.25Ni3.5Co0.2 alloy was annealed at 1123, 1223, and 1323 K for 10 h in 0.3 MPa argon. The microstructure and electrochemical performance of different annealed alloys were investigated systematically by X-Ray Diffraction （XRD）, Scanning Electron Microscopy （SEM）, X-Ray Photoelectron Spectroscopy （XPS）, and electrochemical experiments. The results obtained by XRD and SEM showed that the as-cast and annealed （1123 K） alloys had multiphase structure containing LaNis, （La, Mg）2（Ni, Co）7 and few LaNi2 phases. When annealing temperatures approached 1223 and 1323 K, LaNi2 phase disappeared. The annealed alloys at 1223 and 1323 K were composed of LaNi5, （La, Mg）2（Ni, Co）7 and （La, Mg）（Ni, Co）3 phases. With increasing annealing temperature, the maximum discharge capacity of the alloy decreased monotonously, but the cyclic stability was improved owing to structure homogeneity and grain growth after annealing, as well as the enhancement of anti-oxidation/corrosion ability and the suppression of pulverization during cycling in KOH electrolyte.     

Mass production of magnetocaloric LaFeMnSiB alloys with hydrogenation

LaFe_(11.39)Mn_(0.35)Si_(1.26)B_(0.1)Hxalloys were prepared by hydrogenation.Samples were annealed at 1343Kfor30-90 hto form the NaZn13 phase.La-rich andα-Fe secondary phases were also detected.Saturated hydrogenation at 553 Kand 0.15 MPa of H_2 pressure for 5hwas employed to improve the Curie temperature of the alloys to 279 K.The maximum magnetic entropy change,relative cooling power,and adiabatic temperature change of LaFe_(11.39)Mn_(0.35)Si_(1.26)B_(0.1)H_x annealed at 1343 Kfor 90hafter hydrogen absorption are 6.38J/(kg·K)(magnetic changesμ0ΔH =1.65T),100.1J/kg(μ0ΔH =1.65T),and 2.2 K(μ0ΔH =1.48T),respectively.Although the maximum magnetic entropy change of the LaFe_(11.39)Mn_(0.35)Si_(1.26)B_(0.1)H_x alloys is lower than those of similar alloys with high purity raw materials,the relative cooling power is nearly the same.The effect of impurities of the raw materials used was also discussed.It is assumed that the impurity of 0.2wt.% Al is responsible for the reduced entropy change of the resulted alloys.The LaFe_(11.39)Mn_(0.35)Si_(1.26)B_(0.1)H_x alloys prepared by this method could be a low cost alternative material for room temperature magnetic cooling applications.