我国火力发电机组仿真培训系统的发展状况及展望

我国电厂仿真技术的研究和应用工作始于70年代中期,10几年来已取得了很大的成绩.在电厂工程仿真和仿真培训系统两方面,形成了一整套的科研、开发和应用能力,培养了一批高水平的科技工作者.特别是软件技术水平已进入世界先进行列。然而,我国电厂仿真技术的发展还远远不能满足电力工业高速发展的需要,与世界先进水平相比还存在很大差距.据情组编这期专栏,以总结我国在电厂仿真领域所取得的一些成就和经验,结合国情讨论今后的发展方向,为促进仿真技术更深入地发展服务。今后,本刊还将适当选登这方面的技术性文章.

火力发电机组汽机及其辅助系统能效诊断方法的研究

在火力发电厂的电力生产过程中,火力发电机组设备安装的辅助信息监控系统可以实时对火力发电厂的热力参数数据进行监测和采集。火力发电机组汽机及其辅助系统能效诊断和处理,有利于提高火力发电厂供电效率。本文在对影响引起设备能效指标异常的因素进行分析的基础之上,采用基于故障树分析原理的运行类可调参数诊断方法和可维护故障诊断方法两种方法,对引起机组汽机设备能效指标异常影响因素的诊断方法进行研究。

火力发电厂汽轮机组节能降耗措施浅析

在社会的发展下,人们对于电能的需求也越来越高,火电厂是重要的电能生产部门,直接影响着经济水平的发展,汽轮机是火电厂的重要组成部分,也是耗能大户,对于火力发电厂的经济运行、节能损耗有着直接的影响,火力发电应用到的资源是煤炭资源,为了实现节能减排目标,必须要注意火力发电厂的节能降耗,本文主要分析火力发电厂汽轮机组的节能降耗措施。

Effect of annealing temperature on microstructure and mechanical properties of Mg-Zn-Zr-Nd alloy with large final rolling deformation

In this study,the Mg-3Zn-0.5Zr-χNd(χ=0,0.6)alloys were subjected to final rolling treatment with large deformation of 50%.The impact of annealing temperatures on the microstructure and mechanical properties was investigated.The rolled Mg-3Zn-0.5Zr-0.6Nd alloy exhibited an ultimate tensile strength of 386 MPa,a yield strength of 361 MPa,and an elongation of 7.1%.Annealing at different temperatures resulted in reduced strength and obviously increased elongation for both alloys.Optimal mechanical properties for the Mg-3Zn-0.5Zr-0.6Nd alloy were achieved after annealing at 200℃,with an ultimate tensile strength of 287 MPa,a yield strength of 235 MPa,and an elongation of 26.1%.The numerous deformed microstructures,twins,and precipitated phases in the rolled alloy could impede the deformation at room temperature and increase the work hardening rate.After annealing,a decrease in the work hardening effect and an increase in the dynamic recovery effect were obtained due to the formation of fine equiaxed grains,and the increased volume fraction of precipitated phases,which significantly improved the elongation of the alloy.Additionally,the addition of Nd element could enhance the annealing recrystallization rate,reduce the Schmid factor difference between basal and prismatic slip systems,facilitate multi-system slip initiation and improve the alloy plasticity.

火电大机组发展概况

本文根据有关资料编写介绍国内外和华北电网的200MW及以上容量火电大机组的现状和发展情况,并就国产机组、引进机组和国外进口机组进行相应比较.目前国产和一些进口的200MW机组是电网的主力机组,应当予以充分的重视.

Effects of cold rolling and heat treatment on microstructure and mechanical properties of AA 5052 aluminum alloy

The microstructures and mechanical properties of homogenized-rolled AA5052 aluminum alloys with different rolling reductions and following annealing treatments were investigated by optical microscope, scanning electron microscope, X-ray diffractometer, micro-hardness and tensile tests. The results show that with increasing rolling reduction, the equiaxed grains are elongated along the rolling direction obviously, and accumulation of rolling reduction increases the work hardening effect, which results in the enhanced strength and degraded plasticity. When rolling reduction is 87%, the ultimate tensile strength reaches 325 MPa but elongation is only 2.5%. There are much more secondary phase precipitates after annealing treatment. With an increase of annealing temperature, the amount of precipitates increases and work hardening diminishes continuously. The elongation is improved to ~23% but the tensile strength is decreased to 212 MPa after annealing at 300 °C for 4 h, which are comparable to those of as-homogenized alloy.

Effect of vacuum annealing on microstructure and mechanical properties of TA15 titanium alloy sheets

The mechanical properties, microstructures, and fractographs of TA15 sheets vacuum-annealed under different patterns were investigated. The results indicate that vacuum annealing significantly improves the mechanical properties of the sheets in comparison with those after ambient annealing. With increasing the annealing temperature, the phase boundaries and secondary a-phase increase, whereas the volume fraction of primary a-phase decreases, resulting in increased strength and decreased elongation A relatively fine secondary a-phase is obtained after double annealing. The desirable mechanical properties （i.e., ultimate tensile strength, yield strength, and elongation are 1070 MPa, 958 MPa, and 15%, respectively） are obtained through double annealing （（950 ℃/2 h, AC）＋（600 ℃/2 h, AC））. The fractographs obtained after tensile tests show that the deepest and largest dimples are formed in the specimen annealed at 850 ℃, which indicates that the best plasticity is obtained at this annealing temperature.

Effect of homogenization annealing on microstructure, composition and mechanical properties of 7050/6009 bimetal slab

Homogenization annealing of the 7050/6009 bimetal slab prepared by direct-chill casting was investigated and its effects on microstructural evolution, composition distribution and mechanical properties in the interfacial region of the bimetal were studied. The results show that the optimized homogenization annealing process was 460℃for 24 h. After homogenization annealing, the Zn-rich phases and Al15（FeMn）3Si2phases were precipitated at the interface of the bimetal. The diffusion layer thickness of homogenized bimetal increased by 30 μm from 440 to480℃for 24 h, while it increased by 280 μm from 12 to 36 h at 460℃. The Vickers hardnessesat 6009 alloy side and interface of the bimetal decreased after homogenized annealing and grain coarsening was considered asthedominating softening mechanism.The hardness variation at 7050 alloy side was complicated due to the combined action of solution strengthening, dispersion strengthening and dissolution of reinforced phases.

Effects of rolling and annealing on microstructures and properties of Cu-Mg-Te-Y alloy

Microstructures and element distributions of the as-cast, hot-rolled and cold-rolled Cu-Mg-Te-Y alloys were studied. Effects of rolling process and annealing temperature on the properties of the Cu-Mg-Te-Y alloys were correspondingly investigated. The results indicate that the Mg element is homogeneously distributed in the matrix and the fragmentized Cu2Te phase is dispersed in the matrix after hot rolling. Then, the Cu2Te phase is further stretched to strip shape after the cold rolling process. The microstructures of the cold-rolled alloy keep unchanged for the sample annealed below 390 ℃ for 1 h. However, after annealing at 550 ℃ for 1 h, the copper alloy with fibrous microstructures formed during the cold rolling process recrystallizes, leading to an obvious drop of hardening effect and an increase of electrical conductivity. The Cu-Mg-Te-Y alloy with better comprehensive properties is obtained by annealing at 360-390 ℃.

Effects of non-isothermal annealing on microstructure and mechanical properties of severely deformed 2024 aluminum alloy

Microstructure and mechanical properties of AA2024 after severe plastic deformation （SPD） and non-isothermal annealing were investigated. The non-isothermal treatment was carried out on the severely deformed AA2024, and the interaction between restoration and precipitation phenomena was investigated. Differential scanning calorimetry, hardness and shear punch tests illustrate that static recovery and dissolution of GPB zones/Cu-Mg co-clusters occur concurrently through non-isothermal annealing. Scanning electron microscope and electron backscatter diffraction illustrate that non-isothermal annealing of deformed AA2024 up to 250 ℃ promotes the particle-free regions and also particle stimulated nucleation. Results show that through heating with the rate of 10 ℃/min up to 250 ℃, the ultimate shear strength and the hardness are maximum due to the presence of S＇/S phases which have been detected during non-isothermal differential scanning calorimetry experiment. Also, recrystallization phenomenon occurs in temperature range which includes the dissolution of S＇/S phases. The concurrent recrystallization and dissolution of S＇/S phase at 380 ℃ have been verified by differential scanning calorimetry, mechanical properties, and optical microscope.

Effect of quenching rate on microstructure and stress corrosion cracking of 7085 aluminum alloy

The influence of quenching rate on microstructure and stress corrosion cracking （SCC） of 7085 aluminum alloy was investigated by tensile test, slow strain rate test （SSRT）, combined with scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electrochemical test. The results show that with decreasing the quenching rate, the size and inter-particle distance of the grain boundary precipitates as well as precipitation free zone width increase, but the copper content of grain boundary precipitates decreases. The SCC resistance of the samples increases first and then decreases, which is attributed to the copper content, size and distribution of grain boundary precipitates.

Phase change materials as quenching media for heat treatment of 42CrMo4 steels

In the present work,paraffin phase change material is used as quenchant for the heat treatment of 42CrMo4 alloy and compared with water,air,and CuO doped paraffin.The samples were prepared based on ASTM E 8M-98 standard for tensile test and then heated up to 830°C,kept for 4 h in an electric resistance furnace and then quenched in the mentioned media.Elastic modulus,yield strength,ultimate tensile strength,elongation,and modulus of toughness were determined according to the obtained stress?strain curves.Moreover,the hardness and microstructural evolution were investigated after the heat treatment at different media.The samples quenched in paraffin and CuO-doped paraffin are higher in ultimate tensile strength(1439 and 1306 MPa,respectively)than those quenched in water(1190 MPa)and air(1010 MPa).The highest hardness,with a value of HV 552,belonged to the sample quenched in CuO-doped paraffin.The microstructural studies revealed that the non-tempered steel had a ferrite/pearlite microstructure,while by quenching in water,paraffin and CuO-doped paraffin,ferrite/martensite microstructures were achieved.It is also observed that using the air as quenchant resulted in a three-phase bainite/martensite/ferrite microstructure.

Torch brazing 3003 aluminum alloy with Zn-Al filler metal

Using Zn-Al filler metal with Al content of 2%？22% （mass fraction） and improved CsF-AlF3 flux, wetting properties of Zn-Al filler metal on 3003 Al substrate were investigated. The mechanical property as well as the microstructure of the brazed joints was also studied. The results indicate that excellent joints can be produced by means of torch brazing when the Al content is less than 8%. The metallographic structure in the brazing seam is mainly composed of Al based solid solutions and Zn based solid solutions. The high hardness value of brazing seam of the 3003 aluminum alloy is higher than that of the base metal due to the effect of solid solution strengthening. The results also show that three microstructure zones could be found at the brazing interface; i.e., base metal, diffusing zone and interface zone. The distribution of the solid solution in the brazing seam is the main factor of the tensile strength rather than the diffusion zone width near the interface.

Microstructural evolution and mechanical properties of selective laser melted Ti-6Al-4V induced by annealing treatment

Ti-6Al-4V specimens were fabricated by selective laser melting(SLM)to study the effect of thermal treatment on the phase transformation,elemental diffusion,microstructure,and mechanical properties.The results show that vanadium enriches around the boundary ofαphases with increasing annealing temperature to 973 K,andα′phases transform intoα+βat 973 K.The typicalα′martensite microstructure transforms to fine-scale equiaxed microstructure at 973 K and the equiaxed microstructure significantly coarsens with increasing annealing temperature to 1273 K.The SLM Ti-6Al-4V alloy annealed at 973 K exhibits a well-balanced combination of strength and ductility((1305±25)MPa and(37±3)%,respectively).

Effects of annealing on microstructure and mechanical properties of γ-TiAl alloy fabricated via laser melting deposition

The microstructure evolution and mechanical properties of the as-deposited γ-TiAl-based alloy specimen fabricated via laser melting deposition and as-annealed specimens at different temperatures were investigated.The results show that the microstructure of as-deposited specimen is composed of fineα2(Ti3Al)+γlamellae.With the increase of annealing temperature,the bulk γ m(TiAl)phase gradually changes from single γ phase toγphase+acicularα2 phase,finally small γ phase+lamellar α2+γ phase.Compared with the mechanical properties of as-depositedγ-TiAl alloy(tensile strength 469 MPa,elongation 1.1%),after annealing at 1260℃ for 30 min followed by furnace cooling(FC),the room-temperature tensile strength of the specimen is 543.4 MPa and the elongation is 3.7%,which are obviously improved.

Effect of tempering temperature on microstructure and mechanical properties of AISI 6150 steel

Effect of tempering temperature on the microstructure and mechanical properties of AISI 6150 steel was investigated. All samples were austenitized at 870 ℃ for 45 min followed by oil quenching, and then tempered at temperatures between 200 and 600 ℃ for 60 min. The results show that the microstructure of tempered sample at 200 ℃ mainly consists of tempered martensite. With increasing the tempered temperature, the martensite transforms to the ferrite and carbides. The ultimate tensile strength, the hardness and the retained austenite decrease with increasing tempered temperature, and 0.2% yield strength increases when the temperature increases from 200 to 300 ℃ and then decreases with increasing the temperature, but the elongation and impact energy increase with increasing the tempering temperature.

Effects of niobium addition on microstructure and properties of CPM121 powder metallurgy high-speed steel

Massive vanadium additions as hard phases in powder metallurgy high-speed steels(PM HSS)lead to higher cost and bad machinability.In this study,ultrahigh alloy PM HSS with CPM121(10W-5Mo-4Cr-10V-9Co,wt.%)as the basic composition,was directly compacted and activation sintered with near-full density(>99.0%)using pre-oxidized and ball-mixed element and carbide powders.Niobium-alloyed steels(w(V)+w(Nb)=10 wt.%)show higher hardness and wear resistance,superior secondary-hardening ability and temper resistance.But excess niobium addition(>5 wt.%)leads to coarsened carbides and deteriorated toughness.EPMA results proved that niobium tends to distribute in MC carbides and forces element W to form M6C and WC carbides.Further,the role of rotary forging on properties of niobium-alloyed steels(S3)was researched.After rotary forging with deformation of 40%,the bending strength and fracture toughness of niobium-alloyed steels could be further improved by 20.74%and 43.86%compared with those of sample S3 without rotary forging,respectively.

Effects of non-isothermal annealing on microstructure and mechanical properties of severely deformed aluminum samples:Modeling and experiment

In order to investigate the evolution of microstructure and flow stress during non-isothermal annealing,aluminum samples were subjected to strain magnitudes of 1, 2 and 3 by performing 2, 4 and 6 passes of multi-directional forging. Then, the samples were non-isothermally annealed up to 150, 200, 250, 300 and 350 ℃. The evolution of dislocation density and flow stress was studied via modeling of deformation and annealing stages. It was found that 2, 4 and 6 passes multi-directionally forged samples show thermal stability up to temperatures of 250, 250 and 300 ℃, respectively. Modeling results and experimental data were compared and a reasonable agreement was observed. It was noticed that 2 and 4 passes multi-directionally forged samples annealed non-isothermally up to 350 ℃ have a lower experimental flow stress in comparison with the flow stress achieved from the model.The underlying reason is that the proposed non-isothermal annealing model is based only on the intragranular dislocation density evolution, which only takes into account recovery and recrystallization phenomena. However, at 350℃ grain growth takes place in addition to recovery and recrystallization,which is the source of discrepancy between the modeling and experimental flow stress.

道道利箭射“天狼”——谈怎样打武装直升飞机(下)

打敌武装直升机的基本战法 武装直升机绝非无懈可击。武装直升机作战中的明显弱点是油耗大、航程短;弹药携带量受限,持续作战能力差;相对于其它机种来说飞行高度低、飞行速度慢;机身大都采用全金属半硬壳式结构,装甲防护力不强,除机身底部有加厚装甲。

Microstructures and mechanical properties of the third generation automobile steels fabricated by ART-annealing

The mechanical properties dependence on the microstructure was reviewed and analyzed,and the ultrafine grained duplex microstructure of BCC matrix and large fractioned austenite was given as one of the optimum structures to develop the third generation steel with high strength and high ductility.The medium-Mn steels with different carbon contents processed by austenite reverted transformation(ART-annealing) were studied thoroughly to fabricate the ultrafine duplex steels with large fractioned austenite.The lamellar typed ultrafine structure,the granular typed ultrafine duplex structure and the corresponding mechanical properties of the medium-Mn steels processed by ART-annealing were demonstrated in this paper.It was revealed that the duplex structure with large fraction of austenite and ultrafine grain structure is capable of producing steels with excellent combination of strength and ductility,i.e.,Rm A about 30-50 GPa%,which is about two times of that of the conventional automobile steels and close to that of the TWIP steels.It was concluded that the ART-annealing of the medium-Mn steels would be at least one of the promising ways to fabricate the third generation automobile steels in the near future.