Studies of fracture processes in Cr–Mo–V ferritic steel with various types of microstructures

In this paper, the authors report on analysis of the influence of microstructure on ductile and cleavage fracture mechanisms. The question investigated was whether microstructure observations alone can provide sufficient information to predict the possible fracture mechanism or change in fracture mechanism. Four different microstructures of ferritic steel were tested after four different heat treatments. The microstructures examined were ferritic, ferritic–pearlitic, ferritic–bainitic, and tempered martensitic types. It was concluded that the ratio (S_C/S₀) of the area covered by carbides to the total area of a ferritic grain (measured by taking into account large carbides) is the only possible quantitative measure that can be used to predict cleavage fracture.     

Exploration of alloy 441 chemistry for solid oxide fuel cell interconnect application

Alloy 441 stainless steel (UNS S 44100) is being considered for application as an SOFC interconnect material. There are several advantages to the selection of this alloy over other iron-based or nickel-based alloys: first and foremost alloy 441ss is a production alloy which is both low in cost and readily available. Second, the coefficient of thermal expansion (CTE) more closely matches the CTE of the adjoining ceramic components of the fuel cell. Third, this alloy forms the Laves phase at typical SOFC operating temperatures of 600-800 °C. It is thought that the Laves phase preferentially consumes the Si present in the alloy microstructure. As a result it has been postulated that the long-term area specific resistance (ASR) performance degradation often seen with other ferritic stainless steels, which is associated with the formation of electrically resistive Si-rich oxide subscales, may be avoidable with alloy 441ss. In this paper we explore the physical metallurgy of alloy 441, combining computational thermodynamics with experimental verification, and discuss the results with regards to Laves phase formation under SOFC operating conditions. We show that the incorporation of the Laves phase into the microstructure cannot in itself remove sufficient Si from the ferritic matrix in order to completely avoid the formation of Si-rich oxide subscales. However, the thickness, morphology, and continuity of the Si-rich subscale that forms in this alloy is modified in comparison to non-Laves forming ferritic stainless steel alloys and therefore may not be as detrimental to long-term SOFC performance.     

Microstructural characterization and hydrogenation properties of non-stoichiometric Zr0.9TixV2 alloys

The non-stoichiometric Zr_0.9Ti_xV₂ (x = 0, 0.2, 0.3, 0.4) alloys are designed to explore the effect of non-stoichiometry on phase constituent, microstructure and hydrogenation properties of Zr-based AB₂ Laves alloys. The alloys are prepared by non-consumable arc melting and annealed at 1273 K for 168 h in argon atmosphere to ensure the homogeneity. Phase structure investigation shows the α-Zr/β-Zr phase and V-BCC phase originating from the non-equilibrium solidification can be reduced after annealing, C15-type ZrV₂ becomes the dominant phase. Meanwhile, a small amount of Zr₃V₃O phase generates when x ≤ 0.2 and the β-Zr transforms to α-Zr when x > 0.2. High density annealing twins are observed in ZrV₂ matrix by TEM. Activation behavior, hydrogenation kinetics and PCT characteristics of annealed Zr_0.9Ti_xV₂ are investigated in the temperature range 673–823 K. With the decrease in B/A ratio or increase in Ti content, the initial hydrogen absorption speed decreases obviously, the plateaus of PCT curves become wide and flat, meanwhile the hydrogen absorption capacity and the stability of metal hydrides increases. Twin defects observed in these alloys play an important role in accelerating the hydrogenation kinetics. In addition, phase constituent after hydrogenation is analyzed.     

Microstructure and hydrogen storage properties of non-stoichiometric Zr–Ti–V Laves phase alloys

The non-stoichiometric C15 Laves phase alloys namely Zr_0.9Ti_0.1V_x (x = 1.7, 1.8, 1.9, 2.1, 2.2, 2.3) are designed and expected to investigate the role of defect and microstructure on hydrogenation kinetics of AB₂ type Zr-based alloys. The alloys are prepared by non-consumable arc melting in argon atmosphere and annealed at 1273 K for 168 h to ensure the homogeneity. The microstructure and phase constitute of these alloys are examined by SEM, TEM and XRD. The results indicate the homogenizing can reduce the minor phases α-Zr and abundant V solid solution originating from the non-equilibrium solidification of as-cast alloys. Twin defects with {111}<011 > orientation relationship are observed, and the role of defects on hydrogenation kinetics is discussed. Hydrogen absorption PCT characteristics and hydrogenation kinetics of Zr_0.9Ti_0.1V_x at 673–823 K are investigated by the pressure reduction method using a Sievert apparatus. The results show the hypo-stoichiometric alloys preserve faster hydrogenation kinetics than the hyper-stoichiometric ones due to the decrease of dendritic V. The excess content of Zr₃V₃O phase decreases the hydrogenation kinetics and the stability of hydrides. In addition, the different rate controlled mechanisms during hydrogen absorption are analyzed. The effects of non-stoichiometry on the crystal structure and hydrogen storage properties of Zr_0.9Ti_0.1V_x Laves alloys are discussed.     

超超临界发电技术研究与应用

成熟的超超临界发电技术已成为目前燃煤火电机组发展的主导方向,是满足中国电力可持续发展的重要发电技术。论述了超临界和超超临界发电技术在中国的研究与应用现状及国外超超临界机组的发展概况,介绍了中国首台超超临界发电机组——华能玉环电厂1 000 MW机组的技术特点、设备状况和工程进展,以及中国华能集团公司近年来在超超临界发电技术方面所作的研究开发、示范及推广应用3个层次上的进展,并展望了燃煤发电技术的发展方向。     

Interaction of ZrMo2 with hydrogen at high pressure

The interaction of hydrogen with ZrMo₂ intermetallic compound at pressure up to 2500 bars has been studied. In ZrMo₂–H₂ system desorption isotherms were measured and thermodynamic parameters of hydride phase decomposition were calculated. The structure of ZrMo₂D_4.0 deuteride has been investigated by X-ray and neutron diffraction methods. It was revealed that ordering of deuterium in the cubic lattice of ZrMo₂ led to the formation of superstructure with tetragonal lattice. The occupancy of the positions of deuterium and metal atoms was determined.     

国产S30432钢和T92异种钢焊接接头力学性能和显微组织分析

研究了国产奥氏体S30432钢和马氏体T92异种钢焊接接头的力学性能、各微区的显微组织、硬度分布以及T92钢化学成分变化对焊接接头微观组织的影响,并与进口S30432钢和T92异种钢焊接接头的性能进行了对比.结果表明:国产S30432钢和T92异种钢焊接接头与进口同类型钢焊接接头的力学性能相当,硬度分布情况相同,T92钢侧熔合区的硬度最高,但国产S30432钢和T92异种钢焊接接头的硬度稍低于进口钢.在异种钢焊接接头的T92钢侧熔合区出现块状铁素体带,且发现T92钢不同的Creq当量会影响块状铁素体生成的数量和尺寸.     

Creep-rupture performance of 0.07C–23Cr–45Ni–6W–Ti,Nb austenitic alloy (HR6W) tubes

A series of base metal and cross-weld creep-rupture tests were conducted on the advanced austenitic alloy, HR6W, to evaluate the material for use at advanced ultrasupercritical (A-USC) steam conditions. Creep deformation and rupture were evaluated by traditional methods and data were compared with other studies to evaluate the creep response of the material. Optical and scanning electron microscopy revealed changes in failure mode and precipitation behavior. Thermodynamic predictions of phase stability were conducted and the results were compared with the experimental data. This research confirmed the important role of W and the precipitation of laves phase in the alloy system, but a direct relationship between laves phase content and creep strength was not observed. Furthermore, Cr content was investigated as an additional factor which may be important in the microstructural stability of the alloy which had not been previously considered. Finally, when compared to commercially available stainless steels, this heat of HR6W showed no creep strength advantage for A-USC application.     

浅议超超临界锅炉用耐热钢

本文介绍了超超临界锅炉的发展状况和结构特征,分析了超超临界锅炉用钢的型号及其性能,介绍了国内新型耐热钢的研究状况,对我国超超临界锅炉用耐热钢的发展提出了几点建议.     

Study of the microstructure of the Grade 91 steel after more than 100,000 h of creep exposure at 600 °C

This paper presents results on the evolution of microstructure (both matrix and precipitates) of an ASME Grade 91 steel that has been creep tested for 113,431 h at 600 °C under a load of 80 MPa.     

超临界汽轮机的开发与展望

发展超临界机组是火力发电节约能源、改善环保和提高发电效率、开发大型机组、降低发电成本的必然趋势 ,是发展能与IGCC和PFBC相媲美的超超临界机组的前期技术。超临界机组已具有成熟的技术和良好的经济性能 ,并已为世界所共识。国内电网完全有必要安装 6 0 0MW及更大容量机组。上海汽轮机有限公司在与外商合作的基础上有充分能力开发容量为 6 0 0MW和更大的超临界机组     

超超临界机组低频振荡原因分析及抑制措施

针对汽轮发电机组出现低频振荡事件,分析了振荡发生的原因及机理,提出了用于抑制低频振荡的控制优化方法.对汽机高压调阀进行流量特性试验,优化流量特性曲线,合理设计重叠度,提高控制精度;优化配汽方式,在提高经济性的同时有助于抑制低频振荡;优化控制策略,采用变参数自适应控制结合变负荷智能超调、智能一次调频控制,提高机组调节性能...     

Influence of Laves Phase on Impact Toughness of P92 Steel

对650℃时效500 h、1 000 h、3 000 h和10 000 h的P92钢以及时效后经过760℃回火处理的试样进行了冲击吸收能量、冲击断口和微观组织的试验,并定量分析了Laves相对P92钢冲击性能的影响程度.结果表明：冲击吸收能量、冲击断口的晶状断面率与组织中的Laves相含量之间的变化趋势一致,存在对应关系;Laves相对P92钢热脆化的影响程度取决于时效时间,在短时时效下,Laves相的析出和长大占主导地位,随着时效时间的增加,其影响份额逐渐降低,组织中的其他变化变得逐渐重要,但Laves相的析出和长大仍是主要影响因素;760℃回火可使Laves相发生回溶,并改善了冲击韧性,短期时效试样的冲击韧性可完全恢复到正、回火状态,但冲击吸收能量的组成比例却发生了变化.     

上汽-西门子型百万千瓦超超临界汽轮机

介绍了上海汽轮机有限公司1000MW超超临界汽轮机的技术特点。通过采用高温材料、大容量单轴汽轮机模块以及一系列独特结构和先进技术,使机组的经济性和安全可靠性达到世界先进水平。该机组还能满足今后更高参数、更低背压、空冷、热电联供等不同超超临界电厂的要求,在我国高效洁净燃煤发电领域具有广阔的发展前景。     

大力发展超临界压力机组优化火电结构

通过分析目前我国火电结构存在的“两个基本事实,一个突出矛盾”,认为发展超临压力机组这种已商业化的、成熟的发电是改善火电结构的有效途径;指出发展超 临界压力机组面临着设计、制造和运行等几项技术难点,认为应在掌握新知识和新技术的基础上,努力实现我国发展超临界压力机组的技术跨越。     

超临界机组锅炉试运期间的节能措施与技术

从优化机组运行参数、合理组织优化调试程序、采用新技术等方面论述了超临界机组基建阶段为节能所能做出的措施.     

超大容量超超临界燃煤发电机组的现状及发展趋势

超大容量超超临界燃煤发电机组在提高能源利用率、减少污染物排放的洁净煤发电技术中所具有的优势，及发展现状、发展趋势。     

超超临界锅炉水冷壁T23接头时效性能

对超超临界锅炉水冷壁T23接头进行了500~650℃、0~3 000h的时效试验,分析时效对焊缝组织、硬度和韧性的影响,研究了T23接头在470℃和550℃下的蠕变断裂行为,揭示T23接头的早期失效机理.结果表明:温度对T23接头焊缝性能的影响很大,当时效温度低于550℃时,焊缝长期处于高硬度状态,有明显的时效脆化倾向,当时效温度超过600℃时,焊缝中析出碳化物,硬度降低,冲击韧性逐渐恢复;T23接头脆性失效与楔形蠕变裂纹有关;焊后热处理是防止T23接头失效的有效措施,为了保证焊后热处理的效果和接头的可靠性,建议将250HB作为焊缝硬度控制的上限.     

超（超）临界锅炉机组高温氧化案例分析与启示

通过分析影响高温氧化的各项因素,研究了2013年国内600 MW以上等级超（超）临界锅炉机组高温氧化的典型实例。从材料、温度及介质3个方面对锅炉高温氧化及氧化皮剥落的影响进行了梳理和总结。研究发现：① TP347H材质在晶粒度较低的情况下抗水蒸气氧化性能差;② 存在汽温欠温问题的锅炉,往往也容易出现氧化皮早期剥落的问题;③ 制造厂家给出的壁温控制报警值不能有效指导电厂运行控制以防止氧化皮带来的问题;④ 锅炉采用的给水加氧处理工艺与氧化皮大面积剥落没有直接关联。最后,提出了今后高温氧化问题的研究方向和改进措施。     

1000MW二次再热火电机组管道热效率对系统热经济性的影响

以某1 000MW超超临界二次再热火电机组为研究对象,定量分析了系统管道的散热损失、厂用蒸汽系统损失及工质泄漏损失对单元机组热经济性的影响.结果表明:考虑全部损失时,管道热效率为97.394%,供电标准煤耗为271.935g/(kW·h).与无管道损失时相比,机组管道热效率降低2.606%,供电标准煤耗增加4.584g/(kW·h),说明在二次再热机组热经济性评价中应该考虑管道热效率.