16Cr2Mo1Cu高铬铸铁在亚临界处理中硬化行为研究

研究了亚临界处理对16Cr2Mo1Cu高铬铸铁的组织转变和性能的影响,并利用X射线衍射分析、磁性法和硬度测定法分析了硬化机制.研究表明:16Cr2Mo1Cu高铬铸铁的铸态组织由残余奥氏体、马氏体和M7C3型共晶碳化物组成,其相对含量分别为77.0%,7.2%和15.8%;在亚临界处理过程中,基体组织中的残余奥氏体析出二次碳化物并在冷却过程中转变为马氏体,使该合金在560～600℃的亚临界处理过程中出现二次硬化;在适当的处理温度和保温时间下,16Cr2Mo1Cu高铬铸铁可得到最高的硬度.     

添加Mo对高铬铸铁组织及亚临界处理硬化作用的影响研究

为提升高铬铸铁的综合性能,以无Mo高铬铸铁和含1.0％(质量分数)Mo高铬铸铁为研究对象,对比研究了添加Mo元素对铸态高铬铸铁组织结构以及550℃亚临界处理对其组织及硬度的影响.研究表明:2种铸态高铬铸铁的主要组成相均为奥氏体、马氏体及(Cr,Fe)7C3,但含Mo高铬铸铁中奥氏体含量明显增多.铸态高铬铸铁均以亚共晶方...     

亚临界自然循环汽包炉水位的调节

随着现代锅炉参数的不断提高,汽包内工质的饱和温度维持在较高水平,由于此类锅炉大多数采用非沸腾式省煤器,进入汽包时有一定的欠焓,特别是在变工况运行时进入汽包的工质焓值会发生较大幅度的变化,加之锅炉燃烧状况的变化,机侧用汽量的的变化,高加运行状况的变化等使得机组在变工况运行时的水位调节变的复杂,再加上现代锅炉汽包水容积较小,变工况时水位波动大,此时更容易引起水位保护的动作,造成灭火甚至锅炉干锅、满水的恶性事故。本文着重论述了机组在大幅变工况和启停过程中水位的变化起因以及相应的处理方法。     

近临界水自催化下亚氨基二乙腈水解反应研究

亚氨基二乙腈在没有外加催化剂的近邻界水中可以顺利发生水解.实验测定了亚氨基二乙腈在近临界水中(压力10MPa,温度200～260℃,反应时间10～60min)的水解反应动力学数据并考察了时间、温度、压力和初始反应物/水比对反应物转化率和产物产率的影响.在最佳反应条件下,210℃、压力10MPa、反应时间20min,反应物几乎完全转化,此时亚氨基二乙酸的产率可达到92.3mol%.根据一级反应动力学,得到反应的表观活化能Ea和lnA(min-1)分别为(45.77±5.26)kJ/mol和8.6±0.1.最终反应产物主要包括亚氨基二乙酸和氨以及少量的副产物,反应过程中除生成的氨气外其它气体的生成可以忽略.近临界水中亚氨基二乙腈的水解反应机理和普通碱催化条件的水解反应机理相似.     

600MW亚临界机组启动时振动特性研究

随着经济的迅速发展以及科学技术水平的不断提高,我国的电力工业取得了较大程度上的进步,为我国国民经济的发展以及人民生活水平的提高做出重要贡献。在这种环境之下,人们对电力企业提出了更为严格的要求,期望电力生产更为可靠而有效,600MW亚临界机组便是电力企业谋求发展、满足需求必不可少的设备。然而,目前状况下600Mw亚临界机组仍不完善,还存在着一系列的问题,其中较为突出的一项便是机组启动时出现振动状况,这对整个系统的正常运行造成了一定程度的影响。本文主要针对600MW亚临界机组启动时振动特性进行研究与分析,并在此基础之上提出相应的治理措施。     

混凝土断裂及亚临界扩展的细观机制

通过模型和三点弯曲断裂SEM试验,详细研究了混凝土断裂全过程及亚临界扩展的细观机理。结果表明:混凝土断裂是一个复杂的不规则过程,存在明显的亚临界扩展现象。混凝土亚临界扩展路径是曲折的,并非经典断裂力学假定的平直路径,混凝土亚临界扩展和临界失稳扩展呈现分形特征。用起裂断裂韧性K_ICⁱ和分形等效断裂韧性K_IC^e,f来描述混凝土抵抗初裂和临界失稳扩展的能力。给出了考虑亚临界扩展弯折效应的混凝土亚临界扩展长度、混凝土起裂断裂韧性K_ICⁱ和分形等效断裂韧性K_IC^e,f的计算表达式。计算表明:混凝土失稳断裂时的分形等效断裂韧性K_IC^e,f与混凝土亚临界扩展的分维数D成正比。     

亚临界载荷对樱桃番茄呼吸强度的影响

目的分析单个樱桃番茄在亚临界载荷下受到跌落冲击而发生的延时损伤,以及这种损伤对果品呼吸强度的影响。方法以樱桃番茄为研究对象,设计多组跌落高度实验分析其损伤程度与跌落高度的关系,得出樱桃番茄的临界跌落高度。设计临界高度以下不同高度的对比实验,然后把跌落后的樱桃番茄放入密封的保鲜盒内,在相同的条件下间隔时间测量其CO2/O2浓度的变化。最后,绘制出跌落高度与呼吸速率的关系图,根据数据拟合出亚临界载荷强度与呼吸强度关系的数学模型。结果临界高度以下,樱桃番茄受到损伤冲击后的呼吸速率会发生变化;跌落高度越高,在贮藏初始阶段,樱桃番茄的呼吸速率下降越快,最后趋于平衡;跌落高度越高,呼吸速率越大。结论研究结果对果品包装上的改进具有重要价值。     

600MW亚临界机组锅炉优化燃烧试验研究

介绍了某电厂600MW亚临界机组锅炉燃烧调整试验。对制粉系统进行了优化调整：分析了不同负荷下氧量的变化对锅炉效率的影响,并给出了最佳氧量值;在600MW负荷下进行了二次风箱压力对锅炉效率影响试验,并做出了二次风箱压力对锅炉效率影响曲线;分析了锅炉NOx排放特性。     

亚临界通量操作对黄连解毒汤超滤过程的影响

将临界通量概念引入中药水提液复杂体系,以中药复方黄连解毒汤水提液为实验对象,通过测定中空纤维膜超滤过程的临界通量,考察了亚临界通量操作下的膜系统运行状态.结果表明,在错流流速0.15 m/s,压力0.04 MPa的亚临界通量操作下,膜稳定通量与初始通量相比降低了5.5%;而在0.07 MPa和0.10 MPa的超临界通量操作下,其值分别为32.1%、42.2%.稳定状态下膜相对污染阻力在0.04、0.07和0.10 MPa条件下分别为3.0、7.5和15.8.亚临界通量操作对于优化操作条件,有效降低膜污染,节约生产成本,指导中药水提液膜过滤精制的实际生产应用有着重要的意义.     

浅谈600MW亚临界锅炉运行的优化

锅炉是火力发电厂中最为重要的设备之一,锅炉运行中一直存在不少问题,面临着许多需要优化的地方。本文就600MW亚临界锅炉运行的优化进行深入的研究,包括制粉系统和锅炉本体系统的运行优化,所得经济效益和社会效益明显,给同类锅炉运行优化调整提供了参考。     

Improvement of toughness of high chromium white cast iron: duplex ferritic-austenitic matrix

It is attempted to enhance the impact toughness of industrially used high chromium white cast iron (WCI) without sacrificing wear resistance. The microstructure is engineered by cyclic annealing to obtain features such as duplex grain matrix, where austenite envelops ferrite grain, refined M₇C₃ carbide. The newly cast and heat-treated alloy shows remarkable impact toughness i.e. 13J with improved wear resistance. The fracture micro-mechanism is studied through extensive scanning electron microscopy and it is ascertained that enhanced impact toughness results from crack arrest at duplex grain boundaries. A few other toughness enhancing features are also discussed. The results are compared with standard ASTM grade Class-III high chromium WCI and are found to be encouraging.     

The effect of spray forming on the microstructure and properties of a high chromium white cast iron

The effect of spray forming on the structure and properties of a 17% Cr, 2.5% C white cast iron is described and compared with conventionally cast material of the same composition. Spray forming resulted in a substantial reduction in microstructural scale (eutectic (Cr,Fe)₇C₃ fields of up to 500 m in conventionally cast material were replaced by discrete carbides of typically 2–8 m diameter in the spray cast deposit). Carbide size varied as a function of position in the spray deposit, being approximately twice the size at mid section compared with either surface or interface with the collector. Carbide size was not altered by the gas to metal ratio used to atomise the spray. Spray forming increased transverse rupture stress and work of fracture by 50% compared with the conventionally cast material. Forging of the spray formed material was possible at 950°C, without inducing carbide fracture or void formation in the matrix. Quenching into iced water from 300°C induced extensive macroscopic cracking in the conventionally cast material whereas 400°C was required in the spray cast material to induce similar damage. The relationship between processing, microstructure and mechanical properties is discussed.     

TEM study on precipitation and transformation of secondary carbides in 16Cr–1Mo–1Cu white iron subjected to subcritical treatment

High chromium white irons solidify with a substantially austenitic matrix supersaturated with chromium and carbon. The subcritical heat treatment can destabilize the austenite by precipitating chromium-rich secondary carbides and other special carbides. In the as-cast condition the eutectic carbides are (Fe,Cr)₇C₃ and (Fe_4.3Cr_2.5Mo_0.1)C₃. The initial secondary carbide precipitated is (Fe,Cr)₂₃C₆ after heat-treating at 853 K for 10 h. There are MoC, Fe₂MoC and -carbide precipitating, and (Fe,Cr)₂₃C₆ transforms to M₃C after 16 h at 853 K. The -carbide and (Fe,Cr)₂₃C₆ accomplish transformation to M₃C and the matrix changes from martensitic to pearlitic after 22 h at 853 K. Thereby, in the subcritical heat treatment process, the initial secondary carbide precipitated is (Fe,Cr)₂₃C₆, followed by -carbide, MoC and Fe₂MoC. In addition, there are two in situ transformations from (Fe,Cr)₂₃C₆ and -carbide to M₃C carbides.     

Improving fracture toughness and hardness of Fe2B in high boron white cast iron by chromium addition

The effect of chromium containing 0%, 0.49%, 1.02%, 2.1%, 3.2% (in wt.%) on the morphology, fracture toughness and micro-hardness property of Fe₂B in high boron white cast iron was investigated. The results indicated that, with an increase of chromium addition, the morphology of Fe₂B becomes larger and changes from the block to rod shape, its micro-hardness increases and the fracture toughness increases first and then decreases. Compared with the fracture toughness (3.8 MPa m^1/2) of Fe₂B without chromium addition, the toughness at 2.1 wt.% chromium addition can be improved by above one time, achieving 7.8 Mpa m^1/2, and the result was also qualitatively testified by the micro-cracks in Fe₂B based on scanning electron microscope micrographs.     

烧结Cr15高铬铸铁组织与性能的研究

为研发耐磨性能优良、成本相对低廉的高铬铸铁,本文分别以亚共晶、过共晶的水雾化Cr15高铬铸铁粉末为原料,采用超固相线液相烧结工艺制备了烧结高铬铸铁(SHCCI),并对其显微组织、力学性能和冲击磨粒磨损工况下的耐磨性能进行对比研究。结果表明,烧结高铬铸铁主要由M7C3碳化物、马氏体和奥氏体组成;在亚共晶烧结高铬铸铁中,通过电解腐蚀萃取的M7C3碳化物三维形貌呈珊瑚状,沿晶界均匀分布,材料抗冲击耐磨性能优良;在过共晶烧结高铬铸铁中,优先形成的初生碳化物可能成为共晶碳化物的生长基底,形成核-壳结构的M7C3碳化物,沿晶界相互连接呈网状,严重割裂基体。亚共晶、过共晶烧结高铬铸铁的力学性能分别为:硬度HRC63.9、HRC64.3,冲击韧性7.92、3.04 J/cm^2,抗弯强度2112.65、1624.87 MPa。     

Stepped heat treatment for austempering of high manganese alloyed ductile iron

Abstract

A stepped heat treatment is proposed for overcoming the difficulty of obtaining ductility in an austempered alloyed ductile iron. The method is illustratedfor an iron containing 0·67%Mn, 0·25%Mo, and 0·25%Cu, using an austenitising temperature of 920°C, afirst step austempering temperature of 400°C for 120 min, and a second step austempering temperature of 285°C. The change in the microstructure and phase characteristics with time during the second austempering step are described. Related changes in the mechanical properties compared with a single austempering treatment at 400°C are an increase in the ultimate tensile strength from 770 to 970 MN m^?2, an increase in elongation from 2·5 to 7·5%, and an increase in the unnotched Charpy impact energy from 40 to 150 J.

MST/3119     

Effects of heat treatment processes on microstructure and creep properties of a high nitrogen 15Cr-15Ni austenitic heat resistant stainless steel

Conventional thermo-mechanical treatment (CTMT) and modified thermo-mechanical treatment (MTMT) process were applied for manufacturing a high nitrogen niobium-stabilized 15Cr-15Ni austenitic alloy. CTMT process consists of 5 h of solution treatment at 1270 °C followed by water quenching and subsequent aging at 820 °C for 50 h. MTMT process differs from CTMT process in hot plastic deformation performed immediately after the solution treatment at 1270 °C and longer aging time. Microstructure and creep properties of the steel obtained by both processing routes were investigated. Creep rupture tests at 750 °C showed double increase in rupture time brought about by MTMT process. Examination of crept microstructure by transmission electron microscopy revealed that the improved creep properties in MTMT process were mainly due to improved distribution uniformity of fine nano-sized carbonitride precipitates in the austenitic matrix and that MTMT process has no effects on the number density and distribution of copper precipitates present in the steel. However, the creep ductility in MTMT process drastically reduced comparing to CTMT process. The higher density of grain boundaries due to finer grain recrystallized microstructures and the formation of higher volume fraction of coarser M₂₃C₆ precipitates at the boundaries are believed to be the main reason for the lower creep ductility in MTMT process.     

Effect of aluminum on the primary carbides of a hypereutectic high chromium cast iron

The effect of aluminum on the primary M₇C₃ carbides of a hypereutectic high chromium cast iron containing 4.0 wt% carbon and 20.0 wt% chromium was studied by means of optical microscopy, scanning electron microscope (SEM), energy dispersive X‐ray spectrometry (EDX), water quenching, and differential thermal analysis (DTA). Compared with specimen without aluminum addition, the primary carbides were all refined when different amount of aluminum was added into the melts, but the primary carbides in specimen with 0.3 wt% aluminum were the finest. With the addition of aluminum, aluminum element enriched at the boundary of primary carbides during solidification and was beneficial for the refinement of primary carbides. However, the increase of primary carbide growth time with the increase aluminum content had adverse effect on the refinement of the primary carbides. The comprehensive influence of those two factors leaded to the result that the primary carbides in specimen 1 with 0.3 wt% aluminum were the finest.     

Effects of deep cryogenic treatment on property of 3Cr13Mo1V1.5 high chromium cast iron

Effects of deep cryogenic treatment on the microstructure, hardening behavior and abrasion resistance of 3Cr13Mo1V1.5 high chromium cast iron subjected to sub-critical treatment were investigated in this paper. The results show that deep cryogenic treatment after sub-critical treatment, the hardness and abrasion resistance of high chromium cast iron can be boosted obviously due to abundant retained austenite transforming into martensite and secondary carbides precipitation. In the course of sub-critical treatment with cryogenic treatment, the amount of precipitated secondary carbides was more than that in air cooling, and the secondary hardening peak advanced at a lower temperature. When abrasion resistance reach the maximal, there was about 20% retained austenite in microstructures. Cryogenic treatment can further reduce the austenite content but can not make retained austenite transform to martensite completely.