DZIA-13型锅炉水冷壁管爆裂原因分析

某锅炉水冷壁管在运行过程中发生爆管，通过宏观、微观金相检验和X射线物相分析等检测方法，对其进行了分析。结果表明，爆管系水质管理不当而产生严重水垢，使水冷壁管局部长期超温，显微组织珠光体球化，引起管子蠕变胀粗而最终爆管。     

DZL4-13型锅炉水冷壁管爆裂原因分析

某锅炉水冷壁管在运行过程中发生爆管 ,通过宏观、微观金相检验和X射线物相分析等检测方法 ,对其进行了分析。结果表明 ,爆管系水质管理不当而产生严重水垢 ,使水冷壁管局部长期超温 ,显微组织珠光体球化 ,引起管子蠕变胀粗而最终爆管     

长期服役再热器管T91钢的微观组织老化行为研究

针对国内某电厂350 MW亚临界机组长期服役12万h高温再热器T91钢管试样,通过光学显微镜(OM)、扫描电子显微镜(SEM)、电子背散射衍射(EBSD)以及透射电镜(TEM)等分析手段,研究了长期服役过程中T91钢的微观组织老化行为,并对T91钢的原始态和长期服役状态的组织和性能进行了对比。结果表明:长期服役12万h后T91钢中M_(23)C_6在晶界处发生聚集并长大,其颗粒尺寸从原始态的107.8 nm长大到123.8 nm。晶界处有新的Laves相析出并粗化,Mo元素不断从基体中脱溶,使得铁素体基体内Cr和Mo元素质量分数降低,固溶强化作用减弱。     

超期服役F12耐热钢断裂失效与组织结构的相关性

采用金相、SEM和XRD等方法,对原始及不同服役阶段的F12马氏体耐热钢试样的性能和组织结构进行了分析和比较.结果表明:随着服役时间的延长,试样的力学性能明显下降;在不同服役阶段,F12马氏体耐热钢试样的显微结构发生了明显变化,不仅出现原奥氏体晶界处碳化物的粗化、基体组织中α-Fe的晶格常数减小,且断裂态马氏体组织完全分解,并在晶界粗化的碳化物处形成蠕变孔洞.马氏体组织分解、碳化物粗化和基体组织合金元素贫化是直接导致材料性能下降的原因.     

高温过热器爆管失效分析

通过宏观分析、理化检测和微观组织分析,研究了某电厂锅炉高温过热器爆管产生的原因。研究结果表明:该过热器管局部温度过高,并在该温度下长期运行,使珠光体严重球化,降低材料强度导致爆管。     

某电厂锅炉大弯管爆管事故分析

某钢厂余热锅炉大弯管前后发生2次爆管事故,迫使电厂紧急停炉,为分析爆管事故原因,采用化学成分分析、力学性能测试、宏观和微观组织分析等方法对试样进行了分析,并对现场运行环境参数进行了核查,结果表明:爆管材料的化学成分正常,但力学性能却有所下降,管材金相组织显示珠光体球化严重,经调查现场运行并无超温现象,而宏观形貌却有白色腐蚀物,且腐蚀物中Na离子超标。最终分析认为,该大弯管处于应力集中位置,且运行中存在碱腐蚀,在高温高压下环境下材料组织球化严重,抗高温性能下降,最终致使大弯管失效爆管。     

一起锅炉主蒸汽管爆裂的原因分析

文章采用宏观及微观检验方法对锅炉主蒸汽管爆裂原因进行了分析研究。结果表明，管道由于超温运行，导致其显微组织中珠光体严重球化，并发生了石墨化现象，使材料性能恶化，同时焊缝中存在裂纹等焊接缺陷，减小了承载面积，造成局部应力集中，从而诱发爆裂产生。     

S30432锅炉管高温服役后磁性转变试验研究

采用磁感应强度测量仪、奥氏体氧化物检测仪、光学显微镜、扫描电镜、透射电镜和X射线衍射仪等仪器对较高磁性的S30432高温过热器管进行了取样对比试验研究.结果表明:新管无磁当量和磁感应强度,服役1.9×105 h的运行管出现了较高的磁当量和磁感应强度,磁当量和磁感应强度在管子环向变化较大,服役时间长的管子的磁当量显著大于服役时间短的;引起运行管出现高磁性的原因是管子室温组织中存在一定量的马氏体,马氏体组织呈条带状分布在紧邻晶界两侧,服役时间长的管子中马氏体组织的量明显多于服役时间短的;与新管相比,S30432运行管组织中弥散分布在晶内ε-Cu相的尺寸明显增大、形态也由不规则转变为圆形颗粒.     

长期服役的12%Cr马氏体耐热钢中的碳化物及其变化

以X20CrMoV12.1耐热合金钢管为研究对象,重点研究了管道材料的显微结构变化,特别是碳化物沉淀相的形态和成分变化,探讨了材料性能变化的微观原因.结果表明:12%Cr耐热合金钢主蒸汽管线在550℃高温条件下经180 000 h长期服役后,材料的组织结构发生明显变化,出现马氏体分解,形成板条亚晶结构,表现出典型的蠕变特征;合金碳化物沉淀相大多分布于晶界和板条亚晶界,且相对于原始态粗化严重;晶界和亚晶界分布的碳化结构是M23C6,晶内相对细小的碳化物结构也大多数是M23C6,另有少量方形片状的富V碳化物MX;M23C6碳化物中合金含量随服役时间的延长明显富集,且分布在不同区域的碳化物不仅形态不同,其化学成分也存在明显差异.长期服役过程中碳化物产生这些演变现象与碳化物的粗化进程相关,并受热力学条件和扩散方式的影响.     

700℃先进超超临界汽轮机转子锻件用铁镍基合金的高温组织稳定性研究

对MN1合金和MN2合金进行了700℃和750℃时效处理和高温持久实验。结果表明:MN1合金在700℃下经时效处理后针状η相和γ″相均长大,Laves相析出,其组织稳定性差;当MNI合金的保温时间达到5 000 h或温度提高至750℃时,η相明显粗化,晶界和晶内均析出大量块状Laves相,导致其在700℃下高温持久性能较低;MN2合金在700℃下经时效处理后,细小的γ′相弥散析出于基体,晶界为短棒状η相,此组织在750℃下稳定性良好;MN2合金在700℃、10~5 h条件下的外推持久强度可达127 MPa,可作为700℃超超临界汽轮机转子的备选材料。     

Upper-nose temper embrittlement phenomena in a Mn-Mo-Ni pressure vessel steel

The embrittlement of a Mn-Mo-Ni steel during tempering treatments in the temperature range 630–720°C was studied. Six time-dependent microstructural processes can be recognised that collectively contribute to the deterioration of the mechanical properties. The deterioration of the toughness during tempering in this temperature region is known as upper-nose temper embrittlement. It is associated with the coarsening of the microstructure and also with the formation of a dual phase ferritic-martensitic microstructure. These effects are illustrated with the aid of property-exposure diagrams.     

Long term creep properties and microstructure of SUPER304H,TP347HFG and HR3C for A-USC boilers

Abstract

SUPER304H (18Cr–9Ni–3Cu–Nb–N; ASME CC2328) and TP347HFG (18Cr–12Ni–Nb; ASME SA213) have been developed for high strength oxidation resistant steel tubes to operate at high steam temperatures and pressures. The longest creep rupture tests performed to date (600°C for 85 426 h for SUPER304H; 700°C for 55 858 h for TP347HFG) showed that the stable strength and microstructure were retained, with very little formation of σ-phase compared with conventional austenitic stainless steels and no other brittle phases. The alloy HR3C (25Cr–20Ni–Nb–N; ASME CC2115) has been developed for the high strength and high corrosion resistant steel tubes used in recent ultrasupercritical (USC) boilers with steam temperatures of ～600°C. The longest creep test conducted to date (700°C, 69 MPa for 88 362 h) confirmed a stable creep strength and microstructure at 600–800°C. Superheater and reheater tubes of these alloys installed in the Eddystone No.1 USC power plant since 1991 have been removed and investigated. Updated long term creep rupture properties of the steels and microstructural changes during service are reported. Three steel tubes have been successfully applied as standard materials for superheater and reheater tubes in newly built USC boilers.     

P92钢高温持久强度试验后组织变化对性能的影响

采用扫描电镜和透射电镜对国产P92钢在600℃下经持久强度试验后的显微组织进行了观察,并研究了组织变化对性能的影响．结果表明：试验1429h前硬度下降主要是由于M23C6的粗化,而后由于大量Laves相析出产生的强化作用使硬度重新上升．当试验6063h后,Laves相粗化使强化效果减弱,硬度再次下降,此时MX仍然保持细小的尺寸,具有较好的强化效果．在整个持久试验过程中,板条马氏体的回复、再结晶导致的位错强化减弱,W、Mo从基体的脱溶导致的固溶强化减弱都对硬度下降起一定作用．     

Effective metal temperature in creep life assessment

In assessing remaining creep life of high temperature components, the thermal history, as expressed by the ‘effective metal temperature’ is an important input. This temperature can be derived from quantifiable thermally induced changes such as growth of internal scale or coarsening of carbide particles in the microstructure. Conventional practice is to use this temperature to predict the consequences of a different thermally activated process, i.e. creep. Under isothermal steady-state conditions, this approach is valid. Under the variable loading conditions typical of operating plants, however, effective temperatures for different processes may not be identical. The paper addresses this issue, comparing effective metal temperatures for creep, oxidation and carbide coarsening under several forms of variable loading.     

Effect of high temperature deformation on the microstructure,mechanical properties and hydrogen embrittlement of 2.25Cr–1Mo-0.25 V steel

In this paper, the effects of high temperature deformation on the microstructure, mechanical properties and hydrogen embrittlement (HE) of the 2.25Cr–1Mo-0.25 V steel was investigated by a scanning electron microscope (SEM), a transmission electron microscope (TEM) and tensile tests. The SEM and TEM images demonstrated that high temperature plastic deformation (HTPD) led to the coarsening of carbides and the dislocation density increase. The tensile tests displayed that the HTPD resulted in the cracking susceptibility increase, as indicated by the increased numbers and sizes of cracks at the fractured surface. This was attributed to the coarsening of carbides during high temperature deformation. In contrast, the HTPD highly decreased the loss of ductility compared to the un-deformed specimens, although the amount of ductility losses (elongation or reduction of area) did not change significantly as the HTPD increased. The correlations among carbides, hydrogen and cracks were discussed.     

Two-body abrasion wear mechanism of super bainitic steel

The abrasion wear resistance and wear mechanism of super bainitic steel austempered at different temperatures and time have been investigated by two-body abrasion testings, scanning electron microscopy, X-ray diffraction, transformation electron microscopy and electron backscattering diffraction. The results show that the two-body abrasion wear mechanism is predominantly micro-ploughing abrasion, and the wear resistance is decreased with increasing isothermal temperature which is attributed to the decreased hardness caused by a higher retained austenite content and the coarsening of the microstructure. The sample austempered at 230°C for 2?h with the higher amount of retained austenite and lower carbon concentration exhibits excellent wear resistance, and the transformation induced plasticity effect is observed during wear process which is beneficial for the improving of hardness and wear resistance.     

Simulation of coarsening in three-phase solid oxide fuel cell anodes

Coarsening of the nickel phase is known to occur in solid oxide fuel cell (SOFC) anodes consisting of Ni and yttria-stabilized zirconia (YSZ). However, the exact nature of the coarsening process is not known, nor how it affects three-phase boundaries (TPBs) and the resulting electrochemical performance. We apply a phase-field approach to simulate the microstructural evolution of Ni-YSZ anode functional layers. An experimentally obtained three-dimensional reconstruction of a functional layer from an anode-supported SOFC is used as the initial microstructure. The evolution of the microstructure is characterized quantitatively by examining the TPB density, interfacial area per unit volume, and tortuosity versus time. The assumed TPB contact angles are found to have a strong effect on the microstructural evolution; in particular, reducing the contact angle of nickel on YSZ yields less TPB reduction.     

Microstructural analysis of creep exposed IN617 alloy

Abstract

Ni base alloys such as IN617 are one of the preferred choices for steam turbine components used by fossil fuelled power generation plants. IN617 is a solid solution strengthened Ni based superalloy containing ～23%Cr, 12%Co and 9%Mo with low content of precipitation strengthening elements Al, Ti and Nb. In the 'as received' (solution annealed condition), the microstructure consists of primary carbides (M₂₃C₆) and occasional TiN particles dispersed in a single phase austenitic matrix. Owing to high temperature exposure and the creep deformation processes that occur in service, evolution of the microstructure occurs. This results in secondary precipitation and precipitate coarsening, both on grain boundaries and intragranularly in areas of high dislocation density. The influence of creep deformation on the solution treated IN617 alloy at an operating condition of 650 ～C/574 h, with emphasis on the morphology and distribution of carbide/nitride precipitation is discussed. The applied stress was at an intermediate level.     

Microstructural evolutions of IN738LC during multiple reheat treatment and aging

Abstract

IN738LC is a polycrystalline superalloy which is still widely used for gas turbine blading in many industrial applications. It has been the centre of many research programmes during the last four decades in areas such as alloy design, processing, various degradation regimes and even after heat treatment during repair. The subject of this study has been the microstructural evolution during multiple reheat treatments combined with long term aging. Material has been exposed at two different aging temperatures (875 and 950°C) for a period of 4000 h. This has been followed by a reheat treatment and then further aging, up to a total of 16?000 h. The microstructural evolution of the alloy, γ′ coarsening and carbide transformations, have been investigated in detail after the heat treatments and further aging periods. The results highlighted that although the γ′ structure has largely been recovered by the heat treatments, that of the carbides did not follow a similar trend. This partial recovery of the alloy microstructure and its potential impact on the long term integrity of gas turbine blading which has been heat treated periodically will be discussed in this paper.     

电热辐射管失效分析的研究

介绍了在渗碳气氛中工作的电热辐射管在使用中破坏的形态，断口处的成分及组织变化，探讨了破坏的机理。