核电站一回路主管道材料热老化力学性能的预测概述

从核电站一回路铸造奥氏体不锈钢热老化现象、热老化后力学性能变化趋势及力学性能预测流程等方面,对铸造奥氏体不锈钢热老化后冲击性能、拉伸性能、J-R曲线和断裂韧性力学性能预测的研究现状进行了综述。并对目前力学性能预测方法的不足提出自己的想法。     

铸造奥氏体不锈钢热老化效应的反常现象研究与退火延寿技术探讨

介绍了核电厂用铸造奥氏体不锈钢材料的热老化效应、影响因素及铁素体相的特点等,举例分析并讨论了热老化过程中出现的反常现象。从微观机理分析、应用实例等方面探讨了核电厂铸造奥氏体不锈钢材料的退火延寿技术。     

热老化对AP1000主泵泵壳动态断裂韧性影响研究

为研究热老化对AP1000主泵泵壳的制造材料——铸造奥氏体不锈钢CF8的动态断裂韧性的影响,采用夏比预裂纹试样,利用示波落锤冲击试验系统研究材料动态断裂韧性随老化时间的变化规律。试验结果表明:400℃下的加速热老化使主泵泵壳材料产生明显的脆化效应,降低材料断裂所需消耗的能量;热老化导致材料动态裂纹扩展阻力曲线下降,对应的动态断裂韧度下降,但在热老化前期短时间内阻力曲线下降程度较大,而在热老化时间500h后降幅逐渐减小,出现老化饱和迹象。     

核电主管道不锈钢在高温高压水环境下的疲劳裂纹萌生行为

利用腐蚀疲劳测试系统研究了高温高压水环境下两种压水堆核电站一回路主管道用不锈钢的腐蚀疲劳裂纹萌生行为。结果表明,316LN奥氏体不锈钢的裂纹主要在材料表面的驻留滑移带处萌生,少量裂纹在两簇驻留滑移带交界的亚晶界面处。含有少量铁素体的Z3CN20.09M奥氏体不锈钢的疲劳裂纹依次在试样表面的驻留滑移带处、相界处和点蚀坑处萌生,但主要是在驻留滑移带处。通过研究高温高压水环境下氧化膜的组成和腐蚀疲劳试样横截面的形貌,分析了疲劳裂纹在滑移带处萌生的机理。最后对比分析两种不锈钢裂纹萌生机制的异同,并讨论了铁素体对材料腐蚀疲劳性能的影响。     

核电站离心铸造主管道铁素体含量的检测方法及成分偏析的控制

根据RCC-M要求,CPR1000堆型压水堆核电站核岛主管道的材料为离心铸造的奥氏体-铁素体不锈钢(法国牌号Z3CN20-09M)。该试验按照MC1000章节舍夫勒图(Schaeffler)和MC1340章节的内容测定了主管道的铁素体含量,分析了不同方法检测结果的差异原因。并结合阳江项目主管道的制造经验和RCC-M M3406的内容,从金属学及离心铸造结晶凝固的特点,分析了主管道铁素体含量自管道内壁向外递增分布的原因。总结出舍夫勒图评定铁素体含量与MC1340章节测定铁素体含量方法的适用范围,以及消除主管道铁素体分布不均的方法。     

热老化对316LN不锈钢焊缝微观组织和冲击性能的影响

为研究核电站主管道316LN不锈钢焊缝的热老化,开展了316LN不锈钢在400℃下15000h的加速热老化实验。采用TEM和HREM研究热老化后焊缝微观组织演变,利用冲击实验测定不同热老化时间下焊缝夏比冲击性能;以夏比冲击功作为热老化脆化参量,通过拟合法获得了焊缝热老化脆化动力学公式,利用热老化动力学公式预测焊缝在实际运行温度下服役60年内的夏比冲击功变化。结果表明:经1000h热老化后焊缝中的铁素体已经发生了调幅分解,形成了富Fe的α相和富Cr的α′相,同时在铁素体内析出了G相;焊缝中铁素体调幅分解和G相析出导致焊缝冲击功随时间延长而不断下降;夏比冲击功预测结果显示在运行25年内冲击功下降较快,随后的运行过程中下降过程趋缓。     

相界面对核电Z3CN20-09M不锈钢裂纹萌生和扩展的影响

为研究国产核级主管道不锈钢Z3CN20-09M中奥氏体/铁素体相界面在裂纹萌生与扩展过程中的作用,通过扫描电镜原位拉伸技术对核级主管道不锈钢在拉伸过程中的组织形变、微裂纹的萌生与扩展进行原位观察,对断口进行了分析.研究表明,在拉伸过程中,微裂纹优先在杂质颗粒和相界位置萌生.当铁素体/奥氏体界面垂直于拉伸方向时,裂纹倾向于沿相界萌生,并沿相界扩展;当铁素体/奥氏体界面平行于拉伸方向时,微裂纹在相界开裂,并垂直于界面扩展,主裂纹发生偏折,界面在裂纹扩展过程中起阻碍作用.     

热老化对核电主管道材料冲击性能影响及老化趋势研究

利用示波冲击试验系统研究核电主管道奥氏体-铁素体两相不锈钢铸件材料在老化温度(400℃)下时效3000h过程中冲击断裂性能随时效时间的变化规律。室温冲击实验结果表明:在长期时效过程中,随着时效时间的延长,屈服载荷增加,延性位移减小,表征裂纹稳定扩展速度的卸载角度在时效100h后快速增加。冲击过程中材料的裂纹形成能量、裂纹扩展能量以及总冲击能量均随时效时间的延长先略上升而后逐渐下降,呈现出明显的脆化迹象;相比之下,热老化将主要导致材料裂纹扩展能量的下降。采用脆化动力学公式,对长期时效下热老化趋势进行预测,结果显示采用脆化动力学预测的材料冲击性能下降规律与试验结果基本吻合,但整体偏于保守。SEM结果表明试样表面的微观特征从较浅的韧窝型断裂逐渐演变到典型的解理性脆性断裂,材料在热老化过程中发生了脆化。     

铸造双相不锈钢点腐蚀行为研究

采用化学浸泡腐蚀试验及微观组织和化学成分分析研究了5种铸造双相不锈钢在6%Fe Cl3溶液中的点腐蚀行为,并与316L奥氏体不锈钢进行了对比。结果表明,铸造双相不锈钢的抗点腐蚀性能均优于316L的,腐蚀速率和点腐蚀深度均小于316L奥氏体不锈钢的;双相不锈钢主要耐点蚀能力合金元素在奥氏体和铁素体相内分布不均匀,铬、钼更多地分配于铁素体相内,而镍、氮则更多地分配于奥氏体相内,铁素体相的耐点蚀指数PRE(Cr%+3.3Mo%+16N%)大于奥氏体相;双相不锈钢的耐点腐蚀性能与化学成分有关,随着PRE的增加,双相不锈钢的耐点腐蚀性能提高,铜元素在铁素体内析出的富铜相导致点蚀优先在铁素体内发生和发展。     

超低温用铸造不锈钢（改进型CF8）的开发

一、前言 液化天然气有关装置的各种机器和配管，其构成材料，一般根据低温特性，分别选用碳素钢、低Ni钢、奥氏体不锈钢和奥氏体铸造不锈钢(以下写为铸造不锈制)，还有铝等。     

Oxidation behaviour of steels in advanced gas cooled reactors

Abstract

EDF Energy operates 14 advanced gas cooled reactors (AGRs) in the UK to generate electricity. CO₂ gas is used as the primary coolant in the AGRs, and a range of steels are used as for the structural components: e.g. 9Cr-1Mo ferritic steels and stainless steels. These steels are susceptible to both oxidation and carburisation in CO₂ dominated primary coolant gas under high pressure between 300 and 650 °C. Material degradation is a key concern for lifetime extension of the power stations, and EDF Energy and its predecessors have carried out a series of research programmes to better understand steel oxidation behaviour in AGRs and to develop more realistic lifetime prediction methodologies. These are used to secure safe and reliable operation of the AGRs. In this paper, an overview of oxidation behaviour of steels used in AGRs and some examples from the above programmes are described.     

Applications of Thermoelectric Power Measurement to Deterioration Diagnosis of Nuclear Material and Its Principle

In order to non-destructively evaluate changes in toughness of cast duplex stainless steel, which is frequently used in main coolant pipes of PWR type nuclear power plants, due to thermal aging, we tried to apply thermoelectric power (TEP) measurement. because TEP is sensitive to microstructural material changes, and to clarify the mechanism behind TEP changes due to thermal aging. As a result, TEP of cast duplex stainless steel increased with aging time, and good correlations were found between TEP and toughness. Concerning the mechanism, TEP of high and low Cr content alloys was higher than that of intermediate Cr content alloys. Because high and low Cr areas are created in the ferrite phase due to thermal aging. TEP of the entire material increased. Furthermore, when each Cr fluctuating area acted in parallel, the increase in TEP became larger. According to the Mott-Jones theory, TEP is largely related to the electron density of states at the Fermi level. The electron density of states of Fe–Cr–Ni alloys in the valence band was measured with X-ray photoelectron spectroscopy (XPS). As a result, there was a high correlation between the TEP calculated from the XPS spectrum and the measured TEP. Therefore, we showed experimentally that the electron density of states changed due to variations in Cr concentration, which also affect TEP.     

Continual model of propagation of corrosion cracks for the evaluation of the service life of structures

On the basis of the mechanics of dispersed fracture, we develop a continual model of propagation of corrosion cracks for the evaluation of the service life of structural elements. The results of numerical simulation of the process of crack growth in specimens made of austenitic stainless steel of the 18-8 type performed on the basis of the experimental data available from the literature demonstrate the reliability of the proposed model. We obtain the solutions of the problem of service life of the rectilinear segments of heat-exchange pipes of steam generators of nuclear power plants and apply these solutions to establish a noticeable dependence of the service life on the size of the pipes, pressure in the primary coolant circuit, and chemical compositions of corrosive media.     

The effects of reversion heat treatment on the recovery of thermal aging embrittlement of CF8M cast stainless steels

The thermal aging embrittlement of cast stainless steels (CASSs) is one of the key material property degradation that would limit the long-term operation nuclear power plants. In this study, we investigated the recovery behaviors of thermal aging embrittlement of cast stainless steels (CASSs) by the reversion heat treatment. Two heats of CF8M with different ferrite contents were used and the degree of aging embrittlement was measured by the micro-hardness of ferrite phases. It was found that the micro-hardness values of ferrites in the aged CF8M were significantly reduced after the reversion heat treatment at 550 °C for 30 min. Meanwhile, those of the un-aged CF8M were slightly increased by the reversion heat treatment. Also, the re-aging embrittlement behaviors of the recovered CF8M were similar to the initial aging behaviors. Finally, if the reversion heat treatment was applied to the un-aged CF8M, the degree of the embrittlement was reduced during the thermal aging heat treatment. These changes in the micro-hardness values were explained in view of the dissolution of the Cr-rich region formed during spinodal decomposition and the formation of Mo-rich precipitates in the ferrite phases during the reversion heat treatment.     

Effects of long term thermal aging on high temperature tensile deformation behaviours of duplex stainless steels

Abstract

Tensile deformation behaviours of unaged and thermal aged duplex stainless steels (DSS) were investigated at 350°C in order to understand the effects of long term thermal aging on the high temperature deformation behaviours of DSS. After aging for 20?000?h, the strength of DSS has a slight increase, the plasticity has a considerable decline, and the tensile fracture transfers from ductile to brittle. Nanoindentation tests indicate that ferrite has a considerable increase in hardness, and austenite has only a negligible increase with aging time. Thermal aging embrittlement is primarily concerned with ferrite. After long term thermal aging, spinodal decomposition and G-phase precipitation occur in ferrite and these reactions result in the dramatic decline of the ferrite phases' deformation ability. Cleavage cracks can easily initiate and propagate in ferrite of long term thermal aged DSS.     

恒力吊架力学性能对低温再热蒸汽管道热位移的影响

采用JY—20便携式测试系统,对某火电厂低温再热蒸汽管道恒力吊架的恒定度和载荷偏差进行了测试,探讨了恒力吊架力学性能对低温再热蒸汽管道热位移产生的影响。结果表明:恒力吊架载荷偏差及恒定度不合格是造成低温再热蒸汽管道无法复位的主要原因;更换性能合格的恒力吊架后,恒力吊架的位移指针基本能回复到原位,管道热位移正常,且各主要管种的最大一次应力和二次应力均在其允许值范围内。     

Antibacterial property of Ce-bearing stainless steels

Rare earth (RE) elements inhering in low toxicity have been widely used in biomedicine. The RE elements can also improve the hot workability, corrosion resistance and mechanical properties of stainless steels. However, the antibacterial mechanisms of the RE elements are still under discussion and the antibacterial property of RE-bearing stainless steels has not yet been investigated or reported so far. In this paper several Ce-bearing stainless steels were prepared, the microstructure of the steels was examined, and the antibacterial property of Ce-bearing stainless steels was investigated. It was found that Ce-rich zones were precipitated in the Ce-bearing stainless steels and the volume fraction of the Ce-rich zones increased with increasing Ce content. The Ce-bearing stainless steels showed excellent antibacterial property when the amount of Ce added was above a critical value. Compared to the conventional Cu-bearing antibacterial stainless steels, the Ce-bearing stainless steels investigated presently exhibited good antibacterial ability without any thermal aging treatment. The antibacterial mechanism of Ce-bearing stainless steels is also discussed.     

管道的断裂与落锤撕裂试验

介绍了避免油、气集输管道低应力断裂扩展的上裂原理与速度判据。管道裂纹的扩展速度主要取决于管道钢的转变温度ＦＡＴＴ。ＦＡＴＴ可由落锤撕裂试验测定。论述了落锤撕裂试验的特点、方法和标准，以及该试验在管道钢材、压力容器钢和船体结构钢薄板上的应用情况。     

Precipitation and hot deformation behavior of austenitic heat-resistant steels: A review

The austenitic heat resistant-steels have been considered as important candidate materials for advanced supercritical boilers, nuclear reactors, super heaters and chemical reactors, due to their favorable combination of high strength, corrosion resistance, perfect mechanical properties, workability and low cost.Since the precipitation behavior of the steels during long-term service at elevated temperature would lead to the deterioration of mechanical properties, it is essential to clarify the evolution of secondary phases in the microstructure of the steels. Here, a summary of recent progress in the precipitation behavior and the coarsening mechanism of various precipitates during aging in austenitic steels is made. Various secondary phases are formed under service conditions, like MX carbonitrides, M_(23)C_6 carbides, Z phase, sigma phase and Laves phase. It is found that the coarsening rate of M_(23)C_6 carbides is much higher than that of MX carbonitrides. In order to understand the thermal deformation mechanism, a constitutive equation can be established, and thus obtained processing maps are beneficial to optimizing thermal processing parameters, leading to improved thermal processing properties of steels.