Microstructural Degradation Assessment in Pressure Vessel Steel by Harmonic Generation Technique

The harmonic generation technique has been used to characterize the isothermal degradation of pressure vessel steel. The isothermal degradation was conducted at 630°C with forged 2.25Cr-1Mo steel. The variation in the normalized ultrasonic nonlinearity parameter (β=β₀) was interpreted as having resulted from microstructural evolution, which was supported by the results of electron microscopy and X-ray diffraction, in addition to Vickers hardness and ductile-brittle transition temperature. The normalized ultrasonic nonlinearity parameter increased progressively with the isothermal degradation time due to the increase in the volume fraction of equilibrium M₆C carbide and the variation in the lattice parameter of M₂₃C₆ carbide. It was found that the nonlinearity parameter was very sensitive to the microstructure during the isothermal degradation of 2.25Cr-1Mo steel. The harmonic generation technique has the potential to assess microstructural changes due to isothermal degradation.     

1Cr_(18)Nl_9Ti钢的低周疲劳特性研究

通过对:Cr_(18)Ni_9Ti钢的低周疲劳循环试验,进行了试验结果的回归分析研究,给出了轴向总应变与循环寿命,以及总应变与循环至发生工程裂纹寿命的关系。     

Effect of chemical potential of carbon on phase transformation and corrosion of JLF-1 steel in a static lithium

The corrosion and the phase transformation of RAFM (Reduced Activation Ferritic/Martensitic) steel, JLF-1(Fe-9Cr-2W-0.1C), in static lithium (Li) were investigated. The specimens were exposed to static Li at 600 °C for 250 h. The carbon potential in Li was controlled by the carbide formation on inner surface of the crucible, which was made of Mo and Nb. These materials were expected to form stable carbide, and worked as carbon trap in Li, which resulted in the decrease in the carbon potential of Li. The effect of low carbon potential on the corrosion and the phase transformation was characterized by comparison with the test performed in the crucible made of Fe-9Cr and SUS316L (18Cr-12Ni), which has no effect as carbon traps. The low carbon potential caused by Nb and Mo caused the dissolution of carbon from the surface of JLF-1 specimen to Li. The depth of the phase transformation observed after the test in Nb crucible was deeper than that tested in Mo crucible. This was because the stability of the Nb carbide was larger than that of Mo carbide causing larger driving force for the dissolution of carbides from the surface.     

核一级承压设备疲劳分析方法

基于Miner线性累积损伤理论和雨流计数法,得到单载荷历程作用下疲劳分析的方法,并根据核一级承压设备的特点和核承压设备分析规范的要求,给出了一种适用于核一级承压设备疲劳分析的方法;结合设备实际运行情况,提出了瞬态分组组合的优化疲劳分析的方法,并给出一个案例.结果表明,瞬态分组组合使疲劳分析与设备实际运行情况更加接近,计算结果更加精确.     

1Cr18Ni9Ti不锈钢低周疲劳随动硬化实验研究

为了研究单调加载对1Cr18Ni9Ti不锈钢材料后继循环塑性硬化和流动特性的影响,对该材料进行了带平均应变的低周疲劳实验研究.对不同应变幅值的对称应变及非对称的应变循环进行了屈服面半径和背应力演化分析,揭示了材料的随动硬化和各向同性硬化演化对应变幅值和平均应变的依赖性.实验结果为建立循环加载和单调加载耦合的复杂加载条件下的本构模型提供了实验基础.     

核电用316LN不锈钢的热机械疲劳性能研究

采用热机械疲劳试验方法研究316LN不锈钢的同相热机械疲劳行为,获得材料的疲劳数据。试验结果表明:316LN不锈钢的热机械疲劳行为是一个先强化后软化的过程;滞回曲线呈梭形,形状"饱满",具有良好的塑性变形能力,且随着温度范围增大,变形能力增强;在相同条件下,温度范围增大,材料的疲劳特征表现更为明显;在波动管运行条件下(温度≤320℃),应变对材料的疲劳寿命影响占主要作用;材料在120~320℃和120~230℃条件下的热机械疲劳寿命均大于350℃恒温低周疲劳寿命,说明采用传统的高温低周疲劳试验结果来评价波动管材料的热机械疲劳寿命过于保守。     

Fatigue Crack Initiation in Proton-Irradiated Austenitic Stainless Steel

The effect of irradiation on slip band formation and growth and microcrack initiation behavior under low cycle fatigue in SUS316L austenitic stainless steel was investigated using accelerator-based proton irradiation and a low cycle fatigue test at room temperature in air. The mean space of the slip line in proton-irradiated specimens was 25–40% wider than that in unirradiated specimens under the same number of cycles, possibly due to localized deformation by proton irradiation. The microcrack initiation life of the proton-irradiated specimens was approximately 20% of that of the unirradiated specimens. While the microcrack initiation in the unirradiated specimens was observed at the grain boundary, twin boundary, slip band, and triple junction, that in the proton-irradiated specimens was observed only at the twin boundary and slip band, possibly due to irradiation hardening. The step-height of an extrusion near the microcrack was almost the same in the unirradiated and proton-irradiated specimens regardless of the initiation site (100–150 nm). Therefore, the microcrack initiation was considered to occur when the surface morphology change involving the extrusion exceeded the specific threshold value.     

17-4PH不锈钢回火强化过程研究

将17-4PH钢在1 040℃保温1 h后水淬,于540℃回火不同时间,测试其硬度以研究其析出强化规律,利用原子探针层析技术(APT)研究了强化相析出演化过程。析出强化曲线显示,存在两个析出强化峰。APT分析表明,第1个强化峰是由于析出了大量纳米级富Cu相,第2个强化峰则是由于析出了Cr、V、Nb碳氮化物。APT分析还显示,在富Cu相的周围,Mn、Ni和Al也出现偏聚,而且位于富Cu相和基体的界面。     

A508—3钢回火时显微组织的变化

对 A508-3钢中粒状贝氏体回火转变的研究表明,粒状贝氏体组织具有较高的回火稳定性。回火时板条状贝氏体铁素体基体产生回复及再结晶,并有 Mo_2C 析出;岛状组织中马氏体和奥氏体分解而析出渗碳体。还讨论了显微组织变化对机械性能的影响。     

P92钢高温低周疲劳的实验研究

由于高的热效率和简单的系统组成,超临界水堆(SCWR)被认为是第四代核反应堆的一种选择。超临界水堆的关键问题之一是核心部件尤其是燃料组件包壳的材料。这些材料在高温下的力学性能、腐蚀和应力腐蚀开裂敏感性以及抗辐射性能等对核电厂的安全运行至关重要。本文对SCWR包壳候选材料的F/M类材料P92钢进行了高温低周疲劳实验研究。实验温度为600和650℃,控制方式为总应变控制,应变范围均为±0.2%～±0.6%。实验结果表明,在两种温度下,P92钢均为循环软化材料,但未出现循环稳定现象。由于温度升高,塑性增强,P92钢在650℃下的宏观裂纹出现周次比率随应变范围的增加,下降比较平缓,且650℃下的失效寿命显著高于600℃下的失效寿命。并得到了两种温度下的稳定循环应力-塑性应变的关系以及循环失效寿命和应变的关系。     

国产A508-3钢的低周疲劳性能研究

结合承担的973课题,系统开展了国产A508-3钢的低周疲劳性能研究。其目的是通过低周疲劳性能测试、显微硬度计算、断口形貌观察以及微观结构分析,获得材料的疲劳性能数据,评价国产A508-3钢的疲劳性能,并为下一步辐照性能的研究提供数据基础。研究结果表明,国产A508-3钢的低周疲劳性能符合ASME的设计规范,具有循环软化的特征。     

稀土元素Gd对2308双相不锈钢热变形行为的影响

为解决含Gd双相不锈钢热加工不足问题,本文以含2%Gd的双相不锈钢为研究对象,在不同温度下开展热模拟压缩实验,研究含Gd双相不锈钢热变形行为及组织演变。利用Gleeble-1500D热模拟试验机对含Gd双相不锈钢进行变形量为50%的单道次热变形试验。根据真应力-真应变曲线计算了该合金的热变形激活能Q_d,建立本构方程。同时对热变形后的组织进行了分析,探究稀土元素Gd对含Gd双相不锈钢热变形行为的影响,结果表明,在热变形过程中,合金的动态软化机制主要为动态再结晶。合金包含两种含Gd析出相,即条带状的脆性析出相M₃Gd相和M₁₇Gd₂相（M=Fe、Cr、Ni）,均为六方结构。当变形温度为1 050 ℃时,脆性M3Gd相破坏了基体的连续性,无法与基体协同变形,降低了合金的热塑性,导致合金在热变形过程中出现沿晶开裂。含Gd双相不锈钢适宜的热加工工艺区间的应变速率为0.01~0.1 s^-1,变形温度为950~1 000 ℃。     

6XN不锈钢与825合金的高周疲劳行为研究

采用旋转弯曲疲劳方法完成了6XN不锈钢与825合金在室温和550℃空气中的高周疲劳试验。结果表明:室温时,6XN不锈钢的耐久极限应力大于825合金的耐久极限应力,与静强度顺序一致;550℃高温时,试样氧化速率增加,材料疲劳寿命降低,6XN不锈钢的疲劳寿命下降趋势较大,耐久极限应力接近825合金的耐久极限应力;6XN不锈钢对温度更敏感,而825合金对应力循环次数更敏感;与经验公式比较,2种材料具有较好的抗高周疲劳性能;疲劳过程为裂纹源产生、扩展和断裂,最后断裂区具有韧窝特征。     

304不锈钢的单轴棘轮变形与失效行为研究

对304不锈钢在室温下进行了单轴应变控制下的应变棘轮变形与失效以及低周疲劳试验研究,系统地揭示了材料在循环过程中的材料变形与失效行为。研究表明：材料的应变棘轮变形与失效既不同于单轴拉伸,也不同于相同应变幅值下的对称应变循环加载时的变形与失效,而是强烈地依赖于应变幅值与每一循环周次在最大拉应变处的应变增加量。观察到了一些有意义的结果,     

Effects of Microstructural Evolution on Charpy Impact Properties of Modified Ferritic/Martensitic Steel after Neutron Irradiation

The effects of fast neutron irradiation have been investigated on Charpy impact properties and microstructural evolution of ferritic/martensitic (F/M) 11Cr-0.5Mo-2W, Nb, V stainless steel (PNC-FMS) which were developed by the Japan Atomic Energy Agency for core component applications in advanced fast reactors. One-half-size Charpy specimens were irradiated in the experimental fast reactor JOYO using the material irradiation rig to doses of 4.4 dpa at 773 K and 2.8 dpa at 923 K. Post irradiation Charpy impact tests and microstructural observations by transmission electron microscope were carried out. The results of the Charpy impact tests showed that there was no significant degradation in Charpy impact properties after neutron irradiation at 773 K to 4.4 dpa compared with the as-received specimens, but there was significant degradation in the properties after neutron irradiation at 923 K to 2.8 dpa. The Charpy impact property changes were attributed to matrix softening by recovery of martensite lath structures and to precipitate distributions.     

表面粗糙度对国产316LN钢低周疲劳性能的影响

表面粗糙度对材料服役过程中表面缺陷的形成有着重要影响,由于实验室一般采用光滑试样测试疲劳性能,而真实主管道经过多道工序,其表面粗糙度远大于实验室测试试样,这会给主管道的设计、使用带来风险。本文通过测试不同粗糙度316LN不锈钢的疲劳性能,分析粗糙度(分别为0.08、0.4、1.0μm)对疲劳寿命的影响。结果表明,随着粗糙度的增加,疲劳寿命会相应减少,两者在双对数坐标下呈线性关系。通过断口观察对比和裂纹萌生机理分析可知,粗糙度增加会引起应力集中,增加微裂纹的萌生速度,从而导致疲劳寿命下降。     

屏蔽厂房整环运输变形分析及控制

SC屏蔽厂房是大型筒体结构件,包含内弧板、外弧板及钢筋等构件。SC外径为47.97m,刚性较差,运输过程容易发生变形,需要在运输时进行防变形加固。本文利用有限元分析软件,对SC的变形因素进行了系统分析,本文最后给出了不同数量及分布的运输车对SC变形的影响,并分析得到了主要变形构件及有效的防变形加固措施。     

Detection Method of Fatigue Damage in Carbon Steel Using Laser Ultrasonics

Ultrasonic attenuation was measured by the laser ultrasonic technique among the carbon steel specimens which were subjected to five stages of fatigue damage by constant cyclic tensile stress amplitude. Irradiation of a Q-switched laser was used for ultrasonic generation, and a laser interferometer which consists of a frequency-doubled continuous wave laser and a Fabry-Perot etalon was used for detection of ultrasonic vibration on the specimen surface. From the comparison of the broadband ultrasonic waveforms among five stages of fatigue damage, the attenuation coefficient of the longitudinal wave by the intrinsic material attenuation increased progressively with increasing the number of fatigue cycle. Ultrasonic attenuation at 2.5, 5.0, 7.5 and 10.0MHz were also calculated by Fourier transformation in order to compare the decay of the longitudinal wave among these frequency components. From the results, ultrasonic attenuation increased as the number of fatigue cycle increased, in both broadband and narrowband frequency components. Therefore, the measurement of broadband and narrowband ultrasonic wave obtained by the laser ultrasonic technique would be effective as the detection method of fatigue damage in nuclear power plant components.