核电主管道铸造不锈钢的热老化脆化

为了研究中国核电主管道铸造不锈钢Z3CN20-09M的热老化,在300、350和400℃下,对Z3CN20-09M进行了长达30000h的加速热老化实验.对不同热老化时间下的样品进行了冲击性能和铁素体纳米硬度测定.以夏比冲击功作为热老化脆化参量,利用拟合的方法得出该材料的热老化激活能为51.962kJ·mol-1.通过热老化因子P得出了用夏比冲击功表示的热老化脆化动力学公式.利用热老化激活能和热老化动力学公式预测了Z3CN20-09M在实际运行温度下服役40a内的夏比冲击功和铁素体显微硬度变化.预测结果表明在运行5a内是该材料韧性迅速下降的时期,随后的运行过程中下降过程趋缓.      

长期热老化后核电站主管道材料的力学行为

大型压水堆核电站主管道多采用综合性能优良的铸造奥氏体不锈钢,但该材料在中温下长期服役会发生热老化脆化现象。总结了国内外的最新研究成果,主要综述了长期热老化过程中主管道材料的相变规律及其影响因素,以及长期热老化后材料的纳米硬度、拉伸、冲击和疲劳行为。     

X100级管线钢CO_2气体保护焊接试验研究

通过拉伸、冲击、硬度、焊后热处理等试验方法,研究了不同焊接热输入量对CO_2气体保护焊接条件下X100级管线钢焊接接头力学性能和显微组织的影响。结果表明:随着焊接热输入量增加,显微组织逐渐粗化;当焊接热输入量为1.91 kJ/mm时,焊缝中粒状贝氏体数量增多,针状铁素体数量减少,晶粒和M-A组元尺寸明显粗化,焊接接头的强韧性、硬度均下降;当焊接热输入量为1.17 kJ/mm时,其焊接接头能获得最佳的力学性能和显微组织。经过焊后热处理,距离焊缝2~4 mm处HAZ的HV10硬度为230~240,下降明显,焊缝硬度波动变小,距离焊缝4~6 mm处的HAZ和母材硬度变化不大。     

316LN高氮超低碳奥氏体不锈钢的热变形行为和组织演变

试验的316LN钢（/%:0.011C,0.49Si,1.52Mn,0.016P,0.001S,16.65Cr,13.43Ni,2.18Mo,0.153N）为7.2 t铸锭初轧开坯并锻造成的Φ180 mm圆钢。利用Gleeble-3800热模拟试验机研究了316LN钢在应变速率0.1~50 s^-1、1050~1200℃时的热变形行为和组织演变规律,并通过线性回归分析建立了316LN钢的本构方程。结果表明,变形温度升高有利于动态再结晶的形核,并在热变形过程中促进动态再结晶扩展;热变形过程材料常数α为0.0061,应力指数n为5.5436,表观激活能550.512 kJ/mol,动态再结晶晶粒数量随着变形温度的增加而增多,到1 200℃变形时发生了完全的动态再结晶。     

核岛用P280GH碳锰钢热老化的组织和性能

 P280GH碳锰钢用于制造压水堆核电站核岛蒸汽系统和辅助系统管道,其在280～350 ℃的长时服役过程中易于出现老化现象。为了研究其热老化机理,在400 ℃温度下进行了P280GH碳锰钢的10 000 h的加速热老化试验。测定了不同老化时间下铁素体和珠光体的显微硬度、试样拉伸性能和冲击性能。结果表明,铁素体和珠光体的显微硬度随老化时间的增长而逐渐减小;老化时间少于300 h时,拉伸强度和屈服强度随老化时间增长而增加,老化时间大于300 h后,抗拉强度逐步降低,屈服强度缓慢降低;冲击吸收功随老化时间的增加而减小。上述力学性能变化与热老化过程中的珠光体形貌变化及铁素体中的位错移动有关。     

AP1000主管道冷弯壁厚减薄

提出了一种改进的Johnson-Cook模型,用于室温和低应变速率下AP1000核电站主管道316LN奥氏体不锈钢的塑性变形过程研究.借助有限元软件ANSYS/LS-DYNA,对AP1000核电一回路主管道热段管冷弯成形过程进行模拟仿真,分析管道壁厚、相对弯曲半径、摩擦系数等工艺参数对壁厚减薄率的影响规律,拟合出壁厚减薄率的经验公式.全尺寸主管道冷弯试验结果表明,数值模拟结果准确可靠.      

动态力学法研究热氧老化对含钆有机玻璃性能的影响

对含钆有机玻璃在180℃条件下进行热氧老化实验,老化时间分别为0.25,0.50,1.00,2.00,3.00,5.00,7.00 d,老化前后的试样采用动态热机械分析仪(DMTA)、悬臂梁冲击试验仪和电动塑料洛氏硬度计进行测试,研究其储能模量、损耗模量、玻璃化转变温度、冲击强度和洛氏硬度的变化规律,同时根据储能柔量的垂直位移因子确定临界失效时间来推算含钆有机玻璃在25℃时的使用寿命。研究结果表明,随着热氧老化时间的延长,含钆有机玻璃的储能模量、玻璃化转变温度和洛氏硬度随热氧老化延长而增大,损耗模量和冲击强度随热氧老化时间增加而减小;根据含钆有机玻璃储能柔量的垂直位移因子确定了临界失效时间为10.56 h;利用从动态力学性能得到的寿命方程计算得到含钆有机玻璃在25℃下的使用寿命约为26.55年。     

ITER TF导体铠甲316LN不锈钢管的力学性能

 以ITER TF316LN奥氏体不锈钢无缝管为研究对象,研究了焊接、8%冷变形和650℃、200h的老化处理对316LN不锈钢管性能的影响。分别取母材、焊接接头、经过冷变形和老化处理的焊接接头进行了室温和液氦温度42K下的拉伸和冲击性能的研究,并利用扫描电镜对拉伸和冲击断口的微观形貌进行了观察。结果表明,母材、焊接接头和经过冷变形和老化处理的焊接接头在42K的断后伸长率和冲击韧性依次降低,经过冷变形和老化处理的焊接接头相比母材和未经过任何处理的焊接接头的抗拉强度和屈服强度均高出50~60MPa。42K下,母材的断后伸长率由室温下的48%下降到44%,相反的,焊接接头和经过变形和老化处理的焊接接头的断后伸长率却分别由37%和23%上升到了41%和38%;3种样品在42K下的抗拉强度和屈服强度均是室温下的2~3倍。     

合金元素对316LN不锈钢的力学性能和点蚀性能的影响

研究了N、Cr、Mo和Ni四种合金元素含量的变化对核电主管道用固溶态316LN不锈钢的晶粒尺寸以及常规力学性能和点蚀性能的影响.随着N含量的升高,316LN的晶粒明显细化,其在固溶处理过程中晶粒长大趋势也减小.N含量的升高可改善316LN的力学性能和耐点蚀性能,但是当N质量分数达到0.20%时,其耐点蚀性能又开始变差.晶粒细化对316LN强度的影响远小于N含量对316LN强度的影响.Cr及Ni含量对316LN的晶粒尺寸及抗拉强度、屈服强度等力学性能影响不大;Cr含量增加可轻微改善316LN的抗点蚀能力,Ni元素对316LN的耐点蚀性能影响不大,但可增大钝态的腐蚀速度从而不利于钝化膜的稳定.随Mo含量增加,316LN的晶粒尺寸略有减小,强度增大,延伸率显著降低,耐点蚀能力改善.      

不锈钢316LN中厚板超低温冲击功偏低原因分析及优化建议

利用金相、扫描电镜能谱分析和电子背散射衍射(EBSD)等分析手段对试验用钢316 LN超低温冲击功偏低的原因进行了分析.结果表明,试验用钢316 LN中心层析出的块状σ脆性相是低温冲击功偏低的主要原因.通过Thermo-calc相图理论分析计算,钢板中心层的σ脆性相是铸坯心部高温δ铁素体在后续的变形,及热处理过程中700～950℃停留较长时间析出的.采用合适的热加工工艺可避免高温δ铁素体及σ相的析出,从而提高材料超低温冲击韧性.     

基于应变设计用厚规格X80管线钢组织与性能关系

 针对西气东输三线在强震和断层活跃地区对基于应变设计的抗大变形1219mm×26.4mm X80钢管的迫切需求,通过光学金相、SEM、拉伸和冲击试验研究了抗大变形“铁素体+贝氏体”双相钢的铁素体体积分数、晶粒尺寸对钢板/管的纵向屈服强度、均匀变形伸长率、冲击韧性的影响规律,总结了小批量生产中板管关系的变化特点。发现1219mm×26.4mm X80抗大变形钢管在较大的铁素体体积分数变化范围内可实现技术指标的要求,但较高的铁素体数量不利于钢管的冲击韧性,铁素体体积分数不宜过大;铁素体晶粒细化对提高钢管的强度和改善钢管的断裂韧性十分关键,多边形铁素体细化是十分必要的。     

Influence of high-temperature exposure on the microstructure and mechanical properties of dissimilar metal welds between modified 9Cr-1Mo steel and alloy 800

Transition joints between ferritic steel and austenitic stainless steel are commonly encountered in high-temperature components of power plants. Service failures in these are known to occur as a result, mainly, of thermal stresses due to expansion coefficient differentials. In order to mitigate the problem, a trimetallic configuration involving an intermediate piece of a material such as Alloy 800 between the ferritic and austenitic steels has been suggested. In our work, modified 9Cr-1Mo steel and 316LN stainless steel are used as the ferritic and austenitic components and the thermal behavior of the joints between modified 9Cr-1Mo steel and Alloy 800 is described in this article. The joints, made using the nickel-base filler material INCONEL 82/182 (INCONEL 82 for the root pass by gas-tungsten arc welding and INCONEL 182 for the filler passes by shielded-metal arc welding), were aged at 625 °C for periods up to 5000 hours. The microstructural changes occurring in the weld metal as well as at the interfaces with the two parent materials are characterized in detail. Results of across-the-weld hardness surveys and cross-weld tension tests and weld metal Charpy impact tests are correlated with the structural changes observed. Principally, the results show that (1) the tendency for carbon to diffuse from the ferritic steel into the weld metal is much less pronounced than when 2.25Cr-1Mo steel is used as the ferritic part; and (2) intermetallic precipitation occurs in the weld metal for aging durations longer than 2000 hours, but the weld metal toughness still remains adequate in terms of the relevant specification.     

Effect of Arc Welding Processes on the Weld Attributes of Type 316LN Stainless Steel Weld joint

The present study aims at understanding the effect of various arc welding processes on the evolution of microstructure, mechanical properties, residual stresses and distortion in 9 mm thick type 316LN austenitic stainless steel weld joints. Weld joints of type 316LN stainless steel were fabricated by three different arc welding processes which were commonly employed in the nuclear industry. All the weld joints passed radiographic examination. Microstructural characterization was done using optical and scanning electron microscope. Volume fraction of δ-ferrite was lowest in the A-TIG weld joint. The A-TIG welded joint exhibited adequate strength and maximum impact toughness values in comparison to that of weld joints made by SMAW and FCAW processes. The A-TIG weld joint was found to exhibit lowest residual stresses and distortion compared to that of other welding processes. This was attributed to lower weld metal volume and hence reduced shrinkage in the A-TIG weld joint compared to that of weld joints made by FCAW and SMAW processes which involved v-groove with filler metal addition. Therefore, type 316LN stainless steel A-TIG weld joint consisting of lower δ-ferrite, adequate strength, high impact toughness, lower residual stresses and distortion was suited better for elevated temperature service compared to that of SMAW and FCAW weld joints.     

The influence of post weld heat treatments on the structure,composition and the amount of ferrite in type 316 stainless steel welds

Microstructures of welds of AISI type 316 stainless steel have been examined with a view to establishing the changes that occur during postweld heat treatments in the temperature range 900 to 1100°C. The ferrite content of the weld zone has been estimated using a point count technique in the as-welded condition as well as after heat treatments. In addition, the compositional changes occurring in the ferrite phase have been determined using an electron microprobe analyzer. The ferrite content of the weld decreases continuously with an increase in the aging time. At the same time, the morphology of the ferrite changes from a dendritic network into a distribution of isolated near spherical particles. An analysis of the kinetics of the dissolution and the spheroidization of ferrite suggests that both these processes are controlled by interface diffusion; activation energies for these processes are 132 and 140.5 kJ/mol respectively. The influence of the heat treatment variables on the morphology and composition of the ferrite phase have been discussed.     

QT400-18L球墨铸铁的低温冲击断裂行为

在室温和低温下对QT400-18L球墨铸铁件进行Charpy冲击试验,采用金相显微镜、扫描电镜对冲击断口形貌进行分析,利用透射电镜对断口附近位错密度进行观察分析,探讨了球墨铸铁低温冲击断裂的机制。结果表明:温度对冲击韧性影响较大,随试验温度的降低,冲击吸收的能量显著减小。观察发现,低温冲击断口表现出两种不同的解理断裂刻面:"连续型"和"不连续型"河流形貌。球墨铸铁中裂纹优先在石墨与铁素体基体界面形成,其次在碳化物与基体界面形成。在低温冲击载荷作用下,活动位错源数量少,发生解理断裂。     

Adaptive Neuro-Fuzzy Inference System (ANFIS)-Based Models for Predicting the Weld Bead Width and Depth of Penetration from the Infrared Thermal Image of the Weld Pool

Type 316 LN stainless steel is the major structural material used in the construction of nuclear reactors. Activated flux tungsten inert gas (A-TIG) welding has been developed to increase the depth of penetration because the depth of penetration achievable in single-pass TIG welding is limited. Real-time monitoring and control of weld processes is gaining importance because of the requirement of remoter welding process technologies. Hence, it is essential to develop computational methodologies based on an adaptive neuro fuzzy inference system (ANFIS) or artificial neural network (ANN) for predicting and controlling the depth of penetration and weld bead width during A-TIG welding of type 316 LN stainless steel. In the current work, A-TIG welding experiments have been carried out on 6-mm-thick plates of 316 LN stainless steel by varying the welding current. During welding, infrared (IR) thermal images of the weld pool have been acquired in real time, and the features have been extracted from the IR thermal images of the weld pool. The welding current values, along with the extracted features such as length, width of the hot spot, thermal area determined from the Gaussian fit, and thermal bead width computed from the first derivative curve were used as inputs, whereas the measured depth of penetration and weld bead width were used as output of the respective models. Accurate ANFIS models have been developed for predicting the depth of penetration and the weld bead width during TIG welding of 6-mm-thick 316 LN stainless steel plates. A good correlation between the measured and predicted values of weld bead width and depth of penetration were observed in the developed models. The performance of the ANFIS models are compared with that of the ANN models.     

Intergranular stress corrosion cracking behavior of types 308 and 316 stainless steel weld metals in a simulated boiling water reactor environment

The sensitization behavior of types 308 and 316 stainless steel weld metals as internal overlays for reactor pressure vessels (RPVs) was studied with respect to the effects of postweld heat treatment (PWHT) at about 600 °C during RPV fabrication and low-temperature aging during operation. For the study, a criterion for the rate of intergranular corrosion (IGC) for detecting the susceptibility to intergranular stress corrosion cracking (IGSCC) in high-temperature oxygenated pure water was established by quantitatively evaluating the results from a modified ASTM A262E test. A criterion for expecting satisfactory resistance to IGSCC was found to be an IGC rate of about 1 μm/h. Type 308 weld metal can be sensitized as indicated by an IGC rate >1 μm/h, and can be healed, as indicated by an IGC rate <1 μm/h, depending on the length of PWHT. However, this healed weld metal can be resensitized by exposing it to 500 °C×24 h; in this condition, it shows a relatively high susceptibility to IGSCC. On the contrary, type 316 weld metal was almost immune to sensitization under the same heat treatments. By transmission electron microscopy (TEM), its excellent resistance was attributable to carbon fixation by molybdenum carbide precipitation within ferrite phases during PWHT. Reheat embrittlement of type 316 weld metal was also examined.