Accelerated Stress Corrosion Crack Initiation of Alloys 600 and 690 in Hydrogenated Supercritical Water

The objective of this study is to determine whether stress corrosion crack initiation of Alloys 600 and 690 occurs by the same mechanism in subcritical and supercritical water. Tensile bars of Alloys 690 and 600 were strained in constant extension rate tensile experiments in hydrogenated subcritical and supercritical water from 593 K to 723 K (320 °C to 450 °C), and the crack initiation behavior was characterized by high-resolution electron microscopy. Intergranular cracking was observed across the entire temperature range, and the morphology, structure, composition, and temperature dependence of initiated cracks in Alloy 690 were consistent between hydrogenated subcritical and supercritical water. Crack initiation of Alloy 600 followed an Arrhenius relationship and did not exhibit a discontinuity or change in slope after crossing the critical temperature. The measured activation energy was 121 ± 13 kJ/mol. Stress corrosion crack initiation in Alloy 690 was fit with a single activation energy of 92 ± 12 kJ/mol across the entire temperature range. Cracks were observed to propagate along grain boundaries adjacent to chromium-depleted metal, with Cr₂O₃ observed ahead of crack tips. All measures of the SCC behavior indicate that the mechanism for stress corrosion crack initiation of Alloy 600 and Alloy 690 is consistent between hydrogenated subcritical and supercritical water.     

Oxidation products of INCONEL alloys 600 and 690 in pressurized water reactor environments and their role in intergranular stress corrosion cracking

In this work, thermodynamic arguments for the stability of Ni and Cr compounds developed under pressurized water reactor environments ( and ) were experimentally tested. A mechanism is proposed to explain crack initiation and propagation alloy 600 along the grain boundaries, where Cr₂O₃ has formed from the leaching of Cr from the matrix, leaving behind a porous Ni-rich region. The mechanism is based on the thermodynamic potential for the transformation of a protective NiO surface layer into an amorphous nonprotective Ni(OH)₂ gel. This gel would also form along the grain boundaries and when hydrogenated steam reaches the porous Ni-rich regions. Crack initiation is then favored by tensile stressing of the grain boundary regions, which can easily rupture the gelatinous film. The leaching of matrix Cr to form nonprotective CrOOH gel at the crack tip followed by the exposure of fresh porous Ni to the environment could explain crack propagation in INCONEL alloy 600. The proposed crack initiation mechanism is not expected to occur in alloy 690 where a protective Cr₂O₃ film covers the entire metal surface. However, crack propagation along the grain boundaries in alloy 600 and precracked alloy 690 is expected to be active as hydroxide-forming reactions weaken the boundaries.     

Ti600钛合金置氢后激活能及热塑性研究

采用热模拟实验方法,研究了Ti600钛合金置氢后的热塑性性能,确定了不同含氢量及工艺参数条件下的激活能.研究结果发现,氢含量对置氢Ti600钛合金的峰值应力具有明显影响,当氢含量小于0.2%(质量分数)时,由于此时氢元素对B相的稳定起主导作用,因此随氢含量的增加,峰值应力随之降低.当氢含量大于0.2%(质量分数)时,由于此时氢元素的固溶强化起主导作用,因此随氢含量的增加,峰值应力随之增加.在相同塑性性能的条件下,提高氢含量,可以降低Ti600钛合金的变形温度.根据热模拟实验数据,得到了Ti600钛合金在不同氢含量时的激活能及相关系数,确定了置氢Ti600钛合金的Arrhenius型本构方程.     

The Effect of Temperature on the Preferential Intergranular Oxidation Susceptibility of Alloy 600

Metallurgical and Materials Transactions A - Oxidation studies were performed on solution-annealed Alloy 600 in high-temperature steam at 400 °C and in simulated pressurized water...     

GH600合金试制研讨

本文论述了在非真空状态下，要冶炼GH600的办法，通过二次试生产和不断总结经验，解决了合金锻造塑性问题，从而保证了生产GH600合金的顺利进行。     

GH648合金高温抗氧化性能的研究

GH648是一种时效硬化型镍基高温合金,主要用作航空发动机的启动机900℃以下的抗氧化承力件.在高温下,该合金不仅要有较高的强度,而且还要有较好的抗氧化性能.为此,本文探讨了GH648合金高温氧化机理并简单分析了C元素对合金抗氧化性能的影响.结果表明,GH648合金在空气中氧化时,其氧化膜主要为Cr2O3,该合金的氧化是以Cr在Cr2O3中的扩散为控制因素的;合金在低于900℃的空气中氧化时属于完全抗氧化级.随C含量的升高,合金的抗氧化性能降低.     

GH690合金热加工图及管材热挤压实验研究

采用Gleeble-3500热模拟试验机进行高温等温压缩实验,研究了GH690合金在变形温度为950～1200℃、应变速率为0.001～10.000 s-1条件下的热变形行为,利用动态材料模型构建了GH690合金热加工图,并基于加工图进行GH690合金管材热挤压实验。结果表明:GH690合金有应力峰和动态再结晶软化的特征,在ε≥0.4时,流动应力趋于稳定状态;在热加工图中变形温度为1100～1150℃、应变速率为1.0～2.5 s-1时功率耗散效率达到0.34～0.39,该区域对应的工艺参数适合于进行GH690合金管材热挤压;在热加工图中变形温度为950～1000℃,应变速率在0.94～10.00 s-1之间的区域为不稳定变形区域,热加工时应该避开这一区域。     

Grain Cluster Microstructure and Grain Boundary Character Distribution in Alloy 690

The effects of thermal-mechanical processing (TMP) on microstructure evolution during recrystallization and grain boundary character distribution (GBCD) in aged Alloy 690 were investigated by the electron backscatter diffraction (EBSD) technique and optical microscopy. The original grain boundaries of the deformed microstructure did not play an important role in the manipulation of the proportion of the Σ3 ⁿ (n = 1, 2, 3…) type boundaries. Instead, the grain cluster formed by multiple twinning starting from a single nucleus during recrystallization was the key microstructural feature affecting the GBCD. All of the grains in this kind of cluster had Σ3 ⁿ mutual misorientations regardless of whether they were adjacent. A large grain cluster containing 91 grains was found in the sample after a small-strain (5 pct) and a high-temperature (1100 °C) recrystallization anneal, and twin relationships up to the ninth generation (Σ3⁹) were found in this cluster. The ratio of cluster size over grain size (including all types of boundaries as defining individual grains) dictated the proportion of Σ3 ⁿ boundaries.     

Relative stress corrosion susceptibilities of alloys 690 and 600 in simulated boiling water reactor environments

The relative susceptibilities of alloys 600 and 690 to intergranular stress corrosion cracking (IGSCC) in pure water and a simulated resin intrusion environment at 288 °C were evaluated. A combination of creviced and noncreviced slow-strain-rate, and precracked fracture mechanics tests were employed in the evaluation. Susceptibility was determined as a function of dissolved oxygen content, degree of sensitization, and crevice condition. The results indicated that alloy 600 was susceptible to various degrees of IGSCC in oxygen containing pure water when creviced, and immune to IGSCC when uncreviced. Alloy 690 was immune to IGSCC under all pure water conditions examined. Alloy 600 and alloy 690 were both susceptible to cracking in the simulated resin intrusion environment. Alloy 690, however, exhibited the greatest resistance to SCC of the two alloys.     

Structure,chemistry, and stress corrosion cracking of grain boundaries in alloys 600 and 690

The microstructure in six commercial batches of alloys 600 and 690 has been investigated using scanning electron microscopy (SEM), analytical transmission electron microscopy (ATEM), atom probe field ion microscopy (APFIM), and secondary ion mass spectroscopy (SIMS). The materials were also tested with respect to their resistance to intergranular stress corrosion cracking (IGSCC) in high-purity water at 365 °. Applied microanalytical techniques allowed direct measurement of carbon concentration in the matrix together with determination of grain boundary micro structure and microchemistry in all material conditions. The distribution of oxygen near a crack in material tested with respect to IGSCC was also investigated. The role of carbon and chromium and intergranular precipitates on IGSCC is discussed.     

我国核电事业的发展与Inconel 690合金的研制

阐述我国核电事业发展的必要性，介绍核电蒸发器用管的情况和长钢在我国核电事业发展中的地位。     

GH600合金规模化生产实践及发展民用高温合金的体会

对长钢规模化生产高温合金GH600(UNS N06600)生产成本、周期与不锈钢生产进行了量化对比分析，显示出了规模化生产高温合金会给企业带来巨大的经济效益。从企业角度出发，提出民用高温合金发展亟待解决的三个问题，即深入的市场调研、有效的研发机制和成功的应用典范     

TC4钛合金微弧氧化膜层高温氧化性能研究

利用微弧氧化(MAO)技术在TC4钛合金表面原位制备陶瓷膜层,并通过硅酸钠水溶液对膜层进行了封孔处理。采用X射线衍射仪(XRD)分析了膜层相组成,通过扫描电子显微镜(SEM)观察了膜层表面形貌。通过粘结拉伸测试,比较了膜层在封孔前后与基体的结合强度。利用高温氧化实验,考察了TC4基体及膜层试样封孔前后的抗高温氧化性能。结果表明:微弧氧化膜层与基体间的结合强度较高,经封孔处理及高温氧化100 h后,膜基结合强度降低至4.29 MPa。与TC4基体相比,微弧氧化膜层的高温氧化增重量小,抗高温氧化性能得到了显著的提高。封孔处理提高了微弧氧化膜层的致密性,使其能更好地阻止氧透过膜层向基体内侵入,进一步提高了膜层的抗高温氧化性能。     

饮用水管件用铜合金的研究

为了解决因铋的加入引起的铜合金脆化问题，研究结果表明，通过添加元素Sn、P完全解决了因铋引起的脆化问题，并提出了配方Cu-BilSn3Zn6P0.03。     

冷变形对Inconel 690合金力学行为与组织的影响

 本文研究了Inconel 690合金在冷轧变形过程中的组织演变和形变强化规律。结果表明,在15%和20%之间存在一个临界应变εL,小于临界变形量时,加工硬化能力随着变形量的增加递减,真应力-真应变曲线可用Ludwigson模型描述,位错运动主要是单系滑移,加工硬化主要来自位错的长程应力场。临界应变到40%变形量之间,加工硬化能力随着变形量的增加又增强,真应力-真应变曲线也可用Hollomon方程描述,位错运动出现了多滑移和交滑移,加工硬化主要是位错滑移和林位错交割的短程交互作用。     

Inconel 690镍基合金平衡相的热力学计算和实验分析

采用Thermo-Calc软件研究了经1 t真空感应炉+电渣重熔工艺冶炼的典型Inconel 690镍基合金(%:0.015C、29.42Cr、9.10Fe、0.26Ti、0.16Al)的平衡相析出规律,以及合金成分对M23C6相析出行为的影响。通过扫描电镜、透射电镜、选区电子衍射和X-射线能谱法对固溶和敏化处理的Inconel 690合金的组织进行了实验分析。结果表明,Inconel 690镍基合金平衡态析出相主要为M23C6和M(CN);当固溶温度≥1000℃时,M23C6完全溶解。计算结果指出,合金中碳含量对M23C6析出量的影响最大。     

Cu—Al合金内氧化工艺的研究

对Cu-Al合金的内氧化工艺及其动力学进行了实验研究。结果表明:Cu-Al合金内氧化主要发生在初期较短的一段时间内(本实验条件下10min左右),内氧化动力学曲线具有抛物线特征。提高内氧化温度可大大缩短完成内氧化所用的时间,实际内氧化宜采用较高的温度。与Al的固溶强化相比,Al_2O_3粒子的弥散强化不仅大大提高了电导率,而且显著提高了材料的硬度。实验条件下以1223 K×0.5h内氧化工艺制备的Cu-Al_2O_3复合材料性能最佳,其中电导率可达49m/Ω·mm~2(84.5％IACS),硬度可达HRF98。     

Stress and temperature dependence of creep in Alloy 600 in primary water

The stress and temperature dependence of creep of commercial nickel-base Alloy 600 was investigated through constant load, step-load, and step-temperature creep tests in deaerated primary water containing 40 to 60 cc/kg hydrogen. To analyze creep rates for Alloy 600 in the mill-annealed (MA) condition, effective stresses were estimated using applied stresses and instantaneous strains. The apparent activation area was determined to be 7b ² by the multiple regression analysis of creep rates. The apparent activation energy for creep has a weak stress dependence and was determined to lie between 188 and 281 kJ/mole for the effective stress range of 117 to 232 MPa. Creep rates were better correlated with effective stress than applied stress and the stress exponent of Alloy 600 MA was determined to be 2.2 at 337 °C and 5.1 at 360 °C. The magnitudes of the stress exponent, activation energy, and activation area can be interpreted to support a creep mechanism controlled by dislocation-climb and nonconservative motion of jogs in commercial Alloy 600 MA. The activation area agreed with that determined from carbon in solution, implying thermally activated dislocation glide as another possible creep mechanism.