冷变形316不锈钢在高温水中的应力腐蚀开裂行为

对不同冷变形量的核级316和316L不锈钢在高温水中的应力腐蚀开裂(SCC)行为进行了研究。通过试验,对溶解氧、氯离子和温度对裂纹扩展速率的影响进行了深入探讨和分析。试验结果显示,溶解氧和氯离子能明显加快材料的应力腐蚀开裂速率。当水化学条件一致时,325℃时的裂纹扩展速率较288℃时的裂纹扩展速率高。     

注锌对316不锈钢应力腐蚀裂纹扩展速率的影响

通过使用直流电压降法测量316不锈钢在高温水中的应力腐蚀速率,研究了10、20、40μg/kg乙酸锌对316不锈钢应力腐蚀的影响。实验结果显示,回路内注入10μg/kg乙酸锌时316不锈钢的裂纹扩展速率比加氢时的裂纹扩展速率低5倍,而加入20、40μg/kg乙酸锌后316的裂纹扩展速率上升。     

焊接残余应力对316LN不锈钢应力腐蚀裂纹扩展速率的影响

核电站不锈钢管道焊接过程中引入的残余应力对焊接接头的应力腐蚀开裂性能有较大影响。本文针对一AP1000主管道316LN不锈钢焊接模拟件进行残余应力分析和应力腐蚀裂纹扩展速率测量,得到了焊后原始状态和去应力热处理状态的焊接热影响区材料在高温高压水中的应力腐蚀裂纹扩展速率。实验结果表明,焊接残余应力明显提高了热影响区的应力腐蚀裂纹扩展速率,且在含氢的压水堆一回路正常水化学下焊接残余应力的影响更加显著。     

酸性硫酸根离子介质中奥氏体不锈钢的应力腐蚀行为研究

用慢应变速率法(SSRT)研究奥氏体不锈钢316Ti和316NG在酸性硫酸根离子介质中的应力腐蚀(SCC)行为.结果表明在酸性硫酸根离子环境中,316Ti产生应力腐蚀的临界浓度比316NG的高,但316NG的裂纹扩展速率比316Ti大.用电化学阳极极化法比较了两种奥氏体不锈钢在酸性硫酸根离子介质中的抗腐蚀性能的差异,结合微观分析,探讨了SO2-4离子对奥氏体不锈钢的SSRT-SCC损伤机理.     

316LN在模拟压水堆一回路异常水化学条件下的应力腐蚀敏感性研究

采用慢应变速率拉伸试验（SSRT）法研究了氯离子(Cl^-)和溶解氧对316LN在模拟压水堆（PWR）一回路异常工况下的应力腐蚀开裂（SCC）的影响。结果表明：在饱和氧条件下,随着Cl^-浓度的增大,试样的延伸率降低,SCC敏感指数增大,当Cl^-浓度大于1 mg/L后开始萌生SCC裂纹;溶液除氧后,即使Cl^-浓度增大到10 mg/L也不会引发SCC裂纹。316LN的SCC裂纹萌生于表面的缺陷或贫Cr区,呈穿晶型向基体内扩展。     

敏化处理对316NG奥氏体不锈钢疲劳裂纹扩展行为的影响

在模拟压水堆腐蚀环境条件下,进行了未敏化与725℃敏化处理的316NG奥氏体不锈钢腐蚀疲劳实验。采用扫描电镜(SEM)、能谱分析仪(EDS)、金相显微镜(OM)分析了试样微观结构、偏析相化学成分及裂纹扩展状况,研究了材料疲劳裂纹扩展行为。研究结果表明:敏化处理可显著抑制316NG奥氏体不锈钢在腐蚀环境中的疲劳裂纹扩展;裂纹扩展速率由未经敏化处理的2.21×10~(-4) mm/次减小到敏化处理10min的1.02×10~(-4) mm/次。敏化处理试样的偏析相颗粒数量增多,萌生的支裂纹也增多,导致裂纹扩展速率减小。但是,敏化处理会导致偏析相颗粒中Cr元素含量增加,颗粒附近的基体成为贫铬区,电化学腐蚀加剧,促进裂纹的扩展。     

工质压力及蠕变对冷变形310S不锈钢在超临界水环境下的应力腐蚀开裂行为影响研究

310S不锈钢是一种性能较好的超临界水冷堆候选包壳材料,为丰富310S不锈钢在在超临界水环境下的应力腐蚀性能研究,特别是裂纹扩展速率方面的数据。本研究使用在线监测裂纹扩展的方法,测量了不同冷变形的310S不锈钢在多种工况下的裂纹扩展速率,分析了工质压力、高温蠕变等因素对310S开裂行为的作用。结果显示：超临界水或高温蒸汽的压力变化对310S不锈钢在500℃下的开裂行为的影响较为有限,冷变形作用促进材料的裂纹扩展,材料的高温蠕变行为在超临界水中对应力腐蚀开裂过程中具有较为重要的加速作用,特别是对于高冷变形和高载荷条件下的材料。本研究丰富了超临界水环境下310S的应力腐蚀裂纹扩展速率的数据,证明了提高材料的抗蠕变性能是优化包壳材料服役性能的重要手段之一,包壳设计制造的过程中应当避免较大幅度的冷变形。     

超临界水堆候选材料的腐蚀特性研究

对铁素体/马氏体(F/M)耐热钢P92、奥氏体不锈钢316L和镍基合金690在600℃、23 MPa 超临界水中的腐蚀行为进行了研究.在600℃、23 MPa的超临界水中腐蚀625 h后,690合金、316L不锈钢和P92耐热钢的腐蚀增重速率分别为0.001 02、0.060 6、0.101 27 g/(m2·h).用扫描电子显微镜(SEM)进行观察后发现,超临界环境下F/M耐热钢P92的氧化膜为3层结构,奥氏体不锈钢316L的氧化膜为单层结构,镍基合金690表面生成了一层极薄且有点蚀的氧化膜.     

X-750合金裂纹扩展速率的测量及SO_4~(2-)离子对裂纹扩展速率的影响

利用直流电压降方法(DCPD)测量X-750合金在空气中的疲劳开裂速率和高温高压水环境中的应力腐蚀裂纹扩展速率。介绍利用紧凑拉伸(CT)试样测量裂纹扩展速率的方法。基于滑移-氧化膜破裂-氧化模型,分析裂纹尖端特殊水化学环境形成的原理和过程,探讨水中溶解氧和SO42-离子在该环境形成过程中所起的作用。     

国产690合金与321不锈钢异种金属焊缝的应力腐蚀行为研究

利用慢应变速率试验,采用非标准的漏斗状试样,对国产690合金与321不锈钢异种金属焊接部位(包括690合金热影响区、焊缝、321不锈钢热影响区)在100 mg/L Cl~(-1)除O_2条件下和100 mg/L Cl~(-1)饱和O_2条件下的应力腐蚀行为进行研究。并通过慢应变速率应力-位移曲线和断口形貌对微观组织、氯离子、氧含量对于材料的应力腐蚀(SCC)的影响进行分析。结果表明:690合金热影响区在100 mg/L Cl~(-1)除O_2条件下不易发生SCC,在100 mg/L Cl~(-1)饱和O_2条件下表现出一定的SCC倾向;321不锈钢热影响区在2种条件下均表现出明显的SCC倾向;690合金热影响区的粗大晶粒不利于塑性变形的晶粒间相互协调,导致了热影响区SCC的倾向增大。     

氯和氧对304N在高温水中应力腐蚀开裂的影响

采用慢应变速率拉伸试验（SSRT）与断口形貌分析技术研究304N不锈钢（固溶退火态）在300 ℃高温水中的应力腐蚀行为与机理。结果表明：304N在300 ℃高温水中的最大抗拉强度、延伸率以及断裂吸收能随Cl^-浓度的增大显著降低;随氧浓度的急剧降低而显著增大;304N在高温水中发生应力腐蚀开裂（SCC）主要为穿晶型;随Cl^-浓度增加,304N的应力腐蚀敏感性也迅速增加,在含50 mg/L Cl^-的空气饱和高温水环境中,试样断口形貌表现为完全脆断;在溶解氧浓度急剧降低时,氯致应力腐蚀开裂的敏感性大幅降低,表明溶解氧对304N在高温水中的氯致应力腐蚀开裂具有明显的促进作用。     

FeCrAl铁素体不锈钢在压水堆水化学偏离工况下的应力腐蚀行为

采用慢应变速率拉伸（SSRT）试验方法,研究了FeCrAl铁素体不锈钢在偏离压水堆正常工况下的应力腐蚀行为。结果表明,在含有微量Cu²⁺与Cl^-的高温水介质中,应变速率为2×10^-7s^-1时,FeCrAl铁素体不锈钢将发生显著的应力腐蚀开裂;其在含Cu²⁺和Cl^-的高温水介质中的应力腐蚀开裂主要由点蚀导致。     

不锈钢堆焊层在Cl-溶液中的腐蚀性能研究

采用浸泡腐蚀试验方法,研究了不锈钢堆焊层材料在Cl^-溶液中的腐蚀情况,并通过金相显微镜、扫描电子显微镜、能谱分析观察表面形貌。研究表明,室温条件下堆焊层材料未发生任何腐蚀。在高温条件下,Cl^-的存在诱导了点腐蚀的发生,且随着Cl^-浓度的增加,点腐蚀加剧;较高浓度的Cl^-可导致缝隙内金属元素Cr的流失,缝隙腐蚀加深;应力腐蚀裂纹有沿晶开裂的特征,应力腐蚀敏感性随Cl^-浓度的增加有提高的趋势。     

316LN不锈钢在高温高压水环境下的腐蚀疲劳行为研究

在室温纯水、高温纯水及高温硼锂水环境下开展了316LN不锈钢在不同应变幅加载下的腐蚀实验研究，并获得了3种条件下的腐蚀疲劳寿命曲线。结果表明，316LN不锈钢在加载过程中出现了先硬化后软化现象，且随循环周次增加，应力峰值逐渐下降；高温纯水及高温硼锂水环境下材料的腐蚀疲劳性能下降，加速了材料的腐蚀疲劳失效；在高应变幅条件下高温的软化作用占主要影响，低应变幅条件下腐蚀作用占主要影响；试验后的样品断面上均可观察到疲劳辉纹、滑移变形带及二次裂纹，高温水腐蚀环境会加速裂纹扩展，加速疲劳失效。      

Microstructural Characterization of SCC Crack Tip and Oxide Film for SUS 316 Stainless Steel in Simulated PWR Primary Water at 320°C

Recent studies on stress corrosion cracking (SCC) behaviors of austenitic stainless steels in hydrogenated high-temperature water show that low potential SCC (LPSCC) can occur on cold-worked SUS 316 stainless steel (hereinafter, 316SS). In this study, oxide films and crack tips on cold-worked 316SS exposed to hydrogenated high-temperature water were characterized using analytical transmission electron microscopy (ATEM), grazing incidence X-ray diffraction (GIXRD) and Auger electron spectroscopy (AES) in order to study the corrosion and SCC behaviors of these films and crack tips. A double layer structure was identified for the oxide film after a constant extension rate tensile (CERT) test. The outer layer was composed of large particles (0.2–3 μm) of Fe₃O₄ and the inner layer consisted mainly of fine particles (~10 nm) of FeCr₂O₄. In addition, nickel enrichment was identified at the metal/oxide interface. Particles of Fe₃O₄ were also identified on the crack walls. These results indicate that the same electrochemical reactions had occurred inside and outside the crack. The crack tip area was filled with corrosion products of a chromium-rich oxide. In addition, nickel enrichment was observed at the crack tip. The formation of the nickel-enriched phase indicates that a selective dissolution reaction of iron and chromium occurred at the front of the LPSCC crack.     

Stress corrosion cracking susceptibility of austenitic stainless steels in supercritical water conditions

The presented paper summarizes the results of general corrosion and stress corrosion cracking (SCC) susceptibility tests in supercritical water (SCW), studied for austenitic stainless steel 316L, with the aim to identify maximum SCW temperature usability and specific failure mechanisms prevailing during slow strain-rate tensile (SSRT) tests in ultra-pure demineralized SCW solution with controlled oxygen content. The general corrosion tests clearly revealed the applicability of austenitic stainless steel in SCW to be limited to 550 °C as maximum temperature as oxidation rates of austenitic stainless steels 316L increase dramatically above 550 °C. The SSRT tests were performed using a step-motor controlled loading device in an autoclave at 550 °C SCW. Besides the strain rate (resp. crosshead speed), the oxygen content was varied in the series of tests. The obtained results showed that even at the lowest strain rate, a serious increase of SCC susceptibility, as typically characterized by IGSCC crack growth, was not observed. The fractography confirmed that failure was due to a combination of transgranular SCC and transgranular ductile fracture. Based on fractographic findings a phenomenological map describing the SCC regime of SSRT test parameters could be proposed for AISI 316L.     

Determining factors for anodic polarization curves of typical structural materials of boiling water reactors in high temperature – high purity water

In order to examine the anodic polarization characteristics of typical structural materials of boiling water reactors (BWRs), the anodic polarization curves of type 316L stainless steel (316L SS) and Alloy 182 were measured in deaerated high purity water at 553 K using the previously reported measurement method which was confirmed suitable for high temperature – high purity water. In order to specify which constituent element determines the dissolution characteristics of these materials, the anodic polarization curves of pure iron, pure nickel, and pure chromium were also surveyed. The anodic polarization curve of 316L SS was determined to have active, passive, and transpassive states which were the same as type 304 SS (304 SS) showed. But, Alloy 182 had different polarization characteristics especially near the corrosion potential as it had no active state. From comparison results of the polarization characteristics of these materials and their constituent elements, the corrosion characteristics of these materials were concluded to be mainly determined by the corrosion characteristics of chromium.