高温再热器SA-213TP347H钢管爆管原因分析

通过宏观分析、硬度测量、显微组织观察和扫描电镜与能谱成分分析,对某电厂2号炉高温再热器SA213-TP347H钢管进行爆管原因分析。试验结果表明,爆口管件的化学成分、硬度和拉伸性能符合ASTM A213/A213M对SA213-TP347H钢的规定,爆口处的显微组织为奥氏体,晶界处存在含Fe、Cr、Nb的析出物。对备件管样弯头进行了试验分析,硬度试验表明其弯头处的洛氏硬度超出GB 5310-2008对SA-213TP347H钢的规定;显微组织观察表明弯头处存在较多滑移线,对其进行扫描电镜观察和能谱分析,存在含有S等非金属元素的夹杂。综上所述,爆管原因属材料弯管在生产中未进行固溶处理,晶界上出现含Cr析出物,形成贫Cr区导致晶界弱化,导致晶间应力腐蚀而爆管。     

深度调峰机组TP347H高温过热器管的超温老化

在某630 MW超临界机组深度调峰运行中，TP347H高温过热器管发生局部超温，对机组运行产生严重影响。采用显微组织观察和室温拉伸性能测试，结合温度及应力分布的有限元数值模拟，开展了正常运行与超温运行下TP347H高温过热器管的老化评估。结果表明：深度调峰情况下的传热恶化可能造成过热器管超温，管壁最大热应力甚至可能超过TP347H钢管的屈服强度。TP347H高温过热器管频繁超温和高的热应力作用导致服役态TP347H钢管中析出更多的MX和M₂₃C₆第二相，尤其是M₂₃C₆相颗粒在奥氏体晶界的聚集长大，加剧组织老化。在拉伸过程中，裂纹首先在超温运行管样的奥氏体晶界萌生与扩展，再发生穿晶断裂，奥氏体晶界、晶内存在严重的不均匀变形，从而导致其室温拉伸性能，特别是塑性，显著降低。     

600MW超临界锅炉TP347H高温过热器管爆管的显微分析

对爆管相关资料和数据进行了调查。借助微机控制电子万能实验机、金相显微镜、扫描电镜及能谱仪等仪器设备,从爆管管样、未胀粗管管样和备用管样的拉伸性能、显微组织、晶粒度、第二相等方面对TP347H高温过热器管的爆管原因进行了分析。结果表明:TP347H高过管爆管为高温蠕变失效。TP347H奥氏体不锈钢在长期高温运行过程中于晶界处析出了σ相,且细小的晶粒度促进了σ相在晶界的析出。σ相的析出和大量存在,导致了蠕变孔洞的出现,使得TP347H高过管材质快速老化,导致高温蠕变强度下降,直至爆管。     

600MW超临界锅炉TP347H高温过热器管爆管的显微分析

对爆管相关资料和数据进行了调查。借助微机控制电子万能实验机、金相显微镜、扫描电镜及能谱仪等仪器设备,从爆管管样、未胀粗管管样和备用管样的拉伸性能、显微组织、晶粒度、第二相等方面对TP347H高温过热器管的爆管原因进行了分析。结果表明:TP347H高过管爆管为高温蠕变失效。TP347H奥氏体不锈钢在长期高温运行过程中于晶界处析出了σ相,且细小的晶粒度促进了σ相在晶界的析出。σ相的析出和大量存在,导致了蠕变孔洞的出现,使得TP347H高过管材质快速老化,导致高温蠕变强度下降,直至爆管。     

电站用SA-213TP347HFG钢的焊接工艺研究与应用

针对目前高参数、大容量、高效率机组的快速发展,分析了过热器、再热器等用钢SA-213TP347HFG的焊接性;提出了此类新型细晶粒奥氏体耐热钢焊接时的主要技术难点及解决思路。通过试验研究分析得到合适的焊接工艺,并简述了现场SA-213TP347HFG钢的焊接操作要点,为超临界、超超临界机组中此类钢的焊接提供了参考。     

高温服役后TP347HFG钢的组织与性能

利用金相显微镜、SEM、EDS和万能试验机分析了过热器管TP347HFG钢高温运行1.2×10⁴ h和7.5×10⁴ h后的组织与性能。结果表明,高温服役1.2×10⁴ h和7.5×10⁴ h后,TP347HFG钢仍保持明显的孪晶特征,析出的NbC有利于保持材料的组织稳定性。TP347HFG钢高温服役后力学性能能够保持稳定,随服役时间增加,强度增加而塑性变化不大。     

600MW超临界机组SA-213TP347H高温再热器频繁爆管原因探究

通过宏观检查、化学成分、力学性能、显微组织及扫描电镜与能谱分析,结合设计、制造、安装等阶段存在的隐患分析,深入研究了某电厂SA213-TP347H高温再热器管频繁爆管原因。结果表明:高温再热器管子在弯管处存在不同程度的机械损伤缺陷。爆管管样化学成分、硬度、拉伸性能符合ASTM A213/A213M的规定;爆口处显微组织为奥氏体,晶界处存在含Cr和Nb成分析出物。备品备件硬度偏高,显微组织有明显的孪晶和较多滑移线,加速了敏化,晶界急剧贫Cr化。综上分析,高再频繁爆管的原因既有设计上的因素,也有制造质量的影响,而弯管未进行固溶处理,加速了贫Cr区的形成从而导致晶界抗腐蚀性能降低,导致晶间腐蚀所引起。     

TP347HFG管子冷弯后固溶热处理工艺分析

通过对冷弯弯头受力及应变的分析,参考国内外不同标准对于奥氏体钢管冷弯后固溶工艺的要求,结合实际生产中TP347HFG钢管冷弯后的性能变化,对TP347HFG材料钢管冷弯后固溶工艺提出了建议,为TP347HFG材料在超临界及超超临界机组上的推广应用提供参考.     

600MW机组锅炉末级过热器爆管原因分析

针对某电厂2210 t/h锅炉末级过热器TP347H奥氏体不锈钢爆管试样进行爆口宏观检验、材质成分分析和金相组织检验。综合测试分析认为,在短时超温运行后,晶界析出大量碳化物,使晶界附近形成贫铬区,晶界严重弱化;管外壁的浅表折叠形成残余应力和粗大晶粒形成了应力集中脆性区域。在高温运行工况下,内壁的晶间腐蚀,外壁应力集中脆性区域承载能力的下降和残余应力三者共同作用下,其韧性、强度和有效承载截面逐步减小,最终在介质内压周向应力作用下导致断裂。     

高温再热器SA-213TP347H钢管裂纹原因分析

通过结构分析、断口检查、硬度测试、抗拉试验、显微组织观察及能谱分析,对电厂高温再热器SA-213TP347H钢管进行裂纹原因分析。结果表明:高温再热器在运行中容易晃动,裂纹处于管夹挤压的凹坑;裂纹处管材的拉伸性能、硬度均符合ASME A213/A213M对SA-213TP347H钢的要求;显微组织为奥氏体和沿晶界分布的含Cr碳化物,裂纹是沿晶裂纹,由管外壁向管内扩展;裂纹处腐蚀产物均含有O、S等非金属元素。分析表明:产生裂纹的原因是由于管夹挤压管道,同时管道结构易晃动,增加了挤压变形处的应力,促进了含Cr碳化物沿晶界析出,形成贫Cr区而导致晶界弱化,并在腐蚀性介质的作用下,导致晶间应力腐蚀开裂。     

Correlation Between Microstructure and Corrosion Behavior of Two 90Cu10Ni Alloy Tubes

Two kinds of 90Cu10 Ni tubes with different service lives(more than 3 years and only 1 year,respectively)under identical working conditions were studied by an immersion test in a 3.5 wt% NaCl solution and the electron backscattered diffraction(EBSD) technique.The morphology after immersion showed severer corrosion attack at the grain boundaries of the tube with shorter service life compared with the tube with longer service life.The grain boundary characterization distributions(GBCDs) of the two tubes obtained by EBSD revealed more Σ3 boundaries and twins,and larger random boundary meshes in the tube with longer service life.A short immersion test in a modified Livingston's solution was conducted to evaluate the tendency to corrosion attack of different types of the grain boundaries.SEM and AFM were used to characterize the corrosion morphologies of the boundaries.A strong correlation between varying depths of corrosion grooves and types of the grain boundaries was obtained.The influence of deviation angle of low Σ boundaries on corrosion resistance of the grain boundaries was also discussed.It is concluded that a special ‘‘grain boundary engineering'(GBE) treatment has been performed on the tube with longer service life.It is proposed that the optimized GBCD is responsible for the better service performance of the tube.     

海水腐蚀导致铜镍合金的沿晶析出

半硬态B_(Fe30-1-1)铜镍合金管材在实海暴露过程中随着表面氧化膜的腐蚀脱落,在晶界上出现沿晶析出物,形成较大的沿晶腐蚀倾向。TEM观察表明,这种析出物是调幅分解(Spinodaldecomposition)的产物,其衍衬象为明暗相间的条纹,调幅波长小于50nm。该析出物使材料在拉伸时出现脆性沿晶断口,强度略有上升,但大大恶化了材料的耐海水腐蚀性能。文中根据试验结果阐明了析出物的生成动力,认为是海水腐蚀导致材料的应力状态改变(即应变诱生)及合金元素沿晶界向表层的扩散促使已形核的析出物粗化所致。     

固溶时效处理对Mg-4Sm-3Gd-0.5Zr合金显微组织和耐蚀性能的影响

利用光学显微镜、X射线衍射仪和扫描电镜等方法研究了固溶时效处理前后Mg-4Sm-3Gd-0.5Zr合金(质量分数,%)的显微组织、物相组成和腐蚀形貌,并在质量分数为3.5%的NaCl溶液中进行了静态失重和电化学测试。结果表明,铸态Mg-4Sm-3Gd-0.5Zr合金由α-Mg基体和沿晶界分布的粗大网状共晶相Mg₄₁Sm₅和Mg₅Gd组成,固溶时效处理并没有改变共晶相的种类,但网状共晶组织消失,并且晶内有大量细小弥散的第二相析出,晶界更加清晰。试验合金采用525 ℃×8 h固溶+225 ℃×8 h时效处理后,腐蚀速率从0.185 mg·cm^-2·h^-1降低至到0.116 mg·cm^-2·h^-1,自腐蚀电流密度从1.599×10^-4A·cm^-2降低到0.924×10^-4 A·cm^-2,耐蚀性能明显提高。     

INTERGRANULAR CORROSION AND PHOSPHOR SEGREGATION AT GRAIN BOUNDAR1FS OF NON-SENSITIZED SUPERPURE AUSTENITIC STAINLESS STEEL 00Cr25Ni22Mo2N

The corrosion behaviour and mechanism of superpure austenitic stainless steel00Cr25Ni22Mo2N in urea processing environment was studied using metallography,SEM,TEM,SIMS and AES techniques.The results show that the gas extraction tube made ofnon-sensitized 00Cr25Ni22Mo2N steel suffered intergranular corrosion.Corrosive mediapenetrated not only into the tube wall through grain boundaries but also expanded from theboundary towards the interior of the grain.Neither depletion of Cr nor precipitates were foundat the grain boundaries.However,P(and Si)was segregated at the grain boundaries to a greatextent.Semiquantitative calculation indicates that the P content at the grain boundaries isabout 25 wt-%,three orders of magnitude higher than the content within the grain.Sugges-tion is made that the potential difference between the grain and its boundary due to the segre-gation results in the observed intergranular corrosion.     

时效制度对含钪超高强铝合金晶间腐蚀和剥落腐蚀的影响

通过晶间腐蚀、剥落腐蚀和电化学腐蚀试验,结合扫描电镜和透射电镜等分析手段,研究了含钪Al-Mg-Zn-Cu-Zr合金在不同时效状态下的的晶间腐蚀和剥落腐蚀行为。结果表明,合金抗晶间腐蚀和剥落腐蚀能力随着时效时间的延长而提高,在4.0mol/L NaCl+0.1mol/L HNO3+0.4mol/L KNO3(EXCO)溶液中测试的极化曲线也表现出相同的趋势。透射电镜观察表明,晶界析出相和晶界无沉淀析出带(PFZ)是影响合金腐蚀性能的主要因素。随着时效时间的延长,非平衡相η′和S′相逐渐向平衡相η和S相转变,晶界析出相粗化并呈链状分布,PFZ变宽。晶界粗大平衡相的不均匀分布和PFZ阻断了腐蚀的阳极通道,使合金的腐蚀敏感性降低。     

晶界对低压电解电容器铝箔腐蚀结构的影响

采用扫描电子显微镜和背散射电子取向成像技术分析研究了低压电解电容器用阳极铝箔的腐蚀结构、晶粒尺寸和晶界分布对比电容的影响及相关机理.结果表明,在铝箔的晶界附近,尤其是大角度晶界附近容易出现尺寸较大的腐蚀孔坑或沟道,造成腐蚀结构的不均匀性并降低比电容.该晶界优先腐蚀的现象起因于晶界的高缺陷密度和与之相应的腐蚀电流密度的局部集中.增加晶界密度可以降低杂质原子偏聚程度和电流密度分布的不均匀性,因此在一些特定的电化学腐蚀条件下可以借助减小晶粒尺寸的方式提高比电容.     

Effect of Microstructure on Corrosion Behavior of Mg–Sr Alloy in Hank's Solution

Mg–Sr alloy has been studied as a potential biodegradable material with excellent bioactivity to promote the bone formation. However, its degradation behavior needs to be well controlled to avoid the negative effect, which is important for future application. Therefore in this study, the microstructure and its effect on corrosion behavior of an Mg–1.5 Sr alloy were investigated. The microstructures of the alloy under different processing procedures were characterized by both optical and scanning electron microscopes. The corrosion performance was studied in Hank's solution using immersion,potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) tests. The results showed that the grain size and the amount and distribution of b-Mg_(17)Sr_2 had obvious effects on the corrosion behavior of Mg–Sr alloy. The smaller the grain size was, the more the protective surface layer formed on Mg–Sr alloy, and the higher the corrosion resistance was. For the as-cast Mg–Sr alloy, the network-like second phases precipitated along the grain boundaries could not hinder the corrosion due to their own corrosion cracking accelerating the intergranular corrosion. However, the refinement of second phases increased the corrosion resistance of the as-extruded alloy. After solution treatment at 450 °C for 5 h, the grains in the alloy did not grow much and b-Mg_(17)Sr_2 phases homogenously distributed in the alloy, resulting in the increase in corrosion resistance. However, after aging treatment, large amount of precipitated second phases increased the galvanic corrosion of the alloy, accelerating the development of corrosion.     

法兰开裂原因分析

不锈钢法兰安装到发动机上后在宁波停放5年,检查发现多件法兰表面均存在多条径向裂纹。通过对裂纹及断口形貌观察、金相分析、材料成分检测,分析法兰的断裂原因。结果表明,法兰的开裂模式为应力腐蚀,发生应力腐蚀的原因是由于法兰所用材料牌号与设计要求不符合,用1Cr17Ni7材料代替了304不锈钢,而1Cr17Ni7材料的耐腐蚀及晶间腐蚀性能均比304不锈钢差,同时1Cr17Ni7材料组织存在沿晶分布的网状碳化物,导致其耐晶界腐蚀能力进一步下降。     

Effects of Modified Inclusions and Precipitates Alloyed by Rare Earth Element on Corrosion and Impact Properties in Low Alloy Steel

This study has focused on the morphology and distribution of inclusions and precipitates modified by rare earth (RE) elements, which has a decisive influence on microstructure, corrosion properties and impact behaviors in Q355 low alloy steel. Characterized by the method of electrolytic extraction and ASPEX-scanning electron microscopy (ASPEX-SEM), small-sized spherical RE inclusions have been modified to replace elongated MnS and large-sized Al₂O₃. Q355RE steel after RE alloying has lower corrosion rate and higher value of α/γ, due to the formation of stable and dense rust layers. Q355RE steel also exhibits better resistance to fracture at low temperature, owing to the presence of RE modification to inclusions and its effects on reducing crack initiation and propagation. Nano-scale RE precipitates containing sulfur and phosphorus is observed along grain boundaries by transmission electron microscopy (TEM). The purification of grain boundaries by RE is beneficial to the improvement of corrosion and impact properties.