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1.
将断裂力学原理应用到炉管寿命预测中。利用MTS810试验机,对服役3万h的炉管和未服役炉管的断裂韧性进行了试验分析,并利用扫描电镜进行了断口的形貌分析。研究结果表明:服役后炉管的断裂韧性与未服役炉管相比显著下降,抵抗裂纹扩展能力减弱;服役后的炉管断裂面没有裂纹稳态扩展区和宏观塑形变形,对应于断裂韧性的下降,断裂面微观形貌呈典型的脆性断裂特征。  相似文献   

2.
某石化公司制氢转化炉炉管在运行不到40 000 h后突然破裂起火,在经过宏观检测、表面探伤、力学性能测试,能谱、金相、电镜、X射线、应力等分析后得出结论:由于炉管材料晶界碳化物过多以及疏松空洞的存在削弱了韧性,产生了较多的微观裂纹,加上管外保温材料中存在较多的Na 、Cl-、K 、Mg2 、Ca2 ,便在下猪尾管到下支耳之间的应力较大部位,发生应力腐蚀开裂,58号炉管首先开裂泄漏起火,其它炉管在外部火焰烘烤下短时高温损伤,并变形鼓包直至开裂,这是失效的主要原因和过程.针对失效原因提出了今后使用过程中应采取的防护措施.  相似文献   

3.
通过宏观观察、硬度测试、金相分析、常温和高温拉伸试验、冲击试验和扫描电镜等方法,对高温服役后的Cr9Mo炉管进行性能测试,并分析弯曲原因.结果表明:炉管金相组织明显球化;常温下的伸长率,硬度和冲击性能有所下降,高温下的屈服强度和抗拉强度均比规范值低;热应力导致炉管弯曲.  相似文献   

4.
对水韧状态及硬化状态的ZGMn13钢进行了系列冲击试验,结果表明:高锰钢冲击韧性随试验温度下降而降低,有明显的低温脆性。高锰钢微观断口有:韧窝断口、塑性沿晶断口、解理断口及混合断口。  相似文献   

5.
采用光学显微镜(OM)、能谱仪(EDS)、X射线衍射仪(XRD)、高温显微镜原位观察等实验手段,分析了ZG40Cr25Ni20奥氏体耐热钢烧损原因。结果表明,随着温度升高,奥氏体晶粒不断长大,碳化物Cr23C6不断形成和长大,碳化物中的Cr含量和碳化物硬度不断增加,奥氏体基体中的Cr含量不断减少。温度过高,碳化物溶解,形成孔洞,促进微裂纹沿晶界的扩展,奥氏体晶粒间的结合力逐渐减弱,基体发生过烧,钢的结晶组织遭到破坏,失去金属原有的塑性和强度,造成高温耐热管失效,孔洞和微裂纹的形成及扩展是材料失效的主要原因。此外,高温显微镜原位观察和热处理实验结果表明,ZG40Cr25Ni20耐热钢中碳化物的溶解温度为1030~1250℃。高温显微镜原位观察为碳化物溶解观察和耐热钢失效分析提供了一种新的方法。  相似文献   

6.
对Al含量为0、1.68%、4.72%和7.10%的ZG40Cr25Ni20进行了对比磨损试验。结果表明,Al的加入可以不同程度的提高材料的耐磨性能,Al含量为7.10%时耐磨性最好,其在相同条件下的耐磨性为不含Al时的2.62倍,其次为Al含量为4.72%,其耐磨性比Al含量为1.68%时提高66.40%,试验合金的磨损机理为微观切削。  相似文献   

7.
过滤净化可以提高不锈钢的塑性和韧性指标;它使断裂韧性提高的主要机理是过滤净化减少了夹杂物含量,以及疏松和气孔的数量,提高了合金的致密度,消除了部分裂纹源。  相似文献   

8.
ZG0Cr13Ni4Mo不锈钢铸件微观组织试验研究   总被引:1,自引:0,他引:1  
孙立斌  许庆彦  柳百成 《铸造》2002,51(12):745-749
以长江三峡水轮机叶片所用材料为研究对象,设计并浇注了两种类型的大型试件。用金相显微镜及扫描电镜观察了铸态下微观组织形态,测定了奥氏体晶粒大小、奥氏体晶粒内马氏体板条束个数和马氏体板条间距。分析了ZG0Cr13NiMo不锈钢铸件凝固相变过程,阐明了该材质最终微观组织的特点。试验结果和数值模拟结果对比,可以验证数值模拟结果的可信性。  相似文献   

9.
张玮  王林森  彭芳芳 《电焊机》2021,51(3):47-50
对两个厂家的镍基合金焊条ENiCrCoMo-1进行了工艺性和熔敷金属性能对比试验,并对微观形貌进行了分析。试验结果表明,两个厂家的镍基合金焊条ENiCrCoMo-1工艺性能均良好,熔敷金属成分及力学性能均满足国标要求。此外,由于两个厂家镍基合金焊条ENiCrCoMo-1熔敷金属成分的差异,使其凝固树枝晶及析出相形貌和分布不同,从而导致其性能存在一定的差异。  相似文献   

10.
TP347H钢焊接接头微观组织及断口形貌分析   总被引:2,自引:0,他引:2  
张哲峰  王文先  洪卫 《焊接》2006,(11):40-43
采用了ER316L和H1Cr18Ni9Ti焊丝对TP347H钢的焊接性进行了研究,测试了焊接接头在常温下的力学性能,对焊缝金属和热影响区进行微观组织观察,并对冲击试件进行了SEM断口形貌分析.发现氧化物等杂质容易聚集在热影响区,内充氩不当在焊缝根部极易形成氧化裂纹,焊接参数大容易引起焊缝区未熔合,在启裂处有脆性断裂迹象.通过分析对TP347H钢的焊接性及工艺参数有了更清楚的认识,对大参数火电机组和核电机组材料的焊接具有一定的帮助.  相似文献   

11.
    
Mo2C is normally added to improve the wettability between Ti(C,N) and Ni in Ti(C,N)-based cermets. Due to the increasing price of Mo2C, much attention has been paid to Ti(C,N)-based cermets with WC addition. In this paper, effect of WC content on the microstructure and properties of Ti(C0.7N0.3)-xWC-15wt.%Ni cermets free of Mo2C was studied. The experimental results show that the microstructure is refined obviously with the increase of WC content. The fracture toughness decreases with the increase of WC content when WC content is 10-25 wt.%, and increases when WC content varies from 25 wt.% to 30 wt.%.  相似文献   

12.
    
Room-temperature fracture toughnesses of TiC-added Mo-Si-B alloys were evaluated for samples of three different compositions prepared using a conventional Ar arc-melting technique. The first alloy (TiCp) had a primary phase during solidification of NaCl-type TiC including an amount of Mo, with a Mo solid solution (Moss) volume fraction of approximately 49% and a TiC volume fraction of approximately 19%, while the volume fraction of Mo5SiB2 (T2) was approximately 31% and the remaining 1% was Mo2C including an amount of Ti. The second alloy (T2p) had a primary phase of T2, with volume fractions of Moss, TiC, Mo5SiB2 (T2), and Mo2C of approximately 38%, 4%, 45%, and 13%, respectively. The third alloy (Mop) had a primary phase of Moss, with volume fractions of Moss, TiC, Mo5SiB2 (T2), and Mo2C of approximately 55%, 8%, 32%, and 6%, respectively. Room-temperature fracture toughness was evaluated by three different bending tests using Chevron-notched specimens. Fracture toughness values obtained by the three methods were relatively close with good reproducibility. Consequently, the fracture toughness values of TiCp, T2p, and Mop were evaluated to be ∼15.2 MPa(m)1/2, ∼10.5 MPa(m)1/2, and ∼13.6 MPa(m)1/2, respectively. Fracture surface observations indicated that the Moss phase is subject to severe plastic deformation during the fracture process. The TiC phase was also noted to leave river patterns behind through crack propagation. These fractographic results suggest that not only the ductile-phase toughening by the Moss phase but also an extra-toughening mechanism by the TiC phase are responsible for the goodness of the room-temperature fracture toughness of the MoSiBTiC alloys.  相似文献   

13.
14.
Development of nanostructured hardmetals is a task of great importance. Nevertheless, in spite of some “euphoria” with respect to nanograined hardmetals, their potential application ranges are yet not clear. In some works, near-nano and nano hardmetals are believed can potentially substitute conventional medium- and coarse-grained WC–Co grades. In the present work near-nano hardmetals with WC mean grain size of nearly 200 nm and Co contents of 10–33 wt.% were produced and examined with respect to their hardness, fracture toughness, transverse rupture strength and wear-resistance. The near-nano hardmetal with 10% Co having a hardness of 20 GPa and fracture toughness of 9.5 MPa m1/2 is characterised by exceptionally high wear-resistance obtained by use of the ASTM B611 test in comparison with an ultra-fine grade with 10%. The wear-resistance of the near-nano hardmetals in the ASTM B611 test significantly decreases with increasing the Co content and the wear rates of the difference between the wear rates of the grades with 10% and 33% Co is equal to nearly 44 times. The near-nano hardmetals with 25%, 28% and 33% Co having a moderate hardness and high fracture toughness corresponding to conventional coarse and ultra-coarse-grained mining grades have a very low wear-resistance in laboratory tests on concrete-cutting, granite-cutting and percussion drilling of quartzite. A number of grades with the very similar hardness of 13 ± 0.2 GPa, WC mean grain sizes varying from 0.2 to 4.8 μm and Co contents varying from 3% to 25% were produced and examined by use of the ASTM B611 test. The wear-resistance of the near-nano grade with 25% Co is found to be lower by more than three times compared to the coarsest grade with 3% Co at almost the same hardness. In this case, in spite of the very similar hardness of all the samples, the proportion of the soft binder phase on the surface subjected to abrasive particles when performing the test is significantly higher for the near-nano grade compared to the coarse- and ultra-coarse grained hardmetals. Thus, near-nano and presumably nano hardmetals are expected to never substitute conventional medium- and coarse-grained mining grades. The only application range, where near-nano and nano hardmetals can potentially substitute conventional grades, is an application range of hardnesses of above 18 GPa.  相似文献   

15.
Three Laves phase-based alloys with nominal compositions of Cr2Nb–x Ti(x = 20,30,40,in at%) have been prepared through vacuum non-consumable arc melting.The results show that the microstructures of Cr2Nb-(20,30) Ti alloys are composed of the primary Laves phase C15–Cr2(Nb,Ti) and bcc solid solution phase,while the microstructure of Cr2Nb–40Ti alloy is developed with the eutectic phases C15–Cr2(Nb,Ti)/bcc solid solution.The measured fracture toughness of ternary Laves phase C15–Cr2(Nb,Ti) is about 3.0 MPa m1/2,much larger than 1.4 MPa m1/2for binary Laves phase Cr2 Nb.Meanwhile,the fracture toughness of Cr2Nb–x Ti(x = 20,30,40) alloys increases with increasing Ti content and reaches 10.6 MPa m1/2in Cr2Nb–40Ti alloy.The eutectic microstructure and addition of Ti in Cr2 Nb are found to be effective in toughening Laves phase-based alloys.  相似文献   

16.
The effects of alloying with Zr on the microstructure, mechanical and oxidation properties of Nb-Ti-Si based ultrahigh temperature alloys have been investigated in this study. The microstructures of the all alloys were comprised of primary γ(Nb,X)5Si3 blocks, Nbss and eutectic colonies, and the additions of Zr do not affect the microstructure and phase constituents of Nb-Ti-Si based alloys. Zr improves both the room-temperature toughness and the high-temperature strength. The alloy with addition of 8 at.% Zr shows the highest fracture toughness of 15.01 Mpa·m1/2. The compressive strengths of the alloys are improved to 278.89–293.08 MPa for the Zr-containing alloys when compare with the Zr-free alloy (194.23 MPa). The oxidation resistance of the alloys was also obviously ameliorated with Zr addition, showing a reduced weight gain with the increase of Zr content.  相似文献   

17.
In this work, the microstructure and precipitation phases were primarily characterized by transmission electron microscopy. The mechanical properties were evaluated by tensile and tear test. The results indicated that the samples aged at 145 °C for 45 h or 155 °C for 30 h possessed a preferable combination of strength and plasticity, owing to the precipitation of well-dispersed T1(Al2Cu Li) phases(diameter 150 nm). However, aging at more than 165 °C caused an obvious size growth of T1 plates, leading to the quick reduction in plasticity and toughness. Furthermore, the high Cu/Li ratio resulted in distinct precipitation features, including a shorter incubation time of T1 phase and the aggravated precipitate-free zones.  相似文献   

18.
    
The microstructure and fracture toughness of weld metal under Ti-free and Ti-containing different fluxes were investigated in this study.It was found that the trace element Ti of flux in submerged arc welding produced significant influence on the fracture toughness.The addition of 60 ppm Ti induced the sharp increase in J_(0.2) value from 232.78 to 364.08 kJ/m~2.Microstructure characterization revealed that a large number of oxide inclusions prompted the nucleation of acicular ferrites and refined grains,which improved the fracture toughness of Ti-containing weld metal greatly.Moreover,the crack propagation path was more tortuous and bifurcated due to the small amount of carbide precipitations along grain boundaries and blocky martensite-austenite islands for Ti-containing weld metal.Meanwhile,the large-angle grain boundaries caused crack deflection and increased the resistance of crack propagation compared to Ti-free weld metal.  相似文献   

19.
    
The microstructure evolution and room temperature fracture toughness of as-cast and directionally solidified NiAl-Cr(Fe) alloy were investigated using OM, SEM, EDS, DSC and three-point bending tests. From the as-cast microstructure and DSC result, NiAl-34Cr-4Fe (at.%) is a eutectic alloy which consists of eutectic cells in different sizes. The half-baked mesh-like structure is observed at the cell center, and the radial emanating thicker or longer Cr(Fe) phases embedded within NiAl matrix are observed near or at the cell boundary. In the directional solidification process, the solid-liquid interface morphology has an evolutionary process of planar to cellular, even dendritic interface with increasing the withdrawal rates, and the eutectic cell and the microstructure at the cell center refines gradually. From the transverse microstructure, the characteristic of eutectic cell is similar to that of eutectic cell in as-cast alloy. It can be seen from the longitudinal colony/cell center that the broken (short) Cr(Fe) rods are observed at 6 μm/s, and they evolve to granular Cr(Fe) phases when the withdrawal rate increases further. Moreover, regardless of vacuum induction melting (as-cast) and directional solidification, NiAl-34Cr-4Fe (at.%) eutectic alloy possesses a poor fracture toughness due to the inferior brittleness of both NiAl and Cr(Fe) phases. Meanwhile, the crack propagation and fracture surface are observed to better understand the fracture behavior.  相似文献   

20.
Grain level analysis of crack initiation and propagation in brittle materials   总被引:11,自引:0,他引:11  
A study on the accuracy of cohesive models for capturing dynamic fragmentation of ceramic microstructures is presented. The investigation consists of a combined experimental/numerical approach in which microcracking and damage kinetics are examined by means of plate impact recovery experiments. The numerical analysis is based on a 2-D micromechanical stochastic finite element analysis. The model incorporates a cohesive law to capture microcrack initiation, propagation and coalescence, as well as crack interaction and branching, as a natural outcome of the calculated material response. The stochasticity of the microfracture process is modeled by introducing a Weibull distribution of interfacial strength at grain boundaries. This model accounts for randomness in grain orientation, and the existence of chemical impurities and glassy phase at grain boundaries. Representative volume elements (RVE) of ceramic microstructure with different grain size and shape distributions are considered to account for features observed in real microstructures. Normal plate impact velocity histories are used not only to identify model parameters, but also to determine under what conditions the model captures failure mechanisms experimentally observed. The analyses show that in order to capture damage kinetics a particular distribution of grain boundary strength and detailed modeling of grain morphology are required. Simulated microcrack patterns and velocity histories have been found to be in a good agreement with the experimental observations only when the right grain morphology and model parameters are chosen. It has been found that the addition of rate effects to the cohesive model results in microcrack diffusion not observed experimentally.  相似文献   

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