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1.
采用动电位扫描技术和慢应变速率拉伸试验研究了超高强度钢300M在3.5%NaCl溶液中的应力腐蚀行为,并利用扫描电镜观察了不同外加电位下的断口形貌.300M钢在3.5%NaCl溶液中开路电位下的应力腐蚀开裂机制为阳极溶解型,Cl-的存在明显地增加了材料的应力腐蚀开裂敏感性.阳极电位-600 mV下300M钢溶解速率加快,表现出较高的应力腐蚀开裂敏感性,断面收缩率损失由开路电路下的52.6%升高至99.5%,裂纹起源于表面点蚀坑处,应力腐蚀开裂为阳极溶解型机制.阴极电位-800 mV下材料处于阴极保护电位范围,表现出较低的应力腐蚀开裂敏感性,强度和韧度与空气中拉伸的数值相近,开裂机制为阳极溶解和氢致开裂协同作用.在更低电位(低于-950 mV)下,300M钢的应力腐蚀开裂机制为氢致开裂,在氢和拉应力的共同作用下表现出很大的应力腐蚀开裂敏感性. 相似文献
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本文研究了304L不锈钢氧氯化反应器上封头的应力腐蚀行为,研究结果表明,材料裂纹的产生是由腐蚀引起。在氯离子作用下首先在硅钙类氧化物夹杂物处发生点蚀,成为裂纹源,然后在应力,氯离子和硫离子三种因素作用下产生裂纹,氯离子和硫离子在裂纹处不断积聚,在应力作用下裂纹扩展,最后导致材料失效。 相似文献
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使用恒应变试样浸泡试验、表面分析技术和电化学测试技术研究了CO2分压对N80钢在模拟CO2驱注井环空环境中应力腐蚀行为的影响。研究结果表明:CO2分压对腐蚀速率的影响存在一个拐点,环境温度为25 ℃时拐点约为1 MPa。当CO2分压小于1 MPa时,由于腐蚀产物膜(FeCO3)成形较慢,覆盖率低,随CO2分压的增高,N80钢的自腐蚀电流密度快速增大;当CO2分压大于1 MPa时,腐蚀产物膜能以较快的速率成形,覆盖率高,CO2分压的进一步增高反会使得N80钢的腐蚀电流密度降低。CO2溶于模拟环空溶液中会使溶液pH持续下降,促使N80油管钢在环空环境下发生应力腐蚀开裂。N80钢在CO2注入井环空环境中的应力腐蚀开裂机制是阳极溶解和氢脆共同作用的混合机制。应力腐蚀裂纹在萌生阶段局部阳极溶解作用(点蚀)为主导,该作用下CO2分压为1 MPa时应力腐蚀裂纹最易萌生;在应力腐蚀裂纹生长阶段氢脆作用更强,这种作用导致CO2分压更高时应力腐蚀裂纹更容易生长,应力腐蚀敏感性进一步提高。 相似文献
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研究了激光熔覆和Ni-Al合金涂层及(Ni-Al)+WC复合涂层的热疲劳性能。结果表明,涂层疲劳损伤形式为沿晶应力(氧化)腐蚀。腐蚀产物为Al2O3。每次热循环后,熔覆层中的最终残余应力是残余热应力和相变应力共同作用的结果。由于复合涂层中的残余应力为压应力,而合金涂层中的残余应力为拉应力,因此前热疲劳性能优于后者。 相似文献
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研究了温度对核电用Z3CN20-09M不锈钢在含Cl的高温高压水中的应力腐蚀开裂行为的影响.材料的应力腐蚀开裂敏感性变化趋势与试验温度变化趋势并不一致.320℃时材料的应力腐蚀开裂敏感性最高,290℃时为最低,250℃时开裂敏感性介于两者之间.250℃和320℃条件下腐蚀后试样表面形成了内部致密、外部疏松的双层氧化膜,而在290℃条件下腐蚀后试样形成的是致密的单层氧化膜.大多数点蚀坑产生于铁素体相.应力腐蚀裂纹优先在点蚀坑底部或相界面形核,并倾向于沿相界面或向铁素体内部扩展.铁素体/奥氏体界面对应力腐蚀裂纹的作用取决于裂纹面与相界面的取向关系.当裂纹扩展方向平行于相界面时,裂纹易沿着相界扩展;当裂纹扩展方向垂直于相界面时,相界面对裂纹扩展起阻碍作用. 相似文献
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采用标准中性盐雾腐蚀实验对表面喷丸处理前后两种状态的半固态触变压铸成形(semi-solid molding,SSM)319s铝合金片状试样在中性Na Cl盐雾介质中的耐腐蚀性能进行了测试。采用微距数码相机记录了盐雾腐蚀不同时间后的表面颜色变化和宏观腐蚀产物形貌,通过称重法监测了腐蚀增(减)重和去除腐蚀产物后的平均腐蚀失重随时间的变化规律,并利用扫描电镜(SEM)和能谱仪(EDS)对腐蚀表面微观形貌、腐蚀产物种类和去除表面腐蚀产物后的表面形态和点蚀程度进行了表征和分析。测试研究表明,表面喷丸处理能够明显降低SSM319s铝合金在盐雾气氛中的平均腐蚀失重,经过表面喷丸处理的样品平均腐蚀失重减小50%以上。能谱分析证实表面均匀腐蚀产物主要以Al2O3为主,而点蚀坑内的腐蚀产物为Al2O3和Mg Cl2的混合物。喷丸处理能强烈抑制点蚀坑缺陷的发生和扩展,其原因是喷丸表面形变效应对试样表层疏松、刮痕缺陷的弥合作用以及残余压应力对抗腐蚀性能的有益影响。 相似文献
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采用室温拉伸、光学显微镜和扫描电镜研究了不同恒载荷条件下7055铝合金型材的应力腐蚀性能。结果表明,在腐蚀周期内,随着应力腐蚀载荷的提高,试样的强度并未出现明显的下降,而塑性下降40%。应力腐蚀载荷越接近材料的屈服强度,塑性下降就越明显,抗拉应变和延伸率均有降低。应力腐蚀试样表层部分区域有明显的点蚀、沿晶腐蚀空洞和裂纹;拉伸时,腐蚀缺口处会产生明显的应力集中而成为起裂源,拉伸断口边缘被腐蚀区域为明显的沿晶断裂。 相似文献
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用慢应变速率法测量最大裂纹深度、平均裂纹扩展率、断面收缩率与拉伸率等,研究了碳钢在不同温度、不同介质浓度和不同电位下的非经典应力腐蚀行为。结果表明,最大裂纹深度和平均裂纹扩展速率是较好的评价应力腐蚀的参数。金相显微镜和扫描电镜观察结果表明,应力腐蚀裂纹起始于材料晶界,为沿晶阳极溶解机理。在较高温度和腐蚀电位下,材料仍处于饨化状态,在硝盐介质中,在应变条件下,材料仍遭受应力腐蚀。随介质温度和(或)硝盐浓度的降低,材料的腐蚀形态发生变化,即由应力腐蚀变为一般腐蚀。 相似文献
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采用电化学测试手段(开路电位、交流阻抗谱及动电位极化曲线测试), 结合接触角测试及体视显微镜微观形貌观察探究在80 g·L-1 NaCl溶液中拉应力对L80-13Cr马氏体不锈钢钝化膜溶解与再修复机制的影响.结果表明, 拉应力大小与L80-13Cr的钝化特性存在正相关关系.随着外加拉应力的增大, L80-13Cr马氏体不锈钢的开路电位负移, 电子转移电阻减小, 线性极化电阻减小, 反应速率随着拉应力的增大而增大.而L80-13Cr马氏体不锈钢在高电位下再钝化形成的钝化区会缩短, 自腐蚀电位降低, 维钝电流密度增加.接触角测试和体视显微镜微观形貌观察发现, 拉应力使得表面接触角减小, 不锈钢表面容易发生点蚀.外加拉应力使得L80-13Cr马氏体不锈钢的表面能增加, 促进钝化膜的溶解, 并且抑制钝化膜的再生, 导致材料耐蚀性降低. 相似文献
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The pitting susceptibility of a variously machined binary iron-1 wt pct nickel alloy in 5 M sodium hydroxide solution at 373
K has been measured and correlated with the surface residual macrostress introduced by the machining process. Stresses were
measured using the X-ray diffractometer technique. Tensile surface residual macrostresses increase the corrosion pitting susceptibility
whereas compressive stresses decrease susceptibility. 相似文献
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Laboratory corrosion fatigue studies on smooth and precracked samples indicated that two duplex stainless steels would have
similar service lives in a paper-processing environment; but, in service, one of these alloys has exhibited premature failures.
Since corrosion fatigue experiments had proven unable to detect this failure mechanism, electrochemical measurements and slow
strain rate tensile tests were used to evaluate four alloy composition-dependent failure mechanism hypotheses. No significant
differences were found in the dissolution rates or hydrogen fugacities produced when mechanical processes expose bare surface,
and slow strain rate tensile tests found no indication of a difference in cracking susceptibility for the same hydrogen fugacity.
Electrochemical experiments found that pits nucleate in one phase of the duplex microstructure at lower potentials in the
failure prone alloy, but do not propagate beyond the microscopic dimensions of this phase. These microstructurally limited
“micropits” were found to nucleate fracture in slow strain rate tensile tests, and examination of a service failure confirmed
the presence of microscopic pits at crack initiation sites. The premature failures are attributed to the lower pitting resistance
of the failure prone alloy, and the failure of laboratory experiments to predict this behavior is attributed to the slow kinetics
of pit nucleation in these experiments. A laboratory testing methodology is suggested that will ensure detection of similar
susceptibilities in future corrosion fatigue testing programs. 相似文献
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����ξ ����ϣ ʯ�� �˲� 《钢铁研究学报》2013,25(9):24-29
MS980 is one of advanced high-strength steels, which has a great potential for producing square tubes. Residual stress plays a significant role in determining roll-formed members?? behavior and strength. An experimental study on transverse residual stress of roll-formed shape with square section was conducted via X-ray diffraction method. The distribution of transverse residual stresses at different position in sections was measured and studied, and influence of cold-rolled-sheet and hot-rolled-sheet, different fillet radius, different processes, and different pickling time on circumferential residual stress distribution for square section was investigated. The experimental results show the transverse residual stresses are compressive stress in the corner portion and the tensile stress in the straight edge. Fillet radius, sheet, and process have a significant impact on the distribution of residual stress, but the conventional pickling hardly affects residual stress. 相似文献
15.
The effect of residual stresses and loading frequencies on corrosion fatigue crack growth behavior under synthetic seawater
with a free corrosion potential was examined using center-cracked tension (CCT) and single edge-cracked tension (SECT) specimens
machined from mild steel butt-welded joints and the parent material. A series of fatigue crack growth tests were carried out
with a sinusoidal loading wave form at a stress ratio of 0.05 with a loading frequency of 0.017 to 6.7 Hz. The results show
that the crack growth resistance of a weld metal in the SECT specimen is higher than that in the CCT specimen regardless of
testing conditions. The discrepancy is attributed to the differences in residual stress distribution at the crack tip in the
two specimen geometries. The crack growth rate of the weld metal in the CCT specimen in seawater increased with decreasing
loading frequency. The acceleration of the crack growth rate may be related to the occurrence of brittle striation or cleavage
due to hydrogen embrittlement. It was found that the corrosion fatigue crack growth rate of a welded joint with tensile residual
stress can be predicted using the effective stress intensity factor range, which takes into account both the residual stress
and the loading frequency effects. 相似文献
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The thermal residual stresses that develop in spray atomized and codeposited functionally graded and layered 6061 Al/SiC metal-matrix
composites (MMCs) during cooling from the codeposition temperature to ambient temperature were studied using thermo-elastoplastic
finite element analysis. In an effort to investigate the effect of layered and graded structures on the residual stress distribution,
the composites with homogeneous distribution of SiC particulates were also analyzed. The effect of SiC volume fraction in
the SiC-rich layers and the effect of SiC-rich layer thickness on the residual stresses were investigated. Based on the present
study, it was found that the residual stress distribution is very distinct for the aluminum and the SiC-rich layers in the
layered materials. As the volume fraction of SiC increases in the SiC-rich layer, the magnitude of residual stresses also
increases. The radial stress was found to be tensile in the aluminum layers and compressive in the SiC-rich layers. It was
also found that, as the thickness of the SiC-rich layer increases, the magnitude of radial stress in the aluminum layers increases,
and that in the SiC-rich layers decreases. In the graded material, the lower region of each layer exhibits tensile radial
stress, and the upper region of each layer shows compressive radial stress in order to maintain continuity between layers
during cooldown. In general, the layered and the graded materials have greater residual stresses and more complicated stress
distribution, as compared with those in the composite materials with homogeneous distribution of SiC particulates. 相似文献
18.
S. K. Shekhawat V. Basavaraj V. D. Hiwarkar R. Chakrabarty J. Nemade P. J. Guruprasad K. G. Suresh R. D. Doherty I. Samajdar 《Metallurgical and Materials Transactions A》2014,45(9):3695-3698
Non-grain oriented electrical steel, with minor in-grain orientation gradients, was subjected to interrupted tensile deformations and concurrent microtexture, magnetic property and residual stress measurements. After the upper yield point, clear signatures of mechanical stress relief were observed. Changes in orientation gradients led to annihilation of low-angle (1 to 3 deg) boundaries. Prior deformation compressive residual stresses became tensile and magnetic properties improved. Beyond an optimum true strain of 0.01, this boundary annihilation ceased, compressive stresses were generated, and magnetic properties degraded. 相似文献
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Induction Heat Treatment of Sheet‐Bulk Metal‐Formed Parts Assisted by Water–Air Spray Cooling
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Hans‐Bernward Besserer Andrej Dalinger Dmytro Rodman Florian Nürnberger Philipp Hildenbrand Marion Merklein Hans Jürgen Maier 《国际钢铁研究》2016,87(9):1220-1227
In order to produce components with massive secondary functional elements from sheet metal bulk forming operations, termed sheet‐bulk metal forming, can be applied. Owing to high, three‐dimensional stress and strain states present during sheet‐bulk metal forming, ductile damage occurs in the form of micro‐voids. Depending on the material flow properties, tensile residual stresses can also be present in the components' formed functional elements. During service, the components are subjected to cyclic loading via these functional elements, and tensile residual stresses exert an unfavorable influence on crack initiation and crack growth, and therefore on the fatigue life. Following the forming process, temperature and microstructurally related compressive residual stresses can be induced by local heat treating of the surface. These residual stresses can counteract potential crack initiation on the surface or in the subsurface regions. In the present study, the adjustability of the residual stress state is investigated using a workpiece manufactured by orbital cold‐forming, which possesses an accumulation of material in its edge region. Based on residual stress measurements in the workpiece's edge region using x‐ray diffractometry, it is possible to verify the compressive residual stresses adjusted by varying the cooling conditions. 相似文献