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某再生塔塔体由两部分组成,上部分材特Q345R,下部分材料S31603,其终止焊缝为S31603和Q345R异种钢焊接,在工艺评定弯曲试验时Q345R侧发生开裂.从选择合适的焊接方法、焊接坡口、焊接材料、焊接热输入、预热和层间温度等方面分析、探讨,并制作模拟件,确定合适的焊接工艺,保证了S31603和Q345R异种钢焊接接头的性能. 相似文献
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对不同厚度(20~60 mm)和屈强比(0.7~0.9)的Q500q E钢紧凑拉伸试样进行疲劳裂纹扩展速率试验,并与传统桥梁钢Q345q D进行对比。结果表明:室温下,Q345q D和Q500q E母材的止裂能力明显好于焊缝,Q500q E焊缝的疲劳裂纹扩展速率比Q345q D焊缝的疲劳裂纹扩展速率低,说明有较好的止裂能力;对于相同厚度的钢板,Q500q E母材的疲劳裂纹扩展速率随屈强比的升高而增加。和屈强比为0.7的Q345q D相比,任意厚度和屈强比Q500q E的疲劳裂纹扩展速率均低于Q345q D,说明高性能桥梁钢止裂性优于传统桥梁钢。 相似文献
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对14 mm厚的焊接Q460C高强度结构钢材焊缝区及其热影响区进行不同低温下的三点弯断裂韧性的试验研究,以便获得其焊缝区及其热影响区的断裂韧性指标δm值,同时利用Boltzmann函数对结果进行了拟合分析,得到其韧脆转变温度及其随温度变化的规律,并对试件断口进行扫描电镜分析.结果表明,低温对Q460C结构钢的焊缝区和热影响区断裂韧性有明显的影响,随温度的降低,其断裂韧性也随之呈下降趋势;Q460C焊缝区韧脆转变温度约为-53.6℃,热影响区的约为-40.3℃;在温度低于-20℃时,Q460C焊缝区及热影响区的断口形貌已表现出明显的脆性特征. 相似文献
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轮缘润滑器安装座故检过程中,渗透检测发现T型焊缝处出现宏观裂纹,该结构材料为Q345钢。通过外观检测、裂纹宏观形貌观察、裂纹断口形貌观察、焊接微观组织观察、冲击断口观察等试验,对结构的开裂原因进行分析。试验结果表明:焊接接头微观组织良好,无明显焊接缺陷,可排除由于组织原因引起构件失效的可能;对比裂纹断口形貌与焊缝金属冲击断口形貌,两者存在较大差异,可排除由于承受较大冲击载荷开裂的可能;裂纹微观断口存在大量疲劳条带,表明结构为疲劳开裂;综合考虑裂纹启裂位置的受力情况,可以判定疲劳开裂的原因是承受载荷部位的应力集中问题。 相似文献
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Cleavage fracture is the most dangerous form of fracture. Cleavage fracture usually happens well before general yielding at low nominal fracture stress and strain. Cleavage fracture is often spurred by low temperature and determines the toughness in the lower shelf temperature region. This paper describes a new framework for the micromechanism of cleavage fracture of high strength low alloy (HSLA) steel weld metals. Cleavage fracture not only determines the impact toughness in the lower shelf but also plays a decisive role on the impact toughness in the transition temperature region. The toughness is determined by the extending length of a preceding fibrous crack which is terminated by cleavage fracture. Three non-stop successive stages, i.e. crack nucleation, propagation of a second phase particle-sized crack across the particle/grain boundary, propagation of a grain-sized crack across the grain/grain boundary are explained. The "critical event" of cleavage fracture is emphasized which offers the greatest difficulty during crack formation and controls the cleavage process. The critical event indicates the weakest microstructural component and its critical size which specifies the local cleavage fracture stress sigma(f) for cleavage fracture. In toughness-study it is paramount important to reveal the critical events for various test specimens. Three criteria for crack nucleation, for preventing crack nucleus from blunting and for crack propagation are testified. An active region specified by these criteria is suggested where the combined stress and strain are sufficient to trigger the cleavage fracture. It can be used in statistical analyses. A case study, using the new framework of micromechanism for analyzing toughness of 8% Ni steel welding metals is presented to analyze the experimental results. 相似文献
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针对纯剪断裂试件存在的问题,提出了采用压剪试件实现岩石Ⅱ型裂纹剪切断裂并测试岩石剪切断裂韧度的实验方法,并通过对压剪试件的应力分布和测试结果的分析讨论,提出了岩石Ⅱ型断裂韧度实验的最佳方案,并进而讨论了Ⅱ型裂纹的两种不同断裂型式和断裂判据。 相似文献
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Islam M. A. Knott J. F. Bowen P. 《Journal of Materials Engineering and Performance》2004,13(5):600-606
In general, the low-temperature brittle fracture mode of unembrittled ferritic steel is transgranular cleavage. During temper
embrittlement, impurity elements, such as sulfur (S), phosphorus (P), antimony (Sb), arsenic (As), and tin (Sn), segregate
to prior austenite grain boundaries, which results in a decrease in the grain boundary cohesive strength. As a result, the
brittle transgranular cleavage fracture mode changes to intergranular decohesion in association with the decrease in the critical
fracture (stress (σ
F) as well as the fracture toughness (K). However, the appearance of intergranular facets on the fracture surface does not cause a decrease in the K and σ
F values. In this work, quenched and fully tempered 2.25Cr-1Mo steel (in an unembrittled condition that exhibits almost 100%
brittle transgranular cleavage fracture) has been embrittled for 24, 96, and 210 h at 520 °C to produce different proportions
of intergranular fracture. These unembrittled and embrittled steel specimens were tested to measure K (at −120 and −196 °C) and σ
F (at −196 °C). The experimental results and detailed fractographic observations show that the K and σ
F values decrease with an increase in the area fraction of intergranular fracture, provided that the area fraction of the intergranular
facet on the brittle fracture surface exceeded a certain critical level, approximately 20–22%. 相似文献
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C. C. Chama 《Journal of Materials Engineering and Performance》1995,4(1):70-81
Specimens from a 0.14 % C mild steel were austenitized at 1000 °C for 1 h and thereafter furnace-cooled or isothermally transformed
at 700 °C for 0.5,2, and 8 h. The microconstituents present in the as-received material were ferrite and pearlite and their
amounts did not substantially change even after heat treatment. The impact energy of the as-received and the furnace-cooled
materials increased from 4 to 89 J and from 4 to 108 J, respectively, when the temperature was changed from - 196 to 23 °C.
For these materials, the failure mode was by ductile fracture at 0 and 23 °C and by quasicleavage fracture at - 196 and -
40 °C. The fracture toughness did not show any significant change with isothermal transformation time at 700 °C. The failure
mode of the isothermally transformed materials was always by quasicleavage fracture. 相似文献
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The fracture behavior of SiCp/A356 composite at room and high temperatures was studied.Under tensile stress condition at room temperature, the fracture is mostly a combination of the brittle fracture of SiC particles and ductile fracture of A356 matrix.As the tensile temperature increases, the composite changes the main fracture behavior to the separation fracture of the bonding surface between SiC particles and A356 matrix.When the tensile temperature reaches 573 K, the fracture behavior of the composites is almost the whole separation fracture of the bonding surface, which is the main strengthening mechanism at high temperature.Under the cycle stress condition at room and high temperatures, the main fracture behavior of the composites is always a combination of the brittle fracture of SiC particles and ductile fracture of A356 matrix.However, under the cycle stress at high temperature, cycle behavior of the composites changes from cycle hardening at room temperature to the cycle softening at high temperature. 相似文献
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针对板厚2 mmAZ31B镁合金板材在DZ-3×100三相次级整流点焊机上进行焊接.通过对其焊接接头的拉剪试验、金相显微观察、断口SEM分析、XRD分析,研究了镁合金点焊接头拉剪断裂特征.结果表明,点焊接头拉剪断裂呈现拉剪撕裂和整核断裂两种断裂形式.熔核处断口为韧性-脆性混合型断裂,母材断口处呈现一典型的韧性断裂特征.熔核与母材的物相基本一致.母材焊后,晶界及晶面上析出硬而脆的Mg17Al12金属间化合物,且所占比例远远超过母材基体,熔核区域的断裂倾向增大,Mg17Al12金属间化合物在XRD图谱上衍射峰强. 相似文献
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用金相和扫描电镜分析了钢丝杯锥状断口。结果表明,钢丝杯锥状断口形成机理主要是由于钢丝组织中存在夹杂物、组织疏松、碳偏析以及拉拔工艺不当,导致心部出现"V"型裂纹,沿"V"型裂纹断裂后形成杯锥状断口。 相似文献
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1INTRODUCTIONDuringrecentyears,quiteafewinvestigatorshaveworkedonfractureplanecontrolblastwithnotchedboreholes.Succesfulappl... 相似文献