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1.
M.A. Islam 《Journal of Materials Engineering and Performance》2007,16(1):73-79
Low alloy steels serving for a long time at high temperature, e.g., around 500 °C, are very sensitive to temper embrittlement
due to segregation of various trace elements at prior austenite grain boundaries and/or carbide/matrix interfaces. This type
of segregation in combination with various environmental effects can adversely affect the fracture resistance and fatigue
crack propagation rate with subsequent change in fracture morphology of low alloy steels. This article describes the segregation
behavior of various elements in 2.25Cr-1Mo pressure vessel steel investigated by AES, FEG-STEM, SEM, and EDS analyses. As
confirmed by AES and FEG-STEM, phosphorus is found to be the main embrittling element for isothermal embrittlement. Sulfur
and Mo segregation is only evident after longer embrittlement times. In the step-cooling embrittlement, phosphorus is still
found to be the main embrittling element, but heavy segregation of sulfur in some isolated intergranular facets was also observed.
For P segregation, a Mo-C-P interaction is observed, while sulfur segregation is attributed to site competition between sulfur
and carbon atoms. 相似文献
2.
Low-alloy steels serving for a long time at high temperature (∼500 °C) are very sensitive to temper embrittlement due to segregation
of various trace elements at prior austenite grain boundaries and/or carbide/matrix interfaces. This type of segregation in
combination with various environmental effects can adversely affect the fracture resistance and fatigue crack propagation
rate with subsequent change in the fracture morphology of low-alloy steels. The present work describes the effects of heat
treatments on impurity element segregation and its subsequent effects on fatigue fracture behavior of 2.25Cr-1Mo steel under
different environmental conditions and temperatures. It has been found that either prior impurity element segregation caused
during the heat treatment or hydrogen-induced embrittlement due to the presence of water vapor in laboratory air alone cannot
produce intergranular fracture on the fatigue surfaces of 2.25Cr-1Mo steel at room temperature in air. The occurrence of intergranular
fracture on the fatigue surfaces results from the combined effect of impurity element segregation-induced grain boundary embrittlement
and hydrogen-induced embrittlement, and that the proportion of intergranular fracture is a function of prior impurity element
segregation provided that the grain boundary segregation level exceeds a certain critical value. 相似文献
3.
M. A. Islam M. Novovic P. Bowen J. F. Knott 《Journal of Materials Engineering and Performance》2003,12(3):244-248
Phosphorus is a very common trace element that can segregate at prior austenite grain boundaries and/or carbide/matrix interfaces
of low alloy steels at high temperature (e.g., order of 500 °C) and adversely affect the fracture properties. This paper investigates
segregation of P during reversible temper embrittlement (96 h at 520 °C) of quenched and fully tempered 2.25Cr-1Mo steel by
Auger electron spectroscopy and describes the segregation mechanism. This paper also describes the effect of P segregation
on fracture resistance and fracture mode of unembrittled steels, respectively, by fracture toughness testing over a temperature
range of −196 °C to 20 °C and fractography in scanning electron microscopes. During temper embrittlement phosphorus segregation
has been attributed due to the mechanism of “carbide rejection”. This segregation caused a reduction in fracture toughness
values of the quenched and tempered steels at all test temperatures and an increase in the transition temperature. Phosphorus
segregation also changed the brittle fracture micromechanism of quenched and fully tempered samples from one of transgranular
cleavage to a mixed mode of fracture (transgranular cleavage and intergranular decohesion). The micromechanism of fracture
at temperatures from the upper shelf, however, remained almost unchanged. 相似文献
4.
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
5.
进行了2.25Cr-1Mo-0.25V钢的焊条电弧焊试验,测定其焊缝的成分和冲击吸收功,进行了金相及启裂源观察,对冲击吸收功较低的样品进行脱脆处理.结果表明,冲击吸收功较低的焊缝的Mn,Si,Mo及其杂质元素含量相对较高,Mn,Si,Mo等元素促进杂质元素在晶界上的偏聚,致使晶界性能变坏,断口以沿晶断裂为主,冲击吸收功降低,脱脆处理后,冲击韧性恢复说明焊缝存在高温回火脆性,导致高温回火脆性是由于杂质元素在晶界上的偏聚,因此研制焊条时要严格控制Mn,Si,Mo和杂质元素的含量. 相似文献
6.
Omyma H. Ibrahim Ezzat S. Elshazly 《Journal of Materials Engineering and Performance》2013,22(2):584-589
The effect of microstructure on fracture behavior of 1Cr-0.5Mo and 9Cr-1Mo structural steels was evaluated. 1Cr-0.5Mo steel is used in steam pipes and superheater tubes of power stations. Its microstructure is typically comprised of bainite in a pre-eutectoid ferrite matrix with an average grain size of 10 μm. 9Cr-1Mo steel was developed for applications in steam power stations and as a candidate structural material for first-wall and blanket components of future fusion reactors. Its microstructure consisted of a fully martensitic structure with a prior austenite grain size of 25 μm. The fracture properties were measured using instrumented impact testing at temperatures between ?196 and 300 °C. The total impact fracture energy, the crack initiation and propagation energy, the dynamic yield strength, the brittleness temperature, and the cleavage fracture stress were measured. The bainitic-ferritic alloy steel exhibited much higher resistance to ductile fracture at high test temperatures, while its resistance to brittle fracture at low test temperatures was reduced compared to that of the fully martensitic alloy steel. The results were discussed in terms of the chemical composition and microstructure of the two steel types. 相似文献
7.
A. Abdollah-Zadeh A. Jafari-Pirlari M. Barzegari 《Journal of Materials Engineering and Performance》2005,14(5):569-573
This study focused on tempered martensite embrittlement in a 32NiCrMoV125 steel through examination of the effects of austenite
grain size and tempering temperature on the mechanical properties and fracture morphology of this material. Two different
austenite grain sizes were obtained by austenitizing at 870 and 950 °C. After quenching, the specimens were tempered in the
temperature range of 200–650 °C. The results obtained in this research indicate that by increasing the tempering temperature,
the strength and hardness decrease, but ductility increases. However, impact testing indicated that tempered martensite embrittlement
occurred when samples were tempered in the range of 250–400 °C. Fractography revealed intergranular and quasi-cleavage fracture.
In summary, increasing the austenite grain size decreased strength, but increased impact toughness, except for samples tempered
between 200 and 350 °C. 相似文献
8.
采用电解充氢方法分别对回火脆态和脱脆态2.25Cr-1Mo钢氢致开裂行为进行实验研究,通过甘油测氢法测定了2.25Cr-1Mo钢发生裂纹扩展时钢中扩散的平均氢浓度.为进一步了解回火脆对抗氢致开裂性能的影响,利用有限元软件分别对氢在回火脆态与脱脆态2.25 Cr-1Mo钢中的扩散过程进行模拟分析,系统研究了在应力-氢环境交互作用下裂纹尖端周围的氢扩散规律,并给出了裂纹扩展时裂尖局部位置的氢浓度大小. 相似文献
9.
J.Z.Tan 《金属学报(英文版)》2004,17(2):139-146
Based on the theory of grain boundary segregation,a kinetics model of temper embrittlement caused by long-term service for hot-wall hydrofining reactors was studied.The kinetics model was applied to phosphorus (P) segregation in 2.25Cr-1Mo steel used for a hot-wall hydrofining reactor,and the kinetics of grain boundary segregation of impurity P in the steel exposed to the process environment of the hydrofining reactor was calculated on the basis of the model.The Auger electron spectroscopy test was performed in order to determine the grain boundary concentration of P.The experimental result is agreement with the theoretical calculated data. The results show that the kinetics equation is reasonable for predicting the levels of grain boundary segregation of impurity P in 2.25Cr-1Mo steel used for hot-wall hydrofining reactors. 相似文献
10.
Yifan Feng Renbo Song Zhongzheng Pei Renfeng Song Guoyu Dou 《Metals and Materials International》2018,24(5):1012-1023
The microstructure and impact toughness of the as-cast Fe–24.8Mn–7.3Al–1.2C austenitic steel after solution treatment and subsequent aging treatment were investigated in the present work. Research on the κ-carbides precipitation behavior was carried out by transmission electron microscope. The results show that nano-sized coherent κ-carbides were obtained in the as-solutionized steel after aging treatment, which produced precipitation hardening. After being aging treated at 550 °C for 1 h, the steel with regular hexagonal grain structure exhibited a good combination of yield strength (~?574 MPa) and room-temperature impact toughness (~?168 J). In the present steel, the typical cube-on-cube orientation relationship between austenite and κ-carbides was observed. However, due to the long aging isothermal time and high C content, the coarse intergranular κ′-carbide was formed and grew along the austenite grain boundary, which caused this orientation relationship to be destroyed and a dramatical increase of the coherency strain energy at grain boundary. Furthermore, serious embrittlement of grain boundaries caused that cleavage cracks trend to propagate along the grain boundaries. Accordingly, the room-temperature impact toughness decreased sharply. After aging isothermal time prolonging to 13 h, the Charpy V-notch impact toughness was only ~?5 J and fracture mode turned to fully brittle fracture accompanied with flat facets, shear cracks and well-developed secondary crack. 相似文献
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13.
用焊接热模拟,普通光学金相,透射、扫描电镜及电子探针,X射线和常规拉伸、冲出等手段研究了一种新型Si-Mn-Mo系低碳贝氏体钢焊接热影响区过热区的组织和性能的关系,重点探讨了过热区的脆化机理.结果表明,在焊接热模拟条件下,原始奥氏体晶粒尺寸是影响机械性能的主要因素.少量准下贝氏体与低碳马氏体的混合组织具有最佳的强韧性配合.随线能量增加,影响韧性的主要因素是奥氏体晶粒粗化以及高温时碳原子在奥氏体晶界及其附近的偏聚;而且碳原子的这种偏聚是经过较高线能量热循环后出现沿晶脆性断口的主要原因.粒状贝氏体及粒状组织中的M-A岛不是该钢焊接热影响区过热区脆化的原因. 相似文献
15.
Xiaowei Lei Jing Niu Jianxun Zhang Anqing Fu Yaorong Feng 《Journal of Materials Engineering and Performance》2014,23(4):1231-1239
A crack in thick-walled 2.25Cr-1Mo steel pressure vessel girth weld was found during manufacturing. To investigate the cause of failure, optical microscopy, scanning electron microscopy, energy dispersive spectrometer, transmission electron microscopy, and microhardness tester were used in this study. According to test results, the fracture is classified as reheat cracking with multiple origins. The cracking occurred during surfacing or final post-weld heat treatment process. Coarse-grains in the weld and bulk-carbides precipitated along grain boundaries induced by multiple heating are main causes of the fracture from material aspect, while high level of the hoop stress component and excess localized deformation in stress relief procedure are mechanical aspect causes of the cracking. The fracture surfaces present major intergranular feature with a small fraction of transgranular morphologies. Large numbers of M3C and M23C6 carbides particles were found on the fracture surface, these carbides mainly precipitated on prior austenite-grain boundaries, columnar-grain boundaries, and sub-grain boundaries. Additionally, several proposals were also offered to reduce weld cracking of 2.25Cr-1Mo steel pressure vessels. 相似文献
16.
高强度23MnNiMoCr54链环钢是煤矿设备主要部件,在进行生产测试过程中发生断裂。对该链条钢裂纹部位进行了金相检测、化学元素成分检测、扫描电镜和断口检验和俄歇电子能谱仪分析。结果表明,链条钢的化学元素组成、气体含量、低倍组织和夹杂物含量符合相关技术标准要求;其金相组织为回火屈氏体,实际晶粒度为4级,断口为典型的脆性断口,断裂方式为沿晶脆性断裂。由于链环在生产过程中热处理不当,淬火加热温度过高,产生过热组织,造成链环晶粒粗大,在随后的回火过程中由于加热温度或者加热时间不当,导致晶界处杂质元素偏析,从而形成回火脆性。在晶粒粗大的情况下同时出现回火脆性,导致了链环钢在试验检查时发生沿晶脆性断裂。 相似文献
17.
超细晶粒高强度钢的延迟断裂行为 总被引:5,自引:0,他引:5
对于微合金化处理的42CrMoVNb钢,通过快速循环热处理的方法获得最小2μm的超细奥氏体晶粒,采用缺口拉伸延迟断裂实验研究了超细晶粒试样的延迟断裂行为。结果表明,随着晶粒细化,42CrMoVNb钢的强度和缺口拉伸延迟断裂抗力逐渐提高;但当晶粒细化到2μm时,强度和延迟断裂抗力均不再提高,在高温回火态,当晶粒尺寸在20—4μm范围时,断裂机制主要为穿晶断裂;但当晶粒进一步细化到2μm时,断裂机制转变为沿晶断裂,在低温回火态,不同晶粒尺寸的试样均主要为沿晶断裂,从降低应力集中和夹杂元素晶界偏聚等角度对超细晶粒高强度钢的延迟断裂行为进行了探讨。 相似文献
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19.
J.Z. Tan College of Mechanical Power Engineering Nanjing University of Technology Nanjing China 《金属学报(英文版)》2004,17(2)
Based on the theory of grain boundary segregation, a kinetics model of temper em-brittlement caused by long-term service for hot-wall hydrofining reactors was studied.The kinetics model was applied to phosphorus (P) segregation in 2.25Cr-1Mo steelused for a hot-wall hydrofining reactor, and the kinetics of grain boundary segrea-tion of impurity P in the steel exposed to the process environment of the hydrofiningreactor was calculated on the basis of the model. The Auger electron spectroscopytest was performed in order to determine the grain boundary concentration of P. Theexperimental result is agreement with the theoretical calculated data. The results showthat the kinetics equation is reasonable for predicting the levels of grain boundarysegregation of impurity P in 2.25Cr-1Mo steel used for hot-wall hydrofining reactors. 相似文献
20.
In the present work, slow displacement rate tensile tests were performed to find out the influence of ageing condition and hydrogen-charging on the notched tensile strength and fracture characteristics of T-250 maraging steel aged at various conditions. The influence of embrittling species in the environment on the notched tensile strength was accessed by comparing the measured properties in air, gaseous hydrogen and H2S-saturated solution. The hydrogen diffusivity, permeation flux and apparent solubility of various specimens determined by electrochemical permeation method, were correlated well with the microstructures and mechanical property. The results indicated that the peak-aged (H900) specimen was highly sensitive to hydrogen embrittlement even in gaseous hydrogen. In contrast, the microstructures of over-aged (H1100) specimen comprising of reverted austenite and incoherent precipitates could trap large amount of hydrogen atoms, resulting in decreased hydrogen permeability and hydrogen embrittlement susceptibility. The solution-annealed specimen had the highest diffusion coefficient and the lowest quantity of trapped hydrogen among the specimens, showing high susceptibility to sulfide stress corrosion cracking. In the presence of notches, hydrogen atoms were prone to segregate and trap at grain boundaries, resulting in the formation of intergranular fracture. 相似文献