共查询到20条相似文献,搜索用时 31 毫秒
1.
This study investigates the thermal fatigue cracking behavior of high-silicon spheroidal graphite (SG) cast iron. Irons with
different residual magnesium contents ranging from 0.038 to 0.066 wt pct are obtained by controlling the amount of spheroidizer.
The repeated heating/cooling test is performed under cyclic heating in various temperatures ranging from 650 °C to 800 °C.
Experimental results indicate that the thermal fatigue cracking resistance of high-silicon SG cast iron decreases with increasing
residual magnesium content. The shortest period for crack initiation and the largest crack propagation rate of the specimens
containing 0.054 and 0.060 wt pct residual magnesium contents are associated with heating temperatures of 700 °C and 750 °C.
Heating temperatures outside this range can enhance the resistance to thermal fatigue crack initiation and propagation. When
thermal fatigue cracking occurs, the cracks always initiate at the surface of the specimen. The major path of crack propagation
is generally along the eutectic cell-wall region among the ferrite grain boundaries, which is the location of MgO inclusions
agglomerating together. On the other hand, dynamic recrystallization of ferrite grains occurs when the thermal cycle exceeds
a certain number after testing at 800 °C. Besides, dynamic recrystallization of the ferrite matrix suppresses the initiation
and propagation of thermal fatigue cracking. 相似文献
2.
CHANG Li-min LIU Jian-hua 《钢铁研究学报(英文版)》2006,13(1):36-39
Chromium wear resistant cast iron is widelyusedin engineering, mining and power industry forits high strength,hardness and wear resistance .Inproduction process , some wear-resistant parts ser-ving in alternative stress due to rapid heating andcooling rate ofteninduces thermal fatigue andresultsinfailure .The badthermal fatigue property of chro-mium wear resistant cast iron is due to eutectic car-bides which distribute as continuous net in matrix.Recent researches showthat hot deformation can … 相似文献
3.
利用冷热疲劳试验机模拟分析了冷热循环对不锈钢复合板热疲劳性能的影响,并采用扫描电镜、电子探针和电子背散射衍射仪对热疲劳试样V形缺口及裂纹区域的形貌和成分进行了深入分析。结果表明,不锈钢复合板热疲劳试样经 20~550 ℃ 7 500次冷热循环后,结合界面处V形缺口区出现微裂纹,且微裂纹起裂于V形缺口尖端基层侧。随着冷热循环的继续进行,微裂纹向基层内扩展,但并非沿着结合界面处扩展,而是沿着基层侧扩展。此外,热疲劳裂纹的起裂和扩展与氧化和应力作用有关,微裂纹起裂于热疲劳试样 V 形缺口区域基层侧表层局部氧化孔洞,并在冷热循环的应力作用下向基层内扩展,同时加剧氧化。随着冷热循环的继续进行,晶界氧化逐渐加剧,导致微裂纹扩展成更为明显的裂纹。 相似文献
4.
5.
6.
针对340MPM机组(Multi-Stand Pipe Mill限动芯棒连轧管机组)芯棒服役过程建立三维有限元模型,研究芯棒在服役过程中温度场变化规律.同时,通过对热应力的研究,分析了芯棒热疲劳裂纹萌生机理及裂纹在芯棒内部的扩展规律.对比实测数据与模拟结果,认为所建立的有限元模型能够反映芯棒温度变化趋势.芯棒首次脱管后表面最高温度为630℃,此后经历三次反复的水冷降温和空冷返温过程,冷却结束后表面最高温度为98℃.脱管后,芯棒表面轴向和环向压缩热应力均达到900 MPa,第三次水冷结束时刻,轴向拉伸热应力达到186 MPa,环向拉伸热应力达到221 MPa.芯棒的拉压交变热应力使其表面出现热疲劳裂纹并逐渐扩展,环向裂纹扩展至距表面17.5mm深、轴向裂纹扩展至距表面20mm深时会显著受阻,热应力对轴向裂纹的促进作用强于环向裂纹. 相似文献
7.
Samples of DD3 single crystal superalloy with different dimensions were cast in the directionally solidified furnace with high temperature gradient. The effect of cast dimension on the rotary bending high cycle fatigue (HCF) properties of the alloy was investigated at 800 °C in ambient atmosphere. SEM was used to examine the fracture surface and fracture mechanism of the alloy. The results show that the rotary bending HCF properties of the alloy decreases with increasing cast dimension. The cast dimension has little effect on the HCF fracture mechanism of the alloy. The HCF fracture mechanism of the alloy with different cast dimensions is all quasi-cleavage fracture. The fatigue cracks initiated on the surface or near the surface of the specimens. The crack would propagate along {111} octahedral slip planes. Typical fatigue arc and striation formed on fatigue crack steady propagation. The degeneration of HCF properties is due to the increase of dendrite arm spacing and size of γ′ phase particles and maximal microporosity. 相似文献
8.
XUTao LIFeng CHENHua YUCui-yan 《钢铁研究学报(英文版)》2005,12(4):40-43,49
The formation and growth of thermal fatigue crack in low chromium semi steel were investigated by means of optical microscope and scanning electron microscope, and the function of RE in low-chromium semi steel was analyzed. The results show that the thermal fatigue cracks are mainly generated at eutectic carbides, and the cracks not only grow and spread but also join each other. RE can improve the eutectic carbide‘s morphology, inhibit the generation and propagation of thermal fatigue cracks, and therefore promote the activation energy for the crack‘s propagation, which is especially more noticeable in case of the RE modification in combination with heat treatment. The mathematical model of the crack propagation is put forward. 相似文献
9.
稀土对钢轨钢接触疲劳的影响 总被引:4,自引:1,他引:3
利用接触疲劳磨损试验机械钢轨/车轮接触疲劳作用,了钢轨钢接触疲劳表面区剖面的形貌,显微结构和硬度。结果表明,稀土可延缓钢表面疲劳裂纹的萌生和扩展,推迟表面剥离,减小裂纹贯穿角和裂纹稳定贯穿,缩小塑性化形范围和改善表面加工硬化效果。 相似文献
10.
Effect of RE Modification and Heat Treatment on Impact Fatigue Property of a Wear Resistant White Cast Iron 总被引:5,自引:0,他引:5
Withhigherhardnessandbetterwearresistance ,whitecastironscanbeusedaswearresistantpartsinmanyfields .Inpractice ,thewearresistantpartsareoftenrequiredtobesubjectedtogrindingofabrasivesandrepeatedimpactaction .Therefore ,fatiguecracksareliabletobegeneratedo… 相似文献
11.
12.
13.
14.
采用光学显微镜、扫描电镜、EDS能谱分析和力学性能测试等方法,研究了固溶处理对2205双相不锈钢显微组织与疲劳裂纹扩展规律的影响。结果表明:与原始热轧态相比,在950~1150℃范围固溶处理的试样的疲劳裂纹门槛值显著提高,稳态裂纹扩展速率均有所减小。在950℃固溶处理时,组织中析出少量的σ相,试样的稳态裂纹扩展速率显著降低;随着固溶温度的升高,组织中α相含量逐渐增加,σ相溶解,试样的稳态裂纹扩展速率的变化呈现为先增大后减小的趋势;当固溶温度达到1150℃时,组织中α相含量最高且两相组织明显粗化,试样的稳态裂纹扩展速率达到最小,呈现出最高的抗疲劳裂纹扩展能力。固溶处理引起σ相的析出与溶解、α相含量的增加及组织粗化是引起2205双相不锈钢试样疲劳裂纹扩展性能非单调变化的原因。 相似文献
15.
The crack initiation and propagation behavior of high cobalt molybdenum stainless bearing steel was studied by rotating bending fatigue test with smooth cylindrical specimens and notched specimens (theoretical stress concentration factor Kt=3). The fatigue limit and S- N curve of bearing steel were measured by up- and- down method and group method, respectively. The fractures of the specimens were observed by scanning electron microscopy. The results show that the cracking type of the smooth specimens is single source initiation. The crack source is surface defects and subsurface inclusion. The surface defects are surface roughness, persistent slip band and machining dent, while the subsurface inclusion is Al2O3- CaO- MgO- SiO2 composite inclusion. The fatigue limit of notched specimens is significantly decreased. The cracking type of the notched specimens is multi- source initiation. The notch sensitivity factor qf of bearing steel is 1. 18. The fatigue failure of the smooth specimens is transferred from the surface roughness with high stress amplitude to the persistent slip bands, the machining dents and the inclusions with low stress amplitude. The fatigue crack initiation life accounts for more than 94. 1% of the whole fatigue life. 相似文献
16.
对16Mn钢对焊接头的焊缝及热影响区中疲劳裂纹的萌生与扩展机理进行了研究与讨论.结果发现疲裂纹的萌生与扩展与铁素体组织有关,焊接件疲劳断口很复杂,焊缝中的夹杂物对疲劳裂纹的萌生有重要影响. 相似文献
17.
The influence of microstructure on the thermal fatigue (TF) behavior of MAR-M 509, a cast cobalt-base superalloy, was investigated
using a burner rig and wedge-type specimens which were submitted to thermal shock from 200 °C to 1100 °C. Two microstructures
were studied: a coarse microstructure using specimens machined from bulk castings and a fine microstructure using cast-to-size
specimens. Metallographic observations showed that cast-to-size specimens display a gradient in microstructure since the size
of secondary dendrites increases with the distance to the thin edge. As high-temperature fatigue in this superalloy is controlled
by oxidation-fatigue interactions, the kinetics of interdendritic oxidation was studied at 900 °C. Interdendritic oxidation
was found to be inhibited by a refinement of dendritic microstructure. A fine microstructure was shown to give a much longer
TF life-to-crack initiation and a much lower crack growth rate. This behavior was mainly related to differences in interdendritic
oxidation since interdendritic areas act as crack initiation sites as well as easy crack propagation paths. The influence
of microstructure on crack growth rates was accounted for by using a previously proposed oxidation-fatigue crack growth model
and interdendritic oxidation kinetic data.
Formerly with the Centre des Matériaux, Ecole des Mines de Paris 相似文献
18.
Wearandshellingaretwoimportantformsofdamageforrailsteelssothatmanyresearchesareaimingatthem[1~4].Manyoftheseresearcheswerelimitedtodeterminingthewearandtosurveyingthetopographyofthesamplesurfacesandonlyafewoftheminvestigatedthemicrostructures,themorphol… 相似文献
19.
430不锈钢冷轧酸洗板在折弯加工过程中出现了开裂现象,为了找出裂纹成因,对所使用的430不锈钢冷轧酸洗板进行了化学成分分析、力学性能测试和金相检验,并对样品折弯开裂处的裂纹进行了形貌观察。结果表明,430不锈钢酸洗板折弯开裂的主要原因为基体组织中晶粒大小不均匀,存在异常长大的情况,且晶界处存在大量碳化物析出聚集,促使开裂裂纹沿着晶界由外向内迅速地扩展,导致产品的折弯开裂。通过分析可知,430不锈钢冷轧板材在退火过程中的加热时间过长、材温偏高导致基体内部组织异常。通过控制430不锈钢冷轧板的退火工艺参数:1区加热段温度840~850℃,2区加热段温度870~900℃,在炉时间130~140 S,从而避免了折弯开裂的发牛。 相似文献
20.
《钢铁研究学报(英文版)》2015,(7)
Very high cycle fatigue behavior(107-109 cycles)of 304 Laustenitic stainless steel was studied with ultrasonic fatigue testing system(20kHz).The characteristics of fatigue crack initiation and propagation were discussed based on the observation of surface plastic deformation and heat dissipation.It was found that micro-plasticity(slip markings)could be observed on the specimen surface even at very low stress amplitudes.The persistent slip markings increased clearly along with a remarkable process of heat dissipation just before the fatigue failure.By detailed investigation using a scanning electron microscope and an infrared camera,slip markings appeared at the large grains where the fatigue crack initiation site was located.The surface temperature around the fatigue crack tip and the slip markings close to the fracture surface increased prominently with the propagation of fatigue crack.Finally,the coupling relationship among the fatigue crack propagation,appearance of surface slip markings and heat dissipation was analyzed for a better understanding of ultrasonic fatigue damage behavior. 相似文献