碳化物对热变形中铬半钢的热疲劳抗力的影响

对不同变表中铬半钢的热疲劳行地试验研究,结果表明：共晶碳化物是热疲劳裂纹产生及扩展的主要部位和碳化物破碎程度越大,其热疲劳抗力越高,热疲劳断口属于脆性断裂。     

热变形半钢的热疲劳行为的探讨

本文对不同变形半钢的热疲劳行为进行了探讨，结果表明：共晶碳化物是热疲劳裂纹产生及扩展的主要部位和通道，碳化物破碎越严重，其热疲劳抗力越高，热疲劳断口属于脆性断裂。     

热变形中铬半钢碳化物的形态及冲击疲劳性能

对不同变形量的中铬半钢碳化物的形态及冲击疲劳性能进行了探讨。结果表明：变形量为0－40％时，变形量越大，碳化物破碎越充分，冲击疲劳性能越好。     

热变形量对低铬半钢组织与力学性能的影响

通过对不同热变形量的低铬半钢的组织与性能进行观察、测试及分析，结果表明：热变形能够显著改善低铬半钢的组织与力学性能。其中，40%-50%热变形量的低铬半钢力学性能最好。     

显微组织结构对GJW35钢结硬质合金热疲劳性能的影响

分析了热处理后ＧＪＷ３５钢结硬质合金的显微组织结构，研究了显微组织对合金的热疲劳裂纹萌生及扩展的影响。结果表明，热疲劳裂纹优先在硬质相区中萌生、扩展，钢基体相阻碍裂纹的萌生及扩展。改善显微组织结构，可提高合金的抗热疲劳性能     

H13改进型热作模具钢的组织与性能

 研究了高锰型马氏体热作模具钢SDH3-Mod的室温冲击韧性、回火稳定性和热疲劳性能,并结合透射电镜(TEM)分析了锰对其微观组织的影响。结果表明：SDH3-Mod钢回火组织中残余奥氏体以薄膜状存在于马氏体板条间,提高冲击韧性,延缓裂纹扩展;同时,锰在高温时阻碍碳化物粗化长大和延迟基体的回复再结晶,提高抗回火软化能力和热疲劳性能,使SDH3-Mod性能优于H13。     

无缝钢管连轧机限动芯棒热疲劳性能研究

主要借助于透射电镜研究芯棒的热疲劳行为,并且通过优化热处理工艺来减缓热疲劳裂纹的形成和扩展。研究结果表明,芯棒经冷热疲劳循环后随着循环次数的增加会产生一种循环软化现象,而基体中碳化物的粗化是产生循环软化的主要原因。通过优化材料组织可提高材料的热疲劳性能。     

热变形后的冷却方式对中铬半钢组织与性能的影响

经研究结果得出，１．８３％Ｃ，６．１５％Ｃｒ中铬半钢４０％热变形后的冷却方式对组织与性能的影响，热变形后风冷的中铬半钢的综合机械性能最佳。     

汽车排气系统用铁素体不锈钢的耐热性研究

利用实验室条件下冶炼的Fe-Cr-Nb-Mo铁素体不锈钢,对其高温强度和热疲劳性能进行了研究。研究结果表明:实验钢的高温抗拉强度和屈服强度优于或基本相当于目前所使用的铁素体不锈钢的性能;实验钢的热疲劳裂纹从V形缺口处萌生,夹杂物为裂纹萌生优先区域;热疲劳裂纹长度和扩展速度随热疲劳上限温度的升高而增大;热疲劳裂纹优先沿晶界扩展,高温氧化是疲劳裂纹扩展的主要因素。     

60CrMnMo钢热疲劳裂纹形成及扩展机制的研究

本文借助高频感应加热；金相和电镜（热疲劳试样表面上限温度在７２３－８７３Ｋ，疲劳次数在１０００次内），研究了６０ＣｒＭｎＭｏ钢热疲劳裂纹的形成和扩展过，结果表明：主裂纹在挤入沟处萌生，并使用前沿产生结构疏松；裂纹扩展分为，裂纹与空孔或空孔正断结的忆速不稳定扩展和裂纹沿亚晶界蠕动切断的慢速稳定扩展的两个阶段；并提出了裂纹扩展的数学模型。     

Effect of Hot Deformation on Formation and Growth of Thermal Fatigue Crack in Chromium Wear Resistant Cast Iron

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 …     

斜轧中铬半钢磨球的冲击疲劳和磨损性

通过落球和冲击磨损试验,研究了斜轧1．85％C、5．86％Cr中铬半钢磨球的抗小能量多冲击破坏能力和耐磨性,结果表明：斜轧中铬半钢磨球的冲击疲劳寿命高于铸造半钢磨球,该球经适当的热轧余热热处理,可获得较抗多冲击破坯能力与耐磨性能。     

Fatigue crack initiation and propagation in a quenched and tempered niobium bearing HSLA steel

The fatigue crack initiation and propagation behavior of a niobium bearing HSLA steel heat treated to give two tempered martensitic microstructures presumably with and without fine niobium carbides has been studied by light microscopy, electron microscopy, and strain gage measurements of plastic zone deformation. The high cycle, stress controlled fatigue life of the steel in both heat treated conditions was quite similar with the steel presumably containing the fine niobium carbides having slightly better resistance at low stress amplitudes. This slightly better high cycle resistance is associated with better resistance to fatigue crack initiation for this heat treatment. The fatigue crack propagation behavior of the steel was the opposite. The steel presumably containing the fine niobium carbides exhibited a much faster fatigue crack growth rate than that without them. The difference in growth rates is explained in terms of the plastic work expended during the propagation of the fatigue crack.     

New Duplex Microstructure of Grain Boundary Allotriomorphic Ferrite/Granular Bainite

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Thermal Fatigue Testing of Plasma Transfer Arc Stellite Coatings on Hot Work Tool Steels under Steel Thixoforming Conditions

The thermal fatigue performance of Stellite 12 coating deposited on X32CrMoV33 hot work tool steel via the plasma transfer arc (PTA) process was investigated under steel thixoforming conditions. Stellite 12 coating has made a favorable impact on the thermal fatigue performance of the X32CrMoV33 hot work tool steel. The latter survived steel thixoforming conditions lasting much longer, for a total of 5000 cycles, when coated with a PTA Stellite 12 layer. This marked improvement is attributed to the higher resistance to oxidation and to temper softening of the Stellite 12 alloy. The Cr-rich oxides, which form during thermal cycling, provide adequate protection to high-temperature oxidation. In contrast to hot work tool steel, Stellite 12 alloy enjoys hardening upon thermal exposure under steel thixoforming conditions. This increase in the strength of the coating is produced by the formation of carbides and contributes to the superior thermal fatigue resistance of the Stellite 12 alloy. When the crack finally initiates, it propagates via the fracture of hard interdendritic carbides. The transformation of M₇C₃ to M₂₃C₆, which is more voluminous than M₇C₃, promotes crack propagation.     

Use of the nanoindentation technique for studying microstructure/crack interactions in the fatigue of 4340 steel

The objectives of this research are to study the influence of microstructure on the fatigue crack growth behavior in 4340 steel and to explore the application of the nanoindentation technique for determining the plastic deformation zone at a fatigue crack tip. Two heat treatment conditions were chosen for the steel: annealed and quenched plus tempered. The annealed steel consists of coarse pearlite and proeutectoid ferrite, while the quenched and tempered steel consists of fine tempered martensite. Fatigue crack propagation tests were conducted on disklike compact (DCT) specimens. Subsequently, the nanoindentation technique was applied to quantitatively determine the plastic deformation zone at fatigue crack tips. The plastic deformation zone size determined by the nanoindentation test seems larger than the cyclic deformation zone calculated using the fracture mechanics equation, which involves many assumptions. The fatigue crack growth test results show that the annealed steel has a higher resistance to crack growth than the quenched and tempered steel. The fatigue crack in the annealed steel tends to grow along pearlite domain boundaries, or the cementite/ferrite interfaces within a pearlite domain. In contrast, the fatigue crack in the quenched and tempered steel tends to traverse the fine martensite laths. Consequently, the actual crack path in the annealed steel is rougher than in the quenched and tempered steel and more secondary cracks are observed in the annealed steel.     

基于声发射监测的316LN不锈钢的疲劳损伤评价

疲劳裂纹的萌生与扩展容易导致压力容器及管道的严重疲劳失效.因此就设备的安全可靠性而言,非常有必要对疲劳裂纹扩展过程进行监测,并对疲劳损伤程度进行评估.本文针对316LN不锈钢材料进行疲劳实验研究,利用直流电位法测量实验中的裂纹长度,得到了材料的疲劳裂纹扩展曲线.利用声发射技术对疲劳裂纹扩展过程进行监测,通过声发射多参数分析对疲劳损伤状态进行评价,同时建立了声发射参数与线弹性断裂力学参数之间的关系,并进行寿命预测.研究表明:声发射能够对316LN不锈钢的疲劳裂纹损伤进行有效评估,声发射累积参数如累积计数、累积能量和累积幅值曲线上的转折点标志着疲劳裂纹进入快速扩展阶段,这可以为工程人员提供失效预警;声发射波形和频谱分析表明,噪声信号的幅值较小且信号持续时间较长,信号包含的频率成分比较复杂,而裂纹扩展信号是突发型信号,衰减较快,信号频率主要集中在80~170 kHz范围内;声发射计数率、能量率和幅值率与应力强度因子幅度以及疲劳裂纹扩展速率之间呈线性关系,裂纹长度预测结果与实测值接近.本研究工作对于工程结构的疲劳失效预警和剩余寿命预测具有重要意义.     

0.13C-5Mn中锰钢的裂纹扩展行为

 为了研究基体组织为铁素体和亚稳奥氏体的0.13C-5Mn中锰钢裂纹扩展特性,采用载荷控制对其进行裂纹扩展试验,采用SEM、EBSD等手段表征了裂纹扩展行为。研究结果表明,裂纹扩展机制为滑移和积累损伤双重机制。在裂纹尖端的塑性区内发生亚稳奥氏体转变为马氏体的相变,发生转变的区域远远小于裂纹尖端塑性区尺寸,由于相变吸收了能量以及裂纹闭合效应降低了疲劳裂纹扩展速率。