钨系热作模具钢热疲劳特性的研究

本文研究了钨系热作模具钢3Cr2W8V的热疲劳特性,阐述了一些因素对热疲劳性能的影响,试验结果表明,热疲劳抗力主要取决于材料的高温屈服强度,在强度、塑性及循环热稳定性取得适当配合时最大。     

提高3Cr2W8V钢的铝合金压铸模热疲劳寿命研究

３Ｃｒ２Ｗ８Ｖ钢制作的铝合金压模铸失效形主要是热疲劳破坏。本文目的是通过不同热处理工艺的研究来改善钢的热疲劳性能。试验表明，采用１１８０℃分级淬火，６００℃回火，可较大幅度地提高钢的高温屈服强度、韧性以及热疲劳抗力，从而提高压铸模的使用寿命。     

提高3Cr2W8V钢的铝合金压铸模热疲劳寿命研究

3Cr2W8V钢制作的铝合金压模铸失效形主要是热疲劳破坏，本文目的是通过不同热处理工艺的研究来改善风的热疲劳性能，试验表明，采用1180度分级淬火,600度回火，可较大幅度地提高钢的高温屈服强度，韧性以及热疲劳抗力，从而提高压铸模的使用寿命。     

对3Cr2W8V钢热应力疲劳的再探讨

本文进一步研究了热处理温度和循环温度对3Gr2W8V 钢热疲劳抗力的影响,探讨了热疲劳抗力与常规力学性能之间的联系。结果表明:热疲劳抗力随热处理温度不是单调变化的,分别有一个最佳的淬火温度和最佳的回火温度;随着循环上限温度的升高,热疲劳抗力显著下降,最佳回火温度向高温方向移动,但最佳淬火温度基本不变;在本试验条件下,热疲劳抗力主要受强度控制,在强度和塑性取得适当配合时,热疲劳抗力最大。     

应变滞后能损伤与Uddeholm法热疲劳寿命的相关性

采用应变能研究Uddeholm热疲劳结果表明,当材料的强度、塑性的配合使每一循环所受到的应变能损伤最小时,材料的热疲劳抗力最佳,且可根据材料的常规机械性能及物理性能,予测材料的热疲劳抗力。     

热处理对3Cr2W8V钢热应力疲劳性能的影响

本文通过热疲劳试验,复膜电子金相、扫描断口分析等方法研究了热处理对3Cr2W8V钢热疲劳性能的影响。结果表明:不同热处理状态的钢在热疲劳过程中均有循环软化效应;热疲劳抗力主要受钢的强度及热循环稳定性所控制;热疲劳断口兼有疲劳损伤和氧化腐蚀特征;热疲劳裂纹以沿晶楔入为源,按穿晶——沿晶混合方式扩展。     

热处理对3Cr2W8V钢热疲劳性能的影响

本文通过热疲劳试验、电子金相、扫描断口分析等方法研究了热处理对3Cr2W8V钢热疲劳性能的影响。结果表明:不同热处理状态的钢在热疲劳过程中均有循环软化效应,热疲劳抗力主要受钢的强度及其热循环稳定性控制;热疲劳断口由萌源区和扩展区组成,断口上兼有疲劳损伤和氧化腐蚀的特征;热疲劳裂纹以沿晶楔入为源,按穿晶一沿晶混合方式扩展。     

不同热处理对热模钢H13的组织和性能的影响

本文研究了热模具钢H13（4Cr5MoSiV1)经不同热处理工艺处理后的显微组织和性能，结果表明，H13钢经软氮化处理后，耐磨性，热疲劳抗力较好而冲击韧性较低，250℃等温淬火加回火处理后的冲击韧性最高，热疲劳抗力比政党淬火加回火处理的好，耐磨性较差，300℃等温淬火回火处理的冲吉韧性和疲劳抗力较低，据此，在受冲击载荷情况下，采用250℃等温淬火回火热处理工艺较好，受冲击载荷较小时，采用正常淬火加回火软氮化复合热处理工艺较好。     

热处理和显微组织因素对热作模具钢热疲劳抗力的影响

热疲劳是热作模具的主要失效形式之一。本文阐述了热疲劳抗力与钢的热学性能及力学性能的关系,讨论了奥氏体化温度、回火温度、强韧化处理、表面热处理以及显微组织对热模钢热疲劳抗力的影响。文中对各种试验结果进行了分析,并介绍了若干提高模具热疲劳寿命的实例。     

钢的高温性能和模具的失效分析

本文简要介绍了新型热作模具钢(HD)的高温性能,这种钢的高温强度和热疲劳热磨损抗力优于3Cr2W8V钢,对其原因进行了适当的分析。同时,对铜管热挤压底模进行了失效分析和硬度检验、表层组织分析以及热疲劳热磨损形貌观察,结果表明模具的变形和拉毛失效均与模具材料的高温强度、组织稳定性以及均匀性密切相关,从而说明了HD钢模具使用寿命高的机制。     

燃烧器喷嘴材料热疲劳性能和高温氧化性能研究

采用对比试验方法,通过热疲劳裂纹扩展速率和氧化增重试验,研究了燃煤锅炉燃烧器喷嘴常用的两种材料的热疲劳性能和高温氧化性能,结果表明,铬、锰、硅等元素含量高的新材料ZG40Cr26Ni4Mn3NRe的热疲劳性能和抗高温氧化性能均明显优于原燃烧器喷嘴材料ZG40Cr20Ni5.材料的抗热疲劳性能在很大程度上取决于材料的抗高温氧化性能,热疲劳裂纹在表面缺陷处最易出现,热循环过程中氧化膜的形成和破裂加剧了热疲劳裂纹的萌生和扩展.     

Thermal fatigue behavior of 441 ferritic stainless steel in air and synthetic automotive exhaust gas

The thermal fatigue behavior of 441 ferritic stainless steel was investigated in air and synthetic automotive exhaust gas by the cyclic tests under 100°C–800°C and 900°C conditions. After the fracture failure, the microstructure, oxide film, and precipitated phases were analyzed using optical microscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. In both atmospheres, increasing the maximum temperature from 800°C to 900°C results in lower strength and fatigue life and higher elongation and grain size. At the same maximum temperature, the thermal fatigue life of the specimen is lower in the synthetic exhaust gas than in the air. Both the higher maximum temperature and the synthetic exhaust gas facilitate fatigue failure. The failure mechanism is discussed according to the grain size, thermal stress, high-temperature oxidation rate, and the precipitation of secondary phases. Some precipitated carbides play an important role in the rapid fatigue failure of specimens in the synthetic exhaust gas.

     

Anisotropy of Fatigue Behavior and Tensile Behavior of 5A06 Aluminum Alloy Based on Infrared Thermography

The fatigue behavior during high cycle fatigue testing and the tensile behavior of 5A06 aluminum alloy considering the anisotropy were studied.Two types of specimens including longitudinal specimen(parallel to the rolling direction) and transverse specimen(perpendicular to the rolling direction) were prepared.Infrared thermography was employed to monitor the temperature evolution during the fatigue and tensile tests.The temperature evolution curves in the two directions were contrastively analyzed.It is found that the temperature evolution during fatigue process possesses four stages:initial temperature rise stage,slow temperature decline stage,rapid temperature rise stage,and finial temperature decline stage.The heat generating mechanisms of the four stages are discussed.Obvious differences can be found between the longitudinal specimen and transverse specimen in fatigue strength and fatigue life.The fatigue strength and fatigue life of longitudinal specimen are higher than those of transverse specimen.During the tensile and fatigue testing process,the fracture temperature in the transverse direction are higher than that in the longitudinal direction.The fatigue strength prediction by means of infrared thermography has a good consistency with that by the traditional method.     

Structures and Properties of High-Carbon High Speed Steel by RE-Mg-Ti Compound Modification

The effects of rare earths ( RE )-Mg-Ti compound modification on the structures and properties of high-carbon high speed steel ( HSS ) were researched. The impact toughness (ak), the fracture toughness (Klc)andt hreshold of fatigue crack growth (△Kth)are tested. The thermal fatigue test is done on a self-straining thermal fatigue tester, the wear test is done on a high temperature wear test machine. The results show that the matrix can be reftned by the RE-Mg-Ti compound modification, the euteetic carbides are inclined to spheroidicize and are distributed everdy, the morphology and distribution of eutectic carbides are improved by appropriate RE-Mg-Ti complex modification. After RE-Mg-Ti compound modification, a little effects can be found on the strength, hardness and red hardness, but the fractare toughness(Klc) and threshold of fatigue crack growth (△Kth) are improved in the meantime, the impact toughness (ak) is increased by over one time, and the rasistanee to thermal fatigue and wear resistanee at an elevated temperature are remarkably improved.     

高铬镍合金白口铸铁热疲劳断裂过程的动态观察

用ＨＭ－１００型高温金相显微镜,通过模拟热疲劳的实验方法,动态观察了高铬镍合金白口铸铁热疲劳裂纹的萌生及扩展过程。实验表明：组织为奥氏体加Ｍ２３Ｃ６型碳化物的高铬镍合金白口铸铁热疲劳裂纹主要沿晶界萌生扩展,热疲劳断口为混合型断口。增加含碳量则降低高铬镍合金白口铸铁的热疲劳抗力。     

5CrNiMo钢的等温淬火

本文研究了5CrNiMo钢的马氏体、下贝氏体及低温上贝氏体与马氏体混合组织的回火组织特征和冲击疲劳断口特征.三种组织回火至HRc38等强度条件下,其塑性和韧性基本相等,但下贝氏体组织的冲击疲劳抗力高于马氏体回火组织,因此等温淬火工艺主要适用于以疲劳开裂为主要失效形式的热锤锻模.     

喷丸前后板簧脱碳表层的研究

汽车板簧常有使疲劳强度大幅度下降的脱碳层,而喷丸处理可以有效地改善其疲劳性能。目前用来表征板簧脱碳表面力学特性最常见的指标是Ｘ射线谱线的半高宽和显微硬度,该二参量不仅本身存在缺陷,而且二者给出的结果也不一致。采用Ｘ射线应力分析技术,可以获得金属表面的真实应力———应变关系,从而可以用表面屈服强度对板簧脱碳表面进行研究。采用逐级剥离方法可测得半高宽、显微硬度和表面屈服强度沿脱碳层深度的分布,测量结果表明,脱碳层严重软化,但上述３参量随层深的变化规律存在一定的差异。由于表面屈服强度直接反映材料抵抗塑性形变的能力,因此,表面屈服强度更能正确地表征材料力学特性的分布。     

晶粒度对铝合金疲劳性能的影响

在含有表面粗晶层组织的7A04高强度铝合金锻件上取样,设计一种非均匀材料四点弯曲疲劳试验,研究粗晶组织对7A04铝合金疲劳强度的影响。结果表明,表面粗晶组织会降低7A04铝合金试样表面驻留滑移带的形成抗力,导致疲劳裂纹更容易在粗晶层组织表面萌生,削弱了材料的疲劳性能。