循环泵法兰螺栓断裂分析

通过金相检验、断口分析和化学成分分析等方法对循环泵法兰螺栓的断裂原因进行了分析。结果表明：螺栓早期断裂失效的主要原因是材料使用有误,加上受海水中的氯离子腐蚀引起奥氏体不锈钢螺栓产生应力腐蚀裂纹并扩展所致。     

快卸卡箍螺栓断裂原因分析

通过断口形貌观察、X射线能谱分析、金相检验和硬度检测等试验方法,对某燃油供油导管快卸卡箍螺栓的断裂原因进行了分析,并与螺栓冲击断口和氢致疲劳断口进行了比较分析。结果表明:该快卸卡箍螺栓断口特征与冲击断口和氢致疲劳断口明显不同,其断裂性质为应力腐蚀断裂,裂纹起源于螺栓光杆段的侧表面;螺栓表面加工粗糙且没有防护对裂纹的萌生有一定的影响。对螺栓表面进行防腐处理可有效避免该类故障的再次发生。     

超高强度螺栓断裂失效分析

材质为35CrMnSiA钢的M56超高强螺栓在装配过程中,其螺帽与螺杆的R过渡处发生断裂。经检查,未装配的同批螺栓在螺帽与螺杆的R过渡处也存在微裂纹。借助化学分析、金相检验、扫描电镜和力学性能测试等手段对超高强度螺栓的显微组织、力学性能、宏观和微观断口形貌等进行了研究。结果表明,螺栓在表面处理过程中,表面富氢而产生氢致裂纹,在应力作用下,发生氢脆断裂。     

电站稳压器支承裙座锚固螺栓断裂失效分析

某电站稳压器支承裙座锚固螺栓在安装一段时间后发生断裂,从力学和材料角度对该螺栓断裂原因进行了分析。对断裂螺栓进行了金相组织观察、化学成分分析、力学性能试验以及断口的宏观及微观形貌观察,发现螺栓断口附近组织异常,外部环状带晶粒粗大,硬度和抗拉强度偏低导致裂纹启裂,裂纹逐渐扩展引起螺栓整体失稳断裂;螺栓局部出现组织异常的原因为螺栓热处理过程中控温不当导致局部过热。     

高强度螺栓断裂分析

采用断口分析，金相检验和硬度测定等方法，对高强度螺栓断裂原因进行了分析，断口分析结果表明，断口平坦，呈放射状花样，微观形态主要为准确理花样，表明螺栓的断裂是脆性断裂，同时发现，在断口附近还存在横向内裂纹，内裂纹的断口形态与断裂断口一样，金相分析表明，材料棒中存在严重的中心碳偏析，而中心碳偏析是引起断裂的主要原因。     

252kV GIS机构止动螺栓的断裂失效分析

某批次35Cr Mo合金钢252 k V气体绝缘金属封闭开关设备(GIS)机构电镀锌止动螺栓在合闸试验调节中发生断裂失效,通过化学成分分析、断口分析、硬度测试、氢脆评估试验、金相检验等方法对螺栓断裂原因进行了分析。结果表明:该止动螺栓断裂是由氢脆造成的,而止动螺栓发生氢脆断裂是由螺栓电镀锌后去氢工艺不当造成的。最后提出了预防螺栓氢脆断裂的改进措施。     

镀锌螺栓的断裂分析

镀锌螺栓在组装后放置1～2d于根部或头部发生大量断裂,采用化学成分分析、金相检验、硬度检测及断口分析等方法对螺栓的断裂性质及断裂原因进行了分析。结果表明：螺栓断裂为典型的氢脆断裂;主要原因是螺栓在后期酸洗和电镀过程中除氢不彻底,吸入了大量的氢;次要原因是热处理工艺控制不当,使螺栓心度硬度偏高,增加了其对氢脆的敏感性;两者共同作用最终导致螺栓发生氢脆断裂。     

挤出机摩擦离合器螺栓断裂分析

某挤出机中气动摩擦离合器与减速器端连接的螺栓在使用过程中经常发生断裂,改用另一种材料的螺栓后情况未有很好改善。采用化学成分分析、力学性能测试、断口分析和金相检验等方法,对螺栓断裂的原因进行了分析。结果表明：起裂源位于螺栓的加工刀痕、表面擦伤处及因微动疲劳所致的螺纹微裂纹处,这些部位均存在应力集中,在振动作用下,萌生的裂纹不断扩展,使有效承载面积不断减小,最终引起螺栓疲劳断裂。     

发动机缸盖螺栓断裂原因分析

某发动机缸盖螺栓在装配后发生断裂。通过宏观、微观检验以及化学成分分析、力学性能测试、氢脆试验等对断裂原因进行了分析。结果表明:缸盖螺栓发生了氢脆断裂。其原因是缸盖螺栓在表面磷化后的去氢处理不当,导致装配后缸盖螺栓在拉应力的作用下产生氢脆裂纹,并最终发生断裂。     

螺栓断裂分析

采用多种分析手段对螺栓断口及基体进行分析,并从螺栓的使用环境、受力情况及工作状况分析和探讨了断裂的原因。结果表明,螺栓的断裂是由于缝隙腐蚀引起,在应力腐蚀及腐蚀疲劳的作用下最终导致螺栓断裂,是由多种因素综合所致。     

六角头螺栓断裂分析

采用宏观检验、断口分析、化学成分分析、力学性能测试及金相检验等方法对六角头螺栓的断裂原因进行了分析。结果表明:六角头螺栓在酸洗和电镀工艺后未进行充分的去氢处理,致使六角头螺栓中残存了较多的氢,在应力和氢的共同作用下造成了螺栓的延迟断裂;其次,六角头螺栓表面存在0.2 mm左右的渗碳层,使得螺栓表面硬度提高,增加了螺栓的氢脆敏感性。     

高强度钛合金螺栓断裂失效分析

规格为M4×30 mm高强度钛合金螺栓在正常预紧装配后自行断裂。采用金相检验、扫描电镜断口分析、二次离子质谱分析和螺栓的受力分析等方法对螺栓断裂的原因进行了分析。结果表明,螺栓断裂的性质为低应力脆性断裂,断裂机理为氢致延迟断裂,导致螺栓氢致延迟断裂的原因主要与该批棒材原始氢含量过高有关。     

汽车方向盘自挤螺钉断裂分析

采用断口分析、金相检验、显微硬度测试、化学成分分析、氢脆预载荷试验等方法对某型号乘用车方向盘固定螺钉的断裂原因进行了分析。结果表明：螺钉的断裂性质是氢致延迟断裂,裂纹起源于螺钉头下第一牙底。电镀后驱氢不充分致使螺钉表层残留较高含量的氢,表面渗碳层及首牙处的应力集中构成了导致氢脆的3个敏感因素。     

Participation of hydrogen in slow bending behaviour of 304L stainless steel

Abstract

Three point bending test studies on 304L austenitic stainless steel at 293 and 77 K demonstrated that hydrogen charging promoted the formation of brittle fracture features at 293 K; promoted the formation of larger and shallower microvoids at 77 K; and reduced the energy absorbed by the material at both temperatures, although to a greater degree at 77 K. These observations suggest that although hydrogen redistribution during testing can affect the failure mode of this material, it is not a necessary requirement for hydrogen induced degradation. Furthermore, the observation that embrittlement is more severe at liquid nitrogen temperatures indicates that the effects of low temperatures and hydrogen may interact synergistically. The data presented in this paper are consistent with a model in which the embrittlement process is affected by local hydrogen concentrations.

MST/1930     

Hydrogen Embrittlement Failure of a Galvanized Washer

A galvanized washer used for a locomotive impeller broke into three pieces after an accumulative service of 4–5 h. The washer is fabricated from 42CrMo steel and the fracture surfaces reveal intergranular fracture morphology with microvoid coalescence observed on the facets. Microstructure observation indicates the presence of a severely banded microstructure mainly consisting of untempered martensite and bainite. The average hardness of the failed washer is HRC 59.1. The hardness value is much higher than specified (HBW 260-300) and is in the range of hydrogen embrittlement susceptibility. The significant number of elongated MnS inclusions acting as traps of hydrogen are present in the martensite regions. The delayed fracture associated with the predominance of intergranular fracture micromechanism and the high hardness level and the presence of microstructure susceptible for the hydrogen embrittlement strongly suggest the hydrogen embrittlement being the mostly possible failure mechanism. The likely sources for hydrogen entrapment are the electro-galvanizing process and acid-pickling before galvanizing. The hydrogen was retained in the washer due to absence of baking treatment to remove it or insufficient baking. The incorrect heat treatment process before galvanizing resulting in the high hardness level of the washer is mainly responsible for the occurrence of hydrogen embrittlement on the washer.     

减震器托架断裂失效分析

目的解决减震器托架断裂失效的问题。方法通过化学成分分析、力学性能分析、断口扫描分析、金相组织分析、氢含量测试等手段,确定了减震器托架断裂性质及原因。结果减震器托架发生氢脆断裂。结论由于酸洗过程中材料渗入过量氢,导致氢脆并发生断裂。为防止类似的失效事故再次发生,提供了一些指导性建议。     

Mechanisms of stress-corrosion cracking and liquid-metal embrittlement in Al-Zn-Mg bicrystals

Metallographic and fractographic studies of intercrystalline fracture in high-purity Al-6Zn-3Mg bicrystals in inert, liquid metal, and water environments are described. The effects of variations in grain-boundary microstructure on fracture and the effects of cathodically charging specimens with hydrogen prior to testing in inert environments were also investigated. Mechanisms of liquid-metal embrittlement, stress-corrosion cracking and pre-exposure embrittlement are discussed in the light of these results. The observations suggest that liquid-metal embrittlement and stress-corrosion cracking generally occur by a plastic-flow/microvoid-coalescence process that is more localized than that which occurs in inert environments. It is proposed that adsorbed liquid metal or hydrogen atoms weaken interatomic bonds at crack tips, thereby facilitating the nucleation of dislocations and promoting the coalescence of cracks with voids.     

汽车零部件氢致断裂的分析及预防

对氢脆的机理、氢脆的断口形貌、氢脆的表观形式、影响氢脆的因素、氢脆的预防以及氢脆的检查分别进行了介绍,并通过对汽车生产中典型氢致断裂案例的分析和研究,对氢脆断口形貌提出了判定依据:脆性断口、沿晶断裂、显微气孔、二次裂纹、发线花纹。并依据氢脆发生的机理和主要影响因素,强调对于高强度零件及时有效地进行去氢处理的重要性。     

The effect of baking time,fillet radius,and hardness on the lifecycles of pole fastening screws in an electric motor with hydrogen embrittlement

In order to protect bolts from corrosion, electroplating such as zinc plating is widely used. However, hydrogen can easily penetrate or diffuse into the vacancies and dislocations between the lattices of bolt steel during electroplating. As the diffused hydrogen defects inside the lattice are in gaseous form, small cracks can easily be produced due to high pressure from the hydrogen gas. In this research, in order to determine the root cause of the fracture in pole fastening screws resulting from hydrogen embrittlement in typical electric motors, additional factors that accelerate hydrogen embrittlement fracture were selectively applied, including a small fillet in the head–shank transition and excessive hardness, and parametric study was performed experimentally.