35CrMo钢螺栓断裂原因分析

某电梯用10.9级35CrMo钢螺栓在安装一段时间后发生断裂,采用直读光谱仪、扫描电子显微镜、光学显微镜以及维氏硬度计等仪器设备对螺栓断裂原因进行了分析。结果表明:该螺栓在氢和静拉力的共同作用下发生了氢致延迟断裂。     

某铁路桥梁用20MnTiB钢高强螺栓断裂原因

某铁路主桥钢桁梁杆间20MnTiB钢高强螺栓发生断裂。采用复检试验、化学成分分析、金相检验、硬度测试、力学性能测试和断口分析等方法,分析了螺栓断裂的原因。结果表明：螺栓的断裂形式为氢致断裂,断裂原因是螺栓中锰元素含量偏高,导致耐腐蚀性下降,长期在潮湿环境下服役,致使螺栓发生氢致断裂。     

风力发电机组主轴连接螺栓断裂原因分析

采用宏观检验、化学成分分析、金相检验、力学性能试验、断口分析、有限元分析等方法对某风力发电机组主轴连接螺栓断裂原因进行了分析。结果表明:该主轴连接螺栓断裂模式为氢致脆性断裂;螺栓表面处理前的酸洗工艺控制不当造成大量氢渗入,是导致其氢致脆性断裂的主要原因。     

车用六角头螺栓断裂原因

某车型装配牵引鞍座与瓦楞连接用螺栓在安装扭紧后的静置调试过程中发生断裂,通过断口分析、化学成分分析、氢含量分析、力学性能测试、金相检验等方法,对螺栓的断裂原因进行了分析。结果表明,螺栓断裂模式为氢致脆性断裂。建议螺栓在制造过程中及时除氢。     

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。     

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。     

SWRCH22A钢自攻螺钉断裂原因分析

SWRCH22A钢自攻螺钉在装配一天后发生断裂,通过宏观检验、化学成分分析、金相检验、断口分析及氢含量测试等方法,对其断裂原因进行了分析。结果表明:螺钉的断裂性质为氢致延迟脆性断裂;螺钉经过热处理后的显微组织为回火马氏体和少量残余奥氏体,而马氏体为氢脆敏感组织,且螺钉经过电镀处理,使得其内部氢的质量分数高达0.000 49%,最终导致螺钉于应于集中的螺纹起始位置根部发生氢致延迟脆性断裂。     

N_Ⅳ型平列双扭弹簧延迟断裂分析

某N_Ⅳ型平列双扭弹簧约有0.7%在装配中和装配后发生延迟断裂,采用宏观分析、扫描电镜观察以及工艺分析等方法对扭簧延迟断裂的原因进行了分析。结果表明:扭簧失效是氢致延迟脆性断裂,基体夹杂物相处形成高危应力及电镀后去氢不彻底是导致其断裂的主要原因。     

30MnSi预应力混凝土用钢棒延迟断裂原因

某预应力混凝土用钢棒在静置过程中发生了延迟断裂，采用宏观观察、化学成分分析、硬度测试、扫描电镜和能谱分析、金相检验等方法对其断裂原因进行分析，结果表明：预应力混凝土用钢棒断裂的主要原因为30MnSi材料表面存在结疤及微裂纹等缺陷，这些缺陷为氢致延迟断裂提供了条件。     

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。     

氢气压缩机缸盖螺栓断裂失效分析

某石化公司氢气压缩机缸盖螺栓发生断裂,采用宏、微观断口分析、化学成分分析、金相检验以及力学性能测试等试验手段分析了该氢气压缩机缸盖螺栓的断裂原因。结果表明：断裂起源于螺杆与螺栓头部连接螺纹末端的应力集中处,由于应力集中,加之螺栓强度等级偏低,使螺栓在长期工作过程中的往复交变应力和扭转应力共同作用下发生了低应力高周疲劳断裂。     

汽车螺栓断裂失效分析

对汽车上某一连接发动机和车身的高强度级别螺栓在使用过程中发生的断裂进行了分析.结果表明,螺栓的化学成分和金相组织均正常,其断裂为多源疲劳断裂.经对螺栓使用过程中的受力情况分析,认为螺栓断裂主要是由于该螺栓在安装时预紧力不足或汽车在运行过程中,发动机自身振动和汽车行进中颠簸而使螺栓产生了松动,从而受到交变载荷而在应力集中最为严重的螺纹根部发生疲劳断裂.     

Failure analysis of vessel propeller bolts under fastening stress and cathode protection environment

This paper describes the failure analysis of propeller blade fastening bolts made from martensitic stainless steel 0Cr16Ni5Mo, which was ruptured under service of cathode protection for 5 years. The general crack pattern of the bolts, fractographic features, hydrogen content determination and slow tensile test results are all exhibiting the characteristics of hydrogen embrittlement. Accordingly, hydrogen diffusion driven by hydrogen concentration gradient and stress concentration was identified by experiment and finite element analysis (FEA). The morphology of the crack was intergranular of initiation from bolt cap root surface, and quasi-cleavage of propagation. The hydrogen distribution indicated that the hydrogen concentration in the bolt was in gradient distribution, and the region farther away from the sea water contains less hydrogen content. This revealed that hydrogen entered the bolt top surface through sea water under cathodic protection, and diffused from top to cap. The hydrogen content of the cap where crack initiated was 7.0 ppm, which was much higher than that in bolt shaft with normal content of 1.1 ppm. Results of low tensile test together with fractographic observation showed that the brittleness of the bolt was enhanced by the effect of hydrogen. Stress distribution calculated by FEA analysis indicated that the maximal stress of the bolt was about 1016 MPa, located at cap root surface which was consistent with crack initiation sites. The stress drove hydrogen to accumulate at root surface until cracking occurred. In a sum, the failure was attributed to the hydrogen diffusion, local high stress, and the martensitic microstructure susceptible to hydrogen embrittlement. Remedial measures such as avoiding over protection potential, that increase tempering temperature were suggested. Methods to optimize stress distribution of the bolt were also suggested based on FEA calculation.     

高强螺栓断裂原因分析

对断裂的高强度螺栓断口及其腐蚀产物、螺栓表面存在的微裂纹进行了观察分析；对螺栓材料进行了热处理、氢脆敏感性和力学性能试验。结果表明，引起断裂发生的裂纹源─—微裂纹是Ｃｌ￣－应力腐蚀及氢脆交互作用的结果。断裂螺栓材料变脆是由于时效致使晶界产生铁铬碳化物偏聚引起的。对断口形貌和断裂过程用断裂力学方法提出了解释。     

双头螺栓失效分析

与汽车电机装配在一起的双头螺栓在拧紧后不久便发生断裂。采用扫描电镜、化学分析、金相检验等方法对失效件进行了检测，同时又进行了氢脆试验验证。结果表明，螺栓在进行表面酸洗及电镀时，氢向金属内部扩散和富集，当氢浓度达到一定临界值后，促使氢致裂纹的产生和扩展。在外应力的作用下，即出现氢脆现象导致螺栓断裂。     

Material influence on the stress corrosion cracking of rock bolts

Rock bolt stress corrosion cracking (SCC) has been investigated using the linearly increasing stress test (LIST). One series of experiments determined the threshold stress of various bolt metallurgies (900 MPa for 1355AXRC, and 800 MPa for MAC and MA840B steels). The high values of threshold stress suggest that SCC begins in rock bolts when they are sheared by moving rock strata. SCC only occurred for environmental conditions which produce hydrogen on the sample surface, leading to hydrogen embrittlement and SCC. Different threshold potentials were determined for a range of metallurgies.Cold work was shown to increase the resistance of the steel to SCC. Rock bolt rib geometry does not have a direct impact on the SCC resistance properties of the bolt, although the process by which the ribs are produced can introduce tensile stresses into the bolt which lower its resistance to SCC.     

吐丝机螺栓断裂的失效分析

采用化学成分分析、宏观扣微观检验、金相组织分析和力学性能测定等方法分析了吐丝机用高强度螺栓发生断裂的原因。结果表明,由于机加工不当而在螺纹根部产生表面缺陷,并且这些表面缺陷周围在随后的热处理过程中发生全脱碳,大大降低了螺栓的疲劳强度,导致螺栓在使用过程中早期疲劳断裂。