42CrMoA钢风电螺母调质裂纹形成原因分析
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摘要
针对42CrMoA钢制10. 9级风电螺母调质处理后出现裂纹失效的现象,采用荧光光谱仪、光学显微镜、扫描电镜、洛氏硬度计、拉伸试验机、冲击试验机检测样品的化学成分、组织状态、综合力学性能,分析裂纹形成的原因,并提出改进方法。结果表明:调质裂纹是淬火裂纹,在淬火过程中产生,并在回火过程中氧化;原材料的混晶组织是造成调质裂纹形成的原因,混晶组织在淬火过程中,表面产生马氏体,心部产生块状铁素体及少量网状铁素体,相变应力集中,变形不均匀,导致调质裂纹产生并扩展,且进一步导致材料综合力学性能大幅度下降;混晶组织经完全退火加正火后得到均匀晶粒组织,经调质处理后,无缺陷组织和无裂纹现象出现。
For the phenomenon of crack failure after quenching and tempering of grade 10. 9 wind turbine nuts made of 42 CrMoA steel,the chemical composition,microstructure,and comprehensive mechanical properties of the sample were measured by using fluorescence spectrometer,optical microscope,scanning electron microscope,Rockwell hardness tester,tensile tester,and impact tester. Meanwhile,the causes of cracks were analyzed,and improvement methods were proposed. The results show that the quenched and tempered cracks are quenched cracks generated during the quenching process then oxidized during the tempering process. The mixed grain structure of the raw material is responsible for the appearance of quenched and tempered cracks. The mixed grain structure leads to martensite at sample surface and massive ferrite and few network ferrite in the core during the quenching process. Thus,the phase transition stress is concentrated and the deformation is not uniform,which results in the generation and propagation of quenched and tempered cracks,and the comprehensive mechanical properties of the material are greatly reduced. By applying completely annealing plus normalization,the mixed grain micro structure changes into a uniform grain microstructure,then the material has no defects and no cracks after quenching and tempering.
For the phenomenon of crack failure after quenching and tempering of grade 10. 9 wind turbine nuts made of 42 CrMoA steel,the chemical composition,microstructure,and comprehensive mechanical properties of the sample were measured by using fluorescence spectrometer,optical microscope,scanning electron microscope,Rockwell hardness tester,tensile tester,and impact tester. Meanwhile,the causes of cracks were analyzed,and improvement methods were proposed. The results show that the quenched and tempered cracks are quenched cracks generated during the quenching process then oxidized during the tempering process. The mixed grain structure of the raw material is responsible for the appearance of quenched and tempered cracks. The mixed grain structure leads to martensite at sample surface and massive ferrite and few network ferrite in the core during the quenching process. Thus,the phase transition stress is concentrated and the deformation is not uniform,which results in the generation and propagation of quenched and tempered cracks,and the comprehensive mechanical properties of the material are greatly reduced. By applying completely annealing plus normalization,the mixed grain micro structure changes into a uniform grain microstructure,then the material has no defects and no cracks after quenching and tempering.
引文
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[3]徐钢新,陈亮,李勃,等.多次调质对42CrMo钢组织和力学性能的影响[J].金属热处理,2014,39(5):112-114.Xu Gangxin,Chen Liang,Li Bo,et al.Influence of repeated quenching and tempering on microstructure and mechanical properties of42CrMo steel[J].Heat Treatment of Metals,2014,39(5):112-114.
[4]张宇,刘仁东,王科强,等.42CrMo钢动态CCT曲线及组织转变[J].金属热处理,2012,37(12):37-40.Zhang Yu,Liu Rendong,Wang Keqiang,et al.Dynamic continuous cooling transformation curves and microstructure evolution of 42CrMo steel[J].Heat Treatment of Metals,2012,37(12):37-40.
[5]李秀珍.兆瓦级风机高强度螺栓微裂纹扩展分析与疲劳强度研究[D].长沙:中南大学,2014.
[6]余兆新,蒋佩华,姚志江,等.42CrMo钢螺栓断裂分析[J].金属热处理,2012,37(4):128-130.Yu Zhaoxin,Jiang Peihua,Yao Zhijiang,et al.Fracture analysis of bolt made of 42CrMo steel[J].Heat Treatment of Metals,2012,37(4):128-130.
[7]王长健.42CrMo钢大型厚壁管裂纹形成原因分析[J].金属热处理,2014,39(12):164-166.Wang Changjian.Cracking cause analysis of 42CrMo steel thick wall pipe[J].Heat Treatment of Metals,2014,39(12):164-166.
[8]高雅,孙建林,贠冰,等.Q460C钢组织特性对表面裂纹成因的影响分析[J].材料科学与工艺,2011,19(5):139-143.Gao Ya,Sun Jianlin,Yun Bing,et al.Effect of microstructure characteristic of Q460C steel on surface cracks[J].Materials Science and Technology,2011,19(5):139-143.
[9]聂辉文,聂俊红,曾松盛.锯片基体用50Mn2V钢淬透性不良原因分析[J].机械工程材料,2011,35(5):59-61.Nie Huiwen,Nie Junhong,Zeng Songsheng.Analysis of bad hardenability of 50Mn2V steel for saw blade matrix[J].Materials for Mechanical Engineering,2011,35(5):59-61.
[10]王倩,田加红,丁霞,等.45钢主轴热处理畸变原因分析与改进措施[J].金属热处理,2013,38(5):115-118.Wang Qian,Tian Jiahong,Ding Xia,et al.Distortion and countermeasures of 45 steel mainshaft quenched and tempered[J].Heat Treatment of Metals,2013,38(5):115-118.
[11]杨慧,刘宗昌,王玉峰,等.35CrNi3MoV钢的混晶及防止方法[J].金属热处理,2003,28(12):48-50.Yang Hui,Liu Zongchang,Wang Yufeng,et al.Mixed grain structure of 35CrNi3MoV steel and its countermeasure[J].Heat Treatment of Metals,2003,28(12):48-50.
[12]赵辉,柴武倩,杨强云,等.32高压输电钢脚疲劳失效分析[J].热加工工艺,2015,44(6):232-234.Zhao Hui,Chai Wuqian,Yang Qiangyun,et al.Fatigue failure analysis on32 steel pin of high-voltage transmission[J].Hot Working Technology,2015,44(6):232-234.
[13]董企铭,李炎,江锡堂.20Cr2Ni4A钢混晶组织对其力学性能的影响[J].热加工工艺,1989(5):13-17.Dong Qiming,Li Yan,Jiang Xitang.The effect of mixed grain structure of 20Cr2Ni4A steel on its mechanical properties[J].Hot Working Technology,1989(5):13-17.