材料学硕士论文代写：关于60Si2Mn钢热机械损伤行为的探讨
摘要 3-4
Abstract 4-5
第1章绪论 8-19
1.1课题背景及研究意义 8-9
1.260Si2Mn弹簧钢的性质及应用 9-12
1.3金属材料的热机械性能研究 12-18
1.3.1金属材料的高温拉伸性能研究 12-13
1.3.2金属材料的蠕变研究 13-15
1.3.3金属材料的热机械循环研究及棘轮效应 15-18
1.4本课题主要研究内容 18-19
第2章试验材料及试验方法 19-26
2.1试验材料 19
2.2热处理工艺 19
2.3试样的加工 19-20
2.460Si2Mn钢的拉伸试验 20-21
2.5蠕变及热机械循环试验 21-23
2.5.1蠕变试验 21-22
2.5.2热机械循环试验 22-23
2.660Si2Mn钢制锁钩应力应变分布有限元模型 23-24
2.760Si2Mn钢的硬度测试及组织结构分析 24-26
2.7.1硬度测试 24
2.7.2金相组织观察 24-25
2.7.3扫描电子显微组织观察 25
2.7.4透射电子显微组织观察 25-26
第3章60Si2Mn钢的机械性能与组织 26-37
3.1引言 26
3.2热处理前后60Si2Mn钢的机械性能与组织 26-29
3.2.1回火温度对60Si2Mn钢机械性能的影响 26-27
3.2.2热处理前后60Si2Mn钢室温拉伸性能 27-28
3.2.3热处理前后60Si2Mn钢显微组织 28-29
3.360Si2Mn钢在不同温度下的拉伸性能 29-30
3.460Si2Mn钢在不同温度下的拉伸断口分析 30-36
3.4.1宏观断口分析 30-32
3.4.2微观断口分析 32-36
3.5本章小结 36-37
第4章60Si2Mn钢的蠕变研究 37-47
4.160Si2Mn钢的蠕变曲线 37-39
4.2稳态蠕变速率的计算 39-40
4.360Si2Mn钢的蠕变组织特征 40-43
4.460Si2Mn钢的蠕变断裂特征 43-45
4.5本章小结 45-47
第5章热机械循环对60Si2Mn钢拉伸性能的影响 47-57
5.160Si2Mn钢的热机械循环曲线及特性分析 47-50
5.1.1热机械循环应变损伤特性 47-48
5.1.2循环应力-应变曲线 48-49
5.1.3棘轮安定饱和状态 49-50
5.2热机械循环对60Si2Mn钢常温拉伸性能的影响 50-53
5.2.1拉伸应力-应变曲线比较 50-51
5.2.2热机械循环后的拉伸试样断口形貌 51-53
5.360Si2Mn钢制锁钩应力应变分布的有限元分析 53-55
5.3.160Si2Mn钢制锁钩等效应力的分布 53-54
5.3.2循环应力-应变曲线 54-55
5.4本章小结 55-57
结论 57-58
参考文献 58-65
致谢 65
【摘要】 本文利用RD-50蠕变试验机和热机械循环设备测试了中温回火态60Si2Mn钢在100℃、150℃、200℃、300℃、400℃时的拉伸性能和蠕变规律,以及温度范围为100~400℃和-50~250℃的热机械载荷作用下的变形行为,并利用光学显微镜、扫描电镜(SEM)和透射电镜(TEM)观察分析了该合金在不同热机械载荷作用前后的组织和试样断口形貌。利用Marc2003软件对60Si2Mn钢制锁钩在热机械载荷作用下的应力应变分布进行了有限元分析。拉伸试验结果表明,随拉伸温度的升高,60Si2Mn钢的抗拉强度和屈服强度降低,塑性增加,400℃时与室温相比,合金的屈服极限由1374MPa降为1036MPa,下降了24.6%,而延伸率由9.5%上升到23.4%,增加幅度近150%。而随温度升高,试样断口呈现更明显的韧性断裂特征。蠕变试验结果表明,60Si2Mn钢在100~300℃的蠕变曲线均呈现典型蠕变特点,而在400℃蠕变时,其第一、二阶段不明显,很快进入第三阶段导致断裂。采用幂函数式的Norton公式作为稳速阶段的蠕变率,得到各温度下应力指数分别为:100℃,2.312;150℃,2.179;200℃,2.401;300℃,2.921;400℃,1.089。可见,100~300℃的蠕变机制主要为位错粘滞滑移,400℃下为扩散型。TEM观察的位错形态与此机制相吻合。蠕变断裂试样的断口存在明显的颈缩,由韧窝和平直撕裂棱组成,呈现延性沿晶断裂特征。经100次温度范围为100~400℃的热机械循环试验发现,热机械循环损伤要比单一温度和载荷下等效蠕变损伤严重,循环过程中,材料的应力-应变曲线呈现不闭合的迟滞回线状态,应变逐渐累积;而经温度范围为-50~250℃的热机械循环试验时,材料的应变损伤速率极小。60Si2Mn钢制锁钩的有限元应力应变分析结果表明,锁钩弯角处应力集中程度最大,该处截面(对应124~134节点)上节点130受到最大的等效应力,为锁钩失效的薄弱点;节点130的应力-应变曲线也呈不闭合迟滞回线状态,应变逐渐累积,与材料试验规律一致。
材料学硕士论文代写【Abstract】 The tensile, creep properties of 60Si2Mn steel in medium temperature tempering were performed at temperature of 23℃、100℃、150℃、200℃、300℃and 400℃by 810 Material Test System and RD-50 Creep Eequipment. The damage behaviour of 60Si2Mn steel after thermal-mechanical cycling between 100 and 400℃or between -50 and 250℃were also investigated. The microstructure and fracture pattern of crept and thermal-mechanical cycled specimens were observed by Optical Microscope, Scanning Election Microscope (SEM) and Transmission Electron Microscope (TEM). The distribution of stress and strain during thermal-mechanical cycling in 60Si2Mn steel lock hook was analyzed by means of the MSC.Marc finite element analysis software.The tensile experimental results showed that with increasing temperature, the tensile strength and yield strength of 60Si2Mn steel decreased, while the plasticity increased. The yield strength decreased by 24.6% from 1374MPa to 1036MPa, and the elongation increased by 150% from 9.5% to 23.4% at 400℃comparing with at 23℃. The fracture patterns of specimens exhibited more apparent characteristic of ductile fracture with increasing temperature.The creep experimental results showed that between 100℃and 300℃, the creep curve of 60Si2Mn displayed classical creep characteristic. But at 400℃, the creep curve mainly consisted of the third stage and the fracture of specimen would be take place in a short time. According to the Norton formula, the stress index of the creep specimens at each testing temperature could be obtained as 2.312 at 100℃, 2.179 at 150℃, 2.401 at 200℃, 2.921 at 300℃and 1.089 at 400℃, respectively. Therefore, it could be concluded that the creep mechanism at temperature from100℃to 300℃was mainly viscous slip of dislocation and then changed to diffusion mechanism at 400℃. This conclusion was proved by the observation of dislocation configuration by TEM. Obvious necking-down was observed on the fracture surface of the failure specimen, with disguisable dimple and tear ridges, indicating the intergranular fracture feature.Comparing 100 cycles of thermal-mechanical and pure creep at invariable temperature and load indicated that the thermal-mechanical damage was much more severe. Stress and strain curves appeared to be opened hysteretic loop during cyclic thermal-mechanical load, resulting in accumulate strain. However, the degradation rate of strain was very low for the thermal-mechanical cycling from -50℃to 250℃.The finite element analysis results of the lock hook made by 60Si2Mn steel showed that there was a maximum of stress concentration near the bending angle, corresponding that the node 130 was exerted the most equivalent stress, and was seen as the weak spot. The stress-strain curve of node 130 followed the same law of development with the experimental results.
【关键词】 60Si2Mn钢； 蠕变； 热机械循环； 应力与应变；
【Key words】 60Si2Mn steel； creep； thermal-mechanical cycling； stress and strain；