高强钢表面强化残余应力场实验研究与数值模拟

发布时间：2018-03-07 05:36

本文选题：喷丸强化　切入点：孔冷挤压　出处：《燕山大学》2016年博士论文　论文类型：学位论文

【摘要】：随着高强度钢的应用领域越加广泛,由高强度钢所制备的零部件因为长时间承受交变载荷压力,在表面上形成疲劳裂纹致使失效的情况逐渐增加。为此,采用喷丸、孔冷挤压和渗碳等表面强化对这些承受交变载荷的高强钢零部件进行表面强化处理,采用实验研究与数值模拟相结合的方法,分析残余应力场的分布规律,以提高其使用寿命。本研究不仅具有重要的理论意义,更具有重要的工程意义。本文对不同喷丸与孔冷挤压工艺基于高强度钢试样残余应力场的影响进行了分析,并通过有限元法对喷丸与孔冷挤压后形成的残余应力场开展了数值模拟。研究了不同渗层深度及不同表面碳含量对20CrMn Ti钢试样残余应力场的影响,并采用有限元法对其进行了数值模拟。通过X应力仪测试喷丸、孔冷挤压与渗碳后试样的残余应力,再通过电解抛光法依次测试残余应力的范围。此外,通过X射线衍射仪对喷丸、孔冷挤压与渗碳前后试样晶体结构开展了研究,测定试样表面显微硬度逐层变化情况,观察试样组织形貌。通过ANSYS软件构建有限元模型,对不同喷丸、孔冷挤压和渗碳工艺条件下的残余应力场进行了数值模拟。实验结果表明,伴随喷丸时间的增长,不断增大最大残余应力和强化深度,表面残余应力逐渐降低,相对于小直径弹丸而言,通过大直径弹丸形成的强化深度较大。如果喷丸强度不断增加,最大残余应力、强度也不断上升。通过玻璃丸与陶瓷丸开展二次喷丸增强了试样表面残余应力。喷丸后高强度钢试样表面位错数量有所上涨,试样表面显微硬度也增强。孔冷挤压后孔内表面的晶粒发生变形并纤维化,在材料表面形成强化层,提高了材料表层的硬度,在距孔边大约一个孔径的范围内形成残余压应力,最大残余压应力出现在距孔边大约1mm处。试样经过渗碳处理后,会在表层产生残余压应力层,但压应力的最大值并不处在表层而是处在渗碳层的内部。渗碳淬火后再进行回火处理,明显地降低了试样的残余压应力值;降低渗碳时间和表面碳含量都会使残余压应力值降低,并使残余压应力的最大值向表面移动。模拟结果表明喷丸、孔冷挤压和渗碳后试样的残余应力场发展特点模拟结果和试验结果相同,表明模型的有效性可以运用在各种工艺参数下喷丸、孔冷挤压与渗碳过程中的数值模拟。喷丸工艺的模拟结果显示,不断增加弹丸速度,最大残余压应力、最大残余压应力深度、强化深度依次增长;弹丸弹性模量基于喷丸后残余应力场的影响较小。伴随弹丸直径的增大,最大残余压应力、最大残余压应力深度与强度也会随之提高。随着挤压强度的增加,孔边残余压应力和外部的残余拉应力都随之增大,同时,残余压应力的峰值点到孔边的距离也随着挤压强度的增加而增加。随着孔径的增大,孔边残余压应力峰值的大小逐渐减小,但其分布宽度增加。当孔边距比e/d较小时,孔边残余压应力较小,而外部的残余拉应力较大。伴随e/d的增长,残余压应力也会随之提高,残余拉应力降低,残余压应力的分布区域拓宽。用残余应力场模型对渗碳试样在淬火冷却过程中的瞬时应力进行模拟,试样在冷却到50秒时,应力分布为表面受拉,心部受压;冷却到260s时的应力分布为表面受压,心部受拉;冷却到1300s时的应力分布与260s时一样,表面受压,心部受拉,但压应力的数值明显大于260s时的数值,在距表面大约0.7mm处,压应力达到最大值。
[Abstract]:With more and more application fields of high strength steel, high strength steel by the prepared parts because of long time alternating load pressure, resulting in the failure of the fatigue crack increases gradually formed on the surface. Therefore, the shot peening, strengthening the surface of the alternating load of high-strength steel reinforcement parts Kong Leng extrusion and carburizing and etc. the surface using the method of numerical simulation and experimental research of combining the analysis of the distribution law of residual stress field, to improve their life. This research not only has important theoretical significance, also has important engineering significance. In this paper, different shot peening and cold extrusion process of hole of high strength steel specimen based on the residual stress of the are analyzed, and through the finite element method of residual hole cold extrusion after shot peening and stress field numerical simulation was carried out. Effects of different depth and different surface of carbon The content of the stress field of the 20CrMn Ti steel specimens with residual, and by using the method of finite element numerical simulation is carried out. Through X test peening device, cold extrusion and hole after carburizing residual stress, followed by the test range of residual stress through the electrolytic polishing method. In addition, by means of X ray diffraction instrument for shot peening, hole cold extrusion and carburizing samples before and after the crystal structure was studied by determination of microhardness change layer, microstructure morphology observation. Through the ANSYS software to build the finite element model of different shot peening, residual stress hole cold extrusion and carburizing process under the condition of field simulation experiment results. That, along with the peening time growth, increasing the maximum residual stress and hardening depth, surface residual stress decreased gradually, compared to the small diameter of the projectile, the projectile formation of large diameter reinforcement is relatively large in depth. If Shot peening intensity increasing, the maximum residual stress, strength is also rising. Through the glass and ceramic pill pill to carry out the two shot peening enhances the surface residual stress in specimen after shot peening. High strength steel surface dislocation number of samples increases, the surface microhardness of sample is enhanced. Coldworked hole hole surface after grain deformation and fibrosis, reinforced layer is formed on the surface of the material, improve the surface hardness, formed in the range of about an aperture from the edge of the hole in the residual stress, the residual stress in the distance of hole edge about 1mm. The sample after carburizing, will produce compressive residual stress in the surface layer, maximum but the value of compressive stress in the surface but not in internal. The carburized layer after carburizing and quenching tempering treatment, significantly reduce the residual compressive stress value; reduce carburizing time and surface carbon content will cause the residual The compressive stress decreases, and the maximum value to the mobile surface residual stress. The simulation results show that the shot peening, residual Kong Leng extrusion and carburizing were the stress field characteristics of the development of the simulation results and experimental results show that the same, the validity of the model can be used in all kinds of shot peening parameters, numerical simulation of cold extrusion and hole in the process of carburization. The simulation results show that the shot peening process, increasing the projectile velocity, the maximum compressive residual stress, the residual stress depth, strengthening depth increase in projectile; elastic modulus based on compressive residual stress field of influence is small. With increasing projectile diameter, the maximum compressive residual stress, the maximum residual the compressive stress depth and strength will be increased. With the increase of compressive strength, hole compressive residual stress and residual external tensile stress increases, at the same time, the peak residual stress to the edge of the hole distance Also increased with the increase of compressive strength. When the diameter increases, the hole compressive residual stress peak value decreases, but its distribution width increases. When the hole margin ratio e/d is smaller, the hole compressive residual stress is smaller, while the external residual tensile stress is larger. With the growth of e/d, residual pressure stress also increases, the residual tensile stress is reduced, the regional distribution of residual compressive stress. With the widening of residual stress field model to simulate the instantaneous carburized specimens during quenching process of the stress, the specimen in the cooling to 50 seconds, the stress distribution of surface tension, heart compression; cooling the stress distribution of surface compression to 260s, pulled by heart; cooling to 1300s the stress distribution and 260s, surface pressure, pull by heart, but the values of compressive stress was significantly higher than that of 260s when the distance from the surface, at about 0.7mm, the compressive stress reaches the maximum value.

【学位授予单位】：燕山大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG668

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