脉冲电流处理对HG1钢热疲劳裂纹扩展的影响研究

发布时间：2018-03-28 20:06

本文选题：热作模具钢　切入点：热疲劳　出处：《湖北工业大学》2015年硕士论文

【摘要】：当今社会,随着科技的发展,模具被运用到越来越多的领域,各国的模具行业正在飞速向前发展,模具俨然已经成为国民经济的重要产业了。鉴于热作模具工作环境的恶劣性和复杂性而常常会伴随着热疲劳损伤失效破坏现象的发生,作为热作模具钢来说必须具有较高的高温强度、高的红硬性和回火稳定性、良好的延展性和韧性、高的导热系数、低的热膨胀系数、良好的化学热稳定性等性能特点。针对热作模具钢严重的热疲劳失效,许多科技工作者对热作模具钢的热疲劳失效机理、止裂和修复技术给予了高度的关注,研究了不同的方法来进行止裂修复模具或延缓热疲劳裂纹扩展,从而提高模具使用寿命。而脉冲电流处理技术作为近几年来兴起的一种对模具钢疲劳损伤止裂修复的技术而逐渐被大量推广应用,此技术环保,无污染,节省能源,操作简便迅速,安全,高效,值得大力推广。本文首先采用实际实验与数值模拟有限元相结合的方法对带有预制切口的HG1钢试样通入脉冲电流处理,研究结果表明:施加的脉冲电流使预制切口尖端熔化变成椭圆形,发生钝化现象,增大了切口尖端处的曲率半径,,起到了部分修复的作用,同时还消除了一部分切口尖端的应力集中,达到了止裂修复的目的,为后面实验研究热循环到300次后施加一次脉冲电流的这个最佳时机提供了理论依据。其次,本文还研究了对热疲劳循环过程中的试样施加一次脉冲电流处理后裂纹扩展的情况,采用Uddeholm热疲劳法中的损伤因子来对裂纹情况进行标准评价,它是一种借助计算机图像处理功能,采用Visual Basic编程处理,依据图像中不同颜色的灰度值不同,针对热疲劳后试样的表面裂纹和深度裂纹进行计算机辅助评价分析的方法,通过这种对热疲劳裂纹的评定方法再结合显微硬度的变化情况,研究得出:施加一次脉冲电流处理在本实验条件下对热疲劳裂纹可以起到止裂修复的作用,且热循环到300次后施加一次脉冲电流这个时机最优,同时,热循环到3000次后试样截面发生了软化,表层到心部的硬度呈现先降低后升高且次表层硬度最低的趋势。
[Abstract]:In today's society, with the development of science and technology, mould is applied to more and more fields. Mould has become an important industry of the national economy. Because of the bad and complex working environment of hot work mould, it is often accompanied by the phenomenon of thermal fatigue damage and failure. As a hot working die steel, it must have high high temperature strength, high red hardness and tempering stability, good ductility and toughness, high thermal conductivity, low thermal expansion coefficient, In view of the severe thermal fatigue failure of hot work die steel, many scientific and technological workers have paid great attention to the mechanism of thermal fatigue failure, crack arrest and repair technology of hot work die steel. Different methods for crack arrest and repair die or for delaying thermal fatigue crack propagation are studied. In order to improve the service life of the mould, pulse current treatment technology, as a kind of fatigue damage prevention and repair technology developed in recent years, has been widely used, which is environmentally friendly, pollution-free and energy saving. The operation is simple, rapid, safe and efficient, and it is worth popularizing. Firstly, the method of combining practical experiment with numerical simulation finite element method is used to treat the HG1 steel sample with prefabricated notch by pulse current. The results show that the applied pulse current causes the tip of the prefabricated notch to melt into an ellipse, resulting in passivation, which increases the radius of curvature at the tip of the notch and plays a partial role in repairing it. At the same time, the stress concentration at the tip of a part of the notch is eliminated, and the purpose of crack prevention and repair is achieved, which provides a theoretical basis for the later experimental study on the optimal time of applying a pulse current after 300 cycles. Secondly, In this paper, the crack propagation of the specimen during thermal fatigue cycle is also studied. The damage factor of Uddeholm thermal fatigue method is used to evaluate the crack situation. It is a method of computer aided evaluation and analysis of surface cracks and depth cracks of samples after thermal fatigue according to the gray value of different colors in the image by using Visual Basic programming with the help of the function of computer image processing. Through the evaluation method of thermal fatigue crack and the change of microhardness, it is found that the application of single pulse current treatment can prevent the crack from repairing under the experimental conditions. At the same time, the cross section of the specimen softened after 3000 cycles, and the hardness of the surface to the center decreased first and then increased, and the hardness of the subsurface layer was the lowest.
【学位授予单位】：湖北工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG142.45;TG156.7

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