共查询到20条相似文献,搜索用时 250 毫秒
1.
通过断口分析、低倍检验、高倍组织以及模拟热处理人工断口观察等实验对模具钢在热处理裂纹成因进行了分析。分析表明,模具钢裂纹是在淬火过程中扩展形成的,钢中的白点缺陷和超尺寸夹杂物是引发淬火扩展裂纹的主要原因。由于钢模块在缺陷和裂纹形成后又经历了不同的热处理阶段并在室外放置了较长时间,原始实物断口不可避免的发生一些破坏给断口分析带来一定的困难。本文采用模拟热处理人工断口的方法,即在与钢模块类似的热处理制度下加热人工断口,观察加热温度对断口花样钝化的影响,并与实物断口进行比较,由此判断白点裂纹和淬火扩展裂纹的形成阶段。这种实验分析方法针对工件裂纹受到高温作用影响而使断面发生损坏的裂纹成因失效分析具有一定的推广应用价值。 相似文献
2.
3.
42CrMo钢芯棒在感应淬火及回火后表面出现环向裂纹,通过对其裂纹部位的组织等进行宏观、低倍及高倍观察和分析,找出了环向裂纹产生的原因。 相似文献
4.
5.
6.
7.
8.
9.
10.
连铸坯轧制无缝管横向低倍裂纹分析 总被引:1,自引:0,他引:1
针对由连铸圆管坯轧制的无缝管在横向低倍酸浸试样上存在的大量周向裂纹,通过采用低倍、金相、电镜及能谱各分析手段,进行了全面的研究,找出了导致这些裂纹形成的原因. 相似文献
11.
A method is developed for the simplified evaluation of multiple cracks, based on the d.c. potential drop technique. A subregion containing cracks is considered. The distribution of the potential drop for the cracks except for end cracks in the subregion is measured and calculated numerically by assuming a value for the depths of the end cracks and by assuming any value for the depths of other cracks. Modifying the depths of the other cracks is repeated until the difference between measured and calculated potential drops is minimized, where the depths of the end cracks are fixed. Evaluation of the centre crack in the subregion is made for different assumed depths of the end cracks. To make the evaluation independent of the depths of the end cracks, a subregion is extended to increase successively the number of cracks considered. Multiple cracks are sized well enough by this method. 相似文献
12.
13.
14.
A model is described which accounts reasonably for the observed rate of oxide growth through cracks in silica coatings on 9%Cr steels. It is shown that diffusion through the cracks is rate limiting for narrow cracks and that even for wide cracks the metal penetration rate is far less than for an uncoated surface. The model is also extended to the situation where the protective coating is completely surrounded by oxide. 相似文献
15.
16.
《Science & Technology of Welding & Joining》2013,18(5):440-445
AbstractA method is reported with which heat affected zone (HAZ) cracks in a specific region of spot welded joints, made of advanced high strength steels, could be realised. The influence of HAZ cracks on the fatigue behaviour, which is the focus of the contribution, was studied by evaluating the stiffness characteristics as a function of the number of cycles N in comparison with crack-free specimens, i.e. by analysing HAZ and fatigue cracks on the specimen surface and the surface of fatigue fractures containing beach marks. It was found that the fatigue cracks are not initiated at the HAZ cracks. The number of cycles to failure Nf is not significantly reduced for specimens with HAZ cracks. Overall, the examinations did not reveal any influence of HAZ cracks on the fatigue strength of resistance spot welded joints. 相似文献
17.
18.
焊接接头焊趾部位的疲劳裂纹多呈现为多裂纹形式.针对十字焊接接头,开展变幅载荷谱块下的拉伸疲劳试验,获得了表征裂纹瞬时前沿迹线的海滩条带的演变过程,验证了多裂纹的存在性,并且发现焊接接头焊趾处的多裂纹具有明显的不同步特性.采用有限元仿真技术,在焊趾部位分步插入多个半椭圆形初始裂纹,模拟了多裂纹的演变过程,获得了与试验断口一致的仿真结果.结果表明,裂纹融合导致裂纹前沿形状不断发生变化,最终有向半椭圆形状演变的趋势;焊接结构裂纹萌生和小裂纹扩展阶段在疲劳全过程中的寿命占比较大,具有不可忽略的影响. 相似文献
19.
航空发动机零件存在的较深加工刀痕、磨痕、附着物、表面涂镀层凹凸不平等缺陷和特征,在质量检验过程中会产生疑似裂纹。采用金相分析等手段,初步总结常见疑似裂纹的特点。结果表明:较深的加工刀痕、磨痕导致的疑似裂纹呈一定规律性分布、在疑似裂纹的两端和深度方向底部较钝、可以隐约或清晰地观察疑似裂纹深处的形貌特征,且可以通过表面修磨去除;附着物导致的疑似裂纹一般较宽,疑似裂纹两侧有沿表面渗透的毛刺等特征;表面涂镀层开裂导致的疑似裂纹微观形貌一般呈现龟裂特征。通过显微镜、扫描电镜、修磨验证等手段获取疑似裂纹的特征信息,并结合零件工艺过程、使用履历综合分析判断,可确认疑似裂纹的性质。 相似文献