碳钢焊缝组织石墨化显微图像的自动测量

针对压力锅炉、中温中压机组主蒸汽管道碳钢部件焊缝处金相组织石墨化程度的检测问题,将数字图像处理和模式识别技术运用于显微金相组织测量之中,选择适合的算法,通过用VisualBasic.Net编程,建立了一套对石墨进行形状表征和粒度测量的图像检测系统.系统利用扫描仪将金相照片转换为可进行图像分析的格式,或用CCD摄像机经光学显微镜获取数字化金相图像;针对石墨化部位原始图片灰度区间窄的特征,预处理着重进行全域线性灰度变换,使图像清晰,突出石墨组织;采用基于二维直方图Fisher线形分割的图像分割方法选取二值化阈值,能够更好地分开不同的聚类,且计算量小;图像识别采用边缘检测区域的办法,可提取出要检测的粗大呈黑色的石墨组织.该系统实现了对碳钢石墨化组织中石墨的定量化测量,对石墨各项指标的测量值为精确的数字结果,且检测速度快(不超过5min),效率高.实测结果表明,自动检测系统与金相分析法的分析结果完全吻合.

Auto-Measurement of Digital Image for Graphite in Carbon-Steel Welding Microstructure

On the basis of digital image processing and pattern recognizing techniques, a quantitative auto-measurement system was developed to diagnose the graphitization degree of carbon steel welding microstructure for pressure vessel and main steam pipeline after long-time running under middle temperature and middle pressure. A graphic measurement system was programmed for the shape attribute and the granularity of graphite by using Visual Basic.Net and choosing appropriate algorithms. The system can transform the picture into the mode of graphic analysis by using CCD camera, and can pretreat the pictures focusing on full-linear-gray-transformation to make the picture with narrow gray-level range of the original graphite structure clear and the graphite overhanging. The different clustering can be classified with less calculation by choosing the threshold based on the 2-D histogram. The image recognization can pick the coarse and black graphite structure by using the edge-measuring method. The experiments show that the measurement time is less than 5 minutes and the results have a good agreement with those obtained from metal-microstructure analysis.