钢中夹杂物扫描电镜自动统计分析结果的影响因素探讨

以管线钢、车轮钢、易切削钢为研究对象,考察了利用扫描电镜(SEM)对钢中非金属夹杂物进行自动统计分析时,放大倍数、图像分辨率、采集时间及保护区设置对夹杂物分析结果的影响,并比较了不同的聚焦状态、电子束状态、衬度设置、灰度阈值时夹杂物分析结果的差异,旨在优化选择各种设备参数,提高夹杂物自动统计分析的准确度。分析结果表明:放大倍数从100、200增大到500倍,所检测到的夹杂物数量相应增加,小于2μm的夹杂物增加量占80%以上,500倍时夹杂物增加量接近200倍时的2倍,而测试时间大幅延长至200倍时的5.6倍;图像分辨率从512、1024增大到2048,所检测到的夹杂物数量成倍增加,小于2μm的夹杂物增加量占60%左右,而测试时间延长幅度不大;采集时间延长、设置保护区、聚集好、束流定时补偿均有助于获得更准确的夹杂物分析结果,衬度设置一般推荐Al-40、Fe-200,钢中含稀土夹杂物时采用双阈值设置。

Discussion on influencing factors in automatic statistical analysis of inclusions in steel by scanning electron microscope

The pipeline steel, wheel steel and easy-cutting steel were used as research objectives. The effect of magnification, image resolution, acquisition time and guard zone setting on the analysis results of non-metallic inclusions in steel was studied during the automatic statistical analysis by scanning electron microscope (SEM). The difference of analytical results of inclusions was compared under different conditions including focusing status, electric beam status, calibration level and grey threshold. The aim was to optimize the instrumental parameters and improve the accuracy of automatic statistical analysis of inclusions. The results showed that the number of detected inclusions increased accordingly when the magnification increased from 100 and 200 to 500. The increment of inclusions less than 2μm occupied for over 80%. The number of inclusions at magnification of 500 was about twice of that at magnification of 200. However, the testing time greatly increased by 5.6 times when the magnification increased from 200 to 500. When the image resolution increased from 512 and 1024 to 2048, the number of detected inclusions increased for several times. The increment of inclusions less than 2μm occupied for about 60%. Meanwhile, the testing time was prolonged insignificantly. It was found that the prolonging of acquisition time, the setting of guard zone, good focus status and beam current compensation at regular time intervals were advantageous to improving the accuracy of analytical results of inclusions. The calibration level of Al-40 and Fe-200 was recommended for common steels. Two grey thresholds could be adopted for the steels containing rare earth inclusions.