The preparation of metallographic samples for most materials almost always adopts the method of metallographic sandpaper grinding to remove the damage and deformation layers generated during the cutting process, making sufficient technical preparations for the polishing process of the sample surface. Therefore, the grinding process is a crucial step, and if not handled properly, it will directly affect the quality of sample preparation, and even cause errors in metallographic structure analysis data. Kemai testing engineers share some suggestions on how to use metallographic sandpaper correctly. Friends must keep them for reference.


1、 We suggest that you replace the old metallographic sandpaper in a timely manner

As shown in the figure, what we see is a cross-sectional comparison between the old and new metallographic sandpaper microscopes. The left image shows a new metallographic cross-section, where the abrasive particles are clearly visible standing upright, sharp and sharp like a blade; On the right side is an old metallographic sandpaper, where the abrasive particles have been almost completely ground down, the edges and edges have been removed, and the abrasive particles are almost completely buried in the bonding layer.


I don't know if we don't compare. After the above comparison, it can be seen that the grinding and removal ability of old metallographic sandpaper has significantly decreased. If we continue to use it, it will increase the chances of rubbing the paper base, causing the surface of the ground sample to have a false mirror effect due to its good reflectivity. Please see the comparison chart below:

The left image shows the surface of the sample ground with old sandpaper, while the right image shows the surface of the sample ground with new sandpaper.


Compared to the two, it is obvious that the grinding marks on the right are clearer, with each grinding mark having distinct roots and a three-dimensional visual effect. The wear marks on the left look smoother, with blurry and almost flat surfaces.


On the surface, it seems that the left image has a better effect, but in reality, the visual perception is wrong!


This phenomenon originates from the planarization of the surface wear marks on the sample, resulting in better reflectivity of the sample surface. However, the depth of the deformation layer actually increases, and what the eyes see is only a false image.


In view of this, please remember to replace the metallographic sandpaper with a new one in a timely manner after it is worn out.


2、 We suggest that you thoroughly rinse the sample after each grinding

Usually, a metallographic sample ground with metallographic sandpaper will use 2-3 sandpapers with different particle sizes corresponding to different labels. After grinding with each grade of metallographic sandpaper, the sample must be thoroughly rinsed and must not be omitted. The purpose is to avoid cross contamination of sandpaper abrasives with different particle sizes. When coarse abrasive particles remaining on the surface of the sample are mixed with fine sandpaper, it will cause secondary scratches on the surface of the sample, with deep and numerous scratches that are difficult to remove. Not only does it affect the surface preparation effect of the sample, but it may also cause rework. So, thoroughly rinse the sample after each grinding to avoid cross contamination.


The above is a suggestion from a pulse detection metallographic engineer for you. If it is useful to you, please keep it for future reference.