As we all know, the commonly used grinding consumables in metallographic laboratories are metallographic sandpaper, among which silicon carbide metallographic sandpaper is more commonly used, usually water sandpaper, and only water is needed for grinding. Metallographic sandpaper is a necessary process for rough and fine grinding of conventional metallographic samples. However, there are as many as 20 grades of metallographic sandpaper from coarse to fine, whether it is an American standard, an European standard, or just a national standard. Is it necessary to use every grade to grind it?


With such questions in mind, the editor consulted a beautiful doctoral friend who works at the Aerospace Materials Research Institute, compiled the exchange experiences, and shared them with friends, hoping to provide some help to friends engaged in metallographic sample making work.


Generally speaking, the choice of metallographic sandpaper grinding scheme is related to the type and properties of the material, but it is not closely related because regardless of the hardness of the material, it needs to go through the process of rough grinding, fine grinding, polishing, and corrosion. It is mainly related to the surface roughness, flatness, and presence of burrs on the sample surface. The coarse and fine grinding of metallographic sandpaper generally involves grinding P80-P2000 through 4-6 steps from coarse to fine; If polishing is required, then on this basis, P1500-P4000 needs to be further polished through 2-4 steps to achieve the goal of removing the surface deformation layer of the sample.


Firstly, after receiving the sample, the surface flatness of the sample should be observed with the naked eye. You can also use your nails to press on the burrs, observe the glossiness of the sample, observe rust marks, and roughly determine the type and hardness of the sample to determine the sandpaper label to be used for the starting grinding process.


If the surface of the sample is rough and has obvious cutting marks, metallographic sandpaper with a coarser particle size designation P80 should be selected, starting from this designation.


If the surface of the sample appears relatively flat, you can directly choose from P240 metallographic sandpaper, which can save sandpaper and improve efficiency.


For relatively hard metal samples such as T12 steel, T8 steel, 45 steel, 35 steel, and 20 steel, it is more suitable to choose P80, P240, P400, P600, P800, P1000, P1500, and P2000 metallographic sandpaper for grinding in sequence. During the grinding process, careful observation is carried out while grinding. Based on the actual grinding situation and requirements, P800, P1000, P1500, and P2000 can be omitted in the middle, and diamond polishing fluid can be directly used for the polishing process.


For softer materials such as cast iron, which are relatively soft, it is better to omit P400 and P800 metallographic sandpaper in the above steps. However, in practical work, it is still necessary to add or reduce metallographic sandpaper reasonably based on the grinding situation, and continuously summarize the grinding and polishing experience in order to propose better grinding plans for familiar material samples.

    As for the metallographic sandpaper grinding plan for metallographic samples, there is no unified standard or specification. Different materials and inspection and analysis purposes determine different requirements for sample grinding. Therefore, the plan provided here only provides a selection method for your reference!