How to sample metallographic samples?- Trojan (Suzhou) material technology Co., Ltd.

How to sample metallographic samples?

27-01-2022

The sample should generally not be too large or too high. For the metallographic samples prepared by hand, the size of the grinding surface area is less than 400mm² and the height is 15~20mm. If the sample is too small, the operation will be inconvenient. If the sample is too large, the grinding plane will be too large, which will increase the grinding time and will not be easy to smooth. Due to the different shapes of the materials or parts to be inspected, samples with irregular shapes can be used. For samples not inspecting surface defects, infiltration layers, and coatings, the edges should be rounded to prevent scratches on the metallographic sandpaper and metallographic polishing cloth during grinding, and avoid accidents caused by the flying of samples during polishing. For the test samples of the surface structure, it is strictly forbidden to chamfer to keep the edges and corners intact and to ensure the smoothness of the grinding surface.

There are various methods of sampling. It can be flexibly selected according to the size of the sampled parts, material properties, and current actual conditions. The most commonly used method is metallographic cutting machine grinding wheel (metallographic cutting sheet) cutting. Generally, materials with lower hardness (less than 230HBW) such as low carbon steel, medium carbon steel, gray cast iron, non-ferrous metals, etc. can be machined with saws, cars, planers, etc. For materials with higher hardness (about greater than 450HBW) such as white cast iron, cemented carbide, and brittle materials such as quenched parts, the hammering method can be used to select the size and size from the broken fragments. For large section parts or high manganese steel parts, etc., oxyacetylene flame gas cutting can be used, but a margin larger than 20mm must be reserved so that the heat affected zone of gas cutting can be removed during sample grinding.

Regardless of the sampling method, it is necessary to prevent tissue changes caused by temperature rise, or plastic deformation caused by force.