1) Causes of "pitting" on the surface of the workpiece
Because there are some non-metallic impurities in the steel, which are usually hard and brittle oxides, they are pulled out from the surface of the steel during the polishing process to form pitting corrosion.
The main factors that produce "pitting corrosion" are as follows：
1) The polishing pressure is too high and the polishing time is too long.
2) The purity of steel is not enough, and the content of hard impurities is high.
3) Rust on the mold surface.
4) The black leather is not removed.
2) Measures to eliminate pitting corrosion of workpieces
1) Carefully re-grind the surface. The grit size is one level coarser than the previously used particle size. Use soft and sharp oilstone for the final step of grinding before proceeding to the polishing process.
2) When the size of sand particles is less than 1 mm, avoid using the softest polishing tool.
3) Use the shortest polishing time and the smallest polishing strength possible.