I don't know if the green dot you mentioned can fall off, or just fall off like iron sheet or just a trace. If it is formed on wire, it may come from impurities added in the blank, iron oxide not formed after water treatment and air cooling, and wear. You can check the blank to see if there is any abnormality. The rest is to strengthen temperature and tempering control. It is best to check whether the conduit and guide rail are worn, which is for reference only.