１问题的产生一般来说，在正常条件下生产的低牌号（ＨＴ１００、ＨＴ１５０）灰铸铁，其机械加工性能优良。但在我厂自行研制的专用机床流水线上，加工此类铸件时却经常出现加工困难的现象。机加工认为，有些铸件“太硬”，难以加工。凡加工困难的铸件均剔出报废，有时甚至成? 1 Problem Generation In general, low grade (HT100, HT150) gray cast iron produced under normal conditions has excellent machinability. However, in our own factory developed a special machine tool line, the processing of such castings often appear when the processing difficult phenomenon. Machining that some castings “too hard” and difficult to process. All processing difficult castings are scrapped, and sometimes even into?