Method for detecting inclusion of heavy rail casting blank

The invention discloses a method for detecting impurities in a heavy rail casting blank, which comprises the following steps of: 1) sampling a large square casting blank produced on site as a sample, and taking nine point positions on one section; 2) machining the nine o'clock positions, cutting the nine o'clock positions into square blocks, and preparing to be further observed by a microscope; (3) the machined sample is polished to be flat through an abrasive belt, and then the sample is polished through 240-mesh abrasive paper and 320-mesh abrasive paper till the sample is smooth; 4) finally, polishing the sample which is polished to be smooth, wherein flannelette and a three-lint metallographic polishing agent are used for polishing; 5) observing the polished sample under a lens by using a Chua's microscope, and counting and recording observed inclusions; and (6) the inclusions are divided into three ranges which are smaller than 20 microns, 20-40 microns and 40-60 microns according to the size, and statis