Due to significantly improving service performance of steel components, the QPQ technology, generally consists of liquid nitriding and oxidizing, has been wildly promoted and applied in fields of automobiles, motorcycles, electronic parts, tools and molds. Practical experiences show Cr containing structural steels would have relatively easier cracking surface treated layers than plain carbon steels after QPQ treating. Therefore, the compounds of QPQ treated shafts of 20Cr and 40Cr steels have been studied with XRD，OP，SEM，EDS and micro indentation. The differences of compound layers in morphology and element distribution were paid more attention on both grinding cracking shafts and normal ones. The results show the grinding cracking has an apparent relationship with the segregation of Cr, as well as tiny cracks and holes in original compounds layers.