Cause Analysis on Cracking of 42CrMo Steel Flanges

42CrMo steel has a crack extending along the rolling direction after ring rolling and quenching and tempering,and the maximum width can reach 90 μm. The microstructure near the crack was detected by metallographic microscope and scanning electron microscope with energy dispersive spectrometer. It is found that there are obvious decarburization layers near the crack and iron oxides inside the crack. A large number of large size inclusions are found in the steel matrix, mainly containing Al, Mg, Si, Ca and O. It is determined that the crack is produced during rolling. Due to the large size of inclusions and irregular shape, serious stress concentration will occur near the inclusions in steel deformation, which will lead to cracking. the cleanliness of raw material molten steel without secondary refining is insufficient, and it not suitable for use as ring rolling raw materials.