Causes of magnetic marks on surface of pillar hole of bearing carburized steel roller

During the nondestructive testing of the bearing carburized steel roller, it was found that there were surface magnetic marks of varying degrees in the roller pillar hole. The causes of magnetic marks on the roller surface were analyzed by means of macroscopic observation, chemical composition analysis, metallographic examination, hardness test, macrostructure examination, scanning electron microscope and energy spectrum analysis. The results show that there were hairline defects in the roller. During carburizing and secondary quenching, large stress was generated in the material, which led to the hairline expansion in the roller and finally cracked, forming magnetic marks during nondestructive testing.