Abstract: The bearing roller of G20Cr2Ni4A steel, which was treated by surface carburizing and then quenching and tempering, was fractured after about 2h of test drive. The causes of the fracture of the bearing roller were analyzed using metallographic microscope, Vickers hardness tester, scanning electron microscope, X-fluorescence spectrometer and other testing methods. The results show that the bearing roller microstructure, chemical composition, hardness and carburizing layer thickness are qualified; when the bearing is assembled, the work roll axis is not parallel to the support roll axis causing excessive axial force during the operation of the mill, resulting in the bearing roller cracking failure. Keywords: G20Cr2Ni4A steel; carburization; bearing roller; fracture failure A rolling mill support rolling bearing model 3806/711.2-XRS/HCS/HCEP69, bearing roller material for G20Cr2Ni4A steel, a high-quality low-carbon alloy carburized steel. In the mill plant loading no-load operation 2h, the roller body along the axial fracture, the roller body surface has a serious extrusion deformation and shedding phenomenon. The roller is an inner hollow cylindrical cone, the diameter of the inner bracket round hole is Φ14mm, the diameter of the two ends of the roller body are Φ48mm and Φ50mm, in the form of columnar cone. The surface of the inner bore of the failed and cracked roller has long cracks about 5mm deep along the axial direction. The processing process of the roll body is: forging → turning → 934℃ carburizing → 870℃ direct quenching → 600℃ high temperature tempering → air cooling → 810℃ secondary quenching → 155℃ low temperature tempering → grinding process.  

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