根据相图热学平衡原理和不同气氛碳势的影响，提出了GCr15钢轴承套圈表面脱碳层的形成过程和形成机理。结果表明：炉内气氛碳势等于或大于GCr15钢二相区平衡奥氏体碳含量时，获得正常显微组织；随碳势降低，套圈表面先出现半脱碳层，显微组织变化表现为渗碳体数量减少、铁素体（叠加原始铁素体）增加及团块片状珠光体生成；碳势继续降低后，套圈由外到里生成全脱碳层+半脱碳层。

According to the principle of phase diagram thermal equilibrium and the influence of different atmosphere carbon potential, the formation process and mechanism of decarburization layer on the surface of GCr15 steel bearing ring were put forward. The results show that normal microstructure was obtained when the carbon potential of atmosphere in furnace was equal to or greater than the carbon content of equilibrium austenite in two-phase zone of the GCr15 steel. With the decrease of carbon potential, a semi-decarburized layer first appearred on the surface of the bearing ring, and the change of the microstructure was characterized by the decrease of the number of cementite, the increase of ferrite (superimposed original ferrite) and the formation of agglomerated flake pearlite. After the carbon potential continues to decrease, a full decarburization layer+semi-decarburization layer were formed from the outside to the inside of the bearing.