Effects of Ce on the polishing performance of 1.2311 plastic mold steel

The deterioration of the surface polishing performance for plastic mold steel primarily originates from interfacial damage caused by the property mismatch between inclusions and the matrix. This study combines experimental characterization with theoretical calculations to establish the structure-property relationship governing the Ce-induced enhancement of the polishing performance in 1.2311 mold steel. The results show that Ce transforms irregular Al-Mn-Ca-O-S inclusions (accounting for 76.5%) into spherical RE-oxysulfide inclusions (81.3%), reducing the average inclusion size from 2.05 μm to 1.52 μm and the maximum size from 81.2 μm to 5.2 μm, representing a 25.9% reduction in average size and a dramatic 92.1% reduction in maximum size. The original Al₂O₃ inclusions without Ce lead to spalling and surface pits (surface roughness of R a = 0.184 μm) due to high internal stress and significant interfacial stress difference (599 MPa). In contrast, RE-oxysulfide inclusions in the mold steel enhance plastic deformation compatibility, which can reduce the interfacial stress gradient to 95 MPa and the surface roughness fluctuation by 98.9% ( R a = 0.002 μm). By refining inclusion size and improving deformation compatibility between inclusions and the matrix, Ce effectively reduces the risk of interfacial damage induced by inclusions, thus significantly enhancing the surface polishing performance. This work can provide a theoretical basis for the alloy optimization design of mirror mold steels.