Work

Coupling surface vibratory extrusion and carburizing heat treatment to improve the surface microstructure and mechanical properties of powder metallurgy steel

Year: 2026

Type: article

Abstract: Surface integrity is critical to the reliability of powder metallurgy steels in service environments. However, surface densification, although necessary for structural support, reduces the pore-assisted pathways available for carbon transport during carburizing, making it difficult to achieve both a dense surface layer and effective thermochemical strengthening. To address this issue, a coupled processing route consisting of surface vibratory extrusion and carburizing heat treatment was proposed for Fe-Mo-Cu-C powder metallurgy steel. Surface vibratory extrusion produced a 620 μm densified layer and promoted continuous dynamic recrystallization, generating a high density of grain boundaries and dislocations. These microstructural features increased the effective diffusion coefficient by about 51 % compared with steady-state extrusion. The treated surface developed high-carbon fine-grained martensite and fine dispersed carbides, increasing the surface peak hardness to 882 HV 1.0 , corresponding to a 3.95-fold increase over the untreated state, and extending the effective case depth to 1265 μm. The carbon concentration gradient also contributed to a surface compressive residual stress of 277 MPa. Tribological investigations showed improved friction and wear behavior through a transition from severe pore-induced spalling to mild abrasive wear with frictional oxidation. These results provide useful guidance for designing surface strengthening processes for high-performance powder metallurgy components.

Source: Materials & Design

DOI: 10.1016/j.matdes.2026.116413