Abstract: 【Objective】 To meet the higher requirements for the manufacturing process and performance of powder metallurgy(PM)structural components due to the transformation of automotive technology, chromium-containing PM low-alloy steel has become an important research direction since Chromium-containing steel is a solution with economical, environmentally friendly, and high-performance. This paper investigated the diffusion behavior and hardenability of Cr-containing powder metallurgy steel.【Method】 The study employed both thermodynamic modeling and experimental approaches. Using Thermo-Calc software, the diffusion rates of carbon in various alloy systems(e. g., Fe-Cr-C, Fe-Cr-Mo-C, Fe-Cr-Ni-C) were calculated to assess the influence of Cr and other elements. Experimentally, three material compositions(Fe-Cr(≤3 wt.%)-(Mo)-C) were prepared using pre-alloyed Cr-containing steel powders. Samples were compacted and sintered at 1120°C in a controlled nitrogen-hydrogen atmosphere, and subjected to continuous cooling transformation(CCT) tests via dilatometry. Jominy end-quench tests were conducted to evaluate hardenability, and microstructural analysis was performed using optical microscopy.【Result】 Thermodynamic calculations indicate that the addition of alloying element Cr exerts a certain inhibitory effect on the diffusion of C. With the addition of Mo, the synergistic effect results in a more pronounced influence of the Cr-Mo alloy system on the diffusion of carbon atoms. Within the Cr-Mo alloy system, the inhibitory effect on carbon atom diffusion is particularly evident in the 3 Cr-0.5 Mo alloy system. It has been demonstrated that, under conditions of lower temperature, the rate of diffusion of carbon atoms is notably reduced. The CCT curves demonstrated that Fe-1.8 Cr-0.6C required critical cooling rates of 2.7 K/s for bainite and 10 K/s for full martensite formation. With the addition of 2% Ni, these rates decreased to 0.8 K/s(bainite) and 4 K/s(martensite). The Fe-3 Cr-0.5 Mo-0.5C alloy demonstrated superior hardenability, with critical cooling rates of only 0.1 K/s(bainite) and 1.5 K/s(martensite). Jominy tests confirmed exceptional hardening depth, with Fe-3 Cr-0.5 Mo-0.5C achieving a hardened layer(>400 HV0.1) nearly 20 mm, thereby outperforming conventional wrought steel 20 MnCr5. A thorough examination of the microstructural composition revealed that elevated cooling rates were conducive to the formation of martensite, while intermediate rates resulted in the observation of gradient structures, such as martensite at the boundaries of particles and pearlite within the cores.【Conclusion】 The addition of alloying elements Cr(especially with Mo) significantly inhibits the diffusion of C atoms. At lower temperatures, the Fe-3 Cr-0.5 Mo alloy system exhibits a more pronounced effect on the diffusion of carbon atoms. This finding suggests that during the cooling process after sintering, a greater amount of nonequilibrium martensite can be formed. According to CCT curves and hardenability tests, both alloy materials, Fe-1.8 Cr-2 Ni-0.6C and Fe-3 Cr-0.5 Mo-0.5C, are highly suitable for sinter-hardening processes. In comparison with the standard heat-treated cast(fully dense) material 20 MnCr5, all three Cr-containing sintered materials demonstrate superior hardening capability.