Given the critical role of valve guides in the performance and lifespan of automotive engines, it is crucial to understand and improve their wear resistance. This study focuses on the wear resistance of powder metallurgy valve guides, aiming to systematically analyze the intrinsic relationship between their composition, microstructure, and properties. Three powder metallurgy valve guide samples with different compositions—specifically, a high-MoS2 Fe-C-Mo-Cu-S alloy (1.5 wt.% C, 1.9 wt.% Mo, 1.5 wt.% Cu, 1.4 wt.% S), a low-MoS2 Fe-C-Mo-Cu-S alloy (1.2 wt.% C, 0.3 wt.% Mo, 0.8 wt.% Cu, 0.2 wt.% S), and a Mo-free high-C-Cu Fe-C alloy (1.8 wt.% C, 5 wt.% Cu, 0 wt.% Mo, 0.01 wt.% S)—were studied using field emission scanning electron microscopy, metallographic microscopy, a reciprocating friction testing machine, and a 3D optical profilometer. The results show that the friction coefficient of the high-MoS2 Fe-C-Mo-Cu-S alloy is the highest at 0.5, the low-MoS2 Fe-C-Mo-Cu-S alloy is 0.25, and the Mo-free high-C-Cu Fe-C alloy is the lowest at 0.22. Since the minor wear amount cannot be accurately measured by the gravimetric method, the concave area of the wear-induced average roughness curve is employed to qualitatively indicate the magnitude of material loss: the area of the high-MoS2 Fe-C-Mo-Cu-S alloy is 2964 μm2, the low-MoS2 Fe-C-Mo-Cu-S alloy is 1580 μm2, and the Mo-free high-C-Cu Fe-C alloy is 1502 μm2. The hardness results of the material show that the high-MoS2 Fe-C-Mo-Cu-S alloy reaches 154 HB, the low-MoS2 Fe-C-Mo-Cu-S alloy is 134 HB, and the Mo-free high-C-Cu Fe-C alloy is 145 HB. The porosity results show a difference of about 2% among the three alloys. Based on the microstructure characterization results, it can be concluded that the Mo-free high-C-Cu Fe-C alloy—with high carbon (C) and copper (Cu) content and fine pearlite layers—exhibits excellent wear resistance: high C can improve the hardness of the matrix, while Cu can act as a lubricating phase to enhance the material’s wear resistance. In contrast, although the addition of MoS2 is intended to improve wear resistance, the irregular pearlite generated by MoS2 reduces the wear resistance of the high-MoS2 and low-MoS2 Fe-C-Mo-Cu-S alloys; among them, the high-MoS2 Fe-C-Mo-Cu-S alloy contains a higher amount of MoS2, and large chunks appearing in the tissue easily cause abrasive wear and aggravate material wear during friction. This study provides solid theoretical and practical support for the material selection and performance optimization of powder metallurgy engine valve guides: the identified intrinsic relationship between alloy composition (MoS2, C, and Cu contents), microstructure (pearlite morphology and second-phase distribution), and tribological performance establishes a clear theoretical basis for regulating the wear resistance of such components.
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