Role of Carbon Content in Controlling Mechanical Properties of Cemented Carbides: From Basic Theory to Modern Microstructural Design

Control of carbon content is the most fundamental and critical factor in the microstructural design of WC-Co cemented carbides. It not only dictates the avoidance of harmful phases (η-phase and free carbon) but also determines the solute concentration in the binder phase, which governs the mechanical properties. Historically, based on the foundational work by Suzuki and Hayashi, it was believed that high-carbon alloys exhibited superior transverse rupture strength (TRS) because low-carbon alloys suffered from residual porosity during vacuum sintering. However, the advent of advanced powder processing and Hot Isostatic Pressing (HIP) technology has eliminated these processing defects, leading to a paradigm shift. It is now established that defect-free low-carbon alloys exhibit superior strength due to enhanced solid solution hardening of the binder and effective grain growth inhibition. This review outlines the evolution of carbon control strategies from basic theory to modern applications. In particular, we discuss the critical role of low carbon content in modern ultrafine-grained alloys containing inhibitors (e.g., VC, Cr3C2) to prevent coarse precipitate defects and maximize limiting strength. Furthermore, recent advancements in active microstructural control, such as utilizing high carbon content to induce plate-like WC morphology, are also highlighted.