Molybdenum Carbide

Chemical formula: Mo2C

Melting point: 2687 °C

Density: 8.9 g/cc

The study of molybdenum carbide intensified throughout the 20th century, as part of the development of alloy steels and high-speed steels. Its formation occurs naturally when molybdenum is added to liquid steel and combines with available carbon, giving rise to Mo₂C particles that are distributed throughout the metal matrix. Unlike other carbides that require separate synthesis, this compound spontaneously forms during the casting and solidification of steel. It can also be obtained in isolation by carbothermic reduction of molybdenum oxides in the presence of carbon at high temperatures.

Molybdenum carbide is distinguished by its high thermodynamic stability, which means that its presence influences the properties of steel even in small proportions, greater than 1% by mass. Although its hardness is somewhat lower than that of chromium carbide, its corrosion resistance is greater, making it a valuable reinforcement for steels that require both toughness and chemical resistance. It acts as an alphagenic element, that is, it promotes the formation of martensite, which significantly increases the hardness and wear resistance of the alloy. This property explains its use in certain grades of high-carbon martensitic steel, such as 440C, where it contributes to the fixation of the martensitic microstructure.

Molybdenum carbide plays a fundamental role in high-speed steels (HSS), where its incorporation increases hot hardness and the wear resistance of cutting tools subjected to intensive working conditions. It is also used in small quantities in martensitic stainless steels and in some grades of specialty steels for applications that simultaneously require hardness, mechanical strength, and corrosion resistance.

Since the mid-20th century, industry has attempted numerous times to replace tungsten carbide (WC) with molybdenum carbide, mainly for economic reasons and the availability of raw materials. Tungsten is a strategic resource, primarily used in the manufacture of military components and in applications where no alternative can offer the same level of performance. Molybdenum steels have sometimes been presented as supposedly "more durable and tougher than tungsten steels," although this claim is inaccurate. In practice, tungsten steels are superior in multiple critical parameters, and their prestige in modern metallurgy remains unquestionable. The proliferation of molybdenum steels in industry is due more to the relative scarcity of tungsten than to any intrinsic advantage of Mo₂C. Even so, the abundance and lower cost of molybdenum have allowed its carbide to become a viable alternative in certain high-speed steels and composite materials such as cermets, where it provides a reasonable balance between properties and cost effectiveness.

Molybdenum carbide is an intermediate material within the family of refractory metal carbides. Although it falls short of tungsten carbide's performance in critical applications, it offers an accessible solution in high-speed steels and martensitic stainless steels. Its current relevance lies both in its role as a partial substitute for tungsten in certain contexts and in its ability to simultaneously improve hardness and corrosion resistance. Contemporary research is exploring new applications of Mo₂C in emerging fields such as heterogeneous catalysis, clean energy, and wear-resistant coatings, which could give it a greater role in the future of materials science.