Which alloy is known to improve the red hardness of steel?

Cobalt is known to improve the red hardness of steel significantly. Red hardness is the ability of a material to retain its hardness at elevated temperatures, which is particularly important in applications involving high-speed cutting tools and other high-temperature operations. When added to steel, cobalt contributes to its hardness at elevated temperatures by enhancing the strength and rigidity of the steel structure.

Cobalt-containing steels are also notable for their excellent wear resistance and toughness, which makes them suitable for demanding applications such as high-speed drills and cutting tools. This capability helps maintain the performance of tools in high temperatures that typically lead to softer materials losing their effectiveness.

Other options, like silicon, lead, and manganese, have different functions in alloying steels. Silicon may improve the strength of steel and its deoxidizing properties but does not significantly enhance red hardness. Lead is used primarily to improve machinability, not hardness. Manganese is essential for improving hardenability and tensile strength but does not provide the high red hardness that cobalt does at elevated temperatures. Thus, cobalt stands out as the alloy that specifically enhances red hardness in steel.