D2 Steel Hardness: What HRC Should You Use? The optimal hardness for D2 tool steel is typically 58–60 HRC. Although D2 can reach about 64–65 HRC after quenching, this maximum hardness is too brittle for most cold-work tooling. In real applications, D2 hardness should be selected based on the primary failure mode: wear, chipping, cracking, … Continue reading D2 Steel Hardness Guide: HRC Range, Tempering & Applications