Also known as "razor blade steel". The most typical applications for this type of tool steel is … D-grade of tool steel in the cold-work class can contain approximately 10% to 13% chromium. When hardened and stress relieved, this material’s tensile strength jumps to roughly 1,586 MPa (230 ksi). Surface hardening, treatment of steel by heat or mechanical means to increase the hardness of the outer surface while the core remains relatively soft. It can be hardened to Rockwell 58 hardness, making it one of the hardest stainless steels. The Zero Tolerance 0630 is made of S35VN steel hardened to approximately 60 HRC. The combination of a hard surface and a soft interior is greatly valued in modern engineering because it can withstand very high stress and fatigue, a property that is required in such items as gears and anti-friction bearings. If annealed, grade 420 stainless steel has a tensile strength of around 586 MPa (85 ksi). KnifeArt has nearly 20 years of experience as an online knife retailer, and offers blades ranging from affordable EDC workhorses to exotic custom designs. In order to explain steel hardness correctly, we reached out to the team at KnifeArt.com . Martensitic Stainless Steel Grade 420 Stainless Steel. This type of tool steel does retain its hardness at increased temperature (425 °C / 797 °F max). Available in three grades 440A, 440B, 440C (more common) and … The term hardened steel is often used for a medium or high carbon steel that has been given heat treatment and then quenching followed by tempering.The quenching results in the formation of metastable martensite, the fraction of which is reduced to the desired amount during tempering.This is the most common state for finished articles such as tools and machine parts.