The edge retention and wear resistance of steels are dependant upon hardness nd structure. Until now, two main principles have been adopted to increase the hardness of martensitic stainless steels: 1.Either through the introduction of a structural hardening mechanism into low carbon martensitic grades such as, AISI 630 and XM 16, 2.Or by increasing the carbon content of the martensite and subsequently strengthening it through the presence of primary carbides.
The first option has not allowed to date, the mass production of steels with hardness levels greater than 52/54 HRC. Furthermore, the absence of carbides deleteriously affects cutting quality. The second option has two distinct disadvantages directly linked to the presence of large carbides, which render the steel brittle and reduce corrosion resistance, through chromium depletion of the matrix in the immediate vicinity of the carbides. In X 15 T.N™, (UNS S 42025) nitrogen is used as a partial substitute for carbon, causing hardening by interstitial insertion as well as by the formation of fine nitrides and carbonitrides. In this way, a hardness level (58/60 HRC) is obtained equivalent to a high carbon martensitic steel without chromium depletion, thereby giving a substantial improvement in corrosion resistance, i.e. equivalent or superior to AISI 630 and XM 16.