Boriding of AISI 440B Stainless Steel and Coating Characterization

The AISI 440B (DIN 1.2210, X90CrMoV18) steel is one of the hardest among martensitic stainless steels. This type of steel is used in a variety of industrial applications where wear and corrosion are determinant, such as molds, parts and tools for the automotive and biomedical industries. Their superior mechanical properties are due to its high carbon (0.75-0.95 % C) and chromium (16-18% Cr) contents. Suitable coatings can increase wear resistance and expand these materials usability range. Boride coatings, with their high hardness and wear resistance are good candidates for this purpose. Boride layers were obtained by boriding treatment in a salt bath (a mixture of sodium borate and aluminum). The layer properties, such as hardness, thickness, layer/substrate interface morphology and phases formed are influenced by steel composition. In this work, the layers produced on AISI 440B steel were harder, thinner, with a smoother interface when compared to plain carbon steels due the larger amount of alloying elements. In order to evaluate mechanical properties of borided layers in samples of stainless steel AISI 440B, Optical Microscopy (OM) microstructural analysis, Vickers microhardness tests and micro-adhesive and micro-abrasive wear resistance tests were performed. The layers produced exhibited a hardness close to 2250 HV and excellent wear resistance far superior to that of substrate