M390 is one of the new super steels on the block, manufactured by Bohler-Uddeholm (result of merger of Austrian Bohler and Swedish Uddeholm). It uses third generation powder metal technology and developed for knife blades requiring excellent corrosion resistance and very high hardness for excellent wear resistance. Chromium, molybdenum, vanadium, and tungsten are added to promote sharpness and outstanding edge retention. Unlike ZDP-189 most carbides are formed by vanadium and molybdenum, leaving more ‘free chromium’ to fight corrosion. M390 hardens to 60-62 HRC. Bohler calls this steel “Microclean” and it can be polished to achieve a true mirror. Moderately difficult to sharpen, but won’t take you as long as with S90V.