O2 is O1's higher-manganese, vanadium-bearing sibling, and is identical in commerce to the very common European 1.2842 (90MnCrV8). About 0.90 percent carbon, two percent manganese, half a percent of chromium, and a small vanadium addition give it deep oil hardenability, fine grain, and a reasonable balance of edge retention and toughness in the low-sixties HRC range.
For the cook, O2 / 1.2842 is one of the everyday carbon steels of European cutlery — the steel behind a great many German and Austrian working knives, including a substantial portion of Solingen's traditional output. It sharpens easily, takes a competent edge, and patinas politely. Edge retention is slightly better than O1 thanks to the fine vanadium carbides; toughness at hardness is good, though the manganese-induced inclusions can mean a less perfectly clean apex than the leaner papers and pure carbons.
Among the European maker community it is sometimes treated as the carbon-steel "default": a known quantity, easy to source, easy to heat treat, hard to embarrass with. As with O1, it has been overtaken in performance by newer carbons, but it remains a thoroughly respectable choice.