It seems likely, Roger, that "steel" in this case is marketing exaggeration. Iron, maybe (ferrous sulfate, for example), but not steel. Someone in charge of marketing must have decided that "steel" would sound stronger, thus more effective, than "iron."
Actually I think maybe it is the British meaning of our Iron, as in wine of Iron and tar or Iron and something other. By the way did you get that Eaisly cobalt bottle you said is missing from your collection??? And who do you think got all those Handysides or was it a scam??.......Andy