Hello Vincent -
Ferric chloride will also etch steel as well as cuprous metals.
A blacksmith I know who makes Damascus steel knives uses it to
etch patterns into his handles. I think it takes quite a bit
longer than it does to get a comparable etch on copper, but your
PnP holds up for a very long time if the lines aren’t too fine
and delicate. You will also need to preheat to steel or use some
heat source other than just an iron (such as the many good
suggestions that have been offered here). The blacksmith just
used a hot plate.
He is etching mild steel, however, and I don’t know whether the
reselts would be different on tool steel. Try it and let us know.