Stronger than steel... I guess you won't be nailing it, I guess you'd have to prefab parts so you could drill through with like a carbide endmill since, unlike steel, you can't just use a magnetic drill like you would for field drilling holes.
1. It's very dense
2. The first hole is usually easy enough, but consecutive holes become more and more difficult.
3. This is much less a factor of density than of silica content. Silica sands the metal. Carbide and cobalt bits can help a lot, but the silica always wins.
Worthy note: High silica wood dust, eg from ipe, may as well be considered worse than asbestos. It's evil stuff and will destroy your tools and your lungs inevitably.
Edit: while I don't know the silica content of a wood that's roughly twice the (janka) hardness of ipe, such woods also seem to drill ok, depending on the bit. Two examples are Lignum Vitae and Quebracho. The latter, I think, means axe breaker and was named appropriately.
Edit 2: it's Day of the Insidious and Relentless Typo. Nailing any of the mentioned woods is about as practical as nailing your own hammer. Either the nail will bend before making a dent, or the wood will split.