Like LawrenceA said, there are steels and steels..... and then there is iron.
Each of these have different hardness's depending on the type of steel or iron and the heat treatment of them. They can range in hardness from Brinell Hardness 80 thru BH 745. BH 80 would be something like steel used for water pipe. BH 745 would be something like a fully hardened High Speed Cutting tool.
A cutting tools hardness allows it to cut thru softer steels without a problem so, if the craftsman who made that lock was using the tools I think he was, carving that fancy lock would have taken a lot of time but it would have been possible.
It is also possible that the lock parts were investment (wax) cast to roughly the finished shape and the surfaces on the castings were finished with cutting tools.
Wax casting has been around for thousands of years so, it's nothing new.
It's called wax casting because the shape is originally carved out of wax. The wax is then coated with clay or some other ceramic like material leaving two holes in some unimportant place to create a hollow shell. The wax is then melted out of the shell thru the two holes in the wall of it.
The shell is then fully hardened or glazed.
After heating the shell to almost as hot as the molten metal, the metal is poured into it thru one of the holes while air escapes thru the other hole. It is then allowed to cool. Following cooling, the shell is then broken off of the metal casting.
The process is called "investment casting" because you "invest" the wax pattern which will end up being destroyed in the process.
While I'm at it, hollow castings can also be made using the investment process. To make a hollow casting, things are the same up until the time the metal is poured. The molten metal is poured into the shell and a little time is given to allow the metal to start to harden. It does this from the outer surface, inward.
Before all of the metal is hardened, the shell is turned so that one of the holes is pointed downward. This allows the still molten metal in the interior of the casting to pour back out leaving the hollow casting behind.