I have seen some simple jewelry designs made out of wire, which I'd like to replicate. These designs are made from a single piece of wire bent into a variety of shapes.

For portions of the design, the wire is still perfectly round. However, some parts are smoothly flatted. By smoothly, I mean that there are no creases or hammer marks.

Here's an example of what I'm describing:

How can I achieve this effect? Can I use steel wire, or does it need to be something softer, such as aluminum wire?