OK, the results are in. Hardness is approximately 92 HRB (Rockwell B Scale) as converted from Vickers testing. This is much harder than lead, of course, but not very hard when compared to steels.
Let's compare their tensile strengths to see the difference (it's about the only way to compare with such a large difference). Lead's ultimate tensile strength is around 12 MPa. Our BBs, at 92 HRB, have a tensile strength of ~649 MPa.
For metal people, the microstructure was primarily ferrite, with a small amount of pearlite (this confirms the relatively soft reading).
For those non-metal people, here's how the process went for this:
- Mount the BBs into plastic under heat and pressure. This makes them easy to work with.
- Grind and polish the surface with the BBs, revealing the core and creating a smooth surface.
- Use an acid to etch the surfaces. Etching reveals the structure of a metal, otherwise, it will usually appear to be one solid color.
- Using a tiny pyramid-shaped indenter (Vickers), indentations were made into the surface. I chose this instead of a larger machine since the samples are small. These indentations are measured, which produces a hardness value (HV, Vickers Hardness). This was converted to Rockwell B by the instrument.
- There's your hardness
