It would be material that is hardened from the mill. I use 41L40 bar that is 28-32 rc. It machines well for me. In a lathe I can cut .200 depth of cut, .022 per revelution at 600 surface feet. I get a life of about 150 parts per insert.
Another common material is ETD 150 (LaSalle Steel trademark, I think). The material is produced to a specific tensile strength, in this case 150,000 PSI.
The hardness is usually between Rc 29 and 33. For stronger material, there is ETD 180. Many other companys have similiar products under other trade names. The machinability is maintained to allow production of parts by conventional practices.
Another example is titanium bar TiAl6V4, which is available as a T6 heat treat. Machines very nicely on a suitable lathe. that's about 900 MPa, I think Cheers
I agree with Kenneth. The designation normally used is STA for Solution Treated and Aged, which is approximately equivalent to a T6 treatment for aluminium and magnesium alloys. Ti-6-4 in this condition has a yield strength around 1000 MPa.
