In general, this is why - when I was blacksmithing quite a bit - I
mostly quit trying to recycle steel, especially car parts!
Steel used to mean iron with some carbon (0 to 1%), maybe with a
trace of chrome, moly, nickel, etc. Leaf springs from GM cars were
great medium carbon steel, so too the coilovers. Intake valves (the
lower temp side), usually good stuff.
Now steels are custom cooked for the application, with silicons and
other high temp alloying agents, and as you discovered, a
homogeneous part may actually be heterogeneous with neat tricks like
stir welding, friction welding, or explosive cladding/welding being
used to join unlike metals invisibly and perfectly, with no or
minimal heat zones. Air hardening or high temp steels can be joined
right up against ordinary carbon steels and the only way to find the
transition zone is trial and error (for most of us). Even if you can
identify it, some of the “exotic” alloys (stainless esp.) have
pretty stringent heat treating requirements, with soak, quench, draw
cycles that involve timers, controlled ramp ovens, inert
atmospheres, etc. Far cry from heat it till the magnet doesn’t stick
and drop it in water or oil!
As far as leaving it annealed… well, yeah. Copper is a lot softer
than even annealed steel. I guess it depends on the application. How
detailed is your stamp? What is your backing material when stamping?
I’m pretty overboard on this, probably, but I really only make tools
out of new, O1 or W1 drill stock, and I heat treat and temper all
of them. I figure if I’m taking the time to make that tool, I want
it to outlive me. Good steel from a reputable supplier, olive oil
for the quench (yummy smells) and a perfect surface finish on every
p.s. On a curmudgeonly side note, you can’t always count on getting
quality homogeneous steel from a “new” material supplier either… I
ruined a hammer face on a ball bearing that was embedded in some new
purchased, but obviously recycled, dimensional stock as I was forging
at a bright orange heat… the ball bearing was still at full
hardness I’ve also received air hardening drill rod when ordering
oil hardening from online metals.com, so test a piece any time you
order new stock!