You can do a trigger job to a steel trigger so long as you re-harden it. Basically using a step down approach of stones (Arkansas), abrasive media (Jeweler's Rouge), and sand paper (ultra fine grit) you can remove enough metal and reshape the geometry of the sear. Ultimately in the AR the geometry is the issue, and that's why most people simply go to aftermarket triggers that fix this issue. Since geometry is a large part of the issue in sear work, most people use a jig. You can buy a jig from Brownells, Midway USA, Sinclairs, etc.
To reharden the sear face, you can use Kasenit. You will need to dip it in the powder, heat the metal considerably, and quench it. This will allow the sear to have a very high hardness, so that the friction doesn't round it off and cause hammer follow.
Sintered metal means they start with a powder in a mold, then compress and bake it to get it to stick together. They case harden it after sintering. The two are exclusive. You can sinter metal without case-hardening and you can case-harden without sintering.
All I've done is smooth out the cutting marks. Made a big difference getting rid of that nasty gritty feel, still a lot of creep though but I don't have to worry about exposing the softer steel under the case hardening. It just feels like a well-used AR trigger...
The other AR I have has had different springs installed and it helped a lot. You don't notice the creep so much because the pull is so much lighter.
