I needed to heat treat (harden) some cast iron also. I don't have experience heat treating iron but I remembered that when I tried to drill holes in an old soap pot, It was a BEAR. I needed an English Wheel in a hurry for a project. I couldn't see the big $$$ for a new one (or used) so I made some accessories for my C-press. For the upper wheel, I used a 2x6 cast iron caster wheel. For the bottom anvils, I used 2x3 cast iron casters. All these were rated 1000lb.
What I did (right or wrong) was mount the wheels on a motor-driven shaft and slowly heated them to red-orange (about 5 minutes). Once there, I set my flame to carborizing and held it for another 10 minutes. I tried to keep a dark red glow going the whole time. (Wheel spinning too) After that, I let the wheel air cool in a bucket. (keep the wind off)
I can't tell ya what the hardness is but I went through 2 C2 bits just making very light cuts to make sure the wheels were true on the contact faces before polishing.
The Q&D E-Wheel worked great. I wouldn't try to flatten welds with it but it did a great job of plannishing and rolling some car panels.
Ops! I went back and read your post again. I see that it's a cam. If it were me, I'd send it to my crank and cam guy and have him do it. That cam iron is tricky.
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As others have mentioned, iron and steel alloys are annealed at a temperature that is shown as a rather bright red and almost orange. The heating method doesn't matter, but the metallurgy has to be heated above what is called the transformation temperature.
Transformation temp means that when rapidly cooled the grain structure will transform to a hardened state. To prevent hardening the temperature must be lowered very slowly to prevent re hardening or precipitation hardening as it's called.
Heat your material evenly to the nice red color and immediately bury and cover it well in a large batch of oil dri for the best results. Technically once the material has lowered below 1450F you can pull it out and quench it and go to work.
We're not in a hurry so cover it and walk away for a few hours.
Localized hard spots can be caused by many different conditions. Primarily by a part of the casting that cooled too quickly when poured as the mold essentially sucks heat from the material too quickly and the local transformation occurs.
Funny thing is that iron has a very low or non present carbon constituent in the alloy and therefore will not harden. The melt batch may be a bit contaminated from the crucible it was in or picked up some carbon from the mold it was poured into or contamination from whatever was in the pot from a previous melt.
Another common cause for hard spots in cast iron is sand inclusions from the pouring funnels or the mold. It doesn't take much, maybe a grain or two, but a machining tool isn't going to be able to cut through rock.
Steels:
We all use bits of scrap steel for machining our projects and have no idea what alloy it is. Steel as we know is a hardenable material. Well most steel is. Again it's all about the carbon in it. Low carbon steel can't be hardened. You can heat it as hot as you want then quench it in water and it's still dead soft.
Most of us have machined steel stock and found that there are hard areas on the skin that defy and trash the cutting tools. But the inside of this alloy is soft. Finding this I immediately know that the alloy is a medium or high carbon alloy. Chop saws are notorious for doing this to a bar as the blade causes the metal to get red from the abrasion and it quickly cools as the blade advances. Bingo, you have a hardened area in the steel from the rapid cooling.
If you encounter a hard alloy and want to machine it, the same annealing procedure as iron is used.
Re hardening:
Yes, you can re harden it after machining if you want but the metallurgy may not be the best. But for the things we do it'll most likely be fine if we need a harder structure. **Correct hardening should be determined by the alloy composition as the harden and temper procedurals vary widely per the chemistry and carbon content.
Carbon Points:
Steels are made and have the designation number to determine the chemistry.
1008 to 1018 alloy has no carbon and therefore can't be hardened.
1020 has 2 points of carbon, minimal hardenability
1030 has three, mid level hardenability
1040 has four and hardens nicely
The Moly steels we see like 4130-4140 harden very well and must be tempered back after hardening to prevent cracking.
Spring steels like 1050 to 1090 (nine points of carbon) harden
to extremes.
Some alloys used for gears and splined shafts are suited to furnace carburizing. (pounds carbon into the surface and it soaks in) 8620 is a neat alloy that will carburize the skin to a depth up to 1/16th inch and harden extremely well when quenched. Yet the core remains dead soft for ductility. Perfect stuff for a had gear tooth surface and a soft core to prevent stresses and breakage.
There ya go, a brief intro to metallurgy 101. Actually the above is much less than metallurgy 101...
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