Forged a flatter from 4140 this weekend. After hardening in peanut oil what temp should I temper it? I'm planning on oven tempering.

450 would be a bare minimum.  I would temper the struck end to a blue.  Or I would probably use the same method I use for power hammer tooling thanks to Forgemaster.  I temper ithings hot enough that the oil flashes off.  Better that you have to dress the tool a little more often than have it crack. 

Looking at the steel data charts for that steel, 400f for two hours will give a hardness,,,depending on steel thickness, of 55 RC, to me that is harder than I want for a flatter, I would expect some chipping on the edges if used with a striker younger than me. The chart also show the temps needed for lower RC scale hardness, Those temps would not be attaineable in a home style oven. First off I woiuld test with a file and see if it skates, if not i would reharden. I would heat to a certain color on polished clean parts of the piece to get the tool correct. I want it softer on struck end to prevent chipping.

Chris you did a good job on your flatter. But you should have stayed around for the finalle'.  For those reading Chris was with us (Lyle Wynn, Stan Bryant, David Gaddis) where we forged 5 flatters by hand Saturday.

 

We ground flatters and hardened them yesterday, tempering to dark straw/ gold. As per Ed Brazeal's instrructions goldish should be just right!

 

But then again we used Ed's flatter making anvil and only part of his instructions.

 

BTW...making a flatter is not for the weak person.  It take a lot of heat, lot of beatin', and a lot of sweatin', and then you must be serious. No kidding folks. This is not a regular back yard DIY project.

 

 

Carry on

We never HT flatters just leave them as normalised, they don't need to be hard, they are not a cutting tool, and I certainly would'nt harden the struck end, in fact I would try to anneal it, (by getting the struck end to dull red and burying it in a little pile of dirt on the floor and leaving it there for a few hours to cool slowly).

 

Phil

Would love to see some pictures of the process.

i ended up heat treating my flatter.  I positioned the flatter in my gas forge so that the face of the flatter was facing the burner and the striking end was actually sticking outside of the forge.  I was able to get the face non magnetic without getting the rest of the flatter even to a cherry color.  After confirming that the face was non magnetic i quenched the face in peanut oil.  After letting it quench for about 10 sec or so i removed it and ran a file across the face to test hardness as well as knock the scale off so I could see the temper colors run.  The residual heat was such that the colors ran pretty quick and I was able to get the face a nice brown temper color before quenching the whole thing in oil.   The end result was a flatter with the face still retaining some extra hardness but the struck end was still soft.  I am happy with the result.