Hammer heat treating

Since we were talking about how to heat threat an anvil, it reminded me that I also would like to hear ideas about how people heat treat hammers.
I've modified a couple of hammers and had to heat treat them, but it was just random guessing on my part how to best do it. I'm talking 2 to 3 lb blacksmith hammers of different types.
The last one as a 2 lb harbor freight sledge that I turned into a rounding hammer. I simply heated the whole thing past non-magnetic and quenched it in vegetable oil. I don't believe I made any attempt to temper it after quench. Can't really remember. It doesn't seem to be as hard as it should be, It marks fairly easy if I hit anything other than hot steel.
I've heard one person once talk about running a stream of water down on the face with the idea of making the center of the face harder than the edges. I don't know how much water he was thinking, nor do I understand how you would heat treat the other end if you tried that technique.
Anyone have any experience or suggestions on how to heat treat a hammer?
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snipped-for-privacy@kcwc.com (Curt Welch) wrote:

Not really, but one way to quench both faces would be to have a plumbing arrangement set up that shot water at both ends at once (assuming a water-hardening steel). That (making certain possibly hopeful assumptions about water flow pattern, or perhaps with some sheilds to enforce water flow patterns) would allow for the common one-ended tool trick (my cold chisel, for one) of quench the end, polish, run the colors for temper using the heat retained in the body, and quench fully.
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The first thing is to know what the hammer is made of. It could be water hardening or oil hardening steel. We have made lots and lots of hammers from 1045. I know a guy who has made a thousand or so from 1144 or is it 1141 (Stressproof). But, others may use something like 4140. I think it is unlikely that the Chinese are gonna use anything but cheap simple carbon steel for their hammers. That makes it a water hardening steel in my mind.
Do you know about TTT curves as they relate to how little time you have to get full hardnes with plain carbon steels?
Many people harden hammers with a rosebud torch these days. Oxy-cetylene would be better than oxy-propane, because you can get things up to heat faster when you need it. After forging and/or normalizing, you heat a half inch of the end or so to non magnetic, then quench in cool, not cold water. The eye area never got hard eonugh to harden at all, so it stays soft. Assuming this is a hammer with a pein, do the same thing to the other end. Now the ends should be pretty much file hard. Now, carefully heat one end of the eye area (keeping some water around for control of the other end), and watch the colors run toward that end. Try to do one end at time, looking for, in my opinion, a dark straw. Take you time or the colors may run too fast. Quench the end half inch. Keep swirling the end around for a long time so the latent heat from the eye area can't creep back in to the end and advance the colors.
Pete Stanaitis
Curt Welch wrote:

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In my case, I had no clue what the steel was.
But even if it's oil hardening, isn't it possible you might have to harden in water to get it to cool fast enough?

No, I've never heard of that. But my understanding is that the rate of cooling determines the hardness, and that some allows are water hardening or oil hardening based on how fast they must be cooled. But yet, it seems to me, a large chunk of steel is going to cool far slower (even on the surface) than a small piece simply because it's got more internal thermal energy to dissipate, and all that energy has to travel through the surface to the quenching liquid.
I guess, now that I think about it, how fast the temp of the surface drops will be a trade off between the speed at which the heat is conducted through the metal, vs the speed it is conducted through the steel-quench liquid barrier. So maybe the speed the surface temp drops is more controlled by the type of quench liquid than the size of the steel. The interior will by nature always have to drop slower and end up being softer as far as I can see however.

hot enough?

Ok, so the trick is to find a heat source where you can get the end past non-magnetic without getting the rest there. It does seem tricky however to heat the second side up, without getting the first hot enough to temper it. I guess you just have to cool the first one from time to time as you are heating the second side.

Sounds simple enough. I'll try that on the next one. I used oil for safety (that is would rather under-harden than over harden and crack), but I bet you are right that the cheap Chinese hammers I was playing with were likely just carbon steel and probably needed to be water hardened. I've got enough cheap ball peen I want to turn into something else. I'll try water on that and see what happens.

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If you google "ttt curve for plain carbon steel", you get lots of hits that relate to this issue.
Here's one of the better ones to start with, because it gets right to the point: http://www.azom.com/details.asp?ArticleID14
You only have about one second to get the steel down below about 1000 F. That's why you need a water quench to get it hard.
Read as much about it as you can stand. It gets pretty hairy and then gets pretty close to black magic for mere mortals like myself.
Recently I made a center punch at a demo because I forgot mine. I used a piece of rerod, because that's what was handy. After forging it carefully, I didn't want to crack it in heat treatment, so, I thought I'd do as you did, and oil quench it first and see how hard it got--- just as you said you did. Well, I could NOT find any amount of oil to quench it and I was an antique engine show! So, I preheated a soup can of water to just under boiling and quenched in that. The tool did not harden at all!!! After normalizing, I reheated, quenched in cool water and got a glass hard punch. Speed IS a critical issue.
Pete Stanaitis -------------------------------------

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don't forget guys, back in the olden days blacksmiths shops had a water quench and a brine quench. adding salt to water changed the specific gravity thus changing the cooling rate of said quench. remember, to make carbon steel hard you have to trap the carbon atom inside the iron lattice formation. timing is everything. that is the rate of cooling / iron, steel alloy. have fun,mark
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snipped-for-privacy@webtv.net (Mark Finn) wrote:

I've got a tub of super quench I've played with as well. Just not for hammers. :)
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In that link you provided, it pointed out the "nose" of the curve that you have to miss in the cooling. That's a good thing to know becuase it implies that if you hit that nose (aka don't cool fast enough), you have suddenly lost a good deal of hardness. Which means there must be a fairly sharp discontinuity in the time vs hardness curve if you were to plot that vs some smooth curve which is what I was thinking was more typical. I know you had to cool quickly to get it hard, but I had never seen anything implying there was a time window that was critical to get under which there seems to be - and which seems to match your punch story. And that might well explain why both the hammers I tried to harden aren't as hard as I would expect. I might well have missed that window on both of them.
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snipped-for-privacy@kcwc.com (Curt Welch) wrote:

As it happens, I picked up a TOOL STEELS text book today at an iron in the hat! Now I've got tons of really good stuff to read through!
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Yeah. :)
I bet a guy could heat treat a hammer the same way a track welder heat treats a fresh cut rail end. :) Get it hot with a rosebud then let the rest of the rail quench it. :) They'd get a round patch ~2" in diameter and ~3/8" deep "hot ;)".
Railroad rail is ~1075 plain carbon steel unless otherwise marked on the side of it. "CrMo" and "HiSi are the only other special types that were around when I was working, both made by CF&I. Spark test your hammer heads vs a piece of rail.
A guy could protect the other face from heat by standing it up in wet sand etc. Quenching could be as simple as a big wet sponge the way they do driveshafts and autobody work.
Alvin in AZ
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