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Heat Treating 4340 Power Hammer Dies

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I have been working on getting help heat treating a set of power hammer dies I have made.  The Dies are roughly 2x3x4 (one is slightly larger).  I did some research online and read the posts in heat treating.  The following is the process I have come up with that I hope will yield the best results.  If there is anything that you more experienced heat treaters see that might pose an issue please let me know.


Step 1.  Normalize the material to relieve stress.

Heat dies to 1000-1022 degrees F for 2 hr. Furnace cool to 850 degrees F at 50 degree drop per hour. Then remove and place in vermiculite.  Allow to cool completely.

Step 2.  

Heat dies to slowly to 1550 F, hold until uniform. Quench in oil (I will be using warm vegetable oil) to 200 f.

Step 3.

While still warm (200f), reheat to 850-1200f.  Hold for 2 hours then air cool.


The biggest question I have at this point is what temp. is best for tempering.  I want this material to be on the upper end of it's hardenability.  It seems to me I would want to temper at the lower end of the spectrum.  Is this correct.


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Ok, step back and listen to everyone. You don’t want work hammer die at the top range of hardness. You need harder than soft forging temperature steel. Hard that are too hard can kill you. One chip off the die in the wrong place can be lift ending!

Start of normalized, and if you get too much distortion after a year, rework them. Then harden them and draw them back pretty far. One step at a time, and learn as you go.

Keep it safe!


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Thanks for the input Goods.  Although I asked for a consensus of how hard people recommend power hammer dies I got no specific response.  I started a new thread hoping I could focus on the question at hand so I will keep my response in line with that.

4340 only gets to 60 HRC max, if I were able to process it in some very advanced ways.  So If I heat treat it at home I will only be able to get it into the range of 45-50 HRC Which from some research I have done online is the right hardness for dies.  That is what I mean when I say I want it at the upper end of it's hardenability. 

is your concern that the 50 HRC would make the 4340 too brittle, or that the 50 HRC is too hard?

Edited by Mod30
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Really should have proof read that. Sorry, in the middle of heavy forging heats…

45~50HRC should be safe. I would send it out to a heat treating shop to get it there. 4340 can be pretty quench crack sensitive. Do you have a heat treat furnace? (I would like one one day…)

Keep it fun,


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I do not currently have a furnace. I am still coming up with a plan to dial these dies in.  I don't like the idea of farming it out.  I enjoy trying to figure out the problem.

Thank you for the response!


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I understand that. I’m frustratingly independent. But this is not something to mess with with out experience and the right tools.

(of course, here I stand forging 8lbs of 4140, with a hammer that just a bit small for the job…)


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  • 2 weeks later...

45-50 HRC is a good hardness for a power hammer die and 4340 is fine material for that application. Your original post in this thread does have some errors though. Normalizing is done at temperatures in the 1600-1700 f range. Those you gave were for high temperature tempering. they will not have the same effect as the higher temperature range.

When it comes to heat treatment, especially of critical tools like power hammer dies, control of the heat treat process really is extremely important to getting the outcome you need. Uniformity of temperature during heating, sufficient volume of quench fluid etc all must be considered.

Here are the recommended temperatures for your project:

1. Normalize at 1600 F. Air Cool.

2. Austenitize at 1550 F. Oil Quench.

3. Temper in the range of 600-700 F for a final hardness of 45-50 HRC

You will want a minimum of 10 gallons of oil. you will need to agitate the part vigorously during the quench. 

Paying a commercial heat treater to process these dies to your specification will be much cheaper than buying a furnace with the proper controller needed to properly heat treat these dies. of course, if you have other projects planned for that kind of furnace, you could justify the cost that way.


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