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Adair

4140 dies turned out to not be 4140. What next?

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Hello all, 

I sent some dies to a heat treat shop.  I had 4140 written on the steel.  I have a few hundred dollars invested in machining.  They were heat treated but do not test above 45 Hrc.  I was after 54 Hrc.  The representative in the shop thought they behaved like 4130.  He can case harden them but these dies are for cold work (sheet metal power hammer).  Is there any prudent next step that I might be able to take. I bought the steel new but it was 20 years ago.  I must have mislabeled it.  

-Adair386090781_HeatTreatdies.jpg.487a00dc931fa13b8e701ecc03d549b4.jpg

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Sounds to me like you're stuck with whatcha got. 

The only other thing that pops into my head would be attempting to hardface the dies, but that'd pretty much eliminate the precision you got with the machining, and I (not having any experience with cold working) don't know if the less-hard substrate would hold up to the abuse and not mushroom.

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there is not much of a difference between 4140 and 4130, and surely not 9 RHC points worth, in fact the specs over lap a bit

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Thank you both for helping me face the reality.  I asked them to just send the dies back.  We'll see how long they hold up pounding cold sheetmetal.  I'll be curious until the end of time what steel I actually purchased.  It was soooo long ago.  The first tool steel I ever paid for.  

-Adair

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If they are useless to you in their current hardness try a water quench, then temper immediately.  Read up on this forum about water quenching 4140 in larger sections like power hammer dies, the late great Grant Sarver had much to say about it.  4130 should be similar if that's what you actually have.  Be sure to round EVERY corner and edge.  

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I don't know about that Steve, 10 pts. C is the difference between low 30pts. and medium 40pts.  carbon steel. 

No, case hardening won't work for an impact tool it's only really an abrasion resistance technique. 

Frosty The Lucky.

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Guy I just took a class from uses super quench on his power hammer dies, but those are mild steel. Not sure what that would do to medium carbon.

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According to the specs I looked up: 4140 is stated as requiring between 0.37-.44%  carbon, while 4130 is at 0.28 - 0.33%  So the variance isnt as broad as I suspected, because I assumed a near overlap in specs, but still 4140 is not going to get much harder than 4130. 

Fully hardened Brinell hardness of 197 for 1430 to 205 for 4140, The published maximum hardness is just a lab testing, and not a real world spec. I did get one report stating a maximum Rockwell hardness of 54 to 59 HRC for 4140

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