M390 Heat treat? what to do to increase hardness with low tempering?

S

shqxk

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Mar 26, 2012
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I got result of 59.5HRC tested from my first attempt HTing m390 with brand new Evenheat.

This is the recipe being used.

Preheat 1475F - 10 min > ramp to 2150 soak 30min > plate quench > dryice+ acetone sub-zero > 375F tempering 2 times 2 hour each.

I think the hardness is a little lower than expectation. Any suggestion to increasing hardness with low tempering?
 
Heat to 2050-2075f, soak for 20 min.
Plate quench to ambient.
SLOW cool to -95/100f and hold for 3-4 hours.
Double low temper & check....
 
Thanks you Russ. Seems like the austenitizing I use is better suit for high tempering.
 
I want to say that I just got 62.2HRC with 2065F aust temp with -13F freezer in stead of dry ice sub zero, double 365F tempering. Thanks you again Russ!
 
With the amount of retained austentite generated at the higher temperatures, cry, or high temper would be needed. I found sub zero with z-wear wasn't quite enough, compared to cryo.
 
I have heard several times from different person that M390 is difficult to achieved 62+HRC or even impossible without proper cryogenic. I found that this is not true at all thanks to Russ Andrew.

Straight into 2065F with 30min soak, plate quench and some 360F tempering will get me 62.2-62.4 every time even without any freeze treatment.
 
usually higher hardness gives you lower toughness . The game is to find a good balance between austenitizing temperature , quench, and tempering temperature !! Experiment a bit !
 
Thanks, Mete. I don't do heat treat - send it to Peter's. I was curious because I make skinners which have to withstand abrasives in the fur. M390 at Rc 62 would be ideal for holding an edge but would it chip if I hit a bone?
Tim
 
One of the problems I have is that some don't know how to use a knife . An animal like a boar or elk that rolls in the mud, is cutting through fur and mud .Mud is abrasive on the knife and cut fur gets all over the meat and sticks there ! Turn the blade up side down [now you see why I don't think much of finger grooves ! ] penetrate the skin and slit the skin where you want. Much better way !
Cutting through the mud is very hard on the blade !
 
I was told by the B-U rep at Blade a few years back that dry ice is insufficient for higher alloy steels like Elmax and M390. Whacking that RA is even more critical if using the low temp from what I have read and been told.
 
jdm61 said:
I was told by the B-U rep at Blade a few years back that dry ice is insufficient for higher alloy steels like Elmax and M390. Whacking that RA is even more critical if using the low temp from what I have read and been told.
Click to expand...

...I have no idea why this hasn't sunk in for folks.

Whether the number is 'theoretical' or not, most of these alloys have target Mf's of -130° or thereabouts.

Can't remember if it was @DevinT or @Alpha Knife Supply that said it, but 'good enough' on a custom knife should never be good enough.
 
Ln2 is really the way to go. You can get a new chinese dewar for a couple hundred off eBay, and even the cheapest 10L will hold it for a month or two.
I'll get 50 or so stainless knives ready for HT at once, and get the dewar filled for that batch. My 10L dewar costs about $50 to fill. Even if it only lasts for the one batch, that's $1 or less per knife. Your epoxy costs more than that.
If you don't want to do big batches, you can buy a 1-2L dewar for even less, and get it filled for $5-10

I've experimented with HT on aeb-L and 154cm without cryo, and it can still make a very good knife with the right recipe. But I won't sell one that hasn't seen cryo
 
Agreed. I get 2 Rc points less in z-wear with sub zero compared to cryo.
 
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