Couple of 440c questions

leifjl

leifjl

Joined
Nov 27, 2011
Messages
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Today I got some 440c knives heat treated. I've never used this steel before and was kinda put off when, right out of quenching, I got a hardness reading of 60HRC.
I thought I had screwed up somehow, but decided to continue onto the dry ice quench and then a single temper at 300.
When I checked it again, after the first temper at 300, it tested out at 61.5 HRC.

Is 60 a normal, as quenched, hardness for this steel?

Also, Is 61.5 too hard for this steel, or is this a workable hardness? In other words is this hardness going to end up chipping out a thin edged blade(.010")?


Thanks guys,
Leif
 
What kind of knife, and what will you be cutting?

That's higher than I typically see, but I haven't used 440C at that hardness so cannot comment.

Also, how acute do you intend to go? I'm asking because it'll help others make more educated suggestions.
 
Paring knife, about 3/4" full flat grind to the spine, .090" stock thickness.
I'll go through testing myself but I'd just like to start somewhere in the ballpark first.
 
I'm confused, a temper should of brought out hardness, not make it harder. My guess is a slightly false reading on the initial. I typically test 3 to 4 spot and look for consistency before I make a call.
A 61.5 isn't optimal for 440c and I would do another temper. Tempering also optimizes the chromium and helps to enable its true stainless properties.
 
The whole thing confused me.
That's why I figured I'd ask here.
Those numbers are an average of 3 spots. The dry ice could've brought it up in hardness, but what I'd really like to know is if 60 HRC as quenched is typical or not.
I'll bring the hardness down next temper.
 
If you heated it to proper temp for the right amount of time and air quenched it should of been a little higher, 63 or 64 but there is nothing wrong with 60. Remember it started around 15 or 20 so something went right.
 
Hmm... Is it flexible? I would worry more about the blade breaking than the edge chipping. The pairing knives I have flex quite a lot, but they are inexpensive production pieces. Still, while I don't cook much, I'd expect that flexibility to be necessary given the knifes uses.

I agree with dedub. I would think it would be much harder as quenched, but obviously something did go right. I wonder if the quench can affect the hrc to that extent. Someone must know?

Where's mete when you need him? :)
 
My guess is that the tester was not set up right the first time. I would get out your test block and re-calibrate it. Also, when testing after quench, make sure you are testing hard steel, not decarb over hard steel. Grind a small "window" with a 220 grit belt and test there. The test spot must also have parallel sides.
Cryo can add a point or two in hardness. Dry ice completes the conversion to martensite, but probably does not increase the hardness as much. In either case, it shouldn't raise it enough to be 1.5 points higher after tempering. 300F is too low of a temper normally for 440C. Your final hardness of Rc 61.5 ( assuming it is accurate) is OK for a paring knife, but I would suggest running it through a second temper at 400F.
 
I think something definitely went wrong on that first test.
Either way, I checked it today and it's calibrated, and I re-tempered at 350 and they're now at 60.5, which I'm happy with.
Thanks for the help guys!
 
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