Shallow Hardening Steel Question

J

J.S. Carter

Joined
Jul 4, 2007
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915
:confused: So I'm wondering, on "shallow hardening" steels like 10xx / W1 / W2, how shallow is shallow? and just for giggles lets say we fully quenched and tempered pefectly, and we now have a perfect plate martensite transformation, throughout the whole blade. How many thousandths thick is it? And could you ever sharpen through it?
 
A properly quenched W2 or 1080/1084 blade 1/4" thick will
through harden.
I've not used W1, but it should behave pretty much the
same.
 
"Shallow hardening" is an Industrial term, it could mean only the top inch or so will harden. The only effect it has on knives is quench speed as far as I know.
 
with that said, if you don't use proper oil, those shallow hardening steels will likely not harden all the way through in the thicker sections and you may get what I call an "accidental hamon"
 
It can be difficult to harden those steels even with thin knives, which is why some recommend a deeper hardening steel.
 
Big Medicine said:
Would you mind expanding on "accidental hamon" for a newbie?
Click to expand...

What he's saying is that if you use too slow an oil you will get a good martensitic hardening in the thin section of the blade (say edge to 0.75-0.90" where as the thicker section (.100" +) will only hit a fine grain pearlite structure, Which is what a hamon is, it is a boundary line where the steel transformed from martensite to pearlite. While tough it's nowhere near as tough as a fully hardened plate martensitic structure. (but boy is it pretty!) so with these steels one could use water, brine, or a suitable fast oil, like McMaster Carr's 11 second quench, Brownell's Tough Quench, or Parks #50 to ensure proper hardeness / plate martensite transformation, when quenched from critical temp.
Hope this helps!


Jason
 
A 1" round bar of W1, quenched in water, will typically harden to a depth of .120"
and W2, a depth of .125" (1/8").

So a 1/4" blade hardens to an 1/8" depth from each side = through hardened.
 
The 1/4" blade would harden even better than the mere 1/8 plus 1/8 simply because there is so much less material/residual heat to deal with. With the one inch bar, all that hot steel behind the 1/8 that hardens is the "enemy". In a blade you don't have to deal with that. Thus, I would guess you could get even a slightly thicker blade to through harden.

Best,

John
 
J.S. Carter said:
What he's saying is that if you use too slow an oil you will get a good martensitic hardening in the thin section of the blade (say edge to 0.75-0.90" where as the thicker section (.100" +) will only hit a fine grain pearlite structure, Which is what a hamon is, it is a boundary line where the steel transformed from martensite to pearlite. While tough it's nowhere near as tough as a fully hardened plate martensitic structure. (but boy is it pretty!) so with these steels one could use water, brine, or a suitable fast oil, like McMaster Carr's 11 second quench, Brownell's Tough Quench, or Parks #50 to ensure proper hardeness / plate martensite transformation, when quenched from critical temp.
Hope this helps!


Jason
Click to expand...

Tough Quench is not really fast enough for big W2 blade, IMO. It is an 11-13 second oil depending on how hot you get it. Parks #50 is somewhere in the 7 second tange, if I recall correctly.
 
Wow I'm learning more and more everyday here, would it be ok for 10xx and W1 though or should it be a faster quench as well, prehaps an interupted quench ? anyway Thanks you very much mr Hanson and Mr Frankl That is exactly what I wanted to know!
 
W1, W2 and 1095 need a very fast quench. Other 10xx steels, such as 1084 have much higher manganese, are deeper hardening and can get by with a slower oil but not too slow.
 
Here's some poop on W2 from Cincinnati Tool Steel.
Note Depth of chill, and grain size onfo.
 
Thank you, Russ. Would you mind explaining "depth of chill"? I'm not sure what that is, or what it means for us.

Thanks again,

John
 
Depth of chill is the same as hardening depth. I think the word "chill"
just refers to the depth to which the steel cools fast enough to harden.
 
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