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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making. |
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#1
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deep vs shallow hardening
Could someone give me an explanation and examples of deep hardening versus shallow hardening, in laymans terms? Thanks bruce
__________________ If it isn't sharp it's only a screwdriver. ------------- Birdog Forge,com |
#2
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Basically it has to do with how difficult it is to harden and time allowed to do so. Deep hardening steels can be hardened deeper because they don't need to cool as quickly to harden. For example, if you have a 1" bar of deep hardening allow and one of shallow hardening, and quench them both, the shallow hardening will only be hard for maybe a 1/4" in or so while the deep hardening will be hardened all the way through because it was within the allowed time even though the center holds heat longer.
With the thin cross sections in blades it works a little different, though quenching time still plays a part. It should harden all the way through because the cross section is thin enough, but you have more time with a deep hardening steel to get it down cool enough to harden. A side effect of this is that shallow hardening steels are much easier to get a good hamon on, because the spine doesn't cool quickly enough to harden above the oil/waterline or under the clay, while deep hardening alloys can be anywhere from slightly difficult to near impossible to get a hamon. An example og a shallow hardening steel is 1095, you have around half a second to get it down below approximately 400F. A deep hardening allow is O1, which gives you about a minute to make the same temperature drop. A very deep hardening alloy is just about any stainless or other air hardening steel, they don't even need to be quenched in anything, just remove them from the heat and their own natural cooling rate is fast enough though some people still use cold air or quench plates to squeeze a little extra out of it. Alot of the deeper hardening oil quench steels have a tendency to air harden a little in thin sections. __________________ ~Andrew W. "NT Cough'n Monkey" Petkus |
#3
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Are spring steels, generally, shallow hardening and tool steels deep?
And how does this factor into blade geometry? If at all. Enquiringminds, ya know. b __________________ If it isn't sharp it's only a screwdriver. ------------- Birdog Forge,com |
#4
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I'll venture to say that spring vs tool isn't the determining factor, since 5160 is another deep hardening steel and that's concidered a spring steel, but spring vs tool can be kind of a fuzzy distinction with some steels being counted in both catagories. It has more to do with how high the alloy is. While this isn't written in stone, generally the more alloy components besides iron and carbon, and the higher percentages of them, the more deep hardening it is. The 10xx steels usually only have a little manganese in them and even that is put there to make it slightly more deep hardening if I remember right. I'm sure if I'm wrong on any of this then either Kevin Cashen or Mete will correct me here shortly.
Blade geometry can be effected on shallow hardening steels if the spine is alot thicker then the edge then you might get a differential hardening even if you wanted a full harden, since the thick spine could hold too much heat. On a fairly average blade (what's average?) it shouldn't be an issue. __________________ ~Andrew W. "NT Cough'n Monkey" Petkus Last edited by AwP; 01-24-2005 at 02:02 PM. |
#5
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You're right Andrew. Another way to look at it is that the water hardening ones are the shallowest, oil hardening medium , and air hardening the deepest hardening. The choice becomes important when you are looking for a hamon. Other than that it's not all that important for blades.
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#6
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Thanks guys
__________________ If it isn't sharp it's only a screwdriver. ------------- Birdog Forge,com |
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blade, knife |
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