Just how little should a file bite in after..

[Robert_Phelps]

Just how little should a file bite in after the heat treat/quench? I heard it should skate, and not take off anything but scale.

I used a nicolson 10" ( I think.. it was the biggest Home Depot had) medium coarsness(s'what it said at least), single cut file (pretty new, only worked on one knife with it)

Compared to how it usually bites as I bear down, it did kinda "skate across", but it did leave itty bitty scratches

 

[Will52100]

It's a thing of feel, and hard to explain. The itty bitty scratches could be just a little bit of decarb. Normaly I use a half worn out file and it won't bite at all. I find a fresh file will just barely bite with a bit of pressure but won't dig in. The same stroke that would leave a 1/16" notch in the tange will barely brighten a spot. Experiment and get a feel for it, it's the only way I know how to explain it. I have noticed that if I overheat a blade going into the quench that it feels harder than one that was quenched at criticle.

 

[Kevin R. Cashen]

Depends, what steel is it? 1084, 1095, W2, O1, 52100 anything with more than .8% carbon should feel like your are filing glass if it is fully hard, it should just skate off with no effect. 5160, 1060, 1050 and other steels of similar carbon content should show just a hint of scratching but still skate a file well. I often tell by the sound, if a file does't bite at all it is a high pitched zipping sound, a file that cuts at all will have a duller soft cutting sound.

 

[LRB]

Maybe my age is showing, decaying brain cells and such, but I seem to recall that Mete, Mr. Cashen, and other metalurgists have stressed that to achieve max hardness, one must go above just critical at the quench. At least with the more common steels. I am thinking it was 50o, to 75o, above. If I leave any more marking than a bright spot with a file, I am not satisfied with the hardening process, and although I never really thought much about it, Kevin Cashen is dead right about that sound of the file test. When you hear it, you don't really have to look at the blade for any scratches. You also feel the skip as well as hear it.

 

[Robert_Phelps]

Well, now I'm pretty sure it hardened. (It sharpened really well and passed the brass rod test..also when I cleaned the scale off and tried with the file again it really just skated without any real visable scratching) I didn't want to keep skating with the file to clean off all the scale, so I could really check, because I heard filing on hardened steel ruins files (which would make me buy a new one with money I don't have)

 

[rashid11]

few things:

- if blade is not well protected against decarb during HT, the outer layer will be soft, to the depth of few thou, as carbon gets baked outta steel. Not so bad @ 1450F for plain carbon, much much worse @ 1950F . THis is why PBC, stainless foil envelopes, inert atmospheres etc are used to protect the steel during HT.

- the steel continues to harden for 1-2 hrs AFTER initial quench, in my experience, as transformation continues to take place

 

[Ed Fowler]

The file test is only one indicator of a good edge, don't forget to test for cut.

 

[rashid11]

On a side note it is rather unfortunate that an inexpensive method
for testing hardness has not been developed. the regular diamond-impression
device is expensive and bulky And accuracy is what, -+1.5RC ?

I wonder if we can do something with $10 tuners - the harder steel is, the
higher pitch is shall produce when gently struck ... like a camertone.

Now, due to different sizes & shapes etc, it will be hard to arrive at a formulae.

Ultrasound offers another possibility ?

 

[Kevin R. Cashen]

Well, now I'm pretty sure it hardened. (It sharpened really well and passed the brass rod test..also when I cleaned the scale off and tried with the file again it really just skated without any real visable scratching)...

Now I am confused, is this checking being done before or after the temper? The file should bite after tempering. I am not sure I understand what you mean when you say it sharpened well? A dead soft blade can get scary sharp, it just doesn't like to stay that way, and if the blade was fully hardened it would not have sharpened without some effort. Ease of sharpening should be proportional to overall hardness and carbide condition. If the brass rod test was done before tempering this another indicator of how that method it is good for determining edge geometry but tells very little about overal hardness.

Rashid11, I am not sure what steel you are working with, but it is probably a richer alloy than I am used to, since there is some stubborn austenite action going on if the steel is still hardening after Mf. As has been mentioned before, conversion of metastable austenite into martensite is a dependant upon temperature not time. Retained austenite will hang around and effect hardness long after the quench but then is once again dealt with through temperature. I have watched steel slowly harden over a 5-8 minute period when cooling in the air during marquenchig/martempering procedures, but I could have had full hardness at any point simply by cooling it faster. If you are working with alloys that are still noticeably hardening an hour after they assume room temp, you could probably benefit from some subsequent cold treatments.

 

[LRB]

Rashid11, years back I bought a set of hardness testing files from Sheffield Knifemakers Supply. Their range goes as 40,45,50,55,60,and 65Rc. I have compared testing between them and a Rockwell tester, and they seem dead on, however you are limited with 5 point increments, and have to learn to guesstimate in between scratch results, which I seem to have done fairly well. I have sent samples to a friend who has a Rockwell tester and have been only a point or two from his readings. This file set was about $75.oo. The price is probably higher now, but I have found them well worth the price, and much cheaper than a Rockwell tester.

 

[Dmitry.M]

RASHID11 Unfortuynately camertone (tune fork) will not work. Because the tone depends on mass, shape and metall composition of the blade. The only way is to record initial tone before HT and compare it to one after HT. But it will only indicate the HT effect. Because nobody could predict how the frequency will shift...