My hardness tester has taught me a few things.

[blindhogg]

Well guys, until recently I thought I had hardening knives down to a science. Heat horizontal venturi forge up on 5 psi, for 10-15 mins or so till its good and hot. Slip in a piece of 2" pipe slightly squashed that is welded up on one end as a barrier so direct flame is not on my knife steel (1084 steel). Let that heat up real hot and then slowly crank down the regulator until forge is just barely huffing and insert a thermocouple hooked to my pyrometer for good temperature readings (1600). Insert knife, wait for good color and check w magnet and quench. Been doing it that way for years and years, edge always skated a file and I thought I was doing it right until I checked with my new hardness tester last month. Got readings of 35 to 45 on the C scale. What the hell, I went through all the things that could have gone wrong, pyrometer reading wrong, tempering oven getting too hot, temp too high. All but what the real cause was.
Yep you guessed it, soak time. I did some reading here after my dismal failure and realized it might be my soak time. I had gotten into the habit of not letting it soak much because of the times I used to HT using a blown vertical forge which was super hot and I could not regulate the temps much.
I went back to the smithy today with my new found knowledge acquired here and tried again w temps at 1500, let soak for 10mins and then quenched in my Parks 50 and tempered at 400.
I am now easily getting in the 60's rockwell. Probably still too hard I know but that can easily be fixed. Just wanted to post this so other guys dont make the same bonehead mistakes I have been making.
If anyone has any advice to the way I am currently doing it I am all ears, I have a lot to learn in this endeavor which was evident a few days ago.
CW

 

[daizee]

This is really interesting. When using the propane/brick forge I don't have the heat control you do. The 1084 is looking good so far - I get a little bit of surface decarb, which I hope means it's hot enough. Then I sand through that. Underneath it seems good and hard.

-Daizee

 

[rocketmann]

I am looking at a hardness tester now. What model did you get? Nice shop..

 

[me2]

So the edges were about 45 HRc and would still skate a file? When I heat treated my first blade in a one brick forge, I had the benefit of a hardness tester at work. It warped so bad I had to regrind the tip, heaven knows what the grain looked like, but the hardness was within one point of the specs the steel came with, both after quench and after tempering. Pretty good for stabbing in the dark, and pretty lucky.

Give the blades a good work out at the higher hardness. You might be surprised what you can get away with. I've batoned thin puukko style blades with a hammer with no issues, and they were 64+ HRc. I won't say that's the way to go, but I know I was shocked that I was able to hit that blade hard enough to dent the hammer face with the spine with no breaks. There is no forgiveness however. One crooked, twisting hit, and you get to make 2 or 3 small utility knives.

 

[JBS TOOLMAKER]

Good thread, I have been preaching about this for a while. You can not accurately check hardness with a file if you don't know how hard the file is. Also if the teeth of the file are in poor shape they won't bite anyway. It comes down to quality, do you trust the Q.C. department at Xbrand files ? The only way to test hardness is with a calibrated Rockwell hardness tester. I prefer bench models, I have used the digital portable type they are accurate and are mostly used in Q.C. enviroments so the data can be downloaded for records. The "popper" type which uses a springloaded centerpunch unit and a scope is accurate as long as you "train your eye" to the calibration block. On a day like new years day it probably won't be accurate The cheapest alternative is a set of Rc. testing files I don't have a lot of experiance with them but they are easy to use.
Jason

 

[deker]

Thanks for sharing this Chris. It just goes to show how tricky this all can be!

As for the file skating, don't forget that carbides of various types in your steel can cause the file to skate when the matrix is still very soft.

-d

 

[blindhogg]

I actually am guessing, that the edge on my older blades were somewhat hard. Since the edge is quite a bit thinner than the knife stock it would probably have been at close to the right temperature throughout.
But what fooled me was the knife stock was non magnetic, which I mistakenly thought meant it was ready for quench.
Wrong, just because your steel is non-magnetic does not mean the core is to the right temperature.
I should have realized this long ago because when my knives warped slighlty they were way to easy to bend back into shape when cold.
I just want to share with you guys, dont make the same mistakes I have made.
Get a pyrometer, there dirt cheap now.
ANd for darned sakes soak that blade, Now that I am soaking I can see a significant difference in color.


ROcketman, I have a tabletop hardness tester as available from MSC, it works pretty well and comes with three different test blocks for the C scale.
PS I also did a test when trying to figure out what I did wrong and I saw no real significant difference in hardness readings when I soaked a test block at 1600 then quenched and 1500 and quenched.
So just a little hotter did not seem to hurt me much, thought I would share that.