First HT, first trouble.

D

Dmitry.M

Joined
Jun 13, 2006
Messages
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I had more than 10 year pause in my knifemaking. A month or so ago I decided to start it over again. So I did. I bought a pile of tools, steel, wood and almost everything. I made two blades from A2. For one I even made handle, and all hardware. The only remaining thing was to HT it and finish. I decided to HT it myself as I did years before. I read all datasheet, all insrtuctions. Today I've made an improvized foge and fired it.
Everything was almost perfect. I heated blade to 1400F, than soack for 7-8 minutes and quenched in a front of a fan. Not very strong but big fan, so air flow was pretty even. Checked the hardness - file slides. Ok placed the blade in the oven set it to 500F. Almost 4 hours in the oven. Than slowly cool down. Everything looks great. File still slides, but not that easy. I estimate it ~60.
Anyway, cleaned it up a little and decided to check how it is tough. Tip in to the vise, halfway down. And I pilled the tang....I've got somw juce in my hands. The blade bend like a spring a bit and snapped.:eek: :(
My first blade in 10 years snapped....
Ok, I got some beer and begun investigation. The breackpoint is smooth and grain is even. Pretty fine grain. So I did not overheat it. And than I mentioned colorized corner. Checked the other half - the same pattern. Washed it carefully - still remains. My conclusionn - it is CRACK! And it was there BEFORE HT!!! Because it is oxidized. So my blade snapped where it was a crack. The question is where it came from????????:confused:
I've got the A2 steel from McMaster. It was annealed 1/4" X 1 1/2"X36" ground bar. I did not bind it or cold forge. Just cut with the hacksaw to the shape and removed metal to form the edge. Flat ground. One side 1/4" other 1/16(edge). I did not do anything to make this crack.:( But it is there.
Now I do not want to TH second one I want to understand WHERE for a Gods sake I made a mistake????
I'll try to attach the picture:http://club.foto.ru/gallery/photos/photo.php?photo_id=666344
 
Most likely happened in the heat treat. A gas forge is not the best for heat treating high alloy steels but great for 01, 1095 etc. Your tip probably got hotter than the rest, creating uneven stress. An electric oven would be much better for high alloy steels. Also your quench temp (1400) is way too low for A2. Keep after it, it'll get better :)
 
So the tip could not be OVER heated.... And I checked the temp before quench. It was almost even within 10-15F.
 
Dmitry -

it does look like there was a crack in the blade, indeed. I am not sure how it got there - was it from the beginning in the A2 bar you bought or it was created later.

It is very imprortant not to have any stress risers in the outer "perimiter" of the blade before HT. I usually do a 320 grit all around, making sure not to
have any square corners and choil area is nice and round.

If one profiles the perimeter with 50 grit and leaves it at that, you will have thousands of little scratches , ea a little stress riser and then, with fast quench steels all bets are off.

give me a buzz if you want to chat with a fellow russian knife maker:

two zer0 one 507 1889
 
Check www.crucibleservice.com The heat treatment you did was probably the cause . It should have been 1750-1800 F ,soaked for 20-30 min [for a blade] .That would make a big difference .
 
Not sure how that Rc 60 happened,maybe a dull file? The specs for A-2 are,as mete said, much higher than you used,sounds more like you used O-1 specs.
At the temps you used you might have made some Austenite which cooled down into some sort of mixed structures,but it would have been a poor and weak mix.
Many high alloy steels will often break when they reach the point of bending ,especially if HT was off- that is the nature of A-2 steel in my experience.10XX steels will bend like a spring if done right.
Another thing to think of - If you heated on the charcoal,and you have been out of practice for 10 years,perhaps your guess of the steel temp was off by a good bit.Charcoal has its good points,but temperature control to +/- 20 degrees isn't one of them.A HT oven or temperature controlled forge would be a good idea on anything but simple steels.(It's a good idea on all steels,actually.)
Stacy
 
Does it mean that A2 will snap anyway if bend too much?
The steel I use to work before was pretty close to A2 by composition and it always bend and make cracking-squicking sound before break. And it never break in one "popp" like that one... Unless I overharden it like a glass. I hardley overheated this one... but now I think "may be"....:o
Looks like I need to pot another hundred or so and get some oven... Electrical I quess.
 
You won't regret getting a good HT oven.It will make your life (and your blades) a lot better.
Stacy
 
Stacy, could you answer if A2 wil snap or it will bend first? It might be I just brocke it with my brutal force....
 
A2 is more likely to break instead of bend when HT as a knife blade. If you want a blade that will bend and not break then use a simple carbon steel like 5160, L6, 01, 1084, W1, W2, or any of the other 10XX steels. I use simple carbon steels and prefer them over the high alloy stuff.
 
Thank you SUNFISHMAN , bladsmth, mete, rashid11.
I realized that made a mistake. We'll see if I will rearn from it. Thanks again!
 
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