Destructive testing of blades? What to look for?

S

SeanMK

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Dec 5, 2010
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I made a couple of forged blades a while back, and thats eally as far as I got. Got busy and you know. Starting to get back at it, and I am definitely a beginner. But what should I look for? What am I trying to accomplish, because the first one failed miserably, and the second did marginally better, but still snapped.


Obviously I probably need to look at my heat treat. But I am still in the primitive mode, and financially, as much as I would like to have one, dont see a HT oven in my near future.

Criticize away, as I thought I was better than this, but apparently I went wrong somewhere.
 
Steel is 1084 from Aldo. propane forge. motor oil/hyd fluid quench( a buddy uses this)

Heated to non magnetic, so I dont think I got it too hot(I have tempilstiks ordered at work, 1400 and 1450)

I just remembered I DID NOT temper immediately after the quench. Possible reason?
 
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As a fellow beginner, I know how you feel. A couple of things I was hoping you'd clarify so perhaps a more experienced bladesmith can better address your question...

Did you temper at ALL, or just not immediately after the quench? If you did temper, what temperature and duration? If you didn't temper, that would almost definitely explain the breakage.

Before quenching, did you normalize the blade? What was the temperature of your quenchant?

Also, many here would point you toward using canola oil rather than motor oil as a quenchant. If you dig through the recent threads, you'll find a bit of debate about this but the consensus is that canola is the preferred "back yard"/primitive quenchant, with an engineered quench oil being preferable if you can get your hands on it/afford it.

But like I said... I, too, am a beginner so don't take my suggestions as gospel. Far from it. Hopefully someone experienced will point you in the right direction.
 
Blades was normalized before quench.
Blades were tempered, 3 x at 425deg for an hour each.using my kitchen oven(im single, and the dog doesnt care) also used to additional thermometers along with the oven temp.

quench oil was preheated,though I did not check temp. I think that fills in the holes.
 
Not nearly enough data here to formulate a wild guess, much less an actual reasonable answer.

The first thing to consider before even choosing a steel is, what do you want your knife to do? Is it a chopper, a filet knife, or what? What do you want to cut with it, and how will its geometry work to accomplish this? Poor geometry will lead to almost instant failure no matter what steel or HT regimen you employ. A knife with the appropriate geometry, but cheap, weak steel will perform very well... not for very long, of course, but it will.

What constitutes destruction/failure of the blade? Going dull after a few cuts through cardboard, chipping on the edge when chopping through pine knots, or snapping when you clamp it in a vise and pull with all your might?
 
Blades snapped, first one no flex in it at all. second one flexed a little, then snapped. I put a wench on it and held the table from rolling with one hand, and pulled on the wench with the other. far from "pulling on it with all my might", which is why I am slightly concerned thaat I have made crap. and I am kind of a pefectionist(slightly) but enough that making "crap" bothers me A LOT.

Didnt even get to the edge part.
 
What was the spine thickness, and how far up the blade did you harden it? What do you mean when you say there was no flex at all? Did it not even make it one degree from straight? I assume you are trying to reach 90 degrees. Be sure to use the proper term w/r to flex and bend. This will save those trying to help you a lot of extra questions and incorrect conclusions. The 90 degree test is a bend test usually. Once at 90 degrees, it will only return part way to straight, since it's bent. If it returns all the way to straight, it is flexing. Even a bent blade flexed a little before bending. Even the weakest steel has some ability to return to straight, just not nearly as much as hardened steel. If you already knew this, and it really didn't flex at all, you may have a first, as even my untempered O1 blades flexed a little bit before breaking.
 
Is that an hour with the blade at temp each? It takes a while for the blade to come up to temp even if the oven is up to temp.
 
Blade was in an hou each time, at temp. Put blade in oven turned on, when the preheat buzzer sounded, I started the timer.

Blade may have bent slightly, but surely not noticeably, before fracture. Thats actually why I tried the second blade. I mean, I actually expected blade to bend at least a little bit. I didnt plan on it making to 90deg. but thought I would get at least a little bit away from 2-3 deg.

and to be honest, I know enough about this stuff to get into trouble, and not near enough to say i'm "knowledgeable".

I guess maybe I was looking for some sort of standout answer. "hey dummy, youre doing it all wrong" or something like that.

I kind of want to try the third blade, but I kind of like that one!! I guess I keep reading, and keep trying! and keep saving for the HT oven!!
 
Me2,

spine is 1/8, hardened the entire blade(and tempered) Im waaaay to new at this to even think about getting creative.
 
Your blades unquestionably have some degree of flex. Even glass will flex. It sounds like you are after a bend. If you want your bladez to bend, they will need to have a softer spine. You will have to experiment on the ratio of the hard portion to soft portion. Be aware that fully hardened, edge to spine, blades will not typically bend very much. They will flex to the limit of their strength, bend just a little, then break. Fully hardened blades can flex to 90 degrees, but it takes a good understanding of strenght, hardness, and geometry.
 
James was right it took 10 posts to pull some of the info out of you.


If you're doing a full heat, full quench and full temper, why did you expect it to bend ?
I suspect you are reading too much Ed F.
As long as you did what you did properly, especially not overheat it, that's what happens.

Some sort of heat control would really help.
apparently Kosher salt melts at the right temp.

Try bending a file, it will break too.

Fully hardened and tempered blades are stronger than differential hardening or differential tempering.
I say keep doing it that way for the most useful blade too.

If you had to put a wrench on it to break it, maybe you will never break it by hand.
Crowbars or cutting tools?

If you want to pass the ABS bendy blade test, follow this.
Notice he only quenches the edge.
http://www.caffreyknives.net/journeymanarticle.html
 
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Another question to ask is how long was your blade. A short blade won't have hardly any bend until it snaps but a long blade might give a bit before it breaks.

Why are you trying to have a blade that bends? It won't cut any better than one that doesn't. If you are trying to make a chopper, then you do need some flex in it, but otherwise, if it took a wrench to bend it, I'd say you did well. As Mike Snody says "A bent blade won't go back into the sheath".

How does the grain look at the break? I did some 1084 tests recently. One break right out of quench. One after one hour at 400. One after another hour at 415. And another at one more hour at 425. The grain got much much smaller after each temper cycle.

Jason
 
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