lets break some knives!

C

chad2

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so i have been inspired to break some knives to see the grain structure.

this is a knife that i did 2 years ago when i first started the new heat treating kind of i can not remember exactly but i think i did 2 edge quenches in canola oil and tempered at 350 for two 3 times.

this thing was an absolute pain to break i ended up having to hammer it into a tree and wacked it many times with a mallet, a hammer, and finally numerous times with a 5 foot 2x4 which finally worked. the fractures were only on the ground side of the bevel. this knife had a chisel grind but double edge this is how i do all of my knives i think the reason the fractures are only on that side is because i did not do any normalizing, thermal cycling, or annealing before heat treating.

v7ve.jpg

the grain sizes does not look great but ok.

qa5c.jpg


p7qf.jpg

this shows how many cracks developed

jqob.jpg

this image shows how even the cracks curved away from the flat side of the knife (aka) the side that was not ground for the bevel

i am going to be doing my new heat treat to a piece of 5160 and breaking it also and compairing the results.
 
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I am guess that the stress cracks are from the bevel grinding and not normalizing before heat treating.
 
Be careful about breaking a knife and looking at the "grain structure" on the surface of the fracture. That looks a lot like a piece of structural steel I have that broke in an accident. Low carbon (0.3% max), unhardened, very high load rate, and very high load. No cracks on the surface like yours, but it failed in a different direction. You're knife would have had to fail from spine to edge to have failed the same way this piece did. All I'm saying is don't read too much into it.
 
me2 said:
Be careful about breaking a knife and looking at the "grain structure" on the surface of the fracture. That looks a lot like a piece of structural steel I have that broke in an accident. Low carbon (0.3% max), unhardened, very high load rate, and very high load. No cracks on the surface like yours, but it failed in a different direction. You're knife would have had to fail from spine to edge to have failed the same way this piece did. All I'm saying is don't read too much into it.
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Kind of hard to follow what you are saying, what do you mean?
 
I'm just saying that what you see with just your eyes on a broken piece of steel might be grains, or it might not. It all depends on how it broke and how it was heat treated. Even the coarsest grains you'd find in a carbon steel blade or low alloy blade like 5160 are very small, just barely visible. If you're using procedures to minimize your grain size, you'll quickly get to where they are very difficult to see. An ASTM grain size of 8 has an average grain diameter of less than 0.001". On that sample of structural steel I mentioned, even though it's ASTM size is guaranteed to be 6 or finer, I doubt what I'm seeing on the fracture surface is the grains. It might be, but there's a lot going on there.
 
If the heat treat was done correctly, and it wasn't, why bother. For comparison purposes it won't be a good teacher. Doing the heat treat in the correct manner may not let you "see" the right grain structure either but will give the results. I believe working with the positive does far more good than looking at the negative done work as a learning thing. Frank
 
Breaking a knife by hammering it in a tree and whacking it with a 2X4 isn't going to tell you anything of use. You need a controlled break under a single load.

Place the blade 1/3 back from the tip in a heavy vise. Place a 2-3 foot long piece of pipe over handle ( Oval the pipe a bit if needed). PUT ON SAFETY GLASSES, GLOVES, AND STURDY CLOTHES. Start bending the blade at an even rate and when it reaches the elastic limit, it will break. Just bend one time, not back and forth. Any others in the room need the same safety gear you have on.

The cracks in your blade just show that it received a lot of stress....which your description of the breaking surely would cause.
That they radiate from one side shows which side it failed from.
That they are there at all mainly shows that the blade was edge quenched - the cracks are caused by tearing in unhardened steel, not a shearing break in hardened steel.
The grain looks OK as far as the photo shows. Any knife with the HT done in a controlled manner should show a fine grain. It takes a metallurgical microscope and measurement lenses to tell the actual grain size. Edge quenched blades often just bend, and only the edge shears. There is very little a break test will tell you about an edge quenched blade.....except that they will bend.

To do any sort of comparison testing on blades, they all need to be about the same size, heat treated the same way, and broken the same way. Otherwise, you will be comparing apples to oranges.
 
I'd have to look in my notebooks to get an exact number, but I've broken (tested to destruction) somewhere around 75 blades over the last 10 years... and I definitely think there are things that can be learned from it.

But... IMHO.... if you are doing it with blades that you don't know how you heat-treated, then there's no way you can get any true feedback on what's working for you (or not working).

My $0.02 is: if you don't remember or have notes on how a blade was heat-treated, just test the heck out of it for fun... but don't put too much weight in the results (or break it, LOL). :)
 
Thanks guys. There is deffinantly a lot of knowledge in this forum.

I do think that some of the reason for the way the cracks formed was because when I heat treated this blade I used to lean the blade up against one side, which unfortunately would put the belly of the blade directly next to the heating element on one side . Which I think cause a lot of over heating on that side of the blade.
 
chad2 said:
the grain sizes does not look great but ok.

qa5c.jpg
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That is not by any stretch of the imagination "OK". That is simply awful. Frankly it looks more like cheap cast "pot-metal" than good knife steel. Not only is it extremely coarse to the naked eye, it's wildly inconsistant throughout a very small cross-section. How could one possibly expect to get a fine keen edge on steel in that condition? :confused:

That blade did not snap, it tore apart. That's not a good thing. What you are describing as "cracks" appear to be more like "rips"... there's a huge difference. Well-HT'ed steel should shear along a fairly smooth plain, look milky white or grey, and appear very smooth when broken. It should definitely not look like a close-up of rocky, dirty country road. (that is obviously not a very scientific description, nor a guarantee that the HT is correct)

You have certainly determined how NOT to HT that grade of steel, and I appreciate you sharing your results with us.

I've been following your threads for several weeks now, and I applaud your enthusiasm. But quite honestly, I'm convinced that you know a lot less than you think you do. You currently lack the most basic understanding of why your "failures" failed, and you seem extremely reluctant to listen to the folks who are trying to help you.

That's some thin ice on which to tread. You're doing yourself and the knifemaking community at large a disservice by latching onto one set of ideas that appeals to you and just running with it - without fully understanding it in the first place- rather than putting a lot more homework into understanding WHY and HOW these things actually happen.
 
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Great observation james, yes this blade was not heat treated with the greatest of knowledge behind it. but it is hard for me to believe that you can come up with that observation from such a blurry pic. First it looks different in color because I had just gotten done cleaning it second it looks very incosistent because of the way it was broken. Many many very strong wacks laterally, because of the way I broke it, it created many cracks, hills and valleys in the broken structure, what you are seeing there is the tiny shadows from those hills and valleys. When seen by the naked eye the grain looks very even. I posted the pics because I thought the stress cracks were cool in the way the curved away from the flat side of the blade.
 
james terrio said:
That is not by any stretch of the imagination "OK". That is simply awful. Frankly it looks more like cheap cast "pot-metal" than good knife steel. Not only is it extremely coarse to the naked eye, it's wildly inconsistant throughout a very small cross-section. How could one possibly expect to get a fine keen edge on steel in that condition? :confused:

That blade did not snap, it tore apart. That's not a good thing. What you are describing as "cracks" appear to be more like "rips"... there's a huge difference. Well-HT'ed steel should shear along a fairly smooth plain, look milky white or grey, and appear very smooth when broken. It should definitely not look like a close-up of rocky, dirty country road. (that is obviously not a very scientific description, nor a guarantee that the HT is correct)

You have certainly determined how NOT to HT that grade of steel, and I appreciate you sharing your results with us.

I've been following your threads for several weeks now, and I applaud your enthusiasm. But quite honestly, I'm convinced that you know a lot less than you think you do. You currently lack the most basic understanding of why your "failures" failed, and you seem extremely reluctant to listen to the folks who are trying to help you.

That's some thin ice on which to tread. You're doing yourself and the knifemaking community at large a disservice by latching onto one set of ideas that appeals to you and just running with it - without fully understanding it in the first place- rather than putting a lot more homework into understanding WHY and HOW these things actually happen.
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I am sorry you feel that way. But I hope you dont think this knife was my most resent one because it is not. This knife was a beater I made 2 years ago. My most resent knife which has brought about your unkind words towards me has greatly surpassed the the abilities of this broken knife. Just because I disagree with some of you. does not mean I would ever put any of you down in the way some of you have me. I would also never say that I am better then any of you the way you guys have me. You say I make the knife cummunity look bad? I dont need to do that when people like you are around. Please look through any of these threads that you speak of and show me where i have written something bad about another person, the way you have publicly. I have only brought to light, that people who argu with no knowledge or experience of the other side of the argument, is a very juvenile thing to do.
 
Having the grain size even is only part of the process. The grain size looks pretty rough, and it looks that way because it is. Fine grain does not break with that kind of a pattern. I fully agree with everything that James said. Basically, you are moving too far, and too fast, without an adequate knowledge supply. A little learning can be a dangerous thing. Especially from some of the sources you are using. Just MHO. I would also add, I don't see James putting you down, but rather trying to slow you down to realize that you need to know a good bit more yet than you think you do.
 
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LRB said:
Having the grain size even is only part of the process. The grain size looks pretty rough, and it looks that way because it is. Fine grain does not break with that kind of a pattern. I fully agree with everything that James said. Basically, you are moving too far, and too fast without an adequate knowledge supply. A little learning can be a dangerous thing. Especially from some of the sources you are using. Just MHO.
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Thanks for the tips i will do some more reading.
 
I just want to say that I hope no one that is new to knife making takes anything that I say as fact! I have not and do not proclaim to be a great or even mediocre knife maker. I am very new and am still learning very much every day.

There is so much to learn even in one kind of steel like 5160, that I have had to decide and weed through all of the knowledge that is thrown at me everyday. Just because I have settled a little bit on one set idea of heat treating does not mean that I will not learn a better or more efficient way of heat treating.

My heat treat is a mix of ideas that have been talked over with numerous knife makers by email. None of the information that I post is made up by me, if I have been misinformed then I will admit to being wrong.

I just want to say that I am sorry to you james for what ever I have done and to anyone else that feels I have been offensive towards them this is not my intention. I only want to defend myself and wish I had a fraction of the knowledge that most of you do so that I could help ppl the way you guys have me. Now if I could give a little advice; if the advice that you guys gave was written in more of a helping way and not so much of a duh way. It would be taken better.

Hope that last part makes sense. I only wish to make friends especially with ppl that share my hobby.

Now can we get back to the fun part of this thread and post some pics of blades that have been broken and are heat treated correctly so everyone can know that I am not all that good at heat treating! :) lets see some good grained knives
 
While I'm not really on the same page as you as far as processes/techniques are concerned... I think it's great that you are so jacked up on Mt. Dew about all of this and trying new things. No matter how a guy makes knives, testing his blades is a crucial element in knowing what they will do in application versus just theory.

Just to throw out an example, I had a fella tell me recently that he didn't like flat ground blades because they were too thick--- that they don't have thin edges like his hollow grinds. Well, in theory, a hollow grind would have less meat behind the edge. But in application, the blades he showed me were only ground to around 0.035" - 0.040" and then he put a big, fatty secondary bevel on it.

When I showed him how far back you have to go from the edge on my blades to find 0.035" thickness... he changed his tune a little.

And just for the record--- I do BOTH TYPES OF GRINDS.... so hopefully nobody will see what I just wrote as an attempt to fire up a flat vs hollow debate. That is NOT my point.

My point is that theory is all well and good, but testing and use will help decide if those theories work in application as well. :)


Without getting into a diatribe about grain... a pretty simple way to see some very nice "grain" is to break a HSS drill bit. It will be silky smooth and whitish gray in color.
 
Yep, and was typically heated well over 2000 F before quenching. I wish I'd saved that A2 blade I broke trying to straighten it. It looked the same way.
 
I regret that my observations may seem unkind. It is never my intent to discourage anyone from learning and experimenting, and I certainly am not putting myself up as any sort of expert.
 
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