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Bill Kirkley

Tempering Problem?

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I ground my third knife today from a file. The first knife was forged and heat treated, the second was ground and tempered twice at 400 degrees +- 5 degrees. This time I tempered a file three times at 400 degrees +- five degrees for 1 1/2 hours, letting it cool in the oven to room temperature between cycles. I then ground a knife.

 

I tested the file tang before I ground the blade and it easily bent about 30 degrees and then back to zero. I ground the knife and did the brass rod test on the middle part of the blade and it passed at 30 pounds force. The tip failed, staying deformed. The very tip bent with minimal pressure. I put the knife in a vise to see if the body would bend, and it snapped in two.

 

So, what is going on? is this uneven tempering or over tempering, or something else. Also, the tip did not change color during grinding so I do not think it overheated.

 

I would appreciate any help.

LR Broken Knife.jpg

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Bill,

 

If you didn't blue back the spine of the knife it is just as hard as the edge and will snap. In order for the blade not to snap you need to reduce the hardness everywhere except the edge. I fully aneal my rasp by 3 anealing cycles, then forge my blade as I would 1095 and heat treat it as such. I mainly use Heller Farrier's rasps. Hope this helps.

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Did you normalize prior to HT? I'm planning to do a much better job of that if I make another file knife (or any knife really.) But I may just switch to a more consistent known steel. In my second file knife, I noticed what I think is a very inconsistent grain structure. In the belly of the curve the grain seemed small but the hardness was also much higher. I saw chipping in this area while sharpening. However the edge it took was amazingly keen when I worked the chipps out. However, near the ricasso area the grain structure seemed very large, the steel much softer and the edge folds over after only moderate use. maybe I have this backwards though? Pretty lame really for all the work it was to make. My heat treat process was: heat to critical in a charcoal forge, oil quench in used motor oil, temper once at 415F in the oven (gold color). My process needs work I know. I think part of my problem may have been this was the second knife quenched in the oil and it was still hot but I think normalizing may be more of the issue.

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Take a shot of the grain across the break. That being said, how thick is the knife? Thick blades tempered to the same hardness throughout don't take flexing really well.

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You didn't say how the blade was heated for quenching. If any part of the blade did not reach proper temperature then you might not have had sufficient carbon into solution or if the tip of the blade was allowed to cool below A1 then it might not have hardened enough. I think that you are more likely to be having a hardening problem than a tempering problem.

 

Doug

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I thought a blade that is soft and not hard will bend not snap. A hard blade like a file will snap under pressure. Differential heat treating methods should give the best of both worlds. If you HT then temper steel for a springy effect should that piece not be tough and bend before it snaps. I have seen cross sections of test knives with fine grain that took over 20 bend attempts before being twisted in two.

 

Bill look into the process and review the heat treat methods on Kevin Cashner's site:

 

http://www.cashenblades.com/steel/1095.html

 

He's the go to man on this. IMHO

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I did not heat treat the blade, I just tempered it. I assumed a file was already properly hardened with no tempering. I will post a photo of the grain, it looks fine, but the photo was not clear.

 

I think I figured out why the point end was soft and the middle probably adequately hardened and tempered (it passed the brass rod test). I took a similar file that I did nothing to. The tang would bend and deform and could be straightened without breaking. The smooth portion between the base of the tang and the business portion of the file would bend and deform but broke trying to straighten it. The business part of the file broke with just a little deflection. The point end of my knife was from the smooth part of the file.

 

I am going to try another knife, only tempering it twice for 1.5 hrs and see how that goes.

 

George, if I get a blade that passes the brass rod test do I need to blue the back. I am making a paring knife.

Broken Knife Grain.JPG

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I think the above replies missed your Question Bill?

If I read you right, the first of your 3 knives is the only 1 you ever heated above critical.

The current knife was tempered while still a file in every way. Then you ground it, without overheating based on color, and then started testing without any further heat treating?

 

If I read all of that correctly, I suspect you had a case hardened file. The main body is hardened deeply enough to fracture, but at the tip, you ground through the hardened surface and revealed an unhardened, or lesser hardened core.

James

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With your above reply, I will amend what I posted. Your tip was indeed unhardened, because the file company drew back, or never hardened the "ricasso" and tang of the file for durability during use.

 

With any re-purposed steel, it is always advisable to anneal, forge and/or grind and then do a full heat treat (after testing HT on a sample or 2 first if possible). [Edit: This assumes you are set up to do your own heat treating, which it would seem you are since you did it with Knife #1.]

 

For a short stiff knife like a paring knife you may get away without a blue draw on the spine, but I would go ahead and do it anyway, just to be on the safe side.

James

Edited by James Spurgeon

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Bill,

 

For a pairing knife it would not need to bend.

 

I make large 7 to 10" blade knives from rasps. My process is different. When I make a paring knife using carbon steel it is usually with either 1084 or O1 at 59 to 62 rockwell all the way through. I normally profile the knife, Fully go through all the HT and tempering steps with no blue backing of the blade. I grind after HT on them also, dumping in water after every pass. I really do not use files but farrier's rasps. The steel may be different and my process treats them like large choppers, which they primarily are.

 

If you are using metal or wood files I believe that James has hit it on the nail. Based on his assumption I agree you may have had a case hardened file.

 

For small knives known steel is both easy to find and not that pricey. I do a lot of mystery steel but, I use twice as much known steel. I did not start using mystery steel until I had made about 30 knives out of known steel to get my processes down, and I still mess up every now and again.

 

1385381082433.jpg

Edited by GBrackett

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James, will a case hardened file break or bend? It seems if the core is not hard it should bend.

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If something (anything) is case hardened properly the surface (case) will crack and the inside will deform before breaking. Now the amount of bending before breaking may be different based on the case hardening method/process and base material.

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So, is it correct that the file that broke cleanly with only a small deflection is likely fully hardened?

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I would think so. Bill grind part of it and see if you get a lot of long sparks when grinding. I have found that normally heat treats pretty good for me. I still think you would be better off using known good steel to start out with. It will make your life easier. After you have a few good blades under your belt then use the mystery steel. Without the piece in hand and doing some testing we can only guess at the answer.

Edited by GBrackett

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I have several dozen files I got cheap on eBay. I figured it is better to learn grinding, forging and the process of heat treating on these instead of wrecking up good steel.

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Bill, I hear you. Forging, grinding, and finishing these will give you experience. I used paint stirring sticks to start with. They were free. When it comes to heat treating it's time to use the real deal in order to truly learn the process. My best wishes. And...

 

...remember the more you make, the better you will get!

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Bill, sorry I missed this somehow, I often work with Mystery steel, and I believe in fully annealing everything before I start work, often I use a 'kettle' style barbeque and a bag of charcoal, get this lit and heat up the 'blanks' (files etc.) To yellow in your forge, soak the until the charcoal is at max, then a quick transfer to the barbeque, heap charcoal on top leave on full heat (with lid on for +- 45 mins.) Then choke and leave it with just enough air to keep it going, I do this late afternoon, then go to bed! Lift the lid next morning, often the steel is still warm... Now you should have it soft enough to easily file and grind. Forge into shape or go with stock removal, these blades will have a lot less stress and should harden properly, I quench only the edge 1/3rd of the blade, then temper, only blades I lose are when I skip this process, you can do about 10 in one go and then it's cost effective! Try it and see if it's time well spent or not...

Edited by Miles Hebbard

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I think I figured out why the point end was soft and the middle probably adequately hardened and tempered (it passed the brass rod test). I took a similar file that I did nothing to. The tang would bend and deform and could be straightened without breaking. The smooth portion between the base of the tang and the business portion of the file would bend and deform but broke trying to straighten it. The business part of the file broke with just a little deflection. The point end of my knife was from the smooth part of the file.

 

Yep, that's why the point was easy to bend, it was either never hardened or tempered soft... file tangs don't need to be hard or brittle.

 

 

This time I tempered a file three times at 400 degrees +- five degrees for 1 1/2 hours, letting it cool in the oven to room temperature between cycles. I then ground a knife.

 

File steel is an interesting beast, it is often well over 1% carbon. Just treating it as W1/1095 will often leave you with a somewhat brittle blade, it really seems to need a higher tempering temperature than one would expect... Back when I first started making knives I found a box at my local scrapyard full of about 50 worn out Nickolson black diamond files, and every one of them got turned into either a knife or some other cutting tool over the years. It has been a long time since I made one into a knife, but back when I did, I would temper them at 475-500 degrees Fahrenheit. This would leave me with a blade that was not overly brittle but would still hold a fine edge well. Since you have a few to experiment with, save your broken blade, and make another the same size but temper this one around 475, and compare edge durability and strength/toughness... my bet is you will prefer the second blade's performance over the first's.

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Wish I could find some Nicholson black diamonds ... Great files!

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Miles- I have a store bought propane forge. I'll have to try your charcoal.

 

The way I anneal is to heat it up in the forge to orange-yellow and stick it in vermiculite overnight. I do not have a pyrometer so I use a magnet and canola oil for hardening. As I mentioned above for this small knife I did no annealing or heat treating. I assumed the manufacturer did a better job than I could. I just tempered the file.

 

GEzell-I will try tempering it at 475. I wonder though that because the edge did not chip with 30 pounds pressure on a rod if the three tempers at 1 1/2 hours at 400 are adequate?

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The lower the temp, the longer the time... I don't have any graphs, all my books where pinched during a move a few years ago, so I use memory alone... I do higher temps at less time because I'm allways behind in my work! But the brass rod doesn't fib, so you should be ok.

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Thanks Miles. If I really get into this I will get a pyrometer so I can do a better job heat treating. I may also build a forge more conducive to forge welding.

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I ground another file. It was tempered twice at 400 for an hour and a half (which included the warm up time.) It is a countertop oven that has a convection feature so I used that assuming more even heat.

 

It passed the brass rod test at 30 pounds along the entire blade. The tip does not bend.

 

So, I think the problem with the knife described at the top of this thread is that the tip end of the knife was made in a part of the file that was not fully hardened.

 

I will grind to smaller grit to make it look a little better. I am also going to taper the top of the handle. Then I will put a wooden handle on it.

 

I ground this freehand. I had made a jig but after attending the session at the ABS symposium on grinding a knife I decided to bite the bullet and try and develop the "feel" of freehand grinding. I have a way to go but not too bad for a first, well second, attempt

 

Something interesting is my edge bevel. If my measurements are correct it is 33 degrees. You do remember I was making a small chopping knife, not a paring knife ;-)

LR Dads Knife 1.jpg

LR Dads Knife 2.jpg

LR Dads Knife 3.jpg

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The grinding demo by Master Smith Daniel Warren was something else. Did you notice he started grinding from the point to the ricaso? I had the opportunity to work with him and Bill Wiggins at Bill's shop in February. I got some one on one with both of them. Improved my grinding 1,000%. I put my jig away also.

 

Glad to see the hardness issue worked out. Now time for 10 more!

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