Chipping-Edge gring or Heat Treatment?

David Stifle

David Stifle

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Nov 20, 2008
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I recently finished a 12" W2 bowie. During my chopping test on an oak limb I got some minor chipping. On examination, I noticed I had put a very long shallow v-grind on, similiar to the edge of a meat slicer. I re-profiled the edge and retested, and got no chipping at all.

I heat treated by bringing it up to critical and holding for five minutes or so, then quenched in parks 50. I tempered at 425 for an hour, cooled, and repeated.

I've put the blade through a series of chopping tests and the blade has performed satisfactorily. Still, that initial episode of chipping bothers me. Do you guys think it was caused by testing with an inappropriate edge grind, or could I have missed on my HT? Picture attached.
 

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Hey David, a few questions....

1. By "critical" temperature, what do you mean... in degrees?
2. What is your heat source... kiln or forge?
3. What sort of pre-HT regime did you do... normalize, anneal?
 
Hi Rick,

-Forge: I use a 100 year old hand cranked Champion blower with charcoal or coal
-critical temp: I bring it up to a bright cherry red, run a magnet over it, and put it back for another five minutes or so-holding it at the same color.
-I didn't anneal this one. It came from Aldo and was already annealed, well I think, as it was soft and workable.

My methods have always worked quite well for my primary steel, 5160, but I'm still feeling my way with W2. I would appreciate any tips you have.
 
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Are you sure they were chips, not tiny little dents or something? Also, W2 has a lot more carbon than 5160. That alone can give you fits it you don't know how to deal with it. Or, maybe it doesn't have a lot more. Did you get material certs from Aldo?
 
so did you forge this knife and if so what did you do after forging? Normalize? Anneal?
 
No, they were chips, not big nor deep, but definitly chips. I felt it was due to the edge geometry, which is why I reprofiled it. I didn't get any cert from Aldo. Bill, this was a stock removal blade, I didn't do any normalization or annealment.
 
David Stifle said:
Hi Rick,

-Forge: I use charcoal or coal
-critical temp: I bring it up to a bright cherry red, run a magnet over it, and put it back for another five minutes or so-holding it at the same color.
-I didn't anneal this one. It came from Aldo and was already annealed, well I think, as it was soft and workable.

My methods have always worked quite well for my primary steel, 5160, but I'm still feeling my way with W2. I would appreciate any tips you have.
Click to expand...

I can tell you my opinion based on what I have learned up until now... I won't promise it's the right way, though.... Ha!

I don't think think you(or anyone, for that matter) has the ability to hold temperatures in a coal forge, outside of building some kind of regulated muffle system. I think you may very well have overheated the blade(especially the edge) and are experiencing the symptoms of grain growth.... brittle, chippy edges in thinner geometries.

I don't know about his W2 but Aldo has always cautioned me to normalize(not necessarily anneal) his plain carbon steel. But I really don't think this is your problem.

5160(hypoeutectoid) requires higher temperatures when heat treating. So, I can see where perhaps it could withstand your current process, where W2(hypereutectoid) would not.

It's my opinion that when heat treating, you should use the methods and materials that best suit the equipment you posess. An open forge(solid or gas) is just not capable of nailing heats or soaking. I should reword that to read that the human variable is the weak link. There has been organized testing done on "eyeballing" heat and even Master Smiths were off by an average of 200F... most often overshooting the mark.

I would triple normalize(always) at descending heats to refine grain and skip any attempt to soak your blades more than a few seconds once you feel they are at temperature. Your consistancy will improve and your blades will be better for it.
 
Rick, thanks for all your input. Good stuff. I was seriously temped to send this blade to an Ht house, but being an independent cuss thought I could pull it off. Soo, you don't think my problem is due to testing with a flawed edge geometry, but my heat treatment? I haven't had chipping since I reprofiled the edge. I'll take your advice about normalizing. And, I think in the future I will send my W2 blades out.
 
You don't have to send out your W2. Lots of makers heat treat W2 in a forge. I really think that if you remove the soaking process, it will work out fine. Thicker geometry will support the cutting edge and lessen the likelyhood of chipping. How "meat-slicing" thin are we talking... .015",.010", .005", .002"? What is the shoulder of your cutting edge at now?
 
Ok, thanks Rick. As for how thin the edge was, I think I put a caliper on it, but just don't remember. I also can't remember if I measured the edge after reprofiling or not. I now have a rolled edge on the blade, similiar to what you would see on a katana.
 
i am with rick on this one. Most likely large grain is the largest contributing factor to your edge chipping. I normally heat treat W2 in my forge and quench in water with no soak time at all, yes I break a few blades but less than one in ten. With a 350 degree temper I can chop a piece of oak pallet in two without chipping or rolling using a kitchen knife with the thickness just behind the edge at .015. I use a few steps post forging to reduce grain size, this includes quenching the forged blade in oil from critical twice then three normalizing cycles using reducing heats.
 
All Rick and Bill's advice is good.

Due to the fact that the problem went away when you put a stronger edge on the blade, I suspect it was the edge geometry in this case. That is not to say that your HT regime couldn't use some improvement. Triple cycling W2 ( or any hyper-eutectoid) is very important.
 
Thank you, guys. As usual, when I have a tecnical question I get good, sound professional advice.
 
Great thread so far.

And not to hijack it, but, Bill what sort of hardness are you getting with a water quench and 350 degree temper? I'm guessing a bit north of 60, no? And you still seem to be getting great chopping performance out of a thin edge. Any ideas as to why? And have you toyed with the tempering temps at like 325 and seen chipping there?

Thanks!
 
John Frankl said:
Great thread so far.

And not to hijack it, but, Bill what sort of hardness are you getting with a water quench and 350 degree temper? I'm guessing a bit north of 60, no? And you still seem to be getting great chopping performance out of a thin edge. Any ideas as to why? And have you toyed with the tempering temps at like 325 and seen chipping there?

Thanks!
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Hi John,

My testing tells me that I am somewhere around 62hrc but all I have is some of the hrdness testing files to determine this. It Is my opinion that Having the grain in my blades as fine as possible is helping to give me this kind of performance. Quenching is one of the fastest ways possible to reduce grain size hence the quenches post forging. Normalizing also helps reduce grain size and removes stress from the blade. so three normalizing cycles. Now some of these steps my be redundant but they sure aren't hurting me. I have not tride tempering below 350 degrees.
 
Bill Burke said:
Hi John,

My testing tells me that I am somewhere around 62hrc but all I have is some of the hrdness testing files to determine this. It Is my opinion that Having the grain in my blades as fine as possible is helping to give me this kind of performance. Quenching is one of the fastest ways possible to reduce grain size hence the quenches post forging. Normalizing also helps reduce grain size and removes stress from the blade. so three normalizing cycles. Now some of these steps my be redundant but they sure aren't hurting me. I have not tride tempering below 350 degrees.
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Great results Bill. I have next to no experience with water quenching. I, too quench at least once, pre-HT. Usually, between the second and third normalization cycles.
 
Thanks, Bill. Makes good sense. A couple more if you don't mind :)

1. I use a similar routine for thermal cycling/heat treat, save for the water quenching. How do you get around having your blades curve down on the oil quenches? I like the grain refinement, but this process always seems to make my nice straight bowies start to look like kukris :(

2. I am also assuming you get some reduced hardenability with such fine grain. Are you dealing with this with by using hamon/edge quenching, or are you sometimes going for full hardening? If so, how thick a cross section can you get full hard with this process?

Thanks again!
 
David Stifle said:
I'm confused. You are tempering W2 at 350 degrees? I went with 425. Can someone clarify this?
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David... Bill is shooting for around 62HRC. If he is achieving full hardness (around 67HRC), then 62HRC would be somewhere between 325-400F. If you are shooting for 58-60HRC, then you need to temper between 450-500F. That is assuming all went well in the quench. When you are judging by magnet and eye, those numbers can be off. If that is the case and you don't have access to a hardness tester, then all you can go by is performance. Bill said he is not sure where his HRC is but is happy with his testing. If you are overheating and getting coarse grain, tweeking the temper will not fix the problem. Refinement through recrystalization is the only way.

John Frankl said:
1. I use a similar routine for thermal cycling/heat treat, save for the water quenching. How do you get around having your blades curve down on the oil quenches? I like the grain refinement, but this process always seems to make my nice straight bowies start to look like kukris :(
Click to expand...
If you are clay coating your blades, you can scrape off the spine... that may help. If you are fully hardening, quench spine first. The goal is to stabilize the spine as the thinner edge hardens. Giving it a bit of a head-start is the best way to reduce "tip-dip". BTW, this happens mostly on the classic Bowie/dirk profiles, where the spine is left thick and the bevel is full flat and thin at the edge. Leaving extra stock for the quench can help, too. My tip-dip went away when I switched from vertical quenching to horizontal and plunged spine first.

John Frankl said:
2. I am also assuming you get some reduced hardenability with such fine grain. Are you dealing with this with by using hamon/edge quenching, or are you sometimes going for full hardening? If so, how thick a cross section can you get full hard with this process?
Click to expand...
I can't see normal grain refinment reducing hardenability at all. Perhaps in extreme cases but not by any process knifemakers are capable of. Bill's water quench is hardening to the limit of the steel(at any cross section). The fact that he pays so much attention to his pre-ht is why he is successful.

I'll stop trying to answer for Bill, now..... :o
 
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