Best steel choice for big Bainite Bowie?

Originally posted by Jason Arnold
S5 seems to have been overlooked for years. But, that may be due to the fact that its hard to find in flat bar so stock removers have had to avoid it. And those who forge need to be equipped with precise HT equipment. No eyeball methods allowed. The anneal is especially necessary to have controlled ramping and temp holding.
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Jason, in what sizes are you able to get S5, typically?

Also, can you elaborate a bit on why S5 is a bit tricky to heat treat? What have you experienced?
 
Jason, in what sizes are you able to get S5, typically?
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I was buying S5 in 5/8" round bar.

Also, can you elaborate a bit on why S5 is a bit tricky to heat treat? What have you experienced?
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Well, in that reply I was referring to annealing, but I'm an advocate for precise temp control in general. Necessary, to do it right. Tricky, if you wing it with eyeball methods. I despise variables, so to keep them at a minimum, use precise control.

The primary concern with annealing S5, versus eyeball methods or burying it for slow cooling, is the "ramping down" issue. Kind of like a preheat before ramping up a blade for quench, but backwards. An ash pit/or the like, will not allow one to cool to 1250°F and then hold it there for about 4 hours without deviating a few degrees + or -. Then air cool. There are a couple ways to anneal the material. Both require ramping down over long periods of time, within certain temp ranges.
 
Originally posted by Kevin R. Cashen
The L6 in the same shapes and sizes, in unnotched tests, maxed out the tester, even with multiple hits! It required around 21 Ft lbs to break the notched bar. Weakened by the notch, the L6 behaved like unnotched O1, but unnotched it was unbreakable even in a fully quenched tempered martensite condition. Marquenched, it would max out a much larger tester, this is one of the reasons why I have not felt the need to work with bainite all that much, it just seems to be overkill for a problem that I have not experienced.
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I was thinking about this the other day. Kevin, please correct me if I'm wrong, but if I'm reading between the lines properly, you also believe L6 Bainite would be 'tougher' or more shock resistant than martensitic L6. And, you have not had any toughness problems with martensitic L6 in your blades.

Question: Why not harness the extra strength of bainite to improve blade geometry? I.E., if bainite is say, 25% tougher, make the edge 25% thinner? Right now I'd love to go thinner with my edges, but they'd turn the first time I hit bone. Or why not use bainite to make the blade lighter without sacrificing strength? Thoughts?
 
At this time I would like to reserve judgment on the subject that you bring up. I don't like confrontation at all and at this time there are more than a few people, out there, falling over themselves to extol the superior virtues of bainite. I like to think of knives as cutting tools first, so I put a priority on edge holding. I plan to do exhaustive testing in this field as soon as I can get to it. I have a knee-jerk reaction to anything trendy, sensational or hyped, and can even throw the baby out with the bath water at times.

I will say this, you are on the right track and I think I use the right steel with the right heat treating techniques to allow my edges to get a little thinner than I used to believe possible, but I do it with martensite. I have yet to see the phenomenon, of all these blades breaking like glass in normal use, that prompted this acute phobia that the knife business, has and is spending so much effort to protect against.

You mention both thoughness and strength. I believe I am getting maximum strength from martensite. If, on the other hand, toughness was my absolute top priority I would look more at bainite.
 
Thanks for the quick reply, Kevin. Sorry; wasn't trying to back you into a corner there. I too, have that knee-jerk reaction to something that sounds like the latest bestest thing. But, after hearing it from so many people, I thought I'd at least give it a real try first.

I realize you're a very busy guy. But you can bet I'll be waiting to hear more about any test results you get! :)

Sorry for confusing the terminology again. I guess I'm talking about toughness. I take it you noticed this in my earlier post: "but then again I've never had one of my big Bowies get dull. I always have to sharpen them to remove nicks, chips, and other damage long before they become dull thru abrasive wear. So maybe I shouldn't worry about the wear resistance so much." I tend to use them more for "chopping" rather than "cutting", and I often hit things I shouldn't. (completely by accident, but at the same time unavoidable) And I guess you're probably tired of my story how I did break my first Bowie. :D So unless I'm reading things wrong here, it still sounds like bainite is what I should focus on.
 
I have to agree with Kevin on the issue of bainite. There has been a recent surge of interest in the topic (which is always a good thing!). Though some makers have been offering it up like it was the holy-grail. All so-far in context to full-bainite. Honestly, its getting irritating in so many ways. The only bainite work I have been doing, was with the S5 in a composite style (in sword length). That took me a few years to work on. Originally, it was simply a personal test to myself to figure out, "how the hell?". Later it involved a lot of tweaking and pushing things bit by bit. But now, I'm not so sure I want to even market the blades. Just keep them as a personal achievement. Makes me feel as though I have been pulled onto a bandwagon. What a crappy feeling.

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My whole involvement in these threads has been to teach people what they can get and how to get it. But it must all start with carefully defining what you need rather than following some fad .
 
This seems like the place to ask, since its been discussed before. I have been wondering what specifically nickel does microstructurally in L6 to increase the toughness. Be as specific as you want, and you can answer on email if it would be too lengthy here. I read about nickel increasing toughness in 1994, but havent been able to find an answer as to why. Thanks in advance.
 
me2, yes nickel has long been known to increase toughness in steel but I don't know offhand why. I'll see if I can find out.
 
Hmm, well, nickel will dissolve largely in ferrite and have a solid solution effect, even in the presence of high carbon. I believe due to its lack of aid in hardenability. (Good choice for steels that do not see hardening and tempering treatments. Some added strength there.) But, that doesn't really help us with the toughness question at hand. :cool: At least directly, you could exploit that fact though. Hmm. *I'll get back at that.

*Later: After looking at a couple IT diagrams, I thought of some ideas. You may be able to create a mixed microstructure of mostly martensite and some fine pearlite, using the solid solution to balance out strength and gaining the benefits of added toughness from the mixed martensite/pearlite structure as opposed to a 100% martensite. That's shooting from the hip though, so take it for what its worth. Well, that's all I got, maybe Robert has more.
 
Jason, no that's not the answer because nickel adds toughness even in all martensite structures. BTW in a structure of martensite containing retained austenite the retained austenite adds toughness so it's not all bad.
 
BTW in a structure of martensite containing retained austenite the retained austenite adds toughness so it's not all bad.
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True, probably just be easier to do that then. Especially since HT papers indicate that L6 is naturally prone to retaining austenite. But, the search goes on for the nickel issue...

I'm betting its got something to do with that ferrite strengthening effect. It may just be in comparison to similar alloys that take a hit in ductility when alloyed with other elements for the sake of boosting strength.

I have some info on nickel in steels that work at cold temps, would that help?
 
Maybe, since nickel is such a good austenite stabilizer, it promotes the retained austenite in a stable or ordered manner, allowing for increased toughness even in an otherwise all martensite structure. I have a BS in Materials Science and concentrated in metallurgy, but in all the years I spent in school, no one explained why nickel worked this way. I have only been out of school for 4 years, so I am deferring here to people who I believe have more and different experience.
 
me2, I've been out nof school a lot longer than that and nobody has explained it to me either. As far as low temperature steels - these steels have as much as 9% Ni for service to -300F. Somewhere out there there is probably a research paper that has figured it out . My access to such things is limited now though.It may very well be some effect on martensite.
 
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