bainite

The discussion in rec.knives on austempered swords piqued my curiosity. So I did some looking on bainite and then some thinking. What i read
was to the effect that bainite is tougher than martinsite at a given hardness but has a maximum hardness in the mid to upper 50's Rc scale. And as I;ve started playing with making slip joints, I got to wondering if bainite would make a supperior backspring?
Then I looked at how to get it. The techinque as i understand it is to quench the steel from critical to somewhere between 400 and 700 F then hold it there for some length of time for the bainite to form and allow to cool. Since i've been working with 1095, I wonder if that would allow for sufficently fast cooling to avoid pearlite or if some other alloy would be needed?
And finally, if I tried this how could i tell if i successfully got bainite instead of something else?
Any thought form someone who knows more than me?
ron
ps I'm posting this to bothe rec.knives and alt.crafts.blacksmithing as the initial thread that interested me was in rec.knives and i thought the folks on blacksmithing might be interested. pps if what i'm going for isn't clear, well the thoughts aren't completly formed yet.
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In rec.knives r payne wrote:

So far that's about the hardness readings I've gotten on the factory heat-treated Case chrome-vanadium pocket knife blades. :(
I want to re-do those tests with better prepared "samples". :/

Yes it surely would. :)
No need in my opinion but who am I to judge? (i'm completely Knuts)

That's it, you got it. :)

http://www.panix.com/~alvinj/graphTTT.jpg (from ASM's Tool Steels)
That graph is for 1080 and notice it starts at 1 second that's why the "nose" of the "S" curve is hanging over the edge of the graph.
The trick to turning 1080 into martensite is to cool it quick, right? Picture your starting point being at about the 1400F level (for 1080) and about 1/2" off the left side of the graph for 1/10 second.
The trick to turning 1080 into bainite is to cool it quick -and- cool it no lower than ~550F, then hold it at 550F for 10^4 seconds without the temperature bobbing around too. (salt pot;)
10^4 seconds is about 2+3/4 hours but that graph is for 1080. The TTT graph for 1095 shows a little bit longer time is needed so 3 hours should do it. Before you get that far you'll want a IT/TTT graph for the steel you're working with and talk to Howard Clark.
The nose of the S curve, along with the whole S curve, is shifted to the right with more carbon like 1095. 1018 is next-to-imposible to quench it quick enough, see? :)
Funny thing is, what you would get wouldn't be as good as "work hardened 1018" anyway. :) Let alone case hardened 1018 for certain needs
With 1095 the nose of the S curve is at about 1 second, since the S curve is shifted to the right a little.
With O1 having Mn and Cr in it slows stuff up. The temperature you can go down to is lowered to 425F and the time needed (the S curve) is shifted to the right and needs at least 4 hours for bainite.
The nose of the S curve for O1 is at about 8 seconds.
A2's IT/TTT graph is so shifted to the right and screwed up, I don't even know how to read it. :/ Looks like D2's TTT that way. :/
Also please notice that at about 100F the austenite isn't fully transformed to martensite! Cold treatment! ;)
This ain't rocket science. ;)
The "percentages" are for "how much of the austenite has transformed" to what ever it's going to transform (or decompose) into. "M-point" is a line that below that martensite is the primary product. IMO, there should be another line, a "B-point" at about 900F so the "pearlite and bainite products division point" can be shown.
I don't know why they don't, sometimes they'll label it and use a { or } tho.
Hmmm... just noticed something the "course medium and fine pearlite" sections on another .83%C TTT diagram shows that the fine pearlite is formed at about 900F where "my B-point" should be. Which on the lower side of that is fine bainite. I need to try this on my screwed up re-heat treated files and Old Hickorys etc.
Quench, and pull the sucker back out while it's still glowing bright and then let it air cool? :) Do that a few times then re-heat treat?
Thanks for the questions Ron! :)

Hmmm... I don't know. A hardness test is what industry uses to check their heat treating.
If there's one thing I've learned from my metallurgy class tho, is that if-
"you DO what they say, you'll GET what they say" :)
My hardnesses are right in the middle of the range I'm supposed to be getting including, factoring in, the fact I'm cold treating (raising the hardness) and other farting around like quenching 1095 in oil and silly stuff like that.
When all that's factored in, -theoretically- I should get... X to X+1 hrc.
I'm getting... X.5 hrc. :)

I don't have to know anything? I have a book written by guys that do. ;)
Alvin in AZ <--libertarian and librarian ;) ps- Isothermal Transformation or Time Temperature Transformation some books refer to it as one or the other or sometimes both pps- "one test is worth a thousand expert opinions" -metallurgy instuctor
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snipped-for-privacy@XX.com wrote:

I used to know another vender in the SCA who austempered. He used a hot salt bath on 5160 straight from the oven at quench temp. Said he got consistent high 40s in a third the time of the quench and draw routine. Sorry, can't remember all the details, so we can't test his procedure. I do remember that the salt bath was pretty warm, well over 500 degrees F.
We never had a clangoff, I bake mine to 55.
Charly
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Sounds like he was making "upper bainite" tho. :/

Lower bainite can be that hard too.
What got all this started over on r.k is a story my metallurgy teacher told after I asked about the "grade 5 bolt vs grade 8 bolt fights" that get going on the automotive groups. (that wasn't settled but "will be";)
So... the local copper mine got ahold of him after trying out every bolt on the market including those reccomended and sold through the machine manufacturer. Some sort of screw-type-enclosed material mover. why they weren't using a conveyer belt i don't know. ;)
Anyway this rig used two ~1+1/2"x ~12" bolts for the screw drive pins.
The best they could get would sometimes shear off on start-up or last only a week if "babied along" and they'd gone through a truck load of bolts. When asked to make them some bolts he knew he wouldn't "get to make very many so I charged them accordingly:)". $400 for 4 bolts ...two plus, two more for spares.
Well a year and a half later they wanted him to make them 2 more since the spares were now in service because the originals were so worn-out the screw wasn't staying centered and was rubbing on the outer wall. :)
Not broken... worn out! :)
He had a local machine shop make them up from 4340 and sent them to a former student that now owns a heat treating outfit in Phoenix and they "austempered" them to lower bainite according to "the book".
That's it.
---------
Another story...
A student asked about stainless steel swords and the teacher questioned him about whether they were for looks or what and the student said "they need to be able to take some hitting against each other" and again wanted to know "which stainless steel was best"
I butted in and said "none of the above:)".
The metallurgy teacher agreed and they thought it was funny. So the student asked the teacher "what IS the best then" and he said (without hessitation because he'd been down this raod many times before;)
"4360 austempered to form lower bainite"
I butted in again and said "4360? where in the heck can you get 4360?" well he had no quick answer for that so I said "I know where a guy can get L6 that's supposed to have the optional Moly in it, so it's basically 4370, how would that work?" "the same just a little bit harder" "the same strength?" "about the same, you probably couldn't tell the difference"
Ok, so it's just one guy's opinion, take it for what it cost you? ;)
----------
http://www.AdmiralSteel.com
I just got some L6, called and asked about it being .224" thick instead of 3/16" like the catalog said, wondering if I got some thicker stuff by mistake... she said- "the L6 has some additional thickness" like it was something good! :/ I got -bonus material- what the heck am I complaining about? ;)
3/16" thick was a little bit thicker than I wanted but was willing to "make do". Sure enough not looking forward to working with this dangged thick-ass stuff tho.
Alvin in AZ
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Sounds like you and I are on the same page.
In "Metallurgy Theory and Practice" that i have fig 7-5 shows the I-T for 1095 (or most of it anyway). and from this i believe
1. to get under the "pearlite nose" the temperature needs to drop from critical to below about 950 F in roughly 3/4 second. 2. Martinsite formation starts at around 425 F 3. to get lower bainite and let the reaction go to completion takes around 500 F and nearly 5 hours.
So far as holding the piece at about 500 F, that should be easy enough in an oil bath in an oven. Which leaves the question of whether or not the oil pre-heated to 500 F would cool the steel below the "nose" fast enough to avoid pearlite. Or if not if the pearlite would prove harmful to the spring in the quanties formed?
So far the only thing i can come up with to test with my limited buget and equipment is to guess the hardness with a file. By the I-T graph i'm looking at, bainite formed at 500 F should have a Rc hardness of 57. If it is less than this that would indicate upper bainite or pearlite. If it is harder then some of the austenite transformed to martensite.
But right now this is just theory as it will likely be a few months before i get to experment.
ron
ps- Alvin any other metallurgy books that you recommend?
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Yeah Fig 7-5! :)

Cliff, can a guy heat oil to 500F for 5 hours?
I don't know if the oil would quench 1095 quick enough at that temperature anyway.
Don't have any idea what salt to use that melts at ~350F either. :/

Normally "warm oil quenches fastwer than cold oil" but what extremes that rule of thumb covers I don't know. :/

Pearlite wouldn't be good for springs unless it's at low levels. Tempered martensite or bainite and that's about it for springs.

That sure enough sounds good to me at this time. :)
We're fixing to make some 4140 or maybe 4340 bainite in class. :)
So pretty soon I'll be busting at the seams with information. ;) (or mis-information?)
Did Jominy End Quench tests today on 1060 and 4140 and O1. :)
One thing I noticed way back and I'm for sure on now, Metallurgy Theory and Practice is a lot better book than the one we've got for class. Practical Metallurgy and Materials of Industry.
Ok, so the old clunker has -new- stuff missing but for hobby-use MT&P is the one to beat. :)

A new 5th edition of ASM's "Tool Steels" is out so an older edition might be a good deal. I have a 3rd and 4th and as far as I can tell there ain't much difference between the two when it comes to the simpler steels I mess with.
If you can get your hands on certain volumes of ASM's Metal's Handbook at the library you could copy off everything that you can really use in them without too much trouble.
Parts of: Carbon and Alloy Steels Tool Steels Heat treating
I bought a Desk Edition just because Enco had it on a close-out sale. ;) But I'd already copied off about an inch tall stack of pages out of the multi-volume set. :) A guy could make-do with half that. At the time it was "in library use only" but now a guy can check the volumes out. The set I'm familiar with is called the "red set". The older "blue set" is almost as good.
I've never used it but there is in place some sort of inter-library book loaning system. I actually need to look into using that myself. :)
Alvin in AZ
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if the 500 F oil idea proves less than optimea how does this sound for making backyard bainite-
preheat the oven to 500 F and put a coffee can full of sand to preheat as well. once the spring gets ready dip it in oil breifly (say maybe 1 second) to get under the pearlite nose then move it immediatly to the hot sand and the sand back to the oven. Sounds simple enough to try and within my means. I may give this a shot next weekend if noone has a reason it won't work.
ron
ps Alvin, i should have my first slip joint pictures for you tomorrow or tues. I sent them to mom to scan for me.
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Well I gave it a try. Heated the spring to critical, gave it about a second in oil then into a container of pre-heated sand and into the oven for 5 hours. Since I was drifting hammer eyes to a better sixe, and tempering them at the same time, I set the oven temp to 530 F.

Which is close to how I read the graph for what I did. So I figure I either got bainite or I stayed in the oil a bit long and tempered martensite at 530 F for 5 hours. Since I don't know what to expect from martensite tempered like that, I can't say for sure which it is. Any guesses?? Will this make a suitable spring either way??
ron
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Cool, it should make a good spring either way. :)
We hadn't got to that in class yet.
But there's only one way to know for sure and that is to try it. ;)
A lead pot is what I've been picturing to make bainite.
Alvin in AZ
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snipped-for-privacy@XX.com wrote:

So you dunk the red hot piece of steel in a big pot of molten lead and leave it there for a few hours? This is starting to sound like it is one step away from a meth lab in terms of chemical hazards. :-)
Don't let the EPA hear about it. And wear one of those masks.
--
Del Cecchi
"This post is my own and doesnt necessarily represent IBMs positions,
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One of the old ways was to do it in mercury- supposedly, 'James Black' went blind and crazy from just that heat treatment method. I spoke to Sean Whatshisname that was the research smith at 'Black's Forge', and he said there were pits with high mercuric content that had been excavated there that bear out the story. He was the guy in Bayfield Colorado that was making stainless patternweld- can't remember his last name for the life of me; Scots- really good fighting knives. Hell- I bet you could make a lot of *really good* knives before the blindness, insanity and slow agonizing death. You wouldn't know what happened until you didn't know what happened; ya'know?
Chas
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On Thu, 29 Sep 2005 snipped-for-privacy@XX.com wrote:
[mid to upper 50's]

Phil Wilson has tested many production knives and found in general the hardness is often way under, 5 points or more isn't uncommon.
--
Cliff Stamp
snipped-for-privacy@physics.mun.ca http://www.physics.mun.ca:80/~sstamp /
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