heat treating and annealing vs forging question

Ok, I messed up the heat treatment of a couple of O-1 plane blades. Too hard, edges crumble. I, and others, keep coming back here for advice.
Sometime back someone said the metal was done for, couldn't be recovered. Yet one can forge O-1. So if it's forged at orange or yellow, it's in the same condition as my blades which only reached bright red. Shouldn't annealing my wrecked blades fix them up? (I can see the crystals with a 5x loupe.) Is the problem that there are fractures in the metal that annealing heat can't fix?
I understand that it's a pita to anneal small bits of O-1. Red hot chunk of iron in the vermiculite to slow the rate of cooling, and so forth. Although that confuses me too: the book says 20 degrees per hour, or something like that. I once tossed a marking knife into the fireplace and fished it out the next morning. It re-hardened just fine even though it must have cooled more rapidly than the suggested rate. Just how much leeway is there in the cooling rate?
I took an O-1 chisel blank to my recent blacksmithing class and sneaked a couple of heats to draw a tang. I tried to keep the business end cool, but that blade will have to be annealed too.
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vladimir a t mad scientist com
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Last question first. Full anealling is done with the slow cool as you said for maximum softness. This is not to say that cooling at any rate slower than the TT curve won't make it malleable. Specialized conditions are required to get hardness, not necessarily the other way around.
As for the crumbling, you probably didn't temper it correctly. Not sure the specifics of O1 but you need to reduce hardness to stop it from being brittle and to add strength. Note that hardness (or lack of it) and strength are not the same thing. The right temper will affect both. The wrong one may only affect one (in the manner that you desire).
Even before tempering though you need to normalize the steel to reduce grain size. Repeated air cooling. I'd suggest experimentation to get an idea of what this does. You can use several samples and normalize one, two, three and more times with each test piece, quench and then snap it off in the vice to graphically see the affect. I did this and was a bit amazed at the difference even if I already knew the theory. It brings the lesson home. Multiple quenches have been found to reduce grain in 5160, I don't know if the same would apply to O1.
Lastly, if you are overheating or over soaking the metal at the right temperture, it won't matter what grain you had. It will be course when you quench it. As Don Fogg says "time and temp, time and temp" - it's everything.
Good luck.
GA

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Cool post, GA! :)

Cool, you've even been doing your home work too. ;)
The theory makes what you are seeing "understanding" instead of a "mystery". Many prefer the mystery as an answer. :) Not me. :/

Could help but all that business (O1 or 5160) needs careful temperature control to be helpful rather than making it worse.
A little carbon helps with grain refinement plus the Cr in 5160 give it a double-whammy. ;) 1+1=4 ;)
Manganese is helpful too but there's too much of it in O1 and starts to go negative, so they added the Cr and W because they had to do something. ;) Know that, O1 is more about being a 'cheaper to buy and work with than A2" as a non-deforming, heat treatable steel more than anything else. The other uses are secondary to the big buyers. :/
It's too bad O1's formulation is the one that's has taken over the oil-hardening market. :/ And O2 and O6 aren't even as good, IMO. :/
Cr based A2 is stronger than Mn based O1 for example. :/
O7 is the one to get... just don't know where to get it. :(

...and a learned eye or a cheap-ass magnet? ;)

Alvin in AZ
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After working for months drawing and forging a japanese style short sword, then getting a really nice clay coat differential quench, having the blade come out with an awsome shape and form and topping it all off by snapping the damn thing in two because I didn't have a good understanding of how to reduce the grain and draw the temper in the steel it was made from - I decided I was not going to repeat that mistake on the next one. :-< I wanted to be damn sure I knew what to do with the specific material. I think I've pulled it off on my current project. Took forever to get where I am now because I left them a bit too edge thick and unfinished when I hardend them but I think it's gonna be cool. My big problem now is that I'm getting my expectations higher while working the same project so it never quite seemed good enough yet. I'm about ready to put handles them (two of them) now. That will probably keep me busy for a bit longer ;-) No hurries. It's the end product that matters, not how long I took to get there.

O1 seems to be well liked by makers who what to get a good blade with a decent hamon line.

I'll stick with the magnet for a while longer I think. It's shown me that I don't always "see" it right ;-)
GA
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<snipped good discription of learning curve;>

Cool. :)

A hamon line with an oil hardening steel? Really?

That's backwards from what an oil hardening steel should be IMO.
I use the heck out of O1, even knowing that, because I can't heat treat A2 the way I know it needs to be. :/ Also I can get O1 in precision ground plates in 1/16", 5/64", 3/32", 7/64" and 1/8" and that's the main reason I use the dangged "too high of manganese content for its own good" stuff. ;)

OP, (original poster) you didn't mention using a magnet! :/
Is that the problem you suppose? :)
Alvin in AZ
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Sorry, I'm tripping. Mixing it up with W1. I just bought some 1085 and O1 to try forge welding it. Now the weather is getting better I'm itching to start hammering again. It would be nice to have some pattern weld to play with. Since I don't have a power hammer I'm gonna get together with a friend of mine and one of us will hold and the other hammer with an eight pound sledge. Should make the work go a bit faster that way.

We have to make our sacrifices ;-) You got to use what's available and will work for you.
GA
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On Fri, 20 May 2005 07:43:37 +0000, alvinj wrote:

Nah. I use a little magnet on a telescoping pen thingamajig. I've had success before with plane blades--after studying your posts, I might add. No, this one blade is giving me problems I haven't had before.
Since I posted the original question I tossed both blades (old chippy and new chisel blank) into the fireplace. Rested them in the ashes and covered them with nice coals. Still warm the next morning. Chippy has softened up, ready to re-harden. After I figure out what GA was talking about with repeated air quenches and grain size...
My successfully hardened bench plane blades work very well.
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Lets see if I can explain it without saying anything too stupid ;-) I get the terms mixed up but the idea is simple enough. When you heat the steel up to a given temperture (depends on the alloy) it changes the form of the crystal structure. There are a few different structures that form depending on what you do to it but the point is that once it gets hot enough for quenching it begins to get an enlarged grain size if left too long at that temperture. If quenched with a large grain size then you get a weaker more brittle grain structure. By heating just to the transition stage and then allowing it to air cool, you don't cool it fast enough to get it hard but it will reduce the grain size as it contracts. Done repeatedly, you can get a refined, stronger grain structure - which I'm told will incedentally reduce the hardenablility as well, so you get more control over the hardening process. This is a strong point for those doing differential hardening. The important point is that you get a hardened blade that is less prone to chipping and breaking. Since you have used your method successfully a few times but are having trouble with a particular piece of steel I'm betting you either did something like leaving it hot too long or got it too hot or you're just playing with a different kind of alloy and the rules changed on you. Some steels will get enlarged grain at lower tempertures than others and some have to be tempered at hotter tempertures than others. The best route is to know what you have and then spend some time learning how it wants to be treated (after reading up on the specs for it).
GA
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On Sat, 21 May 2005 20:43:35 -0700, Greyangel wrote:

Aha! Thanks. There's another benefit to the process you describe: I can practice looking for Alvinj's arrest point shadow! :) Also, it takes some of the stress out (of me). "Gotta get this right the first time, just till the magnet lets go, then only a second to get the quench done." Now it looks like "Nah, the shadow didn't look right, pop it back in for another go."
I might now understand why taking something to forging heat doesn't screw up hardening later: the work is basically air cooling while we bang on it, so the grain size isn't growing. Also, the hammering is doing something to the grain size. Close?
dagnabit, I need a reference somewhere in between Richardson/Bealer and hard-core metallurgy textbooks. --Just a gripe; thanks, I've been snipping book recommendations here for a while.
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but it

One of the coolest things to do for me is to normalize a blade after dark on a summer night. I work in the back yard and the process of sitting out at night heating and cooling a piece of steel is a really Zen experience for me. It gives me a chance to really pay attention to the way the metal behaves as it cycles through the tempertures. I've mostly not tuned into Alvin's shadow. I think it depends on the alloy mix. I had one piece of steel from some railroad hardware that I think was a really unique alloy mix. Didn't get hard well unless you got it up around 1700F or so. The shadow effect was really appearent with that stuff. 5160 seems to show it sort of but I'm not as confident that the effect coincides well with the magnetic transition. Straight carbon steel trasitions at lower tempertures than chrome or other alloys and I wouldn't bet my work on seeing a shadow in that at all. Another thing that seems to come into play for me is that I've become a believer in slowly bringing the metal up to temp. When you do this I'm not sure the shadow effect is as appearent. So far the magnet has taught me not to trust my eyes. YMMV.

I think its reasonable that the hammering along with the cooling is breaking down the grain. I'm betting this is what is sometimes refered to as "edge packing" which in the literal sense sounds like crap to me.

If you haven't already been told I'll recommend Dell K. Allen's Metallurgy Theory and Practice. Alvin recommended it to me and I picked it up used off of Amazon for a couple bucks. It's great book for understanding the theory behind it all. A little frustrating in the specifics it leaves out at times but I don't think it was ever intended to be a reference book. It excels at getting the basic mechanics across though.
GA
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