Normalizing after stock removal?

[Quenchcrack]

Terry, You are a gentleman! I see so much confusion and misunderstanding about heat treating I can't pass up the opportunity to help set the record straight. I will readily admit to being a very unskilled knifemaker, however and hope to trade what I know about heat treating for some help in making a better blade. I sold my knife grinder several years ago and the only blades I make now are replica trade knives for buckskinners and trail riders. I can pretty much forge them to shape without grinding.

Spent the afternoon at the forge today but made BBQ tools instead of blades. For the time invested, I can make more $$$ on fireplace and BBQ tools than on knives.

[SteveS]

Just a quick AMEN to what Terry said.

All of us are some where on a continuum between none and complete understanding.

I know a little more than some just behind me and I might attempt to explain what I know - if I think I can. We certainly don't want the professionals among us to spend all their time answering every question.

However, when I'm mistaken I too very much appreciate the correction.

Steve

[Kevin R. Cashen]

Originally Posted by Quenchcrack

There are some things about the iron-carbon phase diagram that appear to be misunderstood by a lot of people. First, no molecules in metals. Metals form crystals, not molecules, and the crystals are made of metallic atoms or alloy atoms. Second, austenite forms over a range of temperatures. Only at the eutectoid composition (.78% carbon) does it form at exactly 1333F. At all other carbon levels it forms over a temperature range that is up to 150 degrees hotter than the Curie (non-magnetic) point. Third, ferrite has a very low solublity for carbon. If you do not fully austenitize the steel, the carbides will not totally dissolve. Annealing at a temperature BELOW the fully austenitic temperature relies on DIFFUSION of carbon which is very slow at that temperature. Annealing ABOVE the fully austenitic temperature allows the carbon to dissolve into the austenite and diffuse more rapidly due to the slightly larger inter-atomic distance of face-center cubic austenite. I think there was a few more points I saw in the previous posts but, mercifully, I have forgotten them and will shut my cake hole now...........

To be even more precise, BCC ferrite (alpha iron) has a lower solubility for carbon; gamma iron easily takes much more carbon into solution. Austenite does form over a range, as Ac1 is a straight line across the iron-iron carbide phase diagram. Acm and A3 define the upper limits of their respective fields and thus form the range at which varying degrees of austenite solution is achieved. The Iron-iron carbide phase diagram is only applicable to ideal equilibrium conditions, and the eutectoid, depending upon the particular diagram you are looking at is a percentage from .77% to .85%.

Almost all steel transformations (with the exception of ones such as the martensitic transformation) are diffusion dependant. This would include those below Ac1 and those above it; the temperature just accelerates the rate of diffusion, due to the inter-atomic FCC spacing that you mentioned.

Below Ac1 is indeed slow, but one can play with the times a bit by starting from different microstructures. Spheroidizing martensitic steels is a much quicker process than other structures that require more diffusion.

[Kevin R. Cashen]

Quenchcrack is correct in pointing out that there is often confusion regarding the Iron-iron carbide equalibrium diagram. It is often refered to when few have access to it visually. I happen have a version of it on my site that I was using in another discussion, involving the eutectic vs. the eutectoid, so I thought I would post it here in hopes that it could be helpful. just ignore the red arrows I added for the the other discussion.

[Quenchcrack]

While admitting that the Fe-C diagram is good only for eqilibrium conditions, we should also remember that it is only for Iron and Carbon and the effects of all alloys and residuals is not reflected. I remember my course in Ternary Metallic Systems and I don't want to go there again! I sort of agree on the comment that almost all transformations are diffusion dependant. All except the one ones that aren't, like Widmanstatten Ferrite (shear and diffusion), Bainite (shear), Martensite (shear). That leaves carbide precipitation either in pearlite formation or in tempering as being diffusion phenomenon. Without resorting to a technical debate that would probably bore most readers, please remember what my objective was: Annealing is not the same as normalizing. It is not interchangeable and may do no good at all prior to hardening. Heating to just non-magnetic may or may not get the steel fully austenitic, depending on the carbon content. If I offended someone or came off as being a know-it-all, please accept my apologies. This forum clearly has enough metallurgists to tend the flock and perhaps my contributions are better made elsewhere.

[AwP]

This forum clearly has enough metallurgists to tend the flock and perhaps my contributions are better made elsewhere.

Don't be silly, when you professional metallurgist types get into a contest on who can teach the most knowledge, there are no losers. It just spurs you both on to dig out even more info to share.

[rhrocker]

Hey guys, I'm really enjoying this, and very glad I started the thread, it's gone WAY beyond where I thought it would go, and I for one appreciate it! The expertise we are seeing here is absolutely unreal. Many thanks to all who are participating, and all who are benefiting. Speaking of the Widmanstatten pattern, I'm holding in my hand right now a 4 billion year old (and no, I have no idea how they know the age) Giobeon meteorite from Namibia. Is thought to have hit the earth several thousand years ago, the meteorite strewn field was discovered by a Capt. J.E. Alexander, in 1838. I have two large slabe, that will yield at least four bolster, plus I have a 5 pound bag of meteorite powder (approx 7.93 Ni, .41 co., .04 P, 2.0 ppm Ga, .12 ppm Ge, 2.3 ppm Ir, the the remaining 90 persent (+) is Fe. I'm going to make a canned mosaic from the powder, using a combo of it, and some more "earthly" metals. Just HAD to mention that since Robert said the word Widmanstatten. I'm pretty excited about it. Will post a photo later of the etched piece if anyone wants to see what that pattern is. Again, thanks for the help guys!

[RJ Martin]

I have been watching this thread closely as well. Some interesting points made here-I am impressed with the phase diagrams for sure!
Still, I am not sure where you guys are with an answer to the question-Stress relieve after grinding (1000/1100F) or anneal, or no treatment at all?

One question I have-Do you guys worry about Carbon loss during these long soaks/cooling cycles performed in a forge? I'm sure you can minimize it, but, I don't even like annealing in my furnace in a protected environment.........

My vote is for a 1-2 hour soak at 1100F after grinding. Safe, yet effective.

What do you guys think?

PS-Quenchcrack, this forum is for the exchange of ideas-Please don't worry about egos when you're stating facts!

[Kevin R. Cashen]

Originally Posted by Quenchcrack

... remember what my objective was: Annealing is not the same as normalizing. It is not interchangeable and may do no good at all prior to hardening. Heating to just non-magnetic may or may not get the steel fully austenitic, depending on the carbon content. If I offended someone or came off as being a know-it-all, please accept my apologies. This forum clearly has enough metallurgists to tend the flock and perhaps my contributions are better made elsewhere...

No, no, not at all. You misunderstand me Quenchcrack, or I misunderstood you. I took your original post as a hint to be more specific and thus a little more accurate with my terms. I am sure you well know how difficult it can be trying to walk that fine line between accurate tech talk and not going over the heads of many aspiring knifemakers. Less technical terms are easier to understand but do tend to lose their accuracy.

I would like to thank you for pointing out the oversight that this thread kind of got side tracked, as far as annealing versus normalizing. You are very much correct in reminding us that annealing IS a softening operation and normalizing is equalizing/refining, regardless of hardeness (when I normalize L6, it hardens to 61 HRC) . It is very much worth mentioning that most folks in industry find what bladesmiths call "normalizing" resembles very little what they know as such. To meet the true and exact definition of normalizing we really need to go to a complete austenitic state and this "dark red" or "barely critical" stuff doesn't seem to fit. Other than "thermal cycling" or "stress relieving", I think we resort to calling it normalizing for lack of a better term.

Keep up the good work, feel free to keep me more accurate, and in no time at all we should have $5 words used with ease here .

[SteveS]

rhrocker,

Me, humble pie Steve, will give you my 2 cent description and methods:

RE: Stress Relief

I've taken to stress relieving my S30V after grinding and before hardening. You see, on warped blades I do a full anneal and re-harden. That is a Veeeerrry long and $$ process. So if a stress relief reduces the chance of warping....

On that steel, I use 1200 for 2 hours then oven cool (as per Crucible).

RE: Normalizing for grain refinement.

I'm of the impression that CPM steels as they come are as fine grained as you need for hardening. Now if you were asking on carbon steels. I would normalize first. A full anneal creates large grains. That is not the optimum condition prior to hardening.

So, carbon steels I normalize first.
High Alloy steels I stress relieve first.

(Boy I sure hope I'm doing it right.)

Steve

[rhrocker]

Hey Steve, thanks. I'm saving up all the valuable info here, on and off topic, this is quite a help for us all. BTW, yesterday I made your convex grinding rubber mouse pad graphite gizmo for my KMG, and used it today, Nice! Thanks for that tip also!

[Quenchcrack]

OK. As long as I haven't P.O.'d anyone.

As far as the 4 million year old asteroid goes, the dating process is really quite simple. They know it is 4 million years old because they found it in a 4 million year old bed of rock. They know it was a 4 million year old bed of rock because there was a 4 million year old asteroid in it.

Stress relieving after grinding: Basically, the stress created by grinding will be limited to the disturbed layer of metal. I would guess this to be .010" or less but a lot more if you have been hogging metal off like you worked on Junk Yard Wars. I think you could get this taken care of with the 1100F for an hour or two as suggested.

Carbon loss during long soaks: I don't have my little heat treating book with me but I believe the diffusion rate of carbon in steel at 1750F is about .006" per hour. As the temperature goes up, the diffusion rate increases considerably. Any time the steel is at an incandescent heat, carbon loss can be a factor. At temperatures in the 1300F range, it is probably not a factor. If you heat treat with stainless foil, or if you have it done in a vacuum furnace, surface decarb is nil. Heat treating in a forge is another matter. If you are going to fine grind or polish the blade after heat treating, the decarburized layer might just go away. If you do not do any finish grinding or polishing, you might indeed have a thin ferrite layer on the surface. Ferrite is soft and weak and can start cracks that can ruin a blade.

I think I mentioned this before elsewhere but if anyone wants a more complete explanation of phase diagrams, continuous cooling curves, and blacksmith heat treating, please go to www.iforgeiron.com, click on Blueprints, and scroll down to "Metallurgy of Heat treating for Blacksmiths". It is not extremely technical but does try to explain some of what we have been discussing. Feel free to copy and distribute the information as I am the author and gave it to the website owner on the condition it could be freely used. It is based on some lecture notes I made way back when I was teaching Material Science.

[Terry Primos]

Originally Posted by Quenchcrack

OK. As long as I haven't P.O.'d anyone.

As far as the 4 million year old asteroid goes, the dating process is really quite simple. They know it is 4 million years old because they found it in a 4 million year old bed of rock. They know it was a 4 million year old bed of rock because there was a 4 million year old asteroid in it.

[rhrocker]

I've read that link of yours Robert and it's good, I got a lot out of it. Just a woodworker however, and not a scientist, so it'll take me a while to digess a lot of what's being said, but I can follow it for the most part. Kevins sword making tutorial (I'd post the link here but probably should get permission from KC first) covers a lot of what you guys are saying in this thread also. This really should become a sticky eventually, it's darn near a tutorial in itself. On the meteorite dating, I was thinking that it was the patterns of the Widmanstatten crystals that gave it's date, but old rocks make sense also. I'll upload a photo of my slab here in a minute, totally off topic, but what the heck, it's steel. Incidently, I tried to rockwell test it, and it showed a big "O" on the scale. No carbon I guess. A picture will follow.

[rhrocker]

Intermission: Here's my pride and joy for the day. This is just a quick sanding and etch to see what I had. Now I hate to cut it up!