reducing grain growth

[Archie Zietman]

Hello.
How does one reduce grain growth in steel or iron? I know that one can shock it by heating it for a few seconds than dipping it in oil to shock it into contracting. is this the way it is done? I have only seen it done in a hot gas forge though. would it work to stick it in the coals for a few secs and then shock-dip-quenchy thingy it the same way a few times?
Thanks,
Archie

[Glenn]

Read the article by quenchcrack BP0078 The Metallurgy of Heat Treating for Blacksmiths


There is also an application called "packing" that may be of interest. One of the metallurgy folks will have to explain that one to you. It is usually associated with chisels and things as I recall.

[Quenchcrack]

Archie, you are talking about two different processes. Preventing grain growth can be done by using a steel with sufficient silicon and aluminum. Vanadium can help too. These elements form nitrides that precipitate at the grain boundaries of the steel. They act like a picket fence and won't allow the grains to grow. However, if you seriously overheat the steel, the nitrides will dissolve and the grains will grow. If you have over heated the steel, you can partially reduce the grain size by heating to about 100 degrees over the upper critical temperature for the carbon content of the steel. For carbon ranges in the .50-.80 %, just heat it a little beyond non-magnetic and let it air cool. If the carbon content is lower, heat it hotter. No need to quench it. Doing this (called normalizing) several times at slightly lower temperatures each time will reduce the grain size somewhat. Do as Glenn suggests and read the Blueprint on Metallurgy of Heat Treating for Blacksmiths. Post your questions here and I will try to answer them.

Packing is probably a discredited procedure regardless of what Alex Bealer said about it. You simply cannot get the iron atoms any closer together than the laws of physics allow.

[JPH]

Hello:

On the grain growth/reduction..all of what QC said except for the "packing"..

Somewhere, a long time ago someone said that it works due to "packing the atoms closer together".. This is wrong, dead wrong, you cannot get atoms closer together with a hand hammer. Not on this planet anyway.
(Funny note here: it has been attributed to me starting this...not hardly, I haver never said anything like that. See the next paragraph)

However, "packing" works to refine the grain structure as it will facilitate grain fracturing into smaller grains. Remember that metallic iron and steel are a man made element. They do not occur on this planet in a "raw" form, only in ores, and only in base elements. They are also a crystal and a lot of folks forget that.

Grain growth in metals is complicated even in the simplest terms to explain. In a nutshell, the bigger the grain, the worse it gets. The smaller the grain, the better off you are. This can be due to impact or thermal techniques. Properly employing both will result in better grain structure than what you can achieve with just one, but even using just one will help improve things.

Hope this helps...

JPH

[Strine]

Interesting stuff and I think the replies are coming from experts but I missed the bit about what grain structure in iron, steel, crystals or the wheat-crop has to do with how I go about making an S hook. For mugs like me what is good grain structure and what is bad? For what purpose can good grains be used for and what can be done with bad grains. How can you tell the difference, one piece of steel looks just like the next bit to me except for maybe the shape of each.

[elkdoc]

The IForgeIron.com tutorial is great. There's more in the 200+ page book, Metallurgy of Steel for Bladesmiths & Others who Heat Treat and Forge Steel by Verhoeven. It is downloadable here:

http://mse.iastate.edu/files/verhoeven/7-5.pdf

Your brain will hurt! :shock:

[oakwoodforge]

Owww! Brain Cramps !
Thanks for the free book elkdoc ! 8)
Some good stuff in there

[elkdoc]

No need for thanks... I'm just passing along links that were passed to me.

Grain growth and reduction is really a fascinating science. Heavy stuff sometimes, but very useful for performance bladesmithing. One of these days I'll get a handle on blade forging enough to get to this part. :lol:

[GobblerForge]

Strine. If you are a hobbiest as I am, then the world of Wizardry and Metalergy are probably equaly mystifying. I was trained traditional and here is my take. If you are making onimental and utilitarian items out of common soft stock as in 1010 and 1020, then don't wory about things like grain size. Your S hook will perform wonderfully. If when you are done making it, on the last heat, brush all the loose scale off. At this point, let it cool naturaly. It should be cool by the time you get done with the next one. If you are making things out of high grade steel and are going to harden and temper, then it matters. Hope this helps. Brad

[Quenchcrack]

I guess I need to clarify my comments because I came to another conclusion regarding edge packing. No, it doesn't work because you get the atoms closer together. HOWEVER.....the concept of packing is quite similar to a process employed in Steel Rolling Mills called Recrystalization Controlled Rolling. It works by heavily working (rolling) the steel at a temperature just above the austenite to ferrite transformation temperature (the A3 for those who care). This crushes the austenite grains. It is then water cooled (this is low carbon stuff) to just below the lower critical temperature (the A1) where the flattened austenite grains transform to many very small ferrite grains. This gives the steel considerable strength (OK, well, so does the precipitation of various metal nitrides but that just complicates this comment). Anyway, when you heat it to harden the steel, the fine ferrite will austenitize very quickly since austenite forms first at the grain boundaries and we just made a lot of them. Additionally, if heat treated properly, it will be a pretty tough martensite that forms. OK, now this process does sound a lot like edge packing and it might be useful but NOT for the reasons most people think. Just for the record, I recently posted a very similar comment on knifenetwork.com where it was immediatly misunderstood and universally ignored. Knock yourselves out... :D

[GobblerForge]

Oh great wizard Quenckcrack. I'm pretty sure I saw some English in there somewhere. Sorry, I couldn't help it. I was curious as to how work hardening falls into the packing world. I know there is heat used to pack and work hardening happens cold but doesn't the steel get harder? When I was tought the prinipals on packing, the concept seems related. I've had some success with it working on chisels and such. Your opinion?
Thanks. Brad

[ThomasPowers]

Packing occurs before heat treat where all the dislocations it causes can renucleate smaller crystals.

Work hardening occurs after the last time up to dislocation climb temperatures and hardens the piece by preventing deformation by introducing dislocations in the crystaline structure.

Halfway right QC?

Been a long time since Dr Ruoff tried to pound that stuff into me...

Thomas

[Quenchcrack]

As ol' Bog Iron said, packing takes place at a black heat or slightly above a black heat. Work hardening must take place below the recrystalization temperature (about 900F). Any distortion applied to the crystal lattice above the recrystalization temperature is instantly remediated by the crystals simply re-forming in a different alignment, hence, no hardening takes place. If you pack the edge cold, you do work harden it. That is how Sythes are usually sharpened and rehardened. However, if you heat it to non-magnetic or above, you exceed the recrystalization temperature and all the work hardening is removed. :mrgreen:

[Tyler Murch]

OK- normalizing 3 times- I need some scientific documentation or explanation from a world class bladesmith (such as JPH) why this is a good thing.

[mcraigl]

Looks like I got some readin' to do. Nice link, mucho appreciated.

[Quenchcrack]

OK- normalizing 3 times- I need some scientific documentation or explanation from a world class bladesmith (such as JPH) why this is a good thing.

Normalizing three times will dissolve more of the big carbides that formed when you annealed it when you really shouldn't have. Grin! Seriously, multiple normalizing does reduce the size of the carbides and will distribute them more evenly through the steel. This results in more uniform hardening and less distortion. The carbon and alloy elements in the steel will segregate in the center of the ingot when it is poured (tool steels are still ingot cast for the most part) and this puts the carbon and other elements in the center of the bar. After hot working it, normalize 2-3 times, each at a lower temperature and you will not only refine the carbides, you can actually reduce the grain size. Yep, go read the tutorial and that book for a complete explanation.

[HWooldridge]

I once saw a master ABS bladesmith temper a blade three times after hardening. He used a torch to bring the edge up to non-magnetic while not spending much time worrying about the spine then quenched in oil. I assume this left a fairly hard edge and a softer spine as hardened. This was followed by polishing away the scale, heating the spine very slowly and watching the colors followed by quenching in water when the temper was correct in his eyes. He did this tempering step three times. It produced a blade that allowed a file to just barely bite on the edge but easily cut the spine area.

I assume this treatment also helps with grain formation - yes?

[Tyler Murch]

I once saw a master ABS bladesmith temper a blade three times after hardening. He used a torch to bring the edge up to non-magnetic while not spending much time worrying about the spine then quenched in oil. I assume this left a fairly hard edge and a softer spine as hardened. This was followed by polishing away the scale, heating the spine very slowly and watching the colors followed by quenching in water when the temper was correct in his eyes. He did this tempering step three times. It produced a blade that allowed a file to just barely bite on the edge but easily cut the spine area.

I assume this treatment also helps with grain formation - yes?

The reason that it is done 3 times is to eliminate any places that possibley didn't get tempered.

[Tyler Murch]

Thanks quenchcrack. That's what I wanted to hear.

[J Hiser]

On 9/15/2006 at 10:55 AM, Quenchcrack said:

Normalizing three times will dissolve more of the big carbides that formed when you annealed it when you really shouldn't have.

Curious about what the correct process is when I’m not finished with a piece but done forging for the day. I’ve been letting the piece sit in the forge after turning it off. While it’s not really annealing, I’m wondering if this is causing carbide formation? Also is there any benefit to normalizing more than 3 times?

[ThomasPowers]

I depending on alloy; yes that *is* really annealing!    Spending time at high temps without forging contributes to grain growth.  There is diminishing returns for multiple normalizations and so 3 is pretty much used to get the most with the least issues with decarburization and scaling from doing it.

Note what alloy you are using contributes hugely to how the various processes affect it---like S-1 where it is NOT recommended to normalize it in the ASM Heat treating handbook!

[anvil]

I've only come across one or two steels where the specs say to normalize more than once.

As far as proper procedure, you can't beat following the specs. 

Check out this apk. "The heat treaters guide companion". It's free and available for Android and iOS.

I believe that is what Thomas is referring to. There is a thread here on it as well.

 

[ThomasPowers]

Nope I was referring to: "Metals Handbook, Vol 2; Heat Treating, Cleaning and Finishing, 8th Edition" put out by ASM; old but most of the alloys I'm interested in are covered in it.  (My phone doesn't do Apps or the internet; It does voice and text with minimal tracking!)

[anvil]

Aren't you an IT? Seems that's what I remember. I find it rather refreshing that you don't have internet on your phone. 

Lol, no matter how old the source, if the "mix" doesn't change, the specs don't change..

[ThomasPowers]

I'm somewhat an introvert and prefer to have all my life off the radar from all the tracking apps and commercials; more so as  I grow older...I generally buy things used and so 99% of the ads don't apply to me and why should I have to see them?  Stepping back from all the pushed consumerism makes it just more obvious how messed up things are---like celebrities who are celebrities just because they are celebrities.  I also don't see the value of getting "local news" from all over the country. If it really doesn't affect me; why do I need to be inundated with it?  I don't like people pushing emotion over reason. I've read the studies that people who watch network news end up having a very unbalanced view of what things are really like in the USA.  (Much like when I spent a month in Indonesia doing an installation and all my Indonesian colleagues kept asking me if I lived in a gated community with armed guards?  They were surprised to learn I lived in a 100+ year old house in the inner city and didn't own a pistol; all their info came from TV.)

So I think I come by the Curmudgeon title naturally...I'm not a luddite; but I don't believe "new" automatically makes things "better".