How to shrink grain size ??

Doug Lester

Well-Known Member
I don't shrink grain size while forging. I wait until after I'm done and am ready to heat treat. By heat treating you can reduce grain size by one of two ways, both involve cycling the steel through crystal phase changes multiple times. One method is multiple quenches, which I don't recommend because quenching can also promote cracking, from microscopic cracks to outright breakage, by multiple routes. To me there is no reason to expose the steel to those forces more often than is required. The other is multiple normalizations, which is austinizing the steel and then letting it air cool and produces less stress in the steel.

Either way that you choose, you have to do it right. First of all, all you want to do is the get the steel to change back and forth from a body centered cube to a face centered cube (austinization). Your are not concerned with getting the carbon in the steel to go back into solution so there's no real reason to do a long soak. All you have to do is to make sure that the steel is austinized throughout before cooling the steel again. The way that it works is that when the new crystals form to change the phase of the crystals they will form on the boundries of the old crystals in a smaller size. Cycling the crystals through these changes will produce progressively smaller crystals-but only if it's done right. Expose the steel to too high a temperature for too long will undue all this and actually grow the grain. You will probably do just about all the grain refinement that can be done in three cycles.

Stress relief also occures by reforming the grains with these methods, especially normalizations. There are also other things, such as alloying and what is used to deoxidize with, that have an impact on these processes but lets not get into that at this time. What I gave you is pretty much what I do.

Doug
 

BarryC

Well-Known Member
You going to start forging Art? Come over some time and I'll let you bang out a knife shaped object.
 
I thermal cycle 2-3 times at 1250-1275 and broken blades show a nice fine grain structure. Do you think I would be better off taking them to the curie point for each cycle?
 

McClellan Made Blades

Well-Known Member
I don't shrink grain size while forging. I wait until after I'm done and am ready to heat treat. By heat treating you can reduce grain size by one of two ways, both involve cycling the steel through crystal phase changes multiple times. One method is multiple quenches, which I don't recommend because quenching can also promote cracking, from microscopic cracks to outright breakage, by multiple routes. To me there is no reason to expose the steel to those forces more often than is required. The other is multiple normalizations, which is austinizing the steel and then letting it air cool and produces less stress in the steel.

Either way that you choose, you have to do it right. First of all, all you want to do is the get the steel to change back and forth from a body centered cube to a face centered cube (austinization). Your are not concerned with getting the carbon in the steel to go back into solution so there's no real reason to do a long soak. All you have to do is to make sure that the steel is austinized throughout before cooling the steel again. The way that it works is that when the new crystals form to change the phase of the crystals they will form on the boundries of the old crystals in a smaller size. Cycling the crystals through these changes will produce progressively smaller crystals-but only if it's done right. Expose the steel to too high a temperature for too long will undue all this and actually grow the grain. You will probably do just about all the grain refinement that can be done in three cycles.

Stress relief also occures by reforming the grains with these methods, especially normalizations. There are also other things, such as alloying and what is used to deoxidize with, that have an impact on these processes but lets not get into that at this time. What I gave you is pretty much what I do.

Doug

Doug,
I've been considering adding another step after normalizing, and that is annealing, will that reduce the size of the grain? Or is it more of a refining step, I've never annealed a blade before, and really haven't seen the need from my testing, BUT I want to make the best blades I can make, and if this step will give my knives benefits of any kind, I want to know! THANKS! Bro, Rex
 

Doug Lester

Well-Known Member
I don't think that annealing would shrink grain size. Sub-critical annealing, spherodizing, could refine carbide size though. Actually I don't anneal anymore as I find that normalizing will soften the steel enough to make grinding easy.

Doug
 

McClellan Made Blades

Well-Known Member
Doug,
I wasn't talking about doing it before grinding, I was thinking about refining the grain structure with 3 normalizing cycles, like I've been doing, then annealing. I'm not sure about what the Phase change and then the slow cooling would do to the grain structure, if anything. I've been getting great results with my current practice, but I'm always looking for ways to improve and of course to learn something new!
Thanks Bro`, Rex
 

Doug Lester

Well-Known Member
I don't see where annealing after normalizations would do anything positive. It is partially the quickness of changing phases that will help refine the grain more. That's one of the positive effects of doing multiple quenches instead of doing doing multiple normalizations. I just don't like the additional opportunities to cause quench cracking. Grain growth is a factor of temperature and time. Even though temperature is much more critical than time, time is a factor and I don't see how the additional time above critical during the slow cool down is going to help anything. If I were to do annealing, I would do it before multiple normalizations to shrink grain size and relieve stress in the steel.

Doug
 

JPH

Member
Hello:

OK..why would you anneal AFTER Normalization? That is to me redundant..sure you can do it but why?

Now I have got to ask...What material? I mean I forge out A-2, D-2 and M-2 on a semi regular basis and that normalization is far different than say what is needed for 1095. So the material does come into play...

I am also an advocate of sub critical forging when ever possible as this also helps prevent grain growth. What material are you using? that would be a great help in getting a more accurate answer to your question..

JPH
 

McClellan Made Blades

Well-Known Member
Hello:

OK..why would you anneal AFTER Normalization? That is to me redundant..sure you can do it but why?

Now I have got to ask...What material? I mean I forge out A-2, D-2 and M-2 on a semi regular basis and that normalization is far different than say what is needed for 1095. So the material does come into play...

I am also an advocate of sub critical forging when ever possible as this also helps prevent grain growth. What material are you using? that would be a great help in getting a more accurate answer to your question..

JPH

Is this Jim? The same Jim that may have written a few books? Let me know if you're the same
Jim I'm thinking of, because if so, I'm very happy that you've joined "The Dog Pound"!

Back to the topic, do keep in mind that this is something I was thinking of trying, in an effort to reduce the grain structure before HT. The steels I use are 1084, W-2 and being that I still have a good bit of 1095, I'm interested in fine tuning my process to get the best possible blade that I can make. I was thinking the Annealing would help after 3 normalization cycles, could the steel benefit any if it was annealed before normalizing? I'm in no way saying this would or could work, this is something I thought of while reading some HT'ing info somewhere.

The way I normalize has been to heat the blade to red, then let it cool back to black 3 times, always at night! Would it better to heat the steel to a specific temp during normalizing? Or is the method I'm using the good? Thanks for helping out, and the more I think about it I'm pretty sure this is the Jim I'm thinking of, not many folks have forged D-2!

I know annealing is beneficial in keeping the steel drill-able and soft enough to grind, my thoughts were that after the stresses of forging, the slow cooling would help out with the grain size. If it is something that isn't necessary, a step that would not realize any benefits in a better blade, I can see why not to do it. Besides, it definitely wouldn't be the first time I was WRONG!!! Thanks, Rex
 
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