Which Tool Steels Wont Grain Refine?

N

nullack

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Nov 17, 2008
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So folks as ya'll know Im a fan of achieving finer grain sizes to improve the mechanical properties of my blades such as achieving higher toughness at the same hardness levels.

Recently it was shown to me that some tool steels wont respond to grain refinement through heat treating. Specifically, I know that grain refinement can be achieved through normalisation and or quenching, but also through working the material by a bunch of deformations.

If we stick to just the heat treating approach for grain refining, do we have a list of what tool steels will, and those that wont, respond to grain refining?

Thanks
 
My opinion, (I'm not an expert):

It isn't so much that certain steels can not respond to grain refinement, it is that certain steels can only achieve a certain level of grain refinement (and it should come that way) and the approach of simply austenitizing three times will result in gross grain growth in some steels such as HSS and D2 and other complex steels with high austenitization temps and carbide volumes. I suspect that S30V and 3V would also be this way. Most tools steels grain refinement should be unnecessary and should be austenitized one time and left alone because it should come from the mill properly setup for HT. The exception would be steels that have been forged and subjected to high temps - then you need to worry about it.

Edit:

I think that steels that don't require long soak at high austenitization temps are good candidates for what you're looking to do.
 
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There are actually two separate issues, carbide size and grain size, D2 for instance can have really fine grain, but 30 micron carbides, so you will not be able to get and retain a really fine edge (1micron edge radius) regardless of what you do to the grain.

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sunshadow said:
There are actually two separate issues, carbide size and grain size, D2 for instance can have really fine grain, but 30 micron carbides, so you will not be able to get and retain a really fine edge (1micron edge radius) regardless of what you do to the grain.

-Page
Click to expand...

It might not get super sharp but it will have teath :D
 
I regularly get D2 sharp enough to "tree top" hair, without any special effort. It will cleave a hanging hair. But super sharp D2 (or any other steel) is really just a neat trick you can do, but unless you're an eye surgeon it is pretty pointless because it won't last.

Plain old shaving sharp is sharp enough for most uses - and D2 can be done to stay shaving sharp though several deer skinnings without touch up. The 30 micron carbides provide a toothy edge that cuts meat better than a polished edge. Users like that large carbide, that is one reason they want D2 and is probably one reason CPM D2 hasn't caught on better. I use an unserrated D2 steak knife that holds up fine to the porcelain plate. The tooth keeps cutting.


D2 frequently beats VG10 and S30V and other high tech steels in real word usage which is why it remains one of the most popular steels requested by knowledgeable users.
 
My Dozier D2 gets super sharp, and takes a mirror polish. Rumors are that it's been grain-refined in the heat treat, but the details are kept secret. D2 does get huge carbides that show up after some wear.

With industry standard heat treat, fracture grain size of D2 is 7.5, but it can definitely be refined.
 
A typical multiple quench can enlarge the grain in air hardening steels, especially high speed steels.
 
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