The "Too fine grained" thread sparked a memory of a question I've had for a while. I've read about the theoretical limit of grain refinement in some steels, 52100 specifically. I have not been able to find the reference for this anywhere. I've discussed it with various makers and no one is sure where it came from, though I heard some good SWAG's. Does anyone know where to find this information? I have access to a good university library if it's in some hard to find book/article.
-
The BladeForums.com 2024 Traditional Knife is available! Price is $250 ea (shipped within CONUS).
Order here: https://www.bladeforums.com/help/2024-traditional/
Grain Size Limit
- Thread starter me2
- Start date
- Joined
- Jan 6, 2005
- Messages
- 9,680
This may be along the lines of your inquiry. There are patents floating around somewhere(I might be able to get the numbers) concerning the research done by R.A. Grange on behalf of U.S. steel. The work was done to refine carbides in bearings, to avoid retained austenite, and involved austempering to produce very fine pearlite or bainite before the final martensitic conversion. Grange clearly states how to use his process to easily obtain grain sizes in excess of 10 down to 14 or better. This was in 1966. I don't know if this is the theoretical limit.
Mete, will be able to bring more to the table than I could... that guy gots big metal brains.:thumbup:
Here is a document on The Influence Of Grain Size On the Mechanical Properties Of Steel. It speaks of limits.
Mete, will be able to bring more to the table than I could... that guy gots big metal brains.:thumbup:
Here is a document on The Influence Of Grain Size On the Mechanical Properties Of Steel. It speaks of limits.
Last edited:
- Joined
- Nov 12, 2012
- Messages
- 88
The above document is very good and the 20nm average size limit seems reasonable. If metal in liquid state is flash cooled it loses all grain structure and becomes an amorphous, glass-like, material; so depending on how the metal is formed you can mess with that limit. Another place to look could be ASM manuals in your library. If the university your library belongs to has an engineering department they should have a large collection of ASM, ASTM, or ASME volumes.
That is some good stuff. I think the limit mentioned in the paper is related to a grain size below which the Hall - Petch relationship does not work in terms of predicting strength changes based on changes in grain size. 20 nm is very fine. The finest I've heard of in knife steels in from friction forged D2, and is about 1/4 the diameter of ASTM size 14 or 15, but even that isn't down to 20 nm.
The theoretical limit I heard was larger than what Grange was able to do. That's why I was trying to find the reference so I could maybe see the theory behind the limit. As far as I can tell, grain size is only limited by the amount of control one has over the processing. The DOE paper does interestingly mention a possible point where not only are there no more gains in properties, but they actually reverse themselves and start getting worse, ie lower strength, lower hardness, lower toughness, lower fatigue limit, etc. Heaven knows how small one has to go before that happens, if it happens in the particular material.
The theoretical limit I heard was larger than what Grange was able to do. That's why I was trying to find the reference so I could maybe see the theory behind the limit. As far as I can tell, grain size is only limited by the amount of control one has over the processing. The DOE paper does interestingly mention a possible point where not only are there no more gains in properties, but they actually reverse themselves and start getting worse, ie lower strength, lower hardness, lower toughness, lower fatigue limit, etc. Heaven knows how small one has to go before that happens, if it happens in the particular material.