Bainite vs Martensite - Which is tougher?

Larrin Larrin
Is there any real significance to the difference in orientation of the carbides in martensite vs. bainite? Is that what causes bainite to be tougher? Aside from the whole plate Martensite and large plate carbides thing.
 
danbot said:
Larrin Larrin
Is there any real significance to the difference in orientation of the carbides in martensite vs. bainite? Is that what causes bainite to be tougher? Aside from the whole plate Martensite and large plate carbides thing.
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Well in the article I concluded that the two have similar toughness, so no I don't think the orientation of the carbides has a significance in terms of properties. :)
 
Larrin said:
Well in the article I concluded that the two have similar toughness, so no I don't think the orientation of the carbides has a significance in terms of properties. :)
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Oops!:oops: Somehow that was lost on me.:p
Thanks again Larrin!
 
This has been discussed here, in the past, here is the best post about it imho:

Stacy E. Apelt - Bladesmith said:
For those who don't know what the fuss is about;
When steel cools down from being austenitized ( at around 1500F) we usually say it has two ways to go - soft pearlite or hard martensite. The doorway is called the pearlite nose, at 1000F. If you pass the nose in the time shown on a TTT chart, you will get martensite, too slow and you get pearlite. However, there is a third structure that is possible with some knife grade steels - Bainite. Bainite forms when you pass the pearlite nose, but don't reach the martensitic start point (around 400F). By holding the blade at some point around 450-475F, the steel forms the bainitic structure. Bainite is tough. The biggest reason we don't hear about it is it takes from ten to thirty hours for it to form. That requires a special equipment.

Before one thinks, "TOUGHER, yeah I want that!", remember that hard rubber is many times tougher than steel, but it doesn't cut worth crap. Bainite can be made into a blade, and some sword makers make bainite swords. About the only plus is a very tough blade that will take impact well and bend. Some of the minus are that bainite will not take as good and edge,the edge won't hold up to use, the cost of a fifteen+ hour burn, and the need for specialized salt pots ( Standard knife kilns and salt pots are not meant to run for those time periods).

Since most knife makers want a sharp knife, and bending is not normally a desirable feature in most knives, there is no real reason to make a bainitic knife. For 99.9% of all knife uses, martensite is the ticket to a good knife. Learning to master the HT to attain a 100% martensitic blade at the target hardness is enough of a challenge for most makers.

I am sure some will say, "But I read about the super bainite swords, made by XXXXX". Yes there is a commercial maker of bainite swords....and when was the last time swords were used in actual sword use? I would be willing to bet that if people needed swords for offensive/defensive reasons, you would see no bainite swords on battlefields. The closest to those conditions comes in modern cutting practice and competitions ( tameshigiri). I don't follow these much, but would think if there was an advantage, the bainite swords would stand out. It is my thoughts that the things that go along with bainite will make the sword a poor cutter. Again, before anyone jumps up and says, " but sensei XXX cut through a 12" rolled tatami with a bainite sword.",that there are those with skill enough to cut with almost anything. One famous samurai was known for throwing his sword on the ground and fighting with the saya, because he did not need a sword to dispatch many of his less skilled opponents.

I did some experiments on trying to attain a martensitic edge with a bainitic spine. Without lab testing, there was no way to really know what I actually got, but the results were not better ( actually a lot worse) than a standard differentially hardened blade.
When I discussed this idea with Kevin, his head spun around....everyone ran from the room....and he replied " You should do that, and let me know how it works out for you." ( just kidding ,Kevin)

I have been told that some ABS tests were done with bainite knives, but IIRC, only one was successful.

If you wanted a tough blade that would bend, make it out of titanium. It would be about the same as a bainite blade without all the trouble.You can sharpen it to a fair edge, but it won't last long in use.


Stacy
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from the thread
https://www.bladeforums.com/threads...nd-disadvantage-of-100-bainitic-knives.714039
 
dirc said:
This has been discussed here, in the past, here is the best post about it imho:



from the thread
https://www.bladeforums.com/threads...nd-disadvantage-of-100-bainitic-knives.714039
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One thing I see in that quote (that relates to Larrin's article) is the 15+ hours for bainite to form. That is true for High alloy steels, but not for low alloy high carbon steels. But even so, it seems that it comes down to a diminishing returns kind of thing. As far as knives are concerned anyway. It's probably great for crowbars though!
 
Thanks to one of your earlier posts, I have the book from 1992, 'Bainite in Steels' by Bhadeshia. It's amazing that a nearly 500 page book is written on the subject, but there are some gems there if one likes to do deep research : -)
 
Bhadeshia's book focuses primarily on low carbon bainite and carbide free bainite designed to have high retained austenite, though there is obviously lots of information on the mechanisms of the transformations, etc. The book is well written but assumes some knowledge of metallurgy.
 
Larrin, I must say that your articles are simply amazing. I’m always interested to learn more about the science of metallurgy.

I was wondering, do you plan on adding a practical section in your site where you could post heat treat protocols for various steels ?

It would be super useful to people like me who are starting to make knives

Thanks
 
I haven't read the article yet and I am sure I won't understand all of it when I do.still thanks for the work.
 
Revolverrodger said:
Larrin, I must say that your articles are simply amazing. I’m always interested to learn more about the science of metallurgy.

I was wondering, do you plan on adding a practical section in your site where you could post heat treat protocols for various steels ?

It would be super useful to people like me who are starting to make knives

Thanks
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the best starting point (imho) to get HT protocols is from the specific steel manufacturer ... then read the knife maker subforum here to get some tweaks or other nuggets

examples:
3v - http://www.crucible.com/PDFs/DataSheets2010/ds3Vv1 2015.pdf
m390 - http://www.bucorp.com/media/Bohler_M390_Microclean.pdf
 
Revolverrodger said:
I was wondering, do you plan on adding a practical section in your site where you could post heat treat protocols for various steels ?

It would be super useful to people like me who are starting to make knives

Thanks
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That is possible. I don't like giving specific recommendations for a couple reasons:
1) Different equipment will give somewhat different results from someone else so the exact temperature/time combinations may not translate perfectly.
2) I would want to have a range of heat treatments along with measured properties to ensure that I was actually giving an optimal heat treatment. For example, I have articles on toughness testing of CruForgeV and Z-Wear where a very good heat treatment could be designed using that information.

For now the hope is that after reading articles on the heat treatment process (austenitizing, tempering, etc) that will allow the maker to know how to read the manufacturer datasheets and how to use them. So you would know answers to questions like: should I use the upper end or the lower end of the hardening temperature recommendation? Maybe I could write an article on specifically how to use the datasheets.
 
Larrin said:
That is possible. I don't like giving specific recommendations for a couple reasons:
1) Different equipment will give somewhat different results from someone else so the exact temperature/time combinations may not translate perfectly.
2) I would want to have a range of heat treatments along with measured properties to ensure that I was actually giving an optimal heat treatment. For example, I have articles on toughness testing of CruForgeV and Z-Wear where a very good heat treatment could be designed using that information.

For now the hope is that after reading articles on the heat treatment process (austenitizing, tempering, etc) that will allow the maker to know how to read the manufacturer datasheets and how to use them. So you would know answers to questions like: should I use the upper end or the lower end of the hardening temperature recommendation? Maybe I could write an article on specifically how to use the datasheets.
Click to expand...

Yes that would be great these datasheets are somewhat obscure
 
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