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Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by Kevin R. Cashen, Sep 23, 2010.
H-K is pretty darned good:thumbup:
Whew! When I first read your thread title, I was afraid you had used my L6 blade as a test and had it explode into a bazillion pieces when quenched!
Then there's the movie!
Thanks for sharing your data Kevin. :thumbup:
that's really cool. Surprising to see such a huge difference thanks for all you do keeping everybody curious
Ahh, but how about the bitter bite of bainite? 1095 was a good year for that.
(running and ducking the broadsword swings)
Hey kevin I know this is off topic but could you look at this? Photo of broken steel
there is a picture in there that I think (hope) is worth your time
So, just out of curiosity...would this test oil be good for something else...say 0-1?
Kevin, what kind of oil is used during the austempering process? Is austempering an acceptable practice when hardening a sword? I have seen some blacksmiths austemper but I do not think they knew what they were actually doing.
Yes, I forgot how bainite can leave a bitter taste in one's mouth.
Nope, it survived despite my best efforts, I will assume you will pick it up at Ricks next month.
It is very hard to tell from just pictures and fracture analysis is an entire complex field of science unto itself so any number of things could be going on there. The lumpy fracture surface is as much an effect of the directed forces caused by your scoring cut, you will notice who closely it follows the shape of your cut mark. If the scoring cut was there before the HT it would be even more interesting with what it tells us about how such factors can steer transformations within the HT itself. One will often get a slightly different look on the tensile side versus the compression side, and this is very much so when there are dual phases. Decarb will always leave a thin line of deformation at the very edge due to a different and more plastic mode of fracture. Pearlite and decarb can illustrate the differences in slow tensile loads and rapid impact loads and let us see the two forms of toughness more clearly. A rather soft steel will fail in a ductile mode and stretch via slip before shear forces get the best of it, but the same piece of steel will fail as if it where much harder, or even brittle, if subjected to sudden loading, due to the fact that it is loaded faster than the ductile processes can occur, thus no accommodation via slip and instead brittle type fracture. When I want to assess fractured ends I always prefer to break it with impact versus bending so that I can get a cleaner look at the surfaces from cleavage fracture without the confusion that the shear based fractures cause.
This, by they way is the cause of much confusion among many makers who arent aware of these processes, causing them to erroneously claim a different grain structure for the edge vs. the spine when all they are really seeing a different mode of fracture from a pearlitic spine.
Mace, any good medium speed oil, heck this prototype oil would probably have worked well for O-1. Houghton type G, Houghto-quench 3430, or Park Metallurgical AAA if you can get it, are all good examples of oils well suited for O1, L6, 5160, 52100 etc
Austempering is greatly misunderstood by many and very often they only think they are achieving the desired results. To properly austemper one MUST make lower bainite as upper bainite is worse than just having pearlite. Lower bainite is however much more difficult to make than its high temp brother. Upper bainite can happen in minutes, but the lower the hold temperature the longer the time required to make the stuff. Lower bainite occurs in the lower temps before Ms (600F and less) so it takes longer and longer (hours not minutes) depending on how strong you want it. This requires a quenching medium capable of pulling the heat out fast enough to avoid both pearlite and upper bainite while still being able to hold the quenching temp above 450F, which is no simple thing. One could also see how some steel would really complicate matters as well due to their ability to quickly make pearlite.
Because of this austempering is best done with martempering oils designed specifically to work at high temperatures, or molten salts. Although many makers feel they are doing fine with heating other oils up and quenching into them, what they are actually getting is a mix of pearlite, upper bainite, perhaps some lower bainite and martensite that converted when they finally went to room temp (at least what converted and did not hang around as retained austenite). So by doing goofy things in an attempt at making bainite without the proper process one can perhaps get a horrible mix of virtually every phase commonly encountered, great for metallography samples, terrible for a blade.
I like this! It is especially true in my case.
Kevin... would a 400X digital USB microscope be of any use to a beginner in examining and trying to read grain structures? I recently picked one up on the interwebz.
Rick, the problem is that fractured grain inspection is nothing like metallographic grain inspection. Fractured grain is very bumpy as it reveals the 3-dimensional outer surfaces of the grains, this makes really high magnification useless due to the depth of field issues, 50X to 100X is the most you could hope for and 100X is already only giving you limited depth.
With metallographic inspection the grains, along with the sample, are cross sectioned and you get a completely flat plain that allows more accurate grain size determination as well as magnifications of 1000X an even beyond.
So a good loop or hand held magnifier will be just as good as anything more fancy for fractured grain inspection.
Thanks Kevin! the reason I scored, and broke it via ductile strain is because I intended to use the two pieces, and I was trying not to get hurt.
Damn:grumpy:... I was hoping you would say you've been fooling us this whole time and metallography was as easy as cut, polish, etch and look! Now, you're probably gonna tell me something crazy like O1 isn't the perfect beginner steel.
Does the R. in "Kevin R. Cashen" stand for Rug-puller? I keep experiencing the sensation of falling when I read your posts.:thumbup:
I knew I liked Karen. She does a surprisingly good job of hitting you where the bruises don't show in public - but of course, hitting you on the head would certainly be a fruitless endeavor for behavior correction.
I'll bet most folks approach removing that 2mm worth at the edge doing their final finish grinding. That means their edge is made up of 12 or 15% pearlite, I'm guessing? NICE.
Of course, maybe you're just not experienced enough to use improper quenchants yet, Kev... don't worry, another 20 years and you'll be able to just make stuff up and be believed, too!
All this really illustrates, is that quench speeds have an effect on the micro structures of the steel, (definitely something to be aware of but),… nothing more nothing less… nothing new.
It simply shows that one of the quenching mediums used was faster and one was slower.