I remember reading this from Howard Clark's :
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.
6 actually has a wider array of uses than saw blades. A203E, and Admirals 8670M also have nickel but they are hardly interchangeble with L6 or 15n20. Both 5160 and 1095 have been used in spring manufacture does this make them similar? Different chemistry, different heat treatment but they look the same, from this perspective any ferrous alloy is similar For years I have seen bladesmiths refer to these steels as the same under different names, I don't get it? Folks loved the Admiral L6 alternative as long as they thought it was L6, I and some other folks pointed out that it didn't behave at all like L6 and then some people got it analyzed and found it was 8670M. Afterwards many were upset by this and felt it was bad steel that they no longer wanted to use it simply because it was not exactly L6. Most are fine with 15n20 being described as just a European name for L6 yet any of the 86XX series come much closer to L6 in chemistry than 15n20. This is just one fo those quircky human nature things that will always puzzle me, kind of like the number of people ready for a revolution when they pay $4 for a gallon of fuel and then crack open 16 oz. of tap water they just happily paid $2 for ??
L6 will laugh at most attempts to machine it unless it is thoroughly spheriodized annealed. Which is the anneal I touched upon in my previous post. I always spheroidize, and how I do it is to soak at 1375F for an hour and then cool no faster than 50F per hour to below 900F. In this condition you should be able to mill it even without coolant (although coolant is always better). Short of spheroidizing L6 will form varying degrees of bainite and even some martensite with almost any other heat treatment.
As far as the L6(aka Haynes25, aka L605) i can attest to the material itself. It is one of the toughest materials on the planet earth. We machine critical components for nuclear and weapon industries out of Haynes25. To put it in perspective, the same part made from 316 Stainless (a very tough stainless) will cost 100.00 that part in L6 will cost 900.00
L6 will take a tremendous beating, will retain an edge(bainite heat treat) and it takes a bit longer to Polish than ordinairy steels due to the microstructure after heat treat and bainite forms on the surface.
I am currently machining a sword for my father out of Haynes25, from a solid bar stock. I have already used up several ceramic inserts roughing it out, but its worth it. Its for my pop.
A sword made from Bugei, a well known and highly respected metal working group, is well worth the money for a forged hand polished sword made from pretty much the toughest commercially available material on earth.
www.mvforge.com..Howard Clark’s forge
