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- Sep 9, 2003
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Mike I have been busy and not on the forums that much, I only noticed your question today. Perhaps I can help shed some light on it. There is actually a lot of misunderstanding about L6 out there and like many things in knifemaking the hype has it either some sort of super alloy or a clunker for edge holding. This is mostly due to a lack of heat treating experience with this specific alloy leading to the latter or permitting the unrealistic beliefs of the former. So I thought we could have a chat about one of my favorite steels - L6.
The “L” in L6 stands for “low alloy” and while it is anything but when compared to simple alloy steels, 5160 or 52100 for example, within the category of tool steels it is very simple when compared with some of the others. L6 was designed to provide increased impact toughness without having to sacrifice strength from hardness. Because of this often some examples given for applications which it could be used include slitting cutters, shear blades, punches and circular saw blades and band saw blades. But the idea that this means a band saw blade or a circular saw blade is L6 is total B.S. and needs to go away. Some time ago industry found that it was much cheaper and more effective to put carbide inserts on a simple softer steel body for circular blades, and if you manage to get a large wood band saw blade not made of space age steel it will more likely be 15n20 than L6.
Which brings me to another common misconception that would be good to clear up, 15n20 is not European L6, other than both having some nickel they couldn’t be more different. 5160, O-1 and L6 all have chromium as well, but nobody is prepared to say they are the same alloys. 15n20 is more like 1075 than it could ever resemble L6. I just wanted to bring this up so that people didn’t have to face the inevitable grief that will ensue should they decide to apply heat treatments interchangeably based on this bit of bad information.
First there are two predominant chemistries floating around the U.S., one originating with Carpenter Specialty steels which they gave the title of R.D.S. (oil tough):
R.D.S.
Carbon: .70%
Manganese: .35%
Silicon: .25%
Chromium: 1.0%
Nickel:1.75%
The other Originating from Crucible Steel Service Centers called Champalloy:
Champalloy
Carbon: .75%
Manganese: .70%
Silicon: .25%
Chromium: .80%
Nickel: 1.50%
Molybdenum: .30%
Now an important note about these numbers, they can deviate a bit in any category and still be called L6, but more importantly while these steel suppliers may have started out making tool steels and developing these chemistries for the specific industrial clients, neither of these steels have been made in the U.S. for quite a while. Steel mills overseas make the stuff and these companies import it and sell it here. Due to this some people may come to the conclusion that you can just buy L6 anywhere and get the same results because it is all just some generic chemical range anyhow. It is the fact that mills can deviate within a range that gives us these different flavors of L6 that will also give us very different results in our heat treating.
I have been using Crucible’s L6 for almost 20 years now and thus have researched it a little more and talked with folks I know at Crucible and gotten the paperwork to trace it origins and I have found much of it coming from two overseas mills. These mills seem to be able to hold a chemistry quite well since this steel has been hands down the most consistent stuff I have worked with in my career. I have yet to encounter any noticeable flaws or significant deviation in its properties or behavior, allowing me to nail a trouble free heat treatment almost every time. Which brings me to my point of scaling my one man shop up to thousands of parts a day, if these suppliers paid no attention to chemistry and simply bought any steel labeled “L6”, there could be some major clients slightly irritated when they processed a few thousand parts in alloy that is the opposite end of the chemistry range that what they thought they bought, and thus we get the two flavors from these suppliers. They do not make the steel differently; they buy steel of different chemistry within the allowable L6 range.
One element within that range that is actually optional is Molybdenum. It is an interesting “optional” due to how powerful its effect on the steels behavior can be. Moly can increase hardenability, lower Ms and greatly increase heat resistance. I don’t know of all of these are good things or not, but if you get very used to working with the moly being there it really is best to be sure it is there the next time if you don’t want to redo your heat treatment.
Carpenter deals mostly with L6 in flat stock and bars while Crucible offers mostly rounds, which makes the latter almost exclusively a forging guys steel. But since rounds are always cheaper than dimensioned flat stock it accounts for the single biggest difference between Carpenter L6 and Crucible L6… the cost! My last batch of Crucible rounds (over 1” dia. for the price) cost around $1.80 per pound, while Carpenter is selling theirs for more than 4 times that cost (I don’t have specific Carpenter prices but if Delbert is reading this he could give you more precise Carpenter numbers)
Why use L6? There are two main reasons to use L6 in making blades and they both come from the nickel- toughness and resistance to etching. If you want a large chopping blade (I used it for all my swords) that can take a pounding at a much higher hardness than many would dare L6 is great, I have maxed out 240 ft lbs on L6 at 56.5 HRC in un-notched Charpy tests and for this reason will no longer do un-notched tests with L6 on my tester, no other steel I work with demands the same respect from me and my tester. If you want a bright silver layer to contrast the dark stuff in your damascus L6 is pretty good.
Why not use L6? If you are going to forge it (which is a given if it comes from Crucible) you will really need the ability to spheroidize it properly if you plan on milling or drilling. I have allowed forgings over ½” thick air cool and got a 61HRC reading. The stuff is NOT designated air hardening but it sure can do one hack of impression of an air hardening steel, though I have found that strength and toughness is miserable from air hardening it despite its hardness reading. Compared to 15n20 or 203E, L6 is a real pain in the @$$ to weld and then properly normalize until you really get the hang of it and compensate for its quirks.
Why do I use it? Perhaps the same reason my wife still loves me, because after all these years I have gotten used to its quirks and thus can do some pretty neat things with it. Why do I prefer Champalloy over R.D.S.? Because Crucible was the first place I called and they promptly sent me some steel, then when I compared I got to really liking the price I was paying! The moly gives me the latitude to do more things in my tempering schedules, and give me more time to be creative in martempering.
As for Tim Zowada, I would like to say that I have finally converted him to the dark side since he now works with Crucibles Champalloy, after hearing me rave about it for years, but the fact is the cost difference finally got to him. For years Tim used the R.D.S. from Carpenter because at double the cost it was still worth it for him to get cleaned square stock ready to stack and weld with no prep time, instead if having to squash it flat like I did. But when the price difference widened to over 3 or 4 times as much he started to reconsider. He just told me on the phone last week that he now likes the Champalloy even better and was sorry he was too lazy to make the switch before now. So the bottom line as to why Tim and I used the different L6- I was too cheap and he was too lazy for either of us to use the other, which is odd because I know I am lazier than Tim.
And finally Admirals “L6 Alternative”, which is not L6 at all, but 8670 modified. It has enough nickel to give a very bright gray color in a damascus etch and hardens a little more deeply than 15n20, but it is not L6 either. However I would like to say that just because this steel is not L6 does not mean that it is bad steel. I have a pile of it in my shop and often use it for applications that are not quite for L6 and not quite 15n20. The only time the steel can be bad is if you treat it like it was L6, but if you treat it like it was 1086M it will behave quite well for what you want it to do.
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