B
Bush Monkey
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Is heat treating damascus steel problematic because different steels require different heat treating formulas in order to maximize their performance?
Is heat treating damascus steel problematic because different steels require different heat treating formulas in order to maximize their performance?
It doesn't have to be, but often is when damascus makers choose steel combinations that are poorly matched for heat treatment.
There are many misconceptions that have arisen over the years that are a result of thinking in absolutes about “damascus.” We can avoid them if we always try to keep this basic premise in mind- damascus, or pattern welding, is not a product but a process. We get in to all kinds of trouble in setting ourselves to be proven wrong whenever we refer to, or even think of, “damascus” as if it were one singular material. The process of pattern welding can include any number of infinite combinations of steels, and any number of procedures to combine them, all ranging from rather terrible to exceptionally good.
I have heard people, who really should have enough time in the field to know better, say something as ridiculously absolute as “damascus steel requires a special quenchant.” What?:31: Perhaps their steel combination required a special quench but other combinations simply use the same quench as the parent alloys. And I know some tool steel mixes that will get impressively hard just cooling in air.
One of the most common misconceptions is the Rockwell thing. For years old timers have said that you can’t Rockwell damascus, but this was because they were still working off from the outdated, and incorrect notion, of hard and soft layers based upon carbon content. I personally work off from a toughness vs. abrasion resistance model, not hard and soft, and my damascus invariably Rockwells even more consistently than either of its two parent steels alone. However, two pattern welded materials that will render a Rockwell tester useless are welded cable (without extended folding) and anything with pure nickel in it. Even 1095 and 1018 will Rockwell if it has been folded to any extend, but the numbers will all be in the low 40’s, unless the 1095 is a mass majority. Once again- a infinite number of possible materials we can call “damascus” some Rockwell beautifully, others not at all.
One area that I have done some serious research the testing on is the cutting ability of hard/soft, versus varying levels of abrasion resistance. Things like pure nickel mixes do cut very aggressively on soft fibrous materials, so if you want to tear up rope and paper in an impressive way they will do it. But if you want to cut on harder things like solid cardboard or wood, it will not hold up so well. I have many micrographs that reveal why this is. The soft nickel layers tend to not just wear at a faster rate, they actually tend to tear and blow out leaving a very toothy edge as it cuts these soft fibrous materials, but something of substance will then apply pressure to the exposed and unsupported rakers of hard steel which will collapse to a dull edge overall. But most puzzling is that so far my tests reveal a surprising lack of gains in impact strength from the nickel, so I have yet to find the anticipated benefits in toughness from pure nickel.
The one misconception that is longest in dying is the idea of layers of differing carbon content. Carbon diffusion is surprising fast at welding temperatures and mixing low carbon material with good blade steel only lowers the overall carbon content. I also have plenty of micrographs showing how well carbon can move between these layers even on the first weld and by the time you are approach 100 layers carbon will be pretty much even throughout. I have also tested some of the popular old mixes that included 1018 and sure enough they are tougher, but that is because they struggle to reach 45 HRC even with a brine quench.
On the subject of this thread, the alloying moves much, much slower via diffusion, so much that the layers can easily keep their alloying autonomy. So if you mix a water hardening steel with a very deep hardening oil quenching steel, you may move their carbon around but the respective hardenability will remain the same and you will have to choose which steel is going to get the proper heat treatment and which one will be sacrificed. This will not merely be problem of edge holding and other blade properties, but what do you suppose that nice straight blade is going to do when one steel hardens with the massive BCT expansion and the other one doesn’t?
There is a reason why the most popular mix going these days is 10XX/15n20, it really works. It works in performance, it works in stunning color contrasts, it welds and forges very well and it heat treats with virtually no comprises.
It has been my experience that if a well made damascus is not seeing every bit as heavy use as any mono-steel blade it is a sad loss. Carbon steels by themselves stain and rust under almost any use, regardless of how careful one is, well made damascus has a very durable finish that does not show this staining nearly as much and is much more fixable if it does. And if the steels are well chosen the stuff can handle any hard use a single steel would, I say this from the perspective of the first smith to win an ABS cutting competition with a damascus blade, and every competition I ever cut in I made it a point to use a damascus blade. This is not to brag myself up, I am a nerd that chops like a girl, this is to emphasis that a well made damascus is the equal of any single steel in hard use. But there is a lot of damascus out there that is not so well made, and it starts with the steel choices.
Thank you for weighing in.
If there are absolutes for heat treating specific types of steel and damascus is made from specific steels then it stands to reason that damascus is not immune to the professed absolutes of heat treating.
The optimal formula for heat treating is either steel specific and using a single heat treating formula for a multi-steel blade is sub-optimal OR the optimal formula for heat treating is not steel specific and heat treating a multi-steel blade using a single heat treating formula is/can be optimal. Unfortunately, we can't have it both ways.
If, heat treating is not steel specific and absolute, then we can discard most of what has been written about heat treating.
I don't know how objective cutting competitions are. Are all or most blades that win these competitions mono-steel blades or multi-steel blades? Tool steels are used in many applications where performance is superior to aesthetics. If well made damascus is "the equal of any single steel in hard use" then it would stand to reason that we would see well made damascus being used hard in applications outside of knifemaking and cutting competitions.
Jeff
O.K. there were three more posts in the time I was typing my last one. I will have some answers for you Knifemaker.ca, in the meantime do not assume you have drawn my ire in any way.
Wow, does that ever open up a pile of questions.
Better start off by saying the last sentence of my reply above wasn't meant to be an attack - sorry if it came across that way. A large measure of my experience has been with stainless Damascus, cable Damascus, thunderforge Damascus and such - hence my experience with varying rockwell reading on a blade. I've also seen it on 1084/15n20 blades, but to a lesser extent. I guess I'm one of those old timers... but I'm not saying you can't rockwell Damascus - just that it's one more thing that can screw up a rockwell test (along with something unnoticed on the anvil, a burr on a pinhole, a tiny bow in the workpiece, less that parallel surfaces....).
I do understand the notion of carbon migration but had presumed it to be material, but incomplete. I stand corrected. How is it then, that with something like 1095/1018, we are still able to etch layers - and if 1095/1018 just makes (for example) 1060, why not just start out with the mono 1060?
My musing about quenchant wasn't suggesting a special quenchant. The question arises that if someone uses steels that have different quench requirements (ex O1 and 1095) do you choose the fast or the slow quenchant - and does the performance of the other steel suffer because of that choice? (You covered this above in part. Is this just an example of the folly of mismatched steel in Damascus?)
Lastly, would I be very much wrong to suggest your ABS competition knife beat out the other blades because of superlative edge geometry and heat treat. If not, I'm interested in how performance characteristics are improved by Damascus in a way that can't be realized with a mono?
My thoughts on (some) Damascus have improved through this thread. Keep talking. I have an open mind?