W2 and O1 overlap on heat-treating temperatures around 1450. What is it about the chemistry of O1 that causes it to need a slower quench or risk cracking? And what things does a person look for when comparing steel for damascus compatibility? I know compatible steels need a similar austenizing temperature but incompatible steels can have similar HT temps.
Mike Krall
The austenitizing temp only becomes a concern when there is not that overlap window you refer to, but for the most part many of the steels we work with will fall in the same 100F range. Two other concerns that should be more critical are the required quench speeds and rate of movement under the hammer.
W2 is basically 1095 with vanadium added so it has a very quick cooling requirement in order to avoid forming pearlite at around 1000F. It was designed and used in a time when water or brine were common quenches in industry; W2 is getting rather scarce these days.
O1 is an entirely different beast, it is a specialized tool steel designed to reach maximum hardness with less intensive quenches in order to minimize stress and distortion in tools, dies, and other more involved applications. It is full of chromium, manganese with additions of vanadium and tungsten. On an I-T curve it has around 10 seconds to avoid pearlite, while W2 has less than 2.
For years I have encountered bladesmiths that just combine any steels they get their hands on willy nilly with no consideration to the heat treatment or other compatibility issues. These are bladesmiths that entirely understand the folly of trying to get the most out of a piece of mystery scrap steel instead of buying a fresh piece of a known alloy, only to turn around and throw the same logic out the window in combining steels in damascus.
Countless times I have suggested common sense should dictate that 1095 and L6 may not be the best combination, only to be piled on by any maker in ear shot that ever made a knife out of it to defend that it is possible. Once again anything is "possible" but is it practical? When I feel this debate coming on I now simply appeal to logic by putting it in the easiest to see terms- If you are making a blade out of 1095 and need to farm out the heat treating are you going to send it to a guy who only heat treats L6? When heat treating a blade out of L6 yourself do you flip to the page for 1095 in the Heat Treater's Guide? If making a mono-steel from either of these steels would you willingly compromise the heat treatment? Why do any of this with your damascus? This is how we end up with public conceptions like "damascus is just for show", or "damascus is pretty but it won't hold an edge like XXXX". And indeed the most common reason given when asking a maker about his choice of steel is the mix is that he wanted a certain look or color, I have yet to hear heat treat mentioned in such an answer, pretty has indeed trumped performance.
The tragic thing is that it doesn't have to. The reason I suggested 15n20 for W2 is that it is basically 1075 with some nickel added, this makes a contrast every bit as good if not better than L6 for steels like 1095, or W2 while still being very well partnered in the heat treatment- there will be no compromises. Often a quick look at the steels chemistry will tell you most of what you need to know about what other steels you should combine it with.
Folks dont realize how often cold shuts, delaminations, cracking or distortion can be traced to the choice of steels to combine; instead they are too quick to blame it on their poor welding skills. Their welding may be good while just their judgment in materials choices may be lacking. I have seen certain combinations literally pull themselves apart from little more than air cooling, and it almost never happens at the weld seems, instead one steel will just split right down the middle in order to accommodate it ornery partner.
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