damascus bar

[ausfire]

I forged this Damascus bar from a small billet of nine layers, alternating mild with spring steel from a car bonnet spring. I have folded and fire welded it twice so it now has 36 layers. I'm thinking it would make a good knife. Is 36 enough, or would another fold be better? I have had little experience with knife making - unsure of where to go from here.

 

[JHCC]

Personally, I like the bold look of low-layer-count damascus. My only concern would be whether or not there was enough carbon migration from the bonnet spring into the mild to make the latter sufficiently hardenable.

[ThomasPowers]

There is NO "magic number of layers" for making a knife.  The design, alloys used and carbon migration are the controlling factors. (Look at San Mai with only 3 layers in the finished billet!  The design makes use of the high carbon center layer for the blade edge and so carbon migration is not an issue/bonus either.)

[Steve Sells]

from page 134, Intro to knifemaking:

There are no high and low carbon content layers to pattern welded steels. Some layers may be softer in the end but that is only due to the nature of that layers alloys. Not all elements migrate as fast as carbon does. According to metallurgist Thomas Nizolek:

When we forge weld steels together, the carbon content in any layer of steel will equalize with that of the surrounding layers of steel very quickly. In Pennsylvanian, February 2009, Laboratory testing was made on a forge welded billet made from 4 alternating bars of W2 and 203E. This examination was done with an electron microscope. In the four layer sample it is evident, based on the pearlite gradient between the layers, that extensive carbon diffusion occurred after the first weld course. Drawn out and folded, the eight-layer sample showed that the pearlite concentration has almost equalized, however ferrite still decorates the prior-austenitic grain boundaries in the 203E layer. By the time the material has reached 16 layers, the carbon content of the sample appears to be uniform.

This appears to prove that carbon migration is happening much faster than most smiths had thought in years past. This means that the patterns we have in a billet made from using only simple carbon steels, must be coming from the other alloy differences, and not from the carbon as we use to think.

Getting a usable blade means paying attention to our steel's alloy content, which includes the amount of carbon. If the carbon content is too low it will not harden. So a 1095 and 1005 mix will not result in a very hard blade, partially due to carbon migration, because using equal parts of 1095 and 1005 will result in the equivalent of about 1045 in the finished billet. The simple math says 0.50 carbon, but remember to account for the loss of carbon to the atmosphere during welding, as well.

Carbon has a stronger attraction to air than to steel. This condition will also cause some of the carbon from the surface layers of our blade to move into the atmosphere. This is another reason to leave the blade thick before hardening.  It allows us enough extra material to still have plenty of thickness left after our final grinding, which removes this de-carb layer as we remove the scaling caused by the quenchant.

[JHCC]

So in other words, carbon diffusion is not the issue, but the final billet will be hardenable only if the bonnet spring and the mild steel combined at a high enough average carbon content. Is that right?

[ThomasPowers]

Yes (why I have some 1.2%C black diamond files squirreled away to use to "juice up a billet".)

Originally Daryl Meier; (IIRC), said that for thin layers 4 welding heats would result in carbon equalization unless blocked by a carbon migration stop layer like pure nickel.

Since I often use thin layers to start, (Bandsaw blade and pallet strapping), I try to use pallet strapping that will quench and snap to not pull down the average C.

[ausfire]

OK. Thanks. I might draw this out a bit longer and flatter and have a go at forging a knife shape.  Heat treatment and etching I'll deal with if necessary.

There is a young guy doing work experience at my forge on Fridays and he is a much better knife maker than I am. I'm not too proud to accept advice from a 17 year old, so we'll see how we go!

[BIGGUNDOCTOR]

Thomas, I believe the Black Diamond Nicholson files are case hardened. When I talked to their materials guy (46 years with them) a few years ago he said they case, and pack harden some files to get more carbon in the teeth.

[ThomasPowers]

These date way back before that!  (AND I had one tested.)  The ones that do NOT have the Nicholson stamp on them!

[BLDSMTH]

Just out of curiosity what about carbon migration in anvil faces with wrought iron body's?

You could always use this bar in a multi bar construction like a viking seax. Use it as the spine and use a file or something for the edge.

[ThomasPowers]

What about it?  Yes it occurs; but the face layer is quite thick compared to most pattern welded billet pieces.

[BLDSMTH]

Couldn't you have just posted your reply instead of a rude comment first? Seems like it would have been easier and less typing. 

[Steve Sells]

what was rude? you just said what about the anvil, and that wasnt really a clear question in there, It seems you are the one getting frogy

[ThomasPowers]

May I commend to your attention: "The Cementation of Iron and Steel" Federico Giolitti  which covers carbon migration extensively including experiments using diamonds as carbon donors, migration without the presence of CO, etc.   Now can I point out that to get good specific answers you need clear specific questions.  Did you want a discussion on the use of shear or blister steel for anvil faces and how carbon migration factors in with those?

[BLDSMTH]

Thomas I am sorry if I came off as a jerk....I believe I took your comment out of context. I should have been more clear with my question and your response was the exact answer to my question so I thought you knew exactly what j was talking about. I am truly sorry!!!

[ThomasPowers]

I've had a lifelong problem with seeing other possibilities with things. I've pointed out to college professors that their question, as written, did not ask what they wanted to ask. I've pointed out to my Dr's office that the form that had everyone sign for months was actually inverted from what they wanted. I read the fine print.  This of course can be highly annoying. (I was overjoyed when my wife started to watch "The Big Bang Theory" and found out that other people were like that too.)

We positively specialize in Straining at gnats and swallowing camels!

[Frosty]

I free associate everything I hear, see and read but swallowing CAMELS Thomas?! Even before I quit smoking  . . . ack . . . GAG! 

Those of us who automatically see many angles to everything can sometimes confuse folks. Thomas can be obscure and I can be way windy. We have reasonably thick skins though and have a lifetime of experience of folk not getting us first time, sometimes ever.

Frosty The Lucky.

[ThomasPowers]

Ok you can handle the staining of gnats---got a single hair brush?

Obscure---you must be thinking of Jude...

[JHCC]

I'm going to consign that last reference to the Hardy hole.

[ThomasPowers]

and not a Hardy-har-har?  I know; my humour is a lost cause.

[ausfire]

Well, back to the Damascus bar …. this is how it looks now. A knife shaped object awaiting further work when I decide what to do.

 

[ausfire]

Well, the above pic was a few weeks ago and the blade has now been etched in Ferric Chloride. I'm quite happy with the pattern. Now a handle is required: