High carbon stuck to low carbon

[Sam Salvati]

This has been messing with my mind for the longest time. If high carbon steel is just stuck to low carbon/iron, can the high carbon really be left at what would regularly be considered too hard? I mean, it just doesn't make sense. If you were trying to get a tougher blade that still had a very hard edge, the edge would just chip and there wouldn't be any benefit? The exposed edge is still going to be super hard, so a spine of mixed steel and iron would be no benefit? Is this sort of construction method stuck up on the "purely aesthetic shelf" along with the folding of modern steels? Talking 2 layers, not laminated.

Then another question comes up. The best illustration of my question when it comes to damascus is O1/L6. Is the choice for these two materials made for the edge holding benefits of the O1 to couple/mingle/mix with the toughness and impact resistance of the L6? Through welding do you get a sort of alloying migration where they will share they're properties and become another steel all together?

 

[TekSec]

Wow, Sam, do you miss Kevin's posts? Great question and I have to admit I've wondered the same thing when it come to edge hardness vs. toughness.

 

[delbert ealy]

Sam,
I work with a lot of O-1 an L-6, and from my observations you do get a very slight increase in cutting ability FOR SLICING CUTS with the mix over pure O-1 if the pattern is other than a straight laminate. For push cuts with a polished edge there is a bit of loss of edge-holding ability. Please keep in mind that the differences are in the hundreths of a percent. Most of the toughness and impact resistance of L-6 is lost when you mix the two in equal parts, but it does seem to have a bit of an edge over pure O-1.
In my experience you dont get serious alloying migration until you hit layer counts over 10,000 and that is far beyond the point which the human eye can discern them in a 1/8" thick piece.
Call me some time and we can chat more about this. I only get to see you at ashokan and then there are so many neat things going on the only way to have a discussion is to stay up until after everyone else has gone to bed.
Thanks,
Del

 

[wnease]

considering that the edge is the thinnest part of a blade that takes the most punishment, i'm not sure why we try to "toughen" the spine anyway or make it of softer, weaker material

 

[john0270]

I think it was mostly done during period times because of lack of heat treating technology(ie tempering ovens), and value of high carbon steel. If the edge of your blade chipped/cracked during combat, it could create a stress riser that would break the blade on the next blow on a mono steel weapon. I am a fan of drawing the spine with a torch to a lower hardness vs clay quenching.

 

[MSCantrell]

Sam, my understanding is 01/L6 go together because the heat treat regimen is nearly identical. So you can heat-treat the blade and know you're doing the most appropriate steps not just for ONE of the steels, but for BOTH.

Same story with 1080/15n20. You could mix O1 and 15n20, and you'd get your light-and-dark contrast because of the differing nickel content, but when you got ready to heat treat, you'd have to decide "Well, do I want to do this right for 15n20 and wrong for O1? Or right for O1 and wrong for 15n20?"

And even worse... (!)... it's not just that half your blade would be heat-treated wrong, apparently the expanding/contracting that happens with hardening can delaminate your steels if you're not hardening both of them together.

This is what I hear... haven't sacrificed a blade to try it myself.
Mike

 

[Stacy E. Apelt - Bladesmith]

The reason to use L-6 or 15N20 is in the color more than the hardness. The chromium will etch much brighter than the O-1 or 1080 will. The slice cutting advantage comes fro the micro-serrated edge. That is the same reason it is less efficient on push cuts ( more friction).

In modern blades the use and function is often secondary to the look and style.

Soft spine/hard edge comes from the days when blades were used.
The Japanese blades have a HC edge and soft core or spine to conserve scarce HC steel, and to prevent a chipping blow from breaking the sword. a crack in the Ha (edge) will only go about 1/4" and stop. The blade can be torqued and bent, but can be stepped on and straightened.The spine is also struck by the opponent's blade. The toughest metal wins that battle,too.A small chip is not a fatal flaw in grading a blade. A deep crack is a fatal flaw......because it might end up being fatal.

Big knives, suck as a D-guard bowie or a snick-or-snee will need a lot of extra toughness in the spine because they are abused from the spine side often. The spine is used to parry a strike from an opponent, as in sword play, as well as being battonned to split wood. A totally hardened blade would not survive such abuse.....and without the knife the owner may not survive.

One more practical advantage was that it was far easier to grind down by hand on natural stones, a soft blade with only a small hard edge than a big hard surface. KMG probably ended a lot of that problem, but hand finishing was surely no more a joy than it is today.It also made scarce and valuable stones last longer.

Stacy