[Aaron Schneiker]

Hi all.

I'm not sure if this topic belongs here or not as it is a question directed more specifically to the folks at Albion, but i'll ask here for the moment.

I was wondering if the heat treatment that is done on the blades is designed based only on the material being used or if each individual blade type gets a specific treatment? Specifically, would a thick cutting blade be tempered for less rigidity and hardness as opposed to a thin pointed thrusting blade? I realize that the each blades geometry is the main factor in how rigid or flexible it is, but I would think that the heat treatment would accentuate these properties. And to put this into more of a historical discussion I will also ask if there was evidence that this was done historically? Did they have the knowledge and temperature control back then to design a treatment tailored to the type of sword they were producing?

Thanks,

-Aaron

[Wolfgang Armbruster]

I'm no expert on smithing or metallurgy, but I'm sure they knew what they were doing back then.
They couldn't determine the temperature exactly but steel changes its clolor according to the heat.
Trial and error was their main method. In the end they knew when to take the blade out of the forge.
Japanese smiths still do it this way. They don't have a thermometer but because of the color of the steel they know when it's time.


To answer your question - Yes I think they could do that.

Here's an excellent article on that topic
http://anvilfire.com/21centbs/armor/atli/index.htm

[Peter Johnsson]

The heat treat methods at Albion is perhaps best explained by Jason.
Basically the same routine is followed on all blades, but it should be appreciated that different mass and geometry will react slightly different to the same heat treat.
We have worked through different steels and tweaked the heat treat methods many times over time. Reviewing routines to increase performance is continually done at a regular basis.

It is impossible to give a good *and* short answer to the question in a historical contex as we know relatively little about how it was actually done. Those few analysis that has been done shows that many different techniques were used, or at least that the reslts varied very much. From what I have read I can not see any trends in the heat treat methods applied to diferent blade types. It seems that the late 15th C saw an introduction of full quenching followed by separate tempering, while in earlie times slack quench was the most common method.

I have my own speculations though....
And these are speculations, based on nothing else than observing the nature of medieval steel and how such a steel would react to basic heat treat routines. We should realise that one single method will produce different results depending on the skill and insights of the individual craftsman. This is the nature of simple steels of variable quality.

If we look at different blade types we can expect them to respond differently to the same type of heat treat.
The most common method seems to have been a slack quench during most of what we call the medeival period. That involves an interruptd cooling of the blade so that remaining heat in the blade leads to a empering of the martensite without the need for a separate annealing after quenching. This method can lead to very variable results depending on the skill of the one doing the heat treat. You can get anything from barely hardened to something that is really quite excellent.

Taking into account different cross sections and the fact that the simple carbon steel of medieval times did not have a high hardenability (meaning that only rather thin sections will reach full hardness, while the core will remain soft), we can see that different blade types will typically react different to the same treatment.
A wide and thin blade will trandsform in a higher degree to martensite, than would a narrow and thick blade.
A soft core is only good in that it will counteract breaking or act in shock absorbing. It is weaker than fine grained tempered martensite, however.
Unhardened steel will give at a lower load than tempered martensite. (all this is rather complex and other factors ill also come into play)
Perhaps it is possible to say in a simplified way that a narrow thick blade (like a type XVII) will have a hard skin and a soft core that will help in shock absorbing. Such a blade can take quite a pounding and would bend rather than break if overstressed.
A wide and thin blade (like a type XIIIa) will be highly flexible if made properly. The full hardness will reach almost to the middle, leabving very little in the way of a soft core. It will be able to work like a leaf spring. it will be much more springy than the type XVII. If properly made such a blade would aslo bend before it breaks, but not as much as the type XVII.
I have a feeling different blade types were developed also to make most of the different results the het treat would give. Stiffness, flexibility and edge retention are three important factors in blade design. Just by varying the cross section but keeping heat treat methods the same and using the same steel, will produce blades with markedly different properties. This effect is most noticeable when using simple steels with low hardenability.
In our time we use steels that have higher hardenability and regularly result in more even results. It is difficult to make direct comparisons between medieval methods ansd thier results and what we do today.

This is all rather short and simplified but might present an idea.

[Wolfgang Armbruster]

That was a interesting read
Thx a lot for this informative post. I have another question that has been bothering me.
If a Type XVa or XVII with a thick spine gets hardened by water-quenching after being heated up for maximum carburizing isn't that a similar effect like the one seen on Katanas?
I mean, the edges and the outer surface get penetrated by the carbon and therefore harder than the inner body which stays softer. That sounds a bit like differential hardening without clay-coating but simply due to the blade geometry.
Should such a blade be tempered at all(given that the steel allows a high degree of hardening)?
Are the edges of such a sword rather martensite or pearlite?

Maybe I' getting it totally wrong, but that's how it sounds to me.

[Peter Johnsson]

The heat treat of a narrow, thick blade of simple cabon steel will get some similar effect as that done with a Katana, yes.
The edge will be hard martensite.
The spine will also be martensite, but slightly softer or a mix of martensite with other structures.
Towards the core you will gradually find a mix from martensite, bainite/troosite to pearlite.

This is an effect of varying cooling speeds depending on mass and surface. Etching such a blade can produce something like the hamon of a japanese sword.

With contemporary steel that have higher hardenability you get a less dramatic effect of varying hardness and a transition to martensite deeper down into the blade.

I am sorry if these posts are very short. A subject like this really demands much more thorough ansvers to be really good.

For us today it is easy to see alternative solutions to many problems relating to blade design. We can choose other steels or other heat treat methods to achieve better results.

If we try to understand the historical aspect of the craft we are better off to try to understand why swords were made the way they were within the limitations of the material and methods of the time.
I do think that new blade types developed not only to become "better thrusters" or "better cutting swords". I think there are intrinsic effects from the blade shape and material used that gave certain effects together with the material used and heat treat method applied.
It is difficult to give clear rules here, but keeping in mind how steel of medieval type reacts in heat treat (as we think they managed this), and apply this to blade types we might see other reasons for the designs than is commonly accepted.

As referense please read this excellent article by Kevin Cashen at the ARMA site:
http://www.thearma.org/essays/impacts.htm

[Wolfgang Armbruster]

Thank you very much for the fast reply
Although I'm far (light years) away from being an expert I think I'm getting a better idea how steel needs to be forged and how it was done.
The idea that different blade types were also developed to perform differently under the same heat-treatment sounds very plausible to me.

[Aaron Schneiker]

thanks much for the clarification and the useful information!

-Aaron