Lancelot Chan wrote: |
Thanks PJ for your info. I've shot Mike an email to see if I can get a replacement with more consistent blade hardness along the length and original sharpness or not. We'll see how it turns out. |
Hey Lance!
One thing to be aware of before you continue your plans: There will always be a varying hardness in the blade towards the forte of a sword made from carbon steel.
This effect is best known and observed in the Japanese Katana. The hamon is always very narrow at the base of the blade and typically grows wider towards the point. This is a nataural effect of changing cooling rates in different thicknesses of the blade. The clay coating of the katana makes this more visible and also manipulates the effect to varying degrees. In a katana this is viewed as part of the beauty and design of the blade. IT is actuallyappreciated as an aspect of quality. A varying hardness in a european sword should not be seen as a flaw. It is part of the design, or a natural cause of the blade shape, if you like. This effect can be made good use of if you let the cross section of the blade vary just right as it grows thinner towards the point. This effect is most easily observable when simple carbon steels are used for the blade, less so when tool steels are used. These modern steels will also show a varying hardness, but less so and probably less than what is obvious when a hardess file is used for testing.
I have spent much time thinking about your test results since I last posted one day ago, Lance. On second thought I do not think the results are that surpricing or perhaps even that detrimental. I cannot really say without seeing how or what you have done in testing.
Without knowing where the tests were made it s very difficult to know if the result shows a flaw or just a natural and actually beneficial effect.
We know that historical european swords show great variation in hardness when tested. I think there is more to this that we often realise.
Results showing varying hardenss is partly an effect like the one you observed in the Brescia Spadona: the blade will always show different hardenss in different parts. It is not so strongly expressed as the Japanese katana, but not totally different either: the spine will be softer and the edges harder, the base will be softer and the point harder. IN a quality ´word this is actually as it should be; expecting otherwise will invite other problems. At the base there might be a rather narrow line that has "full" hardness with most of the material behind it showing a mix of martensite, bainite and fine pearlite. This structure makes for good resiliency in a carbon steel blade. If you test the hardness somewhere behind the edge you will see a lower hardness than if you test the very edge. This is nothing to be concerned about. It is just how these things go.
Most people are not aware of this effect, its reasons or effects. Most only know to expect a hardenss around 55 HRC in a quality sword. At the base of the blade you need a high level of resiliency, not neccesarlily a high hardness.
Archaeolometallurgists who do tests on ancient swords often get strange and surpricing results that seems to show that knowledge of heat treating was low among ancient smiths. Without having direct proof I do suspect that something is overlooked in the procedure of these tests: the areas of martensitic structure could often have been eaten away by rust. Since only the edge and a relatively thin layer of the "skin" of the blade will reach full martensitic structure in a fine grained medium carbon steel and the core will show vaying degrees of fine pearlite, bainite and some traces of martensite in the outer areas, it is easy to draw the conclusion that the quencing was incomplete if the surface layer and the edges has been eaten away by rust.
If the test is also taken at the base of the blade (where most material is left) the structure will surely show a lower level of hardness than the outer two third of the blade (where the cutting is made and more material is eaten away by rust).
When a test on a blade is made the result will be greatly influenced by the insights in the practises of sword heat treatment that the tester might or might not have.
So, in short: do not expect a sword with a carbon steel blade to show a constant hardness along its complete length. This is not natural. If you choose a steel with a higher alloy content, like a modern tool steel, the hardness will vary less since it responds less in variation in cooling rate (that is why you do not make katanas from high alloy steel: they need to be made of a steel with pretty low hardenability to show an attractive hamon).
You can choose to make swords from a number of different steels within certain limits. Whatever you choose it will infliuence most every work procedure the blade goes through: shaping (forging or stock removal), heat trating, finish grinding and sharpening. You cannot pick one aspect, like hardness, and say it is the most important one. Grainsize is equally important for edge retention and resiliency. You cannot test for grain size with a hardness test.
Hardness is just one af many equally important aspects in a sword blade. Grain size, alloy content, edge type, blade type, distribution of mass, dynamic aspects, cross section...I could go on. A thing like hardness must be blanced against all other factors in a blade. Blade shape, cross section, intended function and steel used are perhaps the most important ones.
If you do not trust the makers philosophy and approach in manufacturing procedures, it might be better to turn to some other maker.
I can understand how at first a result of 40-45 HRC in hardness makes you concerned. Now seeing this in perspectve, I am no longer convinced it actually is that detrimental. If this hardenss is read at the base of the blade and some distance away from the edge, this dramatically changes how we should read the result.
Personally I do not find the exact hardness of the forte of the blade that important. As long as it allows for a spring effect and high resiliency, then all is fine.
The failing of the edge of your sword is not at all relatee issue and must be judged separately. That was the result of other issues: the fineness of the cutting sharpenss, the nature of the target and the fact it was not stationary or moderately mobile (like an attached bodypart), but spinning through the air. All those factors will affect the risk of edge failiure. The level of hardenss at the base of the blade is not a an issue here.
These things are very complex and interact on many levels. It is very difficult to answer this on a thread on a forum like this.
Lance, believe me when I say I welcome your thorough methods in testing. I have found them very interesting to take part of and have certainly learned from them.
From past experiences I have learned that topics on forums discussing the quality of swords often leave an echo of undisolved issues. Swords or even makers can get a stigma: "I heard that the sword XXX is ctually a pound too heavy"..."I know from someone who owns such a sword that it is too soft in the blade"..."I heard on a forum swords from this maker fail in cutting tests"...
It is sad to see how often good discssions boils down to ideas of shallow ignorance.
I do hope our thread on this forum will not lead to such conclusions, but that we instead have all gained a broader understanding.
Best
Peter