Want to learn more about steel metallurgy? See our metallurgy courses page. Tempering is used to improve toughness in steel that has been through hardened by heating it to form austenite and then quenching it to form martensite. At these temperatures the martensite decomposes to form iron carbide particles. The higher the temperature, the faster the decomposition for any given period of time.
The micrograph shows a steel after substantial tempering. The black particles are iron carbide. Untempered martensite is a strong, hard, brittle material. The stronger and harder it is, the more brittle it is.
The strength and hardness is a due to elastic strain within the martensite, which is a result of too many carbon atoms being in the spaces between the iron atoms in the martensite. Our Medieval predecessors thought of it as hard or soft iron or as steel being a purer form of iron then the iron with no carbon. They would then strive to add characteristics to the material using ingredients that exhibited these attributes from their surroundings that they desired.
Dr Fabrice Cognot, Phd described it as the medieval craftspersons intention to change the materials temperament as opposed to a modern concept of temper being influenced by the process and recipes described. As we saw in part 1 the medieval smith had an experiential reference base to work from.
Using tradition and simple tools they were able to craft the great metal work we see from this period. Pol Hausbuch MS a illustrates the understanding they had of what types of material and hardness they needed for different objects. We will look at some of these and see the intersection of our understanding of the process with theirs.
Medieval smith tools. We start with the tools to make weapons. Blacksmithing was known as a base art one on which all others must rest for the tools to do most other things must come from the smith. They see the different elements contributing their characteristics to the final product, we recognize factors that we still use today in heat treatment. Today many smiths use brine as a quenchant instead of water, this is due to the problem of steam envelopes being created in a pure water quench.
This will insulate the piece and slow the quench to a point it will not harden. The salt in brine or the other elements in the medieval quench add particulates to the water or base liquid and the steam envelopes collapses before they can form. Modern steels with their high carbon content and alloys often will need specialized quenching oils and additives to not create cracks or fractures in the material itself. In the medium to low carbon content of most medieval steel these recipes would work well.
The last bit in this description addresses the polish as important as well. It is usually beneficial to quench a piece when it has all of the scale from forging removed. This allows for even heating and hardening.
They are in demand as they are very sharp and retain their sharpness well. Another advantage is that weapon metal is easy to work with and does not leave waste, as any remnants can be turned back into powder and re-used. Modern metallurgy is aiming to achieve zero waste products and clean production.
Weapons do not have any miraculous power: on the contrary, they have the power to kill, but swords, blades and knives should not be viewed exclusively in this context. The evolution of weapons is inextricably linked to metallurgical progress. Where did it begin?
With malleable copper, which with one forging gave a thin, sharp edge. And where has this led? To chemical elements being added, to powdered steel, and to production optimisation and automation.
And what does the future hold? Certainly, metallurgists can surprise us; the question is not when, but how. Steel plates. High strength steel Structural and general use steel Boiler and pressure vessel steel Machine building steel Steel for large diameter pipes, offshore structures and energy applications Shipbuilding plate.
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