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It is generally agreed that our ancestors first learned to reduce iron ores to pure iron around 1200 BC. The iron formed without melting in a charcoal fired furnace and sintered together with abundant slag inclusions into a mass called a bloom. It had to be hot forged to remove most of the imputities or ‘slag inclusions’. This bloomery iron was very low in carbon, around 0.06%, and was full of elongated slag inclusions. It was the main source of iron (except in China) up to the late 14th century when European smiths learned to make their furnaces higher, run them hotter and produce a cast iron which was then processed to a wrought iron that was amazingly similar to bloomery iron. Virtually all early steel was made by carburizing the bloomery iron in charcoal fires with the CO / CO2 ratio controlled properly to give high carbon potentials in iron at temperatures above around 850oC where the kinetics of carbon diffusion was appreciable. It was not until the late 18th century that the element C (carbon) was discovered and it was even later that it was learned that the key factor in making hardened steel was adding the element carbon to iron and quenching from high temperatures. Nevertheless early smiths successfully produced martensitic steel as early as 1200 BC |
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Historical Background of Damascus blades |
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There is a general myth in some of the popular literature that genuine Damascus steel blades possess outstanding mechanical properties, often thought superior to modern steels. This idea was shown to be incorrect as long ago as 1924. A famous Swiss collector, Henri Moser, donated 4 genuine Damascus steel swords, one with a non typical carbon content and microstructure, to B. Zschokke, who performed extensive careful experiments including metallographic and chemical analysis in addition to mechanical testing. A series of bending tests compared samples from the swords to a pattern welded blade and a cast blade from the famous German knife centre in Solingen. The 3 good Damascus blades showed significantly inferior bending deflection prior to breakage than the 2 Solingen blades in spite of the fact that the Brinell hardness of the 3 ranged from only 193 to 248, compared to 347 and 463 for the pattern welded and cast Solingen blade, respectively. This is not too surprising in view of the now well known fact that toughness of high carbon steels is inherently low; the Solingen blades had carbon levels of 0.5 to 0.6% compared to 1.3 to 1.9% for the 3 Damascus blades. The reputation of Damascus steel blades being superior to European blades was probably established prior to the 17th century when European blades were still being made by forge welding of carburized iron. It is hard to avoid embrittlement of such blades due to imperfect welding during the forging process as well as difficulty with the carburizing process. |
