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Metal–Crucible Interactions
Published in Nagaiyar Krishnamurthy, Metal–Crucible Interactions, 2023
Crucible steel was also made by melting together pig iron or cast iron, iron, sometimes steel, and often sand, glass, ashes and other fluxes in a crucible. In olden days using charcoal or coal fires, temperatures high enough to melt steel or low-carbon iron could not be reached, but temperatures high enough to melt pig iron were reached. The process therefore consisted of melting pig iron, and by soaking wrought iron or steel in the liquid pig iron long enough, the carbon content of the pig iron was reduced as it slowly transferred into the wrought iron. Crucible steel of this type was produced during the medieval era in south and central Asia. This steel was then forged, filed or polished to make weapons.
Iron
Published in Robert Routledge, Discoveries and Inventions of the Ninteenth Century, 2018
Another method of dealing with the blister steel is to charge crucibles or pots having covers with 50 or 100 lbs. weight of the broken-up bars, and subject the crucibles to a strong heat in a reverberatory furnace, when the metal melts, and at the proper moment the contents of a great number of pots are almost simultaneously poured into a mould to form an ingot. The result is a very uniform steel of the finest texture, known and highly esteemed as cast steel or crucible steel. This steel is much more fusible than iron, but less so than cast iron.
Historical overview on the development of converter steelmaking from Bessemer to modern practices and future outlook
Published in Mineral Processing and Extractive Metallurgy, 2019
Early primitive furnaces were of bowl type and often constructed in a hillside to exploit natural draught of air. In more advanced furnaces air blast was generated by bellows. The bloomery process governed iron/steel making technology for the next millennium and beyond, known, e.g. as Catalan hearth (Thomas 1999). In these early furnaces, formation of metallic iron took place in the solid state, and the product had low carbon content. There was no need for converting to decrease carbon content by oxidation. Ancient blacksmiths knew from experience how to decarburise or carbonise to the desired final carbon content in their forge furnaces. In the course of time, larger bloomeries were erected and equipped with efficient water-driven bellows. Then temperature inside the hearth could rise too high leading to carbon dissolution into iron, the melting point was reached and the iron bloom melted. The blast furnace was thus accidentally discovered. Towards the end of the Medieval Age blast furnace technology was gradually established in Europe. In China liquid iron was known much earlier, about 200 BCE and in India somewhat later. Liquid iron could be utilised in castings but it was difficult to convert iron into steel. Effective decarburisation methods were not available until the eighteenth century. To convert liquid cast iron into steel finery methods were developed, like Osmond and German forges, Walloon, Lancashire and Franche-Comté hearths, from the late Middle Ages to the nineteenth century (Wiborgh 1904). These methods were based on melting of pig iron by combusting charcoal and slow decarburisation refining in semi liquid/semi solid state. In the eighteenth century, more efficient refinery methods were developed. The puddling furnace was a kind of reverberatory furnace. Pig iron was melted by flame from a fireplace, where coal or coke was burnt as fuel. After melting the charge, carbon in the molten iron was oxidised by air by stirring the melt with puddling bars. When the carbon content decreased, the iron solidified and it was gathered by the puddler into a single mass, pulled out and worked under a forge hammer, and then the hot wrought iron would be run through rollers. By using the puddling process, it was possible to produce steel in one stage, faster and with less fuel than with the earlier methods. Another process, crucible steelmaking was developed by clockmaker Benjamin Huntsman in 1740. Cold pig iron was charged with slag-forming flux in small crucibles made of clay and graphite, and then melted by combusting coke. Then low carbon steel was added and melted to get liquid high-carbon steel (e.g. 1% C). The product received was hardenable steel and suitable for tools, mechanical parts etc. Crucible steel remained in a strong position for special grades like tool steels until the first half of twentieth century. The aim of the process was actually not in decarburisation but rather in combination of high- and low-carbon metals. The ancient Indian wootz steel was based on a similar principle (Srinivasan and Ranganathan 2004).