Ancient Japanese Steelmaking Processes
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Ancient Japanese Steelmaking Processes By Shinnosuke Yamamoto * Methods of direct steelmaking were evolved in Japan several thousand years ago. The steel prod uced was used to make famous Japanese swords. Many archaeologists and scientis t s 1 ):'!):!} have carried out resear ch on these ancient iron and steelmaking processes. It cannot be said, h owever, that their origin and theoretical aspects have been thoroughly and fu lly investigated. At the present time, there is strong proof to support opinions that the origin can be traced back to about 2,000 years , ago. The iron and steel making process of that time is generall y call ed the "Tatara" furnace process, and the process was different from that used in the Asia n a rea. This furnace was r ectangu lar in Photo 1. Prototype of the "Tatara" furnace shape with a low shaft, and the furnace body was made of clay with heat-resistant properties. This furnace is s hown in Photo l. This pictures a type of steelmaking furnace, and there was another kind of furnace for making pig iron. This type of furnace is 850 mm X 2,100 mm in diameter and 1,150 mm hig h. Its des ign is shown in Fig. l. There are 18-20 tuyeres on both longitudinal s ides of the furnace, and these tuyeres come out of the bell ows on both sides. The fou ndation part of the furnace does not appear above the ground, but t his foundation is three times as high as the furnace itself so that it can keep complete heat-insulation • and prevention of moisture penetration. As a raw material, only iron sand was cheuged. This, how ever, was a type of magnetite containing titan ium. Its chemical composition is shown in Table l. As can be seen from this table, the impurities con tained in t his iron sand were very few. It con tained on ly sm a ll amounts of s ulphur, phosphorus, vanadium a nd titanium, but the amount of re mainder of these impurities in the finish ed blister Fig. 1. " Tatara" furnace • steel was extremely small. This is shown in Table 2. The life of the furnace, i.e., one cycle, was about During one cycle, the majority of the pig iron 60 hours, and during that time, it was norma l to flows out of a few holes bored in t he lower front obtain 2,900 kilograms of b lister steel and 2,250 pa r t of the furnace, but ordinarily t he rema inder kilograms of pig iron. In order to produce these stays within the "Ker a" lumps which are the blister products, 16,900 kilograms of iron sand and 16,000 steel. Consequently, the "Kera" is a mixture of kilograms of charcoal were cha r ged. The blistel· blister steel, pig iron, acid slag and a small a mount steel was called "Kera" and the pig iron, "Zuku". of charcoal. This "Kera" is s hown in Photo 2. Table 1. Chemical analysis of a typical iron sand (%) T. Fe Fe203 FeO S i02 CaO MgO Ab0 3 Ti02 MilO V20S P S .. Masa " iron sand 59.00 I ~ 24.72 8.40 2.24 1.54 2.34 1. 27 0.05 0.258 0.064 0.009 " A kome" iron sand 52 .07 52.71 19.55 14.50 2.68 0.94 4.98 5.32 0.34 0.369 0.095 0.026 I - Beach iron sand 59 .00 I~ 24.72 4.90 2.36 0.37 1.79 6.98 0.03 0.295 0. 121 0.032 River iron sand 62.55 64.84 22.13 2.24 0.50 1.10 4.51 5.23 Nil. I 0.243 I 0.061 0.014 * Head of the Technical Department and Managing Director, Hitachi Metal Industries, Ltd. 49 Tetsu-to-Hagane Overseas Vol. 1 No.2 September 1961 Table 2. Chemical analysis of blister steel (?o ) C S i Mn P S Ni Cr V Ti Cu As Sn "Kera .. No. I 2.6·1 0.03 tr. 0.015 O.O I ~ nil. 0.05 tr. 0.012 0.003 0.002 tr. "Kera .. No.2 1.44 0.21 0.02 0.005 0.003 nil. tr. tr. 0.014 0.002 0.001 tr. .. Tamahagane " No. 1* 1.56 0.06 tr. 0.023 0.005 nil. tr. tr. 0.024 0.001 0.001 tr. * .. Tamahagane " means a selected bliste r steel. , Photo 2. A raw block of the blister steel" Kera " Photo 3. Pearlite and cementite structure in the blister This piece is 3,000 mm x l,OOO mm and 300 mm thick. steel " Kera" (x 125) (5 6) This piece was taken out after the operation of the "Tatara" furnace had been completed and the re • maining furnace walls were tOl"ll down. The piece wa::; broken into pieces as large as 50-100 mm by a drop hammer pulled up by a water-wheel and then placed in classifications according to quality for different uses. The special feature of the "Ta tara" furnace was that blister steel of high quality could be obtained directly from iron ore, and it was composed of pearlite and cementite structure as shown in Photo 3. The structure of the small • amount of pig iron in the "Kera" is as s hown in Photo 4 and ledeburite is present. " Kera" Refining Theory The first stage or the first period of the opera Photo 4. Ledeburite structure in the blister steel " Kera " tion is the stage of regeneration, and it was begun (x 125) (5'6) by charging the furnace with a large amount of charcoal. Appropriate air blasting from the tuyere charged instead of the iron sand. This kind of group graduall y makes the furnace temperature iron sand containing titanium has such a low high€l", and when it gets to a designated tempera melting point that it melts easily. Soon after it ture, about 7.5 kilogra ms per unit of iron sand are melts, it is reduced to metallic iron having contact charged. The iron sand is charged in layer form with the white hot charcoal, and it changes into alternately with the charcoal, and the amount of molten pig iron by absorbing carbon. At the same charcoal is more than three times that of iron sand. time acid s lag containing iron oxide is formed. The charging work is carried out continuously for These molten materia ls collect in the furnace 6-8 hours in order to in crease the total charged bottom. Then heat is applied to the furnace bottom volume. The iron sand charged in this stage is accelerating the regeneration and the molten the kind which contains titanium and which is materials flow out of the holes in the lower front called "Akome". Sometimes beach iron sand is of the furnace. 50 Tetsu-to-Hagane Overseas Vol. 1 No.2 September 1961 The second stage is t he intermediate period; the proceeding very well , most of the phosphorus is t r ansition period between t h e above-mentioned carried away with t he melted pig iron. stage a nd the third stage, which is the initial step The "Kera" shaping process can be explained in shaping the "Kera". The total ch arged vo lume mo st easily in refere nce to t he well-known F e-C during this stage is more t han three times t hat in equ ilibrium diagram: when the iron sand is direct t he first stage. And in this case, t h e charged iron ly reduced by the white hot charcoal, t he iron sand containing less t itanium in it than in the easily absorbs carbon a nd becomes molten pig iron. first stage is cha rged. In this stage also, in the Tn the equilibrium diagram, Fig. 2, for example, if first half of the operation, practically all of the the molte n iron at .r point drops on top of the molten pig iron and s lag are di scha rged outs ide t h e "Kera" lump, it is cooled and finally arrives at 11 fu rnace. However, t he molten pig iron gradually point on the E-F line. During t his process, for coll ects in the furnace bottom, becomes cooled, and instance, "Ker a" with a car bon co ntent of about turns into half-melted lumps. Because of the 1.15';, is separated at t he? point on the D-F line equilib l' ium r atio, it r eleases carbon to some extent. and "Kel'a" with a carbon co ntent of about 1.43" ;, In the latter half of the process, practically a ll the is separated when the molten iron drops f urther pig iron remains at t he bottom of the furnace. in temperature and reaches II' point. From t hi s This fact is caused by the cooling eff ect of t h e phenomena, it is known why the composition of the "bear" made in the beginning a nd t he widening of "Kera" lump is not uniform. However, it is con the space between the t uyeres which face each sidered t hat unifo rmity can be attained by diffusion other. The reason for widening of this space is as of t he carbon in the high temperature f urnace. foll ows : along with t he rise of f urnace temper a Indil'ect reduction wit h CO gas does not seem to ture, the walls of t he fu rnace a r e eroded by t h e be so predominant in t hi s operation.