" Tatara" Process*
- A Pig Iron- and Steel-Making Process, Transmitted from Ancient Times in Japan -
By lukichi KOZ lIka**
Sy n op sis at " Cha-no-Yu ") were m a d e from it. From Gncient times 111 j ajJa n Ihere are excellent swords called In the following the a uthor d escribes " T a tara" " NijJjJon- t6" as a symbol of " Samurai" . The)' are weLL-knowll and p rocess putting the stress on the direct steelmaking sland high in their aesthetic value aLL over Ihe world. The material of m ethod, " Keraoshi " . " N ijJjJo /l-to" is " Tamahagallc" (c/'ltde steel ) or " H ocho-Ietsu" (c rude wrought iron) produced by " T atara " process which was devel II. The Historical Development of "Tatara )) oped jJeCl.tiiariy ill j ajJa Il alld has bem hallded down to us f rom ollr Process ancestors. This pajJer briefly describes the method of " Totaro " /J I"Qcess and From the a rchaeological viewpoint, it is regarded several malters related to it. that the process was brough t to j a pan for the firsL Lime from the Asia tic Con tinent in the first a nd second I. Introduction centuries. The primitive m ethod of the process ex R aw m ateria l used in " T atara " process is thc isted in the fa bulous age of j a pa n, when our a ncestors. specia l iron sand ca lled " M asa " or "Aka m e" whi ch manufactured by aid of natura l draft a mixture of is mined only in San-in distri ct, sou th-wes t pa rt of iron, steel, sponge iron, slag, a nd charcoal in a hole the m a in isla nd of j apa n . C ha rcoal is used as fu el. which is dug u nderground. After destroying the The sha ft of the furnace is low a nd recta ngula r, a nd furnace, this mixture was forged by ha nd into swords, the body is made of fire clay. Photo. 1 shows the weapons, a nd agricul tural instruments. furnace bod y. By the early 13th cen tury " T atara " process was improved to the present type a nd the process beca me to be operated indoors instea d of outdoors. In this way the direct steelma king industry in j apan was established, earlier than the establishment of it in E uropean countries by one hundred and several decades. Speaking of the development of iron sand sm elting, the development of bellows must be considered. The history of blast in j apa n began with na tural draft , a nd then leather bag bellow, blow pipe, a nd ha nd worked reciprocating bellow " Sashifuigo )) were de veloped . The last one was a lready contrived in the Photo. I. " Tatara" fu rnace eighth century in j apa n, a nd a ft er tha t several inven- • tions a nd improvements were introduced in it. The By " T atara " process a re produced sm a ll lumps o f motive power of bell ow cha nged from ha nd power to crude steel " T ama hagane ", blister steel " H era " treadle as we see a n example in tread bellow, " F umi (" T a ma hagane" incl uded in it), pig iron, etc. In fui go )) (see Photo. 4). W a ter mill had not been used the p rocess there a re two kinds of methods : one is as the power until the early 20th century. It is be direct steelmaki ng method ca ll ed " K eraoshi " by cause the wa ter stream nea r the furnace was regarded which m ore crude steel is p roduced tha n by the other moisturizing the fu rnace, a nd it was too diffi cul t at method , a nd the other is pig iron-making one " Zuku that time to set bl ast pipes over long dista nce. os hi " . But these methods a re so simila r in m a ny Around the la te 17th a nd earl y 18th cen turies, when points tha t the a bove-mentioned products are more the feuda l system in j a pa n was es ta blished, the p rod or less produced by either method . ucts by " T a ta ra " process became a n important Crude steel obtained is formed in to the shell of so urce of revenue in som e p rovinces. Thus the process sword by repeated forgings, while b lis ter steel a nd pig was developed more a nd more, and it became the iron a re converted to wrough t iron " H ocho-tetsu " present accomplished a r t. which is used as the core of sword . The furnace was opera ted by a chiefforem a n called H owever, the products were used not only a s the raw " O motemurage" a nd fo ur assistants. Building of m ateria ls of the sword bu t a lso as importa n t ma teria ls the furnace, cha rging of the m a teria ls, pulling ou t of of hig h q uality tool steels. As pig iron has specia l the p roducts, etc. were carri ed out on " Murage " 's q ua lity, specia l castings (for examp le, teakettle used own responsibili ty. H e opera ted the furnace in ac-
* O rigina ll y publi shed in T etsu-to-H agalli, 52 ( 1966), 1763 in J apanese . English version received April 12, 1967. ** Ya sugi works. Hitachi M eta ls, Ltd ., Yasugi.
( 36 ) Report Transactions ISIJ, Vol. 8, 1968 [ 37)
Section aa
G.L. G.L.
"u '"E • ~
Section bb ....""
G.L.
Charcoal
4352 ""~ Fur. bottom, "Hondoko" ----t Air chamber
------l Dry clay "" Shingles '"'~ Round stone, "Bozuishi" -----+
Ditch ""'"' • '"' Fig. I. "Tatara" furnace, (mm), a scale 1/40
cordance with the art succeeded from his forefathers, adhered on its surface are chipped off. Then it is as well as with his own several experiences. cut off by machine or hammer to select the parts which The operation method was kept secret and handed contain a lmost constant carbon. They are crude down to only his heir, consequently if " Murage " steel called " Tamahagane". died out, the method was not transmitted to the The remainder of the product is used as the raw younger generation. materials of wrought iron, crucible steel, and tool steel. III. Products and Their Treatments The amount of the pig iron produced in the process By " Keraoshi ", direct steelmaking method in is about 20% of the total products. "Tatara" process, an iron block of about 1.1 x2.9x 0.27 m (in thickness) is produced in the furnace. The IV. Construction oj Furnace block called "Kera" (blister steel) is a mixture of The furnace is constructed at the weathered and steel, iron, sponge iron, pig iron, slag, and a few pieces perfectly dried granite zone in San-in district. of charcoal. As Fig. I shows, digging about 3.5 m underground After the furnace is destroyed, the block is pulled is made in the centre of a ditch that is an outlet of out a nd cooled in air, and then foreign substances moisture. On the ditch, round stones (about 40 cm
Report ( 38 ) Transactions lSI], Vol. 8,1968
130-+---430 ---'---';:-Td 320 110 130
"----445 --!---jl/
View a Section b
r---375 - '----!I"
•
View e Section d
10? ~mw~ - ::T ~ tur:re 145 ISO .. ~ .. -
Report Transactions ISH, Vol. 8 , 1968 ( 39 )
Table I. Composition and size distribution of fire clay (% ) with air chambers through the boxes "Tsuburi" which distribute air to each tuyere. 2 3 The tuyere is bored through the furnace wall by Composition ~ I wooden auger when the furnace shape is completed. Si0 69.24 68.54 2 65.59 As shown in Fig. 2, the tuyere is enlarged at the middle A I 0 12.24 13.12 18.63 2 s point of its length, because in this process more amount Fe 0 5.24 4.44 4.82 2 s of air is required, as the operation goes on and the CaO 0 . 15 0.25 0.23 block of blister steel grows. That is one of the char MgO 0.30 0.26 tr. acteristics of direct steelmaking process "Keraoshi ". The distributing air box and the tuyere are joined Si02/Remainders 169. 24JI 7 . 93 68. 54JI8. 07 65.59/23 .68 by a bamboo pipe " Kiro " (3 to 4 cm in dia.) which Mesh I 5 20 32 60 100 · 100 I Total has an iron cap at apex. up up up up up down After the construction the furnace is dried by fire Size distribution 110 .2 45 16.4 17 .5 8.7 2.2 I----WO- woods for about 15 hr, and then the operation of the The corpuscles of the sa mple are el iminated furnace is to be started. __ ~ decantation. Notes The house in which the furnace is installed is called 2 There is no iron sand in the residue. " Tatara " house or "Takadono ". - '-----'------Fig. 3 and Photo. 2 show a " Tatara " house which
• Fig. 3. " Tatara" hOllse, (mm), scale, 1/ 100
en S ,.,.<'> I . I ~ci Stock room of charcoal. Stock room of Iron sands. Stock room of charcoal . 00 "Sumimachi " "Kogan emach i" I "Sumimachi" ': 3 U') :0 0 U') '"3 -~. U') 0> .., '" <'> 0 I :0-:0_.'" '0> 1f----5455---- U-----7273 +------III--t---5455-----i1 :0 ~ -;;v ... v o CIl • ... 0 ... " o 0-" o oo I I 1 o TUyery-~ T o --11------+------l-I+-IL Furnac0lt-::l----""-----!----t Rest I <- room '-.... - / g ~ Rest fur '-....-, room forem en I I Air chamber ~ @ ! ~- f--272S-+-2066 - ~ 3~40--2067-! en o <'> , :><' -i", "g..o..'" ..,0> 2727 Stock 3" 8.. room ~~ Stock yard of fire cla y, -':(b <'> 'Tsuchimachi" Door ii> c======~oDoor of theo======~~~~~====== Report ( 40 ) Transactions ISIJ, Vol. 8, 1968 remains the same as three hundred years ago. column. (see Table 2) The bellow was moved by manpower in ancient V. Another Equipments of " Tatara" Process times. The followings are typical examples. 1. Bellow (I ) Tread bellow" Fumifuigo " (see Photo. 4 and As shown in Photo. 3, reciprocating wooden bellows Fig. 5) are used in the process. Four bellows are worked (2) Balance bellow " Tembinfuigo " (see Photo. 5 in a set by water wheel (see Fig. 4). A set of bellows and Fig. 6) (The shape looks like a balance.) is able to send about I Nm 3 of air in a minute, which However, water wheel power takes the place of is calculated by the numbers of revolutions of water manpower and the reciprocating bellow came to be wheel, and the pressure is 20 to 30 mm by water used in general. 2. Large Drop Hammer, " ado " The hammer is used to cut roughly the block of bl ister steel (see Photo. 6) into pieces of 500 to 300 kg, but not to crush but to cut along with the difference Table 2. Relation between R/min (water wheel) and amount of air R /min of wheel 23 24 25 27 30 31 _A__ m_ o_u_n_t _o_fa_i_r _(JV__ m_ 8_/m__ in_ )~1 __2_2 ___ 2_3____ 2_ 4____ 26____ 29____ 3_ 0_ ... Ph oto. 2. " Tatara" house" Sugaya Tatara " Photo. 4. Tread bellow" Fumifuigo" • Photo. 3. Wooden bellow" Sashifuigo " Fig. 5. Tread bellow " Fumifuigo " Fig. 4. cp Wooden bell ow" Sashifuigo", (mm). - ti!l'lIl!!l!!lLfI.lE. ++-1a::::IEtt~~BH BHHEEIlIHl!I - Water wheel Scale, upper 1/20, below 1/40. c:Jljb Report Transactions ISIJ, Vol. 8, 1968 ( 41 ) in grain size or glaze and fine cracks, etc. So in this and more, a nd at the same time, to cut off impurities work a special art and rich experiences are required. adhered on the surface of the block. Weight of the drop ha mmer is 1.2 to 1.5 t and drop Fig. 8 shows the small drop hammer. distance is 5 m in height. Fig. 7 shows the large These small pieces of the block are further cut by drop hammer. hand into smaller pieces about I kg in weight. In There is another way of cutting the block by quench this way crude steel is obtained (see Photo. 7). Cut ing the block in the pond called "Kanaike". But ting at this stage has another meaning, that is, to this is not used in these days, because the yield of produce the smaller pieces of crude steel containing crude steel is very low. equal amount of carbon. 3. Small Drop Hammer, " Kodo" VI. Raw Materials and Products in " Tatara " Weight of the hammer is 300 to 200 kg a nd thc drop Process distance is I to 1.5 m in height. Operation of the In " Tatara " process two kinds of iron sands are hammer depends on manpower, but it can not work used as raw materials: one is " Masa " which is used so q uickly as general drop hammers. The hammer, therefore, is rolled up by the wheel which a man turns as a mouse turns a mouse wheel. The function is to cut the block above-mentioned into small pieces more • Cast iron 400"' -H--I~~-:! C.L. Photo. 5. Balance bellow" Tcmbinfuigo " Fig. 7. Large drop hammer " Odo ", (mm), scale IfIOO 400 • f------4400---~-I Fig. 6. Balance bellow" Tembinfuigo " Photo. 6. Blist er steel " Kera ", 2 920 X I I 00 X 250 mm Fig. 8. Small drop hammer" Kodo ", (mm), scale 1/ 100 Report ( 42 ) Transactions ISIJ, Vol. 8, 1968 in direct steelmaking process "Keraoshi", and the From the table it is found that "Akame" contains other is "Akame" used chiefly in pig iron-making more Ti02 than " Masa " and that gangue elements process "Zukuoshi ". These iron sands are pro (MgO, A1 20 3, etc.) are not eliminated completely. duced in San-in district only, and they have dif But in the process of" Zukuoshi " such a high Ti02 ferent properties as compared with iron sands pro content is out of the question because the products duced in other places of Japan. When iron sands (pig iron) are taken out from the furnace in a molten are repeatedly dressed by magnetic separator after sta teo crushed under 200 mesh, Ti02 content in the former iron sands is gradually decreased but in the latter the Ti02 content shows a tendency even to increase. 1. "JvJasa" The iron sand called "Masa" is mined in the granite zone which is weathered by rain water. But the iron content is so small as 1 to 2 % . The furnace is operated with such poor ores and this may be re garded to be one of the characteristics of" Tatara " process. As shown in Photo. 8, the efflorescent hill is destroyed by picks , and washed away to mountain river by water jet, then iron sands and another rocks are rubbed and separated each other. These outflows are taken into five wooden ducts (each 8 to 28m long) which are • put in series (see Photo. 9) and dressed by hand with water. Thus it becomes possible to obtain iron sands containing about 60% Fe with water. Table 3 is data of the composition of iron sand " Masa". From the table we can see that impurities m the iron sand are very small. 2. "Akame " Photo. 8. Open cut" Kiriha " This iron sand is used as materials in pig iron making process" Zukuoshi " and gained in the weath ered diorite zone which included 3 to 5% iron. In stead of "Akame", beach iron sands are sometimes used as raw materials in plants situating in the neigh bourhood of the sea. The compositions of these iron sands are shown in Table 4. • Photo. 7. Crude steel" Tamahagane" Photo. 9. Dressing plant" Toyonagashi " Table 3. Compositions of iron sands "Masa" after dressing ( % ) Com posi tionl T.Fe Fe,Os FeO SiO. CaO MgO AI.Os TiO. MnO V.O, P S Description "Nakagura" 59.0 64.45 24.27 8.40 2.24 1.54 2.34 I. 27 0.05 0.258 0 .064 0.009 " Hanaidani " I 59.98 62.45 20.98 10 .02 0 .22 1.27 1.64 1.54 0.19 0.240 0.060 0.018 Report Transactions ISH, Vol. 8, 1968 [ 43 ) Table 4. Compositions of iron sand" Akame" and beach iron sand after magnetic dressing (%) "::om posi tionl· T.Fe Fe20 3 FeO Si02 CaO MgO AI 20 s Ti02 MnO V20, P S Description Zakka (" Akame ") 54.56 5 1.08 18.48 14 .90 1.60 1.74 4.98 6.82 0.05 0.032 0.036 Beach iron sand 57 . 38 50.79 20.41 5.42 0.11 0.76 2.55 6.55 0.35 0.22 0.078 0.026 (" Gotsu") I Table 5. Quality of charcoal Quality I Humidity (%) Volatile matter (%) Fixed C (% ) Ash (%) Powe r (cal) Descri ption For "Tatara" usc 6.21 to 4 . 27 26.91 to 34.34 51 . 96 to 59. 20 1.42t02.00 5500 to 6000 On the market 6 . 70 to 8 . 10 9 .90 to 12.29 78.49 to 80.39 2.53 to 1.61 7300 to 7600 3. Fuel (Charcoal ) (3) Two kinds of pig irons are produced by " Ta Charcoal used in the process is of low grade as tara" process. They are "Hachime" and "Kori shown in Table 5; it contains some, but small wooden me". The former is the pig iron which flows out parts in it. from the furnace during operation. The pig iron tem " Tatara " process successfully utilizes charcoal perature at its flowing out is very low, so that many • which can be rapidly burnt to ashes. So if charcoals gas bubbles are occluded in it. The latter is the pig on the market are charged into the furnace, it is choked iron which remains in the furnace bottom till the and the operation can not be continued finally. final period of operation and shows a dense structure. Both are white pig irons. The chemical compositions 4. Products (in Detail ) are shown in Table 7. In " Tatara " process three kinds of products are Table 7. Compositions of pig iron obtained: ( I) lump steel" Tamahagane" (see Photo. (%) 7), (2) blister steel " Kera " (see Photo. 6), and (3) Composition C Si Mn P S pig Iron. Pig ------iron "Tamahagane" i a crude steel of to kg --- (I) I 60 " Hachime " 3.61 0.03 0.01 0.033 0.010 in weight. The carbon content is almost constant as " Korimc" 3.55 0.02 tr. 0 .043 0.010 shown in Table 6. Table 6. Composition of crude steel" Tamahagane" (% ) These pig irons were used as raw materials of " Nippon-to" after repeated heating in the oxidizing C Si Mn P S flame and forging, or of special castings. ~ I The properties of the pig Irons are itemized as " Tamahagane " 11.0 to 1.6 0.04 tr. 0.008 0.006 follows: (a) They have very good fluidity. As shown in the table, impurities contained are (b) Their carbon-absorbing rate is very big when very small, moreover, such impurities as P and S react they are remelted. with Si0 and are occluded as slag. Therefore, in (c) Their cementite crystal is very large, com •• 2 making Japanese sword" Nippon-to" from " Tama pared with ordinary pig iron with the same carbon , hagane", the slags are squeezed out or broken up into content. microscopical pieces by repeated forging (several thousand times). In this way "Nippon-to" is VII. Practice oj " Keraoshi " (Direct Steelmak produced with the best cutting quality and with the ing Method in " Tatara" Process) best resistance to breaking and bending. The operation is performed by five workers. Two In other words, steel from" T a mahagane " has the of them are head foremen call ed " Murage" who following properties. manage overall furnace operation on their own re (a) Transition points appear very clearly, that is, sponsibility, and their main works are: the steel is very sensitive against heat treatment. (a) to check the degrees of dryness of the furnace (b) C harpy value is very high. and to decide how to carry the furnace operation (c) It has good deep-drawability. (b) to control the blast (d) It can be welded without Aux. (c) to check the chargings T hese facts prove well how "Tamahagane" IS (d) to operate the furnace, especially to take care pure. of iron sands (2) Blister steel " Kera " is a steel block in which (e) to decide how to operate the next process the carbon content is not constant. "Kera" was according to the conditions of blister steel produced used as a raw material of crucible steel in ancient (f) to take the lead in building the furnace for the times, and today is a good material of tool steel of next operation and drying the furnace. the highest grade. Two assistants called" Sumitaki " help the" M ura- Report :;0 (I) 'd o *'" ~ "" >-i >1 po P (Jl po ~ 1st dJ,\' 2nd da\ 2nl dOl\' 4th dav 5th day o· p Da te. IS No\'. 1935 a.m. 5 6 8 10 12 14 16 18 20 22 24 2 5 8 10 12 14 16 18 20 22 24 2 5 8 10 12 14 16 18 20 22 2·\ 2 4 6 8 10 12 14 rr 6 8 10 .. 1 1500 -0) 1 1 ..-(J) 'TI 1 ~ - • • Transactions lSI], Vol. 8 , 1968 ( 45 J ge ". They are engaged in charging of charcoal in to the end of the period the pig iron and slag occa the furnace. sionally run over the furnace bottom and fl ow out from The rest of the workers is " Komawari ", who is the tapping holes. in charge of treatment of fire clay" Kamatsuchi " for In the centre of the furnace the nuclei of blister construction of the furnace. These five men con steel are formed, which promote the blister steel to tinue to work in a " T a tara" house for four days and grow in the fin al period. The furnace wall is eroded nights (which are the standard p eriod of one cycle of and the furnace area is enlarged at the tuyere line to the operation). the mid point of the tuyeres. In a ncient times, more foremen were needed under " Kudari " (The Final Period of the Operation) the necessity of moving the bellows by ma npower, The charging intervals are shortened from 30 to but the adoption of wa ter wheel power made it pos 24 min so that blister steel " Kera " grows up, but sible to minimize the number of them. charging amount is the same as in the preceding Fig. 9 shows the data of " T atara " furnace oper period. As time goes the furnace wa ll becomes thinner ation which was performed on Nov. 18 to 20, 1935. and thinner, and after a bout 70 hr from the begin The operation is divided into four periods as shown ning, the operation can nol be continued. Then the in the figure. furnace is destroyed a nd the blister steel is pulled out " Komori " (The Beginning Period of the Operation) into the air. After that, the furnace bOltom is set, In this period as the furnace tempera lure can not be a nd construction of the furnace for the next opera tion raised fully, iron sands charged react with the furnace is to be started (see Fig. 10). wall a nd become slag, which are collected in the fur As seen in T a ble 8, the total a mo unl of iron sand ~ ace bottom. The heat content of the slag helps the and charcoal charged is about 15 t respectively. ~urna ce temperature rise for the next period of the The lotal products obtained are about 3 t, of which operation. 600 to 700 kg is pig iron a nd 2.3 to 2.4 t blister sleel, " Komoritsugi " (The Second Period of the Operation) The furnace temperature gradually goes up but is Table 8. Charge amounts of materials 111 each period not high enough to reduce iron sands charged, and Period Iron sand (t) (% ) C harcoal (t) (% ) therefore the greater part of lhem becomes slag. But at the end of this period, pig iron begins to be pro First period 1.60 I I I. 26 8 duced little by li ttle in the furnace bottom. Second period 1. 50 10 I. 35 9 " Nobori " (The T hird Peri od of the Opera tion) Third period 3 .60 24 3.38 23 As the heat content of th e slag a nd pig iron increases Final peri od 8.20 55 8.92 60 enough to reduce iron sands, charging amount of iron Total 14. 90 100 14.81 100 sands is increased from 90 to 11 0 kg each time. At 1 1 ] s t per iod after 2 t05 hr from th e beginning of opera tion 2nd period afte r 10 to 15 hi' f," om the beginning o f ope ration I • 3 rd period afte r 20 to 30 hr from th e beg inning of operation Fin al peri od aft er 68 hI' from the beginning of opera ti on Pig iron. sponge iron Fig. 10. Surmise sketches of the centre secti on of the furnace in each period of operation Re por t ( 4 6 ) Transactions ISlJ, Vol. 8, 1968 Table 9. Compositions of iron sand charged in each period (%) composi ~ 1 T.Fe FeO Fe20 a Si02 MnO AI 20 a CaO P S Ti02 V 20 S ------Period First period 56.55 21.52 66.05 7.90 0.57 5.50 0.38 0.056 0.032 2. 15 0.30 Second period 56.96 20.33 60.50 8.18 0 .57 5.90 0.58 0.077 0.027 2.46 0.27 Third period 58.13 21.20 60.46 7.90 0.48 3.86 0.70 0.077 0.020 2.24 0.29 Final period 59.89 22 .85 62.45 7.45 0 .32 2.87 0.42 0.062 0 .018 1. 67 0 .27 Table 10. Compositions of slag in each period (%) ------Com posi ti 0 n I T.Fe FeO Fe 0 Si0 MnO AI 0 CaO P S Ti0 P e riod ~ 2 a 2 2 a 2 Second period 49.52 58.85 5.40 22.52 I. 23 5.40 0. 18 0.02 5.10 Third period 34.40 39 .47 5.32 30.16 2.28 10.81 1.16 0.03 9 .24 Final period 27.20 30.76 4.62 41.30 I. 16 9 . 21 1.49 0.03 9.51 and the latter contains 700 to 800 kg of crude steel the furnace is not so simple. " Tama hagane ". As seen in Table 10, iron content in slag is consider A typical composition s of iron sand charged in ably high, and moreover, iron sands (not fully reduced). each period are shown in Table 9. may sometimes come down to the surface of blister Slag in each period is various in chemical composi steel on account of low shaft. From these facts it is tion, and it is not possible to present its typical or considered that slags or hot iron sands are reacted with mean values. the blister steel directly and bessemerizing reaction Therefore, in Table lOa tendency of slag composi takes place. tions is given for reference. But such reactions cause a decrease in the amount of products, especially" Tamahagane " . According VIII. Consideration of R eaction in the Furnace ly the chief foreman " Murage " endeavours to keep Carbon content in blister steel" Kera " is not uni that operation condition as possible as normal so that form, but crude steel "Tamahagane" obtained by iron sands charged may be reduced to pig iron. In cutting the blister steel into pieces has nearly constant this sense steelmaking by "Tatara" process much carbon contents, through considerably wide range. owes to " Murage " 's own special arts. Phosphorous amounts in "Tamahagane " are less than those in pig iron. IX. "Zukuoshi " (Pig Iron-Making in " Tatara " These phenomena can be explained in reference to Process) the Fe-C equilibrium diagram; in the first period of The purpose of" Zukuoshi " is to produce more pig operation, temperature of the furnace can not be iron than in "Keraoshi", direct steelmaking method. raised enough so that iron sands react with the furnace But both methods are very similar each other in shape wall and become slag, but in the next period, the fur of the furnace as well as in the operation method. If nace temperature sufficiently goes up, and a part of compared, the followings can be said. • iron sands are reduced, absorb carbon, and change In " Zukuoshi " the distance among tuyeres is . into pig iron. shorter, tuyeres are placed closer to each other, In the third period, the furnace wall is eroded, and the furnace is somewhat narrower in width and tuyere distance becomes gradually wide, and blast can higher in height. As far as the furnace operation is not reach the centre part of the furnace. Then semi concerned, blasts a re sent more severely, and" Akame" molten substance (spongelike) is made in the furnace iron sands or beach iron sands are used as raw materi bottom and grows as the operation proceeds. Mean als instead of " M asa " iron sands in " Keraoshi ". while in the upper part of the substance (blister steel), many pieces of molten pig iron, which are reduced by X . Conclusions CO gas or C, exist among charcoals, and these pig iron In the study made above the followings were made fall down toward the bottom. ' '''hen they come to the clear: surface of the substance (blister steel), they hang on it (I) Blister steel " Kera" is not made in the mol and turn to the solid phase because the temperature of ten state but in the semi-melted (at most) state. the blister steel is lower than that of molten pig iron, (2) There are few impurities in the final product while the remaining liquid falls down to the bottom. " Tamahagane" but they are contained in it as slag. Then, while the furnace temperature is constant, (3) In the beginning of the operation, slag is basic carbon content of solid phase is kept constant as a as iron oxide acts as base, but it becomes acidic as the result. operation proceeds. By that reason carbon content in " Tamahagane " (4) Accordingly, slags in crude steel can be di is constant. But the above reaction occurs only in minished by forging it. an idealy normal running, and the actual reaction in (5) Operation is not carried out unnecessarily at Re port Transactions ISIJ, Vol. 8, 1968 ( 47 ) high temperature. At present" Murage "'s age is 70 on an average, (6) Such useless impurities as CaO, Si02, etc. are and the survivors are only two or three. scarcely charged into the furnace. Now the author and his co-workers are forming a (7) Products obtained by " Tatara " process have plan of rehabilitation of the process in order to trans several specialities as mentioned in section VI.-4. mit a tradition to the younger generation, and make Most of the steels produced in a "Tatara" furnace a study to adapt the process to the present arts. had been used as materials of Japanese swords For instance, if we are able to raise the temperature " Nippon-to" till quite recently. But in accordance of sponge iron by about 200°C in a stationary state in with a decrease in demand for the swords the produc the reduction process, we will gain the product as tion of "Tamahagane" fell away, and for these 20 excellent as " Tamahagane ": the melting yield of it years the "Tatara" furnace has not been operated, will be higher than that of sponge iron, and it will consequently "Tamahagane" has not been produced. make by forging superior tool steels which have the same In short, the process has been forgotten in the world. qualities with" Nippon-to". But here is a problem Here is another difficulty: the furnace can not be how to pull it out into the air. Probably there is no operated without the "Murage " 's own art, then if other way except to destroy the furnace just as our an they die out, the process will become extinct, too. cestors thought out this measure some 800 years ago . • • Report