UDC 669.18.001.6

New Development of Steelmaking Equipment in Japan*

By Kazuhiro S. GOTO** and Kazuhiro NAGATA**

Synopsis

Steelmaking equipments newly developed in the past ten years in Japan are summarized with a historical view point. Three new equipments de-veloped in Japan are introduced with their detailed information, together with the details of the improved auxiliary equipments. The reasons of new developments are discussed with some comments on future steelmaking in Japan.

I. Introduction

At the 98th ISIJ Meeting, October 1979, Dr. A. Gamboa of Venezuela has made an impressive speech on the steel industry in Latin America.1 Table 1 is reproduced from his text with additional information2~ about Japanese steel industry.

Dr. Gamboa has estimated the production capacity of steel in Latin America to be 161.7 million t in 2000, considering both favorable and negative con-ditions. This production capacity estimated seems to be comparable with that of Japan in 1980. Thus, it might be worth while to report the present status of steelmaking equipments in Japan, even though there are many different conditions between Vene-zuela and Japan. In the followings, the present au-thors will give numbers and capacities of basic oxygen furnaces, of ladle refining equipments and of con-tinuous casting machines. Then, three new refining equipments developed or very much improved in

Japan will be explained by describing the details of operation. At the end, the new auxiliary equip-ments, such as sublances for LD converters and the oxygen sensors will be discussed in relation to the automatic control of the processes. However, the equipments for desulfurization of hot metals and for dephosphorization will not be included because they are out of the scope of the present paper.

II. Steelmaking Equipments in Japan

In Japan, only basic oxygen converters and basic arc furnaces are used to produce 110 million t of steels in 1979. Table 2 shows the recent changes in number and capacity of basic oxygen converters or LD converters in Japan.3) Although the total pro-duction of steels did not change very much in the past five years, the number of large furnaces has in-creased with a decrease of small furnaces. In 1978, steels of about 90 million t have been produced by 94 LD converters and about 20 million t by electric arc furnaces. Recently, steels tapped out from LD converters or arc furnaces are often further refined by various " ladle refining equipments "

, which are sometimes called " secondary metallurgy " or " injection metal-lurgy ". Table 3 shows the number of these equip-ments existing in Japan.3) Total number of these ladle refining equipments is 58 (excluding electroslag remelting furnaces) and this number is more than half of LD converters. The details how to use these equipments will be given in the following section, but briefly. They are used to remove hydrogen (minimum 1 - 2 ppm) and nitrogen (min. 2O-3O ppm), to accelerate the separation of deoxidation products, to desulfurize down to 5 ppm and to homo-genize both temperature and composition of ordinary steels. For the production of special steels, they are also used to oxidize carbon down to 0.003%, selec-

Table 1. Latin America, Japan ; Steel duction capacity (in 1 000 t of Sanbongi and Komoda2) ).

demand and pro-ingots) (Gamboal>,

Table 2. Number of LD converters in Japan.'

* Presented at the 1st Japan-Venezuela Symposium on Iron- and Steelmaking

1980. * * Tokyo Institute of Technology , Ookayama, Meguro-ku, Tokyo 152.

( 446 ) Report

, ISIJ, Caracas, May 1980. Manuscript received J my 10,

Transactions ISIJ, Vol. 21, 1981 (447)

tively, without oxidation loss of expensive elements such as chromium, manganese, titanium and so on.

When steels are refined by the secondary metal-lurgy, they are cast by continuous casting machines. Table 4 shows the recent change in the production of steels by continuous casting machines in Japan. In 1978, 50% of the total production or 47 million t was

produced via continuous casting. This table gives another interesting information, namely more than half of special steels have been produced by LD con-verters but not by conventional arc furnaces after 1976. In Japan, it seems that the production of special steels via LD and secondary refining furnaces is less expensive than the one via conventional arc furnaces with low efpiciency.4~ (In Japan, special steel includes structural carbon steels for machines.) Figure 1 shows the change in the steel production via continuous casting in Japan from 1970 to 1990.2) This figure indicates that about 80% of steels will be

produced via continuous casting in 1990 in Japan. This prediction seems to be very reliable because it is based on two predictions for 1981 and 1985 made

by The Japan Iron and Steel Federation. However, at least, 15% of steels should be made by ingot casting to meet various different needs of steels with small

quantities even in 1990. The plot at 100% in 1978 is by Oita Works of Nippon Steel Corporation and the plot at 75% in 1978 is by Mizushima Works of Kawasaki Steel Corporation. This figure shows a very rapid increase in the capacity of continuous cast-ing machines in the past decade in Japan. From the above, the new developments in Japanese steelmaking equipments in the past decade may be summarized as follows;

(1) Small basic oxygen converters have been gradually replaced by large furnaces with more than

Table 3. Number of ladle refining

in December of l978.'

equipments in Japan

Fig. 1. Increase in the amount of steel cast via casting route (Sanbongi and Komoda2)).

continuous

Table 4. Steel production by continuous casting in Japans)

( 448 ) Transactions ISIJ, Vol. 21, 1981

200 t per charge. (2) New ladle refining equipments have been

installed and their operations have been very much improved in Japan after 1970.

(3) The capacity of continuous casting machines has increased from 6 % of the total steel production in 1970 to 50% in 1978 and will increase eventually to 80% in 1990 but not more than 85%.

In addition to the above three, the auxiliary equip-ments have also been improved in the past decade. Namely, most of LD converters have been equipped with sublances to measure temperature, carbon con-tent and oxygen content for the dynamic control. Oxygen sensors are also widely used to control the deoxidation processes, and, after that, the shape of sulfides is controlled by rare earth metals in Japan.5)

III. Some New Improvements in Steel making Processes in Japan

1. A Brief History of the Development of Secondary Metal- lurgy

What is the new development in steelmaking tech-nology ? This is a naive question, at first we should solve. Figure 2 shows the increase in the number of ladle refining units installed in the world.6) (BV= Bochumer Verein Vacuum Casting, TN = Thysen-Niederrhein, DH = Dortmund-Horder Hutten-union, RH = Ruhrstahl and Heraus, Finkl-VAD = Finkl & Sons Co. Mannesmann Co. Vacuum Arc Degassing, ASEA=ASEA Co. and SKF Co. Sweden). This figure shows that steels had been manufactured before 1960 only by single type steelmaking furnaces without any further refining. However, according to Fig. 2, new refining equipments have been very rapidly in-troduced to steel works after 1960 and they will be-come more than 300 in 1980. The authors would like to define the introduction of these new equip-ments as the new development in steelmaking tech-nology in the world.

In contrast to this world trend, then, what is the new development in Japan ? This is the second prob-

lem which should be clarified. Figure 3 gives a his-torical presentation of the development of various ladle refining equipments. In this figure, one can see several new refining equipments newly developed in Japan after the development of RH-OB7) in 1969. New developments in Japan include WF process

(Wirefeeder, Nippon Kokan K.K., 1970),8) ABS pro-cess (Al Bullet Shooting, Sumitomo Metal Industries, Ltd., 1972),9) SCAT process (System of Calcium Adding Technique, Sumitomo Metal Industries, Ltd., 1975),10) CAS process (Composition Adjustment by Sealed Argon Bubbling, Nippon Steel Corp., 1975),11) Rapid Al Feeder process (Kawasaki Steel Corp., 1977),12) LF process (Ladle Furnace, Japan Special Steel Co., Ltd., 1971 ),13) SAB process (Sealed Argon Bubbling, Nippon Steel Corp., 1974)14) and CAB

process (Capped Argon Bubbling, Nippon Steel Corp., 1977).15) The development of the above equipments after 1969 can be considered as new developments in steelmaking equipments in Japan. Before the developments of secondary metallurgy, there are a long preparation time or so-called incuba-tion time after that the removal of hydrogen from steels was tried under vacuum in the end of the 19th century.l6) The first successful process in an indus-trial scale was made in 1952 by Bochumer Verein AG in West Germany; the picture of this vacuum treatment is given in Fig. 3.17) This process is really an epochmaking process, because this was the first refining process out of the steelmaking furnace. This invention had stimulated the development of RH18) and DH19> processes for steels of the mass-production type. The second epochmaking new idea is, accord-ing to the author's opinion, the injection of argon into steel through a porous plug at the bottom of ladle in 1950, which is called Gazal Process.20) Since this invention, the injection of gases with powdery refining agents has been widely used to accelerate the reac-tion rate. The third epochmaking invention is ASEA-SKF processe1) made in Sweden. This process is very creative nature, because it is an ideal combination of vacuum, magnetic stirring and heating. This arc heating has solved a fatal weak point of ladle refining, namely temperature decrease during refining.

Although the developments and improvements of steelmaking equipments in foreign countries have dif-ferent histories, Japanese steel industry has been deep-ly stimulated by these epochmaking inventions. In the followings, three typical improvements done in

Japan will be explained in more details.

2. Ladle Furnace by Omori Works, Japan Special Steel Go., Ltd.

In this process, as shown in Fig. 4, refining by slag is combined with argon stirring and submerged arc heating under atmospheric pressure.22) If necessary, the ladle can be evacuated to remove hydrogen from steel. If this ladle furnace is combined with an arc furnace, the reducing period in arc furnace can be completely transferred to the ladle furnace with better reproducibility. If this is combined with the basic oxygen process, this adds the reduction period with

Fig. 2. Number of ladle refi the world (Iida6)).

fling equipments constructed in

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better cleanness of steels and even the possibility of special steel production with better quality than con-ventional electric-arc-furnace steels.23~ Because of the relatively easy operation and the production of better

quality of steels, this process attracted so much atten-tion as to five steel-works in Japan installed the fur-naces of this type, as given in Table 5. Several opera-tion modes have been used22~ by the combination of LF with arc furnace or basic oxygen converters to

produce low alloy steels, high speed steels and stain-less steels. However, in any case, oxidizing slag of the preceding furnace must be removed by flushing in EAF or by reladling in BOF operation to prevent

Fig . 3. A historical

(rearrangedpresentation of the Iida's pictures)).

development of various ladle refining equipments in the world

Fig. 4. Diagrammatic sketch of LF process et a1.22)).

(Ushiyama

(450) Transactions ISIJ, Vol. 21, 1981

the rephosphorization and contamination by dirty slag. Reducing slag is formed either in EAF or in LF. In the BOF operation, all the slag formers are added during reladling into LF together with de-oxidizers. The steel is usually refined for 40 to 80 min to remove sulfur, phosphor and oxygen and to have the target contents of alloying elements.

The desulfurization and deoxidation by LF have been extensively studied by Kajioka et al.24~ with the improvements of impact strength and the reduction of area of heavy plates produced from a 18 t ingot. Figures 5 and 6 give their results on the mechanical

properties in comparison with those of the conven-tional refining processes.

3. RH OB Process : A Very Much Mod/ied RH Process

In 1969, engineers of Muroran Works of NSC have combined their original ideas of oxygen-blowing with the conventional RH process.' By this modifica-tion, the decarburization of high-Cr stainless steels can easily be made without the oxidation loss of ex-

pensive alloying elements. Also, the fluxes are added to absorbed inclusions to make clean steels.25~ Figure 7 shows how to manufacture the Cr-based stainless steels, which consists of 1) desulfurization of hot metal by KR treatment, 2) refining in LD furnace, 3) sepa-ration of slag from steel by tapping and recharging to LD, 4) ferrochromium melting in LD and finally 5) RH-OB process, decarburization under vacuum without chromium 1055.25) (KR is Kajioka Reactor in which hot metal is agitated with an impeller in order to mix with desulfurization agent.) To the steel recharged in LD, high carbon ferro-chromium is added, and it is melted with an oxygen jet and is decarburized down to 0.5-0.6%c without loss of chromium. Then, the steel is further decar-burized by the RH-OB process. Table 6 gives a com-

parison of this process with the previous RH-Ore pro-cess, in which the decarburization was made by ores instead of oxygen blowing. As can be seen from this table, the temperature drop and chromium loss are remarkably reduced by the application of RH-OB

process for steels with lower carbon and nitrogen con-

tents. Soft and workable chromium stainless steels are now manufactured with carbon content of 0.01 N 0.06% and nitrogen content of 50 to 150 ppm. In addition to the RH-OB process, the conventional

RH and DH26~ processes are now used as the ladle refining equipments perform decarburization, denitro-

genization, temperature and composition adjustment, and deoxidation, not only to remove hydrogen from steel, which was the original object of these reactors. Figure 8 shows the several ways to combine the RH

Table 5. LF

and

equipment installed 1976 (Ushiyama et

in Japan al.22) ).

between 1971

Fig. 5. Relationship between impact strength and length of A type inclusions (heavy plates) Yawata) (Ushiyama et al.22)).

total

(NSC;

Fig. 6. Relationship between reduction of area and total length of A type inclusions (heavy plates) (NSC, Yawata) (Ushiyama et al.22)).

Fig. 7. Production steps of stainless steel by the LD-RH

process (Suzuki25)).

.OB

Transactions ISIT, Vol. 21, 1981 (451)

process with basic oxygen converters to produce vari-ous steels; all are used in Nippon Steel Corp.25)

4. Improvement in Q-BOP Operation in Japan

In 1968, Eisenwerk Gesellschaft Maximillians-hutte in West Germany has developed an oxygen bottom blowing converter called OBM (Oxygen Bottom Maxhutte) with 30 t capacity. In 1971, US Steels Corp. has purchased the patent licence and construct-ed three bottom blowing converters of 200 t capacity each and named them Q-BOP. In 1977, Kawasaki Steel Corp. in Japan has constructed two Q-BOP fur-naces of 230 t capacity each. The total production capacity of OBM and Q-BOP in the world became 35 million t in 1977.

A remarkable improvement of Q-BOP operation has been accomplished by Nakanishi and his co-workers through their extensive studies on the reac-tion mechanisms during refining in Q-BOP.27-28) They have clarified the substantial difference between

Q-BOP and LD, that is, steel in Q; BOP is more strongly stirred and in more reducing condition through the refining period. Figure 9 shows the rela-tion between (d [%P] /d ln[%C]) and ISCO value for

Q-BOP and LD,27) where ISCO is defined by

ISCO = 2Qo2 Q°2 2Qo2+4Qd ( W/z)

Here, Qo2 and Qd are the supply rates of oxygen and

propane in Nm3/min, W is the total weight of steel in ton, and z is the uniform-mixing time of the bath in minute, which is measured by the use of radio active tracer of Ag. From the results of their studies, they have concluded that one-point measurement of car-bon content and temperature by the use of the sub-lance sensors would be very reliable for the dynamic control of Q-BOP, because of the uniform tempera-ture and composition of steel during its refining. In 1977, they have already established the SMART sys-

tem for Measuring and Attaining the Refining Tar-

get) having a world record of 1 646 heats with a single bottom-refractory without replacement. By these op-erational improvements, the production costs of low carbon rimming steels has been reduced by 617 yen

per ton of steel, as shown in Table 7, as compared to these by LD converters in Japan.2j

5. Improvements in Auxiliary Equipments in Japan

One of the most important auxiliary equipments of LD converters might be the sublance, which is up-and-down movable with the automatic fixing-and-detaching equipment of sublance-sensors for sampling of slag and steel, and measuring of temperature, car-bon and oxygen contents. Figure 10 shows the sec-tional picture of a LD converter equipped with a sublance. The development of the sublance has started by Japanese steel companies in about 1965 with the help of instrument manufacturing companies. Already in 1976, 40 LD converters have been equipped with the sublance and in 1977, 61 LD converters in Japan. Now, almost all of the LD converters are equipped with sublances and their blowing end-points are auto-matically controlled by the use of sublance. The introduction of sublance has remarkably increased the ratio of successful target values of carbon content and temperature and thus the life time of refractories became very much longer than that before use.

Another new method of automation of steelmaking

process is the automatic control of deoxidation process by the use of oxygen sensors with solid electrolyte.29) In 1977, about 30 000 units of oxygen sensors have been consumed in Japanese steel works to control the deoxidation process combined with the automatic charging machines8-1°,12) of deoxidizers. Figure 11

Table 6. Comparison

OB process

of RH-iron ore

(Suzuk125) ).process and RH-

Fig. 8. Functions of RH-reactor (Suzuki25)).

Fig. 9. Interpretation of oxidizing furnaces in ISCO values (Nakanishi et a1.27)).

terms of

(452) Transactions ISIJ, Vol. 21, 1981

shows a remarkable improvement in the production of capped steel since October of 1976, when the oxygen

sensors have been used with the sublance of LD con-verter.

Iv. Some Reasons of New Developments in Steelmaking Equipments30'

In foreign countries, there are many different rea-sons for the industrial development. However, the followings are some reasons in Japan which have induced the new developments in steelmaking equip-ments.

1. Strong Needs for Better Quality Steels

Defects detected by the ultrasonic test of thick

plates for ships, and for high pressure vessel must be very much reduced. Since the conditions under which steels are used become very severe, higher reliability is required for fatigue fracture after large deformation of steels. (DI cans and thin wires for tires of vehicles, structure steels in ocean, linepipes, etc. )

2. More Cost-down o f Steelmaking

The cost of EAF can be reduced by replacing it by LD but with ladle refining, which is corresponding to reducing period of EAF. The cost of EAF can be reduced by increasing the producibility of EAF with the aid of ladle refining, which is cheaper than that needed for the construction of an additional EAF.

The cost of expensive alloying elements can be very much reduced by prevention of their losses with help of ladle refining.

3. Suitable Steels for Continuous Casting (CC)

The continuous casting needs the complete sepa-ration of deoxidation products, exact casting tem-

perature and homogeneous steel composition, before steels are charged to continuous casting machines. Thus, the increase of the production by CC has in-duced many types of ladle refinings which are very necessary for the production of better quality steels, rimmed or killed, by CC. These needs could be solved by the development of new refractory materials, e.g., high alumina lining, zircon bricks, porous plug, sliding nozzle, etc., and by

Table 7. Cost for blowing low

Q-BOP as compared bongi and Komoda2) ).

carbon rimming steels by with that by BOP (San-

Fig. 10. Mechanism of sublance in converter for steelmak-ing (Goto29)).

Fig. 11. Improvement in cape of oxygen contents

(Goto29)).

ing operation and scattering

by use of oxygen sensors

Transactions ISIJ, Vol. 21, 1981 (453)

cheap production of argon and nitrogen during 1960's in Japan.

V. Concluding Remarks

In the above, new developments of ladle refining processes have been discussed in combination with LD converters. However, sharing 25% of the total crude steel production (35 million t) in 1990, electric arc furnace will supplement the BF-BOP process, taking advantages of the energywise beneficial scrap2~ in Japan.

The furnace capacity will be increased up to 200 N 400 t with ultra high power operation with counter-measures against flicker and noises. Water cooling of the wall will be made by the optimization of the

power input control with automatic charging of mate-rials. The EAF will be used only for melting and the refining will be made by ladle refining processes. Meanwhile, the desulfurization and dephosphoriza-tion of hot metal with soda metallurgy will be more widely used in Japan in the future decade with new improvements. However, other steelmaking methods, such as continuous Steelmaking and open hearth fur-nace with coal gas may have supplemental values de-

pending upon the economic and social conditions of Japan.

Acknowledgements

The authors sincerely express their deep apprecia-tion to Mr. T. Yukawa of Head Office of Nippon

Steel Corp. and to Mr. Y. Miyashita, Technical Re-search Center of Nippon Kokan K.K., for their kind

help to collect the information and for their critical

reading of the manuscript.

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