US3754892A

US3754892A - Continuous method of steel making

Info

Publication number: US3754892A
Application number: US00821385A
Authority: US
Inventors: R Ando; T Fukushima
Original assignee: Nippon Kokan Ltd
Current assignee: JFE Engineering Corp
Priority date: 1968-05-09
Filing date: 1969-05-02
Publication date: 1973-08-28
Anticipated expiration: 1990-08-28
Also published as: NL152602B; FR2009870A1; BE732833A; DE1923596C3; DE1923596A1; GB1234878A; NL6906392A; DE1923596B2; AT308792B

Abstract

Steel is made continuously by mechanically agitating molten pig iron and slag proximate their interface and simultaneously passing oxygen onto that interface whereupon the pig iron is desulphurized and dephosphorized. The pig iron product is then decarbonized by treatment with oxygen.

Description

United States Patent [191 Ando et al." 1*Aug. 28, 1973 [54] CONTINUOUS METHOD OF STEEL 2,767,077 10/1956 Perrin 75/52 MAKING 2,856,280 10/1958 von Bogdandy 75/60 2,962,277 1 1/1960 Morrill 75/60 X -Inventors: y Ando; Tsutomu Fukushima. 2,975,047 3/l96l Leroy et al. 75/60 x both of Kawasaki-shi, Japan 3,013,789 l2/l96l Sayre et a1 266/36 3,171,877 3/1965 Thrin 75/46 X 73 Ass1gnee: Nippon Kokan Kabushlki Kaisha, I 3.172.756 3,1965 aengson 75,60 x 1 Kanagawar Japan 3,303,018 2/l967 Goss 75/60 X a: 3,331,681 7/1967 Mobley 75/60 I Nome gigggggg: 3,567,204 3/1971 Ando et al..... 266/34 p q y 3,592,629 7/1971 Ando et al. 75/58 has been d1scla1med. [22] Filed: y .2, 1969 FOREIGN PATENTS OR APPLlCATlQNS 373,358 2/1962 Japan 75/46 [21] Appl. No; 821,385 594,996 3/1960 Canada 75/60 Prima Examiner-L. Dewa ne Rutled e 30 F A 11 ti P D m Y 8 1 orelgn pp ca on Horny a Assistant Examiner-M. J, Andrews May 9, 1968 Japan 43/30563 Atmmey Flynn and Frishauf 52 US. Cl 75 46 75 52, 75 58, 1 75060 57 ABSTRACT [51] Int. Cl. C2lc 7/00, C2lc 7/06 St l s a sly y ni a ly agitating [58] Field of Search 75/46, 52, 60; molten pig iron and slag proximate their interface and 266/34, 35 simultaneously passing oxygen onto that interface whereupon the pig iron is desulphurized and dephos- [56] References Cit d phorized. The pig iron product is then decarbonized by treatment with oxygen.

8 Claims, 1 Drawing Figure v l CONTINUOUS METHOD, OF STEEL MAKING RELATED APPLICATIONS:

This application is related to application'Ser. No. 818,283, filed Apr. 22, 1969.

FIELD OF INVENTION BACKGROUND OF INVENTION:

With the development of modern metallurgy, there is a tendency of gradually shifting from conventional batch system steel making (for example, flat furnace steel, converter steel, or electric furnace steel) to continuous steel making which is more efficient and economical, and various methods of continuous steel are now being investigated. However, most of these methods of steel making are those developed from the flat furnace or converter type, and the basic reaction conditions and the refining conditions are not changed so much as compared with those which prevailed heretofore. The so-called continuous steel making process involves a mere addition of a conventional method of treatment to the molten pig which is continuously moving. Furthermore, several new methods have recently been published, that is, processes such as spray steel making and the IRSID tank system, that is the tank system of Institut de Recherches do la Siderurgie Francaise.

In the spray steel process, desulphurization, dephosphorization, and decarburization are effected simultaneuously and momentarily, thus it is merely a simple refining method for producing low carbon" steel. Also, as the system becomes larger, higher oxygen pressures are required, which introduces considerable problems.

In the IRSID tank system, oxygen is blown through an oxygen lance or through porous bricks at the bottom of the furnace, and refining is carried out by forming an emulsion of slag metal. In this case, temperature regulation is extremely difficult, and the high-temperature emulsion appears to attack the fireproof material of the furnace, which is a disadvantage in that the continuous operating period must be limited.

Advantageous points of the continuous method of steel making are as follows:

1: Low cost of construction (equipment becomes smaller when plants of equal annual production are compared) I 2: Low operational cost (excellent in thermal efficiency and in available percentage, smaller wear in refractory material, lowering of original unit cost of 0,)

3: Wider allowable operational conditions (substantial proportion of scrap iron can be used, with less fumes produced. Not only having a larger allowance in extent of variation of materials, but also simplerin operation with lesser labor force) 4: Improved reliability in quality of products.

(Efficient control and measurement of the chemical reaction).

Although the continuous method of steel making has such advantageous features, there are present disadvantages such as stated before, so that no satisfactory process has yet been developed. Especially concerning the reliability in the quality of products as well as the wear of the refractory materials, there are considerable problems left unsolved, and at present, no generally acceptable process has been commercialized.

SUMMARY OF INVENTION In accordance with the present invention, there is provided a process for manufacturing steel continuously wherein sulphur and phosphorous are removed from molten iron or molten iron alloy prior to effecting substantial decarburization thereof. Slag and molten iron or molten iron alloy are agitated mechanically proximate their interface and oxygen is passed simultaneously onto their interface. Thereafter, oxygen is injected into the molten iron or molten iron alloy to effect substantial decarburization.

In the process, desulphurization can be accomplished independently by contacting the molten iron or molten iron alloy with a slag forming agent, in the absence of oxygen preferablyjwith the indicated mechanical agitation. The treated iron or iron alloy and slag can then be processed as stated above.

BRIEF DESCRIPTION OF THE DRAWING Advantages of the invention will become apparent to those skilled in the art from the following description considered in conjunction with the drawing wherein:

The FIGURE is a schematic flow diagram illustrating an embodiment wherein desulphurization, dephosphorization and decarburizing are shown.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS As shown in the drawing, pig iron 2 (containing: C=4.3%, Si=0.68%, Mn=0.65%, P=0.l90%, S=0.043%), which is tapped at a rate of 2 tons per minute continuously from blast furnace 1, is passed through line 20 into desulphurization treating tank 3 (capacity [0 tons), which is provided near said blast furnace 1. Calcium carbide (2 kg/min), a slag making agent is passed into tank 3 through feeder 4. Desulphurizing of the pig iron is effected while eccentrically agitating continuously the materials in the area near the slag-metal interface by means of agitating rods 5 made of carbonaceous materials and other refractory materials such as refractory clay of high alumina composition (three rods are fitted). Further details of such an agitation operation are provided in copending application Ser. No. 818,283, filed on Apr. 22, 1969.

Slag can be removed from tank 3 via slag-removing line 17, and can be recycled (not shown) to tank 3 if desired. I

The pig iron thus treated is passed from tank 3 through outlet line 21 to a tank 6 (capacity 10 tons) for dephosphorizing treatment. Slag producing agent a kg/min. of calcined lime, 30 kg/min. of mill scale, 30 kg/min. of soda ash (Na,CO,), l0 kg/min. of fluorite, CaF, or 20 kg/pig ton, l0 kg/per pig ton of mill scale, 3 kg/pig ton of fluorite, CaF,) is passed through feeder 9 and charge line 22 to tank 6, and at the same time oxygen is injected into tank 6 for a total amount of 30 Nmlmin. through oxygen lances 10 (three lances are equipped) provided on tank 6, while agitating by means of an interface agitating device having agitating rods 5 made of carbonaceous materials and other refractory materials as in the case of said tank 3 so as to remove phosphorus by oxidation. The pressure of the oxygen then injected is from about 2kg/cm to about 3kg/cm In this case slag is removed from slag-removing line 17, and can be recycled (not shown) to tank 6 when necessary.

The treated pig iron is then passed from tank 6 through line 11 to steel making furnace 13 (three units) of pure-oxygen, top-blown converter type provided on turret-type, rotating table 12, and the decarburizing refining is effected by conventional processing in which oxygen is injected through lance M. The slag is also removed from tank 6 through line 11. In this way, blank steel of medium carbon content containing 0.25% of C, 0.006% of S, 0.008% of I, a trace of Si, and a trace of Mn, is obtained. Finally, by introducing a ferro alloy as a deoxidizing agent at the final step of steel making, the desired steel product is obtained. The three units of decarburizing steel making furnaces provided on said turret-type rotating table 12 are adapted to cooperate effectively, each operating alternatingly as a decarburizing furnace 13a during receiving pig iron, a furnace 13b during blowing refining, and furnace (not shown) during topping and scrapping.

In the above embodiment, the desulphurization and the dephosphorization are effected using separate treating tanks, 3 and 6, respectively. When desulphuriwhich a large quantity of slag is produced, can be efzation and dephosphorization are carried out, it is preferable, as viewed from such stand points as improvement in thermal efficiency, early forming of slag, and maintenance of fluidity of slag, to utilize slag which is removed continuously from the blast furnace.

In order to increase the effects of the desulphurization, dephosphorization and decarburization to their maximum, it will be sufficient only to increase the number of units of each of the treating tanks (3, 6, and 13), or to increase the capacity of each of said treating tanks. Furthermore, the use of the turret rotating table at the final processing, and the provision of a plurality of steel making furnaces on the table are essential from view points that the amount of scrap used can be selected freely, and that the steel making furnace can be utilized as a ladle. Thus, while one of the steel making furnaces. is under refining operation, another steel making furnace can be used for preheating the scraps, or utilizing it as a ladle for molten steel, or using it as a receiving tank of pig iron which has been subjected to the first processing; thus they have a wide range of utility.

The continuous steel making furnace according to the present invention is characterized by the fact that the desulphurization and dephosphorization process, and that, in said desulfurization and dephosphorization process, the mechanical agitation is effected at the interface of slag and metal. Thus, in the conventional continuous steel making furnace, the principal object thereof is the decarburization, and the steel obtained is a simple blank steel having a low carbon content which requires one further step to finish it into a desired kind of steel. In the continuous steel making furnace according to the present invention, low sulphur and low phosphorus steel can be obtained easily, control of each of these components can be effected readily following the fected at a relatively low temperature, and although the temperature rises so much at the final stage of the decarburization, almost no slag is produced in this stage, so that wear loss due to melting of refractory material in the desulphurizing and dephosphorizing tank is reduced remarkably. In the furnace according to the present invention, resulphurization and re-phosphorization in the decarburization process can be prevented because substantially complete removal of slag is effected in the desulphurization and dephosphorization processing stage or stages.

While the invention has been shown and described in relation to the continuous method of steel making, it should be clear to those skilled in the art that the described method of treatment for dephosphorization and desulphurization is also effective for de-chromiumization and de-manganization.

What is claimed is:

1. A continuous process for manufacturing steel, comprising the sequential steps of a. continuously charging to a refining vessel molten iron or molten iron alloy containing sulphur, phosphorus and carbon,

b. contacting continuously said iron or iron alloy with a slag forming agent in said vessel .while agitating mechanically said iron or iron alloy and said agent at the area proximate the interface thereof, contacting continuously the resulting iron or iron alloy obtained in (b) with a slag forming agent and with oxygen, while agitating mechanically said resulting iron or iron alloy and said agent at the area proximate the interface thereof, said oxygen being charged onto said interface, and

d. charging continuously the resulting product of (c) to a furnace and injecting continuously oxygen into said product to substantially decarburize said product.

2. The process of claim 1, wherein the molten iron is pig iron.

3. The process of claim 11, wherein the slag forming agent of (b) is calcium carbide.

4. The process of claim I, wherein the slag forming agent of (c) comprises a mixture of calcined line, mill scale, soda ash and CaF 5. The process of claim 1, wherein the furnace in (c) is a top-blown oxygen converter furnace.

6. The process of claim 1, wherein the pressure of oxygen in step (c) is from about 2 kg/cm to about 3 kg/cm.

7. The process of claim I, wherein said furnace comprises a plurality of revolving furnace units.

8. The process of claim 5, wherein said furnace comprises a plurality of revolving furnace units.

Claims

2. The process of claim 1, wherein the molten iron is pig iron.
3. The process of claim 1, wherein the slag forming agent of (b) is calcium carbide.
4. The process of claim 1, wherein the slag forming agent of (c) comprises a mixture of calcined line, mill scale, soda ash and CaF2.
5. The process of claim 1, wherein the furnace in (c) is a top-blown oxygen converter furnace.
6. The process of claim 1, wherein the pressure of oxygen in step (c) is from about 2 kg/cm2 to about 3 kg/cm2.
7. The process of claim 1, wherein said furnace comprises a plurality of revolving furnace units.
8. The process of claim 5, wherein said furnace comprises a plurality of revolving furnace units.