US2794731A - Method of reducing refining of cast irons and steels - Google Patents

Description

June 4, 1957 KEIZO IWASE EIAL METHOD OF REDUCING REFINING OF CAST IRONS AND STEELS Filed July 21, 1954 United States Patent METnon or REDUCING REFINING 0F CAST Patented June 4, 1957 ice IRONS AND STEELS 5 with use of a reducing slag as described hereinafter in a melting furnace such as an electric arc furnace hi hfre- Keizo Iwase and Masao Houma Sendai City, Japan asa signers to The Research Institute for Iron, Steel and quency Induction. furnace Crumble furnace heavy 011 other Metals of The Tohoku University Sendai City furnace and the like, and then the tapped molten metal Japan may or may not be treated with ferro-silicon, calcium silicide and the like for inoculation, thus it enables to pro- AllPllmfieil Jilly 1954, serial 444,694 duce cast iron having properties comparable with super- 2 Claims (CL heated cupola cast iron inoculated by calcium silicide or magnesium treated nodular cast iron.

After fundamental investigations, the inventors have This invention relates to a method of reducing refining found out that there exists such relations as listed in the of cast irons and steels. following table between various properties of cast iron The principal object of this invention is to produce and oxygen content dissolved in the cast iron melt:

TABLE Relation between oxygen content and valious properties qfeast iron.

Dissolved Dissolved Oxygen Decreased yg Increased Mark VI V IV III II I II III IV V Macro Structure Inverse Inverse (1O 3Om/m White chilled Grey Grey Grey Grey Grey Grey Chilled White Cast) Needle l'k Graphite g f R}? G 5:15 ar Eutectic Rose Flake Rose Eutectic fi L deand F636 graphite graphite graphite graphite graphite graphite buritxc Matrix and Inner Inner i nodular VII Ferrite Pearlite Pearlite Pearllte Pearlite Pearlite V 83 graphite Strength Toughness Mass Effect Super-heated Cupola Cast Iron Acidic g cupola h Electric Variety Treated Cast Iron Cast p eated b Cu 1 Cast Iron f Nodular of this Iron Clark Cast Iron i B 2151C Cast Iron 9 invention inoculated by Charcoal Iron by Electric Calcium silicide Pig Coke Pig Cast It will be seen from the above that strength decreases from a maximum for a minimum of dissolved oxygen to reach a low point at I and thereafter increases with increasing oxysplendid cast iron which is comparable With the highest grade cast iron obtainable at present.

A further object of this invention is to improve the quality of steel by the reducing refining.

It is known that super-heated cupola cast iron inoculated by calcium silicide and nodular cast iron treated with magnesium has a very high tensile strength. Cast iron having such high tensile strength as super-heated cupola cast iron inoculated by calcium silicide and magnesium treated nodular cast iron could never be obtained until at present by reducing refining in a melting furnace such for example as an electric arc furnace, high frequency induction furnace, crucible furnace by means of slag such as White slag, carbide slag, etc., "and by subgen; Toughness decreases continuously without intermediate low point, and Mass Efiect increases continuously with increasing oxygen.

Electric furnace cast iron obtained by using heretofore common White slag or carbide slag has an oxygen content in the range Within ll, Ill and 1V in the above table. Such electric furnace cast iron is usually deficient in toughness, and contains unevenly distributed graphite of smaller size, and has poor fluidity. It is known that these are mainly due to a larger oxygen content.

Cast iron obtainable by this invention has an oxygen content in the ranges within Ii to V and shows particular-ly superior quality if subjected to inoculation treatment. Deoxidized cast iron melt Within the range of III to V is preferably inoculated. If not inoculated, graphite is finer due to the super-cooling of the melt. The graphite takes eutectic, fine granular, short-flake, quasiflake or nodular form in the structure according to the degree of deoxidation and inoculation.

According to this invention, the inventors have accomplished an epochmaking discovery, based on the fundamental theory which they have established relating to the red-ucingslags which can develop much stronger reducing effect than heretofore used white slag and carbide slag, and the art of producing such slags. By the reducing refining of cast iron melt with a slag according to this invention, a very strong and tough cast iron can be obtained, which is comparable or rather superior to known super-heated cupola cast iron inoculated by caicium silicide'zand magnesium treated nodular cast iron.

The slags which are found to be most suitable in carrying out this invention are ennumerated below:

(1) A mixture of one or more oxides or carbonates of the alkali or alkaline earth metals, and one or more of carbon, silicon (including silicon compounds such as ferro-silicon, and siliceous alloys) or aluminum (including aluminum alloys), and

(2) Calcium cyanarnide containing SiOz, A1203 or CaO.

Further in the economical point of view and considera a turning scrap of cast iron or steel may be used as raw maing the regulation of composition of slag to obtain a re-, quired reducing degree, basicity or acidity, asuitable amount of ordinary used other oxides such as SiOz, Alz Oa, MgO etc., carbonates, or slages such 'as blast furnace clag, cupola slag, open earth slag or electric furnace slag may be added to the above mentioned essential ingredients, and also the substance containing the above main slags as the main constituent may be used in this inventron.

invention since it contains CaCOa. CaCNz sometimes contains considerably small amount of reactive calcium as the result of weathering so that it is advantageous to add C, Si and Al to CaCNz, then it will become a slag such as CaO-C-CaCNz which also constitutes a reducing slag in accordance with this invention. 7

Some examples of compositions of the reducing slag which is the characteristic feature of this invention are as follows: BaCOa-C; NazCOs-C; NazCOs-BaCOs-C; CaCOa-C; CAO-C; BaCOs-Si; BaCOa-C-Si; BaCOs-Al; BaCOa-Si-Al; SrO-C; SI'COa-C-Al; ordinary slag (for example CaO-SiOz-AlzOs)-CaCNz; CaO-CaCNz; C-aCNz-C.

In carrying out the method of this invention, about 1 to 15% of the above slag may be added to raw metal material of suitable constituents and the reducing refining can be conducted, for example, in an electric arc furnace or a high frequency induction furnace. Although it is a particular advantage that the slag can be reacted at asuflicient- Ily low temperature within the range of about l300- C.

to 1350 C., yet the reducing refining may be promoted at a higher temperature so that the use of electric arc furnace is more preferable.

rying out the reducing refining according to this invention. Though a basic furnace is preferable, yet an acidic furnace may also be used without objection.

According to this invention, it is necessary that in the method of preparing the slag, each part of the reducing slag is reactive with slag constituents, before the slag is added with the raw metal material to be refined by reduction. The art of preparing slag is one of the most important points because the object of this invention could never be obtained bymerely charging the above mentioned slag constituents into a melting furnace.

The electric furnace cast iron obtainable with use of white slag or carbide slag for reducing refining is usually brittle, less fluidity, liable to chill, larger mass elfect and poor castability, and the inventors have found the fact that such defects are due to the imperfect art of preparing slag. Cast iron produced according to this invention has higher tensile strength and larger deflection, and considerably good fluidity and castability without substantially mass effect, and the cast iron of low carbon and sili- It is not necessary to maintain reducing atmosphere in the furnace specially in car- Dolomite-C belongs to the reducing slag of this con amounts which should invaiiab ly become white cast iron by heretofore usual smelting process, enables to produce grey cast iron instead of white cast iron by the method of this invention.

The fundamental difference between the method of this invention and the heretofore usual melting process in an electric furnace and cupola will be evident from the following comparison:

1. In the present method, the reducing slag is independent of its form whether it is in the liquid state or solid state. Accordingly the mixture of reducing slag of solid state having such a composition as to have higher melting point than that of cast iron may be arranged on the side wall and bottom surface of the melting furnace and the reducing refining is carried on from the surrounding surface of molten metal by charging the reducing slag, thereby resulting the most effective reducing refining of a larger amount of molten metal in a given time. Such process has never been tried before and the method of this invention enables to use a cupola or reverberatory furnace for the melting purpose.

2. According to the present method, lathe chips or terial with high yield of the required cast iron.

3. On the other hand, in known methods of producing super-heated cupola cast iron inoculated by calcium silicide, which is of the highest quality, selected steel scrap should be used as the raw material, but coke pig iron could never be used. The production of magnesium treated nodular cast iron also needs special high grade raw material.

According to this invention, a large amount of coke pig iron may be used as raw material to obtain a cast iron having the tensile strength of 41 to 42 kgL/mm. and the structure in the form of uniformly dispersed short-flake graphite and sorbitic pearlite, and also a cast iron having tensile strength of about 60 kg./mm. containing substantially no free cementite and having the structure of noduing can be conducted at a lower melting temperature such -as about 1300 C. to about 1350" C., and enables to obtain the above described eutectic graphite cast iron (III'),

' fine granular graphite cast iron (IV) and nodular graphite cast iron (VI'). 7

In contradistinction to the above, the heretofore known method of reducing refining using whiteslag or carbide slag could neither be conducted at such a 10w temperature nor considered its possibility. The properties of cast iron 'deoxidized within the range of (II) to (IV) corresponds 'with those of cast iron which was melted in a cupola under superheated condition and tapped at a temperature above about 0 'C. Thus the cast iron obtained from a melting furnace-by the method of this invention without subjecting inoculation treatment after it has been tapped out of the furnace may have the properties similar to those of super-heated cupola, cast iron so that it should be noted that such non-inoculated cast iron should come within the scope of this invention.

5. The least amount of carbon and silicon which a plain cast iron heretofore produced in an electric furnace by reducing refining with use of white slag or carbide slag would become grey cast iron, not becoming white cast iron or mottled cast iron, are 3.3 to 3.5% of C and about 1.5% of Si for a test piece made in a green sand mold having 10 mm. in diameter.

0n the other hand, the plain cast iron obtained by the method of this invention in a green sand mold of 10 mm.

The method of this invention also can be applied to the smelting of ferro-alloys such as silicon steel and other steels for the purpose of strong deoxidation, thereby improving the various properties of silicon steel and increasing self-hardeningefiect of steel since its pear litic lamellar becomes sorbitic 'lamel lar due to the lowering of the Arr point.

The annexed drawings showthe properties of cast iron obtainable by the method of this invention, in which Figs. 1 and 2 are diagrams showing the mass effect of two test pieces made by the method of this invention, and

Photo. Nos. 1 to 3 show structure of the test pieces made by the method of this invention.

Some examples of this invention are shown in the following:

Example I Raw metal materials-Blast furnace coke pig iron, returned ordinary cast iron such as gate and risers etc., lathe chips, steel scrap etc.

Melting process.-Hrou1t electric furnace, or high frequency induction furnace.

The reducing refining is conducted according to the method of this invention using, for example, the following slags:

(i) In which the ratio of BaCOa to C is 5 tol (ii) In which the ratio of CaO to CaCNz is 1 to 1 (iii) In which the ratio of CaCOa to C is 5 to 1 Any one of the above slags gave the same result.

After tapping, the melt was inoculated with about 0.05% ferro-silicon.

Result.-Chemical compositions, mechanical properties and mass effect are as follows:

Total C percent 3.40. GraphiteC do..--.. 2.70. Combined C do 0.70. Si do.. 1.49. Mn do 0.51. P do 0.128. S do 0.009.

Tensile strength test:

Mold 30 mm. diameter.

Test piece 20 mm. diameter.

Length of parallel portion of the test piece 25 mm.

Load 9.5 tons.

Tensile strength 30.2 kg./mm. Transverse strength testing:

Mold 37 mm. diameter.

Test piece 30 mm. diameter.

Distance between supports 300 mm.

Load 2.1 tons.

Deflection 4.5 mm.

The structure consists of eutectic or fine granular graphite and sorbitic pearlitic matrix.

The mass effect was measured by the Brinell hardness numbers at a cross-section through the central position of a K-shaped test piece 300 mm. long as shown in Fig 1 and it was found that there is substantially no mass effect.

Remarklectric furnace cast iron produced in a basic Hroult furnace with white slag or carbide slag according to heretofore ordinary method has tensile strength of about 25 kg./mm. and deflection of about 2.0 mm. and the mass effect is considerably larger than that of a cast iron obtainable by the method of this invention.

Example 11 Raw metal materials.Same as Example I.

Process for melting-Same as Example I.

Melt after tapping was inoculated with about 0.2% ferro-silicon.

Results-Results of chemical composition, mechanical strength and mass effect are as follows:

Tensile strength (test piece same as Example I) kg./mm. 42.33 Deflection (test piece same as Example I) mm 10.0

The mass effect was shown by the Brinell hardness number tested on the cross-sectional surface cut through the middle of a cube of 20 cm. as shown in Fig. 2, and it was found that every point showed almost equal hardness and the mass eifect is very small.

The structure is shown by Photo. No. 1 (37 mm. diameter, cast) and consists of uniformly dispersed short-flaked graphite and sorbitic pearlite.

Remark-Electric furnace cast iron reducing refined with heretofore method using white slag or carbide slag, even after it was inoculated with ferro-silicon, will become white cast iron or mottled cast iron with the composition shown in this example.

Example III Raw metal materiaL-Same as Example I.

Process of melting-Same as Example II.

Results.Results of chemical composition, mechanical properties and mass effect are as follows:

The structure, under the cast state, is shown by Photo. No. 2 and consists of nodular graphite ferrite and sorbitic pearlite with no free FesC. The structure after short time annealing is shown by the Photo. No. 3, consisting of annealed graphite and ferrite.

By adjusting the amounts of C and Si, a structure consisting of nodular graphite and ferrite under the cast state may be obtained.

Remark-Electric furnace cast iron produced by heretofore ordinary reducing refining method using white slag or carbide slag, even after inoculated with ferrosilicon, is white cast iron or mottled cast iron with the chemical composition in this example.

What we claim is:

l. A method of producing tough cast iron and steel containing short fiake graphite and nodular graphite which comprises reducing-refining the raw metal in a melting furnace with a refining agent containing a substance selected from the group consisting of the oxides and carbonates of the alkali and alkaline earth metals and a substance selected from the group consisting of carbon, silicon and aluminum and a further refining agent comprising CaCN: and a substance selected from the group consisting of SiOz, CaO and A1203.

2. A method of producing tough cast iron and steel containing short flake graphite and nodular graphite which comprises reducing refining the raw metal in a melting furnace with a refining agent comprising a substance selected from the group consisting of the oxides and carbonates of the alkali and alkaline earth metals and a substance selected from the group consisting of carbon, silicon and aluminum and a further refining agent FOREIGN, PATENTS V cvomPrising, N and sioz- 99,495 Great Britain t Nov. 11, 1953 702,776 Great Britainv Jan. 20, 1954 OTHER REFERENCES Refining Metals Electrically, 1st ed., pages 268 to 272, inclusive. Edited by Barton. Published in 1926 by The Penton Publishing Co., Cleveland,'0hi0.

'References Cited in the file of this patent W UNITED STATES, PATENTS Ellis Mar: 30, 1920 Jordan Aug. 5, 1952

Claims (1)

1. A METHOD OF PRODUCING TOUGH CAST ION AND STEEL CONTAINING SHORT FLAKE GRAPHITE AND NODULAR GRAPHITE WHICH COMPRISES REDUCING-REFINING THE RAW METAL IN A MELTING FURNACE WITH A REFINING AGENT CONTAINING A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF THE OXIDES AND CARBONATES OF THE ALKALI AND ALKALINE EARTH METALS AND A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF CARBON, SILICON AND ALUMINUM AND A FURTHER REFINING AGENT COMPRISING CACN2 AND A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF SIO2, CAO AND AL2O3.

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