US2157390A - Method for making cast iron - Google Patents

Description

UNITED STATES PATENT OFFICE 2,157,290 METHOD FOR MAKING oas'r moN William J. Prlestley, New Rochelle, N. Y., assignor to Electro Metallurgical Company, a corporation of West Virg nia No Drawing. Application January 25, 1937, Serial No. 122,235

9 Claims. (Cl. 75-58) The invention relates to cast iron and proterials are substantially additive when they are vides a novel method and means for improving added in this fashion. cast irons of all varieties. The invention will -I have discovered that if graphite, or other be described in connection with gray cast iron form of carbon, is intimately mixed with silicon made in the cupola with little or no steel in the or zirconium, or both, and this intimate mixcharge; but the invention is equally suitable for ture is added in relatively small amount to a use to improve all varieties of cast iron, includmolten cast iron, the iron is improved to 'an exing white and mottled iron and irons of mixed tent, and in a manner, quite different from what or graded structures, when made in any type of could be predicted from the previous knowledge 1 furnace from any kind of charge. I of the individual efiects of the constituents of the 0 Sources of weakness in gray cast iron are the mixture. formation of large graphite flakes and large Specifically, such a mixture refines the grain grains in heavy sections, too deep a chill in light and the graphite flakes in heavy sections, reduces sections, and too large an amount of "eutectid or eliminates chill, suppresses or inhibits the graphite in sections behind a chill. An ideal gray formation of eutectic graphite, inhibits the for- 15 cast iron would have a uniform fine-grained mation of an open grain structure inside heavy structure, uniform chill characteristics, and fine sections, and raises the tensile and transverse I flake graphite uniformly distributed. strength without greatly altering the ductility i It is well known that the chilling characteror hardness of the main body of the casting, the l istics of a cast iron may sometimes be reduced efi'ects obtained depending, of course, on the 20 l by a relatively small addition of graphite in the composition of the melt and the casting condiforehearth or ladle. This eilect is accompanied, tions. however, by a softening of the metal and, in some Although graphite is preferred as the carcases, by a decrease in its tensile and transverse bonaceous ingredient of the mixture, because of 5 strengths. These eflects are illustrated by the its ready solubility in molten iron, other forms of data in Table A. carbon, such as charcoal, coal coke, petroleum Table A Anal is of cast iron ys Tensile Transverse Deflec- Brincll 30 N9. Ladle-addition strength, strength, tion, hardness T. 0. Percent Percent lb/sq. in. lb/sq. in. inches number percent Si Mn 1 None 2.05 2.98 0.6 31,160 3,620 0.18 170 8 2 Graphite 3.05 2.85 0.6 30,425 3,100 0.15 166 4 ounces of graphite per 100 pounds of metal. It is also known that the chilling charactercoke, or carbon black, may be used. The silicon istics can be reduced by adding silicon or zircoor zirconium may be used in any of the com- 40 nium, in small amounts, in cupola, forehearth, or mercial forms of these elements, such as silicon 40 ladle. In order to secure markedly improved remetal, ferrosilicon, 0r silicon-zirconium alloysults by t means, however, it 1 necessary t When ferrosilicon is used, it is particularly aduse so much 01' the silicon addition that the com- Vantageous t use a fellqsilicon C ntaining at position is changed substantially, and the base least 65% silicon. Ferrosilicon having a lower a mixture must be altered to compensate for this proportion of 511100 appears "1 cool the Iron change so that the correct final composition will at least locally, while those having at least be obtained. Sometimes, the chill in light secgenerate emugh heat by exmhermic tions of a casting cannot be suppressed by this actmn to counteract any cooling effect I A mixture of approximately equal parts by expedient without producing undesirably coarse weight pf graphite and grade ferrosilicon eraphite 1n the heavier sectionwill be found to be of most general suitability, al- 0 On occasion, both ferrosilicon (containing 50% though tur containing other proportions silicon) and graphite have been added to cast may be used. If a relatively large amount of the iron, almost simultaneously but not in admixture. mixture is employed, the proportions may range As would be expected, the efiects of the two mafrom 5% carbon and ferrosilicon or its equivalent, to 95% carbon and 5% ferrosilicon or its equivalent; but if only a small amount of mixture is used, the proportions should be between 25% and 75% carbon, remainder ferro- 5 silicon or its equivalent.

The ingredients of the mixture should be finely subdivided and intimately mixed. Particle sizes from that just passing a three mesh screen to fine powder have been used successfully, and somewhat larger particles are useful. The mixture may be used as loose grains or powder.

The amount of mixture to be added will vary, of course, with the type of cast iron and the intensity of the effect desired; but in no case need 15 it be sufficient to alter substantially the chemical composition of the cast iron. Additions of 4 to 8 ounces of the mixture for each 100 pounds of cast iron have given excellent results; but smaller or larger amounts, between the approximate limits of 1 to 16 ounces per 100 pounds of cast iron, are useful, the upper limit being set chiefly by considerations of economy and change of composition. The benefits conferred by the invention are illustrated by the data appearing in Table B:

selected from the group consisting of silicon and zirconium, the amount of said mixture added being between one and sixteen ounces for each 100 pounds of molten cast iron; and castingthe melt.

2. Method of making cast iron which comprises adding to a molten cast iron an eflective amount of an unbonded intimate mixture containing 25% to 75% graphite and the remainder principally ferrosilicon containing at least 65% silicon, the amount of said mixture added being insumcient to change substantially the chemical composition of said molten iron, and casting the melt.

3. Method of making cast iron which comprises adding to a molten cast iron an eflectlve amount of an unbonded intimate mixture consisting essentially of graphite and ferrosilicon in substantially equal amounts by weight, the ferrosllicon containing at least 85% silicon, the

amount of said mixture added being insuflicient to change substantially the chemical composition of said molten iron, and casting the melt.

4. The method of reducing the chill of a highsulfur, low-silicon cast iron containing not less Table B Analysis oi cast iron Tensile Transverse Deflec- Brinell 0 No. Ladle addition Strength, strength, tion, hardness Percent T. 0. Percent lb/sq. in lb/sq. in. inches number percent Mn 1. 58 2. 95 0. 6 32, 786 3, 390 0. 09 1. 56 3. 0. 6 38, 080 3, 730 0. 10 1. 62 2. 90 0. 6 40, 400 3, 760 0. 11 l. 84 3. 16 0. 7 37, 180 2, 340 0. 22 1. 95 3. 20 0. 7 40, 160 2,800 0.30 l. 95 3. 18 0.8 2, 220 0. 19 l. 98 3. 24 0. 8 2, 760 0.28 2. 98 2. 95 0. 6 31, 100 3, 620 0. 18 2.98 2. 95 o. e s, 740 o. 13

40 4 ounces of addition mixture per 100 pounds of cast iron.

" 8 ounces of addition mixture per 100 pounds oi cast iron.

Addition mixture consisted of equal parts by weight of graphite and ierrosilicon containing 85% Si.

In Tables A and B, the symbol T. C." means total carbon; and tensile strength and transverse tests were made in accordance with the standard A. S. T. M. specifications. The transverse tests on samples 6, 7, 8, and 9 were made on supports 18 inches apart; on the remaining samples, on supports 12 inches apart.

The presence of large amounts of strong .carbide-forming elements, in the cast iron, such as more than 10% of chromium, masks or destroys the beneficial effects of the invention by preventing graphitization of the combined carbon.

The chill ordinarily produced in low-silicon irons by the presence of a high sulfur content is reduced or eliminated by the use of the addition mixture of the invention. For instance, a melt of white-iron composition containing 0.75% silicon, 0.28% manganese, 0.31% sulfur, 0.143% phosphorus, 2.86% carbon, remainder iron, was treated by the addition of a small amount of the addition mixture referred to in Table B, and the melt cast. The casting was found to be a mottled iron instead of a white iron.

Modifications of the, invention as described herein will readily occur to those skilled in the art. Accordingly, the invention is not limited to' the specific examples mentioned above by way of example.

I claim:

1. Method of increasing the strength of cast iron which comprises'adding toa molten cast iron an unbonded intimate mixture containingthan 0.1% sulphur, which comprises adding to a melt of said cast iron a small but eflective amount of an unbonded intimate mixture containing 25% to 75% comminuted graphite and the remainder comminuted ferrosilicon containing at least 65% silicon, the amount of said mixture being insufiicient to change substantially the chemical composition of said melt, and casting the melt.

5. Method of making cast iron which comprises adding-to a molten cast iron an eflective amount of an unbonded mixture containing carbon and at least one element selected from the group consisting of silicon and zirconium, the proportions of carbon and said element in said mixture being approximately equal by weight, and the amount of said mixture added being insumcient to change substantially the chemical composition of said molten iron; and casting the melt.

6. Method of making cast iron which comprises adding to a molten cast iron an effective amount of an unbonded mixture containing graphite and silicon, the proportions of graphite and silicon in said mixture being approximately equal by weight, and the amount of said mixture added being insufllcient to change substantially the chemical composition of said molten iron; and casting the melt.

7. Method of making cast iron-which comprises adding to a molten cast iron a small but effective amount of an unbonded mixture containing graphite and ferroeilicon containing at ammoo 3 least 65% silicon; the proportions of graphite and terrosillcon in said mixture being approximately equal by weight, and the amount of said mixture added being insufllcient to change substantially the chemical composition of said molten iron; and casting the melt.

' 8. An agent for treating molten cast-iron in a forehearth or ladle, consisting of an unbonded intimate admixture of powdered materials and 1 composed wholly of carbon and material selected from the group: silicon, ferrosilicon, zirconium, and silicon-zirconium; the carbon being between 25% and 75% of the agent.

9. An agent for treating molten cast-iron in a forehearth or ladle, consisting entirely of an unbonded intimate admixture of powdered graphite and powdered ferrosilicon in approximately equal parts by weight.

WIILIAM J. PRIESTLEY. 10