US2241575A - Method of making cast iron and addition material therefor - Google Patents

Description

Patented M ay'1 3, 1941 UNITED STATES PATENT OFFICE METHOD OF MAKING CAST- IRON AND ADDITION MATERIAL THEREFOR Thomas E. Barlow, Columbus, Ohio, assignor to Battelle Memorial Institute, Columbus, Ohio,

corporation of Ohio No Drawing. Application March 24; 1939,

Serial Nonsense 2 Claims.

lacy type of graphite is frequently associated with patches of ferrite, commonly referred to as snowballs or primary ferri to differentiate from the ferrite which is normally found in certain compositions. Although modified or dendritic cast iron is said to have certain uses such as in the manufacture of heat resistant castings, it

- is found to exhibit lower tensile and transverse;

strength, lower deflection, lower resilience, decreased wear resistance and greater tendency to chill than the so-called normal irons. For these reasons the modifi structure is deemed to be unsuited to the majority of the uses of cast-iron. There are a number of alloys on the market today which will, to some extent, eliminate the tendency of gray iron to modify. One of the most common of these and the one on which the most work has been done is ferrosilicon. Unfortunately, however, the use of ferrosilicon is accompanied by a tendency towards shrinkage,

' blow-holes and porosity. T0 obtainmaximum effects from ferrosilicon, it is frequently necessary to add as much as 1.50 per cent silicon tothe ladle. When adding more than 1.00 per cent silicon the tendency to form blow-holes and shrinks becomes increasingly pronounced. With 1.5 per cent' silicon or more added to the ladle, it is almost impossible to cast completely sound test bars in green sand. The amount of ferrosilicon which may be used without danger of promoting porosityv and low strength is frequently insufficient to offset the tendency of the iron to modify. This is especially true of superheated irons.

Various other alloys have been used as ladle additions for the purpose of preventing modification of cast iron with some success. An alloy of titanium, aluminum, silicon and iron has been somewhat successful but theindications are that it is unduly concentrated to enable it to obtain the best results. The addition of more than 3 ounces of this alloy per hundred pounds of iron seems to be actually harmful.

Calcium silicide has been used as a ladle addition to prevent the modification of the cast iron. However, the fumes ensuing from its use are rather objectionable and there is room for improvement in' the results attainable therewith.

Silicon carbide is somewhat successful for the purpose in question. However, the increase in carbon and silicon resulting from its use tends to offset the beneficial effects thereof.

It has been found that the use of pure aluminum in the foundry for the purpose of preventing modification of cast iron is not advantageous. Apparently, the aluminum accumulates during melting and causes pin-holes and blowholes. Also, the aluminum is so potent as a ladle addition that the slightest excess causes these same casting defects. -It is claimed that if the ladle addition alloy contains-twice as much silicon as aluminum, the two elements flux ofi as a low melting point slag and that this prevents the aluminum content from building up to the danger point. I However, even the combination of silicon and aluminum in the proportions indicated for the production of an alloy to be used in preventing modification of the cast iron leaves something to be desired. I

One of the objects of this invention is to provide a method and an alloy for use therein which will relieve the above-mentioned modified structural deficiencies of the graphite-in the iron.

Another object of this invention is to produce an alloy for the purpose indicated which will be intrinsically beneficial to the physical and mechanical properties of the cast iron, instead of being detrimental or neutral in its effect upo such physical and mechanical properties. p This invention consists in the conception and verification of the-fact that a method of making cast iron can be greatly improved by introducing in'to the cast iron, while it is in molten form, a copper base alloy which preferably contains aluminum and silicon and which may also con-' tain manganese. It has been found that the in- .troductionof such an alloy intoiahe molten cast iron is. far superior to the effects of any of its components when they are added separately. The effect of such a single alloy as an addition material for the cast iron is also superior to the combined effects of all its components when they are added as ferrosilicon, ferromanganese, copper shot'and aluminum wire, for example. The superiority is apparently at least, partly due to (1)- the superior distribution of the individual elements when added as a single alloy and (2) the low melting point of the alloy which is approximately 1500 F. When my alloy is added to cast iron, it not only relieves or eliminates the abovementioned modified structural conditions of the graphite in the iron but it also introduces an alloying element or elements intrinsically beneficial rather, than detrimental or neutral to the improvement of the physical and mechanical properties of the cast Iron.

Copper was decided upon 'as a base for the alloy for three reasons. In the first place, tests have shown that copper in itself has a tendency to relieve the modified condition referred to above. Secondly, copper imparts definite benefits to cast iron, especially in regard to increasing density, decreasing chill, decreasing section sensitivity, increasing machinability and increasing strength and toughness. Also, large additions of copper do not tend to cause foundry defects such as blow-holes, pin-holes, shrinks, etc. In the third place, copper is a low priced metal and is readily available.

Aluminum was chosen as the chief deoxidizing element. It was felt, and later proved, that no harmful effects would result from the use of aluminum when diluted with a large amount of other elements such as copper. Also, when diluted with copper, no difilculty was had in getting uniform distributionof the aluminum in the molten cast iron bath. Another point of some consequence is the fact that a. small amount of aluminum is said to produce better distribution of copper in cast iron.

One undesirable feature of aluminum additions to cast iron is the fact that a finely divided oxide is formed which is frequently difficult to separate from the molten cast iron. These oxide particles frequently cause foundry defects. For thi reason, silicon is added to the alloy and, as indicated, manganese may also be added. When the correct ratio of silicon or of silicon and the manganese to aluminum is present, a low melting point slag is formed which readily separates from the molten metal. In addition, both silicon and manganese have a beneficial effect in regard to elimination of dendritic graphite.- In no case is it necessary to maintain the silicon and manganese contents of the alloy so high as to introduce any weakening effect into the resulting cast iron. In fact, the addition of manganese, especially in the presence of copper, is known to strengthen rather than weaken cast iron.

The range ofcomposition which is best suited for the aluminum, silicon, copper alloys is as follows:

. Percent Aluminum 1 to Silicon 6 to Copper 50-to 93 iron may be present percentages up to 30%.

.However, dilution of this alloy with iron would necessitate a larger addition of the alloy to the molten cast iron and'is therefore not desirable. The cost of producing-the alloy can be materially lowered by introducing the silicon'and manganese as ferrosilicon and ferromanganeseithereby introducing some iron. A150,; ironis a'common impurity in many of the materiais'of manufacture. However, the best results can be .obtained by maintaining the iron content below 10%.

sufficient to-oifset any ordinary tendency of the iron to modify. It is desirable to have the alloy sufliciently dilute to require 1% so as to take advantage of the apparent mass action effect involved. and also to ensure better distribution of the more powerfully deoxidizing elements present .such as aluminum and silicon. However, it is not advisable to have'the alloy so dilute that more than 1% is required because of the reduction of metal temperature effected by large ladle additions. 1 Due to the low melting point of the alloy, '1% can be added with no difficulty and still permit the addition of ferrochromium, ferromolybdenum, ferrovanadium, nickel, copper and other alloys which are frequently added for special purposes. In unusual cases, where a large degree of modification is encountered or where it is desirable to add more copper for special purposes, up to 2% of the alloy can be added withoutexcessive chilling of fairly hot molten iron. It has been found that this alloy unlike other deoxidizers such as silicon and aluminum, is not detrimental when added in excess of the recommended amount.

Aluminum contents of less than 1% would not be sufficient for efiicient deoxidation. Over 10% aluminum in the alloy would tend to introduce an excessive amount of aluminum into the resulting cast iron. Also tests have shown that aluminum contents over. 6% are decreasingly effective and therefore uneconomical after exceeding 10%.

The silicon-content of the alloy should be at least twice that of the aluminum and-at least 6% in order that the aluminum and silicon oxides formed will make a fusible slag which will separate readily from the molten metal; .Also it was found that if the silicon content was 10% or greater, the resulting alloy became extremely friable. This is a very desirable feature in that it permits low cost crushing of the material which will permit the production of the alloy at a. lower cost than would be possible if shotting we're necessary. Also, many authorities are of the opinion that a crushed alloy is more desirable due to the small sizes that may be available. The rate of solution will therefore be more rapid since the ratio of surface to mass is larger. The upper the fact that it is merely a diluent. Thus, the

limit of 25% silicon is based on the fact that a higher percentage would introduce a detrimental amount of silicon into the resulting cast iron. The. optimum percentage of silicon in the alloy is between 10% and 15%.

The manganese content of the alloy can be varied over a fairly wide range, though of course manganese is not absolutely essential and therefore may be absent. It has a beneficial effect both m increasing the effectiveness of the lower aluminum content alloy and also in lowering the final cost of the alley. Manganese is also very helpful in forming a low melting point slag which readily separates from the molten iron. It appears that a very low manganese alloy or even a manganese free alloy will have a considerable degree of the beneficial efiects of these alloys. More than 25% manganese is not advisable because it would raise the final manganese content of the resulting cast iron excessively. Although an, increase in the manganese content of the cast iron acts as a strengthener, the buyers of cast iron frequently set very definite limits on the manganese range.

Any alloy which would tend to raise the manganese content to a marked degree, would, of course, increase the difllculty of maintaining a fixed manganese content in the'cast iron. In some cases it would be. necessary to keep the manganese content of the alloy to a minimum. The

optimum amount of manganese in the alloy is believed to be approximately 10%, although up to 25% may be used.

The percentage of copper in the above alloy should be as high as possible due to its beneficial efiect both as a strengthener and toughener of 'cast iron and also as regard its effect on reduction of chill and section sensitivity and on increasing the machinability. Copper provides, (1) a base to carry the deoxidizing" element and the slag forming elements, (2) a means of introducing a large amount of alloy to the cast iron withoutcausing foundry defects, and (3) introduces beneficial effects other than those obtained from other foundry defects that frequently accompany ladle additions of high melting point alloys. Even if comparable results could be obtained from the independent additions of aluminum,

ferrosillcon, ferromanganese and copper to the ladle, the low melting point of the combined alloy would be an entirely justifiable reason for using it in preference to the separate components.

In the development of my invention, four different alloys were made in a small induction electric furnace lined with a clay graphite crucible. The melting practice was as follows: ,Ferrosilicon and ferromanganese were placed in the bottom of the furnace and covered with copper shot. When this charge was completely molten, the power was shut off, and aluminum was added in the form of wire. The resulting alloy was poured into small dry sand pig molds. In every case the alloy was crushed to pass a 6 mesh screen and was retained on a 28-mesh screen. The alloys were designated as follows:

'Alloy 1:

Percent Aluminum 3 Silicon 9.5 Iron 0.5 Copper 87 Alloy 2:

' Percent Aluminum 3 Y Silirnn 9,5

Manganese; 10 Iron 2.5

' Copper '75 Alloy 3:

Percent Aluminum 6 Silirrm 12 Ir 2 Copper 80 Alloy 4:

. Percent Aluminum 6 Silicon 13 Manganese r 10.5 Ir 2.5 Copper 68 Cast iron melts were made in an 120 lb'. induction electric furnace lined with a magnesia crucible. The charge for each heat was essentially the sameand consisted of pig iron, scrap steel, ferromanganese, ferrosulfide and ferrosilicon. The ferro alloys were added to the charge before melting was complete. Three-40 lb. ladles were poured from each 120 lb. heat. Each ladle of iron was treated with the desired ladle addition as indicated in the following tables. The ladle addition was made to the stream of metal while transferring the metal from the furnace to the ladle. The molten iron'was allowed to cool to 2550 F. before pouring into green sand molds.

areas under the transverse strength-deflectioncurves were used as a measure of resilience.

All values shown in the following tables are the average of four tests.

Averoge'physical properties of cast irons inoculated with ferrosilicon. copper and ferrosilicon, and aluminum-silicon-copper alloy 1 I Trans. Brinell Max. Trans. Resih- Bar No. temp Ladle addition load deg ence- T. S. 13 rs;- C. Si Cu F. Pounds Inches [n.Jbs. Lira/in. I Pct. Pct. Pct.

2550 .045#I-e BL--- 2450 0.235 540 32,500 3.32 1.02 2550 {gagg 2575 0.270 430 30,000 103 3.20 1.07 .95 2550 .45#alloy 1---- 2055 0.278 450 30,500 197 3.30 1.92 .78 2750 .0053 Fest... 2350 0.232 340 32,000 130 3.25 1.30 2750 2405 0.247 390 34,500 191 3.21 1.39 .94 2750 2555 0.201 435 38,500 207 3.17 1.83 1.02 3000 i. l 2340 0.210 330 32,000 3.10 1.93 3000 2510 0.225 350 35,500 200 3.17 1.37 .91 3000 .45#alloy,1 2015 0.234 350 40,500 210 3.15 1.39 1.00

Average physical properties of cast irons inoculated with ferrosilicon, alloy 2 and al 1011 3 Max. Trans. Trans Resili- Emu Bar No. temp. Ladle addition load dteiillggwoe T. 8 hard- T. C. Si Cu F. Pounds Inches In.-lba. Lila/in. Pd. Pct. Pet. 10 2550 .0454 Fe BL--- 2450 275 430 32,500 187 3.29 1.84 11 2550 .454 alloy 2---. 2620 0. 278 460 38, 500 200 3.28 1. 83 76 12. 2550 .451? alloy 3---- 2810 0. 291 510 39,000 m6 3. 24 1. 91 1.07

2750 .0454 Fe 81.... 2320 0.240 360 33,000 191 3.31 1.80 2750 45# alloy 2.--- 2621 0. 279 460 37, 590 204 3. 24 1.84 90 2750 45# alloy 3---- 2670 0:292 490 38, 000 206 3. 24 1.86 .88 3000 .0454 Fe 81.... 2500 0.232 380 32, 500 197 3. 17 1.80 3000 .45# alloy 2---- 2610 0. 242 430 39,5) 214 3. 16 1. 80 91 3000 45# alloy 3-..- 2740 0. 277 600 41,000 213 3. 14 1. 76 76 Average physical properties of cast irons inoculated with. ferrosilicon, alloy 3 and alloy 4 Trans. Brinell Max. Trans. Resili- Bar No. temp Ladle addition load doggeenoe T. S. hlaersg- T. C Si Cu Pounds Inches I'm-lbs. Lba/in. Pct. Pct. Pd. .0455! Fe 51.... 2480 0. 308 620 34, 500 181 3.25 1. 94 .02 .45# alloy 3.... 2685 0.298 520 36,000 200 3.23 1.92 .83 45;! alloy 4...- ,2620 0. 272 460 38, 000 205 .3. 23 1. 94 77 0451! Fe 81.... 2360 0. 239 370 33, 500 193 3. 23 1. 91 02 .45#a1loy 3.... 2720 0.292 500 38,000 202 3.22 1.84- .84 45# alloy 4.-.- 2740 0. 282 490 37, 500 201' 3. 21 1. 89 76 .045# Fe 81.... 2365 0.242 v 370 35, 500 189 3.22 2. 03 .02 45# alloy 3.... 2630 0. 271 465 37, 500 207 3. 20 1. 96 93 .45# alloy 4.-.. 2600 0.204 440 37,000 207 3.22 1.94 .65

cast irons inoculated with ferrosilicon and varying amou nts of alloy 3 Trans Brinell Max. Trans. Reslli- Bar No. temp Ladle addition load dailieenee '1. S. liaergds T. 0 Si Cu F. Pounds Inches I'm-lbs. .Lba/in! Pd. Pd. Pct. 3000 2190 0. 240 350 29, 000 v 179 3. 26 1. 81 3000 2420 0. 334 540 30, 500 170 3. 21 2. 32 3000 2680 0. 317 570 36, 000 197 3. 25 1. 93 3000 N one.... 2330 0. 231 356 30, 000 183 3. 24 1. 92 3000 25# Fe 2260 0. 331 500 30, 500 167 3. 17 2. 49 3000 60;? alloy 3.... 2520 0. 281 465 34, 500 199 3. 24 2. 3000 None 2330 0. 296 310 32, 000 194 3. 1. 84 3000 Fe Si. 2250 0. 322 490 32, 000 172 3. 18 2. 37 3000 80# alloy 3.... 2740 0. 304 550 40, 500 210 3. 17 1. 98 1. 20

Based on the above data alone, it is obvious that the aluminum-silicon-copper alloys and the aluminum-silicon-manganese-copper alloys have I a :beneficial efiect on cast iron. The increase in value for deflection shows that these alloys inhibit the formation of dendritic graphite in cast iron. It will also be apparent that these alloys do not introduce any weakening or detrimental elements such as are introduced by the addition of ferrosilicon in sufiicient quantities to yield comparable deoxidizing effects, the degree of deoxldizing" being indicated by the value for deflection, with low deflection usually indicating dendritic graphite.

That the dendritic graphite was inhibited by the use of'my alloys was verified by examination of the fractures of the bars'which were a clean bright gray characteristic of normal cast iron, instead of being dark and sooty as characteristic of modified cast iron.

Due to the low melting point of my alloys, no dlfficulty was encountered in adding them to molten cast iron, even to small ladles at low temperatures. The optimum or economical amount of these alloys to be added appears to be 1%. The best of those alloys studied were those containing 6% aluminum.

In view of the above and other published and unpublished information concerning the phenomenon of modified cast iron, it is believed that my alloys serve as a deoxidizing agent for cast iron which is superior to previously known deoxidlzing agents and which impart to the cast iron benefits other than those due to deoxidizing alone. It is low in cost and is easily added to and readily absorbed by the molten cast iron without introducing any weakening or detrimental effects or foundry defects such as blow holes and in excess of 50 per cent, the balance being substantially all iron but not exceeding 30 per cent.

2. A material for addition to molten iron, which will be gray iron when cast, for the purpose of inhibiting or decreasing modification of the cast iron comprising a copper base alloy consisting of 1 to 10 per cent aluminum, 6 to 25 per cent silicon, manganese in effective amounts up to 25 per cent and copper in excess of 50 per cent. the balance being substantially all iron :but not exceeding 30 per cent.

THOMAS E. BARLOW.