US2256674A - Method of making malleable cast iron - Google Patents

Description

Patented Sept. 23, 1941 METHOD OF MAKING MALLEABLE CAST IRON Anthony M. Herrmann, Racine, Wis., assignor to Belle City Malleable Iron Company, a corporation of Wisconsin No Drawing. Application December 6, 1939, Serial No. 307,775

Claims.

This invention relates to improvements in the production of malleable iron castings. More specifically it relates to a charge for forming malleable iron castings of a high silicon content.

It is known that a large amount of silicon in an iron reduces the time of annealing, because silicon tends to promote the breaking up of iron carbides during annealing into temper carbon and ferrite. The time of annealing is reduced as above stated with a high silicon content so long as the casting upon cooling and before annealin is free from flake graphite precipitation. However,'there has been considerable difliculty in obtaining this condition, since a high silicon content normally causes graphite precipitation;

Several methods have been devised to obstruct the flake graphite precipitation.

One method has been to chill the casting as rapidly as possible by the use of a chill mold. The disadvantage of this method is that only certain shapes and designs of castings may be produced with a chill mold. Another method involves the use of certain metals in the melt which inhibit the formation of graphite. However, such ingredients are expensive, and the size of section of casting in which these ingredients are effective is limited.

An object of the present invention is to produce an improved malleable iron casting.

A further object is the production of a malleable iron casting which requires a relatively short annealing'period.

Another object is to produce a malleable iron casting of high silicon content in large sections with only a short annealing time.

Still another object is the production of a malleable iron casting of high silicon content without the use of a chill mold or of ingredients obstructing the formation of graphite.

According to my invention I produce malleable iron castings of high silicon content by employing a charge of raw materials in the melt which are completely free or substantially completely free from graphite flakes, nodules, and nuclei. 1 have discovered and proved that ferrous metals will retain, to a certain extent, the characteristics of the metals melted, and that the presence of graphite flakes or nodules in the raw materials which go to make up the melt causes the formation of graphite in the melt upon solidification. Appreciable amounts of graphite flakes, etc. in the charge produce appreciable amounts of graphite flakes in the final product. Conversely, if the charge is free from graphite flakes originally, there is nothing to start the formation of flakes, and the casting upon solidification is free from graphite.

- pig iron and malleable iron scrap, the carbon of which is mainly graphitic. An example of a typical charge is as follows:

railway malleable or agricultural malleaable) The use of materials containing graphitic carbon in the above charge would prevent'the use of a large amount of silicon, since there would result a flake graphite precipitation.

When raw materials forming the charge are free from graphite flakes, nodules, and nuclei, the melt solidifies without flake graphite precipitation. Castings of relatively large section may be produced and possess a strength superior to castings produced under the old process with a long period of annealing. I have found that the following raw materials, free from graphite flakes, nodules, and nuclei, may be used: white cast iron sprue 0r remelt, steel scrap, white cast pig, chilled sections of car wheels, and silvery pig.

Following is a summary of tests carried out under my invention:

Heat N0. 1

Charge Weight Charge Carbon Silicon Pounds Percent White cast iron remelt 530 43 2. 40 l. 00 Steel scrap 260 21 20 20 Silvery pig 112 9 60 19.00 White cast pig 330 27 3. 30 l. 00

Analysis of Heat Carbon 1.79 Silicon 2.45 Manganese q .25 Sulphur Not determined Phosphorus Not determined Tensile strength lbs./sq. in-.. 69,820 Yield point d0 51,666 Elongation Per cent-.. 17.18 Brinell 1 146 Time for annealing was about ten hours.

A test bar 4" x 4" x 9", poured into a sand mold, solidified white. This shows absence of carbon in graphite form. Similar results were obtained with a test bar of the same size, 0.2% (2:156 5feqrro-silicon being added to raise silicon to denum and .60% manganese, making a total o1 .85% manganese, to produce a pearlitic malleable iron, showed the following properties after a 13 hour annealing cycle:

Tensile strength lbs./sq.in 79,010 Yield point do 57,360 Elongation percent 11.3 Brinell 187 Heat No. 3

Charge Charge Carbon Silicon Per cent Steel scrap 9.5 .20 .20

Analysis of heat Carbon 2.14 Silicon 2.38 Manganese .26 Sulphur Not determined Phosphorus Not determined Range of four test bars that small amounts of graphitic carbon may be e Heat No. 2 Analysis of heat Carbon I 2.07 Charge Weight Charge Carbon Silicon Silicon 2.22 P do P M 5 Manganese .23 Sulphur Not determined st lfieh fifii'ffifffiii 1 :9 35 12 3 :12;: Phosphorus Not determined Sil wl ii t e c a pig 800 30 3.00 1.00 Range of four test 'bars 0 b Tensile strength lbs./sq.in 63,000 to 66,000 10 Yield point "00---- 46,500 to 48,000

, Elongation percent 15 to 17 /2 Analysis of heat Brinell 163 to 166 Carbon Duplicate bar bent before failure. Silicon 2.31 15 Time of annealing was. about ten hours.

$3233 The bars tested for strength from theabove Phosphorus Not determined 32 33 232 of the size conformmg to Tensile strength 1bs./Sq.in 68,200 In each of the above heats, test bars measuring Yield point d0 49,20 20 4" x 4" x 9" in size appeared white under frac- Elmlgflfifln 'p iL- 17-18 ture. This indicates the absence of graphitic Brinell 166 carbon, and, consequently, that an iron is being 1 h produced which will be of satisfactory strength g tune of annealing was 7 ours as to! after the short annealing time of 8 to 10 hours.

zhours 10 minutes to 17500 25 A typical charge for production under com- 2 hours at 1750 mercial operating conditions is as follows:

20 minutes to 1400 1 u t 1400 Charge Charge Carbon Silicon 2 hours to 1320 Then withdrawn from oven. .60 19. 00 One test bar was bent 100 before failure. smelscmp ;;3 ;;3 A test bar, to which were added .40% molyb- White cast pig 21.00 4.30 1.00

of carbon and silicon to be present in the casting.

The constituents might well be kept within the following limits:

Percent of charge White cast iron remelt 30-60 Steel scrap 10-50 Silvery pi 3-20 White cast pig 15-50 In the above the white cast iron remelt may have up to 2.5% silicon and from 2 to 2.5% carbon in combined form, the steel scrap about .2% silicon and .2% carbon, the silvery pig from 15 to 20% silicon, and the white pig iron up to 1% silicon and from 3 to 4.3% carbon in combined form.

It is not necessary to use all of the above ingredients or any one of them. The important thing is that there be substantially no carbon in. the ingredients in graphitic form.

I have stated that the raw materials forming the charge should be free from graphite flakes, nodules, and nuclei. This condition need not be maintained too strictly, for I have discovered present in the charge without afiecting the casting. There appears to be a point in percentage of graphitic carbon below which graphitic car bon will not form in the casting, while above this point graphitic carbon will begin to appear.

It is to be noted that the carbon raiser of Heat No. 2 is entirely graphitic carbon. I introduced this into the charge with the hope of finding out how much graphitic carbon could be present in the charge without graphitic carbon in the casting. The white cast pig in the charge was considerably mottled and so also provided some graphitic carbon. However, test bars from this heat were white and free from graphitic carbon.

It will be appreciated from the foregoing description that I have discovered a novel way of producing a malleable cast iron of a high silicon content. The novelty lies in the use of a charge for the casting which includes the usual raw materials containing iron, carbon and silicon, but which materials are completely free from graphitic carbon or are free to the point where the small amount of graphitic carbon does not cause the formation of graphitic carbon in the casting. A casting, formed in this manner, has the decided advantage of requiring a much shorter annealing time for malleabilization. Furthermore, the castings produced under my invention have a very high tensile strength and yield point strength as is evident from the results of the heats tabulated above. These strengths are considerably higher than those obtained with casting produced prior to my invention.

The intention is to limit the invention only within the scope of the appended claims.

What is claimed is:

1. In a method of making malleable cast iron, the step of melting a charge consisting of materials containing in addition to normal impurities only iron, silicon, and carbon, and being substantially free of carbon in graphitic form and proportioned to produce a white cast iron, when cast in a sand mold, containing at least 1.75% carbon and at least 2% silicon.

2. In a method as specified in claim 1, the amount of graphitic carbon in the charge being so small as to be without effect in causing the production of graphitic carbon in the cast iron before malleabilizing.

3. In a method of making malleable cast iron, the step of melting a charge consisting of portions of steel scrap, metal of the group consisting of white cast iron remelt and white pig iron, and iron containing in addition to carbon only a high amount of silicon sufiicient to produce the amount of silicon required for an analysis of at least 2% silicon in a White cast iron, when cast in a sand mold, containing also at least 1.75%

carbon, there being substantially no graphitic carbon in all the aforementioned portions.

4. In a method as specified in claim 3, the amount of graphitic carbon in all the aforementioned portions being so small as to be without efiect in causing the production of graphitic carbon in the cast iron before malleabilizing.

5. In a method of making malleable cast iron containing at least 1.75% carbon and at least 2% silicon,.the step of melting a charge consisting of 30 to 60% of material containing up to 2.5% silicon, 2 to 2.5% carbon in combined form, and the balance substantially all iron; 10 to 50% of material containing about .2% silicon and about .2% carbon and a balance substantially all iron; 3 to 20% of material containing 16 to 19% silicon and the balance substantially all iron; and 15 to 50% of material containing up to 1% silicon, 3 to 4.3% carbon in combined form, and the balance substantially all iron, the above ingredients being so proportioned as to produce a white cast iron, when cast in a sand mold, con-