US2276287A - Production of cast iron - Google Patents

Description

Patented Mar. 17,1942

PRODUCTION OF CAST IRON Henry T. Chandler, New York, N. Y., assignor to Vanadium Corporation of America, New York, N. Y., a corporation of Delaware No Drawing. Application October 11,1940, Serial No. 360,841

11 Claims.

This invention relates generally to the production of cast iron and more particularly to addition alloys for cast iron, which are added to cast iron to improve their engineering and physical properties.

of stabilizing the carbides and restraining carbide decomposition resulting in increased wear resistance, decreased growth at high temperatures, improved strength, hardness and other desirable properties. On the other hand, however, it increases the tendency of the iron to chill, particularly in thin sections, which for some applications is undesirable. As an example, in the production of cast iron automotive cylinder blocks,

it is often desired to have a chromium content of, say, .35 to 50%, in order to impart to the cast iron the desired physical characteristics of strength, hardness and wear resistance along the cylinder bore and valve seats. However, acylinder block has portions, such as flanges and parts of the water jacket, which are of thin section and, when the required amount of chromium alone is used to give the desired characteristics in the bore of the cylinder block, the flanges and other 7 thin parts are chilled to such an extent that either it is diflicult or impossible to machine them or they crack during cooling of the casting.

In order to overcome the chilling tendency of cast iron, whether or not it contains chromium, various other alloying elements have been added. Among these, perhaps the most widely used are nickel and copper. The use of either of these elements nickel or copper together with chromium is open to certain disadvantages. In order to counterbalance the chilling efiect of 35% chromium, it is necessary to use about .'70% nickel. The ratio of nickel to chromium required for balancing the chilling effect of the chromium increases as the percentage of chromium in the cast iron is increased. Thus for an iron containing 50% chromium, about 1.75% nickel is needed and for an iron containing .90% chromium, about 3.0%nickel is required. The use of these amounts of nickel renders the cost excessive for certain types of work. The same is true for copper.

In accordance with the present invention, 1

treat cast iron with an alloy containing chromium, manganese, silicon and iron. The alloy may or may not contain calcium. The use of an addition alloy containing all three elements chromium, manganese and silicon, or all four elements chromium, manganese, silicon and calcium, produces results in the treated cast iron which are entirely different from what would be obtained if the elements were used separately or. as a mere mechanical mixture. Various alloys, for example, ferrochromium, ferromanganese and ferrosilicon, have difierent melting points and different solubilities in cast iron. Thus when these ferro-alloys are added as a mere mechanical mixture, the chromium, manganese and silicon do not act simultaneously on the bath, but in accordance with their respective solubilities and the amounts in which they are present. If the ferrochromium, ferromanganese and ferrosilicon are added successively to the bath, the first added element has an opportunity to react with the constituents of the bath before the other elements are added and, therefore, the later added elements do not have the same bath present on which to react or with which they may alloy.

The distinction between an addition alloy on the one hand and a mere mechanical mixture of alloying elements on the other hand is particularly pronounced where the alloying elements react with each other or with elements present in the bath. Cast iron baths always contain oxygen, nitrogen, sulphur and perhaps other impurities to a greater or lesser extent and these impurities vary with different baths. Where, therefore, separate additions or a mere mechanical mixture of alloying elements is used, it can not be predicted beforehand what the effect of the addition elements in removing or fixing the impurities will be or the degree to which each of the addition elements will be lost by reacting with'the impurities. On the other hand, where my addition alloy is used and the amount of impurities in the different baths varies, the alloying elements in my alloy are so proportioned that after they have performed their deoxidizing function the remaining portions of them are in proportion to produce the desired alloying eflect.

The addition alloys of my invention produce cast iron having properties which are not at all the same but are vastly superior to the properties which may be imparted to cast iron by the addition thereto of a mere mechanical mixture of the various alloying elements or by their separate use.

My alloy when added to cast iron not only I The manganese in my addition alloy also in creases the tendency of the cast iron'to chill, but to a lesser extent than chromium. It stabilizes the carbides at high temperature and refines and hardens the pearlite matrix. It is a somewhat stronger deoxidizer than chromium and combines with sulphur to form manganese sulphide. Since sulphur is a hardener in cast iron, its conversion into the form of manganese sulphide counteracts this tendency to harden the iron.

The silicon is a graphitizer. It strongly retards the tendency of the cast iron to chill. In addition, it is a fairly strong deoxidizer and removes oxygen which otherwise would act as a hardener for the cast iron.

The function of the calcium in .my addition alloy is to act as a powerful deoxidizer and scavenging agent. It is preferred to use calcium or some other scavenging agent, particularly when the cast iron contains substantial amounts of oxygen, sulphur or nitrogen, but its use, although preferable, is not essential and it may be omitted in some instances. It will be noted that each of the elements chromium, manganese, silicon and calcium is a deoxidizer and that the effect of these elements ranges from mildly deoxidizing to strongly deoxidizing. The action of my alloy is, therefore, twofold. A certain amount of the alloying elements is used in reacting with the 0, N and S and perhaps other impurities. The remainder has an alloying effect on the cast iron.

The following is aspecific example of one type of my addition alloy:

Example 1 Percent Chromium 30.0 Manganese 'L 15.0 Silicon 22.0 Calcium 1.25 Carbon 2.0 Iron Balance The composition of my addition alloy may be varied within wide ranges, depending upon what effect it is desired to produce in the cast iron to which it is added. The chromium may be between about 10 and 65% but is preferably between about 25 and 50%. The manganese may be as low as about 2% or as high as about 50%; but for most uses, it lies between about 5 and 30%. The silicon may be between about 5 and 50% but usually is between 10 and 40%; Calcium may or may not be present in the addition alloy but, if present, may be up to about 20% but is preferably not over about 10% by weight of the alloy. The carbon may be between .10% and 10% but is preferably below about 6%.

Further examples of my addition alloy are given in Table I.

TABLE I Addition alloy (r M11 51 0 Ca 0 Percent Percent Percent Percent Percent 6 52 7 9 4. 70 1.22 24 982"". 44 8 13 3.90 1.80 -17 5 46 7 l5 3. 83 2. 2c -l5 30 32 18 22 l. 42 54 -12 32 36 10 23 l. 66 24 ll 4 45 6 25 l. 66 l. 18 4 10 29 15 25 1.31 3. 64 --i 1 30 9 2] 1. 85 0 4 34 31 15 31 49 66 +1 11 27 13 33 97 7. 32 +8 13 3i 4 35 l. 47 8. 0 +16 Do"... '15 8 44 72 13. 90 +29 The column G designates the graphitizing factors of the addition alloys according to the formula TABLE II Cast iron containing addition alloys Test Si Mn 'r.c. c1 cc '1 s. ,125, 13. RN No. 2"dia 1 3 2"dio.

.\. .2.49 .58 3.22 .11 .16 %,45036,050 44,550 207 6.....260 .61 3.22 .33'.16 31182532650 44,975 2% 5 -.2s1 .64 3.10 .30 .10 a1,eso42,4ao 45,725 212 11.-..254 .59 3.26 .09 .21 29,72540,310 42,250 207 4 2.64 3.30 .28 .17 3l,85042,460 42,075 241 .C-- 2.49 .58 3.20 .08 .23 31,45035,500 41,125 212 l0- .2.67 .es 3.21.33 .22 33,27540,900 38,525 22; l .2.6l .62 222 .28 .2: 32,2154o,20o 44,175 223 1)-.-.241 .61 3.21.08 .2: 30,87540,170 40, 211 11..-.250 .61 3.15 .2; .2; ao,15o41,1oo 45, 212

B. H. N.=Brinell hardness number.

Cast irons 5 and 6 were made by adding addition alloys 5 and 6 respectively to the cast iron designated A. Cast iron 4 was made by adding as compared with the untreated cast iron usually in the neighborhood of 2,000 to 3,000 pounds per square inch. Also in all cases with the exception of cast iron 11, the Brinell hardness number was increased by the addition ofmy alloy.

Furthermore, it will be seen from Table III that by the use of my alloy chromium may be.

added to cast iron to impart to it the desirable effects of chromium without, however, increasing the chilling tendency of the iron. In fact, this chilling tendency may be even decreased.

. The effects of the various addition alloys 1, 4,

5, 6, 10 and 11 on chill are shown in the following Table III, as'is also the chilling effect of chromium alone as obtained by, adding ferrochromium to the cast iron.

TABLE I-II Chilling efiect of various addition alloys Chill Chill depth in depth in Chill Percent Alloy No. mm. after mm. in change change in G alloy untreated in mm. chill addn iron 13 6 +7 +116 32 8 6 +2 +33 24 6 l l6 -l5 5 6 1 l6 4 4 6 2 33 4 3 6 3 5O 4 4 8 4 -50 +8 The data for Table III were obtained by employing a chill test specimen 4" long x 2" high x V wide, cast in a core with a thin edge against an iron plate. The depth of chill was measured in millimeters and was the amount of penetration of the white area from the chilled face.

It will be noted from Table III that the addition of-alloys 5, '4, 1, 10 and 11 decreased the depth of chill, whereas alloy 6 increased the depth of chili. In every case, however, the use of the addition alloys improved the tensile strength and other physical properties of the cast iron. Thus by the use of my alloys, I may increase the phys ical properties of cast iron and can either in-. crease or, decrease the tendency of the iron to chill or can retain the tendency to chill substantially unaltered as compared with the untreated cast iron. The fluidity of the molten iron after treatment and its shrinkage characteristics also are materially improved.

The percentages of chromium, manganese, silicon, either with or without calcium which shoud be used in my addition alloy, will depend upon xthe particular properties desired in the cast iron.

The graphitizing factor (G) of any particular addition alloy may be figured according to the arbitrary formula Applying this formula to the addition alloy given in Example 1,

Referring to Table III, it is seen that the addition alloys have been arranged in accordance withjtheir increasing (G) values. Alloy 6 having a (G) value or graphitizing factor of -24 increased the depth 'of chili 33% in the test specimen used. Alloy 5, which had a graphitizing factor of 15, decreased the chill depth 16%. An alloyhav'ing a graphitizing factor of approximately ,',18 would neither increase nor decrease I the chill depth in the chill test specimen, for chromium contents in the treated iron of approximately .30 to 50%. Where, different amounts of chromium are introduced, a different graphitizing factor would be required to produce a balanced alloy, which would neither increase nor decrease the chill when added to a base cast iron. l

Although the percentages of chromium, manganese and silic on-jnay be varied within the ranges given, it is preferred in general commercial practice that they be selected in" such probecause of' section to be cast or composition of the untreated iron it, graphitizes too readily I preferably between +16 and 2Q Where either employ an addition alloy having a high negative graphitizing factor. For example, in castings of extraordinary sizes beyond the usual foundry practice, I may use an addition alloy having a graphitizing factor of say 20 to -35. On the other hand, it may be desired to convert an iron which would normally be white or mottled as cast into one which is gray as cast. In this case,- an addition alloy which has -a graphitizing effect may be used. Thus in treating a' normal white iron composition, the addition alloy may have a graphitizing factor of, say, +5 to +35. By the use of my addition alloy, the range of size of castings of a given quality which is permissible with any given base iron is greatly enlarged.

In using the addition alloy, it is preferably added to the cast iron in the ladle, the amount of addition alloy employed being figured to give the desired chromium content in the cast iron. In general practice, the amount of addition alloy added is sufficient to give in the cast iron a chromium content of about .10% to 1.0% but this may, of course, be varied considerably.

The invention is not restricted to the use of the addition alloys for producing gray cast iron but, due to the independent control of chili made possible by the use of my alloys, the invention is applicable to the production of chilled cast iron parts, such as car wheels, cam shaftsand valve tappets, or in the production of articles where it is desired to have one part chilled and another part machinable.

Addition alloys in accordance with my invention may be made bymelting ferrochromium and silicomanganese in an electric or other furnace under a protective slag. Where the alloy is to cdntain calcium, it may be added to the melt as calcium silicide or calcium"silicomanganese.

' It has been pointed out that according to the present invention the chromium, manganese, s licon and iron are always in the form of an alloy as distinguished from a mere mechanical mixture and that improved results follow from the use of the alloy instead of a mere mechanical mixture of the alloying elements chromium, manganese and silicon. Where calcium: forms a part of my addition composition, it is preferred that at least an effective amount of it be alloyed with the other constituents of the alloy. However, it is notso important that the calcium be I present as an alloy constituent as that the chromium, manganese and silicon be alloyed. The function of the calcium is primarily that of deoxidizing and scavenging the cast iron, whereas the. chromium, manganese and silicon have the additional function of alloying with the cast iron to impart valuable properties thereto as previously described. The calcium, therefore, 21-

- tered in commercial practice.

mix with it an alloy of calcium and silicon or an alloy of calcium, silicon and manganese. The

calcium alloy may or may not contain substantial amounts of iron. When proceeding in this way, the chromium, manganese and silicon are 4 to 65% chromium, about 2 to 50% manganese,

in the form of an alloy but the calcium is merely" 4 admixed mechanically with the chromium, manganese, silicon and iron alloy. The use of a mechanical 'mixture of calcium and the Cr-Mn-Si-Fe alloy enables me to efiectively and cheaply meet the individual conditions encoun- Thus byadding difierent amounts of calcium or othendeoxidizer to the same base alloy I may produce compositions suitable to any particular need without going to the expense of making up a series of base alloys containing different amounts of calcium or other deoxidizer.

The invention has been described with particular reference to addition alloys and compositions containing chromium, manganese, silicon and calcium. As above noted, however, the calcium may be omitted where such a strong deoxidizer or scavenging agent is not required. Where Ca is used it may bealloyed with the iron, chromium, manganese andsilicon or as a mechanical admixture therewith or in part as an alloy constituent and in part as a mechanical mixture. Although I'prefer to use chromium as the carbide'forming and chill inducing element, I may use tungsten, molybdenum, uranium or vanadium. Instead of the preferred graphitizing element silicon, I may use nickel, copper, titanium or zirconium. Other strong deoxidizing and scavenging elements or alloys may be employed in place of calcium, such, for example, as strontium, barium, lithium, aluminum, magnesium, titanium, zirconium or boron.

The claims of this application are directed to alloys or compositions which contain effective amounts of calcium/or other equivalent scavenging agent or to a process for using such alloys about 5 to 50% silicon, and an effective amount up to about 20% calcium, the balance being substantially all iron except for incidental impurities, at least the chromium, manganese, silicon andiron being present in the form of an alloy, the alloy having a graphitizing factor (G) according to the formula the alloy having a graphitizing factor (G) acor compositions. A divisional application, Serial No. 326,019, filed March 26, 1940, which matured into Patent #2,220,063, contains claims which are directed to alloys which do not contain effective amounts of calcium or other equivalent scavenging agent or to a process for using such alloys The invention is not limited to the preferred examples but may be embodied within-the scope of the following claims.

I claim:

l. A preformed alloy for addition to molten cast iron, containing about 0.10 to 10% carbon, about 10 to 65% chromium, about 2 to 50% manganese, about 5 to 50% silicon, and an efiective amount up to about 20% calcium, the balance being substantially all iron except for incidental impurities.

. 2. A composition for addition to molten cast iron, containing about 0.10 to10% carbon, about 10 to 65% chromium, about 2 to 50% manganese, about 5 to 50% silicon, and an efiective amount I up to about 20% calcium, the balance being substantially all iron except for incidental impurities, at least the chromium, manganese, silicon and iron being present in the form of an alloy.

3. A composition for addition to molten cast iron, containing about 0.10 to 10% carbon, about :25 to 50% chromium, about 5. to.30% manganese,

about 10 to 40% silicon, and an effective amount up to.about 10% calcium, the balance being substantially all iron except for incidental impurities, at least the chromium, manganese, silicon cording to the formula G=Si -(Mn+ Cr) between +16-and 20.

6. The process of decreasing the section-sensitivity of cast iron to chill while maintaining its physical properties, which comprises adding to the molten cast iron a composition containing about 0.10 to'l0%'carbon, about 10 to chromium, about 2 to 50% manganese, about 5 to 50% silicon and an effective amount up to about 20% calcium, the balance being substantially all iron except for incidental impurities, at least the chromium, manganese, silicon and iron being present in the form of an alloy.

'7. The process of decreasing the section-sensitivity of cast iron to chill while maintaining its physical properties, which comprises adding to the molten cast iron a composition containing about 0.10 to 10% carbon, about 25 to 50% chromium, about 5 to 30% manganese, about 10 to 40% silicon, and an effective amount up to about 10% calcium, the balance being substantially all iron except for incidental impurities, at least the chromium, manganese, silicon and iron being present in the form of an alloy, the alloy having a graphitizing factor (G) according to the formula G=Si-(Mn+ /2Cr) between +16 and 20.

8. A composition for addition to moltencast iron, containing about 0.10 to 10% carbon, about 10 to 65% of a carbide forming element of the group consisting of chromium, tungsten, molybdenum, uranium and vanadium, about 5 to 50% of a graphitizingelement of the group consist- 65, ing of silicon, nickel, copper, titanium and zirconium, an effective amount up to about 20%. of a scavenging element of the group consisting of calcium, strontium, barium, lithium, aluminum, magnesium, titanium, zirconium and boron and about 5 to 50% manganese, the balance being substantially all iron except for incidental impurities", at least the elements of the carbide forming group and the graphitizing group and the manganese being present in the form of an alloy.

9; An automotive cylinder block of cast ironi carbon, about 10 to 65% chromium, about 2 to 50% manganese, about 5 to 50% silicon, and an effective amount up to about calcium, the balance being substantially all iron except for incidental impurities, at least the chromium,

V manganese, silicon and iron being present in the form of an alloy, the alloy having agraphitizing factor (G) according to the formula.

' G=Si-(Mn+ /2Cr) between and 35 and-casting the cylinder block.

11. A composition for addition to molten cast iron, containing about 0.10 to 10% carbon,

about 10 to 65% chromium, about 2 to manganese, about 5 to 50% silicon, and an efiective amount up to about 20% calcium, the

balance being substantially all iron except for incidental impurities, the chromium, manganese,

silicon and iron being present in the form of an alloy at least a part of the calcium being unalloyed with said chromium-manganese-silicoriiron alloy.

HENRY T. CHANDLER.