US2220063A - Production of cast iron - Google Patents

Description

Patented Nov. 5, 1940 UNITED STATES PATENT OFFICE PRODUCTION OF CAST IRON No Drawing. Original application August 27,

1938, Serial No. 227,182.

Divided and this IP- plication March 26, 1940, Serial No. 326,019

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.

This application is a division of my co-pending application, Serial No. 227,182, filed August 27, 1938, for Production of cast iron.

Various alloying elements have been added to cast iron, in order to improve their strength, hardness, resistance to wear and other physical properties. One element which has been used very extensively is chromium. This has the effect 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, a cylinder 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 thin parts are chilled to such an extent that either it is difficult or impossible to machine them or 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.

elements nickel or copper together with chromium is open to certain disadvantages. In order to counterbalance the chilling effect of chromium, it is necessary to use about 310% nickel. The ratio of nickel to chromium required for balancing the chilling effect of the chromium 50 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 exthey crack during cooling The use of either of these mium, 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, ferro-chromium, ferro-manganese and ferrosilicon, have different 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 ferro-chromium, ferro-manganese and ferrosilicon are added successively to the bath, the first added element has an opportunity to react 25 with the constituents of the bath before the other elements are added and, therefore, the latter added elements do not have the same bath present on which to reactor 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 35 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 difierent 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 effect.

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 llloying elements or by their separate use.

My alloy when added to cast iron not only decreases the section-sensitivity of the cast iron to chill but accomplishes this while retaining or even increasing the physical properties of the cast iron, such as tensile strength, hardness and wear resistance. The chromium increases the tendency of the cast iron to chill and hardens and refines the pearlite matrix of the cast iron. In addition, it is a mild deoxidizer. Cast iron always contains certain amounts of oxygen, nitrogen and sulphur, which afl'ect its physical properties.

The manganese in my addition alloy also increases the tendency of the cast iron' to chill, but to a lesser extent than chromium. It stabilizes the carbides at high temperatures 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. tion, it is a fairly strong deoxidizer and removes oxygen which otherwise would act as a hardner 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 efiect 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 O, N

and S and perhaps other impurities. The remainder has an alloying effect on the cast iron.

The following is a specific example of one type of my addition alloy:

The composition of my addition alloy may be varied within wide ranges, depending upon what efiect it is desired to produce in the cast iron to which it is ad 'd. The chromium may be between about 1 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%.

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

Addition alloy Test Cr Mn Si Ca G No. percent percent percent percent percent The column G designates the graphitizing factors of the addition alloys according to the formula as will be more fully explained hereinafter.

Table II gives the chemical analyses, tensile strengths and Brinell hardness numbers of various cast irons. ignate cast irons made without the use of any addition alloy. Tests 1, 4, 5, 6, 10 and 11 designate cast irons made by adding to base cast irons in the ladle, the addition alloys of Table I, the amount of addition alloy used in each case being figured to produce the desired chromium in the finished cast iron.

TABLE II Cast iron containing addition alloys '1. 3. ms. 'r.s Test 13.11.11.

31 Mn 1 .0. 01 on 2" 1.2" .315" die. die. dia.

B. H. N.-Brin0ll 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 addition alloy 4 to cast iron B. Cast irons 1 and 10 were made by adding addition alloys 1 and 10 respectively to cast iron C. Cast iron 11 was made by adding addition alloy 11 to cast iron D.

It will be noted from Table II that the use of the addition alloys increases the tensile strength 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 of my alloy.

It will be seen 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.

In this table, A, B, C and D des- The effects of the various addition alloys 1, 4, 5, 6, 10 and 11 on chill are shown in the following TableIII, as is also the chilling effect of chromium alone as obtained by adding term-chromium to the cast iron.

Turn III Chilling efiect of various addition alloys Chill depth Chill depth Chill Percent Alloy in mm after m chan chan e G alloy add'n ggg in in chfll 13 6 +7 +116 -32 s 6 +2 +33 -24 c -1 -1c 5 o -1 -1c -4 4 a -2 -33 -4 a c -a -50 -4 4. s --1 --50 +8 The data for Table III were obtained by employing a chill test specimen 4 long x 2" high x A" 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 chili, whereas alloy 6 increased the depth of chill.

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 physical properties of cast iron and can either increase 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 should be used in my addition alloy, will depend upon the 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 with their increasing (G) values. Alloy 6 having a (G) value or graphitizing factor of --24 increased the depth of chill 33% in the test specimen used. Alloy 5, which had a graphitizing factor of 15, decreased the chill depth 16%. An alloy having a graphitizing factor of approximately 18 would neither increase nor decrease the chill depth in the chill test specimen, for chromium contents in the treated iron of approxi-- mately .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.

Although the percentages of chromium, manganese and silicon may be varied within the ranges given, it is preferred in general commercial practice that they be selected in such proportions as to give in the addition alley a ducing element, I may use tungsten, molybdenum,

graphitizing factor (G) between +35 and 35, or preferably between +35 and 20. Where either because of section to be cast or composition of the untreated iron it graphitizes too readily I employ an addition alloy having a. high negative 5 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 20 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 sufi'icient 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 chill 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 shafts and 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 by melting ferro-chromium and silico-manganese in an electric or other furnace under a protective slag. Where the alloy is to contain calcium, it may be added to the melt as calcium silicide or calcium silico-manganese.

The invention has been described with particular reference to addition alloys 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. Although I prefer to use chromium as the carbide forming and chill inuranium or vanadium. Instead of the preferred graphitizing element silicon, I may use nickel, copper, titanium or zirconium. Other strong deoxidizing and scavening elements may be employed in place of calcium, such, for example, as strontium, barium, lithium, aluminum or magnesium.

The claims of this divisional application are directed to alloys which do not contain efiective amounts of calcium or other equivalent scavenging agents or to a process for using such alloys. The claims of the parent application, Serial No. 227,182, are directed to alloys which contain effective amounts of calcium or other equivalent scavenging atent 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:

1. A preformed alloy for addition to molten cast iron, containing about 0.10 to 10% carbon,

balance being substantially all iron except for incidental impurities.

2. A preformed alloy for addition to molten cast iron, containing about 0.10 to 10% carbon, about 25 to 50% chromium, about to 30% manganese, and about to 40% silicon, the balance being substantially all iron except for incidental impurities.

3. A preformed alloy for addition to molten cast iron, containing about 0.10 to 10% carbon, about 10 to 50% chromium, about 2 to 50% manganese, and about 5 to 50% silicon, the

balance being substantially all iron except for incidental impurities, the alloy having a graphitizing factor (G) according to the formula G=Si(Mn+ Cr) between +35 and 35 4. 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, and about 5 to 50% silicon, the balance being substantially all iron except for incidental impurities, the alloy having a graphitizing factor (G) according to the formula G=Si(Mn+ Cr) between +16 and -20 5. 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 preformed alloy containing about 0.10 to 10% carbon, about 10 to 65% chromium, about 2 to 50% manganese and about 5 to 50% silicon, the balance being substantially all iron except for incidental impurities.

6. A preformed alloy for addition to molten cast iron, containing about 0.10 to 10% carbon, about 10 to 50% of a carbide forming element of the group consisting of chromium, tungsten, n-olybdenum, uranium and. vanadium, about 5 to 50% of a graphitizing element of the group consisting of silicon, nickel, copper, titanium and zirconium, and about 5 to 50% of manganese, I

the balance being substantially all iron except for incidental impurities.

7. The process of making automotive cylinder blocks, which comprises adding to molten cast iron a preformed alloy containing about 0.10 to 10% carbon, about 10 to 65% chromium, about 2 to 50% manganese, and about 5 to 50% silicon, the balance being substantially all iron except for incidental impurities, the alloy having a graphitiz-' ing factor (G) according to the formula G=Si(Mn+ /2Cr) between and -35 and casting the cylinder block.

8.-A preformed alloy for addition to cast iron containing about 0.10 to 10% carbon, about 10 to 65% chromium, about 2 to 50% manganese, and

about 15 to 50% silicon, the balance being sub- G=Si(Mn+ or) between +16 and 40 10. An automotive cylinder block of cast iron, in the production of which a preformed alloy is added to molten cast iron, said alloy containing about 0.10 to 10% carbon, about 10 to 65% chromium, about 2 to manganese and about 5 to 50% silicon, the balance being substantially all iron except for incidental impurities.

HENRY T. CHANDLER.