US2516524A

US2516524A - White cast iron

Info

Publication number: US2516524A
Application number: US16139A
Authority: US
Inventors: Millis Keith Dwight
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1948-03-20
Filing date: 1948-03-20
Publication date: 1950-07-25
Anticipated expiration: 1967-07-25
Also published as: DE975234C

Description

Patented July 25, 1950 s im STATES PATENT OFFICE 2,510,524 wnrra cas'r moN Keith Dwight Hillis, Bahway, N. 1., assignor to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware No Drawing.

The present invention relates to white cast irons, and, more particularly, to white cast irons having improved strength especially when produced in the form of sand castings.

It is an object of the present invention to provide a white cast iron having an improved combination of mechanical and physical properties, particularly when produced in the sand cast condition.

It is a further object of the present invention to provide a white iron casting having in the sand cast condition an improved combination of hardness and transverse strength without sacrificing impact properties.

Other objects and advantages of the invention will be made apparent to those skilled in the 4 art from the following description.

Broadly stated, the present invention contemplates a white cast iron composition containing about 2% to about 4.5% carbon, about 0.1% to about 3% silicon, up to about 6% nickel, e. g., 0.01% to 6%, about 0.1% to about 2% manganese, about 0.015% to about 0.5% retained magnesium, up to about 2.5% chromium, e. 3., 0.

to 2.5%, up to about 2% molybdenum, e. g.,

taining about 3% carbon, about 0.75% silicon,

about 0.2% manganese and about 0.02% sulfur. A portion of the melt was cast without further additions. Two other portions of the same melt were cast after the incorporation of sufllcient magnesium to provide retained magnesium contents of 0.04% and 0.06%, respectively, in the final solidified products. The magnesium was introduced as a nickel-magnesium-carbon alloy containing about 11.9% magnesium, 2.8% carbon and the'balance essentially all nickel. All three and impurities usually found in cast Application March 20, 1948, Serial N0. 16,139

5 Claims. (01. 75-123) cast irons were white cast irons in the as-cast condition, as evidenced by the white fracture exhibited by each of the cast irons. The three cast irons had the following properties:

e's roper es Pefi-ent ff HBrill 1300., Lead,

in. lbs

None 0. 088 4, 190 10 371 0.04 0.002 -0.sa0 375 l 1 1.2-inch dia. arbitration bar tested over 12-inch span.

The eflect of magnesium in improving the properties, particularly the transverse breaking load, is further illustrated by the following data determined from a white cast iron containing about 3% carbon, about 0.75% silicon, about 0.2% manganese, and about 0.015% sulfur and from a comparable white cast iron which contained, in addition, 0.13% retained magnesium:

Transverse Properties Percent Izod Impact,

8 it.-1bs. Dell, in. Load, lbs.

None 0.079 4, 580 i!) 0. l3 0. 091 5, 490 27 In order that those skilled in the art may have a better understanding of the invention, the

composition and propertiesof other illustrative white cast irons within the scope of the invention are set forth in Tables I and II, respectively. H

All the cast irons in these tables were sand cast and were tested in the as-cast condition.

TABLE I No Per Cent Per Cent Per Cent Per Cent Per Cent Per Cent O Si Mn Ni 5 Mg as 0.8 0.8 0.8 n. 0. 0. 024 2. 8 2. 1 0. 8 2. 0 U. 012 U. 064 3. 4 1. 8 0. 8 2. 0 0. 016 0. 061 4. 1 l. 3 0. 5 1. 8 0. 02 0. 06

l n. d.-n0t determined.

TABLE III Many white cast irons containing about 0.75% to 2% nickel, about 2.5% to 3.3% carbon, about 0.5% to 296 silicon and over about 0.04% retained magnesium have been tested and exhibited the following high average properties when tested over a 12-inch span:

Transverse breaking load, 5,600 lbs. Transverse deflection, 0.102 in.

Within the aforementioned range of compositions, 9. special range of compositions has been discovered which have particularly outstanding properties which render them especially useful for applications where wear resistance, abrasion resistance and/or high hardness are desired. These compositions contain about 2.5% to 3.3% carbon, about 0.3% to 1.25% silicon, about 3.5% to 5% nickel, about 0.4% to 0.9% manganese, and about 0.05% to 0.1% retained magnesium. The balance of the composition is essentially iron. White cast irons within this special range of compositions have improved properties as compared to similar white cast irons devoid of ma nesium but in which-some other element, e. g., chromium, is employed as a whitener. The improved properties exhibited by these special white east irons are particularly notable in sand castings made therefrom. For certain applications, it may be desirable to employ chill castings. white cast irons having the foregoing s ecial compositions will on the average exhibit properties within the following ranges, the transverse load and deflection being determined on 1.2-inch diameter sand cast arbitration bars tested over a 12-inch span:

Load, lbs, 5000 to 6500 Deflection, in., 0.00 to 0.11 Izod impact. ft.-lbs., to Brinell Hardness No. 550 to 715 The aforementioned special white cast irons are characterized by an unusual microstructure not found in other white cast irons having the same nickel content but devoid of magnesium. As is known to those skilled in the art, the microstructure of analogous white cast irons usually will contain massive carbides arranged in a dendr itic or cellular pattern. In the special white cast irons of the invention, however, the microstructure is characterized by the presence of carbides in the form of laminations or plates. A notable and unusual feature of the mlcrostructure i the discontinuous nature of the carbide phase. The remainder or continuous portion of-the microstructure consists largely of martensite. Tests indicate that the unusual microstructure acabout 405 F.

TABLE III r- Pa- Per- Per- Per- Per- No. cent cent cent cent cent cent Others 0 Si 8 Ni Mn Mg 0.4 0.1! 4.5 0.4 0.07 0.4 0.!!! 4.5 0.4 0.07 0. 6 0. 02 4. 5 0. 5 0. 08 8 29 0.1 0.1 4.7 0.5 none 1 5 Cr 9 3.3 0.5 0.1 4.5 0.5 none 156:

TABLE IV No. Imd Dell. l Impact I BHN i Fracture 5 6,300 0.003 25 600 White 6-- 5,2 0.077 2i 605 Do. 7- 5,85) 0189 20 586 Do. 8 4,881 0.105 28 5 D07 9 1 4,23) 0. 097 25 538 Do.

Lood=Tramverse load in pounds applied midwa between an ports to produce fracture oi bar. y p .=Defled:i|n in inehm at maximum load in transverse test.

Impact=Izod impact value in foot pounds. BHN=Brindl hardness number. I 4.5 Iii-1.5% Cr white iron such as sold under the trade-mark Ni- (Arm of 9 boats counts substantially for the increased strength which has been exhibited by the alloy of the invention.

An, unusual characteristic. of the aforementioned special martensitic white cast iron of the present invention is that the strength and toughness' developed in the sand cast condition are as good. or, in many instances, are even better the chill cast condition. In this respect, the magnesium-containing martensitic white cast iron of the invention diil'ers markedly from the analogous magnesium-free white cast irons of the prior art since these prior art white cast irons are generally stronger, tougher and have a higher deflection in the transverse test in the chill cast condition than in the sand cast condition. It has been found that the laminated or plate-like discontinuous carbide structure described hereinbeiore and which is characteristic of the magnesium-eontaining martensitic white cast iron of the invention is particularly well-defined or prominent when the martensitic white cast iron of the invention is sand cast.

The term white cast iron" is used herein to mean a cast iron (1. e., a eutectiferous alloy of iron and carbon) which has an uncombined or graphitic carbon content not more than about one-half the carbon content in excess of that required to form the matrix, e. g., the eutectoid requirement, and hasa white fracture.

In order that those skilled in the art may have a, better understanding of the properties exhibited by the special martensitic white cast irons of the present invention, the compositions and propel-fies oi martensitic white cast irons within the contemplated range of compositions (Nos. 5, 6 and 7) together with compositions and properties of analogous magnesium-free white cast irons (Nos. 8 and 9), are given in Tables In and IV. All the properties shown in Table III were determined on 1.2-inch diameter arbitiation bars cast in sand, except in the case of Nos. 6 and 'I which were chill cast in iron molds. No. 6 had the same composition as No. 5 but diflered in that it was chill cast whereas No. 5 was sand cast. All the cast irons were subjected to a transverse test over 12-inch centers after a stress relief treatment J Iii-1.5% Cr white iron such as sold under the trade-mark Ni-Hard." (Avaage or 15 beats.)

improved ability of the alloy of the invention to withstand transverse load. It has been found that when tested in the sand cast condition the marfor about 3 hours at tensitic white cast irons of the invention can withstand a transverse load approximately to 35% greater than can be withstood by an analogous magnesium-free white cast iron containing about 1.5% of chromium as a whitening agent.

As is known'to those skilled in the art; the" foundry methods commonly employed to determine the chilling propensity of a given cast iron are the chill block and the step 'bar. Table V contains the results of tests conducted on chill blocks to show the powerful whitening efieot conferred by magnesium in the martensitic white cast iron of the invention. The chill blocks em-' ployed had dimensions of 6"x6"x2" with the chill'being applied on the 6"x2" face and with the remaining faces of the block being cast against sand. In conducting the tests, the melts employed to produce the chill blocks were superheated to 2850*, F. and were cast at 2500 F. The solidified blocks were broken in half in a direction perpendicular to the chill face. and were then examined for depth of chill. The results are illustrated by the data in Table V.

A sand cast step bar having the composition of the aforementioned white cast iron containing 0.13% magnesium was completely white in the largest section of a step bar (the two-inch section) after being superheated to a temperature of 2850 F. and being cast at a temperature of 2650 F. '1

A beneficial eflect which has been found to accompany additions of magnesium to the molten cast iron compositions contemplated by the invention is that magnesium has a very powerful I desulfurizing effect. It has been found that the reduction in sulfur content which takes place when magnesium is introduced into the molten cast iron consumes a part Of the magnesium introduced. Accordingly, when it is desired to.

introduce the amounts of retained magnesium contemplated by the present invention, it is first necessary to introduce a sufficient amount of magnesium to remove a major part of the sulfur present and to reduce the sulfur content of the white cast ironto alowvalue. When0.03 or more retained magnesium is introduced into sulfurcontaining cast irons, the sulfur content will be reduced to about 0.02% or even less (e.g.,0.015%) However, if amounts of retained magnesium less than about 0.03% are introduced, the sulfur level in the resulting solidified cast iron may be higher, for example, 0.08%, depending upon the sulfur content of the iron before the introduction of magnesium. The final sulfur will vary inversely with the amount of retained magnesium. In

addition to the amount of magnesium required for sulfur removal, a suificient excess amount of magnesium must be introduced to provide the required retained amounts of magnesium in the finalcasting. As an empirical approximation, it has been found that of the magnesium actually introduced into the molten cast iron bath one part by weight of magnesium is consumed for each part by weight of sulfur which is removed from the bath. It has been found that this sulfur-removing property is highly effective regardless of the conditions existing when magnesium is introduced into the cast iron melt. Thus, no slag is necessary in order to carry out a the removal of sulfur and the treatment is effecthen held for minutes and. at the end of this time, it was found that the sulfur content was 0.012% and the magnesium content was 0.015%. This loss of magnesium is characteristic of molten magnesium-containing cast irons and is due to a number of factors including oxidation of the magnesium, boiling of! of the magnesium as vapor, etc. It can be said that about 0.03% to about 0.06% magnesium is'lost in about ten min-.

utes when magnesium-containing molten cast iron is held in hand ladies such as are employed in the foundry.

In all instances where it is attempted to introduce magnesiuminto molten iron-base baths, it is important to bear in mind the high reactivity of magnesium and to exercise due precaution in order that reactions of explosive violence be avoided. It has been found that if it is attempted to add magnesium to cast iron melts when the melts are at the ordinary casting heat, reactions of explosive violence take place which will propel the molten metal from the receptacle in which it is contained and result in loss of both molten metal and magnesium without introduction of magnesium into the melt. It has been found that metallic magnesium in the amounts contemplated by the present invention could be introduced directly into cast iron melts when the latter are in a pasty condition at a temperature only slightly above the melting point. When this method is employed, it is then advisable after .the magnesium introduction to raise the temperature of the bath quickly to a suitable casting temperature in order that sound castings be obtained. A method which has been found satisfactory for the purpose of introducing magnesium into the cast iron melts is to first alloy the magnesium with a metallic composition which is soluble in the molten iron to be treated and in which the magnesiumis, in turn, soluble. Satisfactory addition agents are nickel or copper alloys containing up to about 20% of magnesium, e. g., a nickel alloy containing 4% to 20% of magnesium. It is to be pointed out that even in these alloys, the high reactivity of magnesium is still felt. In fact, alloys containing 10% magnesium have been found to burn brightly when placed on top of the molten metal. Recovery of magnesium from the addition agents in terms of magnesium actually retained in the solidified iron casting will vary depending upon the con- .centration of magnesium in the alloy, the temperature of the bath to which the magnesium is added, the composition of the bath, including the nickel and sulfur contents thereof, etc. Generally speaking, the recoveries of magnesium are rather low; for example, in one instance where -vention 0.5% maanesium was added in Uniform or a nickel alloy containin: 20% .of magnesium to a cast iron melt containing 0.05% of suliur, 0.13% or um was actually recovered in the solidified casting- The maanesium-containin: alloy of the inn a an unusual combination of properties, since the transverse strenzth and denection thereof are improved above that or analogous magnesium-tree alloys without any sacrifice of impact or hardness. Because 01 this unusual combination of properties, the magnesiumcontaining white cast iron the invention finds application in a wide number of fields in which the high hardness, wear resistance, abrasion resistance and moderate toughnes of this material may be beneficially employed; For example,

grinding balls, attrition mill plates, rolls, pump parts, mining machinery parts, mullet tires, nozzles, etc., can be made iromthe white cast iron oi the present invention. l

Although the present invention has been de- I scribed in conjunction with preferred embodiments, it is understood that modifications and variations may be resorted to without departing from the spirit and scope oi the invention, as those skilled in the art will readily understand. Variations and modifications apparent to thou skilled in the art are considered to be within the purview and scope of the invention and appended claims.

I claim:

1. A. casting comprisedoi' a white cast iron containing about 2.5% to 3.3% carbon, about 0.5% to 2% silicon, about 0.75% to 2% nickel, about 0.04% to 0.5% mum. less than about 0.020% sulfur and the balance essentially iron.

2. A casting comprised or a white cast iron containing about 2% to 4.5% carbon, about 0.1% to 3% silicon, about 0.1% to about 2% manganese, about 0.01% to 6% nickel, about 0.01%

. 8 2.5% chromium, about 0.01% to about 2% molybdenum, about 0.03% to about 0.5% maznesium, less than about 0.020% suliur'and the balance essentially iron.

8. A casting comprised oi a white cast iron containing about 2.5% to 3.3% carbon, about 0.3% to 1.25% silicon, about 3.5% to 5% nickel, about 0.4% to- 0.9% manganese, not more than about 0.02% sulfur, about 005% to 0.1% magnesium, and the balance essentially iron.

4. A casting comprised 01 a white cast iron containing about 2% to 4.5% carbon, about 0.1% to 3% silicon, about 0.1% to 2% maganese, about 0.03% to about 0.5% magnesium, less than about 0.020% sulfur and the balanc essentially iron.

5. A casting comprised. of a white cast iron containing about 2% to 4.5% carbon, about 0.1%

to 3% silicon, up to about 0% nickel, about 0.1%

to 2% manganese, up to about 2.5% chromium, up to about 2% molybdenum, about 0.03% to 0.5% magnesium, less-than about 0.02% sulfur and the balance essentially iron.

I KEITH DWIGHT MIL-LIB.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

Claims

1. A CASTING COMPRISED OF A WHITE CAST IRON CONTAINING ABOUT 2.5% TO 3.3% CARBON, ABOUT 0.5% TO 2% SILICON, ABOUT 0.75% TO 2% NICKEL, ABOUT 0.04% TO 0.5% MAGNESIUM, LESS THAN ABOUT 0.020% SULFUR AND THE BALANCE ESSENTIALLY IRON.