US2992950A - Malleable cast iron compositions - Google Patents

Description

July 18, 1961 PERAS 2,992,950

MALLEABLE CAST IRON COMPOSITIONS Filed NOV. 2, 1954 FIG. I I FIG. 2

United States Patent@ 2,992,950 MAI LEABLE CAST IRON COMPOSITIONS Lucien Peras, Billancourt France, assignor to Regie Nationale des Usines Renault, Billancourt, France, a French works Filed Nov. 2, 1954, Ser. No. 466,309 Claims priority, application France Nov. 18, 1953 1 Claim. (Cl. 148-35) The present invention relates to malleable cast iron compositions.

In the high resistance malleable cast iron which is the subject of the U.S.A. patent applications Serial No. 335, 579 of February 6, 1953, now Patent No. 2,901,386, and Serial No. 336,187 of February 10, 1935, now Patent No. 2,901,384, it becomes difficult to keep the structure completely white, i.e. free from graphite, when sand-moulding massive parts. This difiiculty is increased by the presence of graphitising elements such as copper. This can be remedied by limiting the carbon and increasing the manganese beyond the maximum proportions provided in malleable cast irons, owing to the new process of graphitisation.

Moreover it has been found that the consecutive treatments of austenisation, followed by martensitic hardening, nucleation tempering and graphitising annealing, in the manner described in said copending applications, give rise to a number of nodules of graphite per unit of volume which is less in proportion as the solidification cooling is slower, that is to say as the casting thicknesses are more considerable and as the amount of heat removed by the mould is reduced, as is the case when dried core sand is substituted for wet green sand. Since the number of nuclei is reduced, there is a costly and notable increase in the time required for graphitisation, the more so since the manganese content has also been increased.

It has been recognised that these disadvantages can be remedied by adding titanium and aluminum separately or simultaneously, but, in these cases, the nodules of graphite which appear in the annealing operation have a star-shaped form prejudicial to good mechanical properties. to the invention that zirconium does not have these disadvantages nd gives rise to nodules of annealing graphite which are of a very rounded, almost spherical shape, whilst remaining numerous and of small dimensions.

The invention relates therefore to a new high resistance malleable cast iron composition for treatment comprising preliminary hardening and nucleation tempering before graphitising annealing as described in said copending applications and which is applicable to massive parts of up to 60 mm. in thickness or diameter, as is the case, more particularly, with cast crank-shafts for internal combustion engines for automobile vehicles. Thus, referring to said applications, this three-phase treatment comprises the steps of effecting martensitic hardening of the casting by austenization with heat at a temperature slightly above that at the end of the eutectoid transformation followed by cooling to produce the martensitic transformation, tempering the thus-produced martensite by heating at a temperature of 400 to 500 C. for a prolonged period of time up to about 48 hours, further heating the thus-treated iron at a higher temperature in the vicinity of 900 C. to effect graphitization of the iron, and cooling to room temperature.

According to one feature of the invention the new On the other hand, it has been shown according 2,992,950 Patented July 18, 1961 composition is comprised within the following percentage limits:

C, 1.6 to 2,6, preferably 2.10

Si, 0.9 to 1.9, preferably 1.40

Mn, 0.7 to 1.7, preferably 1.20

Cu, 0.1 to 2.1, preferably 1.45

Zr, 0.03 to 0.9, preferably 0.60

In addition it contains the customary impurities S, P, etc., in the usual concentrations, for example: 0.04 sulphur and 0.03 phosphorus.

The invention also relates to compositions which, moreover, contain special elements such as Ni in order to improve the hardening capabilities or the structure, and therefore the mechanical properties, without changing the principle of the invention. The invention further relates to cast iron compositions wherein the manganese is partially replaced by chromium, vanadium or molybdenum of equal content in order to make it easier to obtain a white casting structure, but sufiiciently limited to allow graphitisation by the aforesaid processes.

The accompanying drawing illustrates a representative casting which may advantageously be made of a malleable white cast iron composition of the invention. In the drawing:

FIG. 1 is a side elevation of such casting, and

FIG. 2 is an end elevation of the casting.

By way of example, the following composition: C=2.-07, Si=1.40, Mn=1.18, Cu=1.47, Zr=0.60, Ni: 0.18, S=0.040, P=0.027 was cast in wedge moulds made from dried core sand according to the accompanying drawing, the dimensions being: d=50 mm., e=18, f=40, h=20, H=l00, l=1l5. When the casting is fractured, the structure is white to the heart and totally free from graphite. The casting treatment was as follows:

Heating at 820, for 30 minutes, salt hardening, for 2 minutes, cooling in calm air;

Then re-heating to 450, 48 hours cooling in calm air;

Then re-heating to 930, 2 hours, cooling :for 3 hours to 800, then drawing off and cooling in calm air.

The structure is graphitised in homogeneous manner throughout its entire section. The number of graphite nodules is approximately 4,500 per sq. millimetre and the said nodules are of rounded shape proximating to spherical shape.

In order to improve tenacity, the complete graphitisation treatment was followed by the following treatment for quality:

Re-heating to 840, 20 minutes oil hardening;

Re-heating to 680, 20 minutes oil hardening;

Re-heating to 500, 2 hours, cooling in calm air.

The mechanical characteristics discovered in a bottom portion of the casting, which was 17 x 20 mm. in section, are then:

Elastic limit kg./mm. from 71 to 82, average 78;

Breaking load kg./mm. from 77 to 87, average 83;

Expansion percent from 3 to 5, average 4;

Mesnager resilience in kg./cm. from 0.6 to 0.9, average 0.8.

The endurance limit was determined by Moore sample rotary fiexion and was found to be 36 g./mm.

I claim:

A high strength malleablized white iron casting composed largely of iron and containing 1.6 to 2.6% carbon, 0.9 to 1.9% silicon, 0.7 to 1.7% manganese, 0.1 to 2.1% copper, and 0.03 to 0.9% zirconium, said casting having been subjected to heating at about 820 C., quenching at 2,185,894 Hultgren Jan. 2, 1940 about 180 C., cooling, reheating to about 450 0., cool- 2,331,886 Boegehold Oct. 19, 1943 ing, reheating to about 930 C., and cooling to room tem- 2,370,225 Boegehold Feb. 27, 1945 perature, the casting structure before treatment being 2,490,818 Kuniansky Dec. 13, 1949 White and free from graphite and after said treatment said 5 2,651,570 Heine Sept. 8, 1953 casting containing a large number of very fine uniformlydistributed, generally spherical, graphite nodules, and said OTHER REFERENCES casting providing in a unit 17 X 20 mm. in section, an The Foundry, v01. 78, issue 10, pages 94 99 October elastic limit in kg./mrn. of 71 to 82, a breaking load in 1950 kg./mm. of 77 to 87, an expansion of 3 to 5%, and a 10 mesnager resilience in kgJcmz of 0.6 to 0.5L Z1rcon1um 1n Cast Iron, R. Moldenke, Transactions American Foundrymens Assoc., vol. 29, 1920, pp. 391- References Cited in the file of this patent UNITED STATES PATENTS 2,077,117 Lauenstein Apr. 13, 1937 15

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