US2069423A - Ferrous alloy - Google Patents

Description

Feb. 2, 1937. H Z 2,069,423

FERRQUS ALLOY ,Piled March 5, 1932 N). N ,O NOJ/7/S INVENTOR ATITORNE Patented Feb. 2, 1931 I UNITED STATES PATENT OFFICE FEBROUS ALLOY of Ohio Application March 5, 1932, Serial No. 596,971

9 Claims.

This invention relates to the manufacture of ferrous alloys, its principal objects being the production'of an alloy of improved characteristics and the provision of an improved and simplified process of making malleable ferrous alloys.

I have found that in a ferrous alloy which contains substantially less carbon than that normally found in 'white iron for making malleable cast iron and which contains silicon in greater proportions than normally found in high carbon steels, and preferably in 'proportions' greaterthan normally found in'white iron for malleable cast iron, graphite is produced in the iron as it cools in the mold, which graphite is in the form of nodular or temper carbon and with no substantial amounts of flaky carbon. 1 have further found that such alloys may be annealed at a lower temperature and in less time than that required to anneal malleable cast iron. For example, in the 2 production of my malleable ferrous alloy the high temperature portion of the annealing process usually applied in making malleable cast iron may be omitted and the ferrous alloy may be subjected merelyto the second or low temperature portion of the usual annealing process and need not be subjected to emperatures above the critical point during the annealing step.

In describing my new ferrous alloy reference will be made to the diagram which illustrates the relative proportions of carbomand silicon normally found in cast iron and white iron for malleable iron and in my ferrous alloy, the abscissae and ordinates of the graph showing percentages by weights of carbon and silicon respectively.

The letter A designates the range of carbon and silicon normally found in cast iron and the letter B designates that normally found in white iron for malleable cast iron, although in some rare instances malleable iron may have been made containing carbon and silicon in the range shown within the dotted line at C. The line D designates the approximate lower limit of eutectiferous alloys as between carbon, silicon and iron.

With a white iron of the proportions illustrated at B and C and the normal quantities of phosphorus (about .14 to 19%), manganese (.25 to .40%) and sulphur (about .05 to .11%) no graphite is formed in the mold and the cast white iron is normally subjected to an annealing step above its critical temperature after which it is subjected to an annealing step at a temperature under the critical temperature, usually for about 30 hours.

I have found that by selecting a carbon content ranging from about 1% to 1.6% at the low limit for silicon and from about 1% to 1.3% at the high limit for silicon and a silicon content rangingfrom about 1% to 4% as illustrated in the diagram at E, a ferrous alloy is produced which upon cooling in the mold will precipitate carbon in nodular form and which may be'annealed simply by 'sub- 5 jecting the alloy to an annealing step at a temperature below the critical temperature of the alloy. The temperatu're'of annealingwillvary somewhat with the silicon content, as, for example, for the higher silicon material a tempera- 1o ture near 1470" F. will be desirable for the lower silicon materials the temperature may be as little as 1290 F. or 1340 F. With an alloy containing about 1.5 to 2% silicon the annealingstep at a temperature below the critical temperature may 15 be carried out in the usual time required for the second or low temperature annealing step used in producing malleable cast iron, 1. e., about 30 hours. By increasing the silicon content this annealing time may be reduced while with a lower content 20 of silicon a somewhat greater time'of heating may be required. The time and temperature of the annealing mayof course be varied, depending upon the characteristics desired and the annealing may even be omitted, particularly where the 25 higher proportion of silicon is used and where it is desired to retain the particular properties ofcombined carbon unaltered. Also the completely annealed metal may be heat treated to recombine sucnportions of uncombined carbon within the 30 limits of solubility as may be desired or the product may be treated by quenching below the critical point in order to obviate intergranular brittle.- ness and improve its ductility. This latter quenching below the critical point will be particu- 35 larly useful in my product where the silicon is very high.

Nodular carbon may also be formed in the mold when a higher content of silicon is used than the high limit shown in diagram E, al- 40 though the intergranular brittleness after annealing will increase with such higher content of silicon. Where this is not objectionable or where the annealing step may be omitted, such higher silicon alloy may be used. With such an 5 alloy it may be desirable to reduce the phosphorus content to avoid intergranular brittleness. The impurities normally present in white iron may be present in my new alloy although I prefer to reduce the phosphorus and sulphur slightly, 50 although the proportions of these impurities are not essential. It is desirable, however, to maintain a sulphur-manganese balance.

The following are specific examples of some of the alloys which I have found to contain nodular 55 Carbon Silicon Manganese Sulphur Phosphorus The manganese in Examples 2 to 5 was within the range .50 to .46% and the sulphur and phosphorus in all the Examples 1 to 7 were approximatch; the same.

In preparing the metal according to the present invention, any suitable materials may be employed. For instance, a charge of wash metal, presumably containing about 3.75% carbon, rivet scrap containing presumably about .10% carbon and 50% form silicon in such proportions as will give after melting the desired quantities of carbon and silicon. The materials may then be melted in a furnace such as an electric or other suitable furnace with the addition of sufficient ferro manganese to give the desired quantity of manganese.

The melt may then be heated to approximately 3000 F. and poured in a fluid condition, for example at around 2700 F. as the metal enters the mold. Variations may, however, be made in the maximum temperature and in the pouring temperature but it is preferred to use a somewhat higher temperature than that ordinarily used in pouring white or gray iron. After pouring, it is preferred to cool the metal slowly in the mold or to transfer it without previous cooling below the annealing temperature into a furnace maintained at that temperature.

In my new alloy the graphite formed on freezing is in an unexpected form, being present as small, dense nodules instead of flakes and exists in an unexpectedly large quantity. For instance,

I have found that some .45 to .52% of graphitemaybe present in the metal as cast in the form of nodules, the balance of the carbon being combined as pearlite, while in a metal formed from a melt containing 1.86% carbon and 1.36 to 1.65% silicon, only .10 to .13% of the carbon was converted to graphite and that in the form of flaky carbon.

I have found that where the material making up the melt is of a nongraphitic character, proportions of carbon and silicon may be chosen which approach the line D more closely than will be the case where graphitic materials enter into the charge, also where the charge contains graphitic materials more attention must be paid to higher pouring temperatures than where the charge is made entirely of nongraphitic material.

If, because of abnormal cooling rates or abnormal additional constituents, the location of line D of the diagram be displaced, correspond- .ing displacements of the high carbon boundary of the area E can or must be made.

As indicated in the diagram, ordinary malleable iron is a eutectiferous alloy (as between carbon, silicon and iron) and the balance between carbon and silicon is somewhat critical. If too much silicon or too much carbon is present to give a proper balance, flaky graphite will be formed in the mold and the material cannot be used since no amount of annealing will convert the flaky graphite into the nodular form. If the carbon or silicon i's balanced, cementite will be formed in such alloys which requires high temperatures for its speedy graphitization.

My new alloy is a non-eutectiferous alloy and, while it is necessary to maintain a certain degree of balance between carbon and silicon, it is a balance which is not nearly so sensitive, as illustrated in the diagram. With these non-eutectiferous alloys, the graphite separates in the mold in the form of nodules rather than as graphitic flakes.

It is not intended to restrict the invention to the particular alloys described since other low carbon alloys containing no element deleteriously aifecting graphitization may be used as the starting point of my process. For example, some proportion of nickel, aluminum, titanium, zirconium or uranium might be substituted for a portion of the silicon in the low carbon irons referred to above, or such elements as molybdenum and copper may be added for their beneficial effect upon physical properties. Also, certain advantages of the invention may be utilized by using carbon and silicon in ratios somewhat outside the range indicated at'E in the diagram. For example, I have found that an iron alloy containing 1.41% carbon, 3.08% silicon and .16% manganese-when solidified in the mold did not contain either nodular carbonor flaky graphite but could be annealed at temperatures below the critical temperature and in less than six hours, although obviously the time was longer than it would have been if the proeutectoid carbon had been sepathe use of such terms and expressions, of excluding any equivalents of the features shown and described, or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

I claim:

1. An alloy of iron containing about 1.0%-1.5% carbon, more than 2% to about 4% silicon and the balance being substantially all iron, about one-third of said carbon being present in nodular form.

2. An alloy of iron capable of being annealed below the critical temperature, said alloy containing about 1.0%-1.5% carbon, morethan 2% to about 3.5% silicon and the balance being substantially all iron, about one-third of said carbon being present in nodular form, without substantial flake graphite.

3. An unannealed ferrous alloy containing graphitic carbon substantially entirely in the form of nodules and having a total carbon con- 6. A ferrous alloy containing silicon and car- .75

bon within the proportions defined by about 1 to 4% of silicon, 1 to 1.6% or carbon for the low range of silicon and l to 1.4% of carbon tor the high range of silicon, together with .18% to less l alloy and ranging from more than 2 to about 4% of silicon and about 1 to 1.6% of carbon, and substantially all the remainder of iron.

9. A ferrous alloy containing carbon and 5111- con in proportions such as to give a non-eutectiierous alloy and ranging from above 1, to about 4% 01' silicon and about 1 to 1.6% of carbon,

together with manganese in the proportion of about .18 to less than 38%, and substantially all the remainder of iron.

HARRY A. SCHWARTZ.

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