US2034136A - Alloy steel - Google Patents

Description

Patented Mar. 17, 1936 UNITED STATES ALLOY STEEL Alexander Finlayson, Seattle, Wash., assignor to Pacific Car and Foundry Company, Seattle, Wash., a corporation of Washington No Drawing. Application January 15, 1932,

a Serial No. 586,971

14 Claims.

,ThlS invention relates to an improved steel characterized by high strength and ductility. r

The high strength and ductility is most phenomenal when the steel is in a normal condition; that is, in the as cast, as rolled, as forged, or

as cast and annealed states, but without having received any special heat-treatment such as normalizing, quenching, drawing, etc.

The present day carbon or alloy steels after drawing from the quenched or annealed states increase in ductility, but invariably lose in strength, or if they show a slight increase in strength they manifest a marked loss in ductility and resistance to shock. The present invention further contemplates a steel which, after drawing from the annealed condition, shows a marked increase in strength with equal and often increased ductility.

Another object of this invention is the provision of a low carbon steel having tensile strength and ductility in excess of that possessed by the usual carbon steel. Still another object of this invention is the provision of a low carbon copper steel, and a copper-silicon steel, both characterized by high tensile strength and ductility.

This invention also contemplates the provision of a low carbon copper silicon steel characterized by properties of high elastic strength and ductllity and which may be used in the as cast or as forged condition, and withal possesses good machining properties.

The strength of carbon steel is primarily due to the presence of iron carbide and it is well known that the strengthof carbon steel may be modified or affected by the presence of other elements such as manganese, chromium, vanadium, molybdenum, tungsten, etc., depending upon their particular percentages. .With existing processes only a certain ratio of iron and carbon will combine to form carbide of iron, the remainder of these elements retain their freedom, and under certain conditions the free carbon becomes graphitic carbon which segregates and weakens the metal.

This invention consists of a combination of elements with low carbon content which, in the absence of injurious carbides, are free to operate towards the production of the special properties of strength and ductility which we have described.

Marked results are also obtained when copper and silicon in certain ratios are introduced into substantially pure iron; the resultant steel possessing a high degree of elastic strength and exceptional ductility.

The use of copper, however, as an ingredient of steel is attended by certain drawbacks since it is soluble in iron only to a very moderate extent and when used above this limited percentage some of it tends to separate from solid solution during the selective freezing of the steel, thereby greatly reducing ductility and hot malleability. Carbon has a marked effect in further lowering the solubility of copper when present in amounts much over .15% and with the usualamount of silicon (.4% and under), the solubility is so reduced that even 1.0% copper seriously impairs the ductility ofthe metal. It is obvious, therefore, that excessive copper'in a carbon steel alloy is a detriment. However, when the silicon is raised to .8%, or somewhat over, there occurs a. very favorable change, so that when carbon is even a little in excess of .2% the steel will still exhibit good ductility. Either silicon combines with some of the carbon, or it lowers the upper transformation point so that there ,is a lagging or retardation in the action of the forces within the molten mass, known as hysteresis, providing a wider transformation range through which the copper may enter into solid solution. The presence of this comparatively large amount of silicon also greatly increases the tensile properties of this low carbon-copper alloy, which may be tempered and hardened without any increase in carbon. This silicon ratio produces the strength which in other copper steels is obtained by carbon, but it does so without the usual loss in ductility, caused by the copper separating at the freezing point asin the former low silicon copper steels.

In this manner we produce an alloy with low carbon content containing over 1% copper, by means of the addition of silicon in greater ratio as described above, and as will be set forth in 35 detail later. The alloy will have high strength along with high ductility and shock resistant properties. 0

A combination of these elements will have a lower melting and freezing temperature than iron carbide and in certain ratios will enter into solid solution, and their mutual affinities will determine the amounts remaining in solid solution. The lowering of the transformation point also increases the strength characteristic of the alloy.

This invention proposes a combination of elements with copper the chief strengthening agent, but in such ratios with other ingredients as to render the copper non-deleterious in the metal, and thus provide a compound which of itself will function as a strengthening agent in addition to the carbon.

Considering the statement just made, our experiments have proved that an increase in the amount of silicon, to proportions which are more specifically pointed out hereinafter, has this result. .More particularly, this invention proposes the addition of silicon to an amount at least sufficient to combine with the copper whereby to form a constituent which initself essentially increases the strength of the alloy. Tests have shown that the alloy is improved when the silicon content thereof is increased over that normally 5 present in iron, and within the limits specified hereinafter.

- When carbon is present in an alloy to an amoimt slightly in excess of .2%, along with copper and increased silicon in proper ratio, the resultant steel has exhibited good ductility and increased tensile strength. Further, the steel may be tempered and hardened without any increase in carbon content, and it has also been discovered that when the silicon content is increased, and carbon low, as more specifically mentioned hereinafter, the steel may be used in the as cast condition and exhibits excellent machining properties.

To accomplish the results mentioned above it has been found beneficial to add still another element-manganese-into the alloy in the ratio of about four parts manganese to four to six parts copper, which forms a copper-manganese compound which, in combination with the coppersilicon compound described above, produces the total strength of this alloy. If excess'carbon exists in the alloy, however, the manganese will, by the preference of chemical aflinity, combine with it rather than the copperthus forming the deleterious manganese carbides which are difficult to break up and diffuse even with elaborate heat-treatment. ,But the copper-manganese compound precipitates out in the form of a ductile substance giving no evidence of brittleness.

When, however, the manganese exceeds the above ratio a morebrlttle precipitate is liberated. In

practice the manganese should not be much less than half the copper, otherwise poor forging properties will result.

40 We have discovered that manganese has a greater aflinity for copper than it has for carbon since the copper apparently decomposes the manganese carbide uniting with the new free manganese and liberating carbon. The resultsproduced on this alloy by the application of this discovery is an important part of the invention.

As a specific example of the alloy of the present invention, iron is combined with elements in the ratio of carbon .l38%, manganese 1.58%, phosphorus .023%,'sulphur 016%, silicon 1.08%, copper 1.83%. Tests resulted in the following physical properties, after full annealing at 950 degrees centigrade for three hours;

- Yield point 68,250 lbs. per sq. in. Tensile strength 90,000 lbs. per sq. in. Elongation in 2 in. 26.55 per cent Reduction in area 51.35 per cent A second'test, cut from the same coupon, but reheated, or drawn at 500 to 525 degrees centigrade showed increased properties as under;

Without this increased silicon the ductility of this specimen would fall far short of the values given. This alloy steel may be produced in any type of furnace, and the copper may be added either early or late during the operation, while the other elements, silicon and manganese, are preferably added near the finish of the heat, either in the furnace or in the-ladle. Owing to the chemical afllnity of copper and manganese a lesser percentage of manganese is lost in the melting process.

In the foregoing description the properties of this invention in the as cast and "as cast and annealed have been stressed, however, it may be 5 heat-treated and given exceptional qualities. It may also be mechanically formed. It may be either slowly or rapidly cooled depending upon the properties desired. This strengthening is the result of the particular ratio of copper, silicon 10 and manganese, which form compounds of copper silicide and mangano-copper silicide, which precipitate out of solid solution as sub-microscopic particles, the amount of precipitation depending upon the temperature of the metal. as drawn and 15 the mass of the section.

From the above description it is believed that the present invention will be fully apparent to those skilled in the art; the alloy comprises a low carbon, high-silicon copper steel which pos-. 20

sesses the characteristics mentioned herein. The low carbon steel alloy of the'present invention contains copper to an amount approximately equivalent to the empirical combining ratios of the normally alloying constituents of the steel. g5

As set forth in the appended claims, the range of essential alloying ingredients is broadly as follows:

Carbon trace'to .20% Manganese; 14% toabout 1.58% Silicom .6% to 2.5% Copper .5%'to 3.0%

Iron, balance, except for impurities.

Whatisclaimedis: 35

1. A steel alloy containing carbon between .10% and under 20%, manganese between .4% to 1.5%, silicon between .6% and 2.0%, and copper between 1.0% and 2.5%, the balance iron, except for impurities. 40

2. The presence of copper in a steel to the extent of 1.5 to 2.0%, carbon .08 to under 20%, silicon 1.0 to 1.25%, manganese .4 to 1.5%, and the balance iron, except for impm'ities.

3. An alloy steel having high strength and good 45 ductility in annealed condition containing as essential elements copper 1.5% to 2.0%, carbon .08% to under 20%, silicon 1.0% to 1.25%,manganese .4% to 1.5%, and the balance iron except for impurities, such as sulphur and phosphorus.

:4. An alloy steel having high strength and duetility in its annealed state comprising as essential elements copper .5% to 3.0%, carbon trace to under 20%, silicon over .6% up to 2.5%, manganese .4 to approximately 1.58%, and the balance 55 iron except for impurities, such as sulphur and phosphorus.

5. An alloy steel containing carbon trace to under .20%, copper .5% to 3.0%, silicon over .6% up to 2.5%, and manganese 4% to 1.5% as alloying ingredients dispersed in a matrix of iron substantially free from manganese carbide, the balance' iron, except for impurities.

6. As a 'new article of manufacture, an alloy steel having high strength and ductility in its cast condition and containing manganese .4% to 1.5%, copper 1% to 2.5%, silicon .6% to 2.0%, and carbon trace to under .20-%, the copper and silicon being in the form of copper silicide, the balance 7 iron, except for impurities.

'7. As a new article of manufacture, an alloysteel containing carbon trace to under 20%, copper .5% to 3.0%, silicon over-.6% to 2.5%, manganese .4% to 1.5%, and the balance'iromthecop- 75 per content being in amount equal to or greater than the silicon content.

8. As a new article of manufacture, an alloy steel containing carbon .138%, manganese 1.58%, silicon 1.08%, copper 1.83%, phosphorus 023%, sulphur .016%, and the balance iron.

9. An alloy steel containing carbon .08% to less than .12%, manganese .8% to 1.5%, copper .6% to 1.5%, silicon .7% to 1%, and the balance iron except for impurities such as sulphur and phosphorus.

10. A low carbon copper silicon steel adapted on heat-treating to evidence an increase in strength and ductility, said steel containing in addition to iron the following elements only, not over 20% carbon; between .50 to 3.0% copper and between .60% and 2.5% silicon.

11. A low carbon copper silicon steel adapted on heat-treating to evidence an increase in strength and ductility, said steel containing in addition to iron the following elements only, not over 20% carbon; between .50 to 3.0% copper and between .60% and 2.5% silicon with manganese in amounts approximating 4 parts manganese to 25 eacb4tc6partscopper.

12. A low carbon copper silicon steel adapted on heat-treating to evidence an increase in strength and ductility, said steel containing in addition to iron the following elements only, not over 20% carbon; between .50 to 3.0% copper and between .60% and 2.5% silicon with manganese .4 to 1.5%, the manganese and copper being presiron.

14. A low carbon steel adapted on heat-treating to evidence an increase in strength and ductility comprising carbon between .10% and 20%,

silicon between .60% and 2.0% and copper between 1.0% and 2.5% with manganese .4 to 1.5%, said manganese being presentin the ratio of 4 partsmanganese to each 4 to 6 parts copper,ba1- ance substantially all iron.

ALEXANDER FINLAYBON.