US3499757A - Low alloy steel plate containing copper,chromoium,nickel,and molybdenum - Google Patents

Description

United States Pater 20 Claims ABSTRAAIT THE DISCLOSURE High-strength carbon steel plates in the as-rolled condition. The plates have yield strengths of above 50,000 p.s.i. and tensile strengths of 81,000 p.s.i. or higher. Additionally, they exhibit good toughness, particularly at low temperatures, and are readily weldable. The constituents of the steel plates fall essentially within the following ranges:

Elements: Percentage by weight C 0.15-0.25 Mn 1.00-1.50

P (max.) 0.040 S (max) 0.050 Si 0.15-0.50

Cu 0.01-0.47 Ni 0.05-0.35

The copper, chromium and molybdenum should total at least about 0.2%, but preferably should not exceed 0.6%. The total of nickel and chromium should be at least 0.15% and preferably at least 0.20%. For As-inch plate, the carbon should be 0.15-0.25 the manganese LOO-1.20% and the silicon 0.15-0.30%. For -inch plate, the carbon should be 0.18-0.25 the managanese 1.10-1.35%, and the silicon the same as for the %-inch plate, the carbon should be 0.18-0.25 the manganese 0.25%, and the manganese and silicon should be the same as for the -inch plate. For plates of fli-inch and above thicknesses the carbon should be 0.20-0.25 the manganese 1.20-1.50% and the silicon 0.15-0.50%. Normalized plates of essentially the same chemistry exhibit impact strength at -50 F. in excess of 20 foot pounds per standard Charpy V-notch tests.

Cross references to related applications This application is a continuation--in-part of application Ser. No. 642,324, filed May 31, 1967 now abandoned; a continuation-in-part of application Ser. 'No. 415,184, filed Dec. 1, 1964 now abandoned; a continuation-in-part of application Ser. No. 354,764, filed Mar. 25, 1964 now abandoned.

In application Ser. No. 293,576, filed July 3, 1963, now included in Patent No. 3,310,441, issued Mar. 21, 1967, an improvement in heat-treated carbon steel plates was disclosed wherein the notch toughness qualities are improved at low temperatures particularly in the 75 F. and under range. The present invention is concerned with steel plates for a different purpose having generally narrower ranges and a different balance of elements within, however, a similar but, as will be seen, distinctive chemistry. The steels described herein are not hot-rolled high-strength steels of the type which are classified as structural steels. Instead the steel plates are in the asrolled condition, not having been heat treated as distinguished from the steel plates disclosed in the aforementioned application; the properties of the instant steel plates thus being derived principally from their chemistry.

Background of the invention This invention relates to an improvement in carbon steel plates. In particular, the invention relates to improvements to the strength characteristics .of hot-rolled carbon steel plates.

The present invention is also concerned with as rolled flange and fire-box grade steel plate having unexpectedly high tensile strengths. The unusual properties of the flange and fire-box grade steels as well as the properties of the structural grade steels are achieved through chemical control and balance.

in the steel-making industry, steel is considered to be carbon steel when, within the limits of the recognized field of alloy steels, no minimum content of any element is added to obtain a desired alloying effect, when the specified minimum for copper does not exceed 0.40%, or when the maximum content specified for any of the following elements does not exceed the percentages noted: Manganese 1.65, silicon 0.60, copper 0.60. The composition disclosed herein is considered to fall within the foregoing definition of carbon steel in view of the means of producing same. However, the claims of invention as to composition should not necessarily be interpreted as so limited.

Before the development of the steel plates disclosed in US. Patent 3,310,441, the only commercial steel available which provided plate with a minimum tensile strength of 70,000 p.s.i. and notch toughness at F. of 15 foot pound in normalized condition was a steel which contained 2.25% nickel, and was thus a comparatively expensive alloy steel. It was however, discovered that by controlling the residual elements, which almost inevitably occur in carbon steel plate produced from scrap, i.e., copper, nickel, chromium and molybdenum, to comparatively high levels, it was possible to produce a heat-treated carbon steel plate as disclosed in US. Patent 3,310,441 which served the same uses as the known alloy steel plates and could be produced at substantially lower cost. Such steel plate is used primarily for oft-shore drilling rigs in frigid regions such as in the Alaskan shore area, for the storage of refrigerated liquified gas such as propane and ammonia, and in general, for cryogenic uses. All the steel plates for such use and otherwise disclosed in the aforesaid US. Patent 3,310,441, are heat-treated steels, however. Tests run on such steel plates in the as-rolled condition prior to the application of heat treatment failed to disclose the high strength levels of the instant invention. But, on the other hand these tests did indicate that high levels of the socalled residuals produced unexpectedly high strength levels as well as improved weldability and good toughness in the as-rolled plates as well as in the heat-treated plates.

For many years railroad tank cars have been fabricated from steel plate in the as-rolled condition. This has been and currently is a specification of the Interstate Commerce Commission. Until the instant invention, the highest strength carbon steel plate commercially availavle for tank car use was one having 75,000 p.s.i. minumum tensile strength. It was theorized, however, that a steel plate having a tensile strength level about 81,000 p.s.i. or over would permit a substantial reduction of weight in railroad tank cars constructed from standard gauge steel plate. In larger tank cars the hypothesized reduction of weight would be as high as and even more. Needless to say such a reduction of weight would significantly add to the cargo-carrying capacity of the tank car.

Summary of the invention Although no one would have seriously considered it possible to achieve such physical properties in carbon steel plate of the type involved, with the knowledge that surprising increases in strength levels of carbon steel could be obtained through controlling the residual elements to high levels without sacrificing other essential qualities of the steel, it occurred to me that unexpected further increases in strength levels might be consistently obtainable by further modification in the chemistry to permit commercial production of a tough, readily weldable steel having exceptionally high strength levels in the as-rolled condition suitable for tank car use. Because of variations in strength characteristics which occur even in plate produced from the same melt it would be necessary to find a chemfor railroad tank cars guaranteed to minimium tensile D strengths above 81,000 p.s.i. in the as-rolled condition which at the same time has the necessary characteristics of good weldability and toughness. The sheel has already experienced a significant commercial success with fifty to one hundred thousand tons per year presently being produced.

Initially, it was thought that a low-alloy steel, produced to the same chemical analysis as the instant invention, except utilizing a minimum of 0.02% vanadium in lieu of the high residual levels, would be the equivalent of the invention. Although such steel could be produced to over 81,000 p.s.i. tensile strength in the as-rolled condition, in practice it proved inferior in weldability and toughness and has not experienced general commercial acceptance. The necessary chemistry will be described in more detail in the subsequent description of the invention. But it should be understood that the steel plate of this invention differs from the steel plates taught by US. Patent 3,310,441 not only in application as noted above and also in the particular chemical balance, notably in a comparatively higher carbon content and lower manganese to carbon ratio.

I have recently further discovered that plates produced to, about the chemistry taught herein which are normalized by being held at a temperature of about 1550 F. for one hour per inch thickness and air-cooled, provide surprisingly good toughness to temperatures down to F. and are superior as high-strength carbon steel plates for use as pressure vessels both in moderate and lower temperature service. Also, it will be appreciated from the subsequent description of the invention, optimum results are produced for this particular type of steel through a somewhat further modified chemical balance.

In view of the foregoing, it is an object of the invention to provide a high-strength carbon steel plate in the as-rolled condition which may be priced significantly lower than steel plates of comparable capabilities having suitable properties for use in structural applicationsparticularly for fabrication of railroad tank cars.

It is also an object of the instant invention to provide a flange of fire-box grade steel having a minimum tensile strength of 81,000 p.s.i.

It is another object of this invention to provide a highstrength carbon steel of such a type which is readily weldable.

It is a further object of this invention to provide carbonsteel plates of the aforementioned improved qualities and thicknesses up to two inches for structural steel.

It is a yet further object of this invention to provide a tough, weldable, high-strength carbon steel which is superior for use in pressure vessels exposed to moderate and lower temperatures.

A still further object of the invention relates to the production of the foregoing steel, largely from less expensive scrap steel in a melting furnace by the coldcharging process and in the particular chemistry balance achieved through this means of production.

Description of preferred embodiments It has been discovered that the unusual properties of carbon steel plate according to the invention can be achieved by carefully balancing the carbon and manganese levels together with the inclusion of high levels of nickel, chromium, molybdenum and copper within what is presently considered the industrial standards of maximums for residual elements through the careful control of scrap added to the furnace producing the steel. The relative amounts of carbon and manganese have an effect on the yield point, tensile strength, ductility, etc. It has been generally found that the strength level is improved as the ratio of manganese to carbon is increased. However, with the instant invention, increased strength levels are obtained with a lowering of the manganese-to-carbon ratio.

The refinement of the grain structure of these steels is further improved as a result of treating the steel with aluminum. However, the addition of aluminum is optional for structural grade steels although it is pre ferred for flange and fire-box grade steels. Still further, improvement results when the steel contains high levels of the elements nickel, chromium, molybdenum and copper, even though these elements are maintained within the industrial standards of maximums for residual elements. This latter factor not only improves essential physical characteristics of the resulting steel plates, but also permits the use of eighty percent or more scrap in the production of carbon steel plate according to the invention. This is an important factor since, at least currently, the market value of scrap is less than one-half that of pig iron.

Steel in accordance with this invention is prepared in a melting furnace of the open-hearth or electric-arc type. Approximately eighty percent or more of the charge is scrap steel with about one-half of same being purchased scrap and the remaining being scrap generated at the mill from trimmings, diversions, etc. It is important that the chemical constituents of such scrap be known as accurately as possible. However, by experience it has been learned that the copper-nickel-chromium-molybdenum contents in purchased scrap fall in a ratio of roughly 7531. Thus by careful control of scrap in accordance with one of the chemical constituents-say, copper-the other constituents are also controlled within limits. But it should be needless to say that purchased scrap must be carefully inspected and chemically checked by individuals skilled in this art for segregation into identified areas of the scrap yards. Scrap generated in the mill is similarly identified and segregated. At the present time, with such close inspection and segregation, steel plate having characteristics in accordance with the invention may be produced with substantially less than five percent diversions.

It will be appreciated from the foregoing that by controlling the type and amount of scrap, the levels of copper, nickel, chromium and molybdenum contents are similarly controlled. With knowledge of desired amounts of such elements, the object is to employ various grades of scrap in the most economical ratios. Of course, in so doing, the inventory of scrap on hand at the time must be kept in mind. An example of such control is a mixture as follows:

TABLE I Source: Percentage Molds 10.3

Casts 8.7

Total pure iron 19.0

No. 1 busheling u 8.0 No. 1 bundles 3.3 No. 2 heavy melting 8.4 No. 2 bundles 12.0 -Machine shop turnings 9 3 Total purchased scrap 41.0

Common plate 33.3 Pit (sprues and runners) 6.7

Total plant scrap 40.0

The foregoing produced steel which included 0.30% copper, 0.19% nickel, 0.13% chromium and 0.04% molybdeum. The cost of a comparable charge in pig iron for the elements of copper, nickel, chromium and molybdenum added is approximately two and one-half times the foregoing.

It has been found that to produce steel plate economically in accordance with the invention, the preferred minimum percentages of copper, nickel, chromium and molybdenum should be 0.11, 0.10. 0.07, 0.02, respectively. On an individual basis, the respective minimum percentages should be about 0.10, 0.08, 0.04 and 0.01, and the sum of the percentages of copper, chromium and molybdenum should exceed 0.20 but generally should not exceed 0.60. The sum of the nickel and chromium content percentages should be at least 0.15 and preferably at least 0.20. The preferred maximum percentages of copper, nickel, chromium and molybdenum are 0.35, 0.15, 0.15 and 0.05, respectively, and the desired percentage ranges for these constituents are about 0.11-0.27, 0.l0-0.l5, 0.07-0.09 and 0.02-0.03, respectively. However, as will be noted from subsequent tables, one or several of such elements may extend out of these desired ranges.

For the invention herein, the presence of copper follows almost inevitably from economical use of scrap for the charge. But it is not believed that the presence of copper, within the prescribed residual levels, significantly affects as a matter of commercial practicality, the desired characteristics of the steel plate produced. More critical are the nickel and chromium contents which, as indicated above, should preferably total 0.20 percent or more.

Charged into the melting furnace just prior to the tap or into the ladle is standard ferro manganese or other manganese additive whereby the manganese percentage by weight will be 0.70 to 1.60, preferably 0.80 to 1.50 for structural steels, and 0.80 to 1.20 for flange and fire-box grade steels. Where plate from the steel is intended for tank cars, the manganese percentage range will be 1.00- 1.50, the amount depending upon the thickness of the plate to be produced and being on the lower side for thinner plates, say of /s-inch thickness, and on the higher side for thicker plates, say of A- to one-half inch or more in thickness. For the desired quality of steel plate, it has been found that in general the higher the total of copper, nickel, chromium and molybdenum, within the limits of the invention, the less manganese or carbon is required. Ferro silicon or other silicon-containing additive is added at approximately the same time to deoxidize or quite the molten steel. The amount is somewhat lesser for thinner plates than for thicker plates.

In the cold-charging production of steel, the charges are kept in a heated or molten condition for approximately two to four times as long as with the hot-charge method. During the molten period, the carbon content tends to decrease. As noted above, less carbon and manganese are required for strength in the thinner gauges than in the thicker gauges. For this reason, different ranges of carbon and manganese and percentage by weight are specified for different gauges of structural steel plate approximately as shown in the following table:

TABLE II Type A Type B Carbon Manganese Carbon Manganese Gauge range range range range its-WW, incl. 0.15-0.17 1. 05-1. 20 016-0. 18 1. 15-1. 30 Over 1n 0. 17-0. 19 1. 10-1. 25 0. 19-0. 21 1. 25-1. 40 Over %-1", mel .1 0. 10-0 21 1.15-1.30 0. 21-0. 23 1. 30-1. 45 Over 14% 11101.... 0.21-0.23 1. 25-1. 10 0. 22-0. 2-1 1. 30-1. 45 Over 1 -2 ,incl 0. 22-0. 24 1. 301.45 0. 23-0. 25 1. 35-1. 54

Norm-Types A and B steels have minimum yield points of 55,000 and 60,000 lbs./1n. respectively.

The chromium content also tends to become lower While the steel is molten, and for this reason a slightly high chromium content in the initial charge is not considered deleterious.

The specific chemistry of the resulting carbon steel is as follows:

Of course, for the above steels, it will be understood that the carbon content should preferably be maintained the ranges indicated before, depending upon the gauge of the plates. Manganese range for such steels is preferably held between 0.80 to 1.50 percentage by weight for structural steel.

Structural carbon steel plate having the above-disclosed chemistry and produced by conventional hot-rolled processes has properties heretofore only obtainable in steels containing vanadium, columbium, nitrogen or combinations thereof. These unusual properties are disclosed in Table IV.

TABLE IV Yield Tensile Elongation, min. point strength (p.s.i.), (p.s.1.), In 2" In 8" Type min. min. (percent) (percent) A r 55,000 75,000 24. 0 19. 0 B 60, 000 80,000 24. O 19. 0

In carbon steels, it is common for purchasers to specify a certain maximum or minimum copper content. For example, maximum copper content of 0.25 or 0.35% may be specified, or a 0.20% minimum is usual. It is known that the inclusion of copper in amounts from 0.20-0.60% increases the resistance of the steel to atmospheric corrosion and slightly increases the yield point and tensile strength, but adversely affects the ductility. In filling such orders with controlled production, as disclosed herein, the range variations of copper, nickel, chromium and molybdenum, as disclosed in Table III, can easily be obtained in a number of these structural steels as specifically disclosed in Table V.

TABLE v Elongation Yield Tensile Gauge point strength 1112 In 8" Type (1n.) Mn P S Si Cu N1 Cr M0 Al (p.s.i.) (p.s.i.) (percent) (percent) As-rolled carbon steel plate in thicknesses up to one inch having the chemistry of Table III when made accord- TABLE B8658 ing to fine grain melting practice with the inclusion of Oh I 1A 1 about 0.020.055% aluminum, have a minimum tensile ysls] and other qualities of flange and fire-box grades. Such 20 0 Mn P S Cu Si Ni Or Mo A1 steels are suitable for boiler shells, tank car tanks and Q24 L33 m8 Q24 M7 (120 10 Q05 M19 other pressure vessels. These flange and fire-box grade [Ph Sic 1P 0 ti steels are also non-heat treated. Preferably the manganese y a I per 9 content of the flange and fire-box grades is about 0.81.2% Slab N0 3; 21 2 fg Percent l g; and the silicon content is 0.150.3%. Also, the maximum 25 p g m phosphorus and sulfur content should be about 0.035 and 11 56,700 89,300 22 0.04, respectively.

A threefourths inch plate was prepared having the fol- MELT C4040 lowin chemistr and ualities:

y q [Chemical Analysis] IABLE VI 0 Mn P 3 Cu 31 Ni Cr M0 Al C P s 81 of M0 A1 0. 23 1.27 .010 .021 0. 20 0.23 0. 23 0.14 0. 05 0. 015 .23 1.04 .013 .023 .27 .13 .10 .03 .010 0.35 .22 1.00 .011 .024 .10 .10 .10 .00 .020 0.30 lphwcallwpeltlesl Thick- Yield Tensile Percent Elong- Condition of temper: as-rolled slab NO T1955 (111) D Strength in 3" 50, 500 33,300 23 Tensile properties Longitudinal Transverse g/A 2g, 2g, 20 8 21 Yield strength, p.s.i 51,000 53,000 51,600 52,700 57,800 87,900 24 Ultimate strength, p.s.i 82,500 81, 800 82,700 82,400 Elongation in 8 percent 27 28 21 22 Elongation in 2 percent 38 40 40 32 MELT X4502 Reduction in area, percent 57.1 57.2 48.9 49.0

h h [Chemical Analysis] ur no The Welding propertles of the above three fo t s 1 0 Mn P S Cu Si Ni Cr Mo A1 plate were determined to be excellent in terms of transverse and longitudinal tensile strengths. Also, no evidence Q24 L31 .013 of cracking was observed on a 180 bend made in the [Physical Properties] as-welded and stress-relieved conditions.

Thick- Yield Tensile P e t 1 The toughness of this steel ws also determlned with Slab N0 ness (111.) point strength er en 1 5 excellent results. Im act low-temperature V-notch Charpy 64 100 94 400 23 test results were better than conventional structural steels. 03, 700 941300 3 Table VII shows a number of typical melts for the pro- 04,700 37,300 24 duction of plates designed for use in tank cars. Plates Of this steel uniformly had tensile strengths between 81,000 MELT A3841 and 101,000 p.s.i. yield points above 50,000 p.s.i. and an c elongation in eight inches of at least 18%. Bend test hemlcalAnalysls] specimens of such steels can stand being bent cold through 0 P S 011 Si Ni Or M0 Al 180 without cracking 011 the outside of the bent portion 0.23 1.24 0.011 0. 010 0.24 0. 27 0.10 0.12 .07 .021 through an inside diameter of twice the thickness of the [Physical P 0 Mi specimen. It Will be noted that such steel plates are made r p 1 as to fine grain practice. The carbon content is about 18% i Tensile Percent Elong- Slab N0 ness 1n. omt t th of the manganese content 1n the examples and, should p sreng m8 preferably be 1620%. It is of primary importance that g 5 588 85488 21 steel plates for tank car end use be readily weldable 8 20 through standard welding procedures. From experience it has been found that the plates are, in fact, readily weld- MELT 8 9 able.

. Ch 1A 1 It has been found that plates havmg acceptable n11n1- emlca Haws] mum yield strengths and tensile points can be manu- 0 Mn P s Cu 51 Ni CI M0 A1 factured without the high residutl levels specified for 0.23 1.24 0.007 0.024 0.10 0.20 0.12 0.12 0.05 0.010 the steel plates of the lnvention through the addltion of 1 [Physical Properties] vanadium in amounts exceeding 0.02%. However, such plates have not been broadly acceptedbecause they do not slab No 533 Percent ,235 present the advantages and weldabihty of the plates of the invention and the degree of toughness is less.

MELT U3304 [Chemical Analysis] Mn P S Cu Si Ni Cr Mo Al [Physical Properties] Thick- Yield Tensile Percent Elong. Slab No ness (in.) point strength in 8" MELT C4610 [Chemical Analysis] 0 Mn P S Cu Si Ni Cr Me Al [Physical Properties] Thick- Yield Tensile Percent Elong. Slab No ness (in.) point strength in 8 MELT C4590 [Chemical Analysis] C Mn P S Cu Si Ni Cr Me Al [Physical Properties] Thick- Yield Tensile Percent Elong. Slab No. ness (in.) point strength in 8" MELT A2027 [Chemical Analysis] C Mn P S Cu Si Ni Cr Mo Al [Physical Properties] Thiek- Yield Tensile Percent Elong. Slab No ness (in.) point strength in 8 3A Me 61,000 92,700 20 MELT A2941 [Chemical Analysis] 0 Mn P S Cu Si Ni Or Me A] [Physical Properties] Thick- Yield Tensile Percent Elon Slab No ness (in.) point strength n1 8" MELT C3855 [Chemical Analysis] 0 Mn P S Cu Si Ni Cr Me Al [Physical Properties] Thick- Yield Tensile Percent Elong. Slab No ness (in.) point strength in 8 10 For the production of tank-car steel plate, the chemical analysis should be as set forth in Table VIII below:

The nickel and chromium contents must, it has been found, total at least 0.15% and preferably should be at least 0.20%. The carbon, manganese and silicon contents are increased as the thickness of the plate increases. Thus, a As-inch thickness plate should have its carbon content in the range of.0.15 to 0.20%, its manganese content 1.00- 1.20% and its silicon content 0.150.30=%. For a -inch thickness plate, the carbon content should be 0.18-0.25%, the manganese content should be 1.10-1.35 and the silicon content 0.15-0.30%. For plates i/ -inch thick, the carbon content should be 0.20-0.25%, the manganese content 1.10-1.35%, and the silicon content 0.15-0.30%. For thicknesses of %-inch and above, the carbon content should be 0.20-0.25%, the manganese content 1.20- 1.50%, and the silicon content 0.15-0.50%. As the thickness is further increased, the manganese, carbon and silicon content levels should be preferably in the higher portions of the described ranges. From a commercial standpoint, the most important thicknesses are from inch to one inch. However, the steel plates can be produced with the desired characteristics up to two inches in thickness. In producing the tank car steel plate, the socalled residuals of copper, nickel, chromium, and molybdenum are controlled through careful selection of the scrap charge, as previously described, and the manganese, carbon and silicon are controlled through additions to the melt, the amounts of each depending upon the thickness required of the plates to be produced from the melt. As noted with reference to Table VII, the carbon content is between 16 and 20% of the manganese content and preferably about 18%. It is to be appreciated that the physical properties of the steel plate are achieved by carefully controlling the chemistry of the plate rather than through any subsequent heat treatment of the plate.

TABLE IX.MELT B7913 [Chemical analysis] C Mn P S Cu Si Ni Cr Me Al 00 [Physical properties] Charpy V-notch impact Percent strength in Thicknes Yield Tensile Elong. ft.-lbs, at Slab No. (in.) point strength in 8 -50 F.

MELT C3841 [Chemical analysis] C Mn P S On Si Ni Cr Mo Al [Physical properties] [Physical properties] Charpy Charpy V-notch V-notch impact impact Percent strength in Percent strength in Thickness Yield Tensile Elong. it.-lbs. at Thickness Yield Tensile Elong. ft.-lbs. at Slab No. (in.) point strength in 8 -50 F. Slab N0. (in.) point strength in 8" -50 F.

MELT A3064 MELT B7787 [Chemical analysis] [Chemical analysis] 0 Mn P s Cu s1 Ni 0r M0 Al 9 Mn P S 011 Si Ni 0r M0 A1 0. 23 1.35 0. 011 0. 027 0. 23 0. 23 0.12 0. 07 0. 03 0.028 23 39 M10 M17 (124 Q27 13 (108 0-028 [Physical properties] [Physlcal propertles] Charpy Charpy V -notch V-notch lmpact impact Percent strength in Percent strength in Thlckness Yield Tensile Elong. ft.-lbs. at Thickness Yield Tensile Elong. rt-lh at Slab 0 pomt strength In h Slab N0. (1n polnt stlellgt 1n 8 50 F 3 24 9 9 59, 8 00 23 51 55 46 IR 7903 58, 800 85, 800 27 50, 65, 77 i 7903 200 700 26 43 MELT B7732 [Chemical analysis] MELT B8046 0 Mn P s Cu Si Ni Cr Mo A1 C0 [Chemical analysis] 0. 22 1. 34 0. 017 0. 021 0. 25 0. 25 0. 12 0. 08 0, 03 034 O. 01 0 Mn P S Cu Si Ni MO A1 C0 [Physical properties] 0. 24 1. 44 0.011 0. 029 0.20 0. 20 0.10 0.10 0. 04 0. 020 0.01

Cllarpy [Physical properties] V-notch impact Charpy Percent strength in V-noteh Thickness Yield Tensile Elong ft.-lbs. at P c t t hntplact t t tl 8 50 F, er en s reng ln Slab pm 5 rang m Thickness Yield Tensile Elong. ft.-lbs. at 57, 600 377 100 25 4 55, 50 Slab N o. (111.) polnt strength in 8" -50 F.

MELT A2927 [Chemical analysis] MELT B7933 0 Mn P S Cu Si Ni Cr M0 A1 [C emical analysis] 0. 23 1. 35 0.007 0.024 0.23 0. 24 0.11 0.09 0.03 0.032 C Mn P S on Si Ni or Mo A1 00 [Physical properties] 0. 22 1. 40 0.015 0.019 0. 18 0. 27 0. 11 0. 09 0. 03 0. 036 0. 01

Charpy [Physical properties] V-notch impact Charpy Percent strength in Y-notch Thickness Yield Tensile Elollg. ft.-lbs. at Impact Slab N0. (in.) point strength in 8 F. Percent strength in Thickness Yield Tenslle Elong. it.-lbs. at 311 4 300 90, 300 27 2 31 32 0 Slab No. (In) polnt strength In 8" 50 F. 3RD 63, 700 90, 400 22 30, 35, 31

. 7903 62, 700 84, 500 27 40, 45, 48 7903 59, 600 84, 200 29 50, 53, 46 MELT B7767 .7903 57,800 82,700 27 90, 92, 84

Chemical analysis C Mn P S C11 Si Ni CI M0 Al EL 03 5 0. 22 1. 43 0.015 0.025 0.19 0. 27 0.10 0.08 0, 03 0. 035 [Chemical analysis] [Physical properties] C Mn P S Cu Si Ni Cr M0 Al 00 Charpy 0. 23 1. 19 0.014 0.027 0.26 0. 24 0. 13 0.08 0.03 0. 016 0. 01

[Physical properties] Percent strength in Thickness Yield Tensile Elong. ft.-lbs. at DY Slab N0. (in.) point strength in 8" -50 F gg 2 2 Percent strength in g ggwgg g? g? Thlckness Yield Tensile Elong. it.-lbs. at 13/16 001400 371100 23 51: e1: 00 Slab (m9 Strength 111 F l3 16 59, S00 85, 900 28 72 2, 2 13416 58, 000 87 800 27 2 5B .7903 58,700 81,700 23 21, 21, 25 13/16 59,800 87, 800 27 50, 51, 50 13/16 58, 400 87, 200 26 68, 70, 59

70 The success achieved Wlth the tank car plate suggested MELT 3884 the possibility that a similar chemistry might be utilized [Chemical analysis] to produce unique superior high-strength carbon steel C Mn P S Si N of MO A1 plates for pressure vessels or tank cars in moderate and lower-temperature service. Table IX shows the chemical analysis and physlcal propertles of a number of plates The nickel and chromium percentage totals should be at least 0.15 and preferably at least 0.25. The carbon content percentage should be preferably 0.23%. For plates up to 4-inch thickness, the manganese range should preferably be 1.15-1.35, aiming at a percentage of 1.25. For plates over %-inch, the manganese content is preferably 1.25-150, aiming at a 1.40%. The steel plates are made to fine-grain practice and in this connection, the desired percentage of aluminum is 0.025. The carbon content is preferably about 16 to 17% of the manganese content and, in the examples, ranges to 19%. Plate produced in accordance with these specifications is intended for fusion welding and by such techniques is readily weldable. In bend tests, specimens of such steel plates may be bent cold through 180 without cracking on the outside of the bent portion to an inside diameter which is twice the thickness of the specimen. If the test is made on a specimen reduced in thickness, the rolled surface is on the outer curve of the bend.

In the foregoing disclosure and in the claims, percentages are expressed by weight unless indicated otherwise.

Plates from the steels disclosed herein are characterized by high strength characteristics normally associated only with alloy steels or steels containing significant amounts of vanadium, columbium, nitrogen, etc. From the values listed above for tensile strengths, yield points and other characteristics, it will be apparent to one skilled in the art that these higher strength steels exceed standard specifications so that considerable savings are realized.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. A high strength readily weldable carbon steel plate in the as-rolled condition consisting essentially of Element: Percentage by weight Carbon 0.15-0.25

Manganese 1.00-1.50 Phosphorus Up to 0.025 Sulphur Up to 0.040 Silicon 0.15-0.50

Aluminum 0008-0015 Copper 0.01-0.40 Nickel 0.05-0.35

Chromium 005-025 Molybdenum 0.01-0. 15 Iron Balance the total percentage nickel and chromium being at least 0.15%, wherein the carbon content progressively increases from about 0.15% to 0.25%. and the manganese content progressively increases from about 1.00 to 1.50% in functional relationship to the plate gauge as it increases from about inch to 2 inch, said plate having a yield point of at least 50,000 psi. and a tensile strength of at least 81,000 psi.

2. A steel plate in accordance with claim 1 of about thickness wherein the maximum carbon content is 0.20%, the maximum manganese content is 1.20% and the maximum silicon content is 0.30%.

3. A steel plate in accordance with claim 1 of about thickness wherein the carbon content is 0.l8-0.25%, the manganese content is 1.10-1.35 and the maximum silicon content is 0.30%.

4. A steel plate in accordance with claim 1 of about thickness wherein the carbon content is 0.20-0.25%, the manganese content is 1.10-1.35 and the maximum silicon content is 0.30%.

5. A steel plate in accordance with claim 1 of at least about thickness wherein the minimum carbon content is 0.20% and the minimum manganese content is 1.20%.

6. A steel plate in accordance with claim 1 wherein the minimum total content of nickel and chromium is 0.20%.

7. A steel plate in accordance with claim 1 wherein the carbon content is 16-20% of the manganese content.

8. A steel plate in accordance with claim 1 wherein the carbon content is about 18% of the manganese content.

9. A steel plate in accordance with claim 1 wherein the tensile strength is about 87,000 psi.

10. A high strength readily weldable carbon steel plate containing iron, incidental impurities, and about Element: Percentage by weight Carbon 0.22-0.25

Manganese 1.15-1.50 Phosphorus Up to 0.035 Sulphur Up to 0.040 Aluminum Minimum 0.0210

Copper 0.01-0.35 Nickel 0.05-0.25

Chromium 0.05-0.25 Molybdenum 0.01-0.08 Iron Balance the total percentage of nickel and chromium being at least 0.15, said steel plate being in a normalized condition and characterized by a yield point in excess of 50,000 p.s.i., a tensile strength in excess of 81,000 p.s.i. and a minimum Charpy V-notch impact strength at -50 F. of 20 foot-pounds.

11. A steel plate in accordance with claim 10 wherein said plate is normalized by being heated to l525-1650 F. and held a minimum of forty-five minutes per inch thickness, and air cooled.

12. A steel plate in accordance with claim 10 having a thickness of about with a maximum manganese content of 1.35%.

13. A steel plate in accordance with claim 12 having a manganese content of about 1.25%.

14. A steel plate in accordance with claim 10 of over thickness with a minimum manganese content of 1.25%.

15. A steel plate in accordance with claim 14 having a manganese content of about 1.40%.

16. A steel plate in accordance with claim 10 wherein the minimum total content of nickel and chromium is 0.20%.

15 16 17. A steel plate in accordance with claim 10 wherein References Cited the silicon content is about 0.25%.

18. A steel plate in accordance with claim 10 wherein UNITED T F PATENTS the aluminum content is about 0.025%. 2,467,701 4/1949 Rlplch 75124 19. A steel plate in accordance with claim 10 wherein 110,798 11/1963 Keay 75-124 X the carbon content is about 15-19% of the manganese 5 content HYLAND BIZOT, Primary Examiner 20. A steel plate in accordance With claim 10 wherein the carbon content is about 17% of the manganese content.

US. Cl. X.R. 75-125, 128

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent 3,499,757 Dated March 10, 1970 Inventor(s) Louis I. Mandich It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 42, insert after manganese, 1.10 1.35%, and the silicon the same as for the 3/8-inch plate. For 9/l6-inch plate, the carbon should be 0.20-

Column 3, line 33, substitute steel for "sheel Column 7, line 49, substitute was for "we" line 69, substitute residual for residutl SIGNFH AND SEMI-TU smsm (SEAL) Edw M mm 1:. scam-m, .m- Mtesting Officer Gomissiom of Patents FORM PO-1050 (10-69) UsCOMM-DC GONG-P69 i us sovnnmnn numus ornc: 1 an o-lu-ua