US2863763A - Ductile and tough high strength steel - Google Patents

Description

Patented Dec. 9, 1958 DUCTILE AND TOUGH HIGH STRENGTH STEEL Samuel J. Rosenberg and Carolyn R. Irish, Washington, D. C., assignors to the United States of America as represented by the Secretary of the Navy N Drawing. Application March 19, 1957 Serial No. 647,167

5 Claims. (Cl. 75-128) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to high strength alloy steels possessing sufficient ductility and toughness to permit satisfactory use in structural applications.

In order to meet the great variety of uses for steel, many special steels suited to different uses have been developed. in structural applications, for example, it is important to have a steel possessing a high degree of strength.

However, in structural steels now in use, while many possess adequate strength, where extreme strength is involved there may be a definite deficiency in toughness and ductility. The combination of chemical elementsin the present invention develops high strength with sufficient ductility for structural applications by applying a heat treatment to an alloy steel composition in which the percentage of silicon is more than doubled over that usually employed and a small percentage of titanium has been added, as indicated in the following composition Table I giving element percentage ranges:

In general, usual furnace procedures are followed in making the steel of the above indicated alloy. Any of the usual type furnaces may be employed as, for example, the open hearth furnace. It is important that effective deoxidation of the furnace steel be made, good results being obtained by using aluminum addition, to the amount of two pounds per ton of steel. After the ingot is obtained, it is heat soaked, forged and rolled to the desired form according to routine procedure, and then subjected to the following heat treatment.

The alloy is normalized by heating to about 1700 F. and holding at this temperature for at least one half hour per inch of thickness of the workpiece, this treatment being followed by cooling in air. In some cases where machining is required, because of deep hardenability, small and even moderately sized sections may prove difficult to machine after normalizing, in which cases the steel can be annealed by heating to about 1625" F., followed by slow (furnace) cooling to about 800 F. at a rate not exceeding 200 F. per hour and cooling in air below 800 F.

After the normalization step, the steel is hardened by heating to a point above the upper critical temperature (AC3), as 1650" F., holding at this temperature for at least one-half hour, and quenching by fluids, such as oil. The steel is then double tempered-by heating in two successive periods to the 400 F.500 F. temperature range and holding the steel in this range for at least one and one-half hours, after which it is air cooled.

It should be pointed out that while normalizing is a desirable heat treatment it is not essential for hardness, which depends on the heating to 1650 F. followed by quenching and the double tempering steps. However, the preferred procedure includes normalizing to increase uniformity of the steel.

The element percentage range of the alloy steel has been indicated hereinabove; as typical of particular steels tested, examples are given in Table II:

Table 11 Percentages Elements A B C D E 0 42 0 42 0 39 0 40 0 40 O 76 0.76 0. 0.72 0 72 1. 59 1. 59 1. 70 1. 50 1. 50 1. 83 1. 83 1 80 1. 80 1 80 0.79 0 79 0.86 0 83 0 83 0.25 0.25 O 32 0 30 0.30 0 041 O 041 0 10 0 08 0 08 O. 00 0.0022 0. 00 0. 00 0.0011

The composite elemental percentages of many steel specimens approach the following values:

Table III Elements Percentages Carbon 0. 40 Manganese. 0. 75 Silicon 1. 60 Nickel 1. 80 Chromium 0, 85 Molybde 0. 30 Titanium 0. 10

These steels, produced by the indicated process including the normalizing, hardening and double tempering steps, with critical temperatures at about 1600" F.-Ac 1350 F .Ar 540 F.Ms, and with double tempering at successive time periods of one and one-half to four hours, have the properties as indicated in Table IV, which follows, average values being given:

The results are indicative of a definitely high strength level and hardness, which of themselves might not be considered noteworthy; but when these properties are coupled with pronounced ductility, as evidenced by the reduction in area and elongation data, and with a high degree of toughness, as indicated by the impact test data, the steel properties are considered outstanding. The maintenance of toughness on temperature drop to -40 F. from room temperature is also worthy of note, the lowest value for the impact test at either room temperature or 40 F.

Table V Property Value Hardness, Re 55.0 Ultlln te Tensile Strength, p, s. l 302 000 Yield Strength, p. s. L.

Elongation, percent in 1.4 inch 9.0

Reduction of Area, percent 38.2 Irnp1etl-t. Lb

Room Temt 6 Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A low-alloy, high-strength steel for structural application characterized by great hardness, good ductility and toughness when heat treated by quenching from above the upper critical temperature, and double tempered in the 400 F. to 500 F. range, said steel comprising about: 0.35 to 0.45% carbon, 0.50 to 1.50% manganese, 1.30 to 2.00% silicon, 1.50 to 2.50% nickel, 0.70 to 0.90% chromium, 0.20 to 0.40% molybdenum, 0.04 to 0.20% titanium, 0.000 to 0.0025% boron, and the balance of said steel being essentially iron.

2. A low-alloy, high-strength steel for structural applications possessing pronounced great hardness, ductility and toughness containing about: 0.35 to 0.45% carbon,

0.50 to 1.50% manganese, 1.30 to 200% silicon, 1.50 to 2.50% nickel, 0.70 to 0.90% chromium, 0.20 to 0.40% molybdenum, 0.04 to 0.20% titanium, 0.000 to 0.0025% boron, and the balance of said steel being essentially iron.

3. A low-alloy, high-strength steel for structural applications possessing pronounced great hardness, ductility and toughness containing about: carbon 0.39%, manganese 0.75%, silicon 1.70%, nickel 1.80%, chromium 0.86%, molybdenum 0.32%, titanium 0.10%, and the balance of said steel being essentially iron.

4. A low-alloy, high-strength steel for structural applications possessing pronounced great hardness, ductility and toughness containing about: carbon 0.40%, manganese 0.72%, silicon 1.50%, nickel 1.80%, chromium 0.83%, molybdenum 0.30%, titanium 0.08%, boron 0.0011%, and balance of said steel being essentially iron.

5. A process of heat treating a low-alloy steel as set forth in claim 2 which comprises normalizing at a temperature above the upper critical temperature of said steel, hardening by quenching from a temperature in excess of the upper critical temperature of said steel, and tempering by dual successive beatings to between 400 F. and 500 F. followed by air cooling, the sucfiessive heatings being held for at least one and one-half ours.

References Cited in the file of this patent UNITED STATES PATENTS 1,519,388 Walter Dec. 16, 1924 2,283,299 Tisdale May 19, 1942 2,327,490 Bagsar Aug. 24, 1943 2,339,368 Bagsar Jan. 18, 1944 2,673,147 Brezin Mar. 23, 1954 2,791,500 Foley et a1 May 7, 1957 OTHER REFERENCES Grossrnann: Principles of Heat Treatment, 1940 Edition, pp. 143, 106-109 and 110-125.

Claims (1)

1. A LOW-ALLOY, HIGH-STRENGTH STEEL FOR STRUCTURAL APPLICATION CHARACTERIZED BY GREAT HARDNESS, GOOD DUCTILITY AND TOUGHNESS WHEN HEAT TREATED BY QUENCHING FROM ABOVE THE UPPER CRITICAL TEMPERATURE, AND DOUBLE TEMPERED IN THE 400*F. TO 500*F. RANGE, SAID STEEL COMPRISING ABOUT: 0.35 TO 0.45% CARBON, 0.50 TO 1.50% MANGANESE, 1.30 TO 2.00% SILICON, 1.52 TO 2.50% NICKEL, 0.70 TO 0.90% CHROMIUM, 0.20 TO 0.40% MOLYBDENUM, 0.04 TO 0.20% TITANIUM, 0.000 TO 0.0025% BORON, AND THE BALANCE OF SAID STEEL BEING ASSENTIALLY IRON.