US3110586A - High strength normalized steel - Google Patents

Description

United States Patent 3,110,586 HIGH STRENGTH NORMALIZED STEEL John A. Gulya, Lancaster, and Roy Hetherington, In, West Chester, Pa., assignors to Lukens Steel Company, Coatesville, Pa., a corporation of Pennsylvania No Drawing. Filed July 20, 1961, Ser. No. 125,345 4 Claims. (Cl. 75-128) The present invention relates to a normalized and tempered alloy steel providing uniform strength combined with good notch toughness and Weldability through a wide range of section thicknesses without resorting to chemistry changes or accelerated cooling rates from austenitizing temperatures for the larger sections of metal.

Structural and pressure vessel applications frequently require a steel to be used in a broad range of section thicknesses. Unfortunately, available steels are particularly sensitive to section thickness in that they generally exhibit a marked reduction of properties in heavier gauges. Several methods are used to oifset this characteristic property decrease. In some cases, a number of steels are employed together and thereby problems such as inventory, identification, and joining, are multiplied. in other cases, a premium steel is used in lighter sections to provide the required properties in the heavier sections. In still other cases, a steel that is adequate only in the lighter sections will be used, but the heavier sections Will be subjected to rapid cooling from austenitizing temperatures to achieve nearly equivalent properties. This procedure also increases the manufacturing costs and generally provides a material of reduced weldability.

Steels used in structural and pressure vessel applications should exhibit weldability, uniform high strength and notch toughness throughout a wide range of section thicknesses. In order to insure excellent weldability, the amount of carbon should below and the tensile strength and notch toughness of the steel increased with low amounts of selected alloying elements. But, the problem of selecting the proper balance of alloying elements for a steel useful in structural and pressure vessel applications is a difficult one, especially if substantially uniform strengths over a broad range of section thicknesses are to be obtained. This is evidenced in the available steels which exhibit decreased strength accompanied by a marked reduction in notch toughness in the heavier sections.

It is an object of the present invention to provide an improved weldable normalized steel that is characterized by high strength and excellent notch toughness over a broad range of thicknesses ithout resorting to chemistry changes or quenching from austenitizing temperatures for heavier sections.

,It is another object of the present invention to provide a low-carbon, low-alloy steel that is particularly useful in structural and pressure vessel applications having high section thicknesses.

It is still another object of the present invention to provide an economical combination of alloying elements that Will have the above desirable characteristics.

The foregoing problems are avoided to a large extent, and the above objects are achieved in the present invention by the provision of a new, useful, economical combination of alloying elements. In both the normalized, and the normalized and tempered condition, high strength,

3,110,586 Patented Nov. 12, 1963 ice toughness, and weldability are maintained throughout a wide range of section thicknesses by an alloy steel within the following compositional range.

Balance iron and incidental steel-making residuals.

Itwill be apparent that other additives such as 0.25- 0.45% copper for resistance to atmospheric corrosion can be used, replacing a like amount of the iron content. Similarly 0.020.l0% aluminum, other deoxidizers or other commonly used additives to produce fine-grained steels can be included. The preferred alloy will contain the alloying elements in the following ranges.

Element: Percent by weight Carbon 0.12 to 0.20 Manganese"; 0.95 to 1.45 Phosphorus Up to 0.035 Sulphur Up to 0.040 'Silicon 0.11 to 0.30 Nickel 0.70 to 1.00 Chromium 0.40 to 0.65 Molybdenum 0.25 to 0.45 Vanadium 0.03 to 0.08

Balance iron and incidental steel-making residuals.

Sections of plate, approximately one inch and six inches gage were normalized at 1700 -F., allowed to cool to air temperatureand tempered at 1100" F. Treatment times were two and four hours for the one and six inch sections respectively. Analysis of the alloy fol-lows.

Element: 7 Percentage by weight, Carbon 0.14 Manganese 1.22 Phosphorus 0.020 Sulphur 0.024 Silicon 0.17 Nickel g 0.84 Chromium 0. 60 Molybdenum 0.38 Vanadium 0.04- Copper 0.2!5 Balance iron and incidental steel-making residuals.

The test results were as follows:

Yield Tensile Elonga- Reduction Impact, (1,000 (1,000 tion, of Area, tt.-lbs., at p.s.i.) p.s.i.) Percent, Percent 40 Sample 1 (1") 105. 5 120. 9 18. 5 60. 6 20 Sample 2 (6) 99. 5 120. 2 20. 0 56. 3 14 Inorder to demonstrate that the high level of mechanical properties characterizing the alloy can be effectively used in the fabrication and welding of structures, the following test results on welded specimens are cited:

In the standard underbead crack test using E 6010 electrodes, cracking amounting to only 15%. These tests were carried out at 70 F. on 2 X 3" pieces of 1" plate which was split in one-half inch thick samples. In the same tests it is not unusual for the available steels having comparable strengths to exhibit 30 to 50% cracking.

In the foregoing welding test, susceptibility to hydrogen effects appears to be the controlling factor. When welding [with low-hydrogen electrodes, however, hydrogen effects are minimized and joint restraint appears to be the dominant factor. In order to assess alloy steels under such conditions, a test developing greater restraint, such as the standard cruciform test, was used. The results of this test' may be expressed quantitatively by determining the percentage underbead cracking in the third pass. Conducting this test on the subject steel using A diameter 12016 electrodes to deposit a /8" fillet at room temperature resulted in only 20% cracking.

Another important measure of the wel -dability of a steel is the ductility of the heat-aifected-zone of welded joints. While this zone is frequently brittle in the available steels in either or both the as-welded and stressrelieved conditions, the heat-alfected-zone Olf the steel of the present invention is more ductile in either condition than the parent metal. For example, butt Welds were made in /3" plate (machined from the above 1 plate) using the above described 12016 electrodes, half of which were stress-relieved at 1100 F. Standard V- notch Charpy specimens were machined from these samples and tested at -80 F. The following table shows the improved ductility obtained:

Parent metal 11 As-lwelded HAZ 2'8 Stress-relieved HAZ 26 Additional 6" thick samples having the following alloy contents were tested:

The following table indicates the excellent characteristics of these alloys:

Yleld Tensile Elonga- Reduction Impact (1,000 (1,000 tion, of Area, at 40 p.s.i.) p.s.i.) Percent, Percent F. ft.-lbs. in 2' Sample 3 (6") 105. 5 116.3 19 51.0 19 Sample 4 (6) 116. 7, 133. 6 16 50. 5 12 Thus the above .data demonstrate that the low-alloy low-carbon steels of the present invention develop uniformly high strength, toughness and weldability throughout a wide range of section thicknesses Without resorting to drastic changes in alloy content or quenching from austenitizing temperatures for the heavier sections.

In all OLf the above alloys the amount of carbon should be at the maximum of the permissible ranges if abrasion resistance is desired.

Throughout the specification and in the claims, percentages are by 'weight. The specific embodiments are intended to be illustrative but not limiting. All modifications and variations that fall within the meaning and purview of equivalency of the claims are therefore intended to be embraced thereby. It will thus be understood that no limitations of the scope of the invention are contemplated by the employment of specific language and that various alterations and modifications may be made such as would occur to one skilled in the art to which the invention relates.

We claim:

1. An improved weldable normalized steel consisting of Element: Percent by weight Carbon 0.1 to 0.2 8 Manganese 0.9 to 1.45 Phosphorus Up to 0.04 Sulphur Up to 0.05 lSilicon 0.11 to 0.4 0 Nickel 0.5 to 1.00 Chromium 0.35 to 0.70 Molybdenum 0.25 to 0.50 Vanadium 0.02 to 0.10

Balance iron and incidental steel-making residuals.

said steel being characterized in having high uniform strength and toughness through a wide range of thicknesses.

2. An improved weldable normalized steel consisting of Element: Percent by weight Carbon 0.12 to 0.20 Manganese 0.95 to 1.45 Phosphorus Up to 0.035 Sulphur Up to 0.040

v Silicon 0.11 to 0. 30 Nickel 0.70 to 1.00 Chromium 0.40 to 0.6 5 Molybdenum 0.25 to 0.45 Vanadium 0.03 to 0.08

Balance iron and incidental steel-making residuals,

said steel being characterized in having high uniform strength and toughness through a wide range of thicknesses.

3. An improved weldable normalized steel consisting of said steel being characterized in having high uniform strength and toughness through a Wide range of thicknesses.

4. An improved weldable normalized steel consisting of Element: l Percent by weight said steel being characterized in having high uniform Carbon 0.12 to 0.20 strength and toughness through a wide range of thick- Manganese 0.95 to 1.45 nesses. Phosphorus Up to 0.035 Sulphur Up to 0.040 References Cited in the file of this patent 33 3 8-28 5 UNITED STATES PATENTS m 0 70 Gaspali at al A g 28, ch.0m;I.gjjjjjjjjjjjjjjjjjjjjj: 0140 to 0165 2,798,805 Hodge m1 July 9,1957 Molybdenum 0.25 to 0.45 Vanadium 0.03 to 0.08 10 Copper 0.25 to 0.45

Balance iron and incidental steel-making residuals,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,110 586 November 12, 1963 John A, Gulya et a1,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as correc ted below Column 2 line 14 v for "020 to 0. 10" read 0.02 to 0.10 same column 2 in the table at the bottom of the column, the third heading should appear as shown below instead of as in the patent:

Elongation Per-cent in 2 Signed and sealed this 21st day of April 1964.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims (1)

1. AN IMPROVED WELDABLE NORMALIZED STEEL CONSISTING OF ELEMENT PERCENT BY WEIGHT CARBON 0.1 TO 0.28 MANGANESE 0.9 TO 1.45 PHOSPHORUS UP TO 0.04 SULPHUR UP TO 0.05 SILICON 0.11 TO 0.40 NICKEL 0.5 TO 1.00 CHROMIUM 0.35 TO 0.70 MOLYBDENUM 0.25 TO 0.50 VANADIUM 0.02 TO 0.10 BALANCE IRON AND INCIDENTAL STEEL-MAKINE RESIDUALS.