US3294528A - Nickel-copper-titanium steel - Google Patents

Description

United States Patent 3,294,528 NICKEL-C(lIPER-TETANEUM STEEL Robert R. Hayward, Cleveland, (This, and George Raynovich and William H. Richey, Pittsburgh, Pa, assignors to Jones 81 Laughiin Steel Corporation, Pittsburgh, Pa, a. corporation of Pennsylvania No Drawing. Filed May 21, 1962, Ser. No. 197,181 1 (Ilaim. (Cl. 751Z5) This invention relates to low alloy-high strength steels. It is more particularly concerned with such steels containing relatively small amounts of nickel, copper and titanium.

Ordinary carbon steels employed for construction purposes have yield strengths of about 33,000 p.s.i., the particular value depending on the composition of the steel, its section thickness, and other factors well known to metallungists. A number of years ago several low alloy steels were developed which had yield strengths on the order of 50,000 p.s.i., and today there are a variety of such steels, which obtain their strength by the use of alloying elements, principally nickel, chromium and manganese.

While steels of those type-s above mentioned are satisfactory for many purposes, they do not, generally speaking, exhibit high resistance to atmospheric corrosion. Many of them are not readily formed, and many of them have relatively poor notch toughness at low temperatures. An appreciable number are rather difiicult to weld.

It is an object, therefore, of our invention to provide a low alloy-high strength steel having a high degree of formability. It is another object to provide such a steel having improved corrosion resistance. It is another object to provide such a steel having substantial notch toughness at sub-zero temperatures. It is a further object to provide such a steel which may be welded with no more difficulty than plain carbon steels. Other objects of our invention will appear in the course of the description thereof which follows:

The steels of our invention are low carbon steels having maximum carbon content of about 117%. They conform to American Society for Testing Materials standard specification A-Z42-60 for high strength, low alloy structural steel. Their maximum manganese content is 1% and preferably more than about .60%. Their maximum silicon content is .50% and preferably more than .25

Patented Dec. 27, 1966 The steels contain at least 20% copper, which, together With other constituents, increases their resistance to atmospheric corrosion. From a practical standpoint, copper in excess of about .50%, though not harmful, is of little additional value for that purpose. Our steels contain nickel in amounts between about .50% and .80%, and titanium in amounts up to about .06% and preferably above .03%. Phosphorus and sulphur are kept below the normal maximum levels of 04% and .05 respectively.

Table I gives the chemical composition of a number of heats of our steels and Table II itemizes certain physical properties of those steels in several section thicknesses. It is evident from Table II that our steels exhibit yield points above 50,000 p.s.i., and ultimate tensile strengths above 70,000 p.s.i., and display very substantial ductility, as measured by elongation, in thicknesses from .075" to .625. The elongation in all cases is greater than 22% in a gauge length of 8 and even higher for shorter gauge lengths.

We have determined that the yield point of our steel rolled to thicknesses commonly used for structural purposes can be maintained above about 50,000 p.s.i. without detriment to other properties if the titanium content of our steel is controlled in a limited range. Tables I and II show that steels otherwise of our invention, but containing .02% or less titanium, have yield points barely exceeding 50,000 p.s.i., while similar steels containing 04% titanium have somewhat higher yield points.

If the titanium content is increased much beyond that amount, however, we find that it exercises a detrimental effect on the low temperature notch toughness of the steel. We determined that ellect by making a series of small experimental ingots of steel of varying titanium contents as are listed in Table III. Those steels also contain varying amounts of aluminum for a reason to be mentioned. Ingots A3367 and A3368 were of the same basic composition as ingot A3366, and ingots A3370 and A3371 were of the same basic composition as ingot A3369. The titanium contents of the steels of Table III ranged from .01 to .11%. The ingots were rolled into steel samples A" in diameter and the conventional basic properties of those samples were determined and are listed in Table IV.

TABLE I.CIIEMICAL COMPOSITION Heat I-Ieat C Mn P S S1 Cu Ni Ti (Code) TABLE II.'IENSILE TEST RESULTS Heat (Code) Finished Gage Yield Point Tensile Str. Percent Elong.

(p.s.i.) (p.s.l.)

.075 HR ShecL 52, 580 70, 520 32, in 2". .105 HR Shock... 52, 880 73, 080 28, in 2". 375 Plate 50, 980 74, 660 22, in 8. 500 Plate. 51, 750 80, 420 24, in 8". 625 Plate 53, 76, 600 25, in 8". .105 HR Sheet 52, 950 74, 300 30, in 2". .135 HR Sheet- 54, 600 74, 460 30, in 2". .500 Plate 51, 400 74, 500 25, in 8". .150 HR Sheet 52, 560 76, 610 31, in 2. .135 HR Sl1eet 50, 680 74, 060 31, in 2". 313 llate 580 75, 660 23, in 8". 375 Plate 53, 000 79, 700 25, in 8".

TABLE III.-ANALYSIS OF EXPERIMENTAL STEELS TABLE IV.TENSILE TEST RESULTS Ultimate Tensile Strength (p.s.i.)

Heat N0. Lower Yield Elongation Point (p.s.i.)

(percent in 1') Reduction in Area, percent TABLE V.IMPACT TEST RESULTS [Expressed as foot-pounds of energy absorbed] Heat No. 70 40 I -s0 -s -125 -132 140 A3366-2 111, 11s 93, 70 3s, 07 55, 00 35 31 0 A3367-2 120,120 50,39 00,50 23 11 A3368-2 133, 134 104, 71 75, 82 4g, 31 32 10 A3369-2 105,105 88,84 74, 02 g5 5 A3870-2 115,118 73, 57 33,45 s 5 Standard Charpy V-notch samples were prepared and the impact strengths of the various samples were determined at room temperature and at lower temperatures down to -l F. Those values are set out in Table V. Higher titanium contents are seen to have a detrimental effect on impact strength at sub-zero temperatures.

It is well known that impact strength determinations are influence by the amount of reduction the material has received. Because the ingots of Table III were not commercial ingots, we consider the data of Table V to indicate the trend of the changes attributable to titanium contents but not necessarily the magnitude of the impact properties.

We find that if the titanuim content of our steels is controlled to a value of about .05%, the yield point, ductility, and low temperature impact properties of our steels will all be satisfactory for constructional purposes. If the titanium content is much above that figure, the low temperature impact properties of the steel suffer, while if the titanium content is much below that figure, the yield point of the steel suffers. Steel making practices, of course, impose certain tolerances on that figure, and we find that if titanium content is held in the range between .03% and .06%, the steels will be acceptable.

As we have mentioned, the steels listed in Table III contain varying amounts of aluminum. We find that the aluminum in amounts within the limits of that table has no significant effect on the properties of our steel. Aluminum, therefore, may be considered to be an incidental impurity in the steels of our invention.

The steel of our invention is markedly superior to conventional carbon steels in its resistance to atmospheric corrosion. Samples which have been exposed about a year indicate that the corrosion resistance of our steel is four to five times that of plain carbon steel.

The steel of our invention is entirely satisfactory for welding. Susceptibility to underbead cracking was determined for samples from six commercial heats of analyses quite similar to those of heats VN0049 and VN0024 of Table I. The sample plates were of thicknesses rangimg from to /3". In each case, a /2" wide head 4' long was laid on the surface of the sample with either a 7 or diameter welding rod of mild steel. The 4'' head was deposited in 55 seconds using a current of amperes at a potential of 28 volts. The samples were neither preheated nor postheated. All samples were held 96 hours and then were sectioned along the axis of the bead, etched and examined for underbead cracking with a seven power microscope. No cracks were observed in the base metal, and only one sample showed a small crack in the weld. Samples of plate of the same thickness from the same heats were butt welded together by the technique above described and tensile test specimens were cut therefrom across the Weld. All tests exhibited tensile strengths of over 70,000 p.s.i. and broke outside the weld.

We claim:

A rolled steel consisting of carbon up to .15%, manganese between .60% and 1.0%, phosphorus not exceeding .04%, sulphur not exceeding .05%, silicon between .20% and 50%, copper between .20% and about 50%, nickel between 50% and .80%, and titanium between .03% and .06%, the balance being iron and incidental impurities in normal amounts, the steel in the hot rolled condition in thickness not greater than /2" Ibeing characterized by an elongation of at least 22% in an 8" 5 6 [gauge length, an impact strength of at least 15 ft. pounds FOREIGN PATENTS at a temperature of -50 F. and a lower yield point 409 3:80 3/1932 Great Britain of at least 50,000 p.s.i.

625,964 3/ 1944 Great Britain.

References Cited by the Examiner 5 HYLAND BIZOT Primary Examiner UNITED STATES PATENTS MARCUS U. LYONS, ROGER L. CAMPBELL, DAVID 2,140,237 12/ 193 8 Leitner 75125 L. REOK, Examiners.

2,474,766 6/ 1949 Waggoner 75125 I 2,853,379 9/1958 Althouse R. O. DEAN, P. WEINSTEIN, Asszstant Examiners.