US2797162A - Low alloy steel for sub-zero temperature application - Google Patents

Description

LOW ALLOY STEEL FOR SUB ZERG of alloys whose heat treatment is not critical. A more specific object is the provision of low alloy steel articles:

having a mean value of toughness in excess of 15 foot pounds in the Charpy key hole impact tests at tempera- TEMPERATURE APPLICATION 5 tures as low as about -196 C. W The invention by means of which these objects are igfigi $35,535, 33, gfigg figg g g 33:25:35; achieved is based on the discovery that the addition of f New York small properly proportioned quant1t1es of tantalum and optionally columbium to chromium-copper-nickel steels, N Drawillg-v App lily 1954, produces a remarkable lowering of the transition temsenal'No- 444,378 peratures of such alloys. 5

This invention comprises alloys containing 0.02% to 8 Clams" (CL 75 124) 0.15% carbon, 0.20% to 1.20% manganese, 0.05% to 0.60% silicon, 0.20%--to 1.20% copper, 0.25% to 1.50% This invention relates to low alloy steel for use at low chromium, 1.0% to 5.0% nickel, 0.03% to 0.30% temperature, and more particularly to alloys suitable aluminum, up to 0.025% nitrogen and 0.05% to 0. for use in applications where superior impact resistance in the aggregate of tantalum and colum'bium, the tantaat sub-zero temperatures is requiredi lum content being at least 0.04%, the remainder of. the- The trend of modern engineering practice is toward alloys being iron, except for incidental impurities and. the utilization of extremely low temperatures for many 0 small quantities of elements customarily found in steels and diverse operations. Steels with properties which perof good quality. The preferred range of percentages for. mit their efficient use at sub-zero temperatures are needed-T the alloys of this invention is as follows: for chemical apparatus, piping, pressure vessels and for Percent facilities for the storage and transportation of liquid gases. Carbon 0.02-0.10 The low temperature failures of steel articles usually 5 Manganese 0.20-0.60 result from low notched bar impact strength, so that the Silicon 0.10-0.35 notch sensitivity of these materials is the critical factor in Copper 0.20-0. 60 their selection. In general, materials having an impact" Chromium 0.50-0.90 value of at least 15 foot pounds at a :given temperature Nickel 2.00-3.00 as determined by Charpy key hole. impact tests are likely 0 Aluminum 005-020 to have adequate toughness for application at a similar Nitrogen 0.01-0.015 service temperature. Tantalum 0,05-0 1O Several alloys have been proposed for use at low temperatures, but the utility of each one of them has been Molybdenum may be present in quantities less than limited for. various reasons. Of these, au'stenitic and high 0.01% up to 0.50%, and preferentially between 0.1% alloy ferritic steels have the disadvantage of being. quite to 0.2%, if thick sections of the alloys are desired, incostly, of being difficult to fabricate, and of requiring asmuch as the thickness of the material is known to be critical heat treating conditions for optimum properties. a critical factor in lowering the impact strength of such Economical low alloy steels do not retain their toughalloys, which eflect this additional element will counteract. ness to sufiiciently low temperatures. In the case of these 40 The melting of the alloys of the invention does not re a-lloys, variation in the heat treatment, because of its quire special. equipment or procedure, but conformsto criticality, will alter its properties, thereby rendering diflinormal practice, such as, for. example, open hearth, arc cult the reproducibility of the desired properties of the furnace or melting in an induction furnace. The. heats steel. Hitherto, austenitic stainless steel has been the thus produced can then be but worked and normalized. most efficient'steel for low temperature service, but its and further treated by tempering at various temperawide applicability has been limited by economic factors. tures if desired.

TABLE I Charpy keyhole impact test (ft-lb.) alt-183 and 196 C.

Normalized 900 0. Normalized Percent Percent 900 C.

a Cb Temp. 600 O.- Temp. 600 C. Temp. 500 O. Temp. 550 O.- Temp. 650 C;- Added Added 1 Hour 5 Hours 1 Hour 1 Hour 1 Hour 183C 196C. 183 C. 196C 183C. 196 C. 183C. C. 183C 196C 183C 196C 0.10 39.5 2%N1 k@1 8:33 W915? it? '"ifif 0.10 0 10 41.0 30.0 0.10 22.5 23.0 0.05 0.05 36.5 20.8 0.05 0. 05 28.0 23.5 3% Nickel 0.10 0.03 22.3 23.0 0.10 0.03 34.3 33.3 0.25 20.0 0.20 0.05 39.5 32.5

It is the principal object of this invention, therefore, to provide a relatively inexpensive low allow ferritic steel Referring to the attached table of impact test results, Table I, samples of similar composition were heat treatsuitable for use in applications where very low tempera- 7 0 ed in several ways to indicate thatheat treatment is. not

tures are normally encountered, and which will have. low transition temperatures. Another object is the provision critical, and that high. impact values are readily reproducible over a large number of heats in both normalized Patented June 25, 1957- T which are well-suited for use in the fabrication'of articles U i and stress-relieved conditions. The typical nominal composition of each steel sample was:

A further indication of the effects produced by tantalum addition in lowering the transition temperature of low alloy chromium-copper-nickel steels is indicated by the data of Table II. The composition of the samples which do not contain tantalum is similar in everyother that are required to withstand severemechanical stress Percent Carbon 0.03

Manganese 0.30 Silicon 0.20

Chromium 0.80

Copper 0.50

Aluminum 0.15

Nitrogen l 0.013

respect to that of the chromium-copper-nickcl steels containing 3% nickel given on Table I; the impact tests rep sults' represent an average of seven tests from four heats at a --183 C. The notch toughness figures for the tantalum-bearing samples are representative of to 24 tests from a total of 12 heats. In nearly all cases the mean value of tough-.

ness under various heat treatments exceedstheminimnm In addition to the higher impact values obtained by the tantalum-containing alloys, the data in Table II also demonstrate that the alloys which do not contain tantalum are substantially affected by the difference in heat treatment, whereas proportionately similar results are obtained by the alloy of this invention under the different treatments.

The normalizing treatment as practiced in the present invention consists of heating the steel to above the critical temperature but not so high as to produce material grain growth and subsequently cooling at a relatively rapid rate or in some cases, in a liquid coolant. The steel is cooled substantially to room temperature prior to heating for tempering. The exact mechanism whereby the tantalum addition lowers the transition temperature of these alloys is not known, but it is believed that this element produces a grain refinement by forming finely dispersed carbides within the grain structure and by retarding carbide solution and reprecipitation during tempering of the low alloy steel.

Columbium can be effectively added in combination with tantalum up to similar percentages as long as the total of the two elements does not exceed 0.25%. While the composition as hitherto disclosed provides excellent low temperature properties where the finished alloy bars do not exceed 1% inches in thickness, it has been found that the addition of 0.1% to 0.30% molybdenum in creases the toughness of the alloy in slower-cooling, heavier sections.

By the present invention cast or wrought steel articles are produced which may be hot worked and subsequently welded, normalized, or normalized and tempered, and

at low temperatures Their toughness upon prolonged exposure to these temperatures recommends their employment where dependable operation is essential.

What is claimed is: 1. An alloy containing about 0.02% to 0.15% carbon; 0.20% to 1.20% manganese; 0.05% to-0.60% silicon; 0.20% to 1.20% copper; 0.25% to 1.50% chromiurn; 1% to 5% of nickel; 0.03% to 0.30%' aluminum;

up to 0.025% nitrogen and 0.05 to 0.25 in the aggregate of tantalum, and columbium, the tantalum content being at least 0.04%; up to 0.50% of molybdenum;

and the remainder iron and incidental impurities.

2. An alloy containingabout 0.02% to 0.15 carbon;

0.20% to 1.20% manganese; 0.05% to 0.60% silicon;

0.20% to 1.20% copper; 0.25% to 1.50% chromium; 1% to 5% of nickel; 0.03% to 0.30% aluminum; up to 0.025% nitrogen; 0.01% to 0.50%'molybdenurn and 0.05% to 0.25% in the aggregate of tantalum and colurnbium, the tantalum content being at least 0.04%; the

remainder iron and incidental impurities. r

3. An alloy containing about 0.02% to 0.10%. carbon;

0.20% to 0.60% manganese; 0.10% to 0.35% silicon;

the tantalum content being at least 0.04%; the remainder iron andv incidental impurities.

' 5. 'A' welded article which in its normal use is required to withstand mechanical stress at low temperatures down I I 0.20% to 0.60% copper; 0.50% to'0'.90% chromium; 2.00% to 3.00% nickel; 0.05% to 0.20% aluminum;

0.010% to 0.015% nitrogen; an aggregate of 0.05% to 0.10% of tantalum and columbium, thetantalum content being at least 0.04%; the remainder iron and incidental impurities.

4. An alloy containing about'0.'02%' to 0.10% carbon; 0.20% to 0.60% manganese; 0.10% to 0.35% silicon;

' 0.20% to 0.60% copper; 0.50% to .90% chromium; 2.00%

to 3.00% nickel; 0.05% to 0.20% aluminum; 0.010% to 0.015% nitrogen; 0.10% to 0.20% molybdenum; an aggregate of 0.05 to 0.10% of tantalum and columbium,

to about -196 C., which article is composed of an alloy containing about 0.02% to 0.15% carbon; 0.20% to 1.20% manganese; 0.05 to 0.60% silicon; 0.20% to 1.20% copper; 0.25% to 1.50% chromium; 1.0% to 5% of nickel; 0.03% to 0.30% aluminum; up to 0.025% nitrogen and 0.05% to 0.25% in the aggregate of tantalum and columbium, the tantalum content being at least 0.04%; the remainder iron and incidental impurities.

6. A welded article which in its normal use is required to withstand mechanical stress at low temperatures down to about -196 C., which article is composed of an alloy containing about 0.02% to 0.15% carbon; 0.20% to 1.20% manganese; 0.05% to 0.60% silicon; 0.20% to 1.20% copper; 0.25% to 1.50% chromium; 1.0% to 5% nickel; 0.03% to 0.30% aluminum; up to 0.025% nitrogen; 0.01% to 0.50% molybdenum and 0.05% to 0.25% in the aggregate of tantalum and columbium, the tantalum content being at least 0.04%; the remainder iron and incidental impurities.

7. A welded article which in its normal use is required to withstand mechanical stress at low temperatures down to about 196 C., which article is composed of an alloy containing about 0.02% to 0.10% carbon; 0.20% to 0.60% manganese; 0.10% to 0.35% silicon; 0.20 to 0.60% copper; 0.50% to 0.90% chromium; 2.00% to 3.00% nickel; 0.05% to 0.20% aluminum; 0.010% to 0.015% nitrogen; an aggregate of 0.05% to 0.10% of tantalum and columbium, the tantalum content being at least 0.04%; the remainder iron and incidental impurities.

8. A welded article which in its normal use is required to withstand mechanical stress at low temperatures down to about 196 C., which article is composed of an alloy containing about 0.02% to 0.10% carbon; 0.20% to 0.60% manganese; 0.10% to 0.35% silicon; 0.20% to 2,797,162 5 0.60% copper; 0.50% to 0.90% chromium; 2.00% to 3.00% nickel; 0.05% to 0.20% aluminum; 0.010% to 0.015% nitrogen; 0.10% to 0.20% molybdenum; an aggregate of 0.05% to 0.10% of columbium and tantalum, 1,373,908 the tantalum content being at least 0.04%; the remainder 5 2,103,610 iron and incidental impurities. 2,264,35 5

References Cited in the file of this patent UNITED STATES PATENTS Pacz Apr. 5, 1921 Macormac Dec. 28, 1937 Becket et a1. Dec. 2, 1941 Offenhauer May 25, 1954

Claims (1)

1. AN ALLOY CONTAINING ABOUT 0.02% TO 0.15% CARBON; 0.20% TO 1.20% MANGANESE; 0.05% TO 0.60* SILICON; 0.20% TO 1.20% COPPER: 0.25% TO 1.50% CHROMIUM; 1% TO 5% OF NICKEL; 0.03% TO 0.30% ALUMINIUM; UP TO 0.025% NITROGEN AND 0.05% TO 0.25% IN THE AGGREGATE OF TANTALUM AND COLUMBIUM, THE TANTALUM CONTENT BEING AT LEAST 0.04%; UP TO 0.50% OF MOLYBDENUM; AND THE REMAINDER IRON AND INCIDENTAL IMPURITIES.