US2264355A - Steel - Google Patents

Description

Patented Dec. 2, 1941 UNITED STATES PATENT OFFICE STEEL Frederick M. Becket, New York, and Russell Niagara Falls, N. Y., assignon to Electro Metallurgical Company, a corporation of West Virginia No Drawing. Original application June 24, 1936, Serial No. 87.006. Divided and this application November 18, 1938, Serial No. 241,137

Claims. (Cl. 148-31) loyed steels efiects a marked and surprising improvement in the properties of such steels. One important effect of the columbium addition is to refine the grain-size of the steel, and this grain refinement is retained and maintained even at elevated temperatures up to and somewhat above the critical range. Another effect, which is doubtless at least in part a result of the grain refinement, is the improvement of the tensile strength of many of the steels. Further, the impact strength is increased, and this improvement is marked even at subzero temperatures.

There is also an increase in the resistance of the steels to rusting and hot oxidation. The deepdrawing and cold rolling characteristics of the steels are improved. The hardenability of the steels by heat treatment is somewhat decreased, and there is less distortion of the steel when it is rapidly cooled from elevated temperatures. The ratio of yield point to maximum stress is increased, the lncrease depending upon the columbium and carbon contents of the steels: the increase is greater in the steels having the lower carbon and columbium contents.

Steels included in our invention are the plain carbon steels containing carbon in amounts not exceeding 1% and preferably not exceeding 0.6%, silicon in amounts up to 1%, manganese in amounts up to 2%, and suitable amounts of 00- lumbium, the remainder iron.

Suitable amounts of columbium to be added to these steels according to the present invention are from 0.02% to 0.5%. Usually, it will not be necessary or desirable to exceed 0.5%

columbium, and the most useful range is within the limits 0.05% to 0.25%. In general, the greater amounts of columbium should ordinarily be used in the steels containing the greater amounts of carbon, within the ranges specified above.

One of the most valuable properties of the columbium containing steels of the invention is that of retaining its normally fine-grained structure at elevated temperatures, which proper y is attained without detrimentally afiecting other important physical properties. The expedients heretofore customarily employed to refine the grain size of carbon and low-alloyed steels have, in most cases, either detrimentally affected the ening of the grain size at elevated temperatures,

during fabrication for instance, or both. The coarsening of the grain is considerably aggravated in a case carburizing process, and in such a process the addition of columbium to the steel is especially advantageous, as illustrated by the data in Table I which gives the experimentally determined grain number (A. S. T. M. specification El9-33) of the cases of a series of steels after carburizing for eight hours at each of three different temperatures. In each case, the grain size of the core was smaller than that of the case.

Table I Composition of steel Graln No. of case after (remainder iron) carbunzing 8 hours at- Percent Percgnt Perscient Peacgnt Q C.

0.16 0.46 0.29 None 3 m 5 a to s 1 to 4 0.15 0.45 0.27 0.017 3to8 3t08 2to8 0.17 0.48 0.26 0.45 7to8 5to8 51:08 0. 41 0.77 0. 27 None 2 to 4 1 to 4 1 to 4 0.38 0.80 0.27 0.06 5to7 41:07 61:07 0.43 0.74 0.22 0.36 61:08 6to8 6to8 0.77 0. 75 0. 22 None 1 to 3 1 to 3 1 to 3 0.94 0.75 0.25 0.04 5to7 4to6 4to6 0.93 0.73 0.24 0.18 0to7 61:07 51:08 0. 97 0. 72 0. 19 0. 41 5 to 8 5 to 8 5 to 8 0.15 1.50 0.16 None 1to3 lto3 1to3 0.17 1.61 0.33 0.12 51:08 5to8 51:08 0.52 1.68 0.36 0.11 5to8 5to8 41:08

In general, the grain refining efiect is roughly proportional to the columbium content up to a certain optimumamount of columbium, which optimum content depends chiefly on the carbon content of the steel. The grain refinement of a maximum 0.1% carbon steel reaches substantially its greatest degree at about 0.1% columbium; a 0.15% carbon steel at about 0.15% columbium; a 0.35% carbon steel at about 0.18% columbium; and a 0.5% carbon steel at about 0.25% columbium. The presence of chromium, molybdenum, or vanadium reduces somewhat these optimum amounts of columbium.

The influence of columbium on the tensile and impact properties of the steels under consideration is indicated by the data appearing in Tables II and III which show the experimentally determined yield point on thousands of pounds per square inch (Y. P.), maximum stress in thousands of pounds per, square inch (M. S.) percentage elongation in a 2 inch gage length (El. and reduction in area (R. A. all on 0.505 inch diameter A. S. T. M. standard tentoughness of the steels, or failed to prevent coars- 5116 test P and 94150 the Izod impact va ue in foot pounds as determined on a standard Izod machine with an initial energy level of 120 toot pounds and a standard specimen one centimeter square provided with a 45 notch.

above 0.3%, and as other alloyed additions are made, the enects oi columblum on the tensile properties are reduced, particularly if the steels are heat treated.

Table II Compositiion t1): stfel main er on (re Y. P. 1.000 M. s.1,0o EL, R. 1., Izod, lb./sq. in. lb./sq. in. percent percent ft. lb. Percent Percent Percent Percent 0 Mn 81 Cb AS-ROLLED 0.09 0.30 0. 20 None 48 57. 35 63. 76 0.08 0.25 0.2) 0. 60.5 65 26 09 03 0.10 0.33 0.42 0.65 24 58.5 40 80 as AIB COOLED FROM 900 0.

0.00 0.30 0.20 None 4': s0 39 M 82 0. (B 0. 25 0. 20 0. 28 55 60. 5 27 58 95 0. 0. 83 0. 42 0. 55 22. 3 57. 6 40 81 92 QUENCHED IN WATER FROM 900 0.; AND DRAWN AT 150 O.

0. 0. 45 0. 29 None 64. 5 100 17 55 42 0. 15 0. 45 0. 27 0. 017 72. 5 B9 27 03 75 0. 17 0. 48 0. 26 0. 45 71 81. 8 31 71 75 AIR COOLED FROM 925 C.

0. 10 0. 46 0. 29 None 45. 5 66. 8 33 55 72 0. 15 0. 45 0. 27 0. 017 50 67. 5 33 62 72 0. 17 0. 48 0. 2B 0. 45 50 03. 5 69 75 QUENCHED IN WATER FROM 850 0.; AND DRAWN AT 550 C.

0. 41 0. 77 0. 27 None 101. 5 125. 5 19 51 37 0. 38 0. 80 0. 27 0. 06 91. 5 110. 5 21 57 47 0. 43 0. 74 0. 22 0. 36 87 105 M 55 49 COOLED IN AIR FROM 875 C.

0. 41 0. 77 0. 27 None 62 91 25 48 15 0.38 0.80 0.27 0.06 65 90.5 21 57 Z! 0. 43 0. 74 0. 22 0. 64. 5 86 24 56 Table III Composition of steel (remainder iron) 5 E]. R. A. Izod Y. P M. B Percent Percent Percent Percent Percent 0 Mn 81 Cr Cb QUENCHED IN OIL FROM 850 C. C.; DRAWN IN AIR AT 150 0. ---425 C.

GOOLED IN AIR FROM 850 0. 900 C.

It will be observed from the data of Tables II 05 It will also be noted in Tables 11 and III that and III that, in the steels containing up to about 0.3% carbon, the addition of up to about 0.1% columblum increases the yield point, maximum stress, and ratio 01' yield point to maximum stress. The ductility is only slightly affected. As the columblum is increased above 0.1%. the softening effect of the columblum begins to predominate, the yield point and maximum stress are decreased, and the ductility is substantially increased. As the carbon content is increased the addition of columblum raises the impact strength of the steels, and that the improvement is greatest in the high carbon steels.

As mentioned above. the addition oi! columbium to the plain carbon and low alloyed steels considerably increases their impact strength at subzero temperatures. As little as 0.2% columblum raises the impact strength at C. to 10 foot pounds or more.

Table IV contains impact data obtained in the manner described in connection with Tables II and III, except that the samples under the heading 78 C. were cooled about an hour at '18 C. in a bath of acetone and frozen carbon dioxide before testing; and the samples under the heading --100 C. were cooled about an hours at -100 C. in liquid propane which in turn was cooled with liquid air, before testing. After cooling, the specimens were rapidly transferred from the cooling medium to the Izod machine and tested. The time required for the transfer and test was in all cases less than ten seconds.

The presence of columbium substantially increases the resistance of these steels to hot oxidation and, although the columbium steels are not to be considered oxidation resistant in the sense that high chromium steels, for instance, are oxidation resistant, the increase in resistance will be valuable in many uses of the steels. Table V presents data illustrating this effect of columbium.

Table V Composition of steel (remainder iron) Percent loss in wer Per- Per- Per- Perours cent cent cent cent at Mn 8i Cb 0. 09 0. 30 0. 20 None 0. 09 0. 0. 74 None 5. 7 0. 00 0. 41 0. 28 0. 41 4. 4 0. 07 0.41 0.41 0.94 2. 8

The invention is based on the above-described discoveries and comprises new alloy steels and bium throughout, the remainder of the composition being as indicated above; parts of machines and of other apparatus, require to withstand stress at moderately elevated temperatures; articles, composed of the steel of the invention, designed for use to resist impact shock at subzero temperatures; and pressure vessels, composed of the steel of the invention, designed to withstand two or three dimensional stress at subzero temperatures.

It will be appreciated that the specific examples herein are given by way of illustration,

articles composed thereof, having in addition to and that the invention is not limited to or by such examples.

This application is a division of our application Serial No. 87,006, filed June 24, 1936.

We claim:

1. Steel containing carbon in an amount between 0.1% and 1%, manganese in an amount not exceeding 2%, silicon in an amount not exceeding 1%, and 0.02% to 0.25% columbium which imparts to said steel a fine-grained structure which persists at all temperatures up to and somewhat above the critical range, the remainder iron.

2. Steel containing carbon in an amount between 0.1% and 0.6%; manganese in an amount not exceeding 2%; silicon in an amount not exceeding 1%; and 0.05% to 0.25% columbium which imparts to said steel a fine-grained structure which persists at all temperatures up to and somewhat above the critical range but does not impart substantial age hardening properties; the remainder iron.

3. Case carburized article having a core conpact strength at normal and subzero temperatures; the remainder iron.

4. Article used to resist, at subzero temperatures, impact shock or multidimensional stress.

which article is composed of a steel containing carbon in an amount between 0.1% and 1%, manganese in an amount not exceeding 2%, silicon in an amount not exceeding 1%. and 0.02% to' 0.5% columbium which imparts to said article increased impact strength at subzero temperatures; the remainder iron.

5. Article subject to impact stress at elevated temperatures below 500 C. and composed of the steel defined in claim 1.

FREDERICK M. BECKEI. RUSSELL FRANKS. I