US2194178A - Low alloy steel - Google Patents

Description

Patented Mar. 19, 1.940

LOW ALLOY STEEL Frederick M. Becket, New York, and Russell Franks, Niagara Falls, N. Y., assignors 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. 241,136

6 Claims.

This invention relates to steels, and provides new and improved steels characterized by novel and commercially valuable properties.

We have discovered that the addition of cometal of the group consisting of chromium and molybdenum.

Suitable amounts of columbium to be added to these steels according to the present invention lumbium in amounts between 0.02% and 1% to are from 0.02% to 05% y. it Will not be 5 so-called plain carbon" and certain low alnecessary or desirable to exceed 0.5% columbium, loyed steels effects a marked and surprising and the most useful range is within the limits improvement in the properties of such steels. 0.05% to 0.25%. In ge L e greater amounts One important effect of the columbium addition of columbium should ordinarily be used in the m is to refine the grain-size oi the steel, and this steels containing the greater amounts of carbon,

grain refinement is retained and maintained even within the ranges specified above. at elevated temperatures up to and somewhat One of the most valuable properties of the above the critical range. Another effect, which is Columbium Containing Steels 0f the invention is doubtless at least in part a result of the grain that of retaining its normally fi grained 5151116- refinement, is the improvement of the tensile t elevated temperatures. which p op y is 15 strength of many of the steels. Further, the imattained without detrimentally aifecting other pact strength is increased; and this improvement important P y propertiese ped is marked even at SllbZEl'O temperatures. There heretofor customarily p y to i e the is also an increase in the resistance of the steels grain Size of Carbon n low-alloyed Steels e.

t rusting d t oxidation The deep dmwmg in most cases, either detrimentally affected the so and cold rolling characteristics of the steels are toughness of the F or famed to prevent improved. The hardenability of the steels by coarsening of the slze at-,e1evated m heat treatment is somewhat decreased, and there tures' during fabricatmn or both is less distortion of the steel when it is rapidly gisgg g g gg g i fig iz gi ggg gg i gg g z gg i g i f The g such a process the addition of columbmm to the 2 p d di mu .2 s 8 steel is especially advantageous, as illustrated by increase epen ng PDO comm-mum and the date in Table I which gives the experimencarbon contents of the steels. the increase is tally determined m number (A. T Spec 3O greater m the Steels having the lower carbon an ification E19-33) of the cases of a series of steels columblum contents after carburizing for eight hours at each of three Steels included in our invention are those condifferent temperatures. In each case, the grain taining nickel and at least one carbide forming size of the core was smaller than that of the case.

v Table I Composition of steel (remainder iron) gggg y qhg gii ggk Other metals Per- Per- Por- Per- At At At 40 cent cent cent cent 925 0. 975C 1025" C. 40

C 11 Si Cb Percent Percent 0.13 0.42 0.10 None. 1.25 0.44 2t01 M00 1.010 0.34 0.41 0.13 None 1.34 0.41 3:00 310s 20.4 0.14 0.43 0.21 0.00 1.24 0.50 M08 5101 3t 8 45 0.11 0.41 0.31 None 3.40 1.25 3to8 2100 1100 0.32 0.38 0.10 None 3.51 1.49 4101 .3t01 n04 0.14 0.30 0.10 0.03 3.45 1.40 ems M08 M08 0.34 0.01 0.14 0.10 3.53 1.40 4100 (M07 0008 50 regent Iercent 0.18 0.50 0. 22 None 1.74 @2 1 4 to 7 lto 6 lto 5 0.31 0.42 0.00 None 1.14 0.25 s 2001 2100 0.15 0.44 0.23 0.09 1.12 0.22 9 0 0 0.40 0.40 0.20 0.10 1.11 0.14 0 00 am!) iii In general, the grain refining effect is roughly proportional to the columbium content up to a certain optimum amount 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. A moderate excess of columbium above the optimum and below the maximum specified above 1%), will not ordinarily adversely affect the properties of the steel to a serious extent.

The influence of columbium on the tensile and impact properties of the steels under consideration is indicated by the data appearing in Table II which show the experimentally determined yield point in thousands of pounds per square inch (Y. P.), maximum stress in thousands of pounds per square inch (M. 8.), 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 tensile test pieces;

bium is increased above 0.1%, the softening eifect of the columbium begins to predominate, the yield point and maximum stress are decreased, and the ductility is substantially increased. As the carbon content is increased above 0.3%, and as other alloyed additions are made, the eiIects of columbium on the tensile properties are reduced, particularly if the steels are heat treated.

It will be noted in Tables II and III that the addition of columbium raises the impact strength of the steels, and that the improvement is greatest in the high carbon steels and those containing chromium.

As mentioned above, the addition of columbium to the plain carbon and low alloyed steels considerably increases their impact strength at subzero temperatures.

Table III contains impact data obtained in the manner described in connection with Table II, except that the samples under the heading '78 C." were cooled about an hour at -78 C. in a bath of acetone and frozen carbon dioxide 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.

and also the Izod impact value in foot pounds as determined on a standard Izod machine with an initial energy level of foot pounds and a standard specimen one centimeter square pro- 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 vided with a 45 notch. sense that high chromium steels, for instance,

Table II Composition of steel (remainder iron) El Perent Pefizgnt Perscient Peaclent Peggznt Pei-gut Pecgnt Y'P M's git pemeh't If??? quenched in oil from 850 C.900 0.; drawn in air at C.-425 O. 31%? 332% 31%? 3223 iii 1:31:33: it 183 33 35 3:13 31?? 335? 333? iii 3:311:33: ai-1r iii i34 13 ii 13 315 3:32 81% 31:31:: H2 813% """ain' 2% &1 $3. 33 3% Cooled in air from 850" C.-900 o 323 31g 33%? 3233 i352 21:11:: ""i' $5 $3 33 25. 33 3:33 3:32 3155 3132 i3? 31:13:?"535 i3? i3? 3 i3 3 8:13 I 3:32 8:35 1:52 8:52 bfii' 2? *7? 3.3' 23 23 It will be observed from the data of Table II that. in the steels containing up to about 0.3% carbon, the addition of up to about 0.1% columbium increases the yield point, maximum stress, and ratio of yield point to maximum stress. The ductilityis only slightly affected. As the columare oxidation resistant, the increase in resistance will bevaluable in many uses of the steels.

The invention is based on the above-described discoveries and comprises new alloy steels and articles composed thereof, having in addition to 0.02% to 0.5% columbium, substantially the limits of composition indicated in Table IV.

Table IV The articles of the invention include articles deep-drawn from the steel of the invention; articles having a core containing less than 0.5% carbon and a carburized case containing more than 0.8% carbon, and 0.02% to 0.5% columbium throughout, the remainder of the composition being as shown in Table IV; parts of machines and of other apparatus, required 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, and

that the invention is not limited to or by such um and molybdenum in an amount not exceeding a total of 3%, the chromium being less than 2% and the molybdenum not exceeding 1%; 0.05% to nickel; 0.02% to 0.5% columbium which imparts to said steel a fine-grained structure which persists at all temperatures up to and somewhat above the critical range; and the remainder iron.

2. Steel containing carbon in an amount between 0.1% and 0.6%; manganese in an amount not over 1%; silicon in an amount not over 1%; 0.25% to less than 2% chromium; 0.05% to 5% nickel; 0.05% to 0.25% columbium which imparts to said steel 8. fine-grained structure which persists at all temperatures up to'and somewhat above the critical range; the remainder iron.

3. Steel containing carbon in an amount between 0.1% and 0.6%; manganese in an amount not exceeding 1%; silicon in an amount not over 1%; 0.05% to 1% molybdenum; 0.05% to 5%- nickel; 0.02% to 0.25% columbium which imparts to said steel 9. fine-grained structure which persists at all temperatures up to and somewhat above the critical range; the remainder iron.

4. Case carburized article having a core containing less than 0.05% carbon and a carburized case containing more than 0.8% carbon, the core and case being composed of a steel containing, aside from carbon, manganese in an amount not exceeding 2%; silicon in an amount not exceeding 1%; at least one carbide forming metal of the group consisting of chromium and molybdenum in an amount not exceeding a total of 3%, the chromium being less than 2% and the molybdenum not exceeding 1%; 0.05% to 5% nickel; 0.02% to 0.5% columbium which imparts to said article a fine-grained structure, increased ductility, and increased impact strength; the remainder iron.

5. Article used to resist, at subzero temperatures, impact shock or multidimensional stress, which article is composed of a low alloyed 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%; at least one carbide forming metal of the group consisting of chromium and molybdenum in an amount not exceeding a total of 3%, the chromium being less than 2% and the molybdenum not exceeding 1%; 0.05% to 5% nickel; 0.02% to 0.5% columbium which imparts to said article increased impact strength at subzero temperatures; the remainder iron.

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

FREDERICK M. BECKET. RUSSELL FRANKS.

CERTIFICATE OF CORRECTION. Patent No. 2,19h,178. I March 19, 19110.

FREDERICK M. BECKET, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, second column, line 16, claim h,'for "0.05%" read 0.5%; and'that the said Letters Patent should be read with this correction therein that thesam'e may conform to the record of the case in the Patent Office.

Signed and sealed this 9th day of April, A. D. 19,10.

Henry Van Arsdale (Seal) Acting Commissioner of Patents.