US1278082A - Alloy steel. - Google Patents

Description

CHILD HAROLD WILLS, OF DETROIT, MICHIGANZ.

ALLOY STEEL.

No Drawing.

To all whom it may concern:

Be it known that I, CHILD HAROLD. WILLS,-

a citizen of the United States, residing at Detroit, in the county of Wayne and State of Michigan, have invented certain new and useful Improvements in Alloy Steels, of which the following is a. specification.

This invention relates to alloy steels, and particularly to what may be termed commercial steels. The nature of my invention, its objects and advantages Will be best understood from a brief statement of What is comprehended by commercial steels and the properties and characteristics such steels must have to bring them Within this category.

- Broadly speaking, there are four general factors or considerations affecting .the commercial possibilities of all alloy steel: first, the making of the steel itself; second, the manufacture of articlesfrom the steel; third, the performance/of the article produced, 2'. 0., the properties of the finished article; and fourth, the cost, which materially enters into the first twonamed considerations. The second factor may be further classified into three general divisions; namely, the forming of the steel into the article, the heat treatment, and the machining or working. A varying number of considerationsenter into each general factor.

Thus, for example, in steel, it is desirable, on the score of expense and other grounds, that the melting be done by the open hearth method. It is also essential that the alloys be capable of ladle addition, and that segregation, or the formation of pockets of the alloy, be prevented. Segregation frequently occurs, as for example, in manganese steels. Again, the loss of alloys in remelting must be kept Within reasonable limits, as must the amount of the alloy required, as determined for'example, by the output available. In so far as casting is concerned, the ingots should be smooth and should have good preliminary rolling characteristics such as clean surfaces, with a minimum amount of chipping necessary. Finally, the croppage must be kept within reasonable limits, and the scrap after final.

rolling into bar form should be small and capable of being handled without loss. Stated in other words in addition to the Specification of Letters Patent.

the making of the Patented Sept. 2; 1915.

Application filed June 9, 1917. Serial No. 173,719.

other factors above .set forth, the yield should be large. If an alloy steel materially fails to meet these important requirements of the steel maker, it may at once be ruled out as a'commercial steel, although it may be useful for such special purposes as cost of making.

As to the manufacture or.forming of'the alloy steel into the desired articles, the steel should be capable of being forged or'drop hammered at a high temperature, because the greater plasticity of the metal materially cuts down the forging operations. At the same time, however, the steel must be of such a character that no marked or undue crystallization or other detrimental structural change takes place at the high forging temperature. In this connection, the chief difficulty encountered N in commercial alloy steels ,is that at high forging temperatures even under the point at which burning of warrant the high the metal takes place there occurs loss of pidity and structural changes develop which are detrimental to elongation and reduction of area even after the steel has subsequently been heat treated. .The allowable forging temperature limits are thus quite restricted, and because of the diffitculty of maintaining furnace temperatures uniform, as Will be readily understood by those skilled in the art, it frequently happens that the limits are exceeded, with crystallization and consev quent Weakness as-the result. Inaddition to the foregoing, the steel should have good Welding characteristics, should be non-air hardening, and substantially free from the formation of seams and pipes.

As to heat treatment, after forming or forging, using vanadium steel for purposes 1 of illustration, it is customary to subject the steel to three heats, a normalizing heat, a quenching heat, and a drawing heat, to which may be added a fourth heat for case- I hardening purposes, where such is required. .Thechief difliculties encountered in this connection are losses which occur because, in the first place, commercial alloy steels are very sensitive to heat treatment, 2'. 0., the range of temperature within which they must be heat treated is very narrow, and in the second place, it is impossible to maintain furnace temperatures uniform. If the steel be treated at a temperature too low, it lacks the desired properties; if treated at a temperature too high, it will be crystallized, or even burned, 2'. 6., it will undergo certain structural changes which subsequent heat treatment will not rectify. Such stpels will not measure up to the requirements of the service for which they are intended, as the beneficial effects of the alloys are lost. To meet these conditions, it is customary to provide complicated regulating equipment, involving a large item of expense, but even such equipment is not'productive of uniformly satisfactory results,. and the perrentage of losses in manufacture and service, although reduced, is still quite large. It will be apparent that an ideal commercial steel would be one which, instead of being sensitive to heat treatment, would have a wide range of temperature, for reasons which will further appear.

Another factor entering into heat treat ing operations is that minimum crystallization should take place during carburizing.

As to the workability of commercial alloy steels, it is requisite that they can be. readily machined and worked after heat treatment. In this connection, it is also to be observed that the steelshould have superior depth hardening characteristics, so that the metal will be in a uniform condition throughout,

the important advantages of which are that deep cuts can be made without decrease in the unit strength, and also that irregular sections can be quenched with a minimum of warping.

Finally, as to the performance or physical properties of the article produced. The steel should have a high tensile strength and a high elastic limit, with a maximum elongation, so that, for example, accidental bending may occur and re-straightening ac complished without weakening the metal. Stated in other words, the steel should have a-maximum strength with maximum ca- .pacity for cold bending. The steel should also have a very high resistance to impact and shock and to alternating stresses. These properties are essential to a commercial alloy steel, such as used in the manufacture of automobiles, and they must be obtained by the addition of alloys in amounts such as bring the costs within allowable limits.

A steel to be commercial, therefore, must have all of the foregoing characteristics as well as certain other properties not specifi cally mentioned, and if it fails to substantially meet the requirements either in. the

making of the steel, the forming of the steel, the physical properties of the article, or the cost, it may be dismissed as being unsatisfactory. Up to the present, it has been difficult to obtain a commercial steel which was uniformly excellent in all these respects, and it has been necessary to sacrifice to a certain extent some of the most desirable properties, in order to meet other requirements. Stated in other words, com mercial steels at present in use are not Well balanced, and, in addition, it has been impossible to obtain the superexcellent qualities of certain special steels without losing -other properties absolutely essential to a sults. In consequence, breakages frequently occur in service. Again, in nickel steels We find that the steel, although having noncrystallizing characteristics superior to those of vanadium steel, is very hard to machine after heat treatment. The working of such steels, therefore, involves great expense in time, labor and tools. In manganeses steels, such as Hadfield steel, We find super-excellent properties such, for example, as exceedingly high tensile strength and high elastic limit, with an elongation of approximately 50%, and a relatively high reduction in area. Such steels, however, are unworkable and most difficult, if not impos sible to machine. Chrome steels also fall short in some respects, particularly as to crystallization and narrow range of heat treatment.

It is the purpose of my present invention to provide a commercial alloy steel which at the same time has the super-excellent qualities of certain of the special steels, and retains all of the other characteristics neces sary to bring the steel within the commerbeen used in what is known as molybdenum high speed steel, to give such steels increased toughness and hardness and other good tool working qualities. Such steels are, of

course, impractical for commercial purposes, and their field of use strictly limited. The percentage of molybdenum used in such steel is also quite high, and the steel has not met with extended use because of certain defects which develop. Relatively high percentages of molybdenum have also been used in the production of magnet steels, and in other special steels, such as armor plate, big gun steel, and the like, mainly for-the purpose of replacing a portion of the tungsten, and that extensive experiments have been made to observe the efiect of molybdenum on iron. In so far as I am aware, however, no one has made use of molybdenum in the production of commercial steels to obtain the results and advantages herein set forth; this probably because the experiments of early investigators, of the effect of molybdenum on steels in the normal state led to certain conclusions indicating the presence of questionable properties from a commercial standpoint. I have found, however, that the molybdenum commercial steels, upon being heat treated, apparently do not follow the laws of metallurgy, and that results are obtained opposite in character to those which would be naturally predicated from the steel in the normal state.

By the use of molybdenum in alloy steels, in small percenta es, I find, in so far as the manufacture of t e steel is concerned, that all the requirements are well met, and that in addition'the molybdenum does not segregate and apparently has a tendency to prevent segregation of the other ingredients alloyed. The rolling mill yield is also higher and the cost of grinding less.

Most marked results are obtained in the forming of the steel. To illustrate, the forging temperature can be carried considerably higher than is ordinary without fear of destroying properties hitherto unreclaimably lost if the temperature exceeded the allowable narrow limits. In other words, the forging can be done at a higher temperature without burning or over-crystallizing :the steel, and this results in cutting down the forging operations because the metal is more plastic, and it also eliminates the losses heretofore frequently occurring for the reason that the allowable limits of forging'temperature were exceeded during the forging, because of inability to maintain uniform temperature regulation, particularly where articles are being produced in large quantities. An additional saving is eflected by virtue of the fact that with such wider range of forging temperature, the use of the expensive regulating equipment and operators is obviated, because the furnace men can readily approximate the temperature within much less than 200, merely by the color 0 the metal,

Again, the range of temperature for heat treatment is greatly increased, and instead of being confined'within 10 to 20 F. as is the case with present commercial alloy steels, the temperature range is increased to about 200. Stated in other words, the molybdenum prevents detrimental structural changes, such as crystallization, and secondary chemical reactions from taking place until the temperature goes several hundred degrees above the point of recalescence. This isan advantage of the greatest importance, not only because of the saving effected in the cost by the elimination of furnace regulating equipment, but alsobecause the metal will run uniformly under wide variations in temperature which means that the losses in manufacture and in service, ordinarily attributable to exceeding the narrow range of heat treatment, are reduced to a minimum, if not entirelyeliminated. In other words, it is possible to manufacture machine parts, for example, on a large scale and obtain uniform results notwithstanding the impossibility of maintaining uniform temperature conditions.

Furthermore, it appears that the qualities of the steel after forging are far superior than is ordinarily found to be the case, so that it is possible, if desired, to eliminate the normalizing heat preceding the quenching heat. In so far as the drawing heat is concerned, the use of the molybdenum makes it possible to draw at a much higher temperature, which effects a saving because it is much easier to regulate a furnace at high temperatures than it is at low temperatures. 7

As to workability after heat treatment, I find that alloy steels made in accordance with my invention have excellent machining characteristics, having the ease of workability of vanadium steel combined with the superior non-crystallizing characteristics .of

the nickel steels. p

The physical properties of the steel, in contra distinction to ordinary commercial alloy steels, very closely approximate the super-excellent properties of the special steels. ,'ThllS, the tensile strength and the elastic limit are greatly increased, while a maximum elongation is obtained. The cost to obtain like results with the nickel and the vanadium steels, even assuming that no result detrimental to other properties would follow, would-be prohibitive. The steel also has a very high resistance to impact and shock and to alternating stresses without crystallization, the reduction in area is excellent, and the steel can be cold bent double or twisted a number of times, without developing flaws. It appears that by the use of molybdenum in small quantities, the. increase in the physical properties is obtained without a corresponding increase in 'the Brinel-l and machining hardness, which remain well below workable limits. It might also be again observed, that the molybdenum materially increases the depth of hardening, so that the above properties will be found even where considerable reductions in crosssectional areas are made during manufacture. Certain of these properties flow from the fact that the increased temperature range permits of forging, quenching and drawing at a higher temperature; and others from the direct chemical efiect and the indirect chemical eifect of the molybdenum.

In order to demonstrate that the temperature range of heat treatment is greatly in creased without impairment of the physical properties of the steel, the following table of the properties of eight experimental test bars, of the same analysis, is given. The quenching temperatures of the bars varied through 200 1*. Each bar was annealed for three hours at 1020'F. and machined downto .505 from 1 hexagons. The analysis of the steel was:

Si. Mo.

C. Mn. Cr. P. S. .24 .65 A6 .021 .031 .17 .4 1

Ber Quench. Tensile S. i E. L. R. A El. Br.

It will be observed that notwithstanding the extremely wide variation in quenching temperatures, the physical properties vary but little.

To illustrate the efiect of molybdenum on chrome nickel steels, the following tables are given Analysis. 0'. Mn. Cr. r. s. Si. Ni. M0. .33 .80 1.00 .018 .016' .15

' Properties.

'1. 8. EL. El. RA. 144,000 112,500 15.5% 54% Upon the addition of nickel 1.06% and molybdenum 0.56%, the properties were as follows:

rs. EL. E1. an. 180,000 152,000 16% 53% Th this table all bars were quenched at 1500 F. and drawn at 1080 to 1100 F. on 1" hexagon cross sections, and test pieces machined down to .505.

It will be observed that there is a marked increase in tensile strength and elastic limit, and this with a slight increase in elongation and with but a slight loss in the reduction in area.

The commercial value curve of nickel steels, however, begins to drop 00 with higher percentages of nickel, and to get the best results in commercial steels the nickel should be used in small percentages in combination with small percentages of molybdenum. The nickel should be used in quantities less than 5%, above which the steel will lose workability.

The following tables of experimental tests illustrate the effect of small percentages of molybdenum on the physical properties of chrome steels, the depth hardening characteristics of molybdenum, and the modification of the effect of section produced by the molybdenum, all bars being quenched at 1560" and drawn at 1010-1050 F. The bars were hand forged from small ingots 5"x5" x10 to the section indicated. They were then heat treated and standard test bars of .505 diameter were machined from the center section.

Analysis. Section. Properties.

eweslit will be noted that the drop in tensile strength is 16,000} pounds and in elastic limit 34,000 pounds, a very clear indication that the steel has not hardened.

Section. Properties.

rill

W55 P p? Attention is called to the fact that the addition of molybdenum increases the general properties over the first steel, and also decreases the efiect of section, the drop in elastic limit from 5% section to 1% section being 22,000 pounds, as compared to 31,000 pounds where. no molybdenum is used. This indicates that the molybdenum increases the depth of hardening, as does the fact that the decrease in tensile strength is less; These effects are progressive with increasing amounts of molybdenum as shown in the remaining tables of this group.

I Analysis. Section. Properties.

0. "@296 T. S 151,000 Mn. .709 E. L. 130,000 Cr. .94 El. 17%

g. R. A. 58% si. .31

1" rs. 150,000 E. L. 130,000 E1.15% R. A. 55%

1;," 'r s. 142,000 E L. 120,000 E1.15%

Analysis Section. .Iroperties.

' o. .295 a T. s. 107, 500 10111.31 E. L. 157 500 Cr. .92 E1. 14.5 0 P. .021 3.11. 50% S. .025 Si. .31 M0. .515

1" 'r. s. 174,000 E. L. 152,000 131.14% R. A. 4

1 T. s. 170,000 E. L. 150,000 El.13% R. A. 37%

13" 'r. s. 170,000- E. L. 14 ,000 111.11% R. A. 36%

c. .30 1" 'r. s. 150,000 Mn. .72 E.--L. 158, 000 Cr. .95 El. 16% s. .025 R. A. 54% P. .021 1 Si. .032 Mo. .77

'r. s. 171,000 n. L. 145,000 El. 16 a R. A. 53%

'r. s. 172,000 %i h5g0 00 .1 RJA. 411% 1;," 'r. s. 170,000 E. L. 150 00 E1. 14% R. A. 46%

denum in fractional percentages has a very.

marked effect on the physical properties of the steel.

These favorable properties increase with the use of molybdenum up to 1% or a little more, and thereafter the commercial value curve of the steel begins to drop off owing to the development of stiffness, brittleness and other properties, detracting from the workability of the steel, and also because the sensitiveness in the temperature of heat treatment increases.

The independent effect of molybdenum on the properties of commercial steels may be emphasized bythe following comparative tables of tests conducted with 2- hexagon bars, quenched at 1560 F. and drawn at 1020F., the first steel being a plain unal loyed carbon steel containing 23% carbon, .81% manganese, .021 phosphorus, .025 sulfur and .25 silicon; the second steel having added thereto 50% chromium and no molybdenum; the third steel having added thereto no chromium and .7 0% molybdenum; and the fourth steel having added thereto .60% chromium and .70% molybdenum.

, Tensile Elasti Elong. on Red. in

strength. limit. 2". area.

The results of all of the foregoing experimental tests are fully supported in later actual commercial development. ,Thus, for example, the foregoing stock for machme parts which I prefer as giving the most satremarkable physical properties are emphasized by the fact that, in the making of this steel, the blooming mill yield was 81%, 0 which is considerably higher than is the case in present commercial alloy steels, and the cost of preparing the ingot for rolling reduced by more than one-half, and by the further fact that the steel is readily machinable. The increase in properties is most marked when compared with those of one of the best, vanadium steel at present used in autombile crank shafts, the physical properties of which substantially run as follows Tensile strength... 201, 000 to 270,000 pounds. Elastic 1imit.... 180, 000 to 225, 000 pounds. Elongation on 2 7% to 15% Reduction of area. 1.7% to 45% These steels also have increased resistance to dynamic stresses from which it will be readily seen that they are exceedingly desirable for springs.

Furthermore, in case hardening steels l find, in steels made in accordance with my invention, the general penetration of carbon is superior, the increase in penetration of as much as 15% being obtainable which obvi-l ously improves the quality of the case formed during carbonizing.

in conclusion, therefore, it appears that the use of molybdenum in small percentages intensifies the eiiect of the other alloys, increases the most desirable physical properties, and substantially maintains greater elongation, with more excellent reduction in area percentages, and with increase of the resistance to impact and shock and to alternating stresses. Thus, 1 am enabled to obtain the super-excellent qualities such as found in the more special steels, while at the same time the steel has all of the other properties necessary to commercial steels. The net result is a commercial steel which is far superior in properties and is much cheaper both to make and to manufacture, for rea sons given above. My invention is most useful in making ternary and quarternary compounds of alloy steels.

I do not Wish to be understood as limiting myself to steels having the precise proportions of content above given, but I prefer the following proportions, as giving the best commercial results, namely For forging stock for crank shafts, axles, connecting rods, spindles, etc., carbon from 20% to 85%; manganese from 30% to 1,25%; chromium from a fraction of a per cent. to 120%; silicon from .15% to 35%, and molybdenum from a fraction of a per cent. to 1%.

For spring steel, carbon from 38% to 55%; manganese from 40% to 1.25% chromium from a fraction of a per cent. to 2%;

net/aces men, spindles, cams, cam shafts, gears,

springs, parts to be case hardened, die blocks, hammers, parts of forging machines, particularly those undergoing heavy duty, and equivalent articles; as well as certain other classes of steel of a more special nature where the molybdenum is used in substantially the proportions specified, in contradistinction to steels of a similar character in which the molybdenum is embodied in much higher percentages, particularly :Where the molybdenum is added to bring the special steels more Within the class of commercial steels.

1 do not herein specifically claim the sub- .ject matter relating to spring steels specifically described and claimed in divisional application No. 184,942; the subject matter relating to case hardening steels specifically described and claimed in divisional application No. 184,940; nor the subject matter relating to chrome steels specifically described and claimed in divisional application No. 184,941; all filed August 7th, 1917.

1 claim:

1. A commercial steel having a high merit number but readily workable, containing the usual constituents of steel and embodying molybdenum. as an added element.

2. A commercial steel having a high merit number but readily workable, containing the usual constituents of steel and embodying molybdenum as an added element in quantities ranging from'a substantial fraction of 1% to not materially more than 1%.

3. A commercial steel having a Wide range of heat treatment, containing the usual constituents of steel and embodying molybdenum as an added element.

4. A commercial steel having a Wide range of heat treatment, containing the usual constituents of steel and embodying molybdenum as an added element in quantities ranging from a substantial fraction of 1% to not materially more than 1%.

5. A steel having a tensile strength ranging approximately from 120,000 lbs. to 270,000 lbs. and an elastic limit ranging approximately from 100,000 lbs. to 225,000 lbs. which contains molybdenum in addition to the usual constituents as an added element inquantities ranging from a fraction of 1% to not materially more than 1%, the steel being characterized by workability.

6. A. steel having a Wide range of heat treatment and characterized by workability,

5 "substantially containing carbon from .20 to 35%; manganese from .30 to 125%; chrosilicon from .15

to 35%; and molybdenum in relatively large traces up to 1%.

In testimony whereof I signed my name. CH

have hereunto 10 ILD HAROLD WILLS.