US2320040A - Steel product and method for the manufacture thereof - Google Patents

Description

y 2 1943- H. N. LANDIS 2,320,040

STEEL PRODUCT AND METHOD FOR THE MANUFACTURE THEREOF Filed April 11, 1940 2 Sheets-Sheet 2 llll HHIIM INVENTOR.

ATTORNEY.

Patented May 25, 1943 STEEL PRODUCT AND METHOD FOR THE MANUFACTURE THEREOF Henry Neuman Landis, Chicago, Ill., assignor to La Salle Steel Company, Chicago, 111., a corporation of Delaware Application April 11, 1940, Serial No. 329,011

16 Claims.

This invention relates to new and improved steel products and a new and improved method for the manufacture thereof.

The invention more particularly relates to a method of metallurgical treatment whereby to produce a steel of the cold worked type with hitherto unachieved combinations of physical properties, such as; for example, combinations of two or more of the following properties, namely, high tensile strength, extremely satisfactory ductility, true elastic stress-strain curves, a minimum of warpage and distortion, exceptional machinability and wearability The present application is a continuation-inpart of my co-pending application, Serial No. l12,707, filed November 25, 1936, w c in turn is a continuation-in-part of my application Serial No. 42,883, filed September 30, 1935.

One of the objects of this invention is to provide a method of producing steel of the cold Worked type having highly satisfactory physical characteristics.

Another object of the invention is to provide a method for producing a cold worked steel which has combined physical properties of high tensile strength and satisfactory ductility.

' Still a further and very important object of the invention is to provide a new .and improved method for manufacturing steel whereby the resultant product is characterized by excellent wear characteristics.

Another object of this invention is to produce a steel of high tensile strength and satisfactory ductility which has a smooth and satisfactory surface finish without the necessity for subse quent grinding, turning or re-drawing.

Another object of the invention is to provide a method for producing a steel of high tensile strength and satisfactory ductility in a more efficient and economical manner.

It is another object of this invention to produce a cold worked steel having highly improved qualities of machinability.

It is still a further object of this invention to produce new and improved steel products of the cold worked type having a combination of one or more of the properties mentioned above.

An additional and very important object of the invention is to produce new and improved steel products of the cold worked type having the combination of properties of strength, wear resistance, a minimum of warpage or distortion together with excellent machinability.

It is a further object of the invention to provide new and improved sliding frictional members made from the new and improved steel products having the combination of properties of strength, wear resistance, a minimum of warpage and machinability.

Numerous other objects and advantages of the invention will more fully appear during the course and progress of the following specification.

At the present time large tonnages of bar steels are cold worked, that is to say, the cold bars of steel are shaped through rolls or dies and thereby subjected to a pressure which reduces the cross-sectional area of the bar. Steels may be cold worked by various methods such as cold rolling, cold drawing and cold swedging, and such cold working operations may be applied to the steel either in single or multiple passes. In the case of a single pass type of operation the entire reduction in cross-sectional area is achieved in one operation, whereas in the case of multiple pass types of operations the reduction in crosssectional area is achieved by several successive smaller reductions in cross-sectional area.

When bar steels are cold worked crystallographic changes take place in the steel which result in an increase in strength and hardness and a reduction in ductility, .area and impact strength. It further results in an increase in the apparent elastic limit, but the stress-strain curve is sloping and the'yield point is indefinite. A further difliculty which is encountered with cold worked steel is lack of stability. It has been found that most steels of this character harden with age and have a tendency to warp or distort in machining. This has the disadvantage that when cold worked steels are machined into machine parts the resultant parts may, during machining, or even later become warped or distorted. Very often this warpage or distortion is made evident by a growing or increase ,in size of the part or portions thereof. Hence, in the production of bar isteels which are subsequently to be machined orotherwise fabricated into various types of steel products, the art has generally avoided the use of excessive drafts.

It has furthermore been found that the relative increase in strength and decrease in ductility vary with the amount of reduction in area to which the steel is subjected in cold working.

Where steels are subjected to relatively low drafts with an attendant relatively small reduction in cross-sectional area, it is said that the steel is subjected to a light draft, whereas, if the steel is subjected to a relatively high draft with an attendant relatively large reduction in cross-sectional area, it is said that the steel is subjected to a heavy draft. Since the loss of ductility is proportional to the draft," in modern commercial practice the draft is kept at an absolute minimum where ductility is at all important in the metal being processed.

For uses where wear resistance is an essential requirement of steel it has heretofore been customary to use what is known as a "heat treated steel," or a carburized and heat treated steel. Heat treated steel, as the term is employed in the sense just mentioned, means a steel which has been heated above the critical temperature, quenched in a medium such as oil or water, and re-heated to a particular temperature in order to obtain a desired hardness. The heat treated steels which are employed for wear resistance are usually obtained by the heat treatment of high carbon steels containing about .88% to about 1.25% of carbon or low carbon steels with a case of high carbon usually about .88% to 1.25% carbon. Occasionally satisfactory. service has resulted from the heat treatment of carbon alloy steels containing about .40% to about .50% carbon. Lower carbon steels even when heat treated fail to give anything approaching satisfactory results in wear service.

Cold working alone has not heretofore been known to contribute materially toward wear resistance, although it is customary to cold finish "heat treated steels at ordinary drafts of, say, around 7% or perhaps slightly higher. As a matter of fact, excessive cold working has been avoided heretofore for numerous reasons which have already been stated in connection with the discussion of the efiect of cold working generally. Thus, to repeat, it is known that when bar steels are cold worked changes take place in the steel which result in a increase in strength and hardness and a reduction in ductility and impact strength. There is also an increase in the apparent elastic limit, but the stress-strain curve is sloping and the yield point is indefinite. Cold worked steelsare unstable and there is a tendency for such steels to grow, shrink or become distorted. Likewise, they harden with age. Hence, in the production of bar steels which are subsequently to be machined or otherwise fabricated into various types of steel products or machine parts, the art has generally avoided the use of excessive drafts.

The heat treated steels, usually about .40% to about 50% carbon, which are commonly sold to the trade for wear resistance uses, leave much to be desired because they are not sufllciently wear resistant and in the more strenuous types of wear applications, for example, those involving sliding frictional steel members, that is to say, steel members or parts of an apparatus which operate in sliding frictional contact with other members or parts, it is usually customary to resort to case hardening or case carburizing in order to obtain suitable resistance to wear. Such a procedure is costly and very undesirable as compared to any method by which a sliding frictional part or member can be machined directly from a steel to its desired form without a carburizing or case hardening step.

The present invention is based upon the discovery that new and improved steel products can be obtained by a new and improved method of treating steel comprising, first, cold working a steel, for example, abar steel, abnormally or with excessive drafts and thereafter subjecting the cold worked steel to re-heating to a temperature beyond the precipitation hardening range but below the temperature at which substantial recrystallization begins to occur. It has been found that this treatment imparts new and improved properties to steels of many different chemical analyses. Among these properties are strength with satisfactory ductility, high impact values, a minimum of warpage, growth, shrinkage or distortion and machinability. Steels produced in accordance with the invention also have satisfactory elastic stress-strain curves and satisfactory tortional and fatigue values. Furthermore, when this method oi treatment is applied to certain types of steels the steel products obtained have unusual wearability in conjunction with strength, a minimum of distortion and excellent machinability. These products, therefore, are especially valuable for manufacturing numerous machine elements or parts, more particularly sliding frictional elements where wear is an essential property or characteristic. One of the important results of the invention is the fulfillment of a demand for steel products of a type having machinability, strength, wear resistance and a minimum of distortion and which have substantially better wear characteristics than the so-called heat treated steels, and at the same time are less expensive than case carburized or case hardened steels. In other words, the steel products of the class just mentioned made in accordance with this invention occupy a sphere somewhere in between the heat treated steels and the case hardened or case carburized steels. They supply a demand for machine parts such as sliding frictional elements where a heat treated steel is not satisfactory and a case carburized or case hardened steel is too expensive.

The steels preferably employed as starting materials in accordance with this invention are nonaustenitic and have a pearlitic and ferritic grain structure. The bar steels employed as starting materials are preferably hot rolled. The term hot rolled" is applied to bars which have been rolled hot from billets and then air cooled or allowed to cool normally. The products produced in accordance with the invention are characterized by the fact that they retain a pearlitic and ferritic grain structure which may possibly be somewhat elongated due to cold working at abnormally heavy drafts.

The expression "abnormally heavy drafts" is employed herein to describe the cold working of steel under greater compressive pressures to cause a greater reduction in cross-sectional area than in normal practice. The amount of cold working necessary to effect an abnormally heavy draft will vary depending upon the size of the bar to be worked. Generally speaking, the larger the bar the larger is the draft necessary to effect on abnormally heavy draft. For example, in cold working steel bars standard practice on one inch and two inch bars usually involves about a one-sixteenth inch draft. Thus, to produce a one inch round cold drawn bar it is customary t start with a one and one-sixteenth inch diameter bar and subject it to a one-sixteenth inch draft. The reduction in area of the cross-section of the-bar is, therefore, about 11-12%. With a two inch bar the reduction in area of the crosssection would beabout 6%. In accordance with the present invention, however, the abnormally heavy draft used in making bars varying in size all the way from one-fourth inch to two inches should preferably be such as to reduce the crosssectional area of the bar about 20% or more. It will be understood that the invention is also applicable to the treatment of steel in the form of bars of larger size, but where the bar is greater than a two inch size it becomes increasingly difflcult to subject it to an abnormally heavy draft. Furthermore, in the preparation of steel prod ucts for wear usages it has been found in accordance with this invention that even with bars having a maximum thickness of greater than two inches, the amount of cold working must be such as to reduce the cross-sectional area more than about 13%, otherwise suitable wear resistance will not he obtained regardless of the chemical analysis oi the steel.

Even when treating steel bars and rods in the larger sizes it is preferable that the abnormally heavy draft be sufficient to cause an 18-20% reduction in cross-sectional area or more. For practically all purposes where wear resistance is desired, and particularly in making sliding frictional elements, it has been found that the cold working of the steel should preferably be sufficient to reduce the cross-sectional area at least 20%.

The temperature of re-heating after cold working may vary but should be at least, suiiicient to carry the steel through what is called the precipitation hardening range. The precipitation hardening range is well known in the steel art and the term precipitation hardening is used to describe an effect which is invisible and cannot be observed microscopically but which causes certain changes in the physical properties of the steel, namely, an increase in strength, a decrease in impact or Izod, a lowering of ductility and an increase in hardness or Brinell.

This phenomenon in cold worked steels is some:

times called "age hardening. The temperature of re-hea'ting required to carry a steel through the precipitation hardening range will naturally vary .depending upon the chemical composition of the steel as well as other factors, but in most instances with steels cold drawn or cold worked at excessive drafts this temperature will be at least 550 F. The temperature at which recrystallization begins to occur will depend upon the alloying elements present, being higher with some alloying elements than with others.-

For the purpose of the present invention the temperature of re-heating is preferably within the range of about 550 to 1000* F. The in vention is especially applicable to the treatment of steel in the form of bars, rods, tubes and the like. The particular size and shape is immaterial, for example, a bar may be round, square, rectangular, hexagonal or octagonal in crosssection. The period of re-heating may vary widely depending upon the size of the furnace and the amount of steel being re-heated ina given furnace, the size of the bars being heated. and other factors. In general, the time of heating should be sufficient to permit thorough penetration of the heat throughout the steel which will usually require from about one toabout four hours.

tion in area greater than about-20% followed by re-heating to a temperature within the range of about890 F. to about 920 F. and then allowing to cool normally;

3. subjecting a steel to an abnormally heavy draft sufficient to cause a reduction in crosssectional area in excess of about 20% followed by re-heating to a temperature from around 980 F. to about 1000 F. and then allowing to cool normally;

4. subjecting a steel to an abnormally heavy draft sufiicient to cause a reduction in crosssectional area in excess of about 20% followed by re-heating to a temperature of about 800 F. and then allowing to cool normally;

These four procedures will be referred to as treatment No. 1, treatment No. 2, treatment No. 3 and treatment No. 4. I

The invention also has certain outstanding and preferred features as regards the chemical analysis of the steel. It has been found that in order to obtain steel having the combination of properties of strength, wear resistance, a'minimum of warpage or distortion and free machinability the best results are obtained by employing steel containing a substantially greater amount of sulphur than ordinary low sulphur plain carbon steels. To this end the steel employed should preferably contain in excess of about 075% sulphur. For the purpose of this invention a steel containing 075% to about .15% sulphur may be referred to as a medium sulphur steel. A steel containing greater amounts of sulphur may be referred to as a high sulphur'steel. In the practice of this invention it has been found that the high sulphur steels, and particularly those steels containing in excess of about .17 5% sulphur and preferably from about 2% to about .4% sulphur, give excellent results.

It has also been found that in order to obtain wearability in accordance with tests hereinafter described the amount of carbon in the steel should preferably be at least .3%. The maximum amount of carbon will ordinarily be about 55% because steels having a higher content of carbon cannot be subjected to the abnormally heavy drafts required by the practice of the invention. Steels having a lower content of carbon than about .3% are useful for some applications but apparently do not have wear resistance even when treated in accordance with this invention,

even though they are medium sulphur or. high sulphur steels. It is also preferable, in accordance with this invention, that the steel contain in excess of about 1% manganese. The best resuits have been obtained with the so-called manganese-sulphur steels.

The term manganesesulphur steels is used herein to describe steels having a manganese content in excess of about 1.00% and with a medium sulphur content or v high sulphur content.

a steel toabnormal cold working in accordance with any one of the preferred procedures previously mentioned:

Table I TREATMENT #l C 01 d Draft Initial size drawn size Inches Per cent 14 36 56 as 43 it it as 90 31 V4 1e 21 it as 23 1 /i a 29 1V0 Ac 28 "94c 27 54 5'10 21 1% is 23 1% lie 22 9i a 20V V4 23 1 94s 54 23 1% $4 22 2 V4 21 Table II TREATMENT #2 Cold Draft Initial size drawn Inches Per cent is as $6 is 43 it it 36 95 as 31 '/4 is 27 it 56 23 1 $6 21 1140 91c 28 iii: 27 1% M a 24 lo 23 1% ti u 22 1% "51a 20 1% '34s 18 1 410 ,4 23 14 22 2 M 21 Table III TR E A'IMENT #3 01d Draft initial size drawn Inches Per cent M 36 66 it 43 V1 is as K k; 31 A H 27 35 Mr 23 1 it: 21 1 He ii a 28 1% ii a 27 1 it I ia 24 1% Me 23 1% H o 22 4i 20 1% M a 18 1% 0 -31 a 1R 1% ")4 a 17 2 '31 n 17 2140 Mn 17 lie 16 2% 34 n 15 2% 3i 0 l 2}: lie 14 The drafts for the fourth procedure may be the same as those for either the first or second Procedure. It will be understood that the drafts given in the tables are merely typical. They are duction of bars having any specific initial size.

The invention will be further illustrated but is not limited by the following examples:

Example I A steel, which was prepared by the usual hot roll method, by casting, rolling around 1900 to 2000 F. and then allowing to cool normally so that it contained the normalized pearlitic and ferritic structure, had the following analysis:

Per cent Per cent Per cent Per cent mangaphoscarbon new phorus sulphur Per cent Per cent 'lcnsllc Ylf1l1 Bri- Conditlon Strength point 21:155. ragged Izod no" B e f 0 re cold drawing 98, 750 61, 500 27. 0 50. 0 52 207 (.0111 drawn 142, 500 120.500 10.0 45. 5 38 25.5 400 F 134. 500 13.5 44. ii 25 500 F 146, 250 ll. 7 42. 5 21 000 F 140. 500 iii. 0 44. 9 18 269 700 F 127, 650 I5. I 15.5 33 000 F 110, 650 10. 5 50. G 45 241 It will be observed in connection with the elongation of the steel that the cold drawn steel before being heated had an elongation of 10.9% in 2 inches. On being heated, the elongation increased at 400 F. and decreased again at 500 F., and finally began to move steadily upward at around 600 R, which was also the point of maximum hardness. At 900 F. a steel of excellent properties was obtained, having not only a high tensile strength, a high yield point and extensive elongation properties, but also excellent toughness and hardness. Microscopic examination of the grain structure showed that the steel still retained its pearlitic and ferritic structure. This steel also had the property of wear reslstance as tested in the manner hereinafter described.

Example II A manganese alloy steel, prepared by the usual hot roll method, analyzed as follows:

A number of bars of this steel 19; inches round were cold drawn through 0. die to H of an inch, which corresponds to an area reduction of about 40.5%. These were then heated at various temperatures and the properties after cooling observed as described in Example I:

Per cent elong. in 2" Per cent reduced area 7 Tensile strength Yield point Condition Izod 0510 drawn 137, 000 r 53.8 250 Reheat:

Example III A chromium-molybdenum alloy steel, prepared by the usual hot roll method, had the following analysis:

Per cent molybdenum Per cent chromlum Per cent phosphorus Per cent sulphur Per cent manganese Per cent carbon A number of bars of this steel 1 inches round were cold drawn through a die to of an inch, corresponding to an area reduction of about 37% The properties were determined in a manner similar to that described in Example I, as illustrated in the following table:

Tensile strength Yield point Bri- Condition Before cold drawing old drawn 700F It will be observed thatin the case of this steel, 9. temperature of 1050 F. did not substantially change the crystal structure and it is possible to go to higher temperatures before substantial recrystallization occurs.

When the same type of steel was cold drawn Irom 11 g inches to is of an inch, an area re- 1 i Per cent Percent 5 5 Tensile Yield Bri- Cond1t1on strength point eillclirzi g reggged Izod nell Example IV A copper-nickel alloy steel, prepared by the 15 usual hot roll method, had the following analysis:

Per cent Per cent gs Percent Percent Per cent a carbon manganese i sulphur copper nickel p A number of bars of this steel 1 inches round were cold drawn through a die to 1 20f an inch round, corresponding to an area reduction of 40.5%. They were then heated to various temperatures and the properties observed as illustrated in the following table:

Per cent Percent Tens1le Yleld Bri- Condition elong. reduced Izod strength point in area nell 40 0 Here again it will be noted that around 1050 F.

recrystallization had begun and the Izod was rising rapidly.

Example V A plain carbon steel prepared by the hot roll method and containing the usual pearlitic and ferritic grain structure analyzed as follows:

Percent Per cent Per cent Per cent mangaphosoarbon nese phoms sulphur 0.30 0.70 0.016 I 0.027

Bars of this steel 1 inches round were reduced in area by drawing them through a die to 5% of an inch round, corresponding to an area reduction of 42.6%.

The properties of the steel in its original state after being cold drawn and after re-heating at various temperatures were noted as follows:

- Tensile Yield Yemen Percent B 0 o r ondition strength point oily-orig legrlgfd Izod nell Bgforo cold 86 750 rowing 59, 500 31. 3 5S. 8 7O Colddrawm... 130,600 2,000 9.4 36.6 20 22?. 121,500 12.0 35.7 14 to a duction f about 22%, the following results were obtained:

In this case the most desirable combination of'properties occurred when the steel was heated to approximately 900 F.

Other features and advantages of the invention will 'be apparent by reference to the following description and the accompanying drawings, in which:

Figure 1 represents graphically the results of tests made to evaluate and to compare steels of the present invention with known types of steels as to wearability;

Figure 2 illustrates a cam which is one form of sliding frictional element made with wear resistant steels of the type herein described;

Figure 3 illustrates a gear made with a wear resistant steel of the type herein described;

Figure 4 illustrates a stoker helical gear shaft, another type of sliding frictionalelement which may be made with a steel of the type herein described;

Figure 5 illustrates a precision spindle, still another type of sliding frictional element made with a wear resistant steel of the type herein described;

Figure 6 illustrates a worm shaft which is another type of sliding frictional element made with a wear resistant steel of the character herein described;

Figure '7 illustrates a stoker worm gear made with a wear resistant steel of the character herein described;

Figure 8 illustrates an automobile king pin which is another type of sliding frictional element made with a wear resistant steel of the character herein described;

Figure 9 illustrates ajack handle pin which is still another type of sliding frictional element made with a wear resistant steel of the character herein described.

The graphical results illustrated in Figure 1 were obtained from tests'which were made to evaluate the steels of the present invention and to determine their wear resistance properties. At the present time there is no standard test for determining and evaluating wear resistancein steels and since it is practically impossible in a limited period of time to evaluate and compare various types of steels in actual usage, it was necessary to devise a method of testing which would offer a. basis for evaluation and comparison. The tests which were conducted and which afforded an excellent comparison of wear resistance in various types of steels with the wear resistance of steels prepared in accordance with the present invention were carried out on a Falex extreme pressure (EP) lubricant tester manufactured by the Faville-Le Valley Corporation,

Chicago, Illinois.

The Falex tester is ordinarily used for testing lubricants. The basic principle of the equipment is the rotation of a standardized pin having a diameter of about 0.250 inch between two standardized V blocks at a constant speed (293- R. P. M.) in an oil bath. By means of suitable gauges the pressure applied on the pins by the blocks and the torque developed due to the friction between the pin and the blocks are measured. The oil bath temperature can be controlled and/or measured. The loads may be applied either automatically or by hand. When used as a lubricant tester, standardized steel blocks and pins are employed in this apparatus and the test conditions are in accordance with a paper enbricants, bulletin 101-1, American Transit Association Report, October 1938. When testing lubricants an evaluation is made of the pressures at which weld-seizure of standardized pins results due to the failure of the different lubricants.

In testing steels for evaluation in accordance with the present invention, this procedure was was known to occunat 250 lbs. indicated pressure and from this point on resistance to seizure or welding depended entirely upon the test pieces. Since resistance to seizure is a measure of wear resistance it was possible to carry out comparative tests with a number of different types of steels and to evaluate the wear resistance characteristic of these steels.

The steels used in the tests were all machined from the mid radius of bars approximately 1 inch in diameter. All pins were 0250-02495 inch in diameter and ground in the same grinding machine except the case carburized pins. These were ground to an equivalent finish and to the same size by use oi a more applicable grinding wheel.

The following table, Table IV, represents the analyses of the fourteen (14) samples of steel in the order given in the drawings:

Table I Final hardness,

well

Analysis percentage P 8 Mo Rc28 1.50 o- The steels of the above analyses were prepared according to the methods oi treatment given in the following table:

Table V R h tbel o ea ow crys- Steel g rmmd Draft figg g tallizatlon tem- K}: bar area perature after diamcold work eter Inches Inches Per cent 1 Hot rolled nor- 1%; 9111 29 None.

malized. 1 2 do 1% 34 37 Rehcated to 550 F. for about 1% hours.

3 ..do 154s 29 Reheated to 800 F. for about 1%.;

hours.

4 ..do 1} M6 l112 None.

6 ..do 1%; -io Reheated to 890 920 F. for 1%: hours.

6 Hot rolled 1%1 ie 29 Reheated to 800 F. for about 13. hours.

7 .do 1%; $40 29 Reheated to 890- 920 F. for 1% hours. 8..... Hot rolled nor- 1% ,4 37 Reheated to 800 malized. F. for about 1% hours. 9 d0 1%.; Ma 11-12 None. 10.... Heat treated by 7 Do.

, heating above critical ternp e r a t u r e quenching in oil, reheating to 1000 F.

and cold finishing.

11.-.. Hot rolled nor- 1}ie Me ll-l2 D0.

malized.

12.... Hot rolled 1M0 %0 29 Reheated to 890- 920 F. for 1% hours.

13.--- do 1%; Ma 29 Reheated to 890- 920 F. for 1%;

hours.

14..-- Case carburized, None.

Y heatedtol700 F. [or 6 hours and quenched.

Falex procedure previously mentioned, load was applied automatically to 250 lbs. and the machine was allowed to operate at this pressure for 2 minutes to run in the test parts. minute period, load was applied automatically to the test parts in 250 lb. increments with a 1 minute period at each increment until seizure or welding resulted or a pressure of 3000 lbs. was obtained. At each 250 lb. increment the temperature of recorded. Tests were repeated to determine the maximum pressure before weld seizure obtainable on' each grade in order to obtain an average result. In this test the test blocks were standard soft V blocks as indicated in the drawings.

In making anti-weld determinations by the After this 2 the oil and the torque developed were The results obtained speak for themselves and are given in the following table:

These results were used in plotting or repre- 7 senting graphically the results shown in Figure l. The time at which each test pin ran at a given load where failure occurred is indicated by the width of each graph representing a given sample. For instance, in considering the graph in the drawing it will at once be apparent that samples 2, 3, 5, 6 and 14 ran the full test without failure.

Sample No. 1 failed while the pressure was being raised from 250 lbs. to 500 lbs. Sample No. 4 ran the full seconds at 250 lbs. but as shown on the graph, only ran a part of the 60 second period at 500 lbs. Sample No. 9 only ran a part of the 60 second period at 250 lbs. and in the same way the wearability f the other'samples can be determined by inspection of the drawings.

In tests 1 we the steel employed was a high sulphur manganese-sulphur steel. Test 1 shows that merely subjecting such a steel to an abnormally heavy draft does not produce wearability.

0n the other hand, as shown by tests 2 and 3,

when the steel is subjected to an abnormally heavy draft and then re-heated to a temperature beyond the precipitation hardening range but below the temperature at which recrystallization begins to occur, the resultant product has excellent wearibility properties.

Test No. 4 shows that a medium sulphur'manganese-sulphur steel when subjected to cold working but without re-heating does not have substantial wear resistance properties. As shown in test No. 5, the same steel when subjected to abnormal cold working followed by re-heating to a temperature beyond the precipitation hardening range but below the temperature at which recrystallization begins to occur, exhibits very pronounced wearability. Likewise, the same .steel containing a small amount of lead has excellent wearability properties, as shown by test No. 6.

It might be added that in actual wear uses the steels referred to in tests 2 and 3 are superior to the steels referred to in tests 5 and 6.

Tests 7 and 8 illustrate the result obtained with a plain carbon steel with or without lead which. has been subjected to abnormal cold working followed by re-heating to a temperature beyond the precipitation hardening range but below the temperature at which recrystallization begins to occur. It will be observed that this steel exhibited no substantial wearability.

Test 9 illustrates the result obtained with a leaded plain carbon steel without re-heating to' a temperature beyond the precipitation hardening. range but bel the crystallization temperature. As shown, t steel has little wear value. Test 10 illustrates the result obtained with a heat treated steel such as is now used for many wear applications. It will be observed that the products illustrated by'tests 2, 3, 5 and 6 are far superior to the heat treated steel.

Test 11 illustrates that a cold worked steel containing added chromium and nickel has little wear value when tested as herein described. Test 12 illustrates the importance of having the carbon content above about 30%. The steel of test 12 has lower carbon content and although it is substantially the same in other respects as the steels of tests 5 and 6 and has been given substantially the same treatment, it does not have the wear value.

Test 13 should similarly be compared with tests 2 and 3. The steel of test 13 is a high sulphur manganese-sulphur steel and has been given substantially the same treatment as the steels of tests 2 and 3, the only difl'erence being that it has a lower carbon content. This difference, however, apparently has a very substantial effect on the wear value because the steel illustrated in test 13 does not compare with the steels of tests 2 and 3 in wear resistance.

The steel of test 14 is a case hardened or case carburized steel. Within the limits of the test its wear value is as good as the wear value of test samples 2, 3, 5 and 6 but it represents an entirely different type of steel and is much more expensive. Thus, it will be seen that the present invention has provided steel products which have a much better wear value than the heat treated steel of test 10 and are much less expensive than the case carburized steel of test 14. r

The tests represented by the graph of Figure 1 clearly illustrate that the abnormal cold working in itself is not the cause of the increase in wear resistance but rather the increased wear value with a steel of proper chemical analysis is obtained by coupling the abnormal cold working with re-heating to a temperature beyond the precipitation hardening range but below the temperature at which crystallization begins to occur.

Practical tests in which various types of parts or members have been machined from the new steel and substituted for case carburized steel parts have brought out the results demonstrated in the Falex anti-weld test. For example, piston pins made from this steel have operated satisfactorily in an automobile for over 27,000 miles without showing signs of wear.

While the invention is not limited to any theory as regards the application of the process to the production of wear resistant steels it appears from the results obtained that the presence of sulphur in amounts greater that found in ordinary plain carbon steels coupled with the two stage treatment of abnormal working followed by heating, contributes to the wear value. The presence of manganese in greater than normal amounts also contributes to the wear value. Apparentlythis is true regardless of whether or not the steel is a.medium sulphur or'a high sulphur steel, for in one instance it was found that a high manganese, low sulphur steel of the following composition, normalized, had substantial wear resistance when subjected to the two stage treatment herein described: carbon .35%, manganese 1.55%, phosphorus .027%, sulphur .030%, silicon 285%, the remainder being substantially iron; It will be understood that in all of the analyses given in the tables the remainder of the product is substantially iron.

The steel which is being treated preferably has a substantial initial hardness- This hardness should be such that the finished product when treated by the two stage process herein described has a hardness of at least 20 Rockwell C, or about 229 Brinell. For most purposes the initial hardness of the steel .is preferably at least 200 Brinell.

It will be understood that the invention in its broader aspects is not limited to the specific steels described.- The steels may contain other alloying elements, as for example, copper in excess of 0.35% (e. g., up to 1.25%), chromium in excess of 0.25% (e. g., up to 1%), molybdenum in excess of .05% (e. g., up to 35%), beryllium (e. g., up to 1.00%), vanadium in excess of .05% (e. 8., up to .30%), nickel (e. g.,' up to 2.00%) and lead (e. g., up to .50%). The process may have varying eifects upon the product depending upon the chemical analysis of the steel originally employed. As previously stated, in not all cases will a steel'when treated by this two stage procnormally at least 115,000 lbs.

ess have wear value but other valuable properties can be impartedto the steel, such as hardness, impact value and other desirable combinations of physical properties.

In Figures 2 to 9, inclusive, illustrations have been given of various applications of the new wear resistant steels in sliding frictional elements. Preferred steels for this purpose have the following analysis:

Per cent Sulphur .175-.400 Manganese LOO-2.25 Phosphorus 0.00-0.10 Carbon 0.30-0.55 Silicon 0.10-0.40

(Balance substantially all iron.)

A steel having this analysis may be subjected to the two stage treatment according to any one of the four procedures previously mentioned. Ii it is given treatment No. 1, then it is preferably subjected to an abnormal cold working sufllcient to cause a reduction in the cross-sectional area within the range of about 20% to about 45% or higher, followed by re-heating to above 550 F., preferably from 590 F. to 600 F. The resultant product ordinarily has a minimum yield point of 125,000 lbs. per square inch with an elongation in 2 inches of at least 7%, usually around 7% to 11%, and a reduction in area of cross-section upon elongation of at least 26%, usually around 26% to 35%.

If the steel is processed according to procedure No. 2 the temperature of re-heatin'g is somewhat higher, the minimum yield point is usually 100,- 000 lbs. per square inch, the elongation in 2 inches is usually at least 9%, preferably within the range of 9% to 14%, and the reduction in area upon elongation is usually at least 27%,

preferably within the range of about 27% to 37%.

Procedure No. 3' is normally employed with the larger size bars and rods and the minimum yield point of the product is normally at least 80,000 lbs. per square inch, the tensile strength around 100,000 lbs. per square 15% in 2 inches with 35%.

If procedure No. 4 is followed the yield point is per square inch.

As previously indicated, the steel initially employed is preferably a hot rolled or normalized steel which may be produced, for example, by casting and rolling a steel bar at normal rolling practice, e. g., from about 1900" F. to 2200 F. and then allowingthe bar to cool normally in the air so that it contains the normalized pearlitic and ferrltic structure.

To summarize, it will be observed that dependmg upon the particular procedure employed, the

an elongation of around minimum yield point of the resultant product may vary 'all the way from 80,000 lbs. per square inch to 125,000 lbs. per square inch, and the'elongation in 2 inches from about 7% to about 17%. The hardness of the finished product for wear uses should preferably be at least 20 Rockwell C, or about 229 Brinell.

Among the uses for wear resistant steel made in accordance with this invention are'the manu- I facture of armature shafts, centrifugal pump inch, the ductility at least gears andpins, piston rods, sliding rails for printing presses, grinder spindles, speed reducer worm gears and many other types of wear resistance usages, particularly those involving sliding frictional wear.

Thewear resistant steels described herein are particularly desirable for wear resistant usages because they .will give longer life and better service than theheat treated steels of the type heretofore used. Furthermore, they can be used to replace partsformerly made of case hardened or carburized steel and thereby greatly reduce the cost of manufacturing a given apparatus or machine. One of the features of these steels in addition to their wear resistant properties is to be found in their non-warping properties and their ready machinability. By non-warping-is meant the ability to remain dormant without expansion or contraction during or after the machining operation. Cold worked steels as a rule tend to grow or shrink due to the fact that they do not have a true yield point. Certain properties of the steels such as hardness may vary rather widely without substantially affecting their wearability. These steels, as well as other steels made by the two stage method of this invention, because of their high yield point and tensile strength can also be used in strength ap-' plications, for example, in bolts, girders, jacks and other types of apparatus where strength rather than wear is an essential requirement.-

From the standpoint of machinability, the wear resistant steels of this invention possess excellent machining characteristics and are what is known as free machining steels. This term is used to describe steels which are machinable in previously used. Use of these new steels for ma-' which comprises cold working a non-austenitic bar steel containing a normal pearlitic and fer-' ritic structure at abnormally heavy drafts of the character described in this specification and then re-heating the bar to a temperature beyond the precipitation hardening range but below the temperature at which substantial recrystallization begins to occur.

chine parts also eliminates heat treatment of 4 parts after machining aswell as subsequent costly cleaning, straightening and grinding.

In making bar steels in accordance with the present invention it is preferable to employ a unidirectional straightening treatment, as described In my co-pending application Serial No. 256,686, filed February 16, 1939. This may be accomplished, for example, by the following combination of steps involving (1) cold working, (2) unidirectional, and (3) reheating. In some instances the reheating step may be followed by a further step also involving uni-directionalstraightening.

. The expression uni-directional straightening is employed to describe a straightening operation in which the steel is bent or straightened backward and forward in one direction only, as distinguished from the ordinary methods of straightening such as employed in the Medart, Sutton, Schuster or Brightman Flyer straighteners, in which the steel is subjected to stress and strain in all directions. The uni-directional straightening is particularly suited to bar steels where the cold working involves an excessive draft, say, in excess of about 20% area reduction, followed by heating beyond the precipitation hardening range 2. A method of producing an improved bar steel which comprises cold working a non-austenitic bar steel containing a normal pearlitic and ferritic structure at drafts sufficient to cause an area reduction in excess of about 20% of the normal cross-sectional area of the bar, then subjecting the bar to a temperature above the point where maximum precipitation hardness is obtainable and over 550 F. but not higher than the temperature at which substantial recrystalli-' zation begins to occur.

3. A method of producing a wear resistant bar steel which comprises cold working a nonaustenitic bar steel containing in excess of 1% manganese and from 0.3% to 0.55% carbon at abnormally heavy drafts sufficient to cause an area reduction in the cross-sectional area of the bar in excess of approximately 20% of the normal cross-sectional area, then subjecting the bar to a temperature above the point where maximum precipitation hardness is obtainable and over 550 approximately 20% of the normal cross-sectional area, then subjecting the bar to a temperature within the range of about 550 F. to about 1000' F., maintaining said temperature for a period of time sufliciently long to allow penetration of the heat and'thereafter allowing the metal to cool normally.

' 5. A method of producing a wear resistant machinable bar steel which comprises cold working a non-austenitic high sulphur manganese-sulphur alloy steel having substantially the following chemical analysis: sulphur .175%-.400%, manganese 1.00%-2.25%, phosphorus 0.00%-0.10%, carbon 0.30%-0.55%, silicon 0.10%-0.40%, the balance beingsubstantially all iron, and an initial hardness greater than about 200 Brinell at abnormally heavy drafts sufllcient to cause an area reduction in the cross-sectional area of finished bars from A inch to 2 inch sizes in excess of approximately 20% of the normal cross-sectional area, then subjecting the metal to a temperature within the range from about 550 F. to about 1000 F., said temperature being beyond the precipitation hardening range but below the temperature at which substantial recrystallization begins to' occur, maintaining said temperature for a period of time suiliciently long to allow penetration of the heat and thereafter allowing the metal to cool normally.

6. A method of treating a steel which comprises cold working a non-austenitic steel containing a normal pearlitic and ferritic structure atdrafts suilicient to cause an area reduction within the range of about 20% to about 45% then subjecting the metal to a temperature within the range of sufficiently long to allow penetration of the heat, and then allowing the metal to cool normally.

7. A steel having a substantially pearlitic and ferritic structure, a yield point in excess of about 80,000 lbs. per square inch combined with a tensile strength in excess of about 100,000 lbs. per

.square inch, said steel being produced by cold working a steel having a normal pearlitic and ferritic structure at abnormally heavy drafts to cause across-sectional reduction in area greater than 13%, subsequently heating said cold worked steel to a temperature above the precipitation hardening range but below the temperature at which substantial recrystallization begins to ocour and then cooling said steel to retain its pearl itic and ferritic structure.

8. An improved bar steel which is the product obtainable by cold working a non-austenitic bar steel containing a normal pearlitic and ferritic structure at abnormally heavy drafts sufllcient to cause an area reduction in excess of about 20% and then subjecting the steel to a temperature above the point where maximum hardness is obtainable and over 550 F. but belowthe temperature at which substantial recrystallization begins to occur.

9. A wear resistant, freely machinabie, medium sulphur, manganese-sulphur alloy bar steel having a substantially pearlitic and ferritic structure, a yield point in excess of about 80,000 lbs. per square inch coupled with a tensile strength in excess of about 100,000 lbs. per square inch, said steel being produced by cold working a medium sulphur, manganese-sulphur alloy bar steel hav-v ing a normal pearlitic and ferritic structure and containing in excess of 1% manganese, in excess of .0'l5% sulphur and from 0.3% to 0.55% carbon at abnormally heavy drafts suflicient to cause an area reduction in excess of approximately 20% of the normal cross-sectional area of the bar, subsequently heating the bar to a temperature above the point where maximum hardness is obtainable and over 550 F. but below the temperature at which substantial recrystallization begins to occur, maintaining said heat until it has penetrated the bar and then allowing the steel to cool normally.

10. A machinable wear resistant, high sulphur, manganese-sulphur alloy bar steel having a substantially pearlitic and ferritlc structure, said steel being produced by cold working a nonaustenitic, high sulphur, manganese-sulphur, alloy steel having substantially the following chemical analysis: sulphur .1'75%-.-100%, manganese 1.00%-2.25%. phosphorus 0.00%-0.10%, carbon 0.30%-0.55%, silicon'0.10%-0.40%, the balance being substantially all iron, and an initial hardness greater than about 200 Brinell at abnormally heavy drafts sufficient to cause a crosssectional area reduction in excess of approximately 20% and then subjecting the metal to a temperature about 550 F. but below the temperature at which substantial recrystallization begins to occur.

11. A sliding frictional element made from a wear resistant non-austenitic steel produced by cold working at abnormally heavy drafts of the character described in this specification to cause a cross-sectional reduction in area greater than 13% followed by heating the steel to a tempera- I about 550 F. to about 920 F. for a period of time 'ture beyond the precipitation hardening range but below the temperature at which substantial recrystallization begins to occur, said "steel having a carbon content from 0.3% to 0.55%, and a manganese content in excess of 1%.

12. A sliding frictional element made from a wear resistant machinable steel produced by cold working a non-austenitic, high sulphur, manganese-sulphur alloy steel having substantially the following chemical analysis: sulphur .l'75%- .400%, manganese 1.00%-2.25%, phosphorus 0.00%-0.10%, carbon 0.30%-0.55%, silicon 0.10%- 0.40%, the balance being substantially all iron, and an initial hardness greater than about 200 Brinell at abnormally heavy drafts sufilcient to cause a cross-sectional area reduction in excess of approximately 20% followed by heating the cold worked metal to a temperature within the range from 590 F. to 920 F.

13. The method of treating steel bars and rods which comprises subjecting the metal to heavy drafts without destroying the normal crystal structure suflicient to cause an area reduction in excess of about 20% of the normal cross-sectional area of the metal, then subjecting the resultant metal to a uni-directional straightening treatment and thereafter heating it to a temperature beyond the precipitation hardening range but below the temperature at which recrystallization begins to occur.

14. A method of producing an improved bar steel which comprises subjecting a bar steel to heavy drafts sufficient to cause an area reduction in excess of about 20% of the normal cross-sectional area of the metal, then subjecting the bar to a uni-directional straightening treatment and thereafter heating the metal to a temperature within the range of about 550 F. to about 900 F. but no higher than the temperature at which substantial recrystallization begins to take place.

15. A method of producing improved bar steel which comprises subjecting a bar steel having a normalized pearlitic and ferritic grain structure to cold working sufficient to cause an area reduction in excess of about 20% of the normal cross-sectional area of the metal, then subjecting said bar to a uni-directional straightening treatment, thereafter reheating the bar to a temperature within the range of about 550 F. to about 900 F., said temperature being beyond the precipitation hardening stage but below the temperature at which substantial recrystallization takes place, allowing the metal to cool normally and subjecting it to a second uni-directional straightening treatment.

16. As a new article of manufacture, a nonaustenitic alloy steel having a pearlitic-terrific metallographic structure and having improved characteristics of strength. wear-resistance and machinability together with satisfactory ductility and minimum tendency to warp in machining, said alloy steel having been produced by cold ,working an alloy steel of non-austenitic pearliticmaximum hardness is obtainable upon reheating,

and below the point where substantial recrystallization takes place.

HENRY NEUMAN 'LANDIS Patent No. 2,520,0h0.

CERTIFICATE OF CORRECTION.

May 25, 191 5. HENRY NEUMAN LANDIS.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 8, first column, line '56, for "that" read --than--; page 10, first column, line 65, claim 10, for "about" read --above-; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

signed and sealed this 6th day of July, A. D. 1911.5.

' Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.

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