US2362046A - Graphitic steels - Google Patents

Description

' I Graphitic steels are disclosed and Patent No. 2,087,764, granted July 20 1937, on

Patented Nov.- 7,1944

UNITED; STATE.

GRAPHITIC-STEEIQS I Frederick Bonte, Canton, Ohio, assignor to The Timken Roller Bearing Company, Canton, Ohio, a'corporation of Ohio No Drawing. Application October so, 1943, Serial No. 508,3 2 I 5 Claims. ('01. 75 -123 This invention relates to improvements in 'graphitic steels. I

claimed in an application filed by me. The graphitic 'steels described in that patent are characterized generally by the fact that in' the heat treated condition' they contain free graphite and bytheir ability to develop high hardness upon appropriate heat treatment. They p'ossesshigh-resistance towear. Tungsten is, however, one of the critical war materials, and .in any event the relatively high content of tungsten makes thosesteels relatively .expensive.

metal pickup and scoring, they are classed as being 'free machining, and certain of them possess high resistance towear, or abrasion. Such propertiescoupled with other desirable physical properties. have caused the graphitic steels to be used extensively for the making of dies of many It is-among the objects of this invention to provide graphitic steels and articles made therefrom in which the properties generally possessed by such-steels are combined with greater wear resistance than is possessed by molybdenumg'raphitic steels, which are of relatively simple and inexpensive composition and do not require the use of'large amounts of critical alloying elements, which in shapes of relatively great length .or relatively small section, or both, can be hard-,

ened without serious distortion to hardnesses reater than are obtained with the molybdenumkinds, punches, spinning, slitting and forming rolls, broaches, and other. tools used for related purposes, especially where resistance tofatigue and abrasion is requisite.- Notonly have those steels been used satisfactorily and. in large.

amounts; but their use is being extended considerably..

One type of graphitic steel coveredthat I patent which has been used extensively, and

which is being used on an increasingscale, contains abouti1.5 per cent of carbon, about 0.8 per cent of silicon, and a small amount, say about 0.25 per cent, 'of molybdenum. For brevity it may be referred toas molybdenum-graphitic steel That .ste'elis characterized by outstanding resistance to wear and abrasion, and by the fact that it may be quenched without distortion, even in the case ofarticles of varying section. Those properties in combination with others which are possessed in common by graphitic steels have been responsible for its success. Despite the high resistance to .wear that is possessed by molybdenum gra- .phitic steels, still greater wear resistance is de- 'sirablefor some purposes, and in another patent, No. 2,283,664, granted May 19, 1942, I have disclosed and claimed graphitic steels of still greater 1 wear resistance, a typical example of them being a steel containing about 1.5 per ,cent'of carbon,

about 0.5 per cent of molybdenum, about 0.65 per cent of silicon, and about 2.8 per cent of tungsten.

For brevity the steels of this patent may be termed tungsten-graphitic steels. They are exceptionally resistantto 'scufilng, scoring and gra'phiticsteels and which are equivalent to those obtained with the tungsten-graphiticsteels, and

which fabricate easily and in accordance with standard practice in making graphitic steel articles.

. Ihave discovered, and it is upon this that the present invention is predicated, that by the addition of titanium to graphitic steels containing molybdenum in larger amounts than have been customarily used in such steels there is obtained an unexpectedly great improvement in the struc ture, heat treated hardness and wear resistance .of-the steels, more particularly, I have found that by combining molybdenum and titanium in graphitic steel compositions the carbides and gra- 'phitic carbon in heat treated articles arenot only distributed uniformly but are dispersed 'more finely. thanis ordinarily the case in graphitic steels. Also, by appropriate heat treatment the steels provided by the-present invention develop l especially high hardness, which is, I beieve, contrary to the general effect of titanium 'in' plain carbon or low alloy steels; in fact, they can, be

.heat treated to produce hardnesses greater than .titanium steels 'of this invention developed by the standard; molybdenum-graphitic steels and equal to that of the tungsten- Moreover, the molybdenumpossess the out-' standing. ability of the molybdenum-'graphitic graphitic steels.

steels to harden without detrimentaldistortion.

and their wear resistance is several timesthat of the molybdenums raphitic' steels. 'This' is of major importance because, as is well recogmzed in the art, the molybdenum-graphitic steels possess exceptionally good wear resistance. The surprisingly great wear resistance of the present steels is not so great as that of the tungstengraphitic steels, but the steels of this invention are less expensive and they free the critically important element tungsten for other purposes. Additionally, they possess the free machining characteristic of graphitic steels. In consequence of these properties the new steels possess good cutting properties which adapt them to the production of taps, reamers, drills, counter borers, and a wide variety of other tools which do not require red hardness.

Steels and articles made from them in accordance with this invention contain from about 0.5 to 2 per cent of carbon, about 0.5 to 6 per cent of molybdenum, about 0.5 to 1.5 per cent of silicon, and about 0.25 to 2.0 per cent of titanium. Within such ranges it is now preferred for many purposes to form the articles from steels containing about 1.7 to 1.8 per cent of carbon, about 1.4 to 1.6 per cent of molybdenum, about 0.9 to 1.1 per cent of silicon and about 0.4 to 0.6 per cent of titanium, and the steel suitably lies midway of those ranges. Neither the phosphorus nor the sulfur content should exceed about 0.025 per cent, and the manganese content should not be over about 0.45 per cent. The remainder of the steels is iron together with impurities in the amounts customarily encountered in such steels, but it will be understood that other alloying elements may be present provided they do not detrimentally affect the properties which characterize the present invention, for which reason the remainder of the steels may be said to be effectively iron inasmuch as such additional alloying elements do not alter the essential character of products made in accordance with the invention. The foregoing elements are balanced in accordance with customary graphitic steel practice.

The steels provided by this invention may be made in accordance with procedures standard in the art for the production of graphitic steels. Preferably they are made in an electric furnace following standard killed steel practice, the various alloying elements being introduced suitably in the form of ferrc-alloys, or otherwise as desired. It is desirable that the titanium be added only shortly before the heat is poured, at least when it is added as ferro-titanium.

The ingots are treated prior and during hot working in a manner understood in the graphitic steel art, i. e., so that the carbon will remain substantially entirely in the combined form during hot working. Generally speakingthe ingots should be hot worked, as by rolling or forging, at a temperature not over about 1950 F. or 2000 F. to produce shapes of desired form and size for conversion into final products. In case it is necessary to forge the hot rolled material to form dies or other tools the hot rolled shapes should be heated slowly to 2000 F. and held until they have been heated through, after whichthey are forged to shape with care taken that the temperature during forging does not fall below about 1600 F.

The shaped articles are then graphitized by subjecting them to normalizing and annealing treatments. To this end they are normalized by heating above the critical range, for example, at about 1600 F. to cause decomposition and 'difiusion of carbides. They are then cooled, in

accordance with ordinary normalizing practice,

by being removed from the furnace and cooled in air. Thereafter the articles are annealed by reheating them into or above the critical range, say by heating to 1450 F. and holding at that temperature for four hours. The articles are then cooled slowly, advantageously at about 20 F. per hour, to below the critical range, advantageously to about 1100 F. In this manner the carbides are partially decomposed with production of graphitic carbon.

Treated in the manner just described, steels of the preferred composition given hereinabove will contain about 0.4 to 0.7 per cent of free graphite, the remainder of the carbon being in the form of carbides. The graphitic carbon confers surface lubricating qualities desirable in articles provided by the invention, while the carbides provide, upon suitable heat treatment, high hardness and wear resistance. The combination of graphitic carbon and carbides also causes the steels in this condition to be easily machinable. It is characteristic of products provided by this invention that both the graphitic carbon and the carbides are dispersed in uniformly and exceptionally finely divided form throughout the structure, and that when hardened they possess remarkable non-seizing qualities.

After being graphitized the articles are machined or otherwise finished to shape and size, after which they are subjected to a hardening treatment in which they are heated above the critical range and liquid quenched, preferably in 'oil. To this end they may be quenched from about 1475 to 1550 F., depending upon the section. Oil quenched in this manner, steels of the preferred composition specified above regularly develop a hardness of 68 Rockwell C. The hardened articles can be drawn back, or tempered, suitably by heating at about 300 to 350 F. I have successfully quenched articles of uniform section in Water but oil quenching is preferred for most purposes, particularly with articles of varying section.

As indicated above, an important feature of the steels provided by the invention is that tools of variable section or of considerable length and small section can be hardened without distortion. In fact, to repeat, this ability of the steels is equal to that of the molybdenumgraphitic steels, which are outstanding in this particular.

Actual experience has demonstrated amply the superior characteristics of these steels with respect to wear resistance. For example, a 30- pound electric furnace heat of steel in accordance with the invention containing 1.47 per cent of carbon, 0.37 per cent of manganese, 1.02 per cent of molybdenum, 1.06 per cent of silicon and 0.37 per cent of titanium forged easily as described above into stock for making inch diameter spiral reamers. As forged the hardness was 388 Brinell, and after annealing it was 217. The material was quenched into oil from 1525 F. and tempered at 300 F. and its hardness was then 64 Re. An annealed the material contained 0.4 percent of graphitic carbon. The reamers were tested by drilling 147 holes ,4 inch in diameter in inch thick boiler plate and holes of similar diameter in a fiat bar of molybdenum-graphitic steel of the same thickness, and then reaming all of the holes to inch diameter. The reamers withstood this test satisfactorily. r

' H verted into'3 and 2 I was then used for making gagematic discs that There were made also 30-pound electric furnace heats of steels of the following composition:

Heat No. 1; Si Mo Ti Per cent Per cent Per cent Per cent Per cent B into flr-inch rounds and heat G into 3-inch rounds. The three steels were then normalized at 1600fF., annealed'at 1450 F., hardened by quenching into oil from 1525 F., and tempered I at 300 F. The properties in the yariousstates were as follows:

' Heat A was hot forged -into'1 -inch rounds, heat m I drastic gauging operation another'group of discs of the same diameter made from this steel averaged 2,600 pieces as compared with an average Norm. and annealed Hardness HeatNo. after temp.

Hardness Graph. 0, Rc Brinell per cent Heat A was used to make fiat drills used in the laboratory for sampling steel for analysis. Heat B was used for making quenching tests at varifurnace heat was made of steel containing 1.71.

per cent of carbon; 0.34 per cent oimanganese,

- 1.42 per cent of molybdenum, 0.011 per cent of phosphorous, 1.08 per cent of silicon, 0.028 percent of sulfur, and 0.54 per cent of titanium. The steel forged readily into 6-inch square billets with a minimum amount of clean-up necessary. As

:perforating bearing cage blanks. In service the.

-forged the hardness of this heat was.3'l5 Brinell.

fAfter normalizing from'1600 F. andannealing from 1450 F. the hardness was 241 Brinell and the steel contained 0.4 per cent of graphitic carbon. After. quenchin in oil from 1525 F. its hardness was 68 Rc.-

Flat stock x 3 inches was processed into roll support blades for centerless grinders and hardened and drawn to 65/66 Rc. Thisblade supports the work which is being ground, which rotates constantly and moves forwardly, thus exerting upon the blade-a sliding'action under considerable pressure. These blades were used in the roughing grinders, in which the service is par- 'ticularly severe, and it wasunnecessary to remove them for periods of '70 to 80 hours, and then only for regrinding the working surface. Theretofore molybdenum-graphitic steel had been used for these blades with service. Nevertheless, the blades made from the foregoing heat operated at least twice as long and outstanding improvement in of hardened bearing parts while they are being ground, and they are subjected to'considerable wear in being slid into and out of the parts. It

is requisite that they be replaced when their diameter has been reduced 0.0002 inch. Resistance to wear is, therefore, of prime importance. On one operation a-group of 3 -inch diameter discs made from this heat were used for gauging an average of 3,845 pieces before they had worn the allowable amount. This is tobe'comp'ared with 1,260 pieces average gauged by similar discs made from molybdenum-graphitic steel; On, a more of .940 pieces with molybdenum-graphitic steel. In still another case, 2-inch diameter discs made from this heat averaged 4,200 pieces as compared with an average of 1,500 pieces gauged with thestandard molybdenum-graphitic discs that have previously been used for these gauging operations.'

The round stock used for making the aforesaid discs was also processed into center pins that These were hardened and temperedto Re. were tested in an assembly that is used for tapered portion of the pins exerts a wedge-like action on the perforating punches to force them through the sides of the blank; These center pins, therefore, require maximum resistance to wear, and prior to the present invention they were made from molybdenum-graphitic steel. The performance of the pins made from this heat shows similar improvement overth'e standard molybdenum-graphitic pins.

According to the provisions of the patent statutes, I haveexplained the principle and method of practicing my invention and have described what-I now consider to represent its best embodiment. However, I desire to have-it understood that, within the scope of the appended claims, the invention may be practiced otherwise' than as specifically described.

I claim;

1.-As a new article of manufacture, a hot worked and heat treated alloy steel article formed from steel containing about 0.5 to 2 percent of carbon, about 0.5 to 6 per cent' molybdenum,

about 0.5 to 1.5 per cent of silicon, about 0.25"

to 2.0 per cent of titanium, and the remainder effectively iron, and characterized by high surface hardness, by containing graphite and carbides dispersed finely through thestructure, and by high resistance to Wear. l

2. As a new article of manufacture, a hot worked and heat treated "alloy steel article formedfrom steel containing about 1.75 per cent of carbon, not over about 0.45 per cent of manganese, about 1.5 per cent of molybdenum,

on the average from three and one-half to four ,to 65/66 Rc. These the inside diameter were hardened and tempered discs are used for measuring about 1.0 per cent of silicon, and about 0.5 per cent of titanium, and the remainder effectively iron, and characterized by high surface hard ness, by containing graphite and carbidesj'dis- -v persed' finely through the structure,v and by high resistance to wear.

3. Alloy steel containin about 0.5 to 2 per cent of carbon, about.0.5 to 6 per cent-of molybdenum, about 0.5 to 1.5 per cent: of silicon,

and'about 0.25 to 2.01361 cent of titanium, and the remainderefiectively iron, and capable upon annealing of producing graphite and carbides dispersedqfinely through the structure, and upon I hardening heat treatment of developing high hardness deeply and high resistance to wear.

4. Alloy steel containing about 1.7 to 1.8 per cent of carbon, about 1.4 to 1.6 per cent of molybdenum, about 0.9 to 1.1 per cent of silicon, and about 0.4 to 0.6 per cent of titanium, and the remainder eiTectively iron, and characterized by capability of producing graphite and carbides dispersed finely through the structure upon being annealed, and of developing high hardness deeply and high wear resistance upon hardening by heat treatment.

10 hardening by heat treatment.

FREDERICK R. BON'IE.