US2087764A - Ferrous alloys and method of manufacture - Google Patents

Description

Patented July 20, 1931 aos'uun- FERROUS armors AND mrnon or MANUF ACTURE Frederick R. Bonte, Canton, Ohio, assignor to The 'limken Roller Bearing Company, Canton, Ohio, a corporation of Ohio No Drawlng. .Application June 28,1933, Serial No. 678,105. 1933 25 Claims.

This invention relates to,the production of ferrous alloy'articles, and more particularly to a method-of making such articles, and it is a continuation input of my copending application Serial No. 502,624, filed December 15, 19 30,

use in sliding or rotational engagement with another element, such as internal combustion engine parts, e. g., piston rings, moving valve parts, cylinder linings, connecting rods, and the like,

and also as parts for engagement with highfrict ion elements, such as clutch parts, brake drum,

and similar elements, which may be heat treated to reconvert'a desired or predetermined proportion of the graphitic carbon to the combined form for. special purposes, and which maybe made by a process which is simple, easily practiced, in-

expensive, and which minimizes the disadvantages heretofore attendant upon the production of articles of similar composition and structure. Other advantages will be recognized by those skilled in the art from the following description.

The invention is predicated upon my discovery that its stated objects may be attained by hot working an ingot of steel high in carbon and containing a graphitizingelement, i. e., an element which is capable of causing conversion of combined. carbon to graphitic carbon, examples being silicon, molybdenum, nickel, aluminum, and their equivalents, the' carbon and graphitizing' element being so proportioned as to permit the carbon to remain in the combined form during hot working of the ingot, and so'that carbon may be precipitated rapidly in the graphitic state upon heat treatment of the formed article. Alter the ingot has been worked to shape the article, the latter is later heated to a temperature above its critical temperature to convert a substantial proportion of its combined carbon to the graphitic state.

In Great Britain February 24,

An essential stepof the invention therefore' comprises the use of steel compositions such that the ingot is capable of being hot worked, i. e., its carbon content is substantially entirely in the combined form, and yet selecting a composition such that after the article has been formed a substantial amount of the combined'carbon can be converted to the graphitic state by heat. treatment so asto obtain the properties which" characterize articles produced in accordance with the invention. l

In accordance with the invention the percentage of carbon and graphitizin'g element can a be varied to provide the foregoing conditions, it being known that an increase in. either or both of these elements tends to produc'e carbon in the graphitic state. Accordingly, these two elements areso proportioned that during hot working of the ingot the carbon is substantially entirely in'the combined form, as otherwise the ingot can not be worked satisfactorily. If a large percentage of the total carbon is in the graphitic state in-the ingot, such as is the case in ordinary cast iron, the ingot cannot be satisfactorily hot worked to form the desired articles. In accordance with the principle just stated, if the carbon content is raised the content of graphitizing element should, as a general rule, be decreased appropriately so as to provide an ingot which n can be hot worked, i. e;, containing substantially no gr-aphitic carbon-but such that graphitizing may be induced upon subsequent heat treatment. If either the carbon or the graphitizing element, or both, are too low it is impractical to produce graphitic carbon in the desired ranges by heat treating the article fabricated from the ingot. The composition also varies according to the size of the ingot, as will be recognized bythoseskilled in the art.

Although the composition of the steel used in the practice of the invention may be varied in accordance with the change in conditions just noted, it is preferred inmost instances to have the carbon constitute from about 1.5 to 2.0 or 2.5 per cent of the alloy. The amount of gra phitizing element which is used will depend upon the particular element concerned. as will appear 1 more particularly hereinafter. a

Various graphitizing agents maybe used in the practiceof the .invention. These include sili-v 50 con, molybdenum, nickel, aluminum, and their equivalents, all of which may be used in the practice of the invention. They may be used I singly or in combination, although as will appear presently it is usually desirable to use silicon with one or more of the other agents referred to, especially with nickel and molybdenum.

Having reference first to the use of silicon as a graphitizing element, its content is governed by the carbon content. With carbon within the preferred range of about 1.5 to 2.0 or 2.5 per cent it is, in general, preferred to use from about 0.6 to 0.9 per cent of silicon, this element being proportioned with regard to the carbon to effect the conditions stated hereinabove. A simple embodiment, and an advantageous one, is a plain 'carbon steel containing about 1.7 per cent of carbon and about 0.75 per cent of silicon.

In simple steels a too high content of silicon tends to exert its known graphitizing effect, 1. e.,

forming graphitic carbon in the ingot, which may be raised above normal to exert its known effect upon silicon. Thus, with carbon from 1.5 to 2.0 per cent, as much as 1.3 per cent of silicon may be used safely by=increasing the manganese to about 1 per cent. Such a steel may be hot worked satisfactorily :and subsequent graphitization caused, in accordance with the invention. I

Particularly satisfactory results are obtained by soaking the ingots at a temperature not less than about 1800 F. Also, it is important that in reheating the temperature should not exceed about 1975 F. These factors assist in obtaining an ingot in which the carbon is essentially in the combined form, for most satisfactory rolling. The ingot is then hot worked to form articles of desired shape, for example, by rolling or forging to produce plate, sheet, tubes, rod,-bar, orv other forms. Thereafter the article is heat treated at a temperature above its critical point to cause graphitization, for example,"at 1400 F. or above in the case of the plain carbon-silicon steels referred to.

Precipitation of graphitic carbontakes place rapidly, which is a substantial advantage as compared with prior graphitizing procedures, in which graphitizing required long periods of time.

' It appears, in fact, that the extent of graphitization is in general independent of the period of heating, and that, once the article has been brought uniformly to temperature, prolonged heating does not induce any further material graphitization. For. example, pieces of 7 inch round rod formed from an alloy containing 1.52 per cent of carbon, 0.88-per cent of silicon, 0.38 per cent of manganese, and 0.015 percent each of phosphorus and sulfur were heated at 1800 F., and samples-were withdrawn from the furnace after varying periods of time and were. air-, cooled. The sample heated 1 hour showed upon analysis 0.18 per cent of combined carbon, while the sample heated 6 hours had a combined car bon content of 0.16 per cent. The difference in combined carbon content ofthetwo samples is well within the limits of experimental error.

Other samples withdrawn at hourly intervals between those referred to showed substantially similar combined carbon contents. In another test, rod of the same size formed from an alloy containing 1.61 per cent of carbon, 1.06 per cent of silicon, 0.4 per cent of manganese, 0.015 per cent of phosphorus, and 0.014 per cent. of sulfur was heated at 1400 F., and samples were withdrawn and air-cooled as before, at intervals of from 15 minutes up to 4 hours. The sample heated 15 minutes had a combined carbon content of'0.6 per cent, while after 4 hours heating the combined carbon content was but 0.63 per cent. In both instances specimens withdrawn at intermediate times had combined carbon contents similar to those stated, within experimental error.

The foregoing tests are indicative of the rapidity with which the desired result may be obtained. Prolonged heat treatments for the obtaining of graphitization are thus rendered unnecessary. They are indicative of a'further important aspect of the invention, namely the ability to control the result. Thus, the heat treatment at 1800 F. produced much more profound graphitizing than at 1400 F. In this manner,'by suitably selecting the graphitizing temperature, the extent of graphitization and the resultant physical and mechanical properties may be controlled to produce a desired result, since the properties are primarily dependent upon the amounts of combined and graphitic carbon. Furthermore, the properties may be varied, both mechanically, and in regard to the content of g'raphitic carbon, according to whether the articleis furnace cooled or air cooled, i. e., normalized. Thus the inventionprovides for attainment of a wide variety TABLE I Steel A P0.015% S0.014%. Hot rolled to round rod.

Hardness Brinell Combined carbon e e t Treatment p r c n "F.

Fun cool Air cool Fur. cool Air cool The foregoing tests indicate how the mechanical properties may be varied, for the strength, ductility, and related properties change with the Brinell hardness, as known to the skilled in the art. It will be observed also that in each instance the benefits of the invention due to graphitic carbon are also obtained, the different treatments having graphitized from about 60 to about 90 per cent of the total carbon.

The following tests show, how manganese maintains the conditions necessary to the invention when silicon is used in excessive amount. Steel I round bar at a temperature not exceeding about 1950 F. The working operations proceeded satisfactorily. Specimens were then heated and furnace cooled, the results being shown in Table TABLE II .Steel B Strengtlilbs/sq.

Comb.C Elong. Hardness Heated at in 2" 111111011 Yield Ultimate d 'tion weld satisfactorily, and investigationhas shown that the heat conductivity of articles of the type just referred to is distinctly lower than that of many other steels, while the modulus of elasticity in the normalized state compares favorably with ordinary'steels and in the annealed (furnace cooled) condition is distinctly greater than those of ,cast irons.

As indicated hereinabove, the properties of the resultant article may be varied according to the manner in which it is heat treated. With plain carbon steels the structure consists generally of pearlite and graphite, the proportion of the former diminishing, with increase-in the proportionof free ferrite, as graphitization is more and more complete, and this may be controlled according to whether the articles are furnace cooled or air cooled, as indicated. Moreover, a graphitizaticn'treatment consisting of normalizing at 1700" F. is productive of a structure approaching the eutectoid composition, the balance of the carbon being in the-graphitic state, whereby me-- chanical properties characteristic of the eutectoid steels are obtained- The presence of graphite in the structure is desired in most instances, particularly for the production of moving parts, because the graphitic carbon confers valuable lubricating properties. In general, tempering at temperatures up to 1200" F. does not materially alter the graphitic carbon content, although such treatments may be applied advantageously to relieve rolling strains, and for analogous purposes. However, the properties of the articlesmay be further modified to confer necessary mechanical characteristics by heat treatment for the purpose of causing a desired part of the carbon to be returned to the combined form. In this manner thearticles may be hardened for the production of desired mechanical characteristics, thus further widening the-range of applicability of the invention.

The benefits to be derived from such heat treatment of the graphitized articles provided by the invention is well exemplified by the selective hardening of valve tappets. The bearing surfaces of such tappets must be capable of withstanding wear, and one of the present favoredmodes of combatting wear is to form the tappets from gray cast iron with the crown chilled to a hardness of about 48 on the'Rockwell Cf scale.

Tappets were formed from hot rolled 1 inch rods of steel A, thecomposition of which-is given in Table I. After graphitizing the tappets contained 0.76 per cent of graphitic carbon. .The

crowns were then surface heated with an oxyacet ylene flame to rapidly bring the surface layer up to temperature, and they were thenimmediately quenched in water. In this manner the heating Articles produced in accordance with the invenwas local. Crowns heated to approximately 1500 F. and quenched were file hard and showed a Rockwell "0 hardness of 62 to 64. Micrographic examination revealed the wearing surface to be of martensitic character with free graphite preshigher temperatures gave somewhat lower hardness values, although even when heattreated at ent in appreciable amount. 'Treatments at 1800 F. the crown was at least as hard as that of the; cast iron tappets-referred to.

The advantages of such treatment appear from the results. Not only is great hardness obtained, with concomitant desirable properties,.but also the desirable lubricating properties of graphite are realized. As applied tolocalized hardening this further provides the body of the element with the necessary mechanicalproperties for a particular use. .Of course, where it is desirable that the entire article be'hardened that may be done also, and it will be understood that the character of hardening can be varied by the temperature of heat treatment and mode of quenching.

Other graphitlzing elements than silicon may also be used in the practice of the invention, either alone or in co'mbination, as with silicon, and some of them are productive of especially beneficial results.

found to be a particularly powerful and especially advantageous graphitizing agent. This is con trary to expectation because molybdenum is reputed to be a carbide-forming element, and carbide formation defeats graphitization. It has a' tremendous graphitizing power, lowering the graphitizing temperature belowthat needed with silicon alone to produce a given result, and it renders possible graphitization of substantially the entire carbon content, 1. e.', by reducing the combined carbon practically to zero. Particularly is this true of alloys containing silicon with- Thu's, molybdenum, contrary 'to what would have been expected, has been in the preferred rangestated above and from.

about 0.2 to 0.5 per cent of molybdenum.

This aspect of the invention may be seen by consideration of the test lowing tables.

' Composition, see Table I.

Nickel is also a valuable element in the alloys contemplated by this invention. It acts particu-' larly as a graphite refiner, causingthe graphite results given in the fol- 1 to assume the form of small particles instead'of the elongate form which is characteristic of silicon when used alone. Nickelis an especially desirable alloying element I in combination with molybdenum, because of its nodulizing effect upon the graphite and because 'it increases the strength v of the alloys. It may be used in any desired amount, although from 0.75 to 2.0 per cent suf-v fices for many purposes. The combination or nickel and molybdenum' provides alloys having relatively low graphitizing temperatures, which roll very easily and produce substantially no a graphite during the rolling, and which, as indicated, may be substantially entirely graphitized upon appropriate heat treatment. These characteristics may be seen readily from the following tabulations.

1" round bars.

Strength lbs/sq. in. Treatment Comb. Elong. Hardness "F. G in 2 Brinell Yield Ultimate 1500 fur. cool 0. 30 48, 000 90,000 18.7 187 1600 iur. cool- 0. 03 4.4, 000 60, 000 27. 5 137 1700 11.11. 0001. 0.03 41, 750 62, 750 27. 5 137 1800 iur. cooL 0.07 41, 500 65,000 25. 0 143 1500 air c0011.. 0. 73 104, 500 107, 000 12.5 336 1600 air cool... 0. 79 114, 500 9. 0 363 1700 air e001... 0. 76 97,000 174, 000 10.0 303 1800 air 0001- 0. 74 98, 500 174, 000 8.0 341 The mechanical properties of these steels may be advantageously improved by heat treatment, as shown by the following table representing results obtained by heat treatment of specimens at 1550 F. followed by tempering at the temperatures shown.

TABLE V Composition, Table IV, hot worked 1" round bars.

The values given in the'foregoing table show that substantial amounts of carbon remain in the graphitic form, with attendant advantages, while unusually desirable mechanical properties are concurrently obtained.

. Aluminum is another graphitizing agent which is so powerful that it may be used instead of silicon. This element may be used in an amount from about 0.5 to 6 per cent or more, for example, up to 15 per cent. It also is capable-of reducing the content of combined carbon substantially to zero, and it acts also to nodulize the graphite in a manner similar to nickel. In general the properties of these aluminum steels treated according to the invention are equivalent to those of the nickel-molybdenum alloys referred to hereinabove.

The above-explained characteristic rapidity with which graphitization takes place in the practice of this invention-may be further illustrated by tests or inch round rod hot rolled from an alloy containing 1.74 per cent of car bon, 2.24 per cent of aluminum, 0.14 per cent of silicon, 0.015 per cent of phosphorus, and 0.012 per" cent of sulfur. Samples of the rod were heated at 1800 F. and air-cooled. After heating 1 hour the graphitic carbon was reduced to 0.15 per cent, while 6 hours heating reduced it to only 0.14 per cent, showing that long graphitizin'g heat treatment is unnecessary. v

The alloys used in the practice of the invention may also contain other alloying elements used for' special purposes, due regard being had to the 'u necessity for having thecarbon in the combined form during hot working and for the ability to graphitize it in the formed article. For instance, chromium'may be used for its known purposes. Chromium is not a graphitizing element, and actually it tends to stabilize the carbides. That is, it is a powerful agent in preventing graphitization. However, by sufficiently increasing the silicon, or other graphitizing agent, it may advantageously be added to alloys for producing particular mechanical properties, and particularly to provide suitable lubricating properties, due to the graphitic carbon, combined with resistance to wear and abrasion provided by the double carbides characteristic of chromium in ferrous alloys. 1

Chromium and other alloying elements which are added for special purposes but which do not induce graphitization thus do not play any part in the essential phenomena underlying the invention. For this reason the balance of the steels, apart from carbon and graphitizing element, may be considered to be effectively iron, and it is so referred to in the appended claims.

The variations in properties obtainable in the practice of the invention will suggest various uses for the articles. The valuable combination of lubricating properties and resistance to wear and abrasion obtainable with my steels containing chromium has been alluded to. The plain'silicon and nickel steels present pearlitic structures containing excess graphite, and this combination is desirable for use as brake drums, clutch plates, and similar purposes. I

The profound graphitization effected by agents such as molybdenum, or molybdenum-nickel, also opens an interesting field. of applicability. For instance, graphitization being complete, or substantially so, the structures comprise chiefly ferrite and graphite, and thusthey approach wrought iron in nature, with its corrosion resisting and other valuable properties.

As indicated hereinabove, the invention is applicable to the production of articles by hot working, e. g., rolling or forging, and of substantially any desired form, such as tube, bar, plate, etc., for production of any desired-shape. If piston rings, for example, are to be made, the ingot is heated and rolled to rods. The rods are heated to a temperature of about 1650 F. for about two while retaining the full benefits of the invention.

Shafts, valve moving parts, and other moving parts may be formed similarly. In the case of such parts a substantial proportion 'of the total carbon, and in some cases practically all of it, is

converted to graphitic carbon, which acts as a lubricant and increases machinability.

. My invention has the advantage-that articles in which the presence oi a substantial amount of graphitic carbon is desired can be made by fabricating the articles from a high carbon steel ingot,

, and thereafter heat-treating the articles so as to produce the desired amountof graphitic carbon.

Articles can be produced in accordance with the pres ant invention having high ultimate tensile strengths andhigh elongation, as shown by the foregoing test results, both the tensile strength atom-764 oil, water, other liquids or air.

-sider to represent its best embodiment.

According to the provisions of the patent statutes, I have explained the principle of my invention and have described what I now con- However, I desire to have it understood that, within the scope of the appended claims, the inventionv may be practiced otherwise than as specifically described.

I claim:

1. The method of making ferrous articles comprising'forming an article by hot working an in got of steel containing not less than about 1.5 per cent of carbonand also containing a graphitizing element such as silicon, and the remainder of the steel being effectively iron, the carbon and said graphitizing element contents being so proportioned to each other that during hot working the carbon is substantially all in combined form but such that graphitic carbon may be precipitatedrapidly upon annealing, and heating the article at a temperature above its critical temperature to convert a substantial proportion of its carbon content to the graphitic state.

2. The method of making ferrous articles comprising forming an article by hot working an ingot of high carbon steel containing from about 1.5 to 2.0 per cent of carbon, and containing a graphitizing element such as silicon in an amount proportioned to the carbon so that during hot working the carbon is substantially all in combined form but such that graphitic carbon may be precipitated rapidly upon annealing, and the remainder of the steel being effectively iron, and heating the article at a temperature above its critical temperature to convert a substantial proportion of its carbon content to the graphitic state.

3. The method -of making ferrous articles, which comprises forming an article by hot working a high carbon steel ingot containing carbon about 1.50 per cent to 2.0 per cent, silicon about .60 per cent to .90 per cent, and the remainder of the steel being effectively iron, the carbon being in the combined state during hot working, and heating the article at a temperature above its critical temperature to convert a substantial amount of carbon to the'graphitic state.

4. The method of making ferrous articles, which comprises forming an article by hot working a high carbon steel ingot containing about 1.7 per cent carbon, about .75 per cent silicon," and the remainder of the steel being effectively iron, the carbon being in thecombined state during hot working, and heating the article at a temperature above its critical ,temperature .to convert a substantial amount of carbon to the graphitic state.

5. The method of making ferrous articles, which comprises forming an article by hot working a high carbon steel ingot containing carbon about 1.50 per cent to 2 per cent, silicon about .60 per cent to .90 per cent, andthe remainder of the steel being efl'ectively' iron-the carbonv being in the combined'state during hot working, and heating the article above its critical temperature for a time suflicient toproduce about .25 per cent to 1.50 per cent graphitic carbon.

6. A hot-worked article formed of aferrous alloy containing carbon about 1.50 per centto 2.0 per cent, and silicon about .60 per cent to .90 per cent, a substantial amount of the carbon being in the graphitic state.

' 7. A hot-worked" article formed of a ferrous alloy containing about 1.70 per cent carbon and about .75 per cent silicon, a substantial amountv of the carbon being in the graphitic state.

8. A hot-worked article formed of a ferrous alloy containing about 1.70 per cent total carbon and about .75 per cent .silicon, about .25 per cent to 1.50 per cent carbon being in the graphitic state.

9. An internal combustion engine part for use at high temperature while in sliding or rotational engagement with another part, said engine part being formed of a hot-worked high carbon steel containing about 1.50 per cent to 2 per cent carban and about .60 per cent "to .90 per cent silicon, a substantial amount of the carbon being in the graphitic state.

10. An internal combustion engine part for use at high temperature while in sliding or rotational engagement with another part, said engine part comprising forming an article by hot working aningot of an iron-carbon alloy containing not less than about 1.5 per-cent of carbon and also containing a graphitizing element, such as silicon, and the remainder of the alloy being effectively iron, the carbon and said graphitizing element contentsbeing so proportioned to each other that during hot working the carbon is substantially all in combined form but such that graphitic carbon may be precipitated rapidly upon annealing, and heating the article at a temperature above its critical temperature to convert a substantial proportion of, its carbon content to the graphitic state.

13. The method of making ferrous articles comprising forming an article by hot working an ingot of an iron-carbon alloy containing from about 1.5 to 2 per cent of carbon and also containing a graphitizing element, such as silicon,

and the remainder of the alloy being efiectiv'ely iron, the carbon 'and said graphitizingelement contents being so proportioned to each other that during hot working the carbon is substan' tially all in combined form but such that gra phitic carbon may be precipitated rapidly upon annealing, and heating the article at a temperature above its critical temperature to convert a substantial proportion of its carbon content to the graphitic state.

14. The method of making ferrous articles comprising forming an article by hot working an ingot of an iron-carbon alloy containing from about 1.5 to 2 per cent of carbon'and also containing a graphitizing element, such as silicon, and the remainder of the alloy being effectively .iron, the carbon and said graphitizing element contents being so proportioned to each other that during-hot working the carbon is substantially all in combined form but such that graphitic carbon may be precipitated rapidly upon annealing, heating the articleat a temperature above its critical. temperature to convert a substantial proportion of its carbon content to the graphitic state, and thereafter heat treating th said article.

15. A hot worked and subsequently annealed article of manufacture, the article being formed from an iron-carbon alloy containing not less than about 1.5 per cent of carbon, a graphitizing element, such as silicon, so proportioned to the carbon that during thehot working of the alloy the carbon was substantially all in combined form and a substantial pro-portion of which is in graphitic form as a consequence of the annealing of the article, the remainder of the alloy being eifectively iron.

16. A hot worked and subsequently annealed articleof manufacture, the article being formed from an iron-carbon alloy containing from about 1.5 to 2 per cent of carbon, a graphitizing element, such as silicon, so proportioned to the carbon that during the hot working of the alloy the carbon was substantially all in combined form and a substantial proportion of which is in graphitic form 'as a consequence of the annealing ofthe article, the remainder of the alloy being effectively iron.

1'7. A hot worked and subsequently annealed and heat treated article of manufacture, the article being formed from an iron-carbon alloy containing from about 1.5 to 2 per cent of carbon, a graphitizing element such as silicon, so proportioned to the carbon that during the hot working of the alloy the carbon was substantially all in combined form and a substantial proportion of which is in graphitic form as a consequence of the annealing of the article, the remainder of the alloy being effectively iron.

18. An internal combustion engine part for use at high temperature while in sliding or rotational engagement with another part, said engine part being formed from a graphitizable hot worked iron-carbon alloy containing a graphitizing agent and not less than about 1.5 percent of carbon, a substantial amount of the carbon being in the graphitic state.

19. The method which comprises hot working a graphitizable ferrous base alloy containing a graphitizing agent and more than about 1.5 per cent of carbon.

20. As a new article of manufacture, a hot worked graphitizable ferrous base alloy containing a graphitizing agent and more than about 1.5 per cent of carbon.

21. The method which comprises hot working a ferrous base alloy containing more than 1.5 per cent of carbon, and containing a graphitizing agent in an amount adapted to permit gra phitization of the formed article, and heating the article to a temperature adapted to convert a substantial proportion of the carbon to the graphitic state.

22. A hot Worked article formed ofa ferrous base alloy containing more than 1.5 per cent of carbon, and a graphitizing agent in an amount adapted to permit graphitization of the article, a substantial amount of the carbon having been converted to the graphitic state.

23. That. method which comprises hot working a ferrous base alloy containing more than about 1.5 per cent of carbon, and containing a graphi- 'working the carbon is substantially all in the .combined state but such that graphitic carbon may be'precipitated upon annealing, heating the article to convert a substantial proportion of the carbon to thegraphitic state, and then heating at a temperature to re-dissolve carbon.

25. A hot worked and heat treated article formed from a graphitizable ferrous base alloy containing a graphitizing agentand more than about 1.5 per cent of carbon, the article having been heated to cause precipitation of a substantial proportion of graphitic carbon, and further heated to re-dissolve carbon.

FREDERICK R. BONTE.