US3825416A

US3825416A - Self-lubricating iron base alloy

Info

Publication number: US3825416A
Application number: US00270398A
Authority: US
Inventors: Y Mizutani; K Tozawa
Original assignee: Toyota Central R&D Labs Inc
Current assignee: Toyota Central R&D Labs Inc
Priority date: 1971-07-09
Filing date: 1972-07-10
Publication date: 1974-07-23
Anticipated expiration: 1991-07-23
Also published as: GB1388194A; DE2233487B2; DE2233487A1; JPS5130529B1

Abstract

TO % OF EITHER SULPHUR OR SELENIUM, THE BALANCE BEING ESSENTIALLY IRON, AND ALL CONTENTS BEING IN WEIGHT PERCENT. THE ALLOY IS ABRASION RESISTANT AND CAN BE USED OVER A WIDE RANGE OF TEMPERATURES.
A SELF-LUBRICATING IRON BASE ALLOY CONTAINS A TOTAL OF FROM 5 TO 30% OF ONE OR MORE METALS SELECTED FROM THE GROUP GROUP CONSISTING OF TI, ZR, V, NB, TA, MO AND W, AND 0.5

D R A W I N G

Description

United States Patent US. Cl. 3 Claims AB TRAC OF THE DISCLOSURE .A self-lubricating iron base alloy contains a total of from 5 to 30% of one or more-metals selected from the group consisting of Ti, Zr, V, Nb, Ta, Mo and W, and 0.5 to 5% of either su1phur-or selenium, the balance being essentially iron, and all contents being in weight percent. The alloy is abrasion resistant and can be used over a wide range of temperatures.

BACKGR OF'TI-IE INvENTIoN Compounds of sulphur or selenium with a metal selected from-Group IVa, Va and VIa of the periodic table are known to be excellent lubricants. Examples are TiS Tlsez, ZI'SZ, ZI'SBZ, VS, VSe, NbS2, Nbsez, T2152, Tase M08 MoSe WS and WSe These compounds have proved to beexcellent solid' lubricants in the following forms: a

1. a coating applied on the surface of a material to be subjected to friction,

2. a composite material in which the sulphide or selenide is bonded in the form. of a layer on a base metal using an adhesive such as an organic resin, and

3. a solution-in a lubricant which serves as a solvent.

The compounds listed when-used as described above suffer-from the..followingdrawbacks, the drawbacks beinglisted in the same order as above:

1. A coating tends to flake or peel from a base metal so that the lubrication characteristic decreases with Wear.

2. When incorporated in a resin, the maximum temperature to which the composition can be raised without damage to the lubrication property is that which the resin will tolerate. As is well known, very few resins can be usedat temperatures above about 150 C.

3. Segregation of the selenide'or sulphide in the liquid is likely to-occur, as a result of which the lubricating compound is not uniformly distributed at the frictional interface, so that severe wear of the metal which it is desired to protect may occur,

SUMMARY OF THE INVENT ON An iron-based alloy contains a total of 5 to 30% by weight of at least one of the metals, Ti, Zr, V, Nb, Ta, Mo and W and from 0.5 to 5% by weight of sulphur or selenium. The sulphur or selenium is preferably added in the form of iron sulphide or iron selenide to a melt containing iron and at least one of the metals listed above.

The alloys prepared in this way are themselves lubricants; consequently, they introduce no danger of flaking or peeling or degradation when used at elevated temperature. Moreover, the subject alloys retain their uniform lubricating characteristics even when worn.

Accordingly, an object of the present invention is to provide an improved iron-based alloy possessing inherent lubricating characteristics.

Another object of the present invention is to provide an improved iron-based alloy which retains its lubricating characteristics over a wide temperature range.

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A further object of the present invention is to provide an improved iron-based alloy which retains its lubricating characteristics even after subjection to severe wear.

Still another object of the present invention is to provide an improved iron-based alloy having a uniform lubricating characteristic over its entire surface.

Yet another object of the present invention is to provide an improved method for preparing an alloy having a high lubricating characteristic which is effective over a wide temperature range and which is retained even when a bearing or other piece made of the alloy is worn.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the composition possessin the features, properties, and the relation of constituents, which are exemplified in the following detailed disclosure, and

the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF DRAWINGS For a fuller understanding of the invention, reference is' had to the following description taken in connection with the accompanying drawings, in which:

FIGS. 1 through 6 are graphs showing the coefficient .of friction of iron-based alloys in accordance with the present invention as a function of metallic additive concentration. The alloys of FIGS. 1 through 5 contain sulphur while the alloy of FIG. 6 contains selenium.

DESCRIPTION or THE PREFERRED EMBODIMENTS Alloys in accordance with the present invention are prepared by melting iron, preferably electrolytic iron, in

a crucible, adding a non-ferrous metal, designated as,

at a speed of 7.9 m./sec. and a pressure of 3 kg./cm.

The metal against which the specimens were pressed was hardened 0.5% carbon steel. Table 1 gives the content of non-ferrous metal (X) and S or Se, iron constituting the remainder of the alloy. In the last column, the

coefficient of friction is listed.

TABLE 1 Composition, percent Example Frictional of alloy coeflicient Alloy FeX+S alloy Sor Se V:7+Mo:7

Fe-X-Se alloy 9 Taz2-10 11 WIS-IO The above data show that the coetficient of friction decreases with increase in the amount of non-ferrous metal in the alloy. These data are further illustrated in FIGS. 1 through 6.

TABLE 2 Alloy example number (from Table 1) NOTE-The coefficient before the third element in each alloy gives the percentage of the element.

In the Figures, the open circles designate the coefficient of friction of the alloys as cast, and the closed circles indicate the coefficient of friction of the alloys after having been annealed for 2 hours at 900 C. subsequent to casting. In FIG. 4, the broken line running through the triangles designates the amount of molybdenumsulphide compound (MoS in the alloy, the amount being measured by X-ray diffraction and shown on an arbitrary scale.

As is apparent from Table l and from the Figures, the coefiicient of friction of an alloy decreases with increase in the amount of metal (X). The coefficient of friction decreases sharply to about 0.3 as the non-ferrous metal content increases to about As the non-ferrous metal content is increased further, the coefficient of friction decreases to an essentially constant value of about 0.2. It should be recognized that a value of 0.2 is sufficiently low for most purposes. As an indication of the improvement resulting from the incorporation of sulphur or selenium, the alloys consisting of 85% iron-% vanadium and 97.5% iron, 2.5% molybdenum seized immediately after the beginning of friction tests.

It is evident from FIG. 4 that the coefiicient of friction decreases as the content of molybdenum sulphide increases. The value of x in (MoS was found to be about 2 according to X-ray diffraction and EPMA analysis. From this Figure, it follows that the sharp decrease in the coefficient of friction is achieved by incorporating greater amounts of non-ferrous metal and sulphur or selenium. There is no point in increasing the non-ferrous metal content beyond 30% because the coefficient of friction approaches a constant value when the content (X) is from 15 to Moreover, when the content of non-ferrous metal is increased beyond 30% increased brittleness and poor machinability result. Also, the cost of the alloy increases. As to the lower limit of nonferrous metal content, quantities below 5% do not give sufficient decrease in the coefficient of friction for most purposes. The most desirable range for the non-ferrous metal content is from 10 to 20% from the viewpoint of low coefficient of friction, machinability, work absorption, and cost.

Y The quantity of sulphur or selenium to be incorporated in an alloy should be commensurate with the quantity of non-ferrous metal since the lowering of the coefficient of friction appears to be due to the formation of a nonferrous metal-sulphur compound.- Where the non-ferrous metal content ranges from 5 to 30%, the quantity of sulphur or selenium should be inthe range'from- 0.5 to 5%. Where the quantity of non-ferrous metal is 10 to 20%, the amount of" sulphur or selenium, should be 1 to 3%. Sulphur or selenium contents below 0.5% give no appreciable improvement in coefficient of friction while if the quantity of sulphur or selenium exceeds 5%, an ironsulphur compound will be formed in quantity such as to cause red shortness of the alloy. 7

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficientlyattained and, since certain changes may be made in carrying out the above method and in the composition set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shownin the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention hereindescribed,.,and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed is: Y

1. A self-lubricating iron-base alloy consisting essen-. tially of a least one non-ferrous metal selected from the, group consisting of Ti, Zr, V, Nb, Ta, Mo and W, the quantity of non-ferrous metal lying between 5 and 30% by weight, and 0.5 to 5% by weight of an element selected from the group consisting of S and Se, the balance .being iron. e

2. The alloy as defined in claim 1, wherein said iron is electrolytic iron.

3. A self-lubricating iron-base alloy consisting essentially of at least one non-ferrous metal selected from the group consisting of Ti, Zr, V, Nb, Ta, Moand W, the quantity of non-ferrous metal lying between 10 and 20% by weight, and from 1% to 3% by weight of an element selected from the group consisting of S and Se, the balance being iron. 1

References Cited 7 4 UNITED'STATES PATENTS 2,009,713 7/1935, Palmer 123 AA 2,162,596 6/1939 Wyman 7s 123 1 s. c1. X.R;"" 75-123 G, 126 L, 126 M