US3321338A - Friction elements especially resistant to wear by abrasion - Google Patents

Description

United States Patent 3,321,338 FRICTION ELEMENTS ESPECIALLY RESISTANT TO WEAR BY ABRASION Jacques Caubet, Saint-Etienne, France, assignor to Automobiles M. Berliet, Lyon, France, and Hydromecanique et Frottement, Saint-Etienne, France, both French corporations No Drawing. Filed Dec. 10, 1964, Ser. No. 417,495 Claims priority, application France, Dec. 11, 1963, 956,874, Patent 1,386,446; Feb. 27, 1964, 965,390, Patent 85,297; Feb. 28, 1964, 965,616, Patent 85,370; June 22, 1964, 979,152, Patent 85,994; June 23, 1964, 979,316, Patent 86,012

7 Claims. (Cl. 14811.5)

For a long time past, efforts have been made to produce friction elements, the rate of wear of which would remain low with no or very doubtful lubrication, and in the presence of abrasive grains. This preoccupation has been common to numerous industries which have found themselves facing the problems presented, for example, by the wear of parts such as gears and bearings working in the atmosphere of cement works, the oscillation shafts of springs on railway rolling stock, the oscillation shafts of the suspension of road vehicles or of public works machines, mining equipment, amongst others.

The properties of resistance to Wear of hypereutectoid steels containing at least 12% of manganese, commonly known as Hadfield steels have been known for a very long time. At the present time, these steels are generally employed in the condition of super-temper, that is to say with a stable austenitic structure and then, under the effect of the forces due to friction, to abrasion or to shocks, the superficial austenite becomes converted to a kind of very hard martensite which has a remarkable resistance to wear.

However, this method of utilization is subject to two conditions which limit its use. On the one hand, the initial forces must exceed a certain threshold below which the cold-hammering does not take place, and on the other hand, an initial wear must be permitted which is generally very considerable during the period of time necessary for the formation of the cold-hammered layer. An example of the first disadvantage is given by the balls of ball-mills, which have a good resistance in cement ball-mills, but remain austenitic and Wear rapidly in plaster mills.

The second disadvantage makes it impossible to utilize Hadfield steels for parts, the precise initial dimensions of which must be preserved as far as possible.

Similar phenomena are observed on austenitic stainless steels, such as for example the common stainless steels comprising substantial proportions of addition elements such as chromium and nickel, and on the hypereutectoid alloy steels containing by weight 11 to 14% of magnanese, l to 1.3% of carbon, not more than 0.6% of silicon, impurities in the usual proportions, the remainder being constituted by iron.

Finally, as regards hardening, titanium and its alloys exhibit similar properties together with the drawbacks which result from them.

All the metals and alloys enumerated above have the common property of hardening by cold-hammering, subsequently showing a great density of planes of slip in their superficial crystalline structure.

Starting from a metallic material having the above properties, the object of the present invention is to obtain parts which present immediately, as soon as they are put to use, a good resistance to seizure and to wear.

According to the invention, parts made of a metallic material capable of hardening by cold-hammering or coldrolling and having in its superficial crystalline structure a high density of plane of slip, to a deep cold-hammer- 3,321,338 Patented May 23, 1967 ing carried out in such manner that it produces on the surface of the parts striations which are substantially perpendicular to the direction of application of the friction. After the cold-hammering or cold-rolling operation, there is effected a superficial incorporation of at least one element chosen from the groups of metalloids and transition metals, metalloids and transition metals possessing one of two properties, one of which consists of the capacity to deposit on the surface of the parts an ionic compound produced by reaction with the underlying metal, while the other has the capacity of inserting its atoms in the structure of the underlying metal, forming a solid insertion solution. This incorporation is obtained by means of at least one thermal treatment effected in a fluid, such as a salt bath or a gaseous atmosphere, which contains the element to be incorporated.

The cold-hammering can be carried out either by knurling or by hammering. In the case of knurling, which is preferably used when the parts to be cold-hammered are flat or round surfaces, the rollers must be cut so that the striations which they impress by forging on the surface of the part are arranged in a direction substantially perpendicular to the direction of application of the friction. In the case where the parts to be cold-hardened are neither flat nor round, it is preferable to employ a hammer with a striated striking face.

There will be employed with advantage as an approximate minimum cold-hardening load on a roller a diameter 20 mm. and a length of 10 mm., a load substantially equal in kilopond (9.81 Newton) to the elastic limit of the material to be cold-hardened, in kp./ sq. mm. For the approximate maximum charge, there will preferably be chosen that which, taking account of the geometric form of the part to be cold-hardened and assuming the roller to be smooth, gives hertzian pressures equal to three times the elastic limit of the material.

The thermal treatment or treatments are carried out in such manner that there is obtained a superficial incorporation of one or of two metalloids, or of a transition metal capable either of depositing on the surface of the part an ionic compound by reaction with the underlying metal, or of inserting its atoms into the" structure of the underlying metal while forming a solid insertion solution. These transition metals or these metalloids may be, for example, nitrogen, sulphur, selenium, 'telluriu-m, amongst others.

The introduction of a metalloid or of a transition metal as defined above, into the cold-hardened layer is obtained by a heat treatment of the knurled part in a salt bath or in gaseous atmosphere for a period of time anywhere from one hour to as long as six hours at a temperature between 400 C. and 590 C.

For the superficial incorporation of sulphur, the coldhardened part is treated with a bath of sulphur salts or a gaseous sulphur atmosphere for a period of time of at least two hours and at a temperature higher than 500 C.

A treatment of this kind can for example be ap lied by means of a process known in France under the commercial name of Sulfinuz. However, all the identical or similar processes using salt baths or a gaseous medium producing superficial structure layers of compositions similar or identical with those which are obtained by the Sulfinuz process may be employed. 3

In the case of the Sulfinuz process, the parts are preheated to about 300 to 350 C. and are then immersed for a period of 2 to 6 hours in a salt bath maintained at an approximate temperature of 570 C. and are composed of an inactive base such as the alkali and alkaline earth chlorides and carbonates, permitting a melting point to be obtained of less than 500 C. of sulphur compounds, the action of which is preponderant and buffer cyanides or cyanates which protect the sulphur compounds by keeping the bath in a reducing medium. In certain particular cases, the treatment temperature in salt baths or in a gaseous atmosphere may, depending on the composition of the bath, for example when it contains a sulphide and a ferro-cy-anide, be less than 570 C., the sulphuretting action being then capable of taking place from 400 C.

The approximate composition of a Sulfinuz bath is given below by way .of example:

7 Percent Sulphide 0.5 Alkaline cyanides 8 Alkaline cyanates 27 Alkaline chlorides 33 Alkaline carbonates 31.5

As regards ferrous alloys, the incorporation of nitrogen can be effected by means of any nitriding process which is effective below a maximum temperature of 580 C., beyond which temperature the decomposition of the austenite is too great and introduces excessive brittleness.

According to the invention, it is also possible to make use of the process known by the commercial name of Tenifer or of all identical or similar processes using salt baths or gaseous media producing superfiicial layers of structures and of compositions similar or identical to those which are obtained by the Tenifer process.

The latter, also known in the anglo-saxon countries by the name of Tufftride is a process of mild nitridation which makes it possible to obtain on the steel parts, an outer layer comprising iron carbide and iron nitride covering a ditfusionlayer of nitrogen in the steel. This result can be obtained for example by immersing the part for a sufficient pre-determined period, for example for two hours, in a salt bath heated to a temperature comprised between 550 and 580 C., for erample 565 C., comprising about 32 to 35% of alkali cyanates, for example 45 of potassium cyanate, and 50 to 55% approx. of alkali cyanides, for example 55 of potassium cyanide, the bath being stirred by blowing-in air.

The results obtained are substantially identical with those which are recorded after a sulphurizing treatment, such as the Sulfinuz process.

Furthermore, and again in accordance with the invention, the cold-hardened parts can advantageously be successively subjected to a nitridation such as the Tenifer treatment and then to a sulphurizing treatment, for example according to the Sulfinuz process.

Various possibilities of the application of the method according to the invention will be brought out from the following examples:

Example 1 A shaft and rings of 15 40 mm. were machined from a steel in the super-tempered state containing, by weight, 1.2% of carbon and 14.5% of manganese. Immediately after the lathe operation, the bearing surfaces of the shaft and the corresponding surfaces of the rings were knurled with a tool which pressed two rollers of 20 mm. against the parts with a force of 400 kg., giving two families of striations of 0.15 mm. in depth and 1 mm. apart, respectively inclined by -15 to the direction of the gen erator lines.

The knurled wheels made 14 to-and-fro passages under these conditions.

As the knurling operation causes a slight swelling of about 0.05 mm., the part is easily brought back to its initial dimension by a light polishing with emery cloth.

The parts, shaft and rings, cold-hardened in this way, have in section under metallographic examination, extremely dense networks of lines of shear, this is to say having for example four lines of shear per square of 0.01 mm. sides, and penetrating to a depth of more than 0.3 mm. The micro-hardness indicates that in the zone of shear, the initial hardness of 70 kg./sq. mm. has increased to 190 kg./sq. mm., the hardness of the core not being modified.

The parts were then immersed for 3 hours in a sulphurizing and cyaniding bath of the Sulfinuz type at a temperature of 585 i-S C. After this treatment, a first examination of metallography and micro-hardness shows that the core-hardness has passed from 70 to 125 kg./ sq. mm., this increase being due to the conventional decomposition of the austenite and the precipitation of the carbides of iron and manganese. In the superficial zone of the lines of shear obtained by knurling, the hardness remains unchanged, and all the old shear lines, even the deepest, are the centres of fine and dense precipitations.

The tests of the shaft and the rings thus treated show performances which are extraordinarily improved and without common measure with those which are obtained, all other things being equal, either with non-Sulfinuzed knurled Hadfield steel or with non-knurled Sulfinuzed Hadfield steel.

In the example described above, the shaft of '40 mm. oscillated in a ring of 40 mm. in length with a clearance of 0.1 mm. on the diameter. The whole was assembled without lubrication and immersed in water. The amplitude of the oscillations was 90 and their frequency was 2 cycles/sec. The load was 2,000 kp.

Under these conditions, a shaft and a ring of knurled non-Sulfinuzed Hadfield steel showed traces of seizure with a great increase in the coefficient of friction at the end of 12 hours. A ring and a shaft of non-knurled but Sulfinuzed Hadfield steel showed defects by scaling at the end of 30 hours; on the other hand, the shaft and the ring treated according to the example of the process according to the invention were able to oscillate for 500 hours, while retaining a perfect state of surface and without variation of the coefiicient of friction.

Example 2 A part of Hadfield steel, cold-hardened and knurled, was plunged into a bath of molten salts at 560 C., containing cyanides and unstable isomers of potassium cyanate. After immersion in this bath, of which one of the types is known by the commercial name of Tenifer, the same precipitates are found along the planes of shear, without increase in the micro-hardness, over the first four-tenths of a millimeter of the surface of the part, as those which were observed on the cold-hardened parts subjected to a sulphurizing treatment.

Example 3 A shaft and rings of the same dimensions as those of Example 1 were machined from a standard stainless steel containing, by weight, 18% of chromium, 8% of nickel and 3% of molybdenum. Tested under the treatments according to the invention, substantially under the same conditions of tests as the parts of Example 1, that is to say with an amplitude of oscillations of a frequency of one cycle per sec. and a load of 2,000 kp., the whole immersed in water at 20 C., seizure inevitably occurs in less than a few minutes. On the other hand, when knurled and subjected to the sulphurizing treatment, an identical shaft can oscillate for more than 50 hours while retaining a satisfactory surface condition. The same advantage was obtained by means of nitridation.

Example 4 Parts of titanium or of titanium alloy were subjected to cold-hardening followed in some cases by a sulphurizing thermal treatment and in the other cases by a nitriding treatment. After these applications of the process according to the invention, they all showed equally as soon as they were put into use, a good resistance to seizure and to wear.

Thus, in a titanium alloy of the type Ti A, in accordance with French standards, there were taken two male and female oscillation test samples similar to those described in Example 1. These samples were knurled according to the invention with wheels of 20 mm. and 10 mm. in width, the striations being inclined by at least 60 to the direction of slip. The wheels must necessarily be made of high-speed steel previously Sulfinuzed so as to prevent them from adhering to the titanium. When Sulfinuzed, samples of this kind have been capable of oscillating without incident for 10 hours under a load of 200 kp., the amplitude being 90, the frequency one cycle/sec, the temperature ambient and the medium, water. Under the same conditions, the same sample pieces of titanium not treated according to the invention, seize-up instantly.

Example 5 A piece of Hadfield steel, after the cold-hardening operation, is immersed for two hours in a bath of nitriding salts at 560 C., the bath being constituted by a mixture of alkali cyanates and cyanides following the Tenifer process. After this mild nitridation, the part is subjected to the sulphurizing action of a bath such as that of the process known "by the commercial name of Sulfinuz, this process comprising a treatment of at least two hours in a sulphurizing 'bath or a sulphurizing atmosphere at a temperature exceeding 500 C. The results obtained are superior to those which are recorded on cold-hardened parts subjected only either to a sulphurizing treatment or to a nitriding treatment.

What is claimed is:

1. A method for producing metallic parts having a high resistance to seizure and to wear by friction, wherein parts made from a metallic material chosen from the group of metals capable of hardening by cold-hammering While exhibiting in its superficial crystalline structure a high density of planes of shear, and consisting of austenitic stainless steels, hyper-eutectoid alloy steels containing at least 11% by weight of manganese, titanium, and titanium alloys containing a major part of titanium, are subjected to a deep cold-hardening executed in such manner that it produces, on the surface of the part, striations substantially perpendicular to the direction of the friction, following which the part is subjected to the superficial incorporation of at least one element chosen from the group of the metalloids and transition metals, which metalloids and transition metals possess one of the two properties consisting firstly in the capacity of depositing at the surface of the parts an ionic compound by reaction with the underlying metal, and secondly of the capacity of inserting its atoms into the structure of the underlying metal while forming a solid insertion solution, the metalloid group consisting of nitrogen, carbon and sulphur and the transition metal group of selenium and tellurium, the superficial incorporation being obtained by maintaining a contact during a period comprised between 1 and 6 hours at a temperature from 400 to 590 C. between said part and a fluid such as a salt bath or a gaseous atmosphere, which contains the element to be incorporated.

2. A method for producing metallic parts having a high resistance to seizure and to wear by friction which comprises forming a metallic part of a metal capable of hardening by cold-hammering while exhibiting in its superficial crystalline structure a high density of planes of shear and selected from the group consisting of austenitic stainless steels, hyper-eutectoid alloy steels containing at least 11% by weight manganese, titanium, and titanium alloys containing a major part of titanium; subjecting the part to a deep cold-hardening executed in such a manner that it produces on the surface of the part striations substantially perpendicular to the direction of frictional wear; subjecting the striated part to superficial incorporation of at least one element selected from the group consisting of nitrogen, carbon, sulfur, selenium, and tellurium, by maintaining contact between said metal part and a fluid containing such element for a period of time between one and six hours at a temperature of about 400 to 590 C.

3. A method in accordance with claim 1 wherein the deep cold-hardening is eifected by knurling.

4. A method according to claim 1 wherein the deep cold-hardening is effected 'by hammering with a striated hammer.

5. A method in accordance with claim 1, wherein the case where the element is sulphur, the parts are subjected to a thermal treatment of at least two hours in sulphurizing bath or a sulphurizing atmosphere at a temperature higher than 500 C.

6. A method in accordance with claim 1 wherein in the case of incorporation of nitrogen, the said incorporation is obtained by means of any nitriding process which is eflt'ective below a maximum temperature of 580 C.

7. A method in accordance with claim 6, wherein after the nitridation, the part is subjected to a treatment for at least two hours in a sulphurizing bath at a temperature of at least 400 C.

References Cited by the Examiner UNITED STATES PATENTS 2,707,159 4/1955 Foucry et al. 1486.24 X 3,009,843 1l/l961 Nachtman et al. l48l2.1 3,022,204 2/ 1962 Muller et al. l48l5.5 3,208,885 9/1965 Muller 14815.5

FOREIGN PATENTS 782,263 9/1957 Great Britain.

DAVID L. RE'CK, Primary Examiner.

H. F. SAITO, Assistant Examiner.

Claims (1)

1. A METHOD FOR PRODUCING METALLIC PARTS HAVING A HIGH RESISTANCE TO SEIZURE AND TO WEAR BY FRICTION, WHEREIN PARTS MADE FROM A METALLIC MATERIAL CHOSEN FROM THE GROUP OF METALS CAPABLE OF HARDENING BYCOLD-HAMMERING WHILE EXHIBITING IN ITS SUPERFICIAL CRYSTALLINE STRUCTURE A HIGH DENSITYOF PLANES OF SHEAR, AND CONSISTING OF AUSTENITIC STAINLESS STEELS, HYPER-EUTECTOID ALLOY STEELS CONTAINING AT LEAST 11% BY WEIGHT OF MANGANESE, TITANIUM, AND TITANIUM ALLOYS CONTAINING AMOJOR PART OF TITANIUM, ARE SUBJECTED TO A DEEP COLD-HARDENING EXECUTED IN SUCH MANNER THAT IT PRODUCES, ON THE SURFACE OF THE PART, STRIATIONS SUBSTANTIALLY PERPENDICULAR TO THE DIRECTION OF THE FRICTION, FOLLOWING WHICH THE PART IS SUBJECTED TO THE SUPERFICIAL INCORPORATION OF AT LEAST ONE ELEMENT CHOSEN FROM THE GROUP OF THE METALLOIDS AND TRANSITION METALS, WHICH METALLOIDS AND TRANSITION METALS POSSESS ONE OF THE TWO PROPERTIES CONSISTING FIRSTLY IN THE CAPACITY OF DEPOSITING AT THE SURFACE OF THE PARTS AN IONIC COMPOUND BY REACTION WITH THE UNDERLYING METAL, AND SECONDLY OF THE CAPACITY OF INSERTING ITS ATOMS INTO THE STRUCTURE OF THE UNDERLYING METAL WHILE FORMING A SOLID INSERTION SOLUTION, THE METALLOID GROUP CONSISTING OF NITROGEN, CARON AND SULPHUR AND THE TRANSITION METAL GROUP OF SELENIUM AND TELLURIUM, THE SUPERFICIAL INCORPORATION BEING OBTAINED BY MAINTAINING A CONTACT DURING A PERIOD COMPRISED BETWEEN 1 AND 6 HOURS AT A TEMPERATURE FROM 400 TO 590*C. BETWEEN SAID PART AND A FLUID SUCH AS A SALT BATH OR A GASEOUS ATMOSPHERE, WHICH CONTAINS THE ELEMENT TO BE INCORPORATED.