US3329487A - Sintered three-phase welding alloy of fe3w3c, wc, and fe - Google Patents

Description

United States Patent 3,329,487 SINTERED THREE-PHASE WELDING ALLOY 0F Fc W C, WC, Fe

John J. Sowko, Pittsburgh, and Phillip G. Barrho,

McMurray, Pa., assignors to Firth Sterling, Inc., Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. 15, 1965, Ser. No. 433,257 14 Claims. (Cl. 29182.7)

This invention relates to a hard metal composition that may be provided in solid form, as in the form of a rod, for coating ferrous metal surfaces to provide them with a wear and abrasive resistant facing and to one that can be employed for relatively inaccessible areas. A phase of our invention relates to a hard metal composition that can be used in a solid or unitary form in directly applying surface facing to a ferrous metal member or surface.

There has been a need for a hard metal composition that can be formed into a suitable shape such as a rod and directly used in this form in applying an abrasion and Wear-resistant surface to an item, such as a coal crushing hammer, a plow for mixing abrasive materials or to provide a wear resistant facing on any surface that erodes due to abrasion. Heretofore, there have been two approaches to the problem; one involves the employment of carbide powders in a plasma gun, and the other involves the use of a steel tube having crushed carbide particles carried as a core therein. Difficulty has been encountered in attempting to use carbide powders from the standpoint of obtaining a proper flow through the plasma gun and from the standpoint of bonding the powders to the metal surface. In attempting such a type of application, the surface of the metal member is first pre-alloyed to make it susceptible to some adherence with the hard metal particles, but even after doing so, a relatively poor bond is obtained. Also, there is a tendency to burn or warp the metal piece to which the application is being made. Although some success has been attained in using the second method and this method has been heretofore the only one having some practicability, difiiculty has been encountered in obtaining good and uniform characteristics of the surface application. Further, both methods are not practical from the standpoint of relatively inaccessible areas and it has been necessary to make the application to a fiat surface member or one which presents a flat surface to the application.

In endeavoring to solve the problem, we conceived of the idea of developing a hard metal composition that could be formed into a suitable shape, such as a rod in solid or integral form, and then melted by a conventional apparatus, such as an acetylene torch, a Heliarc welding apparatus, etc. We found that it was important to develop a composition that could be directly bonded to the surface of the member, without the need for any special fluxing agents and surface treatment or alloying of the member, with the only condition being the provision of a clean surface at the point of application.

We have been able to solve the problem, not only from the standpoint of successfully, simply and effectively applying a hard metal surface or facing, but also from the standpoint of providing a facing that has an unusually high combination of hardness with strength.

It has been an object of our invention to solve the problem presented in applying a hard, wear and abrasive resistant surface to a suitable member, such as a mixing plow, which will have excellent properties as applied, and which will have an excellent bonded strength in its application and use;

Another object of our invention has been to simplify the procedure in applying a hard metal facing to a ferrous metal member or surface;

3,329,487 Patented July 4, 1967 Another object of our invention has been to provide a new hard metal composition that can be used as a unitary or solid piece in applying a wear and abrasive resistant surface thereto; I

A further object of our invention has been to provide a hard metal facing for a ferrous metal member or a metal member having ferrous metal surface which will have an optimum combination of strength and hardness as well as molecular adherence;

A still further object of our invention has been to provide a hard metal composition that will stand up under use as a surface coating on a metal member that is subjected to wear and tear and temperature variations during its use;

These and other objects of our invention will appear to those skilled in the art from the drawings, the description and the claims.

In the drawings, FIGURE 1 is a side view of a solid or unitary member of a composition of our invention which may be used in applying a metal facing where the operation is conducted in a relatively non-oxidizing atmosphere;

FIGURE 2 is a view similar to and on the scale of FIGURE 1 showing a product of our invention which is provided with an outer fluxing or de-oxidizing coating and which is thus suitable for utilization in an oxidizing ambient atmosphere during its application to the surface of a member or part;

FIGURE 3 is a triangular coordinate chart showing a comparison of hard metal alloys disclosed and discussed herein; and

FIGURE 4 is a 1500 micrograph through an optimum hard metal composition of our invention showing its structure.

. Since it is well recognized that a carbide metal has a coefiicient of thermal expansion that is much lower than ferrous metals, for example, about one-half that of steel, we determined that this was an important factor in attaining a solution to the problem. This is particularly true, since products, such as sandslinger liners, plows, etc., are subjected to variations in temperature in use and often becomes heated up to well above the temperature of the ambient atmosphere. In addition, we found it was also important from the standpoint of obtaining an effective bond between the ferrous metal surface and the hard metal composition and metal material.

We have been able to develop a composition which meets all requirements and accomplishes the objects of the invention and which extends the field of application and utilization of hard metal facings. This composition in its broader aspects has the following content:

In making the composition, powders of tungsten and iron are mixed and then extruded or pressed to shape in a cold state. If they are to be extruded, they can be mixed with Vaseline and if they are to be pressed, they can be mixed with paraflin. The initial powders may be ballmilled while wet with the petroleum temporaly binder for about 72 hours. The pressing or extruding may be accomplished at a pressure of, for example, about 15 tons per square inch. After pressing or extrusion, the shape, such as a rod is then dried as in the air and may be half or pre-sintered at about 1100" F. to remove or to driveoff the paratfin or Vaseline, asthe case may be. The shape may then be finally sintered in a graphite or carbon boat having arcuate or concave grooves in its bottom and an 3 alundum packing, using a hydrogen or reducing atmosphere. The arcuate grooves tend to hold the shape straight and minimize camber. The shrinkage is about .865 perpendicular and about .800 parallel to the direction to found that if the iron content is too low, such that the tungsten is combined with the iron eta, wear-resistance is low. The composition A of Tables II and III, has a thermal expansion of 5 l0 inches per square inch at which the shape has been pressed in its formation. The 5 76 to 600 F., a melting point of about 2850 F., and initial powders may be ball-milled while wet for about amagnetic characteristic at 1800 F. 72 hours and finally sintered at about 2425 to 2600 F. It has been found that a composition of our invention for 15 minutes in the boat. has superior abrasion resistance, as compared to a con- The composition of our invention has an excellent ventional tungsten carbide containing cobalt, and that combination of strength and hardness. Although the tung- 10 within its range of content, has a maximum of strength sten carbide tends to increase hardness, a maximum with hardness. As will be noted from Table II, composistrength is attained within the range of our composition. tions A, F and G, each of which has substantially an It has been determined that the tungsten, itself, tends to equal proportion or content of tungsten and iron, have increase hardness but with a rather sudden drop-off of the highest combination of hardness with cross breaking strength. It has also been determined that the iron, itstrength, although the other compositions, such as B, C, self, tends to decrease hardness but with a decrease of D, E and H, have improved properties for a hard metal strength. composition. Composition A represents the optimum Our composition has a content such that the sintered content. product has fine tungsten carbide particles imbedded in Composition I has been added by way of comparison an iron eta with fine grain double carbide fully dispersed and represents a composition which is in full solution, throughout an iron binder structure. If the iron content see particularly Table III. Although it has a good hardis too low, all the tungsten is combined with the iron eta ness, its cross break strength is totally unsatisfactory, as to cause a lower wear resistance and bonding strength; indicated by Table II. In other words, it is important, in the content of iron is critical, in that it must be in an accordance with our invention, to provide an eta phase amount to form an iron eta with a slight excess to give composition which contains an excess of iron and to avoid bonding strength and resilience. The very uniform disa fully eutectic composition, as represented by composipersion is important in achieving the results and is extion I. The use of iron is highly important and critical, emplified by the micrograph of FIGURE 4 of the drawin that it has been determined that it combines with the ings. It is necessary to avoid conversion of the elements ferrous metal surface to which it is being applied in soluor ingredients into a full solution form as represented, tion to readily, and without fluxes or an intervening alby composition I of the following Table III. In our work, loyed surface, provide a gOOd molecular bond therewith we have found that the forming of iron eta first and then that is somewhat resilient or that provides a cushioning sintering with iron will not produce the desired results. connection, such that differences in the rate of expansion The composition of our invention thus constitutes a threeand contraction of the metal member or workpiece and phase alloy of free iron, free tungsten carbide, and iron the hard metal facing will not cause breaking or damage. tungsten carbide eta phase as represented by W Fe C. We have been the first to successfully provide a com- In the micrograph of FIGURE 4, the dark phase is idenposition for a solid or integral hard metal body, such as tified as eta, the gray phase as WC and the white phase rod 10 of FIGURE 1, that can be directly used to apply as Fe. a hard metal facing to a ferrous metal surface. For ob- T able ll Content Sintering Strength Composition Temp., Density Hardness C/Bxlo,

F. RWA p.s.i. WC W Fe Table III Composition A Composition I WC WC Fe WC In the various tables, the percentages of the compositions involved are percentages by weight. The iron content is critical to provide bonding ability and strength with that about two passes are desirable, for example, using about amperes with an MG set (DC), and reversthe ferrous metal surface. The iron content provides a 70 ing polarity. A workpiece positioned at an angle as great resilient or cushioning type of molecular bonding with a ferrous surface of a workpiece, such that the metal workpiece and the hard metal wear resistant surface thereon may expand and contract without breaking away from each other and spoiling the product. It has also been as 45 with respect to the rod can be thus coated without difficulty.

The solid shape or rod 10 may be used by heating it and the surface of the workpiece simultaneously, so that both are substantially molten, and then by moving the rod slightly so that the molten globules of the hard metal composition will leave the end of the rod and adhere to the surface workpiece. The workpiece may be at an ambient temperature or may be preheated to about 1000 F. when starting the Welding operation. The application may be effected by employing a Heliweld or a Heliarc apparatus, using alternating current and thoriated tungsten, with a flow of argon. We have also employed a direct-current reverse polarity process using about the same current to 50 to 160 amperes. If a protective gaseous atmosphere is provided, the rod of FIGURE 1 may be employed. However, if a welding torch is used, then it may be desirable to employ a coated product, such as disclosed in FIG- URE 2; by way of example, a rod of about A of an inch in diameter may be provided with a flux coating 11 of about of an inch in thickness. The temperature used may be within a range of about 2850 to 2900 F. A thickness of application of about .010 to .050 of an inch has been successfully obtained, and the finished product can be bent up to about 125 without adversely affecting the coating. If a torch is used, the rod should be about one size larger than a conventional steel tube containing crushed carbide, and the flame should be adjusted so that it is slightly reducing rather than neutral or oxidizing.

The ferrous metal surface to which the hard metal facing is to be applied should be cleaned, as by sand blasting with silicon carbide or aluminum grit, and this is preferably also done after the first pass and before any subsequent passes.

Where there is no assurance of a non-oxidizing atmosphere during the melting-on application of the hard surface composition, we have successfully used a coated rod such as shown in FIGURE 2. This coating may be made up of powdered carbon wetted with sodium silicate or water glass so as to produce a viscous mixture or emulsion. The rod of FIGURE 1 may be, for example, dipped or the mixture applied in any other suitable manner as an outer layer about the rod and, after the application, allowed to dry. To facilitate the removal of moisture, baking may also be used.

The composition of our invention has outstanding characteristics of relatively high hardness with relatively small grains. It has a high abrasion resistance, in that the hard granules are well anchored in the matrix. It alsohas superior wear-resistance compared to an ordinary carbide. Although cobalt or nickel may form a double carbide eta phase, they will produce an entirely different structure with different physical properties, and will not assure the easy bonding action with the metal surface or provide a cushioning type of bond for the facing coat. A transient liquid phase is formed during the relataively rapid final sintering which may be accomplished in about 15 minutes at the above indicated temperature. Once the iron eta has been formed, however, it has been found impossible to sinter it at the same low temperature and the same rapidity; it is impossible to achieve the structure of finely dispersed double carbide with tungsten carbide particles embedded in an iron matrix. The powders used in our composition may be of a size to pass a 150 or finer mesh screen.

Summarized briefly, "our invention involves a sintered carbide hard metal alloy containing as its ingredients about 45 to 50% by weight of tungsten carbide and about to 30% by weight each of tungsten and iron. These ingredients are mixed in powdered form and with a pctroleum temporary binder for compacting purposes. They are then compacted and pre-shaped under a high pressure followed by a preliminary sintering at a relatively low temperature of about 1100 F. to dn've-ofi? the petroleum binder. Finally, they are sintered in a carbon boat at about 2425 to 2600 F. for about 15 minutes. The resultant alloy is of a three-phase structure in which a Fe W C solution is in a major proportion or dominates, in which tungsten carbide is in an intermediate proportion and both of which are dispersed through a binder of a minor proportion of iron. That is, the alloy product has a structure in the form of an iron eta solution and tungsten carbide dispersed through a binder of iron.

This structure is essentially retained when the alloy product or solid hard metal shape is then melted or applied in a molten condition to a ferrous metal surface member and solidified thereon. On solidification, it provides a molecularlyadhering abrasion-resisting facing characterized by its maximum hardness in combination with a good or the best possible cross breaking strength, and that has a somewhat resilient molecular bond with the metal surface. This alloy is further characterized as a pressed-out shape of compressed and sintered powders whose density, as formed, is between about 12.7 to 13.9, whose Rock-well A hardness is about 86 to 90, and whose cross breaking strength is about 102,000 to 215,000 p.s.i. The optimum proportioning of the ingredients is 50% by weight of tungsten carbide and 25% each by weight (substantial equal proportioning) of tungsten and iron. In the final structure, the ingredients, although containing a major proportion of the iron eta in solution form as Fe W C, also contains free tungsten carbide and iron. In this connection, the iron eta solution may be about 50 to 54% by Weight, the tungsten carbide about 36 to 39% by weight and the iron about 7 to 14% by weight.

What we claim is:

1. A sintered carbide hard metal welding alloy containing as its ingredients about 45 to 50% by weight of WC and about 20 to 30% each by Weight of W and Fe, said alloy having a three-phase structure of Fe W C solution and WC dispersed Within an Fe binder.

2. A sintered carbide hard metal welding alloy as defined in claim 1 which is characterized by its high hardness and high bending strength, and by its molecular adherency and abrasion-resistance as applied to a ferrous metal surface.

3. A sintered carbide hard metal welding alloy as defined in claim 2 which is characterized by a hardness of at least about 86 Rockwell A and a cross-breaking strength of at least about 102,000 p.s.i.

4. A sintered carbide hard welding alloy metal shape containing as its ingredients about 45 to 55% by weight of WC and about 20 to 30% each by weight of W and Fe, and whose structure is in the form of a major proportion of Fe W C solution by weight and an intermediate proportion of WC by weight dispersed throughout a binder of a minor proportion by weight of Fe.

5. A hard metal welding composition of solid form for application in a melted condition to a ferrous metal surface member to, on solidification, provide the member with a molecularly-adherent, abrasion-resistant facing which contains about 45 to 50% by weight of WC and about 2.0 to 30% each by weight of W and Fe, and wherein the structure has an iron eta phase, a tungsten carbide phase, and an iron phase, and the iron content is sufficient to avoid a fully eutectic structure.

6. A hard metal abrasive Welding facing for a ferrous metal surface member that is applied in the molten form to the surface of the member as a pre-sintered and preshaped solid alloy metal containing in its structure a major proportion by weight of an iron tungsten carbide eta and an intermediate proportion by weight of tungsten carbide dispersed throughout a binder of a minor proportion of iron, and said facing as applied being characterized by its maximum hardness in combination with a good cross-breaking strength, by its molecular-adherency to the ferrous metal surface and by its resilient molecular bond with the metal surface.

7. A hard metal abrasive welding facing as defined in claim 6 wherein the basic ingredients of the facing as utilized in the sintered product comprise, about 45 to 50% by weight of tungsten carbide and about 20 to 30% by weight each of tungsten and iron.

8. A sintered carbide hard metal welding alloy shape for application in a melted condition to a ferrous metal surface member to, on solidification, provide a molecularly-adherent abrasion-resistant facing thereon which consists of a mixture of about 45 to 50% by weight of tungsten carbide powder, and about 20 to 30% by Weight each of tungsten and iron powders pressed and sintered, and characterized when applied to the ferrous metal surface, by its high molecular and resilient bond with the surface member and by its maximum hardness with a good cross-breaking strength.

9. A sintered hard metal welding alloy shape as defined in claim 8 wherein the sintered welding alloy shape has a structure in the form of an iron eta solution and tungsten carbide dispersed throughout a binder of iron.

10. A sintered hard metal welding alloy shape as defined in claim 9 wherein the iron eta constitutes a major proportion by weight of the structure, the tungsten carbide constitutes an intermediate proportion by weight and the iron binder constitutes a minor proportion by Weight of the structure.

11. A sintered hard metal welding alloy shape as defined in claim 10 wherein the iron eta of the structure is about 49 to 54% by weight, the tungsten carbide of the structure is about 36 to 39% by Weight and the iron binder is about 7 to 14% by weight.

12. A sintered carbide hard metal welding shape containing as its ingredients about 45 to 55% by weight of WC and about to by weight each of W and Fe as introduced and mixed in powder form, compressed and sintered, whose density is between about 12.7 and 13.9, Whose Rockwell A hardness is about 86 to 91 and whose cross-breaking strength is about 102,000 to 215,000 p.s.i.

13. A sintered hard metal welding shape as defined in claim 12 wherein the ingredients are in the amount of by weight of WC and 25% by weight each of W and Fe.

14. A sintered hard metal welding shape as defined in claim 12 wherein the metal structure has a major proportion of its ingredients by Weight in the form of an eutectic, has an appreciable proportion of tungsten carbide and a minor proportion of iron by weight, and wherein the solution structure and the tungsten carbide are dispersed throughout the iron.

No references cited.

CARL D. QUARFORTH, Primary Examiner. L. DEWAYNE RUTLEDGE, Examiner.

A. I. STEINER, Assistant Examiner.

Claims (2)

1. 4. A SINTERED CARBIDE HARD WELDING ALLOY METAL SHAPE CONTAINING AS ITS INGREDIENTS ABOUT 45 TO 55% BY WEIGHT OF WC AND ABOUT 20 TO 30% EACH BY WEIGHT OF W AND FE, AND WHOSE STRUCTURE IS IN THE FORM OF A MAJOR PROPORTION OF FE3W3C SOLUTION BY WEIGHT AND AN INTERMEDIATE PROPORTION OF WC BY WEIGHT DISPERSED THROUGHOUT A BINDER OF A MINOR PROPORTION BY WEIGHT OF FE.
2. 8. A SINTERED CARBIDE HARD METAL WELDING ALLOY SHAPE FOR APPLICATION IN A MELTED CONDITION TO A FERROUS METAL SURFACE MEMBER TO, ON SOLIDFICATION, PROVIDE A MOLECULARLY-ADHERENT ABRASION-RESISTANT FACING THEREON WHICH CONSISTS OF A MIXTURE OF ABOUT 45 TO 50% BY WEIGHT OF TUNGSTEN CARBIDE POWDER, AND ABOUT 20 TO 30% BY WEIGHT EACH OF TUNGSTEN AND IRON POWDERS PRESSED AND SINTERED, AND CHARACTERIZED WHEN APPLIED TO THE FERROUS METAL SURFACE, BY ITS HIGH MOLECULAR AND RESILLIENT BOND WITH THE SURFACE MEMBER AND BY ITS MAXIMUM HARDNESS WITH A GOOD CROSS-BREAKING STRENGTH.

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