US 3778580 A
A method for hardfacing a metal workpiece to provide a hardfaced work surface varying in composition over a cross section of the face thereof said method utilizing consumable guide nozzles and electroslag welding procedures.
Description (OCR text may contain errors)
[ Dec. 11, 1973 United States' Patent 11 1 Bierwith [5 METHOD FOR PROVIDING ALLOYED 2,191,469 2/1940 Hopkins......................
ZONES ()N A HARDFACED WORKPIECE 3,665,143 5/1972 Uj11c 3,518,397 6/1970 Hannahs  Inventor: Stanton F. Bierwith, San Leandro,
e y n a t n 0 W uA we S r m i r e 8 .m .m m mx E Ym m m TS PA 0 e h .m L s d n a S I a nd .m mm C a m mm mm GT m e n b S S A l 3 7 Attorney-George L. Church et a1.
Appl. No.: 239,071
ABSTRACT  Int. B23h 9/18  Field of Search.................... 219/146, 145, 137, A metlwd for hardfac'ng metal Pmv'de 219/126, 77 76, 73; 37/142; 76/DIG 11, 1; a hardfaced work surface varying in composition over a cross section of the face thereof said method utilizing consumable guide nozzles and electroslag welding procedures.
2,191,471 219/76 2 Claims, 6 Drawing Figures PATENTEI] DEC 1 1 I975 SHEET 1 BF 3 FIG. 11
PATENTED DEC 1 1 I975 SBEET 3 OF 3 FIG. HZ
EATENIEU I 3.778580 SHIIET 30F 3 FIG. I
34 33 32 a IO FIG. II
METHOD FOR PROVIDING ALLOYED ZONES ON A HARDFACED WORKPIECE BACKGROUND OF THE INVENTION The present invention relates to a procedure of hardfacing metal workpieces such as digging tools. In particular the present method provides a hardfaced tool having a variation in metallurgy across the work surface of the tool. More particularly, the present invention relates to methods and compositions for manufacturing hardfaced tools utilizing electroslag welding techniques and consumable guide nozzles that are particularly suitable for use in the manufacture of digging tools and the like. The manufacture of tools and implements used in mining present particular problems to the toolmaking industry. For example, excavator teeth must have a wear surface which has a high resistance to abrasion while at the same time having good tensile strength properties.
It is generally known in the art that the metallic alloys which provide a metalsurface having high resistance to abrasion and wear often are brittle and deficient in tensile properties. Thus a hardfaced tool having outstanding resistance to abrasion and therefore good wear properties often easily breaks when subject to tension. On the other hand, tolls hard-faced with metal alloys which have good tensile properties are often found to be rather poor with regard to resistance to abration and wear and have a rather short life when subject to uses where high abrasion and wear are encountered. The prior art provides many alloy compositions and particular types of forged steel which are proposed to have either good wear properties or resistance to abrasion. Sometools are disclosed to provide a combination of reasonable wear properties along with good tensile strength properties. a
One method of improving the wear properties of a hardfaced metal workpiece recently proposed has been hardfacing utilizing the electroslag welding techniques. One version of a method of providing hardfacing by electroslag welding is provided by B. E. Patent in the text Electroslag Welding, second Edition, published by the American Welding Society Inc., New York. Particularly on pages 144 to 152 of this text a procedure for hardfacing a work tool or workpiece is set forth.
Also, in the patent literature, U. S. Pat. No. 2,909,778 to Landis et al. proposes a method of electro arc welding using particular types of electrodes. U. S. Pat. No. 2,510,960, U. S. Pat. No. 2,345,758, U. S. Pat. No. 3,325,619, U. S. Pat. No. 3,534,390, U. S. Pat. No. 3,531,620, U. S. Pat. No. 3,491,225, U. S. Pat. No. 3,448,241, U. S. Pat. No. 3,215,809 and U. S. Pat. No. 3,118,053 provide particular welding electrodes or consumable nozzles particularly suited for electric arc and/or electroslag welding techniques and provide alloys which have particularly attractive wear and strength properties. Also, U. S. Pat. No. 3,518,397 to .l. R. Hannahs provides an electroslag welding technique using consumable nozzles wherein metal workpieces can be welded together to provide a high strength weld.
Also, in the art are U. S. Pat. No. 2,137,471 and U. S. Pat. No. 3,023,130 which provide hardfacing techniques using particular electrodes containing tungsten carbide particles or similar metal carbide particles which provide hardfaced tools withoutstanding abrasion characteristics.
Electroslag welding as mentioned above comprises generally a process whereby heat is generated by passing an electric arc between electrodes and a ground base. The passing of a current through the electrode melts the electrode to provide a weld pool suitable for fusing metal articles together or which when properly held in a cavity or gap can provide a hardfacing for the metal workpiece being treated. Recent developments in the area of electroslag welding have also provided consumable guide nozzles which can be made up of particular metal alloys which when added to the consumable electrode provide a final hardface alloy which may have attractive abrasion resistance and good wear properties.
The consumable guide nozzles disclosed in the art generally comprise a steel tube around which is provided a larger tube containing the metal particles directed for use in the electroslag welding technique. The final weld on the face of the workpiece contains an alloy of the metal in the electrode wire fed into the electroslag welding apparatus and the metal components which form the consumable guide nozzles used during the welding process. The consumable guide nozzle also serve the purpose of directing the electrode wire into the slag pool.
One recentinnovation comprises the art of hardfacing digging implements such as teeth used in bucketwheel excavators. New applications for bucketwheel excavators such as in the tundra of the frozen north as well as the tar sand of the frozen north such as those found in Alberta, Canada have made new demands on technology to provide bucketwheel excavator teeth which have good resistance to abrasion as well as being able to stand the impact in mining normally experienced under temperatures of up to -S0F. By the methods of the present invention, hardfaced tools suitable for use in extremes of temperature and abrasion while maintaining good wear properties and good tensile strength properties have now been provided.
DESCRIPTION OF THE INVENTION The present invention provides a method for manufacturing hardfaced work tools in which the facing on the work surface of the tool can be custom tailored to provide specific properties in designated areas of the work surface. Specifically, the present invention comprises a method for hard-facing workpieces which utilizes consumable guide nozzles in electroslag weld hardfacing. These consumable guide nozzles contain particular metal alloy compositions which provide the specific metallurgy designed into a particular area of the workpiece being manufactured.
It is well known to the art that certain metallic alloy compositions are particularly resistant to wear and abrasion but are also found to be brittle and therefore have poor tensile properties. On the other hand, certain metallic alloys used in hardfacing known to have good impact and tensile properties have lesser hardness characteristics and therefore are not as resistant to abrasion and'wear as the harder more brittle alloys. In the prior art, normally one alloy or the other alloy would be selected in order to provide a hardfacing which had one or the other desired properties. In some circumstances, a blend of the components of each alloy can be provided to make a hardfaced workpiece having a compromise of all the physical properties required. However, by the methods of the present invention, a
hardfaced workpiece is provided which in effect is custom tailored. That is, a hardfaced workpiece is provided which has the particular metallic alloy custom tailored in the hardface to be centered in the area where specific characteristics are required. In the present invention, the area of a tool where the work surface is subject to high abrasion is hardfaced using consumable guide nozzles utilized in electroslag weld hardfacing which contain a metal alloy designed specifically for its resistance to abrasion. Another area of the same workpiece may require high tensile properties. To meet this requirement, a consumable guide nozzle is provided which contains a high nickel and chrome content.
In carrying out the method of the present invention, electroslag welding techniques are preferred. In the process of electroslag welding as used in the present invention, consumable guide nozzles containing metal alloys designed to make up the final composition of hardfaced element are selectively provided.
In the electroslag hardfacing technique of the present invention, two or more consumable guide nozzles can be placed in the area to be hardfaced in order to provide specific metallurgy required in designated areas of the hardfaced workpiece. As an example, consumable guide nozzle A is prepared by blending together fine particles passing through a 120 screen mesh of 60 percent tungsten carbide, 30 percent ferrochrome, 5 percent by weight ferromolybdenum and 5 percent by weight ferrovanadium. This consumable guide nozzle when utilized in electroslag hardfacing techniques provides a hardface surface area particularly resistant against abrasive wear. A second guide nozzle designated as composition B is prepared by blending 49 percent ferrochrome, 49 percent silicon carbide and 2 percent cobalt. This nozzle is used in electroslag welding techniques of hardfacing in an area where a medium resistance to abrasion is required and where substantial tensile properties are required. Nozzle A and nozzle B as disclosed herein when used in hardfacing a workpiece needing the combination of resistance to abrasion and wear as well as high tensile strength properties when properly applied to the area where the need is shown can provide a custom tailored workpiece having a hardsurfaced area meeting the requirements for its use.
Referring to the drawings, FIG. I is a consumable guide nozzle made up of the metallic particle composition known as composition A. FIG. II is a consumable guide nozzle made up of the metallic particle composition known as composition B. FIG. III illustrates a bucketwheel excavator tooth having disposed in a cavity or gap formed to provide for the hardfacing of the wear surface of the tooth as shown consumable electroslag guide nozzles A and B in place for electroslag wled hardsurfacing. FIG. IV illustrates an electroslag welding apparatus well known in the art showing consumable guide nozzles A and B in placein the cavity of workiece 10 to be hardfaced. FIG. V illustrates the finished product of workpiece l0 havinga hardfacing on the work surface thereof as shown containing the custom tailored alloy on the surface. FIG. VI is another vicw ofthe same workpiece in FIG. V illustrating the cross section of custom tailored metal alloy hardfacing.
By the method of the present invention, a forged or cast steel or other metal alloy workpiece can be hardfaced in a manner to provide a unique custom tailored work surface on that workpiece. Specifically, it has been discovered that by the method of the present invention a workpiece such as a bucketwheel excavator tooth used in mining can be hardfaced in a manner whereby the area of the work surface of the tooth which is most subject to severe abrasions contains a metallic alloy composition specifically designed to have high resistance to abrasive wear. While at the same time on the same hardfacing in an adjacent section thereto, a metallic alloy is provided which has acceptable wear properties while at the same time having high tensile properties thereby providing for strength in the area of the workpiece where it is more specifically required.
By the method of the present invention, a workpiece having a hardfacing on the work surface thereof is provided whereby the hard surface composition is custom tailored to provide the properties most needed in the particular area of the workpiece. The example given in the illustration of FIGS. I through VII give one embodiment of this invention. A bucketwheel excavator tooth having a narrow tip and a broad base both of which are subject to abrasion is custom tailored so that the tip of the tooth having the most severe exposure to abrasion contains a hardfacing alloy which is most suitable for resistance to wear. At the same time, the hardfacing on that tooth also contains an alloy toward the center of the tooth where improved tensile strength is required. Finally, the base portion of the tooth is hardfaced with a metallic alloy which has high tensile strength.
To better define in detail this embodiment of the methods and the compositions of the present invention, referring again to the drawings, FIG. I illustrates a consumable guide nozzle which generally can comprise an elongated outer shell 5 having a hollow tube 6 located within the shell. The shell is also filled with fine particulate blend of metal alloys 7.
The consumable guide can be of any shape suitable to fit the area to be hardfaced. For purposes of the present illustration the consumable nozzle of FIG. I contains the composition disclosed for consumable nozzle A given above and is therefore designated as nozzle A in FIGS. I, II and IV herein presented.
FIG. II illustrates a consumable guide nozzle B similar to that of FIG. I having outer shell 4 and inner hollow tube 8 with the variation that the metal particulate composition of 9 which fills outer shell 4 is of a different blend of metal particles in order to provide a hardface composition having different physical properties.
FIG. III illustrates a bucketwheel excavator tooth of one type 10 shown in position to be hard surfaced having a depression or gap in the area of the work surface of the tooth. The depression 19 has disposed therein consumable electrodes A and B of FIGS. I and II respectively.
FIG. IV illustrates an electroslag'welding apparatus of the type that can be used in providing the custom hardfacing of the present invention. Specifically, in FIG. IV is shown a forged steel excavator tooth l0 suitable for use in the bucket wheel excavator used for mining tar sands or the like. The tooth is placed on workbench II in a position so that consumable guide nozzles 15 which are nozzles A and B of FIGS. I and II respectively are located within the indentation provided on the work surface of workpiece 10 to be hardfaced.
Immediately below the consumable nozzles is sump 16 which is a depression in bench 22 nornally provided when electroslag welding procedures are employed. Consumable electrode wires 13 are fed through guide nozzle 15 to the space between the workpiece and heat exchange means 17 which can be a copper shoe having a fluid circulating therethrough to maintain a certain surface temperature on the heat exchange medium.
In the process of hardfacing by way of electoslag welding as shown in FIG. IV, electrode wire 13 travels through straightening mechanism 20 and wire feeding mechanism 21 to the interior of consumable nozzles into the electroslag tool. Consumable nozzles 15 are releasably connected to extension 14 of the wire feeding mechanism 21. Heat exchange shoe 17 has a means for coolant inlet and outlet as shown at 18. The placing of the heat exchange means 17 adjacent to the depression in the surface of workpiece 10 provides a cavity or .gap to maintain the electroslag weld in the area of the surface of the workpiece to be hardfaced.
Welding current to electrodes 13 is supplied from the conventional power supply 30 through cables 31 to lugs on extension 23. The power passes through the lugs to consumable guides 15 and thereafter through the electroslag welding pool into workbench 11 and back to the power supply through cable 22. The consumable guide nozzles 15 which are also nozzles A and B can be made to oscillate across the thickness of the cavity formed on workpiece 10 to thereby distribute the heat evenly across the area being hardfaced as well as provide for a uniform transition of metallic alloy from the alloy composition of consumable nozzle A to the alloy composition of consumable nozzle B.
The rate at which electrode 13 is fed into the weld is regulated by control of apparatus 25 which has a connection to the wire feeding mechanism 21 by cable 26. Control apparatus 25 is also provided with means to adjust the welding voltage remotely through cable 27 and to regulate through cable 28 the velocity at which the consumable guides 15 move across the thickness of the cavity of the workpiece 10. The welding current is determined by setting the wire speed control. The wire feed mechanism 21 is powered by motor 29 in response to signals from unit 25 conducted through connection 26.
A detailed descriptionvof the apparatus shown in FIG. IV is provided in U. S. Pat. No. 3,518,397 issued June 20, 1968. The electroslag welding techniques disclosed in this patent reference as well as the electroslag technology disclosed in the reference text Electroslag Welding edited by B. E. Patent, American Welding Society, Inc., New York, New York, Reinhold Publishing Corporation, 1962 is suitable for use in the method of the present invention.
FIG. V illustrates the finished custom tailored hardfaced bucketwheel excavator tooth 10 suitable for mining tar sands. The composition across the hardface area of workpiece 10 is shown where the metallic alloy consumable nozzle A is primarily disposed in area 32 of the surface hardfaced on workpiece l0. Metallic alloy of consumable nozzle B is primarily provided in area 34 of FIG. V on workpiece 10. In area 33 of FIG. V there is provided an integration of the alloys of consumable nozzles A and B to provide a transition of the characteristics of each of the metal alloys of consumable nozzles A and B.
FIG. VI illustrates another view of the same workpiece as shown in FIG. V illustrating the custom tailored hardfacing on the bucketwheel excavator tooth 10 showing the composition across the area of hardfacing with the primary alloy of consumable nozzle A being in the area 32 and that of consumable nozzle B being in the area of 34 with area 33 providing an amalgamation of the two alloys to provide for a transition of the properties of consumable nozzles A and B over the whole of the surface of the metal workpiece manufactured.
In the preferred embodiment of the method of the present invention automatic electroslag welding equipment is employed. Standard electroslag welding techniques normally practiced in the art and using an electrode wire of any type from which welding arc is produced under the shielding of a granular flux are applicable. A filler steel wire of metallic alloys desired in part or in whole to provide the hardfacing matrix on the work face of the tool being hardfaced is also used. The filler electrode wire and/or the consumable guide nozzles can be composed of or contain oxidizing agents such as ferromanganese and ferrosilicon. They can also contain denitrifying agents such as ferrozircon or slag producing materials for facilitating welding operations and for adjusting basicity of the slag in the weld pool. Metals such as nickel chromium, molybdenum, titanium, zirconium and others are included among the components in the electrode wire and or consumable nozzles.
Again referring to the drawing in FIG. IV, a metal workpiece such as a forged steel tooth 10 designed for use on a bucketwheel excavator and having an indentation on its face is first preheated to a temperature in the range of 500-l00OF. and more preferably 600-700F. and placed in the proper relation to consumable nozzles 15 which are comprised of a compacted alloy of particles having a size distribution in the range of -140 mesh and each containing the components disclosed for nozzles A and B respectively above. In preparing these nozzles, the metallic particle blends were combined in a sodium silicate liquid carrier, compressed into the outer shell and the guide tube was inserted through the center of the filled shell. The whole shell was heated until the silicate bound the metal particles into a solid mass in the shell. I-Ieat exchange shoe 17 is affixed adjacent to the work surface of workpiece l0 and the cavity or gap formed between the cooling shoe and the workpiece provides the walls in which the electroslag weld pool is formed. About 50 grams of metal powder of the same alloy as that in electrodes 13 is placed in sump 16 in FIG. IV. Electroslag welding is initiated by supplying electric power into the electrodes at 55 volts and 400 amps wherein an arc is initiated between the electrode and the powdered metal in the sump. Thereafter 50 grams of flux material is added and the electroslag welding procedure begun. Electrode wires are fed at a rate to provide that the entire cavity is filled over a period of 5.5 minutes. The amperage of the electrode is programmed so that during the 5.5 minute period or welding the amperage continually increases in a linear manner until it reaches 1,000 amperes at the end of the 5.5 minutes. The voltage is programmed to decrease over the same period of time until it reaches 32 volts at the end of 5.5 minutes. The consumable nozzles are oscillated across the face of the workpiece at the rate of 6 oscillations per minute. At the end of the welding step a forged bucketwheel excavator tooth having a custom tailored hardfaced work surface is recovered.
The invention claimed is:
l. A method for hardfacing a metallic workpiece to provide said workpiece with a hardfaced work surface having a variedmetallurgical composition thereover comprising the steps of:
a. placing the work surface to be hardfaced in a vertical position;
b. placing a heat exchange means adjacent and complementary to said work surface to form a gap and retain molten weld metal therebetween;
c. placing adjacent to one area of the work surface within said gap a consumable guide nozzle having means for passing a consumable electrode wire therethrough said consumable guide nozzle containing a predetermined metallurgical composition comprised of fine metal particles adhered to a ho]- low metal guide tube;
d. placing adjacent to a contiguous area of the same work surface of said workpiece, a second consumable guide nozzle having means for passing a consumable electrode wire therethrough said second guide nozzle containing a different predetermined metallurgical composition from that of said first guide nozzle said metallurgical composition comprised of fine metal granules adhered to hollow metal guide tube;
e. feeding an electrode wire through each consumable guide nozzle;
f. passing an electrical current through said electrode wires to deposit weld metal and concurrently melt said consumable guide nozzles and positioning said first and second guide nozzles so that upon melting said first and second guide nozzles form separate zones of different metalurgical composition fused to the surface of the workpiece and connected by a fused zone of a metalurgical composition formed by a blending of the melted metal from said first and second guide nozzles.
2. A method according to claim 1 wherein the workpiece is a bucketwheel excavator tooth.