Method for making a clad metal product

A process for producing clad products that utilizes wrought or cast components eliminating the need for costly metal powders and a can to contain them. A sleeve circumscribes a core leaving a space therebetween. Powder is introduced into the space and is sealed therein. The resultant billet is extruded generating a clean metallurgical bond between the core and the sleeve. The space need not be evacuated prior to heating the billet. Resultant clad welding rod permits higher operating amperages.

TECHNICAL FIELD 
The instant invention relates to clad metal forms in general and, more 
particularly, to a technique for fabricating clad product using powder as 
in intermediate layer. 
BACKGROUND ART 
Clad metal tubing, that is, a tube comprised of a tubular core or wire 
material internally or externally circumscribed by a dissimilar sleeve 
material, has been commercially available for many years. Offering a large 
array of differing physical and chemical characteristics, a composite 
structure may be fabricated to suit particular needs. The strengh of the 
core material matched with selected properties of the cladding affords the 
engineer custom designed options that are superior to single material 
designs. 
Various methods have been developed to coat metal surfaces. However, 
limitations exist with each presently known method. To illustrate, weld 
overlaying is commonly used to coat internal surfaces of articles of 
manufacture but such cladding requires essentially flat or cylindrical 
surfaces having little detail. There are also size limitations for such 
internal linings that are related to access by welding equipment. Similar 
limitations apply to the related processes, flame and plasma spraying 
which, although useful for internal cladding, provide coatings that may 
not be dense enough or thick enough for many applications. Welding and 
spraying methods can not be readily used to apply coatings of reactive 
metals such as titanium. 
Although generally used on flat plate, explosive bonding and braze bonding 
are other methods that may be used for internal cladding. However, these 
processes are of limited use since they require precise mating of part and 
cladding. 
Hot isostatic pressing is generally considered useful for forming powdered 
metal articles and is also useful for external metal cladding. It is 
conceivable that this process could also be used for the internal cladding 
of metal articles; however, the equipment used with this process is 
extremely sophisticated and requires considerable capital investment. 
Composite tubing can be prepared by simultaneous extrusion of a powdered 
metal and a solid shell. This method is applicable to many materials. 
Unfortunately, high production costs translate into high selling prices 
and as a consequence limit the usage of these materials. 
Turning now more particularly to extruding methods, a major difficulty is 
caused by the need for an intermediate can. The can must be first 
fabricated, positioned in place, processed and ultimately removed; each 
step increasing the cost of the technique. Moreover, as the diameter of 
the ultimate product becomes smaller, i.e. welding electrode, the use of a 
can becomes less desirable. 
Representative examples of the prior powder art include U.S. Pat. No. 
2,390,452 which teaches a method for welding dissimilar materials and U.S. 
Pat. Nos. 3,652,235 and 3,753,704 (a continuation-in-part thereof) which 
disclose an isostatic method of fabricating a clad product. U.S. Pat. No. 
4,016,008 utilizes an internal metal liner or can which is generally 
removed. U.S. Pat. No. 4,065,306 utilizes an expandable bladder. 
The instant invention is directed toward the expeditious production of 
tubular or rod goods of relatively lower cost and compatible quality when 
compared to existing methods. 
SUMMARY OF THE INVENTION 
Accordingly, there is provided a method for making a billet for extrusion 
without the need for a can to contain the cladding powder. As a result, 
smaller quantities of powder are needed. 
Essentially, the method utilizes wrought or cast material for both the core 
and the sleeve. A space between the core and the sleeve is filled with a 
small quantity of powder that is consolidated during extrusion. By 
eliminating cans and bladders, the thickness of the space is not 
dimensionally critical. This permits relative ease of assembly of the 
extrusion billet. 
The utilization of the powder insert the core and the sleeve follows for 
dissimilar materials to be bonded together to form a composite cladded 
tube and rod. Inasmuch as physical dimensions are less critical with the 
instant method, the disclosed technique is useful for an entire array of 
shaped products such as tubes, pipe, squares, rod, wire and welding 
electrodes. 
The advantages of the instant invention are: 
(A) Ease of assembly. 
(B) No preparation and removal of a can. 
(C) Produces material that can be produced economically on conventional hot 
and cold working mill equipment and rotary forges. 
(D) Requires minimal machining to produce component parts. 
(E) Good bonding affinity between the core and the sleeve. 
(F) No large quantity of powder required for the sleeve material. 
(G) Method is amenable to tube and welding rod and wire products. 
(H) Method permits a thin cladding layer to be placed on the outside 
diameter, the inside diameter or both surfaces of a tube. 
(I) Method permits many alloy considerations without the attendant 
production of costly powders.

PREFERRED MODE FOR CARRYING OUT THE INVENTION 
FIGS. 1 and 2 are cross sectional views of a billet 10 prior to extrusion. 
The billet 10 consists of a core 12, an external sleeve 14 and powder 16 
disposed therebetween in the resultant annular space 22. End caps 18 seal 
in the powder 16. The axis of symmetry is representated by reference 
numeral 20. 
The billet 10 may be prepared by vertically orienting the core 12 and 
sliding a spacer (not shown) having a thickness equal to the predetermined 
thickness of the space 22 over the core 12. The sleeve 14 is then slid 
over the spacer. One end cap 18 is welded to the top of the core 12 and 
the sleeve 14. All welds should be air tight. The billet 10 is then 
inverted, the spacer removed and the powder 16 is introduced to the space 
22. 
A small quantity of titanium sponge may be introduced into the space 22 
before the powder 16 is fed into it. The titanium sponge serves as an 
oxygen getter during the subsequent sintering and billet heating process. 
This eliminates the need for evacuation of the biller 10 after powder 
filling. Eventually the titanium containing end portions of the extruded 
product may be cut off. 
Depending on the materials selected the powder 16 may be a prealloyed, 
blended or single elemental powder. 
To assist in filling the space 22, the billet 10 should be vibrated and a 
funnel used to feed the powder into the space 22. 
After the space 22 has been filled with the powder 16 and additional 
titanium sponge, another end cap 18 is welded on the sleeve 14 and core 12 
to complete the assembly of the billet 10. Rounding or radiusing the 
leading end of the billet 10 aids the extrusion process. 
In the instant invention, metal powders in small quantities are used to 
fill the air gap between the two major components of the clad products 
(irrespective of whether inside diameter or outside diameter clad material 
is being made). It has been demonstrated experimentally that the powder 
can be similar in or identical composition to either of the major 
components or dissimilar to both components. 
Using previous techniques, clad tubing may be made by co-extrusion of two 
dissimilar metals that have been shrunk or press fitted together so that a 
metallurgical bond is achieved on extrusion or working. The use of 
interference fits to join the dissimilar metals requires costly very close 
tolerance machining, a means to heat or cool one of the components, and a 
pressing device for assembly. Contrary to current practice, powder is used 
in the instant invention to permit lower cost "sloppy" tolerance between 
the components to be joined and assembly can be accomplished without the 
use of presses. A role of the powder is that of a filler to compensate for 
differences in machined sizes of component parts. 
Further cost reductions are achieved in the instant invention because the 
material used for the components can be static or centrifugally cast or 
made from wrought or extruded products. The versatility of the method can 
be visualized with the following hypothetical example: assume that a tube 
is being centrifugally cast as a sleeve for cladding on the outside 
diameter of some core material. The desired wall thickness of the tube 
centrifugally cast may be nominally one inch (2.54 cm) wall thickness but 
due to casting flaws or variability in the amount of metal cast, final 
wall thickness of the tube may be greater than or less than the desired 
thickness. The instant method provides latitude in accomodating the 
dimensional variations by using slightly more or less powder as required 
to achieve component wall thickness (in this case one inch [2.54 cm ]). 
Ten experimental extrusion billets were prepared as described above. 
Details are provided in the table below: 
__________________________________________________________________________ 
Extrusion Billet Make-Up 
Heat 
Temperature 
Die Size 
Throttle 
Outer 
I.D. 
.degree.F. 
(.degree.C.) 
in. 
(mm) 
% Sleeve Powder 
Core 
__________________________________________________________________________ 
2 2150 
(1177) 
0.750 
(19.1) 
34 INCOLOY 
INCOLOY 
INCONEL 
alloy 825 
alloy 825 
alloy 625 
3 2150 
(1177) 
0.750 
(19.1) 
34 INCOLOY 
INCONEL 
INCONEL 
alloy 825 
alloy 671 
alloy 600 
1 2150 
(1177) 
0.750 
(19.1) 
34 INCOLOY 
INCOLOY 
INCONEL 
alloy 825 
alloy 825 
alloy 600 
4 2150 
(1177) 
0.750 
(19.1) 
34 INCOLOY 
INCONEL 
INCONEL 
alloy 825 
alloy 671 
alloy 625 
5 2150 
(1177) 
0.750 
(19.1) 
34 INCOLOY 
NICKEL 
INCONEL 
alloy 825 
123 alloy 600 
6 2150 
(1177) 
0.750 
(19.1) 
34 INCOLOY 
NICKEL 
INCONEL 
ALLOY 825 
123 ALLOY 625 
7 2050 
(1121) 
0.750 
(19.1) 
34 INCOLOY 
INCOLOY 
INCONEL 
alloy 825 
alloy 825 
alloy 600 
8 2050 
(1121) 
0.750 
(19.1) 
34 INCOLOY 
INCOLOY 
INCONEL 
alloy 825 
alloy 825 
alloy 625 
9 2050 
(1121) 
0.750 
(19.1) 
34 INCOLOY 
NICKEL 
INCONEL 
alloy 825 
123 alloy 600 
10 2050 
(1121) 
0.750 
(19.1) 
34 INCOLOY 
NICKEL 
INCONEL 
alloy 825 
123 alloy 625 
__________________________________________________________________________ 
Extrusion Comments: 
#4 Melted. Suspect extrusion temperature too high for 625 core 
#6 Same as #4 
#8 Press malfunction 
INCOLOY and INCONEL are trademarks of assignee 
The billets were extruded on Loewy.RTM. hydropress (750-ton) {3,336N} 
capacity) to an 0.750 inch (19.1 mm) diameter at an extrusion ratio of 
21:1. 
The combination of high extrusion temperatures, high extrusion ratios and 
the alloy combinations within the billets caused some initial problems. 
There was evidence of melting in some of the rods but good metallurgical 
bonds were obtained in all of the alloy combinations. 
Photomicrographs of the extruded materials showed that sound metallurgical 
bonds were obtained with the three powders used. Thus, it can be concluded 
that the powder used to fill the annular space may be similar or identical 
in composition to one of the components or dissimilar to both materials. 
Accordingly, actual commercial practice will dictate the choice of 
components to obtain the desired mechanical and chemical properties of the 
finished product. Diffusion across boundary lines is minimal and not 
believed to pose any difficulties. Samples of the as-extruded rods were 
hot rolled from 0.750 inch (19.1 mm) diameter to 0.650 inch (16.5 mm) 
diameter as starting stock for cold rolling exteriments. They were 
annealed for 0.5 hour at 1850.degree. F. (1010.degree. C.) and cold rolled 
to 0.500 inch (12.7 mm) squares. The percent reduction was 24% cold work. 
The material rolled without incident. Photomicrographs showed that the 
bond integrity was maintained. Samples 4 and 6 that experienced melting 
were actually improved after cold rolling but some evidence of melting was 
still evident. 
The above experiments had the width of the annular space as a variable. No 
effect was observed and it can be concluded that there could be a minimum, 
consistent with the ease of filling. If the powder used is of the same 
composition of one of the components comprising the core or sleeve, then 
its thickness can be apparently greatly expanded without detrimental 
effects on the final product. 
Additional experiments were run to determine the applicability of the 
instant invention to clad or duplex welding electrodes. It is known that 
certain existing welding nickel-base electrodes are amperage limiting. Due 
to excess heating of the electrode, the welder must either turn down the 
amperage setting or waste the portion of the electrode that overheats. 
This inefficiency causes loss of both material and the welder's time. 
By utilizing the instant method, it has been determined that a nickel-iron 
duplex electrode may be processed to wire and flux coated to produce 
electrodes that may be used at more than 20% higher amperage settings than 
current electrodes without overheating. 
The resultant wire has either nickel or iron sheathing the other component. 
Nickel is the preferred sheathing material because it has a lower 
electrical resistivity thus allowing for higher electrical currents to be 
carried without overheating. In addition, nickel does not oxidize as does 
iron. 
As with the production of tubing, the wire billet uses a metal powder 
between the components. This use of the powder permits the use of more 
lineral machining and rolling tolerances for preparation of the component 
parts. The powder aids in metallurgical bonding of tube component parts. 
An additional benefit over conventional methods of making duplex billets 
is that the costly requirement that the billet be extruded to a billet for 
hot rolling to wire rod has been eliminated. The duplex billet may 
directly rotary forged to a rectangular section for hot rolling or hot 
rolled directly to wire rod. As a last step conventional wire drawing 
processes may be utilized in reducing the wire to final size. 
A series of comparison tests were conducted to determine the efficacy of 
the instant method with respect to welding electrodes. 
Method 1 
A nickel tube (31/2 inch [89 mm] outside diameter, 21/2 inch [57 mm] inside 
diameter.times.61/2 inch [165 mm] long) was machined to have a 2.35+0.010 
inch (60 mm) inside diameter. An iron (1010 HR Steel) rod was machined to 
a 2.35-0.010 inch (60 mm) diameter and the two pieces were fit together 
and both ends welded at their mating surfaces. Both materials were acid 
pickled for oxide removal and solvent cleaned before assembly. Note that 
this method of billet assembly requires that both pieces require machining 
to close tolerance that adds to the cost of production. 
Method 2 
A nickel tube (31/2 inch [89 mm] outside diameter, 3 inch [76 mm] inside 
diameter.times.61/2 inch [165 mm] long) was used as the outer sleeve. An 
iron rod was machined 2.35.+-.0.020 inch (60 mm) diameter. Note that 
tolerances were much more liberal, which cuts machining costs. An end cap 
was welded to join the sleeve and core. The iron core was centered inside 
the nickel sleeve. The space was filled with Nickel 123 (essentially pure 
nickel) powder. Vibration was used to further pack the loose powder. The 
loose powder does not have the density of wrought nickel so that while the 
calculations show the nickel to be 58% of the weight, in actuality, the 
nickel weight approached 55%. After filling the space with powder, a cap 
was welded on the open end. The same cleaning procedures were used on this 
billet. 
Both billets were charged into a furnace at 1950.degree. F. (1066.degree. 
C.) and heated four hours at temperature. Each billet was upset forged in 
an extrusion press at 500 tons (2224N) against a blank die. After ejection 
from the press, both billets were reheated at 1950.degree. F. 
(1066.degree. C.) for about one hour and hot rolled to a 0.680 inch (17 
mm) diameter rod. Material from Method 1 showed cracking of the nickel 
caused by breaking up to the core during rolling. The materials did not 
seem to roll as one and metallurgically bond but seemed to come apart as 
rolling progressed. The billet from Method 2 containing the nickel powder 
was rolled without incident to a high quality rod. 
The 0.680 inch (17 mm) diameter hot rolled rod of Method 2 was annealed at 
1850.degree. F. (1010.degree. C.)/0.5 hour, air cooled and cold rolled on 
an 8 inch (203 mm) rod mill to about 0.5 inch (18 mm), round cornered 
square, reannealed as above, cold rolled to 0.25 inch (6.3 mm) round, 
annealed as above, cold rolled on a 4 inch (102 mm) rod mill to 0.125 inch 
(3 mm) round cornered square. All cold work was done without incident. 
The material was then cold drawn to 0.093 inch (2 mm) diameter using dry 
soap as a lubricant. A review of the cross sectional profiles of the wire 
as it was being processed indicated that the material became fully dense 
and would behave as a solid wire. 
Comparing existing commercial electrodes with those made in accordance with 
this invention, calculations were undertaken to show the effects of 
electrode heating during welding. The material heating effect caused by 
the electrode carrying a current while welding is shown by the expression: 
EQU P.sub.H =I.sup.2 R [1] 
where 
P.sub.H=heat generated in watts 
I=applied welding current in amperes 
R=resistance of the material in ohms 
##EQU1## 
where .rho.=resistivity in ohms.times.10.sup.-6 cm 
L=electrode length in centimeters 
A=cross section of electrode in square centimeters (0.04383 cm.sup.2) 
EQU .rho..sub.Ni= 6.84 .times.10.sub.-6.sup.-6 ohm cm 
EQU .rho..sub.Fe= 9.7.times.10.sub.-6.sup.-6 ohm cm 
EQU .rho..sub.NiFe 258 =30-35.times.10 ohm cm 
NiFe 258 is a conventional alloyed wire consisting of about 55% nickel and 
45% iron. 
The table below compares the heat generated by the various compositions: 
______________________________________ 
.sup.P H = I.sup.2 R, Watts 
Material 
Length, cm 
R, Ohms at 60 Amps 
at 90 Amps 
______________________________________ 
Ni 30 0.00468 16.85 37.91 
Ni 10 0.00156 5.62 12.64 
Fe 30 0.00628 22.61 50.87 
Fe 10 0.00209 7.52 16.93 
NiFe 258 
30 0.02259 81.32 182.98 
NiFe 258 
10 0.00753 27.11 60.99 
______________________________________ 
It may be seen from the data in the preceding table that NiFe 258 produces 
about five times more heat than the nickel sheathed material and would 
produce about three and one-half times more heat than would an iron 
sheathed rod. 
The nickel sheathed material would generate only about 75% as much heat as 
the iron sheathed electrode. The nickel sheathed electrode would also be 
protected from surface oxidation since iron oxidizes. Accordingly, it is 
preferable to put nickel on the outside surface. 
Obviously, the nickel sheathed material could be used at higher amperage 
setting significantly higher than the NiFe 258 or higher settings than the 
iron. This is important to the welding industry. 
0.093 inch (2.4 mm) diameter wire was made into 0.125 inch (3.2 mm) 
diameter coated electrodes for welding. They were compared to NI-ROD.RTM. 
welding electrode 55 and NI-ROD.RTM. welding electrode 55X. (NI-ROD is a 
trademark of assignee.) These commercially available electrodes are made 
from NiFe 258 alloy. Tests indicated that the clad electrodes would 
operate at 110-120 amperes as compared to 90 amperes for the conventional 
electrodes. 
While in accordance with the provisions of the statute, there is 
illustrated and described herein specific embodiments of the invention, 
those skilled in the art will understand that changes may be made in the 
form of the invention covered by the claims and that certain features of 
the invention may sometimes be used to advantage without a corresponding 
use of the other features.