Composite metal articles

A method of forming a composite article having a first and a second metal components, and a resultant composite metal article, wherein a flux coating is applied over at least a substantially oxide-free bond surface of the first component, the first component with said flux coating is preheated and, with said first component positioned in a mould to fill a portion of a cavity of the mould, a melt for providing the second component is poured into the mould so as to flow over said bond surface; the first component being preheated to a first temperature and the melt being poured at a second temperature such that, on flowing over the bond surface, the melt displaces said flux coating and wets said bond surface, and that such initial temperature equilibration between said surface and the melt results in an interface temperature therebetween at least equal to the liquidus temperature of the melt, thereby resulting on solidification of the melt in attainment of a bond between the components.

The invention relates to composite metal articles. The invention 
particularly relates to articles of two different metals securely bonded 
together, with one metal protecting the other in a manner required for a 
particular application. 
A wide variety of procedures has been proposed for providing composite 
metal articles to enable use of desirable properties of two dissimilar 
metals. Thus, articles of a metal of low corrosion resistance frequently 
are protected by hard-facing or cladding with a wear or corrosion 
resistant metal such as stainless steel. Alternatively, tough but readily 
machinable metals can be similarly protected by application of a material 
which provides in a composite article the required wear resistance. In the 
latter case, the tough metal supports and retains a relatively brittle 
abrasion resistant material which may fracture under impact loading, while 
also enabling machining and fixing of the composite article in a manner 
possible only with difficulty for an article of abrasion resistant 
material alone. 
Hardfacing by weld deposition of metal to provide a composite article, 
while widely used, is relatively slow, labour intensive, relatively costly 
and subject to a number of practical limitations. However, recourse to 
hardfacing is necessary in many applications because of the lack of an 
economic and/or practical alternative. A variety of alternative proposals 
is set out in U.K. patent specifications Nos. 888404, 928928, 977207, 
1053913, 1152370, 1247197 and 2044646 and in U.S. Pat. Nos. 3,279,006 and 
3,342,564. 
U.K. Pat. No. 888404 proposes a process for clad steel products, such as of 
mild or low alloy steel and a stainless steel, clad by casting a melt of 
one of the steels around a solid of the other steel. The solid other metal 
is mechanically or chemically cleaned prior to the casting process, while 
casting is performed under a substantial vacuum. However, it is made clear 
that no complete bond is made merely by the casting process. The composite 
article thus has to be hot-rolled to weld the two steels together; the 
bonding being effected by the hot rolling. The process thus suffers from 
the disadvantages of having to be performed under vacuum, a procedure not 
well suited to many production situations; while the need for hot rolling 
limits the choice of materials with which the process can be applied, as 
well as the form of the resultant composite article. 
U.K. Pat. No. 928928 is concerned with liners for grinding mills, and 
points out the problems resulting from making the liner solely from an 
abrasion resistant material such as carbidic cast iron, either unalloyed, 
or an alloyed cast iron such as nickel-chromium white cast iron. It thus 
proposes a composite liner of such material and a backing of a softer and 
tougher metal or alloy, produced by a double casting operation in which a 
first metal is cast, and the second metal is cast against the first metal. 
Evidently cognizant of the difficulty of achieving a bond between a solid 
and a cast metal, and being unable with a brittle cast iron to have 
recourse to hot rolling to overcome this difficulty, U.K. Pat. No. 928928 
teaches that the first metal, typically the carbidic cast iron, is only 
partially solidified when the second metal is cast against it. 
U.K. Pat. No. 928928 recognises the adverse consequences of oxidation of 
the surface of the first metal against which the second metal is to be 
cast. For this purpose, a chill mould is used to achieve rapid cooling of 
the first metal to its partially solidified condition. However, to further 
offset oxidation, a flux can be used to protect that surface; the flux 
being present in the mould before pouring the first metal or added in 
liquid form with the first metal. 
Due to the backing being cast in the proposal of U.K. Pat. No. 928928, its 
properties will be inferior to those of a wrought backing. Also, the need 
for the first metal to be only partially solidified when casting the 
second metal provides a substantial constraint. Thus, close temperature 
control is imperative due to rapid cooling of the melt of the first metal 
and the need to cast the second metal while the first is only partially 
solidified. Pouring of the second metal with the first still too hot, that 
is, still containing liquid, will result in mixing of the metals, and loss 
of properties due to dilution; while, if the first metal is too cool, 
sound bonding is not likely. Also, the process necessitates two melts 
available at the same time and at well-controlled temperatures and, while 
some foundries will be able to meet this need, there remains the problem 
of coordinating pouring from the two ladles necessary. Additionally, there 
is the practical problem of feeding solidification shrinkage in the cast 
first metal with metal of the same composition. In the disclosure of U.K. 
Pat. No. 928928, such shrinkage can only be fed from the second metal, so 
that the first metal ultimately will contain regions of dissimilar 
composition. Additionally, the process of U.K. Pat. No. 928928 
necessitates the surface of the first metal being horizontal, with severe 
limitations on the range of composite articles able to be produced. 
Further, the second metal has to be fed horizontally over that surface to 
avoid excessive mixing of the two melts; while flow-rate of the second 
metal over that surface has to be controlled so as to disturb the first 
metal as little as possible, for the same reason. 
U.K. Pat. No. 977207 proposes a process for seamlessly clad products, such 
as pipes or rods, in which respective parts are of a soft steel such as 
stainless steel and a mild steel. In this process, a component of one of 
those steels is heated under vacuum or a non-oxidizing atmosphere and, 
while maintaining such environment, it is plunged rapidly into a melt of 
the second steel. The temperature of heating of the component of the first 
steel is to be to a temperature such that, on being plunged into the melt 
of the second steel, its surface becomes a semi-molten or highly viscous 
melt such that, on cooling of the two steels, they are welded together. 
The need for operation under a vacuum or a non-oxidizing atmosphere is a 
severe constraint, typically necessitating a sealed vessel in which the 
process is performed to exclude oxidation on heating the first component 
to near the melting point of the second metal. Also, the process again is 
limited in the range of shapes or forms of composite articles able to be 
produced. Additionally, the process is not amenable to use where the two 
metals differ significantly in melting point. 
The severe disadvantages of operating with a non-oxidizing atmosphere also 
applies to the similar disclosures of U.K. Pat. Nos. 1053913 and 1152370. 
These disclosures differ essentially in the composition of their 
respective wear resistant materials; U.K. Pat. No. 1053913 proposes 
chromium-boron white cast irons containing molybdenum and vanadium, while 
U.K. Pat. No. 1152370 proposes nickel-boron cast irons containing 
molybdenum and vanadium. In each case the solid cast iron, in the form of 
crushed pig and pellets, is sealed to prevent atmospheric oxidation in a 
housing in which it is to provide a lining and heated therein under an 
inert atmosphere so as to melt. The housing is spun to centrifugally 
distribute the molten cast iron, and the housing and melt thereafter are 
cooled. In addition to the disadvantage of the need for an inert 
atmosphere, and spinning of the housing until the cast iron has 
solidified, the disclosure of each of U.K. Pat. Nos. 1053913 and 1152370 
has other disadvantages. The housing, of necessity, must have a melting 
point substantially above that of the cast iron, as the heating of the 
housing has to be limited to a temperature below that at which distortion 
or deformation of the housing will occur, particularly when spun. 
Additionally, the disclosure has severe limitations in relation to the 
shape of the resultant composite article, given the reliance on 
centrifugal distribution of the cast iron melt; while there is no 
disclosure as to how as a practical matter the higher melting point 
housing can be provided with externally distributed cast iron. 
U.K. Pat. No. 1247197 is similar overall to U.K. Pat. Nos. 1053913 and 
1152370. It differs principally in its use of eutectic Fe-C, plus higher 
melting point alloys, to form the cast iron. 
U.S. Pat. Nos. 3,342,564 and 3,279,006 relate respectively to a composite 
article and a method for its production in which a melt of one metal is 
cast to fill a mould containing a solid second metal. Again, a vacuum or 
non-oxidizing atmosphere is necessary, due to the second metal being 
preheated to an elevated temperature such that melting of its surface 
occurs on casting of the first metal, and the need to protect against 
oxidation of the second metal. 
Finally, U.K. Pat. No. 2044646 proposes hot welding together of a soft 
steel and a martensitic white cast iron. The welding together can be 
achieved by casting the white iron onto soft-steel plate, with the latter 
possibly being preheated. Alternatively, the cast iron can be cast first 
and, while still hot, the soft steel cast thereagainst. However, in the 
first of these alternatives, hot welding is likely only if surface melting 
of the soft-steel occurs, a situation not suggested by the optional nature 
of possibly preheating the soft steel. Also, oxidation of the soft-steel 
occurs to such an extent that, even with melting of the surface of the 
soft-steel, a sound bond between the soft-steel and cast iron is hard to 
achieve. Similar considerations apply in the second case, except that 
oxidation is of the cast iron during its cooling. Indeed, it is only by 
mechanical interlocking resulting from perforations or the like in the one 
metal, against which the other is cast, that the two metals are likely to 
be adequately secured together. However, such interlocking obviates the 
advantage of a soft-steel backing in protecting the brittle cast iron 
under impact loading, as the interlocking gives rise to localized stress 
concentration in the cast iron. 
The present invention seeks to provide an improved composite metal article, 
and a processs for its production which is more amenable to simple foundry 
practice and which enables a wider choice of metals. 
The invention provides a method of forming a composite metal article, 
wherein a first metal component for the article is preheated and, with the 
first component positioned in a mould cavity to fill a portion of the 
cavity, a melt for providing a second metal component is poured so as to 
flow into the cavity over a surface of the first component; the 
temperature of said surface of the first component and the temperature of 
the melt being controlled so as to achieve wetting of said surface by the 
melt and attainment of a bond between the components on solidification and 
cooling of the melt which is strengthened by diffusion between the 
components and is substantially free of a fusion layer of said surface of 
the first component. 
The required bond substantially free of a fusion layer is achieved if the 
surface of the first component is wetted by the melt which is to form the 
second component. Such wetting of that surface is found to occur if: 
(a) a favourable surface energy relationship exists between the surface of 
the first component and the melt--a condition obtained if the surface is 
substantially free of oxide contamination but precluded by such 
contamination, and 
(b) the first component has a relatively high melting point and its 
surface, with the melt cast thereagainst, attains a sufficiently high 
temperature, most preferably a temperature equal to or greater than the 
liquidus temperature of the melt. 
The bond generally is sharply defined but typically exhibits some solid 
state diffusion between the components. Also, while a fusion layer 
resulting from melting of the first layer substantially is avoided, the 
bond may be characterised by microdissolution, as distinct from melting, 
of the first component in the melt prior to solidification of the latter. 
Additionally, some epitaxial growth from the surface of the first 
component can occur, although this has not been seen to characterize the 
bond to any visible extent. 
Thus, it is found that the attainment of a sound bond by casting a melt of 
a metal against a solid component is dependent, inter alia, upon the 
temperature prevailing at the surface of the solid component against which 
the melt is cast, and also the absence of oxidation of that surface. In 
general, the prior art has endeavoured to protect against oxidation by use 
of a vacuum or non-oxidizing atmosphere; a vacuum generally being 
preferred. However, as a practical matter, casting under vacuum is not 
well suited to industrial foundry practice and necessitates expensive 
apparatus. Particularly in repetitive casting operations, it also 
substantially increases production time. Similar comments apply to casting 
under a non-oxidizing atmosphere since, to provide adequate protection of 
the first component, casting under such atmosphere must be performed in a 
closed vessel similar to that necessary when operating under vacuum. That 
is, particularly when the solid first component is heated, as is necessary 
for a sound bond, the precautions necessary to protect its surface against 
oxidation increase with temperature and it is necessary that the melt for 
the second component be cast against the surface substantially in the 
absence of oxide on the surface. 
It is found that a sound bond is achieved if the surface of the first 
component is cleaned to remove any oxide film and then protected, until 
the melt for the second component is cast against it, by a film of a 
suitable flux. A variety of fluxes can be used, while these can be applied 
in different ways. However, the flux most preferably is an active flux in 
that it not only prevents oxidation of the surface of the first component, 
but also cleans that surface of any oxide contamination remaining, or 
occurring, after cleaning of that surface. Suitable fluxes include Comweld 
Bronze Flux, which has a melting point of about 635.degree. C. and 
contains 84% boric acid and 7% sodium metaborate, Liquid Air Formula 305 
Flux (650.degree. C., 65% boric acid, 30% anhydrous borax) and CIG G.P. 
Silver Brazing Flux (485.degree. C. and containing boric acid plus 
borates, fluorides and fluoborates). Less active fluxes, such as anhydrous 
borax (740.degree. C.), which simply provide a protective film but do not 
remove existing oxide contamination of the surface, can also be used 
provided that such combination first is mechanically or chemically 
removed. 
As indicated above, the temperature prevailing at the surface of the solid 
component against which the melt is cast is an important parameter. By 
this is meant the temperature at the interface between the components on 
casting the melt. However, while important, this parameter is secondary to 
the need for that surface of the solid component to be free of oxide, 
since attainment of an otherwise sufficient interface temperature will not 
achieve a sound bond if that surface is oxidized. 
The interface temperature attained is dependent on a number of factors. 
These include the temperature to which the solid component is preheated, 
the degree of superheating of the melt when cast, the area of the surface 
of the solid component against which the melt is cast, and the mass of the 
solid and cast components. Also, where the respective metals of those 
components differ, further variables include the respective thermal 
conductivity, specific heat and density of those metals. However, 
notwithstanding the complex inter-relationships arising from these 
parameters, it has been found that a satisfactory bond can be achieved 
when the solid component is preheated to a temperature of at least about 
350.degree. C. The solid component preferably is preheated to a 
temperature of at least about 500.degree. C. 
It is highly preferred that the temperature to which the solid component is 
preheated and the degree of superheating of the melt are such that, on 
casting the melt, an interface temperature equal to or in excess of the 
liquidus temperature for the melt is achieved. It is found that the 
substantially instantaneous interface temperature is not simply the 
arithmetic mean of the preheat and melt temperatures, weighted if 
necessary for differences in thermal conductivity, specific heat and 
density, as could be expected. Such arithmetic mean in fact results in 
erroneously low determination of substantially instantaneous interface 
temperature, since the calculation assumes that heat transfer from the 
melt to the solid component is solely by conduction. Calculation of the 
Nusselt number for the melt shows that convection that transfer in the 
melt also is important and, when this is taken into account, it shows the 
substantially instantaneous interface temperature may be up to about 
150.degree. C. to 200.degree. C. higher than the arithmetic mean of the 
preheat temperature of the solid component and the melt temperature. 
The requirement that an interface temperature equal to or above the 
liquidus temperature of the melt be attained means that the invention 
principally is applicable where the solid first component has a melting 
range commencing at a temperature at least equal to the liquidus of the 
melt to provide the second component. Also, it is to be borne in mind that 
while reference is made in the preceding paragraph to the substantially 
instantaneous interface temperature, that reference is by way of example. 
That is, the required interface temperature need not be attained 
instantaneously, and may be briefly delayed such as due to a temperature 
gradient with the first component. It also should be noted that the 
invention can be used where the melt to provide the second component is of 
substantially the same composition as the first component; the first and 
second components thus having substantially the same melting range. In 
such case, it remains desirable that the surface of the first component 
against which the melt is cast still attains, on casting of the melt, a 
temperature at least equal to the liquidus temperature of the melt, but 
that the body of the first component acts as a heat sink which quickly 
reduces that surface temperature before significant fusion of the surface 
occurs. Similarly, the invention can be applied where the first component 
has a melting range commencing below that of the material for the second 
component, provided such quick cooling can prevent significant surface 
fusion of the first component; although such lower melting range first 
component is not preferred. 
Attainment of a sufficient interface temperature is achieved by a balance 
between preheating of the first component, and the extent of superheating 
of the melt to provide the second component. The preheating preferably is 
to a temperature in excess of 350.degree. C., more preferably to at least 
500.degree. C. The melt preferably is superheated to a temperature of at 
least 200.degree. C., most preferably at least 250.degree. C., above its 
liquidus temperature. However, in the case of aluminium bronzes such as 
hereinafter designated which are highly prone to oxidation, it can be 
desirable to drop these limits to 100.degree. C. and 150.degree. C. 
respectively, with a corresponding increase in preheating of the 
substrate. 
The use of a flux and attainment of a sufficient interface temperature 
enables a sound bond to be achieved between similar metals and also 
between dissimilar metals. We have found that these factors enable such 
bond to be achieved in casting a stainless steel against a mild steel, or 
an alloy steel such as a stainless steel. A sound bond also similarly is 
round to be achieved in casting a cast iron, for example, a white cast 
iron such as a chromium white cast iron, against a mild steel, an alloy 
steel such as a stainless steel, or cast iron such as a white cast iron. 
Additionally, cobalt-base alloys similarly can be cast against a mild 
steel or an alloy steel to achieve a sound bond therebetween. Moreover, 
similar results can be achieved in casting nickel alloys, such as low 
melting point nickel-boron alloys, and aluminium bronzes against mild 
steel or alloy steels. 
Stainless steels with which excellent results can be achieved, either as 
the solid first component or the cast second component, include those such 
as austenitic grades equivalent to AISI 316 or AS 2074-H6A, having 0.08 
wt.% maximum carbon, 18 to 21 wt.% chromium, 10 to 12 wt.% nickel and 2 to 
3 wt.% molybdenum, the balance substantially being iron. AISI 304 
stainless steel, with 0.08 wt.% maximum carbon, 18 to 21 wt.% chromium, 8 
to 11 wt.% nickel, and the balance substantially iron, also can be used. 
Suitable cobalt base alloys include those of compositions typified by 
(Co,Cr).sub.7 C.sub.3 carbides in an eutectic structure and a work 
hardenable matrix, such as compositions comprising 28 to 31 wt.% chromium, 
3.5 to 5.5 wt.% tungsten, 3.0 wt.% maximum iron, 3.0 wt.% maximum nickel, 
2.0 wt.% maximum manganese, 2.0 wt.% maximum silicon, 1.5 wt.% maximum 
molybdenum, 0.9 to 1.4 wt.% carbon and the balance substantially cobalt. A 
cobalt base alloy having the nominal composition 29 wt.% chromium, 6.3 
wt.% tungsten, 2.9 wt.% iron, 9.0 wt.% nickel, 1.0 wt.% carbon and the 
balance substantially cobalt, also has been found to be suitable. 
Cast irons used as the second component include chromium white irons, of 
hypo- or hyper-eutectic composition. For these the carbon content can 
range from about 2.0 to 5.0 wt.% while the chromium content can be 
substantially in excess of chromium additions used to decrease 
graphitization in cast iron. The chromium content preferably is in excess 
of 14 wt.% and may be as high as from 25 to 30 wt.%. Conventional alloying 
elements normally used in chromium white iron can be present in the 
component of that material. Particular chromium white irons found to be 
suitable in the present invention include: 
(a) AS 2027 grade Cr-15, Mo-3, cast iron having 2.4 to 3.6 wt.% carbon, 0.5 
to 1.5 wt.% manganese, 1.0 wt.% maximum silicon, 14 to 17 wt.% chromium 
and 1.5 to 3.5 wt.% molybdenum, the balance apart from incidental 
impurities being iron. 
(b) AS 2027 grade Cr-27 cast iron having 2.3 to 3.0 wt.% carbon, 0.5 to 1.5 
wt.% manganese, 1.0 wt.% maximum silicon, 23 to 30 wt.% chromium, and 1.5 
wt.% maximum molybdenum, the balance apart from incidental impurities 
being iron. 
(c) austenitic chromium carbide iron having 2.5 to 4.5 wt.% carbon, 2.5 to 
3.5 wt.% manganese, 1.0 wt.% maximum silicon, 25 to 29 wt.% chromium, and 
0.5 to 1.5 wt.% molybdenum, the balance apart from incidental impurities 
being iron. 
(d) complex chromium carbide iron having 4.0 to 5.0 wt.% carbon, 1.0 wt.% 
maximum manganese, 0.5 to 1.5 wt.% silicon, 18 to 25 wt.% chromium, 5.0 to 
7.0 wt.% molybdenum, 0.5 to 1.5 wt.% vanadium, 5.0 to 10.0 wt.% niobium, 
and 1.0 to 5.0 wt.% tungsten, the balance apart from incidental impurities 
being iron. 
(e) complex chromium carbide iron having 3.5 to 4.5 wt.% carbon, 1.0 wt.% 
maximum manganese, 0.5 to 1.5 wt.% silicon, 23 to 30 wt.% chromium, 0.7 to 
1.1 wt.% molybdenum, 0.3 to 0.5 wt.% vanadium, 7.0 to 9.0 wt.% niobium, 
and 0.2 to 0.5 wt.% nickel, the balance apart from incidental impurities 
being iron. 
Suitable nickel alloys include nickel-boron alloys conventionally applied 
by hard-facing and characterized by chromium borides and chromium carbides 
in a relatively low melting point matrix. Particularly preferred 
compositions are those substantially of eutectic composition and having 11 
to 16 wt.% chromium, 3 to 6 wt.% silicon, 2 to 5 wt.% boron, 0.5 to 1.5 
wt.% carbon and optionally 3 to 7 wt.% iron the balance, apart from 
incidental impurities being nickel. Exemplary compositions are: 
(a) 77 wt.% nickel, 14 wt.% chromium, 4.0 wt.% silicon; 3.5 wt.% boron and 
1.0 wt.% carbon, plus incidental impurities; and 
(b) 13.5 wt.% chromium, 4.7 wt.% iron, 4.25 wt.% silicon, 3.0 wt.% boron, 
0.75 wt.% carbon and, apart from incidental impurities, a balance of 
nickel. 
Aluminium bronze compositions suitable for use in the invention vary 
extensively but, excluding impurities, are typified by: 
(a) 86 wt.% minimum copper, 8.5 to 9.5 wt.% aluminium and 2.5 to 4.0 wt.% 
iron (UNS No. C95200); 
(b) 86 wt.% minimum copper, 9.0 to 11.0 wt.% aluminium, and 0.8 to 1.5 wt.% 
iron (UNS No. C95300); 
(c) 83 wt.% minimum copper, 10.0 to 11.5 wt.% aluminium, 3.0 to 5.0 wt.% 
iron, 2.5 wt.% maximum nickel (plus any cobalt), and 0.5 wt.% maximum 
manganese (UNS No. C95400); 
(d) 78 wt.% minimum copper, 10.0 to 11.5 wt.% aluminium, 3.0 to 5.0 wt.% 
iron, 3.0 to 5.5 wt.% nickel (plus any cobalt), and 3.5 wt.% maximum 
manganese (UNS No. C95500); 
(e) 71 wt.% minimum copper, 7.0 to 8.5 wt.% aluminium, 2.0 to 4.0 wt.% 
iron, 11.0 to 14.0 wt.% manganese, 1.5 to 3.0 wt.% nickel, 0.10 wt.% 
maximum silicon, and 0.03 wt.% maximum lead 
(f) 79 wt.% minimum copper, 8.5 to 9.5 wt.% aluminium, 3.5 to 4.5 wt.% 
iron, 0.8 to 1.5 wt.% manganese, 0.10 wt.% maximum silicon and 0.03 wt.% 
maximum lead (UNS No. C95800); and 
(g) 12.5 to 13.5 wt.% aluminium, 3.5 to 5.0 wt.% iron, 2.0 wt.% maximum 
manganese, 0.5 wt.% maximum other elements, balance substantially copper 
(UNS No. C62500). 
The aluminium bronze alloys exhibit poor castability, as is appreciated. A 
problem with their use in the present invention is the pronounced tendency 
for their melts to oxidize, and this can complicate their use in the 
invention as in other applications. However, protecting the melt against 
oxidation, such as by melting under a flux cover, enables these alloys 
also to be cast against and securely bonded to a solid first component, 
such as a mild steel substrate. However, because of the tendency for the 
melt to oxidize, it can be advantageous to limit the extent of 
superheating of the melt and to achieve the required first component/melt 
interface temperature by increasing the temperature to which the first 
component is preheated. 
The specifically itemised castable metals suitable for use in the invention 
as the second component will be recognised as surfacing materials 
conventionally applied by hardfacing by weld deposition. Typically, such 
metals are applied to provide wear resistant facings. However, in the case 
of stainless steels, which can provide abrasion resistance at low or 
medium temperatures, the purpose of its use in a composite article may be 
in part or wholly to achieve corrosion resistance for the other component 
of the article. Thus, while principally concerned with composite articles 
having abrasion resistance by appropriate selection of the metal of one 
component, the invention also is concerned with articles for use in 
environments other than those in which abrasion resistance is required. 
Also, as indicated by the ability to cast for example a cast iron against 
a cast iron, the composite article of the invention can be applied to 
rebuilding a worn or damaged part of an article; the first and second 
components in that case being of substantially the same or similar 
composition if required. In such rebuilding, the worn or damaged part of 
an article can be machined, if required, to provide a more regular surface 
thereof against which a melt of rebuilding metal is to be cast. However, 
such machining may not be necessary for a sound bond to be achieved, 
provided that an oxide-free surface is available against which to cast the 
melt. 
The solid first component may be preheated in the mould or prior to being 
placed in the mould while the type of mould used can vary with the nature 
of the preheating. When heated in the mould, the preheating may be by 
induction coils, or by flame heating. When heated prior to being placed in 
the mould, resistance, induction or flame heating can be used or, 
alternatively, the solid first component can be preheated in a muffle or 
an induction furnace. What is important, in each case, is that at least 
the surface of that component against which the melt for the second 
component is to be cast is thoroughly cleaned mechanically and/or 
chemically and protected, prior to preheating to a temperature at which 
re-oxidation will occur, by a suitable flux. Normally, in such cases, the 
flux is applied as a slurry, such as by the flux being painted on at least 
that surface of the solid first component. Alternatively, the flux can be 
sprinkled on the surface in powder form; provided, where preheating then 
is to be by a flame, the surface has been partially heated to a 
temperature at which the flux becomes tacky. Particularly where the 
surface of the first component against which the melt is to be cast is of 
complex form, the flux alternatively can be applied by dipping the first 
component into a bath of molten flux. In each of these methods of applying 
the flux, the first component can be stored, once coated with the flux, 
until required for preheating. Alternatively, the component may be 
preheated immediately after the flux is applied. 
Where the flux is applied by dipping the solid first component in a bath of 
molten flux, a variant on the above described methods of preheating can be 
adopted. In this, the preheating can be effected at least in part by the 
solid first component being soaked in the bath of molten flux until it 
attains a sufficient temperature, which may be below, substantially at, or 
above the required preheat temperature. The component then can be 
transferred to the mould and, after further induction or flame heating or 
after being allowed to cool to the required preheat temperature, the melt 
to provide the second component is cast thereagainst. 
Where preheating of the solid first component is at least in part by flame 
heating, that component may be positioned in a mould defining a firing 
port enabling a heating flame to extend into the mould cavity and over 
that component; the flame preheating the component and also heating the 
mould. While not essential, a reducing flame can be used to maintain in 
the mould a reducing atmosphere so as to further preclude oxidation of the 
surface of the first component. The flame may be provided by a burner 
adjacent to the firing port for generating the reducing flame. 
The mould for use in flame heating may be constructed in portions which are 
separable. The portions may be spaced by opposed side walls and, at one 
end of those walls, the firing port can be defined, with an outlet port 
for exhausting combustion gases from the flame being defined at the other 
ends of the side walls. The side walls may be separable from the mould 
portions or each may be integral with the same or a respective mould 
portion. Preferably, an inlet duct is provided at the firing port for 
guiding the flame into the interior of the mould. Where the first 
component has an extensive surface over which the melt is to be cast, such 
as a major face of a flat plate substrate, the width of the firing port in 
a direction parallel to that surface may be substantially equal to the 
dimension of the substrate surface in that direction. The duct may have 
opposed side walls which diverge toward the firing port to cause the 
reducing flame to fan out to a width extending over substantially the full 
surface of the substrate to which the melt is to be cast. Also, the duct 
may have top and bottom walls which converge toward the firing port to 
assist in attaining such flame width. The duct may be separable from the 
mould, integral with one mould portion or longitudinally separable with a 
part thereof integral with each mould portion. 
The flame heating may be maintained until completion of casting of the 
melt. After pouring the melt and before the latter has solidified, the 
burner may be adjusted to give a hotter, slightly lean flame. 
Solidification of the top surface of the melt can be delayed by such lean 
flame, so that the melt solidifies preferentially from the melt/first 
component interface, rather than simultaneously from that interface and 
top surface. Such solidification also can minimise void formation due to 
shrinkage in the unfed cast metal. 
In such flame preheating, the pouring arrangement most conveniently is such 
as to rapidly distribute the melt over all parts of the surface of the 
first component on which it is to be cast and to maximise turbulence in 
the melt. Such rapid distribution and turbulence promotes heat transfer 
and a high, uniform temperature at the interface between the poured melt 
and the surface first component. Rapid distribution and turbulence also 
facilitates breaking-up and removal of any oxide film on the melt. It also 
would remove any residual oxide film of that surface, although reliance on 
this action without prior cleaning and use of a flux produces a quite 
inferior bond. 
Rapid distribution of the melt over the substrate surface of the first 
component and turbulence in the melt can be generated by a mould having a 
pouring basin into which the melt is received, and from which the melt 
flows via a plurality of sprues of which the outlets are spaced over that 
surface. This arrangement functions to evenly and simultaneously pour the 
melt onto all areas of the surface; thereby reducing the distance the melt 
has to flow and aiding in achieving a high and uniform temperature at the 
melt-first component interface. The arrangement also increases turbulence 
in the melt over, and facilitates wetting of, that surface. 
One advantage of a reducing flame in such preheating of the first component 
is that it offsets any tendency for oxidation of the melt resulting from 
its rapid distribution and turbulence. Also, such turbulence can cause 
erosion, by localized macrodissolution of metal of the first component, at 
points of impingement of the melt with the surface of that component. It 
therefore can be beneficial to use an arrangement for pouring the melt 
which establishes substantially non-turbulent, progressive mould filling. 
In one such arrangement, the invention uses a mould having a horizontally 
extending gate which causes the melt to enter a mould cavity in a plane 
substantially parallel to, and slightly above, the surface of the first 
component on which the melt is to be cast. This enables the melt to 
progress in substantially non-turbulent flow across the surface, with 
minimum division of the flow, thereby inhibiting oxidation of the melt. 
Thus, the exposure of fresh, non-oxidized metal of the melt to an 
oxidizing environment is minimised. 
The placement of the gate most conveniently is such that the initial melt 
which enters the mould flow across the surface of the pre-heated first 
component, further heating that surface. Subsequent incoming liquid metal 
displaces the initial metal which entered the mould cavity, thereby 
ensuring that maximum heat is imparted to the surface before 
solidification commences. Just prior to pouring, the mould cavity may be 
closed with a cope-half mould, with the molten metal being run into the 
cavity through a vertical down sprue and horizontal runner system. For 
small castings, this system permits several castings to be made in the 
same moulding box from a single vertical down-sprue feeding into separate 
runners for each casting. Such casting practice can be used to produce a 
bond interface on a horizontal, inclined or even vertical, surface of the 
first component. 
In such arrangement providing substantially non-turbulent flow of the melt 
in the mould, flame heating again can be used. However, in this instance, 
it is necessary to position the first component (which may have been 
partially preheated) in the drag portion of the mould and, before 
positioning the cope portion of the mould, to effect flame heating from 
above. As an alternative, the mould can be fully assembled and preheating 
effected or completed therein by induction heating. 
Where flame heating is used, it is preferred that the flux be applied by 
dipping in a melt of the flux or by painting on a slurry of the flux. If, 
as an alternative, it is required to apply the flux as a powder, it is 
preferable that the first component be slightly heated to about 
150.degree. to 200.degree. C., such as in a muffle furnace, so that the 
flux becomes tacky and is not blown from the surface of the first 
component by the heating flame. 
When the flux is applied by dipping the first component into a bath of 
molten flux, the flux is applied at least over the surface of that 
component against which the melt is to be cast. Preferably, the component 
is immersed in the bath so as to be fully coated with flux and also at 
least partially preheated in that bath. Once a flux coating is provided, 
the first component then is positioned in a mould and a melt to provide 
the second component poured into the mould so that the melt flows over the 
surface of the first component. Preferably the first component is 
suspended in the bath of molten flux until its temperature exceeds the 
melting point of the flux. The component is then withdrawn from the flux 
bath with a coating of a thin, adherent layer of the flux thereon. The 
melt displaces the thin flux coating, remelting the latter if necessary, 
thereby exposing the clean surface of the first component so that wetting 
and bonding take place. Clearly, the flux employed must have a melting 
point which is sufficiently low to permit quick remelting of the flux, if 
frozen at the time the melt is poured into the mould. At the same time the 
molten flux must be able to withstand temperatures sufficiently high that 
the steel substrate can be adequately preheated. A sufficient temperature 
can be achieved with several fluxes during suspension, or dipping, of the 
first component in the bath of molten flux. However, where the temperature 
of the flux bath is insufficient for this, or where the heat loss from the 
first component between forming the flux coating and pouring the melt is 
too great, the first component can be further preheated in the mould, such 
as by induction or flame heating.

With reference to FIGS. 1 and 2, mould 10, formed from a bonded sand 
mixture, has a lower mould portion 12 in which is positioned a ductile 
first component or substrate 14 on which a wear-resistant component is to 
be cast. A layer 16 of ceramic fibre insulating material insulates the 
underside of substrate 14 from the mould portion 12, while a layer 18 of 
such material lines the side walls of portion 12 around the above 
substrate 14. Mould 10 also has an upper portion 20, spaced above portion 
12 by opposed bricks 22. The spacing provided between portions 12,20 by 
bricks 22 is such as to define a transverse passage 24 through mould 10. 
Across one end of passage 24, the mould is provided with an inlet duct 26; 
the junction of the latter with passage 24 defining a firing port 28. A 
burner 30, operable for example on gas or oil, is positioned adjacent to 
the outer end of duct 26 for generating a flame for preheating substrate 
14 and mould portions 12,20. 
Duct 26 has sidewalls 32 which diverge from the outer end to firing port 
28. This arrangement causes the flame of burner 30 to fan out horizontally 
across substantially the full width of port 28 and, within mould 10, to 
pass through passage 24 over substantially the entire upper surface of 
substrate 14. Upper and lower walls 34,35 converge to port 28, and so 
assist in attaining such flame width in mould 10. The flame most 
conveniently extends through the end of passage 24 remote from port 28; 
with combustion gases also discharging from that remote end. 
Upper portion 20 of the mould has a section 36 defining a pouring basin 37 
into which is received the melt of wear-resistant metal to be cast on the 
upper surface of substrate 14. From basin 37, the melt is able to flow 
under gravity through throat 38, along runners 39, and through the several 
sprues 40 in portion 20. The lower ends of sprues 40 are distributed 
horizontally, such that the melt is poured evenly and simultaneously onto 
all areas of the upper surface of substrate 14. 
FIG. 3 shows a mould pattern for use in producing the upper portion 20 of a 
mould similar to that of FIGS. 1 and 2. In FIG. 3 corresponding parts are 
shown by the same numeral primed. 
Castings made in a mould as shown in FIGS. 1 and 2 include steel substrates 
measuring 300 mm.times.300 mm and 10 mm thick. The steel plates were 
inserted in the lower mould portion with insulation under and around the 
plates as described earlier. The moulds were levelled, flux was sprinkled 
on the steel to cover its upper surface, the mould built up in the manner 
discussed, and the mould was initially gently heated to make the flux 
tacky and adhere to the surface. Two sizes of castings were made using a 
high chromium white cast iron, one type had 40 mm overlay on 10 mm steel 
plate, the other had 20 mm on 10 mm. 
For the 4:1 ratio castings, the substrate was preheated by means of the 
burner generating a reducing flame in the mould, and 30 kg of high 
chromium white iron was poured at a temperature of approximately 
1600.degree. C. into the pouring basin. The iron surface was kept liquid 
for about 8 minutes and the burner was then turned off. A thermocouple 
against the bottom surface of the substrate reached a temperature of 
1250.degree. C. approximately 2 mins. after pouring. Ultra-sonic 
measurement indicated 100% bonding, which was subsequently confirmed by 
surface grinding of the edges and of a diagonal cut through the casting, 
as well as extraction of 50 mm diameter cores by electro-discharge 
machining. The bond was free of any fusion layer due to melting of the 
steel. 
For the 2:1 ratio castings, the substrate was preheated and 15 kg of the 
iron was poured at a temperature of about 1600.degree. C. The white iron 
surface could not be kept liquid as long as with the 4:1 ratio castings, 
but was liquid for about 5 minutes. The thermocouple against the bottom of 
the plate reached 1115.degree. C. approximately 3 minutes after pouring. 
For this size casting sound bonding over the full interface between the 
substrate and cast metal again is achieved. 
In addition to the castings described above, a number of further castings 
were made on 200 mm.times.50 mm.times.10 mm steel substrates. The most 
suitable pouring mould in this case was found to be in the shape of a 
funnel with a long narrow slot at the bottom. The slot extended for the 
full length of the substrate and was narrow enough for the liquid iron to 
issue from its full length simultaneously. With a preheat of 350.degree. 
C. and a liquid iron pour temperature of 1570.degree. C., bonding was 
achieved over more than 95% of the total area. By increasing the preheat 
temperature, bonding over 100% of the area can readily be achieved with 
this size of substrate. 
The castings described have been shown to give complete bonding on 300 
mm.times.300 mm.times.10 mm test plates of mild steel with white iron to 
steel ratios of 4:1 to 2:1. Higher and lower ratios are possible; the 
lower ratios depending in part on substrate thickness and the rate of heat 
loss from the metal for optimum bonding. 
Inherent in the invention is a high degree of freedom with respect to the 
geometrical shape of the substrate and the finished article. The invention 
has significant advantages compared to other methods in that it enables 
the direct casting of hard, wear-resistant metals, such as high chromium 
white iron, onto ductile steel substrates. The finished article can 
combine the wall documented wearing qualities of for example white iron 
with the good mechanical strength and toughness, machining properties and 
weldability of low carbon steel. The direct metallurgical bond between the 
white iron and the steel results in very high bond strength. The invention 
is especially suitable for producing hardfacing layers of thickness 
exceeding those which may be conveniently laid down by welding processes. 
The temperature to which the substrate is preheated can vary considerably. 
The temperature is limited by the need to prevent oxidation, the melting 
point of the material of the substrate, the need to minimise grain growth, 
and the type of flux. Within these limits, a high preheat temperature is 
advantageous. The minimum preheat temperature will depend on the thickness 
ratio of cast component to substrate, and on the size and shape of the 
components. For the above-mentioned 4:1 castings, a preheat temperature of 
500.degree. C. was found to be just sufficient; while for the 2:1 
castings, a minimum preheat of 600.degree. C. was found to be necessary. 
An important parameter is the temperature at the interface between the cast 
liquid and the substrate. This enables a lowering of melt temperature with 
a corresponding increase in substrate preheat temperature, and vice versa. 
However, it is preferable for the melt to be superheated sufficiently to 
allow any flux and any dislodged scale to rise to the surface of the cast 
melt, and to attain the required interface temperature for a satisfactory 
bond between the substrate and cast component. For all casting alloys, 
with the exception of aluminium bronzes discussed herein, superheating by 
at least 200.degree. C. above the liquidus temperature is preferred, most 
preferable at least 250.degree. C. above that temperature, in order to 
achieve the required interface temperature on casting. 
Particularly with the flux provided over the substrate surface on which the 
melt is to be cast, the reducing flame need provide only a mildly reducing 
atmosphere over that surface during preheating. For such atmosphere, a 
flame provided by an air deficiency of between 5% and 10% can be used. 
With reference to FIG. 4, there is shown at A an underside view of the cope 
portion 50 of mould 52, and the top plan view of drag portion 54 thereof. 
In each of several mould cavities 56, there is a respective chamfered 
substrate 58, of which the upper surface of each has been painted with a 
flux slurry. As shown at B, substrates 58 are preheated by flame from 
above, prior to positioning cope portion 50, using a reflector 60 to 
facilitate preheating. As shown at C, cope portion 50 then is positioned 
and a melt to be cast against the upper surface of each substrate is 
poured into the mould via cope opening 62. The melt flows horizontally via 
gates 64, to each cavity 56, and flows along each substrate 58 across the 
full width of each. As indicated at D, the resultant composite articles 66 
are knocked-out, and thereafter dressed in the normal manner. 
Operation as depicted in FIG. 4 has been used to produce various sizes of 
hammer tips for use in sugar cane shredder hammer mills. The hammer tips 
were made with mild steel substrates and a facing bonded thereto of high 
chromium white cast iron. Dimensions of hammer tips produced have been as 
follows: 
______________________________________ 
Substrate dimensions (mm) 
Cast overlay thickness (mm) 
______________________________________ 
80 .times. 90 .times. 25 (thick) 
25 
90 .times. 90 .times. 25 (thick) 
20 
76 .times. 50 .times. 20 (thick) 
18 
______________________________________ 
Risers have been employed in producing the hammer tips to ensure fully 
sound castings were produced. In these types of hammer tip, substantial 
chamfers have been machined into the substrates prior to pouring, in order 
to permit the production of hammer tips with a more complete coverage of 
wear-resistant alloy on the working face than has hitherto been possible 
with brazed composites. These hammer tips have also used pre-machined 
substrates, wherein drilled and tapped holes required for subsequent 
fixing of the hammer tip to the hammer head have been formed prior to 
production of the composite. The threaded holes have been protected with 
threaded metal inserts during the casting operation. The flexibility of 
being able to use pre-machined bases in this way has overcome the problems 
associated with drilling and tapping blind holes in an already bonded 
composite. 
The hammer tips were found to be characterized by a sound diffusion bond, 
using casting temperatures comparable to those indicated with reference to 
FIGS. 1 to 3. 
The bonds were diffusion bonds exhibiting no fusion layer due to melting of 
the substrate surfaces. 
With reference to FIG. 5, there is shown at A a furnace 70 providing a bath 
of molten flux 72 in which is immersed a tubular steel component 74. The 
latter is preheated to a required temperature in flux 70. As indicated at 
B and C, heated component 74 coated with flux, is withdrawn from furnace 
70 and, after draining excess flux, component 74 is lowered into the drag 
half 76 of a mould and the cope half 78 of the latter is positioned. In 
the arrangement illustrated, the mould includes a core 80 which extends 
axially through component 74, to leave an annular cavity 82 between core 
80 and the inner surface of component 74. With cope half 78 positioned as 
shown at D, a melt of superheated metal is cast as at E, via cope opening 
84, to fill cavity 82. 
Trials with the above described Liquid Air flux (m.p. 650.degree. C.) have 
been carried out in a procedure essentially as described with reference to 
FIG. 5, using steel substrates comprising: 
(a) 200 mm long.times.50 mm wide.times.10 mm thick, for which bonding has 
been produced with cast overlay thicknesses of 40 mm, 30 mm and 20 mm 
(i.e. 4:1, 3:1 and 2:1 casting ratios); and 
(b) 80 mm square.times.25 mm thick, for which good bonding has been 
produced with a cast overlay thickness of 25 mm (i.e. 1:1 casting ratio). 
It has been found that the flux layer which adheres to the substrate upon 
its withdrawal from the molten flux bath is relatively thick, and that 
mechanical scraping away of the majority of this adherent flux to leave 
only a very thin layer produced a better bond. A lower melting point flux 
can be used and has the advantages of being more fluid at the required 
working temperature, thereby draining better upon withdrawal of the 
substrate as well as being more readily remelted during casting. However, 
in the latter regard, it should be noted that it is not necessary that the 
flux freezes between removal of the substrate from the bath and casting 
the melt or the application of flame or other preheating. Also, use of a 
lower melting point flux facilitates production of even smaller casting 
ratio articles than described herein. 
While the articles described herein are of planar form, it should be noted 
that the invention can be used to provide articles of a variety of forms. 
Thus, the invention can be used in the production of, for example, 
cylindrical articles having a wear-resistant material cast on the internal 
and/or external surface thereof, curved elbows, T-pieces and the like. 
Representative further composite articles further exemplifying the 
flexibility and range of possibilities with the present invention are set 
out in the following table, in which: 
Method I designates manufacture in accordance with the procedures described 
with reference to FIGS. 1 to 3, and 
Methods II and III designate manufacture in accordance with FIGS. 4 and 5, 
respectively. 
TABLE 
__________________________________________________________________________ 
Substrate Component 
Cast Component Method 
__________________________________________________________________________ 
A. Alloy White Cast Iron 
1. 200 .times. 50 .times. 10 mild steel 
Each of 40, 30, 20 and 10 mm 
Each of I, flame preheating 
plates on substrate main faces. 
and III, flux bath preheating. 
2. 300 .times. 300 .times. 20 mm thick 
Each of 40 and 20 mm on 
I, flame preheating. 
steel plates substrate main faces. 
3. 900 .times. 75 .times. 50 mm steel bar 
50 mm thickness on main face 
I, flame preheating articles 
(heat/abrasion resistant alloy 
for use as sinter plant 
complex Cr--carbide iron). 
griller bars. 
4. Steel plate of: Cast on substrate mainfaces 
Both I and II, flame pre- 
(a) 80 .times. 70 .times. 25 mm 
25 mm heating - articles for use 
(b) 90 .times. 80 .times. 25 mm 
25 mm as hammer tips in sugar cane 
(c) 76 .times. 50 .times. 20 mm 
20 mm shredder. 
(d) 90 .times. 90 .times. 20 mm 
25 mm 
5. Round steel bar of: 
Cast on cylindrical cladding 
(a) 40 mm diameter 
30 mm wall thickness 
(b) 50 mm diameter 
25 mm wall thickness 
III, flux bath preheating. 
(c) 60 mm diameter 
20 mm wall thickness 
(d) 70 mm diameter 
15 mm wall thickness 
6. Hollow steel pipes of: 
Cast to provide: 
(a) 100 mm outside diameter, 
Internal claddings of each of 
and 10 mm wall thickness. 
15 mm and 19 mm. 
(b) 75 mm outside diameter, 
External cladding of 12.5 mm 
and 10 mm wall thickness. 
with simultaneous internal 
claddings of each of 3.5 and 
III, flux bath heating. 
7.5 mm thicknesses. 
(c) 90.degree. pipe bend of 75 mm 
Internal cladding of 7 to 10 mm 
outside diameter, 5 mm 
thickness. 
wall thickness and 63 mm 
centreline radius of curvature. 
7. AISI 304 stainless steel, 
Cast 25 mm on main substrate 
II, induction preheating. 
90 .times. 90 .times. 10 mm thick 
faces. 
8. Composite substrate 90 .times. 
Cast 25 mm on main substrate 
II, induction preheating. 
90 .times. 25 mm with 15 mm 
white iron overlay surface. 
thick base of mild steel 
and 10 mm thick white 
iron overlay 
B. Stainless Steel 
9. (a) 90 .times. 90 .times. 10 mm thick 
AISI 316 stainless steel cast 
II, induction preheating. 
mild steel 25 mm on main substrate surface. 
(b) 90 .times. 90 .times. 70 mm thick 
Cast on main face 70 mm thickness. 
II, induction preheating 
- plate and III, flux bath 
preheating. 
C. Cobalt Base Alloy 
10. 
90 .times. 90 .times. 10 mm thick 
Cast on main substrate face 
II, induction preheating. 
mild steel 25 mm thickness. 
D. Aluminium Bronze Alloy 
90 .times. 90 .times. 10 mm thick 
Cast 25 mm on substrate main 
II, with flame preheating 
mild steel plates 
faces. and II with induction 
preheating. 
E. Nickel Alloy 
90 .times. 90 .times. 10 mm thick 
Cast 25 mm on substrate main 
II, with induction 
mild steel plate 
faces. preheating. 
__________________________________________________________________________ 
With each of the examples detailed in the table, sound bonds were achieved 
in each case. It was found that attainment of a sound bond was relatively 
insensitive to the choice of flux, or the method of preheating, in any of 
those cases. Generally, preheating of the substrate component was to a 
temperature of about 800.degree. C., with the melt poured at a temperature 
of about 1600.degree. C. for all alloys except aluminium bronze. The 
above-mentioned CIG Silver Brazing Flux and Liquid Air 305 Flux both were 
found to be highly suitable, particularly in method III. 
The melt used in Example 12 was 14.7 wt.% aluminium, 4.3 wt.% iron, 1.6 
wt.% manganese, the balance, apart from other elements at 0.5 wt.% 
maximum, being copper. As with other aluminium bronze compositions 
detailed herein, this melt exhibited a tendency to oxidation, and 
precautions are necessary to prevent this. To the extent that this 
difficulty could be overcome, sound bonding at clean interface surfaces 
results. The melt liquidus is approximately 1050.degree. C. and the melt 
was poured at 1350.degree. C. with the substrate preheated to about 
800.degree. C. The problem of melt oxidation can be reduced by lowering 
the melt superheating, with a corresponding increase in substrate 
preheating and/or use of a flux cover for the melt. 
The melt used in Example 13 had a composition of 13.5 wt.% chromium, 4.7 
wt.% iron, 4.25 wt.% silicon, 3.0 wt.% boron, 0.75 wt.% carbon and the 
balance substantially nickel. This melt had a liquidus temperature of 
approximately 1100.degree. C., and was poured at approximately 
1600.degree. C. with the substrate preheated to approximately 800.degree. 
C. 
The bond achieved with the present invention was found to be of good 
strength. This is illustrated for a composite article comprising AISI 316 
stainless steel cast against and bonded to mild steel. For such article, 
bond strengths of about 440 MPa were obtained with test specimens machined 
to have a minimum cross-section at the bond zone. Also with such article, 
an ultimate tensile strength of about 420 MPa was obtained in a testpiece 
with 56 mm parallel length, with the bond about halfway along that length; 
the total elongation of 50 mm gauge length being 32%. For articles in 
which the cast metal component is brittle, it is found that the bond is 
stronger than the component of the article of the cast metal. Thus, with 
hypoeutectic chromium white iron cast against and bonded to mild steel, 
bend tests showed fracture paths passed through the white iron, and not 
the bond zone.