WEARFACING MATERIALS
A surfacing operation using a copper-base alloy
filler metal produces a relatively soft surface. Work-
hardening bronzes are soft when applied and give
excellent resistance against frictional wear. Other types
of alloys are available that produce a surface that is
corrosion and wear resistant at high temperatures. Wear-
facing materials are produced by many different manu-
facturers; therefore, be sure that the filler alloys you
select for a particular surfacing job meet Navy specifi-
cations.
Two types of hard-surfacing materials in general use
in the Navy are iron-base alloys and tungsten carbide.
Iron-Base Alloys
These materials contain nickel, chromium, manga-
nese, carbon, and other hardening elements. They are
used for a number of applications requiring varying
degrees of hardness. A Steelworker frequently works
with iron-base alloys when he builds up and resurfaces
parts of construction equipment.
Tungsten Carbide
You use this for building up wear-resistant surfaces
on steel parts. Tungsten carbide is one of the hardest
substances known to man. Tungsten carbide can be
applied in the form of inserts or of composite rod. Inserts
are not melted but are welded or brazed to the base
metal, as shown in figure 6-18. The rod is applied with
the same surfacing technique as that used for oxygas
welding; a slightly carburizing flame adjustment is nec-
essary.
WEARFACING PROCEDURES
Proper preparation of the metal surfaces is an im-
portant part of wearfacing operations. Make sure that
scale, rust, and foreign matter are removed from the
metal surfaces. You can clean the metal surfaces by
grinding, machining, or chipping. The edges of grooves,
corners, or recesses should be well rounded to prevent
base metal overheating and to provide a good cushion
for the wearfacing material.
Weafacing material is applied so it forms a thin
layer over the base metal. The thickness of the deposit
is usually from one sixteenth to one eighth of an inch
and is seldom over one fourth of an inch. It is generally
deposited in a single pass. Where wear is extensive, it
may become necessary to use a buildup rod before
wearfacing. If in doubt as to when to use a buildup rod,
you should check with your leading petty officer.
Preheating
Most parts that require wearfacing can be preheated
with a neutral welding flame before surfacing. You
should use a neutral flame of about 800°F. Do not
preheat to a temperature higher than the critical tem-
perature of the metal or to a temperature that can cause
the formation of scale.
Application
In general, the torch manipulations and the wearfac-
ing procedures are similar to brazing techniques. How-
ever, higher temperatures (about 2200°F) are necessary
for wearfacing, and tips of one or two sizes larger than
normal are used.
To begin, you heat a small area of the part with a
sweeping torch movement until the surface of the base
metal takes on a sweating or wet appearance. When the
surface of the base metal is in this condition, bring the
end of the surfacing alloy into the flame and allow it to
melt. Do not stir or puddle the alloy; let it flow. When
the surface area has been properly sweated, the alloy
flows freely over the surface of the base metal.
Being able to recognize a sweated surface is essen-
tial for surfacing. Sweating occurs when you heat the
steel with a carburizing flame to a white heat tempera-
ture. This carburizes an extremely thin layer of the base
metal, approximately 0.001 inch thick. The carburized
layer has a lower melting point than the base metal. As
a result, it becomes a liquid, while the underlying metal
remains a solid. This liquid film provides the medium
for flowing the filler metal over the surface of the base
metal. The liquid film is similar to and serves the same
purpose as a tinned surface in soldering and braze weld-
ing.
When you heat steel with a carburizing flame, it first
becomes red. As heating continues, the color becomes
lighter and lighter until a bright whiteness is attained. At
this point, a thin film of liquid, carburized metal appears
on the surface. Surfacing alloy added at this time flows
over the sweated surface and absorbs the film of carbur-
ized metal. This surface condition is not difficult to
recognize, but you should make several practice passes
before you try wearfacing for the first time.
When you use an oxygas torch for surfacing with
chromium cobalt, the torch flame should have an excess
fuel-gas feather about three times as long as the inner
6-16