e l a b o r a t e preparations, fluxes, and special
INTIMACY OF CONTACT
techniques because its characteristics are such that
the welding operation can be easily performed.
In the second basic requirement for coalescence,
Other metals require special preparatory steps,
intimacy of contact, the welding processes may be
complex welding sequences, skillful use of a specific
divided into two groups: pressure processes and
welding technique, and extensive heat treatments
nonpressure processes. In PRESSURE
PROCESSES, we get intimacy of contact by
applying pressure while the contact surfaces are at
Many factors influence the weldability of a
a high enough temperature to allow plastic flow of
the metal. In NONPRESSURE PROCESSES, a
metal. Here are some of the more important ones
that must be taken into account and, insofar as
space is left between the surfaces to be joined. This
space is filled, either progressively or all at once,
of the metals involved (that is, the kind and
with molten metal. The molten metal may be
obtained from a filler metal (welding rod or
percentage of elements present) and the effect of
electrode), by melting the surfaces to be joined, or
radical temperature changes on the various
by combining a filler metal and melted base metal.
elements; (2) the expansion and contraction
characteristics of the base metals; (3) the filler metal
All nonpressure processes involve fusion, and
(welding rod or electrode); (4) the joint design; and
are often referred to as FUSION PROCESSES.
(5) the welding procedure.
However, this term is somewhat misleading since
some pressure processes also involve fusion.
The Navy uses a large number of different
metals and alloys. Each of these materials has
The various welding processes differ not only in
characteristics or properties that make its use
d e s i r a b l e for certain applications.
the way coalescence is achieved, but also in their
ability to produce a satisfactory joint in a given kind
characteristics and properties of a given alloy are
of metal under the conditions in which the weld
partly determined by the kind and amount of
must be made. Many factors influence the selection
elements present. The effect welding has on these
of a welding process for a particular application.
elements and their reaction during and after the
Some important factors to be considered are the
application of heat have a tremendous influence on
relative cost, the amount of welding required, the
the weldability of the metal in question.
location and position of welds, the service conditions
the welded structure must withstand, and the
In steel, carbon is probably the most important
qualifications of the person who does the welding.
element that limits weldability. Carbon gives steel
Probably the most important single factor, however,
hardenability; that is, when certain carbon steels are
is the weldability of the metal.
heated above a critical temperature and then cooled
rapidly, they be come much harder. At the same
time they lose ductility. In fact, the metal may
become extremely brittle. With few exceptions, the
The term WELDABILITY means the capacity
temperatures used in welding exceed the critical
of a metal to be fabricated by a welding process into
temperature of carbon steels.
a structure that will perform its purpose
hardening may occur when the mass of relatively
satisfactorily. Weldability also means the degree of
cold metal surrounding the weld area conducts heat
simplicity or complexity of the procedures and
away so fast that rapid cooling occurs. Thus, certain
techniques used to produce welds with properties
steels may become hardened by many of the welding
that are equal to or better than the properties of the
base material. For example, mild steel can be
welded by most welding processes, but the welds
When the percentage of carbon is less than 0.25
produced may not be equally satisfactory, and one
percent, its effect in producing hardness is slight.
m e t h o d may be more complicated or more
But when the carbon content exceeds 0.25 percent,
expensive than another. While it is possible to weld
or when such elements as manganese, vanadium,
mild steel through the use of a variety of welding
chromium, molybdenum, or titanium are present,
processes, some metals such as aluminum and its
along with a lesser carbon percentage, the
alloys can be satisfactorily welded with only a few
weldability of the steel is decreased. Special steps
welding processes. Mild steel does not require
should be taken to control preheat, interpass