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le, one opens from a few hours to a few days after.
The latter condition may prove the most serious, as
shear inspection will not reveal the trouble and such
stock may rupture further when brought to forging
heat.
Fins or ragged edges should be avoided in shearing
as they may "lap in" during forging. Often it is necessary
to grind badly finned edges. This difficulty can
usually be eliminated by closer alignment of shears
and maintenance of proper knife edges.
Heating Requires Attention.
During heating of stock in the furnace at the hammer
much more material is ruined than is generally
assumed. It is a simple matter for the operator to
detect when steel is being burnt, and to immediately
remedy conditions before the loss is great, but it is
not so readily apparent when the over-heating is only
sufficient to cause incipient burning, or to seriously
impair the structure of the steel beyond the point of
reclamation by heat treatment to develop satisfactory
properties. Usually there is no warning during too
rapid heating of "tender" steels, of the ill effects which
such practice produces.
In steels of higher alloying contents, particularly
chrome-nickel, with and without additional elements
such as vanadium, molybdenum, etc., internal defects
will result from rapid heating. The condition becomes
more acute as the carbon content increases. Pre-heating
slowly to a temperature between 600 deg. F. and
1200 deg. F. and then finish heating to forging temperature
is necessary- This can best be accomplished
by the use of a separate furnace for pre-heating, although
in some cases entirely satisfactory results may
be obtained by pre-heating on the front of the hearth
of the forging furnace, or "double rowing".
Under-heating is less frequently encountered on
account of handicaps promptly manifested to the hammerman.
The result is decreased production, misalignment
of dies, decreased life of dies and rods, increased
maintenance costs on equipment, and at times
die and rod breakage.
Forging furnaces should be so designed as to permit
proper time cycle for soaking stock to constant
head and to operate under soft rather than cutting
flame, avoiding direct flame impingement on the
charge and excessive air.
Cold Shuts and Laps.
During forging operations there are many manners
in which defects may be introduced into forgings, and
controversies as to whether their origin is in the steel
itself or in its fabrication often take place. In some
cases a decision may lie simple, in others almost impossible.
Cold shuts and laps are often claimed to
be seams, forging bursts, pipe; and vice versa. In
most cases one familiar with the method of forging
should be able to decide whether defects are laps,
shuts or seams. In other cases a careful study of the
flow of metal in the various operations under the hammer
should determine the cause of the trouble. Seams
or laps in rolled bars or billets always exist parallel
to the direction of rolling. If the flow of metal has
been such that the defect must have existed in a direction
other than longitudinal with the rolled product
the evidence is quite conclusive as to its origin. If
surface defects are characteristic of a certain position
in forgings the fault is unlikely to be in the steel — it
Fbrging-Stamping - Heat Treating
January, 1925
is improbable that pieces forged would have defects in
the same spot on the bar, billet or slab.
Enumeration or discussion of all defects encountered
under the hammer is impossible, but a number of
frequent sources of trouble might be briefly considered.
During drawing, fullering or edging operations,
ridges or fins may be formed which fold over and form
laps or shuts during finishing. Excessive working on
the flat of the die or in round sections may produce internal
ruptures, often mistaken for pipe- .Rapid wash
heating may produce similar flaws. Restricted flow
of metal in dies and too rapid heating may cause shattered
hearts, and this may .be aggravated by segregation.
Improper reduction in fullers, edgers, blocking
impressions, or preliminary die forging, may result in
forcing such large excess of metal through the flash
line in the finishing dies as to result in rupture which
may or may not be revealed in trimming, and often not
discovered until after heat treatment or failure in service
Incorrect distribution of metal for the finishing
impression frequently causes stock in finishing operation
to tend to flow from small to large sections, resulting
in bad distortion of flow lines, poor flash distribution,
and even splits, which are often attributed to
piped steel. Bending operations, with improper gathering
of stock, may produce crinkling or folding on the
concave side of the bend, which produces lapping in
the finished part. Likewise, unsatisfactorily executed
splitting operations may produce tears which may be
lapped in finishing.
Front axle forgings probably embody as many
faults as any forging produced. Predominating among
imperfections in this part are laps, shuts, flange cracks,
separation along flash line, web ruptures, cross cracks
and shattered centers. Trouble encountered in eyebeam
sections may often be attributed to faulty preliminary
forging operations, resulting in the squirting
of metal from the flanges through the parting line and
out in the flash, leaving shattered flanges. Flaws at or
near the flange and web are often due to improper
flow, resulting from too sharp filleting. Badly strained
condition along the flash line is intensified by cold
trimming. Quite uniformly spaced cross checks have
been encountered practically throughout the length of
the eye-beam section. Steel defects could not exist in
stock in such a direction as to be responsible. The use
of sharp cornered square stock has rendered the material
more susceptible to over-heating or incipient
burning on the four corners while bringing up to forging
heat; heat treatment and stretching have seriously
strained if not lightly ruptured the metal; the final
pickling with its hydrogen impregnation has brought
about the final ruptures or in some cases has merely
rendered visible previously existing ones.
Considerable progress has been made in the study
of flow of metal and in making practical application
of the same in die design. Flow should be smooth
around all corners, avoiding throws into the surface.
Its proper regulation is of vital importance in effecting
increased resistance to stress, shock, vibration, and in
such parts as gears in governing distortion arising in
heat treatment. Coarse etching constitutes a most
satisfactory means of study. Sections, after machining
and grinding free from tool marks, are etched in
a solution of from 50 to 1U0 per cent hydrochloric acid
at approximately boiling temperature for a period usually
from one-half to one and one-half hours, washed
and dried for examination. For photographing, a