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November, 1925
Forging- Stamping - Heat Treating
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D e v e l o p m e n t s in D r o p F o r g i n g P r o d u c t i o n
A Brief Review of the Most Prevalent Defects in Rolled Steel
Found by Regular Bar Inspection—Accurate Checks
BEFORE using under the hammer, stock must be
first sheared to suitable lengths or multiples.
It is impossible on steels of higher alloying content
to draw a definite line as to what analyses will
and what will not satisfactorily cold shear. Such
variables as size, condition of shears, high or low
side of range in hardening elements, and even weather
conditions have pronounced effect. Under most favorable
conditions it may be assumed that standard analyses
of chrome-vanadium, chrome-carbon, low-chromenickel
and 3y-\ per cent nickel steels will cold shear
in sizes up to 2y> in. round or square with a carbon
content up to .45 maximum.
With carbon as high as .50 or .55 these types
can usually be sheared cold with safety in sizes up
to iy in. round or square. These limits are given
more in the nature of a warning than as a recommendation.
A little heating before shearing steel
approximating these limits is by no means an extravagance.
In extremely cold weather much improvement
may even be effcted on certain types of
steel by raising temperatures but slightly, from yard
to room temperature for instance, or just sufficient to
relieve the intense chill from the steel. Requiring
special attention in cold shearing are capacity of
shears, their alignment, condition of knives and hold
down,
Trouble in cold shearing may be evidenced in several
forms. The stock may break off sharply, or spall
on the corners, it may show a very fine crack across
the sheared surface or it may be strained to such an
extent upon shearing that while no crack is perceptible,
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 sotck 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 edge.
Heating.
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
saisfactory properties. Usually there is no warning
during too rapid heating of "tender" steels, of the ill
effects which such practice produces.
*From U-loy News.
Possible on Forging Qualities of Steel
PART II
399
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. Preheating
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 be 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 is improbable that pieces forged would have defects
in the same spot on the bar, billet or slab.
Frequent Sources of Trouble.
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