BBBBflt] «BlJIUrIrlr - Clpdigital.org

434 Fbrging-Stamping - Heat Treating
F a i l u r e o f Billets D u r i n g F o r g i n g
A lot of 20 forged medium carbon steel billets
with a cross section of 24 in. by 24 in. and an approximate
weight of 1.500 lbs. was used by a ma-
FIG. 1—Showing location of cracks in forged billet.
chine company in manufacturing crankshafts, etc.
The carbon content varied from .35 to .50 per cent.
Next to the last of these billets, when taken out of
By R. B. WILHELM
December. 1925
the furnace, showed cracks in two planes perpendicular
to the longitudinal axis of the billet and also a
diagonal one in the front. A sketch showing the
location of the cracks is given in Fig. 1. AAiter dividing
the billet in plane B-B, crack D, (Fig. 1), appeared.
Fig. 2 represents crack A in the front and
crack D in section B-B. The aspect of the fracture
clearly reveals that the crack extended almost over
the entire section except the corners. Fig. 3 shows
the cracks C as indicated in Fig. 1.
Due to the fact that the heating of the billet had
been done very carefully, some inherent defee: was
supposed to be the cause of the failure, as the first 18
similar billets, heated exactly in the same manner,
did not show the slightest defect.
Before heating the last billet of this lot it was
subjected to a thorough examination. A suspicious
spot in the surface is shown in Fig. 4 where the scale
FIG. 2—Upper—Crack A, Lower—Crack D as indicated in Fig. 1. FIG. 3—Crack C indicated in Fig 1 FIG 4 Cracked
scale, a suspicious spot on the surface. FIG. 5—The crack shown was revealed upon polishing and etching the surface
shown in Fig. 4.