On the fracture surface of these samples one can observe different fracture mecha- 
) nisms. In the samples without hydrogen the fracture occurs by dimples, nucleated on 
Cee graphite particles and MnS inclusions. On the previously hydrogen charged = samples, 
hE one can observe a variation of the fracture mode related to the distance from the 
405 Une, periphery to the center of the sample, On the central region of the transversal sec- 
tion, the fracture occurred by nucleation and growth of dimples (figure 4-a), : while 
near the periphery the fracture occurred predominantly by cleavage (figure 4-c), At 
the intermediate region, the fracture is mixed, with dimples and cleavage (figure 4- 
b). This fracture mode variation results from the hydrogen concentration gradient , 
caused by the hydrogen charging procedure. 
properties 
| TH | 
Te. 
5 5 
3 er 
a a : a BEN oA 
; : a 
! | ) ) 
Figure 4 — Fracture surfaces of 
_— 
samples after hydrogen 
wal charging. Blackheart 
il 46 malleable iron. 
ve a) central region of 
N the specimen: dimples. 
Sila b) intermediate region: 
. cleavage and dimples, 
¢) periphery: cleavage. 
AEE 5 
pepe 12) 
The cleavage facets induced by the hydrogen, as it happens in steels (17, 18), pre- 
oo sent differences related to the cleavage which occurs in impact tests, The hydrogen 
induced cleavage shows a higher river marking aspect (figure 5) and this characteris- 
tic could be utilized in a failure analysis to detect the possible hydrogen influen- 
ce on the fracture mechanism. 
Prakt. Met. Sonderbd. 21 (1990) 
(b 
a 
125