stress direction, These cracks are transgranular and extremely sharp, growing asso- 
ciated with small plastic deformation levels of the matrix (figures 7-a and 7-b). Fi- 
gure 7-c shows the crack propagation. 
band hydrogen 
fm i” Se pre “Ag, BD 38: 
aia fo ©) 
\nitlation a- 
dund the cavi- 
erns of the cle- 
ite interface 
ne can observe 
cating the og 
723s further 
ze, associated 
3.2 10 identify i 
& without hydro- (0) , 
neg Figure 6 — Fracture sequence of samples without hydrogen. 
he growth of the 
te (Figure 6-0), The preferential localization of the cleavage cracks around the graphite, observed 
und Mas inclu- in the tensile specimen and in the samples with interrupted tests, shows that the hy- 
gg BE drogen embrittlement is strongly influenced by the presence of graphite particles. 
se In order to investigate this effect in more detail, the nodule number in blackheart 
CEES a1 1eable iron and in ductile iron was varied (Table II). One can observe in both al- 
loys that the hydrogen embrittlement tendency is reduced with increasing nodule num- 
sui TF par, This is particularly evident in the sample with a high number of secondary gra- 
ol BI phite particles. It was also observed in this sample that the cleavage facets nuclea- 
ora tion is not located around the eutectic graphite particles, as occurred in the sam- 
co FEE Glee without secondary graphite. 
„a from the 
Prakt. Met. Sonderbd. 21 (1990) 
‚a! 
vb’ 
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1207