Hydrogen embrittlement has been widely studied in steels, mainly in quenched and tem- tin 0 
pered steels, although no systematic investigations have been reported about its ef- nal 
fect in cast irons. The hydrogen influence is strongly dependent upon the microstruc- Ee 
ture and the results obtained with steels cannot be always applied directly to cast 
irons. Furthermore, cast irons, besides the presence of graphite particles, have a TE 
high silicon content matrix (1,5 - 2,5%). en 
In low carbon or spheroidized steels, with low strength and high ductility levels, el 
the presence of hydrogen causes elongation decrease, generally without fracture mode Eo 
change, which remains by dimples (6-8). Only for high hydrogen content the fracture ER 
mode changes to quasi-cleavage, cleavage or to intergranular (9-11). The tens 
Referring to the graphite particles, in nickel alloys it was found out that the pre- neni 
cipitation of small graphite particles at grain boundaries enhances the resistance to In order 
hydrogen embrittlement (12). These graphite particles act as "irreversible traps',re- oir 
moving the hydrogen from the grain boundaries. ar 
In cast irons it was observed that hydrogen delays the dissolution of graphite during TE 
the austenitization of ferritic ductile iron (13) and decreases the graphitization ra- 
te during malleable iron annealing (14). These findings suggest that also in cast 
irons there is a strong interaction between hydrogen and the graphite particles,which 
could affect the hydrogen embrittlement. 
This paper reports the results from investigations of the effects of hydrogen on 
blackheart malleable iron and ductile iron, mainly in ferritic matrix. The susceptibi- 
lity to hydrogen embrittlement was evaluated by slow tensile tests, Scanning Electron 
Microscope (SEM) examination of fracture surfaces and incremental loading experiments. 
2, Experimental Procedures 
The irons were melted in a 350 kg medium frequency induction furnace, and cylindrical Bigure 2 
test bars with 20 mm diameter and 80 mm length were poured in green sand moulds. The GEL 
following chemical compositions were obtained: ling tin 
-blackheart malleable iron: 2,54%C - 1,427Si - 0,27%Mn - 0,10%s - 0,020ZP Was not 
-ductile irom: 3.,50%C - 2,55%Si - 0,20%Mn - 0,0207ZS - 0,040%ZP - 0,0447Mg. a. 
Ladle additions of 0,010% Bi, 0,005% Al and 0,0027 B to blackheart malleable melts rine 
were performed. Observe 
The blackheart malleable iron annealing was conducted according to the usual heat oe 
treatment procedures (15), comprising First and Second Graphitization Stages. This or 
procedure results in a ferritic matrix, with graphite particles and manganese sulfide oo 
inclusions. Some samples were submitted to previous treatment (4009C, 4 h) before an- . N 
nealing, to increase the number of graphite particles. or 
The ductile iron melts were innoculated with 0,3% or with 0,87 FeSi75, in order to ob- 
Prakt. Met. Sonderbd. 21 (1990) 
120