“tz — tain different nodule numbers, Ferritic and tempered martensite microstructures were 
TSE | obtained by annealing (7409C - 4 h) or quenching and tempering (9009C =- 2 h, oil; 
JRE 5609C - 2,5 h, air) treatments. In order to obtain samples with a high nodule ‘count 
UL cast (secondary graphite), quenched samples were submitted to a tempering at 6509C for 20h 
Hydrogen was introduced by cathodic charging or by a pickling process. A 4% H,S0, so- 
lution with 0,25 g/1 NaAsO, was used for cathodic charging, with a current density of 
Y levels, 7,5 Affen“, for 24 h. The pickling treatment was performed with 60 g/l HCl solution, du- 
‘Tacture node ring 0,5 to 72 h. The mechanical tests were done up to a maximum of 15 minutes. after 
the fracture hydrogen charging. 
The tensile tests were carried out with a strain rate of 50 x 107071, using speci- 
‘hat the pre- mens with a 40 mm gage length and 8 mm diameter (DIN 50 125). 
a In order to investigate the crack initiation and propagation, interrupted tests with 
A the samples of Figure 1 (16) were performed. The upper face of the sample was metal- 
lographically prepared before cathodic charging. Next, an increasing loading by com- 
Ti during pression were applied and then the polished surface was examined by SEM. 
articles.which 
Figure 1 ~ Increasing loading sample (16). 
‚drogen on 
ST 3. Results and Discussions 
eine! Figure 2 indicates the results of mechanical properties for ferritic blackheart mal- 
SUT leable iron,with pickling treatment, showing the elongation reduction as the pick- 
ling time increases. A significant influence related to the solution concentration 
m was not observed, 
For specimens cathodically charged, the results in Table I show that the elongation 
Me nelts decreases with increasing charging time and current density. It is also possible to 
observe the reversibility of the embrittlement with the 2009C heat treatment. 
gual heat During the tensile test of the previously hydrogen charged samples, it is possible to 
sages. This observe the development of small superficial cracks (figure 3). Some of these cracks 
inanese sulfide are blunted when they hit the graphite nodules, due to the increase in the radius of 
4) before an“ the crack. The fracture of the sample occurs because of the propagation of one of 
these cracks. 
Coen CO or 
Prakt. Met. Sonderbd. 21 (1990) 
102