PSI - Issue 59

Jesús Toribio et al. / Procedia Structural Integrity 59 (2024) 198–205 Jesús Toribio / Procedia Structural Integrity 00 ( 2024) 000 – 000

200

3

where c 0 is the equilibrium hydrogen concentration in the metal in the absence of any stresses. This equation is also the stationary solution of the diffusion problem. 3. Experimental programme A high strength pearlitic steel was used, whose chemical composition and mechanical properties are respectively given in Tables 1 and 2. It presents a coarse pearlitic microstructure, with a pearlite interlamellar spacing of 0.3  m, an average size of the cleavage facet of 75  m, and an average pearlite colony size of about 15  m.

Table 1. Chemical composition (wt %) of the steel. C Mn Si P S

Cr

Ni

Mo

0.85

0.60

0.26

0.010

0.030

0.02

0.02

0.001

Table 2. Mechanical properties of the steel. Young's Modulus E (GPa) Yield Strength (MPa) UTS (MPa)

Ramberg-Osgood parameters  =  e +  p =  / E +(  / P ) n P (MPa) n

Elong. at UTS (%)

199

600

1151

6.1

2100

4.9

Four notched geometries were used of different depth and radii, as sketched in Fig. 1, so as to achieve very different triaxiality (constraint) levels in the vicinity of the notch tip.

L/2

x = a - r

R

r

a

A

D/2

Fig. 1. Axisymmetric notched geometries used in the experiments.

The samples were subjected to slow strain rate testing with displacement rates between 10 – 10 and 2.10 – 6 m/s. The test environment was an aqueous solution of 1 g/l calcium hydroxide plus 0.1 g/l sodium chloride. The pH value was 12.5 and tests were performed at a constant electrochemical potential of – 1200 mV SCE (saturated calomel electrode) to achieve HE environmental conditions.