PSI - Issue 54

Magdalena Eškinja et al. / Procedia Structural Integrity 54 (2024) 123–134 M. Eškinja et al. / Structural Integrity Procedia 00 (2019) 000 – 000

125

3

tempering temperature to 610°C for 110 min. After heat treatments, specimens were mechanically grounded and decarburized layers were removed in order to machine the specimens for performing hydrogen related experiments.

Table 1. Chemical composition of HMoS and LMoS (%wt). Material C Si Mn Cr Mo

S

P

Ni

Fe

HMoS LMoS

0.21 0.31

0.04 0.09

0.84

0.98 0.94

0.97 0.16

0.002 0.008

0.005 0.009

0.14

Bal. Bal.

0.7

0.009

Fig. 1. SEM micrographs of (a) HMoS and (b) LMoS, showing tempered martensitic lath microstructure for both steels, and corresponding orientation EBSD maps (c, d) in as-received condition.

Figure 1 shows scanning electron microscopy (SEM) images of the a) HMoS and b) LMoS specimens, exhibiting a typical lath martensite microstructure, comprised from blocks and packets inside prior austenite grain boundaries (PAGB). Electron backscatter diffraction (EBSD) results implied no significant difference in the microstructure, and the grain size of lath martensite and prior austenite grains (PAGs) was similar for both alloys. 2.2. Mechanical Properties To investigate mechanical properties of the steels in air and in hydrogen environment uniaxial tensile tests were performed at ambient temperature. The chosen strain rate was 1 ˟ 10 -6 s -1 due to the fact that at low strain rates