PSI - Issue 13

Vishal Singh et al. / Procedia Structural Integrity 13 (2018) 1427–1432 Author name / Structural Integrity Procedia 00 (2018) 000–000

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3

Table 1. Chemical composition of investigated steels

Element (wt. %)

C

S

P

Mn

Si

Cr

Ni

Mo

Cu

Al

V

Nb

Fe

316L

0.019 0.016 0.026 1.629 0.328 16.74 10.26 2.022 --

--

-- --

-- --

SA508

0.19

0.002 0.018 1.3

0.23

0.17

0.7

0.44

0.13 0.02

Balance

0.054 0.001 0.012 1.498 0.230 --

--

0.086 --

0.029 0.0355 0.0572

X65 X80

0.04

0.001 0.012 1.8

0.24

0.05

0.19

0.18

0.18 --

0.018

0.482

The tests were interrupted at regular intervals (in terms of number of cycles) to take the images of the crack path in front of the notch. The detailed experimental procedure used for short fatigue crack propagation can be found elsewhere (Singh et al. (2018)). 3. Results and discussion Fig. 1 presents the microstructures of all the steels investigated in the present work. AISI 316L austenitic steel was characterized with an average grain size of ~50 µm. SA508 Grade 3 Class I steel was characterized as upper bainitic microstructure with an average grain size of ~20 um. API 5L X65 steel was composed of ferrite, pearlite and some bainite, with average grain size of ~10 um. API 5L X80 steel was containing ferrite and bainite with average grain size of ~6 um. Small fraction of martensite/austenite (M/A) islands and stringers were also obtained in SA508, X65 and X80 steels samples. Tensile characteristics of all the materials with and without hydrogen charging are presented in Table 2.

Table 2. Tensile properties of investigated steels with and without hydrogen environment

Uncharged UTS, MPa

Hydrogen charged

Material

YS, MPa

Elongation, %

YS, MPa

UTS, MPa

Elongation, %

316L

315 523 523 625

541 663 610 665

86 28 25 22

303 540 552 650

567 642 601 670

81 22 21 12

SA508

X65 X80

(a)

(b)

(c)

(d)

Fig. 1. (a) Optical image of 316L and SEM images of (b) SA508, (c) X65, and (d) X80 steels