PSI - Issue 7

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Ning Wang et al. / Procedia Structural Integrity 7 (2017) 376–382 N. Wang et l. / Structural Integrity Procedia 00 (201 ) 0 0–000

378

Table 2. Tensile properties of the 25Cr2Ni2MoV steel.

Reduction of area ψ , [ % ]

Ultimate Tensile Strength [MPa]

Yield Strength, [MPa]

Elastic Modulus [GPa]

Elongation δ , [ % ]

894

793

16.62

71.16

212

3. Results and discussion 3.1. S-N curves

600

Hydrogen-assisted As-received As-received, runout

560

440 Alternative stress, σ a (MPa) 480 520

400

10 5

10 6

10 7

10 8

10 9

Number of cycles to failure, N f

Fig. 2 S-N Curves The S – N curves of two series of specimens are shown in Fig. 2. Runout data are represented with arrows. With the decrease of stress amplitude, the fatigue lifetime increases gradually up to the VHCF regime, the S – N curves show a continuously decreasing mode. Current data are still limited to judge on the existence of conventional fatigue limit. As shown in Fig. 2, there is a significant influence associated with hydrogen charging on the fatigue life. The fatigue strength of hydrogen charged specimens is obviously lower than those as-received ones.

(a)

(b)

Fig. 3 (a) As-received specimen ( σ a =510 MPa, N f =2 × 10

7 cycles), (b) hydrogen charged specimen ( σ =460 MPa, N

f =3.11 × 10

7 cycles)