PSI - Issue 52

Long Jin et al. / Procedia Structural Integrity 52 (2024) 12–19 Author name / Structural Integrity Procedia 00 (2019) 000–000

14

3

(a)

(b)

3μm

3μm

Fig. 2. SEM images showing the microstructures of as-received (a) and aged at 450°C for 1000h (b) material

Table 1. Chemical composition of 16MND5 low alloy steel (in wt%)

C

Mn

Ni

Mo

Si

Cr

0.18

1.37

0.75

0.50

0.17

0.12

Cu

Al

N

P

Fe

0.03

0.016

0.010

0.003

Bal.

2.2. Mechanical properties test Three as-received and three aged tensile tests were performed on a 200kN hydraulic tension-compression test machine at ambient temperature. Hardness was measured under 1000 gf for 15 s dwelling on a Vickers hardness test machine with at least ten random measuring points on each specimen. The cylindrical fatigue specimens with uniform gage of 16mm in length and 8mm in diameter were machined according to ASTM E-606 in Fig. 3. The surface of the fatigue specimens was polished to a roughness of 0.2 μ m. The low cycle fatigue tests were carried out on a servo-hydraulic fatigue testing machine MTS Land Mark370.10 at ambient temperature, and the strain signal was collected by a knife-edge extensometer with a 15 mm gage length. The wave form was triangular and the stress ratio is R = -1. Five strain amplitudes, 0.3 %, 0.45 %, 0.5 %, 0.65 %, and 0.8 %, were employed with the same strain rate of 0.004 mm/mm s -1 in the fatigue test.

Fig. 3. Shape and dimension of the fatigue specimen