PSI - Issue 60

B Shashank Dutt et al. / Procedia Structural Integrity 60 (2024) 690–699 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

692

3

0.07 mm/s. During testing, loads, crack opening displacement and crack lengths were recorded. J -R curves were determined as per ASTM E1820 standard. After fracture testing, all the specimens were broken in to two pieces. The initial and final crack lengths were determined optically by using a nine-point average method.

Table 1. Chemical composition (wt %)

C

Mn 0.45

Si

Ni

P

S

Cr

Mo 0.99

V

Nb

N

Fe

0.10

0.22

0.21

0.01

0.002

9.09

0.20

0.07

0.047

Bal.

3. Results and Discussion

3.1 Tensile properties and fracture results

The stress-strain curves at different temperatures ranging from 300 °C and 550 °C are plotted in Figure 1 and tensile test results are given in Table 2. In the temperature range 300-550 C, decrease in strength values with increase in test temperatures was observed. Decrease ductility was observed at 350 °C, followed by increase in ductility above 400 °C. Similar trends in tensile results were observed by Choudhary (2013), Roy et al. (2009) and Verma et al. (2015). Modulus of toughness were determined from area under the stress strain curves are mentioned in Fig.1. From True stress- true strain plots, strain hardening parameters were determined as per Hollomon equation (1).

Table 2. Tensile properties of P91 steel

YS (MPa)

UTS (MPa) 853 ±6 810 ±5 673 ±3 638 ±4 547 ±5 478 ±6

% Total elongation

Youngs Modulus

strain hardening exponent (n)

Strength coefficient (K)

Modulus of toughness MJ.m -3

Test temperature (°C)

300 350 400 450 500 550

612 ±5 576 ±4 547 ±6 511 ±3 486 ±4 457 ±3

11 ±1 9 ±1 12 ±2 13 ±1 21 ±2 24 ±2

197 ±4 193 ±3 188 ±5 184 ±4 179 ±5 173 ±3

0.29 ±0.04 0.32 ±0.03 0.35 ±0.02 0.37 ±0.04 0.35 ±0.03 0.27 ±0.02

1664 ±5 1772 ±6 1826 ±4 1841 ±5 1597 ±3 1123 ±6

74 ±3 66 ±4 45 ±3 82 ±5 62 ±2 80 ±5

n K



 

(1) Where K is strength coefficient and n is strain hardening exponent. The n and K values are mentioned in table 2. From strain hardening parameters, plastic strain energy density was estimated using equation 2. Strain energy density was observed to decrease with temperatures as revealed in Figure 2.

1

( )   n u 

K

E



(2)

p

( 1) n

Where ϵ u is the true plastic strain at maximum true plastic stress before onset of necking.