PSI - Issue 33

Wei Song et al. / Procedia Structural Integrity 33 (2021) 795–801 Author name / Structural Integrity Procedia 00 (2019) 000–000

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cubic (bcc) configuration. It will undergo metallurgical SSPT during heating and cooling. Generally, the determination of phase transformation volumes and the final fractions of phases mainly depends on the cooling time and cooling rate from the CCT diagram, which was shown in Fig 4(a). It should be noted that the temperature histories from 800 ℃ to 500 ℃ (t 8/5 ) are critical to forming the final phase microstructures. To further obtain the parameters of phase transition process, the dilatometry experiments were conducted by Gleeble 3800 thermomechanical simulator equipped with a dilatometer, as shown in Fig 4(b). The Koistinen-Marburger (K-M) models, were adopted to simulate diffusion type and displacive reactions for solid-state transformations in the heating and cooling phases:     1 1 3 1 3 1 exp ( ) / ( ) n A c c c c c f k A T A A A T A        ， (1) where A f is metallurgical phase proportion of austenite, T is the function of temperature. 1 c A (cementite disappearance) and 3 c A (α-ferrite disappearance temperature) are 790 ℃ and 855 ℃ from dilatometry results, respectively. The Koistinen-Marburger equation is given for the austenite-martensite transformation, as follows:     0 1 exp M s s f b M T T M          ， (2)

(a)

Centerline

Y

Z

X

Constraints

(b)

Evenmatched

Weld center

Undermatched

Fig. 3 A schematic diagram of local metal removed and residual stress measurement. (a) The location of measurement; (b) arrangement of strain gauges.

(a)

(b)

1.8

100 200 300 400 500 600 700 800 900

Speed of cooling: 10 ° C/s Peak temperature: 1200 ° C Speed of cooling: 20 ° C/s Speed of heating: 200 ° C/s

10CrNi3MoV

Ac 3 =820 ° C

1.5

Ac 1 =707 ° C

1.2

F+P

Temperature ( ° C )

0.9

A

Austenite

B

heating

0.6

Ms =450° C

M

Martensite

0.3

Themal strain /%

cooling

0.0

 vol

10CrNi3MoV

t 8/5 =2.8 s

t 8/5 =15 s

Ac 1

Ac 3

M f

M s

-0.3

0

200 400 600 800 1000 1200

1

10

100

1000

10000

Time (s)

Temperature ( ° C)