PSI - Issue 33

Saki Hayashi et al. / Procedia Structural Integrity 33 (2021) 1162–1172 Hayashi et al / Structural Integrity Procedia 00 (2019) 000 – 000

1165

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would segregate at grain boundary more readily than Sn by Hongbing Peng (2014) and boron has a possibility to prevent the toughness deterioration caused by Sn segregation.

Table 1. Chemical compositions of steels used [mass%].

Mark

remark Low-Sn

C

Si

Mn 1.3 1.3 1.3 1.3 1.3 1.3

P

S

Ti

B

Sn

D

0.05 0.05 0.05 0.05 0.05 0.05

0.23 0.23 0.23 0.23 0.23 0.23

0.012 0.012 0.012 0.012 0.012 0.012

0.005 0.005 0.005 0.005 0.005 0.005

0.020 0.020 0.020 0.020 0.020 0.020

0

0.010 0.010

F

Low-Sn_B

0.0010

H

Mid-Sn High-Sn

0 0

0.10 0.20 0.10 0.20

I J

Mid-Sn_B High-Sn_B

0.0010 0.0010

K

Next, for heat treatment, a reproduction thermal cycle test specimen, as shown in Fig. 1 was taken from the center of the steel plate in a direction parallel to the rolling direction. Several thermal cycles simulating HAZ microstructure subjected to SAW (Submerged Arc Welding) on a steel plate of 25 mm thickness were applied to the middle part of this specimen by induction heating system (Advance Riko, Inc.; MN16-0026-0). An example of thermal cycle is shown in Fig. 2. The peak temperature and holding time of the first cycle is 1400 °C and 1 second, and the peak temperature of the second cycle simulating the following welding pass was heated to 400 °C, which is the typical temperature at which temper embrittlement occurs. In order to observe the toughness change by grain boundary segregation, several holding time conditions are being set. The weld heat transfer equation used in this report is based on the Yurioka’s formula (2004) which is commonly used in japan and derived fr om Rosenthal equation (1941) for weld heat transfer point heat sources with consideration of finite thickness effects, the addition of the temperature rise due to preheating or interpass temperature ( T ph - T ∞ ) to T w , and the consideration of heat dissipation from the weld zone and plate surface ( α 1 and α 2 ). = ∞ + ∙ {(− 1 ) ∙ ( 2 ℎ )} + ( ℎ − ∞ ) ∙ {(− 2 ) ∙ ( 2 ℎ )} (1) = 2 (− 2 ) [ 1 (− 2 ) + ∑ { 1 (− 2 ) + 1 ′ (− ′ 2 )} ∞ =1 ] (2) 2.3. Fracture toughness Fracture toughness of each specimen after thermal histories was evaluated by CTOD test using three-point bending specimens as shown in Fig. 3. It has to be noted that this specimen has only a notch and does not have fatigue crack. CTOD is one of the most common fracture toughness parameters which can be applied for elastic-plastic status. In Temperature, T [ C˚] Time, t [s] 1400 ℃ 400 ℃ Holding time=1sec. Holding time =5,50,500,5000sec. Cooling rate is determined by eq.(1) under condition of SAW with 3.0kJ/mm 1st cycle 2nd cycle Fig. 1. Configuration of specimen for simulated HAZ test. Fig. 2. Schematic illustration of heat treatment condition.