PSI - Issue 28

1924 7 In the Master Curve approach the increase of the DBTT is captured by a shift of reference temperature ( � ). This shift is added to the safety factor associated to this method where the �� � � � ���� IAEA (2005) and Wallin (1984). The increase in ductile to brittle transition temperature depends on thermal fluence, chemical composition of the alloy and temperature. The composition of the different steel grades is given in Table 2, and the strength and ductility requirements in Table 3. For the simulation purposes the stress-strain diagram in indicates the stress-strain relation at room temperature, this was scaled at higher temperatures by the yield strength data for high temperatures from ASME (2017). The room temperature stress-strain diagram for SA-508gr.3cl.1 was taken from Kim et al. (2015). For SA-508gr.4N no such curve was found, and therefore a curve was derived using the yield stress and ultimate stress values from ASME, Table 3. Stiffness modulus, Poisson ratio and other relevant material data was assumed equal between the two grades. Casper Versteylen et al. / Procedia Structural Integrity 28 (2020) 1918–1929 Versteylen/ Structural Integrity Procedia 00 (2020) 000–000

Table 2. The maximum values of all alloying element according to ASME (2017).

C

Mn

P

S

Ni

Cr

Mo

V

Cu

SA-508 gr.3 SA-508 gr.4N

0.25 0.23

1.50 0.40

0.025 0.020

0.025 0.020

1.00 3.90

0.25 2.00

0.60 0.60

0.05 0.03

0.20 0.25

Table 3. The minimal yield and ultimate strength of forged steels according to ASME (2017).

� ( MPa ) � ( MPa ) Red. Area min. % 450 620 45

SA-508 gr.3 SA-508 gr.4N

690

795

45

2.4. Chemical factor

The irradiation causes a shift in the DBTT Tanguy et al. (2005), which depends on the chemical composition of the alloy and the fluence. The thermal fluence after 40 years for the case considered is 10 19 nꞏcm -2 Uitslag Doolaard et al. (2019). The shift in reference temperature can be calculated using procedures laid out in ASME XI on page 505 ASME XI (2017). � is a material property which is known for SA-508gr.3 steel, but more research is needed to provide reliable data for SA-508gr.4N. Kim et al. compared fracture toughness tests which indicates a lower reference temperature for SA-508gr.4N compared to SA-508gr.3 Kim et al. (2016). As first assumption � shall be assumed to be equal between both steel grades, but this value needs to be determined and introduced to the ASME code if SA-508gr.4N will be applied in future reactors. In previous work a different method was applied which lead to a ∆ �� of 60.6 ºC Uitslag-Doolaard (2019). This value is close to the 57.42 ºC which is calculated in the report using the procedure of ASME XI (2017).