PSI - Issue 28

6

Versteylen/ Structural Integrity Procedia 00 (2020) 000–000

Casper Versteylen et al. / Procedia Structural Integrity 28 (2020) 1918–1929

1923

Table 1. width (c).

Postulated crack sizes for different analyses, all cracks are semi-elliptical an identified only by the depth (a) and

Postulated crack

a ( mm )

c ( mm )

AR ( a/c )

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

ASME postulated crack

62.5 56.3 68.8 62.5 62.5

187.5 168.8 206.3

1/3 1/3 1/3 2/3 1/3

ASME -10% ASME +10%

AR 2/3

93.3

SA-508gr.4N

187.5

Fig. 2. The mesh of the RPV containing six cracks at locations 4, 5, 6, 7, 8, and 9. Fig. 3. The mes of the RPV contain ng six cr cks t l cations 4, 5, 6, 7, 8, and 9.

2.3. Material properties

The RPV steel for which the master curve has been fitted is SA-508 IAEA (2005), Wallin (2002), Wallin (1984), Tanguy (2003) Tanguy et al. (2005). The fracture toughness and the ductile brittle transition temperature (DBTT) of this material depends on the chemical composition and the microstructure of the material. A newer grade of this steel SA-508gr.4N contains more Nickel and Chromium compared to SA-508gr.3 and less Manganese. These elements suppress the formation of bainite during continuous cooling Yang et al.( 2018). It is therefore easier to make a pure martensite microstructure for SA-508gr.4N. The ductile to brittle transition temperature for the martensite microstructure is actually higher than for the bainite microstructure. This is related to the high angle grain boundaries of the martensite laths which disrupt cleavage crack propagation Yang et al.( 2018). For these reasons this type of steel is very promising. The chemical factor of this steel is seems to be lower, despite the higher Chromium content. The DBTT of SA-508gr.4N will therefore increase less with fluence.