PSI - Issue 23

Aleš Materna et al. / Procedia Structural Integrity 23 (2019) 425–430 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

426

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propose an optimum temperature profile for regeneration annealing of the WWER-440 reactor internals (namely the core barrel, the core basket and the block of guide tubes). The main structural material for the reactor internals is chromium-nickel titanium-stabilized austenitic stainless steel 08Ch18N10T. These internals are fabricated in various shapes such as bars, sheets and forgings with different degree of cold-work hardening of steel. Prior the annealing of the irradiated specimens, the effect of annealing temperature on mechanical properties of unirradiated 08Ch18N10T steel as well as the reliability of the proposed methodology for evaluation of mechanical properties recovery was tested on rectangular specimens with three levels of hardness induced by the different thickness reduction. In the previous work by Petelova et al. (2018), hardness change after 6 hours of annealing at temperatures varying from 550 °C to 900 °C was examined and anomalous behaviour was found at 700 °C. While for most temperatures in given range the hardness decreases after annealing, annealing at 700 °C had only small effect on the measured hardness within the observed scatter. Therefore, more detailed study on the effect of the annealing temperature 700 °C with progressively increasing annealing times was performed and results are presented in this paper. In addition, the finite element analysis of the variation of the local hardness in cold-worked specimens was performed and, as a result, specific places on specimen’s surface were recommended to avoid during hardness measurements. Nomenclature ( ) , equivalent true (logarithmic) plastic strain HV3 Vickers hardness at 3 kgf HV5 Vickers hardness at 5 kgf HIT indentation hardness

2. Material and methods

2.1. 08Ch18N10T stainless steel

08Ch18N10T is a titanium stabilized chromium-nickel austenitic stainless steel with chemical composition (see Table 1) similar to AISI 321.

Table 1. Chemical composition of 08Ch18N10T austenitic stainless steel (in wt %). in wt % C Mn S P Ni Cr

Ti

≤ 0.08

1.0 – 2.0

≤ 0.02

≤ 0.035

9.0 – 11.0

17.0 – 19.0 ≥ 5C ≤ 0.6

08Ch18N10T

2.2. Hardening of 08Ch18N10T steel

Hardening was carried out at room temperature using a universal tensile testing machine. Two quenched plates pressed rectangular specimens of original size 12×12×60 mm to two various final thicknesses: 10.8 mm and 9.6 mm using pressure forces 450 kN and 800 kN respectively (see Table 2).

Table 2. Three hardening states of 08Ch18N10T steel used in the present study. Thickness reduction [%] Final thickness [mm]

Pressure force [kN]

0 (undeformed)

12

0

10 20

10.8

450 800

9.6