| The fracture toughness of the thermal cycle simulates weld HAZ (heat-affected zone) of SA 508 Cl.3 RPV (reactor pressure vessel) steel was evaluated in the ductile-brittle transition region. Reference temperature(T_0), and master curve for each region in the weld HAZ were determined from the three point bending tests at low temperatures, by using the Weibull`s statistical method as described in ASTM E1921. Most specimens were conformed to validate at the test temperatures. It was shown that the new test method, which evaluates the fracture toughness in the transition region, was effectively applicable to the weld HAZ. The fracture toughness test results indicated that the coarse grained HAZ region near the weld fusion line possesses relatively good fracture toughness. In contrast, the minimum toughness value was noted at the subcritically reheated HAZ region adjacent to the base metal. The volume fraction of tempered martensite, mean sizes of grains and precipitates were quantitatively analysed as microstructural factors, a discussion on the effects of these factors on fracture toughness of the weld HAZ is presented. |
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