FORECASTING OF STRUCTURAL TRANSFORMATIONS IN HEAT AFFECTED ZONE STEEL OF 15Kh2NMFA AT ANTI-CORROSION CLADDING

Using mathematical modeling based on existing parametric regression equations the prediction of microstructure-phase transformations in heat affected zone( HAZ) metal of base material (steel 15Kh2NMFA) of WWER-1000 reactor vessel in arc cladding of protective anti-corrosion layer was carried out as well as performed comparative analysis of modeling results with obtained experimental data of dilatometric and metallographic analysis. The comparison of results ensures formation of bainite-martensite structure in HAZ metal of WWER-1000 reactor vessel, however a value of content of martensite in calculation and experimental determination is different on ~ 40…50%. To clarify the calculated results, a thermokinetic diagram of the decomposition of supercooled austenite was constructed for characteristic cooling rates (3; 4, and 5 °C/s) during the welding/surfacing thermal cycle. As a result, adequate parameters of the microstructure-phase composition in the HAZ of steel 15Kh2NMFA at corrosion-resistant cladding were obtained.

Application of Master Curve Approach to WWER-1000 RPV Materials

Part of the IRLA (International Residual Life Assessment) project was concentrated on a detailed analysis of existing and available fracture toughness data of WWER-1000 (Water-Water-Energetical-Reactor) reactor pressure vessel materials – steel 15Kh2NMFA (Ni-Cr-Mo-V) type and its welding metals. A wide database of standard fracture toughness data from testing specimens with thicknesses between 10 and 150 mm were collected. Together, 34 different materials were tested – 20 base metals of 15Kh2NMFA(A) grade and 14 weld metals — 11 of SAW (submerged arc weld) type welds (4 welds with 08KhGNMTA grade wire, 4 welds with 10KhGNMAA grade wire and 3 welds with 12Kh2NMAA grade wire; weld with narrow gap, U-groove as well as V-groove technologies were prepared), 1 of EAW (electroslag automatic weld) with 16KhNMFA type wire and finally 2 SMAW welds (manual arc weld) with RT-45A and RT-45B electrodes, respectively. Altogether, this database contains 398 static fracture toughness data from base metals and 121 from weld metals – KIC or KJC types in accordance on testing conditions. This database was primarily analysed with respect to design fracture toughness curves given in WWER standards. Then, data were re-calculated in accordance with the “Master Curve” approach and results were compared with these requirements. Comparison of standard “design fracture toughness” and “Master” curves are presented.