Susceptibility of reactor steels to reheat cracking in the heat affected zone as determined by the simulation method

The behavior was investigated of low-alloy steels used for the WWER-440 and WWER-1000 reactor vessels. The steels included the 15Kh2MFAA Cr-Mo-V steel and the 15Kh2NMFAA Cr-Ni-Mo-V steel. The phenomena occurring during welding and heat treatment were studied using the SMITWELD simulator. The resistance of the steels to high-temperature reheat cracking in the heat affected zone was examined by isothermal pressure testing. Appreciable transformation strengthening and embrittlement of the coarse-grain part of the heat affected zone was observed. The degradation phenomena are intensified by increasing the thermal power of the overlaying process. The 15Kh2NMFAA steel is more resistant to high-temperature reheat cracking in the heat affected zone. One-layer submerged arc overlaying with a strip electrode can be applied to manufacture metal-clad pressure vessels from the steel without the hazard of cracking in the heat affected zone. (M.D.). 4 figs., 5 tabs., 5 refs