Vanadium effect on steel structural stability in creep-rupture tests

A comparative study of structure changes in the process of creep-rupture tests is performed for 12KhGNU and 12KhGNMT steels at temperatures of 350 and 460 deg C. It is established that vanadium alloying increases essentially the characteristics of long-term rupture strength. The methods of thermomagnetic analysis and electron microscopy show that steel strain at 350 deg C results in partial decomposition of the carbide phase. The effect of Cr, Mn, Ni, Mo, V, Nb, Si on changes in the steel phase composition was studied in the process of loading at 350 deg C. Only V and Nb of the studied elements prevent the carbide phase decomposition. Loading of 12KhGNM steel at 460 deg C is accompanied by coagulation and a noticeable coarsening of carbide particles. Vanadium addition delays the coalescence process at this temperature. A conclu;ion is made that under loading temperature below the temperature of interstitial impurities atmosphere condensation around dislocations (Tk), the process of the carbide phase partial decomposition is essential for the long-term rupture strength, while at the temperature above Tk the coalescence of carbide particles becames the determining process. Vanadium stabilizes the carbide phase in both temperature ranges