Influence of the original structure and aging temperature and time on the formation of sigma-phase in tubes of 12Kh18N12T steel

An investigation was made of 32x6 mm steam superheater tubes of 12Kh18N12T steel containing 0.09% C and 0.50% Ti. It was established that the aging temperature, the length of the hold at the selected temperature, and the grain size of the original metal influence the formation of σ-phase. The microhardness of specimens taken from the tubes before and after straightening in relation to the investigated factors is shown. It is shown that an increase in aging temperature and time in combination with a coarse-grained structure of steam superheater tubes of 12Kh18N12T steel leads to precipitation of σ-phase in the grain boundaries, which may cause embrittlement of the tube metal in service of it