Working zone of the industrial heat treatment furnace was checked

and the small-scale heating furnace with accurate temperature control was applied to simulate the low temperature heating zone of the industrial heat treatment furnace.Moreover

the optical microscope

scanning electron microscope and transmission electron microscope were used to observe the microstructure of the samples which have suffered different heat treatment processes.The results show that

the positive deviation of temperature in the furnace and the obvious low temperature at the bottom of furnace were the main reasons for metallographic " unqualified" for P92 steel.The mechanical properties of the samples after normalizing at 970℃and 1 070℃ nearly had no difference

the microstructure of both the samples were fine tempered martensite

which is qualified.With an increase in normalizing temperature

the width of martensite laths increased

the strengthening phases precipitated obviously

the persistent strength increased and the minimum creep rate decreased.