The effect of N content on creep rupture properties, mainly creep rupture ductility, of 12% Cr heat resisting steels was studied. The creep rupture strength became higher with increasing N content below the temperature of 600°C. But, the increase in N content led to the decrease in creep rupture strength above the temperature of 650°C. The creep rupture ductility decreased with increasing N content and creep rupture time, and it was much more remarkable for reduction of area than for rupture elongation.
To clarify the cause that creep rupture ductility decreased with increasing N content and creep rupture time, the multilinear regression analysis was carried out. As the result, it was found that the amount of precipitates and the strength level of matrix affected the decrease in creep rupture ductility.
