Effect of Nb, Ti, Mo and B on Creep Rupture Strength of 16Cr-10Ni Heat Resisting Steel with Vanadium

Abstract

The influence of individual and combined additions of molybdenum, niobium, boron and titanium on the creep rupture strength and the rupture elongation of 16Cr-10Ni-0.4V heat resisting steel, and their correlation with microstructures have been studied.
Chemical composition of the steels used has been selected by the design of experiment and the relationship between the creep rupture strength and the chemical composition has been analysed by computer. Aregression equation has been developed which satisfactorily predicts the 700°C1000 hr creep rupture strength from the chemical composition. The additions of molybdenum, niobium and boron to this steel have a remarkable effect in increasing the creep rupture strength. Molybdenum, boron and titanium additions have been found to improve the creep rupture elongation.
It has been presumed from electron microscopic studies that molybdenum accelerates slightly the coarsening of the precipitated carbide, but increases the creep rupture strength through the so-called solid solution strengthening, and that niobium and boron make a distribution of precipitated carbide more uniform in matrix, that is one of the causes of their strenghthening effect.