Effect of titanium on second phase precipitation behavior in 9-12Cr ferritic/martensitic heat resistant steels

Effect of titanium addition from 0.003 to 0.140 wt.% on precipitation behavior of MX-type phase in 9-12Cr ferritic/martensitic heat resistant steels was studied. The results show that large titanium-containing MX particles with about 1 mu m form from liquid metal during the solidification process in high titanium steel. After normalizing at 1100 degrees C for 1 h, cooled in air and tempering at 750 degrees C for 1 h, nanometer-sized MX precipitates distribute densely near martensitic lath boundaries in the high titanium steel. Two kinds of nanometer-sized MX precipitates distribute densely and homogeneously in the matrix within lath in low titanium and ultra low carbon steels after the same heat treatment. The relatively larger nanosized MX precipitates have a size more than 30 nm and contain titanium. The number density of the relatively larger nanosized MX precipitates increases with the increasing of titanium content. The relatively smaller nanosized MX precipitates are about 10 nm in size and have two kinds of different shapes: one is cubic and contains titanium, and another rectangular without titanium.