PRECIPITATION OF TITANIUM NITRIDE IN LOW-ALLOYED STEEL DURING SOLIDIFICATION

The microsegregation of titanium and manganese and the precipitation o f titanium nitride during dendritic solidification were investigated o n an Fe-0.051%Ti-0.77%Mn alloy. Carbon and nitrogen were introduced in to the liquid sample via the gas phase. The material solidifies as del ta ferrite at a carbon mass content of about 0.08% but predominantly a s austenite at greater than or equal to 0.3%. At ferritic solidificati on, an about 3fold enrichment of the titanium in the residual melt bet ween secondary dendrite arms is attained by segregration, whereas in t he corners between some dendrites or grains in maximum a 10 fold enric hment was detected. TIN particles of 0.5 to 1.0 mu m size are formed o nly in the regions of maximum segregation where the supersaturation is higher than 15fold. An equal supersaturation has been calculated for homogeneous nucleation in the melt. The number of particles is moderat e at 0.016% nitrogen but. low at 0.008%. At austenitic solidification, the titanium content in the residual melt increases to more than the 30fold of the starting value, Particles formed in the melt grow to dia meters in the 2 mu m range.