Precipitation of titanium nitride in low-alloyed steel during cooling and deformation

Abstract

The precipitation of titanium nitride in undeformed solid carbon-manganese steel has been investigated by means of metallography and electron microscopy at in-situ melted samples the cooling of which was interrupted at different temperatures for a defined time. The deformation-induced precipitation of titanium nitride was studied on samples which were in-situ melted in a torsion plastometer, deformed after solidification, re-deformed after a holding time, and quenched. Additionally, 50 mm slabs were investigated after direct rolling in a pilot plant, partially with a preceding soaking. In the range of delta ferrite fast homogenization of segregated titanium takes place. No TiN nuclei were formed. In undeformed austenite some large precipitates were formed indicating the solidification structure. In the 1200 to 1100 °C range particle sizes between 20 and 70 nm were reached. A high density of deformation-induced particles smaller than 10 nm could be obtained at or below 1050 °C. The density of the particles increased with decreasing deformation temperature. After fast cooling, below 1000 °C also in undeformed material finely dispersed precipitates were formed.