Abstract: Large TiN inclusions were found in the hot-rolled medium carbon steel plates with titanium microalloying. Therefore, the slab of titanium microalloyed medium carbon steel was taken as the research object. The TiN inclusions in slab were observed by means of optical microscope (OM), scanning electron microscope (SEM), ASPEX, stereomicroscope (ST), and microhardness tester (MH), and the distribution law of TiN inclusions in the thickness direction of the slab was summarized. An innovative combination of micro-labeling and dendrite erosion was adopted to confirm that the large-grained titanium nitride in slab was precipitated between dendrites. The three-dimensional morphology of TiN inclusions in slab was observed by large sample electrolysis, and it was proved that with the increase of TiN particle size, the morphology presented dendritic, confirming that the large TiN inclusions grew in a dendritic manner. The TiN inclusions obtained by ultrasonic cleaning and electrolysis were found to be fragile. Chain-like TiN inclusions were found in the rolled products, verifying that the TiN inclusions in the dendritic state in slab were broken into chains during the rolling deformation process. The TiN in slab of the studied steel was marked, and the heating furnace process was simulated, proving that under the existing heating furnace process conditions, the TiN inclusions were difficult to dissolve.

Key words: TiN inclusions; slab; titanium microalloying; dendritic crystal; micro-marking positioning