Sima Aminorroaya

TEM characterization of precipitates in the segregated regions of a low-carbon, low-manganese, titanium-added steel.

A concentric solidification technique has been employed to simulate sulphide precipitation at the centreline of a continuously cast low‐carbon, low‐manganese, titanium‐added steel slab. Selected precipitates were identified using transmission electron microscopy following sample preparation by focused ion beam milling techniques. FeTiS2 and hexagonal MnS containing iron atoms form in close proximity to each other in super‐saturated areas of the concentrically solidified sample. The presence of FeTiS2 precipitates in low‐carbon steel has been verified for the first time, and the crystal structure determined by electron diffraction analysis as a trigonal CdI2‐type with a P3 m1 space group and lattice parameters of a= 0.341 nm and c= 0.569 nm.

A novel approach to simulate segregation at the centreline of continuously cast steel using laser-scanning confocal microscopy

A concentric solidification technique was employed to simulate the segregation of alloying elements that occur during solidification at the centreline of continuously cast steel. Microstructural development of low carbon steel upon solidification has been observed in situ in a laser‐scanning confocal microscope. Sulphide precipitates that formed in the last remaining liquid were identified, and evidence is provided that segregation occurring at the centreline of steel slabs can reasonably be simulated by the use of the concentric solidification technique.

Simulation of microsegregation and the solid/liquid interface progression in the concentric solidification technique

A concentric solidification technique was employed to simulate experimentally the segregation of alloying elements during solidification at the centerline of continuously cast steel. Microstructural development of low carbon steel upon solidification has been observed in situ in a laser-scanning confocal microscope. Microscopic analyses following in situ observations, demonstrate that segregation occurring at steel slabs can reasonably be simulated by the use of the concentric solidification technique. The validity of these experimental simulations has been correlated with mathematical analyses using the Thermo-Calc and DICTRA (Diffusion Controlled Transformation) modeling tools. The effect of cooling rate on the sequence of events during solidification of Fe–0.18%C and Fe–4.2 wt%Ni peritectic alloys was studied and compared with the experimental observations.

TEM analysis of centreline sulphide precipitates modified by titanium additions to low carbon steel

Elongated inclusions, particularly MnS, contribute significantly to reduced ductility and toughness in hot rolled steel but earlier research indicated that these properties can be improved by titanium additions. Such additions to a steel result in titanium being dissolved in manganese sulphide or MnS being replaced by TiS and/or titanium carbosulphides. In the present study, a steel was designed to decrease alloying element segregation and to evaluate the effect of titanium on centreline sulphide precipitates. Precipitates were identified by using scanning electron microscopy and characterized by the use of transmission electron microscopy following sample preparation by focused ion beam milling techniques. Iron–titanium‐sulphides form in close proximity to MnS precipitates that contain iron. Evidence is provided that an increase in the titanium content of steel leads to an increase in the percentage of titanium contained in the iron sulphides and a decrease in the iron content of MnS inclusions.