Solidification microstructures and phase transformations in Al-Ti-Si-Mn deoxidized steel weld metals

Controlled undercooling of liquid iron in contact with Al2O3 substrates under varying oxygen partial pressures

“…From the analysis of weld pool solidification, it is well reported that the amount of equiaxed zone depends on the type of inclusions or inoculant particles and that the lattice disregistry between inclusions and solid metal may define undercooling. [2,3,4] In Al-alloy casting, [7,8] a fine, uniform, and equiaxed microstructure can be achieved by inoculation, but because the inoculants are potent and the nucleation undercooling is very low, the classical spherical-cap model is not useful in explaining the results. Alternative models have shown that the adsorption of solutes in the substrate/melt interface as well as the reaction between the substrates and the melt can have effects on solidification that are not expected from the classical nucleation theory.…”

“…Most of these articles came from the field of welding [2,3,4] but there are some references to the production of steel with 100 pct equiaxed structure in Posco [5] and Sumitomo. [6] There are also some interesting insights into the mechanisms of heterogeneous nucleation from the external inoculation process that has been long used in the production of aluminum.…”

Refinement of Solidification Microstructure and Austenite Grain by Fine Inclusion Particles

“…The present results coupled with previous one 5) suggest that the dendrite arm length also decreases with the dissolved Ce content. In a previous study, 5) it was found that the area fraction of equiaxed crystals increases with an increase of Ce 2 An Fe-0.15 or 0.30%C-1%Mn-1%Ni alloy was deoxidized at 1 600°C with Ti, Ce, Mg or Zr and cooled to 1 470°C (Cϭ0.15 %) and 1 460°C (Cϭ0.30 %) at 50 K · min Ϫ1 , followed by rapid quenching. These quenching temperatures determined by the cooling curves correspond to the start of the single g-phase, namely, the temperatures in the single g-phase just below the dϩg and gϩliquid two phases, respectively.…”

“…1) However, if the austenite is bounded by an orientation relationship with the d-ferrite, the austenite cannot grow across the primary d-ferrite solidification boundaries. It is reported 2) that in the presence of Al 2 O 3 inclusions, nucleation of austenite phase becomes energetically more favorable and thus steel solidifies directly as austenite in interdendritic liquid.…”

“…The mean primary arm length, l¯1, mean primary arm spacing, l ළ 1 , and density of dendrite were measured from solidification structure etched in an Oberhöffer solution and/or a saturated picric acid and CuCl 2 solution. The observation area was about 200 mm 2 , which corresponded to the half of the cross section area of vertically sliced sample. The observation number of dendrite was about 20 to 50.…”