Mixing time is a parameter that describes the degree of agitation in a gas-stirred ladle. The literature is not conclusive on the effect of the tracer injection position on the mixing time under equal stirring conditions. This work conducted a systematic and comprehensive study on the effect of the tracer position on the mixing time for centric injection. Results in the form of a mixing time map indicate that the diagonal formed between the inlet and the upper wall region gets the fastest mixing, and specifically in the eye of the toroid of the circulation loop is the best position to mix solute rapidly. In contrast, the dead zones at the lower near-wall part of the ladle have the poorest mixing behavior for the tracer addition. The study also tested the ladle's axisymmetric assumption since two points were at different angular positions, but the same axial and radial points presented similar mixing time.

Mechanical characterization by multiscale indentation of dense particle reinforced Ni/Al2O3 metal matrix nanocomposites (MMNC) obtained by high-kinetic processing (HKP) of ball milling of the powders with a systematic variation of alumina nanoparticles fractions (from 1 to 20 vol.%) and spark plasma sintering (SPS) is here reported. The morphology and particle size distribution of powder were evaluated as a function of milling time at 2 h intervals up to 10 h. Samples from the processed powders after 10 h were densified by SPS. The mechanical properties of the sintered samples were obtained by micro and nanoindentation using diamond tips of Vickers and Berkovich geometry, respectively. The combination of HKP and SPS allowed obtaining a homogeneous dispersion of Al2O3 nanoparticles in the nickel matrix and effective reinforcing effects, which is the particular case of Ni/10 vol.% Al2O3 and Ni/15 vol.% Al2O3 samples. The highest hardness (4.68 ± 0.37 GPa) was obtained for Ni/15vol% Al2O3 MMNC, which is almost twice that of pure nickel (2.45 ± 0.22 GPa) processed at the same conditions. The highest elastic modulus (346 ± 30 GPa) was obtained for the Ni/10vol% Al2O3 sample. The analysis of the load-depth curves confirmed the reinforcing of the MMNCs as a function of the alumina particles content. Discussion of the possible reinforcing mechanisms is also included. The Ni/Al2O3 MMNC sintered specimens exhibit outstanding mechanical property results, which make them candidates for various high-temperature applications.

This article demonstrates that the enthalpy-porosity technique was successfully applied to determine the melting of DRI (direct-reduced iron) and Al pellets in a liquid of the same composition under static and forced-convection bath conditions. It also confirms that this study accurately represents the entire pellet-melting process, from shell formation to complete melting. The pellet’s internal thermal gradients and movement due to molten-steel flow were calculated using a dynamic mesh. The technique was first validated using experimental data by obtaining melting curves for aluminum spheres in their own baths at different temperatures under static bath conditions. The total melting times for the aluminum spheres in their own baths were 10 s at 750 °C, 18 s at 700 °C, and 33 s at 680 °C, showing good agreement with experimental data. The melting time for the DRI pellet in the liquid steel bath at 1500 °C was 9 s with forced convection and 11 s in the static bath. This test case shows that the technique can represent, within the same domain, actual bath stirring conditions and the melting of many solid particles, as occurs in many metallurgical processes, which is the future of simulating these complex systems.