Dissolution of Al_2TiO_5 inclusions in CaO-SiO_2-Al_2O_3 slags at 1823 K

Al-Ti-O inclusions always clog submerged nozzles in Ti-bearing Al-killed steel.A typical synthesized Al2TiO5 inclusion was immersed in a CaO-SiO2-Al2O3 molten slag for different durations at 1823 K.The Al2TiO5 dissolution paths and mechanism were revealed by scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS）.Decreased amounts of Ti and Al and increased amounts of Si and Ca at the dissolution boundary prove that inclusion dissolution and slag penetration simultaneously occur.SiO2 diffuses or penetrates the inclusion more quickly than CaO,as indicated by the w（CaO）/w（SiO2） value in the reaction region.A liquid product （containing 0.7-1.2 w（CaO）/w（SiO2）,15wt%-20wt% Al2O3,and 5wt%-15wt% TiO2） forms on the inclusion surface when Al2TiO5 is dissolved in the slag.Al2TiO5 initially dissolves faster than the diffusion rate of the liquid product toward the bulk slag.With increasing reaction time,the boundary reaches its largest distance,the Al2TiO5 dissolution rate equals the liquid product diffusion rate,and the dissolution process remains stable until the inclusion is completely dissolved.

Physical and numerical investigation on fluid flow and inclusion removal behavior in a single-strand tundish

Aiming at the problem that the existence of inclusions in the tundish continuous casting process can easily lead to quality defects of the slab,the stainless steel continuous casting tundish was taken as the research object.The effects of flow control device,inclusion density and inclusion size on the mixing characteristics of molten steel and inclusion behavior in tundish were studied.The results showed that compared with the tundish without flow control device,the average residence time of molten steel was prolonged by about 49 s,the dead zone volume fraction was reduced by 8.93%,and the piston fluid integral rate was increased by 12.68%.In the turbulence inhibitor(TI)tundish with weir-dam combination,the removal rate of inclusions with a density of 2700 kg m^(-3) and a particle size of 5 lm is 63.32%,while the removal rate of large inclusions with a density of 150μm could reach 89.04%.When the inclusion particle size was 10-50μm and the density was 2700-4500 kg m^(-3),the effect of inclusion density on inclusion removal rate was small.At the same time,when weir-dam combination TI tundish was set,the inclusions were mainly limited to the slag-metal interface of the first and second chambers of the tundish.The removal rate of inclusions in the first chamber was generally improved,with 10μm inclusions accounting for 47.67% and 150μm inclusions accounting for 60.69%.Furthermore,it has the best effect on the removal of small-size inclusions,especially those less than 70μm.

Effect of Magnesium on Evolution of Oxide and Sulphide in Liquid Iron at 1873K

To reveal the effects of magnesium on the evolution of oxide and sulphide inclusions in liquid iron, both thermodynamic calculations and deoxidization experiments were carried out. The samples extracted from the liquid iron were polished and analyzed by optical microscopy and scanning electron microscopy. The results showed that magne sium could modify oxide and sulphide inclusions simultaneously. Spherical MgO and irregular spinel inclusions were observed in the samples. The elongated MnS inclusions were replaced by small MgO · MgS or MgO · MgS · MnS complex inclusions, and the sulphides were distributed dispersively. The evolution mechanisms of inclusions were discussed comprehensively, and a proposed model for the formation of oxysulphide was set up.

Modification of Inclusions in Liquid Iron by Mg Treatment

Effect of Mg addition on the compositions of inclusions were studied. The results show that Mg can minimize the inclusions of steel obviously. Under the present condition, Mg deoxidation products of low-S content experimental steel would be changed in the order of Al2O3→MgAl2O4→Mg–Al–O–S→Mg–O–S. Mg deoxidation products of high-S content experimental steel generate Mg–S(–O)+MnS type inclusions, except for usual oxysulfide. And it is consistent with the results of thermodynamics calculation. Mg is preferred to react with oxide, compared with sulfide. The reaction reaches the equilibrium after 1 min or 5 min. It shows that the number and diameter of inclusions in all experimental steel samples are well under control, helping to improve the properties of steel.

Aluminum,titanium and oxygen control during electroslag remelting of stainless steel based on thermodynamic analysis

Experimental investigation and thermodynamic calculation were carried out to study the effect of slag on alloying elements during electroslag remelting with developing a thermodynamic model to control titanium and aluminum in in got.The thermodynamic model based on ion and molecule coexistence theory and conservation law of element atoms was established to analyze the change in aluminum and titanium along the height of ingot.The results show that low CaO slag is suitable for electroslag remelting of metal containing high titanium-to-aluminum ratio.As electroslag remelting process consists of slag temperature-rising and temperature-stable periods,TiO2 should be added into water-cooled copper mold during temperature-rising period in order to keep the thermodynamic equilibrium between titanium and aluminum,and the amount of TiO2 is the difference value calculated by the reaction between titanium and alumina at 1477 and 1677℃.

Interface characteristics between TiN and matrix and their effect on solidification structure

Heterogeneous nucleation is an effective way to promote the dispersion and precipitation of second-phase particles in steel and refine the grain size of the solidification structure.Not only refining as-cast structure grain size,but TiN in ferritic stainless steel can also pin grain boundaries and restrain the overgrowth of grains during rolling.The interface characteristics between TiN and heterogeneous phases(high-melting inclusions and ferrite phase)were studied based on the wetting angles between molten steel with different compositions and TiN substrate,and on the matching degree between TiN and ferrite lattice.It was found that,for the molten steel with the same composition,the wetting angle with the TiN substrate was significantly smaller than the contact angles with the other three substrates,while the wetting angle between ferrite phase and TiN was the smallest.The lattice matching was compared among MgAl_(2)O_(4),TiN andδmatrix by means of a high-resolution transmission electron microscope,which revealed that a coherent or semi-coherent interface was formed between the crystal plane(400)of MgAl_(2)O_(4)and the crystal plane(200)of TiN,as well as between the crystal plane(200)of TiN and the crystal plane(110)ofδmatrix,with a lattice misfit of 5.1%and 3.4%,respectively.Finally,these two characteristics between TiN and ferrite phase were both explained from the perspective of interfacial energy.The microstructure refinement mechanism from high temperature to room temperature can be better reflected by the proposed wetting–lattice misfit theory.